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diff --git a/40472-0.txt b/40472-0.txt index 9be811d..9f096f8 100644 --- a/40472-0.txt +++ b/40472-0.txt @@ -1,42 +1,4 @@ -Project Gutenberg's The History of Creation, Vol. I (of 2), by Ernst Haeckel - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The History of Creation, Vol. I (of 2) - Or the Development of the Earth and its Inhabitants by the - Action of Natural Causes - -Author: Ernst Haeckel - -Translator: E. Ray Lankester - -Release Date: August 14, 2012 [EBook #40472] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF CREATION, VOL I *** - - - - -Produced by Adrian Mastronardi, Turgut Dincer, Jason Palmer -and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - - - +*** START OF THE PROJECT GUTENBERG EBOOK 40472 *** +------------------------------------------------------------------+ | Transcriber’s note: | @@ -11094,361 +11056,4 @@ D. APPLETON & CO., PUBLISHERS, 1, 3, & 5 BOND STREET, NEW YORK. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The History of Creation, Vol. I (of 2) - Or the Development of the Earth and its Inhabitants by the - Action of Natural Causes - -Author: Ernst Haeckel - -Translator: E. Ray Lankester - -Release Date: August 14, 2012 [EBook #40472] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF CREATION, VOL I *** - - - - -Produced by Adrian Mastronardi, Turgut Dincer, Jason Palmer -and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - - - - - +------------------------------------------------------------------+ - | Transcriber's note: | - | | - | This book was published in two volumes, of which this is the | - | first. The second volume was released as Project Gutenberg ebook | - | #40473, available at http://www.gutenberg.org/ebooks/40473 | - | | - | Numbers enclosed in square brackets, e.g. [1], relate to | - | footnotes, which have been placed at the end of the text. | - | Numbers enclosed in parentheses, e.g. (1), relate to works | - | referred to in the text and listed at the end of volume II. | - | | - | In the text versions of these two volumes, words in _italics_ | - | are enclosed in underscores, +bold+ words are enclosed in plus | - | signs, and words in =Gothic script= are enclosed in equal signs. | - | Curly brackets are used to represent subscripts, e.g. k{1}. | - +------------------------------------------------------------------+ - - - - - THE HISTORY OF CREATION. - - - - -[Illustration: Development of a Calcareous Sponge (Olynthus).] - - - - - THE - HISTORY OF CREATION: - - _OR THE DEVELOPMENT OF THE EARTH AND ITS - INHABITANTS BY THE ACTION OF NATURAL CAUSES._ - - A POPULAR EXPOSITION OF - THE DOCTRINE OF EVOLUTION IN GENERAL, AND OF THAT OF - DARWIN, GOETHE, AND LAMARCK IN PARTICULAR. - - FROM THE GERMAN OF - ERNST HAECKEL, - PROFESSOR IN THE UNIVERSITY OF JENA. - - THE TRANSLATION REVISED BY - E. RAY LANKESTER, M.A., FELLOW OF EXETER COLLEGE, OXFORD. - - _IN TWO VOLUMES._ - VOL. I. - - NEW YORK: - D. APPLETON AND COMPANY, - 1, 3, AND 5 BOND STREET. - 1880. - - - - - A sense sublime - Of something far more deeply interfused, - Whose dwelling is the light of setting suns, - And the round ocean, and the living air, - And the blue sky, and in the mind of man; - A motion and a spirit that impels - All thinking things, all objects of all thought, - And rolls through all things. - - In all things, in all natures, in the stars - Of azure heaven, the unenduring clouds, - In flower and tree, in every pebbly stone - That paves the brooks, the stationary rocks, - The moving waters and the invisible air. - - WORDSWORTH. - - - - -CONTENTS OF VOL. I. - - - CHAPTER I. - - NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION, - OR DESCENT-THEORY. - PAGE - General Importance and Essential Nature of the Theory of - Descent as reformed by Darwin.--Its Special Importance to - Biology (Zoology and Botany).--Its Special Importance to - the History of the Natural Development of the Human - Race.--The Theory of Descent as the Non-Miraculous History - of Creation.--Idea of Creation.--Knowledge and - Belief.--History of Creation and History of - Development.--The Connection between the History of - Individual and Palæontological Development.--The Theory of - Purposelessness, or the Science of Rudimentary - Organs.--Useless and Superfluous Arrangements in - Organisms.--Contrast between the two entirely Opposed - Views of Nature: the Monistic (mechanical, causal) and the - Dualistic (teleological, vital).--Proof of the former by - the Theory of Descent.--Unity of Organic and Inorganic - Nature, and the Identity of the Active Causes in - both.--The Importance of the Theory of Descent to the - Monistic Conception of all Nature 1 - - - CHAPTER II. - - SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT. - HISTORY OF CREATION ACCORDING TO LINNÆUS. - - The Theory of Descent, or Doctrine of Filiation, as the - Monistic Explanation of Organic Natural Phenomena.--Its - Comparison with Newton's Theory of Gravitation.--Limits of - Scientific Explanation and of Human Knowledge in - general.--All Knowledge founded originally on Sensuous - Experience, _à posteriori_.--Transition of _à posteriori_ - knowledge, by inheritance, into _à priori_ - knowledge.--Contrast between the Supernatural Hypotheses - of the Creation according to Linnæus, Cuvier, Agassiz, - and the Natural Theories of Development according to - Lamarck, Goethe, and Darwin.--Connection of the former - with the Monistic (mechanical), of the latter with the - Dualistic Conception of the Universe.--Monism and - Materialism.--Scientific and Moral Materialism.--The - History of Creation according to Moses.--Linnæus as the - Founder of the Systematic Description of Nature and - Distinction of Species.--Linnæus' Classification and - Binary Nomenclature.--Meaning of Linnæus' Idea of - Species.--His History of Creation.--Linnæus' view of the - Origin of Species 24 - - - CHAPTER III. - - THE HISTORY OF CREATION ACCORDING TO CUVIER - AND AGASSIZ. - - General Theoretical Meaning of the Idea of - Species.--Distinction between the Theoretical and - Practical Definition of the Idea of Species.--Cuvier's - Definition of Species.--Merits of Cuvier as the Founder of - Comparative Anatomy.--Distinction of the Four Principal - Forms (types or branches) of the Animal Kingdom, by Cuvier - and Bär.--Cuvier's Services to Palæontology.--His - Hypothesis of the Revolutions of our Globe, and the Epochs - of Creation separated by them.--Unknown Supernatural - Causes of the Revolutions, and the subsequent New - Creations.--Agassiz's Teleological System of Nature.--His - Conception of the Plan of Creation, and its six Categories - (groups in classification).--Agassiz's Views of the - Creation of Species.--Rude Conception of the Creator as a - man-like being in Agassiz's Hypothesis of Creation.--Its - internal Inconsistency and Contradictions with the - important Palæontological Laws discovered by Agassiz 47 - - - CHAPTER IV. - - THEORY OF DEVELOPMENT ACCORDING TO GOETHE - AND OKEN. - - Scientific Insufficiency of all Conceptions of a Creation - of Individual Species.--Necessity of the Counter Theories - of Development.--Historical Survey of the most Important - Theories of Development.--Aristotle.--His Doctrine of - Spontaneous Generation.--The Meaning of - Nature-philosophy.--Goethe.--His Merits as a - Naturalist.--His Metamorphosis of Plants.--His Vertebral - Theory of the Skull.--His Discovery of the Mid Jawbone in - Man.--Goethe's Interest in the Dispute between Cuvier and - Geoffroy St. Hilaire.--Goethe's Discovery of the two - Organic Formative Principles, of the Conservative - Principle of Specification (by Inheritance), and of the - Progressive Principle of Transformation (by - Adaptation).--Goethe's Views of the Common Descent of all - Vertebrate Animals, including Man.--Theory of Development - according to Gottfried Reinhold Treviranus.--His Monistic - Conception of Nature.--Oken.--His - Nature-philosophy.--Oken's Theory of Protoplasm.--Oken's - Theory of Infusoria (Cell Theory).--Oken's Theory of - Development 72 - - - CHAPTER V. - - THEORY OF DEVELOPMENT ACCORDING TO KANT AND - LAMARCK. - - Kant's Dualistic Biology.--His Conception of the Origin of - Inorganic Nature by Mechanical Causes, of Organic Nature - by Causes acting for a Definite Purpose.--Contradiction of - this Conception with his leaning towards the Theory of - Descent.--Kant's Genealogical Theory of Development.--Its - Limitation by his Teleology.--Comparison of Genealogical - Biology with Comparative Philology.--Views in favour of - the Theory of Descent entertained by Leopold Buch, Bär, - Schleiden, Unger, Schaafhausen, Victor Carus, - Büchner.--French Nature-philosophy.--Lamarck's Philosophic - Zoologique.--Lamarck's Monistic (mechanical) System of - Nature.--His Views of the Interaction of the two Organic - Formative Tendencies of Inheritance and - Adaptation.--Lamarck's Conception of Man's Development - from Ape-like Mammals.--Geoffroy St. Hilaire's, Naudin's, - and Lecoq's Defence of the Theory of Descent.--English - Nature-philosophy.--Views in favour of the Theory of - Descent entertained by Erasmus Darwin, W. Herbert, Grant, - Freke, Herbert Spencer, Hooker, Huxley.--The Double Merit - of Charles Darwin 100 - - - CHAPTER VI. - - THEORY OF DEVELOPMENT ACCORDING TO LYELL - AND DARWIN. - - Charles Lyell's Principles of Geology.--His Natural - History of the Earth's Development.--Origin of the - Greatest Effects through the Multiplication of the - Smallest Causes.--Unlimited Extent of Geological - Periods.--Lyell's Refutation of Cuvier's History of - Creation.--The Establishment of the Uninterrupted - Connection of Historical Development by Lyell and - Darwin.--Biographical Notice of Charles Darwin.--His - Scientific Works.--His Theory of Coral - Reefs.--Development of the Theory of Selection.--A Letter - of Darwin's.--The Contemporaneous Appearance of Darwin's - and Alfred Wallace's Theory of Selection.--Darwin's Study - of Domestic Animals and Cultivated Plants.--Andreas - Wagner's Notions as to the Special Creation of Cultivated - Organisms for the good of Man.--The Tree of Knowledge in - Paradise.--Comparison between Wild and Cultivated - Organisms.--Darwin's Study of Domestic - Pigeons.--Importance of Pigeon Breeding.--Common Descent - of all Races of Pigeons 125 - - - CHAPTER VII. - - THE THEORY OF SELECTION (DARWINISM). - - Darwinism (Theory of Selection) and Lamarckism (Theory of - Descent).--The Process of Artificial Breeding.--Selection - of the Different Individuals for After-breeding.--The - Active Causes of Transmutation.--Change connected with - Food and Transmission by Inheritance connected with - Propagation.--Mechanical Nature of these Two Physiological - Functions.--The Process of Natural Breeding: Selection in - the Struggle for Existence.--Malthus' Theory of - Population.--The Proportion between the Numbers of - Potential and Actual Individuals of every Species of - Organisms.--General Struggle for Existence, or Competition - to attain the Necessaries of Life.--Transforming Force of - the Struggle for Existence.--Comparison of Natural and - Artificial Breeding.--Selection in the Life of - Man.--Military and Medical Selection 149 - - - CHAPTER VIII. - - TRANSMISSION BY INHERITANCE AND PROPAGATION. - - Universality of Inheritance and Transmission by - Inheritance.--Special Evidences of the same.--Human Beings - with four, six, or seven Fingers and Toes.--Porcupine - Men.--Transmission of Diseases, especially Diseases of the - Mind.--Original Sin.--Hereditary Monarchies.--Hereditary - Aristocracy.--Hereditary Talents and Mental - Qualities.--Material Causes of Transmission by - Inheritance.--Connection between Transmission by - Inheritance and Propagation.--Spontaneous Generation and - Propagation.--Non-sexual or Monogonous - Propagation.--Propagation by Self-Division.--Monera and - Amoeba.--Propagation by the formation of Buds, by the - formation of Germ-Buds, by the formation of - Germ-Cells.--Sexual or Amphigonous Propagation.--Formation - of Hermaphrodites.--Distinction of Sexes, or - Gonochorism.--Virginal Breeding, or - Parthenogenesis.--Material Transmission of Peculiarities - of both Parents to the Child by Sexual - Propagation.--Difference between Transmission by - Inheritance in Sexual and in Asexual Propagation 175 - - - CHAPTER IX. - - LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND - NUTRITION. - - Distinction between Conservative and Progressive - Transmission by Inheritance.--Laws of Conservative - Transmission: Transmission of Inherited - Characters.--Uninterrupted or Continuous - Transmission.--Interrupted or Latent - Transmission.--Alternation of - Generations.--Relapse.--Degeneracy.--Sexual - Transmission.--Secondary Sexual Characters.--Mixed or - Amphigonous Transmission.--Hybrids.--Abridged or - Simplified Transmission.--Laws of Progressive Inheritance: - Transmission of Acquired Characters.--Adapted or Acquired - Transmission.--Fixed or Established - Transmission.--Homochronous Transmission (Identity in - Epoch).--Homotopic Transmission (Identity in - Part).--Adaptation and Mutability.--Connection between - Adaptation and Nutrition.--Distinction between Indirect - and Direct Adaptation 203 - - - CHAPTER X. - - LAWS OF ADAPTATION. - - Laws of Indirect or Potential Adaptation.--Individual - Adaptation.--Monstrous or Sudden Adaptation.--Sexual - Adaptation.--Laws of Direct or Actual - Adaptation.--Universal Adaptation.--Cumulative - Adaptation.--Cumulative Influence of External Conditions - of Existence and Cumulative Counter-Influence of the - Organism.--Free Will.--Use and Non-use of - Organs.--Practice and Habit.--Correlative - Adaptation.--Correlation of Development.--Correlation of - Organs.--Explanation of Indirect or Potential Adaptation - by the Correlation of the Sexual Organs and of the other - parts of the Body.--Divergent Adaptation.--Unlimited or - Infinite Adaptation 227 - - - CHAPTER XI. - - NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION - OF LABOUR AND PROGRESS. - - Interaction of the two Organic Formative Causes, - Inheritance and Adaptation.--Natural and Artificial - Selection.--Struggle for Existence, or Competition for the - Necessaries of Life.--Disproportion between the Number of - Possible or Potential, and the Number of Real or Actual - Individuals.--Complicated Correlations of all Neighbouring - Organisms.--Mode of Action in Natural - Selection.--Homochromic Selection as the Cause of - Sympathetic Colourings.--Sexual Selection as the Cause of - the Secondary Sexual Characters.--Law of Separation or - Division of Labour (Polymorphism, Differentiation, - Divergence of Characters).--Transition of Varieties into - Species.--Idea of Species.--Hybridism.--Law of Progress or - Perfecting (Progresses, Teleosis) 252 - - - CHAPTER XII. - - LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS. - PHYLOGENY AND ONTOGENY. - - Laws of the Development of Mankind: Differentiation and - Perfecting.--Mechanical Cause of these two Fundamental - Laws.--Progress without Differentiation, and - Differentiation without Progress.--Origin of Rudimentary - Organs by Non-use and Discontinuance of - Habit.--Ontogenesis, or Individual Development of - Organisms.--Its General Importance.--Ontogeny, or the - Individual History of Development of Vertebrate Animals, - including Man.--The Fructification of the Egg.--Formation - of the Three Germ Layers.--History of the Development of - the Central Nervous System, of the Extremities, of the - Branchial Arches, and of the Tail of Vertebrate - Animals.--Causal Connection and Parallelism of Ontogenesis - and Phylogenesis, that is, of the Development of - Individuals and Tribes.--Causal Connection of the - Parallelism of Phylogenesis and of Systematic - Development.--Parallelism of the three Organic Series of - Development 280 - - - CHAPTER XIII. - - THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE - EARTH. SPONTANEOUS GENERATION. THE CARBON THEORY. THE - PLASTID THEORY. - - History of the Development of the Earth.--Kant's Theory of - the Development of the Universe, or the Cosmological Gas - Theory.--Development of Suns, Planets, and Moons.--First - Origin of Water.--Comparison of Organisms and - Anorgana.--Organic and Inorganic Substances.--Degrees of - Density, or Conditions of Aggregation.--Albuminous - Combinations of Carbon.--Organic and Inorganic - Forms.--Crystals and Formless Organisms without - Organs.Stereometrical Fundamental Forms of Crystals and - of Organisms.--Organic and Inorganic Forces.--Vital - Force.--Growth and Adaptation in Crystals and in - Organisms.--Formative Tendencies of Crystals.--Unity of - Organic and Inorganic Nature.--Spontaneous Generation, or - Archigony.--Autogony and Plasmogony.--Origin of Monera by - Spontaneous Generation.--Origin of Cells from Monera.--The - Cell Theory.--The Plastid Theory.--Plastids, or - Structural-Units.--Cytods and Cells.--Four Different Kinds - of Plastids 316 - - - CHAPTER XIV. - - MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE - ICE-PERIOD OF THE EARTH. - - Chorological Facts and Causes.--Origin of most Species in - one Single Locality.--"Centres of Creation."--Distribution - by Migration.--Active and Passive Migrations of Animals - and Plants.--Means of Transport.--Transport of Germs by - Water and by Wind.--Continual Change of the Area of - Distribution by Elevations and Depressions of the - Ground.--Chorological Importance of Geological - Processes.--Influence of the Change of Climate.--Ice or - Glacial Period.--Its Importance to Chorology.--Importance - of Migrations for the Origin of New Species.--Isolation of - Colonists.--Wagner's Law of Migration.--Connection between - the Theory of Migration and the Theory of - Selection.--Agreement of its Results with the Theory of - Descent 350 - - - - -LIST OF ILLUSTRATIONS. - - - PLATES. - PAGE - - Development of a Calcareous Sponge (Olynthus) _Frontispiece_ - - I.--Life History of a Simplest Organism _To face page_ 184 - - II., III.--Germs or Embryos of Four Vertebrates " 306 - - - FIGURES. - - 1.--Propagation of Moneron 186 - - 2.--Propagation of Amoeba 188 - - 3.--Egg of Mammal 189 - - 4.--First Development of Mammal's Egg 190 - - 5.--The Human Egg Enlarged 297 - - 6.--Development of Mammal's Egg 299 - - 7.--Embryo of a Mammal or Bird 304 - - - - -AUTHOR'S PREFACE TO THE ENGLISH EDITION. - - -I am desirous of prefacing the English edition of the "History of -Creation" with a few remarks which may serve to explain the origin and -object of this book. In the year 1866 I published, under the title -"Generelle Morphologie," a somewhat comprehensive work, which -constituted the first attempt to apply the general doctrine of -development to the whole range of organic morphology (Anatomy and -Biogenesis), and thus to make use of the vast march onwards which the -genius of Charles Darwin has effected in all biological science by his -reform of the Descent Theory and its establishment through the doctrine -of selection. At the same time, in the "Generelle Morphologie," the -first attempt was made to introduce the Descent Theory into the -systematic classification of animals and plants, and to found a "natural -system" on the basis of genealogy; that is, to construct hypothetical -pedigrees for the various species of organisms. - -The "Generelle Morphologie" found but few readers, for which the -voluminous and unpopular style of treatment, and its too extensive Greek -terminology, may be chiefly to blame. But a proportionately large -measure of approval has met the "Natürliche Schöpfungsgeschichte" in -Germany. This book took its origin in the shorthand notes of a course of -lectures which treated, before a mixed audience and in a popular form, -the most important topics discussed in the "Generelle Morphologie." The -notes were subsequently revised, and received considerable additions. -The book appeared first in 1868, its fourth edition in 1873, and has -been translated into several languages. I hope that it may also find -sympathy in the fatherland of Darwin, the more so since it contains -special morphological evidence in favour of many of the important -doctrines with which this greatest naturalist of our century has -enriched science. Proud as England may be to be called the fatherland of -Newton, who, with his law of gravitation, brought inorganic nature under -the dominion of natural laws of cause and effect, yet may she with even -greater pride reckon Charles Darwin among her sons--he who solved the -yet harder problem of bringing the complicated phenomena of organic -nature under the sway of the same natural laws. - -The reproach which is now oftenest made against the Descent Theory is -that it is not securely founded, not sufficiently proven. Not only its -distinct opponents maintain that there is a want of satisfactory proofs, -but even faint-hearted and wavering adherents declare that Darwin's -hypothesis is still wanting fundamental proof. Neither the former nor -the latter estimate rightly the immeasurable weight which the great -series of phenomena of comparative anatomy and ontogeny, palæontology -and taxonomy, chorology and oecology, cast into the scale in favour of -the doctrine of filiation. Darwin's Theory of Selection, which -completely explains the origin of species through the combined action of -Inheritance and Adaptation in the struggle for existence, also appears -to these persons not sufficient. They demand, over and above, that the -descent of species from common ancestral forms shall be proved in a -particular case; that, in contradistinction to the _synthetic_ proofs -adduced for the Descent Theory, the _analytic_ proof of the genealogical -continuity of the several species shall be brought forward. - -This "analytical solution of the problem of the origin of species" I -have myself endeavoured to afford in my recently published "Monograph of -the Calcareous Sponges." For five consecutive years I have investigated -this small but highly instructive group of animals in all its forms in -the most careful manner, and I venture to maintain that the monograph, -which is the result of those studies, is the most complete and accurate -morphological analysis of an entire organic group which has up to this -time been made. Provided with the whole of the material for study as yet -brought together, and assisted by numerous contributions from all parts -of the world, I was able to work over the whole group of organic forms -known as the Calcareous Sponges in that greatest possible degree of -fulness which appeared indispensable for the proof of the common origin -of its species. This particular animal group is especially fitted for -the analytical solution of the species problem, because it presents -exceedingly simple conditions of organisation, because in it the -morphological conditions possess a greatly superior, and the -physiological conditions an inferior, import, and because all species of -Calcispongiæ are remarkable for the fluidity and plasticity of their -form. With a view to these facts, I made two journeys to the sea-coast -(1869 to Norway, 1871 to Dalmatia), in order to study as large a number -of individuals as possible in their natural circumstances, and to -collect specimens for comparison. Of many species, I compared several -hundred individuals in the most careful way. I examined with the -microscope and measured in the most accurate manner the details of form -of all the species. As the final result of these exhaustive and almost -endless examinations and measurements it appeared that "good species," -in the ordinary dogmatic sense of the systematists, have no existence at -all among the Calcareous Sponges; that the most different forms are -connected one with another by numberless gradational transition forms; -and that all the different species of Calcareous Sponges are derived -from a single exceedingly simple ancestral form, the Olynthus. A drawing -of the Olynthus and its earliest stages of development (observe -especially the highly important Gastrula) is given in the frontispiece -of the present edition. Illustrations of the various structural details -which establish the derivation of all Calcareous Sponges from the -Olynthus, are given in the atlas of sixty plates which accompanies my -monograph of the group. In the gastrula, moreover, is now also found the -common ancestral form from which all the tribes of animals (the lowest -group, that of the protozoa, alone being excepted) can without -difficulty be derived. It is one of the most ancient and important -ancestors of the human race! - -If we take for the limitation of genus and species an average standard, -derived from the actual practice of systematists, and apply this to the -whole of the Calcareous Sponges at present known, we can distinguish -about twenty-one genera, with one hundred and eleven species (as I have -done in the second volume of the Monograph). I have, however, shown that -we may draw up, in addition to this, another systematic arrangement -(more nearly agreeing with the arrangement of the Calcispongiæ hitherto -in vogue) which gives thirty-nine genera and two hundred and eighty-nine -species. A systematist who gives a more limited extension to the "ideal -species" might arrange the same series of forms in forty-three genera -and three hundred and eighty-one species, or even in one hundred and -thirteen genera and five hundred and ninety species; another systematist -on the other hand, who takes a wider limit for the "abstract species," -would use in arranging the same series of forms only three genera, with -twenty-one species, or might even satisfy himself with one genus and -seven species. The delimitation of species and genera appears to be so -arbitrary a matter, on account of endless varieties and transitional -forms in this group, that their number is entirely left to the -subjective taste of the individual systematist. In truth, from the point -of view of the theory of descent, it appears altogether an unimportant -question as to whether we give a wider or a narrower signification to -allied groups of forms--whether we choose, that is to say, to call them -genera or species, varieties or sub-species. The main fact remains -undeniable, viz., the common origin of all the species from one -ancestral form. The many-shaped Calcareous Sponges furnish, in the very -remarkable conditions of their varieties of aggregation (metrocormy), a -body of evidence in favour of this view which could hardly be more -convincing. Not unfrequently the case occurs of several different forms -growing out from a single "stock" or "cormus"--forms which until now -have been regarded by systematists, not only as belonging to different -species, but even to different genera. Fig. 10 in the frontispiece -represents such a composite stock. This solid and tangible piece of -evidence in favour of the common descent of different species ought, one -would think, to satisfy the most determined sceptic! - -In point of fact, I have a right to expect of my opponents that they -shall carefully consider the "exact empirical proof" here brought -forward for them, as they have so eagerly demanded. The opponents of the -doctrine of filiation, who have too little power of weighing evidence, -or possess too little knowledge to appreciate the overpowering weight of -proof afforded by the synthetical argument (comparative anatomy, -ontogeny, taxonomy, etc.), may yet be able to follow me along the path -of analytical proof, and attempt to upset the conclusion as to the -common origin of all species of all Calcareous Sponges which I have -given in my Monograph. I must, however, repeat that this conclusion is -based on the most minute investigation of an extraordinarily rich mass -of material,--that it is securely established by thousands of the most -careful microscopical observations, measurements, and comparisons of -every single part, and that thousands of collected microscopic -preparations render, at any moment, the most searching criticism of my -results confirmatory of their correctness. One may hope, then, that -opponents will endeavour to confront me on the ground of this "exact -empiricism," instead of trying to damn my "nature-philosophical -speculations." One may hope that they will endeavour to bring forward -some evidence to show that the latter do not follow as the legitimate -consequences of the former. May they, however, spare me the -empty--though by even respectable naturalists oft-repeated--phrase, that -the monistic nature-philosophy, as expounded in the "General -Morphology," and in the "History of Creation," is wanting in actual -proofs. The proofs are there. Of course those who turn their eyes away -from them will not see them. Precisely that "exact" form of analytical -proof which the opponents of the descent theory demand is to be found, -by anybody who wishes to find it, in the "Monograph of the Calcareous -Sponges." - - - ERNST HEINRICH HAECKEL. - - _Jena, June 24th, 1873._ - - - - -NOTE. - - -Feeling sure that such a book as Professor Haeckel's -"Schöpfungsgeschichte" would do a great deal of good, if placed in the -hands of the English reading public, and of commencing students of -Natural History, I gladly undertook to revise for the publishers the -present translation, which was made by a young lady. I have not -attempted to escape a difficulty by ignoring the German names made use -of by Professor Haeckel for classes, orders, and genera, but have -adopted English equivalents. I do not submit these names as a maturely -considered English nomenclature, they appear here simply as necessary -parts of a close rendering of the German work. I do, however, hold that -some such series of English terms is both possible and useful, and do -not doubt--in spite of the pretended hostility of the genius of our -language, and the curious sentimental objection that English names are -_unscientific_--that we shall before long make use of plain English in -speaking of the various groups of plants and animals--much to the gain -of the larger public, and without detriment to the latinized -nomenclature established for the purposes of the professional student. - - - E. R. L. - - _Oxford, October, 1874._ - - - - -THE HISTORY OF CREATION. - - - - -CHAPTER I. - -NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION, OR DESCENT-THEORY. - - - General Importance and Essential Nature of the Theory of - Descent as reformed by Darwin.--Its Special Importance to - Biology (Zoology and Botany).--Its Special Importance to - the History of the Natural Development of the Human - Race.--The Theory of Descent as the Non-Miraculous - History of Creation.--Idea of Creation.--Knowledge and - Belief.--History of Creation and History of - Development.--The Connection between the History of - Individual and Palæontological Development.--The Theory - of Purposelessness, or the Science of Rudimentary - Organs.--Useless and Superfluous Arrangements in - Organisms.--Contrast between the two entirely opposed - Views of Nature: the Monistic (mechanical, causal) and - the Dualistic (teleological, vital).--Proof of the former - by the Theory of Descent.--Unity of Organic and Inorganic - Nature, and the Identity of the Active Causes in - both.--The Importance of the Theory of Descent to the - Monistic Conception of all Nature. - - -The intellectual movement to which the impulse was given, thirteen years -ago, by the English naturalist, Charles Darwin, in his celebrated work, -"On the Origin of Species,"(1) has, within this short period, assumed -dimensions which cannot but excite the most universal interest. It is -true the scientific theory set forth in that work, which is commonly -called briefly Darwinism, is only a small fragment of a far more -comprehensive doctrine--a part of the universal Theory of Development, -which embraces in its vast range the whole domain of human knowledge. - -But the manner in which Darwin has firmly established the latter by the -former is so convincing, and the direction which has been given by the -unavoidable conclusions of that theory to all our views of the universe, -must appear to every thinking man of such deep significance, that its -general importance cannot be over estimated. There is no doubt that this -immense extension of our intellectual horizon must be looked upon as by -far the most important, and rich in results, among all the numerous and -grand advances which natural science has made in our day. - -When our century, with justice, is called the age of natural science, -when we look with pride upon the immensely important progress made in -all its branches, we are generally in the habit of thinking more of -immediate practical results, and less of the extension of our general -knowledge of nature. We call to mind the complete reform, so infinitely -rich in consequences to human intercourse, which has been effected by -the development of machinery, by railways, steamships, telegraphs, and -other inventions of physics. Or we think of the enormous influence which -chemistry has brought to bear upon medicine, agriculture, and upon all -arts and trades. - -But much as we may value this influence of modern science upon practical -life, still it must, estimated from a higher and more general point of -view, stand most assuredly below the enormous influence which the -theoretical progress of modern science will have on the entire range of -human knowledge, on our conception of the universe, and on the -perfecting of man's culture. - -Think of the immense revolutions in all our theoretical views which we -owe to the general application of the microscope. Think of the cell -theory, which explains the apparent unity of the human organism as the -combined result of the union of a mass of elementary vital units. Or -consider the immense extension of our theoretical horizon which we owe -to spectral analysis and to the mechanical theory of heat. But among all -these wonderful theoretical advances, the theory wrought out by Darwin -occupies by far the highest rank. - -Every one of my readers has heard of the name of Darwin. But most -persons have probably only an imperfect idea of the real value of his -theory. If a reader estimates as of equal value all that has been -written upon Darwin's memorable work since its appearance, the value of -the theory will appear very doubtful to him, supposing that he has not -been engaged in the organic natural sciences, and has not penetrated -into the inner secrets of zoology and botany. The criticisms of it are -so full of contradictions, and for the most part so defective, that we -ought not to be at all astonished that even now, after the lapse of -thirteen years since the appearance of Darwin's work, it has not gained -half that importance which is justly due to it, and which sooner or -later it certainly will attain. - -Most of the innumerable writings which have been published during these -years, both for and against Darwinism, are the productions of persons -who are entirely wanting in the necessary amount of biological, and -especially of zoological, knowledge. Although almost all of the more -celebrated naturalists of the present day are adherents of the theory, -yet only a few of them have endeavoured to procure its acceptance and -recognition in larger circles. Hence the odd contradictions and the -strange opinions which may still be heard everywhere about Darwinism. -This is the reason which induces me to make Darwin's theory, and those -further doctrines which are connected with it, the subject of these -pages, which, I hope, will be generally intelligible. I hold it to be -the duty of naturalists, not merely to meditate upon improvements and -discoveries in the narrow circle to which their speciality confines -them, not merely to pore over their one study with love and care, but -also to seek to make the important general results of it fruitful to the -mass, and to assist in spreading the knowledge of physical science among -the people. The highest triumph of the human mind, the true knowledge of -the most general laws of nature, ought not to remain the private -possession of a privileged class of savans, but ought to become the -common property of all mankind. - -The theory which, through Darwin, has been placed at the head of all our -knowledge of nature, is usually called the Doctrine of Filiation, or the -Theory of Descent. Others term it the Transmutation Theory. Both -designations are correct. For this doctrine affirms, that _all -organisms_ (viz., all species of animals, all species of plants, which -have ever existed or still exist on the earth) _are derived from one -single, or from a few simple original forms, and that they have -developed themselves from these in the natural course of a gradual -change_. Although this theory of development had already been brought -forward and defended by several great naturalists, and especially by -Lamarck and Goethe, in the beginning of our century, still it was -through Darwin, thirteen years ago, that it received its complete -demonstration and causal foundation; and this is the reason why now it -is commonly and exclusively (though not quite correctly) designated as -_Darwin's Theory_. - -The great and really inestimable value of the Theory of Descent appears -in a different light, accordingly as we merely consider its more -immediate connection with organic natural science, or its larger -influence upon the whole range of man's knowledge of the universe. -Organic natural science, or Biology, which as Zoology treats of animals, -as Botany of plants, is completely reformed and founded anew by the -Theory of Descent. For by this theory we are made acquainted with the -active causes of organic forms, while up to the present time Zoology and -Botany have simply been occupied with the facts of these forms. We may -therefore also term the theory of descent a _mechanical explanation of -organic forms_, or the science of the true causes of Organic Nature. - -As I cannot take for granted that my readers are all familiar with the -terms "organic and inorganic nature," and as the contrast of both these -natural bodies will, in future, occupy much of our attention, I must say -a few words in explanation of them. We designate as _Organisms_, or -_Organic bodies_, all _living creatures_ or _animated bodies_; therefore -all plants and animals, man included; for in them we can almost always -prove a combination of various parts (instruments or organs) which work -together for the purpose of producing the phenomena of life. Such a -combination we do not find in _Anorgana_, or inorganic natural -bodies--the so-called dead or _inanimate bodies_, such as minerals or -stones, water, the atmospheric air, etc. Organisms always contain -albuminous combinations of carbon in a semi-fluid condition of -aggregation, which are always wanting in the Anorgana. Upon this -important distinction rests the division of all natural history into two -great and principal parts--_Biology_, or the science of Organisms -(Zoology and Botany), and _Anorganology_, or the science of Anorgana -(Mineralogy, Geology, Meteorology, etc.). - -The great value of the Theory of Descent in regard to Biology consists, -as I have already remarked, in its explaining to us the origin of -organic forms in a mechanical way, and pointing out their active causes. -But however highly and justly this service of the Theory of Descent may -be valued, yet it is almost eclipsed by the immense importance which a -single necessary inference from it claims for itself alone. This -necessary and unavoidable inference is the theory of the _animal descent -of the human race_. - -The determination of the position of man in nature, and of his relations -to the totality of things--this question of all questions for mankind, -as Huxley justly calls it--is finally solved by the knowledge that man -is descended from animals. In consequence of Darwin's reformed Theory of -Descent, we are now in a position to establish scientifically the -groundwork of a _non-miraculous history of the development of the human -race_. All those who have defended Darwin's theory, as well as all its -thoughtful opponents, have acknowledged that, as a matter of necessity, -it follows from his theory that the human race, in the first place, must -be traced to ape-like mammals, and further back to the lower vertebrate -animals. - -It is true Darwin himself did not express at first this most important -of all the inferences from his theory. In his work, "On the Origin of -Species," not a word is found about the animal descent of man. The -courageous but cautious naturalist was at that time purposely silent on -the subject, for he anticipated that this most important of all the -conclusions of the Theory of Descent was at the same time the greatest -obstacle to its being generally accepted and acknowledged. Certain it is -that Darwin's book would have created, from the beginning, even much -more opposition and offence, if this most important inference had at -once been clearly expressed. It was not till twelve years later, in his -work on "The Descent of Man, and Selection in Relation to Sex," that -Darwin openly acknowledged that far-reaching conclusion, and expressly -declared his entire agreement with those naturalists who had, in the -meantime, themselves formed that conclusion. Manifestly the effect of -this conclusion is immense, and _no_ science will be able to escape from -the consequences. Anthropology, or the science of man, and consequently -all philosophy, are thereby thoroughly reformed in all their various -branches. - -It will be a later task in these pages to discuss this special point. I -shall not treat of the theory of the animal descent of man till I have -spoken of Darwin's theory, and its general foundation and importance. To -express it in one word, that most important, but (to most men) at first -repulsive, conclusion is nothing more than a special deduction, which we -must draw from the general inductive law of the descent theory (now -firmly established), according to the stern commands of inexorable -logic. - -Perhaps nothing will make the full meaning of the theory of descent -clearer than calling it the "_non-miraculous history of creation_." I -have therefore chosen that name for this work. It is, however, correct -only in a certain sense, and it must be borne in mind that, strictly -speaking, the expression "non-miraculous history of creation" contains a -"_contradictio in adjecto_." - -In order to understand this, let us for a moment examine somewhat more -closely what we understand by _creation_. If we understand the creation -to mean the _coming into existence of a body_ by a creative power or -force, we may then either think of the _coming into existence of its -substance_ (corporeal matter), or of the _coming into existence of its -form_ (the corporeal form). - -Creation in the former sense, as the _coming into existence of matter_, -does not concern us here at all. This process, if indeed it ever took -place, is completely beyond human comprehension, and can therefore never -become a subject of scientific inquiry. Natural science teaches that -matter is eternal and imperishable, for experience has never shown us -that even the smallest particle of matter has come into existence or -passed away. Where a natural body seems to disappear, as for example by -burning, decaying, evaporation, etc., it merely changes its form, its -physical composition or chemical combination. In like manner the coming -into existence of a natural body, for example, of a crystal, a fungus, -an infusorium, depends merely upon the different particles, which had -before existed in a certain form or combination, assuming a new form or -combination in consequence of changed conditions of existence. But never -yet has an instance been observed of even the smallest particle of -matter having vanished, or even of an atom being added to the already -existing mass. Hence a naturalist can no more imagine the coming into -existence of matter, than he can imagine its disappearance, and he -therefore looks upon the existing quantity of matter in the universe as -a given fact. If any person feels the necessity of conceiving the coming -into existence of this matter as the work of a supernatural creative -power, of the creative force of something outside of matter, we have -nothing to say against it. But we must remark, that thereby not even the -smallest advantage is gained for a scientific knowledge of nature. Such -a conception of an immaterial force, which at the first creates matter, -is an article of faith which has nothing whatever to do with human -science. _Where faith commences, science ends._ Both these arts of the -human mind must be strictly kept apart from each other. Faith has its -origin in the poetic imagination; knowledge, on the other hand, -originates in the reasoning intelligence of man. Science has to pluck -the blessed fruits from the tree of knowledge, unconcerned whether these -conquests trench upon the poetical imaginings of faith or not. - -If, therefore, science makes the "history of creation" its highest, most -difficult, and most comprehensive problem, it must accept as its idea of -creation the second explanation of the word, viz., _the coming into -being of the form_ of natural bodies. In this way geology, which tries -to investigate the origin of the inorganic surface of the earth as it -now appears, and the manifold historical changes in the form of the -solid crust of the earth, may be called the history of the creation of -the earth. In like manner, the history of the development of animals and -plants, which investigates the origin of living forms, and the manifold -historical changes in animal and vegetable forms, may be termed the -history of the creation of organisms. As, however, in the idea of -creation, although used in this sense, the unscientific idea of a -creator existing outside of matter, and changing it, may easily creep -in, it will perhaps be better in future to substitute for it the more -accurate term, _development_. - -The great value which the _History of Development_ possesses for the -scientific understanding of animal and vegetable forms, has now been -generally acknowledged for many years, and without it it would be -impossible to make any sure progress in organic morphology, or the -theory of forms. But by the history of development, only one part of -this science has generally been understood, namely, that of organic -individuals, usually called Embryology, but more correctly and -comprehensively, _Ontogeny_. But, besides this, there is another history -of development of organic species, genera, and tribes (phyla), which has -the most important relations to the former. - -The subject of this is furnished to us by the science of petrifactions, -or palæontology, which shows us that each tribe of animals and plants, -during different periods of the earth's history, has been represented by -a series of entirely different genera and species. Thus, for example, -the tribe of vertebrated animals was represented by classes of fish, -amphibious animals, reptiles, birds, and mammals, and each of these -groups, at different periods, by quite different kinds. This -palæontological history of the development of organisms, which we may -term _Phylogeny_, stands in the most important and remarkable relation -to the other branch of organic history of development, I mean that of -individuals, or Ontogeny. On the whole, the one runs parallel to the -other. In fact, the history of individual development, or Ontogeny, is a -short and quick recapitulation of palæontological development, or -Phylogeny, dependent on the laws of Inheritance and Adaptation. - -As I shall have, later, to explain this most interesting and important -coincidence more fully, I shall not dwell further upon it here, and -merely call attention to the fact that it can only be explained and its -causes understood by the Theory of Descent, while without that theory it -remains completely incomprehensible and inexplicable. The Theory of -Descent in the same way shows us _why_ individual animals and plants -must develop at all, and why they do not come into life at once in a -perfect and developed state. No supernatural history of creation can in -any way explain to us the great mystery of organic development. To this -most weighty question, as well as to all other biological questions, the -Theory of Descent gives us perfectly satisfactory answers--and always -answers which refer to purely mechanical causes, and point to purely -physico-chemical forces as the causes of phenomena which we were -formerly accustomed to ascribe to the direct action of supernatural, -creative forces. Hence, by our theory the mystic veil of the miraculous -and supernatural, which has hitherto been allowed to hide the -complicated phenomena of this branch of natural knowledge, is removed. -All the departments of Botany and Zoology, and especially the most -important portion of the latter, Anthropology, become reasonable. The -dimming mirage of mythological fiction can no longer exist in the clear -sunlight of scientific knowledge. - -Of special interest among general biological phenomena are those which -are quite irreconcilable with the usual supposition, that every organism -is the product of a creative power, acting for a definite object. -Nothing in this respect caused the earlier naturalists greater -difficulty than the explanation of the so-called "_rudimentary -organs_,"--those parts in animal and vegetable bodies which really have -no function, which have no physiological importance, and yet exist in -form. These parts deserve the most careful attention, although most -unscientific men know little or nothing about them. Almost every -organism, almost every animal and plant possesses, besides the obviously -useful arrangements of its organization, other arrangements the purpose -of which it is utterly impossible to make out. - -Examples of this are found everywhere. In the embryos of many ruminating -animals--among others, in our common cattle--fore-teeth, or incisors, -are placed in the mid-bone of the upper jaw, which never fully develop, -and therefore serve no purpose. The embryos of many whales--which -afterwards possess the well-known whalebone instead of teeth--yet have -before they are born, and while they take no nourishment, teeth in their -jaws, which set of teeth never comes into use. Moreover, most of the -higher animals possess muscles which are never employed; even man has -such rudimentary muscles. Most of us are incapable of moving our ears as -we wish, although the muscles for this movement exist, and although -individual persons who have taken the trouble to exercise these muscles -do succeed in moving their ears. It is still possible, by special -exercise, by the persevering influence of the will upon the nervous -system, to reanimate the almost extinct activity in the existing but -imperfect organs, which are on the road to complete disappearance. On -the other hand, we can no longer do this with another set of small -rudimentary muscles, which still exist in the cartilage of the outer -ear, but which are always perfectly inactive. Our long-eared ancestors -of the tertiary period--apes, semi-apes, and pouched animals, like most -other mammals, moved their large ear-flaps freely and actively; their -muscles were much more strongly developed and of great importance. In a -similar way, many varieties of dogs and rabbits, under the influence of -civilized life, have left off "pricking up" their ears, and thereby have -acquired imperfect auricular muscles and loose-hanging ears, although -their wild ancestors moved their stiff ears in many ways. - -Man has also these rudimentary organs on other parts of his body; they -are of no importance to life, and never perform any function. One of the -most remarkable, although the smallest organ of this kind, is the little -crescent-like fold, the so-called "plica semilunaris," which we have in -the inner corner of the eye, near the root of the nose. This -insignificant fold of skin, which is quite useless to our eye, is the -imperfect remnant of a third inner eyelid which, besides the upper and -under eyelid, is highly developed in other mammals, and in birds and -reptiles. Even our very remote ancestors of the Silurian period, the -Primitive Fishes, seem to have possessed this third eyelid, the -so-called nictitating membrane. For many of their nearest kin, who still -exist in our day but little changed in form, viz., many sharks, possess -a very strong nictitating membrane, which they can draw right across the -whole eyeball, from the inner corner of the eye. - -Eyes which do not see form the most striking example of rudimentary -organs. These are found in very many animals, which live in the dark, as -in caves or underground. Their eyes often exist in a well-developed -condition, but they are covered by membrane, so that no ray of light -can enter, and they can never see. Such eyes, without the function of -sight, are found in several species of moles and mice which live -underground, in serpents and lizards, in amphibious animals (Proteus, -Cæcilia), and in fishes; also in numerous invertebrate animals, which -pass their lives in the dark, as do many beetles, crabs, snails, worms, -etc. - -An abundance of the most interesting examples of rudimentary organs is -furnished by Comparative Osteology, or the study of the skeletons of -vertebrate animals, one of the most attractive branches of Comparative -Anatomy. In most of the vertebrate animals we find two pairs of limbs on -the body, a pair of fore-legs and a pair of hind-legs. Very often, -however, one or the other pair is imperfect; it is seldom that both are, -as in the case of serpents and some varieties of eel-like fish. But some -serpents, viz., the giant serpents (Boa, Python), have still in the -hinder portion of the body some useless little bones, which are the -remains of lost hind-legs. - -In like manner the mammals of the whale tribe (Cetacea), which have only -fore-legs fully developed (breast-fins,), have further back in their -body another pair of utterly superfluous bones, which are remnants of -undeveloped hind-legs. The same thing occurs in many genuine fishes, in -which the hind-legs have in like manner been lost. - -Again, in our slow-worm (Anguis), and in some other lizards, no -fore-legs exist, although they have a perfect shoulder apparatus within -their bodies, which should serve as a means of affixing the legs. -Moreover, in various vertebrate animals, the single bones of both pairs -of legs are found in all the different stages of imperfection, and often -the degenerate bones and those muscles belonging to them are partially -preserved, without their being able in any way to perform any function. -The instrument is still there, but it can no longer play. - -Moreover, we can, almost as generally, find rudimentary organs in the -blossoms of plants, inasmuch as one part or another of the male organs -of propagation--the stamen and anther, or of the female organs of -propagation--the style, germ, etc.--is more or less imperfect or -abortive. Among these we can trace, in various closely connected species -of plants, the organ in all stages of degeneration. Thus, for example, -the great natural family of lip-blossomed plants (Labiatæ), to which the -balm, peppermint, marjoram, ground-ivy, thyme, etc., belong, are -distinguished by the fact that their mouth-like, two-lipped flower -contains two long and two short stamens. But in many exceptional plants -of this family, _e.g._ in different species of sage, and in the -rosemary, only one pair of stamens is developed; the other pair is more -or less imperfect, or has quite disappeared. Sometimes stamens exist, -but without the anthers, so that they are utterly useless. Less -frequently the rudiment or imperfect remnant of a fifth stamen is found, -physiologically (for the functions of life) quite useless, but -morphologically (for the knowledge of the form and of the natural -relationship) a most valuable organ. In my "General Morphology of -Organisms,"(4) in the chapter on "Purposelessness, or Dysteleology," I -have given a great number of other examples (Gen. Morph. ii. 226). - -No biological phenomenon has perhaps ever placed zoologists or botanists -in greater embarrassment than these rudimentary or abortive organs. They -are instruments without employment, parts of the body which exist -without performing any service--adapted for a purpose, but without in -reality fulfilling that purpose. When we consider the attempts which the -earlier naturalists have made in order to explain this mystery, we can -scarcely help smiling at the strange ideas to which they were led. Being -unable to find a true explanation, they came, for example, to the -conclusion that the Creator had placed these organs there "for the sake -of symmetry," or they believed that it had appeared unwise and -unsuitable to the Creator (seeing that their nearest kin did possess -such organs) that these organs should be completely wanting in -creatures, where they are incapable of performing a function, and where -it cannot be otherwise from the special mode of life. In compensation -for the non-existing function, he had at least furnished them with the -outward but empty form; nearly in the same manner as civil officers, in -uniform, are furnished with an innocent sword, which is never drawn from -the scabbard. I scarcely believe, however, that any of my readers will -be content with such an explanation. - -Now, it is precisely this widely spread and mysterious phenomenon of -rudimentary organs, in regard to which all other attempts at explanation -fail, which is perfectly explained, and indeed in the simplest and -clearest way, by Darwin's _Theory of Inheritance_ and _Adaptation_. We -can trace the important laws of inheritance and adaptation in the -domestic animals which we breed, and the plants which we cultivate; and -a series of such laws of inheritance have already been established. -Without going further into this at present, I will only remark that some -of them perfectly explain, in a mechanical way, the coming into -existence of rudimentary organs, so that we must look upon the -appearance of such structures as an entirely natural process, arising -from the _disuse of the organs_. - -By _adaptation_ to special conditions of life, the formerly active and -really working organs have gradually ceased to be used or employed. In -consequence of their not being exercised they have become more and more -imperfect, but in spite of this have always been handed down from one -generation to another by _inheritance_, until at last they vanish -partially or entirely. Now, if we admit that all the vertebrate animals -mentioned above are derived from one common ancestor, possessing two -seeing eyes and two well developed pairs of legs, the different stages -of suppression and degeneration of these organs are easily accounted for -in such of the descendants as could no longer use them. In like manner -the various stages of suppression of the stamens, originally existing to -the number of five (in the flower-bud), among the Labiatæ is explained, -if we admit that all the plants of this family sprung from one common -ancestor, provided with five stamens. - -I have here spoken somewhat fully of the phenomena of rudimentary -organs, because they are of the utmost general importance, and because -they lead us to the great, general, and fundamental questions in -philosophy and natural science, for the solution of which the Theory of -Descent has now become the indispensable guide. As soon, in fact, as, -according to this theory, we acknowledge the exclusive activity of -physico-chemical causes in living (organic) bodies, as well as in -so-called inanimate (inorganic) nature, we concede exclusive dominion to -that view of the universe, which we may designate as the _mechanical_, -and which is opposed to the _teleological_ conception. If we compare -all the ideas of the universe prevalent among different nations at -different times, we can divide them all into two sharply contrasted -groups--a _causal_ or _mechanical_, and a _teleological_ or -_vitalistic_. The latter has prevailed generally in Biology until now, -and accordingly the animal and vegetable kingdoms have been considered -as the products of a creative power, acting for a definite purpose. In -the contemplation of every organism the unavoidable conviction seemed to -press itself upon us, that such a wonderful machine, so complicated an -apparatus for motion as exists in the organism, could only be produced -by a power analogous to, but infinitely more perfect than, the power of -man in the construction of his machines. - -However sublime the former idea of a Creator, and his creative power, -may have been; however much it may be attempted to divest it of all -human analogy, yet in the end this analogy still remains unavoidable and -necessary in the teleological conception of nature. In reality the -Creator must himself be conceived of as an organism, that is, as a being -who, analogous to man, even though in an infinitely more perfect form, -reflects on his constructive power, lays down a plan of his mechanisms, -and then, by the application of suitable materials, makes them answer -their purpose. Such conceptions necessarily suffer from the fundamental -error of _anthropomorphism_, or man-likening. In such a view, however -exalted the Creator may be imagined, we assign to him the human -attributes of designing a plan, and therefrom suitably constructing the -organism. This is, in fact, quite clearly expressed in that view which -is most sharply opposed to Darwin's theory, and which has found among -naturalists its most distinguished representative in Agassiz. His -celebrated work, "An Essay on Classification,"(5) which is entirely -opposed to Darwin's, and appeared almost at the same time, has -elaborated quite consistently, and to the utmost extent, these -anthropomorphic conceptions of the Creator. - -I maintain with regard to the much-talked-of "purpose in nature," that -it really has no existence but for those persons who observe phenomena -in animals and plants in the most superficial manner. Without going more -deeply into the matter, we can see at once that the rudimentary organs -are a formidable obstacle to this theory. And, indeed, everyone who -makes a really close study of the organization and mode of life of the -various animals and plants, and becomes familiar with the reciprocity or -interaction of the phenomena of life, and the so-called "economy of -nature," must necessarily come to the conclusion that this -"purposiveness" no more exists than the much-talked-of "beneficence" of -the Creator. These optimistic views have, unfortunately, as little real -foundation as the favourite phrase, the "moral order of the universe," -which is illustrated in an ironical way by the history of all nations. -The dominion of the "moral" popes, and their pious inquisition, in the -mediæval times, is not less significant of this than the present -prevailing militarism, with its "moral" apparatus of needle-guns and -other refined instruments of murder. - -If we contemplate the common life and the mutual relations between -plants and animals (man included), we shall find everywhere, and at all -times, the very opposite of that kindly and peaceful social life which -the goodness of the Creator ought to have prepared for his creatures--we -shall rather find everywhere a pitiless, most embittered _Struggle of -All against All_. Nowhere in nature, no matter where we turn our eyes, -does that idyllic peace, celebrated by the poets, exist; we find -everywhere a struggle and a striving to annihilate neighbours and -competitors. Passion and selfishness--conscious or unconscious--is -everywhere the motive force of life. The well-known words of the German -poet-- - - "Die Welt ist vollkommen überall - Wo der Mensch nicht hinkommt mit seiner Qual."[1] - -are beautiful, but, unfortunately, not true. Man in this respect -certainly forms no exception to the rest of the animal world. The -remarks which we shall have to make on the theory of "Struggle for -Existence" will sufficiently justify this assertion. It is, in fact, -Darwin who has placed this important point, in its high and general -significance, very clearly before our eyes, and the chapter in his -theory which he himself calls "Struggle for Existence" is one of the -most important parts of it. - -Whilst, then, we emphatically oppose the vital or teleological view of -animate nature which presents animal and vegetable forms as the -productions of a kind Creator, acting for a definite purpose, or of a -creative, natural force acting for a definite purpose, we must, on the -other hand, decidedly adopt that view of the universe which is called -the _mechanical_ or _causal_. It may also be called the _monistic_, or -_single-principle_ theory, as opposed to the _twofold principle_, or -_dualistic_ theory, which is necessarily implied in the teleological -conception of the universe. The mechanical view of nature has for many -years been so firmly established in certain domains of natural science, -that it is here unnecessary to say much about it. It no longer occurs to -physicists, chemists, mineralogists, or astronomers, to seek to find in -the phenomena which continually appear before them in their scientific -domain the action of a Creator acting for a definite purpose. They -universally, and without hesitation, look upon the phenomena which -appear in their different departments of study as the necessary and -invariable effects of physical and chemical forces which are inherent in -matter. Thus far their view is purely _materialistic_, in a certain -sense of that "word of many meanings." - -When a physicist traces the phenomena of motion in electricity or -magnetism, the fall of a heavy body, or the undulations in the waves of -light, he never, in the whole course of his research, thinks of looking -for the interference of a supernatural power. In this respect, Biology, -as the science of so-called "_animated_" natural bodies, was formerly -placed in sharp opposition to the above-mentioned inorganic natural -sciences (Anorganology). It is true modern Physiology, the science of -the phenomena of motion in animals and plants, has completely adopted -the mechanical view; but Morphology, the science of the forms of animals -and plants, has not been affected at all by it. Morphologists, in spite -of the position of physiology, have continued, as before, in opposition -to the mechanical view of functions, to look upon the forms of animals -and plants as something which cannot be at all explained mechanically, -but which must owe its origin necessarily to a higher, supernatural -creative power, acting for a definite purpose. - -In this general view it is quite indifferent whether the creative power -be worshipped as a personal god, or whether it be termed the power of -life (vis vitalis), or final cause (causa finalis). In any case, to -express it in one word, its supporters have recourse to a _miracle_ for -an explanation. They throw themselves into the arms of a poetic faith, -which as such can have no value in the domain of scientific knowledge. - -All that was done before Darwin, to establish a natural mechanical -conception of the origin of animals and plants, has been in vain, and -until his time no theory gained a general recognition. Darwin's theory -first succeeded in doing this, and thus has rendered an immense service. -For the idea of the _unity of organic and inorganic nature_ is now -firmly established; and that branch of natural science which had longest -and most obstinately opposed mechanical conception and explanation, -viz., the science of the structure of animate forms, is launched on to -identically the same road towards perfection as that along which all the -rest of the natural sciences are travelling. The unity of _all_ natural -phenomena is by Darwin's theory finally established. - -This unity of all nature, the animating of all matter, the -inseparability of mental power and corporeal substance, Goethe has -asserted in the words: "Matter can never exist and be active without -mind, nor can mind without matter." These first principles of the -mechanical conception of the universe have been taught by the great -monistic philosophers of all ages. Even Democritus of Abdera, the -immortal founder of the Atomic theory, clearly expressed them about 500 -years before Christ; but the great Dominican friar, Giordano Bruno, did -so even more explicitly. For this he was burnt at the stake, by the -Christian inquisition in Rome, on the 17th of Feb., 1600, on the same -day on which, 36 years before, Galileo, his great fellow-countryman and -fellow-worker, was born. Such men, who live and die for a great idea, -are usually stigmatized as "materialists"; but their opponents, whose -arguments were torture and the stake, are praised as "spiritualists." - -By the Theory of Descent we are for the first time enabled to conceive -of the unity of nature in such a manner that a mechanico-causal -explanation of even the most intricate organic phenomena, for example, -the origin and structure of the organs of sense, is no more difficult -(in a general way) than is the mechanical explanation of any physical -process; as, for example, earthquakes, the courses of the wind, or the -currents of the ocean. We thus arrive at the extremely important -conviction that _all natural bodies_ which are known to us are _equally -animated_, that the distinction which has been made between animate and -inanimate bodies does _not_ exist. When a stone is thrown into the air, -and falls to earth according to definite laws, or when in a solution of -salt a crystal is formed, the phenomenon is neither more nor less a -mechanical manifestation of life than the growth and flowering of -plants, than the propagation of animals or the activity of their senses, -than the perception or the formation of thought in man. This final -triumph of the monistic conception of nature constitutes the highest and -most general merit of the Theory of Descent, as reformed by Darwin. - - - - -CHAPTER II. - - SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT. - HISTORY OF CREATION ACCORDING TO LINNÆUS. - - - The Theory of Descent, or Doctrine of Filiation, as the - Monistic Explanation of Organic Natural Phenomena.--Its - Comparison with Newton's Theory of Gravitation.--Limits - of Scientific Explanation and of Human Knowledge in - general.--All Knowledge founded originally on Sensuous - Experience, _a posteriori_.--Transition of _a posteriori_ - knowledge, by Inheritance, into _a priori_ - knowledge.--Contrast between the Supernatural Hypotheses - of the Creation according to Linnæus, Cuvier, Agassiz, - and the Natural Theories of Development according to - Lamarck, Goethe, and Darwin.--Connection of the former - with the Monistic (mechanical), of the latter with the - Dualistic Conception of the Universe.--Monism and - Materialism.--Scientific and Moral Materialism.--The - History of Creation according to Moses.--Linnæus as the - Founder of the Systematic Description of Nature and - Distinction of Species.--Linnæus' Classification and - Binary Nomenclature.--Meaning of Linnæus' Idea of - Species.--His History of Creation.--Linnæus' view of the - Origin of Species. - - -The value which every scientific theory possesses is measured by the -number and importance of the objects which can be explained by it, as -well as by the simplicity and universality of the causes which are -employed in it as grounds of explanation. On the one hand, the greater -the number and the more important the meaning of the phenomena explained -by the theory, and the simpler, on the other hand, and the more general -the causes which the theory assigns as explanations, the greater is its -scientific value, the more safely we are guided by it, and the more -strongly are we bound to adopt it. - -Let us call to mind, for example, that theory which has ranked up to the -present time as the greatest achievement of the human mind--the Theory -of Gravitation, which Newton, two hundred years ago, established in his -Mathematical Principles of Natural Philosophy. Here we find that the -object to be explained is as large as one can well imagine. He undertook -to reduce the phenomena of the motion of the planets, and the structure -of the universe, to mathematical laws. As the most simple cause of these -intricate phenomena of motion, Newton established the law of weight or -attraction, the same law which is the cause of the fall of bodies, of -adhesion, cohesion, and many other phenomena. - -If we apply the same standard of valuation to Darwin's theory, we must -arrive at the conclusion that this theory, also, is one of the greatest -achievements of the human mind, and that it may be placed quite on a -level with Newton's Theory of Gravitation. Perhaps this opinion will -seem a little exaggerated, or at any rate very bold, but I hope in the -course of this treatise to convince the reader that this estimate is not -too high. In the preceding chapter, some of the most important and most -general phenomena in organic nature, which have been explained by -Darwin's theory, have been named. Among them are the variations in form -which accompany the individual development of organisms, most varied and -complicated phenomena, which until now presented the greatest -difficulties in the way of mechanical explanation, that is, in the -tracing of them to active causes. We have mentioned the _rudimentary -organs_, those exceedingly remarkable structures in animals and plants -which have no object and refute every teleological explanation seeking -for the final purpose of the organism. A great number of other phenomena -might have been mentioned, which are no less important, and are -explained in the simplest manner by Darwin's reformed Theory of Descent. -For the present I will only mention the phenomena presented to us by the -_geographical distribution of animals and plants_ on the surface of our -planet, as well as the _geological distribution of the extinct and -petrified organisms_ in the different strata of the earth's crust. These -important palæontological and geographical phenomena, which were -formerly only known to us as _facts_, are now traced to their active -_causes_ by the Theory of Descent. - -The same statement applies further to all the general laws of -_Comparative Anatomy_, especially to the great law of _division of -labour_ or _separation_ (polymorphism, or differentiation), a law which -determines the form or structure of human society, as well as the -organization of individual animals and plants. It is this law which -necessitates an ever _increasing variety_, as well as a _progressive -development_ of organic forms. This law of the division of labour has, -up to the present time, been only recognized as a fact, and it, like the -law of progressive development, or the law of progress which we perceive -active everywhere in the history of nations (as also in that of animals -and plants), is explained by Darwin's Doctrine of Descent. Then, if we -turn our attention to the great whole of organic nature, if we compare -all the individual groups of phenomena of this immense domain of life, -it cannot fail to appear, in the light of the Doctrine of Descent, no -longer as the ingeniously designed work of a Creator building up -according to a definite purpose, but as the necessary consequence of -active causes, which are inherent in the chemical combination of matter -itself, and in its physical properties. - -In fact, we can most positively assert, and I shall justify this -assertion in the course of these pages, that by the Doctrine of -Filiation, or Descent, we are enabled for the first time to reduce all -organic phenomena to a single law, and to discover a single active cause -for the infinitely intricate mechanism of the whole of this rich world -of phenomena. In this respect, Darwin's theory stands quite on a level -with Newton's Theory of Gravitation; indeed, it even rises higher than -Newton's theory! - -The grounds of explanation are equally simple in the two theories. In -explaining this most intricate world of phenomena, Darwin does not make -use of new or hitherto unknown properties of matter, nor does he, as one -might suppose, make use of discoveries of new combinations of matter or -of new forces of organization; but it is simply by extremely ingenious -combination, by the synthetic comprehension, and by the thoughtful -comparison of a number of well-known facts, that Darwin has solved the -"holy mystery" of the living world of forms. The consideration of the -interchanging relations which exist between two general properties of -organisms, viz., _Inheritance and Adaptation_, is what has here been of -the first importance. Merely by considering the relations between these -two vital actions or physiological functions of organisms, also further -by considering the reciprocal interaction which all animals and plants, -living in one and the same place, necessarily exert on one -another--solely by the correct estimate of these simple facts, and by -skilfully combining them, Darwin has succeeded in finding the true -active causes (causæ efficientes) of the immensely intricate world of -forms in organic nature. - -In any case we are in duty bound to accept this theory till a better one -be found, which will undertake to explain the same amount of facts in an -equally simple manner. Until now we have been in utter want of such a -theory. The fundamental idea that all different animal and vegetable -forms must be descended from a few or even from one single, most simple -primary form, was indeed not new. This idea was long since distinctly -formulated--first by the great Lamarck, at the beginning of our century. -But Lamarck in reality only expressed the hypothesis of the Doctrine of -Filiation, without establishing it by an explanation of the active -causes. And it is just the demonstration of these causes which marks the -extraordinary progress which Darwin's theory has made beyond that of -Lamarck. In the physiological properties of Inheritance and Adaptation -of organic matter, Darwin discovered the true cause of the genealogical -relationship of organisms. It was not possible for the genius of Lamarck -in his day to command that colossal material of biological facts which -has been collected by the patient zoological and botanical -investigations of the last fifty years, and which has been used by -Darwin as an overpowering apparatus of evidence. - -Darwin's theory is therefore not what his opponents frequently represent -it as being--an unwarranted hypothesis taken up at random. It is not for -zoologists or botanists to accept or reject this as an explanatory -theory, as they please; they are rather compelled and obliged to accept -it, according to the general principle observed in all natural sciences, -that we must accept and retain for the explanation of phenomena any -theory which, though it has only a feeble basis, is compatible with the -actual facts--until it is replaced by a better one. If we do not adopt -it, we renounce a scientific explanation of phenomena, and this is, in -fact, the position which many biologists still maintain. They look upon -the whole domain of animate nature as a perfect mystery, and upon the -origin of animals and plants, the phenomena of their development and -affinities, as quite inexplicable and miraculous; in fact, they will not -allow that there _can_ be a true understanding of them. - -Those opponents of Darwin who do not exactly wish to renounce a -scientific explanation are in the habit of saying, "Darwin's theory of -the common origin of the different species is only _one_ hypothesis; we -oppose to it _another_, the hypothesis that the individual animal and -vegetable species have not developed one from another by descent, but -that they have come into existence independently of one another, by a -still undiscovered law of nature." But as long as it is not shown how -this coming into existence is to be conceived of, and what that "law of -nature" is--as long as not even _probable_ grounds of explanation can be -brought forward to account for the independent coming into existence of -animal and vegetable species, so long this counter-hypothesis is in fact -no hypothesis, but an empty unmeaning phrase. Darwin's theory ought, -moreover, not to be called an hypothesis. For a scientific hypothesis is -a supposition, postulating the existence of unknown properties or -motional phenomena of natural bodies, which properties have not as yet -been observed by the experience of the senses. But Darwin's theory does -not assume such unknown conditions; it is based upon general properties -of organisms that have long been recognized, and--as has been -remarked--it is the exceedingly ingenious and comprehensive combination -of a number of phenomena which had hitherto stood isolated, which gives -the theory its extraordinarily great and intrinsic value. By it we are -for the first time in a position to demonstrate an active cause for all -the known morphological phenomena in the animal and vegetable kingdoms; -and, in fact, this cause is always one and the same, viz., the alternate -action of Adaptation and Inheritance, therefore a physiological, that -is, a physico-chemical or mechanical, relationship. For these reasons -the acceptance of the Doctrine of Filiation, as mechanically established -by Darwin, is a binding and unavoidable necessity for the whole domain -of zoology and botany. - -As, therefore, in my opinion the immense importance of Darwin's theory -lies in the fact that it has _mechanically explained those organic -phenomena of forms_ which had hitherto been unexplained, it is perhaps -necessary that I should here say a few words about the different ideas -connected with the word "explanation." It is very frequently said, in -opposition to Darwin's theory, that it does indeed explain those -phenomena by Inheritance and Adaptation, but that it does not at the -same time explain those properties of organic matter, and that therefore -we do not arrive at first causes. This objection is quite correct, but -it applies equally to _all_ explanations of phenomena. We _nowhere_ -arrive at a knowledge of first causes. The origin of every simple salt -crystal, which we obtain by evaporating its mother liquor, is no less -mysterious to us, as far as concerns its first cause, and in itself no -less incomprehensible than the origin of every animal which is developed -out of a simple cell. In explaining the most simple physical or chemical -phenomena, as the falling of a stone, or the formation of a chemical -combination, we arrive, by discovering and establishing the active -causes--for example, the gravitation or the chemical affinity--at other -remoter phenomena, which in themselves are mysterious. This arises from -the limitation or relativity of our powers of understanding. We must not -forget that human knowledge is absolutely limited, and possesses only a -relative extension. It is, in its essence, limited by the very nature of -our senses and of our brains. - -All knowledge springs from sensuous perceptions. In opposition to this -statement, the innate, _à priori_ knowledge of man may be brought up; -but we can see that the so-called _à priori_ knowledge can by Darwin's -theory be proved to have been acquired _à posteriori_, being based on -experience as its first cause. Knowledge which is based originally upon -purely empirical observations, and which is therefore a purely sensuous -experience, but has then been transmitted from generation to generation -by inheritance, appears in later generations as if it were independent, -innate, and _à priori_. In our late animal ancestors, all our so-called -"_à priori_ knowledge" was originally acquired _à posteriori_, and only -gradually became _à priori_ by inheritance. It is based in the first -instance upon experiences, and by the laws of Inheritance and Adaptation -we can positively prove that knowledge _à priori_ and knowledge _à -posteriori_ cannot rightly be placed in opposition, as is usually done. -On the contrary, sensuous experience is the original source of _all_ -knowledge. For this reason alone, all our knowledge is limited, and we -can never apprehend the _first causes_ of any phenomena. The force of -crystallization, the force of gravitation, and chemical affinity remain -in themselves just as incomprehensible as do Adaptation and Inheritance. - -Seeing that Darwin's theory explains from a single point of view the -totality of all those phenomena of which we have given a brief survey, -that it demonstrates one and the same quality of the organism as the -active cause in all cases, we must allow that it gives us for the -present _all_ that we can desire. Moreover, we have good reason to hope -that at some future time we shall learn to explain the first causes at -which Darwin has arrived, namely, the properties of Adaptation and -Inheritance; and that we shall succeed in discovering in the composition -of albuminous matter certain molecular relations as the remoter, simpler -causes of these phenomena. There is indeed no prospect of this in the -immediate future, and we content ourselves for the present with the -tracing back of organic phenomena to two mysterious properties, just as -in the case of Newton's theory we are satisfied with tracing the -planetary motions to the force of gravitation, which itself is likewise -a mystery to us and not cognizable in itself. - -Before commencing our principal task, which is the careful discussion of -the Doctrine of Descent, and the consequences that arise out of it, let -us take an historical retrospect of the most important and most widely -spread of those views, which before Darwin men had elaborated -concerning organic creation, and the coming into existence of the many -animal and vegetable species. In doing this I have no intention of -entertaining the reader with a statement of all the innumerable stories -about the creation which have been current among the different human -species, races, or tribes. However interesting and gratifying this task -would be, from an ethnographical point of view, as well as in a history -of civilization, it would lead us here much too far from our subject. -Besides, the great majority of all these legends about creation bear too -clearly the stamp of arbitrary fiction, and of a want of a close -observance of nature, to be of interest in a scientific treatment of the -history of creation. I shall therefore only select the Mosaic history -from among those that are not founded on scientific investigation, on -account of the unparalleled influence which it has gained in the western -civilized world; and then I shall immediately take up the scientific -hypothesis about creation, which originated with Linnæus as late as the -commencement of last century. - -All the different conceptions which man has ever formed about the coming -into existence of the different animal and vegetable species may -conveniently be divided into two great contrasted groups--the natural -and supernatural histories of creation. - -These two groups, on the whole, correspond with the two different -principal forms of the human notions of the universe which we have -already contrasted as the _monistic and the dualistic_ conception of -nature. In the usual dualistic or teleological (vital) conception of the -universe, organic nature is regarded as the purposely executed -production of a Creator working according to a definite plan. Its -adherents see in every individual species of animal and plant an -"embodied creative thought," the material expression of a _definite -first cause_ (causa finalis) acting for a set purpose. They must -necessarily assume supernatural (not mechanical) processes for the -origin of organisms. With justice, we may therefore designate their -scheme of the world's growth as the _Supernatural History of Creation_. -Among all such teleological histories of creation, that of Moses has -gained the greatest influence, since even so distinguished a naturalist -as Linnæus has claimed admittance for it in Natural Science. Cuvier's -and Agassiz's views of creation also belong to this group, as do in fact -those of the great majority of both scientific and unscientific men. - -On the other hand, the theory of development carried out by Darwin, -which we shall have to treat of here as the _Non-miraculous_ or _Natural -History of Creation_, and which has already been put forward by Goethe -and Lamarck, must, if carried out logically, lead to the monistic or -mechanical (causal) conception of the universe. In opposition to the -dualistic or teleological conception of nature, our theory considers -organic, as well as inorganic, bodies to be the necessary products of -natural forces. It does not see in every individual species of animal -and plant the embodied thought of a personal Creator, but the expression -for the time being of a mechanical process of development of matter, the -expression of a necessarily active cause, that is, of a mechanical cause -(causa efficiens). Where teleological Dualism seeks the arbitrary -thoughts of a capricious Creator in the miracles of creation, causal -Monism finds in the process of development the necessary effects of -eternal immutable laws of nature. - -The Monism here maintained by us is often considered identical with -Materialism. Now, as Darwinism, and in fact the whole theory of -development, has been designated as "_materialistic_," I cannot avoid -here at once guarding myself against this ambiguous word, and against -the malice with which, in certain quarters, it is employed to stigmatize -our doctrine. - -By the word "_Materialism_," two completely different things are very -frequently confounded and mixed up, which in reality have nothing -whatever to do with each other, namely, scientific and moral -materialism. Scientific materialism, which is identical with our Monism, -affirms in reality no more than that everything in the world goes on -naturally--that every effect has its cause, and every cause its effect. -It therefore assigns to causal law--that is, the law of a necessary -connection between cause and effect--its place over the entire series of -phenomena that can be known. At the same time, scientific materialism -positively rejects every belief in the miraculous, and every conception, -in whatever form it appears, of supernatural processes. Accordingly, -nowhere in the whole domain of human knowledge does it recognize real -metaphysics, but throughout only physics; through it the inseparable -connection between matter, form, and force becomes self evident. This -scientific materialism has long since been so universally acknowledged -in the wide domain of inorganic science, in Physics and Chemistry, in -Mineralogy and Geology, that no one now doubts its sole authority. But -in Biology, or Organic science, the case is very different; here its -value is still continually a matter of dispute in many quarters. There -is, however, nothing else which can be set up against it, excepting the -metaphysical spectre of a vital power, or empty theological dogma. If we -can prove that all nature, so far as it can be known, is only _one_, -that the same "great, eternal, iron laws" are active in the life of -animals and plants, as in the growth of crystals and in the force of -steam, we may with reason maintain the monistic or mechanical view of -things throughout the domain of Biology--in Zoology and Botany--whether -it be stigmatized as "materialism" or not. In such a sense all exact -science, and the law of cause and effect at its head, is purely -materialistic. - -_Moral_, or _ethical Materialism_, is something quite distinct from -scientific materialism, and has nothing whatever in common with the -latter. This real materialism proposes no other aim to man in the course -of his life than the most refined possible gratification of his senses. -It is based on the delusion that purely material enjoyment can alone -give satisfaction to man; but as he can find that satisfaction in no one -form of sensuous pleasure, he dashes on weariedly from one to another. -The profound truth that the real value of life does not lie in material -enjoyment, but in moral action--that true happiness does not depend upon -external possessions, but only in a virtuous course of life--this is -unknown to ethical materialism. We therefore look in vain for such -materialism among naturalists and philosophers, whose highest happiness -is the intellectual enjoyment of Nature, and whose highest aim is the -knowledge of her laws. We find it in the palaces of ecclesiastical -princes, and in those hypocrites who, under the outward mask of a pious -worship of God, solely aim at hierarchical tyranny over, and material -spoliation of, their fellow-men. Blind to the infinite grandeur of the -so-called "raw material," and the glorious world of phenomena arising -from it--insensible to the inexhaustible charms of Nature, and without a -knowledge of her laws--they stigmatize all natural science, and the -culture arising from it, as sinful "materialism," while really it is -this which they themselves exhibit in a most shocking form. Satisfactory -proofs of this are furnished, not only by the whole history of the -Catholic Popes, with their long series of crimes, but also by the -history of the morals of orthodoxy in every form of religion. - -In order, then, to avoid in future the usual confusion of this utterly -objectionable Moral Materialism with our Scientific Materialism, we -think it necessary to call the latter either _Monism_ or _Realism_. The -principle of this _Monism_ is the same as what Kant terms the -"principle of mechanism," and of which he expressly asserts, that -_without it there can be no natural science at all_. This principle is -quite inseparable from our Non-miraculous History of Creation, and -characterizes it as opposed to the teleological belief in the miracles -of a Supernatural History of Creation. - -Let us now first of all glance at the most important of all the -supernatural histories of creation, I mean that of Moses, as it has been -handed down to us in the Bible, the ancient document of the history and -laws of the Jewish people. The Mosaic history of creation, since in the -first chapter of Genesis it forms the introduction to the Old Testament, -has enjoyed, down to the present day, general recognition in the whole -Jewish and Christian world of civilization. Its extraordinary success is -explained not only by its close connection with Jewish and Christian -doctrines, but also by the simple and natural chain of ideas which runs -through it, and which contrasts favourably with the confused mythology -of creation current among most of the other ancient nations. First the -Lord God creates the earth as an inorganic body; then he separates light -from darkness, then water from the dry land. Now the earth has become -inhabitable for organisms, and plants are first created, animals -later--and among the latter the inhabitants of the water and the air -first, afterwards the inhabitants of the dry land. Finally God creates -man, the last of all organisms, in his own image, and as the ruler of -the earth. - -Two great and fundamental ideas, common also to the non-miraculous -theory of development, meet us in this Mosaic hypothesis of creation, -with surprising clearness and simplicity--the idea of separation or -_differentiation_, and the idea of progressive development or -_perfecting_. Although Moses looks upon the results of the great laws of -organic development (which we shall later point out as the necessary -conclusions of the Doctrine of Descent) as the direct actions of a -constructing Creator, yet in his theory there lies hidden the ruling -idea of a progressive development and a differentiation of the -originally simple matter. We can therefore bestow our just and sincere -admiration on the Jewish lawgiver's grand insight into nature, and his -simple and natural hypothesis of creation, without discovering in it a -so-called "divine revelation." That it cannot be such is clear from the -fact that two great fundamental errors are asserted in it, namely, -first, the _geocentric_ error that the earth is the fixed central point -of the whole universe, round which the sun, moon, and stars move; and -secondly, the _anthropocentric_ error, that man is the premeditated aim -of the creation of the earth, for whose service alone all the rest of -nature is said to have been created. The former of these errors was -demolished by Copernicus' System of the Universe in the beginning of the -16th century, the latter by Lamarck's Doctrine of Descent in the -beginning of the 19th century. - -Although the geocentric error of the Mosaic history was demonstrated by -Copernicus, and thereby its authority as an absolutely perfect divine -revelation was destroyed, yet it has maintained, down to the present -day, such influence, that it forms in many wide circles the principle -obstacle to the adoption of a natural theory of development. Even in our -century, many naturalists, especially geologists, have tried to bring -the Mosaic theory into harmony with the recent results of natural -science, and have, for example, interpreted Moses' seven days of -creation as seven great geological periods. However, all these ingenious -attempts at interpretation have so utterly failed, that they require no -refutation here. The Bible is no scientific book, but consists of -records of the history, the laws, and the religion of the Jewish people, -the high merit of which, as a history of civilization, is not impaired -by the fact that in all scientific questions it has no commanding -importance, and is full of gross errors. - -We may now make a great stride over more than three thousand years, from -Moses, who died about the year 1480 before Christ, to Linnæus, who was -born in the year 1707 after Christ. During this whole period no history -of creation was brought forward that gained any lasting importance, or -the closer examination of which would here be of any interest. Indeed, -during the last fifteen hundred years, since Christianity gained its -supremacy, the Mosaic history of creation, together with the dogmas -connected with it, has become so generally predominant, that the 19th -century is the first that has dared positively to rise against it. Even -the great Swedish naturalist, Linnæus, the founder of modern natural -history, linked his System of Nature most closely to the Mosaic history -of creation. - -The extraordinary progress which Charles Linnæus made in the so-called -descriptive natural sciences, consists, as is well known, in his having -established a system of nomenclature of animals and plants, which he -carried out in a manner so perfectly logical and consistent, that down -to the present day it has remained in many respects the standard for all -succeeding naturalists engaged in the study of the forms of animals and -plants. Although Linnæus' system was artificial, although in classifying -animal and vegetable species he only sought and employed single parts as -the foundation for his divisions, it has, nevertheless, gained the -greatest success; firstly, in consequence of its being carried out -consistently, and secondly, by its nomenclature of natural bodies, which -has become extremely important, and at which we must here briefly -glance. - -Before Linnæus' time, many vain attempts had been made to throw light -upon the endless chaos of different animal and vegetable forms (then -known) by adopting for them suitable names and groupings; but Linnæus, -by a happy hit, succeeded in accomplishing this important and difficult -task, when he established the so-called "_binary nomenclature_." The -binary nomenclature, or the twofold designation, as Linnæus first -established it, is still universally applied by all zoologists and -botanists, and will, no doubt, maintain itself, for a long time to come, -with undiminished authority. It consists in this, that every species of -animal and plant is designated by two names, which stand to each other -in the same relation as do the christian and surnames of a man. The -special name which corresponds with the christian name, and expresses -the idea of "a species," serves as the common designation of all -individual animals or plants, which are equal in all essential matters -of form, and are only distinguished by quite subordinate features. The -more general name, on the other hand, corresponding with the surname, -and which expresses the idea of a genus, serves for the common -designation of all the most nearly similar kinds or species. - -According to Linnæus' plan, the more general and comprehensive generic -name is written first; the special subordinate name of the species -follows it. Thus, for example, the common cat is called Felis domestica; -the wild cat, Felis catus; the panther, Felis pardus; the jaguar, Felis -onca; the tiger, Felis tigris; the lion, Felis leo. All these six kinds -of animals of prey are different species of one and the same -genus--Felis. Or, to add an example from the vegetable kingdom, -according to Linnæus' designation the pine is Pinus abies; the fir, -Pinus picea; the larch, Pinus larix; the Italian pine, Pinus pinea; the -Siberian stone pine, Pinus cembra; the knee timber, Pinus mughus; the -common pine, Pinus silvestris. All these seven kinds of pines are -different species of one and the same genus--Pinus. - -Perhaps this advance made by Linnæus may seem to some only of -subordinate importance in the practical distinction and designation of -the variously formed organisms. But in reality it was of the very -greatest importance, both from a practical and theoretical point of -view. For now, for the first time, it became possible to arrange the -immense mass of different organic forms according to their greater or -less degree of resemblance, and to obtain an easy survey of the general -outlines of such a "system." Linnæus facilitated the tabulation and -survey of this "system" of plants and animals still more by placing -together the most nearly similar genera into so-called orders (ordines); -and by uniting the most nearly similar orders into still more -comprehensive main divisions or classes. Thus, according to Linnæus, -each of the two organic kingdoms were broken up into a number of -classes, the vegetable kingdom into twenty-four, and the animal kingdom -into six. Each class again contains several orders. Every single order -may contain a number of genera, and, again, every single genus several -species. - -Valuable as was Linnæus' binary nomenclature in a _practical_ way, in -bringing about a comprehensive systematic distinction, designation, -arrangement, and division of the organic world of forms, yet the -incalculable _theoretical_ influence which it gained forthwith in -relation to the history of creation was no less important. Even now all -the important fundamental questions as to the history of creation turn -finally upon the decision of the very remote and unimportant question, -_What really are kinds or species?_ Even now the _idea of organic -species_ may be termed the central point of the whole question of -creation, the disputed centre, about the different conceptions of which -Darwinists and Anti-Darwinists fight. - -According to Darwin's opinion, and that of his adherents, the different -species of one and the same genus of animals and plants are nothing else -than differently developed descendants of one and the same original -primary form. The different kinds of pine mentioned above would -accordingly have originated from a single primæval form of pine. In like -manner the origin of all the species of cat mentioned above would be -traced to a single common form of Felis, the ancestor of the whole -genus. But further, in accordance with the Doctrine of Descent, all the -different genera of one and the same order ought also to be descended -from one common primary ancestor, and so, in like manner, all orders of -a class from a single primary form. - -On the other hand, according to the idea of Darwin's opponents, all -species of animals and plants are quite independent of each other, and -only the individuals of each species have originated from a single -primary form. But if we ask them how they conceive these original -primary forms of each species to have come into existence, they answer -with a leap into the incomprehensible, "They were created." - -Linnæus himself defined the idea of species in this manner by saying, -"There are as many different species as there were different forms -created in the beginning by the infinite Being." ("Species tot sunt -diversæ, quot diversas formas ab initio creavit infinitum ens.") In this -respect, therefore, he follows most closely the Mosaic history of -creation, which in the same way maintains that animals and plants were -created "each one after its kind." Linnæus, accepting this, held that -originally of each species of animals and plants either a single -individual or a pair had been created; in fact a pair, or, as Moses -says, "a male and a female" of those species which have separate sexes, -but of those species in which each individual combines both sexual -organs (hermaphrodites), as for instance the earthworm, the garden and -vineyard snails, as well as the great majority of plants, a single -individual. - -Linnæus further follows the Mosaic legend in regard to the flood, by -supposing that the great general flood destroyed all existing organisms, -except those few individuals of each species (seven pairs of the birds -and of clean animals, one pair of unclean animals) which Noah saved in -the ark, and which were placed again on land, on Mount Ararat, after the -flood had subsided. He tried to explain the geographical difficulty of -the living together of the most different animals and plants, as -follows: Mount Ararat, in Armenia, being situated in a warm climate, and -rising over 16,000 feet in height, combines in itself the conditions for -a temporary common abode of such animals as live in different zones. -Accordingly, animals accustomed to the polar regions could climb up the -cold mountain ridges, those accustomed to a warm climate could go down -to the foot of the mountain, and the inhabitants of a temperate zone -could remain midway up the mountain. From this point it was possible for -them to spread north and south over the earth. - -It is scarcely necessary to remark that this Linnæan hypothesis of -creation, which evidently was intended to harmonize most closely with -the prevailing belief in the Bible, requires no serious refutation. When -we consider Linnæus' clearness and sagacity in other matters, we may -doubt whether he believed it himself. As to the simultaneous origin of -all individuals of each species from one pair of ancestors respectively -(or in the case of the hermaphrodite species, from one original -hermaphrodite), it is clearly quite untenable; for, apart from other -reasons, in the first days after the creation, the few animals of prey -would have sufficed to have utterly demolished all the herbivorous -animals, as the herbivorous animals must have destroyed the few -individuals of the different species of plants. The existence of such an -equilibrium in the economy of nature as obtains at present cannot -possibly be conceived, if only one individual of each species, or only -one pair, had originally and simultaneously been created. - -Moreover, how little importance Linnæus himself attached to this -untenable hypothesis of creation is clear, among other things, from the -fact that he recognized _Hybridism_ (crossing) as a source of the -production of new species. He assumed that a great number of independent -new species had originated by the interbreeding of two different -species. Indeed, such hybrids are not at all rare in nature, and it is -now proved that a great number of species, for example, of the genus -Rubus (bramble), mullen (Verbascum), willow (Salix), thistle (Cirsium), -are hybrids of different species of these genera. We also know of -hybrids between hares and rabbits (two species of the genus Lepus), -further of hybrids between different species of dog (genus Canis), etc., -which can be propagated as independent species. - -It is certainly very remarkable that Linnæus asserted the physiological -(therefore mechanical) origin of new species in this process of -hybridism. It clearly stands in direct opposition to the supernatural -origin of the other species by creation, which he accepted as put -forward in the Mosaic account. The one set of species would therefore -have originated by dualistic (teleological) creation, the other by -monistic (mechanical) development. - -The great and well merited authority which Linnæus gained by his -systematic classification and by his other services to Biology, was -clearly the reason why his views of creation also remained, throughout -the whole of the last century, undisputed and generally recognized. If -throughout systematic Zoology and Botany the distinctions, -classification, and designations of species, introduced by Linnæus, and -the dogmatic ideas connected therewith had not been maintained--more or -less unaltered--we should be at a loss to understand how his idea of an -independent creation of single species could have stood, by itself down -to the present day. It is only owing to his great authority, and through -his attaching himself to the prevailing Biblical belief, that his -hypothesis of creation has retained its position so long. - - - - -CHAPTER III. - -THE HISTORY OF CREATION ACCORDING TO CUVIER AND AGASSIZ. - - - General Theoretical Meaning of the Idea of - Species.--Distinction between the Theoretical and - Practical Definition of the Idea of Species.--Cuvier's - Definition of Species.--Merits of Cuvier as the Founder - of Comparative Anatomy.--Distinction of the Four - Principal Forms (types or branches) of the Animal - Kingdom, by Cuvier and Bär.--Cuvier's Services to - Palæontology.--His Hypothesis of the Revolutions of our - Globe, and the Epochs of Creation separated by - them.--Unknown Supernatural Causes of the Revolutions, - and the subsequent New Creations.--Agassiz's Teleological - System of Nature.--His Conception of the Plan of - Creation, and its six Categories (groups in - classification).--Agassiz's Views of the Creation of - Species.--Rude Conception of the Creator as a man-like - being in Agassiz's Hypothesis of Creation.--Its internal - Inconsistency and Contradictions with the important - Palæontological Laws discovered by Agassiz. - - -The real matter of dissension in the contest carried on by naturalists -as to the origin of organisms, their creation and development, lies in -the conceptions which are entertained about the _nature of species_. -Naturalists either agree with Linnæus, and look upon the different -species as distinct forms of creation, independent of one another, or -they assume with Darwin their blood-relationship. If we share Linnæus' -view (which was discussed in our last chapter), that the different -organic species came into existence independently--that they have no -blood-relationship--we are forced to admit that they were created -independently, and we must either suppose that every single organic -individual was a special act of creation (to which surely no naturalist -will agree), or we must derive all individuals of every species from a -single individual, or from a single pair, which did not arise in a -natural manner, but was called into being by command of a Creator. In so -doing, however, we turn aside from the safe domain of a rational -knowledge of nature, and take refuge in the mythological belief in -miracles. - -If, on the other hand, with Darwin, we refer the similarity of form of -the different species to real blood-relationship, we must consider all -the different species of animals and plants as the altered descendants -of one or a few most simple original forms. Viewed in this way, the -Natural System of organisms (that is, their tree-like and branching -arrangement and division into classes, orders, families, genera, and -species) acquires the significance of a real genealogical tree, whose -root is formed by those original archaic forms which have long since -disappeared. But a truly natural and consistent view of organisms can -assume no supernatural act of creation for even those simplest original -forms, but only a coming into existence by _spontaneous generation_[2] -(archigony, or generatio spontanea). From Darwin's view of the nature of -species, we arrive therefore at a _natural theory of development_; but -from Linnæus' conception of the idea of species, we must assume a -_supernatural dogma of creation_. - -Most naturalists after Linnæus, whose great services in -systematic and descriptive natural history won for him such high -authority, followed in his footsteps, and without further inquiry into -the origin of organization, they assumed, in the sense of Linnæus, an -independent creation of individual species, in conformity with the -Mosaic account of creation. The foundation of their conception was based -upon Linnæus' words: "There are as many different species as there were -different forms created in the beginning by the Infinite Being." We must -here remark at once, without going further into the definition of -species, that all zoologists and botanists in their classificatory -systems, in the practical distinction and designation of species of -animals and plants, never troubled, or even could trouble, themselves in -the slightest degree about this assumed creation of the parent forms. In -reference to this, one of our first zoologists, the ingenious Fritz -Müller, makes the following striking observation: "Just as in Christian -countries there is a catechism of morals, which every one knows by -heart, but which no one considers it his duty to follow, or expects to -see followed by others,--so zoology also has its dogmas, which are just -as generally professed as they are denied in practice." (Für Darwin, p. -71.)(16) - -Linnæus' venerated dogma of species is just such an irrational dogma, -and for that very reason it is powerful. Although most naturalists -blindly submitted to it, yet they were, of course, never in a position -to demonstrate the descent of individuals belonging to one species from -the common, originally created, primitive form. Zoologists and -botanists, in their systems of nomenclature, confined themselves -entirely to the similarity of forms, in order to distinguish and name -the different species. They placed in one species all organic -individuals which were very similar, or almost identical in form, and -which could only be distinguished from one another by very unimportant -differences. On the other hand, they considered as different species -those individuals which presented more essential or more striking -differences in the formation of their bodies. But of course this opened -the flood-gates to the most arbitrary proceedings in the systematic -distinctions of species. For as all the individuals of one species are -never completely alike in all their parts, but as every species varies -more or less, no one could point out which degree of variation -constituted a really "good species," or which degree indicated a "mere -variety." - -This dogmatic conception of the idea of species, and the arbitrary -proceedings connected with it, necessarily led to the most perplexing -contradictions, and to the most untenable suppositions. This is clearly -demonstrable in the case of the celebrated Cuvier (born in 1769), who -next to Linnæus has exercised the greatest influence on the study of -zoology. In his conception and definition of the idea of species, he -agreed on the whole with Linnæus, and shared also his belief in an -independent creation of individual species. Cuvier considered their -immutability of such importance that he was led to the foolish -assertion--"The immutability of species is a necessary condition of the -existence of scientific natural history." As Linnæus' definition of -species did not satisfy him, he made an attempt to give a more exact -and, for systematic practice, a more useful definition, in the following -words: "All those individual animals and plants belong to one species -which can be proved to be either descended from one another, or from -common ancestors, or which are as similar to these as the latter are -among themselves." - -In dealing with this matter, Cuvier reasoned in the following -manner:--"In those organic individuals, of which we know that they are -descended from one and the same common form of ancestors--in which, -therefore, their common ancestry is empirically proved--there can be no -doubt that they belong to one species, whether they differ much or -little from one another, or whether they are almost alike or very -unlike. Moreover, all those individuals also belong to this species -which differ no more from the latter (those proved to be derived from a -common stock) than these differ from one another." In a closer -examination of this definition of species given by Cuvier, it becomes at -once evident that it is neither theoretically satisfactory nor -practically applicable. Cuvier, with this definition, began to move in -the same circle in which almost all subsequent definitions of species -have moved, through the assumption of their immutability. - -Considering the extraordinary authority which George Cuvier has gained -in the science of organic nature, and in consequence of the almost -unlimited supremacy which his views exercised in zoology, during the -first half of our century, it seems appropriate here to examine his -influence a little more closely. This is all the more necessary as we -have to combat, in Cuvier, the most formidable opponent to the Theory of -Descent and the monistic conception of nature. - -One of the many and great merits of Cuvier is that he stands forth as -the founder of Comparative Anatomy. While Linnæus established the -distinction of species, genera, orders, and classes mostly upon external -characters, and upon separate and easily discoverable signs in the -number, size, place, and form of individual organic parts of the body, -Cuvier penetrated much more deeply into the essence of organization. He -demonstrated great and wide differences in the inner structure of -animals, as the real foundation of a scientific knowledge and -classification of them. He distinguished natural families in the classes -of animals, and established his natural system of the animal kingdom on -their comparative anatomy. - -The progress from Linnæus' artificial system to Cuvier's natural system -was exceedingly important. Linnæus had arranged all animals in a single -series, which he divided into six classes, two classes of Invertebrate, -and four classes of Vertebrate animals. He distinguished these -artificially, according to the nature of their blood and heart. Cuvier, -on the other hand, showed that in the animal kingdom there were four -great natural divisions to be distinguished, which he termed Principal -Forms, or General Plans, or Branches of the animal kingdom -(Embranchments), namely--1. The Vertebrate animals (Vertebrata); 2. The -Articulate animals (Articulata); 3. The Molluscous animals (Mollusca); -and 4. The Radiate animals (Radiata). He further demonstrated that in -each of these four branches a peculiar plan of structure or type was -discernible, distinguishing each branch from the three others. In the -Vertebrate animals it is distinctly expressed by the form of the -skeleton, or bony framework, as also by the structure and position of -the dorsal nerve-chord, apart from many other peculiarities. The -Articulate animals are characterized by their ventral nerve-chord and -their dorsal heart. In Molluscs the sack-shaped and non-articulate body -is the distinguishing feature. The Radiate animals, finally, differ -from the three other principal forms by their body being the combination -of four or more main sections united in the form of radii (antimera). - -The distinction of these four principal forms of animals, which has -become extremely productive in the development of zoology, is commonly -ascribed entirely to Cuvier. However, the same thought was expressed -almost simultaneously, and independently of Cuvier, by Bär, one of the -greatest naturalists, and still living, who did the most eminent service -in the study of animal development. Bär showed that in the development -of animals, also, four different main forms (or types) must be -distinguished.(20) These correspond with the four plans of structure in -animals, which Cuvier distinguished on the ground of comparative -anatomy. Thus, for example, the individual development of all Vertebrate -animals agrees, from the commencement, so much in its fundamental -features that the germs or embryos of different Vertebrate animals (for -example, of reptiles, birds, and mammals) in their earlier stages cannot -be distinguished at all. It is only at a late stage of development that -there gradually appear the more marked differences of form which -separate those different classes and orders from one another. The plan -of structure, which shows itself in the individual development of -Articulate animals (insects, spiders, crabs), is from the beginning -essentially the same in all Articulate animals, but different from that -of all Vertebrate animals. The same holds good, with certain -limitations, in Molluscous and Radiated animals. - -Neither Bär, who arrived at the distinction of the four animal types or -principal forms through the history of the individual development -(Embryology), nor Cuvier, who arrived at the same conclusion by means -of comparative anatomy, recognized the true cause of this difference. -This is disclosed to us by the Theory of Descent. The wonderful and -astonishing similarity in the inner organization and in the anatomical -relations of structure, and the still more remarkable agreement in the -embryonic development of all animals belonging to one and the same type -(for example, to the branch of the Vertebrate animals), is explained in -the simplest manner by the supposition of their common descent from a -single primary original form. If this view is not accepted, then the -complete agreement of the most different Vertebrate animals, in their -inner structure and their manner of development, remains perfectly -inexplicable. In fact it can only be explained by the law of -_inheritance_. - -Next to the comparative anatomy of animals and the systematic zoology -founded anew by it, it was specially to the science of petrifactions, or -Palæontology, that Cuvier rendered great service. We must draw special -attention to this, because these very palæontological views, and the -geological ideas connected with them, were held almost universally in -the highest esteem during the first half of the present century, and -caused the greatest hindrance to the working out of a truly natural -history of creation. - -Petrifactions, the scientific study of which Cuvier promoted at the -beginning of our century in a most extensive manner, and established -quite anew for the Vertebrate animals, play one of the most important -parts in the "non-miraculous history of creation." For these remains and -impressions of extinct animals and plants, preserved to us in a -petrified condition, are the true "monuments of the creation," the -infallible and indisputable records which fix the correct history of -organisms upon an irrefragable foundation. All petrified or fossil -remains and impressions tell us of the forms and structure of such -animals and plants as are either the progenitors and ancestors of the -present living organisms, or they are the representatives of extinct -collateral lines, which, together with the present living organisms, -branched off from a common stem. - -These inestimable records of the history of creation throughout a long -period played a subordinate part in science. Their true nature was -indeed correctly understood, even more than five hundred years before -Christ, by the great Greek philosopher, Xenophanes of Colophon, the same -who founded the so-called Eleatic philosophy, and who was the first to -demonstrate with convincing precision that all conceptions of personal -gods result in more or less rude anthropomorphism. - -Xenophanes for the first time, asserted that the fossil impressions of -animals and plants were real remains of formerly living creatures, and -that the mountains in whose rocks they were found must at an earlier -date have stood under water. But although other great philosophers of -antiquity, and among them Aristotle, also possessed this true knowledge, -yet throughout the illiterate Middle Ages, and even with some -naturalists of the last century, the idea prevailed that petrifactions -were so-called freaks of nature (lusus naturæ), or products of an -unknown formative power or instinct of nature (nisus formativus, vis -plastica). Respecting the nature of this mysterious and mystic creative -power, the strangest ideas were formed. Some believed that this -constructive power--the same to which they also ascribed the coming -into existence of the present species of animals and plants--had made -numerous attempts to create organisms of different forms, but that these -attempts had only partially succeeded, had often failed, and that -petrifactions were nothing more than such unsuccessful attempts. -According to others, petrifactions originated from the influence of the -stars upon the interior of the earth. - -Others, again, had the still cruder notion that the Creator had first -made models (out of mineral substances--for example, of gypsum or clay) -of those forms of animals and plants which he afterwards executed in -organic substances, and into which he breathed his living breath; -petrifactions were accordingly such rude inorganic models. Even as late -as the last century these crude ideas prevailed, and it was assumed, for -example, that there existed a special "seminal air," which was said to -penetrate into the earth with the water, and by fructifying the stones -formed petrifactions or "stony flesh" (caro fossilis). - -It took a very long time before the simple and natural view was -accepted, namely, that petrifactions are in reality nothing but what -they appear to simple observation--the indestructible remains of extinct -organisms. It is true the celebrated painter, Leonardo da Vinci, in the -15th century, ventured to assert that the mud which was constantly -deposited by water was the cause of petrifactions, as it surrounded the -indestructible shells of mussels and snails which lay at the bottom of -the waters, and gradually turned them into solid stone. The same idea -was maintained in the 16th century by a Parisian potter, Palissy by -name, who became celebrated on account of his invention of china. -However, the so-called "professional men" were very far from paying any -regard to these correct assertions of a simple and healthy human -understanding; it was not till the end of the last century that it was -generally accepted, in consequence of the foundation of the Neptunian -geology by Werner. - -The foundation of a more strictly scientific palæontology, however, -belongs to the beginning of our century, when Cuvier published his -classic researches on petrified Vertebrate animals, and when his great -opponent, Lamarck, made known his remarkable investigations on fossil -Invertebrate animals, especially on petrified snails and clams. In -Cuvier's celebrated work "On the Fossil Bones" of Vertebrate -animals--principally of mammals and reptiles--we see that he had already -arrived at the knowledge of some very important and general -palæontological laws, which are of great consequence to the history of -creation. Foremost among them stands the assertion that the extinct -species of animals, whose remains we find petrified in the different -strata of the earth's crust, lying one above another, differ all the -more strikingly from the still living kindred species of animals the -deeper those strata lie--in other words, the earlier the animals lived -in past ages. In fact, in every perpendicular section of the stratified -crust of the earth we find that the different strata, deposited by the -water in a certain historical succession, are characterized by different -petrifactions, and that these extinct organisms become more like those -of the present day the higher the strata lie; in other words, the more -recent the period in the earth's history in which they lived, died, and -became encrusted by the deposited and hardened strata of mud. - -However important this general observation of Cuvier's was in one -sense, yet in another it became to him the source of a very serious -error. For as he considered the characteristic petrifactions of each -individual group of strata (which had been deposited during one main -period of the earth's history) to be entirely different from those of -the strata lying above or below, and as he erroneously believed that one -and the same species of animal was never found in two succeeding groups -of strata, he arrived at the false idea, which was accepted as a law by -most subsequent naturalists, that a series of quite distinct periods of -creation had succeeded one another. Each period was supposed to have had -its special animal and vegetable world, each its peculiar specific Fauna -and Flora. - -Cuvier imagined that the whole history of the earth's crust, since the -time when living creatures had first appeared on the surface, must be -divided into a number of perfectly distinct periods, or divisions of -time, and that the individual periods must have been separated from one -another by peculiar revolutions of an unknown nature (cataclysms, or -catastrophes). Each revolution was followed by the utter annihilation of -the till then existing animals and plants, and after its termination a -completely new creation of organic forms took place. A new world of -animals and plants, absolutely and specifically distinct from those of -the preceding historical periods, was called into existence at once, and -now again peopled the globe for thousands of years, till it again -perished suddenly in the crash of a new revolution. - -About the nature and causes of these revolutions, Cuvier expressly said -that no idea could be formed, and that the present active forces in -nature were not sufficient for their explanation. Cuvier points out four -active causes as the natural forces, or mechanical agents, at present -constantly but slowly at work in changing the earth's surface: first, -_rain_, which washes down the steep mountain slopes and heaps up débris -at their foot; secondly, _flowing waters_, which carry away this débris -and deposit it as mud in stagnant waters; thirdly, the sea, whose -breakers gnaw at the steep _sea_ coasts, and throw up "dunes" on the -flat sea margins; finally and fourthly, _volcanos_, which break through -and heave up the strata of the earth's hardened crust, and pile up and -scatter about the products of their eruptions. Whilst Cuvier recognizes -the constant slow transformation of the present surface of the earth by -these four mighty causes, he asserts at the same time that they would -not have sufficed to effect the revolutions of the remote ages, and that -the anatomical structure of the earth's surface cannot be explained by -the necessary action of those mechanical agents: the great and -marvellous revolutions of the whole earth's surface must, according to -him, have been rather the effects of very peculiar causes, completely -unknown to us; the usual thread of development was broken by them, and -the course of nature altered. - -These views Cuvier explained in a special work "On the Revolutions of -the Earth's Surface, and the Changes which they have wrought in the -Animal World." They were maintained, and generally accepted for a long -time, and became the greatest obstacle to the development of a natural -history of the creation. For if such all-destructive revolutions had -actually occurred, of course a continuity of the development of species, -a connecting thread in the organic history of the earth, could not be -admitted at all, and we should be obliged to have recourse to the -action of supernatural forces; that is, to the interference of miracles -in the natural course of things. It is only through miracles that these -revolutions of the earth could have been brought about, and it is only -through miracles that, after their cessation and at the commencement of -each new period, a new animal and vegetable kingdom could have been -created. But science has no room for miracles, for by miracles we -understand an interference of supernatural forces in the natural course -of development of matter. - -Just as the great authority which Linnæus gained by his system of -distinguishing and naming organic species led his successors to a -complete ossification, as it were, of the dogmatic idea of species and -to a real abuse of the systematic distinction implied by it, so the -great services which Cuvier had rendered to the knowledge and -distinction of extinct species became the cause of a general adoption of -his theory of revolutions and catastrophes, and of the false views of -creation connected therewith. The consequence of this was that, during -the first half of our century, most zoologists and botanists clung to -the opinion that a series of independent periods in the organic history -of the earth had existed; that each period was distinguished by distinct -and peculiar kinds of animal and vegetable species; that these were -annihilated at the termination of the period by a general revolution; -and that, after the cessation of the latter, a new world of different -species of animals and plants was created. - -It is true some independent thinkers, above all the great physical -philosopher, Lamarck, even at an early period, set forth a series of -weighty reasons which refuted Cuvier's theory of cataclysms, and -pointed to a perfectly continuous and uninterrupted developmental -history of all the organic inhabitants of the earth through all ages. -They maintained that the animal and vegetable species of each period -were derived from those of the preceding period, and were only the -altered descendants of the former. This true conception, however, being -opposed to Cuvier's great authority, was then unable to make way. Nay, -even after Cuvier's theory of catastrophes had been completely cast out -from the domain of geology by Lyell's classic Principles of Geology, -which appeared in 1830, still his idea of the specific distinctness of a -series of organic creations maintained its influence, in many ways, in -the science of Palæontology. (Gen. Morph. ii. 312.) - -By a curious coincidence, thirteen years ago, almost at the same time -that Cuvier's History of Creation received its death-blow by Darwin's -book, another celebrated naturalist made an attempt to re-establish it, -and to adopt it in the roughest manner, as a part of a -teleologico-theological system of nature. This was the Swiss geologist, -Louis Agassiz, who attained a great reputation by his theory of glaciers -and the ice-period, borrowed from Schimper and Charpentier, and who has -been living in North America for many years. He commenced in 1858 to -publish a work planned on a very large scale, which bears the title of -"Contributions to the Natural History of the United States of North -America." The first volume of this work, although large and costly, -owing to the patriotism of the Americans, had an unprecedented sale; its -title is, "An Essay on Classification."(5) - -In this essay Agassiz not only discusses the natural series of -organisms, and the different attempts of naturalists at classification, -but also all the general biological phenomena which have reference to -it. The history of the development of organisms, both the embryonal and -the palæontological, comparative anatomy, the general economy of nature, -the geographical and topographical distribution of animals and -plants--in short, almost all the general phenomena of organic nature are -discussed in Agassiz's Essay on Classification, and are explained in a -sense and from a point of view which is thoroughly opposed to that of -Darwin. While Darwin's chief merit lies in the fact that he demonstrates -natural causes for the coming into existence of animal and vegetable -species, and thereby establishes the mechanical or monistic view of the -universe as regards this most difficult branch of the history of -creation, Agassiz, on the contrary, strives to exclude every mechanical -hypothesis from the subject, and to put the supernatural interference of -a personal Creator in the place of the natural forces of matter; -consequently, to establish a thoroughly teleological or dualistic view -of the universe. It will not be out of place if I examine a little more -closely Agassiz's biological views, and especially his ideas of -creation, because no other work of our opponents treats the important -fundamental questions with equal minuteness, and because the utter -untenableness of the dualistic conception of nature becomes very evident -from the failure of this attempt. - -The organic _species_, the various conceptions of which we have above -designated as the real centre of dispute in the opposed views of -creation, is looked upon by Agassiz, as by Cuvier and Linnæus, as a form -unchangeable in all its essential characteristics. The species may -indeed change and vary within certain narrow limits; never in essential -qualities, but only in unessential points. No new species could ever -proceed from the changes or varieties of a species. Not one of all -organic species, therefore, is ever derived from another, but each -individual species has been separately created by God. Each individual -species, as Agassiz expresses it, is "an embodied creative thought" of -God. - -In direct opposition to the fact established by palæontological -experience, that the duration of the individual organic species is most -unequal, and that many species continue unchanged through several -successive periods of the earth's history, while others only existed -during a small portion of such a period, Agassiz maintains that one and -the same species never occurs in two different periods, but that each -individual period is characterized by species of animals and plants -which are quite peculiar, and belong to it exclusively. He further -shares Cuvier's opinion that the whole of these inhabitants were -annihilated by the great and universal revolutions of the earth's -surface, which divide two successive periods, and that after its -destruction a new and specifically different assemblage of organisms was -created. This new creation Agassiz supposes to have taken place in this -manner: viz., that at each creation all the inhabitants of the earth, in -their full average number of individuals, and in the peculiar relations -corresponding to the economy of nature, were, as a whole, suddenly -placed upon the earth by the Creator. In saying this he puts himself in -opposition to one of the most firmly established and most important laws -of animal and vegetable geography--namely, to the law that each species -has a single original locality of origin, or a so-called "centre of -creation," from which it has gradually spread over the rest of the -earth. Instead of this, Agassiz assumes each species to have been -created at several points of the earth's surface, and that in each case -a large number of individuals was created. - -The "natural system" of organisms, the different groups and categories -of which arranged above one another--namely, the branches, classes, -orders, families, genera, and species--we consider, in accordance with -the Theory of Descent, as different branches and twigs of the organic -family-tree, is, according to Agassiz, the direct expression of the -divine plan of creation, and the naturalist, while investigating the -natural system, repeats the creative thoughts of God. In this Agassiz -finds the strongest proof that man is the image and child of God. The -different stages of groups or categories of the natural system -correspond with the different stages of development which the divine -plan of creation had attained. The Creator, in projecting and carrying -out this plan, starting from the most general ideas of creation, plunged -more and more into specialities. For instance, when creating the animal -kingdom, God had in the first place four totally distinct ideas of -animal bodies, which he embodied in the different structures of the four -great, principal forms, types, or branches of the animal kingdom; -namely, vertebrate animals, articulate animals, molluscous animals, and -radiate animals. The Creator then, having reflected in what manner he -might vary these four different plans of structure, next created within -each of the four principal forms, several different classes--for -example, in the vertebrate animal form, the classes of mammals, birds, -reptiles, amphibious animals, and fishes. Then God further reflected -upon the individual classes, and by various modifications in the -structure of each class, he produced the individual orders. By further -variation in the order, he created natural families. As the Creator -further varied the peculiarities of structure of individual parts in -each family, genera arose. In further meditation on his plan of -creation, he entered so much into detail that individual species came -into existence, which, consequently, are embodied creative thoughts of -the most special kind. It is only to be regretted that the Creator -expressed these most special and most deeply considered "creative -thoughts" in so very indistinct and loose a manner, and that he -imprinted so vague a stamp upon them, and permitted them to vary so -freely that not one naturalist is able to distinguish the "good" from -the "bad species," or a genuine species from varieties, races, etc. -(Gen. Morph. ii. 373.) - -We see, then, according to Agassiz's conception, that the Creator, in -producing organic forms, goes to work exactly as a human architect, who -has taken upon himself the task of devising and producing as many -different buildings as possible, for the most manifold purposes, in the -most different styles, in various degrees of simplicity, splendour, -greatness, and perfection. This architect would perhaps at first choose -four different styles for all these buildings, say the Gothic, -Byzantine, Chinese, and Rococo styles. In each of these styles he would -build a number of churches, palaces, garrisons, prisons, and -dwelling-houses. Each of these different buildings he would execute in -ruder and more perfect, in greater and smaller, in simpler and grander -fashion, etc. However, the human architect would perhaps, in this -respect, be better off than the divine Creator, as he would have perfect -liberty in the number of graduated subordinate groups. The Creator, -however, according to Agassiz, can only move within six groups or -categories: the species, genus, family, order, class, and type. More -than these six categories do not exist for him. - -When we read Agassiz's book on classification, and see how he carries -out and establishes these strange ideas, we can scarcely understand how, -with all the appearance of scientific earnestness, he can persevere in -his idea of the divine Creator as a man-like being (anthropomorphism), -for by his explanation of details he produces a picture of the most -absurd nonsense. In the whole series of these suppositions the Creator -is nothing but an all-mighty man, who, plagued with _ennui_, amuses -himself with planning and constructing most varied toys in the shape of -organic species. After having diverted himself with these for thousands -of years, they become tiresome to him, he destroys them by a general -revolution of the earth's surface, and thus throws the whole of the -useless toys in heaps together; then, in order to while away his time -with something new and better, he calls a new and more perfect animal -and vegetable world into existence. But in order not to have the trouble -of beginning the work of creation over again, he keeps, in the main, to -his original plan of creation, and creates merely new species, or at -most only new genera, and much more rarely new families, new orders, or -classes. He never succeeds in producing a new style or type, and always -keeps strictly within the six categories or graduated groups. - -When, according to Agassiz, the Creator has thus amused himself for -thousands of millions of years with constructing and destroying a series -of different creations, at last (but very late) he is struck with the -happy thought of creating something like himself, and so makes man in -his own image. The end of all the history of creation is thus arrived at -and the series of revolutions of the earth is closed. Man, the child and -image of God, gives him so much to do, causes him so much pleasure and -trouble, that he is wearied no longer, and therefore need not undertake -a new creation. It is clear that if, according to Agassiz, we once -assign to the Creator entirely human attributes and qualities, and -regard his work of creation as entirely analogous to human creative -activity, we are necessarily obliged to admit such utterly absurd -inferences as those just stated. - -The many intrinsic contradictions and perversities in Agassiz's view of -creation--a view which necessarily led him to the most decided -opposition to the Theory of Descent--must excite our astonishment all -the more because, in his earlier scientific works, he had in many -respects actually paved the way for Darwin, especially by his researches -in Palæontology. Among the numerous investigations which created general -interest in the then young science of Palæontology, those of Agassiz, -especially his celebrated work on "Fossil Fish," rank next in importance -to Cuvier's work, which formed the foundation of the science. The -petrified fish, with which Agassiz has made us acquainted, have not only -an extremely great importance for the understanding of all groups of -Vertebrate animals, and their historical development, but we have -arrived through them at a sure knowledge of important general laws of -development, some of which were first discovered by Agassiz. He it was -who drew special attention to the remarkable parallelism between the -embryonal and the palæontological development--between ontogeny and -phylogeny, which I have already (p. 10) claimed as one of the strongest -pillars of the Theory of Descent. No one before had so distinctly stated -as Agassiz did, that, of the Vertebrate animals, fishes alone existed, -at first, that amphibious animals came later, and that birds and mammals -appeared only at a much later period, further, that among mammals, as -among fishes, imperfect and lower orders had appeared first, but more -perfect and higher orders at a later period. Agassiz, therefore, showed -that the palæontological development of the whole Vertebrate group was -not only parallel with the embryonic, but also with the systematic -development, that is, with the graduated series which we see everywhere -in the system, ascending from the lower to the higher classes, orders, -etc. - -In the earth's history lower forms appeared first, the higher forms -later. This important fact, as well as the agreement of the embryonic -and palæontological development, is explained quite simply and naturally -by the Doctrine of Descent, and without it is perfectly inexplicable. -This cause holds good also in the great law of _progressive -development_, that is, of the historical progress of organization, which -is traceable, broadly and as a whole, in the historical succession of -all organisms, as well as in the special perfecting of individual parts -of animal bodies. Thus, for example, the skeleton of Vertebrate animals -acquired at first slowly, and by degrees, that high degree of perfection -which it now possesses in man and the other higher Vertebrate animals. -This progress, acknowledged in point of fact by Agassiz, necessarily -follows from Darwin's Doctrine of Descent, which demonstrates its active -causes. If this doctrine is correct, the perfecting and diversification -of animal and vegetable species must of necessity have gradually -increased in the course of the organic history of the earth, and could -only attain its highest perfection in most recent times. - -The above-mentioned laws of development, together with some other -general ones, which have been expressly admitted and justly emphasized -by Agassiz, and some of which have first been set forth by him, are, as -we shall see later, only explicable by the Theory of Descent, and -without it remain perfectly incomprehensible. The conjoint action of -Inheritance and Adaptation, as explained by Darwin, can alone be their -true cause. But they all stand in sharp and irreconcilable opposition to -the hypothesis of creation maintained by Agassiz, as well as to the idea -of a personal Creator who acts for a definite purpose. If we seriously -wish to explain those remarkable phenomena and their inter-connection by -Agassiz's theory, then we are necessarily driven to the curious -supposition that the Creator himself has developed, together with the -organic nature which he created and modelled. We can, in that case, no -longer rid ourselves of the idea that the Creator himself, like a human -being, designed, improved, and finally, with many alterations, carried -out his plans. "Man grows as higher grow his aims," and the same -supposition, so unworthy of a God, must be applied to him. Although, -from the reverence with which, in every page, Agassiz speaks of the -Creator, it might appear that, on his theory, we attain to the sublimest -conception of the divine activity in nature, yet the contrary is in -truth the case. The divine Creator is degraded to the level of an -idealized man, of an organism progressing in development! - -Considering the wide popularity and great authority which Agassiz's work -has gained, and which is perhaps justified on account of earlier -scientific services rendered by the author, I have thought it my duty -here to show the utter untenableness of his general conceptions. So far -as this work pretends to be a scientific history of creation, it is -undoubtedly a complete failure. But still it has great value, being the -only detailed attempt, adorned with scientific arguments, which an -eminent naturalist of our day has made to found a teleological or -dualistic history of creation. The utter impossibility of such a history -has thus been made obvious to every one. No opponent of Agassiz could -have refuted the dualistic conception of organic nature and its origin -more strikingly than he himself has done by the intrinsic contradictions -which present themselves everywhere in his theory. - -The opponents of the monistic or mechanical conception of the world have -welcomed Agassiz's work with delight, and find in it a perfect proof of -the direct creative action of a personal God. But they overlook the fact -that this personal Creator is only an idealized organism, endowed with -human attributes. This low dualistic conception of God corresponds with -a low animal stage of development of the human organism. The more -developed man of the present day is capable of, and justified in, -conceiving that infinitely nobler and sublimer idea of God which alone -is compatible with the monistic conception of the universe, and which -recognizes God's spirit and power in all phenomena without exception. -This monistic idea of God, which belongs to the future, has already been -expressed by Giordano Bruno in the following words:--"A spirit exists in -all things, and no body is so small but contains a part of the divine -substance within itself, by which it is animated." It is of this noble -idea of God that Goethe says:--"Certainly there does not exist a more -beautiful worship of God than that which needs no image, but which -arises in our heart from converse with Nature." By it we arrive at the -sublime idea of the Unity of God and Nature. - - - - -CHAPTER IV. - -THEORY OF DEVELOPMENT ACCORDING TO GOETHE AND OKEN. - - - Scientific Insufficiency of all Conceptions of a Creation - of Individual Species.--Necessity of the Counter Theories - of Development.--Historical Survey of the Most Important - Theories of Development.--Aristotle.--His Doctrine of - Spontaneous Generation.--The Meaning of Natural - Philosophy.--Goethe.--His Merits as a Naturalist.--His - Metamorphosis of Plants.--His Vertebral Theory of the - Skull.--His Discovery of the Mid Jawbone in - Man.--Goethe's Interest in the Dispute between Cuvier and - Geoffroy St. Hilaire.--Goethe's Discovery of the Two - Organic Formative Principles, of the Conservative - Principle of Specification (by Inheritance), and of the - Progressive Principle of Transformation (by - Adaptation).--Goethe's Views of the Common Descent of all - Vertebrate Animals, including Man.--Theory of Development - according to Gottfried Reinhold Treviranus.--His Monistic - Conception of Nature.--Oken.--His Natural - Philosophy.--Oken's Theory of Protoplasm.--Oken's Theory - of Infusoria (Cell Theory).--Oken's Theory of - Development. - - -All the different ideas which we may form of a separate and independent -origin of the individual organic species by creation lead us, when -logically carried out, to a so-called _anthropomorphism_, that is, to -imagining the Creator as a man-like being, as was shown in our last -chapter. The Creator becomes an organism who designs a plan, reflects -upon and varies this plan, and finally forms creatures according to this -plan, as a human architect would his building. If even such eminent -naturalists as Linnæus, Cuvier, and Agassiz, the principal -representatives of the dualistic hypothesis of creation, could not -arrive at a more satisfactory view, we may take it as evidence of the -insufficiency of all those conceptions which would derive the various -forms of organic nature from a creation of individual species. - -Some naturalists, indeed, seeing the complete insufficiency of these -views, have tried to replace the idea of a personal Creator by that of -an unconsciously active and creative Force of Nature; yet this -expression is evidently merely an evasive phrase, as long as it is not -clearly shown what this force of nature is, and how it works. Hence -these attempts, also, have been absolute failures. In fact, whenever an -independent origin of the different forms of animals and plants has been -assumed, naturalists have found themselves compelled to fall back upon -so many "acts of creation," that is, on supernatural interferences of -the Creator in the natural course of things, which in all other cases -goes on without interference. - -It is true that several teleological naturalists, feeling the scientific -insufficiency of a supernatural "_creation_," have endeavoured to save -the hypothesis by wishing it to be understood that creation "is nothing -else than a way of coming into being, unknown and inconceivable to us." -The eminent Fritz Müller has cut off from this sophistic evasion every -chance of escape by the following striking remark:--"It is intended here -only to express in a disguised manner the shamefaced confession, that -they neither have, nor care to have, _any opinion_ about the origin of -species. According to this explanation of the word, we might as well -speak of the creation of cholera, or syphilis, of the creation of a -conflagration, or of a railway accident, as of the creation of man." -(Jenaische Zestscrift, bd. v. p. 272.) - -In the face, then, of these hypotheses of creation, which are -scientifically insufficient, we are forced to seek refuge in the -_counter-theory of development_ of organisms, if we wish to come to a -rational conception of the origin of organisms. We are forced and -obliged to do so, even if the theory of development only throws a -glimmer of probability upon a mechanical, natural origin of the animal -and vegetable species; but all the more if, as we shall see, this theory -explains all facts simply and clearly, as well as completely and -comprehensively. The theories of development are by no means, as they -often falsely are represented to be, arbitrary fancies, or wilful -products of the imagination, which only attempt approximately to explain -the origin of this or that individual organism; but they are theories -founded strictly on science, which explain in the simplest manner, from -a fixed and clear point of view, the whole of organic natural phenomena, -and more especially the origin of organic species, and demonstrate them -to be the necessary consequences of mechanical processes in nature. - -As I have already shown in the second chapter, all these theories of -development coincide naturally with that general theory of the universe -which is usually designated as the uniform or _monistic_, often also as -the _mechanical_ or causal, because it only assumes mechanical causes, -or _causes working by necessity_ (causæ efficientes), for the -explanation of natural phenomena. In like manner, on the other hand, the -supernatural hypotheses of creation which we have already discussed -coincide completely with the opposite view of the universe, which in -contrast to the former is called the twofold or _dualistic_, often the -_teleological_ or vital, because it traces the organic natural phenomena -to final causes, acting and _working for a definite purpose_ (causæ -finales). It is this deep and intrinsic connection of the different -theories of creation with the most important questions of philosophy -that incites us to their closer examination. - -The fundamental idea, which must necessarily lie at the bottom of all -natural theories of development, is that of a _gradual development of -all (even the most perfect) organisms_ out of a single, or out of a very -few, quite simple, and quite imperfect original beings, which came into -existence, not by supernatural creation, but by _spontaneous -generation_, or archigony, out of inorganic matter. In reality, there -are two distinct conceptions united in this fundamental idea, but which -have, nevertheless, a deep intrinsic connection--namely, first, the idea -of spontaneous generation (or archigony) of the original primary beings; -and secondly, the idea of the progressive development of the various -species of organisms from those most simple primary beings. These two -important mechanical conceptions are the inseparable fundamental ideas -of every theory of development, if scientifically carried out. As it -maintains the derivation of the different species of animals and plants -from the simplest, common primary species, we may term it also the -Doctrine of Filiation, or _Theory of Descent_; as there is also a change -of species connected with it, it may also be termed the _Transmutation -Theory_. - -While the supernatural histories of creation must have originated -thousands of years ago, in that very remote primitive age when man, -first developing out of the monkey-state, began for the first time to -think more closely about himself, and about the origin of the world -around him, the natural theories of development, on the other hand, are -necessarily of much more recent origin. These views are met with only -among nations of a more matured civilization, to whom, by philosophic -culture, the necessity of a knowledge of natural causes has become -apparent; and even among these, only individual and specially gifted -natures can be expected to have recognized the origin of the world of -phenomena, as well as its course of development, as the necessary -consequences of mechanical, naturally active causes. In no nation have -these preliminary conditions, for the origin of a natural theory of -development, ever existed in so high a degree as among the Greeks of -classic antiquity. But, on the other hand, they lacked a close -acquaintance with the facts of the processes and forms of nature, and, -consequently, the foundation based upon experience, for a satisfactory -unravelling of the problem of development. Exact investigation of -nature, and the knowledge of nature founded on an experimental basis, -was of course almost unknown to antiquity, as well as to the Middle -Ages, and is only an acquisition of modern times. We have therefore here -no special occasion to examine the natural theories of development of -the various Greek philosophers, since they were wanting in the knowledge -gained by experience, both of organic and inorganic nature, and since -they almost always, as the consequence, lost themselves in airy -speculations. - -One man only must be mentioned here by way of exception,--Aristotle, the -greatest and the only truly great naturalist of antiquity and the Middle -Ages, one of the grandest geniuses of all time. To what a degree he -stands there alone, during a period of more than two thousand years, in -the region of empirico-philosophical knowledge of nature, and especially -in his knowledge of organic nature, is proved to us by the precious -remains of his but partially surviving works. In them many traces are -found of a theory of natural development. Aristotle assumes, as a matter -of certainty, that spontaneous generation was the natural manner in -which the lower organic creatures came into existence. He describes -animals and plants originating from matter itself, through its own -original force; as, for example, moths from wool, fleas from putrid -dung, wood-lice from damp wood, etc. But as the distinction of organic -species, which Linnæus only arrived at two thousand years later, was -unknown to him, he could form no ideas about their genealogical -relations. - -The fundamental notion of the theory of development, that the different -species of animals and plants have been developed from a common primary -species by transformation, could of course only be clearly asserted -after the kinds of species themselves had become better known, and after -the extinct species had been carefully examined and compared with the -living ones. This was not done until the end of the last and the -beginning of the present century. It was not until the year 1801 that -the great Lamarck expressed the theory of development, which he, in -1809, further elaborated in his classical "Philosophie Zoologique." -While Lamarck and his countryman, Geoffroy St. Hilaire, in France, -opposed Cuvier's views, and maintained a natural development of organic -species by transformation and descent, Goethe and Oken at the same time -pursued the same course in Germany, and helped to establish the theory -of development. As these naturalists are generally called -nature-philosophers (Naturphilosophen), and as this ambiguous -designation is correct in a certain sense, it appears to me appropriate -here to say a few words about the correct estimate of the -"Natur-philosophie." - -Although for many years in England the ideas of natural science and -philosophy have been looked upon as almost equivalent, and as every -truly scientific investigator of nature is most justly called there a -"natural philosopher," yet in Germany for more than half a century -natural science has been kept strictly distinct from philosophy, and the -union of the two into a true philosophy of nature is recognized only by -the few. This misapprehension is owing to the fantastic eccentricities -of earlier German natural-philosophers, such as Oken, Schelling, etc.; -they believed that they were able to construct the laws of nature in -their own heads, without being obliged to take their stand upon the -grounds of actual experience. When the complete hollowness of their -assumptions had been demonstrated, naturalists, in "the nation of -thinkers," fell into the very opposite extreme, believing that they -would be able to reach the high aim of science, that is, the knowledge -of truth, by the mere experience of the senses, and without any -philosophical activity of thought. - -From that time, but especially since 1830, most naturalists have shown a -strong aversion to any general, philosophical view of nature. The real -aim of natural science was now supposed to consist in the knowledge of -details, and it was believed that this would be attained in the study of -biology, when the forms and the phenomena of life, in all individual -organisms, had become accurately known, by the help of the finest -instruments and means of observation. It is true that among these -strictly empirical, or so-called exact naturalists, there were always -very many who rose above this narrow point of view, and sought the final -aim in a knowledge of the general laws of organization. Yet the great -majority of zoologists and botanists, during the thirty or forty years -preceding Darwin, refused to concern themselves about such general laws; -all they admitted was, that perhaps in the far distant future, when the -end of all empiric knowledge should have been arrived at, when all -individual animals and plants should have been thoroughly examined, -naturalists might begin to think of discovering general biological laws. - -If we consider and compare the most important advances which the human -mind has made in the knowledge of truth, we shall soon see that it is -always owing to philosophical mental operations that these advances have -been made, and that the experience of the senses which certainly and -necessarily precedes these operations, and the knowledge of details -gained thereby, only furnish the basis for those general laws. -Experience and philosophy, therefore, by no means stand in such -exclusive opposition to each other as most men have hitherto supposed; -they rather necessarily supplement each other. The philosopher who is -wanting in the firm foundation of sensuous experience, of empirical -knowledge, is very apt to arrive at false conclusions in his general -speculations, which even a moderately informed naturalist can refute at -once. On the other hand, the purely empiric naturalists, who do not -trouble themselves about the philosophical comprehension of their -sensuous experiences, and who do not strive after general knowledge, can -promote science only in a very slight degree, and the chief value of -their hard-won knowledge of details lies in the general results which -more comprehensive minds will one day derive from them. - -From a general survey of the course of biological development since -Linnæus' time, we can easily see, as Bär has pointed out, a continual -vacillation between these two tendencies, at one time a prevalence of -the empirical--the so-called exact--and then again of the philosophical -or speculative tendency. Thus at the end of the last century, in -opposition to Linnæus' purely empirical school, a natural-philosophical -reaction took place, the moving spirits of which, Lamarck, Geoffroy St. -Hilaire, Goethe, and Oken, endeavoured by their mental work to introduce -light and order into the chaos of the accumulated empirical raw -material. In opposition to the many errors and speculations of these -natural philosophers, who went too far, Cuvier then came forward, -introducing a second, purely empirical period. It reached its most -one-sided development between the years 1830-1860, and there now -followed a second philosophical reaction, caused by Darwin's work. Thus -during the last ten years, men again have begun to endeavour to obtain a -knowledge of the general laws of nature, to which, after all, all -detailed knowledge of experience serves only as a foundation, and -through which alone it acquires its true value. It is through philosophy -alone that natural knowledge becomes a true science, that is, a -philosophy of nature. (Gen. Morph. i. 63-108.) - -Jean Lamarck and Wolfgang Goethe stand at the head of all the great -philosophers of nature who first established a theory of organic -development, and who are the illustrious fellow-workers of Darwin. I -turn first to our beloved Goethe, who, among all, stands in the closest -relations to us Germans. However, before I explain his special services -to the theory of development, it seems to me necessary to say a few -words about his importance as a naturalist in general, as it is commonly -very little known. - -I am sure most of my readers honour Goethe only as a poet and a man; -only a few have any conception of the high value of his scientific -works, and of the gigantic stride with which he advanced before his own -age--advanced so much that most naturalists of that time were unable to -follow him. In several passages of his scientific writings he bitterly -complains of the narrow-mindedness of professed naturalists, who do not -know how to value his works (who cannot see the wood for the trees), and -who cannot rouse themselves to discover the general laws of nature among -the mass of details. He is only too just when he utters the -reproach--"The philosophers will very soon discover that observers -rarely rise to a stand-point from which they can survey so many -important objects." It is true, at the same time, that their want of -appreciation was caused by the false road into which Goethe was led in -his theory of colours. - -This theory of colours, which he himself designates as the favourite -production of his leisure, however much that is beautiful it may -contain, is a complete failure in regard to its foundations. The exact -mathematical method by means of which alone it is possible, in inorganic -sciences, but above all in physics, to raise a structure step by step on -a thoroughly firm basis, was altogether repugnant to Goethe. In -rejecting it he allowed himself not only to be very unjust towards the -most eminent physicists, but to be led into errors which have greatly -injured the fame of his other valuable works. It is quite different in -the organic sciences, in which we are but rarely able to proceed, from -the beginning, upon a firm mathematical basis; we are rather compelled, -by the infinitely difficult and intricate nature of the problem, at the -first to form inductions--that is, we are obliged to endeavour to -establish general laws by numerous individual observations, which are -not quite complete. A comparison of kindred series of phenomena, or the -method of combination, is here the most important instrument for -inquiry, and this method was applied by Goethe with as much success as -with conscious knowledge of its value, in his works relating to the -philosophy of nature. - -The most celebrated among Goethe's writings relating to organic nature -is his _Metamorphosis of Plants_, which appeared in 1790, a work which -distinctly shows a grasp of the fundamental idea of the theory of -development, inasmuch as Goethe, in it, was labouring to point out a -single organ, by the infinitely varied development and metamorphosis of -which the whole of the endless variety of forms in the world of plants -might be conceived to have arisen; this fundamental organ he found in -the _leaf_. If at that time the microscope had been generally employed, -if Goethe had examined the structure of organisms by the means of the -microscope he would have gone still further, and would have seen that -the leaf is itself a compound of individual parts of a lower order, that -is, of _cells_. He would then not have declared that the leaf, but that -the _cell_ is the real fundamental organ by the multiplication, -transformation, and combination (synthesis) of which, in the first -place, the leaf is formed; and that, in the next place, by -transformation, variation, and combination of leaves there arise all -the varied beauties in form and colour which we admire in the green -parts, as well as in the organs of propagation, or the flowers of -plants. Goethe here showed that in order to comprehend the whole of the -phenomena, we must in the first place compare them, and, secondly, -search for a simple type, a simple fundamental form, of which all other -forms are only infinite variations. - -Something similar to what he had here done for the metamorphosis of -plants he then did for the Vertebrate animals, in his celebrated -_vertebral theory of the skull_. Goethe was the first to show, -independently of Oken, who almost simultaneously arrived at the same -thought, that the skull of man and of all Vertebrate animals, in -particular mammals, is nothing more than a bony case, formed of the same -bones,--that is, vertebræ,--out of which the spine also is composed. The -vertebræ of the skull are like those of the spine, bony rings lying -behind each other, but in the skull are peculiarly changed and -specialized (differentiated). Although this idea has been strongly -modified by recent discoveries, yet in Goethe's day it was one of the -greatest advances in comparative anatomy, and was not only one of the -first advances towards the understanding of the structure of Vertebrate -animals, but at the same time explained many individual phenomena. When -two parts of a body, such as the skull and spine, which appear at first -sight so different, were proved to be parts originally the same, -developed out of one and the same foundation, one of the difficult -problems of the philosophy of nature was solved. Here again we meet the -notion of a single type--the conception of a single principle, which -becomes infinitely varied in the different species, and in the parts of -individual species. - -But Goethe did not merely endeavour to search for such far-reaching -laws, he also occupied himself most actively for a long time with -numerous individual researches, especially in comparative anatomy. Among -these, none is perhaps more interesting than the discovery of the _mid -jawbone in man_. As this is, in several respects, of importance to the -theory of development, I shall briefly explain it here. There exist in -all mammals two little bones in the upper jaw, which meet in the centre -of the face, below the nose, and which lie between the two halves of the -real upper jawbone. These two bones, which hold the four upper cutting -teeth, are recognized without difficulty in most mammals; in man, -however, they were at that time unknown, and celebrated comparative -anatomists even laid great stress upon this want of a mid jawbone, as -they considered it to constitute the principal difference between men -and apes--the want of a mid jawbone was, curiously enough, looked upon -as the most human of all human characteristics. But Goethe could not -accept the notion that man, who in all other corporeal respects was -clearly only a mammal of higher development, should lack this mid -jawbone. - -By the general law of induction as to the mid jawbone he arrived at the -special deductive conclusion that it must exist in man also, and Goethe -did not rest until, after comparing a great number of human skulls, he -really found the mid jawbone. In some individuals it is preserved -throughout a whole lifetime, but usually at an early age it coalesces -with the neighbouring upper jawbone, and is therefore only to be found -as an independent bone in very youthful skulls. In human embryos it can -now be pointed out at any moment. In man, therefore, the mid jawbone -actually exists, and to Goethe the honour is due of having first firmly -established this fact, so important in many respects; and this he did -while opposed by the celebrated anatomist, Peter Camper, one of the most -important professional authorities. The way by which Goethe succeeded in -establishing this fact is especially interesting; it is the way by which -we continually advance in biological science, namely, by way of -induction and deduction. _Induction_ is the inference of a general law -from the observation of numerous individual cases; _deduction_, on the -other hand, is an inference from this general law applied to a single -case which has not yet been actually observed. From the collected -empirical knowledge of those days, the inductive conclusion was arrived -at that all mammals had mid jawbones. Goethe drew from this the -deductive conclusion, that man, whose organization was in all other -respects not essentially different from mammals, must also possess this -mid jawbone; and on close examination it was actually found. The -deductive conclusion was confirmed and verified by experience. - -Even these few remarks may serve to show the great value which we must -ascribe to Goethe's biological researches. Unfortunately most of his -labours devoted to this subject are so hidden in his collected works, -and his most important observations and remarks so scattered in numerous -individual treatises--devoted to other subjects--that it is difficult to -find them out. It also sometimes happens that an excellent, truly -scientific remark is so much interwoven with a mass of useless -philosophical fancies, that the latter greatly detract from the former. - -Nothing is perhaps more characteristic of the extraordinary interest -which Goethe took in the investigation of organic nature than the lively -way in which, even in his last years, he followed the dispute which -broke out in France between Cuvier and Geoffroy de St. Hilaire. Goethe, -in a special treatise which was only finished a few days before his -death, in March, 1832, has given an interesting description of this -remarkable dispute and its general importance, as well as an excellent -sketch of the two great opponents. This treatise bears the title -"Principes de Philosophic Zoologique par M. Geoffroy de Saint Hilaire"; -it is Goethe's last work, and forms the conclusion of the collected -edition of his works. The dispute itself was, in several respects, of -the highest interest. It turned essentially upon the justification of -the theory of development. It was carried on, moreover, in the bosom of -the French Academy, by both opponents, with a personal vehemence almost -unheard of in the dignified sessions of that learned body; this proved -that both naturalists were fighting for their most sacred and deepest -convictions. The conflict began on the 22nd of February, and was -followed by several others; the fiercest took place on the 19th of July, -1830. Geoffroy, as the chief of the French nature-philosophers, -represented the theory of natural development and the monistic -conception of nature. He maintained the mutability of organic species, -the common descent of the individual species from common primary forms, -and the unity of their organization--or the unity of the plan of -structure, as it was then called. - -Cuvier was the most decided opponent of these views, and according to -what we have seen, it could not be otherwise. He endeavoured to show -that the nature-philosophers had no right to rear such comprehensive -conclusions on the basis of the empirical knowledge then possessed, and -that the unity of organization--or plan of structure of organisms--as -maintained by them, did not exist. He represented the teleological -(dualistic) conception of nature, and maintained that "the immutability -of species was a necessary condition for the existence of a scientific -history of nature," Cuvier had the great advantage over his opponent, -that he was able to bring towards the proof of his assertions things -obvious to the eye; these, however, were only individual facts taken out -of their connection with others. Geoffroy was not able to prove the -higher and general connection of individual phenomena which he -maintained, by equally tangible details. Hence Cuvier, in the eyes of -the majority, gained the victory, and decided the defeat of the -nature-philosophy and the supremacy of the strictly empiric tendency for -the next thirty years. - -Goethe of course supported Geoffroy's views. How deeply interested he -was, even in his 81st year, in this great contest is proved by the -following anecdote related by Soret:-- - -"Monday, Aug. 2nd, 1830.--The news of the outbreak of the revolution of -July arrived in Weimar to-day, and has caused general excitement. In the -course of the afternoon I went to Goethe. 'Well?' he exclaimed as I -entered, 'what do you think of this great event? The volcano has burst -forth, all is in flames, and there are no more negotiations behind -closed doors.' 'A dreadful affair,' I answered; 'but what else could be -expected under the circumstances, and with such a ministry, except that -it would end in the expulsion of the present royal family?' 'We do not -seem to understand each other, my dear friend,' replied Goethe. 'I am -not speaking of those people at all; I am interested in something very -different, I mean the dispute between Cuvier and Geoffroy de Saint -Hilaire, which has broken out in the Academy, and which is of such great -importance to science.' This remark of Goethe's came upon me so -unexpectedly, that I did not know what to say, and my thoughts for some -minutes seemed to have come to a complete standstill. 'The affair is of -the utmost importance,' he continued, 'and you cannot form any idea of -what I felt on receiving the news of the meeting on the 19th. In -Geoffroy de Saint Hilaire we have now a mighty ally for a long time to -come. But I see also how great the sympathy of the French scientific -world must be in this affair, for, in spite of the terrible political -excitement, the meeting on the 19th was attended by a full house. The -best of it is, however, that the synthetic treatment of nature, -introduced into France by Geoffroy, can now no longer be stopped. This -matter has now become public through the discussions in the Academy, -carried on in the presence of a large audience; it can no longer be -referred to secret committees, or be settled or suppressed behind closed -doors.'" - -In my book on "The General Morphology of Organisms" I have placed as -headings to the different books and chapters a selection of the numerous -interesting and important sentences in which Goethe clearly expresses -his view of organic nature and its constant development. I will here -quote a passage from the poem entitled, "The Metamorphosis of Animals" -(1819). - - "All members develop themselves according to eternal laws, - And the rarest form mysteriously preserves the primitive type, - Form therefore determines the animal's way of life, - And in turn the way of life powerfully reacts upon all form. - Thus the orderly growth of form is seen to hold - Whilst yielding to change from externally acting causes."[3] - -Here, clearly enough, the contrast between two different organic -constructive forms is intimated, which are opposed to one another, and -which by their interaction determine the form of the organism; on the -one hand, a common inner original type, firmly maintaining itself, -constitutes the foundation of the most different forms; on the other -hand, the externally active influence of surroundings and mode of life, -which influence the original type and transform it. This contrast is -still more definitely pointed out in the following passage:-- - -"An inner original community forms the foundation of all organization; -the variety of forms, on the other hand, arises from the necessary -relations to the outer world, and we may therefore justly assume an -original difference of conditions, together with an uninterruptedly -progressive transformation, in order to be able to comprehend the -constancy as well as the variations of the phenomena of form." - -The "original type" which constitutes the foundation of -every organic form "as the inner original community" is the _inner -constructive force_, which receives the original direction of -form-production--that is, the tendency to give rise to a particular -form--and is propagated by _Inheritance_. The "uninterruptedly -progressive transformation," on the other hand, which "springs from the -necessary relations to the outer world," acting as an _external -formative force_, produces, by _Adaptation_ to the surrounding -conditions of life, the "infinite variety of forms" (Gen. Morph. i. 154; -ii. 224). The internal formative tendency of _Inheritance_, which -retains the unity of the original type, is called by Goethe in another -passage the _centripetal force_ of the organism, or its tendency to -specification; in contrast with this he calls the external formative -tendency of _Adaptation_, which produces the variety of organic forms, -the _centrifugal force_ of organisms, or their tendency to variation. -The passage in which he clearly indicates the "equilibrium" of these two -extremely important organic formative tendencies, runs as follows: "The -idea of _metamorphosis_ resembles the vis centrifuga, and would lose -itself in the infinite, if a counterpoise were not added to it: I mean -the tendency to _specification_, the strong power to preserve what once -has come into being, a vis centripeta, which in its deepest foundation -cannot be affected by anything external." - -Metamorphosis, according to Goethe, consists not merely, as the word is -now generally understood, in the changes of form which the organic -individual experiences during its individual development, but, in a -wider sense, in the transformation of organic forms in general. His idea -of metamorphosis is almost synonymous with the theory of development. -This is clear, among other things, from the following passage:--"The -triumph of physiological metamorphosis manifests itself where the whole -separates and transforms itself into families, the families into genera, -the genera into species, and then again into other varieties down to the -individual. This operation of nature goes on ad infinitum; she cannot -rest inactive, but neither can she keep and preserve all that she has -produced. From seeds there are always developed varying plants, -exhibiting the relations of their parts to one another in an altered -manner." - -Goethe had, in truth, discovered two great mechanical forces of nature, -which are the active causes of organic formations, his two organic -formative tendencies--on the one hand the conservative, centripetal, and -internal formative tendency of Inheritance or specification; and on the -other hand the progressive, centrifugal, and external formative tendency -of Adaptation, or metamorphosis. This profound biological intuition -could not but lead him naturally to the fundamental idea of the Doctrine -of Filiation, that is, to the conception that the organic species -resembling one another in form are actually related by blood, and that -they are descended from a common original type. In regard to the most -important of all animal groups, namely that of Vertebrate animals, -Goethe expresses this doctrine in the following passage (1796):--"Thus -much then we have gained, that we may assert without hesitation that all -the more perfect organic natures, such as fishes, amphibious animals, -birds, mammals, and man at the head of the last, were all formed upon -one original type, which only varies more or less in parts which are -none the less permanent, and still daily changes and modifies its form -by propagation." - -This sentence is of interest in more than one way. The theory that all -"the more perfect organic natures," that is all Vertebrate animals, are -descended from one common prototype, that they have arisen from it by -propagation (Inheritance) and transformation (Adaptation), may be -distinctly inferred. But it is especially interesting to observe that -Goethe admits no exceptional position for man, but rather expressly -includes him in the tribe of the other Vertebrate animals. The most -important special inference of the Doctrine of Filiation, that man is -descended from other Vertebrate animals, may here be recognized in the -germ.(3) - -This exceedingly important fundamental idea is expressed by Goethe still -more clearly in another passage (1807), in the following words:--"If we -consider plants and animals in their most imperfect condition, they can -scarcely be distinguished. But this much we can say, that the creatures -which by degrees emerge as plants and animals out of a common phase, -where they are barely distinguishable, arrive at perfection in two -opposite directions; so that the plant in the end reaches its highest -glory in the tree, which is immovable and stiff, the animal in man, who -possesses the greatest elasticity and freedom." This remarkable passage -not only indicates most explicitly the genealogical relationship between -the vegetable and animal kingdoms, but contains the germ of the -monophyletic hypothesis of descent, the importance of which I shall have -to explain hereafter. (Compare Chapter XVI. and the Pedigree, p. 398.) - -At the time when Goethe in this way sketched the fundamental features of -the Theory of Descent, another German philosopher, Gottfried Reinhold -Treviranus, of Bremen (born 1776, died 1837), was zealously engaged at -the same work. As Wilhelm Focke has recently shown, Treviranus, even in -the earliest of his greater works, "The Biology or Philosophy of Animate -Nature," which appeared at the beginning of the present century, had -already developed monistic views of the unity of nature, and of the -genealogical connection of the species of organisms, which entirely -correspond with our present view of the matter. In the first three -volumes of the Biology, which appeared successively in 1802, 1803, and -1805 (therefore several years before Oken's and Lamarck's principal -works), we find numerous passages which are of interest in this respect. -I shall here quote only a few of the most important. - -In speaking of the principal question of our theory, the question of the -origin of organic species, Treviranus makes the following -remarks:--"Every form of life can be produced by physical forces in one -of two ways: either by coming into being out of formless matter, or by -modification of an already existing form by a continued process of -shaping. In the latter case the cause of this modification may lie -either in the influence of a dissimilar male generative matter upon the -female germ, or in the influence of other powers which operate only -after procreation. In every living being there exists the capability of -an endless variety of form-assumption; each possesses the power to adapt -its organization to the changes of the outer world, and it is this power -put into action by the change of the universe that has raised the simple -zoophytes of the primitive world to continually higher stages of -organization, and has introduced a countless variety of species into -animate nature." - -By _zoophytes_, Treviranus here means organisms of the lowest order and -of the simplest character, namely, those neutral primitive beings which -stand midway between animals and plants, and on the whole correspond -with our _protista_. "These zoophytes," he remarks in another passage, -"are the original forms out of which all the organisms of the higher -classes have arisen by gradual development. We are further of opinion -that every species, as well as every individual, has certain periods of -growth, of bloom, and of decay, but that the decay of a species is -_degeneration_, not dissolution, as in the case of the individual. From -this it appears to us to follow that it was not the great catastrophes -of the earth (as is generally supposed) which destroyed the animals of -the primitive world, but that many survived them, and it is more -probable that they have disappeared from existing nature, because the -species to which they belonged have completed the circle of their -existence, and have become changed into other kinds." - -When Treviranus, in this and other passages, points to _degeneration_ as -the most important cause of the transformation of the animal and -vegetable species, he does not understand by it what is now commonly -called degeneration. With him "degeneration" is exactly what we now call -_Adaptation_ or _modification_, by the action of external formative -forces. That Treviranus explained this trans-transformation of organic -species by Adaptation, and its preservation by Inheritance, and thus the -whole variety of organic forms by the interaction of Adaptation and -Inheritance, is clear also from several other passages. How profoundly -he grasped the mutual dependence of all living creatures on one another, -and in general the _universal connection between cause and effect_--that -is, the monistic causal connection between all members and parts of the -universe--is further shown, among others, by the following remarks in -his Biology:--"The living individual is dependent upon the species, the -species upon the fauna, the fauna upon the whole of animate nature, and -the latter upon the organism of the earth. The individual possesses -indeed a peculiar life, and so far forms its own world. But just because -its life is limited it constitutes at the same time an organ in the -general organism. Every living body exists in consequence of the -universe, but the universe, on the other hand, exists in consequence of -it." - -It is self-evident that so profound and clear a thinker as Treviranus, -in accordance with this grand mechanical conception of the universe, -could not admit for man a privileged and exceptional position in nature, -but assumed his gradual development from lower animal forms. And it is -equally self-evident, on the other hand, that he did not admit a chasm -between organic and inorganic nature, but maintained the absolute unity -of the organization of the whole universe. This is specially attested by -the following sentence:--"Every inquiry into the influence of the whole -of nature on the living world must start from the principle, that all -living forms are products of physical influences, which are acting even -now, and are changed only in degree, or in their direction." Hereby, as -Treviranus himself says, "The fundamental problem of biology is solved," -and we add, solved in a purely mechanical or monistic sense. - -Neither Treviranus nor Goethe is commonly considered the most eminent of -the German nature-philosophers, but Lorenz Oken, who, in establishing -the vertebral theory of the skull, came forward as a rival to Goethe, -and did not entertain a very kindly feeling towards him. Although they -lived for some time in the same neighbourhood, yet the natures of these -two men were so very different, that they could not well be drawn -towards each other. Oken's "Manual of the Philosophy of Nature," which -may be designated as the most important production of the -nature-philosophy school then existing in Germany, appeared in 1809, the -same year in which Lamarck's fundamental work, the "Philosophie -Zoologique," was published. As early as 1802, Oken had published an -"Outline of the Philosophy of Nature." As we have already intimated, in -Oken's as in Goethe's works, a number of valuable and profound thoughts -are hidden among a mass of erroneous, very eccentric, and fantastic -conceptions. Some of these ideas have only quite recently and gradually -become recognized in science, many years after they were first -expressed. I shall here quote only two thoughts, which are almost -prophetic, and which at the same time stand in the closest relation to -the theory of development. - -One of the most important of Oken's theories, which was formerly very -much decried, and was most strongly combatted, especially by the -so-called "exact experimentalists," is the idea that the phenomena of -life in all organisms proceed from a common chemical substance, so to -say, from a general simple _vital-substance_, which he designated by the -name _Urschleim_, or _original slime_. By it he meant, as the name -indicates, a mucilaginous substance, an albuminous combination, which -exists in a semi-fluid condition of aggregation, and possesses the -power, by adaptation to different conditions of existence in the outer -world and by interaction with its material, of producing the most -various forms. Now, we need only change the expression "original slime" -(Urschleim) into _Protoplasm_, or _cell-substance_, in order to arrive -at one of the grandest results which we owe to microscopic -investigations during the last ten years, more especially to those of -Max Schultze. By these investigations it has been shown that in all -living bodies, without exception, there exists a certain quantity of -mucilaginous albuminous matter, in a semi-fluid condition; and that this -nitrogen-holding carbon-compound is exclusively the original seat and -agent of all the phenomena of life, and of all production of organic -forms. All other substances which appear in the organism, besides these, -are either formed by this active matter of life, or have been introduced -from without. The organic egg, the original cell out of which every -animal and plant is first developed, consists essentially only of one -round little lump of such albuminous matter. Even the yolk of an egg is -nothing but albumen, mixed with granules of fat. Oken was therefore -right when, more divining than knowing, he made the assertion--"Every -organic thing has arisen out of slime, and is nothing but slime in -different forms. This primitive slime originated in the sea, from -inorganic matter in the course of planetary-evolution." - -Another equally grand idea of the same philosopher is closely connected -with his theory of primitive slime, which coincides with the extremely -important _Protoplasm theory_. For Oken, as early as 1809, asserted that -the primitive slime produced in the sea by spontaneous generation, at -once assumed the form of microscopically small bladders, which he called -"_Mile_," or "_Infusoria_." "Organic nature has for its basis an -infinity of such vesicles." These little bladders arise from original -semi-fluid globules of the primitive slime, by the fact of their -periphery becoming condensed. The simplest organism, as well as every -animal and every plant of higher kind, is nothing else than "an -accumulation (synthesis) of such infusorial bladders, which by various -combinations assume various forms, and thus develop into higher -organisms." Here again we need only translate the expression _little -bladder_, or _infusorium_, by the word _cell_, and we arrive at the Cell -theory, one of the grandest biological theories of our century. -Schleiden and Schwann, about thirty years ago, were the first to furnish -experiential proof that all organisms are either simple cells, or -accumulations (syntheses) of such cells, and the more recent protoplasm -theory has shown that protoplasm (the original slime) is the most -essential (and sometimes the only) constituent part of the genuine cell. -The properties which Oken ascribes to his Infusoria are exactly the -properties of cells, the properties of elementary beings, by whose -accumulation, combination, and varying development, the higher organisms -are formed. - -These two extremely fruitful thoughts of Oken, on account of the absurd -form in which he expressed them, were at first little heeded, or -entirely misunderstood, and it was reserved for a much later era to -establish them by actual observation. The supposition that the -individual species of plants and animals originated from common -prototypes by a slow and gradual development of the higher organisms out -of lower ones, was of course most closely connected with these ideas. -Man's descent from lower organisms was likewise asserted by Oken--"Man -has been developed, not created." Although many arbitrary perversities -and extravagant fancies may be found in Oken's philosophy of nature, -they must not prevent us paying our just admiration to these grand -ideas, which were so far in advance of their age. This much is clearly -evident from the statements of Goethe and Oken which we have quoted, and -from the views of Lamarck and Geoffroy which have to be discussed next, -that during the first decade of our century no doctrine approached so -nearly to the natural Theory of Descent, newly established by Darwin, as -the much decried "Natur-philosophie." - - - - -CHAPTER V. - -THEORY OF DEVELOPMENT ACCORDING TO KANT AND LAMARCK. - - - Kant's Dualistic Biology.--His Conception of the Origin - of Inorganic Nature by Mechanical Causes, of Organic - Nature by Causes acting for a Definite - Purpose.--Contradiction of this Conception with his - leaning towards the Theory of Descent.--Kant's - Genealogical Theory of Development.--Its Limitation by - his Teleology.--Comparison of Genealogical Biology with - Comparative Philology.--Views in favour of the Theory of - Descent entertained by Leopold Buch, Bär, Schleiden, - Unger, Schaafhausen, Victor Carus, Büchner.--French - Nature-philosophy.--Lamarck's Philosophie - Zoologique.--Lamarck's Monistic (mechanical) System of - Nature.--His Views of the Interaction of the Two Organic - Formative Tendencies of Inheritance and - Adaptation.--Lamarck's Conception of Man's Development - from Ape-like Mammals.--Geoffroy St. Hilaire's, Naudin's, - and Lecoq's Defence of the Theory of Descent.--English - Nature-philosophy.--Views in favour of the Theory of - Descent, entertained by Erasmus Darwin, W. Herbert, - Grant, Freke, Herbert Spencer, Hooker, Huxley.--The - Double Merit of Charles Darwin. - - -The teleological view of nature, which explains the phenomena of the -organic world by the action of a personal Creator acting for a definite -purpose, necessarily leads, when carried to its extreme consequences, -either to utterly untenable contradictions, or to a twofold (dualistic) -conception of nature, which most directly contradicts the unity and -simplicity of the supreme laws which are everywhere perceptible. The -philosophers who embrace teleology must necessarily assume two -fundamentally different natures: an _inorganic_ nature, which must be -explained by causes acting _mechanically_ (causæ efficientes), and an -_organic_ nature, which must be explained by _causes acting for a -definite purpose_ (causæ finales). (Compare p. 34.) - -This dualism meets us in a striking manner when considering the -conceptions of nature formed by Kant, one of the greatest German -philosophers, and his ideas of the coming into being of organisms. A -closer examination of these ideas is forced upon us here, because in -Kant we honour one of the few philosophers who combine a solid -scientific culture with an extraordinary clearness and profundity of -speculation. The Königsberg philosopher gained the highest celebrity, -not only among speculative philosophers as the founder of critical -philosophy, but acquired a brilliant name also among naturalists by his -mechanical cosmogeny. Even in the year 1755, in his "General History of -Nature, and Theory of the Heavens,"(22) he made the bold attempt "to -discuss the constitution and the mechanical origin of the whole -universe, according to Newton's principles," and to explain them -mechanically by the natural course of development, to the exclusion of -all miracles. This cosmogeny of Kant, or "cosmological gas theory," -which we shall briefly discuss in a future chapter, was at a later day -fully established by the French mathematician Laplace and the English -astronomer Herschel, and enjoys at the present day almost universal -recognition. On account of this important work alone, in which exact -knowledge is coupled with most profound speculation, Kant deserves the -honourable name of a natural philosopher in the best and purest sense of -the word. - -If we read Kant's Criticism of the Teleological Faculty of Judgment, his -most important biological work, we perceive that in contemplating -organic nature he always maintains what is essentially the teleological -or dualistic point of view; whilst for inorganic nature he, -unconditionally and without reserve, assumes the mechanical or monistic -method of explanation. He affirms that in the domain of inorganic nature -all the phenomena can be explained by mechanical causes, by the moving -forces of matter itself, but not so in the domain of organic nature. In -the whole of Anorganology (in Geology and Mineralogy, in Meteorology and -Astronomy, in the physics and chemistry of inorganic natural bodies), -all phenomena are said to be explicable merely by _mechanism_ (causa -efficiens), without the intervention of a final purpose. In the whole -domain of Biology, on the other hand--in Botany, Zoology, and -Anthropology--mechanism is not considered sufficient to explain to us -all their phenomena; but we are supposed to be able to comprehend them -only by an assumption of a _final cause_ acting for a definite purpose -(causa finalis). In several passages Kant emphatically remarks that, -from a strictly scientific point of view, _all_ phenomena, without -exception, require a mechanical interpretation, and that _mechanism -alone can offer a true explanation_. But at the same time he thinks, -that in regard to living natural bodies, animals and plants, our human -power of comprehension is limited, and not sufficient for arriving at -the real cause of organic processes, especially at the origin of organic -forms. The _right_ of human reason to explain all phenomena mechanically -is unlimited, he says, but its _power_ is limited by the fact that -organic nature can be conceived only from a teleological point of view. - -Some passages are, however, very remarkable, in which Kant in a -surprising manner deviates from this mode of viewing things, and -expresses, more or less distinctly, the fundamental idea of the Theory -of Descent. He even asserts the necessity of a genealogical conception -of the series of organisms, if we at all wish to understand it -scientifically. The most important and remarkable of these passages -occurs in his "Methodical System of the Teleological Faculty of -Judgment" (§ 79), which appeared in 1790 in the "Criticism of the -Faculty of Judgment." Considering the extraordinary interest which this -passage possesses, both for forming a correct estimate of Kant's -philosophy, as well as for the Theory of Descent, I shall here insert it -_verbatim_. - -"It is desirable to examine the great domain of organized nature by -means of a methodical comparative anatomy, in order to discover whether -we may not find in it something resembling a system, and that too in -connection with the mode of generation, so that we may no longer be -compelled to stop short with a mere consideration of forms as they -are--which gives us no insight into their generation--and need no longer -give up in despair all hope of gaining a full insight into this -department of nature. The agreement of so many kinds of animals in a -certain common plan of structure, which seems to be visible not only in -their skeletons, but also in the arrangement of the remaining parts--so -that a wonderfully simple typical form, by the shortening and -lengthening of some parts, and by the suppression and development of -others, might be able to produce an immense variety of species--gives us -a ray of hope, though feeble, that here perhaps some result may be -obtained, by the application of the principle of the _mechanism of -nature_, without which, in fact, no science can exist. This analogy of -forms (in so far as they seem to have been produced in accordance with a -common prototype, notwithstanding their great variety) strengthens the -supposition that they have an actual blood-relationship, due to -origination from a common parent; a supposition which is arrived at by -observation of the graduated approximation of one class of animals to -another, beginning with the one in which the principle of purposiveness -seems to be most conspicuous, that is man, and extending down to the -polyps, and from these even down to mosses and lichens, and arriving -finally at raw matter, the lowest stage of nature observable by us. From -this matter and its forces the whole apparatus of Nature seems to have -descended according to mechanical laws (such as those which she follows -in the production of crystals); yet this apparatus, as seen in organic -beings, is so incomprehensible to us, that we feel ourselves compelled -to conceive for it a different principle. But it would seem that the -archæologist of Nature is at liberty to regard the great _Family_ of -creatures (for as a Family we must conceive it, if the above-mentioned -continuous and connected relationship has a real foundation) as having -sprung from the immediate results of her earliest revolutions, judging -from all the laws of their mechanism known to or conjectured by him." - -If we take this remarkable passage out of Kant's "Criticism of the -Teleological Faculty of Judgment," and consider it by itself, we cannot -but be astonished to find how profoundly and clearly the great thinker, -even in 1790, had recognized the inevitable necessity of the Doctrine of -Descent, and designated it as the only possible way of explaining -organic nature by mechanical laws--that is, by true scientific -reasoning. On account of this one passage taken by itself, we might -place Kant beside Goethe and Lamarck, as one of the first founders of -the Doctrine of Descent; and considering the high authority which Kant's -Critical Philosophy most justly enjoys, this circumstance might perhaps -induce many a philosopher to decide in favour of the theory. But as soon -as we consider this passage in connection with the other train of -thoughts in the "Criticism of the Faculty of Judgment," and balance it -against other directly contradictory passages, we see clearly that Kant, -in these and some similar (but weaker) sentences, went beyond himself, -and abandoned the teleological point of view which he usually adopts in -Biology. - -Directly after the admirable passage which I have just quoted, there -follows a remark which completely takes off its edge. After having quite -correctly maintained the origin of organic forms out of raw matter by -mechanical laws (in the manner of crystallization), as well as a gradual -development of the different species by descent from one common original -parent, Kant adds, "But he (the archæologist of nature, that is the -palæontologist) must for this end ascribe to the common mother an -organization ordained purposely with a view to the needs of all her -offspring, otherwise the possibility of suitability of form in the -products of the animal and vegetable kingdoms (_i.e._ teleological -adaptation) cannot be conceived at all." This addition clearly -contradicts the most important fundamental thought of the preceding -passage, viz., that a purely mechanical explanation of organic nature -becomes possible through the Theory of Descent. And that the -teleological conception of organic nature predominated with Kant, is -shown by the heading of the remarkable § 79, which contains the two -contradictory passages cited: "_Of the Necessary Subordination of the -Mechanical to the Teleological Principle, in the explanation of a thing -as a purpose or object of Nature._" - -He expresses himself most decidedly against the mechanical explanation -of organic nature in the following passage (§ 74): "It is quite certain -that we cannot become sufficiently acquainted with organized creatures -and their hidden potentialities by aid of purely mechanical natural -principles, much less can we explain them; and this is so certain, that -we may boldly assert that it is absurd for man even to conceive such an -idea, or to hope that a Newton may one day arise able to make the -production of a blade of grass comprehensible, according to natural laws -ordained by no intention; such an insight we must absolutely deny to -man." Now, however, this impossible Newton has really appeared seventy -years later in Darwin, whose Theory of Selection has actually solved the -problem, the solution of which Kant had considered absolutely -inconceivable! - -In connection with Kant and the German philosophers whose theories of -development have already occupied us in the preceding chapter, it seems -justifiable to consider briefly some other German naturalists and -philosophers, who, in the course of our century, have more or less -distinctly resisted the prevailing teleological views of creation, and -vindicated the mechanical conception of things which is the basis of the -Doctrine of Filiation. Sometimes general philosophical considerations, -sometimes special empirical observations, were the motives which led -these thinking men to form the idea that the various individual species -of organisms must have originated from common primary forms. Among them -I must first mention the great German geologist, Leopold Buch. Important -observations as to the geographical distribution of plants led him to -the following remarkable assertion in his excellent "Physical -Description of the Canary Islands":-- - -"The individuals of genera, on continents, spread and widely diffuse -themselves, and by the difference of localities, nourishment, and soil, -form varieties; and being in consequence of their isolation never -crossed by other varieties, and so brought back to the main type, they -in the end become a permanent and a distinct species. Then, perhaps, in -other ways, they once more become associated with other descendants of -the original form--which have likewise become new varieties--and both -now appear as very distinct species, no longer mingling with one -another. Not so on islands. Being commonly confined in narrow valleys or -within the limit of small zones, individuals can reach one another and -destroy every commencing production of a permanent variety. Much in the -same way the peculiarities or faults in language, originating with the -head of some family, become, through the extension of the family, -indigenous throughout a whole district. If the district is separated and -isolated, and if the language is not brought back to its former purity -by constant connection with that spoken in neighbouring districts, a -dialect will be the result. If natural obstacles, forests, constitution, -form of government, unite the inhabitants of the separate district still -more closely, and separate them still more completely from their -neighbours, the dialect is fixed, and becomes a completely distinct -language." (Uebersicht der Flora auf den Canarien, S. 133.) - -We perceive that Buch is here led to the fundamental idea of the Theory -of Descent by the phenomena of the geography of plants, a department of -biological knowledge which in fact furnishes a mass of proofs in favour -of it. Darwin has minutely discussed these proofs in two separate -chapters of his book (the 11th and 12th). Buch's remark is further of -interest, because it leads us to the exceedingly instructive comparison -of the different branches of language with the species of organisms, a -comparison which is of the greatest use to Comparative Philology, as -well as to Comparative Botany and Zoology. Just as, for example, the -different dialects, provincialisms, branches, and off-shoots of the -German, Slavonic, Greco-Latin, and Irano-Indian parent language, are -derived from a single common Indo-Germanic parent tongue, and just as -their _differences_ are explained by _Adaptation_, and their common -_fundamental characters_ explained by _Inheritance_, so in like manner -the different species, genera, families, orders, and classes of -Vertebrate animals are derived from a single common vertebrate form of -animal. Here also Adaptation is the cause of differences, Inheritance -the cause of community of character. This interesting parallelism in the -divergent development of the forms of speech and the forms of organisms -has been discussed in the clearest manner by one of our first -comparative philologists, the talented Augustus Schleicher, whose -premature death, four years ago, remains an irreparable loss, not only -to our University of Jena, but to the whole of monistic science.(6) - -Among other eminent German naturalists who have expressed their belief -in the Theory of Descent more or less distinctly, arriving at their -conclusion in very various ways, I must next mention Carl Ernst Bär, -the great reformer of animal embryology. In a lecture delivered in 1834, -entitled "The Most General Laws of Nature in All Development," he shows, -in the clearest way, that only in a very childish view of nature could -organic species be regarded as permanent and unchangeable types, and -that really they can be only passing series of generations, which have -developed by transformation from a common original form. The same -conception again received firm support from Baer, in 1859, through a -consideration of the laws of the geographical distribution of organisms. - -J. M. Schleiden, who founded, thirty years ago, in Jena, a new epoch in -Botany by his strictly empirico-philosophical and truly scientific -method, illustrated the philosophical significance of the conception of -organic species in his incisive "Outlines of Scientific Botany,"(7) and -showed that it had only a subjective origin in the general _law of -specification_. The different species of plants are only the specified -productions of the formative tendencies of plants, which arise from the -various combinations of the fundamental forces of organic matter. - -The eminent botanist, F. Unger, of Vienna, was led by his profound and -comprehensive investigations on extinct vegetable species, to a -palæontological history of the development of the vegetable kingdom, -which distinctly asserts the principle of the Theory of Descent. In his -"Attempt at a History of the World of Plants" (1852), he maintains the -derivation of all different species of plants from a few primary forms, -and perhaps from a single original plant, a simple vegetable cell. He -shows that this view is founded on the genetic connection of all -vegetable forms, and is necessary, not merely upon philosophical -grounds, but upon those of experience and observation.(8) - -Victor Carus, of Leipzig, in the Introduction to his excellent "System -of Animal Morphology,"(9) published in 1853, in which he endeavours to -establish in a philosophical manner the universal constructive laws of -the animal body through comparative anatomy and the history of -development, makes the following remark:--"The organisms buried in the -most ancient geological strata must be looked upon as the ancestors from -whom the rich diversity of forms of the present creation have originated -by continued generation, and by accommodation to progressive and very -different conditions of life." - -In the same year (1853) Schaaffhausen, the anthropologist of Bonn, in an -Essay "On the Permanence and Transformation of Species," declared -himself decidedly in favour of the Theory of Descent. According to him, -the living species of animals and plants are the transformed descendants -of extinct species, from which they have arisen by gradual modification. -The divergence or separation of the most nearly allied species takes -place by the destruction of the connecting intermediate stages. -Schaaffhausen also maintained, with distinctness, the origin of the -human race from animals, and its gradual development from ape-like -animals, the most important deduction from the Doctrine of Filiation. - -Lastly, we have still to mention among the German Nature-philosophers -the name of Louis Büchner, who, in his celebrated work, "Force and -Matter" (1855), also independently developed the principles of the -Theory of Descent, taking his stand mainly on the ground of the -undeniable evidences of fact which are furnished by the palæontological -and individual development of organisms, as well as by their -comparative anatomy and by the parallelism of these series of -development. Büchner showed very clearly that, even from such data -alone, the derivation of the different organic species from common -primary forms followed as a necessary conclusion, and that the origin of -these original primary forms could only be conceived of as the result of -a spontaneous generation. - -We now turn from the German to the French Nature-philosophers, who have -likewise held the Theory of Descent, since the beginning of the present -century. At their head stands Jean Lamarck, who occupies the first place -next to Darwin and Goethe in the history of the Doctrine of Filiation. -To him will always belong the immortal glory of having for the first -time worked out the Theory of Descent, as an independent scientific -theory of the first order, and as the philosophical foundation of the -whole science of Biology. Although Lamarck was born as early as 1744, he -did not begin the publication of his theory until the commencement of -the present century, in 1801, and established it more fully only in -1809, in his classic "Philosophie Zoologique."(2) This admirable work is -the first connected exposition of the Theory of Descent carried out -strictly into all its consequences. By its purely mechanical method of -viewing organic nature, and the strictly philosophical proofs brought -forward in it, Lamarck's work is raised far above the prevailing -dualistic views of his time; and with the exception of Darwin's work, -which appeared just half a century later, we know of none which we could -in this respect place by the side of the "Philosophie Zoologique." How -far it was in advance of its time is perhaps best seen from the -circumstance that it was not understood by most men, and for fifty -years was not spoken of at all. Cuvier, Lamarck's greatest opponent, in -his "Report on the Progress of Natural Sciences," in which the most -unimportant anatomical investigations are enumerated, does not devote a -single word to this work, which forms an epoch in science. Goethe, also, -who took such a lively interest in the French nature-philosophy and in -"the thoughts of kindred minds beyond the Rhine," nowhere mentions -Lamarck, and does not seem to have known the "Philosophie Zoologique" at -all. The great reputation which Lamarck gained as a naturalist he does -not owe to his highly important general work, but to numerous special -treatises on the lower animals, particularly on Molluscs, as well as to -an excellent "Natural History of Invertebrate Animals," which appeared, -in seven volumes, between the years 1815-1822. The first volume of this -celebrated work contains in the general introduction a detailed -exposition of his theory of filiation. I can, perhaps, give no better -idea of the extraordinary importance of the "Philosophie Zoologique" -than by quoting _verbatim_ some of the most important passages -therefrom:-- - -"The systematic divisions of classes, orders, families, genera, and -species, as well as their designations, are the arbitrary and artificial -productions of man. The kinds or species of organisms are of unequal -age, developed one after the other, and show only a relative and -temporary persistence; species arise out of varieties. The differences -in the conditions of life have a modifying influence on the -organization, the general form, and the parts of animals, and so has the -use or disuse of organs. In the first beginning only the very simplest -and lowest animals and plants came into existence; those of a more -complex organization only at a later period. The course of the earth's -development, and that of its organic inhabitants, was continuous, not -interrupted by violent revolutions. Life is purely a physical -phenomenon. All the phenomena of life depend on mechanical, physical, -and chemical causes, which are inherent in the nature of matter itself. -The simplest animals and the simplest plants, which stand at the lowest -point in the scale of organization, have originated and still originate -by spontaneous generation. All animate natural bodies or organisms are -subject to the same laws as inanimate natural bodies or anorgana. The -ideas and actions of the understanding are the motional phenomena of the -central nervous system. The will is in truth never free. Reason is only -a higher degree of development and combination of judgments." - -These are indeed astonishingly bold, grand, and far-reaching views, and -were expressed by Lamarck sixty years ago; in fact, at a time when their -establishment, by a mass of facts, was not nearly as possible as it is -in our day. Indeed Lamarck's work is really a complete and strictly -monistic (mechanical) system of nature, and all the important general -principles of monistic Biology are already enunciated by him: the unity -of the active causes in organic and inorganic nature; the ultimate -explanation of these causes in the chemical and physical properties of -matter itself; the absence of a special vital power, or of an organic -final cause; the derivation of all organisms from some few, most simple -original forms, which have come into existence by spontaneous generation -out of inorganic matter; the coherent course of the whole earth's -history; the absence of violent cataclysmic revolutions; and in general -the inconceivableness of any miracle, of any supernatural interference, -in the natural course of the development of matter. - -The fact that Lamarck's wonderful intellectual feat met with scarcely -any recognition, arises partly from the immense length of the gigantic -stride with which he had advanced beyond the next fifty years, partly -from its defective empirical foundation, and from the somewhat one-sided -character of some of his arguments. Lamarck quite correctly recognizes -_Adaptation_ as the first mechanical cause which effects the continual -transformation of organic forms, while he traces with equal justice the -similarity in form of different species, genera, families, etc., to -their blood-relationship, and thus explains it by _Inheritance_. -Adaptation, according to him, consists in this, that the perpetual, slow -change of the outer world causes a corresponding change in the actions -of organisms, and thereby also causes a further change in their forms. -He lays the greatest stress upon the effect of _habit_ upon the use and -disuse of organs. This is certainly of great importance in the -transformation of organic forms, as we shall see later. However, the way -in which Lamarck wished to explain exclusively, or at any rate mainly, -the change of forms, is after all in most cases not possible. He says, -for example, that the long neck of the giraffe has arisen from its -constantly stretching out its neck at high trees, and from the endeavour -to pick the leaves off their branches; as giraffes generally inhabit dry -districts, where only the foliage of trees afford them nourishment, they -were forced to this action. In like manner the long tongues of -wood-peckers, humming-birds, and ant-eaters, are said by him to have -arisen from the habit of fetching their food out of narrow, small, and -deep crevices or channels. The webs between the toes of the webbed feet -in frogs and other aquatic animals have arisen solely from the constant -endeavour to swim, from striking their feet against the water, and from -the very movements of swimming. Inheritance fixed these habits on the -descendants, and finally, by further elaboration, the organs were -entirely transformed. However correct, as a whole, this fundamental -thought may be, yet Lamarck lays the stress too exclusively on _habit_ -(use and non-use of organs), certainly one of the most important, but -not the only cause of the change of forms. Still this cannot prevent our -acknowledging that Lamarck quite correctly appreciated the mutual -co-operation of the two organic formative tendencies of Adaptation and -Inheritance. What he failed to grasp is the exceedingly important -principle of "Natural Selection in the Struggle for Existence," with -which Darwin, fifty years later, made us acquainted. - -It still remains to be mentioned as a special merit of Lamarck, that he -endeavoured to prove the _development of the human race_ from other -primitive, ape-like mammals. Here again it was, above all, to habit that -he ascribed the transforming, the ennobling influence. He assumed that -the lowest, original men had originated out of men-like apes, by the -latter accustoming themselves to walk upright. The raising of the body, -the constant effort to keep upright, in the first place led to a -transformation of the limbs, to a stronger differentiation or separation -of the fore and hinder extremities, which is justly considered one of -the most essential distinctions between man and the ape. Behind, the -calf of the leg and the flat soles of the feet were developed; in -front, the arms and hands, for the purpose of seizing objects. The -upright walk was then followed by a freer view over the surrounding -objects, and led consequently to an important progress in mental -development. Human apes thereby soon gained a great advantage over the -other apes, and further, over surrounding organisms in general. In order -to maintain the supremacy over them, they formed themselves into -companies, and there arose, as in the case of all animals living in -company, the desire of communicating to one another their desires and -thoughts. Thus arose the necessity of language, which, consisting at -first of rough and disjointed sounds, soon became more connected, -developed, and articulate. The development of articulate speech now in -turn became the strongest lever for a further progressive development of -the organism, and above all, of the brain, and so ape-like men became -gradually and slowly transformed into real men. In this way the actual -descent of the lowest and rudest primitive men from the most highly -developed apes was distinctly maintained by Lamarck, and supported by a -series of the most important proofs. - -The honour of being the chief French nature-philosopher is not usually -assigned to Lamarck, but to Etienne Geoffroy St. Hilaire (the elder), -born in 1771, the same in whom Goethe was especially interested, and -with whom we have already become acquainted as Cuvier's most prominent -opponent. He developed his ideas about the transformation of organic -species as far back as the end of the last century, but published them -only in the year 1828, and then in the following years, especially in -1830, defended them bravely against Cuvier. Geoffroy St. Hilaire in all -essentials adopted Lamarck's Theory of Descent, yet he believed that -the transformation of animal and vegetable species was less effected by -the action of the organism itself (by habit, practice, use, or disuse of -organs) than by the "monde ambiant," that is, by the continual change of -the outer world, especially of the atmosphere. He conceives the organism -as passive, in regard to the vital conditions of the outer world, while -Lamarck, on the contrary, regards it as active. Geoffroy thinks, for -example, that birds originated from lizard-like reptiles, simply by a -diminution of the carbonic acid in the atmosphere, in consequence of -which the breathing process became more animated and energetic through -the increased proportion of oxygen in the atmosphere. Thus there arose a -higher temperature of the blood, an increased activity of the nerves and -muscles, and the scales of the reptiles became the feathers of the -birds, etc. This conception is based upon a correct thought, but -although the change of the atmosphere, as well as the change of every -other external condition of existence, certainly effects directly or -indirectly the transformation of the organism, yet this single cause is -by itself too unimportant for such effects to be ascribed to it. It is -even less important than practice and habit, upon which Lamarck lays too -much stress. Geoffroy's chief merit consists in his having vindicated -the monistic conception of nature, the unity of organic forms, and the -deep genealogical connection of the different organic types in the face -of Cuvier's powerful influence. I have already mentioned in the -preceding chapter (pp. 87, 88) the celebrated disputes between the two -great opponents in the Academy of Paris, especially the fierce conflicts -on the 22nd of February, and on the 19th of July, in which Goethe took -so lively an interest. On that occasion Cuvier remained the -acknowledged victor, and since that time very little, or rather nothing, -more has been done in France to further the development of the Doctrine -of Filiation, and complete the monistic theory of development. This is -evidently to be ascribed principally to the repressive influence -exercised by Cuvier's great authority. Even at the present day the -majority of the French naturalists are the disciples and blind followers -of Cuvier. In no civilized country of Europe has Darwin's doctrine had -so little effect and been so little understood as in France, so that in -the further course of our examination we need not take the French -naturalists into consideration. At most, there are two distinguished -botanists, among the recent French naturalists, whom we may mention as -having ventured to express themselves in favour of the mutability and -transformation of species. These two men are Naudin (1852) and Lecoq -(1854). - -Having discussed the early services of German and French -nature-philosophy in establishing the doctrine of descent, we turn to -the third great country of Europe, to free England, which during the -last ten years has become the chief seat and starting-point for the -further working out and definite establishment of the theory of -development. Englishmen, who now take such an active part in every great -scientific progress of humanity, and are the first to promote the -eternal truths of natural science, at the beginning of the century took -but little part in the continental nature-philosophy and its most -important progress, the Theory of Descent. Almost the only earlier -English naturalist whom we have here to mention is Erasmus Darwin, the -grandfather of the reformer of the Theory of Descent. In 1795 he -published, under the title of "Zoonomia," a scientific work in which he -expresses views very similar to those of Goethe and Lamarck, without, -however, then knowing anything about these two men. It is evident that -the Theory of Descent at that time pervaded the intellectual atmosphere. -Erasmus Darwin lays great stress upon the transformation of animal and -vegetable species by their own vital action and by their becoming -accustomed to changed conditions of existence, etc. Next, W. Herbert, in -1822, expressed the opinion that species of animals and plants are -nothing but varieties which have become permanent. In like manner Grant, -in Edinburgh, in 1826, declared that new species proceed from existing -species by continued transformation. In 1841 Freke maintained that all -organic beings must be descended from a single primitive type. In 1852 -Herbert Spencer demonstrated minutely, and in a very clear and -philosophic manner, the necessity of the Doctrine of Filiation, and -established it more firmly in his excellent "Essays," which appeared in -1858, and in his "Principles of Biology," which was published at a later -date. He has, at the same time, the great merit of having applied the -theory of development to psychology, and of having shown that the -emotional and intellectual faculties could only have been acquired by -degrees and developed gradually. Lastly, we have to mention that in 1859 -Huxley, the first of English zoologists, spoke of the Theory of Descent -as the only hypothesis of creation reconcilable with scientific -physiology. The same year produced the "Introduction to the Flora of -Tasmania," in which Hooker, the celebrated English botanist, adopts the -Theory of Descent, supporting it with important observations of his -own. - -All the naturalists and philosophers with whom we have become acquainted -in this brief historical survey, as men adopting the Theory of -Development, merely arrived at the conception that all the different -species of animals and plants which at any time have lived, and still -live, upon the earth, are the gradually changed and transformed -descendants of one or some few original and very simple prototypes, -which latter arose out of inorganic matter by spontaneous generation. -But none of them succeeded in placing this fundamental element of the -doctrine of descent in relation with some cause, nor in satisfactorily -explaining the transformation of organic species by the true -demonstration of its mechanical antecedents. Charles Darwin was the -first who solved this most difficult problem, and this forms the broad -gulf which separates him from his predecessors. - -The special merit of Charles Darwin is, in my opinion, twofold: in the -first place, the doctrine of descent, the fundamental idea of which was -already clearly expressed by Goethe and Lamarck, has been developed by -him much more comprehensively, has been traced much more minutely in all -directions, and carried out much more strictly and connectedly than by -any of his predecessors; and secondly, he has established a new theory, -which reveals to us the natural causes of organic development, the -acting causes (causæ efficientes) of organic form-production, and of the -changes and transformations of animal and vegetable species. This is the -theory which we call the Theory of Selection, or more accurately, the -Theory of Natural Selection (selectio naturalis). - -When we reflect that (with the few exceptions above mentioned) the -whole science of Biology, before Darwin's time, was elaborated in -accordance with the opposite views, and that almost all zoologists and -botanists regarded the absolute independence of organic species as a -self-evident inference from the results of all study of forms, we shall -certainly not lightly value the twofold merit of Darwin. The false -doctrine of the constancy and independent creation of individual species -had gained such high authority, was so generally recognized, and was, -moreover, so much favoured by delusive appearances, accepted by -superficial observation, that, indeed, no small degree of courage, -strength, and intelligence was required to rise as a reformer against -its omnipotence, and to dash to pieces the structure artificially -erected upon it. But, in addition to this, Darwin added to Lamarck's and -Goethe's doctrine of descent the new and highly important principle of -"natural selection." - -We must sharply distinguish the two points--though this is usually not -done--first, Lamarck's Theory of Descent, which only asserts _that_ all -animal and vegetable species are descended from common, most simple, and -spontaneously generated prototypes; and secondly, Darwin's Theory of -Selection, which shows us _why_ this progressive transformation of -organic forms took place, and what causes, acting mechanically, effected -the uninterrupted production of new forms, and the ever increasing -variety of animals and plants. - -Darwin's immortal merit cannot be justly estimated until a later period, -when the Theory of Development, after overthrowing all other theories of -creation, will be recognized as the supreme principle of explanation in -Anthropology, and, consequently, in all other sciences. At present, -while in the hot contest for truth the name of Darwin is the watchword -to the advocates of the natural theory of development, his merits are -inaccurately appreciated on both sides, for some persons overestimate -them as much as others underestimate them. - -His merit is overestimated when he is regarded as the founder of the -Theory of Descent, or of the whole of the Theory of Development. We have -seen from the historical sketch in this and the preceding chapters, that -the Theory of Development, as such, is not new; all philosophers who -have refused to be led captive by the blind dogma of a supernatural -creation, have been compelled to assume a natural development. But the -Theory of Descent constituting the specially biological part of the -universal Theory of Development, had already been so clearly expressed -by Lamarck, and carried out so fully by him to its most important -consequences, that we must honour him as the real founder of it. Hence -it is only the Theory of Selection, and not that of Descent, which may -be called _Darwinism_; but this is in itself of so much importance, that -its value can scarcely be overestimated. - -Darwin's merit is naturally underestimated by all his opponents. But it -is scarcely possible in this matter to point to scientific opponents, -who are entitled by profound biological culture to pronounce an opinion. -For among all the works opposed to Darwin and the Theory of Descent yet -published, with the exception of that of Agassiz, not one deserves -consideration, much less refutation; all have so evidently been written -either without thorough knowledge of biological facts, or without a -clear philosophical understanding of the question in hand. We need not -trouble ourselves at all about the attacks of theologians and other -unscientific men, who really know nothing whatever of nature. - -The only eminent scientific adversary who still remains opposed to -Darwin and the whole theory of development is Louis Agassiz; but the -principle of his opposition in reality deserves notice only as a -philosophical curiosity. In a French translation of his "Essay on -Classification,"(5) which we have spoken of before, published in Paris -in 1869, Agassiz has most formally announced his opposition to -Darwinism, which he had previously expressed in many ways. To this -translation he has appended a treatise of sixteen pages, bearing the -title, "Le Darwinisme. Classification de Haeckel." This curious chapter -contains the most wonderful things; as, for example, "Darwin's idea is a -conception _à priori_. Darwinism is a burlesque of facts. Science would -renounce the claim which it has hitherto possessed to the confidence of -earnest minds if such sketches were to be accepted as indications of a -true progress." The following passage, however, is the climax of this -strange polemic: "Darwinism shuts out almost the whole mass of acquired -knowledge in order to retain and assimilate to itself that only which -may serve its doctrine." - -Surely this is what we may call turning the whole affair topsy-turvy! -The biologist who knows the facts must be astounded at Agassiz's courage -in uttering such sentences--sentences without a word of truth in them, -and which he cannot himself believe! The impregnable strength of the -Theory of Descent lies just in the fact that all biological facts are -explicable only through it, and that without it they remain -unintelligible miracles. All our "laborious knowledge" in comparative -anatomy and physiology--in embryology and palæontology--in the doctrine -of the geographical and topographical distribution of organisms, etc., -constitutes an irrefutable testimony to the truth of the Theory of -Descent. - -In my General Morphology, especially in the sixth book (in the General -Phylogeny), I have minutely refuted Agassiz's "Essay on Classification" -in all essential points. The twenty-fourth chapter I have devoted to a -very detailed and strictly scientific discussion of that section which -Agassiz himself considers the most important (the groups or categories -of systematic zoology and botany), and have shown that this part of his -work is purely chimerical, without any trace of real foundation. Agassiz -takes good care not to venture anywhere to touch upon my refutation, -because, forsooth, he is not in a position to produce anything -substantial against it. He fights not with arguments, but with phrases. -However, such opposition will not delay the complete victory of the -Theory of Development, but only accelerate it. - - - - -CHAPTER VI. - -THEORY OF DEVELOPMENT ACCORDING TO LYELL AND DARWIN. - - - Charles Lyell's Principles of Geology.--His Natural - History of the Earth's Development.--Origin of the - Greatest Effects through the Multiplication of the - Smallest Causes.--Unlimited Extent of Geological - Periods.--Lyell's Refutation of Cuvier's History of - Creation.--The Establishment of the Uninterrupted - Connection of Historical Development by Lyell and - Darwin.--Biographical Notice of Charles Darwin.--His - Scientific Works.--His Theory of Coral Reefs.--Development - of the Theory of Selection.--A Letter of Darwin's.--The - Contemporaneous Appearance of Darwin's and Alfred - Wallace's Theory of Selection.--Darwin's Study of Domestic - Animals and Cultivated Plants.--Andreas Wagner's notions - as to the Special Creation of Cultivated Organisms for the - good of Man.--The Tree of Knowledge in - Paradise.--Comparison between Wild and Cultivated - Organisms.--Darwin's Study of Domestic - Pigeons.--Importance of Pigeon Breeding.--Common Descent - of all Races of Pigeons. - - -During the thirty years, from 1830 until 1859, when Darwin's work -appeared, the ideas of creation introduced by Cuvier remained -predominant in the sciences of organic nature. People rested satisfied -with the unscientific assumption, that in the course of the earth's -history, a series of inexplicable revolutions had periodically -annihilated the whole world of animals and plants, and that at the end -of each revolution, and the beginning of a new period, a new enlarged, -and improved edition of the organic population had appeared. Although -the number of these editions of creation was altogether problematical, -and in truth could not be fixed at all, and although the numerous -advances which, during this time, were made in all the departments of -zoology and botany demonstrated more and more that Cuvier's hypothesis -was unfounded and untenable, and that Lamarck's natural theory of -development was nearer the truth, yet the former maintained its -authority almost universally among biologists. This must, above all, be -ascribed to the veneration which Cuvier had acquired, and strikingly -illustrates how injurious to the progress of humanity a faith in any -definite authority may become. Authority, as Goethe once admirably said, -perpetuates the individual, which as an individual should pass away, -rejects and allows to pass that which should be held fast, and is the -main obstacle to the advance of humanity. - -It is only by having regard to the great weight of Cuvier's authority, -and to the mighty potency of human indolence, which is with difficulty -induced to depart from the broad and comfortable way of everyday -conceptions, and to enter upon new paths not yet made easy, that we can -comprehend how it is that Lamarck's Theory of Descent did not gain its -due recognition until 1859, after Darwin had given it a new foundation. -The soil had long been prepared for it by the works of Charles Lyell, -another English naturalist, whose views are of great importance for the -natural history of creation, and must accordingly here be briefly -explained. - -In 1830 Charles Lyell published, under the title of "Principles of -Geology," a work in which he thoroughly reformed the science of Geology -and the history of the earth's development, and effected this reform in -a manner similar to that in which, thirty years later, Darwin in his -work reformed the science of Biology. Lyell's great treatise, which -radically destroyed Cuvier's hypothesis of creation, appeared in the -same year in which Cuvier celebrated his triumph over the -nature-philosophy, and established his supremacy in the domain of -morphology for the following thirty years. Whilst Cuvier, by his -artificial hypothesis of creation and his theory of catastrophes -connected with it, directly obstructed the path of the theory of natural -development, and cut off all chance of a natural explanation, Lyell once -more opened a free road, and brought forward convincing geological -evidence to show that Cuvier's dualistic conceptions were as unfounded -as they were superfluous. He demonstrated that those changes of the -earth's surface, which are still taking place before our eyes, are -perfectly sufficient to explain everything we know of the development of -the earth's crust in general, and that it is superfluous and useless to -seek for mysterious causes in inexplicable revolutions. He showed that -we need only have recourse to the hypothesis of exceedingly long periods -of time in order to explain the formation of the crust of the earth in -the simplest and most natural manner by means of the very same causes -which are still active. Many geologists had previously imagined that the -highest chains of mountains which rise on the surface of the earth could -owe their origin only to enormous revolutions transforming a great part -of the earth's surface, especially to colossal volcanic eruptions. Such -chains of mountains as those of the Alps or the Cordilleras were -believed to have arisen direct from the fiery fluid of the interior of -the earth, through an enormous chasm in the broken crust. Lyell, on the -other hand, showed that we can explain the formation of such enormous -chains of mountains quite naturally by the same slow and imperceptible -risings and depressions of the earth's surface which are still -continually taking place, and the causes of which are by no means -miraculous. Although these depressions and risings may perhaps amount -only to a few inches, or at most a few feet, in the course of a century; -still, in the course of some millions of years they are perfectly -sufficient to raise up the highest chains of mountains, without the aid -of mysterious and incomprehensible revolutions. In like manner, the -meteorological action of the atmosphere, the influence of rain and snow, -and, lastly, the breakers on the coasts, which by themselves seem to -produce an insignificant effect, must cause the greatest changes if we -only allow sufficiently long periods for their action. The -multiplication of the smallest causes produces the greatest effects. -Drops of water produce a cavity in a rock. - -I shall afterwards be obliged again to recur to the immeasurable length -of geological periods which are necessary for this purpose, for, as we -shall see, Darwin's theory, as well as that of Lyell, renders the -assumption of immense periods absolutely necessary. If the earth and its -organisms have actually developed in a natural way, this slow and -gradual development must certainly have taken a length of time which -surpasses our powers of comprehension. But as many men see in this very -circumstance one of the principal difficulties in the way of those -theories of development, I beg leave here to remark that we have not a -single rational ground for conceiving the time requisite to be limited -in any way. Not only many ordinary persons, but even eminent -naturalists, make it their chief objection to these theories, that they -arbitrarily claim too great a length of time: yet the ground of -objection is scarcely intelligible. For it is absolutely impossible to -see what can, in any way, limit us in assuming long periods of time. We -have long known, even from the structure of the stratified crust of the -earth alone, that its origin and the formation of neptunic rocks from -water must have taken, at least, several millions of years. From a -strictly philosophical point of view, it makes no difference whether we -hypothetically assume for this process ten millions or ten thousand -billions of years. Before us and behind us lies eternity. If the -assumption of such enormous periods is opposed to the feelings of many, -I regard this simply as the consequence of false notions which are -impressed upon us from our earliest youth concerning the short history -of the earth, which is said to embrace only a few thousands of years. -Albert Lange, in his "History of Materialism,"(12) has convincingly -shown that from a strictly philosophical point of view it is far less -objectionable in a scientific hypothesis to assume periods which are too -long than periods which are too short. Every process of development is -the more intelligible the longer it is assumed to last. A short and -limited period is the most improbable. - -I have no space here to enter minutely into Lyell's great work, and will -therefore mention only its most important result, which is, that he -completely refuted Cuvier's history of creation with its mythical -revolutions, and established in its place the constant and slow -transformation of the earth's crust by the continued action of forces, -which are still working on the earth's surface, viz., the movement of -water and the volcanic fluid of the interior of earth. Lyell thus -demonstrated a continuous and uninterrupted connection of the whole -history of the earth, and he proved it so irrefutably, and established -so convincingly the supremacy of the "existing causes," that is, of the -causes which are still active in the transformation of the earth's -crust, that Geology in a short time completely renounced Cuvier's -hypothesis. - -Now, it is remarkable that Palæontology, the science of petrifactions, -so far as it was pursued by botanists and zoologists, remained -apparently unaffected by this great progress in geology. Biology still -continued to assume repeated new creations of the whole animal and -vegetable kingdoms, at the beginning of every new period of the earth's -history, although this hypothesis of individual creations, shoved into -the world one after the other, without the assumption of Cuvier's -cataclysms, became pure nonsense, and lost its foundation. It is -evidently perfectly absurd to assume a distinct new creation of the -whole world of animals and plants at definite epochs, without the crust -of the earth itself experiencing any considerable general revolution. -And although this conception is most closely connected with Cuvier's -theory of catastrophes, still it prevailed when the latter had been -completely destroyed and abandoned. - -It was reserved for the great English naturalist, Charles Darwin, to -remove this contradiction, and to show that the organic beings of the -earth have a history as continuous and connected as the inorganic crust -of the earth; that animals and plants have arisen from one another by as -gradual a transmutation as that by which the varying forms of the -earth's crust, the forms of the continents, and of the seas surrounding -and separating them, have arisen out of earlier and quite different -forms. In this respect we may truly say that in the domain of Zoology -and Botany Darwin made the same progress as Lyell, his great countryman, -in the domain of Geology. Both proved the _uninterrupted connection of -the historical development_, and demonstrated a gradual transmutation of -the different conditions succeeding one another. - -The special merit of Darwin, as I have already remarked in a preceding -chapter, is twofold. In the first place, he has treated the Theory of -Descent, put forth by Lamarck and Goethe, in a much more comprehensive -manner, as a whole, and carried it out in a much more connected manner, -than had been done by any one of his predecessors. Secondly, he has -established the causal foundation of this Theory of Descent by the -Theory of Selection, which is peculiarly his own; that is, he has -demonstrated the acting _causes of the changes_ which the Theory of -Descent simply stated, as _facts_. The Theory of Descent, introduced -into Biology in 1809, by Lamarck, asserts that all the different species -of animals and plants are descended from a single or some few most -simple prototypes, produced by spontaneous generation. The Theory of -Selection, established in 1859 by Darwin, shows us _why_ this must be -so; it points out the acting causes in a manner with which Kant would -have been delighted, and indeed, in the domain of organic nature, Darwin -has become the Newton whose advent Kant thought himself entitled -prophetically to deny. - -Now, before we approach Darwin's theory, it will perhaps be of interest -to notice a few details as to the personal character of this great -naturalist, as to his life, and the way in which he was led to form his -doctrine. Charles Robert Darwin was born at Shrewsbury, on the Severn, -on the 12th of February, 1809; therefore, at present he is sixty-three -years old. In his seventeenth year (1825) he entered the University of -Edinburgh, and two years later Christ's College, Cambridge. When -scarcely twenty-two years old, in 1831, he was invited to take part in a -scientific expedition which was sent out by England, in order to survey -accurately the southernmost point of South America, and to examine -several parts of the South Seas. This expedition, like many other -voyages of inquiry fitted out in a praiseworthy manner by England, had -scientific objects, and at the same time was intended to solve practical -problems relating to navigation. The vessel, commanded by Captain -Fitzroy, appropriately bore the symbolic name of the _Beagle_. The -voyage of the _Beagle_, which lasted five years, was of the highest -importance to the full development of Darwin's genius; for in the very -first year, when he set his foot on the soil of South America, the -outline of the doctrine of descent dawned upon him. Darwin himself has -described this voyage in a work which is written in a very attractive -style, and the perusal of which I strongly recommend to the reader. This -book of travel, which lies far above the usual average in interest, not -only shows in a very charming manner Darwin's amiable character, but we -can in many ways recognize the various steps by which he arrived at his -conceptions. The result of the voyage was, first, a large scientific -work, the zoological and geological portion of which belong in a great -measure to Darwin; and secondly, a celebrated work by him alone on Coral -Reefs, which in itself would have sufficed to secure to him a lasting -reputation. It is well known that the islands in the South Seas consist -for the most part of coral reefs, and are surrounded by them. Formerly -no satisfactory explanation could be given of their different and -remarkable forms, and of their relation to those islands which are not -formed of corals. It was reserved for Darwin to solve this difficult -problem, for together with the constructive action of the coral -zoophytes, he assumed geological risings and depressions of the bottom -of the sea to account for the origin of the different forms of reefs. -Darwin's Theory of the Origin of Coral Reefs, like his later one as to -the Origin of Organic Species, is a theory which fully explains the -phenomenon, and for this purpose assumes only the simplest natural -causes, without hypothetically supporting it with any unknown processes. -Among the remaining works of Darwin, I must not pass over his excellent -monograph on Cirrhipedia, a curious class of marine animals, which in -their outward appearance resemble mussels, and were actually considered -by Cuvier as Molluscs possessing two shells, while in truth they -belonged to the Crustacea (crabs). - -The extraordinary hardships to which Darwin had been exposed during his -voyage in the _Beagle_ had injured his health to such a degree, that -after his return home he was obliged to withdraw from the restless -turmoil of London life, and since then has lived in quiet retirement on -his estate at Down, near Bromley, in Kent. This seclusion from the -restless activity of the great city certainly exercised a beneficial -influence upon Darwin, and it is probable that we owe to it, at least -partially, the formation of the Theory of Selection. Undisturbed by the -various engagements which in London would have wasted his strength, he -was enabled to concentrate his attention upon the great problem to -which his mind had been turned during his voyage in the _Beagle_. In -order to show what kind of observations during the voyage principally -gave rise to the fundamental idea of the Theory of Selection, and in -what manner he afterwards worked it out, I shall insert here a passage -from a letter which he addressed to me on the 8th of October, 1864. - - -_Letter from Charles Darwin to Haeckel, 8th October, 1864._ - -"In South America three classes of facts were brought strongly before my -mind. _Firstly_, the manner in which closely allied species replace -species in going southward. _Secondly_, the close affinity of the -species inhabiting the islands near South America to those proper to the -continent. This struck me profoundly, especially the difference of the -species in the adjoining islets in the Galopagos Archipelago. _Thirdly_, -the relation of the living Edentata and Rodentia to the extinct species. -I shall never forget my astonishment when I dug out a gigantic piece of -armour like that of the living armadillo. - -"Reflecting on these facts, and collecting analogous ones, it seemed to -me probable that allied species were descended from a common parent. But -for some years I could not conceive how each form became so excellently -adapted to its habits of life. I then began systematically to study -domestic productions, and after a time saw clearly that man's selective -power was the most important agent. I was prepared, from having studied -the habits of animals, to appreciate the struggle for existence, and my -work in geology gave me some idea of the lapse of past time. Therefore, -when I happened to read "Malthus on Population," the idea of natural -selection flashed on me. Of all the minor points, the last which I -appreciated was the importance and cause of the principle of -divergence." - - -During the leisure and retirement in which Darwin lived after his -return, he occupied himself, as we see from this letter, first and -specially with the study of organisms in their cultivated state; that -is, domestic animals and garden plants. This was undoubtedly the most -likely way to arrive at the Theory of Selection. In this, as in all his -labours, Darwin proceeded with extreme care and accuracy. With wonderful -caution and self-denial, he published nothing on this subject during a -period of twenty-one years, from 1837 to 1858, not even a preliminary -sketch of his theory, which he had written as early as 1844. He was -always anxious to collect still more certain experimental proofs, in -order to be able to establish his theory in a complete form, and on the -broadest possible foundation of experience. While he was thus aiming at -the greatest possible perfection, which might perhaps have led him never -to publish his theory at all, he was fortunately disturbed by a -countryman of his, who, independently of Darwin, had discovered the -Theory of Selection, and in 1858 sent its outlines to Darwin himself, -with the request to hand them to Lyell for publication in some English -journal. This was Alfred Wallace, one of the boldest and most -distinguished scientific travellers of modern times. For many years -Wallace had wandered alone in the wilds of the Sunda Islands, in the -dense primitive forests of the Indian Archipelago; and during this close -and comprehensive study of one of the richest and most interesting parts -of the earth, with its great variety of animals and plants, he had -arrived at exactly the same general views regarding the origin of -organic species as Darwin. Lyell and Hooker, both of whom had long known -Darwin's work, now induced him to publish a short extract from his -manuscripts simultaneously with the manuscript sent him by Wallace. They -appeared in the _Journal of the Linnean Society_, August, 1858. - -Darwin's great work "On the Origin of Species," in which the Theory of -Selection is carried out in detail, appeared in November, 1859. Darwin -himself, however, characterizes this book (of which a fifth edition -appeared in 1869, and the German translation by Bronn as early as -1860)(1) as only a preliminary extract from a larger and more detailed -work, which is to contain a mass of facts in favour of his theory, and -comprehensive and experimental proofs. The first part of the larger work -promised by Darwin appeared in 1868, under the title, "The Variations of -Animals and Plants in the State of Domestication," and has been -translated into German by Victor Carus.(14) It contains a rich abundance -of the most valuable evidence as to the extraordinary changes of organic -forms which man can produce by cultivation and artificial selection. -However much we are indebted to Darwin for this abundance of convincing -facts, still we do not by any means share the opinion of those -naturalists who hold that the Theory of Selection requires for its -actual proof these further details. It is our opinion that Darwin's -first work, which appeared in 1859, already contains sufficient proof. -The unassailable strength of his theory does not lie in the immense -amount of individual facts that may be adduced as proofs, but in the -harmonious connection of all the great and general phenomena of organic -nature, which agree in bearing testimony to the truth of the Theory of -Selection. - -Darwin, at first, intentionally did not notice the important conclusion -from his Theory of Descent, namely, the descent of the human race from -other mammals. It was not till this highly important conclusion had been -definitely established by other naturalists as the necessary sequel of -the doctrine of descent, that Darwin himself expressly endorsed it, and -thereby completed his system. This was done in the highly interesting -work, "The Descent of Man, and Sexual Selection," which appeared as late -as 1871, and has likewise been translated into German by Victor -Carus.(48) - -The careful study which Darwin devoted to _domestic animals and -cultivated plants_ was of the greatest importance in establishing the -Theory of Selection. The infinitely varied changes of form which man has -produced in these domesticated organisms by artificial selection are of -the very highest importance for a right understanding of animal and -vegetable forms; and yet this study has, down to the most recent times, -been most grossly neglected by zoologists and botanists. Without -entering upon the discussion of the significance to be attached to the -idea of species itself, they have filled not only bulky volumes, but -whole libraries, with descriptions of individual species, and with most -childish controversies as to whether these species are good, or -tolerably good, and bad, or tolerably bad. If naturalists instead of -spending their time on these useless fancies had duly studied cultivated -organisms, and had examined the transmutation of the living forms, -instead of the individual dead ones, they would not have been led -captive so long by the fetters of Cuvier's dogma. But as cultivated -organisms are so extremely inconvenient to the dogmatic conception of -the permanence of species, naturalists to a great extent intentionally -did not concern themselves about them, and even celebrated naturalists -have often expressed the opinion that cultivated organisms, domesticated -animals and garden plants, are artificial productions of man, and that -their formation and transformation could not decide anything about the -nature of species and about the origin of the forms of species that live -in a natural state. - -This perverse view went so far that, for example, Andreas Wagner, a -zoologist of Munich, quite seriously made the following ridiculous -assertion:--"Animals and plants in their wild state have been called -into being by the Creator as distinctly different and unchangeable -species; but in the case of domestic animals and cultivated plants this -was not necessary, because he formed them from the beginning for the use -of man. The Creator formed man out of a clod of earth, breathed the -living breath into his nostrils, and then created for him the different -useful domestic animals and garden plants, among which he thought well -to save himself the trouble of distinguishing species." Unfortunately, -Andreas Wagner does not tell us whether the _Tree of Knowledge_ in -Paradise was a "good" wild species, or, as a cultivated plant, "no -species" at all. As the Tree of Knowledge was placed by the Creator in -the centre of Paradise, we might be inclined to believe that it was a -highly favoured cultivated plant, and therefore no species at all. But -since, on the other hand, the fruit of the Tree of Knowledge was -forbidden to man, and since many men, as Wagner himself clearly shows, -have never eaten of the fruit, it was evidently not created for the use -of man, and therefore in all probability was a _real species!_ What a -pity Wagner has not given us any information about this important and -difficult problem! - -Now, however ridiculous this view may appear to us, it is only the -logical sequence of a false view (which is widely spread) of the special -nature of cultivated organisms, and one may occasionally hear similar -objections from naturalists of great reputation. I must most decidedly, -and at once, condemn this utterly false conception. It is the same -perverseness which is committed by physicians who maintain that diseases -are artificial productions, and not natural phenomena. It has been a -work of hard labour to combat this prejudice, and it is only in recent -times that men have generally adopted the view that diseases are nothing -but natural changes of the organisms, or really natural phenomena of -life, which are produced by changed and abnormal conditions of -existence. Disease, therefore, is not a life beyond Nature's realm (vita -præter naturam), as the early physicians used to say, but a natural life -under conditions which produce illness and threaten the body with -danger. Just in the same manner, cultivated organic forms are not -artificial works of man, but natural productions which have arisen under -the influence of peculiar conditions of life. Man by his culture can -never directly produce a new organic form, but he can breed organisms -under new conditions of life, which are such as to influence and -transform them. All domestic animals and all garden plants are -originally descended from wild species, which have been transformed by -the peculiar conditions of culture. - -A thorough comparison of cultivated forms (races and varieties) with -organisms not altered by cultivation (species and varieties), is of the -utmost importance to the theory of selection. What is most surprising in -such a comparison is the remarkably short time in which man can produce -a new form, and the high degree in which this form, produced by man, can -deviate from the original form. While wild animals and plants, one year -after another, appear to the zoologist and botanist approximately in the -same form, so as to have given rise to the false doctrine of the -constancy of species, domestic animals and garden plants, on the other -hand, display the greatest changes within a few years. The perfection -which gardeners and farmers have attained in the art of selection now -enables them, in the space of a few years, arbitrarily to create -entirely new animal and vegetable forms. For this purpose it is only -necessary to keep and propagate the organism under the influence of -special conditions--which are capable of producing new formations--and -even at the end of a few generations new species may be obtained, which -differ from the original form in a much higher degree than so-called -good species in a wild state differ from one another. This fact is -extremely important, and we cannot lay sufficient stress upon it. The -assertion is not true that cultivated forms descended from one and the -same primary form do not differ from one another as much as wild animal -and vegetable species differ among themselves. If we only make -comparisons, without prejudice, we can very easily perceive that a -number of races or varieties which have been derived from a single -cultivated form, within a short series of years, differ from one another -in a higher degree than so-called good species (bonæ species), or even -different genera of one family, in the wild state. - -In order to establish this extremely important fact as firmly as -possible by experiments, Darwin decided to make a special study of the -whole extent of variation in form in a single group of domesticated -animals, and for this purpose he chose the _domestic pigeons_, which are -in many respects especially suited for such a study. For a long time he -kept on his estate all possible races and varieties of pigeons which he -was able to procure, and he was helped in this by rich contributions -from all parts of the world. He also joined two London pigeon clubs, the -members of which passionately, and with truly artistic skill, carry on -the breeding of the different forms of pigeons. Lastly, he formed -connections with some of the most celebrated pigeon-fanciers; so that he -could command the richest experimental material. - -The art of, and fancy for, pigeon breeding is very ancient. Even more -than 3,000 years before Christ, it was carried on by the Egyptians. The -Romans, under the emperors, laid out enormous sums upon the breeding of -pigeons, and kept accurate pedigrees of their descent, just as the Arabs -keep genealogical pedigrees of their horses, and the Mecklenburg -aristocracy of their own ancestors. In Asia, too, among the wealthy -princes, pigeon breeding was a very ancient fancy; in 1600, the court of -Akber Khan possessed more than 20,000 pigeons. Thus in the course of -several centuries, and in consequence of the various methods of breeding -practised in the different parts of the world, there has arisen out of -one single originally tamed form, an immense number of different races -and varieties, which in their most divergent forms are extremely -different from one another, and are often curiously characterized. - -One of the most striking races of pigeons is the well-known fan-tailed -pigeon, which spreads its tail like the peacock, and carries a number of -(from thirty to forty) feathers placed in the form of radii, while other -pigeons possess much fewer tail feathers--generally twelve. We may here -mention that the number of feathers on the tails of birds is considered -by naturalists of great value as a systematic distinction, so that whole -orders can thereby be distinguished. For example, singing birds, almost -without exception, possess twelve tail feathers; chirping birds -(Strisores) ten, etc. Several races of pigeons, moreover, are -characterized by a tuft of neck feathers, which form a kind of periwig; -others by grotesque transformation of their beaks and feet, by peculiar -and often very remarkable decorations, as, for example, skinny lappets, -which develop on the head; by a large crop, which is formed by the -gullet being strongly inclined forward, etc. Remarkable, also, are the -strange habits which many pigeons have acquired; for example, the turtle -pigeons and the trumpeters with their musical accomplishments, the -carriers with their topographical instinct. The tumblers have the -strange habit of ascending into the air in great numbers, then turning -over and falling down through the air as if dead. The ways and habits of -these endless races of pigeons--the form, size, and colour of the -individual parts of their bodies, and their proportions, differ in a -most astonishing degree from one another; in a much higher degree than -is the case with the so-called good species, or even with the perfectly -distinct genera, of wild pigeons. And what is of the greatest -importance, is the fact that these differences are not confined to the -external form, but extend even to the most important internal parts; -there even occur great modifications of the skeleton and of the -muscular tissues. For example, we find great differences in the number -of vertebræ and ribs, in the size and shape of the gaps in the -breast-bones, in the size and shape of the merry-thought, in the lower -jaw, in the facial bones, etc. In short, the bony skeleton, which -morphologists consider a very permanent part of the body, and which -never varies to such an extent as the external parts--shows such great -changes, that many races of pigeons might be described as special -genera, and this would doubtless be done if all these different forms -had been found in a wild and natural state. - -How far the differences of the races of pigeons have been carried is -best shown by the fact that all pigeon breeders are unanimously of -opinion that each peculiar or specially marked race of pigeons must be -derived from a corresponding wild original species. It is true every one -assumes a different number of original species. Yet Darwin has most -convincingly and acutely proved that all these pigeons, without -exception, must be derived from a single wild primary species--from the -blue rock-pigeon (_Columba livia_). In like manner, it can be proved of -most of the domestic animals and cultivated plants, that all the -different races are descendants of a single original wild species which -has been brought by man into a cultivated condition. - -An example similar to that of the domestic pigeons is furnished among -mammals by our tame _rabbit_. All zoologists, without exception, have -long considered it proved that all its races and varieties are descended -from the common wild rabbit, that is, from a single primary species. And -yet the extreme forms of these races differ to such a degree from one -another, that every zoologist, if he met with them in a wild state, -would unhesitatingly designate them not only as an entirely distinct -"good species," but even as species of entirely different genera of the -Leporid family. Not only does the colour, length of hair, and other -qualities of the fur of the different tame races of rabbits vary -exceedingly, and form extremely broad contrasts, but, what is still more -important, the typical form of the skeleton and its individual parts do -so also, especially the form of the skull and the jaw (which is of such -importance in systematic arrangement); further, the relative proportion -of the length of the ears, legs, etc. In all these respects the races of -tame rabbits avowedly differ from one another far more than all the -different forms of wild rabbits and hares which are scattered over all -the earth, and are the recognized "good species" of the genus _Lepus_. -And yet, in the face of these clear facts, the opponents of the theory -of development maintain that the wild species are not descended from a -common prototype, although they at once admit it in the case of the tame -races. With opponents who so intentionally close their eyes against the -clear light of truth, no further dispute can be carried on. - -While in this manner it appears certain that the domestic races of -pigeons, of tame rabbits, of horses, etc., notwithstanding the -remarkable difference of their varieties, are descended in each case -from but one wild, so-called "species"; yet, on the other hand, it is -certainly probable that the great variety of races of some of the -domestic animals, especially dogs, pigs, and oxen, must be ascribed to -the existence of several wild prototypes, which have become mixed. It -is, however, to be observed that the number of these originally wild -primary species is always much smaller than that of the cultivated forms -proceeding from their mingling and selection, and naturally they were -originally derived from a single primary ancestor, common to the whole -genus. In no case is each separate cultivated race descended from a -distinct wild species. - -In opposition to this, almost all farmers and gardeners maintain, with -the greatest confidence, that each separate race bred by them must be -descended from a separate wild primary species, because they clearly -perceive the differences of the races, and attach very high importance -to the inheritance of their qualities; but they do not take into -consideration the fact that these qualities have arisen only by the slow -accumulation of small and scarcely observable changes. In this respect -it is extremely instructive to compare cultivated races with wild -species. - -Many naturalists, and especially the opponents of the Theory of -Development, have taken the greatest trouble to discover some -morphological or physiological mark, some characteristic property, -whereby the artificially bred and cultivated races may be clearly and -thoroughly distinguished from wild species which have arisen naturally. -All these attempts have completely failed, and have led only with -increasing certainty to the result, that such a distinction is -altogether impossible. I have minutely discussed this fact, and -illustrated it by examples in my criticism of the idea of species. (Gen. -Morph. ii. 323-364.) - -I may here briefly touch on yet another side of this question, because -not only the opponents, but even a few of the most distinguished -followers of Darwin--for example, Huxley--have regarded the phenomena of -_bastard-breeding_, or _hybridism_, as one of the weakest points of -Darwinism. Between cultivated races and wild species, they say, there -exists this difference, that the former are capable of producing -fruitful bastards, but that the latter are not. Two different cultivated -races, or wild _varieties of one species_, are said in all cases to -possess the power of producing bastards which can fruitfully mix with -one another, or with one of their parent forms, and thus propagate -themselves; on the other hand, _two really different species_, two -cultivated or wild _species_ of one genus, are said _never_ to be able -to produce from one another bastards which can be fruitfully crossed -with one another, or with one of their parent species. - -As regards the first of these assertions, it is simply refuted by the -fact that there are organisms which do not mix at all with their own -ancestors, and therefore can produce no fruitful descendants. Thus, for -example, our cultivated guinea-pig does not bear with its wild Brazilian -ancestor; and again, the domestic cat of Paraguay, which is descended -from our European domestic cat, no longer bears with the latter. Between -different races of our domestic dogs, for example, between the large -Newfoundland dogs and the dwarfed lap-dogs, breeding is impossible, even -for simple mechanical reasons. A particularly interesting instance is -afforded by the Porto-Santo rabbit (Lepus Huxleyi). In the year 1419, a -few rabbits, born on board ship of a tame Spanish rabbit, were put on -the island of Porto Santo, near Madeira. These little animals, there -being no beasts of prey, in a short time increased so enormously that -they became a pest to the country, and even compelled a colony to remove -from the island. They still inhabit the island in great numbers; but in -the course of four hundred and fifty years they have developed into a -quite peculiar variety--or if you will have it, into a "good -species"--which is distinguished by a peculiar colour, a rat-like shape, -small size, nocturnal life, and extraordinary wildness. The most -important fact, however, is that this new species, which I call _Lepus -Huxleyi_, no longer pairs with its European parent rabbit, and no longer -produces bastards with it. - -On the other hand, we now know of numerous examples of fruitful genuine -bastards; that is, of mixings that have proceeded from the crossing of -two entirely different species, and yet propagate themselves with one -another as well as with one of their parent species. A number of such -bastard species (species Hybridæ) have long been known to botanists; for -example, among the genera of the thistle (Cirsium), the laburnum -(Cytisus), the bramble (Rubus), etc. Among animals also they are by no -means rare, perhaps even very frequent. We know of fruitful bastards -which have arisen from the crossing of two different species of a genus, -as among several genera of butterflies (Zygæna, Saturnia), the family of -carps, finches, poultry, dogs, cats, etc. One of the most interesting is -the hare-rabbit (Lepus Darwinii), the bastard of our indigenous hare and -rabbit, many generations of which have been bred in France, since 1850, -for gastronomic purposes. I myself possess such hybrids, the products of -pure in-breeding, that is, both parents of which are themselves hybrids -by a hare-father and a rabbit-mother. I possess them through the -kindness of Professor Conrad, who has repeatedly made these experiments -in breeding on his estate. The half-blood hybrid thus bred, which I name -in honour of Darwin, appears to propagate itself through many -generations by pure in-breeding, just as well as any genuine species. -Although on the whole it is more like its mother (rabbit), still in the -formation of the ears and of the hind-legs, it possesses distinct -qualities of its father (hare). Its flesh has an excellent taste, rather -resembling that of a hare, though the colour is more like that of a -rabbit. But the hare (Lepus timidus) and the rabbit (Lepus cuniculus) -are two species of the genus Lepus, so different that no systematic -zoologist will recognize them as varieties of one species. Both species, -moreover, live in such different ways, and in their wild state entertain -so great an aversion towards one another, that they do not pair so long -as they are left free. If, however, the newly-born young ones of both -species are brought up together, this aversion is not developed; they -pair with one another and produce the _Lepus Darwinii_. - -Another remarkable instance of the crossing of different species (where -the two species belong even to different genera!) is furnished by the -fruitful hybrids of sheep and goats which have for a long time been bred -in Chili for industrial purposes. On what unessential circumstances in -the sexual mingling the fertility of the different species depend, is -shown by the fact that he-goats and sheep in their mingling produce -fruitful hybrids, while the ram and she-goat pair very rarely, and then -without result. The phenomena of hybridism to which undue importance has -been erroneously attributed are thus utterly unmeaning, so far as the -idea of species is concerned. The breeding of hybrids does not enable -us, any more than other phenomena, thoroughly to distinguish cultivated -races from wild species; and this circumstance is of the greatest -importance in the Theory of Selection. - - - - -CHAPTER VII. - -THE THEORY OF SELECTION (DARWINISM). - - - Darwinism (Theory of Selection) and Lamarckism (Theory of - Descent).--The Process of Artificial Breeding.--Selection - of the Different Individuals for After-breeding.--The - Active Causes of Transmutation.--Change connected with - Food, and Transmission by Inheritance connected with - Propagation.--Mechanical Nature of these Two - Physiological Functions.--The Process of Natural - Breeding: Selection in the Struggle for - Existence.--Malthus' Theory of Population.--The - Proportion between the Numbers of Potential and Actual - Individuals of every Species of Organisms.--General - Struggle for Existence, or Competition to attain the - Necessaries of Life.--Transforming Force of the Struggle - for Existence.--Comparison of Natural and Artificial - Breeding.--Selection in the Life of Man.--Military and - Medical Selection. - - -It is, properly speaking, not quite correctly that the Theory of -Development, with which we are occupied in these pages, is usually -called Darwinism. For, as we have seen from the historical sketch in the -previous chapters, the most important foundation of the Theory of -Development--that is, the Doctrine of Filiation, or Descent--had already -been distinctly enunciated at the beginning of our century, and had been -definitely introduced into science by Lamarck. The portion of the Theory -of Development which maintains the common descent of all species of -animals and plants from the simplest common original forms might, -therefore, in honour of its eminent founder, and with full justice, be -called _Lamarckism_, if the merit of having carried out such a principle -is to be linked to the name of a single distinguished naturalist. On the -other hand, the Theory of Selection, or breeding, might be justly called -_Darwinism_, being that portion of the Theory of Development which shows -us in what way and _why_ the different species of organisms have -developed from those simplest primary forms. (Gen. Morph. ii. 166.) - -It is true we find the first trace of an idea of natural selection even -forty years before the appearance of Darwin's work. For in the year 1818 -there was published a paper "On a woman of the white race whose skin -partly resembled that of a negro," which had been read before the Royal -Society as early as 1813. Its author, Dr. W. C. Wells, states that -negroes and mulattoes are distinguished from the white race by their -immunity from certain tropical diseases. On this occasion he remarks -that all animals have a tendency to change up to a certain degree, and -that farmers, by availing themselves of this tendency, and also by -selection, improve their domestic animals; and then he adds, that what -is done in this latter case "by art, seems to be done with equal -efficiency, though more slowly, by nature, in the formation of varieties -of mankind fitted for the country which they inhabit. Of the accidental -varieties of man which would occur among the first few and scattered -inhabitants of the middle regions of Africa, some one would be better -fitted than the others to bear the diseases of the country. This race -would consequently multiply, while the others would decrease; not only -from their inability to sustain the attacks of disease, but from their -incapacity of contending with their more vigorous neighbours. The -colour of this vigorous race I take for granted, from what has been -already said, would be dark. But the same disposition to form varieties -still existing, a darker and a darker race would in the course of time -occur; and as the darkest would be the best fitted for the climate, this -would at length become the most prevalent, if not the only race, in the -particular country in which it had originated." He then extends these -same views to the white inhabitants of colder climates. Although Wells -clearly expresses and recognizes the principle of natural selection, yet -it is applied by him only to the very limited problem of the origin of -human races, and not at all to that of the origin of animal and -vegetable species. Darwin's great merit in having independently -developed the Theory of Selection, and having brought it to complete and -well merited recognition, is as little affected by the earlier and long -forgotten remark of Wells, as by some other fragmentary observations -about natural selection made by Patrick Mathew, and hidden in his book -on "Timber for Shipbuilding, and the Cultivation of Trees," which -appeared in 1831. The celebrated traveller, Alfred Wallace, who -developed the Theory of Selection independently of Darwin, and had -published it in 1858, simultaneously with Darwin's first contribution, -likewise stands far behind his greater and elder countryman in regard to -profound conception, as well as to extended application of the theory. -In fact Darwin, by his extremely comprehensive and ingenious development -of the whole doctrine, has acquired a fair claim to see the theory -connected with his own name. - -This Theory of Selection, Darwinism in its proper sense, to the -consideration of which we now turn our attention, rests essentially (as -has already been intimated in the last chapter) upon the comparison of -those means which man employs in the breeding of domestic animals and -the cultivation of garden plants, with those processes which in free -nature, outside the cultivated state, lead to the coming into existence -of new species and new genera. We must therefore, in order to understand -the latter processes, first turn to the artificial breeding by man, as -was, in fact, done by Darwin himself. We must inquire into the results -to which man attains by his artificial breeding, and what means are -applied in order to obtain those results; and we must then ask -ourselves, "Are there in nature similar forces and causes acting -similarly to those resorted to by man?" - -First, in regard to artificial breeding, we start from the fact last -discussed above, viz., that its products in some cases differ from one -another much more than the productions of natural breeding. It is a fact -that races or varieties often differ from one another in a much greater -degree and in much more important qualities than many so-called species, -or "good species,"--nay, sometimes even more than so-called "good -genera" in their natural state. Compare, for example, the different -kinds of apples which the art of horticulture has derived from one and -the same original apple-form, or compare the different races of horses -which their breeders have derived from one and the same original form of -horse, and it will be easily observed that the differences of the most -different forms are extremely important, and much more important than -the so-called "specific differences," which are referred to by -zoologists and botanists when comparing wild forms for the purpose of -distinguishing several so-called "good species." - -Now, by what means does man produce this extraordinary difference or -divergence of several forms which are proved to be descended from the -same primary form? In order to answer this question, let us follow a -gardener who desires to produce a new form of a plant, which is -distinguished by the beautiful colour of its flowers. He will first of -all make a selection from a great number of plants which are seedlings -from one and the same parent. He will pick out those plants which -exhibit most distinctly the colour of flower he desires. The colour of -flowers is a very changeable thing. Plants, for example, which as a rule -have a white flower, frequently show deviations into the blue or red. -Now, supposing the gardener wishes to obtain the red colour in a plant -usually producing white flowers, he will very carefully, from among the -many different individuals which are the descendants of one and the same -seed-plant, select those which most distinctly show a reddish tint, and -sow them exclusively, in order to produce new individuals of the same -kind. He would cast aside and no longer cultivate the other seedlings -which show a white or less distinct red colour. He will propagate -exclusively the individual plants whose blossoms show the red most -markedly, and he will sow the seeds produced by these selected plants. -From the seedlings of this second generation, he will again carefully -select those in which the red, which is now visible in the majority of -them, is most distinctly displayed. If such a selection is carried on -during a series of six or ten generations, and if the flower which shows -the deepest red is most carefully selected, the gardener in the sixth or -tenth generation will obtain the desired plants with flowers of a pure -red. - -The farmer wishing to breed a special race of animals, for example, a -kind of sheep distinguished by particularly fine wool, proceeds in the -same manner. The only process applied in the improvement of wool -consists in this, that the farmer with the greatest care and -perseverance selects from a whole flock of sheep those individuals which -have the finest wool. These only are used in breeding, and among the -descendants of these selected sheep, those again are chosen which have -the finest wool, etc. If this careful selection is carried on through a -series of generations, the selected breeding-sheep are in the end -distinguished by a wool which differs very strikingly from the wool of -the original parent, and this is exactly the advantage which the breeder -desired. - -The differences of the individuals that come into consideration in this -artificial selection are very slight. An ordinary unpractised man is -unable to discover the exceedingly minute differences of individuals -which a practised breeder perceives at the first glance. The business of -a breeder is not easy; it requires an exceedingly sharp eye, great -patience, and an extremely careful manner of treating the organisms to -be bred. In each individual generation, the differences of individuals -are perhaps not seen at all by the uninitiated; but by the accumulation -of these minute differences during a series of generations, the -deviation from the original form becomes in the end very great. It -becomes so great that the artificially produced form may in the end -differ far more from the original form than do two so-called "good -species" in their natural state. The art of breeding has now made such -progress, that man can often at discretion produce certain peculiarities -in cultivated species of animals and plants. To practised gardeners and -farmers, you may give distinct commissions, and say, for example, I wish -to have this species of plant with this or that colour, and with this or -that shape. Where breeding has reached the perfection which it has -attained in England, gardeners and farmers are frequently able to -furnish to order the desired result within a definite period, that is, -at the end of a number of generations. Sir John Sebright, one of the -most experienced English pigeon-breeders, could assert that in three -years he would produce any form of feather, but that he required six -years to obtain any desired form of the head and beak. In the process of -breeding the merino-sheep of Saxony, the animals are three times placed -on a table beside one another, and most carefully compared and studied. -Each time only the best sheep with the finest wool are selected, so that -in the end, out of a great multitude, there remain only some few -animals, but their wool is exquisitely fine, and only these last are -used in breeding. We see, therefore, that the causes through which, in -artificial breeding, great effects are produced, are unusually simple, -and these great effects are obtained simply by accumulating the -differences which in themselves are very insignificant, and become -surprisingly increased by a continually repeated selection. - -Before we pass on to a comparison of this artificial with natural -breeding, let us see what natural qualities of the organisms are made -use of by the artificial breeder or cultivator. We can trace all the -different qualities which here come into play to physiological -fundamental qualities of the organism, which are common to all animals -and plants, and are most closely connected with the functions of -_propagation_ and _nutrition_. These two fundamental qualities are -_transmissivity_, or the capability of _transmitting by inheritance_, -and _mutability_, or the capability of _adaptation_. The breeder starts -from the fact that all the individuals of one and the same species are -different, though in a very slight degree, a fact which is as true of -organisms in a wild as in a cultivated state. If you look about you in a -forest consisting of only a single species of tree, for example of -beech, you will certainly not find in the whole forest two trees of this -kind which are absolutely identical or perfectly equal in the form of -their branches, the number of their branches and leaves, blossoms and -fruits. Special differences occur everywhere, just as in the case of -men. There are no two men who are absolutely identical, perfectly equal -in size, in the formation of their faces, the number of their hairs, -their temperament, character, etc. The very same is true of individuals -of all the different species of animals and plants. It is true that in -most organisms the differences are very trifling to the eye of the -uninitiated. Everything here essentially depends on the exercise of the -faculty of discovering these often very minute differences of form. The -shepherd, for example, knows every individual of his flock, solely by -accurately observing their features, while the uninitiated are incapable -of distinguishing at all the different individuals of one and the same -flock. This fact of the individual difference is the extremely important -foundation on which the whole of man's power of breeding rests. If -individual differences did not exist everywhere, man would not be able -to produce a number of different varieties or races from one and the -same original stock. We must, at the outset, hold fast the principle -that the phenomenon is quite universal; we must necessarily assume it -even where, with the imperfect capabilities of our senses, we are unable -to discover differences. Among the higher plants (the phanerogams, or -flower-plants), where the individual stocks show such numerous -differences in the number of branches or leaves, and in the formation of -the stem and branches, we can almost always easily perceive these -differences. But this is not the case in the lower plants, such as -mosses, algæ, fungi, and in most animals, especially the lower ones. The -distinction of all the individuals of one species is here, for the most -part, extremely difficult or altogether impossible. But there is no -reason for ascribing individual differences only to those organisms in -which we can perceive them at once. We may, on the contrary, with full -certainty assume such individuality as a universal quality of all -organisms, and we can do this all the more surely since we are able to -trace the mutability of individuals to the mechanical conditions of -nutrition. We can show that by influencing nutrition we are able to -produce striking individual differences where they would not exist if -the conditions of nutrition had not been altered. The many complicated -conditions of nutrition are never absolutely identical in two -individuals of a species. - -Now, just as we see that the mutability or capability of adaptation has -a causal connection with the general relations of nutrition in animals -and plants, so too we find the second fundamental phenomenon of life, -with which we are here concerned, namely, the capability of -_transmitting by inheritance_, to have a direct connection with the -phenomenon of _propagation_. The second thing that a farmer or gardener -does in artificial breeding, after he has selected, and has consequently -availed himself of the mutability, is to endeavour to hold fast and -develop the modified forms by Inheritance. He starts from the universal -fact that children resemble their parents, that "the apple does not fall -far from the tree." This phenomenon of Inheritance has hitherto been -scientifically examined only to a very small extent, which may partly -arise from the fact that the phenomenon is of such everyday occurrence. -Every one considers it quite natural that every species should produce -its like; that a horse should not suddenly produce a goose, or a goose a -frog. We are accustomed to look upon these everyday occurrences of -Inheritance as self-evident. But this phenomenon is not so simply -self-evident as it appears at first sight, and in the examination of -Inheritance the fact is very frequently overlooked that the different -descendants, derived from one and the same parents, are in reality -_never_ quite identical, and also never absolutely like the parents, but -are always slightly different. We cannot formulate the principle of -Inheritance, as "Like produces like," but we must limit the expression -to "Similar things produce similar things." The gardener, as well as the -farmer, avails himself of the fact of Inheritance in its widest form, -and indeed with special regard to the fact that not only those qualities -of organisms are transmitted by inheritance which they have inherited -from _their_ parents but those also which they themselves have -_acquired_. This is an important point upon which very much depends. An -organism can transmit to its descendants not only those qualities of -form, colour, and size which it has inherited from its parents, but it -can also transmit changes of these qualities, which it has acquired -during its own life through the influence of outward circumstances, such -as climate, nourishment, training, etc. - -These are the two fundamental qualities of animals and plants of which -the breeder must avail himself in order to produce new forms. The -theoretical principle of breeding is, indeed, extremely simple, but in -detail the practical application of this simple principle is difficult -and immensely complicated. A thoughtful breeder, acting according to a -definite plan, must understand the art of correctly estimating, in every -case, the general interaction between the two fundamental qualities of -heirship and mutability. - -Now, if we examine the real nature of those two important properties of -life, we find that we can trace them, like all physiological functions, -to physical and chemical causes, to the properties and the phenomena of -motion of those substances of which the bodies of animals and plants -consist. As we shall hereafter have to show in the more accurate -consideration of these two functions, the transmission by _Inheritance_, -if we express ourselves quite generally, is essentially dependent upon -the material continuity and partial identity of the matter in the -producing and produced organism, the parents and the child. In every act -of breeding a certain quantity of protoplasm or albuminous matter is -transferred from the parents to the child, and along with it there is -transferred the individually _peculiar molecular motion_. These -molecular phenomena of motion in the protoplasm, which call forth the -phenomena of life, and are their active and true cause, differ more or -less in all living individuals; they are of infinite variety. - -_Adaptation_, or transmutation is, on the other hand, essentially the -consequence of material influences, which the substance of the organism -experiences from the material surrounding it,--in the widest sense of -the word from the _conditions_ of life. The external influences of the -latter are communicated to the individual parts of the body by the -molecular processes of nutrition. In every act of Adaptation the -individual molecular motion of the protoplasm, peculiar to each part, -disturbs and modifies the whole individual, or part of it, by -mechanical, physical, or chemical influences. The innate, inherited -vital actions of the protoplasm--that is, the molecular phenomena of -motion of the smallest albuminous particles--are therefore more or less -modified by it. The phenomenon of Adaptation, or transmutation, depends -therefore upon the material influence which the organism experiences -from its surroundings, or its conditions of existence; while the -transmission by Inheritance is due to the partial identity of the -producing and produced organism. These are the real, simple, mechanical -foundations of the artificial process of breeding. - -Now Darwin asked himself, Does there exist a similar process of -selection in nature, and are there forces in nature which take the place -of man's activity in artificial selection? Is there a natural tendency -among wild animals and plants which acts selectingly, in a similar -manner to the artificial selection practised by the designing will of -man? All here depended upon the discovery of such a relation, and Darwin -succeeded in this so satisfactorily, that we consider his theory of -selection completely sufficient to explain, mechanically, the origin of -the wild species of animals and plants. That relation which in free -nature influences the forms of animals and plants, by selecting and -transforming them, is called by Darwin the "_Struggle for Existence_." - -The "Struggle for Existence" has rapidly become a watchword of the day. -Yet this designation is, perhaps, in many respects not very happily -chosen, and the phenomena might probably have been more accurately -described as "_Competition for the Means of Subsistence_." For under the -name of "Struggle for Life," many relations are comprehended which -properly and strictly speaking do not belong to it. As we have seen from -the letter inserted in the last chapter, Darwin arrived at the idea of -the "Struggle for Existence" from the study of Malthus' book "On the -Conditions and the Consequences of the Increase of Population." It was -proved in that important work, that the number of human beings, on the -average, increases in a geometrical progression, while the amount of -articles of food increase only in an arithmetical progression. This -disproportion gives rise to a number of inconveniences in the human -community, which cause among men a continual competition to obtain the -necessary means of life, which do not suffice for all. - -Darwin's theory of the struggle for life is, to a certain extent, a -general application of Malthus' theory of population to the whole of -organic nature. It starts from the consideration that the number of -_possible_ organic individuals which might arise from the germs -produced, is far greater than the number of _actual_ individuals which, -in fact, do simultaneously live on the earth's surface. The number of -possible or _potential individuals_ is given us by the number of the -eggs and organic germs produced by organisms. The number of these germs, -from each of which, under favourable circumstances, an individual might -arise, is very much larger than the number of real or actual -_individuals_--that is, of those that really arise from these germs, -come into life, and propagate themselves. By far the greater number of -germs perish in the earliest stage of life, and it is only some favoured -organisms which manage to develop, and actually survive the first period -of early youth, and finally succeed in propagating themselves. This -important fact is easily proved by a comparison of the number of eggs in -a given species with the number of individuals which exist of this -species. These numerical relations show the most striking contrast. -There are, for example, species of fowls which lay great numbers of -eggs, and yet are among the rarest of birds; and the bird which is said -to be the commonest (the most widely spread) of all, the stormy petrel -(_Procellaria glacialis_), lays only a single egg. The relation is the -same in other animals. There are many very rare invertebrate animals, -which lay immense quantities of eggs; and others again which produce -only very few eggs, and yet are among the commonest of animals. Take, -for example, the proportion which is observed among the human -tape-worms. Each tape-worm produces within a short period millions of -eggs, while man, in whom these tape-worms are lodged, forms a far -smaller number of eggs, and yet fortunately there are fewer tape-worms -than human beings. In like manner, among plants there are many splendid -orchids, which produce thousands of seeds and yet are very rare, and -some kinds of asters (Compositæ), which have but few seeds, are -exceedingly common. - -This important fact might be illustrated by an immense number of -examples. It is evidently, therefore, not the number of actually -existing germs which indicates the number of individuals which -afterwards come into life and maintain themselves in life; but rather -the case is this, that the number of adult individuals is limited by -other circumstances, especially by the relations in which the organism -stands to its organic and inorganic surroundings. Every organism, from -the commencement of its existence, struggles with a number of hostile -influences: it struggles against animals which feed on it, and to which -it is the natural food, against animals of prey and parasites; it -struggles against inorganic influences of the most varied kinds, against -temperature, weather, and other circumstances; but it also struggles -(and this is much the most important!), above all, against organisms -most like and akin to itself. Every individual, of every animal and -vegetable species, is engaged in the fiercest competition with every -other individual of the same species which lives in the same place with -it. In the economy of nature the means of subsistence are nowhere -scattered in abundance, but are very limited, and far from sufficient -for the number of organisms which might develop from the germs produced. -Therefore the young individuals of most species of animals and -vegetables must have hard work in obtaining the means of subsistence; -this necessarily causes a competition among them in order to obtain the -indispensable supplies of life. - -This great competition for the necessaries of life goes on everywhere -and at all times, among human beings and animals as well as among -plants; in the case of the latter this circumstance, at first sight, is -not so clearly apparent. If we examine a field which is richly sown with -wheat, we can see that of the numerous young plants (perhaps some -thousands) which shoot up on a limited space, only a very small -proportion preserve themselves in life. A competition takes place for -the space of ground which each plant requires for fixing its root, a -competition for sunlight and moisture. And in the same manner we find -that, among all animal species, all the individuals of one and the same -species compete with one another to obtain these indispensable means of -life, or the conditions of existence in the wide sense of the word. They -are equally indispensable to all, but really fall to the lot of only a -few--"Many are called, but few are chosen." The fact of the great -competition is quite universal. You need only to cast a glance at human -society, where this competition exists everywhere, and in all the -different branches of human activity. Here, too, a struggle is brought -about by the free competition of the different labourers of one and the -same class. Here too, as everywhere, this competition benefits the -thing, or the work, which is the object of competition. The greater and -more general the competition, the more quickly improvements and -inventions are made in the branch of labour, and the higher is the grade -of perfection of the labourers themselves. - -The position of the different individuals in this struggle for life is -evidently very unequal. Starting from the inequality of individuals, -which is a recognized fact, we must in all cases necessarily suppose -that all the individuals of one and the same species do not have equally -favourable prospects. Even at the beginning they are differently placed -in this competition by their different strengths and abilities, -independently of the fact that the conditions of existence are -different, and act differently at every point of the earth's surface. We -evidently have an infinite combination of influences, which, together -with the original inequality of the individuals during the competition -for the conditions of existence, favour some individuals and prejudice -others. The favoured individuals will gain the victory over the others, -and while the latter perish more or less early, without leaving any -descendants, the former alone will be able to survive and finally to -propagate the species. As, therefore, it is clear that in the struggle -for life the favoured individuals succeed in propagating themselves, we -shall (even as the result of this relation) perceive in the next -generation differences from the preceding one. Some individuals of this -second generation, though perhaps not all of them, will, by inheritance, -receive the individual advantage by which their parents gained the -victory over their rivals. - -But now--and this is a very important law of inheritance--if such a -transmission of a favourable character is continued through a series of -generations, it is not simply transmitted in the original manner, but it -is constantly increased and strengthened, and in a last generation it -attains a strength which distinguishes this generation very essentially -from the original parent. Let us, for example, examine a number of -plants of one and the same species which grow together in a very dry -soil. As the hairs on the leaves of plants are very useful for receiving -moisture from the air, and as the hairs on the leaves are very -changeable, the individuals possessing the thickest hair on their leaves -will have an advantage in this unfavourable locality where the plants -have directly to struggle with the want of water, and in addition to -this have to compete with one another for the possession of what little -water there may be. These alone hold out, while the others possessing -less hairy leaves perish; the more hairy ones will be propagated, and -their descendants will, on the average, be more distinguished by their -thick and strong hairs than the individuals of the first generation. If -this process is continued for several generations in one and the same -locality, there will arise at last such an increase of this -characteristic, such an increase of the hairs on the surface of the -leaf, that an entirely new species seems to present itself. It must here -be observed, that in consequence of the interactions of all the parts of -every organism, generally one individual part cannot be changed without -at the same time producing changes in other parts. If, for instance, in -our imaginary example, the number of the hairs on the leaves is greatly -increased, a certain amount of nourishment is thereby withdrawn from -other parts; the material which might be employed to form flowers or -seeds is diminished, and a smaller size of the flower or seed will then -be the direct or indirect consequence of the struggle for life, which in -the first place only produced a change in the leaves. Thus the struggle -for life, in this instance, acts as a means of selecting and -transforming. The struggle of the different individuals to obtain the -necessary conditions of existence, or, taking it in its widest sense, -the inter-relations of organisms to the whole of their surroundings, -produce mutations of form such as are produced in the cultivated state -by the action of man's selection. - -This agency will perhaps appear at first sight small and insignificant, -and the reader will not be inclined to concede to the action of such -relations the weight which it in reality possesses. I must therefore -find space in a subsequent chapter to put forward further examples of -the immense and far-reaching power of transformation exhibited in -natural selection. For the present I will confine myself to simply -placing side by side the two processes of artificial and natural -selection, and clearly explaining the agreement and the differences of -the two. - -Both natural and artificial selection are quite simple natural, -mechanical relations of life, which depend upon the _interaction_ of two -physiological functions, namely, on _Adaptation_ and _Inheritance_, -functions which, as such, must again be traced to physical and chemical -properties of organic matter. The difference between the two forms of -selection consists in this: in artificial selection the will of man -makes the selection according to a _plan_, whereas in natural selection, -the struggle for life (that universal inter-relation of organisms) acts -_without a plan_, but otherwise produces quite the same result, namely, -a selection of a particular kind of individuals for propagation. The -alterations produced by artificial selection are turned to the advantage -of _those who make the selection_; in natural selection, on the other -hand, to the advantage of the _selected organism_. - -These are the most essential differences and agreements of the two modes -of selection; it must, however, be further observed that there is -another difference, viz., in the duration of time required for the two -processes of selection. Man in his artificial selection can produce very -important changes in a very short time, while in natural selection -similar results are obtained only after a much longer time. This arises -from the fact that man can make his selection with much greater care. -Man is able with the greatest nicety to pick out individuals from a -large number, drop the others, and to employ only the privileged beings -for propagation, which is not the case in natural selection. In natural -conditions, besides the privileged individuals which first succeed in -propagating themselves, some few or many of the less distinguished -individuals will propagate themselves by the side of the former. -Moreover, man can prevent the crossing of the original and the new form, -which in natural selection is often unavoidable. If such a crossing, -that is, a sexual connection, of the new variety with the original forms -takes place, the offspring thereby produced generally returns to the -original character. In natural selection, such a crossing can be avoided -only when the new variety by migration separates from the original and -isolates itself. - -Natural selection therefore acts much more slowly; it requires much -longer periods than the artificial process of selection. But it is an -essential consequence of this difference, that the product of artificial -selection disappears much more easily, and that the new form returns -rapidly to the earlier one, which is not the case in natural selection. -The new species arising from natural selection maintain themselves much -more permanently, and return much less easily to the original form, than -is the case with products of artificial selection, and accordingly -maintain themselves during a much longer time than the artificial races -produced by man. But these are only subordinate differences, which are -explained by the different conditions of natural and artificial -selection, and in reality are connected only with differences in the -duration of time. The nature of the transformation and the means by -which it is produced are entirely the same in both artificial and -natural selection. (Gen. Morph. ii. 248.) - -The thoughtless and narrow-minded opponents of Darwin are never tired of -asserting that his theory of selection is a groundless conjecture, or at -least an hypothesis which has yet to be proved. That this assertion is -completely unfounded, may be perceived even from the outlines of the -doctrine of selection which have just been discussed. Darwin assumes no -kind of unknown forces of nature, nor hypothetical conditions, as the -acting causes for the transformation of organic forms, but solely and -simply the universally recognized vital activities of all organisms, -which we term _Inheritance_ and _Adaptation_. Every naturalist -acquainted with physiology knows that these two phenomena are directly -connected with the functions of propagation and nutrition, and, like all -other phenomena of life, are purely mechanical processes of nature, that -is, they depend upon the molecular phenomena of motion in organic -matter. That the interaction of these two functions effect a continual, -slow transmutation of organic forms, is a necessary result of the -struggle for existence. But this, again, is no more a hypothetical -relation, nor one requiring a proof, than is the interaction of -Inheritance and Adaptation. The struggle for life is a mathematical -necessity, arising from the disproportion between the limited number of -places in nature's household, and the excessive number of organic germs. -The origin of new species is moreover greatly favoured by the active or -passive _migrations_ of animals and plants, which takes place everywhere -and at all times, without being, however, entitled to rank as -_necessary_ agents in the process of natural selection. - -The origin of new species by natural selection, or, what is the same -thing, by the interaction of Inheritance and Adaptation in the struggle -for life, is therefore a _mathematical necessity_ of nature which needs -no further proof. Whoever, in spite of the present state of our -knowledge, still seeks for _proofs_ for the Theory of Selection, only -shows that he either does not thoroughly understand the theory, or is -not sufficiently acquainted with the biological facts--has not the -requisite amount of experimental knowledge in Anthropology, Zoology, and -Botany. - -If, as we maintain, natural selection is the great active cause which -has produced the whole wonderful variety of organic life on the earth, -all the interesting phenomena of _human life_ must also be explicable -from the same cause. For man is after all only a most highly-developed -vertebrate animal, and all aspects of human life have their parallels, -or, more correctly, their lower stages of development in the animal -kingdom. The whole history of nations, or what is called "Universal -History," must therefore be explicable by means of "natural -selection,"--must be a physico-chemical process, depending upon the -interaction of Adaptation and Inheritance in the struggle for life. And -this is actually the case. We shall give further proofs of this later -on. - -It appears of interest here to remark that not only _natural_ selection, -but also _artificial_ selection exercises its influence in many ways in -universal history. A remarkable instance of _artificial selection in -man_, on a great scale, is furnished by the ancient Spartans, among -whom, in obedience to a special law, all newly-born children were -subject to a careful examination and selection. All those that were -weak, sickly, or affected with any bodily infirmity, were killed. Only -the perfectly healthy and strong children were allowed to live, and they -alone afterwards propagated the race. By this means, the Spartan race -was not only continually preserved in excellent strength and vigour, but -the perfection of their bodies increased with every generation. No doubt -the Spartans owed their rare degree of masculine strength and rough -heroic valour (for which they are eminent in ancient history) in a -great measure to this artificial selection. - -Many tribes also among the Red Indians of North America (who at present -are succumbing in the struggle for life to the superior numbers of the -white intruders, in spite of a most heroic and courageous resistance) -owe their rare degree of bodily strength and warlike bravery to a -similar careful selection of the newly-born children. Among them, also, -all children that are weak or affected with any infirmity are -immediately killed, and only the perfectly strong individuals remain in -life, and propagate the race. That the race becomes greatly -strengthened, in the course of very many generations, by this artificial -selection cannot in itself be doubted, and is sufficiently proved by -many well known facts. - -The opposite of this artificial selection of the wild Redskins and the -ancient Spartans is seen in the individual selection which is -universally practised in our modern military states, for the purpose of -maintaining standing armies, and which, under the name of _military -selection_, we may conveniently consider as a special form of selection. -Unfortunately, in our day, militarism is more than ever prominent in our -so-called "civilization"; all the strength and all the wealth of -flourishing civilized states are squandered on its development; whereas -the education of the young, and public instruction, which are the -foundations of the true welfare of nations and the ennobling of -humanity, are neglected and mismanaged in a most pitiable manner. And -this is done in states which believe themselves to be the privileged -leaders of the highest human intelligence, and to stand at the head of -civilization. As is well known, in order to increase the standing army -as much as possible, all healthy and strong young men are annually -selected by a strict system of recruiting. The stronger, healthier, and -more spirited a youth is, the greater is his prospect of being killed by -needle-guns, cannons, and other similar instruments of civilization. All -youths that are unhealthy, weak, or affected with infirmities, on the -other hand, are spared by the "military selection," and remain at home -during the war, marry, and propagate themselves. The more useless, the -weaker, or infirmer the youth is, the greater is his prospect of -escaping the recruiting officer, and of founding a family. While the -healthy flower of youth dies on the battle-field, the feeble remainder -enjoy the satisfaction of reproduction and of transmitting all their -weaknesses and infirmities to their descendants. According to the laws -of transmission by inheritance, there must necessarily follow in each -succeeding generation, not only a further extension, but also a more -deeply-seated development of weakness of body, and what is inseparable -from it, a condition of mental weakness also. This and other forms of -artificial selection practised in our civilized states sufficiently -explain the sad fact that, in reality, weakness of the body and weakness -of character are on the perpetual increase among civilized nations, and -that, together with strong, healthy bodies, free and independent spirits -are becoming more and more scarce. - -To the increasing enervation of modern civilized nations, which is the -necessary consequence of military selection, there is further added -another evil. The progress of modern medical science, although still -little able really to cure diseases, yet possesses and practises more -than it used to do the art of prolonging life during lingering, chronic -diseases for many years. Such ravaging evils as consumption, scrofula, -syphilis, and also many forms of mental disorders, are transmitted by -inheritance to a great extent, and transferred by sickly parents to some -of their children, or even to the whole of their descendants. Now, the -longer the diseased parents, with medical assistance, can drag on their -sickly existence, the more numerous are the descendants who will inherit -incurable evils, and the greater will be the number of individuals, -again, in the succeeding generation, thanks to that artificial "_medical -selection_," who will be infected by their parents with lingering, -hereditary disease. - -If any one were to venture the proposal, after the examples of the -Spartans and Redskins, to kill, immediately upon their birth, all -miserable, crippled children to whom with certainty a sickly life could -be prophesied, instead of keeping them in life injurious to them and to -the race, our so-called "humane civilization" would utter a cry of -indignation. But the same "humane civilization" thinks it quite as it -should be, and accepts without a murmur, that at the outbreak of every -war (and in the present state of civilized life, and in the continual -development of standing armies, wars must naturally become more -frequent) hundreds and thousands of the finest men, full of youthful -vigour, are sacrificed in the hazardous game of battles. The same -"humane civilization" at present praises the abolition of capital -punishment as a "liberal measure!" And yet capital punishment for -incorrigible and degraded criminals is not only just, but also a benefit -to the better portion of mankind; the same benefit is done by destroying -luxuriant weeds, for the prosperity of a well cultivated garden. As by -a careful rooting out of weeds, light, air, and ground is gained for -good and useful plants, in like manner, by the indiscriminate -destruction of all incorrigible criminals, not only would the struggle -for life among the better portion of mankind be made easier, but also an -advantageous artificial process of selection would be set in practice, -since the possibility of transmitting their injurious qualities by -inheritance would be taken from those degenerate outcasts. - -Against the injurious influence of artificial military and medical -selection, we fortunately have a salutary counterpoise, in the -invincible and much more powerful influence of _natural selection_, -which prevails everywhere. For in the life of man, as well as in that of -animals and plants, this influence is the most important transforming -principle, and the strongest lever for progress and amelioration. The -result of the struggle for life is that, in the long run, that which is -better, because more perfect, conquers that which is weaker and -imperfect. In human life, however, this struggle for life will ever -become more and more of an intellectual struggle, not a struggle with -weapons of murder. The organ which, above all others, in man becomes -more perfect by the ennobling influence of natural selection, is the -_brain_. The man with the most perfect understanding, not the man with -the best revolver, will in the long run be victorious; he will transmit -to his descendants the qualities of the brain which assisted him in the -victory. Thus then we may justly hope, in spite of all the efforts of -retrograde forces, that the progress of mankind towards freedom, and -thus to the utmost perfection, will, by the happy influence of natural -selection, become more and more certain. - - - - -CHAPTER VIII. - -TRANSMISSION BY INHERITANCE AND PROPAGATION. - - - Universality of Inheritance and Transmission by - Inheritance.--Special Evidences of the same.--Human - Beings with four, six, or seven Fingers and - Toes.--Porcupine Men.--Transmission of Diseases, - especially Diseases of the Mind.--Original - Sin.--Hereditary Monarchies.--Hereditary - Aristocracy.--Hereditary Talents and Mental - Qualities.--Material Causes of Transmission by - Inheritance.--Connection between Transmission by - Inheritance and Propagation.--Spontaneous Generation and - Propagation.--Non-sexual or Monogonous - Propagation.--Propagation by Self-Division.--Monera and - Amoebæ.--Propagation by the formation of Buds, by the - formation of Germ-Buds, by the formation of - Germ-Cells.--Sexual or Amphigonous - Propagation.--Formation of Hermaphrodites.--Distinction - of Sexes, or Gonochorism.--Virginal Breeding, or - Parthenogenesis.--Material Transmission of Peculiarities - of both Parents to the Child by Sexual - Propagation.--Difference between Transmission by - Inheritance in Sexual and in Asexual Propagation. - - -The reader has, in the last chapter, become acquainted with natural -selection according to Darwin's theory, as the constructive force of -nature which produces the different forms of animal and vegetable -species. By natural selection we understand the interaction which takes -place in the struggle for life between the _transmission by inheritance_ -and the _mutability_ of organisms, between two physiological functions -which are innate in all animals and plants, and which may be traced to -other processes of life--the functions of propagation and nutrition. All -the different forms of organisms, which people are usually inclined to -look upon as the products of a creative power, acting for a definite -purpose, we, according to the Theory of Selection, can conceive as the -necessary productions of natural selection, working without a -purpose,--as the unconscious interaction between the two properties of -Mutability and Hereditivity. Considering the importance which -accordingly belongs to these vital properties of organisms, we must -examine them a little more closely, and employ a chapter with the -consideration of Transmission by Inheritance. (Gen. Morph. ii. 170-191.) - -Strictly speaking, we must distinguish between Hereditivity -(Transmissivity) and Inheritance (Transmission). Hereditivity is the -power of transmission, the capability of organisms to transfer their -peculiarities to their descendants by propagation. Transmission by -Inheritance, or Inheritance simply, on the other hand, denotes the -exercise of the capability, the actual transmission. - -Hereditivity and Transmission by Inheritance are such universal, -everyday phenomena, that most people do not heed them, and but few are -inclined to reflect upon the operation and import of these phenomena of -life. It is generally thought quite natural and self-evident that every -organism should produce its like, and that children should more or less -resemble their parents. Heredity is usually only taken notice of and -discussed in cases relating to some special peculiarity, which appears -for the first time in a human individual without having been inherited, -and then is transmitted to his descendants. It shows itself in a -specially striking manner in the case of certain diseases, and in -unusual and irregular (monstrous) deviations from the usual formation of -the body. - -Among these cases of the inheritance of monstrous deviations, those are -specially interesting which consist in an abnormal increase or decrease -of the number five in the fingers or toes of man. It is not unfrequently -observed in families through several generations, that individuals have -six fingers on each hand, or six toes on each foot. Less frequent is the -number of four or seven fingers or toes. The unusual formation arises at -first from a single individual who, from unknown causes, is born with an -excess of the usual number of fingers and toes, and transmits these, by -inheritance, to a portion of his descendants. In one and the same family -it has happened that, throughout three, four, or more generations, -individuals have possessed six fingers and toes. In a Spanish family -there were no less than forty individuals distinguished by this excess. -The transmission of the sixth finger or toe is not permanent or enduring -in all cases, because six-fingered people always intermarry again with -those possessing five fingers. If a six-fingered family were to -propagate by pure in-breeding, if six-fingered men were always to marry -six-fingered women, this characteristic would become permanent, and a -special six-fingered human race would arise. But as six-fingered men -usually marry five-fingered women, and _vice versâ_, their descendants -for the most part show a very mixed numerical relation, and finally, -after the course of some generations, revert again to the normal number -of five. Thus, for example, among eight children of a six-fingered -father and a five-fingered mother, two children may have on both hands -and feet six fingers and toes, four children may have a mixed number, -and two children may have the usual number of five on both hands and -feet. In a Spanish family, each child except the youngest had the number -six on both hands and feet; the youngest, only, had the usual number on -both hands and feet, and the six-fingered father of the child refused to -recognize the last one as his own. - -The power of inheritance, moreover, shows itself very strikingly in the -formation and colour of the human skin and hair. It is well known how -exactly the nature of the complexion in many families--for instance, a -peculiar soft or rough skin, a peculiar luxuriance of the hair, a -peculiar colour and largeness of the eyes--is transmitted through many -generations. In like manner, peculiar local growths or spots on the -skin, the so-called moles, freckles, and other accumulations of pigment -which appear in certain places, are frequently transmitted through -several generations so exactly, that in the descendants they appear on -the same spots on which they existed in the parents. The porcupine men -of the Lambert family, who lived in London last century, are especially -celebrated. Edward Lambert, born in 1717, was remarkable for a most -unusual and monstrous formation of the skin. His whole body was covered -with a horny substance, about an inch thick, which rose in the form of -numerous thorn-shaped and scale-like processes, more than an inch long. -This monstrous formation of the outer skin, or epidermis, was -transmitted by Lambert to his sons and grandsons, but not to his -granddaughters. The transmission in this instance remained in the male -line, as is often the case. In like manner, an excessive development of -fat in certain parts of the body is often transmitted only in the -female line. I scarcely need call to mind how exactly the characteristic -formation of the face is transmitted by inheritance; sometimes it -remains within the male, sometimes within the female line; sometimes it -is blended in both. - -The phenomena of transmission by inheritance of pathological conditions, -especially of the different forms of human diseases, are very -instructive and generally known. Diseases of the respiratory organs, the -glands, and of the nervous system, are specially liable to be -transmitted by inheritance. Very frequently there suddenly appears in an -otherwise healthy family a disease until then unknown among them; it is -produced by external causes, by conditions of life causing disease. This -disease, brought about in an individual by external cause, is propagated -and transmitted to his descendants, and some or all of them then suffer -from the same disease. In case of diseases of the lungs, for instance in -consumption, this sad transmission by inheritance is well known, and it -is the same with diseases of the liver, with syphilis, and diseases of -the mind. The latter are specially interesting. Just as peculiar -characteristic features of man--pride, ambition, frivolity, etc.--are -transmitted to the descendants strictly by inheritance, so too are the -peculiar abnormal manifestations of mental activity, which are usually -called fixed ideas, despondency, imbecility, and generally "diseases of -the mind." This distinctly and irrefragably shows that the soul of man, -just as the soul of animals, is a purely mechanical activity, the sum of -the molecular phenomena of motion in the particles of the brain, and -that it is transmitted by inheritance, together with its substratum, -just as every other quality of the body is materially transmitted by -propagation. - -When this exceedingly important and undeniable fact is mentioned, it -generally causes great offence, and yet in reality it is silently and -universally acknowledged. For upon what else do the ideas of "hereditary -sin," "hereditary wisdom," and "hereditary aristocracy," etc., rest than -upon the conviction that the _quality of the human mind_ is transmitted -by propagation--that is, by a purely _material_ process--through the -body, from the parents to the descendants? The recognition of this great -importance of transmission by inheritance is shown in a number of human -institutions, as for example, among many nations in the division into -castes, such as the castes of warriors, castes of priests, and castes of -labourers, etc. It is evident that the institution of such castes -originally arose from the notion of the great importance of hereditary -distinctions possessed by certain families, which it was presumed would -always be transmitted by the parents to the children. The institution of -an hereditary aristocracy and an hereditary monarchy is to be traced to -the notion of such a transmission of special excellencies. However, it -is unfortunately not only virtues, but also vices that are transmitted -and accumulated by inheritance; and if, in the history of the world, we -compare the different individuals of the different dynasties, we shall -everywhere find a great number of proofs of the transmission of -qualities by inheritance, but fewer of transmissions of virtues than of -vices. Look only, for example, at the Roman emperors, at the Julii and -the Claudii, or at the Bourbons in France, Spain, and Italy! - -In fact, scarcely anywhere could we find such a number of striking -examples of the remarkable transmission of bodily and mental features by -inheritance, as in the history of the reigning houses in hereditary -monarchies. This is specially true in regard to the diseases of the mind -previously mentioned. It is in reigning families that mental disorders -are hereditary in an unusual degree. Thus Esquirol, distinguished for -his knowledge of mental diseases, proved that the number of insane -individuals in the reigning houses was, in proportion to the number -among the ordinary population, as 60 to 1; that is, that disorders of -the brain occur 60 times more frequently in the privileged families of -the ruling houses than among ordinary people. If equally accurate -statistics were made of the hereditary nobility, the result would -probably be that here also we should find an incomparably larger -contingent of mental diseases than among the common, ignoble portion of -mankind. This phenomenon can scarcely astonish us if we consider what -injury these privileged castes inflict upon themselves by their -unnatural, one-sided education, and by their artificial separation from -the rest of mankind. By this means many dark sides of human nature are -specially developed and, as it were, artificially bred, and, according -to the laws of transmission by inheritance, are propagated through -series of generations with ever-increasing force and dominance. - -It is sufficiently obvious from the history of nations how in successive -generations of many dynasties, for example, of the princes of Saxon -Thuringia and of the Medici, the noble solicitude for the most perfect -human accomplishments in science and art were retained and transmitted -from father to son; and how, on the other hand, in many other dynasties, -for centuries a special partiality for the profession of war, for the -oppression of human freedom, and for other rude acts of violence, have -been hereditary. In like manner talents for special mental activities -are transmitted in many families for generations, as, for instance, -talent for mathematics, poetry, music, sculpture, the investigation of -nature, philosophy, etc. In the family of Bach there have been no less -than twenty-two eminent musicians. Of course the transmission of such -peculiarities of mind depends upon the material process of reproduction, -as does the transmission of mental qualities in general. In this case -again, the vital phenomenon, the manifestation of force (as everywhere -in nature), is directly connected with definite relations in the -admixture of the material components of the organism. It is this -definite proportion and molecular motion of matter which is transmitted -by generation. - -Now, before we examine the numerous, and in some cases most interesting -and important, laws of transmission by inheritance, let us make -ourselves acquainted with the actual nature of the process. The -phenomena of transmission by inheritance are generally looked upon as -something quite mysterious, as peculiar processes which cannot be -fathomed by natural science, and the causes and actual nature of which -cannot be understood. It is precisely in such a case that people very -generally assume supernatural influences. But even in the present state -of our physiology it can be proved with complete certainty that all the -phenomena of inheritance are entirely natural processes, that they are -produced by mechanical causes, and that they depend on the material -phenomena of motion in the bodies of organisms, which we may consider as -a part of the phenomena of propagation. All the phenomena of Heredity -and the laws of Transmission by Inheritance can be traced to the -material process of _Propagation_. - -Every organism, every living individual, owes its existence _either_ to -an act of unparental or _Spontaneous Generation_ (Generatio Spontanea, -Archigonia), or to an act of Parental Generation or _Propagation_ -(Generatio Parentalis, Tocogonia). In a future chapter we shall have to -consider Spontaneous Generation, or Archigony. At present we must occupy -ourselves with Propagation, or Tocogony, a closer examination of which -is of the utmost importance for understanding transmission by -inheritance. Most of my readers probably only know those phenomena of -Propagation which are seen universally in the higher plants and animals, -the processes of Sexual Propagation, or Amphigony. The processes of -Non-sexual Propagation, or Monogony, are much less generally known. The -latter, however, are far more suited to throw light upon the nature of -transmission by inheritance in connection with propagation. - -For this reason, we shall first consider only the phenomena of -_non-sexual_ or _monogonic propagation_ (Monogonia). This appears in a -variety of different forms, as for example, self-division, formation of -buds, the formation of germ-cells or spores (Gen. Morph. ii. 36-58). It -will be most instructive, first, to examine the propagation of the -simplest organisms known to us, which we shall have to return to later, -when considering the question of spontaneous generation. These very -simplest of all organisms yet known, and which, at the same time, are -the simplest imaginable organisms, are the _Monera_ living in water; -they are very small living corpuscles, which, strictly speaking, do not -at all deserve the name of organism. For the designation "organism," -applied to living creatures, rests upon the idea that every living -natural body is composed of organs, of various parts, which fit into -one another and work together (as do the different parts of an -artificial machine), in order to produce the action of the whole. During -late years we have become acquainted with _Monera_, organisms which are, -in fact, not composed of any organs at all, but consist entirely of -shapeless, simple, homogeneous matter. The entire body of one of these -Monera, during life, is nothing more than a shapeless, mobile, little -lump of mucus or slime, consisting of an albuminous combination of -carbon. Simpler or more imperfect organisms we cannot possibly conceive. - -The first complete observations on the natural history of a Moneron -(Protogenes primordialis) were made by me at Nice, in 1864. Other very -remarkable Monera I examined later (1866) in Lanzarote, one of the -Canary Islands, and in 1867 in the Straits of Gibraltar. The complete -history of one of these Monera, the orange-red _Protomyxa aurantiaca_, -is represented in Plate I, and its explanation is given in the Appendix. -I have found some curious Monera also in the North Sea, off the -Norwegian coast, near Bergen. Cienkowski has described (1865) an -interesting Moneron from fresh waters, under the name of _Vampyrella_. -But perhaps the most remarkable of all Monera was discovered by Huxley, -the celebrated English zoologist, and called _Bathybius Hæckelii_. -"Bathybius" means, living in the deep. This wonderful organism lives in -immense depths of the ocean, which are over 12,000--indeed, in some -parts 24,000 feet below the surface, and which have become known to us -within the last ten years, through the laborious investigations made by -the English. There, among the numerous Polythalamia and Radiolaria -which inhabit the fine calcareous mud of these abysses, the Bathybius is -found in great quantities, sometimes in the shape of roundish, formless -lumps of mucus, sometimes in the form of a network of mucus, covering -fragments of stone and other objects. Small particles of chalk are -frequently embedded in these mucous gelatinous masses, and are, perhaps, -products of their secretion. The entire body of this remarkable -Bathybius consists solely of shapeless plasma, or protoplasm, as in the -case of the other Monera--that is, it consists of the same albuminous -combination of carbon, which in infinite modifications is found in all -organisms, as the essential and never-failing seat of the phenomena of -life. I have given a detailed description and drawing of the Bathybius -and other Monera in my "Monographie der Moneren," 1870,(15) from which -the drawing in Fig. 9 is taken. - -[Illustration: Life history of a simplest organism. Pl. I. - -E. Haeckel del. _Prototmyxa aurantiaca._ Lagesse sc.] - -In a state of rest most Monera appear as small globules of mucus or -slime, invisible, or nearly so, to the naked eye; they are at most as -large as a pin's head. When the Moneron moves itself, there are formed -on the upper surface of the little mucous globule, shapeless, fingerlike -processes, or very fine radiated threads; these are the so-called false -feet, or pseudopodia. The false feet are simple, direct continuations of -the shapeless albuminous mass, of which the whole body consists. We are -unable to perceive different parts in it, and we can give a direct proof -of the absolute simplicity of the semi-fluid mass of albumen, for with -the aid of the microscope we can follow the Moneron as it takes in -nourishment. When small particles suited for its nourishment--for -instance, small particles of decayed organic bodies or microscopic -plants and infusoria--accidentally come into contact with the Moneron, -they remain hanging to the sticky semi-fluid globule of mucus, and here -create an irritation, which is followed by a strong afflux of the mucous -substance, and, in consequence, they become finally completely inclosed -by it, or are drawn into the body of the Moneron by displacement of the -several albuminous particles, and are there digested, being absorbed by -simple diffusion (endosmosis). - -[Illustration: FIG. 1.--Propagation of the simplest organism, a Moneron, -by self-division. _A._ The entire Moneron, a Protamoeba. _B._ It falls -into two halves by a contraction in the middle. _C._ Each of the two -halves has separated from the other, and now represents an independent -individual.] - -Just as simple as the process of nutrition is the _propagation_ of these -primitive creatures, which in reality we can neither call animals nor -plants. All Monera propagate themselves only in an asexual manner by -monogony; and in the simplest case, by that kind of monogony which we -place at the head of the different forms of propagation, that is, by -self-division. When such a little globule, for example a Protamoeba or -a Protogenes, has attained a certain size by the assimilation of foreign -albuminous matter, it falls into two pieces; a pinching in takes place, -contracting the middle of the globule on all sides, and finally leads to -the separation of the two halves (compare Fig. 1). Each half then -becomes rounded off, and now appears as an independent individual, which -commences anew the simple course of the vital phenomena of nutrition and -propagation. In other Monera (Vampyrella), the body in the process of -propagation does not fall into two, but into four equal pieces, and in -others, again (Protomonas, Protomyxa, Myxastrum), at once into a number -of small globules of mucus, each of which again, by simple growth, -becomes like the parent body. Here it is evident that the process of -_propagation is nothing but a growth of the organism beyond its own -individual limit of size_. - -The simple method of propagation of the Moneron by self-division is, in -reality, the most universal and most widely spread of all the different -modes of propagation; for by the same simple process of division, -_cells_ also propagate themselves. Cells are those simple organic -individuals, a large number of which constitute the bodies of most -organisms, the human body not excepted. With the exception of the -organisms of the lowest order, which have not even the perfect form of a -cell (Monera), or during life only represent a single cell (many -Protista and single-celled plants), the body of every organic individual -is composed of a great number of cells. Every organic cell is to a -certain degree an independent organism, a so-called "elementary -organism," or an "individual of the first order." Every higher organism -is, in a measure, a society or a state of such variously shaped -elementary individuals, variously developed by division of labour.(39) -Originally every organic cell is only a single globule of mucus, like a -Moneron, but differing from it in the fact that the homogeneous -albuminous substance has separated itself into two different parts, a -firmer albuminous body, the _cell-kernel_ (nucleus), and an external, -softer albuminous body, the _cell-substance_ or _body_ (protoplasma). -Besides this, many cells later on form a third (frequently absent) -distinct part, inasmuch as they cover themselves with a capsule, by -exuding an outer pellicle or _cell-membrane_ (membrana). All other forms -of cells, besides these, are of subordinate importance, and are of no -further interest to us here. - -Every organism composed of many cells was originally a single cell, and -it becomes many-celled owing to the fact that the original cell -propagates itself by self-division, and that the new individual cells -originating in this manner remain together, and by division of labour -form a community or a state. The forms and vital phenomena of all -many-celled organisms are merely the effect or the expression of all the -forms and vital phenomena of all the individual cells of which they are -composed. The egg, from which most animals and plants are developed, is -a simple cell. - -[Illustration: FIG. 2.--Propagation of a single-celled organism, -Amoeba sphærococcus, by self-division. _A._ The enclosed Amoeba, a -simple globular cell consisting of a lump of protoplasm (_c_), which -contains a kernel (_b_) and a kernel speck (_a_), and is surrounded by a -cell-membrane or capsule. _B._ The free Amoeba, which has burst and -left the cyst or cell-membrane. _C._ It begins to divide by its kernel -forming two kernels, and by the cell-substance between the two becoming -contracted. _D._ The division is completed by the cell-substance -likewise falling into two halves (_Da_ and _Db_).] - -The single-celled organisms, that is, those which during life retain the -form of a single cell, for example the Amoebæ, as a rule propagate -themselves in the simplest way by self-division. This process differs -from the previously described self-division of the Moneron only in the -fact that at the commencement the firmer cell-kernel (nucleus) falls -into two halves, by a pinching in at its middle. The two young kernels -separate from each other and act now as two distinct centres of -attraction upon the surrounding softer albuminous matter, that is, the -cell-substance (protoplasma). By this process finally the latter also -divides into two halves, and there now exist two new cells, which are -like the mother cell. If the cell was surrounded by a membrane, this -either does not divide at all, as in the case of egg-cleavage (Fig. 3, -4), or it passively follows the active pinching in of the protoplasm; -or, lastly, every new cell exudes a new membrane for itself. - -[Illustration: FIG. 3.--Egg of a mammal (a simple cell). _a._ The small -kernel speck or nucleolus (the so-called germ-spot of the egg). _b._ -Kernel or nucleus (the so-called germ-bladder of the egg). _c._ -Cell-substance or protoplasm (the so-called yolk of the egg). _d._ -Cell-capsule or membrane (membrane of the yolk) of the egg; called in -mammals, on account of its transparency, Membrana pellucida.] - -The non-independent cells which remain united in communities or states, -and thus constitute the body of higher organisms, are propagated in the -same manner as are independent single-celled organisms, for example, -Amoeba (Fig. 2). Just as in that case, the cell with which most -animals and plants commence their individual existence, namely, the egg, -multiplies itself by simple division. When an animal, for instance a -mammal (Fig. 3, 4), develops out of an egg, this process of development -always begins by the simple egg-cell (Fig. 3) forming an accumulation of -cells (Fig. 4) by continued self-division. The outer covering, or cell -membrane, of the globular egg remains undivided. First, the cell-kernel -of the egg (the so-called germinal vesicle) divides itself into two -kernels, then follows the cell-substance (the yolk of the egg) (Fig. 4 -_A_). In like manner, the two cells, by continued self-division, -separate into four (Fig. 4 _B_), these into eight (Fig. 4 _C_), into -sixteen, thirty-two, etc., and finally there is produced a globular mass -of very numerous little cells (Fig. 4 _D_). These now, by further -increase and heterogeneous development (division of labour), gradually -build up the compound many-celled organism. Every one of us, at the -commencement of our individual development, has undergone the very same -process as that represented in Fig. 4. The egg of a mammal--represented -in Fig. 3, and its development in Fig. 4--might as well be that of a -man, as of an ape, dog, horse, or any other placental mammal. - -[Illustration: FIG. 4.--First commencement of the development of a -mammal's egg, the so-called "cleavage of the egg" (propagation of the -egg-cell by repeated self-division). _A._ The egg, by the formation of -the first furrow, falls into two cells. _B._ These separate by division -into four cells. _C._ The latter have divided into eight cells. _D._ By -repeated division a globular accumulation of numerous cells has -arisen.] - -Now, when one examines this simplest form of propagation, this -self-division, it surely cannot be considered wonderful that the -products of the division of the original organism should possess the -same qualities as the parental individual. For they are parts or halves -of the parental organism, and the matter or substance in both halves is -the same, and as both the young individuals have received an equal -amount and the same quality of matter from the parent individual, one -can but consider it natural that the vital phenomena, the physiological -qualities should be the same in both children. In fact, in regard to -their form and substance, as well as to their vital phenomena, the two -produced cells can in no respect be distinguished from one another, or -from the mother cell. They have _inherited_ from her the same nature. - -But this same simple propagation by self-division is not only confined -to simple cells--it is the same also in the higher many-celled -organisms; for example, in the coral zoophytes. Many of them which -exhibit a high complexity of composition and organization, nevertheless, -propagate themselves by simple division. In this case the whole -organism, with all its organs, falls into two equal halves as soon as by -growth it has attained a certain size. Each half again develops itself, -by growth, into a complete individual. Here, again, it is surely -self-evident that the two products of division will share the qualities -of the parental organism, as they themselves are in fact halves of that -parent. - -Next to propagation by division we come to propagation by the _formation -of buds_. This kind of monogony is exceedingly widely spread. It occurs -both in the case of simple cells (though not frequently) and in the -higher organisms composed of many cells. The formation of buds is -universal in the vegetable kingdom, less frequent in the animal kingdom. -However, here also it occurs in the tribe of Plant-like Animals, -especially among the Coral Zoophytes, and among the greater portion of -the Hydroid Polyps very frequently, further also among some worms -(Planarian Worms, Ring-Worms, Moss Animals, Tunicates). Most branching -animal-trees or colonies, which are exceedingly like branching plants, -arise like those plants, by the formation of buds. - -Propagation by the _formation of buds_ (Gemmatio) is essentially -distinguished from propagation by division, in the fact that the two -organisms thus produced by budding are not of equal age, and therefore -at first are not of equal value, as they are in the case of division. In -division we cannot clearly distinguish either of the two newly produced -individuals as the parental, that is as the producer, because, in fact, -both have an equal share in the composition of the original parental -individual. If, on the other hand, an organism sends out a bud, then the -latter is the child of the former. The two individuals are of unequal -size and of unequal form. If, for instance, a cell propagates itself by -the formation of buds, we do not see the cell fall into two equal -halves, but there appears at one point of it a protuberance, which -becomes larger and larger, more or less separates itself from the -parental cell, and then grows independently. In like manner we observe -in the budding of a plant or animal, that a small local growth arises on -a part of the mature individual, which growth becomes larger and larger, -and likewise more or less separates itself from the parental organism by -an independence in its growth. The bud, after it has attained a certain -size, may either completely separate itself from the parental -individual, or it may remain connected with it and form a stock or -colony, whilst at the same time its life may be quite independent of -that of its parent. While the growth which starts the propagation, in -the case of self-division, is a total one affecting the whole body, it -is in the formation of buds only partial, affecting merely a portion of -the parental organism. But here, also, the bud--the newly-produced -individual which remains so long most directly connected with the -parental organism, and which proceeds from it--retains the essential -qualities and the original tendency of development of its parent. - -A third mode of non-sexual propagation, that of the _formation of -germ-buds_ (Polysporogonia), is intimately connected with the formation -of buds. In the case of the lower, imperfect organisms, among animals, -especially in the case of the Plant-like animals and Worms, we very -frequently find that in the interior of an individual composed of many -cells, a small group of cells separates itself from those surrounding -it, and that this small isolated group gradually develops itself into -an individual, which, becomes like the parent, and sooner or later comes -out of it. Thus, for example, in the body of the Fluke-worms -(Trematodes) there often arise numerous little bodies consisting of many -cells, that is _germ-buds_, or _polyspores_, which, at an early stage -separate themselves completely from the parent body, and leave it when -they have attained a certain stage of development. - -The formation of germ-buds is evidently but little different from real -budding. But, on the other hand, it is connected with a fourth kind of -non-sexual propagation, which almost forms a transition to sexual -reproduction, namely, the _formation of germ-cells_ (Monosporogonia), -which is often briefly called formation of spores (sporogonia). In this -case it is no longer a group of cells, but a single cell, which -separates itself from the surrounding cells in the interior of the -producing organism, and which only becomes further developed after it -has come out of its parent. After this _germ-cell_, or monospore (or, -briefly, spore), has left the parental individual, it multiplies by -division, and thus forms a many-celled organism, which by growth and -gradual development attains the hereditary qualities of the parental -organism. This occurs very generally among lower plants (Cryptogama). - -Although the formation of germ-cells very much resembles the formation -of germ buds, it evidently and very essentially differs from the latter, -and also from the other forms of non-sexual propagation which have -previously been mentioned, by the fact that only a very small portion of -the producing organism takes part in the propagation and, accordingly, -in the transmission by inheritance. In the case of self-division, where -the whole organism falls into two halves, in the formation of buds, -where a considerable portion of the whole body, already more or less -developed, separates from the producing individual, we easily understand -that the forms and vital phenomena should be the same in the producing -and produced organism. It is much more difficult to understand in the -formation of germ-buds, and more difficult still in the formation of -germ-cells, how this very small, quite undeveloped portion of the body, -this group of cells, or this single cell, not only directly takes with -it certain parental qualities into its independent existence, but also -after its separation from the parental individual develops into a -many-celled body, and in this repeats the forms and vital phenomena of -the original producing organism. This last form of monogonic -propagation--that of the germ cells, or spore-formation--leads us -directly to a form of propagation which is the most difficult of all to -explain, namely, sexual propagation. - -_Sexual or amphigonic propagation_ (Amphigonia) is the usual method of -propagation among all higher animals and plants. It is evident that it -has only developed, at a very late period of the earth's history, from -non-sexual propagation, and apparently in the first instance from the -method of propagation by germ-cells. In the earliest periods of the -organic history of the earth, all organisms propagated themselves in a -non-sexual manner, as numerous lower organisms still do, especially all -those which are at the lowest stage of organization, and which, strictly -speaking, can be considered neither as animals nor as plants, and which -therefore, as primary creatures, or Protista, are best excluded from -both the animal and vegetable kingdoms. In the case of the higher -animals and plants, the increase of individuals, as a rule, is at -present brought about in the majority of cases by sexual propagation. - -In all the chief forms of non-sexual propagation mentioned above--in -fission, in the formation of buds, germ buds, and germ cells--the -separated cell or group of cells was able by itself to develop into a -new individual, but in the case of sexual propagation the cell must -first be fructified by another generative substance. The fructifying -male sperm must first mix with the female germ-cell (the egg) before the -latter can develop into a new individual. These two different -generative substances, the male sperm and the female egg, are either -produced by one and the same individual hermaphrodite -(Hermaphroditismus), or by two different individuals (sexual separation, -Gonochorismus) (Gen. Morph. ii. 58, 59). - -The simpler and more ancient form of sexual propagation is through -double-sexed individuals (Hermaphroditismus). It occurs in the great -majority of plants, but only in a minority of animals, for example, in -the garden snails, leeches, earth-worms, and many other worms. Every -single individual among hermaphrodites produces within itself materials -of both sexes--eggs and sperm. In most of the higher plants every -blossom contains both the male organ (stamens and anther) and the female -organs (style and germ). Every garden snail produces in one part of its -sexual gland eggs, and in another part sperm. Many hermaphrodites can -fructify themselves; in others, however, copulation and reciprocal -fructification of both hermaphrodites is necessary for causing the -development of the eggs. This latter case is evidently a transition to -sexual separation. - -_Sexual separation_ (Gonochorismus,) which characterizes the more -complicated of the two kinds of sexual reproduction, has evidently been -developed from the condition of hermaphroditism at a late period of the -organic history of the world. It is at present the universal method of -propagation of the higher animals, and occurs, on the other hand, only -in the minority of plants (for example, in many aquatic plants, _e.g._ -Hydrocharis, Vallisneria; and in trees, _e.g._ Willows, Poplars). Every -organic individual, as a non-hermaphrodite (Gonochoristus), produces -within itself only one of two generative substances, either the male or -the female. The female individuals, both in animals and plants, produce -eggs or egg-cells. The eggs of plants in the case of flowering plants -(Phanerogama), are commonly called "embryo sacs"; in the case of -flowerless plants (Cryptogama), "fruit spores." In animals, the male -individual secretes the fructifying sperm (sperma); in plants, the -corpuscles, which correspond to the sperm. In the Phanerogama, these are -the pollen grains, or flower-dust; in the Cryptogama, a sperm, which, -like that of most animals, consists of floating vibratile cells actively -moving in a fluid--the zoosperms, spermatozoa, or sperm-cells. - -The so-called _virginal reproduction_ (Parthenogenesis) offers an -interesting form of transition from sexual reproduction to the -non-sexual formation of germ-cells (which most resembles it); it has -been demonstrated to occur in many cases among Insects, especially by -Siebold's excellent investigations. In this case germ-cells, which -otherwise appear and are formed exactly like egg-cells, become capable -of developing themselves into new individuals without requiring the -fructifying seed. The most remarkable and most instructive of the -different partheno-genetic phenomena are furnished by those cases in -which the same germ-cells, according as they are fructified or not, -produce different kinds of individuals. Among our common honey bees, a -male individual (a drone) arises out of the eggs of the queen, if the -egg has not been fructified; a female (a queen, or working bee), if the -egg has been fructified. It is evident from this, that in reality there -exists no wide chasm between sexual and non-sexual reproduction, but -that both modes of reproduction are directly connected. The -parthenogenesis of Insects must probably be regarded as a _relapse_ from -the sexual mode of propagation (possessed by the original parents of the -insects) to the earlier condition of non-sexual propagation. (Gen. -Morph. ii. 86.) In any case, however, sexual reproduction, both in -plants and animals, which seems such a wonderful process, has only -arisen at a later date out of the more ancient process of non-sexual -reproduction. In both cases heredity is a necessary part of the -phenomenon. - -In all the different modes of propagation the essential point of the -process is invariably a detachment of a portion of the parental organism -possessing the capability of leading an individual, independent -existence. We may, therefore, in all cases expect, _à priori_, that the -produced individuals--which are, in fact, as is commonly said, "the -flesh and blood" of the parents--will receive the vital characteristics -and qualities of form which the parental individuals possess. It is -simply a larger or smaller quantity of the parental material, in fact of -its albuminous protoplasm, or cell-substance, which passes to the -produced individual. But together with the material, its vital -properties--that is, the molecular motions of the plasma--are -transmitted, which then manifest themselves in its form. Inheritance by -sexual breeding loses very much of the mysterious and wonderful -character which it at first sight possesses for the uninitiated, if we -consider the above-mentioned series of the different modes of -propagation, and their connection one with another. It at first appears -exceedingly wonderful that in the sexual propagation of man, and of all -higher animals, the small egg, the minute cell, often invisible to the -naked eye, is able to transfer to the produced organism all the -qualities of the maternal organism, and, no less mysterious, that at -the same time the essential qualities of the paternal organism are -transferred to the offspring by means of the male sperm, which -fructifies the egg-cell by means of a viscid substance in which minute -thread-like cells or zoosperms move about. But as soon as we compare the -connected stages of the different kinds of propagation, in which the -produced organism separates itself more and more as a distinct growth -from the parental individual, and more or less early enters upon its -independent career; as soon as we consider, at the same time, that the -growth and development of every higher organism only depends upon the -increase of the cells composing it--that is, upon their simple -propagation by division--it becomes quite evident that all these -remarkable processes belong to one series. - -The life of every organic individual is nothing but a connected chain of -very complicated material phenomena of motion. These motions must be -considered as changes in the position and combination of the molecules, -that is, of the smallest particles of animated matter (of atoms placed -together in the most varied manner). The specific, definite tendency of -these orderly, continuous, and inherent motions of life depends, in -every organism, upon the chemical mingling of the albuminous generative -matter to which it owes its origin. In man, as in the case of the higher -animals which propagate themselves in a sexual manner, the individual -vital motion commences at the moment in which the egg-cell is fructified -by the spermatic filaments of the seed, in which process both generative -substances actually mix; and here the tendency of the vital motion is -determined by the specific, or more accurately, by the individual -nature of the sperm as well as of the egg. There can be no doubt as to -the purely mechanical material nature of this process. But here we stand -full of wonder and astonishment before the infinite and inconceivable -delicacy of this albuminous matter. We are amazed at the undeniable fact -that the simple egg-cell of the maternal organism, and a single paternal -sperm-thread, transfer the molecular individual vital motion of these -two individuals to the child so accurately, that afterwards the minutest -bodily and mental peculiarities of both parents reappear in it. - -Here we stand before a mechanical phenomenon of nature of which Virchow, -whose genius founded the "cellular pathology," says with full justice: -"If the naturalist cared to follow the custom of historians and -preachers, and to clothe phenomena, which are in their way unique, with -the hollow pomp of ponderous and sounding words, this would be the -opportunity for him; for we have now approached one of those great -mysteries of animal nature, which encircle the region of animal life as -opposed to all the rest of the world of phenomena. The question of the -formation of cells, the question of the excitation of a continuous and -equable motion, and, finally, the questions of the independence of the -nervous system and of the soul--these are the great problems on which -the human mind can measure its strength." To comprehend the relation of -the male and female to the egg-cell is almost as much as to solve all -those mysteries. The origin and development of the egg-cell in the -mother's body, the transmission of the bodily and mental peculiarities -of the father to it by his seed, touch upon all the questions which the -human mind has ever raised about man's existence. And, we add, these -most important questions are solved, by means of the Theory of Descent, -in a purely mechanical and purely monistic sense! - -There can then be no further doubt that, in the sexual propagation of -man and all higher organisms, inheritance, which is a purely mechanical -process, is directly dependent upon the material continuity of the -producing and produced organism, just as is the case in the simplest -non-sexual propagation of the lower organisms. However, I must at once -take this opportunity of drawing attention to an important difference -which inheritance presents in sexual and non-sexual propagation. It is a -fact long since acknowledged, that the individual peculiarities of the -producing organism are much more accurately transmitted to the produced -organism by non-sexual than by sexual propagation. Gardeners have for a -long time made use of this fact in many ways. When, for instance, a -single individual of a species of tree with stiff, upright branches -accidentally produces down-hanging branches, a gardener, as a rule, -cannot transmit this peculiarity by sexual, but only by non-sexual -propagation. The twigs cut off such a weeping tree and planted as -cuttings or slips, afterwards produce trees having likewise hanging -branches, as, for example, the weeping willows and beeches. Seedlings, -on the other hand, which have been reared out of the seed of such a -weeping tree, generally have the original stiff and upright form of -branches possessed by their ancestors. The same may be observed in a -very striking manner in the so-called "copper-coloured trees," that is, -varieties of trees which are characterized by a red or reddish brown -colour of the leaves. Off-shoots from such copper-coloured trees (for -example, the copper beech), which have been propagated by cuttings in a -non-sexual manner, show the peculiar colour and nature of the leaves -which distinguished the parental individual, while others reared from -seeds of such a copper-coloured tree return to the green-coloured -condition of leaf. - -This difference in inheritance will seem very natural when we consider -that the material connection between the producing and produced -individuals is much closer and lasts much longer in non-sexual than in -sexual propagation. The special tendency of the molecular motion of life -can therefore fix itself much longer and more thoroughly in the filial -organism, and be more strictly transmitted by non-sexual than by sexual -propagation. All these phenomena, considered in connection, clearly -prove that the transmission of bodily and mental peculiarities is a -purely material and mechanical process. By propagation a greater or -lesser quantity of albuminous particles, and together with them the -individual form of motion inherent in these molecules of protoplasm, are -transmitted from the parental organism to the offspring. As this form of -motion remains continuous, the more delicate peculiarities inherent in -the parental organism must sooner or later reappear in the filial -organism. - - - - -CHAPTER IX. - -LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND NUTRITION. - - - Distinction between Conservative and Progressive - Transmission by Inheritance.--Laws of Conservative - Transmission: Transmission of Inherited - Characters.--Uninterrupted or Continuous - Transmission.--Interrupted or Latent - Transmission.--Alternation of - Generations.--Relapse.--Degeneracy.--Sexual - Transmission.--Secondary Sexual Characters.--Mixed or - Amphigonous Transmission.--Hybrids.--Abridged or - Simplified Transmission.--Laws of Progressive - Inheritance: Transmission of Acquired - Characters.--Adapted or Acquired Transmission.--Fixed or - Established Transmission.--Homochronous Transmission - (Identity in Epoch).--Homotopic Transmission (Identity in - Part).--Adaptation and Mutability.--Connection between - Adaptation and Nutrition.--Distinction between Indirect - and Direct Adaptation. - - -In the last chapter we considered Transmission by Inheritance, one of -the two universal vital activities of organisms, Adaptation and -Inheritance, which by their interaction produce the different species of -organisms, and we have endeavoured to trace this very mysterious vital -activity to a more general physiological function of organisms, namely, -to Propagation. This latter in its turn, like other vital phenomena of -animals and plants, depends on physical and chemical relations. It is -true they appear at times exceedingly complicated, but can nevertheless -in reality be traced to simple mechanical causes--that is, to the -relations of attraction and repulsion in the particles or molecules--in -fact, to the motional phenomena of matter. - -Now, before we turn our attention to the second function, the phenomenon -of Adaptation or Mutability, which counteracts the Transmission by -Inheritance, it seems appropriate first to cast one more glance at the -various manifestations of Heredity, which we may perhaps even now -denominate the "_laws of transmission by inheritance._" Unfortunately, -up to the present time very little has been done for this most important -subject, either in zoology or in botany, and almost all we know of the -different laws of inheritance is confined to the experiences of -gardeners and farmers. It is not therefore to be wondered at, that on -the whole these exceedingly interesting and important phenomena have not -been investigated with desirable scientific accuracy, or reduced to the -form of scientific laws. Accordingly, what I shall relate of the -different laws of transmission are only some preliminary fragments taken -out of the infinitely rich store which lies open to our inquiry. - -We may first divide all the different phenomena of inheritance into two -groups, which we may distinguish as the transmission of _inherited_ -characters, and the transmission of _acquired_ characters; and we may -call the former the _conservative_ transmission, and the latter the -_progressive_ transmission by inheritance. This distinction depends upon -the exceedingly important fact that the individuals of every species of -animals and plants can transmit to their descendants, not only those -qualities which they themselves have inherited from their ancestors, but -also the peculiar, individual qualities which they have acquired during -their own life. The latter are transmitted by progressive, the former -by conservative inheritance. We have now first to examine the phenomena -of _conservative inheritance_, that is, the transmission of such -qualities as the organism has already received from its parents or -ancestors. (Gen. Morph. ii. 180.) - -Among the phenomena of conservative inheritance we are first struck by -that which is its most general law, and which we may term the _law of -uninterrupted or continuous transmission_. It is so universal among the -higher animals and plants, that the uninitiated might overestimate its -action and consider it as the only normal law of transmission by -inheritance. This law simply consists in the fact that among most -species of animals and plants, every generation is, on the whole, like -the preceding--that the parents are as like the grandparents as they are -like the children. "Like produces like," as is commonly said, but more -accurately "similar things produce similar things." For, in reality, the -descendants of every organism are never absolutely equal in all points, -but only similar in a greater or less degree. This law is so generally -known, that I need not give any examples of it. - -The _law of interrupted or latent transmission_ by inheritance, which -might also be termed alternating transmission, is in a measure opposed -to the preceding law. This important law appears principally active -among many lower animals and plants, and manifests itself in contrast to -the former in the fact that the offspring are not like their parents, -but very dissimilar, and that only the third or a later generation -becomes similar to the first. The grandchildren are like the -grandparents, but quite unlike the parents. This is a remarkable -phenomenon, and, as is well known, occurs also very frequently, though -in a less degree, in human families. Every one of my readers doubtless -knows some members of a family who, in this or that peculiarity, much -more resemble the grandfather or grandmother than the father or mother. -Sometimes it lies in bodily peculiarities, for example, features of -face, colour of hair, size of body--sometimes in mental qualities, for -example, temperament, energy, understanding--which are transmitted in -this manner. This fact may be observed in domestic animals as well as in -the case of man. Among the domestic animals most liable to vary--as the -dog, horse, and ox--breeders very frequently find that the product by -breeding resembles the grandparents far more than it does its own -parental organism. If we express this general law and the succession of -generations by the letters of the alphabet, then A = C = E, whilst -B = D = F, and so on. - -This very remarkable fact appears in a more striking way in the lower -animals and plants than in the higher, and especially in the well-known -phenomenon of _alternation of generations_ (metagenesis). Here we very -frequently find--for example, among the Planarian worms, sea-squirts or -Tunicates, Zoophytes, and also among ferns and mosses--that the organic -individual in the first place produces, by propagation, a form -completely different from the parental form, and that only the -descendants of this generation, again, become like the first. This -regular change of generation was discovered by the poet Chamisso, on his -voyage round the world in 1819, among the _Salpæ_, cylindrical -tunicates, transparent like glass, which float on the surface of the -sea. Here the larger generation, the individuals of which live isolated -and possess an eye of the form of a horse-shoe, produce in a non-sexual -manner (by the formation of buds) a completely different and smaller -generation. The individuals of this second smaller generation live -united in chains and possess a cone-shaped eye. Every individual of such -a chain produces, in a sexual manner (hermaphrodite) again, a non-sexual -solitary form of the first and larger generation. Among the Salpæ, -therefore, it is always the first, third, and fifth generation, and in -like manner the second, fourth, and sixth generations, that are entirely -like one another. However, it is not always only one, but in other cases -a number of generations, which are thus leapt over; so that the first -generation resembles the fourth and seventh, the second resembles the -fifth and eighth, the third resembles the sixth and ninth, and so on. -Three different generations alternate with one another; for example, -among the neat _little sea-buoys_ (Doliolum), small tunicates closely -related to the Salpæ. In this case it is A = D = G, further, B = E = H, -and C = F = I. Among the plant-lice (Aphides), each sexual generation is -followed by a succession of from eight to ten or twelve non-sexual -generations, which are like one another, but differ from the sexual -generations. Then, again, a sexual generation reappears like the one -long before vanished. - -If we further follow this remarkable law of latent or interrupted -inheritance, and take into consideration all the phenomena appertaining -to it, we may comprise under it also the well-known phenomena of -_reversion_. By the term "reversion" or "atavism" we understand the -remarkable fact known to all breeders of animals, that occasionally -single and individual animals assume a form which has not existed for -many generations, but belongs to a generation which has long since -disappeared. One of the most remarkable instances of this kind is the -fact that in some horses there sometimes appear singular dark stripes, -similar to those of the zebra, quagga, and other wild species of African -horses. Domestic horses of the most different races and of all colours -sometimes show such dark stripes; for example, a stripe along the back, -a stripe across the shoulders, and the like. The sudden appearance of -these stripes can only be explained by the supposition that it is the -effect of a latent transmission, a relapse into the ancient original -form, which has long since vanished, and was once common to all species -of horses; the original form, undoubtedly, was originally striped like -the zebras, quaggas, etc. In like manner, certain qualities in other -domestic animals sometimes appear quite suddenly, which once marked -their wild ancestors, now long since extinct. In plants, also, such a -relapse can be observed very frequently. All my readers probably know -the wild yellow toad-flax (Linaria vulgaris), a plant very common in our -fields and hedges. Its dragon-mouthed yellow flower contains two long -and two short stamens. But sometimes there appears a single blossom -(Peloria) which is funnel-shaped, and quite regularly composed of five -individual and equal sections, with five corresponding stamens. This -Peloria can only be explained as a relapse into the long since extinct -and very ancient common form of all those plants which, like the -toad-flax, possess dragon-mouthed, two-lipped flowers, with two long and -two short stamens. The original form, like the Peloria, possessed a -regular five-spurred blossom, with five equal stamens, which only later -and by degrees have become unequal (compare p. 17). All such relapses -are to be brought under the law of interrupted or latent transmission, -although the number of intervening generations may be enormous. - -When cultivated plants or domestic animals become wild, when they are -withdrawn from the conditions of cultivated life, they experience -changes which appear not only as adaptations to their new mode of life, -but partially also as relapses into the ancient original form out of -which the cultivated forms have been developed. Thus the different kinds -of cabbage, which are exceedingly different in form, may be led back to -the original form, by allowing them to grow wild. In like manner, dogs, -horses, heifers, etc., when growing wild, often revert more or less to a -long extinct generation. An immensely long succession of generations may -pass away before this power of latent transmission becomes extinguished. - -A third law of conservative transmission may be called the _law of -sexual transmission_, according to which each sex transmits to the -descendants of the same sex peculiarities which are not inherited by the -descendants of the other sex. The so-called secondary sexual characters, -which in many respects are of extraordinary interest, everywhere furnish -numerous examples of this law. Subordinate or secondary sexual -characters are those peculiarities of one of the two sexes which are not -directly connected with the sexual organs themselves; such characters, -which exclusively belong to the male sex, are, for example, the antlers -of the stag, the mane of the lion, and the spur of the cock. The human -beard, an ornament commonly denied to the female sex, belongs to the -same class. Similar characteristics by which the female sex is alone -distinguished are, for example, the developed breasts, with the -lactatory glands of female mammals and the pouch of the female opossum. -The bodily size, also, and complexion, differs in female animals of many -species from that of the male. All these secondary sexual qualities, -like the sexual organs themselves, are transmitted by the male organism -only to the male, not to the female, and _vice versâ_. Contrary facts -are rare exceptions to the rule. - -A fourth law of transmission, which has here to be mentioned, in a -certain sense contradicts the last, and limits it, viz., the _law of -mixed or mutual_ (amphigonous) _transmission_. This law tells us that -every organic individual produced in a sexual way receives qualities -from both parents, from the father as well as from the mother. This -fact, that personal qualities of each of the two sexes are transmitted -to both male and female descendants, is very important, Goethe mentions -it of himself, in the beautiful lines-- - - "Von Vater hab ich die Statur, des Lebens ernstes Führen - Von Mütterchen die Frohnatur und Lust zu fabuliren." - - "From my father I have my stature and the serious tenour of my life, - From my mother a joyous nature and a turn for poetizing." - -This phenomenon, I suppose, is so well-known to all, that I need not -here enter upon it. It is according to the different portions of their -character which father and mother transmit to their children, that the -individual differences among brothers and sisters are chiefly -determined. - -The very important and interesting phenomenon of _hybridism_ also -belongs to this law of mixed or amphigonous transmission. It alone, -when rightly estimated, is quite sufficient to refute the prevailing -dogma of the constancy of species. Plants, as well as animals, belonging -to quite different species, may sexually mingle with one another and -produce descendants which in many cases can again propagate themselves, -and that indeed either (more frequently) by mingling with one of the two -parental species, or (more rarely) by pure in-breeding, hybrid mixing -with hybrid. The latter is well established, for example, in the hybrids -of hares and rabbits (Lepus Darwinii, p. 147). The hybrids of a horse -and a donkey, two different species of the same genus (Equus), are well -known. These hybrids differ according as the father or the mother -belongs to the one or the other species--the horse or the donkey. The -mule produced by a mare and a he-donkey has qualities quite different -from those of the jinny (Hinnus), the hybrid of a horse and she-donkey. -In both cases the hybrid produced by the crossing of two different -species is a mixed form, which receives qualities from both parents; but -the qualities of the hybrid are different, according to the form of the -crossing. In like manner, mulattoes produced by a European and a negress -show a different mixture of characters from the hybrids produced by a -negro with a European female. In these phenomena of hybrid-breeding, as -well as in the other laws of transmission previously mentioned, we are -as yet unable to show the acting causes in detail; but no naturalist -doubts the fact that the causes are in all cases purely mechanical and -dependent upon the nature of organic matter itself. If we possessed more -delicate means of investigation than our rude organs of sense and -auxilliary instruments, we should be able to discover those causes, and -to trace them to the chemical and physical properties of matter. - -Among the phenomena of conservative transmission, we must now mention, -as the fifth law, the _law of abridged or simplified transmission_. This -law is very important in regard to embryology or ontogeny, that is in -regard to the history of the development of organic individuals. -_Ontogeny_, or the history of the development of individuals, as I have -already mentioned in the first chapter (p. 10), and as I subsequently -shall explain more minutely, is nothing but a short and quick repetition -of _Phylogeny_ dependent on the laws of transmission and -adaptation--that is, a repetition of the palæontological history of -development of the whole organic tribe, or phylum, to which the organism -belongs. If, for example, we follow the individual development of a man, -an ape, or any other higher mammal within the maternal body from the -egg, we find that the foetus or embryo arising out of the egg passes -through a series of very different forms, which on the whole agrees -with, or at least runs parallel to, a series of forms which is presented -to us by the historical chain of ancestors of the higher mammals. Among -these ancestors we may mention certain fishes, amphibians, marsupials, -etc. But the parallelism or agreement of these two series of development -is never quite complete; on the contrary, in ontogeny there are always -gaps and leaps which indicate the omission of certain stages belonging -to the phylogeny. Fritz Müller, in his excellent work, "Für Darwin,"(16) -has clearly shown in the case of the Crustacea, or crabs, that "the -historical record preserved in the individual history of development is -gradually obscured, in proportion as development takes a more and more -direct route from the egg to the complete animal." This process of -obscuring and shortening is determined by the law of abridged -transmission, and I mention it here specially because it is of great -importance for the understanding of embryology, and because it explains -the fact, at first so strange, that the whole series of forms which our -ancestors have passed through in their gradual development are no longer -visible in the series of forms of our own individual development from -the egg. - -Opposed to the laws of the conservative transmission, hitherto -discussed, are the phenomena of the transmission of the second series, -that is, the _laws of progressive transmission by inheritance_. As -already mentioned, they depend upon the fact that the organism transmits -to its descendants not only those qualities which it has inherited from -its own ancestors, but also a number of those individual qualities which -it has acquired during its own lifetime. Adaptation is here seen to be -connected with transmission by inheritance (Gen. Morph. ii. 186). - -At the head of these important phenomena of progressive transmission, we -may mention the _law of adapted or acquired transmission_. In reality it -asserts nothing more than what I have said above, that in certain -circumstances the organism is capable of transmitting to its descendants -all the qualities which it has acquired during its own life by -adaptation. This phenomenon, of course, shows itself most distinctly -when the newly acquired peculiarity produces any considerable change in -the inherited form. This is the case in the examples I mentioned in the -preceding chapter as to transmission in general, in the case of the men -with six fingers and toes, the porcupine men, copper beeches, weeping -willows, etc. The transmission of acquired diseases, such as -consumption, madness, and albinism, likewise form very striking -examples. Albinoes are those individuals who are distinguished by the -absence of colouring matter, or pigments, in the skin. They are of -frequent occurrence among men, animals, and plants. In the case of -animals of a definite dark colour, individuals are not unfrequently born -which are entirely without colour, and in animals possessing eyes, this -absence of pigment extends even to the eyes, so that the iris of the -eye, which is commonly of a bright or intense colour, is colourless, but -appears red, on account of the blood-vessels being seen through it. -Among many animals, such as rabbits and mice, albinoes with white fur -and red eyes are so much liked that they are propagated in great numbers -as a special race. This would be impossible were it not for the law of -the transmission of adaptations. - -Which of the changes acquired by an organism are transmitted to its -descendants, and which are not, cannot be determined _à priori_, and we -are unfortunately not acquainted with the definite conditions under -which the transmission takes place. We only know in a general way that -certain acquired qualities are much more easily transmitted than others, -for example, more easily than the mutilations caused by accidents. These -latter are generally not transmitted by inheritance, otherwise the -descendants of men who have lost their arms or legs would be born -without the corresponding arm or leg; but here, also, exceptions occur, -and a race of dogs without tails has been produced by consistently -cutting off the tails of both sexes of the dog during several -generations. A few years ago a case occurred on an estate near Jena, in -which by a careless slamming of a stable door the tail of a bull was -wrenched off, and the calves begotten by this bull were all born without -a tail. This is certainly an exception; but it is very important to note -the fact, that under certain unknown conditions such violent changes are -transmitted in the same manner as many diseases. - -In very many cases the change which is transmitted and preserved by -adapted transmission is constitutional or inborn, as in the case of -albinism mentioned before. The change then depends upon that form of -adaptation which we call the indirect or potential. A very striking -instance is furnished by the hornless cattle of Paraguay, in South -America. A special race of oxen is there bred which is entirely without -horns. It is descended from a single bull, which was born in 1770 of an -ordinary pair of parents, and the absence of horns was the result of -some unknown cause. All the descendants of this bull produced with a -horned cow were entirely without horns. This quality was found -advantageous, and by propagating the hornless cattle among one another, -a hornless race was obtained, which at present has almost entirely -supplanted the horned cattle in Paraguay. The case of the otter-sheep of -North America forms a similar example. In the year 1791 a farmer, by -name Seth Wright, lived in Massachusetts, in North America; in his -normally formed flock of sheep a lamb was suddenly born with a -surprisingly long body and very short and crooked legs. It was therefore -unable to take any great leaps, and especially unable to leap across a -hedge into a neighbour's garden--a quality which seemed advantageous to -the owner, as the territories were divided by hedges. It therefore -occurred to him to transmit this quality to other sheep, and by -crossing this ram with normally shaped ewes, he produced a whole race -of sheep, all of which had the qualities of the father, short and -crooked legs and a long body. None of them could leap across the hedges, -and they therefore were much liked and propagated in Massachusetts. - -A second law, which likewise belongs to the series of progressive -transmissions, may be called the _law of established or habitual -transmission_. It manifests itself in this, that qualities acquired by -an organism during its individual life are the more certainly -transmitted to its descendants the longer the causes of that change have -been in action, and that this change becomes the more certainly the -property of all subsequent generations the longer the cause of change -acts upon these latter also. The quality newly acquired by adaptation or -mutation must be established or constituted to a certain degree before -we can calculate with any probability that it will be transmitted at all -to the descendants. In this respect transmission resembles adaptation. -The longer a newly acquired quality has been transmitted by inheritance, -the more certainly will it be preserved in future generations. If, -therefore, for example, a gardener by methodical treatment has produced -a new kind of apple, he may calculate with the greater certainty upon -preserving the desired peculiarity of this sort the longer he has -transmitted the same by inheritance. The same is clearly shown in the -transmission of diseases. The longer consumption or madness has been -hereditary in a family the deeper is the root of the evil, and the more -probable it is that all succeeding generations will suffer from it. - -We may conclude the consideration of the phenomena of inheritance with -the two very important laws of _homotopic_ and _contemporaneous -transmission by inheritance_. We understand by them the fact that -changes acquired by an organism during its life, and transmitted to its -descendants, appear in the same part of the body in which the parental -organism was first affected by them, and that they also appear in the -offspring at the same age as that at which they did so in the parent. - -_The law of contemporaneous or homochronous transmission_, which Darwin -calls the law of "transmission in corresponding periods of life," can -be shown very clearly in the transmission of diseases, especially of -such as are recognized as very destructive, on account of their -hereditary character. They generally appear in the organism of the child -at the time corresponding with that in which the parental organism -contracted the disease. Hereditary diseases of the lungs, liver, teeth, -brain, skin, etc., usually appear in the descendants at the same period, -or a little earlier than they showed themselves in the parental -organism, or were contracted by it. The calf gets its horns at the same -period of life as its parents did. In like manner the young stag -receives its antlers at the same period of life in which they appeared -in its father or grandfather. In every one of the different sorts of -vine the grapes ripen at the same time as they did in the case of their -progenitors. It is well known that the time of ripening varies greatly -in the different sorts; but as all are descended from a single species, -this variation has been acquired by the progenitors of the several -sorts, and has then been transmitted by inheritance. - -The _law of homotopic transmission_, which is most closely connected -with the last mentioned law, and which might be called the law of -transmission in corresponding parts of the body, may also be very -distinctly recognized in pathological cases of inheritance. Large moles, -for example, or accumulations of pigment in several parts of the skin, -tumours also, often appear during many generations, not only at the same -period of life, but also in the same part of the skin. Excessive -development of fat in certain parts of the body is likewise transmitted -by inheritance. Above all, it is to be noted that numerous examples of -this, as well as of the preceding law, may be found everywhere in the -study of embryology. Both the _law of homochronous and homotopic -transmission are fundamental laws of embryology, or ontogeny_. For these -laws explain the remarkable fact that the different successive forms of -individual development in all generations of one and the same species -always appear in the same order of succession, and that the variations -of the body always take place in the same parts. This apparently simple -and self-evident phenomenon is nevertheless exceedingly wonderful and -curious; we cannot explain its real causes, but may confidently assert -that they are due to the direct transmission of the organic matter from -the parental organism to that of the offspring, as we have seen above in -the case of the process of transmission in general, by a consideration -of the details of the various modes of reproduction. - -Having thus, then, considered the most important laws of Inheritance, we -now turn to the second series of phenomena bearing on natural selection, -viz., to those of Adaptation or Variation. These phenomena, taken as a -whole, stand in a certain opposition to the phenomena of Inheritance, -and the difficulty which arises in examining them consists mainly in -the two sets of phenomena being so completely intercrossed and -interwoven. We are but seldom able to say with certainty--of the -variations of form which occur before our eyes--how much is owing to -Inheritance, and how much to Adaptation. All characters of form, by -which organisms are distinguished, are caused _either_ by Inheritance or -by Adaptation; but as both functions are continually interacting with -each other, it is extremely difficult for the systematic inquirer to -recognize the share belonging to each of the two functions in the -special structure of individual forms. This is, at present, all the more -difficult, because we are as yet scarcely aware of the immense -importance of this fact, and because most naturalists have neglected the -theory of Adaptation, as well as that of Inheritance. The laws of -Inheritance, which we have just discussed, as well as the laws of -Adaptation, which we shall consider directly, in reality form only a -small portion of the phenomena existing in this domain, but which have -not as yet been investigated; and since every one of these laws can -interact with every other, it is clear that there is an infinite -complication of physiological actions, which are at work in the -construction of organisms. - -But now, as to the phenomenon of variation or adaptation in general, we -must, as in the case of inheritance, view it as a quite universal, -physiological fundamental quality of all organisms, without -exception--as a manifestation of life which cannot be separated from the -idea of organism. Strictly speaking, we must here also, as in the case -of inheritance, distinguish between Adaptation itself and Adaptability. -By Adaptation (Adaptio), or Variation (Variatio), we understand the fact -that the organism, in consequence of influences of the surrounding -outer world, assumes certain new peculiarities in its vital activity, -composition, and form which it has not inherited from its parents; these -acquired individual qualities are opposed to those which have been -inherited, or, in other words, those which have been transmitted to it -from its parents or ancestors. On the other hand, we call Adaptability -(Adaptabilitas), or Variability (Variabilitas), the capability inherent -in all organisms to acquire such new qualities under the influence of -the outer world. (Gen. Morph. ii. 191.) - -The undeniable fact of organic adaptation or variation is universally -known, and can be observed at every moment in thousands of phenomena -surrounding us. But just because the phenomena of variation by external -influences appear so self-evident, they have hitherto undergone scarcely -any accurate scientific investigation. To them belong all the phenomena -which we look upon as the results of contracting and giving up habits, -of practice and giving up practices, or as the results of training, of -education, of acclimatization, of gymnastics, etc. Many permanent -variations brought about by causes producing disease, that is to say, -many diseases, are nothing but dangerous adaptations of the organism to -injurious conditions of life. In the case of cultivated plants and -domestic animals, variation is so striking and powerful that the breeder -of animals and the gardener found their whole mode of proceeding upon -it, or rather upon the interaction between these phenomena and those of -Inheritance. It is also well known to every one that animals and plants, -in their wild state, are subject to variation. Every systematic treatise -on a group of animals or plants, if it were to be quite complete and -exhaustive, ought to mention in every individual species the number of -variations which differ more or less from the prevailing or typical form -of the species. Indeed, in every careful systematic special treatise one -finds, in the case of most species, mention of a number of such -variations, which are described sometimes as individual deviations, and -sometimes as so-called races, varieties, degenerate species, or -subordinate species, and which often differ exceedingly from the -original species, solely in consequence of the adaptation of the -organism to the external conditions of life. - -If we now endeavour to fathom the general causes of these phenomena of -Adaptation, we arrive at the conclusion that in reality they are as -simple as the causes of the phenomena of Inheritance. We have shown that -the nature of the process of propagation furnishes the real explanation -of the facts of Transmission by Inheritance, that is, the transmission -of parental matter to the body of the offspring; and in like manner we -can show that the physiological function of _nutrition_, or _change of -substance_, affords a general explanation of Adaptation or Variation. -When I here point to "nutrition" as the fundamental cause of variation -and adaptation, I take this word in its widest sense, and I understand -by it the whole of the material changes which the organism undergoes in -all its parts through the influences of the surrounding outer world. -Nutrition thus comprises not only the reception of actual nutritive -substances and the influence of different kinds of food, but also, for -example, the action upon the organism of water and of the atmosphere, -the influence of sunlight, of temperature, and of all those -meteorological phenomena which are implied in the term "climate." The -indirect and direct influence of the nature of the soil and of the -dwelling-place also belong to it; and further, the extremely important -and varied influence which is exercised upon every animal and every -plant by the surrounding organisms, friends and neighbours, enemies and -robbers, parasites, etc. All these and many other very important -influences, all of which more or less modify the organism in its -material composition, must be taken into consideration in studying the -change of substance which goes on in living things. Adaptation, -accordingly, is the consequence of all those material variations which -are produced in the change of substance of the organism by the external -conditions of existence, or by the influences of the surrounding -external world. - -How very much every organism is dependent upon the whole of its external -surroundings, and changed by their alteration, is, in a general way, -well known to every one. Only think how much the human power of action -is dependent upon the temperature of the air, or how much the -disposition of our minds depends upon the colour of the sky. Accordingly -as the sky is cloudless and sunny, or covered with large heavy clouds, -our state of mind is cheerful or dull. How differently do we feel and -think in a forest during a stormy winter night and during a bright -summer day! All the different moods of our soul depend upon purely -material changes of our brain, upon movements of molecular plasma, which -are started through the medium of the senses by the different influences -of light, warmth, moisture, etc. "We are a plaything to every pressure -of the air." No less important and deeply influential are the effects -produced upon our mind and body by the different quality and quantity -of food. Our mental activity, the activity of our understanding and of -our imagination, is quite different accordingly as we have taken tea or -coffee, wine or beer, before or during our work. Our moods, wishes, and -feelings are quite different when we are hungry and when we are -satisfied. The national character of Englishmen and Gauchos, in South -America, who live principally on meat and food rich in nitrogen, is -wholly different from that of the Irish, feeding on potatoes, and that -of the Chinese, living on rice, both of whom take food deficient in -nitrogen. The latter also form much more fat than the former. Here, as -everywhere, the variations of the mind go hand in hand with the -corresponding transformations of the body; both are produced by purely -material causes. But all other organisms, in the same way as man, are -varied and changed by the different influences of nutrition. It is well -known that we can change in an arbitrary way the form, size, colour, -etc., of our cultivated plants and domestic animals, by change of food; -that, for example, we can take from or give to a plant definite -qualities, accordingly as we expose it to a greater or less degree of -sunlight and moisture. As these phenomena are generally widely known, -and as we shall proceed presently to the consideration of the different -laws of adaptation, we will not dwell here any longer on the general -facts of variation. - -As the different laws of transmission may be naturally divided into the -two series of conservative and progressive transmission, so we may also -distinguish between two series of the laws of adaptation, first, the -series of laws of _indirect_, and secondly, the series of laws of -_direct_ adaptation. The latter may also be called the laws of actual, -and the former the laws of potential, adaptation. - -The first series, comprising the phenomena of _indirect_ (potential) -adaptation, has, on the whole, hitherto been little attended to, and -Darwin has the merit of having directed special attention to this series -of changes. It is somewhat difficult to place this subject clearly -before the reader; I will endeavour to make it clear hereafter by -examples. Speaking quite generally, indirect or potential adaptation -consists in the fact that certain changes in the organism, effected by -the influence of nutrition (in its widest sense) and of the external -conditions of existence in general, show themselves not in the -individual form of the respective organism, but in that of its -descendants. Thus, especially in organisms propagating themselves in a -sexual way, the reproductive system, or sexual apparatus, is often -influenced by external causes (which little affect the rest of the -organism), to such a degree that its descendants show a complete -alteration of form. This can be seen very strikingly in artificially -produced monstrosities. Monstrosities can be produced by subjecting the -parental organism to certain extraordinary conditions of life, and, -curiously enough, such an extraordinary condition of life does not -produce a change of the organism itself, but a change in its -descendants. This cannot be called transmission by inheritance, because -it is not a quality existing in the parental organism that is -transmitted by inheritance. It is, on the contrary, a change affecting -the parental organism, but not perceptible in it, that appears in the -peculiar formation of its descendants. It is only the impulse to this -new formation which is transmitted in propagation through the egg of the -mother or the sperm of the father. The new formation exists in the -parental organism only as a possibility (potential); in the descendants -it becomes a reality (actual). - -As this very important and very general phenomenon had hitherto been -entirely neglected, people were inclined to consider all the visible -variations and transformations of organic forms as phenomena of -adaptation of the second series, that is, as phenomena of _direct_ or -actual adaptation. The essence of this latter kind of adaptation -consists in the fact that the change affecting the organism (through -nutrition, etc.) shows itself immediately by some transformation, and -does not only make itself apparent in the descendants. To this class -belong all the well-known phenomena in which we can directly trace the -transforming influence of climate, food, education, training, etc., in -their effects upon the individual itself. - -We have seen how the two series of phenomena of progressive and -conservative transmission, in spite of their difference in principle, in -many ways interfere with and modify each other, and in many ways -co-operate with and cross each other. The same is the case, in a still -higher degree, in the two series of phenomena of indirect and direct -adaptation, which are opposed to each other and yet closely connected. -Some naturalists, especially Darwin and Carl Vogt, ascribe to the -indirect or potential adaptation by far the more important and almost -exclusive influence. But the majority of naturalists have hitherto been -inclined to take the opposite view, and to attribute the principal -influence to direct or actual adaptation. I consider this controversy, -in the mean while, as almost useless. It is but seldom that we are in a -condition, in any individual case of variation, to judge how much of it -belongs to direct and how much to indirect adaptation. We are, on the -whole, still too little acquainted with these exceedingly important and -intricate relations, and can only assert, in a general way, that the -transformation of organic forms is to be ascribed _either_ to direct -adaptation alone, _or_ to indirect adaptation alone, or lastly, to the -co-operation of both direct _and_ indirect adaptation. - - - - -CHAPTER X. - -LAWS OF ADAPTATION. - - - Laws of Indirect or Potential Adaptation.--Individual - Adaptation.--Monstrous or Sudden Adaptation.--Sexual - Adaptation.--Laws of Direct or Actual - Adaptation.--Universal Adaptation.--Cumulative - Adaptation.--Cumulative Influence of External Conditions - of Existence and Cumulative Counter-Influence of the - Organism.--Free Will.--Use and Non-use of - Organs.--Practice and Habit.--Correlative - Adaptation.--Correlation of Development.--Correlation of - Organs.--Explanation of Indirect or Potential Adaptation - by the Correlation of the Sexual Organs and of the other - parts of the Body.--Divergent Adaptation.--Unlimited or - Infinite Adaptation. - - -In the last chapter we reduced into two groups the phenomena of -Adaptation or Variation, which, in connection and interaction with the -phenomena of Heredity, produce all the endless variety of forms in -animals and plants--first, the group of indirect or potential, and -secondly, the group of direct or actual Adaptation. We shall occupy -ourselves with a closer examination of the different laws which we can -discover in these two groups of the phenomena of variation. Let us first -take into consideration the remarkable and very important, although -hitherto much neglected, phenomena of indirect variation. - -_Indirect or potential adaptation_ manifests itself, it will be -remembered, in the striking and exceedingly important fact that organic -individuals experience transformations and assume forms in consequence -of changes of nutrition which have not operated on them themselves, but -upon their parental organism. The transforming influence of the external -conditions of existence, of climate, of nutrition, etc., shows its -effects here not directly in the transformation of the organism itself, -but indirectly in that of its descendants. (Gen. Morph. ii. 202.) - -As the principal and most universal of the laws of indirect variation -must be mentioned _the law of individual adaptation_, or the important -proposition that all organic individuals from the commencement of their -individual existence are unequal, although often very much alike. As a -proof of this proposition, I may at once point to the fact, that in the -human race in general all brothers and sisters, all children of the same -parents, are unequal from their birth. No one will venture to assert -that two children at their birth are perfectly alike; that the size of -the individual parts of their bodies, the number of hairs on their -heads, the number of cells composing their outer skins or epidermis, the -number of blood-cells are the same in both children, or that both -children have come into the world with the same abilities or talents. -But what more specially proves this law of individual difference, is the -fact that in the case of those animals which produce several young ones -at a time,--for instance, dogs and cats,--all the young of each birth -differ from one another more or less strikingly in size and colour of -the individual parts of the body, or in strength, etc. Now this law is -universal. All organic individuals from their beginning are -distinguished by certain, though often extremely minute, differences, -and the cause of these individual differences, though in detail usually -utterly unknown to us, depends partly or entirely on certain influences -which the organs of propagation in the parental organism have undergone. - -A second law of indirect adaptation, which we shall call _the law of -monstrous or sudden adaptation_, is of less importance and less general -than the law of individual adaptation. Here the divergences of the -child-organism from the parental form are so striking that, as a rule, -we may designate them as monstrosities. In many cases they are produced, -as has been proved by experiments, by the parental organism having been -subject to a certain treatment, and placed under peculiar conditions of -nutrition; for example, when air and light are withdrawn from it, or -when other influences powerfully acting upon its nutrition are changed -in a certain way. The new condition of existence causes a strong and -striking modification of form, not directly of the organism itself, but -only of that of its descendants. The mode of this influence in detail we -cannot discover, and we can only in a very general way detect a causal -connection between the abnormal formation of the child and a certain -change in the conditions of existence of its parents exerting a special -influence upon the organs of propagation in the latter. The previously -mentioned phenomenon of albinism probably belongs to this group of -abnormal or sudden variations, also the individual cases of human beings -with six fingers and toes, the case of the hornless cattle, as well as -those of sheep and goats with four or six horns. The abnormal deviation -in all these cases probably owes its origin to a cause which at first -only affected the reproductive system of the parental organism, the egg -of the mother or the sperm of the father. - -A third curious manifestation of indirect adaptation may be termed _the -law of sexual adaptation_. Under this name we indicate the remarkable -fact that certain influences, which act upon the male organs of -propagation only, affect the structure of the male descendants, and in -like manner other influences, which act upon the female organs of -propagation only, manifest their effect only in the change of structure -of the female descendants. This remarkable phenomenon is still very -obscure, and has not as yet been investigated, but is probably of great -importance in regard to the origin of "secondary sexual -characteristics," to which we have already made allusion. - -All the phenomena of sexual, monstrous, and individual adaptation, which -we may comprise under the name of the laws of _indirect or potential -adaptation_, are as yet very little known to us in their real nature and -in their deeper causal connection. Only this much we can at present -maintain with certainty, that numerous and important transformations in -organic forms owe their existence to this process. Many and striking -variations of form solely depend on causes which at first only affect -the nutrition of the parental organism, and specially its organs of -propagation. Evidently the relations in which the sexual organs stand to -other parts of the body are of the greatest importance. We shall have -more to say of these presently, when we speak of the law of correlative -adaptation. How powerfully the variations in the conditions of life and -nutrition affect the propagation of organisms is rendered obvious by the -remarkable fact that numerous wild animals which we keep in our -zoological gardens, and exotic plants which are grown in our botanical -gardens, are no longer able to reproduce themselves. This is the case, -for example, with most birds of prey, parrots, and monkeys. The -elephant, also, and the animals of prey of the bear genus, in captivity -hardly ever produce young ones. In like manner many plants in a -cultivated state become sterile. The two sexes may indeed unite, but no -fructification, or no development of the fructified germ, takes place. -From this it follows with certainty that the changed mode of nutrition -in the cultivated state is able completely to destroy the capability of -reproduction, and therefore to exercise the greatest influence upon the -sexual organs. In like manner other adaptations or variations of -nutrition in the parental organism may cause, not indeed a complete want -of descendants, but still important changes in their form. - -Much better known than the phenomena of indirect or potential adaptation -are those of _direct or actual adaptation_, to the consideration of -which we now turn our attention. To them belong all those changes of -organisms which are generally considered to be the results of practice, -habit, training, education, etc.; also those changes of organic forms -which are effected directly by the influence of nutrition, of climate, -and other external conditions of existence. As has already been remarked -in direct or actual adaptation, the transforming influence of the -external cause affects the form of the organism itself, and does not -only manifest itself in that of the descendants. (Gen. Morph. ii. 207.) - -We may place _the law of universal adaptation_ at the head of the -different laws of direct or actual adaptation, because it is the chief -and most comprehensive among them. It may be briefly explained in the -following proposition: "All organic individuals become unequal to one -another in the course of their life by adaptation to different -conditions of life, although the individuals of one and the same species -remain mostly very much alike." A certain inequality of organic -individuals, as we have seen, was already to be assumed in virtue of the -law of individual (indirect) adaptation. But, beyond this, the original -inequality of individuals is afterwards increased by the fact that every -individual, during its own independent life, subjects and adapts itself -to its own peculiar conditions of existence. All different individuals -of every species, however like they may be in their first stages of -life, become in the further course of their existence less like to one -another. They deviate from one another in more or less important -peculiarities, and this is a natural consequence of the different -conditions under which the individuals live. There are no two single -individuals of any species which can complete their life under exactly -the same external circumstances. The vital conditions of nutrition, of -moisture, air, light; further, the vital conditions of society, the -inter-relations with surrounding individuals of the same or other -species, are different in every individual being; and this difference -first affects the functions, and later changes the form of every -individual organism. If the children of a human family show, even at the -beginning, certain individual inequalities which we may consider as the -consequence of individual (indirect) adaptation, they will appear still -more different at a later period of life, when each child has passed -through different experiences, and has adapted itself to different -conditions of life. The original difference of the individual processes -of development, evidently becomes greater the longer the life lasts and -the more various the external conditions which influence the separate -individuals. This may be demonstrated in the simplest manner in man, as -well as in domestic animals and cultivated plants, in which the vital -conditions may be arbitrarily modified. Two brothers, of whom one is -brought up as a workman and the other as a priest, develop quite -differently in body as well as in mind; in like manner, two dogs of one -and the same birth, of which one is trained as a sporting dog and the -other chained up as a watch dog. The same observation may also readily -be made as to organic individuals in a natural state. If, for instance, -one carefully compares all the trees in a fir or beech forest, which -consists of trees of a single species, one finds that among all the -hundreds or thousands of trees, there are not two individual trees -completely agreeing in size of trunk and other parts, in the number of -branches, leaves, etc. Everywhere we find individual inequalities which, -in part at least, are merely the consequences of the different -conditions of life under which the trees have developed. It is true we -can never say with certainty how much of this dissimilarity in all the -individuals of every species may have originally been caused by indirect -individual adaptation, and how much of it acquired under the influence -of direct or universal adaptation. - -A second series of phenomena of direct adaptation, which we may comprise -under _the law of cumulative adaptation_, is no less important and -general than universal adaptation. Under this name I include a great -number of very important phenomena, which are usually divided into two -quite distinct groups. Naturalists, as a rule, have distinguished, -first, those variations of organisms which are produced directly by the -permanent influence of external conditions (by the constant action of -nutrition, of climate, of surroundings, etc.), and secondly, those -variations which arise from habit and practice, from accustoming -themselves to definite conditions of life, and from the use and non-use -of organs. The latter influences have been set forth especially by -Lamarck as important causes of the change of organic forms, while the -former have for a very long time been recognized as such more generally. - -The sharp distinction usually made between these two groups of -cumulative adaptation, and which even Darwin still maintains, disappears -as soon as we reflect more accurately and deeply upon the real nature -and causal foundation of these two, apparently very different, series of -adaptations. We then arrive at the conviction that in both cases there -are always two different active causes to be dealt with: on the one hand -the _external influence_ or _action_ of adaptative conditions of life, -and on the other hand the _internal reaction of the organism_ which -subjects and adapts itself to that condition of life. If cumulative -adaptation is considered from the first point of view alone, and the -transforming actions of the permanent external conditions of life are -traced to those conditions solely, then the principal stress is laid -unduly upon the external factor, and the necessary internal reaction of -the organism is not taken into proper consideration. If, on the other -hand, cumulative adaptation is unjustly regarded solely in relation to -its second factor, and the transforming action of the organism itself, -its reaction against the external influences, its change by practice, -habit, use, or non-use of organs, is put into the foreground, then we -forget that this reaction is first called into play by the action of -external conditions of existence. Hence it seems that the distinction -made between these two groups lies only in the different manner of -viewing them, and I believe that they can, with full justice, be -considered as one. The most essential fact in these phenomena of -cumulative adaptation is that the change of the organism which manifests -itself first in the functions, and at a later period in the form, is the -result either of long enduring, or of often repeated, influences of an -external cause. The smallest cause, by cumulation of its action, can -attain the greatest results. - -There are innumerable examples of this kind of direct adaptation. In -whatever direction we may examine the life of animals and plants, we -discover on all hands evident and undeniable changes of this kind. Let -me first mention some of those phenomena of adaptation occasioned -directly by nutrition itself. Every one knows that the domestic animals -which are bred for certain purposes can be variously modified, according -to the different quantity and quality of the food given to them. If a -farmer in breeding sheep wishes to produce fine wool, he gives them -different food from what he would give if he wished to obtain good flesh -or an abundance of fat. Choice race and carriage horses receive better -food than dray and cart horses. Even the bodily form of man--for -example, the amount of fat--is quite different according to his -nutrition. Food containing much nitrogen produces little fat, that -containing little nitrogen produces a great deal of fat. People who, by -means of Banting's system, at present so popular, wish to become thin -eat only meat and eggs--no bread, no potatoes. The important variations -that can be produced among cultivated plants, solely by changing the -quantity and quality of nourishment, are well known. The same plant -acquires an altogether different appearance, according as it is placed -in a dry and warm place, exposed to the sunlight or placed in a cool -damp spot in the shade. Many plants, if transferred to the sea shore, -get in a short space of time thick, fleshy leaves, and the same plants -placed in a particularly dry and hot locality get thin hairy leaves. All -these variations arise directly from the cumulative influence of changed -nutrition. - -But it is not only the quantity and quality of the articles of nutrition -which affect and powerfully change and transform the organism, but it is -affected also by all the other external conditions of existence, above -all by its nearest organic surroundings, the society of friendly or -hostile organisms. One and the same kind of tree develops itself quite -differently in an open locality, where it is free on all sides, and in a -forest where it must adapt itself to its surroundings, where it is -pressed on all sides by its nearest neighbours, and is forced to shoot -upwards. In the former case, the branches of the tree spread widely out; -in the latter, the trunk extends upwards, and the top of the tree -remains small and contracted. How powerfully all these circumstances, -and how powerfully the hostile or friendly influence of surrounding -organisms, of parasites, etc., affect every animal and every plant, is -so well known, that it appears superfluous to quote further examples. -The change of form, or transformation which is thereby effected, is -never solely the direct result of the external influence, but must -always be traced to the corresponding reaction, and to the activity of -the organism itself, which consists in contracting a habit, or practice, -and in the use or non-use of organs. The fact that these latter -phenomena, as a rule, have been considered distinct from the former, is -owing first to the one-sided manner of viewing them already mentioned, -and secondly to the wrong notion which has been formed as to the nature -and the influence of the activity of the will in animals. - -The activity of the will, which is the organ of habit, of practice, of -the use or non-use of organs among animals, is, like every other -activity of the animal soul, dependent upon material processes in the -central nervous system, upon peculiar motions which emanate from the -albuminous matter of the ganglion cells, and the nervous fibres -connected with them. The will, as well as the other mental activities, -in higher animals, in this respect is different from that of men only in -quantity, not in quality. The will of the animal, as well as that of -man, is never free. The widely spread dogma of the freedom of the will -is, from a scientific point of view, altogether untenable. Every -physiologist who scientifically investigates the activity of the will in -man and animals, must of necessity arrive at the conviction that _in -reality the will is never free_, but is always determined by external or -internal influences. These influences are for the most part ideas which -have been either formed by Adaptation or by Inheritance, and are -traceable to one or other of these two physiological functions. As soon -as we strictly examine the action of our own will, without the -traditional prejudice about its freedom, we perceive that every -apparently free action of the will is the result of previous ideas, -which are based on notions inherited or otherwise acquired, and are -therefore, in the end, dependent on the laws of Adaptation and -Inheritance. The same also applies to the action of the will in all -animals. As soon as their will is considered in connection with their -mode of life, in its relation to the changes which the mode of life is -subject to from external conditions, we are at once convinced that no -other view is possible. Hence the changes of the will which follow the -changes of nutrition, and which, in the form of practice, habit, etc., -produce variations in structure, must be reckoned among the other -material processes of cumulative adaptation. - -Whilst an animal's will is adapting itself to changed conditions of -existence by the acquisition of new habits, practices, etc., it not -unfrequently effects the most remarkable transformations of the organic -form. Numerous instances of this may be found everywhere in animal life. -Thus, for example, many organs in domestic animals are suppressed, when -in consequence of a changed mode of life they cease to act. Ducks and -fowls in a wild state fly exceedingly well, but lose this facility more -or less in a cultivated state. They accustom themselves to use their -legs more than their wings, and in consequence the muscles and skeleton -used in flying are essentially changed in their development and form. -Darwin has proved this by a very careful comparative measurement and -weighing of the respective parts of the skeleton in the different races -of domestic ducks, which are all descended from the wild duck (_Anas -boschas_). The bones of the wings in tame ducks are weaker, the bones of -the legs, on the other hand, are more strongly developed than in wild -ducks. In ostriches and other running birds which have become completely -unaccustomed to fly, the consequence is that their wings are entirely -crippled and degenerate into mere "rudimentary organs" (p. 12). In many -domestic animals, especially in many races of dogs and rabbits, we find -that in the cultivated state they have acquired pendulous ears. This is -simply a consequence of a diminished use of the auricular muscles. In a -wild state these animals have to exert their ears very much in order to -discover an approaching foe, and this is accompanied by a strong -development of the muscular apparatus, which keeps the outer ears in an -upright position, and by which they can turn them in all directions. In -a domestic state the same animals no longer require to listen so -attentively, they prick up or turn their ears only a little; the -auricular muscles cease to be used, gradually become weakened, and the -ears hang down flabbily, or become rudimentary. - -As in these cases the function, and consequently the form also, of the -organ becomes degenerated through disuse, so, on the other hand, it -becomes more developed by greater use. This is particularly striking if -we compare the brain, and the mental activity belonging to it, in wild -animals and those domestic animals which are descended from them. The -dog and horse, which are so vastly improved by cultivation, show an -extraordinary degree of mental development, in comparison with their -wild original ancestors, and evidently the change in the bulk of the -brain, which is connected with it, is mainly determined by persistent -exercise. It is also well known how quickly and powerfully muscles grow -and change their form by continual practice. Compare, for example, the -arms and legs of a trained gymnast with those of an immovable book-worm. - -How powerfully external influences affect the habits of animals and -their mode of life, and in this way still further change their forms, is -very strikingly shown in many cases among amphibious animals and -reptiles. Our commonest indigenous snake, the ringed snake, lays eggs -which require three weeks' time to develop. But when it is kept in -captivity, and no sand is strewn in the cage, it does not lay its eggs, -but retains them until the young ones are developed. The difference -between animals producing living offspring and those laying eggs is here -effaced simply by the change of the ground upon which the animal lives. - -The water-salamanders, or tritons, which have been artificially made to -retain their original gills, are extremely interesting in this respect. -The tritons are amphibious animals, nearly akin to frogs, and possess, -like the latter, in their youth external organs of -respiration--gills--with which they, while living in water, breathe the -air dissolved in the water. At a later date a metamorphosis takes place -in tritons, as in frogs. They leave the water, lose their gills, and -accustom themselves to breathe with their lungs. But if they are -prevented from doing this by being kept shut up in a tank, they do not -lose their gills. The gills remain, and the water salamander continues -through life in that low stage of development, beyond which its lower -relations, the gilled salamanders, or Sozobranchiata, never pass. The -gilled salamander attains its full size, its sexual development, and -reproduces itself without losing its gills. - -Great interest was caused a short time ago, among zoologists, by the -axolotel (Siredon pisciformis), a gilled salamander from Mexico, nearly -related to the triton; it had already been known for a long time, and -been bred on a large scale in the zoological garden in Paris. This -animal possesses external gills, like the young salamander, but retains -them all its life, like all other Sozobranchiata. This gilled salamander -generally remains in the water, with its aquatic organs of respiration, -and also propagates itself there. But in the Paris garden, unexpectedly -from among hundreds of these animals, a small number crept out of the -water on to the dry land, lost their gills, and changed themselves into -gill-less salamanders, which are not to be distinguished from a -North-American genus of tritons (Amblystoma), and breathe only through -lungs. In this exceedingly curious case we can directly follow the great -stride from water-breathing to air-breathing animals, a stride which can -indeed be observed every spring in the individual history of development -of frogs and salamanders. Just as every separate frog and every separate -salamander transforms itself from an amphibious animal breathing through -gills, at a later period into one breathing through lungs, so the whole -group of frogs and salamanders have arisen from animals breathing -through gills, and akin to the Siredon. The Sozobranchiata have remained -up to the present day in that low stage of development. Ontogeny here -explains phylogeny; the history of the development of individuals -explains that of the whole group (p. 10). - -To the law of accumulative adaptation there closely follows a third law -of direct or actual adaptation, _the law of correlative adaptation_. -According to this important law, actual adaptation not only changes -those parts of the organism which are directly affected by its -influence, but other parts also not directly affected by it. This is the -consequence of organic solidarity, and especially of the unity of the -nutrition existing among all the parts of every organism. If, for -example, the hairiness of the leaves increases in a plant by its being -transferred to a dry locality, then this change reacts upon the -nutrition of other parts, and it may result in a shortening of the parts -of the stalk, and produce a more contracted form of the whole plant. In -some races of pigs and dogs--for example, in the Turkish dog--which by -adaptation to a warmer climate have more or less lost their hair, the -teeth also have degenerated. Whales and Endentata (armadillos), which by -their curious skin-covering are removed from the other mammals, also -show the greatest deviations in the formation of their teeth. Further, -those races of domestic animals (oxen and pigs) which have acquired -short legs have, as a rule, also a short and compact head. Among other -examples, the races of pigeons which have the longest legs are also -characterized by the longest beaks. The same correlation between the -length of the legs and beaks is universal in the order of stilted-birds -(Grallatores), in storks, cranes, snipe, etc. The correlations which -thus exist between different parts of the organism are most remarkable, -but their real cause is unknown to us. In general, we can of course say, -the changes of nutrition affecting an individual part must necessarily -react on the other parts, because the nutrition of every organism is a -connected, centralized activity. But why just this or that part should -exhibit this or that particular correlation is in most cases quite -unknown to us. We know a great number of such correlations in nutrition; -they are especially seen in those changes of animals and plants which -give rise to an absence of pigment (noticed previously)--in albinoes. -The want of the usual colouring matter goes hand in hand with certain -changes in the formation of other parts; for example, of the muscular -and osseous system, consequently of organic systems which are not at all -ultimately connected with the system of the outer skin. Very frequently -albinoes are more feebly developed, and consequently the whole structure -of the body is more delicate and weak than in coloured animals of the -same species. The organs of the senses and nervous system are in like -manner curiously affected when there is this want of pigment. White cats -with blue eyes are nearly always deaf. White horses are distinguished -from coloured horses by their special liability to form sarkomatous -tumours. In man, also, the degree of the development of pigment in the -outer skin greatly influences the susceptibility of the organism for -certain diseases; so that, for instance, Europeans with a dark -complexion, black hair, and brown eyes become more easily acclimatized -to tropical countries, and are less subject to the diseases there -prevalent (inflammation of the liver, yellow fever, etc.) than Europeans -of white complexion, fair hair, and blue eyes. (Compare above, p. 150.) - -Among these correlations in the formation of different organs, those are -specially remarkable which exist between the sexual organs and other -parts of the body. No change of any part reacts so powerfully upon the -other parts of the body as a certain treatment of the sexual organs. -Farmers who wish to obtain an abundant formation of fat in pigs, sheep, -etc., remove the sexual organs by cutting them out (castration), and -this is indeed done to animals of both sexes. The result is an -excessive development of fat. The same is done to the singers in certain -religious corporations. These unfortunates are castrated in early youth, -in order that they may retain their high boyish voices. In consequence -of this mutilation of the genitals, the larynx remains in its youthful -stage of development. The muscular tissues of the body remain at the -same time weakly developed, while below the skin an abundance of fat -accumulates. But this mutilation also powerfully reacts upon the -development of the nervous system, the energy of the will, etc., and it -is well known that human castrates, or eunuchs, as well as castrated -animals, are utterly deficient in the special psychical character which -distinguishes the male sex. Man is a man, both in body and soul, solely -through his male generative glands. - -These most important and influential correlations between the sexual -organs and the other parts of the body, especially the brain, are found -equally in both sexes. This might be expected even _à priori_, because -in most animals the two kinds of organs develop themselves from the same -foundation, and at the beginning are not different. In man, as in the -rest of the vertebrate animals, the male and female organs in the -original state of the germ are entirely the same, and the differences of -the two sexes only gradually arise in the course of embryonic -development (in man, in the ninth week of embryonic life), by one and -the same gland developing in the female as the ovary, and in the male as -the testicle. Every change of the female ovary, therefore, has a no less -important reaction upon the whole female organism than every change of -the testicle has upon the male organism. Virchow has expressed the -importance of this correlation in his admirable essay on "Das Weib und -die Zelle" ("Woman and the Cell"), in the following words:--"Woman is -woman only by her sexual glands; all the peculiarities of her body and -mind, of her nutrition and her nervous activity, the sweet delicacy and -roundness of her limbs, the peculiar formation of the pelvis, the -development of the breasts, the continuance of the high voice, that -beautiful ornament of hair on her head, with the scarcely perceptible -soft down on the rest of the skin--then again, the depth of feeling, the -truth of her direct perceptions, her gentleness, devotion, and -fidelity--in short, all the feminine qualities which we admire and -honour in a true woman are but a dependence of the ovary. Take this -ovary away, and the man-woman stands before us--a loathly abortion." - -The same close correlation between the sexual organs and the other parts -of the body occurs among plants as generally as among animals. If one -wishes to obtain an abundance of fruit from a garden plant, the growth -of the leaves is curtailed by cutting off some of them. If, on the other -hand, an ornamental plant with a luxuriance of large and beautiful -leaves is desired, then the development of the blossoms and fruit is -prevented by cutting off the flower buds. In both cases one system of -organs develops at the cost of the others. Thus, also, most variations -in the formation of leaves in wild plants result in corresponding -transformations of the generative parts or blossoms. The great -importance of this "compensation of development," of this "correlation -of parts," has been already set forth by Goethe, by Geoffroy St. -Hilaire, and other nature-philosophers. It rests mainly upon the fact -that direct or actual adaptation cannot produce an important change in a -single part of the body, without at the same time affecting the whole -organism. - -The correlative adaptation between the reproductive organs and the other -parts of the body deserves a very special consideration, because it is, -above all others, likely to throw light upon the obscure and mysterious -phenomena of indirect or potential adaptation, which have already been -considered. For just as every change of the sexual organs powerfully -reacts upon the rest of the body, so on the other hand every important -change in another part of the body must necessarily more or less react -on the sexual organs. This reaction, however, will only become -perceptible in the formation of the offspring which arise out of the -changed generative parts. It is, in fact, precisely those remarkable and -imperceptible changes of the genital system (in themselves utterly -insignificant changes)--changes of the eggs and the sperm--brought about -by such correlations, which have the greatest influence upon the -formation of the offspring, and all the phenomena of indirect or -potential adaptation previously mentioned may in the end be traced to -correlative adaptation. - -A further series of remarkable examples of correlative adaptation is -furnished by the different animals and plants which become degenerated -through parasitic life or parasitism. No other change in the mode of -life so much affects the shapes of organisms as the adoption of a -parasitical life. Plants thereby lose their green leaves; as, for -instance, our native parasitical plants, Orobanche, Lathræa, Monotropa. -Animals which originally have lived freely and independently, but -afterwards adopt a parasitical mode of life on other animals or plants, -in the first place cease to use their organs of motion and their organs -of sense. The loss of this activity is succeeded by the loss of the -organs themselves, and thus we find, for example, many crabs, or -crustacea, which in their youth possess a tolerably high degree of -organization, viz., legs, antennæ, and eyes, in old age completely -degenerate, living as parasites, without eyes, without apparatus of -motion, and without antennæ. The lively, active form of youth, has -become a shapeless, motionless lump. Only the most necessary organs of -nutrition and propagation retain their activity; all the rest of the -body has degenerated. Evidently these complete transformations are, to a -large extent, the direct consequences of cumulative adaption, of the -non-use and defective exercise of the organs, but a great portion of -them must certainly be attributed also to correlative adaptation. -(Compare Plate X. and XI.) - -A seventh law of adaptation, the fourth in the group of direct -adaptation, is _the law of divergent adaptation_. By this law we -indicate the fact that parts originally formed alike have developed in -different ways under the influence of external conditions. This law of -adaptation is extremely important for the explanation of the phenomenon -of division of labour, or polymorphism. We can see this very easily in -our own selves; for instance, in the activity of our two hands. We -usually accustom our right hand to quite different work from that which -we give our left, and in consequence of the different occupation there -arises a different formation of the two hands. The right hand, which we -use much more than the left, shows a stronger development of the nerves, -muscles, and bones. The same applies to the whole arm. In most human -beings the bones and flesh of the right arm are, in consequence of their -being more employed, stronger and heavier than those of the left arm. -Now, as the special use of the right arm has been adopted and -transmitted by inheritance for thousands of years among Europeans, the -stronger shape and size of the right arm have already become hereditary. -P. Harting, an excellent Dutch naturalist, has shown by measuring and -weighing newly-born children, that even in them the right arm is more -developed than the left. - -According to the same law of divergent adaptation, both eyes also -frequently develop differently. If, for example, a naturalist accustoms -himself always to use one eye for the microscope (it is better to use -the left), then that eye will acquire a power different from that of the -other, and this division of labour is of great advantage. The one eye -will become more short-sighted, and better suited for seeing things near -at hand; the other eye becomes, on the contrary, more long-sighted, more -acute for looking at an object in the distance. If, on the other hand, -the naturalist alternately uses both eyes for the microscope, he will -not acquire the short-sightedness of the one eye and the compensatory -degree of long-sight in the other, which is attained by a wise -distribution of these different functions of sight between the two eyes. -Here then again the function, that is the activity, of originally -equally-formed organs can become divergent by habit; the function reacts -again upon the form of the organ, and thus we find, after a long -duration of such an influence, a change in the more delicate parts and -the relative growth of the divergent organs, which in the end becomes -apparent even in their coarser outlines. - -Divergent adaptation can very easily be perceived among plants, -especially in creepers. Branches of one and the same creeping plant, -which originally were formed alike, acquire a completely different form -and extent, a completely different degree of curvature and diameter of -spiral winding, according as they twine themselves round a thinner or a -thicker bar. The divergent change of form of parts originally identical -in form, which tending in different directions develop themselves under -different external conditions, can be distinctly demonstrated in many -other examples. As this divergent adaptation interacts with progressive -inheritance, it becomes the cause of a division of labour among the -different organs. - -An eighth and last law of adaptation we may call _the law of unlimited -or infinite adaptation_. By it we simply mean to express that we know of -no limit to the variation of organic forms occasioned by the external -conditions of existence. We can assert of no single part of an organism, -that it is no longer variable, or that if it were subjected to new -external conditions it would not be changed by them. It has never yet -been proved by experience that there is a limit to variation. If, for -example, an organ degenerates from non-use, this degeneration ends -finally in a complete disappearance of the organ, as is the case with -the eyes of many animals. On the other hand, we are able, by continual -practice, habit, and the ever-increasing use of an organ, to bring it to -a degree of perfection which we should at the beginning have considered -to be impossible. If we compare the uncivilized savages with civilized -nations, we find among the former a development of the organs of -sense--sight, smell, and hearing--such as civilized nations can hardly -conceive of. On the other hand, the brain, that is mental activity, -among more civilized nations is developed to a degree of which the wild -savages have no idea. - -There appears indeed to be a limit given to the adaptability of every -organism, by the "type" of its tribe or phylum; that is, by the -essential fundamental qualities of this tribe, which have been inherited -from a common ancestor, and transmitted by conservative inheritance to -all its descendants. Thus, for example, no vertebrate animal can acquire -the ventral nerve-chord of articulate animals, instead of the -characteristic spinal marrow of the vertebrate animals. However, within -this hereditary primary form, within this inalienable type, the degree -of adaptability is unlimited. The elasticity and fluidity of the organic -form manifests itself, within the type, freely in all directions, and to -an unlimited extent. But there are some animals, as, for example, the -parasitically degenerate crabs and worms, which seem to pass even the -limit of type, and have forfeited all the essential characteristics of -their tribe by an astonishing degree of degeneration. As to the -adaptability of man, it is, as in all other animals, also unlimited, and -since it is manifested in him above all other animals, in the -modifications of the brain, there can be absolutely no limit to the -knowledge which man in a further progress of mental cultivation may not -be able to exceed. The human mind, according to the law of unlimited -adaptation, enjoys an infinite perspective of becoming ever more and -more perfect. - -These remarks are sufficient to show the extent of the phenomena of -Adaptation, and the great importance to be attached to them. The laws of -Adaptation, or the facts of Variation caused by the influence of -external conditions, are just as important as the laws of Inheritance. -All phenomena of Adaptation, in the end, can be traced to conditions of -nutrition of the organism, in the same way as the phenomena of -Inheritance are referable to conditions of reproduction; but the latter, -as well as the former, may further be traced to chemical and physical, -that is to mechanical, causes. According to Darwin's Theory of Selection -the new forms of organisms, the transformations which artificial -selection produces in the state of cultivation, and which natural -selection produces in the state of nature, arise solely by the -interaction of such causes. - - - - -CHAPTER XI. - -NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION OF LABOUR AND -PROGRESS. - - - Interaction of the Two Organic Formative Causes, - Inheritance and Adaptation.--Natural and Artificial - Selection.--Struggle for Existence, or Competition for - the Necessaries of Life.--Disproportion between the - Number of Possible or Potential, and the Number of Real - or Actual Individuals.--Complicated Correlations of all - Neighbouring Organisms.--Mode of Action in Natural - Selection.--Homochromic Selection as the Cause of - Sympathetic Colourings.--Sexual Selection as the Cause of - the Secondary Sexual Characters.--Law of Separation or - Division of Labour (Polymorphism, Differentiation, - Divergence of Characters).--Transition of Varieties into - Species.--Idea of Species.--Hybridism.--Law of Progress - or Perfectioning (Progressus, Teleosis). - - -In order to arrive at a right understanding of Darwinism, it is, above -all, necessary that the two organic functions of _Inheritance and -Adaptation_, which we spoke of in our last chapter, should be more -closely examined. If we do not, on the one hand, examine the purely -mechanical nature of these two physiological activities, and the various -action of their different laws, and if, on the other hand, we do not -consider how complicated the interaction of these different laws of -Inheritance and Adaptation must be, we shall not be able to understand -how these two functions, by themselves, have been able to produce all -the variety of animal and vegetable forms, which, in fact, they have. -We have, at least, hitherto been unable to discover any other formative -causes besides these two, and if we rightly understand the necessary and -infinitely complicated interaction of Inheritance and Adaptation, we do -not require to look for other unknown causes for the change of organic -forms. These two fundamental causes are, as far as we can see, -completely sufficient. - -Even long before Darwin had published his Theory of Selection, some -naturalists, and especially Goethe, had assumed the interaction of two -distinct formative tendencies--a conservative or preserving, and a -progressive or changing formative tendency--as the causes of the variety -of organic forms. The former was called by Goethe the centripetal or -specifying tendency, the latter the centrifugal tendency, or the -tendency to metamorphosis (p. 89). These two tendencies completely -correspond with the two processes of Inheritance and Adaptation. -_Inheritance_ is the _centripetal_ or _internal formative tendency_ -which strives to keep the organic form in its species, to form the -descendants like the parents, and always to produce identical things -from generation to generation. _Adaptation_, on the other hand, which -counteracts inheritance, is the _centrifugal_ or _external formative -tendency_, which constantly strives to change the organic forms through -the influence of the varying agencies of the outer world, to create new -forms out of those existing, and entirely to destroy the constancy or -permanency of species. Accordingly as Inheritance or Adaptation -predominates in the struggle, the specific form either remains constant -or changes into a new species. The degree of constancy of form in the -different species of animals and plants, which obtains at any moment, -is simply the necessary result of the momentary predominance which -either of these two formative powers (or physiological activities) has -acquired over the other. - -If we now return to the consideration of the process of selection or -choice, the outlines of which we have already examined, we shall be in a -position to see clearly and distinctly that both artificial and natural -selection rest solely upon the interaction of these two formative -tendencies. If we carefully watch the proceedings of an artificial -selector--a farmer or a gardener--we find that only these two -constructive forces are used by him for the production of new forms. The -whole art of artificial selection rests solely upon a thoughtful and -wise application of the laws of Inheritance and Adaptation, and upon -their being applied and regulated in an artistic and systematic manner. -Here the will of man constitutes the selecting force. - -The case of natural selection is quite similar, for it also employs -merely these two organic constructive forces, these ingrained -physiological properties of Adaptation and Heredity, in order to produce -the different species. But the selecting principle or force, which in -_artificial_ selection is represented by the conscious _will of man_ -acting for a definite purpose, consists in _natural_ selection of the -unconscious _struggle for existence_ acting without a definite plan. -What we mean by "struggle for existence" has already been explained in -the seventh chapter. It is the recognition of this exceedingly important -identity which constitutes one of the greatest of Darwin's merits. But -as this relation is very frequently imperfectly or falsely understood, -it is necessary to examine it now more closely, and to illustrate by a -few examples the operation of the struggle for life, and the operation -of natural selection _by means of_ the struggle for life (Gen. Morph. -ii. 231). - -When considering the struggle for life, we started from the fact that -the number of germs which all animals and plants produce is infinitely -greater than the number of individuals which actually come to life and -remain alive for a longer or shorter time. Most organisms produce during -life thousands or millions of germs, from each of which, under -favourable circumstances, a new individual might arise. In most animals -and plants these germs are eggs, that is cells, which for their -development require sexual fructification. But among the Protista, the -lowest organisms, which are neither animals nor plants, and which -propagate themselves only in a non-sexual manner, the germ-cells, or -spores, require no fructification. Now, in all cases the number of -unsexual, as well as of sexual germs, is out of all proportion to the -number of actually living individuals of every species. - -Taken as a whole, the number of living animals and plants on our earth -remains always about the same. The number of places in the economy of -nature is limited, and in most parts of the earth's surface these places -are always approximately occupied. Certainly there occur everywhere and -in every year fluctuations in the absolute and in the relative number of -individuals of all species. However, taken as a whole, these -fluctuations are of little importance, and it is broadly the fact that -the total number of all individuals remains, on an average, almost -constant. There is a constant fluctuation, which depends on the fact -that in one year or another one or other series of animals and plants -predominates, and that every year the struggle for life somewhat alters -their relations. - -Every single species of animals and plants would have densely peopled -the whole earth's surface in a short time, if it had not had to struggle -against a number of enemies and hostile influences. Even Linnæus -calculated that if an annual plant only produced two seeds (and there is -not one which produces so few), it would have yielded in twenty years a -million of individuals. Darwin has calculated of elephants, which of all -animals seem the slowest to increase, that in seven hundred and fifty -years the descendants of a single pair would amount to nineteen millions -of individuals; this is supposing that every elephant, during its period -of fertility (from the 30th to the 90th year), produced only three pairs -of young ones, and survived itself to its hundredth year. In like manner -the increase of the number of human beings--if calculated on the average -proportion of births to population, and no hindrances to the natural -increase stood in the way--would be such as to double the total in -twenty-five years. In every century the total number of men would have -increased sixteen-fold; whereas we know that the total number of human -beings increases but slowly, and that the increase of population is very -different in different countries. While European tribes spread over the -whole globe, other tribes or species of men every year draw nearer to -their complete extinction. This is the case especially with the redskins -of America, and with the copper-coloured natives of Australia. Even if -these races were to propagate more abundantly than the white Europeans, -yet they would sooner or later succumb to the latter in the struggle for -life. But of all human individuals, as of all other organisms, by far -the majority perish at the earliest period of their lives. Of the -immense quantity of germs which every species produce, only very few -actually succeed in developing, and of these few it is again only a very -small portion which attain to the age in which they can reproduce -themselves (compare p. 161). - -From the disproportion between the immense excess of organic germs and -the small number of chosen individuals which are actually able to -continue in existence beside one another, there follows of necessity -that universal struggle for life, that constant fight for existence, -that perpetual competition for the necessaries of life, of which I gave -a sketch in my seventh chapter. It is this struggle for life which -brings natural selection into play, which in its turn is made use of by -the interaction of the phenomena of Inheritance and Adaptation as a -sifting agency, and which thus causes a continual change in all organic -forms. In this struggle for acquiring the necessary conditions of -existence, those individuals will always overpower their rivals who -possess any individual privilege, any advantageous quality, of which -their fellow competitors are destitute. It is true we are able only in -the fewest cases (in those animals and plants best known to us) to form -an approximate conception of the infinitely complicated interaction of -the numerous circumstances, all of which here come into combination. -Only think how infinitely varied and complicated are the relations of -every single human being to the rest of mankind, and in general, to the -whole of the surrounding outer world. But similar relations prevail also -among all animals and plants which live together in one place. All -influence one another actively or passively. Every animal and every -plant struggles directly with a number of enemies, beasts of prey, -parasitic animals, etc. Plants standing together struggle with one -another for the space of ground requisite for their roots, for the -necessary amount of light, air, moisture, etc. In like-manner, animals -living together struggle with one another for their food, -dwelling-place, etc. In this most active and complicated struggle, any -personal superiority, however small, any individual advantage, may -possibly decide the issue in favour of the one possessing it. This -privileged individual remains the victor in the struggle, and propagates -itself, while its fellow-competitors perish before they succeed in -propagating themselves. The personal advantage which gave it the victory -is transmitted by inheritance to its descendants, and by a further -development may become so strongly marked as to cause us to consider the -later generations as a new species. - -The infinitely complicated correlations which exist between the -organisms of every district, and which must be looked upon as the real -conditions of the struggle for life, are mostly unknown to us, and are -very difficult to discover. We have hitherto been able to trace them -only to a certain point in individual cases, as in the example given by -Darwin of the relations between cats and red clover in England. The red -clover (_Trifolium pratense_), which in England is among the best fodder -for cattle, requires the visit of humming-bees in order to attain the -formation of seeds. These insects, while sucking the honey from the -bottom of the flower, bring the pollen in contact with the stigma, and -thus cause the fructification of the flower, which never takes place -without it. Darwin has shown by experiments, that red clover which is -not visited by humming-bees does not yield a single seed. The number of -bees is determined by the number of their enemies, the most destructive -of which are the field-mice. The more the field-mice predominate, the -less the clover is fructified. The number of field-mice, again, is -dependent upon the number of their enemies, principally cats. Hence in -the neighbourhood of villages and towns, where many cats are kept, there -are plenty of bees. A great number of cats, therefore, is evidently of -great advantage for the fructification of clover. This example may be -followed still further, as has been done by Carl Vogt, if we consider -that cattle which feed on red clover are one of the most important -foundations of the wealth of England. Englishmen preserve their bodily -and mental powers chiefly by making excellent meat--roast beef and -beefsteak--their principal food. The English owe the superiority of -their brains and minds over those of other nations in a great measure to -their excellent meat. But this is clearly indirectly dependent upon the -cats, which pursue the mice. We may, with Huxley, even trace the chain -of causes to those old maids who cherish and keep cats, and, -consequently, are of the greatest importance to the fructification of -the clover and to the prosperity of England. From this example we can -see that the further it is traced the wider is the circle of action and -of correlation. We can with certainty maintain that there exist a great -number of such correlations in every plant and in every animal, only we -are not always able to point out and survey their concatenation as in -the last instance. - -Another remarkable example of important correlations is the following, -given by Darwin. In Paraguay, there are no wild oxen and horses, as in -the neighbouring parts of South America, both north and south of -Paraguay. This surprising circumstance is explained simply by the fact -that in that country a kind of small fly is very frequent, and is in the -habit of laying its eggs in the navel of newly-born calves and foals. -The newly-born animals die in consequence of this attack, and the small -deadly fly is therefore the cause of oxen and horses never becoming wild -in that district. Supposing that this fly were destroyed by some -insect-eating bird, then these large mammals would grow wild in -Paraguay, as well as in the neighbouring parts of South America; and as -they would eat a quantity of certain species of plants, the whole flora, -and, consequently again, the whole fauna of the country would become -changed. It is hardly necessary to state, that at the same time the -whole economy, and consequently the character, of the human population -would alter. - -Thus the prosperity, nay, even the existence of whole populations can be -indirectly determined by a single small animal or vegetable form in -itself extremely insignificant. There are small coral islands whose -human inhabitants live almost entirely upon the fruit of a species of -palm. The fructification of this palm is principally effected by -insects, which carry the pollen from the male to the female palm trees. -The existence of these useful insects is endangered by insect-eating -birds, which in their turn are pursued by birds of prey. The birds of -prey, however, often succumb to the attack of a small parasitical mite, -which develops itself in millions in their feathers. This small, -dangerous parasite, again, may be killed by parasitical moulds. Moulds, -birds of prey, and insects would in this case favour the prosperity of -the palm, and consequently of man; birds, mites, and insect-eating birds -would, on the other hand, endanger it. - -Interesting examples in relation to the change of correlations in the -struggle for life are furnished also by those isolated oceanic islands, -uninhabited by man, on which at different times goats and pigs have been -placed by navigators. These animals become wild, and having no enemies, -they increase in number so excessively, that the rest of the animal and -vegetable population suffer in consequence, and the island finally may -become almost a waste, because there is insufficient food for the large -mammals which increase too numerously. In some cases on an island thus -overrun with goats and pigs, other navigators have let loose a couple of -dogs, who enjoyed this superabundance of food, and they again increased -so numerously, and made such havoc among the herds, that after several -years the dogs themselves lacked food, and they also almost died out. -The equilibrium of species continually changes in this manner in -nature's economy, accordingly as one or another species increases at the -expense of the rest. In most cases the relations of different species of -animals and plants to one another are much too complicated for us to be -able to follow them, and I leave it to the reader to picture to himself -what an infinitely complicated machinery is at work in every part of the -world in consequence of this struggle. The impulses which started the -struggle, and which altered and modified it in different places, are in -the end seen to be the impulses of self-preservation--in fact, the -instinct leading individuals to preserve themselves (the instinct of -obtaining food), and the instinct leading them to preserve the species -(instinct of propagation). It is these two fundamental instincts of -organic self-preservation of which Schiller, the idealist (not Goethe, -the realist!) says: - - "Meanwhile, until philosophy - Sustains the structure of the world, - Her workings will be carried on - By hunger and by love."[4] - -It is these two powerful fundamental instincts which, by their varying -activity, produce such extraordinary differences in species through the -struggle for life. They are the foundations of the phenomena of -Inheritance and Adaptation. We have, in fact, traced all phenomena of -Inheritance to propagation, all phenomena of Adaptation to nutrition, as -the two wider classes of material phenomena to which they belong. - -The struggle for life in natural selection acts with as much selective -power as does the will of man in artificial selection. The latter, -however, acts according to a plan and consciously, the former without a -plan and unconsciously. This important difference between artificial and -natural selection deserves especial consideration. For we learn by it to -understand how _arrangements serving a purpose can be produced by -mechanical causes acting without an object, as well as by causes acting -for an object_. The products of natural selection are arranged even more -for a purpose than the artificial products of man, and yet they owe -their existence not to a creative power acting for a definite purpose, -but to a mechanical relation acting unconsciously and without a plan. -If we had not thoroughly considered the interaction of Inheritance and -Adaptation under the influence of the struggle for life, we should not -at first be inclined to expect such results from this natural process of -selection as are, in fact, furnished by it. It may therefore be -appropriate here to mention a few especially striking examples of the -activity of natural selection. - -Let us first take _Darwin's homochromic selection_ of animals, or the -so-called "sympathetic selection of colours," into consideration. -Earlier naturalists have remarked that numerous animals are of nearly -the same colour as their dwelling-place, or the surroundings in which -they permanently live. Thus, for example, plant-lice and many other -insects living on leaves are of a green colour. The inhabitants of the -deserts, the jerboa, or leaping mice, foxes of the desert, gazelles, -lions, etc., are mostly of a yellow or yellowish-brown colour, like the -sand of the desert. The polar animals, which live on the ice and snow, -are white or grey, like ice and snow. Many of these animals change their -colour in summer and winter. In summer, when the snow partly vanishes, -the fur of these polar creatures becomes brownish-grey or blackish, like -the naked earth, while in winter it again becomes white. Butterflies and -insects which hover round the gay and bright flowers are like them in -colour. Now, Darwin explains this surprising circumstance quite simply -by the fact that such colours as agree with the colour of the habitation -are of the greatest use to the animals concerned. If these animals are -animals of prey, they will be able to approach the object of their -pursuit more safely and with less likelihood of observation, and, in -like manner, those animals which are pursued will be able to escape -more easily, if their colour is as little different as possible from -that of their surroundings. If therefore originally an animal species -varied so as to present cases of all colours, those individuals whose -colour most resembled the surroundings must have been most favoured in -the struggle for life. They remained more unobserved, maintained and -propagated themselves, while those individuals or varieties differently -coloured died out. - -I have tried to explain, by the same sympathetic selection of colour, -the wonderful fact that the majority of pelagic animals--that is, of -those which live on the surface of the open sea--are bluish, or -completely colourless and transparent, like glass and water itself. Such -colourless, glassy animals are met with in the most different classes. -To them belong, among fish, the Helmicthyidæ, through whose crystalline -bodies the words of a book can be read; among the molluscs, the finned -snails (Heteropods) and sea-butterflies, or whales-food (Pteropods); -among worms, the Salpæ, Alciope, and Sagitta; further, a great number of -pelagic crabs (Crustacea), and the greater part of the Medusæ -Umbrella-jellies, (Discomedusæ); Comb-jellies, (Ctenophora). All of -these pelagic animals, which float on the surface of the ocean, are -transparent and colourless, like glass and like the water itself, while -their nearest kin live at the bottom of the ocean, and are coloured and -opaque like the inhabitants of the land. This remarkable fact, like the -sympathetic colouring of the inhabitants of the earth, can be explained -by natural selection. Among the ancestors of the pelagic glass-like -animals which showed a different degree of colourlessness and -transparency, those that were the most colourless and transparent must -have been most favoured in the active struggle for life which takes -place on the surface of the ocean. They were enabled to approach their -prey the most easily unobserved, and were themselves least observed by -their enemies. Hence they could preserve and propagate themselves more -easily than their more coloured and opaque relatives; and finally, by -accumulative adaptation and transmission by inheritance, through natural -selection, in the course of many generations their bodies would attain -that degree of crystal-like transparency and colourlessness which we at -present admire in them. (Gen. Morph. ii. 242.) - -No less interesting and instructive than homochromic selection is that -species of natural selection which Darwin calls "_sexual selection_," -which explains the origin of the so-called "secondary sexual -characters." We have already mentioned these subordinate sexual -characteristics, so instructive in many respects. They comprise those -peculiarities of animals and plants which belong only to one of the two -sexes, and which do not stand in any direct relation to the act of -propagation itself (compare above, p. 244). Such secondary sexual -characters occur in great variety among animals. We all know how -striking is the difference of the two sexes in size and colour in many -birds and butterflies. The male sex is generally the larger and more -beautiful. It often possesses special decorations or weapons; as for -example, the spur and comb of the cock, the antlers of the stag and -deer, etc. All these peculiarities of the two sexes have nothing -directly to do with propagation itself, which is effected by the -"primary sexual characters," or actual sexual organs. - -Now, the origin of these remarkable "secondary sexual characters" is -explained by Darwin simply by a choice or selection which takes place -in the propagation of animals. In most animals the number of individuals -of both sexes is unequal; either the number of the female or the number -of the male individuals is greater, and, as a rule, when the season of -propagation approaches, a struggle takes place between the rivals for -the possession of the animals of the other sex. It is well known with -what vigour and vehemence this struggle is fought out among the higher -animals--among mammals and birds--especially among those of polygamous -habits. Among gallinaceous birds, where for one cock there are several -hens, a severe struggle takes place between the competing cocks for as -large a harem as possible. The same is the case with many ruminating -animals. Among stags and deer, for instance, at the period of rut, -deadly struggles take place between the males for the possession of the -females. The secondary sexual character which here distinguishes the -males--the antlers of stags and deer--not possessed by the female, is, -according to Darwin, the consequence of that struggle. Here the motive -and cause determining the struggle is not, as in the case of the -struggle for individual existence, self-preservation, but the -preservation of the species--propagation. There are numerous passive -weapons of defence, as well as active weapons for attack. The lion's -mane, not possessed by the female, is evidently such a weapon of -defence; it is an excellent means of protection against the bites which -the male lions try to inflict on each other's necks when fighting for -the females; consequently those males with the strongest manes have the -greatest advantage in the sexual struggle. The dewlap of the ox and the -comb of the cock are similar defensive weapons. Active weapons of -attack, on the other hand, are the antlers of the stag, the tusks of -the boar, the spur of the cock, and the hugely developed pair of jaws in -the male stag-beetle; all are instruments employed by the males in the -struggle for the females, for annihilating or chasing away their rivals. - -In the cases just mentioned, it is the bodily "struggle to the death" -which determines the origin of the secondary sexual characters. But, -besides these mortal struggles, there are other important competitions -in sexual selection, which no less influence the structure of the -rivals. These consist principally in the fact that the courting sex -tries to please the other by external finery, by beauty of form, or by a -melodious voice. Darwin thinks that the beautiful voices of singing -birds have principally originated in this way. Many male birds carry on -a regular musical contest when they contend for the possession of the -females. It is known of several singing birds, that in the breeding -season the males assemble in numbers round the females, and let their -songs resound before them, and that then the females choose the singers -who best please them for their mates. Among other songsters, individual -males pour out their songs in the loneliness of the forest in order to -attract the females, and the latter follow the most attractive calls. A -similar musical contest, though certainly less melodious, takes place -among crickets and grasshoppers. The male cricket has on its belly two -instruments like drums, and produces with these the sharp chirping notes -which the ancient Greeks curiously enough thought beautiful music. Male -grasshoppers, partly by using their hind-legs like the bow of a violin -against their wing coverings, and partly by rubbing their wing coverings -together, bring out tones which are, indeed, not melodious to us, but -which please the female grasshoppers so much that they choose the male -who fiddles the best. - -Among other insects and birds it is not song or, in fact, any musical -accomplishment, but finery or beauty of the one sex which attracts the -other. Thus we find that, among most gallinaceous birds, the cocks are -distinguished by combs on their heads, or by a beautiful tail, which -they can spread out like a fan; as for example, in the case of the -peacock and turkey-cock. The magnificent tail of the bird of paradise is -also an exclusive ornament of the male sex. In like manner, among very -many other birds and very many insects, principally among butterflies, -the males are distinguished from the females by special colours or other -decorations. These are evidently the results of sexual selection. As the -females do not possess these attractions and decorations, we must come -to the conclusion that they have been acquired by degrees by the males -in the competition for the females, which takes its origin in the -selective discrimination of the females. - -We may easily picture to ourselves, in detail, the application of this -interesting conclusion to the human community. Here, also, the same -causes have evidently influenced the development of the secondary sexual -characters. The characteristics distinguishing the man, as well as those -distinguishing the woman, owe their origin, certainly for the most part, -to the sexual selection of the other sex. In antiquity and in the Middle -Ages, especially in the romantic age of chivalry, it was the bodily -struggles to the death--the tournaments and duels--which determined the -choice of the bride; the strongest carried home the bride. In more -recent times, however, in our so-called "polished" or "highly -civilized" society, competing rivals prefer to contend indirectly by -means of musical accomplishments, instrumental performances and song, by -bodily charms, natural beauty, or artificial decoration. But by far the -most important of these different forms of sexual selection in man is -that form which is the most exalted, namely, _psychical selection_, in -which the mental excellencies of the one sex influence and determine the -choice of the other. The most highly intellectually developed types of -men have, throughout generations, when choosing a partner in life, been -guided by her excellencies of soul, and have thus transmitted these -qualities to their posterity, and they have in this way, more than by -any other thing, helped to create the deep chasm which at present -separates civilized men from the rudest savages, and from our common -animal ancestors. In fact, both the part played by the prevalence of a -higher standard of sexual selection, and the part played by the due -division of labour between the two sexes, is exceedingly important, and -I believe that here we must seek for the most powerful causes which have -determined the origin and the historical development of the races of -man. (Gen. Morph. ii. 247.) As Darwin, in his exceedingly interesting -work, published in 1871, on "The Origin of Man and Sexual -Selection,"(48) has discussed this subject in the most masterly manner, -and has illustrated it by most remarkable examples, I refer for further -detail to that work. - -But now let us look again at two extremely important organic laws which -can be explained by the theory of selection, as necessary consequences -of natural selection in the struggle for existence. I mean the law of -_division of labour_, or _differentiation_, and the law of _progress_, -or _perfecting_. When the phenomena due to these two laws first became -known, through observation of the historical development, the individual -development, and the comparative anatomy of animals and plants, -naturalists were inclined to trace them to a direct creative influence. -It was supposed to be part of the plan of the Creator, acting for a -definite purpose, in the course of time to develop the forms of animals -and plants more and more variously, and to bring them more and more to a -state of perfection. We shall evidently make a great advance in the -knowledge of nature if we reject this teleological and anthropomorphic -conception, and if we can prove the two laws of Division of Labour and -Perfecting to be the necessary consequences of natural selection in the -struggle for life. - -The first great law which follows directly and of necessity from natural -selection, is that of _separation_, or _differentiation_, which is -frequently called _division of labour_, or _polymorphism_, and which -Darwin speaks of as _divergence of character_. (Gen. Morph. ii. 249.) We -understand by it the general tendency of all organic individuals to -develop themselves more and more diversely, and to deviate from the -common primary type. The cause of this general inclination towards -differentiation and the formation of heterogeneous forms from -homogeneous beginnings is, according to Darwin, simply to be traced to -the circumstance that the struggle for life between every two organisms -rages all the more fiercely the nearer the relation in which they stand -to one another, or the more nearly alike they are. This is an -exceedingly important, and in reality an exceedingly simple relation, -but it is usually not duly considered. - -It must be obvious to every one, that in a field of a certain size, -beside the corn-plants which have been sown, a great number of weeds -can exist, and, moreover, in places which could not have been occupied -by corn-plants. The more dry and sterile places of the ground, in which -no corn-plant would thrive, may still furnish sustenance to weeds of -different kinds; and such species and individuals of weeds will more -readily be able to exist in such conditions, in proportion as they are -suited to adapt themselves to the different parts of the ground. It is -the same with animals. It is evident that a much greater number of -animal individuals can live together in one and the same limited -district, if they are of various and different natures, than if they are -all alike. There are trees (for example, the oak) on which a couple of -hundred of different species of insects live together. Some feed on the -fruits of the tree, others on the leaves, others again on the bark, the -root, etc. It would be quite impossible for an equal number of -individuals to live on this tree if all were of one species; if, for -example, all fed on the bark, or only upon the leaves. Exactly the same -is the case in human society. In one and the same small town, only a -certain number of workmen can exist, even when they follow different -occupations. The division of labour, which is of the greatest use to the -whole community, as well as to the individual workman, is a direct -consequence of the struggle for life, of natural selection; for this -struggle can be sustained more easily the more the activities, and -hence, also, the forms of the different individuals deviate from one -another. The different function naturally produces its reaction in -changing the form, and the physiological division of labour necessarily -determines the morphological differentiation, that is, the "divergence -of character."(37) - -Now, I beg the reader again to remember that all species of animals and -plants are variable, and possess the capability of adapting themselves -to different places or to local relations. The varieties or races of -each species, according to the laws of adaptation, deviate all the more -from the original primary species, the greater the difference of the new -conditions to which they adapt themselves. If we imagine these -varieties--which have proceeded from a common primary form--to be -disposed in the shape of a branching, radiating bunch, then those -varieties will be best able to exist side by side and propagate which -are most distant from one another, which stand at the ends of the -series, or at the opposite sides of the bunch. Those forms, on the other -hand, occupying a middle position--presenting a state of -transition--have the most difficult position in the struggle for life. -The necessaries of life differ most in the two extremes, in the -varieties most distant from one another, and consequently these will get -into the least serious conflict with one another in the general struggle -for life. But the intermediate forms, which have deviated less from the -original primary form, require nearly the same necessaries of life as -the original form, and therefore, in competing for them, they will have -to struggle most with, and be most seriously threatened by, its members. -Consequently, when numerous varieties of a species live side by side on -the same spot of the earth, the extremes, or those forms deviating most -from one another, can much more easily continue to exist beside one -another than the intermediate forms which have to struggle with each of -the different extremes. The intermediate forms will not be able to -resist, for any length of time, the hostile influences which the extreme -forms victoriously overcome. These alone maintain and propagate -themselves, and at length cease to be any longer connected with the -original primary species through intermediate forms of transition. Thus -arise "good species" out of varieties. Thus, then, the struggle for life -necessarily favours the general divergence of organic forms, that is, -the constant tendency of organisms to form new species. This fact does -not rest upon any mystic quality, or upon an unknown formative tendency, -but upon the interaction of Inheritance and Adaptation in the struggle -for life. As the intermediate forms, that is, the individuals in a state -of transition, of the varieties of every species die out and become -extinct, the process of divergence constantly goes further, and from the -extremes forms develop which we distinguish as new species. - -Although all naturalists have been obliged to acknowledge the -variability and mutability of all species of animals and plants, yet -most of them have hitherto denied that the modification or -transformation of the organic form surpasses the original limit of the -characters of the species. Our opponents cling to the -proposition--"However far a species may exhibit deviations from its -usual form in a collection of varieties, yet the varieties of it are -never so distinct from one another as two really good species." This -assertion, which Darwin's opponents usually place at the head of their -arguments, is utterly untenable and unfounded. This will become quite -clear as soon as we critically compare the various attempts to define -the idea of species. No naturalist can answer the question as to what is -in reality a "genuine or good species" ("bona species"); yet every -systematic naturalist uses this expression every day, and whole -libraries have been written on the question as to whether this or that -observed form is a species or a variety, whether it is a really good or -a bad species. The most general answer to this question used to be the -following: "To one species belong all those individuals which agree in -all essential characteristics. Essential characteristics of species are -those which remain permanent or constant, and never become modified or -vary." But as soon as a case occurred in which the characteristic--which -had hitherto been considered essential--did become modified, then it was -said, "This characteristic is not essential to the species, for -essential characteristics never vary." Those who argued thus evidently -moved in a circle, and the naïveté with which this circular method of -defining species is laid down in thousands of books as an unassailable -truth, and is still constantly repeated, is truly astonishing. - -All other attempts which have been made to arrive at a definite and -logical determination of the idea of organic "species" have, like the -last, been utterly futile, and led to no results. Considering the nature -of the case, it cannot be otherwise. The idea of species is just as -truly a relative one and not absolute, as is the idea of variety, genus, -family, order, class, etc. I have proved this in detail in the criticism -of the idea of species in my "General Morphology" (Gen. Morph. ii. -323-364). I will waste no more time on this unsatisfactory discussion, -and now only add a few words about the _relation of species to -hybridism_. Formerly it was regarded as a dogma, that two good species -could never produce hybrids which could reproduce themselves as such. -Those who thus dogmatized almost always appealed to the hybrids of a -horse and donkey, the mule and the hinny, which, truly enough, are -seldom able to reproduce themselves. But the truth is that such -unfruitful hybrids are rare examples, and in the majority of cases -hybrids of two totally different species are fruitful and able to -reproduce themselves. They can almost always fruitfully mix with one or -other of the parent species, and sometimes also among themselves; and in -this way completely new forms can originate according to the laws of -"mixed transmission by inheritance." - -Thus, in fact, _hybridism is a source of the origin of new species_, -distinct from the source we have hitherto considered--natural selection. -I have already spoken occasionally of these _hybrid species_ (species -hybridæ), especially of the hare-rabbit (Lepus Darwinii), which has -arisen from the crossing of a male hare and a female rabbit; the -goat-sheep (Capra ovina), which has arisen from the pairing of a he-goat -and ewe; also the different species of thistles (Cirsium), brambles -(Rubus), etc. It is possible that many wild species have originated in -this way, as even Linnæus assumed. At all events, these hybrid species, -which can maintain and propagate themselves as well as pure species, -prove that hybridism cannot serve in any way to give an absolute -definition to the idea of species. - -I have already mentioned (p. 47) that the many vain attempts to define -the idea of species theoretically have nothing whatever to do with the -practical distinction of species. The extensive practical application of -the idea of species, as it is carried out in systematic zoology and -botany, is very instructive as furnishing an example of human folly. -Hitherto, by far the majority of zoologists and botanists, in -distinguishing and describing the different forms of animals and plants, -have endeavoured, above all things, to distinguish accurately kindred -forms as so many "good species." However, it has been found scarcely -possible, in any group, to make an accurate and consistent distinction -of such "genuine or good species." There are no two zoologists, no two -botanists, who agree in all cases as to which of the nearly related -forms of a genus are good species, and which are not. All authors have -different views about them. In the genus _Hieracium_, for example, one -of the commonest genera of European plants, no less than 300 species -have been distinguished in Germany alone. The botanist Fries, however, -only admits 106, Koch only 52, as "good species," and others accept -scarcely 20. The differences in the species of brambles (Rubus) are -equally great. Where one botanist makes more than a hundred species, a -second admits only about one half of that number, a third only five or -six, or even fewer species. The birds of Germany have long been very -accurately known. Bechstein, in his careful "Natural History of German -Birds," has distinguished 367 species, L. Reichenbach 379, Meyer and -Wolff 406, and Brehm, a clergyman learned in ornithology, distinguishes -even more than 900 different species. - -Thus we see that here, and, in fact, in every other domain of systematic -zoology and botany, the most arbitrary proceedings prevail, and, from -the nature of the case, must prevail. For it is quite impossible -accurately to distinguish varieties and races from so-called "good -species." _Varieties are commencing species._ The variability or -adaptability of species, under the influence of the struggle for life, -necessitates the continual and progressive separation or differentiation -of varieties, and the perpetual delimitation of new forms. Whenever -these are maintained throughout a number of generations by inheritance, -whilst the intermediate forms die out, they form independent "new -species." The origin of new species by division of labour, or -separation, divergence, or differentiation of varieties, is therefore a -_necessary consequence of natural selection_.(37) - -The same kind of interest attaches to a second great law which we deduce -from natural selection, and which is, indeed, closely connected with the -law of Divergence, but in no way identical with it; namely, the law of -_Progress_ (progressus), or _Perfecting_ (teleosis). (Gen. Morph. ii. -257.) This great and important law, like the law of differentiation, had -long been empirically established by palæontological experience, before -Darwin's Theory of Selection gave us the key to the explanation of its -cause. The most distinguished palæontologists have pointed out the law -of progress as the most general result of their investigations of fossil -organisms. This has been specially done by Bronn, whose investigations -on the laws of construction(18) and the laws of the development(19) of -organisms, although little heeded, are excellent, and deserve most -careful consideration. The general results of the law of differentiation -and the law of progress, at which Bronn arrived by a purely mechanical -hypothesis, and by exceedingly accurate, laborious, and careful -investigations, are brilliant confirmations of the truth of these two -great laws which we deduce as necessary inferences from the theory of -selection. - -The law of progress or of perfecting establishes the exceedingly -important fact, on the ground of palæontological experience, that in -successive periods of this earth's history, a continual increase in the -perfection of organic formations has taken place. Since that -inconceivably remote period in which life on our planet began with the -spontaneous generation of Monera, organisms of all groups, both -collectively as well as individually, have continually become more -perfectly and highly developed. The steadily increasing variety of -living forms has always been accompanied by progress in organization. -The lower the strata of the earth in which the remains of extinct -animals and plants lie buried, that is, the older the strata are, the -more simple and imperfect are the forms which they contain. This applies -to organisms collectively, as well as to every single large or small -group of them, setting aside, of course, those exceptions which are due -to the process of degeneration, which we shall discuss hereafter. - -As a confirmation of this law I shall mention only the most important of -all animal groups, the tribe of vertebrate animals. The oldest fossil -remains of vertebrate animals known to us belong to the lowest class, -that of Fishes. Upon these there followed later more perfect Amphibious -animals, then Reptiles, and lastly, at a much later period, the most -highly organized classes of vertebrate animals, Birds and Mammals. Of -the latter only the lowest and most imperfect forms, without placenta, -appeared at first, such as are the pouched animals (Marsupials), and -afterwards, at a much later period, the more perfect mammals, with -placenta. Of these, also, at first only the lower kinds appeared, the -higher forms later; and not until the late tertiary period did man -gradually develop out of these last. - -If we follow the historical development of the vegetable kingdom we -shall find the same law operative there. Of plants there existed at -first only the lowest and most imperfect classes, the Algæ or tangles. -Later there followed the group of Ferns or Filicinæ (ferns, pole-reeds, -scale-plants, etc.). But as yet there existed no flowering plants, or -Phanerogama. These originated later with the Gymnosperms (firs and -cycads), whose whole structure stands far below that of the other -flowering plants (Angiosperms), and forms the transition from the group -of fern-like plants to the Angiosperms. These latter developed at a -still later date, and among them there were at first only flowering -plants without corolla (Monocotyledons and Monochlamyds); only later -were there flowering plants with a corolla (Dichlamyds). Finally, again, -among these the lower polypetalous plants preceded the higher -gamopetalous plants. The whole series thus constitutes an irrefutable -proof of the great law of progressive development. - -Now, if we ask what is the cause of this fact, we again, just as in the -case of differentiation, come back to natural selection in the struggle -for life. If once more we consider the whole process of natural -selection, how it operates through the complicated interaction of the -different laws of Inheritance and Adaptation, we shall recognize not -only divergence of character, but also the perfecting of structure to be -the direct and necessary result of it. We can trace the same thing in -the history of the human race. Here, too, it is natural and necessary -that the progressive division of labour constantly furthers mankind, and -urges every individual branch of human activity into new discoveries and -improvements. This progress itself universally depends on -differentiation, and is consequently, like it, a direct result of -natural selection in the struggle for life. - - - - -CHAPTER XII. - -LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS. PHYLOGENY AND -ONTOGENY. - - - Laws of the Development of Mankind: Differentiation and - Perfecting.--Mechanical Cause of these two Fundamental - Laws.--Progress without Differentiation, and - Differentiation without Progress.--Origin of Rudimentary - Organs by Non-use and Discontinuance of - Habit.--Ontogenesis, or Individual Development of - Organisms.--Its General Importance.--Ontogeny, or the - Individual History of Development of Vertebrate Animals, - including Man.--The Fructification of the Egg.--Formation - of the three Germ Layers.--History of the Development of - the Central Nervous System, of the Extremities, of the - Branchial Arches, and of the Tail of Vertebrate - Animals.--Causal Connection and Parallelism of - Ontogenesis and Phylogenesis, that is of the Development - of Individuals and Tribes.--Causal Connection of the - Parallelism of Phylogenesis and of Systematic - Development.--Parallelism of the three Organic Series of - Development. - - -If man wishes to understand his position in nature, and to comprehend as -natural facts his relations to the phenomena of the world cognisable by -him, it is absolutely necessary that he should compare human with -extra-human phenomena, and, above all, with animal phenomena. We have -already seen that the exceedingly important physiological laws of -Inheritance and Adaptation apply to the human organism in the same -manner as to the animal and vegetable kingdoms, and in both cases -interact with one another. Consequently, natural selection in the -struggle for life acts so as to transform human society, just as it -modifies animals and plants, and in both cases constantly produces new -forms. The comparison of the phenomena of human and animal -transformation is especially interesting in connection with the laws of -divergence and progress, the two fundamental laws which, at the end of -the last chapter, we proved to be direct and necessary consequences of -natural selection in the struggle for life. - -A comparative survey of the history of nations, or what is called -"universal history," will readily yield to us, as the first and most -general result, evidence of a continually _increasing variety_ of human -activities, both in the life of individuals and in that of families and -states. This differentiation or separation, this constantly increasing -divergence of human character and the form of human life, is caused by -the ever advancing and more complete division of labour among -individuals. While the most ancient and lowest stages of human -civilization show us throughout the same rude and simple conditions, we -see in every succeeding period of history, among different nations, a -greater variety of customs, practices, and institutions. The increasing -division of labour necessitates an increasing variety of forms -corresponding to it. This is expressed even in the formation of the -human face. Among the lowest tribes of nations, most of the individuals -resemble one another so much that European travellers often cannot -distinguish them at all. With increasing civilization the physiognomy of -individuals becomes differentiated, and finally, among the most highly -civilized nations, the English and Germans, the divergence in the -characters of the face is so great that we very rarely mistake one face -for another. - -The second great fundamental law which is obvious in the history of -nations is the great law of progress or perfecting. Taken as a whole, -the history of man is the history of his _progressive development_. It -is true that everywhere and at all times we may notice individual -retrogressions, or observe that crooked roads towards progress have been -taken, which lead only towards one-sided and external perfecting, and -thus deviate more and more from the higher goal of internal and enduring -perfecting. However, on the whole, the movement of development of all -mankind is and remains a progressive one, inasmuch as man continually -removes himself further from his ape-like ancestors, and continually -approaches nearer to his own ideal. - -Now, if we wish to know what causes actually determine these two great -laws of development in man, namely, the law of divergence and the law of -progress, we must compare them with the corresponding laws of -development in animals, and on a close examination we shall inevitably -come to the conclusion that the phenomena, as well as their causes, are -exactly the same in the two cases. The course of development in man, -just as in that of animals, being directed by the two fundamental laws -of differentiation and perfecting, is determined solely by purely -mechanical causes, and is solely the necessary consequence of natural -selection in the struggle for life. - -Perhaps in the preceding discussion the question has presented itself to -some--"Are not these two laws identical? Is not progress in all cases -necessarily connected with divergence?" This question has often been -answered in the affirmative, and Carl Ernst Bär, for example, one of the -greatest investigators in the domain of the history of development, has -set forth the following proposition as one of the principal laws in the -ontogenesis of the animal body:--"The degree of development (or -perfecting) depends on the stage of separation (or differentiation) of -the parts."(20) Correct as this proposition may be on the whole, yet it -is not universally true. In many individual cases it can be proved that -divergence and progress by no means always coincide. _Every progress is -not a differentiation, and every differentiation is not a progress._ - -Naturalists, guided by purely anatomical considerations, had already set -forth the law relating to progress in organization, that the perfecting -of an organism certainly depends, for the most part, upon the division -of labour among the individual organs and parts of the body, but that -there are also other organic transformations which determine a progress -in organization. One, in particular, which has been generally -recognized, is the _numerical diminution of identical parts_. If, for -example, we compare the lower articulated animals of the crustacean -group, which possess numerous pairs of legs, with spiders which never -have more than four pairs of legs, and with insects which always possess -only three pairs of legs, we find this law, for which a great number of -examples could be adduced, confirmed. The numerical diminution of pairs -of legs is a progress in the organization of articulated animals. In -like manner the numerical diminution of corresponding vertebral joints -in the trunk of vertebrate animals is a progress in their organization. -Fishes and amphibious animals with a very large number of identical -vertebral joints are, for this very reason, less perfect and lower than -birds and mammals, in which the vertebral joints, as a whole, are not -only very much more differentiated, but in which the number of -corresponding vertebræ is also much smaller. Further, according to the -same law of numerical diminution, flowers with numerous stamens are more -imperfect than the flowers of kindred plants with a smaller number of -stamens, etc. If therefore originally a great number of homogeneous -parts exist in an organic body, and if, in the course of very many -generations, this number be gradually decreased, this transformation -will be an example of perfecting. - -Another law of progress, which is quite independent of differentiation, -nay, even appears to a certain extent opposed to it, is the law of -_centralization_. In general the whole organism is the more perfect the -more it is organized as a unit, the more the parts are subordinate to -the whole, and the more the functions and their organs are centralized. -Thus, for example, the system of blood-vessels is most perfect where a -centralized heart exists. In like manner, the dense mass of marrow which -forms the spinal cord of vertebrate animals, and the ventral cord of the -higher articulated animals, is more perfect than the decentralized chain -of ganglia of the lower articulated animals, and the scattered system of -ganglia in the molluscs. Considering the difficulty of explaining these -complicated laws of progress in detail, I cannot here enter upon a -closer discussion of them, and must refer to Bronn's excellent -"Morphologischen Studien," and to my "General Morphology" (Gen. Morph. -i. 370, 550; ii. 257-266). - -Just as we have become acquainted with phenomena of progress, quite -independent of divergence, so we shall, on the other hand, very often -meet with divergencies which are not perfecting, but which are rather -the contrary, that is retrogressions or degenerations. It is easy to see -that the changes which every species of animal and plant experiences -cannot always be improvements. But rather many phenomena of -differentiation, which are of direct advantage to the organism itself, -are yet, in a wider sense, detrimental, inasmuch as they lessen its -general capabilities. Frequently a relapse to simpler conditions of life -takes place, and by adaptation to them a divergence in a retrograde -direction. If, for instance, organisms which have hitherto lived -independently accustom themselves to a parasitical life, they thereby -degenerate or retrograde. Such animals, which hitherto had possessed a -well-developed nervous system and quick organs of sense, as well as the -power of moving freely, lose these when they accustom themselves to a -parasitical mode of life; they consequently retrograde more or less. -There the differentiation viewed by itself is a degeneration, although -it is advantageous to the parasitical organism. In the struggle for life -such an animal, which has accustomed itself to live at the expense of -others, by retaining its eyes and apparatus of motion, which are of no -more use to it, would only expend so much material uselessly; and when -it loses these organs, then a great quantity of nourishment which was -employed for the maintenance of these parts, benefits other parts. In -the struggle for life between the different parasites, therefore, those -which make least pretensions will have advantage over the others, and -this favours their degeneration. - -Just as this is found to be the case with the whole organism, so it is -also with the parts of the body of an individual organism. A -differentiation of parts, which leads to a partial degeneration, and -finally even to the loss of individual organs, is, when looked at by -itself, a degeneration, but yet may be advantageous to the organism in -the struggle for life. It is easier to fight when useless baggage is -thrown aside. Hence we meet everywhere, in the more highly-developed -animal and vegetable bodies, processes of divergence, the essence of -which is that they cause the degeneration, and finally the loss, of -particular parts. And at this point the most important and instructive -of all the series of phenomena bearing upon the history of organisms -presents itself to us, namely, that of _rudimentary or degenerate -organs_. - -It will be remembered that even in my first chapter I considered this -exceedingly remarkable series of phenomena, from a theoretical point of -view, as one of the most important and most striking proofs of the truth -of the doctrine of descent. We designated as rudimentary organs those -parts of the body which are arranged for a definite purpose and yet are -without function. Let me remind the reader of the eyes of those animals -which live in the dark in caves and underground, and which consequently -never can use them. In these animals we find real eyes hidden under the -skin, frequently developed exactly as are the eyes of animals which -really see; and yet these eyes never perform any function, indeed -cannot, simply for the reason that they are covered by an opaque -membrane, and consequently no ray of light falls upon them (compare -above, p. 13). In the ancestors of these animals, which lived in open -daylight, the eyes were well developed, covered by a transparent horny -capsule (cornea), and actually served the purpose of seeing. But as the -animals gradually accustomed themselves to an underground mode of life, -and withdrew from the daylight and no longer used their eyes, these -became degenerated. - -Very clear examples of rudimentary organs, moreover, are the wings of -animals which cannot fly; for example, the wings of the running birds, -like the ostrich, emeu, cassowary, etc., the legs of which have become -exceedingly developed. These birds having lost the habit of flying, have -consequently lost the use of their wings; however, the wings are still -there, although in a crippled form. We very frequently find such -crippled wings in the class of insects, most members of which can fly. - -From reasons derived from comparative anatomy and other circumstances, -we can with certainty draw the inference that all insects now living -(all dragon-flies, grasshoppers, beetles, bees, bugs, flies, -butterflies, etc.) have originated from a single common parental form, -from a primary insect which possessed two well-developed pairs of wings, -and three pairs of legs. Yet there are very many insects in which either -one or both pairs of wings have become more or less degenerated, and -many in which they have even completely disappeared. For example, in the -whole order of flies, or Diptera, the hinder pair of wings--in the -bee-parasites, or Strepsiptera, on the other hand, the fore pair of -wings--have become degenerated or entirely disappeared. Moreover, in -every order of insects we find individual genera, or species, in which -the wings have more or less degenerated or disappeared. The latter is -the case especially in parasites. The females have frequently no wings, -whereas the males have; for instance, in the case of glow-worms -(Lampyris), Strepsiptera, etc. This partial or complete degeneration of -the wings of insects has evidently arisen from natural selection in the -struggle for life. For we find insects without wings living under -circumstances where flying would be useless, or even decidedly injurious -to them. If, for example, insects living on islands fly about much, it -may easily happen that when flying they are blown into the sea by the -wind, and if (as is always the case) the power of flying is differently -developed in different individuals, then those which fly badly have an -advantage over those which fly well; they are less easily blown into the -sea, and remain longer in life than the individuals of the same species -which fly well. In the course of many generations, by the action of -natural selection, this circumstance must necessarily lead to a complete -suppression of the wings. If this conclusion had been arrived at on -purely theoretical grounds, we might be pleased to find its truth -established by facts. For upon isolated islands the proportion of -wingless insects to those possessing wings is surprisingly large, much -larger than among the insects inhabiting continents. Thus, for example, -according to Wollaston, of the 550 species of beetles which inhabit the -island of Madeira, 220 are wingless, or possess such imperfect wings -that they can no longer fly; and of the 29 genera which belong to that -island exclusively, no less than 23 contain such species only. It is -evident that this remarkable circumstance does not need to be explained -by the special wisdom of the Creator, but is sufficiently accounted for -by natural selection, because in this case the hereditary disuse of the -wings, the discontinuance of flying in the presence of dangerous winds, -has been very advantageous in the struggle for life. In other wingless -insects the want of wings has been advantageous for other reasons. -Viewed by itself, the loss of wings is a degeneration, but in these -special conditions of life it is advantageous to the organism in the -struggle for life. - -Among other rudimentary organs I may here, by way of example, further -mention the lungs of serpents and serpent-like lizards. All vertebrate -animals possessing lungs, such as amphibious animals, reptiles, birds, -and mammals, have a pair of lungs, a right and a left one. But in cases -where the body is exceedingly thin and elongated, as in serpents and -serpent-like lizards, there is no room for the one lung by the side of -the other, and it is an evident advantage to the mechanism of -respiration if only one lung is developed. A single large lung here -accomplishes more than two small ones side by side would do; and -consequently, in these animals, we invariably find only the right or -only the left lung fully developed. The other is completely aborted, -although existing as a useless rudiment. In like manner, in all birds -the right ovary is aborted and without function; only the left one is -developed, and yields all the eggs. - -I mentioned in the first chapter that man also possesses such useless -and superfluous rudimentary organs, and I specified as such the muscles -which move the ears. Another of them is the rudiment of the tail which -man possesses in his 3--5 tail vertebræ, and which, in the human embryo, -stands out prominently during the first two months of its development -(compare Plates II. and III.). It afterwards becomes completely hidden. -The rudimentary little tail of man is an irrefutable proof of the fact -that he is descended from tailed ancestors. In woman the tail is -generally by one vertebra longer than in man. There still exist -rudimentary muscles in the human tail which formerly moved it. - -Another case of human rudimentary organs, only belonging to the male, -and which obtains in like manner in all male mammals, is furnished by -the mammary glands on the breast, which, as a rule, are active only in -the female sex. However, cases of different mammals are known, -especially of men, sheep, and goats, in which the mammary glands were -fully developed in the male sex, and yielded milk as food for their -offspring. I have already mentioned before (p. 12) that the rudimentary -auricular muscles in man can still be employed to move their ears, by -some persons who have perseveringly practised them. In fact, rudimentary -organs are frequently very differently developed in different -individuals of the same species; in some they are tolerably large, in -others very small. This circumstance is very important for their -explanation, as is also the other circumstance that generally in -embryos, or in a very early period of life, they are much larger and -stronger in proportion to the rest of the body than they are in fully -developed and fully grown organisms. This can, in particular, be easily -pointed out in the rudimentary sexual organs of plants (stamens and -pistil), which I have already mentioned. They are proportionately much -larger in the young flower-bud than in the mature flower. - -I have remarked (p. 15) that rudimentary or suppressed organs were the -strongest supports of the monistic or mechanical conception of the -universe. If its opponents, the dualists and teleologists, understood -the immense significance of rudimentary organs, it would put them into a -state of despair. Their ludicrous attempts to explain that rudimentary -organs were given to organisms by the Creator "for the sake of -symmetry," or "as a formal provision," or "in consideration of his -general plan of creation," sufficiently prove the utter impotence of -their perverse conception of the universe. I must here repeat that, even -if we knew absolutely nothing of the other phenomena of development, we -should be obliged to believe in the truth of the Theory of Descent, -solely on the ground of the existence of rudimentary organs. Not one of -its opponents has been able to throw even a feeble glimmer of an -acceptable explanation upon these exceedingly remarkable and important -phenomena. There is scarcely any highly developed animal or vegetable -form which has not some rudimentary organs, and in most cases it can be -shown that they are the products of natural selection, and that they -have become suppressed by disuse. It is the reverse of the process of -formation in which new organs arise from adaptation to certain -conditions of life, and by the use of parts as yet incompletely -developed. It is true our opponents usually maintain that the origin of -altogether new parts is completely inexplicable by the Theory of -Descent. However, I distinctly assert that to those who possess a -knowledge of comparative anatomy and physiology this matter does not -present the slightest difficulty. Every one who is familiar with -comparative anatomy and the history of development will find as little -difficulty about the origin of completely new organs as about the utter -disappearance of rudimentary organs. The disappearance of the latter, -viewed by itself, is the converse of the origin of the former. Both -processes are particular phenomena of differentiation, which, like all -others, can be explained quite simply and mechanically by the action of -natural selection in the struggle for life. - -The infinitely important study of rudimentary organs and their origin, -the comparison of their palæontological and embryological development, -now naturally leads us to the consideration of one of the most important -and instructive of all biological phenomena, namely, the parallelism -which the phenomena of progress and divergence present to us in three -different series. When, in the last chapter, we spoke of perfecting and -division of labour, we understood by those words progress and -separation, and those changes effected by them, which in the long and -slow course of the earth's history have led to a continual variation of -the flora and fauna, to the origin of new and to the disappearance of -ancient species of animals and plants. Now, if we follow the origin, the -development, and the life of every single organic individual, we meet -with exactly the same phenomena of progress and differentiation. The -individual development, or the _ontogenesis_ of every single organism, -from the egg to the complete form is nothing but a growth attended by a -series of diverging and progressive changes. This applies equally to -animals, plants, and protista. If, for example, we consider the ontogeny -of any mammal, of man, of an ape, or of a pouched animal, or if we -follow the individual development of any other vertebrate animal of -another class, we everywhere find essentially the same phenomena. Every -one of these animals develops itself originally out of a single cell, -the egg. This cell increases by self-division, and forms a number of -cells, and by the growth of this accumulation of cells, by the divergent -development of originally identical cells, by the division of labour -among them, and by their perfecting, there arises the perfect organism, -the complicated composition of which excites our admiration. - -It seems to me here indispensable to draw attention more closely to -those infinitely important and interesting processes which accompany -_ontogenesis, or the individual development of organisms_, and -especially to that of vertebrate animals, man included. I wish -especially to recommend these exceedingly remarkable and instructive -phenomena to the reader's most careful consideration, first, because -they are among the strongest supports of the Theory of Descent, and -secondly, because, considering their immense general importance, they -have hitherto been properly considered only by a few privileged persons. - -We cannot indeed but be astonished when we consider the deep ignorance -which still prevails, in the widest circles, about the facts of the -individual development of man and organisms in general. These facts, the -universal importance of which cannot be estimated too highly, were -established, in their most important outlines, even more than a hundred -years ago, in 1759, by the great German naturalist Caspar Friedriech -Wolff, in his classical "Theoria Generationis." But, just as Lamarck's -Theory of Descent, founded in 1809, lay dormant for half a century, and -was only awakened to new and imperishable life in 1859, by Darwin, in -like manner Wolff's Theory of Epigenesis remained unknown for nearly -half a century; and it was only after Oken, in 1806 had published his -history of the development of the intestinal tube, and after Meckel, in -1812, had translated Wolff's work (written in Latin) on the same subject -into German, that Wolff's theory of epigenesis became more generally -known, and formed the foundation of all subsequent investigations of the -history of individual development. The study of ontogenesis now received -a great stimulus, and soon there appeared the classical investigations -of the two friends, Christian Pander (1817) and Carl Ernst Bär (1819). -Bär, in his remarkable "Entwickelungsgeschichte der Thiere,"(20) worked -out the ontogeny of vertebrate animals in all its important facts. He -carried out a series of such excellent observations, and illustrated -them by such profound philosophical reflections, that his work became -the foundation for a thorough understanding of this important group of -animals, to which, of course, man also belongs. The facts of embryology -alone would be sufficient to solve the question of man's position in -nature, which is the highest of all problems. Look attentively at and -compare the eight figures which are represented on the adjoining Plates -II. and III., and it will be seen that the philosophical importance of -embryology cannot be too highly estimated. - -We may well ask, What do our so-called "educated" circles, who think so -much of the high civilization of the 19th century, know of these most -important biological facts, of these indispensable foundations for -understanding their own organism? How much do our speculative -philosophers and theologians know about them, who fancy they can arrive -at an understanding of the human organism by mere guesswork or divine -inspiration? What indeed do the majority of naturalists, not excepting -the majority of the so-called "zoologists" (including the -entomologists!), know about them? - -The answer to this question tells much to the shame of the persons above -indicated, and we must confess, willingly or unwillingly, that these -invaluable facts of human ontogeny are, even at the present day, utterly -unknown to most people, or are in no way valued as they deserve to be. -It is in the face of such a condition of things as this that we see -clearly upon what a wrong and one-sided road the much vaunted culture of -the 19th century still moves. Ignorance and superstition are the -foundations upon which most men construct their conception of their own -organism and its relation to the totality of things; and these palpable -facts of the history of development, which might throw the light of -truth upon them, are ignored. It is true these facts are not calculated -to excite approval among those who assume a thorough difference between -man and the rest of nature, and who will not acknowledge the animal -origin of the human race. That origin must be a very unpleasant truth to -members of the ruling and privileged castes in those nations among which -there exists an hereditary division of social classes, in consequence of -false ideas about the laws of inheritance. It is well known that, even -in our day, in many civilized countries the idea of hereditary grades of -rank goes so far, that, for example, the aristocracy imagine themselves -to be of a nature totally different from that of ordinary citizens, and -nobles who commit a disgraceful offence are punished by being expelled -from the caste of nobles, and thrust down among the pariahs of "vulgar -citizens." What are these nobles to think of the noble blood which flows -in their privileged veins, when they learn that all human embryos, those -of nobles as well as commoners, during the first two months of -development, are scarcely distinguishable from the tailed embryos of -dogs and other mammals? - -As the object of these pages is solely to further the general knowledge -of natural truths, and to spread, in wider circles, a natural conception -of the relations of man to the rest of nature, I shall be justified if I -do not pay any regard to the widely-spread prejudice in favour of an -exceptional and privileged position for man in creation, and simply give -here the embryological facts from which the reader will be able to draw -conclusions affirming the groundlessness of those prejudices. I wish all -the more to entreat him to reflect carefully upon these facts of -ontogeny, as it is my firm conviction that a general knowledge of them -can only promote the intellectual advance, and thereby the mental -perfecting, of the human race. - -Amidst all the infinitely rich and interesting material which lies -before us in the ontogeny of vertebrate animals, that is, in the history -of their individual development, I shall here confine myself to showing -some of those facts which are of the greatest importance to the Theory -of Descent in general, as well as in its special application to man. Man -is at the beginning of his individual existence a simple egg, a single -little cell, just the same as every animal organism which originates by -sexual generation. The human egg is essentially the same as that of all -other mammals, and cannot be distinguished from the egg of the higher -mammals. The egg represented in Fig. 5 might be that of a man or an ape -as well as of a dog, a horse, or any other mammal. Not only the form and -structure, but even the size of the egg in most mammals is the same as -in man, namely, about the 120th part of an inch in diameter, so that the -egg under favorable circumstances, with the naked eye, can just be -perceived as a small speck. The differences which really exist between -the eggs of different mammals and that of man do not consist in the -form, but in the chemical mixture, in the molecular composition of the -albuminous combination of carbon, of which the egg essentially consists. -These minute individual differences of all eggs, which depend upon -indirect or potential adaptation (and especially upon the law of -individual adaptation), are indeed not directly perceptible to the -exceedingly imperfect senses of man, but are cognisable through indirect -means, as the primary causes of the difference of all individuals. - -[Illustration: FIG. 5.--The human egg a hundred times enlarged. _a._ The -kernel speck, or nucleolus (the so-called germinal spot of the egg). -_b._ Kernel, or nucleus (the so-called germinal vesicle of the egg). -_c._ Cell-substance, or protoplasm (so-called yolk of the egg). _d._ -Cell-membrane (the yolk-membrane of the egg; in mammals, on account of -its transparency, called zona pellucida). The eggs of other mammals are -of the same form.] - -The human egg is, like that of all other mammals, a small globular -bladder, which contains all the constituent parts of a simple organic -cell (Fig. 5). The most essential parts of it are the mucous -cell-substance, or the protoplasma (_c_), which in an egg is called the -"yolk," and the cell-kernel, or nucleus (_b_), surrounded by it, which -is here called by the special name of the "germinal vesicle." The latter -is a delicate, clear, glassy globule of albumen, of about 1-600th part -of an inch in diameter, and surrounds, a still smaller, sharply-marked, -rounded granule (_a_), the kernel-speck, or the nucleolus of the cell -(in the egg it is called the "germinal spot"). The outside of the -globular egg-cell of a mammal is surrounded by a thick pellucid -membrane, the cell-membrane or yolk-membrane, which here bears the -special name of zona pellucida (_d_). The eggs of many lower animals -(for example of many Medusæ) differ from this in being _naked_ cells, as -the outer covering, or cell-membrane, is wanting. - -As soon as the egg (ovulum) of the mammal has attained its full -maturity, it leaves the ovary of the female, in which it originates, and -passes into the oviduct, and through this narrow passage into the wider -pouch or womb (uterus). If, meanwhile, the egg is fructified by the male -seed (sperm), it develops itself in this pouch into an embryo, and does -not leave it until perfectly developed and capable of coming into the -world at birth as a young mammal. - -The variations of form and transformations which the fructified egg must -go through within the uterus before it assumes the form of the mammal -are exceedingly remarkable, and proceed from the beginning in man, in -precisely the same way as in the other mammals. At first the fructified -egg of the mammal acts as a single-celled organism, which is about to -propagate independently and increase itself; for example, an Amoeba -(compare Fig. 2, p. 188). In point of fact the simple egg-cell becomes -two, by the process of cell-division which I have previously described. -There arise from the single germinal spot (the small kernel-speck of the -original simple egg-cell) two new kernel-specks, and then in like -manner, out of the germinal vesicle (the nucleus), two new cell-kernels. -Then, and not until then, does the globular protoplasma first separate -itself by an equatorial furrow into two halves, in such a manner that -each half encloses one of the two kernels, together with its -kernel-speck. Thus the simple egg-cell, within the original cellular -membrane, has become two naked cells, each possessing its own kernel -(Fig. 6). - -[Illustration: FIG. 6.--First commencement of the development of a -mammal's egg, the so-called "yolk-cleavage" (propagation of the egg-cell -by repeated self-division). _A._ The egg, by the formation of the first -furrow, falls into two cells. _B._ These by division fall into four -cells. _C._ These latter have fallen into eight cells. _D._ By continued -division a globular mass of numerous cells has arisen.] - -The same process of cell-division now repeats itself several times in -succession. In this way, from two cells (Fig. 6 _A_) there arise four -(Fig. 6 _B_); from four, eight (Fig. 6 _C_); from eight, sixteen; from -these, thirty-two, etc. Each time the division of the kernel-speck -precedes that of the kernel; this, again, precedes that of the -cell-substance, or protoplasma. As the division of the latter always -commences with the formation of a superficial annular _furrow_, or -cleft, the whole process is usually called the _furrowing of the egg_, -or yolk-cleavage, and the products of it, that is, the cells arising -from the continued halving, are called the _cleavage spheres_. However, -the whole process is nothing more than a simple, oft-repeated _division -of cells_, and the products of it are actual, naked _cells_. Finally, -through the continued division or "furrowing" of the mammal's egg there -arises a mulberry-shaped ball, which is composed of a great number of -small spheres, naked cells, containing kernels (Fig. 6 _D_). These cells -are the materials out of which the body of the young mammal is -constructed. Every one of us has once been such a simple mulberry-shaped -ball, composed only of small equi-formal cells. - -The further development of the globular lump of cells, which now -represents the young body of the mammal, consists first in its changing -into a globular bladder, as fluid accumulates within it. This bladder is -called the germ-bladder (vesicula blastodermica). Its wall is at first -composed of merely equi-formal cells. But soon, at one point on the -wall, arises a disc-shaped thickening, as the cells here increase -rapidly, and this thickening is now the foundation of the actual body of -the germ or embryo, while the other parts of the germ-bladder serve only -for its nutrition. The thickened disc, or foundation of the embryo, soon -assumes an oblong, and then a fiddle-shaped form, in consequence of its -right and left walls becoming convex (Fig. 7, p. 304). At this stage of -development in the first form of their germ or embryo, not only all -mammals, including man, but even all vertebrate animals in -general--birds, reptiles, amphibious animals, and fishes--can either not -be distinguished from one another at all, or only by very unessential -differences, such as the arrangement of the egg-coverings. In all the -whole body consists of nothing but a quite simple, oblong, oval, or -violin-shaped thin disc, which is composed of three closely connected -membranes or plates, lying one above another. Each of the three plates -or layers of the germ consists simply of cells all exactly like one -another; but each layer has a different function in the building up of -the vertebrate animal body. Out of the upper or outer germ-layer arises -solely the outer skin (epidermis), together with the central parts of -the nervous system (spinal marrow and brain); out of the lower or inner -layer arises only the inner delicate skin (epithelium) which lines the -whole intestinal tube from the mouth to the anus, together with all the -glands connected with it (lung, liver, salivary glands, etc.); out of -the middle germ-layer lying between the two others arise all the other -organs, muscles, bones, blood-vessels. Now, the processes by which the -various and exceedingly complicated parts of the fully-formed body of -vertebrate animals arise out of such simple material--out of the three -germ-layers composed only of cells--are, in the first place, the -repeated division, and consequently the increase of cells; in the second -place, the division of labour or differentiation of these cells; and -thirdly, the union of the variously developed or differentiated cells, -for the formation of the different organs. Thus arises the gradual -progress or perfecting which can be traced step by step in the -development of the embryonic body. The simple embryonic cells, which are -to constitute the body of the vertebrate animal, stand in the same -relation to each other as citizens who wish to found a state. Some take -to one occupation, others to another, and work together for the good of -the whole. By this division of labour, or differentiation, and the -perfecting (the organic progress) which is connected with it, it becomes -possible for the whole state to accomplish undertakings which would have -been impossible to the single individual. The whole body of the -vertebrate animal, like every other many-celled organism, is a -republican state of cells, and consequently it can accomplish organic -functions which the individual cell, as a solitary individual (for -example, an Amoeba, or a single-celled plant), could never perform. - -No sensible person supposes that carefully devised institutions, which -have been established for the good of the whole, as well as for the -individual, in every human state, are the results of the action of a -personal and supernatural Creator, acting for a definite purpose. On the -contrary, every one knows that these useful institutions of organization -in the state are the consequences of the co-operation of the individual -citizens and their common government, as well as of adaptation to the -conditions of existence of the outer world. Just in the same way we must -judge of the many-celled organism. In it also all the useful -arrangements are solely the natural and necessary result of the -co-operation, differentiation, and perfecting of the individual -citizens--the cells--and by no means the artificial arrangements of a -Creator acting for a definite purpose. If we rightly consider this -comparison, and pursue it further, we can distinctly see the perversity -of that dualistic conception of nature which discovers the action of a -creative plan of construction in the various adaptations of the -organization of living things. - -Let us pursue the individual development of the vertebrate animal body a -few stages further, and see what is next done by the citizens of this -embryonic organism. In the central line of the violin-shaped disc, which -is composed of the three cellular germ-layers, there arises a straight -delicate furrow, the so-called "primitive streak," by which the -violin-shaped body is divided into two equal lateral halves--a right and -a left part or "antimer." On both sides of that streak or furrow, the -upper or external germ-layer rises in the form of a longitudinal fold, -and both folds then grow together over the furrow in the central line, -and thus form a cylindrical tube. This tube is called the marrow-tube, -or medullary canal, because it is the foundation of the central nervous -system, the _spinal marrow_ (medulla spinalis). At first it is pointed -both in front and behind, and it remains so for life in the lowest -vertebrate animal, the brainless, skull-less Lancelet (Amphioxus). But -in all other vertebrate animals, which we distinguish from the latter as -skulled animals, or Craniota, a difference between the fore and hinder -end of the marrow tube soon becomes visible, the fore end becoming -dilated, and changing into a roundish bladder, the foundation of the -_brain_. - -In all Craniota, that is, in all vertebrate animals possessing skull and -brain, the brain, which is at first only the bladder-shaped dilatation -of the anterior end of the spinal marrow, divides into five bladders -lying one behind the other, four superficial, transverse in-nippings -being formed. These _five brain-bladders_, out of which afterwards arise -all the different parts of the intricately constructed brain, can be -seen in their original condition in the embryo represented in Fig. 7. It -is just the same whether we examine the embryo of a dog, a fowl, a -lizard, or any other higher vertebrate animal. For the embryos of the -different skulled animals (at least the three higher classes of them, -the reptiles, birds and mammals) cannot be in any way distinguished at -the stage represented in Fig. 7. The whole form of the body is as yet -exceedingly simple, being merely a thin, leaf-like disc. Face, legs, -intestines, etc., are as yet completely wanting. But the five bladders -are already quite distinct from one another. - -[Illustration: FIG. 7.--Embryo of a mammal or bird, in which the five -brain-bladders have just commenced to develop. _v._ Fore brain. _z._ -Twixt brain. _m._ Mid brain. _h._ Hind brain. _n._ After brain. _p._ -Spinal-marrow. _a._ Eye-bladders. _w._ Primitive vertebræ. _d._ -Spinal-axis or notochord.] - -The _first_ bladder, the _fore brain_ (_a_), is in so far the most -important that it principally forms the hemispheres of the so-called -larger brain (cerebrum), that part which is the seat of the higher -mental activities. The more these activities are developed in the series -of vertebrate animals, the more do the two lateral halves of the fore -brain, or the hemispheres, grow at the expense of the other bladders, -and overlap them in front and from above. In man, where they are most -strongly developed, agreeing with his higher mental activity, they -eventually almost entirely cover the other parts from above (compare -Plates II. and III.) The _second_ bladder, the _twixt brain_ (_z_), -forms that portion of the brain which is called the _centre of sight_, -and stands in the closest relation to the eyes (_a_), which grow right -and left out of the fore brain in the shape of two bladders, and later -lie at the bottom of the twixt brain. The _third_ bladder, the _mid -brain_ (_m_), for the most part vanishes in the formation of the -so-called _four bulbs_, a bossy portion of the brain, which is strongly -developed in reptiles and birds (Fig. _E_, _F_, Plate II.), whereas in -mammals it recedes much more (Fig. _G_, _H_, Plate III.). The _fourth_ -bladder, the _hind brain_ (_h_), forms the so-called _little -hemispheres_, together with the middle part of the _small brain_ -(cerebellum), a part of the brain as to the function of which the most -contradictory conjectures are entertained, but which seems principally -to regulate the co-ordination of movements. Lastly, the _fifth_ bladder, -the _after brain_ (_n_), develops into that very important part of the -central nervous system which is called the _prolonged marrow_ (medulla -oblongata). It is the central organ of the respiratory movements, and of -other important functions, and an injury to it immediately causes death, -whereas the large hemispheres of the fore brain (or the organ of the -"soul," in a restricted sense) can be removed bit by bit, and even -completely destroyed, without causing the death of the vertebrate -animal--only its higher mental activities disappearing in consequence. - -These five brain bladders, in all vertebrate animals which possess a -brain at all, are originally arranged in the same manner and develop -gradually in the different groups so differently, that it is afterwards -very difficult to recognize the corresponding parts in the -fully-developed brains. In the early stage of development which is -represented in Fig. 7, it seems as yet quite impossible to distinguish -the embryos of the different mammals, birds, and reptiles, from one -another. But if we compare the much more developed embryos on Plates II. -and III. with one another, we can clearly see an inequality in their -development, and especially it will be perceived that the brain of the -two mammals (_G_ and _H_) already strongly differ from that of birds -(_F_) and of reptiles (_E_). In the two latter the mid brain -predominates, but in the former the fore brain. Even at this stage the -brain of the bird (_F_) is scarcely distinguishable from that of the -tortoise (_E_), and in like manner the brain of the dog (_G_) is as yet -almost the same as that of man (_H_). If, on the other hand, we compare -the brains of these four vertebrate animals in a fully developed -condition, we find them so very different in all anatomical particulars, -that we cannot doubt for a moment as to which animal each brain belongs. - -I have here explained the original equality, the gradual commencement, -and the ever increasing separation or differentiation of the embryos in -the different vertebrate animals, taking the brain as a special example, -just because this organ of the soul's activity is of special interest. -But I might as well have discussed in its stead the heart, or the liver, -or the limbs, in short, any other part of the body, since the same -wonder of creation is here ever repeated, namely, this, that all parts -are originally the same in the different vertebrate animals, and that -the variations by which the different classes, orders, families, genera, -etc., differ and deviate from one another, are only gradually developed. - -There are certainly few parts of the body which are so differently -constructed as the _limbs or extremities_ of the vertebrate animals. -Now, I wish the reader to compare in Fig. _A-H_ on Plates II. and III., -the four extremities (_bv_) of the embryos with one another, and he will -scarcely be able to perceive any important differences between the human -arm (_H bv_), the wing of a bird (_F bv_), the slim foreleg of a dog (_G -bv_), and the plump foreleg of the tortoise (_E bv_). In comparing the -hinder extremities (_bh_) in these figures he will find it equally -difficult to distinguish the leg of a man (_H bh_), of a bird (_F bh_), -the hind-leg of a dog (_G bh_), and that of a tortoise (_E bh_). The -fore as well as the hinder extremities are as yet short, broad -lumps, at the ends of which the foundations of the five toes are placed, -connected as yet by a membrane. At a still earlier stage (Fig. _A-D_) -the five toes are not marked out at all, and it is quite impossible to -distinguish even the fore and hinder extremities from one another. The -latter, as well as the former, are nothing but simple roundish -processes, which have grown out of the side of the trunk. At the very -early stage represented in Fig. 7 they are completely wanting, and the -whole embryo is a simple trunk without a trace of limbs. - -[Illustration: Pl. II. Germs or Embryos of four Vertebrates. - -_v._ Fore-brain. _z._ Twixt-brain. _m._ Mid-brain. _h._ Hind-brain. _n._ -After-brain. _w._ Spine. _r._ Spinal-cord.] - -[Illustration: Pl. III. Germs or Embryos of four Vertebrates. - -_na._ Nose. _a._ Eyes. _o._ Ear. _k__{1} _k__{2} _k__{3}. Gill-arches. -_s._ Tail. _bv._ Fore-leg. _bh._ Hind-leg.] - -I wish especially to draw attention in Plates II. and III., which -represents embryos in early stages of development (Fig. _A-D_)--and in -which we are not able to recognize a trace of the full-grown animal--to -an exceedingly important formation, which originally is common to all -vertebrate animals, but which at a later period is transformed into the -most different organs. Every one surely knows the _gill-arches_ of fish, -those arched bones which lie behind one another, to the number of three -or four, on each side of the neck, and which support the gills, the -respiratory organs of the fish (double rows of red leaves, which are -popularly called "fishes' ears.") Now, these gill-arches originally -exist exactly the same in man (_D_), in dogs (_C_), in fowls (_B_), and -in tortoises (_A_), as well as in all other vertebrate animals. (In Fig. -_A-D_ the three gill-arches of the right side of the neck are marked -_k__{1} _k__{2} _k__{3}). Now, it is only in fishes that these remain in -their original form, and develop into respiratory organs. In the other -vertebrate animals they are partly employed in the formation of the face -(especially the jaw apparatus), and partly in the formation of the organ -of hearing. - -Finally, when comparing the embryos on Plates II. and III., we must not -fail to give attention again to the _human tail_ (_s_), an organ which, -in the original condition, man shares with all other vertebrate animals. -The discovery of tailed men was long anxiously expected by many monistic -philosophers, in order to establish a closer relationship between man -and the other mammals. And in like manner their dualistic opponents -often maintained with pride that the complete want of a tail formed one -of the most important bodily distinctions between men and animals, -though they did not bear in mind the many tailless animals which really -exist. Now, man in the first months of development possesses a real tail -as well as his nearest kindred, the tailless apes (orang-outang, -chimpanzee, gorilla), and vertebrate animals in general. But whereas, in -most of them--for example, the dog (_C_, _G_)--in the course of -development it always grows longer, in man (Fig. _D_, _H_) and in -tailless mammals, at a certain period of development, it degenerates and -finally completely disappears. However, even in fully developed men, the -remnant of the tail is seen in the three, four, or five tail vertebræ -(vertebræ coccygeæ) as an aborted or rudimentary organ, which forms the -hinder or lower end of the vertebral column (p. 289). - -Most persons even now refuse to acknowledge the most important deduction -of the Theory of Descent, that is, the palæontological development of -man from ape-like, and through them from still lower, mammals, and -consider such a transformation of organic form as impossible. But, I -ask, are the phenomena of the individual development of man, the -fundamental features of which I have here given, in any way less -wonderful? Is it not in the highest degree remarkable that all -vertebrate animals of the most different classes--fishes, amphibious -animals, reptiles, birds, and mammals--in the first periods of their -embryonic development cannot be distinguished at all, and even much -later, at a time when reptiles and birds are already distinctly -different from mammals, that the dog and the man are almost identical? -Verily, if we compare those two series of development with one another, -and ask ourselves which of the two is the more wonderful, it must be -confessed that _ontogeny_, or the short and quick history of development -of the _individual_, is much more mysterious than _phylogeny_, or the -long and slow history of development of the _tribe_. For one and the -same grand change of form is accomplished by the latter in the course of -many thousands of years, and by the former in the course of a few -months. Evidently this most rapid and astonishing transformation of the -individual in ontogenesis, which we can actually point out at any moment -by direct observation, is in itself much more wonderful and astonishing -than the corresponding, but much slower and gradual transformation which -the long chain of ancestors of the same individual has gone through in -phylogenesis. - -The two series of organic development, the ontogenesis of the individual -and the phylogenesis of the tribe to which it belongs, stand in the -closest causal connection with each other. I have endeavoured, in the -second volume of the "General Morphology,"(4) to establish this theory -in detail, as I consider it exceedingly important. As I have there -shown, _ontogenesis, or the development of the individual, is a short -and quick repetition_ (recapitulation) _of phylogenesis, or the -development of the tribe to which it belongs, determined by the laws of -inheritance and adaptation_; by tribe I mean the ancestors which form -the chain of progenitors of the individual concerned. (Gen. Morph. ii. -110-147, 371.) - -In this intimate connection of ontogeny and phylogeny, I see one of the -most important and irrefutable proofs of the Theory of Descent. No one -can explain these phenomena unless he has recourse to the laws of -Inheritance and Adaptation; by these alone are they explicable. These -laws, which we have previously explained, are _the laws of abbreviated, -of homochronic, and of homotopic inheritance_, and here deserve renewed -consideration. As so high and complicated an organism as that of man, or -the organism of every other mammal, rises upwards from a simple cellular -state, and as it progresses in its differentiation and perfecting it -passes through the same series of transformations which its animal -progenitors have passed through, during immense spaces of time, -inconceivable ages ago. I have already pointed out this extremely -important parallelism of the development of individuals and tribes (p. -10). Certain very early and low stages in the development of man, and -the other vertebrate animals in general, correspond completely in many -points of structure with conditions which last for life in the lower -fishes. The next phase which follows upon this presents us with a change -of the fish-like being into a kind of amphibious animal. At a later -period the mammal, with its special characteristics, develops out of the -amphibian, and we can clearly see, in the successive stages of its later -development, a series of steps of progressive transformation which -evidently correspond with the differences of different mammalian orders -and families. Now, it is precisely in the same succession that we also -see the ancestors of man, and of the higher mammals, appear one after -the other in the earth's history; first fishes, then amphibians, later -the lower, and at last the higher mammals. Here, therefore, the -embryonic development of the individual is completely parallel to the -palæontological development of the whole tribe to which it belongs, and -this exceedingly interesting and important phenomenon can be explained -only by the interaction of the laws of Inheritance and Adaptation. - -The example last mentioned, of the parallelism of the palæontological -and of the individual developmental series, now directs our attention to -a third developmental series, which stands in the closest relations to -these two, and which likewise runs, on the whole, parallel to them. I -mean that series of development of forms which constitutes the object of -investigation in _comparative anatomy_, and which I will briefly call -the _systematic developmental series of species_. By this we understand -the chain of the different, but related and connected forms, which exist -_side by side_ at any one period of the earth's history; as for example, -at the present moment. While comparative anatomy compares the different -forms of fully-developed organisms with one another, it endeavours to -discover the common prototypes which underlie, as it were, the manifold -forms of kindred genera, classes, etc., and which are more or less -concealed by their particular differentiation. It endeavours to make out -the series of progressive steps which are indicated in the different -degrees of perfection of the divergent branches of the tribe. To make -use again of the same particular instance, comparative anatomy shows us -how the individual organs and systems of organs in the tribe of -vertebrate animals--in the different classes, families, and species of -it--have unequally developed, differentiated, and perfected themselves. -It shows us how far the succession of classes of vertebrate animals, -from the Fishes upwards, through the Amphibia to the Mammals, and here -again, from the lower to the higher orders of Mammals, forms a -progressive series or ladder. This attempt to establish a connected -anatomical developmental series we may discover in the works of the -great comparative anatomists of all ages--in the works of Goethe, -Meckel, Cuvier, Johannes Müller, Gegenbaur, and Huxley. - -The developmental series of mature forms, which comparative anatomy -points out in the different diverging and ascending steps of the organic -system, and which we call the systematic developmental series, is -parallel to the palæontological developmental series, because it deals -with the _result_ of palæontological development, and it is parallel to -the individual developmental series, because this is parallel to the -palæontological series. If two parallels are parallel to a third, they -must be parallel to one another. - -The varied differentiation, and the unequal degree of perfecting which -comparative anatomy points out in the developmental series of the -System, is chiefly determined by the ever increasing variety of -conditions of existence to which the different groups adapt themselves -in the struggle for life, and by the different degrees of rapidity and -completeness with which this adaptation has been effected. Conservative -groups which have retained their inherited peculiarities most -tenaciously remain, in consequence, at the lowest and rudest stage of -development. Those groups progressing most rapidly and variously, and -which have adapted themselves to changed conditions of existence most -readily have attained the highest degree of perfection. The further the -organic world developed in the course of the earth's history, the -greater must the gap between the lower conservative and the higher -progressive groups have become, as in fact may be seen too in the -history of nations. In this way also is explained the historical fact, -that the most perfect animal and vegetable groups have developed -themselves in a comparatively short time to a considerable height, while -the lowest or most conservative groups have remained stationary -throughout all ages in their original simple stage, or have progressed, -but very slowly and gradually. The series of man's progenitors clearly -shows this state of things. The sharks of the present day are still very -like the primary fish, which are among the most ancient vertebrate -progenitors of man, and the lowest amphibians of the present day (the -gilled salamanders and salamanders) are very like the amphibians which -first developed themselves out of fishes. So, too, the later ancestors -of man, the Monotremata and Marsupials, the most ancient mammals, are at -the same time the most imperfect animals of the class which still exist. - -The laws of inheritance and adaptation known to us are completely -sufficient to explain this exceedingly important and interesting -phenomenon, which may be briefly designated as the _parallelism of -individual, of palæontological, and of systematic development_. No -opponent of the Theory of Descent has been able to give an explanation -of this extremely wonderful fact, whereas it is perfectly explained, -according to the Theory of Descent, by the laws of Inheritance and -Adaptation. - -If we examine this parallelism of the three organic series of -development more accurately, we have to add the following special -qualifications. _Ontogeny_, or the history of the individual development -of every organism (embryology and metamorphology), presents us with a -simple _unbranching_ or graduated chain of forms; and so it is with that -_portion of phylogeny_ which comprises the palæontological history of -development of the _direct ancestors only_ of an individual organism. -But _the whole of phylogeny_--which meets us in the _natural system_ of -every organic tribe or phylum, and which is concerned with the -investigation of the palæontological development _of all_ the branches -of this tribe--forms a _branching_ or tree-shaped developmental series, -a veritable pedigree. If we examine and compare the branches of this -pedigree, and place them together according to the degree of their -differentiation and perfection, we obtain the tree-shaped, branching, -_systematic developmental series of comparative anatomy_. Strictly -speaking, therefore, the latter is parallel to _the whole of phylogeny_, -and consequently is only partially parallel to ontogeny; for ontogeny -itself is parallel only to _a portion_ of phylogeny. - -All the phenomena of organic development above discussed, especially the -threefold genealogical parallelism, and the laws of differentiation and -progress, which are evident in each of these three series of organic -development, and, further, the whole history of rudimentary organs, are -exceedingly important proofs of the truth of the Theory of Descent. For -by it alone can they be explained, whereas its opponents cannot even -offer a shadow of an explanation of them. Without the Doctrine of -Filiation, the fact of organic development in general cannot be -understood. We should therefore, for this reason alone, be forced to -accept Lamarck's Theory of Descent, even if we did not possess Darwin's -Theory of Selection. - - - - -CHAPTER XIII. - -THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE EARTH. SPONTANEOUS -GENERATION. THE CARBON THEORY. THE PLASTID THEORY. - - - History of the Development of the Earth.--Kant's Theory - of the Development of the Universe, or the Cosmological - Gas Theory.--Development of Suns, Planets, and - Moons.--First Origin of Water.--Comparison of Organisms - and Anorgana.--Organic and Inorganic Substances.--Degrees - of Density, or Conditions of Aggregation.--Albuminous - Combinations of Carbon.--Organic and Inorganic - Forms.--Crystals and Formless Organisms without - Organs.--Stereometrical Fundamental Forms of Crystals and - of Organisms.--Organic and Inorganic Forces.--Vital - Force.--Growth and Adaptation in Crystals and in - Organisms.--Formative Tendencies of Crystals.--Unity of - Organic and Inorganic Nature.--Spontaneous Generation, or - Archigony.--Autogony and Plasmogony.--Origin of Monera by - Spontaneous Generation.--Origin of Cells from - Monera.--The Cell Theory.--The Plastid Theory.--Plastids, - or Structural Units.--Cytods and Cells.--Four Different - Kinds of Plastids. - - -In our considerations hitherto we have endeavoured to answer the -question, "By what causes have new species of animals and plants arisen -out of existing species?" We have answered this question according to -Darwin's theory, that natural selection in the struggle for -existence--that is, the interaction of the laws of Inheritance and -Adaptation--is completely sufficient for producing mechanically the -endless variety of the different animals and plants, which have the -appearance of being organized according to a plan for a definite -purpose. Meanwhile the question must have already repeatedly presented -itself to the reader, how did the first organisms, or that one original -and primæval organism arise, from which we derive all the others? - -This question Lamarck(2) answered by the hypothesis of _spontaneous -generation_, or _archigony_. But Darwin passes over and avoids this -subject, as he expressly remarks that he has "nothing to do with the -origin of the soul, nor with that of life itself." At the conclusion of -his work he expresses himself more distinctly in the following -words:--"I imagine that probably all organic beings which ever lived on -this earth descended from some primitive form, which was first called -into life by the Creator." Moreover, Darwin, for the consolation of -those who see in the Theory of Descent the destruction of the whole -"moral order of the universe," appeals to the celebrated author and -divine who wrote to him, that "he has gradually learnt to see that it is -just as noble a conception of the Deity to believe that he created a few -original forms capable of self-development into other and needful forms, -as to believe that he required a fresh act of creation to supply the -voids caused by the action of his laws." - -Those to whom the belief in a supernatural creation is an emotional -necessity may rest satisfied with this conception. They may reconcile -that belief with the Theory of Descent; for in the creation of a single -original organism possessing the capability to develop all others out of -itself by inheritance and adaptation, they can really find much more -cause for admiring the power and wisdom of the Creator than in the -independent creation of different species. - -If, taking this point of view, we were to explain the origin of the -first terrestrial organisms, from which all the others are descended, as -due to the action of a personal Creator acting according to a definite -plan, we should of course have to renounce all scientific knowledge of -the process, and pass from the domain of true science to the completely -distinct domain of poetical faith. By assuming a supernatural act of -creation we should be taking a leap into the inconceivable. Before we -decide upon this latter step, and thereby renounce all pretension to a -scientific knowledge of the process, we are at all events in duty bound -to endeavour to examine it in the light of a mechanical hypothesis. We -must at least examine whether this process is really so wonderful, and -whether we cannot form a tenable conception of a completely -non-miraculous origin of the first primary organism. We might then be -able entirely to reject miracle in creation. - -It will be necessary for this purpose, first of all, to go back further -into the past, and to examine the history of the creation of the earth. -Going back still further, we shall find it necessary to consider the -history of the creation of the whole universe in its most general -outlines. All my readers undoubtedly know that from the structure of the -earth, as it is at present known to us, the notion has been derived, and -as yet has not been refuted, that its interior is in a fiery fluid -condition, and that the firm crust, composed of different strata, on the -surface of which organisms are living, forms only a very thin pellicle -or shell round the fiery fluid centre. We have arrived at this idea by -different confirmatory experiments and reasonings. In the first place, -the observation that the temperature of the earth's crust continually -increases towards the centre is in favour of this supposition. The -deeper we descend, the greater the warmth of the ground, and in such -proportion, that with every 100 feet the temperature increases about one -degree. At a depth of six miles, therefore, a heat of 1500° would be -attained, sufficient to keep most of the firm substances of our earth's -crust in a molten, fiery, fluid state. This depth, however, is only the -286th part of the whole diameter of the earth (1717 miles). We further -know that springs which rise out of a considerable depth possess a very -high temperature, and sometimes even throw water up to the surface in a -boiling state. Lastly, very important proofs are furnished by volcanic -phenomena, the eruption of fiery fluid masses of stone bursting through -certain parts of the earth's crust. All these phenomena lead us with -great certainty to the important assumption that the firm crust of the -earth forms only quite a small fraction, not nearly the one-thousandth -part of the whole diameter of the terrestrial globe, and that the rest -is still for the most part in a molten or fiery fluid state. - -Now if, starting with this assumption, we reflect on the ancient history -of the development of the globe, we are logically carried back a step -further, namely, to the assumption that at an earlier date the whole -earth was a fiery fluid body, and that the formation of a thin, -stiffened crust on the surface was only a later process. Only gradually, -by radiating its intrinsic heat into the cold space of the universe, has -the surface of the glowing ball become condensed into a thin crust. -That the temperature of the earth in remote times was much higher than -it is now, is proved by many phenomena. Among other things, this is -rendered probable by the equal distribution of organisms in remote times -of the earth's history. While at present, as is well known, the -different populations of animals and plants correspond to the different -zones of the earth and their appropriate temperature, in earlier times -this was distinctly not the case. - -We see from the distribution of fossils in the remoter ages, that it was -only at a very late date, in fact, at a comparatively recent period of -the organic history of the earth (at the beginning of the so-called -cænolithic or tertiary period), that a separation of zones and of the -corresponding organic populations occurred. During the immensely long -primary and secondary periods, tropical plants, which require a very -high degree of temperature, lived not only in the present torrid zone, -under the equator, but also in the present temperate and frigid zones. -Many other phenomena also demonstrate a gradual decrease of the -temperature of the globe as a whole, and especially a late and gradual -cooling of the earth's crust about the poles. Bronn, in his excellent -"Investigations of the Laws of Development of the Organic World," has -collected numerous geological and palæontological proofs of this fact. - -These phenomena and the mathematico-astronomical knowledge of the -structure of the universe justify the theory that, inconceivable ages -ago, long before the first existence of organisms, the whole earth was a -fiery fluid globe. Now, this theory corresponds with the grand theory of -the origin of the universe, and especially of our planetary system, -which, on the ground of mathematical and astronomical facts, was put -forward in 1755 by our critical philosopher Kant,(22) and was later more -thoroughly established by the celebrated mathematicians, Laplace and -Herschel. This cosmogeny, or theory of the development of the universe, -is now almost universally acknowledged; it has not been replaced by a -better one, and mathematicians, astronomers, and geologists have -continually, by various arguments, strengthened its position. - -Kant's cosmogeny maintains that _the whole universe, inconceivable ages -ago, consisted of a gaseous chaos_. All the substances which are found -at present separated on the earth, and other bodies of the universe, in -different conditions of density--in the solid, semi-fluid, liquid, and -elastic fluid or gaseous states of aggregation--originally constituted -together one single homogeneous mass, equally filling up the space of -the universe, which, in consequence of an extremely high degree of -temperature, was in an exceedingly thin gaseous or nebulous state. The -millions of bodies in the universe which at present form the different -solar systems did not then exist. They originated only in consequence of -a universal rotatory movement, or rotation, during which a number of -masses acquired greater density than the remaining gaseous mass, and -then acted upon the latter as central points of attraction. Thus arose a -separation of the chaotic primary nebula, or gaseous universe, into a -number of rotating nebulous spheres, which became more and more -condensed. Our solar system was such a gigantic gaseous or nebulous -ball, all the particles of which revolved round a common central point, -the solar nucleus. The nebulous ball itself, like all the rest, in -consequence of its rotatory movement, assumed a spheroidal or a -flattened globular form. - -While the centripetal force attracted the rotating particles nearer and -nearer to the firm central point of the nebulous ball, and thus -condensed the latter more and more, the centrifugal force, on the other -hand, always tended to separate the peripheral particles further and -further from it, and to hurl them off. On the equatorial sides of the -ball, which was flattened at both poles, this centrifugal force was -strongest, and as soon as, by increase of density, it attained -predominance over the centripetal force, a circular nebulous ring -separated itself from the rotating ball. This nebulous ring marked the -course of future planets. The nebulous mass of the ring gradually -condensed, and became a planet, which revolved round its own axis, and -at the same time rotated round the central body. In precisely the same -manner, from the equator of the planetary mass, as soon as the -centrifugal force gained predominance over the centripetal force, new -nebulous rings were ejected, which moved round the planets as the latter -moved round the sun. These nebulous rings, too, became condensed into -rotating balls. Thus arose the moons, only one of which moves round our -earth, whilst four move round Jupiter, and six round Uranus. The ring of -Saturn still shows us a moon in its early stage of development. As by -increasing refrigeration these simple processes of condensation and -expulsion repeated themselves over and over again, there arose the -different solar systems, the planets rotating round their central suns, -and the satellites or moons moving round their planets. - -The original gaseous condition of the rotating bodies of the universe -gradually changed, by increasing refrigeration and condensation, into -the fiery fluid or molten state of aggregation. By the process of -condensation, a great quantity of heat was emitted, and the rotating -suns, planets, and moons, soon changed into glowing balls of fire, like -gigantic drops of melted metal, which emitted light and heat. By loss of -heat, the melted mass on the surface of the fiery fluid ball became -further condensed, and thus arose a thin, firm crust, which enclosed a -fiery fluid nucleus. In all essential respects our mother earth probably -did not differ from the other bodies of the universe. - -In view of the object of these pages, it will not be of especial -interest to follow in detail the _history of the natural creation of the -universe_, with its different solar and planetary systems, and to -establish it mathematically by the different astronomical and geological -proofs. The outlines of it, which I have just mentioned, must be -sufficient here, and for further details I refer to Kant's[5] "General -History of Nature and Theory of the Heavens."(22) I will only add that -this wonderful theory, which might be called _the cosmological gas -theory_, harmonizes with all the general series of phenomena at present -known to us, and stands in no irreconcilable contradiction to any one of -them. Moreover, it is purely mechanical or monistic, makes use -exclusively of the inherent forces of eternal matter, and entirely -excludes every supernatural process, every prearranged and conscious -action of a personal Creator. Kant's Cosmological Gas Theory -consequently occupies a similar supreme position in _Anorganology_, -especially in _Geology_, and forms the crown of our knowledge in that -department, in the same way as Lamarck's Theory of Descent does in -_Biology_, and especially in _Anthropology_. Both rest exclusively upon -mechanical or unconscious causes (causæ efficientes), in no case upon -prearranged or conscious causes (causæ finales). (Compare above, p. -100-106.) Both therefore fulfil all the demands of a scientific theory, -and consequently will remain generally acknowledged until they are -replaced by better ones. - -I will, however, not deny that Kant's grand cosmogeny has some weak -points, which prevent our placing the same unconditional confidence in -it as in Lamarck's Theory of Descent. The notion of an original gaseous -chaos filling the whole universe presents great difficulties of various -kinds. A great and unsolved difficulty lies in the fact that the -Cosmological Gas Theory furnishes no starting-point at all in -explanation of the first impulse which caused the rotary motion in the -gas-filled universe. In seeking for such an impulse, we are -involuntarily led to the mistaken questioning about a "first beginning." -We can as little imagine a _first beginning_ of the eternal phenomena of -the motion of the universe as of its final end. - -The universe is unlimited and immeasurable in both space and time. It is -eternal, and it is infinite. Nor can we imagine a beginning or end to -the uninterrupted and eternal motion in which all particles of the -universe are always engaged. The great laws of the _conservation of -force_(38) and the _conservation of matter_, the foundations of our -whole conception of nature, admit of no other supposition. The universe, -as far as it is cognisable to human capability, appears as a connected -chain of material phenomena of motion, necessitating a continual change -of forms. Every form, as the temporary result of a multiplicity of -phenomena of motion, is as such perishable, and of limited duration. -But, in the continual change of forms, matter and the motion inseparable -from it remain eternal and indestructible. - -Now, although Kant's Cosmological Gas Theory is not able to explain the -development of motion in the whole universe in a satisfactory manner, -beyond that gaseous state of chaos, and although many other weighty -considerations may be brought forward against it, especially by -chemistry and geology, yet we must on the whole acknowledge its great -merit, inasmuch as it explains in an excellent manner, by due -consideration of development, the whole structure of all that is -accessible to our observation, that is, the anatomy of the solar -systems, and especially of our planetary system. It may be that this -development was altogether different from what Kant supposes, and our -earth may have arisen by the aggregation of numberless small meteorides, -scattered in space, or in any other manner, but hitherto no one has as -yet been able to establish any other theory of development, or to offer -one in the place of Kant's cosmogeny. - -After this general glance at the monistic cosmogeny, or the -non-miraculous history of the development of the universe, let us now -return to a minute fraction of it, to our mother earth, which we left as -a ball flattened at both poles and in a fiery fluid state, its surface -having condensed by becoming cooled into a very thin firm crust. The -crust, on first cooling, must have covered the whole surface of the -terrestrial sphere as a continuous smooth and thin shell. But soon it -must have become uneven and hummocky; for, since during the continued -cooling, the fiery fluid nucleus became more and more condensed and -contracted, and consequently the diameter of the earth diminished, the -thin cold crust, which could not closely follow the softer nuclear mass, -must have fallen in, in many places. An empty space would have arisen -between the two, had not the pressure of the outer atmosphere forced -down the fragile crust towards the interior, breaking it in so doing. -Other unevennesses probably arose from the fact that, in different -parts, the cooled crust during the process of refrigeration contracted -also itself, and thus became fissured with cracks and rents. The fiery -fluid nucleus flowed up to the external surface through these cracks, -and again became cooled and stiff. Thus, even at an early period there -arose many elevations and depressions, which were the first foundations -of mountains and valleys. - -After the temperature of the cooled terrestrial ball had fallen to a -certain degree, a very important new process was effected, namely, the -_first origin of water_. Water had until then existed only in the form -of steam in the atmosphere surrounding the globe. The water could -evidently not condense into a state of fluid drops until the temperature -of the atmosphere had considerably decreased. Now, then, there began a -further transformation of the earth's crust by the force of water. It -continually fell in the form of rain, and in that form washed down the -elevations of the earth's crust, filling the depressions with the mud -carried along, and, by depositing it in layers, it caused the extremely -important neptunic transformations of the earth's crust, which have -continued since then uninterruptedly, and which in our next chapter we -shall examine a little more closely. - -It was not till the earth's crust had so far cooled that the water had -condensed into a fluid form, it was not till the hitherto dry crust of -the earth had for the first time become covered with liquid water, that -the origin of the first organisms could take place. For all animals and -all plants--in fact, all organisms--consist in great measure of fluid -water, which combines in a peculiar manner with other substances, and -brings them into a semi-fluid state of aggregation. We can therefore, -from these general outlines of the inorganic history of the earth's -crust, deduce the important fact, that at a certain definite time life -had its beginning on earth, and that terrestrial organisms did not exist -from eternity, but at a certain period came into existence for the first -time. - -Now, how are we to conceive of this origin of the first organisms? This -is the point at which most naturalists, even at the present day, are -inclined to give up the attempt at natural explanation, and take refuge -in the miracle of an inconceivable creation. In doing so, as has already -been remarked, they quit the domain of scientific knowledge, and -renounce all further insight into the eternal laws which have determined -nature's history. But before despondingly taking such a step, and before -we despair of the possibility of any knowledge of this important -process, we may at least make an attempt to understand it. Let us see if -in reality the origin of a first organism out of inorganic matter, the -origin of a living body out of lifeless matter, is so utterly -inconceivable and beyond all experience. In one word, let us examine the -question of _spontaneous generation, or archigony_. In so doing, it is -above all things necessary to form a clear idea of the principal -properties of the two chief groups of natural bodies, the so-called -inanimate or inorganic, and the animate or organic bodies, and then -establish what is common to, and what are the differences between, the -two groups. It is desirable to go somewhat carefully into the -_comparison of organisms and anorgana_, since it is commonly very much -neglected, although it is necessary for a right understanding of nature -from the monistic point of view. It will be most advantageous here to -look separately at the three fundamental properties of every natural -body; these are matter, form, and force. Let us begin with _matter_. -(Gen. Morph. iii.) - -By chemistry we have succeeded in analysing all bodies known to us into -a small number of elements or simple substances, which cannot be further -divided, for example, carbon, oxygen, nitrogen, sulphur, and the -different metals: potassium, sodium, iron, gold, etc. At present we know -about seventy such elements or simple substances. The majority of them -are unimportant and rare; the minority only are widely distributed, and -compose not only most of the anorgana, but also all organisms. If we -compare those elements which constitute the body of organisms with those -which are met with in anorgana, we have first to note the highly -important fact that in animal and vegetable bodies no element occurs but -what can be found outside of them in inanimate nature. There are no -special organic elements or simple organic substances. - -The chemical and physical differences existing between organisms and -anorgana, consequently, do not lie in their material foundation; they do -not arise from the different nature of the _elements_ composing them, -but from the different manner in which the latter are united by -chemical _combination_. This different manner of combination gives rise -to certain physical peculiarities, especially in density of substance, -which at first sight seems to constitute a deep chasm between the two -groups of bodies. Inorganic or inanimate natural bodies, such as -crystals and the amorphous rocks, are in a state of density which we -call the firm or solid state, and which we oppose to the liquid state of -water and to the gaseous state of air. It is familiar to every one that -these three different degrees of density, or states of aggregation of -anorgana, are by no means peculiar to the different elements, but are -the results of a certain degree of temperature. Every inorganic solid -body, by increase of temperature, can be reduced to the liquid or melted -state, and, by further heat, to the gaseous or elastic state. In the -same way most gaseous bodies, by a proper decrease of temperature can -first be converted into a liquid state, and further, into a solid state -of density. - -In opposition to these three states of density of anorgana, the living -body of all organisms--animals as well as plants--is in an altogether -peculiar fourth state of aggregation. It is neither solid like stone, -nor liquid like water, but presents rather a medium between these two -states, which may therefore be designated as the firm-fluid or swollen -state of aggregation (viscid). In all living bodies, without exception, -there is a certain quantity of water combined in a peculiar way with -solid matter, and owing to this characteristic combination of water with -solid matter we have that soft state of aggregation, neither solid nor -liquid, which is of great importance in the mechanical explanation of -the phenomena of life. Its cause lies essentially in the physical and -chemical properties of a simple, indivisible, elementary substance, -namely, _carbon_ (Gen. Morph. i. 122-130). - -Of all elements, carbon is to us by far the most important and -interesting, because this simple substance plays the largest part in all -animal and vegetable bodies known to us. It is that element which, by -its peculiar tendency to form complicated combinations with the other -elements, produces the greatest variety of chemical compounds, and among -them the forms and living substance of animal and vegetable bodies. -Carbon is especially distinguished by the fact that it can unite with -the other elements in infinitely manifold relations of number and -weight. By the combination of carbon with three other elements, with -oxygen, hydrogen, and nitrogen (to which generally sulphur, and -frequently, also, phosphorus is added), there arise those exceedingly -important compounds which we have become acquainted with as the first -and most indispensable substratum of all vital phenomena, the albuminous -combinations, or albuminous bodies (protean matter). - -We have before this (p. 185) become acquainted with the simplest of all -species of organisms in the Monera, whose entire bodies when completely -developed consist of nothing but a semi-fluid albuminous lump; they are -organisms which are of the utmost importance for the theory of the first -origin of life. But most other organisms, also, at a certain period of -their existence--at least, in the first period of their life--in the -shape of egg-cells or germ-cells, are essentially nothing but simple -little lumps of such albuminous formative matter, known as plasma, or -protoplasma. They then differ from the Monera only by the fact that in -the interior of the albuminous corpuscle the cell-kernel, or nucleus, -has separated itself from the surrounding cell-substance (protoplasma). -As we have already pointed out, the cells, with their simple attributes, -are so many citizens, who by co-operation and differentiation build up -the body of even the most perfect organism; this being, as it were, a -cell republic (p. 301). The fully developed form and the vital phenomena -of such an organism are determined solely by the activities of these -small albuminous corpuscles. - -It may be considered as one of the greatest triumphs of recent biology, -especially of the theory of tissues, that we are now able to trace the -wonder of the phenomena of life to these substances, and that we can -demonstrate the _infinitely manifold and complicated physical and -chemical properties of the albuminous bodies to be the real cause of -organic or vital phenomena_. All the different forms of organisms are -simply and directly the result of the combination of the different forms -of cells. The infinitely manifold varieties of form, size, and -combination of the cells have arisen only gradually by the division of -labour, and by the gradual adaptation of the simple homogeneous lumps of -plasma, which originally were the only constituents of the cell-mass. -From this it follows of necessity that the fundamental phenomena of -life--nutrition and generation--in their highest manifestations, as well -as in their simplest expressions, must also be traced to the material -nature of that albuminous formative substance. The other vital -activities are gradually evolved from these two. Thus, then, the general -explanation of life is now no more difficult to us than the explanation -of the physical properties of inorganic bodies. All vital phenomena and -formative processes of organisms are as directly dependent upon the -chemical composition and the physical forces of organic matter as the -vital phenomena of inorganic crystals--that is, the process of _their_ -growth and _their_ specific formation--are the direct results of their -chemical composition and of their physical condition. The _ultimate -causes_, it is true, remain in _both_ cases concealed from us. When gold -and copper crystallize in a cubical, bismuth and antimony in a -hexagonal, iodine and sulphur in a rhombic form of crystal, the -occurrence is in reality neither more nor less mysterious to us than is -every elementary process of organic formation, every self-formation of -the organic cell. In this respect we can no longer draw a fundamental -distinction between organisms and anorgana, a distinction of which, -formerly, naturalists were generally convinced. - -Let us secondly examine the agreements and differences which are -presented to us in the _formation_ of organic and inorganic natural -bodies (Gen. Morph. i. 130). Formerly the simple structure of the latter -and the composite structure of the former were looked upon as the -principal distinction. The body of all organisms was supposed to consist -of dissimilar or heterogeneous parts, of instruments or organs which -worked together for the purposes of life. On the other hand, the most -perfect anorgana, that is to say, crystals, were supposed to consist -entirely of continuous or homogeneous matter. This distinction appears -very essential. But it loses all importance through the fact that in -late years we have become acquainted with the exceedingly remarkable and -important Monera.(15) (Compare above, p. 185.) The whole body of these -most simple of all organisms--a semi-fluid, formless, and simple lump of -albumen--consists, in fact, of only a single chemical combination, and -is as perfectly simple in its structure as any crystal, which consists -of a single inorganic combination, for example, of a metallic salt or of -a silicate of the earths and alkalies. - -As naturalists believed in differences in the inner structure or -composition, so they supposed themselves able to find complete -differences in the external forms of organisms and anorgana, especially -in the mathematically determinable crystalline forms of the latter. -Certainly crystallization is pre-eminently a quality of the so-called -anorgana. Crystals are limited by plane surfaces, which meet in straight -lines and at certain measurable angles. Animal and vegetable forms, on -the contrary, seem at first sight to admit of no such geometrical -determination. They are for the most part limited by curved surfaces and -crooked lines, which meet at variable angles. But in recent times we -have become acquainted, among Radiolaria(23) and among many other -Protista, with a large number of lower organisms, whose body, in the -same way as crystals, may be traced to a mathematically determinable -fundamental form, and whose form in its whole, as well as in its parts, -is bounded by definite geometrically determinable planes and angles. In -my general doctrine of _Fundamental Forms, or Promorphology_, I have -given detailed proofs of this, and at the same time established a -general system of forms, the ideal stereometrical type-forms, which -explain the real forms of inorganic crystals, as well as of organic -individuals (Gen. Morph. i. 375-574). Moreover, there are also perfectly -amorphous organisms, like the Monera, Amoeba, etc., which change their -forms every moment, and in which we are as little able to point out a -definite fundamental form as in the case of the shapeless or amorphous -anorgana, such as non-crystallized stones, deposits, etc. We are -consequently unable to find any essential difference in the external -forms or the inner structure of anorgana and organisms. - -Thirdly, let us turn to the _forces_ or the _phenomena of motion_ of -these two different groups of bodies (Gen. Morph. i. 140). Here we meet -with the greatest difficulties. The vital phenomena, known as a rule -only in the highly developed organisms, in the more perfect animals and -plants, seem there so mysterious, so wonderful, so peculiar, that most -persons are decidedly of opinion that in inorganic nature there occurs -nothing at all similar, or in the least degree comparable to them. -Organisms are for this very reason called animate, and the anorgana, -inanimate natural bodies. Hence, even so late as the commencement of the -present century, the science which investigates the phenomena of life, -namely physiology, retained the erroneous idea that the physical and -chemical properties of matter were not sufficient for explaining these -phenomena. In our own day, especially during the last ten years, this -idea may be regarded as having been completely refuted. In physiology, -at least, it has now no place. It now never occurs to a physiologist to -consider any of the vital phenomena as the result of a mysterious _vital -force_, of an active power working for a definite purpose, standing -outside of matter, and, so to speak, taking only the physico-chemical -forces into its service. Modern physiology has arrived at the strictly -monistic conviction that all of the vital phenomena, and, above all, the -two fundamental phenomena of nutrition and propagation are purely -physico-chemical processes, and directly dependent on the material -nature of the organism, just as all the physical and chemical qualities -of every crystal are determined solely by its material composition. Now, -as the elementary substance which determines the peculiar material -composition of organisms is carbon, we must ultimately reduce all vital -phenomena, and, above all, the two fundamental phenomena of nutrition -and propagation to the properties of the carbon. _The -peculiar-chemico-physical properties, and especially the semi-fluid -state of aggregation, and the easy decomposibility of the exceedingly -composite albuminous combinations of carbon, are the mechanical causes -of those peculiar phenomena of motion which distinguish organisms from -anorgana, and which in a narrow sense are usually called "life."_ - -In order to understand this "_carbon theory_," which I have established -in detail in the second book of my General Morphology, it is necessary, -above all things, closely to examine those phenomena of motion which are -common to both groups of natural bodies. First among them is the -_process of growth_. If we cause any inorganic solution of salt slowly -to evaporate, crystals are formed in it, which slowly increase in size -during the continued evaporation of the water. This process of growth -arises from the fact that new particles continually pass over from the -fluid state of aggregation into the solid, and, according to certain -laws, deposit themselves upon the firm kernel of the crystal already -formed. From such an apposition of particles arise the mathematically -definite crystalline shapes. In like manner the growth of organisms -takes place by the accession of new particles. The only difference is -that in the growth of organisms, in consequence of their semi-fluid -state of aggregation, the newly-added particles penetrate into the -interior of the organism (inter-susception), whereas anorgana receive -homogeneous matter from without only by apposition or an addition of new -particles to the surface. This important difference of growth by -inter-susception and by apposition is obviously only the necessary and -direct result of the different conditions of density or state of -aggregation in organisms and anorgana. - -Unfortunately I cannot here follow in detail the various exceedingly -interesting parallels and analogies which occur between the formation of -the most perfect anorgana, the crystals, and the formation of the -simplest organisms, the Monera and their next kindred forms. For this I -must refer to a minute comparison of organisms and anorgana, which I -have carried out in the fifth chapter of my General Morphology (Gen. -Morph. i. 111-160). I have there shown in detail that there exist no -complete differences between organic and inorganic natural bodies, -neither in respect to form and structure, nor in respect to matter and -force; and that the actually existing differences are dependent upon the -peculiar nature of the _carbon_; and that there exists no insurmountable -chasm between organic and inorganic nature. We can perceive this most -important fact very clearly if we examine and compare the origin of the -forms in crystals and in the simplest organic individuals. In the -formation of crystal individuals, two different counteracting formative -tendencies come into operation. The _inner constructive force_, or the -inner formative tendency, which corresponds to the Heredity of -organisms, in the case of the crystal is the direct result of its -material constitution or of its chemical composition. The form of the -crystal, so far as it is determined by this inner original formative -tendency, is the result of the specific and definite way in which the -smallest particles of the crystallizing matter unite together in -different directions according to law. That independent inner formative -force, which is directly inherent in the matter itself, is directly -counteracted by a second formative force. The _external constructive -force_, or the external formative tendency, may be called Adaptation in -crystals as well as in organisms. Every crystal individual during its -formation, like every organic individual, must submit and adapt itself -to the surrounding influences and conditions of existence of the outer -world. In fact, the form and size of every crystal is dependent upon its -whole surroundings, for example, upon the vessel in which the -crystallization takes place, upon the temperature and the pressure of -the air under which the crystal is formed, upon the presence or absence -of heterogeneous bodies, etc. Consequently, the form of every single -crystal, like the form of every single organism, is the result of the -interaction of two opposing factors--the _inner_ formative tendency, -which is determined by the chemical constitution of the _matter itself_, -and of the _external_ formative tendency, which is dependent upon the -influence of _surrounding_ matter. Both these constructive forces -interact similarly also in the organism, and, just as in the crystal, -are of a purely mechanical nature and directly inherent in the substance -of the body. If we designate the growth and the formation of organisms -as a process of life, we may with equal reason apply the same term to -the developing crystal. The teleological conception of nature, which -looks upon organisms as machines of creation arranged for a definite -purpose, must logically acknowledge the same also in regard to the -forms of crystals. The differences which exist between the simplest -organic individuals and inorganic crystals are determined by the _solid_ -state of aggregation of the latter, and by the _semi-fluid_ state of the -former. Beyond that the causes producing form are exactly the same in -both. This conviction forces itself upon us most clearly, if we compare -the exceedingly remarkable phenomena of growth, adaptation, and the -"correlation of parts" of developing crystals with the corresponding -phenomena of the origin of the simplest organic individuals (Monera and -cells). The analogy between the two is so great that, in reality, no -accurate boundary can be drawn. In my General Morphology I have quoted -in support of this a number of striking facts (Gen. Morph. i. 146, 156, -158.) - -If we vividly picture to ourselves this "_unity of organic and inorganic -nature_" this essential agreement of organisms and anorgana in matter, -form, and force, and if we bear in mind that we are not able to -establish any one fundamental distinction between these two groups of -bodies (as was formerly generally assumed), then the question of -spontaneous generation will lose a great deal of the difficulty which at -first seems to surround it. Then the development of the first organism -out of inorganic matter will appear a much more easily conceivable and -intelligible process than has hitherto been the case, whilst an -artificial absolute barrier between organic or animate, and inorganic or -inanimate nature was maintained. - -In the question of _spontaneous generation, or archigony_, which we can -now answer more definitely, it must be borne in mind that by this -conception we understand generally the _non-parental generation of an -organic individual_, the origin of an organism independent of a -parental or producing organism. It is in this sense that on a former -occasion (p. 183) I mentioned spontaneous generation (archigony) as -opposed to parental generation or propagation (tocogony). In the latter -case the organic individual arises by a greater or less portion of an -already existing organism separating itself and growing independently. -(Gen. Morph. ii. 32.) - -In spontaneous generation, which is often also called original -generation (generatio spontanea, æquivoca, primaria etc.), we must first -distinguish two essentially different kinds, namely, _autogeny_ and -_plasmogeny_. By _autogeny_ we understand the origin of a most simple -organic individual in an _inorganic formative fluid_, that is, in a -fluid which contains the fundamental substances for the composition of -the organism dissolved in simple and loose combinations (for example, -carbonic acid, ammonia, binary salts, etc.). On the other hand, we call -spontaneous generation _plasmogeny_ when the organism arises in an -_organic formative fluid_, that is, in a fluid which contains those -requisite fundamental substances dissolved in the form of complicated -and fluid combinations of carbon (for example, albumen, fat, hydrate of -carbon, etc.). (Gen. Morph. i. 174, ii. 33.) - -Neither the process of autogeny, nor that of plasmogeny, has yet been -directly observed with perfect certainty. In early, and also in more -recent times, numerous and interesting experiments have been made as to -the possibility or reality of spontaneous generation. Almost all these -experiments refer not to autogeny, but to plasmogeny, to the origin of -an organism out of already formed organic matter. It is evident, -however, that this latter process is only of subordinate interest for -our history of creation. It is much more important for us to solve the -question, "Is there such a thing as autogeny? Is it possible that an -organism can arise, not out of pre-existing organic, but out of purely -inorganic, matter?" Hence we can quietly lay aside all the numerous -experiments which refer only to plasmogeny, which have been carried on -very zealously during the last ten years, and which for the most part -have had a negative result. For even supposing that the reality of -plasmogeny were strictly proved, still autogeny would not be explained -by it. - -The experiments on autogeny have likewise as yet furnished no certain -and positive result. Yet we must at the outset most distinctly protest -against the notion that these experiments have proved the impossibility -of spontaneous generation in general. Most naturalists who have -endeavoured to decide this question experimentally, and who, after -having employed all possible precautionary measures, under -well-ascertained conditions, have seen no organisms come into being, -have straightway made the assertion, on the ground of these negative -results: "That it is altogether impossible for organisms to come into -existence by themselves without parental generation." This hasty and -inconsiderate assertion they have supported by the negative results of -their experiments, which, after all, could prove nothing except that, -under these or those highly artificial circumstances created by the -experimenters themselves, no organism was developed. From these -experiments, which have been for the most part made under the most -unnatural conditions, and in a highly artificial manner, we can by no -means draw the conclusion that spontaneous generation in general is -impossible. The impossibility of such a process can, in fact, never be -proved. For how can we know that in remote primæval times there did not -exist conditions quite different from those at present obtaining, and -which may have rendered spontaneous generation possible? Indeed, we can -even positively and with full assurance maintain that the general -conditions of life in primæval times must have been entirely different -from those of the present time. Think only of the fact that the enormous -masses of carbon which we now find deposited in the primary coal -mountains were first reduced to a solid form by the action of vegetable -life, and are the compressed and condensed remains of innumerable -vegetable substances, which have accumulated in the course of many -millions of years. But at the time when, after the origin of water in a -liquid state on the cooled crust of the earth, organisms were first -formed by spontaneous generation, those immeasurable quantities of -carbon existed in a totally different form, probably for the most part -dispersed in the atmosphere in the shape of carbonic acid. The whole -composition of the atmosphere was therefore extremely different from the -present. Further, as may be inferred upon chemical, physical, and -geological grounds, the density and the electrical conditions of the -atmosphere were quite different. In like manner the chemical and -physical nature of the primæval ocean, which then continuously covered -the whole surface of the earth as an uninterrupted watery sheet, was -quite peculiar. The temperature, the density, the amount of salt, etc., -must have been very different from those of the present ocean. In any -case, therefore, even if we do not know anything more about it, there -remains to us the supposition, which can at least not be disputed, that -at that time, under conditions quite different from those of to-day, a -spontaneous generation, which now is perhaps no longer possible, may -have taken place. - -But it is necessary to add here that, by the recent progress of -chemistry and physiology, the mysterious and miraculous character which -at first seems to belong to this much disputed and yet inevitable -process of spontaneous generation, has been to a great extent, or almost -entirely, destroyed. Not fifty years ago, all chemists maintained that -we were unable to produce artificially in our laboratories any -complicated combination of carbon, or so-called "organic combination." -The mystic "vital force" alone was supposed to be able to produce these -combinations. When, therefore, in 1828, Wöhler, in Göttingen, for the -first time refuted this dogma, and exhibited pure "organic" urea, -obtained in an artificial manner from a purely inorganic body (cyanate -of ammonium), it caused the greatest surprise and astonishment. In more -recent times, by the progress of synthetic chemistry, we have succeeded -in producing in our laboratories a great variety of similar "organic" -combinations of carbon, by purely artificial means--for example alcohol, -acetic acid, formic acid. Indeed, many exceedingly complicated -combinations of carbon are now artificially produced, so that there is -every likelihood, sooner or later, of our producing artificially the -most complicated, and at the same time the most important of all, -namely, the albuminous combinations, or plasma-bodies. By the -consideration of this probability, the deep chasm which was formerly -and generally believed to exist between organic and inorganic bodies is -almost or entirely removed, and the way is paved for the conception of -spontaneous generation. - -Of still greater, nay, the very greatest importance to the hypothesis of -spontaneous generation are, finally, the exceedingly remarkable -_Monera_, those creatures which we have already so frequently mentioned, -and which are not only the simplest of all observed organisms, but even -the simplest of all imaginable organisms. I have already described these -wonderful "_organisms without organs_," when examining the simplest -phenomena of propagation and inheritance. We already know seven -different genera of these Monera, some of which live in fresh water, -others in the sea (compare above, p. 184; also Plate I. and its -explanation in the Appendix). In a perfectly developed and freely motile -state, they one and all present us with nothing but a simple little lump -of an albuminous combination of carbon. The individual genera and -species differ only a little in the manner of propagation and -development, and in the way of taking nourishment. Through the discovery -of these organisms, which are of the utmost importance, the supposition -of a spontaneous generation loses most of its difficulties. For as all -trace of organization--all distinction of heterogeneous parts--is still -wanting in them, and as all the vital phenomena are performed by one and -the same homogeneous and formless matter, we can easily imagine their -origin by spontaneous generation. If this happens through _plasmogeny_, -and if plasma capable of life already exists, it then only needs to -individualize itself in the same way as the mother liquor of crystals -individualizes itself in crystallization. If, on the other hand, the -spontaneous generation of the Monera takes place by true _autogeny_, -then it is further requisite that that plasma capable of life, that -primæval mucus, should be formed out of simpler combinations of carbon. -As we are now able artificially to produce, in our laboratories, -combinations of carbon similar to this in the complexity of their -constitution, there is absolutely no reason for supposing that there are -not conditions in free nature also, in which such combinations could -take place. Formerly, when the doctrine of spontaneous generation was -advocated, it failed at once to obtain adherents on account of the -composite structure of the simplest organisms then known. It is only -since we have discovered the exceedingly important Monera, only since we -have become acquainted in them with organisms not in any way built up of -distinct organs, but which consist solely of a single chemical -combination, and yet grow, nourish, and propagate themselves, that this -great difficulty has been removed, and the hypothesis of spontaneous -generation has gained a degree of probability which entitles it to fill -up the gap existing between Kant's cosmogony and Lamarck's Theory of -Descent. Even among the Monera at present known there is a species which -probably, even now, always comes into existence by spontaneous -generation. This is the wonderful _Bathybius Hæckelii_, discovered and -described by Huxley. As I have already mentioned (p. 184), this Moneron -is found in the greatest depths of the sea, at a depth of between 12,000 -and 24,000 feet, where it covers the ground partly as retiform threads -and plaits of plasma, partly in the form of larger or smaller irregular -lumps of the same material.[6] - -Only such homogeneous organisms as are yet not differentiated, and are -similar to inorganic crystals in being homogeneously composed of one -single substance, could arise by spontaneous generation, and could -become the primæval parents of all other organisms. In their further -development we have pointed out that the most important process is the -formation of a _kernel_ or _nucleus_ in the simple little lump of -albumen. We can conceive this to take place in a purely physical manner, -by the condensation of the innermost central part of the albumen. The -more solid central mass, which at first gradually shaded off into the -peripheral plasma, becomes sharply separated from it, and thus forms an -independent, round, albuminous corpuscle, the kernel; and by this -process the Moneron becomes a _cell_. Now, it must have become evident -from our previous chapters, that the further development of all other -organisms out of such a cell presents no difficulty, for every animal -and every plant, in the beginning of its individual life, is a simple -cell. Man, as well as every other animal, is at first nothing but a -simple egg-cell, a single lump of mucus, containing a kernel (p. 297, -Fig. 5). - -In the same way as the kernel of the organic cell arose in the interior -or central mass of the originally homogeneous lump of plasma, by -separation, so, too, the first _cell-membrane_ was formed on its -surface. This simple, but most important process, as has already been -remarked, can likewise be explained in a purely physical manner, either -as a chemical deposit, or as a physical condensation in the uppermost -stratum of the mass, or as a secretion. One of the first processes of -adaptation effected by the Moneron originating by spontaneous generation -must have been the condensation of an external crust, which as a -protecting covering shut in the softer interior from the hostile -influences of the outer world. As soon as, by condensation of the -homogeneous Moneron, a cell-kernel arose in the interior and a membrane -arose on the surface, all the fundamental parts of the unit were -furnished, out of which, by infinitely manifold repetition and -combination, as attested by actual observation, the body of higher -organisms is constructed. - -As has already been mentioned, our whole understanding of an organism -rests upon the cell theory established thirty years ago by Schleiden and -Schwann. According to it, every organism is either a simple cell or a -cell-community, a republic of closely connected cells. All the forms and -vital phenomena of every organism are the collective result of the forms -and vital phenomena of all the single cells of which it is composed. By -the recent progress of the cell theory it has become necessary to give -the elementary organisms, that is, the "organic" individuals of the -first order, which are usually designated as _cells_, the more general -and more suitable name of _form-units_, or _plastids_. Among these -form-units we distinguish two main groups, namely, the cytods and the -genuine cells. The _cytods_ are, like the Monera, pieces of plasma -without a kernel (p. 186, Fig. 1). _Cells_, on the other hand, are -pieces of plasma containing a kernel or nucleus (p. 188, Fig. 2). Each -of these two main groups of plastids is again divided into two -subordinate groups, according as they possess or do not possess an -external covering (skin, shell, or membrane). We may accordingly -distinguish the following four grades or species of plastids, namely: 1. -_Simple cytods_ (p. 186, Fig. 1 _A_); 2. _Encased cytods_; 3. _Simple -cells_ (p. 188, Fig. 2 _B_); 4. _Encased cells_ (p. 188, Fig. 2 _A_). -(Gen. Morph. i. 269-289.) - -Concerning the relation of these four forms of plastids to spontaneous -generation, the following is the most probable:--1. The _simple cytods_ -(Gymnocytoda), naked particles of plasma without kernel, like the still -living Monera, are the only plastids which directly come into existence -by spontaneous generation. 2. The _enclosed cytods_ (Lepocytoda), -particles of plasma without kernel, which are surrounded by a covering -(membrane or shell), arose out of the simple cytods either by the -condensation of the outer layers of plasma or by the secretion of a -covering. 3. The _simple cells_ (Gymnocyta), or naked cells, particles -of plasma with kernel, but without covering, arose out of the simple -cytods by the condensation of the innermost particles of plasma into a -kernel, or nucleus, by differentiation of a central kernel and -peripheral cell-substance. 4. The _enclosed cells_ (Lepocyta), or -testaceous cells, particles of plasma with kernel and an outer covering -(membrane or shell), arose either out of the enclosed cytods by the -formation of a kernel, or out of the simple cells by the formation of a -membrane. All the other forms of form-units, or plastids, met with, -besides these, have only subsequently arisen out of these four -fundamental forms by natural selection, by descent with adaptation, by -differentiation and transformation. - -By this _theory of plastids_, by deducing all the different forms of -plastids, and hence, also, all organisms composed of them, from the -Monera, we obtain a simple and natural connection in the whole series of -the development of nature. The origin of the first Monera by spontaneous -generation appears to us as a simple and necessary event in the process -of the development of the earth. We admit that this process, as long as -it is not directly observed or repeated by experiment, remains a pure -hypothesis. But I must again say that this hypothesis is indispensable -for the consistent completion of the non-miraculous history of creation, -that it has absolutely nothing forced or miraculous about it, and that -certainly it can never be positively refuted. It must be taken into -consideration that the process of spontaneous generation, even if it -still took place daily and hourly, would in any case be exceedingly -difficult to observe and establish with absolute certainty as such. With -regard to the Monera, we find ourselves placed before the following -alternative: _either_ they are actually directly derived from -pre-existing, or "created," most ancient Monera, and in this case they -would have had to propagate themselves unchanged for many millions of -years, and to have maintained their original form of simple particles of -plasma; _or_, the _present_ Monera have originated much later in the -course of the organic history of the earth, by repeated acts of -spontaneous generation, and in this case spontaneous generation may take -place now as well as then. The latter supposition has evidently much -more probability on its side than the former. - -If we do not accept the hypothesis of spontaneous generation, then at -this one point of the history of development we must have recourse to -the miracle of a _supernatural creation_. The Creator must have created -the first organism, or a few first organisms, from which all others are -derived, and as such he must have created the simplest Monera, or -primæval cytods, and given them the capability of developing further in -a mechanical way. I leave it to each one of my readers to choose between -this idea and the hypothesis of spontaneous generation. To me the idea -that the Creator should have in this one point arbitrarily interfered -with the regular process of development of matter, which in all other -cases proceeds entirely without his interposition, seems to be just as -unsatisfactory to a believing mind as to a scientific intellect. If, on -the other hand, we assume the hypothesis of spontaneous generation for -the origin of the first organisms, which in consequence of reasons -mentioned above, and especially in consequence of the discovery of the -Monera, has lost its former difficulty, then we arrive at the -establishment of an uninterrupted natural connection between the -development of the earth and the organisms produced on it, and, in this -last remaining lurking-place of obscurity, we can proclaim the _unity of -all Nature, and the unity of her laws of Development_ (Gen. Morph. i. -164). - - - - -CHAPTER XIV. - -MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE ICE-PERIOD OF -THE EARTH. - - - Chorological Facts and Causes.--Origin of most Species in - one Single Locality: "Centres of Creation."--Distribution - by Migration.--Active and Passive Migrations of Animals - and Plants.--Means of Transport.--Transport of Germs by - Water and by Wind.--Continual Change of the Area of - Distribution by Elevations and Depressions of the - Ground.--Chorological Importance of Geological - Processes.--Influence of the Change of Climate.--Ice or - Glacial Period.--Its Importance to Chorology.--Importance - of Migrations for the Origin of New Species.--Isolation - of Colonists.--Wagner's Law of Migration.--Connection - between the Theory of Migration and the Theory of - Selection.--Agreement of its Results with the Theory of - Descent. - - -As I have repeatedly said, but cannot too much emphasize, the actual -value and invincible strength of the Theory of Descent does not lie in -its explaining this or that single phenomenon, but in the fact that it -explains _all_ biological phenomena, that it makes _all_ botanical and -zoological series of phenomena intelligible in their relations to one -another. Hence every thoughtful investigator is the more firmly and -deeply convinced of its truth the more he advances from single -biological observations to a general view of the whole domain of animal -and vegetable life. Let us now, starting from this comprehensive point -of view, survey a biological domain, the varied and complicated -phenomena of which may be explained with remarkable simplicity and -clearness by the theory of selection. I mean _Chorology_, or the theory -of the _local distribution of organisms over the surface of the earth_. -By this I do not only mean the _geographical_ distribution of animal and -vegetable species over the different parts and provinces of the earth, -over continents and islands, seas, and rivers; but also their -_topographical_ distribution in a _vertical_ direction, their ascending -to the heights of mountains, and their descending into the depths of the -ocean. (Gen. Morph. ii. 286.) - -The strange chorological series of phenomena which show the horizontal -distribution of organisms over parts of the earth, and their vertical -distribution in heights and depths, have long since excited general -interest. In recent times Alexander Humboldt(39) and Frederick Schouw -have especially discussed the geography of plants, and Berghaus and -Schmarda the geography of animals, on a large scale. But although these -and several other naturalists have in many ways increased our knowledge -of the distribution of animal and vegetable forms, and laid open to us a -new domain of science, full of wonderful and interesting phenomena, yet -Chorology as a whole remained, as far as their labours were concerned, -only a desultory knowledge of a mass of individual _facts_. It could not -be called a science as long as the _causes_ for the explanation of these -facts were wanting. These causes were first disclosed by the theory of -selection and its doctrine of the _migrations_ of animal and vegetable -species, and it is only since the works of Darwin and Wallace that we -have been able to speak of an independent _science of Chorology_. - -If all the phenomena of the geographical and topographical distribution -of organisms are examined by themselves, without considering the gradual -development of species, and if at the same time, following the customary -superstition, the individual species of animals and plants are -considered as forms independently created and independent of one -another, then there remains nothing for us to do but to gaze at those -phenomena as a confused collection of incomprehensible and inexplicable -miracles. But as soon as we leave this low stand-point, and rise to the -height of the theory of development, by means of the supposition of a -blood-relationship between the different species, then all at once a -clear light falls upon this strange series of miracles, and we see that -all chorological facts can be understood quite simply and clearly by the -supposition of a common descent of the species, and their passive and -active migrations. - -The most important principle from which we must start in chorology, and -of the truth of which we are convinced by due examination of the theory -of selection, is that, as a rule, every animal and vegetable species has -arisen only _once_ in the course of time and only in _one_ place on the -earth--its so-called "centre of creation"--by natural selection. I share -this opinion of Darwin's unconditionally, in respect to the great -majority of higher and perfect organisms, and in respect to most animals -and plants in which the division of labour, or differentiation of the -cells and organs of which they are composed, has attained a certain -stage. For it is quite incredible, or could at best only be an -exceedingly rare accident, that all the manifold and complicated -circumstances--all the different conditions of the struggle for life, -which influence the origin of a new species by natural selection--should -have worked together in exactly the same agreement and combination more -than once in the earth's history, or should have been active at the same -time at several different points of the earth's surface. - -On the other hand, I consider it to be very probable that certain -exceedingly imperfect organisms of the simplest structure, forms of -species of an exceedingly indifferent nature, as, for example, many -single-celled Protista, but especially the Monera, the simplest of them -all, should have several times or simultaneously arisen in their -specific form in several parts of the earth. For the few and very simple -conditions by which their specific form was changed in the struggle for -life may surely have often been repeated, in the course of time, -independently in different parts of the earth. Further, those higher -specific forms also, which have not arisen by natural selection, but by -_hybridism_ (the previously-mentioned hybrid species, pp. 147 and 275), -may have repeatedly arisen anew in different localities. As, however, -this proportionately small number of organisms does not especially -interest us here, we may, in respect of chorology, leave them alone, and -need only take into consideration the distribution of the great majority -of animal and vegetable species in regard to which the _single origin of -every species in a single locality_, in its so-called "central point of -creation," can be considered as tolerably certain. - -Every animal and vegetable species from the beginning of its existence -has possessed the tendency to spread beyond the limited locality of its -origin, beyond the boundary of its "centre of creation," or, in other -words, beyond its _primæval home_, or its natal place. This is a -necessary consequence of the relations of population and over-population -(pp. 161 and 256). The more an animal or vegetable species increases, -the less is its limited natal place sufficient for its sustenance, and -the fiercer the struggle for life; the more rapid the _over-population_ -of the natal spot, the more it leads to _emigration_. These _migrations_ -are common to all organisms, and are the real cause of the wide -distribution of the different species of organisms over the earth's -surface. Just as men leave over-crowded states, so all animals and -plants migrate from their over-crowded primæval homes. - -Many distinguished naturalists, especially Lyell(11) and Schleiden, have -before this repeatedly drawn attention to the great importance of these -very interesting migrations of organisms. The means of transport by -which they are effected are extremely varied. Darwin has discussed these -most excellently in the eleventh and twelfth chapters of his work, which -are exclusively devoted to "geographical distribution." The means of -transport are partly active, partly passive; that is to say, the -organism effects its migration partly by free locomotion due to its own -activity, and partly by the movements of other natural bodies in which -it has no active share. - -It is self-evident that _active migrations_ play the chief part in -animals able to move freely. The more freely an animal's organization -permits it to all move in directions, the more easily the animal species -can migrate, and the more rapidly it will spread over the earth. -_Flying_ animals are of course most favoured in this respect, among -vertebrate animals especially birds, and among articulated animals, -insects. These two classes, as soon as they came into existence, can -have more easily spread over the whole earth than any other animal, and -this fact partly explains the extraordinary uniformity of structure -which characterizes these two great classes of animals. For, although -they contain an exceedingly large number of different species, and -although the insect class alone is said to possess more different -species than all other classes of animals together, yet all the -innumerable species of insects, and in like manner, also, the different -species of birds, agree most strikingly in all essential peculiarities -of their organization. Hence, in the class of insects, as well as in -that of birds, we can distinguish only a very small number of large -natural groups or orders, and these few orders differ but very little -from one another in their internal structure. The orders of birds with -their numerous species are not nearly as distinct from one another as -the orders of the mammalian class, containing much fewer species; and -the orders of insects, which are extremely rich in genera and species, -resemble one another much more closely in their internal structure than -do the much smaller orders of the crab class. The general parallelism -between birds and insects is also very interesting in relation to -systematic zoology; and the great importance of their richness in forms, -for scientific morphology, lies in the fact that they show us how, -within the narrowest anatomical sphere, and without profound changes of -the essential internal organization, the greatest variety in external -bodily forms can be attained. The reason of this is evidently their -flying mode of life and their free locomotion. In consequence of this -birds, as well as insects, have spread very rapidly over the whole -surface of the earth, have settled in all possible localities -inaccessible to other animals, and variously modified their specific -form by superficial adaptation to particular local relations. - -Next to the flying animals, those animals, of course, have spread most -quickly and furthest which were next best able to migrate, that is, the -best runners among the inhabitants of the land, and the best swimmers -among the inhabitants of the water. However, the power of such active -migrations is not confined to those animals which throughout life enjoy -free locomotion. For the fixed animals also, such as corals, tubicolous -worms, sea-squirts, lily encrinites, sea-acorns, barnacles, and many -other lower animals which adhere to seaweeds, stones, etc., enjoy, at -least at an early period of life, free locomotion. They all migrate -before they adhere to anything. Their first free locomotive condition of -early life is generally that of a "ciliated" larva, a roundish, cellular -corpuscle, which, by means of a garb of movable "flimmer-hairs," (Latin, -"cilia") swarms about in the water and bears the name of Planula. - -But the power of free locomotion, and hence, also, of active migration, -is not confined to animals alone, but many plants likewise enjoy it. -Many lower aquatic plants, especially the class of the Tangles (Algæ), -swim about freely in the water in early life, like the lower animals -just mentioned, by means of a vibratile hairy coat, a vibrating whip, or -a covering of tremulous fringes, and only at a later period adhere to -objects. Even in the case of many higher plants, which we designate as -creepers and climbing plants, we may speak of active migration. Their -elongated stalks and perennial roots creep or climb during their long -process of growth to new positions, and by means of their widespread -branches they acquire new habitations, to which they attach themselves -by buds, and bring forth new colonies of individuals of their species. - -Influential as these active migrations of most animals and many plants -are, yet alone they would by no means be sufficient to explain the -chorology of organisms. _Passive migrations_ have ever been by far the -more important, and of far greater influence, in the case of most plants -and in that of many animals. Such passive changes of locality are -produced by extremely numerous causes. Air and water in their eternal -motion, wind and waves with their manifold currents, play the chief -part. The wind in all places and at all times raises light organisms, -small animals and plants, but especially their young germs, animal eggs -and plant seeds, and carries them far over land and seas. Where they -fall into the water they are seized by currents or waves and carried to -other places. It is well known, from numerous examples, how far in many -cases trunks of trees, hard shelled fruits, and other not readily -perishable portions of plants are carried away from their original home -by the course of rivers and by the currents of the sea. Trunks of palm -trees from the West Indies are brought by the Gulf Stream to the British -and Norwegian coasts. All large rivers bring down driftwood from the -mountains, and frequently alpine plants are carried from their home at -the source of the river into the plains, and even further, down to the -sea. Frequently numerous inhabitants live between the roots of the -plants thus carried down, and between the branches of the trees thus -washed away there are various inhabitants which have to take part in the -passive migration. The bark of the tree is covered with mosses, lichens, -and parasitic insects. Other insects, spiders, etc., even small -reptiles and mammals, are hidden within the hollow trunk or cling to the -branches. In the earth adhering to the fibres of the roots, in the dust -lying in the cracks of the bark, there are innumerable germs of smaller -animals and plants. Now, if the trunk thus washed away lands safely on a -foreign shore or on a distant island, the guests who had to take part in -the involuntary voyage can leave their boat and settle in the new -country. A very remarkable kind of water-transport is formed by the -floating icebergs which annually become loosened from the eternal ice of -the Polar Sea. Although these cold regions are thinly peopled, yet many -of their inhabitants, who were accidentally upon an iceberg while it was -becoming loosened, are carried away with it by the currents, and landed -on warmer shores. In this manner, by means of loosened blocks of ice -from the northern Polar Sea, often whole populations of small animals -and plants have been carried to the northern shores of Europe and -America. Nay, even polar foxes and polar bears have been carried in this -way to Iceland and to the British Isles. - -Transport by air is no less important than transport by water in this -matter of passive migration. The dust covering our streets and roofs, -the earth lying on dry fields and dried-up pools, the light moist soil -of forests, in short, the whole surface of the globe contains millions -of small organisms and their germs. Many of these small animals and -plants can without injury become completely dried up, and awake again to -life as soon as they are moistened. Every gust of wind raises up with -the dust innumerable little creatures of this kind, and often carries -them away to other places miles off. But even larger organisms, and -especially their germs, may often make distant passive journeys through -the air. The seeds of many plants are provided with light feathery -processes, which act as parachutes and facilitate their flight in the -air, and prevent their falling. Spiders make journeys of many miles -through the air on their fine filaments, their so-called gossamer -threads. Young frogs are frequently raised by whirlwinds into the air by -thousands, and fall down in a distant part as a "shower of frogs." -Storms may carry birds and insects across half the earth's -circumference. They drop in the United States, having risen in England. -Starting from California, they only come to rest in China. But, again, -many other organisms may make the journey from one continent to another -together with the birds and insects. Of course all parasites, the number -of which is legion, fleas, lice, mites, moulds, etc., migrate with the -organisms upon which they live. In the earth which often remains -sticking to the claws of birds there are also small animals and plants -or their germs. Thus the voluntary or involuntary migration of a single -larger organism may carry a whole small flora and fauna from one part of -the earth to another. - -Besides the means of transport here mentioned, there are many others -which explain the distribution of animal and vegetable species over the -large tracts of the earth's surface, and especially the general -distribution of the so-called cosmopolitan species. But these alone -would not nearly be sufficient to explain all chorological facts. How is -it, for example, that many inhabitants of fresh water live in various -rivers or lakes far away and quite apart from one another? How is it -that many inhabitants of mountains, which cannot exist in plains, are -found upon entirely separated and far distant chains of mountains? It -is difficult to believe, and in many cases quite inconceivable, that -these inhabitants of fresh water should have in any way, actively or -passively, migrated over the land lying between the lakes, or that the -inhabitants of mountains in any way, actively or passively, crossed the -plains lying between their mountain homes. But here geology comes to our -help, as a mighty ally, and completely solves these difficult problems -for us. - -The history of the earth's development shows us that the distribution of -land and water on its surface is ever and continually changing. In -consequence of geological changes of the earth's crust, _elevations_ and -_depressions_ of the ground take place everywhere, sometimes more -strongly marked in one place, sometimes in another. Even if they happen -so slowly that in the course of centuries the seashore rises or sinks -only a few inches, or even only a few lines, still they nevertheless -effect great results in the course of long periods of time. And -long--immeasurably long--periods of time have not been wanting in the -earth's history. During the course of many millions of years, ever since -organic life existed on the earth, land and water have perpetually -struggled for supremacy. Continents and islands have sunk into the sea, -and new ones have arisen out of its bosom. Lakes and seas have slowly -been raised and dried up, and new water basins have arisen by the -sinking of the ground. Peninsulas have become islands by the narrow neck -of land which connected them with the mainland sinking into the water. -The islands of an archipelago have become the peaks of a continuous -chain of mountains by the whole floor of their sea being considerably -raised. - -Thus the Mediterranean at one time was an inland sea, when, in the place -of the Straits of Gibraltar, an isthmus connected Africa with Spain. -England, even during the more recent history of the earth, when man -already existed, has repeatedly been connected with the European -continent and been repeatedly separated from it. Nay, even Europe and -North America have been directly connected. The South Sea at one time -formed a large Pacific Continent, and the numerous little islands which -now lie scattered in it were simply the highest peaks of the mountains -covering that continent. The Indian Ocean formed a continent which -extended from the Sunda Islands along the southern coast of Asia to the -east coast of Africa. This large continent of former times Sclater, an -Englishman, has called _Lemuria_, from the monkey-like animals which -inhabited it, and it is at the same time of great importance from being -the probable cradle of the human race, which in all likelihood here -first developed out of anthropoid apes. The important proof which Alfred -Wallace has furnished,(36) by the help of chorological facts, that the -present Malayan Archipelago consists in reality of two completely -different divisions, is particularly interesting. The western division, -the Indo-Malayan Archipelago, comprising the large islands of Borneo, -Java, and Sumatra, was formerly connected by Malacca with the Asiatic -continent, and probably also with the Lemurian continent just mentioned. -The eastern division, on the other hand, the Austro-Malayan Archipelago, -comprising Celebes, the Moluccas, New Guinea, Solomon's Islands, etc., -was formerly directly connected with Australia. Both divisions were -formerly two continents separated by a strait, but they have now for -the most part sunk below the level of the sea. Wallace, solely on the -ground of his accurate chorological observations, has been able in the -most acute manner to determine the position of this former strait, the -south end of which passes between Balij and Lombok. - -Thus, ever since liquid water existed on the earth, the boundaries of -water and land have eternally changed, and we may assert that the -outlines of continents and islands have never remained for an hour, nay, -even for a minute, exactly the same. For the waves eternally and -perpetually break on the edge of the coast, and whatever the land in -these places loses in extent, it gains in other places by the -accumulation of mud, which condenses into solid stone and again rises -above the level of the sea as new land. Nothing can be more erroneous -than the idea of a firm and unchangeable outline of our continents, such -as is impressed upon us in early youth by defective lessons on -geography, which are devoid of a geological basis. - -I need hardly draw attention to the fact that these geological changes -of the earth's surface have ever been exceedingly important to the -migrations of organisms, and consequently to their Chorology. From them -we learn to understand how it is that the same or nearly related species -of animals and plants can occur on different islands, although they -could not have passed through the water separating them, and how other -species living in fresh water can inhabit different enclosed -water-basins, although they could not have crossed the land lying -between them. These islands were formerly mountain peaks of a connected -continent, and these lakes were once directly connected with one -another. The former were separated by geological depressions, the latter -by elevations. Now, if we further consider how often and how unequally -these alternating elevations and depressions occur on the different -parts of the earth, and how, in consequence of this, the boundaries of -the geographical tracts of distribution of species become changed, and -if we further consider in what exceedingly various ways the active and -passive migrations of organisms must have been influenced by them, then -we shall be in a position to completely understand the great variety of -the picture which is at present offered to us by the distribution of -animal and vegetable species. - -There is yet another important circumstance to be mentioned here, which -is likewise of great importance for a complete explanation of this -varied geographical picture, and which throws light upon many very -obscure facts, which, without its help, we should not be able to -comprehend. I mean the gradual _change of climate_ which has taken place -during the long course of the organic history of the earth. As we saw in -our last chapter, at the beginning of organic life on the earth a much -higher and more equal temperature must have generally prevailed than at -present. The differences of zones, which in our time are so very -striking, did not exist at all in those times. It is probable that for -many millions of years but one climate prevailed over the whole earth, -which very closely resembled, or even surpassed, the hottest tropical -climate of the present day. The highest north which man has yet reached -was then covered with palms and other tropical plants, the fossil -remains of which are still found there. The temperature of this climate -at a later period gradually decreased; but still the poles remained so -warm that the whole surface of the earth could be inhabited by -organisms. It was only at a comparatively very recent period of the -earth's history, namely, at the beginning of the tertiary period, that -there occurred, as it seems, the first perceptible cooling of the -earth's crust at the poles, and through this the first differentiation -or separation of the different zones of temperature or climatic zones. -But the slow and gradual decrease of temperature continued to extend -more and more within the tertiary period, until at last, at both poles -of the earth, the first permanent ice caps were formed. - -I need scarcely point out in detail how very much this change of climate -must have affected the geographical distribution of organisms, and the -origin of numerous new species. The animal and vegetable species, which, -down to the tertiary period, had found an agreeable tropical climate all -over the earth, even as far as the poles, were now forced either to -adapt themselves to the intruding cold, or to flee from it. Those -species which adapted and accustomed themselves to the decreasing -temperature became new species simply by this very acclimatization, -under the influence of natural selection. The other species, which fled -from the cold, had to emigrate and seek a milder climate in lower -latitudes. The tracts of distribution which had hitherto existed must by -this have been vastly changed. - -However, during the last great period of the earth's history, during the -quaternary period (or diluvial period) succeeding the tertiary one, the -decrease of the heat of the earth from the poles did not by any means -remain stationary. The temperature fell lower and lower, nay, even far -below the present degree. Northern and Central Asia, Europe, and North -America from the north pole, were covered to a great extent by a -connected sheet of ice, which in our part of the earth seems to have -reached the Alps. In a similar manner the cold also advancing from the -south pole covered a large portion of the southern hemisphere, which is -now free from it, with a rigid sheet of ice. Thus, between these vast -lifeless ice continents there remained only a narrow zone to which the -life of the organic world had to withdraw. This period, during which -man, or at least the human ape, already existed, and which forms the -first period of the so-called _diluvial epoch_, is now universally known -as the _ice_ or _glacial period_. - -The ingenious Carl Schimper is the first naturalist who clearly -conceived the idea of the ice period, and proved the great extent of the -former glaciation of Central Europe by the help of the so-called -boulders, or erratic blocks of stone, as also by the "glacier tables." -Louis Agassiz, stimulated by him, and considerably supported by the -independent investigations of the eminent geologist Charpentier, -afterwards undertook the task of carrying out the theory of the ice -period. In England, the geologist Forbes distinguished himself in this -matter, and also was the first to apply it to the theory of migrations -and the geographical distribution of species dependent upon migration. -Agassiz, however, afterwards injured the theory by his one-sided -exaggeration, inasmuch as, from his partiality to Cuvier's theory of -cataclysms, he endeavoured to attribute the destruction of the whole -animate creation then existing, to the sudden coming on of the cold of -the ice period and the "revolution" connected with it. - -It is unnecessary here to enter into detail as to the ice period itself, -and into investigations about its limits, and I may omit this all the -more reasonably since the whole of our recent geological literature is -full of it. It will be found discussed in detail in the works of -Cotta,(31) Lyell,(30) Vogt,(27) Zittel,(32) etc. Its great importance to -us here is that it helps us to explain the most difficult chorological -problems, as Darwin has correctly perceived. - -For there can be no doubt that this glaciation of the present temperate -zones must have exercised an exceedingly important influence on the -geographical and topographical distribution of organisms, and that it -must have entirely changed it. While the cold slowly advanced from the -poles towards the equator, and covered land and sea with a connected -sheet of ice, it must of course have driven the whole living world -before it. Animals and plants had to migrate if they wished to escape -being frozen. But as at that time the temperate and tropical zones were -probably no less densely peopled with animals and plants than at -present, there must have arisen a fearful struggle for life between the -latter and the intruders coming from the poles. During this struggle, -which certainly lasted many thousands of years, many species must have -perished and many become modified and been transformed into new species. -The hitherto existing tracts of distribution of species must have become -completely changed, and the struggle have been continued, nay, indeed, -must have broken out anew and been carried on in new forms, when the ice -period had reached and gone beyond its furthest point, and when in the -post-glacial period the temperature again increased, and organisms began -to migrate back again towards the poles. - -In any case this great change of climate, whether a greater or less -importance be ascribed to it, is one of those occurrences in the history -of the earth which have most powerfully influenced the distribution of -organic forms. But more especially one important and difficult -chorological circumstance is explained by it in the simplest manner, -namely, the specific agreement of many of our Alpine inhabitants with -some of those living in polar regions. There is a great number of -remarkable animal and vegetable forms which are common to these two far -distant parts of the earth, and which are found nowhere in the wide -plains lying between them. Their migration from the polar lands to the -Alpine heights, or _vice versa_, would be inconceivable under the -present climatic circumstances, or could be assumed at least only in a -few rare instances. But such a migration could take place, nay, was -obliged to take place, during the gradual advance and retreat of the -ice-sheet. As the glaciation encroached from Northern Europe towards our -Alpine chains, the polar inhabitants retreating before it--gentian, -saxifrage, polar foxes, and polar hares--must have peopled Germany, in -fact all Central Europe. When the temperature again increased, only a -portion of these Arctic inhabitants returned with the retreating ice to -the Arctic zones. Another portion of them climbed up the mountains of -the Alpine chain instead, and there found the cold climate suited to -them. The problem is thus solved in a most simple manner. - -We have hitherto principally considered the _theory of the migrations_ -of organisms in so far as it explains the radiation of every animal and -vegetable species from a single primæval home, from a "central point of -creation," and the dispersion of these species over a greater or less -portion of the earth's surface. But these migrations are also of great -importance to the theory of development, because we can perceive in them -a very important means for the _origin of new species_. When animals and -plants migrate they meet in their new home, in the same way as do human -emigrants, with conditions which are more or less different from those -which they have inherited throughout generations, and to which they have -been accustomed. The emigrants must either submit and adapt themselves -to these new conditions of life or they perish. By adaptation their -peculiar specific character becomes the more changed the greater the -difference between the new and the old home. The new climate, the new -food, but above all, new neighbours in the forms of other animals and -plants, influence and tend to modify the inherited character of the -immigrant species, and if it is not hardy enough to resist the -influences, then sooner or later a new species must arise out of it. In -most cases this transformation of an immigrant species takes place so -quickly under the influence of the altered struggle for life, that even -after a few generations a new species arises from it. - -Migration has an especial influence in this way on all organisms with -separate sexes. For in them the origin of new species by natural -selection is always rendered difficult, or delayed, by the fact that the -modified descendants occasionally again mix sexually with the unchanged -original form, and thus by crossing return to the first form. But if -such varieties have migrated, if great distances or barriers to -migration--seas, mountains, etc.--have separated them from the old home, -then the danger of a mingling with the primary form is prevented, and -the isolation of the emigrant form, which becomes a new species by -adaptation, prevents its breeding with the old stock, and hence prevents -its return in this way to the original form. - -The importance of migration for the isolation of newly-originating -species and the prevention of a speedy return to the primary form has -been especially pointed out by the philosophic traveller, Moritz Wagner, -of Munich. In a special treatise on "Darwin's Theory and the Law of the -Migration of Organisms,"(40) Wagner gives from his own rich experience a -great number of striking examples which confirm the theory of migration -set forth by Darwin in the eleventh and twelfth chapters of his book, -where he especially discusses the effect of the complete isolation of -emigrant organisms in the origin of new species. Wagner sets forth the -simple causes which have "locally bounded the form and founded its -typical difference," in the following three propositions:--1. The -greater the total amount of change in the hitherto existing conditions -of life which the emigrating individuals find on entering a new -territory, the more intensely must the innate variability of every -organism manifest itself. 2. The less this increased individual -variability of organisms is disturbed in the peaceful process of -reproduction by the mingling of numerous subsequent immigrants of the -same species, the more frequently will nature succeed, by -intensification and transmission of the new characteristics, in forming -a new variety or race, that is, a commencing species. 3. The more -advantageous the changes experienced by the individual organs are to the -variety, the more readily will it be able to adapt itself to the -surrounding conditions; and the longer the undisturbed breeding of a -commencing variety of colonists in a new territory continues without its -mingling with subsequent immigrants of the same species, the oftener a -new species will arise out of the variety. - -Every one will agree with these three propositions of Moritz Wagner's. -But we must consider his view, that the migration and the subsequent -isolation of the emigrant individuals is a _necessary_ condition for the -origin of new species, to be completely erroneous. Wagner says, "without -a long-enduring separation of colonists from their former species, the -formation of a new race cannot succeed--selection, in fact, cannot take -place. Unlimited crossing, unhindered sexual mingling of all individuals -of a species will always produce uniformity, and drive varieties, whose -characteristics have not been fixed throughout a series of generations, -back to the primary form." - -This sentence, in which Wagner himself comprises the main result of his -investigations, he would be able to defend only if all organisms were of -separate sexes, if every origin of new individuals were possible only by -the mingling of male and female individuals. But this is by no means the -case. Curiously enough, Wagner says nothing of the numerous -hermaphrodites which, possessing both the sexual organs, are capable of -self-fructification, and likewise nothing of the countless organisms -which are not sexually differentiated. - -Now, from the earliest times of the organic history of the earth, there -have existed thousands of organic species (thousands of which still -exist) in which no difference of sex whatever exists, and, in fact, in -which no sexual propagation takes place, and which exclusively reproduce -themselves in a non-sexual manner by division, budding, formation of -spores, etc. All the great mass of Protista, the Monera, Amoebæ, -Myxomycetes, Rhizopoda, etc., in short, all the lower organisms which we -shall have to enumerate in the domain of Protista, standing midway -between the animal and vegetable kingdoms, propagate themselves -_exclusively in a non-sexual manner_. And this domain comprises a class -of organisms which is one of the richest in forms, nay, even in a -certain respect the richest of all in forms, as all possible geometrical -fundamental forms are represented in it. I allude to the wonderful class -of the Rhizopoda, or Ray-streamers, to which the lime-shelled Acyttaria -and the flint-shelled Radiolaria belong. (Compare chapter xvi.) - -It is self-evident, therefore, that Wagner's theory is quite -inapplicable to all these non-sexual organisms. Moreover, the same -applies to all those hermaphrodites in which every individual possesses -both male and female organs and is capable of self-fructification. This -is the case, for instance, in the Flat-worms, flukes, and tape-worms, -further in the important Sack-worms (Tunicates), the invertebrate -relatives of the vertebrate animals, and in very many other organisms of -different groups. Many of these species have arisen by natural -selection, without a "crossing" of the originating species with its -primary form having been possible. - -As I have already shown in the eighth chapter, the origin of the two -sexes, and consequently sexual propagation in general, must be -considered as a process which began only in later periods of the organic -history of the earth, being the result of differentiation or _division -of labour_. The most ancient terrestrial organisms can have propagated -themselves only in the simplest non-sexual manner. Even now all -Protista, as well as all the countless forms of cells, which constitute -the body of higher organisms, multiply themselves only by non-sexual -generation. And yet there arise here "new species" by differentiation in -consequence of natural selection. - -But even if we were to take into consideration the animal and vegetable -species with separate sexes, in this case too we should have to oppose -Wagner's chief proposition, that "the _migration_ of organisms and their -formation of colonies is the _necessary condition of natural -selection_." August Weismann, in his treatise on the "Influence of -Isolation upon the Formation of Species,"(24) has already sufficiently -refuted that proposition, and has shown that even in one and the same -district one bi-sexual species may divide itself into several species by -natural selection. In relation to this question, I must again call to -mind the great influence which _division of labour, or differentiation_, -possesses, being one of the necessary results of natural selection. All -the different kinds of cells constituting the body of the higher -organisms, the nerve cells, muscle cells, gland cells, etc., all these -"good species," these "bonæ species" of elementary organisms, have -arisen solely by division of labour, in consequence of natural -selection, although they not only never were locally isolated, but ever -since their origin have always existed in the closest local relations -one with another. Now, the same reasoning that applies to these -elementary organisms, or "individuals of the first order," applies also -to the many-celled organisms of a higher order which only at a later -date have arisen as "good species" from among their fellows. - -We are therefore of the same opinion as Darwin and Wallace, that the -migration of organisms and their isolation in their new home is a very -advantageous condition for the origin of new species; but we cannot -admit, as Wagner asserts, that it is a _necessary_ condition, and that -without it no species can arise. Wagner sets up this opinion, "that -migration is a necessary condition for natural selection," as a special -"_law of migration_"; but we consider it sufficiently refuted by the -above-mentioned facts. We have, moreover, already pointed out that in -reality the origin of new species by natural selection is a -_mathematical and logical necessity_ which, without anything else, -follows from the simple combination of three great facts. These three -fundamental facts are--the Struggle for Life, the Adaptability, and the -Hereditivity of organisms. - -We cannot here enter into detail concerning the numerous interesting -phenomena furnished by the geographical and topographical distribution -of organic species, which are all wonderfully explained by the theory of -selection and migration. For these I refer to the writings of Darwin,(1) -Wallace,(36) and Moritz Wagner,(40) in which the important doctrine of -the _limits of distribution_--seas, rivers, and mountains--is -excellently discussed and illustrated by numerous examples. Only three -other phenomena must be mentioned here on account of their special -importance. First, the close relation of forms, that is, the striking -"family likeness" existing between the characteristic local forms of -every part of the globe, and their extinct fossil ancestors in the same -part of the globe; secondly, the no less striking "family likeness" -between the inhabitants of island groups and those of the neighbouring -continent from which the islands were peopled; lastly and thirdly, the -peculiar character presented in general by the flora and fauna of -islands taken as a whole. - -All these chorological facts given by Darwin, Wallace, and -Wagner--especially the remarkable phenomena of the limited local fauna -and flora, the relations of insular to continental inhabitants, the wide -distribution of the so-called "cosmopolitan species," the close -relationship of the local species of the present day with the extinct -species of the same limited territory, the demonstrable radiation of -every species from a single central point of creation--all these, and -all other phenomena furnished to us by the geographical and the -topographical distribution of organisms, are explained in a simple and -thorough manner by the theory of selection and migration, while without -it they are simply incomprehensible. Consequently, in the whole of this -series of phenomena we find a new and weighty proof of the truth of the -Theory of Descent. - - - [1] The world is perfect save where Man - Comes in with his strife. - - [2] Archebiosis (Bastian), Abiogenesis (Huxley). - - [3] Alle Glieder bilden sich aus nach ew'gen Gesetzen, - Und die seltenste Form bewahrt im Geheimniss das Urbild. - Also bestimmt die Gestalt die Lebensweise des Thieres. - Und die Weise zu leben, sie wirkt auf alle Gestalten - Mächtig zurück. So zeiget sich fest die geordnete Bildung, - Welche zum Wechsel sich neigt durch äusserlich wirkende Wesen. - - [4] "Einstweilen bis den Bau der Welt - Philosophie zusammenhält, - Erhält sich ihr Getriebe - Durch Hunger und durch Liebe." - - [5] "Allgemeine Naturgeschichte und Theorie des Himmels." - - [6] We must wait for fuller information on the subject of - Bathybius, at the hands of the naturalists of the _Challenger_ - expedition, before accepting it finally as a distinct - organism.--_Editor._ - - -END OF VOL. I. - - - - -WORKS OF PROFESSOR ERNST HAECKEL. - - - FREEDOM IN SCIENCE AND TEACHING. From the German of ERNST - HAECKEL. With a Prefatory Note by T. H. Huxley, F.R.S. 1 - vol., 12mo. - - THE EVOLUTION OF MAN. A Popular Exposition of the - Principal Points of Human Ontogeny and Phylogeny. From - the German of ERNST HAECKEL, Professor in the University - of Jena, author of "The History of Creation," etc. With - numerous Illustrations. In two vols., 12mo. Cloth. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The History of Creation, Vol. I (of 2) - Or the Development of the Earth and its Inhabitants by the - Action of Natural Causes - -Author: Ernst Haeckel - -Translator: E. Ray Lankester - -Release Date: August 14, 2012 [EBook #40472] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF CREATION, VOL I *** - - - - -Produced by Adrian Mastronardi, Turgut Dincer, Jason Palmer -and the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive) - - - - - - - - - - +------------------------------------------------------------------+ - | Transcriber's note: | - | | - | This book was published in two volumes, of which this is the | - | first. The second volume was released as Project Gutenberg ebook | - | #40473, available at http://www.gutenberg.org/ebooks/40473 | - | | - | Numbers enclosed in square brackets, e.g. [1], relate to | - | footnotes, which have been placed at the end of the text. | - | Numbers enclosed in parentheses, e.g. (1), relate to works | - | referred to in the text and listed at the end of volume II. | - | | - | In the text versions of these two volumes, words in _italics_ | - | are enclosed in underscores, +bold+ words are enclosed in plus | - | signs, and words in =Gothic script= are enclosed in equal signs. | - | Curly brackets are used to represent subscripts, e.g. k{1}. | - +------------------------------------------------------------------+ - - - - - THE HISTORY OF CREATION. - - - - -[Illustration: Development of a Calcareous Sponge (Olynthus).] - - - - - THE - HISTORY OF CREATION: - - _OR THE DEVELOPMENT OF THE EARTH AND ITS - INHABITANTS BY THE ACTION OF NATURAL CAUSES._ - - A POPULAR EXPOSITION OF - THE DOCTRINE OF EVOLUTION IN GENERAL, AND OF THAT OF - DARWIN, GOETHE, AND LAMARCK IN PARTICULAR. - - FROM THE GERMAN OF - ERNST HAECKEL, - PROFESSOR IN THE UNIVERSITY OF JENA. - - THE TRANSLATION REVISED BY - E. RAY LANKESTER, M.A., FELLOW OF EXETER COLLEGE, OXFORD. - - _IN TWO VOLUMES._ - VOL. I. - - NEW YORK: - D. APPLETON AND COMPANY, - 1, 3, AND 5 BOND STREET. - 1880. - - - - - A sense sublime - Of something far more deeply interfused, - Whose dwelling is the light of setting suns, - And the round ocean, and the living air, - And the blue sky, and in the mind of man; - A motion and a spirit that impels - All thinking things, all objects of all thought, - And rolls through all things. - - In all things, in all natures, in the stars - Of azure heaven, the unenduring clouds, - In flower and tree, in every pebbly stone - That paves the brooks, the stationary rocks, - The moving waters and the invisible air. - - WORDSWORTH. - - - - -CONTENTS OF VOL. I. - - - CHAPTER I. - - NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION, - OR DESCENT-THEORY. - PAGE - General Importance and Essential Nature of the Theory of - Descent as reformed by Darwin.--Its Special Importance to - Biology (Zoology and Botany).--Its Special Importance to - the History of the Natural Development of the Human - Race.--The Theory of Descent as the Non-Miraculous History - of Creation.--Idea of Creation.--Knowledge and - Belief.--History of Creation and History of - Development.--The Connection between the History of - Individual and Palaeontological Development.--The Theory of - Purposelessness, or the Science of Rudimentary - Organs.--Useless and Superfluous Arrangements in - Organisms.--Contrast between the two entirely Opposed - Views of Nature: the Monistic (mechanical, causal) and the - Dualistic (teleological, vital).--Proof of the former by - the Theory of Descent.--Unity of Organic and Inorganic - Nature, and the Identity of the Active Causes in - both.--The Importance of the Theory of Descent to the - Monistic Conception of all Nature 1 - - - CHAPTER II. - - SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT. - HISTORY OF CREATION ACCORDING TO LINNAEUS. - - The Theory of Descent, or Doctrine of Filiation, as the - Monistic Explanation of Organic Natural Phenomena.--Its - Comparison with Newton's Theory of Gravitation.--Limits of - Scientific Explanation and of Human Knowledge in - general.--All Knowledge founded originally on Sensuous - Experience, _a posteriori_.--Transition of _a posteriori_ - knowledge, by inheritance, into _a priori_ - knowledge.--Contrast between the Supernatural Hypotheses - of the Creation according to Linnaeus, Cuvier, Agassiz, - and the Natural Theories of Development according to - Lamarck, Goethe, and Darwin.--Connection of the former - with the Monistic (mechanical), of the latter with the - Dualistic Conception of the Universe.--Monism and - Materialism.--Scientific and Moral Materialism.--The - History of Creation according to Moses.--Linnaeus as the - Founder of the Systematic Description of Nature and - Distinction of Species.--Linnaeus' Classification and - Binary Nomenclature.--Meaning of Linnaeus' Idea of - Species.--His History of Creation.--Linnaeus' view of the - Origin of Species 24 - - - CHAPTER III. - - THE HISTORY OF CREATION ACCORDING TO CUVIER - AND AGASSIZ. - - General Theoretical Meaning of the Idea of - Species.--Distinction between the Theoretical and - Practical Definition of the Idea of Species.--Cuvier's - Definition of Species.--Merits of Cuvier as the Founder of - Comparative Anatomy.--Distinction of the Four Principal - Forms (types or branches) of the Animal Kingdom, by Cuvier - and Baer.--Cuvier's Services to Palaeontology.--His - Hypothesis of the Revolutions of our Globe, and the Epochs - of Creation separated by them.--Unknown Supernatural - Causes of the Revolutions, and the subsequent New - Creations.--Agassiz's Teleological System of Nature.--His - Conception of the Plan of Creation, and its six Categories - (groups in classification).--Agassiz's Views of the - Creation of Species.--Rude Conception of the Creator as a - man-like being in Agassiz's Hypothesis of Creation.--Its - internal Inconsistency and Contradictions with the - important Palaeontological Laws discovered by Agassiz 47 - - - CHAPTER IV. - - THEORY OF DEVELOPMENT ACCORDING TO GOETHE - AND OKEN. - - Scientific Insufficiency of all Conceptions of a Creation - of Individual Species.--Necessity of the Counter Theories - of Development.--Historical Survey of the most Important - Theories of Development.--Aristotle.--His Doctrine of - Spontaneous Generation.--The Meaning of - Nature-philosophy.--Goethe.--His Merits as a - Naturalist.--His Metamorphosis of Plants.--His Vertebral - Theory of the Skull.--His Discovery of the Mid Jawbone in - Man.--Goethe's Interest in the Dispute between Cuvier and - Geoffroy St. Hilaire.--Goethe's Discovery of the two - Organic Formative Principles, of the Conservative - Principle of Specification (by Inheritance), and of the - Progressive Principle of Transformation (by - Adaptation).--Goethe's Views of the Common Descent of all - Vertebrate Animals, including Man.--Theory of Development - according to Gottfried Reinhold Treviranus.--His Monistic - Conception of Nature.--Oken.--His - Nature-philosophy.--Oken's Theory of Protoplasm.--Oken's - Theory of Infusoria (Cell Theory).--Oken's Theory of - Development 72 - - - CHAPTER V. - - THEORY OF DEVELOPMENT ACCORDING TO KANT AND - LAMARCK. - - Kant's Dualistic Biology.--His Conception of the Origin of - Inorganic Nature by Mechanical Causes, of Organic Nature - by Causes acting for a Definite Purpose.--Contradiction of - this Conception with his leaning towards the Theory of - Descent.--Kant's Genealogical Theory of Development.--Its - Limitation by his Teleology.--Comparison of Genealogical - Biology with Comparative Philology.--Views in favour of - the Theory of Descent entertained by Leopold Buch, Baer, - Schleiden, Unger, Schaafhausen, Victor Carus, - Buechner.--French Nature-philosophy.--Lamarck's Philosophic - Zoologique.--Lamarck's Monistic (mechanical) System of - Nature.--His Views of the Interaction of the two Organic - Formative Tendencies of Inheritance and - Adaptation.--Lamarck's Conception of Man's Development - from Ape-like Mammals.--Geoffroy St. Hilaire's, Naudin's, - and Lecoq's Defence of the Theory of Descent.--English - Nature-philosophy.--Views in favour of the Theory of - Descent entertained by Erasmus Darwin, W. Herbert, Grant, - Freke, Herbert Spencer, Hooker, Huxley.--The Double Merit - of Charles Darwin 100 - - - CHAPTER VI. - - THEORY OF DEVELOPMENT ACCORDING TO LYELL - AND DARWIN. - - Charles Lyell's Principles of Geology.--His Natural - History of the Earth's Development.--Origin of the - Greatest Effects through the Multiplication of the - Smallest Causes.--Unlimited Extent of Geological - Periods.--Lyell's Refutation of Cuvier's History of - Creation.--The Establishment of the Uninterrupted - Connection of Historical Development by Lyell and - Darwin.--Biographical Notice of Charles Darwin.--His - Scientific Works.--His Theory of Coral - Reefs.--Development of the Theory of Selection.--A Letter - of Darwin's.--The Contemporaneous Appearance of Darwin's - and Alfred Wallace's Theory of Selection.--Darwin's Study - of Domestic Animals and Cultivated Plants.--Andreas - Wagner's Notions as to the Special Creation of Cultivated - Organisms for the good of Man.--The Tree of Knowledge in - Paradise.--Comparison between Wild and Cultivated - Organisms.--Darwin's Study of Domestic - Pigeons.--Importance of Pigeon Breeding.--Common Descent - of all Races of Pigeons 125 - - - CHAPTER VII. - - THE THEORY OF SELECTION (DARWINISM). - - Darwinism (Theory of Selection) and Lamarckism (Theory of - Descent).--The Process of Artificial Breeding.--Selection - of the Different Individuals for After-breeding.--The - Active Causes of Transmutation.--Change connected with - Food and Transmission by Inheritance connected with - Propagation.--Mechanical Nature of these Two Physiological - Functions.--The Process of Natural Breeding: Selection in - the Struggle for Existence.--Malthus' Theory of - Population.--The Proportion between the Numbers of - Potential and Actual Individuals of every Species of - Organisms.--General Struggle for Existence, or Competition - to attain the Necessaries of Life.--Transforming Force of - the Struggle for Existence.--Comparison of Natural and - Artificial Breeding.--Selection in the Life of - Man.--Military and Medical Selection 149 - - - CHAPTER VIII. - - TRANSMISSION BY INHERITANCE AND PROPAGATION. - - Universality of Inheritance and Transmission by - Inheritance.--Special Evidences of the same.--Human Beings - with four, six, or seven Fingers and Toes.--Porcupine - Men.--Transmission of Diseases, especially Diseases of the - Mind.--Original Sin.--Hereditary Monarchies.--Hereditary - Aristocracy.--Hereditary Talents and Mental - Qualities.--Material Causes of Transmission by - Inheritance.--Connection between Transmission by - Inheritance and Propagation.--Spontaneous Generation and - Propagation.--Non-sexual or Monogonous - Propagation.--Propagation by Self-Division.--Monera and - Amoeba.--Propagation by the formation of Buds, by the - formation of Germ-Buds, by the formation of - Germ-Cells.--Sexual or Amphigonous Propagation.--Formation - of Hermaphrodites.--Distinction of Sexes, or - Gonochorism.--Virginal Breeding, or - Parthenogenesis.--Material Transmission of Peculiarities - of both Parents to the Child by Sexual - Propagation.--Difference between Transmission by - Inheritance in Sexual and in Asexual Propagation 175 - - - CHAPTER IX. - - LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND - NUTRITION. - - Distinction between Conservative and Progressive - Transmission by Inheritance.--Laws of Conservative - Transmission: Transmission of Inherited - Characters.--Uninterrupted or Continuous - Transmission.--Interrupted or Latent - Transmission.--Alternation of - Generations.--Relapse.--Degeneracy.--Sexual - Transmission.--Secondary Sexual Characters.--Mixed or - Amphigonous Transmission.--Hybrids.--Abridged or - Simplified Transmission.--Laws of Progressive Inheritance: - Transmission of Acquired Characters.--Adapted or Acquired - Transmission.--Fixed or Established - Transmission.--Homochronous Transmission (Identity in - Epoch).--Homotopic Transmission (Identity in - Part).--Adaptation and Mutability.--Connection between - Adaptation and Nutrition.--Distinction between Indirect - and Direct Adaptation 203 - - - CHAPTER X. - - LAWS OF ADAPTATION. - - Laws of Indirect or Potential Adaptation.--Individual - Adaptation.--Monstrous or Sudden Adaptation.--Sexual - Adaptation.--Laws of Direct or Actual - Adaptation.--Universal Adaptation.--Cumulative - Adaptation.--Cumulative Influence of External Conditions - of Existence and Cumulative Counter-Influence of the - Organism.--Free Will.--Use and Non-use of - Organs.--Practice and Habit.--Correlative - Adaptation.--Correlation of Development.--Correlation of - Organs.--Explanation of Indirect or Potential Adaptation - by the Correlation of the Sexual Organs and of the other - parts of the Body.--Divergent Adaptation.--Unlimited or - Infinite Adaptation 227 - - - CHAPTER XI. - - NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION - OF LABOUR AND PROGRESS. - - Interaction of the two Organic Formative Causes, - Inheritance and Adaptation.--Natural and Artificial - Selection.--Struggle for Existence, or Competition for the - Necessaries of Life.--Disproportion between the Number of - Possible or Potential, and the Number of Real or Actual - Individuals.--Complicated Correlations of all Neighbouring - Organisms.--Mode of Action in Natural - Selection.--Homochromic Selection as the Cause of - Sympathetic Colourings.--Sexual Selection as the Cause of - the Secondary Sexual Characters.--Law of Separation or - Division of Labour (Polymorphism, Differentiation, - Divergence of Characters).--Transition of Varieties into - Species.--Idea of Species.--Hybridism.--Law of Progress or - Perfecting (Progresses, Teleosis) 252 - - - CHAPTER XII. - - LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS. - PHYLOGENY AND ONTOGENY. - - Laws of the Development of Mankind: Differentiation and - Perfecting.--Mechanical Cause of these two Fundamental - Laws.--Progress without Differentiation, and - Differentiation without Progress.--Origin of Rudimentary - Organs by Non-use and Discontinuance of - Habit.--Ontogenesis, or Individual Development of - Organisms.--Its General Importance.--Ontogeny, or the - Individual History of Development of Vertebrate Animals, - including Man.--The Fructification of the Egg.--Formation - of the Three Germ Layers.--History of the Development of - the Central Nervous System, of the Extremities, of the - Branchial Arches, and of the Tail of Vertebrate - Animals.--Causal Connection and Parallelism of Ontogenesis - and Phylogenesis, that is, of the Development of - Individuals and Tribes.--Causal Connection of the - Parallelism of Phylogenesis and of Systematic - Development.--Parallelism of the three Organic Series of - Development 280 - - - CHAPTER XIII. - - THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE - EARTH. SPONTANEOUS GENERATION. THE CARBON THEORY. THE - PLASTID THEORY. - - History of the Development of the Earth.--Kant's Theory of - the Development of the Universe, or the Cosmological Gas - Theory.--Development of Suns, Planets, and Moons.--First - Origin of Water.--Comparison of Organisms and - Anorgana.--Organic and Inorganic Substances.--Degrees of - Density, or Conditions of Aggregation.--Albuminous - Combinations of Carbon.--Organic and Inorganic - Forms.--Crystals and Formless Organisms without - Organs.Stereometrical Fundamental Forms of Crystals and - of Organisms.--Organic and Inorganic Forces.--Vital - Force.--Growth and Adaptation in Crystals and in - Organisms.--Formative Tendencies of Crystals.--Unity of - Organic and Inorganic Nature.--Spontaneous Generation, or - Archigony.--Autogony and Plasmogony.--Origin of Monera by - Spontaneous Generation.--Origin of Cells from Monera.--The - Cell Theory.--The Plastid Theory.--Plastids, or - Structural-Units.--Cytods and Cells.--Four Different Kinds - of Plastids 316 - - - CHAPTER XIV. - - MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE - ICE-PERIOD OF THE EARTH. - - Chorological Facts and Causes.--Origin of most Species in - one Single Locality.--"Centres of Creation."--Distribution - by Migration.--Active and Passive Migrations of Animals - and Plants.--Means of Transport.--Transport of Germs by - Water and by Wind.--Continual Change of the Area of - Distribution by Elevations and Depressions of the - Ground.--Chorological Importance of Geological - Processes.--Influence of the Change of Climate.--Ice or - Glacial Period.--Its Importance to Chorology.--Importance - of Migrations for the Origin of New Species.--Isolation of - Colonists.--Wagner's Law of Migration.--Connection between - the Theory of Migration and the Theory of - Selection.--Agreement of its Results with the Theory of - Descent 350 - - - - -LIST OF ILLUSTRATIONS. - - - PLATES. - PAGE - - Development of a Calcareous Sponge (Olynthus) _Frontispiece_ - - I.--Life History of a Simplest Organism _To face page_ 184 - - II., III.--Germs or Embryos of Four Vertebrates " 306 - - - FIGURES. - - 1.--Propagation of Moneron 186 - - 2.--Propagation of Amoeba 188 - - 3.--Egg of Mammal 189 - - 4.--First Development of Mammal's Egg 190 - - 5.--The Human Egg Enlarged 297 - - 6.--Development of Mammal's Egg 299 - - 7.--Embryo of a Mammal or Bird 304 - - - - -AUTHOR'S PREFACE TO THE ENGLISH EDITION. - - -I am desirous of prefacing the English edition of the "History of -Creation" with a few remarks which may serve to explain the origin and -object of this book. In the year 1866 I published, under the title -"Generelle Morphologie," a somewhat comprehensive work, which -constituted the first attempt to apply the general doctrine of -development to the whole range of organic morphology (Anatomy and -Biogenesis), and thus to make use of the vast march onwards which the -genius of Charles Darwin has effected in all biological science by his -reform of the Descent Theory and its establishment through the doctrine -of selection. At the same time, in the "Generelle Morphologie," the -first attempt was made to introduce the Descent Theory into the -systematic classification of animals and plants, and to found a "natural -system" on the basis of genealogy; that is, to construct hypothetical -pedigrees for the various species of organisms. - -The "Generelle Morphologie" found but few readers, for which the -voluminous and unpopular style of treatment, and its too extensive Greek -terminology, may be chiefly to blame. But a proportionately large -measure of approval has met the "Natuerliche Schoepfungsgeschichte" in -Germany. This book took its origin in the shorthand notes of a course of -lectures which treated, before a mixed audience and in a popular form, -the most important topics discussed in the "Generelle Morphologie." The -notes were subsequently revised, and received considerable additions. -The book appeared first in 1868, its fourth edition in 1873, and has -been translated into several languages. I hope that it may also find -sympathy in the fatherland of Darwin, the more so since it contains -special morphological evidence in favour of many of the important -doctrines with which this greatest naturalist of our century has -enriched science. Proud as England may be to be called the fatherland of -Newton, who, with his law of gravitation, brought inorganic nature under -the dominion of natural laws of cause and effect, yet may she with even -greater pride reckon Charles Darwin among her sons--he who solved the -yet harder problem of bringing the complicated phenomena of organic -nature under the sway of the same natural laws. - -The reproach which is now oftenest made against the Descent Theory is -that it is not securely founded, not sufficiently proven. Not only its -distinct opponents maintain that there is a want of satisfactory proofs, -but even faint-hearted and wavering adherents declare that Darwin's -hypothesis is still wanting fundamental proof. Neither the former nor -the latter estimate rightly the immeasurable weight which the great -series of phenomena of comparative anatomy and ontogeny, palaeontology -and taxonomy, chorology and oecology, cast into the scale in favour of -the doctrine of filiation. Darwin's Theory of Selection, which -completely explains the origin of species through the combined action of -Inheritance and Adaptation in the struggle for existence, also appears -to these persons not sufficient. They demand, over and above, that the -descent of species from common ancestral forms shall be proved in a -particular case; that, in contradistinction to the _synthetic_ proofs -adduced for the Descent Theory, the _analytic_ proof of the genealogical -continuity of the several species shall be brought forward. - -This "analytical solution of the problem of the origin of species" I -have myself endeavoured to afford in my recently published "Monograph of -the Calcareous Sponges." For five consecutive years I have investigated -this small but highly instructive group of animals in all its forms in -the most careful manner, and I venture to maintain that the monograph, -which is the result of those studies, is the most complete and accurate -morphological analysis of an entire organic group which has up to this -time been made. Provided with the whole of the material for study as yet -brought together, and assisted by numerous contributions from all parts -of the world, I was able to work over the whole group of organic forms -known as the Calcareous Sponges in that greatest possible degree of -fulness which appeared indispensable for the proof of the common origin -of its species. This particular animal group is especially fitted for -the analytical solution of the species problem, because it presents -exceedingly simple conditions of organisation, because in it the -morphological conditions possess a greatly superior, and the -physiological conditions an inferior, import, and because all species of -Calcispongiae are remarkable for the fluidity and plasticity of their -form. With a view to these facts, I made two journeys to the sea-coast -(1869 to Norway, 1871 to Dalmatia), in order to study as large a number -of individuals as possible in their natural circumstances, and to -collect specimens for comparison. Of many species, I compared several -hundred individuals in the most careful way. I examined with the -microscope and measured in the most accurate manner the details of form -of all the species. As the final result of these exhaustive and almost -endless examinations and measurements it appeared that "good species," -in the ordinary dogmatic sense of the systematists, have no existence at -all among the Calcareous Sponges; that the most different forms are -connected one with another by numberless gradational transition forms; -and that all the different species of Calcareous Sponges are derived -from a single exceedingly simple ancestral form, the Olynthus. A drawing -of the Olynthus and its earliest stages of development (observe -especially the highly important Gastrula) is given in the frontispiece -of the present edition. Illustrations of the various structural details -which establish the derivation of all Calcareous Sponges from the -Olynthus, are given in the atlas of sixty plates which accompanies my -monograph of the group. In the gastrula, moreover, is now also found the -common ancestral form from which all the tribes of animals (the lowest -group, that of the protozoa, alone being excepted) can without -difficulty be derived. It is one of the most ancient and important -ancestors of the human race! - -If we take for the limitation of genus and species an average standard, -derived from the actual practice of systematists, and apply this to the -whole of the Calcareous Sponges at present known, we can distinguish -about twenty-one genera, with one hundred and eleven species (as I have -done in the second volume of the Monograph). I have, however, shown that -we may draw up, in addition to this, another systematic arrangement -(more nearly agreeing with the arrangement of the Calcispongiae hitherto -in vogue) which gives thirty-nine genera and two hundred and eighty-nine -species. A systematist who gives a more limited extension to the "ideal -species" might arrange the same series of forms in forty-three genera -and three hundred and eighty-one species, or even in one hundred and -thirteen genera and five hundred and ninety species; another systematist -on the other hand, who takes a wider limit for the "abstract species," -would use in arranging the same series of forms only three genera, with -twenty-one species, or might even satisfy himself with one genus and -seven species. The delimitation of species and genera appears to be so -arbitrary a matter, on account of endless varieties and transitional -forms in this group, that their number is entirely left to the -subjective taste of the individual systematist. In truth, from the point -of view of the theory of descent, it appears altogether an unimportant -question as to whether we give a wider or a narrower signification to -allied groups of forms--whether we choose, that is to say, to call them -genera or species, varieties or sub-species. The main fact remains -undeniable, viz., the common origin of all the species from one -ancestral form. The many-shaped Calcareous Sponges furnish, in the very -remarkable conditions of their varieties of aggregation (metrocormy), a -body of evidence in favour of this view which could hardly be more -convincing. Not unfrequently the case occurs of several different forms -growing out from a single "stock" or "cormus"--forms which until now -have been regarded by systematists, not only as belonging to different -species, but even to different genera. Fig. 10 in the frontispiece -represents such a composite stock. This solid and tangible piece of -evidence in favour of the common descent of different species ought, one -would think, to satisfy the most determined sceptic! - -In point of fact, I have a right to expect of my opponents that they -shall carefully consider the "exact empirical proof" here brought -forward for them, as they have so eagerly demanded. The opponents of the -doctrine of filiation, who have too little power of weighing evidence, -or possess too little knowledge to appreciate the overpowering weight of -proof afforded by the synthetical argument (comparative anatomy, -ontogeny, taxonomy, etc.), may yet be able to follow me along the path -of analytical proof, and attempt to upset the conclusion as to the -common origin of all species of all Calcareous Sponges which I have -given in my Monograph. I must, however, repeat that this conclusion is -based on the most minute investigation of an extraordinarily rich mass -of material,--that it is securely established by thousands of the most -careful microscopical observations, measurements, and comparisons of -every single part, and that thousands of collected microscopic -preparations render, at any moment, the most searching criticism of my -results confirmatory of their correctness. One may hope, then, that -opponents will endeavour to confront me on the ground of this "exact -empiricism," instead of trying to damn my "nature-philosophical -speculations." One may hope that they will endeavour to bring forward -some evidence to show that the latter do not follow as the legitimate -consequences of the former. May they, however, spare me the -empty--though by even respectable naturalists oft-repeated--phrase, that -the monistic nature-philosophy, as expounded in the "General -Morphology," and in the "History of Creation," is wanting in actual -proofs. The proofs are there. Of course those who turn their eyes away -from them will not see them. Precisely that "exact" form of analytical -proof which the opponents of the descent theory demand is to be found, -by anybody who wishes to find it, in the "Monograph of the Calcareous -Sponges." - - - ERNST HEINRICH HAECKEL. - - _Jena, June 24th, 1873._ - - - - -NOTE. - - -Feeling sure that such a book as Professor Haeckel's -"Schoepfungsgeschichte" would do a great deal of good, if placed in the -hands of the English reading public, and of commencing students of -Natural History, I gladly undertook to revise for the publishers the -present translation, which was made by a young lady. I have not -attempted to escape a difficulty by ignoring the German names made use -of by Professor Haeckel for classes, orders, and genera, but have -adopted English equivalents. I do not submit these names as a maturely -considered English nomenclature, they appear here simply as necessary -parts of a close rendering of the German work. I do, however, hold that -some such series of English terms is both possible and useful, and do -not doubt--in spite of the pretended hostility of the genius of our -language, and the curious sentimental objection that English names are -_unscientific_--that we shall before long make use of plain English in -speaking of the various groups of plants and animals--much to the gain -of the larger public, and without detriment to the latinized -nomenclature established for the purposes of the professional student. - - - E. R. L. - - _Oxford, October, 1874._ - - - - -THE HISTORY OF CREATION. - - - - -CHAPTER I. - -NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION, OR DESCENT-THEORY. - - - General Importance and Essential Nature of the Theory of - Descent as reformed by Darwin.--Its Special Importance to - Biology (Zoology and Botany).--Its Special Importance to - the History of the Natural Development of the Human - Race.--The Theory of Descent as the Non-Miraculous - History of Creation.--Idea of Creation.--Knowledge and - Belief.--History of Creation and History of - Development.--The Connection between the History of - Individual and Palaeontological Development.--The Theory - of Purposelessness, or the Science of Rudimentary - Organs.--Useless and Superfluous Arrangements in - Organisms.--Contrast between the two entirely opposed - Views of Nature: the Monistic (mechanical, causal) and - the Dualistic (teleological, vital).--Proof of the former - by the Theory of Descent.--Unity of Organic and Inorganic - Nature, and the Identity of the Active Causes in - both.--The Importance of the Theory of Descent to the - Monistic Conception of all Nature. - - -The intellectual movement to which the impulse was given, thirteen years -ago, by the English naturalist, Charles Darwin, in his celebrated work, -"On the Origin of Species,"(1) has, within this short period, assumed -dimensions which cannot but excite the most universal interest. It is -true the scientific theory set forth in that work, which is commonly -called briefly Darwinism, is only a small fragment of a far more -comprehensive doctrine--a part of the universal Theory of Development, -which embraces in its vast range the whole domain of human knowledge. - -But the manner in which Darwin has firmly established the latter by the -former is so convincing, and the direction which has been given by the -unavoidable conclusions of that theory to all our views of the universe, -must appear to every thinking man of such deep significance, that its -general importance cannot be over estimated. There is no doubt that this -immense extension of our intellectual horizon must be looked upon as by -far the most important, and rich in results, among all the numerous and -grand advances which natural science has made in our day. - -When our century, with justice, is called the age of natural science, -when we look with pride upon the immensely important progress made in -all its branches, we are generally in the habit of thinking more of -immediate practical results, and less of the extension of our general -knowledge of nature. We call to mind the complete reform, so infinitely -rich in consequences to human intercourse, which has been effected by -the development of machinery, by railways, steamships, telegraphs, and -other inventions of physics. Or we think of the enormous influence which -chemistry has brought to bear upon medicine, agriculture, and upon all -arts and trades. - -But much as we may value this influence of modern science upon practical -life, still it must, estimated from a higher and more general point of -view, stand most assuredly below the enormous influence which the -theoretical progress of modern science will have on the entire range of -human knowledge, on our conception of the universe, and on the -perfecting of man's culture. - -Think of the immense revolutions in all our theoretical views which we -owe to the general application of the microscope. Think of the cell -theory, which explains the apparent unity of the human organism as the -combined result of the union of a mass of elementary vital units. Or -consider the immense extension of our theoretical horizon which we owe -to spectral analysis and to the mechanical theory of heat. But among all -these wonderful theoretical advances, the theory wrought out by Darwin -occupies by far the highest rank. - -Every one of my readers has heard of the name of Darwin. But most -persons have probably only an imperfect idea of the real value of his -theory. If a reader estimates as of equal value all that has been -written upon Darwin's memorable work since its appearance, the value of -the theory will appear very doubtful to him, supposing that he has not -been engaged in the organic natural sciences, and has not penetrated -into the inner secrets of zoology and botany. The criticisms of it are -so full of contradictions, and for the most part so defective, that we -ought not to be at all astonished that even now, after the lapse of -thirteen years since the appearance of Darwin's work, it has not gained -half that importance which is justly due to it, and which sooner or -later it certainly will attain. - -Most of the innumerable writings which have been published during these -years, both for and against Darwinism, are the productions of persons -who are entirely wanting in the necessary amount of biological, and -especially of zoological, knowledge. Although almost all of the more -celebrated naturalists of the present day are adherents of the theory, -yet only a few of them have endeavoured to procure its acceptance and -recognition in larger circles. Hence the odd contradictions and the -strange opinions which may still be heard everywhere about Darwinism. -This is the reason which induces me to make Darwin's theory, and those -further doctrines which are connected with it, the subject of these -pages, which, I hope, will be generally intelligible. I hold it to be -the duty of naturalists, not merely to meditate upon improvements and -discoveries in the narrow circle to which their speciality confines -them, not merely to pore over their one study with love and care, but -also to seek to make the important general results of it fruitful to the -mass, and to assist in spreading the knowledge of physical science among -the people. The highest triumph of the human mind, the true knowledge of -the most general laws of nature, ought not to remain the private -possession of a privileged class of savans, but ought to become the -common property of all mankind. - -The theory which, through Darwin, has been placed at the head of all our -knowledge of nature, is usually called the Doctrine of Filiation, or the -Theory of Descent. Others term it the Transmutation Theory. Both -designations are correct. For this doctrine affirms, that _all -organisms_ (viz., all species of animals, all species of plants, which -have ever existed or still exist on the earth) _are derived from one -single, or from a few simple original forms, and that they have -developed themselves from these in the natural course of a gradual -change_. Although this theory of development had already been brought -forward and defended by several great naturalists, and especially by -Lamarck and Goethe, in the beginning of our century, still it was -through Darwin, thirteen years ago, that it received its complete -demonstration and causal foundation; and this is the reason why now it -is commonly and exclusively (though not quite correctly) designated as -_Darwin's Theory_. - -The great and really inestimable value of the Theory of Descent appears -in a different light, accordingly as we merely consider its more -immediate connection with organic natural science, or its larger -influence upon the whole range of man's knowledge of the universe. -Organic natural science, or Biology, which as Zoology treats of animals, -as Botany of plants, is completely reformed and founded anew by the -Theory of Descent. For by this theory we are made acquainted with the -active causes of organic forms, while up to the present time Zoology and -Botany have simply been occupied with the facts of these forms. We may -therefore also term the theory of descent a _mechanical explanation of -organic forms_, or the science of the true causes of Organic Nature. - -As I cannot take for granted that my readers are all familiar with the -terms "organic and inorganic nature," and as the contrast of both these -natural bodies will, in future, occupy much of our attention, I must say -a few words in explanation of them. We designate as _Organisms_, or -_Organic bodies_, all _living creatures_ or _animated bodies_; therefore -all plants and animals, man included; for in them we can almost always -prove a combination of various parts (instruments or organs) which work -together for the purpose of producing the phenomena of life. Such a -combination we do not find in _Anorgana_, or inorganic natural -bodies--the so-called dead or _inanimate bodies_, such as minerals or -stones, water, the atmospheric air, etc. Organisms always contain -albuminous combinations of carbon in a semi-fluid condition of -aggregation, which are always wanting in the Anorgana. Upon this -important distinction rests the division of all natural history into two -great and principal parts--_Biology_, or the science of Organisms -(Zoology and Botany), and _Anorganology_, or the science of Anorgana -(Mineralogy, Geology, Meteorology, etc.). - -The great value of the Theory of Descent in regard to Biology consists, -as I have already remarked, in its explaining to us the origin of -organic forms in a mechanical way, and pointing out their active causes. -But however highly and justly this service of the Theory of Descent may -be valued, yet it is almost eclipsed by the immense importance which a -single necessary inference from it claims for itself alone. This -necessary and unavoidable inference is the theory of the _animal descent -of the human race_. - -The determination of the position of man in nature, and of his relations -to the totality of things--this question of all questions for mankind, -as Huxley justly calls it--is finally solved by the knowledge that man -is descended from animals. In consequence of Darwin's reformed Theory of -Descent, we are now in a position to establish scientifically the -groundwork of a _non-miraculous history of the development of the human -race_. All those who have defended Darwin's theory, as well as all its -thoughtful opponents, have acknowledged that, as a matter of necessity, -it follows from his theory that the human race, in the first place, must -be traced to ape-like mammals, and further back to the lower vertebrate -animals. - -It is true Darwin himself did not express at first this most important -of all the inferences from his theory. In his work, "On the Origin of -Species," not a word is found about the animal descent of man. The -courageous but cautious naturalist was at that time purposely silent on -the subject, for he anticipated that this most important of all the -conclusions of the Theory of Descent was at the same time the greatest -obstacle to its being generally accepted and acknowledged. Certain it is -that Darwin's book would have created, from the beginning, even much -more opposition and offence, if this most important inference had at -once been clearly expressed. It was not till twelve years later, in his -work on "The Descent of Man, and Selection in Relation to Sex," that -Darwin openly acknowledged that far-reaching conclusion, and expressly -declared his entire agreement with those naturalists who had, in the -meantime, themselves formed that conclusion. Manifestly the effect of -this conclusion is immense, and _no_ science will be able to escape from -the consequences. Anthropology, or the science of man, and consequently -all philosophy, are thereby thoroughly reformed in all their various -branches. - -It will be a later task in these pages to discuss this special point. I -shall not treat of the theory of the animal descent of man till I have -spoken of Darwin's theory, and its general foundation and importance. To -express it in one word, that most important, but (to most men) at first -repulsive, conclusion is nothing more than a special deduction, which we -must draw from the general inductive law of the descent theory (now -firmly established), according to the stern commands of inexorable -logic. - -Perhaps nothing will make the full meaning of the theory of descent -clearer than calling it the "_non-miraculous history of creation_." I -have therefore chosen that name for this work. It is, however, correct -only in a certain sense, and it must be borne in mind that, strictly -speaking, the expression "non-miraculous history of creation" contains a -"_contradictio in adjecto_." - -In order to understand this, let us for a moment examine somewhat more -closely what we understand by _creation_. If we understand the creation -to mean the _coming into existence of a body_ by a creative power or -force, we may then either think of the _coming into existence of its -substance_ (corporeal matter), or of the _coming into existence of its -form_ (the corporeal form). - -Creation in the former sense, as the _coming into existence of matter_, -does not concern us here at all. This process, if indeed it ever took -place, is completely beyond human comprehension, and can therefore never -become a subject of scientific inquiry. Natural science teaches that -matter is eternal and imperishable, for experience has never shown us -that even the smallest particle of matter has come into existence or -passed away. Where a natural body seems to disappear, as for example by -burning, decaying, evaporation, etc., it merely changes its form, its -physical composition or chemical combination. In like manner the coming -into existence of a natural body, for example, of a crystal, a fungus, -an infusorium, depends merely upon the different particles, which had -before existed in a certain form or combination, assuming a new form or -combination in consequence of changed conditions of existence. But never -yet has an instance been observed of even the smallest particle of -matter having vanished, or even of an atom being added to the already -existing mass. Hence a naturalist can no more imagine the coming into -existence of matter, than he can imagine its disappearance, and he -therefore looks upon the existing quantity of matter in the universe as -a given fact. If any person feels the necessity of conceiving the coming -into existence of this matter as the work of a supernatural creative -power, of the creative force of something outside of matter, we have -nothing to say against it. But we must remark, that thereby not even the -smallest advantage is gained for a scientific knowledge of nature. Such -a conception of an immaterial force, which at the first creates matter, -is an article of faith which has nothing whatever to do with human -science. _Where faith commences, science ends._ Both these arts of the -human mind must be strictly kept apart from each other. Faith has its -origin in the poetic imagination; knowledge, on the other hand, -originates in the reasoning intelligence of man. Science has to pluck -the blessed fruits from the tree of knowledge, unconcerned whether these -conquests trench upon the poetical imaginings of faith or not. - -If, therefore, science makes the "history of creation" its highest, most -difficult, and most comprehensive problem, it must accept as its idea of -creation the second explanation of the word, viz., _the coming into -being of the form_ of natural bodies. In this way geology, which tries -to investigate the origin of the inorganic surface of the earth as it -now appears, and the manifold historical changes in the form of the -solid crust of the earth, may be called the history of the creation of -the earth. In like manner, the history of the development of animals and -plants, which investigates the origin of living forms, and the manifold -historical changes in animal and vegetable forms, may be termed the -history of the creation of organisms. As, however, in the idea of -creation, although used in this sense, the unscientific idea of a -creator existing outside of matter, and changing it, may easily creep -in, it will perhaps be better in future to substitute for it the more -accurate term, _development_. - -The great value which the _History of Development_ possesses for the -scientific understanding of animal and vegetable forms, has now been -generally acknowledged for many years, and without it it would be -impossible to make any sure progress in organic morphology, or the -theory of forms. But by the history of development, only one part of -this science has generally been understood, namely, that of organic -individuals, usually called Embryology, but more correctly and -comprehensively, _Ontogeny_. But, besides this, there is another history -of development of organic species, genera, and tribes (phyla), which has -the most important relations to the former. - -The subject of this is furnished to us by the science of petrifactions, -or palaeontology, which shows us that each tribe of animals and plants, -during different periods of the earth's history, has been represented by -a series of entirely different genera and species. Thus, for example, -the tribe of vertebrated animals was represented by classes of fish, -amphibious animals, reptiles, birds, and mammals, and each of these -groups, at different periods, by quite different kinds. This -palaeontological history of the development of organisms, which we may -term _Phylogeny_, stands in the most important and remarkable relation -to the other branch of organic history of development, I mean that of -individuals, or Ontogeny. On the whole, the one runs parallel to the -other. In fact, the history of individual development, or Ontogeny, is a -short and quick recapitulation of palaeontological development, or -Phylogeny, dependent on the laws of Inheritance and Adaptation. - -As I shall have, later, to explain this most interesting and important -coincidence more fully, I shall not dwell further upon it here, and -merely call attention to the fact that it can only be explained and its -causes understood by the Theory of Descent, while without that theory it -remains completely incomprehensible and inexplicable. The Theory of -Descent in the same way shows us _why_ individual animals and plants -must develop at all, and why they do not come into life at once in a -perfect and developed state. No supernatural history of creation can in -any way explain to us the great mystery of organic development. To this -most weighty question, as well as to all other biological questions, the -Theory of Descent gives us perfectly satisfactory answers--and always -answers which refer to purely mechanical causes, and point to purely -physico-chemical forces as the causes of phenomena which we were -formerly accustomed to ascribe to the direct action of supernatural, -creative forces. Hence, by our theory the mystic veil of the miraculous -and supernatural, which has hitherto been allowed to hide the -complicated phenomena of this branch of natural knowledge, is removed. -All the departments of Botany and Zoology, and especially the most -important portion of the latter, Anthropology, become reasonable. The -dimming mirage of mythological fiction can no longer exist in the clear -sunlight of scientific knowledge. - -Of special interest among general biological phenomena are those which -are quite irreconcilable with the usual supposition, that every organism -is the product of a creative power, acting for a definite object. -Nothing in this respect caused the earlier naturalists greater -difficulty than the explanation of the so-called "_rudimentary -organs_,"--those parts in animal and vegetable bodies which really have -no function, which have no physiological importance, and yet exist in -form. These parts deserve the most careful attention, although most -unscientific men know little or nothing about them. Almost every -organism, almost every animal and plant possesses, besides the obviously -useful arrangements of its organization, other arrangements the purpose -of which it is utterly impossible to make out. - -Examples of this are found everywhere. In the embryos of many ruminating -animals--among others, in our common cattle--fore-teeth, or incisors, -are placed in the mid-bone of the upper jaw, which never fully develop, -and therefore serve no purpose. The embryos of many whales--which -afterwards possess the well-known whalebone instead of teeth--yet have -before they are born, and while they take no nourishment, teeth in their -jaws, which set of teeth never comes into use. Moreover, most of the -higher animals possess muscles which are never employed; even man has -such rudimentary muscles. Most of us are incapable of moving our ears as -we wish, although the muscles for this movement exist, and although -individual persons who have taken the trouble to exercise these muscles -do succeed in moving their ears. It is still possible, by special -exercise, by the persevering influence of the will upon the nervous -system, to reanimate the almost extinct activity in the existing but -imperfect organs, which are on the road to complete disappearance. On -the other hand, we can no longer do this with another set of small -rudimentary muscles, which still exist in the cartilage of the outer -ear, but which are always perfectly inactive. Our long-eared ancestors -of the tertiary period--apes, semi-apes, and pouched animals, like most -other mammals, moved their large ear-flaps freely and actively; their -muscles were much more strongly developed and of great importance. In a -similar way, many varieties of dogs and rabbits, under the influence of -civilized life, have left off "pricking up" their ears, and thereby have -acquired imperfect auricular muscles and loose-hanging ears, although -their wild ancestors moved their stiff ears in many ways. - -Man has also these rudimentary organs on other parts of his body; they -are of no importance to life, and never perform any function. One of the -most remarkable, although the smallest organ of this kind, is the little -crescent-like fold, the so-called "plica semilunaris," which we have in -the inner corner of the eye, near the root of the nose. This -insignificant fold of skin, which is quite useless to our eye, is the -imperfect remnant of a third inner eyelid which, besides the upper and -under eyelid, is highly developed in other mammals, and in birds and -reptiles. Even our very remote ancestors of the Silurian period, the -Primitive Fishes, seem to have possessed this third eyelid, the -so-called nictitating membrane. For many of their nearest kin, who still -exist in our day but little changed in form, viz., many sharks, possess -a very strong nictitating membrane, which they can draw right across the -whole eyeball, from the inner corner of the eye. - -Eyes which do not see form the most striking example of rudimentary -organs. These are found in very many animals, which live in the dark, as -in caves or underground. Their eyes often exist in a well-developed -condition, but they are covered by membrane, so that no ray of light -can enter, and they can never see. Such eyes, without the function of -sight, are found in several species of moles and mice which live -underground, in serpents and lizards, in amphibious animals (Proteus, -Caecilia), and in fishes; also in numerous invertebrate animals, which -pass their lives in the dark, as do many beetles, crabs, snails, worms, -etc. - -An abundance of the most interesting examples of rudimentary organs is -furnished by Comparative Osteology, or the study of the skeletons of -vertebrate animals, one of the most attractive branches of Comparative -Anatomy. In most of the vertebrate animals we find two pairs of limbs on -the body, a pair of fore-legs and a pair of hind-legs. Very often, -however, one or the other pair is imperfect; it is seldom that both are, -as in the case of serpents and some varieties of eel-like fish. But some -serpents, viz., the giant serpents (Boa, Python), have still in the -hinder portion of the body some useless little bones, which are the -remains of lost hind-legs. - -In like manner the mammals of the whale tribe (Cetacea), which have only -fore-legs fully developed (breast-fins,), have further back in their -body another pair of utterly superfluous bones, which are remnants of -undeveloped hind-legs. The same thing occurs in many genuine fishes, in -which the hind-legs have in like manner been lost. - -Again, in our slow-worm (Anguis), and in some other lizards, no -fore-legs exist, although they have a perfect shoulder apparatus within -their bodies, which should serve as a means of affixing the legs. -Moreover, in various vertebrate animals, the single bones of both pairs -of legs are found in all the different stages of imperfection, and often -the degenerate bones and those muscles belonging to them are partially -preserved, without their being able in any way to perform any function. -The instrument is still there, but it can no longer play. - -Moreover, we can, almost as generally, find rudimentary organs in the -blossoms of plants, inasmuch as one part or another of the male organs -of propagation--the stamen and anther, or of the female organs of -propagation--the style, germ, etc.--is more or less imperfect or -abortive. Among these we can trace, in various closely connected species -of plants, the organ in all stages of degeneration. Thus, for example, -the great natural family of lip-blossomed plants (Labiatae), to which the -balm, peppermint, marjoram, ground-ivy, thyme, etc., belong, are -distinguished by the fact that their mouth-like, two-lipped flower -contains two long and two short stamens. But in many exceptional plants -of this family, _e.g._ in different species of sage, and in the -rosemary, only one pair of stamens is developed; the other pair is more -or less imperfect, or has quite disappeared. Sometimes stamens exist, -but without the anthers, so that they are utterly useless. Less -frequently the rudiment or imperfect remnant of a fifth stamen is found, -physiologically (for the functions of life) quite useless, but -morphologically (for the knowledge of the form and of the natural -relationship) a most valuable organ. In my "General Morphology of -Organisms,"(4) in the chapter on "Purposelessness, or Dysteleology," I -have given a great number of other examples (Gen. Morph. ii. 226). - -No biological phenomenon has perhaps ever placed zoologists or botanists -in greater embarrassment than these rudimentary or abortive organs. They -are instruments without employment, parts of the body which exist -without performing any service--adapted for a purpose, but without in -reality fulfilling that purpose. When we consider the attempts which the -earlier naturalists have made in order to explain this mystery, we can -scarcely help smiling at the strange ideas to which they were led. Being -unable to find a true explanation, they came, for example, to the -conclusion that the Creator had placed these organs there "for the sake -of symmetry," or they believed that it had appeared unwise and -unsuitable to the Creator (seeing that their nearest kin did possess -such organs) that these organs should be completely wanting in -creatures, where they are incapable of performing a function, and where -it cannot be otherwise from the special mode of life. In compensation -for the non-existing function, he had at least furnished them with the -outward but empty form; nearly in the same manner as civil officers, in -uniform, are furnished with an innocent sword, which is never drawn from -the scabbard. I scarcely believe, however, that any of my readers will -be content with such an explanation. - -Now, it is precisely this widely spread and mysterious phenomenon of -rudimentary organs, in regard to which all other attempts at explanation -fail, which is perfectly explained, and indeed in the simplest and -clearest way, by Darwin's _Theory of Inheritance_ and _Adaptation_. We -can trace the important laws of inheritance and adaptation in the -domestic animals which we breed, and the plants which we cultivate; and -a series of such laws of inheritance have already been established. -Without going further into this at present, I will only remark that some -of them perfectly explain, in a mechanical way, the coming into -existence of rudimentary organs, so that we must look upon the -appearance of such structures as an entirely natural process, arising -from the _disuse of the organs_. - -By _adaptation_ to special conditions of life, the formerly active and -really working organs have gradually ceased to be used or employed. In -consequence of their not being exercised they have become more and more -imperfect, but in spite of this have always been handed down from one -generation to another by _inheritance_, until at last they vanish -partially or entirely. Now, if we admit that all the vertebrate animals -mentioned above are derived from one common ancestor, possessing two -seeing eyes and two well developed pairs of legs, the different stages -of suppression and degeneration of these organs are easily accounted for -in such of the descendants as could no longer use them. In like manner -the various stages of suppression of the stamens, originally existing to -the number of five (in the flower-bud), among the Labiatae is explained, -if we admit that all the plants of this family sprung from one common -ancestor, provided with five stamens. - -I have here spoken somewhat fully of the phenomena of rudimentary -organs, because they are of the utmost general importance, and because -they lead us to the great, general, and fundamental questions in -philosophy and natural science, for the solution of which the Theory of -Descent has now become the indispensable guide. As soon, in fact, as, -according to this theory, we acknowledge the exclusive activity of -physico-chemical causes in living (organic) bodies, as well as in -so-called inanimate (inorganic) nature, we concede exclusive dominion to -that view of the universe, which we may designate as the _mechanical_, -and which is opposed to the _teleological_ conception. If we compare -all the ideas of the universe prevalent among different nations at -different times, we can divide them all into two sharply contrasted -groups--a _causal_ or _mechanical_, and a _teleological_ or -_vitalistic_. The latter has prevailed generally in Biology until now, -and accordingly the animal and vegetable kingdoms have been considered -as the products of a creative power, acting for a definite purpose. In -the contemplation of every organism the unavoidable conviction seemed to -press itself upon us, that such a wonderful machine, so complicated an -apparatus for motion as exists in the organism, could only be produced -by a power analogous to, but infinitely more perfect than, the power of -man in the construction of his machines. - -However sublime the former idea of a Creator, and his creative power, -may have been; however much it may be attempted to divest it of all -human analogy, yet in the end this analogy still remains unavoidable and -necessary in the teleological conception of nature. In reality the -Creator must himself be conceived of as an organism, that is, as a being -who, analogous to man, even though in an infinitely more perfect form, -reflects on his constructive power, lays down a plan of his mechanisms, -and then, by the application of suitable materials, makes them answer -their purpose. Such conceptions necessarily suffer from the fundamental -error of _anthropomorphism_, or man-likening. In such a view, however -exalted the Creator may be imagined, we assign to him the human -attributes of designing a plan, and therefrom suitably constructing the -organism. This is, in fact, quite clearly expressed in that view which -is most sharply opposed to Darwin's theory, and which has found among -naturalists its most distinguished representative in Agassiz. His -celebrated work, "An Essay on Classification,"(5) which is entirely -opposed to Darwin's, and appeared almost at the same time, has -elaborated quite consistently, and to the utmost extent, these -anthropomorphic conceptions of the Creator. - -I maintain with regard to the much-talked-of "purpose in nature," that -it really has no existence but for those persons who observe phenomena -in animals and plants in the most superficial manner. Without going more -deeply into the matter, we can see at once that the rudimentary organs -are a formidable obstacle to this theory. And, indeed, everyone who -makes a really close study of the organization and mode of life of the -various animals and plants, and becomes familiar with the reciprocity or -interaction of the phenomena of life, and the so-called "economy of -nature," must necessarily come to the conclusion that this -"purposiveness" no more exists than the much-talked-of "beneficence" of -the Creator. These optimistic views have, unfortunately, as little real -foundation as the favourite phrase, the "moral order of the universe," -which is illustrated in an ironical way by the history of all nations. -The dominion of the "moral" popes, and their pious inquisition, in the -mediaeval times, is not less significant of this than the present -prevailing militarism, with its "moral" apparatus of needle-guns and -other refined instruments of murder. - -If we contemplate the common life and the mutual relations between -plants and animals (man included), we shall find everywhere, and at all -times, the very opposite of that kindly and peaceful social life which -the goodness of the Creator ought to have prepared for his creatures--we -shall rather find everywhere a pitiless, most embittered _Struggle of -All against All_. Nowhere in nature, no matter where we turn our eyes, -does that idyllic peace, celebrated by the poets, exist; we find -everywhere a struggle and a striving to annihilate neighbours and -competitors. Passion and selfishness--conscious or unconscious--is -everywhere the motive force of life. The well-known words of the German -poet-- - - "Die Welt ist vollkommen ueberall - Wo der Mensch nicht hinkommt mit seiner Qual."[1] - -are beautiful, but, unfortunately, not true. Man in this respect -certainly forms no exception to the rest of the animal world. The -remarks which we shall have to make on the theory of "Struggle for -Existence" will sufficiently justify this assertion. It is, in fact, -Darwin who has placed this important point, in its high and general -significance, very clearly before our eyes, and the chapter in his -theory which he himself calls "Struggle for Existence" is one of the -most important parts of it. - -Whilst, then, we emphatically oppose the vital or teleological view of -animate nature which presents animal and vegetable forms as the -productions of a kind Creator, acting for a definite purpose, or of a -creative, natural force acting for a definite purpose, we must, on the -other hand, decidedly adopt that view of the universe which is called -the _mechanical_ or _causal_. It may also be called the _monistic_, or -_single-principle_ theory, as opposed to the _twofold principle_, or -_dualistic_ theory, which is necessarily implied in the teleological -conception of the universe. The mechanical view of nature has for many -years been so firmly established in certain domains of natural science, -that it is here unnecessary to say much about it. It no longer occurs to -physicists, chemists, mineralogists, or astronomers, to seek to find in -the phenomena which continually appear before them in their scientific -domain the action of a Creator acting for a definite purpose. They -universally, and without hesitation, look upon the phenomena which -appear in their different departments of study as the necessary and -invariable effects of physical and chemical forces which are inherent in -matter. Thus far their view is purely _materialistic_, in a certain -sense of that "word of many meanings." - -When a physicist traces the phenomena of motion in electricity or -magnetism, the fall of a heavy body, or the undulations in the waves of -light, he never, in the whole course of his research, thinks of looking -for the interference of a supernatural power. In this respect, Biology, -as the science of so-called "_animated_" natural bodies, was formerly -placed in sharp opposition to the above-mentioned inorganic natural -sciences (Anorganology). It is true modern Physiology, the science of -the phenomena of motion in animals and plants, has completely adopted -the mechanical view; but Morphology, the science of the forms of animals -and plants, has not been affected at all by it. Morphologists, in spite -of the position of physiology, have continued, as before, in opposition -to the mechanical view of functions, to look upon the forms of animals -and plants as something which cannot be at all explained mechanically, -but which must owe its origin necessarily to a higher, supernatural -creative power, acting for a definite purpose. - -In this general view it is quite indifferent whether the creative power -be worshipped as a personal god, or whether it be termed the power of -life (vis vitalis), or final cause (causa finalis). In any case, to -express it in one word, its supporters have recourse to a _miracle_ for -an explanation. They throw themselves into the arms of a poetic faith, -which as such can have no value in the domain of scientific knowledge. - -All that was done before Darwin, to establish a natural mechanical -conception of the origin of animals and plants, has been in vain, and -until his time no theory gained a general recognition. Darwin's theory -first succeeded in doing this, and thus has rendered an immense service. -For the idea of the _unity of organic and inorganic nature_ is now -firmly established; and that branch of natural science which had longest -and most obstinately opposed mechanical conception and explanation, -viz., the science of the structure of animate forms, is launched on to -identically the same road towards perfection as that along which all the -rest of the natural sciences are travelling. The unity of _all_ natural -phenomena is by Darwin's theory finally established. - -This unity of all nature, the animating of all matter, the -inseparability of mental power and corporeal substance, Goethe has -asserted in the words: "Matter can never exist and be active without -mind, nor can mind without matter." These first principles of the -mechanical conception of the universe have been taught by the great -monistic philosophers of all ages. Even Democritus of Abdera, the -immortal founder of the Atomic theory, clearly expressed them about 500 -years before Christ; but the great Dominican friar, Giordano Bruno, did -so even more explicitly. For this he was burnt at the stake, by the -Christian inquisition in Rome, on the 17th of Feb., 1600, on the same -day on which, 36 years before, Galileo, his great fellow-countryman and -fellow-worker, was born. Such men, who live and die for a great idea, -are usually stigmatized as "materialists"; but their opponents, whose -arguments were torture and the stake, are praised as "spiritualists." - -By the Theory of Descent we are for the first time enabled to conceive -of the unity of nature in such a manner that a mechanico-causal -explanation of even the most intricate organic phenomena, for example, -the origin and structure of the organs of sense, is no more difficult -(in a general way) than is the mechanical explanation of any physical -process; as, for example, earthquakes, the courses of the wind, or the -currents of the ocean. We thus arrive at the extremely important -conviction that _all natural bodies_ which are known to us are _equally -animated_, that the distinction which has been made between animate and -inanimate bodies does _not_ exist. When a stone is thrown into the air, -and falls to earth according to definite laws, or when in a solution of -salt a crystal is formed, the phenomenon is neither more nor less a -mechanical manifestation of life than the growth and flowering of -plants, than the propagation of animals or the activity of their senses, -than the perception or the formation of thought in man. This final -triumph of the monistic conception of nature constitutes the highest and -most general merit of the Theory of Descent, as reformed by Darwin. - - - - -CHAPTER II. - - SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT. - HISTORY OF CREATION ACCORDING TO LINNAEUS. - - - The Theory of Descent, or Doctrine of Filiation, as the - Monistic Explanation of Organic Natural Phenomena.--Its - Comparison with Newton's Theory of Gravitation.--Limits - of Scientific Explanation and of Human Knowledge in - general.--All Knowledge founded originally on Sensuous - Experience, _a posteriori_.--Transition of _a posteriori_ - knowledge, by Inheritance, into _a priori_ - knowledge.--Contrast between the Supernatural Hypotheses - of the Creation according to Linnaeus, Cuvier, Agassiz, - and the Natural Theories of Development according to - Lamarck, Goethe, and Darwin.--Connection of the former - with the Monistic (mechanical), of the latter with the - Dualistic Conception of the Universe.--Monism and - Materialism.--Scientific and Moral Materialism.--The - History of Creation according to Moses.--Linnaeus as the - Founder of the Systematic Description of Nature and - Distinction of Species.--Linnaeus' Classification and - Binary Nomenclature.--Meaning of Linnaeus' Idea of - Species.--His History of Creation.--Linnaeus' view of the - Origin of Species. - - -The value which every scientific theory possesses is measured by the -number and importance of the objects which can be explained by it, as -well as by the simplicity and universality of the causes which are -employed in it as grounds of explanation. On the one hand, the greater -the number and the more important the meaning of the phenomena explained -by the theory, and the simpler, on the other hand, and the more general -the causes which the theory assigns as explanations, the greater is its -scientific value, the more safely we are guided by it, and the more -strongly are we bound to adopt it. - -Let us call to mind, for example, that theory which has ranked up to the -present time as the greatest achievement of the human mind--the Theory -of Gravitation, which Newton, two hundred years ago, established in his -Mathematical Principles of Natural Philosophy. Here we find that the -object to be explained is as large as one can well imagine. He undertook -to reduce the phenomena of the motion of the planets, and the structure -of the universe, to mathematical laws. As the most simple cause of these -intricate phenomena of motion, Newton established the law of weight or -attraction, the same law which is the cause of the fall of bodies, of -adhesion, cohesion, and many other phenomena. - -If we apply the same standard of valuation to Darwin's theory, we must -arrive at the conclusion that this theory, also, is one of the greatest -achievements of the human mind, and that it may be placed quite on a -level with Newton's Theory of Gravitation. Perhaps this opinion will -seem a little exaggerated, or at any rate very bold, but I hope in the -course of this treatise to convince the reader that this estimate is not -too high. In the preceding chapter, some of the most important and most -general phenomena in organic nature, which have been explained by -Darwin's theory, have been named. Among them are the variations in form -which accompany the individual development of organisms, most varied and -complicated phenomena, which until now presented the greatest -difficulties in the way of mechanical explanation, that is, in the -tracing of them to active causes. We have mentioned the _rudimentary -organs_, those exceedingly remarkable structures in animals and plants -which have no object and refute every teleological explanation seeking -for the final purpose of the organism. A great number of other phenomena -might have been mentioned, which are no less important, and are -explained in the simplest manner by Darwin's reformed Theory of Descent. -For the present I will only mention the phenomena presented to us by the -_geographical distribution of animals and plants_ on the surface of our -planet, as well as the _geological distribution of the extinct and -petrified organisms_ in the different strata of the earth's crust. These -important palaeontological and geographical phenomena, which were -formerly only known to us as _facts_, are now traced to their active -_causes_ by the Theory of Descent. - -The same statement applies further to all the general laws of -_Comparative Anatomy_, especially to the great law of _division of -labour_ or _separation_ (polymorphism, or differentiation), a law which -determines the form or structure of human society, as well as the -organization of individual animals and plants. It is this law which -necessitates an ever _increasing variety_, as well as a _progressive -development_ of organic forms. This law of the division of labour has, -up to the present time, been only recognized as a fact, and it, like the -law of progressive development, or the law of progress which we perceive -active everywhere in the history of nations (as also in that of animals -and plants), is explained by Darwin's Doctrine of Descent. Then, if we -turn our attention to the great whole of organic nature, if we compare -all the individual groups of phenomena of this immense domain of life, -it cannot fail to appear, in the light of the Doctrine of Descent, no -longer as the ingeniously designed work of a Creator building up -according to a definite purpose, but as the necessary consequence of -active causes, which are inherent in the chemical combination of matter -itself, and in its physical properties. - -In fact, we can most positively assert, and I shall justify this -assertion in the course of these pages, that by the Doctrine of -Filiation, or Descent, we are enabled for the first time to reduce all -organic phenomena to a single law, and to discover a single active cause -for the infinitely intricate mechanism of the whole of this rich world -of phenomena. In this respect, Darwin's theory stands quite on a level -with Newton's Theory of Gravitation; indeed, it even rises higher than -Newton's theory! - -The grounds of explanation are equally simple in the two theories. In -explaining this most intricate world of phenomena, Darwin does not make -use of new or hitherto unknown properties of matter, nor does he, as one -might suppose, make use of discoveries of new combinations of matter or -of new forces of organization; but it is simply by extremely ingenious -combination, by the synthetic comprehension, and by the thoughtful -comparison of a number of well-known facts, that Darwin has solved the -"holy mystery" of the living world of forms. The consideration of the -interchanging relations which exist between two general properties of -organisms, viz., _Inheritance and Adaptation_, is what has here been of -the first importance. Merely by considering the relations between these -two vital actions or physiological functions of organisms, also further -by considering the reciprocal interaction which all animals and plants, -living in one and the same place, necessarily exert on one -another--solely by the correct estimate of these simple facts, and by -skilfully combining them, Darwin has succeeded in finding the true -active causes (causae efficientes) of the immensely intricate world of -forms in organic nature. - -In any case we are in duty bound to accept this theory till a better one -be found, which will undertake to explain the same amount of facts in an -equally simple manner. Until now we have been in utter want of such a -theory. The fundamental idea that all different animal and vegetable -forms must be descended from a few or even from one single, most simple -primary form, was indeed not new. This idea was long since distinctly -formulated--first by the great Lamarck, at the beginning of our century. -But Lamarck in reality only expressed the hypothesis of the Doctrine of -Filiation, without establishing it by an explanation of the active -causes. And it is just the demonstration of these causes which marks the -extraordinary progress which Darwin's theory has made beyond that of -Lamarck. In the physiological properties of Inheritance and Adaptation -of organic matter, Darwin discovered the true cause of the genealogical -relationship of organisms. It was not possible for the genius of Lamarck -in his day to command that colossal material of biological facts which -has been collected by the patient zoological and botanical -investigations of the last fifty years, and which has been used by -Darwin as an overpowering apparatus of evidence. - -Darwin's theory is therefore not what his opponents frequently represent -it as being--an unwarranted hypothesis taken up at random. It is not for -zoologists or botanists to accept or reject this as an explanatory -theory, as they please; they are rather compelled and obliged to accept -it, according to the general principle observed in all natural sciences, -that we must accept and retain for the explanation of phenomena any -theory which, though it has only a feeble basis, is compatible with the -actual facts--until it is replaced by a better one. If we do not adopt -it, we renounce a scientific explanation of phenomena, and this is, in -fact, the position which many biologists still maintain. They look upon -the whole domain of animate nature as a perfect mystery, and upon the -origin of animals and plants, the phenomena of their development and -affinities, as quite inexplicable and miraculous; in fact, they will not -allow that there _can_ be a true understanding of them. - -Those opponents of Darwin who do not exactly wish to renounce a -scientific explanation are in the habit of saying, "Darwin's theory of -the common origin of the different species is only _one_ hypothesis; we -oppose to it _another_, the hypothesis that the individual animal and -vegetable species have not developed one from another by descent, but -that they have come into existence independently of one another, by a -still undiscovered law of nature." But as long as it is not shown how -this coming into existence is to be conceived of, and what that "law of -nature" is--as long as not even _probable_ grounds of explanation can be -brought forward to account for the independent coming into existence of -animal and vegetable species, so long this counter-hypothesis is in fact -no hypothesis, but an empty unmeaning phrase. Darwin's theory ought, -moreover, not to be called an hypothesis. For a scientific hypothesis is -a supposition, postulating the existence of unknown properties or -motional phenomena of natural bodies, which properties have not as yet -been observed by the experience of the senses. But Darwin's theory does -not assume such unknown conditions; it is based upon general properties -of organisms that have long been recognized, and--as has been -remarked--it is the exceedingly ingenious and comprehensive combination -of a number of phenomena which had hitherto stood isolated, which gives -the theory its extraordinarily great and intrinsic value. By it we are -for the first time in a position to demonstrate an active cause for all -the known morphological phenomena in the animal and vegetable kingdoms; -and, in fact, this cause is always one and the same, viz., the alternate -action of Adaptation and Inheritance, therefore a physiological, that -is, a physico-chemical or mechanical, relationship. For these reasons -the acceptance of the Doctrine of Filiation, as mechanically established -by Darwin, is a binding and unavoidable necessity for the whole domain -of zoology and botany. - -As, therefore, in my opinion the immense importance of Darwin's theory -lies in the fact that it has _mechanically explained those organic -phenomena of forms_ which had hitherto been unexplained, it is perhaps -necessary that I should here say a few words about the different ideas -connected with the word "explanation." It is very frequently said, in -opposition to Darwin's theory, that it does indeed explain those -phenomena by Inheritance and Adaptation, but that it does not at the -same time explain those properties of organic matter, and that therefore -we do not arrive at first causes. This objection is quite correct, but -it applies equally to _all_ explanations of phenomena. We _nowhere_ -arrive at a knowledge of first causes. The origin of every simple salt -crystal, which we obtain by evaporating its mother liquor, is no less -mysterious to us, as far as concerns its first cause, and in itself no -less incomprehensible than the origin of every animal which is developed -out of a simple cell. In explaining the most simple physical or chemical -phenomena, as the falling of a stone, or the formation of a chemical -combination, we arrive, by discovering and establishing the active -causes--for example, the gravitation or the chemical affinity--at other -remoter phenomena, which in themselves are mysterious. This arises from -the limitation or relativity of our powers of understanding. We must not -forget that human knowledge is absolutely limited, and possesses only a -relative extension. It is, in its essence, limited by the very nature of -our senses and of our brains. - -All knowledge springs from sensuous perceptions. In opposition to this -statement, the innate, _a priori_ knowledge of man may be brought up; -but we can see that the so-called _a priori_ knowledge can by Darwin's -theory be proved to have been acquired _a posteriori_, being based on -experience as its first cause. Knowledge which is based originally upon -purely empirical observations, and which is therefore a purely sensuous -experience, but has then been transmitted from generation to generation -by inheritance, appears in later generations as if it were independent, -innate, and _a priori_. In our late animal ancestors, all our so-called -"_a priori_ knowledge" was originally acquired _a posteriori_, and only -gradually became _a priori_ by inheritance. It is based in the first -instance upon experiences, and by the laws of Inheritance and Adaptation -we can positively prove that knowledge _a priori_ and knowledge _a -posteriori_ cannot rightly be placed in opposition, as is usually done. -On the contrary, sensuous experience is the original source of _all_ -knowledge. For this reason alone, all our knowledge is limited, and we -can never apprehend the _first causes_ of any phenomena. The force of -crystallization, the force of gravitation, and chemical affinity remain -in themselves just as incomprehensible as do Adaptation and Inheritance. - -Seeing that Darwin's theory explains from a single point of view the -totality of all those phenomena of which we have given a brief survey, -that it demonstrates one and the same quality of the organism as the -active cause in all cases, we must allow that it gives us for the -present _all_ that we can desire. Moreover, we have good reason to hope -that at some future time we shall learn to explain the first causes at -which Darwin has arrived, namely, the properties of Adaptation and -Inheritance; and that we shall succeed in discovering in the composition -of albuminous matter certain molecular relations as the remoter, simpler -causes of these phenomena. There is indeed no prospect of this in the -immediate future, and we content ourselves for the present with the -tracing back of organic phenomena to two mysterious properties, just as -in the case of Newton's theory we are satisfied with tracing the -planetary motions to the force of gravitation, which itself is likewise -a mystery to us and not cognizable in itself. - -Before commencing our principal task, which is the careful discussion of -the Doctrine of Descent, and the consequences that arise out of it, let -us take an historical retrospect of the most important and most widely -spread of those views, which before Darwin men had elaborated -concerning organic creation, and the coming into existence of the many -animal and vegetable species. In doing this I have no intention of -entertaining the reader with a statement of all the innumerable stories -about the creation which have been current among the different human -species, races, or tribes. However interesting and gratifying this task -would be, from an ethnographical point of view, as well as in a history -of civilization, it would lead us here much too far from our subject. -Besides, the great majority of all these legends about creation bear too -clearly the stamp of arbitrary fiction, and of a want of a close -observance of nature, to be of interest in a scientific treatment of the -history of creation. I shall therefore only select the Mosaic history -from among those that are not founded on scientific investigation, on -account of the unparalleled influence which it has gained in the western -civilized world; and then I shall immediately take up the scientific -hypothesis about creation, which originated with Linnaeus as late as the -commencement of last century. - -All the different conceptions which man has ever formed about the coming -into existence of the different animal and vegetable species may -conveniently be divided into two great contrasted groups--the natural -and supernatural histories of creation. - -These two groups, on the whole, correspond with the two different -principal forms of the human notions of the universe which we have -already contrasted as the _monistic and the dualistic_ conception of -nature. In the usual dualistic or teleological (vital) conception of the -universe, organic nature is regarded as the purposely executed -production of a Creator working according to a definite plan. Its -adherents see in every individual species of animal and plant an -"embodied creative thought," the material expression of a _definite -first cause_ (causa finalis) acting for a set purpose. They must -necessarily assume supernatural (not mechanical) processes for the -origin of organisms. With justice, we may therefore designate their -scheme of the world's growth as the _Supernatural History of Creation_. -Among all such teleological histories of creation, that of Moses has -gained the greatest influence, since even so distinguished a naturalist -as Linnaeus has claimed admittance for it in Natural Science. Cuvier's -and Agassiz's views of creation also belong to this group, as do in fact -those of the great majority of both scientific and unscientific men. - -On the other hand, the theory of development carried out by Darwin, -which we shall have to treat of here as the _Non-miraculous_ or _Natural -History of Creation_, and which has already been put forward by Goethe -and Lamarck, must, if carried out logically, lead to the monistic or -mechanical (causal) conception of the universe. In opposition to the -dualistic or teleological conception of nature, our theory considers -organic, as well as inorganic, bodies to be the necessary products of -natural forces. It does not see in every individual species of animal -and plant the embodied thought of a personal Creator, but the expression -for the time being of a mechanical process of development of matter, the -expression of a necessarily active cause, that is, of a mechanical cause -(causa efficiens). Where teleological Dualism seeks the arbitrary -thoughts of a capricious Creator in the miracles of creation, causal -Monism finds in the process of development the necessary effects of -eternal immutable laws of nature. - -The Monism here maintained by us is often considered identical with -Materialism. Now, as Darwinism, and in fact the whole theory of -development, has been designated as "_materialistic_," I cannot avoid -here at once guarding myself against this ambiguous word, and against -the malice with which, in certain quarters, it is employed to stigmatize -our doctrine. - -By the word "_Materialism_," two completely different things are very -frequently confounded and mixed up, which in reality have nothing -whatever to do with each other, namely, scientific and moral -materialism. Scientific materialism, which is identical with our Monism, -affirms in reality no more than that everything in the world goes on -naturally--that every effect has its cause, and every cause its effect. -It therefore assigns to causal law--that is, the law of a necessary -connection between cause and effect--its place over the entire series of -phenomena that can be known. At the same time, scientific materialism -positively rejects every belief in the miraculous, and every conception, -in whatever form it appears, of supernatural processes. Accordingly, -nowhere in the whole domain of human knowledge does it recognize real -metaphysics, but throughout only physics; through it the inseparable -connection between matter, form, and force becomes self evident. This -scientific materialism has long since been so universally acknowledged -in the wide domain of inorganic science, in Physics and Chemistry, in -Mineralogy and Geology, that no one now doubts its sole authority. But -in Biology, or Organic science, the case is very different; here its -value is still continually a matter of dispute in many quarters. There -is, however, nothing else which can be set up against it, excepting the -metaphysical spectre of a vital power, or empty theological dogma. If we -can prove that all nature, so far as it can be known, is only _one_, -that the same "great, eternal, iron laws" are active in the life of -animals and plants, as in the growth of crystals and in the force of -steam, we may with reason maintain the monistic or mechanical view of -things throughout the domain of Biology--in Zoology and Botany--whether -it be stigmatized as "materialism" or not. In such a sense all exact -science, and the law of cause and effect at its head, is purely -materialistic. - -_Moral_, or _ethical Materialism_, is something quite distinct from -scientific materialism, and has nothing whatever in common with the -latter. This real materialism proposes no other aim to man in the course -of his life than the most refined possible gratification of his senses. -It is based on the delusion that purely material enjoyment can alone -give satisfaction to man; but as he can find that satisfaction in no one -form of sensuous pleasure, he dashes on weariedly from one to another. -The profound truth that the real value of life does not lie in material -enjoyment, but in moral action--that true happiness does not depend upon -external possessions, but only in a virtuous course of life--this is -unknown to ethical materialism. We therefore look in vain for such -materialism among naturalists and philosophers, whose highest happiness -is the intellectual enjoyment of Nature, and whose highest aim is the -knowledge of her laws. We find it in the palaces of ecclesiastical -princes, and in those hypocrites who, under the outward mask of a pious -worship of God, solely aim at hierarchical tyranny over, and material -spoliation of, their fellow-men. Blind to the infinite grandeur of the -so-called "raw material," and the glorious world of phenomena arising -from it--insensible to the inexhaustible charms of Nature, and without a -knowledge of her laws--they stigmatize all natural science, and the -culture arising from it, as sinful "materialism," while really it is -this which they themselves exhibit in a most shocking form. Satisfactory -proofs of this are furnished, not only by the whole history of the -Catholic Popes, with their long series of crimes, but also by the -history of the morals of orthodoxy in every form of religion. - -In order, then, to avoid in future the usual confusion of this utterly -objectionable Moral Materialism with our Scientific Materialism, we -think it necessary to call the latter either _Monism_ or _Realism_. The -principle of this _Monism_ is the same as what Kant terms the -"principle of mechanism," and of which he expressly asserts, that -_without it there can be no natural science at all_. This principle is -quite inseparable from our Non-miraculous History of Creation, and -characterizes it as opposed to the teleological belief in the miracles -of a Supernatural History of Creation. - -Let us now first of all glance at the most important of all the -supernatural histories of creation, I mean that of Moses, as it has been -handed down to us in the Bible, the ancient document of the history and -laws of the Jewish people. The Mosaic history of creation, since in the -first chapter of Genesis it forms the introduction to the Old Testament, -has enjoyed, down to the present day, general recognition in the whole -Jewish and Christian world of civilization. Its extraordinary success is -explained not only by its close connection with Jewish and Christian -doctrines, but also by the simple and natural chain of ideas which runs -through it, and which contrasts favourably with the confused mythology -of creation current among most of the other ancient nations. First the -Lord God creates the earth as an inorganic body; then he separates light -from darkness, then water from the dry land. Now the earth has become -inhabitable for organisms, and plants are first created, animals -later--and among the latter the inhabitants of the water and the air -first, afterwards the inhabitants of the dry land. Finally God creates -man, the last of all organisms, in his own image, and as the ruler of -the earth. - -Two great and fundamental ideas, common also to the non-miraculous -theory of development, meet us in this Mosaic hypothesis of creation, -with surprising clearness and simplicity--the idea of separation or -_differentiation_, and the idea of progressive development or -_perfecting_. Although Moses looks upon the results of the great laws of -organic development (which we shall later point out as the necessary -conclusions of the Doctrine of Descent) as the direct actions of a -constructing Creator, yet in his theory there lies hidden the ruling -idea of a progressive development and a differentiation of the -originally simple matter. We can therefore bestow our just and sincere -admiration on the Jewish lawgiver's grand insight into nature, and his -simple and natural hypothesis of creation, without discovering in it a -so-called "divine revelation." That it cannot be such is clear from the -fact that two great fundamental errors are asserted in it, namely, -first, the _geocentric_ error that the earth is the fixed central point -of the whole universe, round which the sun, moon, and stars move; and -secondly, the _anthropocentric_ error, that man is the premeditated aim -of the creation of the earth, for whose service alone all the rest of -nature is said to have been created. The former of these errors was -demolished by Copernicus' System of the Universe in the beginning of the -16th century, the latter by Lamarck's Doctrine of Descent in the -beginning of the 19th century. - -Although the geocentric error of the Mosaic history was demonstrated by -Copernicus, and thereby its authority as an absolutely perfect divine -revelation was destroyed, yet it has maintained, down to the present -day, such influence, that it forms in many wide circles the principle -obstacle to the adoption of a natural theory of development. Even in our -century, many naturalists, especially geologists, have tried to bring -the Mosaic theory into harmony with the recent results of natural -science, and have, for example, interpreted Moses' seven days of -creation as seven great geological periods. However, all these ingenious -attempts at interpretation have so utterly failed, that they require no -refutation here. The Bible is no scientific book, but consists of -records of the history, the laws, and the religion of the Jewish people, -the high merit of which, as a history of civilization, is not impaired -by the fact that in all scientific questions it has no commanding -importance, and is full of gross errors. - -We may now make a great stride over more than three thousand years, from -Moses, who died about the year 1480 before Christ, to Linnaeus, who was -born in the year 1707 after Christ. During this whole period no history -of creation was brought forward that gained any lasting importance, or -the closer examination of which would here be of any interest. Indeed, -during the last fifteen hundred years, since Christianity gained its -supremacy, the Mosaic history of creation, together with the dogmas -connected with it, has become so generally predominant, that the 19th -century is the first that has dared positively to rise against it. Even -the great Swedish naturalist, Linnaeus, the founder of modern natural -history, linked his System of Nature most closely to the Mosaic history -of creation. - -The extraordinary progress which Charles Linnaeus made in the so-called -descriptive natural sciences, consists, as is well known, in his having -established a system of nomenclature of animals and plants, which he -carried out in a manner so perfectly logical and consistent, that down -to the present day it has remained in many respects the standard for all -succeeding naturalists engaged in the study of the forms of animals and -plants. Although Linnaeus' system was artificial, although in classifying -animal and vegetable species he only sought and employed single parts as -the foundation for his divisions, it has, nevertheless, gained the -greatest success; firstly, in consequence of its being carried out -consistently, and secondly, by its nomenclature of natural bodies, which -has become extremely important, and at which we must here briefly -glance. - -Before Linnaeus' time, many vain attempts had been made to throw light -upon the endless chaos of different animal and vegetable forms (then -known) by adopting for them suitable names and groupings; but Linnaeus, -by a happy hit, succeeded in accomplishing this important and difficult -task, when he established the so-called "_binary nomenclature_." The -binary nomenclature, or the twofold designation, as Linnaeus first -established it, is still universally applied by all zoologists and -botanists, and will, no doubt, maintain itself, for a long time to come, -with undiminished authority. It consists in this, that every species of -animal and plant is designated by two names, which stand to each other -in the same relation as do the christian and surnames of a man. The -special name which corresponds with the christian name, and expresses -the idea of "a species," serves as the common designation of all -individual animals or plants, which are equal in all essential matters -of form, and are only distinguished by quite subordinate features. The -more general name, on the other hand, corresponding with the surname, -and which expresses the idea of a genus, serves for the common -designation of all the most nearly similar kinds or species. - -According to Linnaeus' plan, the more general and comprehensive generic -name is written first; the special subordinate name of the species -follows it. Thus, for example, the common cat is called Felis domestica; -the wild cat, Felis catus; the panther, Felis pardus; the jaguar, Felis -onca; the tiger, Felis tigris; the lion, Felis leo. All these six kinds -of animals of prey are different species of one and the same -genus--Felis. Or, to add an example from the vegetable kingdom, -according to Linnaeus' designation the pine is Pinus abies; the fir, -Pinus picea; the larch, Pinus larix; the Italian pine, Pinus pinea; the -Siberian stone pine, Pinus cembra; the knee timber, Pinus mughus; the -common pine, Pinus silvestris. All these seven kinds of pines are -different species of one and the same genus--Pinus. - -Perhaps this advance made by Linnaeus may seem to some only of -subordinate importance in the practical distinction and designation of -the variously formed organisms. But in reality it was of the very -greatest importance, both from a practical and theoretical point of -view. For now, for the first time, it became possible to arrange the -immense mass of different organic forms according to their greater or -less degree of resemblance, and to obtain an easy survey of the general -outlines of such a "system." Linnaeus facilitated the tabulation and -survey of this "system" of plants and animals still more by placing -together the most nearly similar genera into so-called orders (ordines); -and by uniting the most nearly similar orders into still more -comprehensive main divisions or classes. Thus, according to Linnaeus, -each of the two organic kingdoms were broken up into a number of -classes, the vegetable kingdom into twenty-four, and the animal kingdom -into six. Each class again contains several orders. Every single order -may contain a number of genera, and, again, every single genus several -species. - -Valuable as was Linnaeus' binary nomenclature in a _practical_ way, in -bringing about a comprehensive systematic distinction, designation, -arrangement, and division of the organic world of forms, yet the -incalculable _theoretical_ influence which it gained forthwith in -relation to the history of creation was no less important. Even now all -the important fundamental questions as to the history of creation turn -finally upon the decision of the very remote and unimportant question, -_What really are kinds or species?_ Even now the _idea of organic -species_ may be termed the central point of the whole question of -creation, the disputed centre, about the different conceptions of which -Darwinists and Anti-Darwinists fight. - -According to Darwin's opinion, and that of his adherents, the different -species of one and the same genus of animals and plants are nothing else -than differently developed descendants of one and the same original -primary form. The different kinds of pine mentioned above would -accordingly have originated from a single primaeval form of pine. In like -manner the origin of all the species of cat mentioned above would be -traced to a single common form of Felis, the ancestor of the whole -genus. But further, in accordance with the Doctrine of Descent, all the -different genera of one and the same order ought also to be descended -from one common primary ancestor, and so, in like manner, all orders of -a class from a single primary form. - -On the other hand, according to the idea of Darwin's opponents, all -species of animals and plants are quite independent of each other, and -only the individuals of each species have originated from a single -primary form. But if we ask them how they conceive these original -primary forms of each species to have come into existence, they answer -with a leap into the incomprehensible, "They were created." - -Linnaeus himself defined the idea of species in this manner by saying, -"There are as many different species as there were different forms -created in the beginning by the infinite Being." ("Species tot sunt -diversae, quot diversas formas ab initio creavit infinitum ens.") In this -respect, therefore, he follows most closely the Mosaic history of -creation, which in the same way maintains that animals and plants were -created "each one after its kind." Linnaeus, accepting this, held that -originally of each species of animals and plants either a single -individual or a pair had been created; in fact a pair, or, as Moses -says, "a male and a female" of those species which have separate sexes, -but of those species in which each individual combines both sexual -organs (hermaphrodites), as for instance the earthworm, the garden and -vineyard snails, as well as the great majority of plants, a single -individual. - -Linnaeus further follows the Mosaic legend in regard to the flood, by -supposing that the great general flood destroyed all existing organisms, -except those few individuals of each species (seven pairs of the birds -and of clean animals, one pair of unclean animals) which Noah saved in -the ark, and which were placed again on land, on Mount Ararat, after the -flood had subsided. He tried to explain the geographical difficulty of -the living together of the most different animals and plants, as -follows: Mount Ararat, in Armenia, being situated in a warm climate, and -rising over 16,000 feet in height, combines in itself the conditions for -a temporary common abode of such animals as live in different zones. -Accordingly, animals accustomed to the polar regions could climb up the -cold mountain ridges, those accustomed to a warm climate could go down -to the foot of the mountain, and the inhabitants of a temperate zone -could remain midway up the mountain. From this point it was possible for -them to spread north and south over the earth. - -It is scarcely necessary to remark that this Linnaean hypothesis of -creation, which evidently was intended to harmonize most closely with -the prevailing belief in the Bible, requires no serious refutation. When -we consider Linnaeus' clearness and sagacity in other matters, we may -doubt whether he believed it himself. As to the simultaneous origin of -all individuals of each species from one pair of ancestors respectively -(or in the case of the hermaphrodite species, from one original -hermaphrodite), it is clearly quite untenable; for, apart from other -reasons, in the first days after the creation, the few animals of prey -would have sufficed to have utterly demolished all the herbivorous -animals, as the herbivorous animals must have destroyed the few -individuals of the different species of plants. The existence of such an -equilibrium in the economy of nature as obtains at present cannot -possibly be conceived, if only one individual of each species, or only -one pair, had originally and simultaneously been created. - -Moreover, how little importance Linnaeus himself attached to this -untenable hypothesis of creation is clear, among other things, from the -fact that he recognized _Hybridism_ (crossing) as a source of the -production of new species. He assumed that a great number of independent -new species had originated by the interbreeding of two different -species. Indeed, such hybrids are not at all rare in nature, and it is -now proved that a great number of species, for example, of the genus -Rubus (bramble), mullen (Verbascum), willow (Salix), thistle (Cirsium), -are hybrids of different species of these genera. We also know of -hybrids between hares and rabbits (two species of the genus Lepus), -further of hybrids between different species of dog (genus Canis), etc., -which can be propagated as independent species. - -It is certainly very remarkable that Linnaeus asserted the physiological -(therefore mechanical) origin of new species in this process of -hybridism. It clearly stands in direct opposition to the supernatural -origin of the other species by creation, which he accepted as put -forward in the Mosaic account. The one set of species would therefore -have originated by dualistic (teleological) creation, the other by -monistic (mechanical) development. - -The great and well merited authority which Linnaeus gained by his -systematic classification and by his other services to Biology, was -clearly the reason why his views of creation also remained, throughout -the whole of the last century, undisputed and generally recognized. If -throughout systematic Zoology and Botany the distinctions, -classification, and designations of species, introduced by Linnaeus, and -the dogmatic ideas connected therewith had not been maintained--more or -less unaltered--we should be at a loss to understand how his idea of an -independent creation of single species could have stood, by itself down -to the present day. It is only owing to his great authority, and through -his attaching himself to the prevailing Biblical belief, that his -hypothesis of creation has retained its position so long. - - - - -CHAPTER III. - -THE HISTORY OF CREATION ACCORDING TO CUVIER AND AGASSIZ. - - - General Theoretical Meaning of the Idea of - Species.--Distinction between the Theoretical and - Practical Definition of the Idea of Species.--Cuvier's - Definition of Species.--Merits of Cuvier as the Founder - of Comparative Anatomy.--Distinction of the Four - Principal Forms (types or branches) of the Animal - Kingdom, by Cuvier and Baer.--Cuvier's Services to - Palaeontology.--His Hypothesis of the Revolutions of our - Globe, and the Epochs of Creation separated by - them.--Unknown Supernatural Causes of the Revolutions, - and the subsequent New Creations.--Agassiz's Teleological - System of Nature.--His Conception of the Plan of - Creation, and its six Categories (groups in - classification).--Agassiz's Views of the Creation of - Species.--Rude Conception of the Creator as a man-like - being in Agassiz's Hypothesis of Creation.--Its internal - Inconsistency and Contradictions with the important - Palaeontological Laws discovered by Agassiz. - - -The real matter of dissension in the contest carried on by naturalists -as to the origin of organisms, their creation and development, lies in -the conceptions which are entertained about the _nature of species_. -Naturalists either agree with Linnaeus, and look upon the different -species as distinct forms of creation, independent of one another, or -they assume with Darwin their blood-relationship. If we share Linnaeus' -view (which was discussed in our last chapter), that the different -organic species came into existence independently--that they have no -blood-relationship--we are forced to admit that they were created -independently, and we must either suppose that every single organic -individual was a special act of creation (to which surely no naturalist -will agree), or we must derive all individuals of every species from a -single individual, or from a single pair, which did not arise in a -natural manner, but was called into being by command of a Creator. In so -doing, however, we turn aside from the safe domain of a rational -knowledge of nature, and take refuge in the mythological belief in -miracles. - -If, on the other hand, with Darwin, we refer the similarity of form of -the different species to real blood-relationship, we must consider all -the different species of animals and plants as the altered descendants -of one or a few most simple original forms. Viewed in this way, the -Natural System of organisms (that is, their tree-like and branching -arrangement and division into classes, orders, families, genera, and -species) acquires the significance of a real genealogical tree, whose -root is formed by those original archaic forms which have long since -disappeared. But a truly natural and consistent view of organisms can -assume no supernatural act of creation for even those simplest original -forms, but only a coming into existence by _spontaneous generation_[2] -(archigony, or generatio spontanea). From Darwin's view of the nature of -species, we arrive therefore at a _natural theory of development_; but -from Linnaeus' conception of the idea of species, we must assume a -_supernatural dogma of creation_. - -Most naturalists after Linnaeus, whose great services in -systematic and descriptive natural history won for him such high -authority, followed in his footsteps, and without further inquiry into -the origin of organization, they assumed, in the sense of Linnaeus, an -independent creation of individual species, in conformity with the -Mosaic account of creation. The foundation of their conception was based -upon Linnaeus' words: "There are as many different species as there were -different forms created in the beginning by the Infinite Being." We must -here remark at once, without going further into the definition of -species, that all zoologists and botanists in their classificatory -systems, in the practical distinction and designation of species of -animals and plants, never troubled, or even could trouble, themselves in -the slightest degree about this assumed creation of the parent forms. In -reference to this, one of our first zoologists, the ingenious Fritz -Mueller, makes the following striking observation: "Just as in Christian -countries there is a catechism of morals, which every one knows by -heart, but which no one considers it his duty to follow, or expects to -see followed by others,--so zoology also has its dogmas, which are just -as generally professed as they are denied in practice." (Fuer Darwin, p. -71.)(16) - -Linnaeus' venerated dogma of species is just such an irrational dogma, -and for that very reason it is powerful. Although most naturalists -blindly submitted to it, yet they were, of course, never in a position -to demonstrate the descent of individuals belonging to one species from -the common, originally created, primitive form. Zoologists and -botanists, in their systems of nomenclature, confined themselves -entirely to the similarity of forms, in order to distinguish and name -the different species. They placed in one species all organic -individuals which were very similar, or almost identical in form, and -which could only be distinguished from one another by very unimportant -differences. On the other hand, they considered as different species -those individuals which presented more essential or more striking -differences in the formation of their bodies. But of course this opened -the flood-gates to the most arbitrary proceedings in the systematic -distinctions of species. For as all the individuals of one species are -never completely alike in all their parts, but as every species varies -more or less, no one could point out which degree of variation -constituted a really "good species," or which degree indicated a "mere -variety." - -This dogmatic conception of the idea of species, and the arbitrary -proceedings connected with it, necessarily led to the most perplexing -contradictions, and to the most untenable suppositions. This is clearly -demonstrable in the case of the celebrated Cuvier (born in 1769), who -next to Linnaeus has exercised the greatest influence on the study of -zoology. In his conception and definition of the idea of species, he -agreed on the whole with Linnaeus, and shared also his belief in an -independent creation of individual species. Cuvier considered their -immutability of such importance that he was led to the foolish -assertion--"The immutability of species is a necessary condition of the -existence of scientific natural history." As Linnaeus' definition of -species did not satisfy him, he made an attempt to give a more exact -and, for systematic practice, a more useful definition, in the following -words: "All those individual animals and plants belong to one species -which can be proved to be either descended from one another, or from -common ancestors, or which are as similar to these as the latter are -among themselves." - -In dealing with this matter, Cuvier reasoned in the following -manner:--"In those organic individuals, of which we know that they are -descended from one and the same common form of ancestors--in which, -therefore, their common ancestry is empirically proved--there can be no -doubt that they belong to one species, whether they differ much or -little from one another, or whether they are almost alike or very -unlike. Moreover, all those individuals also belong to this species -which differ no more from the latter (those proved to be derived from a -common stock) than these differ from one another." In a closer -examination of this definition of species given by Cuvier, it becomes at -once evident that it is neither theoretically satisfactory nor -practically applicable. Cuvier, with this definition, began to move in -the same circle in which almost all subsequent definitions of species -have moved, through the assumption of their immutability. - -Considering the extraordinary authority which George Cuvier has gained -in the science of organic nature, and in consequence of the almost -unlimited supremacy which his views exercised in zoology, during the -first half of our century, it seems appropriate here to examine his -influence a little more closely. This is all the more necessary as we -have to combat, in Cuvier, the most formidable opponent to the Theory of -Descent and the monistic conception of nature. - -One of the many and great merits of Cuvier is that he stands forth as -the founder of Comparative Anatomy. While Linnaeus established the -distinction of species, genera, orders, and classes mostly upon external -characters, and upon separate and easily discoverable signs in the -number, size, place, and form of individual organic parts of the body, -Cuvier penetrated much more deeply into the essence of organization. He -demonstrated great and wide differences in the inner structure of -animals, as the real foundation of a scientific knowledge and -classification of them. He distinguished natural families in the classes -of animals, and established his natural system of the animal kingdom on -their comparative anatomy. - -The progress from Linnaeus' artificial system to Cuvier's natural system -was exceedingly important. Linnaeus had arranged all animals in a single -series, which he divided into six classes, two classes of Invertebrate, -and four classes of Vertebrate animals. He distinguished these -artificially, according to the nature of their blood and heart. Cuvier, -on the other hand, showed that in the animal kingdom there were four -great natural divisions to be distinguished, which he termed Principal -Forms, or General Plans, or Branches of the animal kingdom -(Embranchments), namely--1. The Vertebrate animals (Vertebrata); 2. The -Articulate animals (Articulata); 3. The Molluscous animals (Mollusca); -and 4. The Radiate animals (Radiata). He further demonstrated that in -each of these four branches a peculiar plan of structure or type was -discernible, distinguishing each branch from the three others. In the -Vertebrate animals it is distinctly expressed by the form of the -skeleton, or bony framework, as also by the structure and position of -the dorsal nerve-chord, apart from many other peculiarities. The -Articulate animals are characterized by their ventral nerve-chord and -their dorsal heart. In Molluscs the sack-shaped and non-articulate body -is the distinguishing feature. The Radiate animals, finally, differ -from the three other principal forms by their body being the combination -of four or more main sections united in the form of radii (antimera). - -The distinction of these four principal forms of animals, which has -become extremely productive in the development of zoology, is commonly -ascribed entirely to Cuvier. However, the same thought was expressed -almost simultaneously, and independently of Cuvier, by Baer, one of the -greatest naturalists, and still living, who did the most eminent service -in the study of animal development. Baer showed that in the development -of animals, also, four different main forms (or types) must be -distinguished.(20) These correspond with the four plans of structure in -animals, which Cuvier distinguished on the ground of comparative -anatomy. Thus, for example, the individual development of all Vertebrate -animals agrees, from the commencement, so much in its fundamental -features that the germs or embryos of different Vertebrate animals (for -example, of reptiles, birds, and mammals) in their earlier stages cannot -be distinguished at all. It is only at a late stage of development that -there gradually appear the more marked differences of form which -separate those different classes and orders from one another. The plan -of structure, which shows itself in the individual development of -Articulate animals (insects, spiders, crabs), is from the beginning -essentially the same in all Articulate animals, but different from that -of all Vertebrate animals. The same holds good, with certain -limitations, in Molluscous and Radiated animals. - -Neither Baer, who arrived at the distinction of the four animal types or -principal forms through the history of the individual development -(Embryology), nor Cuvier, who arrived at the same conclusion by means -of comparative anatomy, recognized the true cause of this difference. -This is disclosed to us by the Theory of Descent. The wonderful and -astonishing similarity in the inner organization and in the anatomical -relations of structure, and the still more remarkable agreement in the -embryonic development of all animals belonging to one and the same type -(for example, to the branch of the Vertebrate animals), is explained in -the simplest manner by the supposition of their common descent from a -single primary original form. If this view is not accepted, then the -complete agreement of the most different Vertebrate animals, in their -inner structure and their manner of development, remains perfectly -inexplicable. In fact it can only be explained by the law of -_inheritance_. - -Next to the comparative anatomy of animals and the systematic zoology -founded anew by it, it was specially to the science of petrifactions, or -Palaeontology, that Cuvier rendered great service. We must draw special -attention to this, because these very palaeontological views, and the -geological ideas connected with them, were held almost universally in -the highest esteem during the first half of the present century, and -caused the greatest hindrance to the working out of a truly natural -history of creation. - -Petrifactions, the scientific study of which Cuvier promoted at the -beginning of our century in a most extensive manner, and established -quite anew for the Vertebrate animals, play one of the most important -parts in the "non-miraculous history of creation." For these remains and -impressions of extinct animals and plants, preserved to us in a -petrified condition, are the true "monuments of the creation," the -infallible and indisputable records which fix the correct history of -organisms upon an irrefragable foundation. All petrified or fossil -remains and impressions tell us of the forms and structure of such -animals and plants as are either the progenitors and ancestors of the -present living organisms, or they are the representatives of extinct -collateral lines, which, together with the present living organisms, -branched off from a common stem. - -These inestimable records of the history of creation throughout a long -period played a subordinate part in science. Their true nature was -indeed correctly understood, even more than five hundred years before -Christ, by the great Greek philosopher, Xenophanes of Colophon, the same -who founded the so-called Eleatic philosophy, and who was the first to -demonstrate with convincing precision that all conceptions of personal -gods result in more or less rude anthropomorphism. - -Xenophanes for the first time, asserted that the fossil impressions of -animals and plants were real remains of formerly living creatures, and -that the mountains in whose rocks they were found must at an earlier -date have stood under water. But although other great philosophers of -antiquity, and among them Aristotle, also possessed this true knowledge, -yet throughout the illiterate Middle Ages, and even with some -naturalists of the last century, the idea prevailed that petrifactions -were so-called freaks of nature (lusus naturae), or products of an -unknown formative power or instinct of nature (nisus formativus, vis -plastica). Respecting the nature of this mysterious and mystic creative -power, the strangest ideas were formed. Some believed that this -constructive power--the same to which they also ascribed the coming -into existence of the present species of animals and plants--had made -numerous attempts to create organisms of different forms, but that these -attempts had only partially succeeded, had often failed, and that -petrifactions were nothing more than such unsuccessful attempts. -According to others, petrifactions originated from the influence of the -stars upon the interior of the earth. - -Others, again, had the still cruder notion that the Creator had first -made models (out of mineral substances--for example, of gypsum or clay) -of those forms of animals and plants which he afterwards executed in -organic substances, and into which he breathed his living breath; -petrifactions were accordingly such rude inorganic models. Even as late -as the last century these crude ideas prevailed, and it was assumed, for -example, that there existed a special "seminal air," which was said to -penetrate into the earth with the water, and by fructifying the stones -formed petrifactions or "stony flesh" (caro fossilis). - -It took a very long time before the simple and natural view was -accepted, namely, that petrifactions are in reality nothing but what -they appear to simple observation--the indestructible remains of extinct -organisms. It is true the celebrated painter, Leonardo da Vinci, in the -15th century, ventured to assert that the mud which was constantly -deposited by water was the cause of petrifactions, as it surrounded the -indestructible shells of mussels and snails which lay at the bottom of -the waters, and gradually turned them into solid stone. The same idea -was maintained in the 16th century by a Parisian potter, Palissy by -name, who became celebrated on account of his invention of china. -However, the so-called "professional men" were very far from paying any -regard to these correct assertions of a simple and healthy human -understanding; it was not till the end of the last century that it was -generally accepted, in consequence of the foundation of the Neptunian -geology by Werner. - -The foundation of a more strictly scientific palaeontology, however, -belongs to the beginning of our century, when Cuvier published his -classic researches on petrified Vertebrate animals, and when his great -opponent, Lamarck, made known his remarkable investigations on fossil -Invertebrate animals, especially on petrified snails and clams. In -Cuvier's celebrated work "On the Fossil Bones" of Vertebrate -animals--principally of mammals and reptiles--we see that he had already -arrived at the knowledge of some very important and general -palaeontological laws, which are of great consequence to the history of -creation. Foremost among them stands the assertion that the extinct -species of animals, whose remains we find petrified in the different -strata of the earth's crust, lying one above another, differ all the -more strikingly from the still living kindred species of animals the -deeper those strata lie--in other words, the earlier the animals lived -in past ages. In fact, in every perpendicular section of the stratified -crust of the earth we find that the different strata, deposited by the -water in a certain historical succession, are characterized by different -petrifactions, and that these extinct organisms become more like those -of the present day the higher the strata lie; in other words, the more -recent the period in the earth's history in which they lived, died, and -became encrusted by the deposited and hardened strata of mud. - -However important this general observation of Cuvier's was in one -sense, yet in another it became to him the source of a very serious -error. For as he considered the characteristic petrifactions of each -individual group of strata (which had been deposited during one main -period of the earth's history) to be entirely different from those of -the strata lying above or below, and as he erroneously believed that one -and the same species of animal was never found in two succeeding groups -of strata, he arrived at the false idea, which was accepted as a law by -most subsequent naturalists, that a series of quite distinct periods of -creation had succeeded one another. Each period was supposed to have had -its special animal and vegetable world, each its peculiar specific Fauna -and Flora. - -Cuvier imagined that the whole history of the earth's crust, since the -time when living creatures had first appeared on the surface, must be -divided into a number of perfectly distinct periods, or divisions of -time, and that the individual periods must have been separated from one -another by peculiar revolutions of an unknown nature (cataclysms, or -catastrophes). Each revolution was followed by the utter annihilation of -the till then existing animals and plants, and after its termination a -completely new creation of organic forms took place. A new world of -animals and plants, absolutely and specifically distinct from those of -the preceding historical periods, was called into existence at once, and -now again peopled the globe for thousands of years, till it again -perished suddenly in the crash of a new revolution. - -About the nature and causes of these revolutions, Cuvier expressly said -that no idea could be formed, and that the present active forces in -nature were not sufficient for their explanation. Cuvier points out four -active causes as the natural forces, or mechanical agents, at present -constantly but slowly at work in changing the earth's surface: first, -_rain_, which washes down the steep mountain slopes and heaps up debris -at their foot; secondly, _flowing waters_, which carry away this debris -and deposit it as mud in stagnant waters; thirdly, the sea, whose -breakers gnaw at the steep _sea_ coasts, and throw up "dunes" on the -flat sea margins; finally and fourthly, _volcanos_, which break through -and heave up the strata of the earth's hardened crust, and pile up and -scatter about the products of their eruptions. Whilst Cuvier recognizes -the constant slow transformation of the present surface of the earth by -these four mighty causes, he asserts at the same time that they would -not have sufficed to effect the revolutions of the remote ages, and that -the anatomical structure of the earth's surface cannot be explained by -the necessary action of those mechanical agents: the great and -marvellous revolutions of the whole earth's surface must, according to -him, have been rather the effects of very peculiar causes, completely -unknown to us; the usual thread of development was broken by them, and -the course of nature altered. - -These views Cuvier explained in a special work "On the Revolutions of -the Earth's Surface, and the Changes which they have wrought in the -Animal World." They were maintained, and generally accepted for a long -time, and became the greatest obstacle to the development of a natural -history of the creation. For if such all-destructive revolutions had -actually occurred, of course a continuity of the development of species, -a connecting thread in the organic history of the earth, could not be -admitted at all, and we should be obliged to have recourse to the -action of supernatural forces; that is, to the interference of miracles -in the natural course of things. It is only through miracles that these -revolutions of the earth could have been brought about, and it is only -through miracles that, after their cessation and at the commencement of -each new period, a new animal and vegetable kingdom could have been -created. But science has no room for miracles, for by miracles we -understand an interference of supernatural forces in the natural course -of development of matter. - -Just as the great authority which Linnaeus gained by his system of -distinguishing and naming organic species led his successors to a -complete ossification, as it were, of the dogmatic idea of species and -to a real abuse of the systematic distinction implied by it, so the -great services which Cuvier had rendered to the knowledge and -distinction of extinct species became the cause of a general adoption of -his theory of revolutions and catastrophes, and of the false views of -creation connected therewith. The consequence of this was that, during -the first half of our century, most zoologists and botanists clung to -the opinion that a series of independent periods in the organic history -of the earth had existed; that each period was distinguished by distinct -and peculiar kinds of animal and vegetable species; that these were -annihilated at the termination of the period by a general revolution; -and that, after the cessation of the latter, a new world of different -species of animals and plants was created. - -It is true some independent thinkers, above all the great physical -philosopher, Lamarck, even at an early period, set forth a series of -weighty reasons which refuted Cuvier's theory of cataclysms, and -pointed to a perfectly continuous and uninterrupted developmental -history of all the organic inhabitants of the earth through all ages. -They maintained that the animal and vegetable species of each period -were derived from those of the preceding period, and were only the -altered descendants of the former. This true conception, however, being -opposed to Cuvier's great authority, was then unable to make way. Nay, -even after Cuvier's theory of catastrophes had been completely cast out -from the domain of geology by Lyell's classic Principles of Geology, -which appeared in 1830, still his idea of the specific distinctness of a -series of organic creations maintained its influence, in many ways, in -the science of Palaeontology. (Gen. Morph. ii. 312.) - -By a curious coincidence, thirteen years ago, almost at the same time -that Cuvier's History of Creation received its death-blow by Darwin's -book, another celebrated naturalist made an attempt to re-establish it, -and to adopt it in the roughest manner, as a part of a -teleologico-theological system of nature. This was the Swiss geologist, -Louis Agassiz, who attained a great reputation by his theory of glaciers -and the ice-period, borrowed from Schimper and Charpentier, and who has -been living in North America for many years. He commenced in 1858 to -publish a work planned on a very large scale, which bears the title of -"Contributions to the Natural History of the United States of North -America." The first volume of this work, although large and costly, -owing to the patriotism of the Americans, had an unprecedented sale; its -title is, "An Essay on Classification."(5) - -In this essay Agassiz not only discusses the natural series of -organisms, and the different attempts of naturalists at classification, -but also all the general biological phenomena which have reference to -it. The history of the development of organisms, both the embryonal and -the palaeontological, comparative anatomy, the general economy of nature, -the geographical and topographical distribution of animals and -plants--in short, almost all the general phenomena of organic nature are -discussed in Agassiz's Essay on Classification, and are explained in a -sense and from a point of view which is thoroughly opposed to that of -Darwin. While Darwin's chief merit lies in the fact that he demonstrates -natural causes for the coming into existence of animal and vegetable -species, and thereby establishes the mechanical or monistic view of the -universe as regards this most difficult branch of the history of -creation, Agassiz, on the contrary, strives to exclude every mechanical -hypothesis from the subject, and to put the supernatural interference of -a personal Creator in the place of the natural forces of matter; -consequently, to establish a thoroughly teleological or dualistic view -of the universe. It will not be out of place if I examine a little more -closely Agassiz's biological views, and especially his ideas of -creation, because no other work of our opponents treats the important -fundamental questions with equal minuteness, and because the utter -untenableness of the dualistic conception of nature becomes very evident -from the failure of this attempt. - -The organic _species_, the various conceptions of which we have above -designated as the real centre of dispute in the opposed views of -creation, is looked upon by Agassiz, as by Cuvier and Linnaeus, as a form -unchangeable in all its essential characteristics. The species may -indeed change and vary within certain narrow limits; never in essential -qualities, but only in unessential points. No new species could ever -proceed from the changes or varieties of a species. Not one of all -organic species, therefore, is ever derived from another, but each -individual species has been separately created by God. Each individual -species, as Agassiz expresses it, is "an embodied creative thought" of -God. - -In direct opposition to the fact established by palaeontological -experience, that the duration of the individual organic species is most -unequal, and that many species continue unchanged through several -successive periods of the earth's history, while others only existed -during a small portion of such a period, Agassiz maintains that one and -the same species never occurs in two different periods, but that each -individual period is characterized by species of animals and plants -which are quite peculiar, and belong to it exclusively. He further -shares Cuvier's opinion that the whole of these inhabitants were -annihilated by the great and universal revolutions of the earth's -surface, which divide two successive periods, and that after its -destruction a new and specifically different assemblage of organisms was -created. This new creation Agassiz supposes to have taken place in this -manner: viz., that at each creation all the inhabitants of the earth, in -their full average number of individuals, and in the peculiar relations -corresponding to the economy of nature, were, as a whole, suddenly -placed upon the earth by the Creator. In saying this he puts himself in -opposition to one of the most firmly established and most important laws -of animal and vegetable geography--namely, to the law that each species -has a single original locality of origin, or a so-called "centre of -creation," from which it has gradually spread over the rest of the -earth. Instead of this, Agassiz assumes each species to have been -created at several points of the earth's surface, and that in each case -a large number of individuals was created. - -The "natural system" of organisms, the different groups and categories -of which arranged above one another--namely, the branches, classes, -orders, families, genera, and species--we consider, in accordance with -the Theory of Descent, as different branches and twigs of the organic -family-tree, is, according to Agassiz, the direct expression of the -divine plan of creation, and the naturalist, while investigating the -natural system, repeats the creative thoughts of God. In this Agassiz -finds the strongest proof that man is the image and child of God. The -different stages of groups or categories of the natural system -correspond with the different stages of development which the divine -plan of creation had attained. The Creator, in projecting and carrying -out this plan, starting from the most general ideas of creation, plunged -more and more into specialities. For instance, when creating the animal -kingdom, God had in the first place four totally distinct ideas of -animal bodies, which he embodied in the different structures of the four -great, principal forms, types, or branches of the animal kingdom; -namely, vertebrate animals, articulate animals, molluscous animals, and -radiate animals. The Creator then, having reflected in what manner he -might vary these four different plans of structure, next created within -each of the four principal forms, several different classes--for -example, in the vertebrate animal form, the classes of mammals, birds, -reptiles, amphibious animals, and fishes. Then God further reflected -upon the individual classes, and by various modifications in the -structure of each class, he produced the individual orders. By further -variation in the order, he created natural families. As the Creator -further varied the peculiarities of structure of individual parts in -each family, genera arose. In further meditation on his plan of -creation, he entered so much into detail that individual species came -into existence, which, consequently, are embodied creative thoughts of -the most special kind. It is only to be regretted that the Creator -expressed these most special and most deeply considered "creative -thoughts" in so very indistinct and loose a manner, and that he -imprinted so vague a stamp upon them, and permitted them to vary so -freely that not one naturalist is able to distinguish the "good" from -the "bad species," or a genuine species from varieties, races, etc. -(Gen. Morph. ii. 373.) - -We see, then, according to Agassiz's conception, that the Creator, in -producing organic forms, goes to work exactly as a human architect, who -has taken upon himself the task of devising and producing as many -different buildings as possible, for the most manifold purposes, in the -most different styles, in various degrees of simplicity, splendour, -greatness, and perfection. This architect would perhaps at first choose -four different styles for all these buildings, say the Gothic, -Byzantine, Chinese, and Rococo styles. In each of these styles he would -build a number of churches, palaces, garrisons, prisons, and -dwelling-houses. Each of these different buildings he would execute in -ruder and more perfect, in greater and smaller, in simpler and grander -fashion, etc. However, the human architect would perhaps, in this -respect, be better off than the divine Creator, as he would have perfect -liberty in the number of graduated subordinate groups. The Creator, -however, according to Agassiz, can only move within six groups or -categories: the species, genus, family, order, class, and type. More -than these six categories do not exist for him. - -When we read Agassiz's book on classification, and see how he carries -out and establishes these strange ideas, we can scarcely understand how, -with all the appearance of scientific earnestness, he can persevere in -his idea of the divine Creator as a man-like being (anthropomorphism), -for by his explanation of details he produces a picture of the most -absurd nonsense. In the whole series of these suppositions the Creator -is nothing but an all-mighty man, who, plagued with _ennui_, amuses -himself with planning and constructing most varied toys in the shape of -organic species. After having diverted himself with these for thousands -of years, they become tiresome to him, he destroys them by a general -revolution of the earth's surface, and thus throws the whole of the -useless toys in heaps together; then, in order to while away his time -with something new and better, he calls a new and more perfect animal -and vegetable world into existence. But in order not to have the trouble -of beginning the work of creation over again, he keeps, in the main, to -his original plan of creation, and creates merely new species, or at -most only new genera, and much more rarely new families, new orders, or -classes. He never succeeds in producing a new style or type, and always -keeps strictly within the six categories or graduated groups. - -When, according to Agassiz, the Creator has thus amused himself for -thousands of millions of years with constructing and destroying a series -of different creations, at last (but very late) he is struck with the -happy thought of creating something like himself, and so makes man in -his own image. The end of all the history of creation is thus arrived at -and the series of revolutions of the earth is closed. Man, the child and -image of God, gives him so much to do, causes him so much pleasure and -trouble, that he is wearied no longer, and therefore need not undertake -a new creation. It is clear that if, according to Agassiz, we once -assign to the Creator entirely human attributes and qualities, and -regard his work of creation as entirely analogous to human creative -activity, we are necessarily obliged to admit such utterly absurd -inferences as those just stated. - -The many intrinsic contradictions and perversities in Agassiz's view of -creation--a view which necessarily led him to the most decided -opposition to the Theory of Descent--must excite our astonishment all -the more because, in his earlier scientific works, he had in many -respects actually paved the way for Darwin, especially by his researches -in Palaeontology. Among the numerous investigations which created general -interest in the then young science of Palaeontology, those of Agassiz, -especially his celebrated work on "Fossil Fish," rank next in importance -to Cuvier's work, which formed the foundation of the science. The -petrified fish, with which Agassiz has made us acquainted, have not only -an extremely great importance for the understanding of all groups of -Vertebrate animals, and their historical development, but we have -arrived through them at a sure knowledge of important general laws of -development, some of which were first discovered by Agassiz. He it was -who drew special attention to the remarkable parallelism between the -embryonal and the palaeontological development--between ontogeny and -phylogeny, which I have already (p. 10) claimed as one of the strongest -pillars of the Theory of Descent. No one before had so distinctly stated -as Agassiz did, that, of the Vertebrate animals, fishes alone existed, -at first, that amphibious animals came later, and that birds and mammals -appeared only at a much later period, further, that among mammals, as -among fishes, imperfect and lower orders had appeared first, but more -perfect and higher orders at a later period. Agassiz, therefore, showed -that the palaeontological development of the whole Vertebrate group was -not only parallel with the embryonic, but also with the systematic -development, that is, with the graduated series which we see everywhere -in the system, ascending from the lower to the higher classes, orders, -etc. - -In the earth's history lower forms appeared first, the higher forms -later. This important fact, as well as the agreement of the embryonic -and palaeontological development, is explained quite simply and naturally -by the Doctrine of Descent, and without it is perfectly inexplicable. -This cause holds good also in the great law of _progressive -development_, that is, of the historical progress of organization, which -is traceable, broadly and as a whole, in the historical succession of -all organisms, as well as in the special perfecting of individual parts -of animal bodies. Thus, for example, the skeleton of Vertebrate animals -acquired at first slowly, and by degrees, that high degree of perfection -which it now possesses in man and the other higher Vertebrate animals. -This progress, acknowledged in point of fact by Agassiz, necessarily -follows from Darwin's Doctrine of Descent, which demonstrates its active -causes. If this doctrine is correct, the perfecting and diversification -of animal and vegetable species must of necessity have gradually -increased in the course of the organic history of the earth, and could -only attain its highest perfection in most recent times. - -The above-mentioned laws of development, together with some other -general ones, which have been expressly admitted and justly emphasized -by Agassiz, and some of which have first been set forth by him, are, as -we shall see later, only explicable by the Theory of Descent, and -without it remain perfectly incomprehensible. The conjoint action of -Inheritance and Adaptation, as explained by Darwin, can alone be their -true cause. But they all stand in sharp and irreconcilable opposition to -the hypothesis of creation maintained by Agassiz, as well as to the idea -of a personal Creator who acts for a definite purpose. If we seriously -wish to explain those remarkable phenomena and their inter-connection by -Agassiz's theory, then we are necessarily driven to the curious -supposition that the Creator himself has developed, together with the -organic nature which he created and modelled. We can, in that case, no -longer rid ourselves of the idea that the Creator himself, like a human -being, designed, improved, and finally, with many alterations, carried -out his plans. "Man grows as higher grow his aims," and the same -supposition, so unworthy of a God, must be applied to him. Although, -from the reverence with which, in every page, Agassiz speaks of the -Creator, it might appear that, on his theory, we attain to the sublimest -conception of the divine activity in nature, yet the contrary is in -truth the case. The divine Creator is degraded to the level of an -idealized man, of an organism progressing in development! - -Considering the wide popularity and great authority which Agassiz's work -has gained, and which is perhaps justified on account of earlier -scientific services rendered by the author, I have thought it my duty -here to show the utter untenableness of his general conceptions. So far -as this work pretends to be a scientific history of creation, it is -undoubtedly a complete failure. But still it has great value, being the -only detailed attempt, adorned with scientific arguments, which an -eminent naturalist of our day has made to found a teleological or -dualistic history of creation. The utter impossibility of such a history -has thus been made obvious to every one. No opponent of Agassiz could -have refuted the dualistic conception of organic nature and its origin -more strikingly than he himself has done by the intrinsic contradictions -which present themselves everywhere in his theory. - -The opponents of the monistic or mechanical conception of the world have -welcomed Agassiz's work with delight, and find in it a perfect proof of -the direct creative action of a personal God. But they overlook the fact -that this personal Creator is only an idealized organism, endowed with -human attributes. This low dualistic conception of God corresponds with -a low animal stage of development of the human organism. The more -developed man of the present day is capable of, and justified in, -conceiving that infinitely nobler and sublimer idea of God which alone -is compatible with the monistic conception of the universe, and which -recognizes God's spirit and power in all phenomena without exception. -This monistic idea of God, which belongs to the future, has already been -expressed by Giordano Bruno in the following words:--"A spirit exists in -all things, and no body is so small but contains a part of the divine -substance within itself, by which it is animated." It is of this noble -idea of God that Goethe says:--"Certainly there does not exist a more -beautiful worship of God than that which needs no image, but which -arises in our heart from converse with Nature." By it we arrive at the -sublime idea of the Unity of God and Nature. - - - - -CHAPTER IV. - -THEORY OF DEVELOPMENT ACCORDING TO GOETHE AND OKEN. - - - Scientific Insufficiency of all Conceptions of a Creation - of Individual Species.--Necessity of the Counter Theories - of Development.--Historical Survey of the Most Important - Theories of Development.--Aristotle.--His Doctrine of - Spontaneous Generation.--The Meaning of Natural - Philosophy.--Goethe.--His Merits as a Naturalist.--His - Metamorphosis of Plants.--His Vertebral Theory of the - Skull.--His Discovery of the Mid Jawbone in - Man.--Goethe's Interest in the Dispute between Cuvier and - Geoffroy St. Hilaire.--Goethe's Discovery of the Two - Organic Formative Principles, of the Conservative - Principle of Specification (by Inheritance), and of the - Progressive Principle of Transformation (by - Adaptation).--Goethe's Views of the Common Descent of all - Vertebrate Animals, including Man.--Theory of Development - according to Gottfried Reinhold Treviranus.--His Monistic - Conception of Nature.--Oken.--His Natural - Philosophy.--Oken's Theory of Protoplasm.--Oken's Theory - of Infusoria (Cell Theory).--Oken's Theory of - Development. - - -All the different ideas which we may form of a separate and independent -origin of the individual organic species by creation lead us, when -logically carried out, to a so-called _anthropomorphism_, that is, to -imagining the Creator as a man-like being, as was shown in our last -chapter. The Creator becomes an organism who designs a plan, reflects -upon and varies this plan, and finally forms creatures according to this -plan, as a human architect would his building. If even such eminent -naturalists as Linnaeus, Cuvier, and Agassiz, the principal -representatives of the dualistic hypothesis of creation, could not -arrive at a more satisfactory view, we may take it as evidence of the -insufficiency of all those conceptions which would derive the various -forms of organic nature from a creation of individual species. - -Some naturalists, indeed, seeing the complete insufficiency of these -views, have tried to replace the idea of a personal Creator by that of -an unconsciously active and creative Force of Nature; yet this -expression is evidently merely an evasive phrase, as long as it is not -clearly shown what this force of nature is, and how it works. Hence -these attempts, also, have been absolute failures. In fact, whenever an -independent origin of the different forms of animals and plants has been -assumed, naturalists have found themselves compelled to fall back upon -so many "acts of creation," that is, on supernatural interferences of -the Creator in the natural course of things, which in all other cases -goes on without interference. - -It is true that several teleological naturalists, feeling the scientific -insufficiency of a supernatural "_creation_," have endeavoured to save -the hypothesis by wishing it to be understood that creation "is nothing -else than a way of coming into being, unknown and inconceivable to us." -The eminent Fritz Mueller has cut off from this sophistic evasion every -chance of escape by the following striking remark:--"It is intended here -only to express in a disguised manner the shamefaced confession, that -they neither have, nor care to have, _any opinion_ about the origin of -species. According to this explanation of the word, we might as well -speak of the creation of cholera, or syphilis, of the creation of a -conflagration, or of a railway accident, as of the creation of man." -(Jenaische Zestscrift, bd. v. p. 272.) - -In the face, then, of these hypotheses of creation, which are -scientifically insufficient, we are forced to seek refuge in the -_counter-theory of development_ of organisms, if we wish to come to a -rational conception of the origin of organisms. We are forced and -obliged to do so, even if the theory of development only throws a -glimmer of probability upon a mechanical, natural origin of the animal -and vegetable species; but all the more if, as we shall see, this theory -explains all facts simply and clearly, as well as completely and -comprehensively. The theories of development are by no means, as they -often falsely are represented to be, arbitrary fancies, or wilful -products of the imagination, which only attempt approximately to explain -the origin of this or that individual organism; but they are theories -founded strictly on science, which explain in the simplest manner, from -a fixed and clear point of view, the whole of organic natural phenomena, -and more especially the origin of organic species, and demonstrate them -to be the necessary consequences of mechanical processes in nature. - -As I have already shown in the second chapter, all these theories of -development coincide naturally with that general theory of the universe -which is usually designated as the uniform or _monistic_, often also as -the _mechanical_ or causal, because it only assumes mechanical causes, -or _causes working by necessity_ (causae efficientes), for the -explanation of natural phenomena. In like manner, on the other hand, the -supernatural hypotheses of creation which we have already discussed -coincide completely with the opposite view of the universe, which in -contrast to the former is called the twofold or _dualistic_, often the -_teleological_ or vital, because it traces the organic natural phenomena -to final causes, acting and _working for a definite purpose_ (causae -finales). It is this deep and intrinsic connection of the different -theories of creation with the most important questions of philosophy -that incites us to their closer examination. - -The fundamental idea, which must necessarily lie at the bottom of all -natural theories of development, is that of a _gradual development of -all (even the most perfect) organisms_ out of a single, or out of a very -few, quite simple, and quite imperfect original beings, which came into -existence, not by supernatural creation, but by _spontaneous -generation_, or archigony, out of inorganic matter. In reality, there -are two distinct conceptions united in this fundamental idea, but which -have, nevertheless, a deep intrinsic connection--namely, first, the idea -of spontaneous generation (or archigony) of the original primary beings; -and secondly, the idea of the progressive development of the various -species of organisms from those most simple primary beings. These two -important mechanical conceptions are the inseparable fundamental ideas -of every theory of development, if scientifically carried out. As it -maintains the derivation of the different species of animals and plants -from the simplest, common primary species, we may term it also the -Doctrine of Filiation, or _Theory of Descent_; as there is also a change -of species connected with it, it may also be termed the _Transmutation -Theory_. - -While the supernatural histories of creation must have originated -thousands of years ago, in that very remote primitive age when man, -first developing out of the monkey-state, began for the first time to -think more closely about himself, and about the origin of the world -around him, the natural theories of development, on the other hand, are -necessarily of much more recent origin. These views are met with only -among nations of a more matured civilization, to whom, by philosophic -culture, the necessity of a knowledge of natural causes has become -apparent; and even among these, only individual and specially gifted -natures can be expected to have recognized the origin of the world of -phenomena, as well as its course of development, as the necessary -consequences of mechanical, naturally active causes. In no nation have -these preliminary conditions, for the origin of a natural theory of -development, ever existed in so high a degree as among the Greeks of -classic antiquity. But, on the other hand, they lacked a close -acquaintance with the facts of the processes and forms of nature, and, -consequently, the foundation based upon experience, for a satisfactory -unravelling of the problem of development. Exact investigation of -nature, and the knowledge of nature founded on an experimental basis, -was of course almost unknown to antiquity, as well as to the Middle -Ages, and is only an acquisition of modern times. We have therefore here -no special occasion to examine the natural theories of development of -the various Greek philosophers, since they were wanting in the knowledge -gained by experience, both of organic and inorganic nature, and since -they almost always, as the consequence, lost themselves in airy -speculations. - -One man only must be mentioned here by way of exception,--Aristotle, the -greatest and the only truly great naturalist of antiquity and the Middle -Ages, one of the grandest geniuses of all time. To what a degree he -stands there alone, during a period of more than two thousand years, in -the region of empirico-philosophical knowledge of nature, and especially -in his knowledge of organic nature, is proved to us by the precious -remains of his but partially surviving works. In them many traces are -found of a theory of natural development. Aristotle assumes, as a matter -of certainty, that spontaneous generation was the natural manner in -which the lower organic creatures came into existence. He describes -animals and plants originating from matter itself, through its own -original force; as, for example, moths from wool, fleas from putrid -dung, wood-lice from damp wood, etc. But as the distinction of organic -species, which Linnaeus only arrived at two thousand years later, was -unknown to him, he could form no ideas about their genealogical -relations. - -The fundamental notion of the theory of development, that the different -species of animals and plants have been developed from a common primary -species by transformation, could of course only be clearly asserted -after the kinds of species themselves had become better known, and after -the extinct species had been carefully examined and compared with the -living ones. This was not done until the end of the last and the -beginning of the present century. It was not until the year 1801 that -the great Lamarck expressed the theory of development, which he, in -1809, further elaborated in his classical "Philosophie Zoologique." -While Lamarck and his countryman, Geoffroy St. Hilaire, in France, -opposed Cuvier's views, and maintained a natural development of organic -species by transformation and descent, Goethe and Oken at the same time -pursued the same course in Germany, and helped to establish the theory -of development. As these naturalists are generally called -nature-philosophers (Naturphilosophen), and as this ambiguous -designation is correct in a certain sense, it appears to me appropriate -here to say a few words about the correct estimate of the -"Natur-philosophie." - -Although for many years in England the ideas of natural science and -philosophy have been looked upon as almost equivalent, and as every -truly scientific investigator of nature is most justly called there a -"natural philosopher," yet in Germany for more than half a century -natural science has been kept strictly distinct from philosophy, and the -union of the two into a true philosophy of nature is recognized only by -the few. This misapprehension is owing to the fantastic eccentricities -of earlier German natural-philosophers, such as Oken, Schelling, etc.; -they believed that they were able to construct the laws of nature in -their own heads, without being obliged to take their stand upon the -grounds of actual experience. When the complete hollowness of their -assumptions had been demonstrated, naturalists, in "the nation of -thinkers," fell into the very opposite extreme, believing that they -would be able to reach the high aim of science, that is, the knowledge -of truth, by the mere experience of the senses, and without any -philosophical activity of thought. - -From that time, but especially since 1830, most naturalists have shown a -strong aversion to any general, philosophical view of nature. The real -aim of natural science was now supposed to consist in the knowledge of -details, and it was believed that this would be attained in the study of -biology, when the forms and the phenomena of life, in all individual -organisms, had become accurately known, by the help of the finest -instruments and means of observation. It is true that among these -strictly empirical, or so-called exact naturalists, there were always -very many who rose above this narrow point of view, and sought the final -aim in a knowledge of the general laws of organization. Yet the great -majority of zoologists and botanists, during the thirty or forty years -preceding Darwin, refused to concern themselves about such general laws; -all they admitted was, that perhaps in the far distant future, when the -end of all empiric knowledge should have been arrived at, when all -individual animals and plants should have been thoroughly examined, -naturalists might begin to think of discovering general biological laws. - -If we consider and compare the most important advances which the human -mind has made in the knowledge of truth, we shall soon see that it is -always owing to philosophical mental operations that these advances have -been made, and that the experience of the senses which certainly and -necessarily precedes these operations, and the knowledge of details -gained thereby, only furnish the basis for those general laws. -Experience and philosophy, therefore, by no means stand in such -exclusive opposition to each other as most men have hitherto supposed; -they rather necessarily supplement each other. The philosopher who is -wanting in the firm foundation of sensuous experience, of empirical -knowledge, is very apt to arrive at false conclusions in his general -speculations, which even a moderately informed naturalist can refute at -once. On the other hand, the purely empiric naturalists, who do not -trouble themselves about the philosophical comprehension of their -sensuous experiences, and who do not strive after general knowledge, can -promote science only in a very slight degree, and the chief value of -their hard-won knowledge of details lies in the general results which -more comprehensive minds will one day derive from them. - -From a general survey of the course of biological development since -Linnaeus' time, we can easily see, as Baer has pointed out, a continual -vacillation between these two tendencies, at one time a prevalence of -the empirical--the so-called exact--and then again of the philosophical -or speculative tendency. Thus at the end of the last century, in -opposition to Linnaeus' purely empirical school, a natural-philosophical -reaction took place, the moving spirits of which, Lamarck, Geoffroy St. -Hilaire, Goethe, and Oken, endeavoured by their mental work to introduce -light and order into the chaos of the accumulated empirical raw -material. In opposition to the many errors and speculations of these -natural philosophers, who went too far, Cuvier then came forward, -introducing a second, purely empirical period. It reached its most -one-sided development between the years 1830-1860, and there now -followed a second philosophical reaction, caused by Darwin's work. Thus -during the last ten years, men again have begun to endeavour to obtain a -knowledge of the general laws of nature, to which, after all, all -detailed knowledge of experience serves only as a foundation, and -through which alone it acquires its true value. It is through philosophy -alone that natural knowledge becomes a true science, that is, a -philosophy of nature. (Gen. Morph. i. 63-108.) - -Jean Lamarck and Wolfgang Goethe stand at the head of all the great -philosophers of nature who first established a theory of organic -development, and who are the illustrious fellow-workers of Darwin. I -turn first to our beloved Goethe, who, among all, stands in the closest -relations to us Germans. However, before I explain his special services -to the theory of development, it seems to me necessary to say a few -words about his importance as a naturalist in general, as it is commonly -very little known. - -I am sure most of my readers honour Goethe only as a poet and a man; -only a few have any conception of the high value of his scientific -works, and of the gigantic stride with which he advanced before his own -age--advanced so much that most naturalists of that time were unable to -follow him. In several passages of his scientific writings he bitterly -complains of the narrow-mindedness of professed naturalists, who do not -know how to value his works (who cannot see the wood for the trees), and -who cannot rouse themselves to discover the general laws of nature among -the mass of details. He is only too just when he utters the -reproach--"The philosophers will very soon discover that observers -rarely rise to a stand-point from which they can survey so many -important objects." It is true, at the same time, that their want of -appreciation was caused by the false road into which Goethe was led in -his theory of colours. - -This theory of colours, which he himself designates as the favourite -production of his leisure, however much that is beautiful it may -contain, is a complete failure in regard to its foundations. The exact -mathematical method by means of which alone it is possible, in inorganic -sciences, but above all in physics, to raise a structure step by step on -a thoroughly firm basis, was altogether repugnant to Goethe. In -rejecting it he allowed himself not only to be very unjust towards the -most eminent physicists, but to be led into errors which have greatly -injured the fame of his other valuable works. It is quite different in -the organic sciences, in which we are but rarely able to proceed, from -the beginning, upon a firm mathematical basis; we are rather compelled, -by the infinitely difficult and intricate nature of the problem, at the -first to form inductions--that is, we are obliged to endeavour to -establish general laws by numerous individual observations, which are -not quite complete. A comparison of kindred series of phenomena, or the -method of combination, is here the most important instrument for -inquiry, and this method was applied by Goethe with as much success as -with conscious knowledge of its value, in his works relating to the -philosophy of nature. - -The most celebrated among Goethe's writings relating to organic nature -is his _Metamorphosis of Plants_, which appeared in 1790, a work which -distinctly shows a grasp of the fundamental idea of the theory of -development, inasmuch as Goethe, in it, was labouring to point out a -single organ, by the infinitely varied development and metamorphosis of -which the whole of the endless variety of forms in the world of plants -might be conceived to have arisen; this fundamental organ he found in -the _leaf_. If at that time the microscope had been generally employed, -if Goethe had examined the structure of organisms by the means of the -microscope he would have gone still further, and would have seen that -the leaf is itself a compound of individual parts of a lower order, that -is, of _cells_. He would then not have declared that the leaf, but that -the _cell_ is the real fundamental organ by the multiplication, -transformation, and combination (synthesis) of which, in the first -place, the leaf is formed; and that, in the next place, by -transformation, variation, and combination of leaves there arise all -the varied beauties in form and colour which we admire in the green -parts, as well as in the organs of propagation, or the flowers of -plants. Goethe here showed that in order to comprehend the whole of the -phenomena, we must in the first place compare them, and, secondly, -search for a simple type, a simple fundamental form, of which all other -forms are only infinite variations. - -Something similar to what he had here done for the metamorphosis of -plants he then did for the Vertebrate animals, in his celebrated -_vertebral theory of the skull_. Goethe was the first to show, -independently of Oken, who almost simultaneously arrived at the same -thought, that the skull of man and of all Vertebrate animals, in -particular mammals, is nothing more than a bony case, formed of the same -bones,--that is, vertebrae,--out of which the spine also is composed. The -vertebrae of the skull are like those of the spine, bony rings lying -behind each other, but in the skull are peculiarly changed and -specialized (differentiated). Although this idea has been strongly -modified by recent discoveries, yet in Goethe's day it was one of the -greatest advances in comparative anatomy, and was not only one of the -first advances towards the understanding of the structure of Vertebrate -animals, but at the same time explained many individual phenomena. When -two parts of a body, such as the skull and spine, which appear at first -sight so different, were proved to be parts originally the same, -developed out of one and the same foundation, one of the difficult -problems of the philosophy of nature was solved. Here again we meet the -notion of a single type--the conception of a single principle, which -becomes infinitely varied in the different species, and in the parts of -individual species. - -But Goethe did not merely endeavour to search for such far-reaching -laws, he also occupied himself most actively for a long time with -numerous individual researches, especially in comparative anatomy. Among -these, none is perhaps more interesting than the discovery of the _mid -jawbone in man_. As this is, in several respects, of importance to the -theory of development, I shall briefly explain it here. There exist in -all mammals two little bones in the upper jaw, which meet in the centre -of the face, below the nose, and which lie between the two halves of the -real upper jawbone. These two bones, which hold the four upper cutting -teeth, are recognized without difficulty in most mammals; in man, -however, they were at that time unknown, and celebrated comparative -anatomists even laid great stress upon this want of a mid jawbone, as -they considered it to constitute the principal difference between men -and apes--the want of a mid jawbone was, curiously enough, looked upon -as the most human of all human characteristics. But Goethe could not -accept the notion that man, who in all other corporeal respects was -clearly only a mammal of higher development, should lack this mid -jawbone. - -By the general law of induction as to the mid jawbone he arrived at the -special deductive conclusion that it must exist in man also, and Goethe -did not rest until, after comparing a great number of human skulls, he -really found the mid jawbone. In some individuals it is preserved -throughout a whole lifetime, but usually at an early age it coalesces -with the neighbouring upper jawbone, and is therefore only to be found -as an independent bone in very youthful skulls. In human embryos it can -now be pointed out at any moment. In man, therefore, the mid jawbone -actually exists, and to Goethe the honour is due of having first firmly -established this fact, so important in many respects; and this he did -while opposed by the celebrated anatomist, Peter Camper, one of the most -important professional authorities. The way by which Goethe succeeded in -establishing this fact is especially interesting; it is the way by which -we continually advance in biological science, namely, by way of -induction and deduction. _Induction_ is the inference of a general law -from the observation of numerous individual cases; _deduction_, on the -other hand, is an inference from this general law applied to a single -case which has not yet been actually observed. From the collected -empirical knowledge of those days, the inductive conclusion was arrived -at that all mammals had mid jawbones. Goethe drew from this the -deductive conclusion, that man, whose organization was in all other -respects not essentially different from mammals, must also possess this -mid jawbone; and on close examination it was actually found. The -deductive conclusion was confirmed and verified by experience. - -Even these few remarks may serve to show the great value which we must -ascribe to Goethe's biological researches. Unfortunately most of his -labours devoted to this subject are so hidden in his collected works, -and his most important observations and remarks so scattered in numerous -individual treatises--devoted to other subjects--that it is difficult to -find them out. It also sometimes happens that an excellent, truly -scientific remark is so much interwoven with a mass of useless -philosophical fancies, that the latter greatly detract from the former. - -Nothing is perhaps more characteristic of the extraordinary interest -which Goethe took in the investigation of organic nature than the lively -way in which, even in his last years, he followed the dispute which -broke out in France between Cuvier and Geoffroy de St. Hilaire. Goethe, -in a special treatise which was only finished a few days before his -death, in March, 1832, has given an interesting description of this -remarkable dispute and its general importance, as well as an excellent -sketch of the two great opponents. This treatise bears the title -"Principes de Philosophic Zoologique par M. Geoffroy de Saint Hilaire"; -it is Goethe's last work, and forms the conclusion of the collected -edition of his works. The dispute itself was, in several respects, of -the highest interest. It turned essentially upon the justification of -the theory of development. It was carried on, moreover, in the bosom of -the French Academy, by both opponents, with a personal vehemence almost -unheard of in the dignified sessions of that learned body; this proved -that both naturalists were fighting for their most sacred and deepest -convictions. The conflict began on the 22nd of February, and was -followed by several others; the fiercest took place on the 19th of July, -1830. Geoffroy, as the chief of the French nature-philosophers, -represented the theory of natural development and the monistic -conception of nature. He maintained the mutability of organic species, -the common descent of the individual species from common primary forms, -and the unity of their organization--or the unity of the plan of -structure, as it was then called. - -Cuvier was the most decided opponent of these views, and according to -what we have seen, it could not be otherwise. He endeavoured to show -that the nature-philosophers had no right to rear such comprehensive -conclusions on the basis of the empirical knowledge then possessed, and -that the unity of organization--or plan of structure of organisms--as -maintained by them, did not exist. He represented the teleological -(dualistic) conception of nature, and maintained that "the immutability -of species was a necessary condition for the existence of a scientific -history of nature," Cuvier had the great advantage over his opponent, -that he was able to bring towards the proof of his assertions things -obvious to the eye; these, however, were only individual facts taken out -of their connection with others. Geoffroy was not able to prove the -higher and general connection of individual phenomena which he -maintained, by equally tangible details. Hence Cuvier, in the eyes of -the majority, gained the victory, and decided the defeat of the -nature-philosophy and the supremacy of the strictly empiric tendency for -the next thirty years. - -Goethe of course supported Geoffroy's views. How deeply interested he -was, even in his 81st year, in this great contest is proved by the -following anecdote related by Soret:-- - -"Monday, Aug. 2nd, 1830.--The news of the outbreak of the revolution of -July arrived in Weimar to-day, and has caused general excitement. In the -course of the afternoon I went to Goethe. 'Well?' he exclaimed as I -entered, 'what do you think of this great event? The volcano has burst -forth, all is in flames, and there are no more negotiations behind -closed doors.' 'A dreadful affair,' I answered; 'but what else could be -expected under the circumstances, and with such a ministry, except that -it would end in the expulsion of the present royal family?' 'We do not -seem to understand each other, my dear friend,' replied Goethe. 'I am -not speaking of those people at all; I am interested in something very -different, I mean the dispute between Cuvier and Geoffroy de Saint -Hilaire, which has broken out in the Academy, and which is of such great -importance to science.' This remark of Goethe's came upon me so -unexpectedly, that I did not know what to say, and my thoughts for some -minutes seemed to have come to a complete standstill. 'The affair is of -the utmost importance,' he continued, 'and you cannot form any idea of -what I felt on receiving the news of the meeting on the 19th. In -Geoffroy de Saint Hilaire we have now a mighty ally for a long time to -come. But I see also how great the sympathy of the French scientific -world must be in this affair, for, in spite of the terrible political -excitement, the meeting on the 19th was attended by a full house. The -best of it is, however, that the synthetic treatment of nature, -introduced into France by Geoffroy, can now no longer be stopped. This -matter has now become public through the discussions in the Academy, -carried on in the presence of a large audience; it can no longer be -referred to secret committees, or be settled or suppressed behind closed -doors.'" - -In my book on "The General Morphology of Organisms" I have placed as -headings to the different books and chapters a selection of the numerous -interesting and important sentences in which Goethe clearly expresses -his view of organic nature and its constant development. I will here -quote a passage from the poem entitled, "The Metamorphosis of Animals" -(1819). - - "All members develop themselves according to eternal laws, - And the rarest form mysteriously preserves the primitive type, - Form therefore determines the animal's way of life, - And in turn the way of life powerfully reacts upon all form. - Thus the orderly growth of form is seen to hold - Whilst yielding to change from externally acting causes."[3] - -Here, clearly enough, the contrast between two different organic -constructive forms is intimated, which are opposed to one another, and -which by their interaction determine the form of the organism; on the -one hand, a common inner original type, firmly maintaining itself, -constitutes the foundation of the most different forms; on the other -hand, the externally active influence of surroundings and mode of life, -which influence the original type and transform it. This contrast is -still more definitely pointed out in the following passage:-- - -"An inner original community forms the foundation of all organization; -the variety of forms, on the other hand, arises from the necessary -relations to the outer world, and we may therefore justly assume an -original difference of conditions, together with an uninterruptedly -progressive transformation, in order to be able to comprehend the -constancy as well as the variations of the phenomena of form." - -The "original type" which constitutes the foundation of -every organic form "as the inner original community" is the _inner -constructive force_, which receives the original direction of -form-production--that is, the tendency to give rise to a particular -form--and is propagated by _Inheritance_. The "uninterruptedly -progressive transformation," on the other hand, which "springs from the -necessary relations to the outer world," acting as an _external -formative force_, produces, by _Adaptation_ to the surrounding -conditions of life, the "infinite variety of forms" (Gen. Morph. i. 154; -ii. 224). The internal formative tendency of _Inheritance_, which -retains the unity of the original type, is called by Goethe in another -passage the _centripetal force_ of the organism, or its tendency to -specification; in contrast with this he calls the external formative -tendency of _Adaptation_, which produces the variety of organic forms, -the _centrifugal force_ of organisms, or their tendency to variation. -The passage in which he clearly indicates the "equilibrium" of these two -extremely important organic formative tendencies, runs as follows: "The -idea of _metamorphosis_ resembles the vis centrifuga, and would lose -itself in the infinite, if a counterpoise were not added to it: I mean -the tendency to _specification_, the strong power to preserve what once -has come into being, a vis centripeta, which in its deepest foundation -cannot be affected by anything external." - -Metamorphosis, according to Goethe, consists not merely, as the word is -now generally understood, in the changes of form which the organic -individual experiences during its individual development, but, in a -wider sense, in the transformation of organic forms in general. His idea -of metamorphosis is almost synonymous with the theory of development. -This is clear, among other things, from the following passage:--"The -triumph of physiological metamorphosis manifests itself where the whole -separates and transforms itself into families, the families into genera, -the genera into species, and then again into other varieties down to the -individual. This operation of nature goes on ad infinitum; she cannot -rest inactive, but neither can she keep and preserve all that she has -produced. From seeds there are always developed varying plants, -exhibiting the relations of their parts to one another in an altered -manner." - -Goethe had, in truth, discovered two great mechanical forces of nature, -which are the active causes of organic formations, his two organic -formative tendencies--on the one hand the conservative, centripetal, and -internal formative tendency of Inheritance or specification; and on the -other hand the progressive, centrifugal, and external formative tendency -of Adaptation, or metamorphosis. This profound biological intuition -could not but lead him naturally to the fundamental idea of the Doctrine -of Filiation, that is, to the conception that the organic species -resembling one another in form are actually related by blood, and that -they are descended from a common original type. In regard to the most -important of all animal groups, namely that of Vertebrate animals, -Goethe expresses this doctrine in the following passage (1796):--"Thus -much then we have gained, that we may assert without hesitation that all -the more perfect organic natures, such as fishes, amphibious animals, -birds, mammals, and man at the head of the last, were all formed upon -one original type, which only varies more or less in parts which are -none the less permanent, and still daily changes and modifies its form -by propagation." - -This sentence is of interest in more than one way. The theory that all -"the more perfect organic natures," that is all Vertebrate animals, are -descended from one common prototype, that they have arisen from it by -propagation (Inheritance) and transformation (Adaptation), may be -distinctly inferred. But it is especially interesting to observe that -Goethe admits no exceptional position for man, but rather expressly -includes him in the tribe of the other Vertebrate animals. The most -important special inference of the Doctrine of Filiation, that man is -descended from other Vertebrate animals, may here be recognized in the -germ.(3) - -This exceedingly important fundamental idea is expressed by Goethe still -more clearly in another passage (1807), in the following words:--"If we -consider plants and animals in their most imperfect condition, they can -scarcely be distinguished. But this much we can say, that the creatures -which by degrees emerge as plants and animals out of a common phase, -where they are barely distinguishable, arrive at perfection in two -opposite directions; so that the plant in the end reaches its highest -glory in the tree, which is immovable and stiff, the animal in man, who -possesses the greatest elasticity and freedom." This remarkable passage -not only indicates most explicitly the genealogical relationship between -the vegetable and animal kingdoms, but contains the germ of the -monophyletic hypothesis of descent, the importance of which I shall have -to explain hereafter. (Compare Chapter XVI. and the Pedigree, p. 398.) - -At the time when Goethe in this way sketched the fundamental features of -the Theory of Descent, another German philosopher, Gottfried Reinhold -Treviranus, of Bremen (born 1776, died 1837), was zealously engaged at -the same work. As Wilhelm Focke has recently shown, Treviranus, even in -the earliest of his greater works, "The Biology or Philosophy of Animate -Nature," which appeared at the beginning of the present century, had -already developed monistic views of the unity of nature, and of the -genealogical connection of the species of organisms, which entirely -correspond with our present view of the matter. In the first three -volumes of the Biology, which appeared successively in 1802, 1803, and -1805 (therefore several years before Oken's and Lamarck's principal -works), we find numerous passages which are of interest in this respect. -I shall here quote only a few of the most important. - -In speaking of the principal question of our theory, the question of the -origin of organic species, Treviranus makes the following -remarks:--"Every form of life can be produced by physical forces in one -of two ways: either by coming into being out of formless matter, or by -modification of an already existing form by a continued process of -shaping. In the latter case the cause of this modification may lie -either in the influence of a dissimilar male generative matter upon the -female germ, or in the influence of other powers which operate only -after procreation. In every living being there exists the capability of -an endless variety of form-assumption; each possesses the power to adapt -its organization to the changes of the outer world, and it is this power -put into action by the change of the universe that has raised the simple -zoophytes of the primitive world to continually higher stages of -organization, and has introduced a countless variety of species into -animate nature." - -By _zoophytes_, Treviranus here means organisms of the lowest order and -of the simplest character, namely, those neutral primitive beings which -stand midway between animals and plants, and on the whole correspond -with our _protista_. "These zoophytes," he remarks in another passage, -"are the original forms out of which all the organisms of the higher -classes have arisen by gradual development. We are further of opinion -that every species, as well as every individual, has certain periods of -growth, of bloom, and of decay, but that the decay of a species is -_degeneration_, not dissolution, as in the case of the individual. From -this it appears to us to follow that it was not the great catastrophes -of the earth (as is generally supposed) which destroyed the animals of -the primitive world, but that many survived them, and it is more -probable that they have disappeared from existing nature, because the -species to which they belonged have completed the circle of their -existence, and have become changed into other kinds." - -When Treviranus, in this and other passages, points to _degeneration_ as -the most important cause of the transformation of the animal and -vegetable species, he does not understand by it what is now commonly -called degeneration. With him "degeneration" is exactly what we now call -_Adaptation_ or _modification_, by the action of external formative -forces. That Treviranus explained this trans-transformation of organic -species by Adaptation, and its preservation by Inheritance, and thus the -whole variety of organic forms by the interaction of Adaptation and -Inheritance, is clear also from several other passages. How profoundly -he grasped the mutual dependence of all living creatures on one another, -and in general the _universal connection between cause and effect_--that -is, the monistic causal connection between all members and parts of the -universe--is further shown, among others, by the following remarks in -his Biology:--"The living individual is dependent upon the species, the -species upon the fauna, the fauna upon the whole of animate nature, and -the latter upon the organism of the earth. The individual possesses -indeed a peculiar life, and so far forms its own world. But just because -its life is limited it constitutes at the same time an organ in the -general organism. Every living body exists in consequence of the -universe, but the universe, on the other hand, exists in consequence of -it." - -It is self-evident that so profound and clear a thinker as Treviranus, -in accordance with this grand mechanical conception of the universe, -could not admit for man a privileged and exceptional position in nature, -but assumed his gradual development from lower animal forms. And it is -equally self-evident, on the other hand, that he did not admit a chasm -between organic and inorganic nature, but maintained the absolute unity -of the organization of the whole universe. This is specially attested by -the following sentence:--"Every inquiry into the influence of the whole -of nature on the living world must start from the principle, that all -living forms are products of physical influences, which are acting even -now, and are changed only in degree, or in their direction." Hereby, as -Treviranus himself says, "The fundamental problem of biology is solved," -and we add, solved in a purely mechanical or monistic sense. - -Neither Treviranus nor Goethe is commonly considered the most eminent of -the German nature-philosophers, but Lorenz Oken, who, in establishing -the vertebral theory of the skull, came forward as a rival to Goethe, -and did not entertain a very kindly feeling towards him. Although they -lived for some time in the same neighbourhood, yet the natures of these -two men were so very different, that they could not well be drawn -towards each other. Oken's "Manual of the Philosophy of Nature," which -may be designated as the most important production of the -nature-philosophy school then existing in Germany, appeared in 1809, the -same year in which Lamarck's fundamental work, the "Philosophie -Zoologique," was published. As early as 1802, Oken had published an -"Outline of the Philosophy of Nature." As we have already intimated, in -Oken's as in Goethe's works, a number of valuable and profound thoughts -are hidden among a mass of erroneous, very eccentric, and fantastic -conceptions. Some of these ideas have only quite recently and gradually -become recognized in science, many years after they were first -expressed. I shall here quote only two thoughts, which are almost -prophetic, and which at the same time stand in the closest relation to -the theory of development. - -One of the most important of Oken's theories, which was formerly very -much decried, and was most strongly combatted, especially by the -so-called "exact experimentalists," is the idea that the phenomena of -life in all organisms proceed from a common chemical substance, so to -say, from a general simple _vital-substance_, which he designated by the -name _Urschleim_, or _original slime_. By it he meant, as the name -indicates, a mucilaginous substance, an albuminous combination, which -exists in a semi-fluid condition of aggregation, and possesses the -power, by adaptation to different conditions of existence in the outer -world and by interaction with its material, of producing the most -various forms. Now, we need only change the expression "original slime" -(Urschleim) into _Protoplasm_, or _cell-substance_, in order to arrive -at one of the grandest results which we owe to microscopic -investigations during the last ten years, more especially to those of -Max Schultze. By these investigations it has been shown that in all -living bodies, without exception, there exists a certain quantity of -mucilaginous albuminous matter, in a semi-fluid condition; and that this -nitrogen-holding carbon-compound is exclusively the original seat and -agent of all the phenomena of life, and of all production of organic -forms. All other substances which appear in the organism, besides these, -are either formed by this active matter of life, or have been introduced -from without. The organic egg, the original cell out of which every -animal and plant is first developed, consists essentially only of one -round little lump of such albuminous matter. Even the yolk of an egg is -nothing but albumen, mixed with granules of fat. Oken was therefore -right when, more divining than knowing, he made the assertion--"Every -organic thing has arisen out of slime, and is nothing but slime in -different forms. This primitive slime originated in the sea, from -inorganic matter in the course of planetary-evolution." - -Another equally grand idea of the same philosopher is closely connected -with his theory of primitive slime, which coincides with the extremely -important _Protoplasm theory_. For Oken, as early as 1809, asserted that -the primitive slime produced in the sea by spontaneous generation, at -once assumed the form of microscopically small bladders, which he called -"_Mile_," or "_Infusoria_." "Organic nature has for its basis an -infinity of such vesicles." These little bladders arise from original -semi-fluid globules of the primitive slime, by the fact of their -periphery becoming condensed. The simplest organism, as well as every -animal and every plant of higher kind, is nothing else than "an -accumulation (synthesis) of such infusorial bladders, which by various -combinations assume various forms, and thus develop into higher -organisms." Here again we need only translate the expression _little -bladder_, or _infusorium_, by the word _cell_, and we arrive at the Cell -theory, one of the grandest biological theories of our century. -Schleiden and Schwann, about thirty years ago, were the first to furnish -experiential proof that all organisms are either simple cells, or -accumulations (syntheses) of such cells, and the more recent protoplasm -theory has shown that protoplasm (the original slime) is the most -essential (and sometimes the only) constituent part of the genuine cell. -The properties which Oken ascribes to his Infusoria are exactly the -properties of cells, the properties of elementary beings, by whose -accumulation, combination, and varying development, the higher organisms -are formed. - -These two extremely fruitful thoughts of Oken, on account of the absurd -form in which he expressed them, were at first little heeded, or -entirely misunderstood, and it was reserved for a much later era to -establish them by actual observation. The supposition that the -individual species of plants and animals originated from common -prototypes by a slow and gradual development of the higher organisms out -of lower ones, was of course most closely connected with these ideas. -Man's descent from lower organisms was likewise asserted by Oken--"Man -has been developed, not created." Although many arbitrary perversities -and extravagant fancies may be found in Oken's philosophy of nature, -they must not prevent us paying our just admiration to these grand -ideas, which were so far in advance of their age. This much is clearly -evident from the statements of Goethe and Oken which we have quoted, and -from the views of Lamarck and Geoffroy which have to be discussed next, -that during the first decade of our century no doctrine approached so -nearly to the natural Theory of Descent, newly established by Darwin, as -the much decried "Natur-philosophie." - - - - -CHAPTER V. - -THEORY OF DEVELOPMENT ACCORDING TO KANT AND LAMARCK. - - - Kant's Dualistic Biology.--His Conception of the Origin - of Inorganic Nature by Mechanical Causes, of Organic - Nature by Causes acting for a Definite - Purpose.--Contradiction of this Conception with his - leaning towards the Theory of Descent.--Kant's - Genealogical Theory of Development.--Its Limitation by - his Teleology.--Comparison of Genealogical Biology with - Comparative Philology.--Views in favour of the Theory of - Descent entertained by Leopold Buch, Baer, Schleiden, - Unger, Schaafhausen, Victor Carus, Buechner.--French - Nature-philosophy.--Lamarck's Philosophie - Zoologique.--Lamarck's Monistic (mechanical) System of - Nature.--His Views of the Interaction of the Two Organic - Formative Tendencies of Inheritance and - Adaptation.--Lamarck's Conception of Man's Development - from Ape-like Mammals.--Geoffroy St. Hilaire's, Naudin's, - and Lecoq's Defence of the Theory of Descent.--English - Nature-philosophy.--Views in favour of the Theory of - Descent, entertained by Erasmus Darwin, W. Herbert, - Grant, Freke, Herbert Spencer, Hooker, Huxley.--The - Double Merit of Charles Darwin. - - -The teleological view of nature, which explains the phenomena of the -organic world by the action of a personal Creator acting for a definite -purpose, necessarily leads, when carried to its extreme consequences, -either to utterly untenable contradictions, or to a twofold (dualistic) -conception of nature, which most directly contradicts the unity and -simplicity of the supreme laws which are everywhere perceptible. The -philosophers who embrace teleology must necessarily assume two -fundamentally different natures: an _inorganic_ nature, which must be -explained by causes acting _mechanically_ (causae efficientes), and an -_organic_ nature, which must be explained by _causes acting for a -definite purpose_ (causae finales). (Compare p. 34.) - -This dualism meets us in a striking manner when considering the -conceptions of nature formed by Kant, one of the greatest German -philosophers, and his ideas of the coming into being of organisms. A -closer examination of these ideas is forced upon us here, because in -Kant we honour one of the few philosophers who combine a solid -scientific culture with an extraordinary clearness and profundity of -speculation. The Koenigsberg philosopher gained the highest celebrity, -not only among speculative philosophers as the founder of critical -philosophy, but acquired a brilliant name also among naturalists by his -mechanical cosmogeny. Even in the year 1755, in his "General History of -Nature, and Theory of the Heavens,"(22) he made the bold attempt "to -discuss the constitution and the mechanical origin of the whole -universe, according to Newton's principles," and to explain them -mechanically by the natural course of development, to the exclusion of -all miracles. This cosmogeny of Kant, or "cosmological gas theory," -which we shall briefly discuss in a future chapter, was at a later day -fully established by the French mathematician Laplace and the English -astronomer Herschel, and enjoys at the present day almost universal -recognition. On account of this important work alone, in which exact -knowledge is coupled with most profound speculation, Kant deserves the -honourable name of a natural philosopher in the best and purest sense of -the word. - -If we read Kant's Criticism of the Teleological Faculty of Judgment, his -most important biological work, we perceive that in contemplating -organic nature he always maintains what is essentially the teleological -or dualistic point of view; whilst for inorganic nature he, -unconditionally and without reserve, assumes the mechanical or monistic -method of explanation. He affirms that in the domain of inorganic nature -all the phenomena can be explained by mechanical causes, by the moving -forces of matter itself, but not so in the domain of organic nature. In -the whole of Anorganology (in Geology and Mineralogy, in Meteorology and -Astronomy, in the physics and chemistry of inorganic natural bodies), -all phenomena are said to be explicable merely by _mechanism_ (causa -efficiens), without the intervention of a final purpose. In the whole -domain of Biology, on the other hand--in Botany, Zoology, and -Anthropology--mechanism is not considered sufficient to explain to us -all their phenomena; but we are supposed to be able to comprehend them -only by an assumption of a _final cause_ acting for a definite purpose -(causa finalis). In several passages Kant emphatically remarks that, -from a strictly scientific point of view, _all_ phenomena, without -exception, require a mechanical interpretation, and that _mechanism -alone can offer a true explanation_. But at the same time he thinks, -that in regard to living natural bodies, animals and plants, our human -power of comprehension is limited, and not sufficient for arriving at -the real cause of organic processes, especially at the origin of organic -forms. The _right_ of human reason to explain all phenomena mechanically -is unlimited, he says, but its _power_ is limited by the fact that -organic nature can be conceived only from a teleological point of view. - -Some passages are, however, very remarkable, in which Kant in a -surprising manner deviates from this mode of viewing things, and -expresses, more or less distinctly, the fundamental idea of the Theory -of Descent. He even asserts the necessity of a genealogical conception -of the series of organisms, if we at all wish to understand it -scientifically. The most important and remarkable of these passages -occurs in his "Methodical System of the Teleological Faculty of -Judgment" (Sec. 79), which appeared in 1790 in the "Criticism of the -Faculty of Judgment." Considering the extraordinary interest which this -passage possesses, both for forming a correct estimate of Kant's -philosophy, as well as for the Theory of Descent, I shall here insert it -_verbatim_. - -"It is desirable to examine the great domain of organized nature by -means of a methodical comparative anatomy, in order to discover whether -we may not find in it something resembling a system, and that too in -connection with the mode of generation, so that we may no longer be -compelled to stop short with a mere consideration of forms as they -are--which gives us no insight into their generation--and need no longer -give up in despair all hope of gaining a full insight into this -department of nature. The agreement of so many kinds of animals in a -certain common plan of structure, which seems to be visible not only in -their skeletons, but also in the arrangement of the remaining parts--so -that a wonderfully simple typical form, by the shortening and -lengthening of some parts, and by the suppression and development of -others, might be able to produce an immense variety of species--gives us -a ray of hope, though feeble, that here perhaps some result may be -obtained, by the application of the principle of the _mechanism of -nature_, without which, in fact, no science can exist. This analogy of -forms (in so far as they seem to have been produced in accordance with a -common prototype, notwithstanding their great variety) strengthens the -supposition that they have an actual blood-relationship, due to -origination from a common parent; a supposition which is arrived at by -observation of the graduated approximation of one class of animals to -another, beginning with the one in which the principle of purposiveness -seems to be most conspicuous, that is man, and extending down to the -polyps, and from these even down to mosses and lichens, and arriving -finally at raw matter, the lowest stage of nature observable by us. From -this matter and its forces the whole apparatus of Nature seems to have -descended according to mechanical laws (such as those which she follows -in the production of crystals); yet this apparatus, as seen in organic -beings, is so incomprehensible to us, that we feel ourselves compelled -to conceive for it a different principle. But it would seem that the -archaeologist of Nature is at liberty to regard the great _Family_ of -creatures (for as a Family we must conceive it, if the above-mentioned -continuous and connected relationship has a real foundation) as having -sprung from the immediate results of her earliest revolutions, judging -from all the laws of their mechanism known to or conjectured by him." - -If we take this remarkable passage out of Kant's "Criticism of the -Teleological Faculty of Judgment," and consider it by itself, we cannot -but be astonished to find how profoundly and clearly the great thinker, -even in 1790, had recognized the inevitable necessity of the Doctrine of -Descent, and designated it as the only possible way of explaining -organic nature by mechanical laws--that is, by true scientific -reasoning. On account of this one passage taken by itself, we might -place Kant beside Goethe and Lamarck, as one of the first founders of -the Doctrine of Descent; and considering the high authority which Kant's -Critical Philosophy most justly enjoys, this circumstance might perhaps -induce many a philosopher to decide in favour of the theory. But as soon -as we consider this passage in connection with the other train of -thoughts in the "Criticism of the Faculty of Judgment," and balance it -against other directly contradictory passages, we see clearly that Kant, -in these and some similar (but weaker) sentences, went beyond himself, -and abandoned the teleological point of view which he usually adopts in -Biology. - -Directly after the admirable passage which I have just quoted, there -follows a remark which completely takes off its edge. After having quite -correctly maintained the origin of organic forms out of raw matter by -mechanical laws (in the manner of crystallization), as well as a gradual -development of the different species by descent from one common original -parent, Kant adds, "But he (the archaeologist of nature, that is the -palaeontologist) must for this end ascribe to the common mother an -organization ordained purposely with a view to the needs of all her -offspring, otherwise the possibility of suitability of form in the -products of the animal and vegetable kingdoms (_i.e._ teleological -adaptation) cannot be conceived at all." This addition clearly -contradicts the most important fundamental thought of the preceding -passage, viz., that a purely mechanical explanation of organic nature -becomes possible through the Theory of Descent. And that the -teleological conception of organic nature predominated with Kant, is -shown by the heading of the remarkable Sec. 79, which contains the two -contradictory passages cited: "_Of the Necessary Subordination of the -Mechanical to the Teleological Principle, in the explanation of a thing -as a purpose or object of Nature._" - -He expresses himself most decidedly against the mechanical explanation -of organic nature in the following passage (Sec. 74): "It is quite certain -that we cannot become sufficiently acquainted with organized creatures -and their hidden potentialities by aid of purely mechanical natural -principles, much less can we explain them; and this is so certain, that -we may boldly assert that it is absurd for man even to conceive such an -idea, or to hope that a Newton may one day arise able to make the -production of a blade of grass comprehensible, according to natural laws -ordained by no intention; such an insight we must absolutely deny to -man." Now, however, this impossible Newton has really appeared seventy -years later in Darwin, whose Theory of Selection has actually solved the -problem, the solution of which Kant had considered absolutely -inconceivable! - -In connection with Kant and the German philosophers whose theories of -development have already occupied us in the preceding chapter, it seems -justifiable to consider briefly some other German naturalists and -philosophers, who, in the course of our century, have more or less -distinctly resisted the prevailing teleological views of creation, and -vindicated the mechanical conception of things which is the basis of the -Doctrine of Filiation. Sometimes general philosophical considerations, -sometimes special empirical observations, were the motives which led -these thinking men to form the idea that the various individual species -of organisms must have originated from common primary forms. Among them -I must first mention the great German geologist, Leopold Buch. Important -observations as to the geographical distribution of plants led him to -the following remarkable assertion in his excellent "Physical -Description of the Canary Islands":-- - -"The individuals of genera, on continents, spread and widely diffuse -themselves, and by the difference of localities, nourishment, and soil, -form varieties; and being in consequence of their isolation never -crossed by other varieties, and so brought back to the main type, they -in the end become a permanent and a distinct species. Then, perhaps, in -other ways, they once more become associated with other descendants of -the original form--which have likewise become new varieties--and both -now appear as very distinct species, no longer mingling with one -another. Not so on islands. Being commonly confined in narrow valleys or -within the limit of small zones, individuals can reach one another and -destroy every commencing production of a permanent variety. Much in the -same way the peculiarities or faults in language, originating with the -head of some family, become, through the extension of the family, -indigenous throughout a whole district. If the district is separated and -isolated, and if the language is not brought back to its former purity -by constant connection with that spoken in neighbouring districts, a -dialect will be the result. If natural obstacles, forests, constitution, -form of government, unite the inhabitants of the separate district still -more closely, and separate them still more completely from their -neighbours, the dialect is fixed, and becomes a completely distinct -language." (Uebersicht der Flora auf den Canarien, S. 133.) - -We perceive that Buch is here led to the fundamental idea of the Theory -of Descent by the phenomena of the geography of plants, a department of -biological knowledge which in fact furnishes a mass of proofs in favour -of it. Darwin has minutely discussed these proofs in two separate -chapters of his book (the 11th and 12th). Buch's remark is further of -interest, because it leads us to the exceedingly instructive comparison -of the different branches of language with the species of organisms, a -comparison which is of the greatest use to Comparative Philology, as -well as to Comparative Botany and Zoology. Just as, for example, the -different dialects, provincialisms, branches, and off-shoots of the -German, Slavonic, Greco-Latin, and Irano-Indian parent language, are -derived from a single common Indo-Germanic parent tongue, and just as -their _differences_ are explained by _Adaptation_, and their common -_fundamental characters_ explained by _Inheritance_, so in like manner -the different species, genera, families, orders, and classes of -Vertebrate animals are derived from a single common vertebrate form of -animal. Here also Adaptation is the cause of differences, Inheritance -the cause of community of character. This interesting parallelism in the -divergent development of the forms of speech and the forms of organisms -has been discussed in the clearest manner by one of our first -comparative philologists, the talented Augustus Schleicher, whose -premature death, four years ago, remains an irreparable loss, not only -to our University of Jena, but to the whole of monistic science.(6) - -Among other eminent German naturalists who have expressed their belief -in the Theory of Descent more or less distinctly, arriving at their -conclusion in very various ways, I must next mention Carl Ernst Baer, -the great reformer of animal embryology. In a lecture delivered in 1834, -entitled "The Most General Laws of Nature in All Development," he shows, -in the clearest way, that only in a very childish view of nature could -organic species be regarded as permanent and unchangeable types, and -that really they can be only passing series of generations, which have -developed by transformation from a common original form. The same -conception again received firm support from Baer, in 1859, through a -consideration of the laws of the geographical distribution of organisms. - -J. M. Schleiden, who founded, thirty years ago, in Jena, a new epoch in -Botany by his strictly empirico-philosophical and truly scientific -method, illustrated the philosophical significance of the conception of -organic species in his incisive "Outlines of Scientific Botany,"(7) and -showed that it had only a subjective origin in the general _law of -specification_. The different species of plants are only the specified -productions of the formative tendencies of plants, which arise from the -various combinations of the fundamental forces of organic matter. - -The eminent botanist, F. Unger, of Vienna, was led by his profound and -comprehensive investigations on extinct vegetable species, to a -palaeontological history of the development of the vegetable kingdom, -which distinctly asserts the principle of the Theory of Descent. In his -"Attempt at a History of the World of Plants" (1852), he maintains the -derivation of all different species of plants from a few primary forms, -and perhaps from a single original plant, a simple vegetable cell. He -shows that this view is founded on the genetic connection of all -vegetable forms, and is necessary, not merely upon philosophical -grounds, but upon those of experience and observation.(8) - -Victor Carus, of Leipzig, in the Introduction to his excellent "System -of Animal Morphology,"(9) published in 1853, in which he endeavours to -establish in a philosophical manner the universal constructive laws of -the animal body through comparative anatomy and the history of -development, makes the following remark:--"The organisms buried in the -most ancient geological strata must be looked upon as the ancestors from -whom the rich diversity of forms of the present creation have originated -by continued generation, and by accommodation to progressive and very -different conditions of life." - -In the same year (1853) Schaaffhausen, the anthropologist of Bonn, in an -Essay "On the Permanence and Transformation of Species," declared -himself decidedly in favour of the Theory of Descent. According to him, -the living species of animals and plants are the transformed descendants -of extinct species, from which they have arisen by gradual modification. -The divergence or separation of the most nearly allied species takes -place by the destruction of the connecting intermediate stages. -Schaaffhausen also maintained, with distinctness, the origin of the -human race from animals, and its gradual development from ape-like -animals, the most important deduction from the Doctrine of Filiation. - -Lastly, we have still to mention among the German Nature-philosophers -the name of Louis Buechner, who, in his celebrated work, "Force and -Matter" (1855), also independently developed the principles of the -Theory of Descent, taking his stand mainly on the ground of the -undeniable evidences of fact which are furnished by the palaeontological -and individual development of organisms, as well as by their -comparative anatomy and by the parallelism of these series of -development. Buechner showed very clearly that, even from such data -alone, the derivation of the different organic species from common -primary forms followed as a necessary conclusion, and that the origin of -these original primary forms could only be conceived of as the result of -a spontaneous generation. - -We now turn from the German to the French Nature-philosophers, who have -likewise held the Theory of Descent, since the beginning of the present -century. At their head stands Jean Lamarck, who occupies the first place -next to Darwin and Goethe in the history of the Doctrine of Filiation. -To him will always belong the immortal glory of having for the first -time worked out the Theory of Descent, as an independent scientific -theory of the first order, and as the philosophical foundation of the -whole science of Biology. Although Lamarck was born as early as 1744, he -did not begin the publication of his theory until the commencement of -the present century, in 1801, and established it more fully only in -1809, in his classic "Philosophie Zoologique."(2) This admirable work is -the first connected exposition of the Theory of Descent carried out -strictly into all its consequences. By its purely mechanical method of -viewing organic nature, and the strictly philosophical proofs brought -forward in it, Lamarck's work is raised far above the prevailing -dualistic views of his time; and with the exception of Darwin's work, -which appeared just half a century later, we know of none which we could -in this respect place by the side of the "Philosophie Zoologique." How -far it was in advance of its time is perhaps best seen from the -circumstance that it was not understood by most men, and for fifty -years was not spoken of at all. Cuvier, Lamarck's greatest opponent, in -his "Report on the Progress of Natural Sciences," in which the most -unimportant anatomical investigations are enumerated, does not devote a -single word to this work, which forms an epoch in science. Goethe, also, -who took such a lively interest in the French nature-philosophy and in -"the thoughts of kindred minds beyond the Rhine," nowhere mentions -Lamarck, and does not seem to have known the "Philosophie Zoologique" at -all. The great reputation which Lamarck gained as a naturalist he does -not owe to his highly important general work, but to numerous special -treatises on the lower animals, particularly on Molluscs, as well as to -an excellent "Natural History of Invertebrate Animals," which appeared, -in seven volumes, between the years 1815-1822. The first volume of this -celebrated work contains in the general introduction a detailed -exposition of his theory of filiation. I can, perhaps, give no better -idea of the extraordinary importance of the "Philosophie Zoologique" -than by quoting _verbatim_ some of the most important passages -therefrom:-- - -"The systematic divisions of classes, orders, families, genera, and -species, as well as their designations, are the arbitrary and artificial -productions of man. The kinds or species of organisms are of unequal -age, developed one after the other, and show only a relative and -temporary persistence; species arise out of varieties. The differences -in the conditions of life have a modifying influence on the -organization, the general form, and the parts of animals, and so has the -use or disuse of organs. In the first beginning only the very simplest -and lowest animals and plants came into existence; those of a more -complex organization only at a later period. The course of the earth's -development, and that of its organic inhabitants, was continuous, not -interrupted by violent revolutions. Life is purely a physical -phenomenon. All the phenomena of life depend on mechanical, physical, -and chemical causes, which are inherent in the nature of matter itself. -The simplest animals and the simplest plants, which stand at the lowest -point in the scale of organization, have originated and still originate -by spontaneous generation. All animate natural bodies or organisms are -subject to the same laws as inanimate natural bodies or anorgana. The -ideas and actions of the understanding are the motional phenomena of the -central nervous system. The will is in truth never free. Reason is only -a higher degree of development and combination of judgments." - -These are indeed astonishingly bold, grand, and far-reaching views, and -were expressed by Lamarck sixty years ago; in fact, at a time when their -establishment, by a mass of facts, was not nearly as possible as it is -in our day. Indeed Lamarck's work is really a complete and strictly -monistic (mechanical) system of nature, and all the important general -principles of monistic Biology are already enunciated by him: the unity -of the active causes in organic and inorganic nature; the ultimate -explanation of these causes in the chemical and physical properties of -matter itself; the absence of a special vital power, or of an organic -final cause; the derivation of all organisms from some few, most simple -original forms, which have come into existence by spontaneous generation -out of inorganic matter; the coherent course of the whole earth's -history; the absence of violent cataclysmic revolutions; and in general -the inconceivableness of any miracle, of any supernatural interference, -in the natural course of the development of matter. - -The fact that Lamarck's wonderful intellectual feat met with scarcely -any recognition, arises partly from the immense length of the gigantic -stride with which he had advanced beyond the next fifty years, partly -from its defective empirical foundation, and from the somewhat one-sided -character of some of his arguments. Lamarck quite correctly recognizes -_Adaptation_ as the first mechanical cause which effects the continual -transformation of organic forms, while he traces with equal justice the -similarity in form of different species, genera, families, etc., to -their blood-relationship, and thus explains it by _Inheritance_. -Adaptation, according to him, consists in this, that the perpetual, slow -change of the outer world causes a corresponding change in the actions -of organisms, and thereby also causes a further change in their forms. -He lays the greatest stress upon the effect of _habit_ upon the use and -disuse of organs. This is certainly of great importance in the -transformation of organic forms, as we shall see later. However, the way -in which Lamarck wished to explain exclusively, or at any rate mainly, -the change of forms, is after all in most cases not possible. He says, -for example, that the long neck of the giraffe has arisen from its -constantly stretching out its neck at high trees, and from the endeavour -to pick the leaves off their branches; as giraffes generally inhabit dry -districts, where only the foliage of trees afford them nourishment, they -were forced to this action. In like manner the long tongues of -wood-peckers, humming-birds, and ant-eaters, are said by him to have -arisen from the habit of fetching their food out of narrow, small, and -deep crevices or channels. The webs between the toes of the webbed feet -in frogs and other aquatic animals have arisen solely from the constant -endeavour to swim, from striking their feet against the water, and from -the very movements of swimming. Inheritance fixed these habits on the -descendants, and finally, by further elaboration, the organs were -entirely transformed. However correct, as a whole, this fundamental -thought may be, yet Lamarck lays the stress too exclusively on _habit_ -(use and non-use of organs), certainly one of the most important, but -not the only cause of the change of forms. Still this cannot prevent our -acknowledging that Lamarck quite correctly appreciated the mutual -co-operation of the two organic formative tendencies of Adaptation and -Inheritance. What he failed to grasp is the exceedingly important -principle of "Natural Selection in the Struggle for Existence," with -which Darwin, fifty years later, made us acquainted. - -It still remains to be mentioned as a special merit of Lamarck, that he -endeavoured to prove the _development of the human race_ from other -primitive, ape-like mammals. Here again it was, above all, to habit that -he ascribed the transforming, the ennobling influence. He assumed that -the lowest, original men had originated out of men-like apes, by the -latter accustoming themselves to walk upright. The raising of the body, -the constant effort to keep upright, in the first place led to a -transformation of the limbs, to a stronger differentiation or separation -of the fore and hinder extremities, which is justly considered one of -the most essential distinctions between man and the ape. Behind, the -calf of the leg and the flat soles of the feet were developed; in -front, the arms and hands, for the purpose of seizing objects. The -upright walk was then followed by a freer view over the surrounding -objects, and led consequently to an important progress in mental -development. Human apes thereby soon gained a great advantage over the -other apes, and further, over surrounding organisms in general. In order -to maintain the supremacy over them, they formed themselves into -companies, and there arose, as in the case of all animals living in -company, the desire of communicating to one another their desires and -thoughts. Thus arose the necessity of language, which, consisting at -first of rough and disjointed sounds, soon became more connected, -developed, and articulate. The development of articulate speech now in -turn became the strongest lever for a further progressive development of -the organism, and above all, of the brain, and so ape-like men became -gradually and slowly transformed into real men. In this way the actual -descent of the lowest and rudest primitive men from the most highly -developed apes was distinctly maintained by Lamarck, and supported by a -series of the most important proofs. - -The honour of being the chief French nature-philosopher is not usually -assigned to Lamarck, but to Etienne Geoffroy St. Hilaire (the elder), -born in 1771, the same in whom Goethe was especially interested, and -with whom we have already become acquainted as Cuvier's most prominent -opponent. He developed his ideas about the transformation of organic -species as far back as the end of the last century, but published them -only in the year 1828, and then in the following years, especially in -1830, defended them bravely against Cuvier. Geoffroy St. Hilaire in all -essentials adopted Lamarck's Theory of Descent, yet he believed that -the transformation of animal and vegetable species was less effected by -the action of the organism itself (by habit, practice, use, or disuse of -organs) than by the "monde ambiant," that is, by the continual change of -the outer world, especially of the atmosphere. He conceives the organism -as passive, in regard to the vital conditions of the outer world, while -Lamarck, on the contrary, regards it as active. Geoffroy thinks, for -example, that birds originated from lizard-like reptiles, simply by a -diminution of the carbonic acid in the atmosphere, in consequence of -which the breathing process became more animated and energetic through -the increased proportion of oxygen in the atmosphere. Thus there arose a -higher temperature of the blood, an increased activity of the nerves and -muscles, and the scales of the reptiles became the feathers of the -birds, etc. This conception is based upon a correct thought, but -although the change of the atmosphere, as well as the change of every -other external condition of existence, certainly effects directly or -indirectly the transformation of the organism, yet this single cause is -by itself too unimportant for such effects to be ascribed to it. It is -even less important than practice and habit, upon which Lamarck lays too -much stress. Geoffroy's chief merit consists in his having vindicated -the monistic conception of nature, the unity of organic forms, and the -deep genealogical connection of the different organic types in the face -of Cuvier's powerful influence. I have already mentioned in the -preceding chapter (pp. 87, 88) the celebrated disputes between the two -great opponents in the Academy of Paris, especially the fierce conflicts -on the 22nd of February, and on the 19th of July, in which Goethe took -so lively an interest. On that occasion Cuvier remained the -acknowledged victor, and since that time very little, or rather nothing, -more has been done in France to further the development of the Doctrine -of Filiation, and complete the monistic theory of development. This is -evidently to be ascribed principally to the repressive influence -exercised by Cuvier's great authority. Even at the present day the -majority of the French naturalists are the disciples and blind followers -of Cuvier. In no civilized country of Europe has Darwin's doctrine had -so little effect and been so little understood as in France, so that in -the further course of our examination we need not take the French -naturalists into consideration. At most, there are two distinguished -botanists, among the recent French naturalists, whom we may mention as -having ventured to express themselves in favour of the mutability and -transformation of species. These two men are Naudin (1852) and Lecoq -(1854). - -Having discussed the early services of German and French -nature-philosophy in establishing the doctrine of descent, we turn to -the third great country of Europe, to free England, which during the -last ten years has become the chief seat and starting-point for the -further working out and definite establishment of the theory of -development. Englishmen, who now take such an active part in every great -scientific progress of humanity, and are the first to promote the -eternal truths of natural science, at the beginning of the century took -but little part in the continental nature-philosophy and its most -important progress, the Theory of Descent. Almost the only earlier -English naturalist whom we have here to mention is Erasmus Darwin, the -grandfather of the reformer of the Theory of Descent. In 1795 he -published, under the title of "Zoonomia," a scientific work in which he -expresses views very similar to those of Goethe and Lamarck, without, -however, then knowing anything about these two men. It is evident that -the Theory of Descent at that time pervaded the intellectual atmosphere. -Erasmus Darwin lays great stress upon the transformation of animal and -vegetable species by their own vital action and by their becoming -accustomed to changed conditions of existence, etc. Next, W. Herbert, in -1822, expressed the opinion that species of animals and plants are -nothing but varieties which have become permanent. In like manner Grant, -in Edinburgh, in 1826, declared that new species proceed from existing -species by continued transformation. In 1841 Freke maintained that all -organic beings must be descended from a single primitive type. In 1852 -Herbert Spencer demonstrated minutely, and in a very clear and -philosophic manner, the necessity of the Doctrine of Filiation, and -established it more firmly in his excellent "Essays," which appeared in -1858, and in his "Principles of Biology," which was published at a later -date. He has, at the same time, the great merit of having applied the -theory of development to psychology, and of having shown that the -emotional and intellectual faculties could only have been acquired by -degrees and developed gradually. Lastly, we have to mention that in 1859 -Huxley, the first of English zoologists, spoke of the Theory of Descent -as the only hypothesis of creation reconcilable with scientific -physiology. The same year produced the "Introduction to the Flora of -Tasmania," in which Hooker, the celebrated English botanist, adopts the -Theory of Descent, supporting it with important observations of his -own. - -All the naturalists and philosophers with whom we have become acquainted -in this brief historical survey, as men adopting the Theory of -Development, merely arrived at the conception that all the different -species of animals and plants which at any time have lived, and still -live, upon the earth, are the gradually changed and transformed -descendants of one or some few original and very simple prototypes, -which latter arose out of inorganic matter by spontaneous generation. -But none of them succeeded in placing this fundamental element of the -doctrine of descent in relation with some cause, nor in satisfactorily -explaining the transformation of organic species by the true -demonstration of its mechanical antecedents. Charles Darwin was the -first who solved this most difficult problem, and this forms the broad -gulf which separates him from his predecessors. - -The special merit of Charles Darwin is, in my opinion, twofold: in the -first place, the doctrine of descent, the fundamental idea of which was -already clearly expressed by Goethe and Lamarck, has been developed by -him much more comprehensively, has been traced much more minutely in all -directions, and carried out much more strictly and connectedly than by -any of his predecessors; and secondly, he has established a new theory, -which reveals to us the natural causes of organic development, the -acting causes (causae efficientes) of organic form-production, and of the -changes and transformations of animal and vegetable species. This is the -theory which we call the Theory of Selection, or more accurately, the -Theory of Natural Selection (selectio naturalis). - -When we reflect that (with the few exceptions above mentioned) the -whole science of Biology, before Darwin's time, was elaborated in -accordance with the opposite views, and that almost all zoologists and -botanists regarded the absolute independence of organic species as a -self-evident inference from the results of all study of forms, we shall -certainly not lightly value the twofold merit of Darwin. The false -doctrine of the constancy and independent creation of individual species -had gained such high authority, was so generally recognized, and was, -moreover, so much favoured by delusive appearances, accepted by -superficial observation, that, indeed, no small degree of courage, -strength, and intelligence was required to rise as a reformer against -its omnipotence, and to dash to pieces the structure artificially -erected upon it. But, in addition to this, Darwin added to Lamarck's and -Goethe's doctrine of descent the new and highly important principle of -"natural selection." - -We must sharply distinguish the two points--though this is usually not -done--first, Lamarck's Theory of Descent, which only asserts _that_ all -animal and vegetable species are descended from common, most simple, and -spontaneously generated prototypes; and secondly, Darwin's Theory of -Selection, which shows us _why_ this progressive transformation of -organic forms took place, and what causes, acting mechanically, effected -the uninterrupted production of new forms, and the ever increasing -variety of animals and plants. - -Darwin's immortal merit cannot be justly estimated until a later period, -when the Theory of Development, after overthrowing all other theories of -creation, will be recognized as the supreme principle of explanation in -Anthropology, and, consequently, in all other sciences. At present, -while in the hot contest for truth the name of Darwin is the watchword -to the advocates of the natural theory of development, his merits are -inaccurately appreciated on both sides, for some persons overestimate -them as much as others underestimate them. - -His merit is overestimated when he is regarded as the founder of the -Theory of Descent, or of the whole of the Theory of Development. We have -seen from the historical sketch in this and the preceding chapters, that -the Theory of Development, as such, is not new; all philosophers who -have refused to be led captive by the blind dogma of a supernatural -creation, have been compelled to assume a natural development. But the -Theory of Descent constituting the specially biological part of the -universal Theory of Development, had already been so clearly expressed -by Lamarck, and carried out so fully by him to its most important -consequences, that we must honour him as the real founder of it. Hence -it is only the Theory of Selection, and not that of Descent, which may -be called _Darwinism_; but this is in itself of so much importance, that -its value can scarcely be overestimated. - -Darwin's merit is naturally underestimated by all his opponents. But it -is scarcely possible in this matter to point to scientific opponents, -who are entitled by profound biological culture to pronounce an opinion. -For among all the works opposed to Darwin and the Theory of Descent yet -published, with the exception of that of Agassiz, not one deserves -consideration, much less refutation; all have so evidently been written -either without thorough knowledge of biological facts, or without a -clear philosophical understanding of the question in hand. We need not -trouble ourselves at all about the attacks of theologians and other -unscientific men, who really know nothing whatever of nature. - -The only eminent scientific adversary who still remains opposed to -Darwin and the whole theory of development is Louis Agassiz; but the -principle of his opposition in reality deserves notice only as a -philosophical curiosity. In a French translation of his "Essay on -Classification,"(5) which we have spoken of before, published in Paris -in 1869, Agassiz has most formally announced his opposition to -Darwinism, which he had previously expressed in many ways. To this -translation he has appended a treatise of sixteen pages, bearing the -title, "Le Darwinisme. Classification de Haeckel." This curious chapter -contains the most wonderful things; as, for example, "Darwin's idea is a -conception _a priori_. Darwinism is a burlesque of facts. Science would -renounce the claim which it has hitherto possessed to the confidence of -earnest minds if such sketches were to be accepted as indications of a -true progress." The following passage, however, is the climax of this -strange polemic: "Darwinism shuts out almost the whole mass of acquired -knowledge in order to retain and assimilate to itself that only which -may serve its doctrine." - -Surely this is what we may call turning the whole affair topsy-turvy! -The biologist who knows the facts must be astounded at Agassiz's courage -in uttering such sentences--sentences without a word of truth in them, -and which he cannot himself believe! The impregnable strength of the -Theory of Descent lies just in the fact that all biological facts are -explicable only through it, and that without it they remain -unintelligible miracles. All our "laborious knowledge" in comparative -anatomy and physiology--in embryology and palaeontology--in the doctrine -of the geographical and topographical distribution of organisms, etc., -constitutes an irrefutable testimony to the truth of the Theory of -Descent. - -In my General Morphology, especially in the sixth book (in the General -Phylogeny), I have minutely refuted Agassiz's "Essay on Classification" -in all essential points. The twenty-fourth chapter I have devoted to a -very detailed and strictly scientific discussion of that section which -Agassiz himself considers the most important (the groups or categories -of systematic zoology and botany), and have shown that this part of his -work is purely chimerical, without any trace of real foundation. Agassiz -takes good care not to venture anywhere to touch upon my refutation, -because, forsooth, he is not in a position to produce anything -substantial against it. He fights not with arguments, but with phrases. -However, such opposition will not delay the complete victory of the -Theory of Development, but only accelerate it. - - - - -CHAPTER VI. - -THEORY OF DEVELOPMENT ACCORDING TO LYELL AND DARWIN. - - - Charles Lyell's Principles of Geology.--His Natural - History of the Earth's Development.--Origin of the - Greatest Effects through the Multiplication of the - Smallest Causes.--Unlimited Extent of Geological - Periods.--Lyell's Refutation of Cuvier's History of - Creation.--The Establishment of the Uninterrupted - Connection of Historical Development by Lyell and - Darwin.--Biographical Notice of Charles Darwin.--His - Scientific Works.--His Theory of Coral Reefs.--Development - of the Theory of Selection.--A Letter of Darwin's.--The - Contemporaneous Appearance of Darwin's and Alfred - Wallace's Theory of Selection.--Darwin's Study of Domestic - Animals and Cultivated Plants.--Andreas Wagner's notions - as to the Special Creation of Cultivated Organisms for the - good of Man.--The Tree of Knowledge in - Paradise.--Comparison between Wild and Cultivated - Organisms.--Darwin's Study of Domestic - Pigeons.--Importance of Pigeon Breeding.--Common Descent - of all Races of Pigeons. - - -During the thirty years, from 1830 until 1859, when Darwin's work -appeared, the ideas of creation introduced by Cuvier remained -predominant in the sciences of organic nature. People rested satisfied -with the unscientific assumption, that in the course of the earth's -history, a series of inexplicable revolutions had periodically -annihilated the whole world of animals and plants, and that at the end -of each revolution, and the beginning of a new period, a new enlarged, -and improved edition of the organic population had appeared. Although -the number of these editions of creation was altogether problematical, -and in truth could not be fixed at all, and although the numerous -advances which, during this time, were made in all the departments of -zoology and botany demonstrated more and more that Cuvier's hypothesis -was unfounded and untenable, and that Lamarck's natural theory of -development was nearer the truth, yet the former maintained its -authority almost universally among biologists. This must, above all, be -ascribed to the veneration which Cuvier had acquired, and strikingly -illustrates how injurious to the progress of humanity a faith in any -definite authority may become. Authority, as Goethe once admirably said, -perpetuates the individual, which as an individual should pass away, -rejects and allows to pass that which should be held fast, and is the -main obstacle to the advance of humanity. - -It is only by having regard to the great weight of Cuvier's authority, -and to the mighty potency of human indolence, which is with difficulty -induced to depart from the broad and comfortable way of everyday -conceptions, and to enter upon new paths not yet made easy, that we can -comprehend how it is that Lamarck's Theory of Descent did not gain its -due recognition until 1859, after Darwin had given it a new foundation. -The soil had long been prepared for it by the works of Charles Lyell, -another English naturalist, whose views are of great importance for the -natural history of creation, and must accordingly here be briefly -explained. - -In 1830 Charles Lyell published, under the title of "Principles of -Geology," a work in which he thoroughly reformed the science of Geology -and the history of the earth's development, and effected this reform in -a manner similar to that in which, thirty years later, Darwin in his -work reformed the science of Biology. Lyell's great treatise, which -radically destroyed Cuvier's hypothesis of creation, appeared in the -same year in which Cuvier celebrated his triumph over the -nature-philosophy, and established his supremacy in the domain of -morphology for the following thirty years. Whilst Cuvier, by his -artificial hypothesis of creation and his theory of catastrophes -connected with it, directly obstructed the path of the theory of natural -development, and cut off all chance of a natural explanation, Lyell once -more opened a free road, and brought forward convincing geological -evidence to show that Cuvier's dualistic conceptions were as unfounded -as they were superfluous. He demonstrated that those changes of the -earth's surface, which are still taking place before our eyes, are -perfectly sufficient to explain everything we know of the development of -the earth's crust in general, and that it is superfluous and useless to -seek for mysterious causes in inexplicable revolutions. He showed that -we need only have recourse to the hypothesis of exceedingly long periods -of time in order to explain the formation of the crust of the earth in -the simplest and most natural manner by means of the very same causes -which are still active. Many geologists had previously imagined that the -highest chains of mountains which rise on the surface of the earth could -owe their origin only to enormous revolutions transforming a great part -of the earth's surface, especially to colossal volcanic eruptions. Such -chains of mountains as those of the Alps or the Cordilleras were -believed to have arisen direct from the fiery fluid of the interior of -the earth, through an enormous chasm in the broken crust. Lyell, on the -other hand, showed that we can explain the formation of such enormous -chains of mountains quite naturally by the same slow and imperceptible -risings and depressions of the earth's surface which are still -continually taking place, and the causes of which are by no means -miraculous. Although these depressions and risings may perhaps amount -only to a few inches, or at most a few feet, in the course of a century; -still, in the course of some millions of years they are perfectly -sufficient to raise up the highest chains of mountains, without the aid -of mysterious and incomprehensible revolutions. In like manner, the -meteorological action of the atmosphere, the influence of rain and snow, -and, lastly, the breakers on the coasts, which by themselves seem to -produce an insignificant effect, must cause the greatest changes if we -only allow sufficiently long periods for their action. The -multiplication of the smallest causes produces the greatest effects. -Drops of water produce a cavity in a rock. - -I shall afterwards be obliged again to recur to the immeasurable length -of geological periods which are necessary for this purpose, for, as we -shall see, Darwin's theory, as well as that of Lyell, renders the -assumption of immense periods absolutely necessary. If the earth and its -organisms have actually developed in a natural way, this slow and -gradual development must certainly have taken a length of time which -surpasses our powers of comprehension. But as many men see in this very -circumstance one of the principal difficulties in the way of those -theories of development, I beg leave here to remark that we have not a -single rational ground for conceiving the time requisite to be limited -in any way. Not only many ordinary persons, but even eminent -naturalists, make it their chief objection to these theories, that they -arbitrarily claim too great a length of time: yet the ground of -objection is scarcely intelligible. For it is absolutely impossible to -see what can, in any way, limit us in assuming long periods of time. We -have long known, even from the structure of the stratified crust of the -earth alone, that its origin and the formation of neptunic rocks from -water must have taken, at least, several millions of years. From a -strictly philosophical point of view, it makes no difference whether we -hypothetically assume for this process ten millions or ten thousand -billions of years. Before us and behind us lies eternity. If the -assumption of such enormous periods is opposed to the feelings of many, -I regard this simply as the consequence of false notions which are -impressed upon us from our earliest youth concerning the short history -of the earth, which is said to embrace only a few thousands of years. -Albert Lange, in his "History of Materialism,"(12) has convincingly -shown that from a strictly philosophical point of view it is far less -objectionable in a scientific hypothesis to assume periods which are too -long than periods which are too short. Every process of development is -the more intelligible the longer it is assumed to last. A short and -limited period is the most improbable. - -I have no space here to enter minutely into Lyell's great work, and will -therefore mention only its most important result, which is, that he -completely refuted Cuvier's history of creation with its mythical -revolutions, and established in its place the constant and slow -transformation of the earth's crust by the continued action of forces, -which are still working on the earth's surface, viz., the movement of -water and the volcanic fluid of the interior of earth. Lyell thus -demonstrated a continuous and uninterrupted connection of the whole -history of the earth, and he proved it so irrefutably, and established -so convincingly the supremacy of the "existing causes," that is, of the -causes which are still active in the transformation of the earth's -crust, that Geology in a short time completely renounced Cuvier's -hypothesis. - -Now, it is remarkable that Palaeontology, the science of petrifactions, -so far as it was pursued by botanists and zoologists, remained -apparently unaffected by this great progress in geology. Biology still -continued to assume repeated new creations of the whole animal and -vegetable kingdoms, at the beginning of every new period of the earth's -history, although this hypothesis of individual creations, shoved into -the world one after the other, without the assumption of Cuvier's -cataclysms, became pure nonsense, and lost its foundation. It is -evidently perfectly absurd to assume a distinct new creation of the -whole world of animals and plants at definite epochs, without the crust -of the earth itself experiencing any considerable general revolution. -And although this conception is most closely connected with Cuvier's -theory of catastrophes, still it prevailed when the latter had been -completely destroyed and abandoned. - -It was reserved for the great English naturalist, Charles Darwin, to -remove this contradiction, and to show that the organic beings of the -earth have a history as continuous and connected as the inorganic crust -of the earth; that animals and plants have arisen from one another by as -gradual a transmutation as that by which the varying forms of the -earth's crust, the forms of the continents, and of the seas surrounding -and separating them, have arisen out of earlier and quite different -forms. In this respect we may truly say that in the domain of Zoology -and Botany Darwin made the same progress as Lyell, his great countryman, -in the domain of Geology. Both proved the _uninterrupted connection of -the historical development_, and demonstrated a gradual transmutation of -the different conditions succeeding one another. - -The special merit of Darwin, as I have already remarked in a preceding -chapter, is twofold. In the first place, he has treated the Theory of -Descent, put forth by Lamarck and Goethe, in a much more comprehensive -manner, as a whole, and carried it out in a much more connected manner, -than had been done by any one of his predecessors. Secondly, he has -established the causal foundation of this Theory of Descent by the -Theory of Selection, which is peculiarly his own; that is, he has -demonstrated the acting _causes of the changes_ which the Theory of -Descent simply stated, as _facts_. The Theory of Descent, introduced -into Biology in 1809, by Lamarck, asserts that all the different species -of animals and plants are descended from a single or some few most -simple prototypes, produced by spontaneous generation. The Theory of -Selection, established in 1859 by Darwin, shows us _why_ this must be -so; it points out the acting causes in a manner with which Kant would -have been delighted, and indeed, in the domain of organic nature, Darwin -has become the Newton whose advent Kant thought himself entitled -prophetically to deny. - -Now, before we approach Darwin's theory, it will perhaps be of interest -to notice a few details as to the personal character of this great -naturalist, as to his life, and the way in which he was led to form his -doctrine. Charles Robert Darwin was born at Shrewsbury, on the Severn, -on the 12th of February, 1809; therefore, at present he is sixty-three -years old. In his seventeenth year (1825) he entered the University of -Edinburgh, and two years later Christ's College, Cambridge. When -scarcely twenty-two years old, in 1831, he was invited to take part in a -scientific expedition which was sent out by England, in order to survey -accurately the southernmost point of South America, and to examine -several parts of the South Seas. This expedition, like many other -voyages of inquiry fitted out in a praiseworthy manner by England, had -scientific objects, and at the same time was intended to solve practical -problems relating to navigation. The vessel, commanded by Captain -Fitzroy, appropriately bore the symbolic name of the _Beagle_. The -voyage of the _Beagle_, which lasted five years, was of the highest -importance to the full development of Darwin's genius; for in the very -first year, when he set his foot on the soil of South America, the -outline of the doctrine of descent dawned upon him. Darwin himself has -described this voyage in a work which is written in a very attractive -style, and the perusal of which I strongly recommend to the reader. This -book of travel, which lies far above the usual average in interest, not -only shows in a very charming manner Darwin's amiable character, but we -can in many ways recognize the various steps by which he arrived at his -conceptions. The result of the voyage was, first, a large scientific -work, the zoological and geological portion of which belong in a great -measure to Darwin; and secondly, a celebrated work by him alone on Coral -Reefs, which in itself would have sufficed to secure to him a lasting -reputation. It is well known that the islands in the South Seas consist -for the most part of coral reefs, and are surrounded by them. Formerly -no satisfactory explanation could be given of their different and -remarkable forms, and of their relation to those islands which are not -formed of corals. It was reserved for Darwin to solve this difficult -problem, for together with the constructive action of the coral -zoophytes, he assumed geological risings and depressions of the bottom -of the sea to account for the origin of the different forms of reefs. -Darwin's Theory of the Origin of Coral Reefs, like his later one as to -the Origin of Organic Species, is a theory which fully explains the -phenomenon, and for this purpose assumes only the simplest natural -causes, without hypothetically supporting it with any unknown processes. -Among the remaining works of Darwin, I must not pass over his excellent -monograph on Cirrhipedia, a curious class of marine animals, which in -their outward appearance resemble mussels, and were actually considered -by Cuvier as Molluscs possessing two shells, while in truth they -belonged to the Crustacea (crabs). - -The extraordinary hardships to which Darwin had been exposed during his -voyage in the _Beagle_ had injured his health to such a degree, that -after his return home he was obliged to withdraw from the restless -turmoil of London life, and since then has lived in quiet retirement on -his estate at Down, near Bromley, in Kent. This seclusion from the -restless activity of the great city certainly exercised a beneficial -influence upon Darwin, and it is probable that we owe to it, at least -partially, the formation of the Theory of Selection. Undisturbed by the -various engagements which in London would have wasted his strength, he -was enabled to concentrate his attention upon the great problem to -which his mind had been turned during his voyage in the _Beagle_. In -order to show what kind of observations during the voyage principally -gave rise to the fundamental idea of the Theory of Selection, and in -what manner he afterwards worked it out, I shall insert here a passage -from a letter which he addressed to me on the 8th of October, 1864. - - -_Letter from Charles Darwin to Haeckel, 8th October, 1864._ - -"In South America three classes of facts were brought strongly before my -mind. _Firstly_, the manner in which closely allied species replace -species in going southward. _Secondly_, the close affinity of the -species inhabiting the islands near South America to those proper to the -continent. This struck me profoundly, especially the difference of the -species in the adjoining islets in the Galopagos Archipelago. _Thirdly_, -the relation of the living Edentata and Rodentia to the extinct species. -I shall never forget my astonishment when I dug out a gigantic piece of -armour like that of the living armadillo. - -"Reflecting on these facts, and collecting analogous ones, it seemed to -me probable that allied species were descended from a common parent. But -for some years I could not conceive how each form became so excellently -adapted to its habits of life. I then began systematically to study -domestic productions, and after a time saw clearly that man's selective -power was the most important agent. I was prepared, from having studied -the habits of animals, to appreciate the struggle for existence, and my -work in geology gave me some idea of the lapse of past time. Therefore, -when I happened to read "Malthus on Population," the idea of natural -selection flashed on me. Of all the minor points, the last which I -appreciated was the importance and cause of the principle of -divergence." - - -During the leisure and retirement in which Darwin lived after his -return, he occupied himself, as we see from this letter, first and -specially with the study of organisms in their cultivated state; that -is, domestic animals and garden plants. This was undoubtedly the most -likely way to arrive at the Theory of Selection. In this, as in all his -labours, Darwin proceeded with extreme care and accuracy. With wonderful -caution and self-denial, he published nothing on this subject during a -period of twenty-one years, from 1837 to 1858, not even a preliminary -sketch of his theory, which he had written as early as 1844. He was -always anxious to collect still more certain experimental proofs, in -order to be able to establish his theory in a complete form, and on the -broadest possible foundation of experience. While he was thus aiming at -the greatest possible perfection, which might perhaps have led him never -to publish his theory at all, he was fortunately disturbed by a -countryman of his, who, independently of Darwin, had discovered the -Theory of Selection, and in 1858 sent its outlines to Darwin himself, -with the request to hand them to Lyell for publication in some English -journal. This was Alfred Wallace, one of the boldest and most -distinguished scientific travellers of modern times. For many years -Wallace had wandered alone in the wilds of the Sunda Islands, in the -dense primitive forests of the Indian Archipelago; and during this close -and comprehensive study of one of the richest and most interesting parts -of the earth, with its great variety of animals and plants, he had -arrived at exactly the same general views regarding the origin of -organic species as Darwin. Lyell and Hooker, both of whom had long known -Darwin's work, now induced him to publish a short extract from his -manuscripts simultaneously with the manuscript sent him by Wallace. They -appeared in the _Journal of the Linnean Society_, August, 1858. - -Darwin's great work "On the Origin of Species," in which the Theory of -Selection is carried out in detail, appeared in November, 1859. Darwin -himself, however, characterizes this book (of which a fifth edition -appeared in 1869, and the German translation by Bronn as early as -1860)(1) as only a preliminary extract from a larger and more detailed -work, which is to contain a mass of facts in favour of his theory, and -comprehensive and experimental proofs. The first part of the larger work -promised by Darwin appeared in 1868, under the title, "The Variations of -Animals and Plants in the State of Domestication," and has been -translated into German by Victor Carus.(14) It contains a rich abundance -of the most valuable evidence as to the extraordinary changes of organic -forms which man can produce by cultivation and artificial selection. -However much we are indebted to Darwin for this abundance of convincing -facts, still we do not by any means share the opinion of those -naturalists who hold that the Theory of Selection requires for its -actual proof these further details. It is our opinion that Darwin's -first work, which appeared in 1859, already contains sufficient proof. -The unassailable strength of his theory does not lie in the immense -amount of individual facts that may be adduced as proofs, but in the -harmonious connection of all the great and general phenomena of organic -nature, which agree in bearing testimony to the truth of the Theory of -Selection. - -Darwin, at first, intentionally did not notice the important conclusion -from his Theory of Descent, namely, the descent of the human race from -other mammals. It was not till this highly important conclusion had been -definitely established by other naturalists as the necessary sequel of -the doctrine of descent, that Darwin himself expressly endorsed it, and -thereby completed his system. This was done in the highly interesting -work, "The Descent of Man, and Sexual Selection," which appeared as late -as 1871, and has likewise been translated into German by Victor -Carus.(48) - -The careful study which Darwin devoted to _domestic animals and -cultivated plants_ was of the greatest importance in establishing the -Theory of Selection. The infinitely varied changes of form which man has -produced in these domesticated organisms by artificial selection are of -the very highest importance for a right understanding of animal and -vegetable forms; and yet this study has, down to the most recent times, -been most grossly neglected by zoologists and botanists. Without -entering upon the discussion of the significance to be attached to the -idea of species itself, they have filled not only bulky volumes, but -whole libraries, with descriptions of individual species, and with most -childish controversies as to whether these species are good, or -tolerably good, and bad, or tolerably bad. If naturalists instead of -spending their time on these useless fancies had duly studied cultivated -organisms, and had examined the transmutation of the living forms, -instead of the individual dead ones, they would not have been led -captive so long by the fetters of Cuvier's dogma. But as cultivated -organisms are so extremely inconvenient to the dogmatic conception of -the permanence of species, naturalists to a great extent intentionally -did not concern themselves about them, and even celebrated naturalists -have often expressed the opinion that cultivated organisms, domesticated -animals and garden plants, are artificial productions of man, and that -their formation and transformation could not decide anything about the -nature of species and about the origin of the forms of species that live -in a natural state. - -This perverse view went so far that, for example, Andreas Wagner, a -zoologist of Munich, quite seriously made the following ridiculous -assertion:--"Animals and plants in their wild state have been called -into being by the Creator as distinctly different and unchangeable -species; but in the case of domestic animals and cultivated plants this -was not necessary, because he formed them from the beginning for the use -of man. The Creator formed man out of a clod of earth, breathed the -living breath into his nostrils, and then created for him the different -useful domestic animals and garden plants, among which he thought well -to save himself the trouble of distinguishing species." Unfortunately, -Andreas Wagner does not tell us whether the _Tree of Knowledge_ in -Paradise was a "good" wild species, or, as a cultivated plant, "no -species" at all. As the Tree of Knowledge was placed by the Creator in -the centre of Paradise, we might be inclined to believe that it was a -highly favoured cultivated plant, and therefore no species at all. But -since, on the other hand, the fruit of the Tree of Knowledge was -forbidden to man, and since many men, as Wagner himself clearly shows, -have never eaten of the fruit, it was evidently not created for the use -of man, and therefore in all probability was a _real species!_ What a -pity Wagner has not given us any information about this important and -difficult problem! - -Now, however ridiculous this view may appear to us, it is only the -logical sequence of a false view (which is widely spread) of the special -nature of cultivated organisms, and one may occasionally hear similar -objections from naturalists of great reputation. I must most decidedly, -and at once, condemn this utterly false conception. It is the same -perverseness which is committed by physicians who maintain that diseases -are artificial productions, and not natural phenomena. It has been a -work of hard labour to combat this prejudice, and it is only in recent -times that men have generally adopted the view that diseases are nothing -but natural changes of the organisms, or really natural phenomena of -life, which are produced by changed and abnormal conditions of -existence. Disease, therefore, is not a life beyond Nature's realm (vita -praeter naturam), as the early physicians used to say, but a natural life -under conditions which produce illness and threaten the body with -danger. Just in the same manner, cultivated organic forms are not -artificial works of man, but natural productions which have arisen under -the influence of peculiar conditions of life. Man by his culture can -never directly produce a new organic form, but he can breed organisms -under new conditions of life, which are such as to influence and -transform them. All domestic animals and all garden plants are -originally descended from wild species, which have been transformed by -the peculiar conditions of culture. - -A thorough comparison of cultivated forms (races and varieties) with -organisms not altered by cultivation (species and varieties), is of the -utmost importance to the theory of selection. What is most surprising in -such a comparison is the remarkably short time in which man can produce -a new form, and the high degree in which this form, produced by man, can -deviate from the original form. While wild animals and plants, one year -after another, appear to the zoologist and botanist approximately in the -same form, so as to have given rise to the false doctrine of the -constancy of species, domestic animals and garden plants, on the other -hand, display the greatest changes within a few years. The perfection -which gardeners and farmers have attained in the art of selection now -enables them, in the space of a few years, arbitrarily to create -entirely new animal and vegetable forms. For this purpose it is only -necessary to keep and propagate the organism under the influence of -special conditions--which are capable of producing new formations--and -even at the end of a few generations new species may be obtained, which -differ from the original form in a much higher degree than so-called -good species in a wild state differ from one another. This fact is -extremely important, and we cannot lay sufficient stress upon it. The -assertion is not true that cultivated forms descended from one and the -same primary form do not differ from one another as much as wild animal -and vegetable species differ among themselves. If we only make -comparisons, without prejudice, we can very easily perceive that a -number of races or varieties which have been derived from a single -cultivated form, within a short series of years, differ from one another -in a higher degree than so-called good species (bonae species), or even -different genera of one family, in the wild state. - -In order to establish this extremely important fact as firmly as -possible by experiments, Darwin decided to make a special study of the -whole extent of variation in form in a single group of domesticated -animals, and for this purpose he chose the _domestic pigeons_, which are -in many respects especially suited for such a study. For a long time he -kept on his estate all possible races and varieties of pigeons which he -was able to procure, and he was helped in this by rich contributions -from all parts of the world. He also joined two London pigeon clubs, the -members of which passionately, and with truly artistic skill, carry on -the breeding of the different forms of pigeons. Lastly, he formed -connections with some of the most celebrated pigeon-fanciers; so that he -could command the richest experimental material. - -The art of, and fancy for, pigeon breeding is very ancient. Even more -than 3,000 years before Christ, it was carried on by the Egyptians. The -Romans, under the emperors, laid out enormous sums upon the breeding of -pigeons, and kept accurate pedigrees of their descent, just as the Arabs -keep genealogical pedigrees of their horses, and the Mecklenburg -aristocracy of their own ancestors. In Asia, too, among the wealthy -princes, pigeon breeding was a very ancient fancy; in 1600, the court of -Akber Khan possessed more than 20,000 pigeons. Thus in the course of -several centuries, and in consequence of the various methods of breeding -practised in the different parts of the world, there has arisen out of -one single originally tamed form, an immense number of different races -and varieties, which in their most divergent forms are extremely -different from one another, and are often curiously characterized. - -One of the most striking races of pigeons is the well-known fan-tailed -pigeon, which spreads its tail like the peacock, and carries a number of -(from thirty to forty) feathers placed in the form of radii, while other -pigeons possess much fewer tail feathers--generally twelve. We may here -mention that the number of feathers on the tails of birds is considered -by naturalists of great value as a systematic distinction, so that whole -orders can thereby be distinguished. For example, singing birds, almost -without exception, possess twelve tail feathers; chirping birds -(Strisores) ten, etc. Several races of pigeons, moreover, are -characterized by a tuft of neck feathers, which form a kind of periwig; -others by grotesque transformation of their beaks and feet, by peculiar -and often very remarkable decorations, as, for example, skinny lappets, -which develop on the head; by a large crop, which is formed by the -gullet being strongly inclined forward, etc. Remarkable, also, are the -strange habits which many pigeons have acquired; for example, the turtle -pigeons and the trumpeters with their musical accomplishments, the -carriers with their topographical instinct. The tumblers have the -strange habit of ascending into the air in great numbers, then turning -over and falling down through the air as if dead. The ways and habits of -these endless races of pigeons--the form, size, and colour of the -individual parts of their bodies, and their proportions, differ in a -most astonishing degree from one another; in a much higher degree than -is the case with the so-called good species, or even with the perfectly -distinct genera, of wild pigeons. And what is of the greatest -importance, is the fact that these differences are not confined to the -external form, but extend even to the most important internal parts; -there even occur great modifications of the skeleton and of the -muscular tissues. For example, we find great differences in the number -of vertebrae and ribs, in the size and shape of the gaps in the -breast-bones, in the size and shape of the merry-thought, in the lower -jaw, in the facial bones, etc. In short, the bony skeleton, which -morphologists consider a very permanent part of the body, and which -never varies to such an extent as the external parts--shows such great -changes, that many races of pigeons might be described as special -genera, and this would doubtless be done if all these different forms -had been found in a wild and natural state. - -How far the differences of the races of pigeons have been carried is -best shown by the fact that all pigeon breeders are unanimously of -opinion that each peculiar or specially marked race of pigeons must be -derived from a corresponding wild original species. It is true every one -assumes a different number of original species. Yet Darwin has most -convincingly and acutely proved that all these pigeons, without -exception, must be derived from a single wild primary species--from the -blue rock-pigeon (_Columba livia_). In like manner, it can be proved of -most of the domestic animals and cultivated plants, that all the -different races are descendants of a single original wild species which -has been brought by man into a cultivated condition. - -An example similar to that of the domestic pigeons is furnished among -mammals by our tame _rabbit_. All zoologists, without exception, have -long considered it proved that all its races and varieties are descended -from the common wild rabbit, that is, from a single primary species. And -yet the extreme forms of these races differ to such a degree from one -another, that every zoologist, if he met with them in a wild state, -would unhesitatingly designate them not only as an entirely distinct -"good species," but even as species of entirely different genera of the -Leporid family. Not only does the colour, length of hair, and other -qualities of the fur of the different tame races of rabbits vary -exceedingly, and form extremely broad contrasts, but, what is still more -important, the typical form of the skeleton and its individual parts do -so also, especially the form of the skull and the jaw (which is of such -importance in systematic arrangement); further, the relative proportion -of the length of the ears, legs, etc. In all these respects the races of -tame rabbits avowedly differ from one another far more than all the -different forms of wild rabbits and hares which are scattered over all -the earth, and are the recognized "good species" of the genus _Lepus_. -And yet, in the face of these clear facts, the opponents of the theory -of development maintain that the wild species are not descended from a -common prototype, although they at once admit it in the case of the tame -races. With opponents who so intentionally close their eyes against the -clear light of truth, no further dispute can be carried on. - -While in this manner it appears certain that the domestic races of -pigeons, of tame rabbits, of horses, etc., notwithstanding the -remarkable difference of their varieties, are descended in each case -from but one wild, so-called "species"; yet, on the other hand, it is -certainly probable that the great variety of races of some of the -domestic animals, especially dogs, pigs, and oxen, must be ascribed to -the existence of several wild prototypes, which have become mixed. It -is, however, to be observed that the number of these originally wild -primary species is always much smaller than that of the cultivated forms -proceeding from their mingling and selection, and naturally they were -originally derived from a single primary ancestor, common to the whole -genus. In no case is each separate cultivated race descended from a -distinct wild species. - -In opposition to this, almost all farmers and gardeners maintain, with -the greatest confidence, that each separate race bred by them must be -descended from a separate wild primary species, because they clearly -perceive the differences of the races, and attach very high importance -to the inheritance of their qualities; but they do not take into -consideration the fact that these qualities have arisen only by the slow -accumulation of small and scarcely observable changes. In this respect -it is extremely instructive to compare cultivated races with wild -species. - -Many naturalists, and especially the opponents of the Theory of -Development, have taken the greatest trouble to discover some -morphological or physiological mark, some characteristic property, -whereby the artificially bred and cultivated races may be clearly and -thoroughly distinguished from wild species which have arisen naturally. -All these attempts have completely failed, and have led only with -increasing certainty to the result, that such a distinction is -altogether impossible. I have minutely discussed this fact, and -illustrated it by examples in my criticism of the idea of species. (Gen. -Morph. ii. 323-364.) - -I may here briefly touch on yet another side of this question, because -not only the opponents, but even a few of the most distinguished -followers of Darwin--for example, Huxley--have regarded the phenomena of -_bastard-breeding_, or _hybridism_, as one of the weakest points of -Darwinism. Between cultivated races and wild species, they say, there -exists this difference, that the former are capable of producing -fruitful bastards, but that the latter are not. Two different cultivated -races, or wild _varieties of one species_, are said in all cases to -possess the power of producing bastards which can fruitfully mix with -one another, or with one of their parent forms, and thus propagate -themselves; on the other hand, _two really different species_, two -cultivated or wild _species_ of one genus, are said _never_ to be able -to produce from one another bastards which can be fruitfully crossed -with one another, or with one of their parent species. - -As regards the first of these assertions, it is simply refuted by the -fact that there are organisms which do not mix at all with their own -ancestors, and therefore can produce no fruitful descendants. Thus, for -example, our cultivated guinea-pig does not bear with its wild Brazilian -ancestor; and again, the domestic cat of Paraguay, which is descended -from our European domestic cat, no longer bears with the latter. Between -different races of our domestic dogs, for example, between the large -Newfoundland dogs and the dwarfed lap-dogs, breeding is impossible, even -for simple mechanical reasons. A particularly interesting instance is -afforded by the Porto-Santo rabbit (Lepus Huxleyi). In the year 1419, a -few rabbits, born on board ship of a tame Spanish rabbit, were put on -the island of Porto Santo, near Madeira. These little animals, there -being no beasts of prey, in a short time increased so enormously that -they became a pest to the country, and even compelled a colony to remove -from the island. They still inhabit the island in great numbers; but in -the course of four hundred and fifty years they have developed into a -quite peculiar variety--or if you will have it, into a "good -species"--which is distinguished by a peculiar colour, a rat-like shape, -small size, nocturnal life, and extraordinary wildness. The most -important fact, however, is that this new species, which I call _Lepus -Huxleyi_, no longer pairs with its European parent rabbit, and no longer -produces bastards with it. - -On the other hand, we now know of numerous examples of fruitful genuine -bastards; that is, of mixings that have proceeded from the crossing of -two entirely different species, and yet propagate themselves with one -another as well as with one of their parent species. A number of such -bastard species (species Hybridae) have long been known to botanists; for -example, among the genera of the thistle (Cirsium), the laburnum -(Cytisus), the bramble (Rubus), etc. Among animals also they are by no -means rare, perhaps even very frequent. We know of fruitful bastards -which have arisen from the crossing of two different species of a genus, -as among several genera of butterflies (Zygaena, Saturnia), the family of -carps, finches, poultry, dogs, cats, etc. One of the most interesting is -the hare-rabbit (Lepus Darwinii), the bastard of our indigenous hare and -rabbit, many generations of which have been bred in France, since 1850, -for gastronomic purposes. I myself possess such hybrids, the products of -pure in-breeding, that is, both parents of which are themselves hybrids -by a hare-father and a rabbit-mother. I possess them through the -kindness of Professor Conrad, who has repeatedly made these experiments -in breeding on his estate. The half-blood hybrid thus bred, which I name -in honour of Darwin, appears to propagate itself through many -generations by pure in-breeding, just as well as any genuine species. -Although on the whole it is more like its mother (rabbit), still in the -formation of the ears and of the hind-legs, it possesses distinct -qualities of its father (hare). Its flesh has an excellent taste, rather -resembling that of a hare, though the colour is more like that of a -rabbit. But the hare (Lepus timidus) and the rabbit (Lepus cuniculus) -are two species of the genus Lepus, so different that no systematic -zoologist will recognize them as varieties of one species. Both species, -moreover, live in such different ways, and in their wild state entertain -so great an aversion towards one another, that they do not pair so long -as they are left free. If, however, the newly-born young ones of both -species are brought up together, this aversion is not developed; they -pair with one another and produce the _Lepus Darwinii_. - -Another remarkable instance of the crossing of different species (where -the two species belong even to different genera!) is furnished by the -fruitful hybrids of sheep and goats which have for a long time been bred -in Chili for industrial purposes. On what unessential circumstances in -the sexual mingling the fertility of the different species depend, is -shown by the fact that he-goats and sheep in their mingling produce -fruitful hybrids, while the ram and she-goat pair very rarely, and then -without result. The phenomena of hybridism to which undue importance has -been erroneously attributed are thus utterly unmeaning, so far as the -idea of species is concerned. The breeding of hybrids does not enable -us, any more than other phenomena, thoroughly to distinguish cultivated -races from wild species; and this circumstance is of the greatest -importance in the Theory of Selection. - - - - -CHAPTER VII. - -THE THEORY OF SELECTION (DARWINISM). - - - Darwinism (Theory of Selection) and Lamarckism (Theory of - Descent).--The Process of Artificial Breeding.--Selection - of the Different Individuals for After-breeding.--The - Active Causes of Transmutation.--Change connected with - Food, and Transmission by Inheritance connected with - Propagation.--Mechanical Nature of these Two - Physiological Functions.--The Process of Natural - Breeding: Selection in the Struggle for - Existence.--Malthus' Theory of Population.--The - Proportion between the Numbers of Potential and Actual - Individuals of every Species of Organisms.--General - Struggle for Existence, or Competition to attain the - Necessaries of Life.--Transforming Force of the Struggle - for Existence.--Comparison of Natural and Artificial - Breeding.--Selection in the Life of Man.--Military and - Medical Selection. - - -It is, properly speaking, not quite correctly that the Theory of -Development, with which we are occupied in these pages, is usually -called Darwinism. For, as we have seen from the historical sketch in the -previous chapters, the most important foundation of the Theory of -Development--that is, the Doctrine of Filiation, or Descent--had already -been distinctly enunciated at the beginning of our century, and had been -definitely introduced into science by Lamarck. The portion of the Theory -of Development which maintains the common descent of all species of -animals and plants from the simplest common original forms might, -therefore, in honour of its eminent founder, and with full justice, be -called _Lamarckism_, if the merit of having carried out such a principle -is to be linked to the name of a single distinguished naturalist. On the -other hand, the Theory of Selection, or breeding, might be justly called -_Darwinism_, being that portion of the Theory of Development which shows -us in what way and _why_ the different species of organisms have -developed from those simplest primary forms. (Gen. Morph. ii. 166.) - -It is true we find the first trace of an idea of natural selection even -forty years before the appearance of Darwin's work. For in the year 1818 -there was published a paper "On a woman of the white race whose skin -partly resembled that of a negro," which had been read before the Royal -Society as early as 1813. Its author, Dr. W. C. Wells, states that -negroes and mulattoes are distinguished from the white race by their -immunity from certain tropical diseases. On this occasion he remarks -that all animals have a tendency to change up to a certain degree, and -that farmers, by availing themselves of this tendency, and also by -selection, improve their domestic animals; and then he adds, that what -is done in this latter case "by art, seems to be done with equal -efficiency, though more slowly, by nature, in the formation of varieties -of mankind fitted for the country which they inhabit. Of the accidental -varieties of man which would occur among the first few and scattered -inhabitants of the middle regions of Africa, some one would be better -fitted than the others to bear the diseases of the country. This race -would consequently multiply, while the others would decrease; not only -from their inability to sustain the attacks of disease, but from their -incapacity of contending with their more vigorous neighbours. The -colour of this vigorous race I take for granted, from what has been -already said, would be dark. But the same disposition to form varieties -still existing, a darker and a darker race would in the course of time -occur; and as the darkest would be the best fitted for the climate, this -would at length become the most prevalent, if not the only race, in the -particular country in which it had originated." He then extends these -same views to the white inhabitants of colder climates. Although Wells -clearly expresses and recognizes the principle of natural selection, yet -it is applied by him only to the very limited problem of the origin of -human races, and not at all to that of the origin of animal and -vegetable species. Darwin's great merit in having independently -developed the Theory of Selection, and having brought it to complete and -well merited recognition, is as little affected by the earlier and long -forgotten remark of Wells, as by some other fragmentary observations -about natural selection made by Patrick Mathew, and hidden in his book -on "Timber for Shipbuilding, and the Cultivation of Trees," which -appeared in 1831. The celebrated traveller, Alfred Wallace, who -developed the Theory of Selection independently of Darwin, and had -published it in 1858, simultaneously with Darwin's first contribution, -likewise stands far behind his greater and elder countryman in regard to -profound conception, as well as to extended application of the theory. -In fact Darwin, by his extremely comprehensive and ingenious development -of the whole doctrine, has acquired a fair claim to see the theory -connected with his own name. - -This Theory of Selection, Darwinism in its proper sense, to the -consideration of which we now turn our attention, rests essentially (as -has already been intimated in the last chapter) upon the comparison of -those means which man employs in the breeding of domestic animals and -the cultivation of garden plants, with those processes which in free -nature, outside the cultivated state, lead to the coming into existence -of new species and new genera. We must therefore, in order to understand -the latter processes, first turn to the artificial breeding by man, as -was, in fact, done by Darwin himself. We must inquire into the results -to which man attains by his artificial breeding, and what means are -applied in order to obtain those results; and we must then ask -ourselves, "Are there in nature similar forces and causes acting -similarly to those resorted to by man?" - -First, in regard to artificial breeding, we start from the fact last -discussed above, viz., that its products in some cases differ from one -another much more than the productions of natural breeding. It is a fact -that races or varieties often differ from one another in a much greater -degree and in much more important qualities than many so-called species, -or "good species,"--nay, sometimes even more than so-called "good -genera" in their natural state. Compare, for example, the different -kinds of apples which the art of horticulture has derived from one and -the same original apple-form, or compare the different races of horses -which their breeders have derived from one and the same original form of -horse, and it will be easily observed that the differences of the most -different forms are extremely important, and much more important than -the so-called "specific differences," which are referred to by -zoologists and botanists when comparing wild forms for the purpose of -distinguishing several so-called "good species." - -Now, by what means does man produce this extraordinary difference or -divergence of several forms which are proved to be descended from the -same primary form? In order to answer this question, let us follow a -gardener who desires to produce a new form of a plant, which is -distinguished by the beautiful colour of its flowers. He will first of -all make a selection from a great number of plants which are seedlings -from one and the same parent. He will pick out those plants which -exhibit most distinctly the colour of flower he desires. The colour of -flowers is a very changeable thing. Plants, for example, which as a rule -have a white flower, frequently show deviations into the blue or red. -Now, supposing the gardener wishes to obtain the red colour in a plant -usually producing white flowers, he will very carefully, from among the -many different individuals which are the descendants of one and the same -seed-plant, select those which most distinctly show a reddish tint, and -sow them exclusively, in order to produce new individuals of the same -kind. He would cast aside and no longer cultivate the other seedlings -which show a white or less distinct red colour. He will propagate -exclusively the individual plants whose blossoms show the red most -markedly, and he will sow the seeds produced by these selected plants. -From the seedlings of this second generation, he will again carefully -select those in which the red, which is now visible in the majority of -them, is most distinctly displayed. If such a selection is carried on -during a series of six or ten generations, and if the flower which shows -the deepest red is most carefully selected, the gardener in the sixth or -tenth generation will obtain the desired plants with flowers of a pure -red. - -The farmer wishing to breed a special race of animals, for example, a -kind of sheep distinguished by particularly fine wool, proceeds in the -same manner. The only process applied in the improvement of wool -consists in this, that the farmer with the greatest care and -perseverance selects from a whole flock of sheep those individuals which -have the finest wool. These only are used in breeding, and among the -descendants of these selected sheep, those again are chosen which have -the finest wool, etc. If this careful selection is carried on through a -series of generations, the selected breeding-sheep are in the end -distinguished by a wool which differs very strikingly from the wool of -the original parent, and this is exactly the advantage which the breeder -desired. - -The differences of the individuals that come into consideration in this -artificial selection are very slight. An ordinary unpractised man is -unable to discover the exceedingly minute differences of individuals -which a practised breeder perceives at the first glance. The business of -a breeder is not easy; it requires an exceedingly sharp eye, great -patience, and an extremely careful manner of treating the organisms to -be bred. In each individual generation, the differences of individuals -are perhaps not seen at all by the uninitiated; but by the accumulation -of these minute differences during a series of generations, the -deviation from the original form becomes in the end very great. It -becomes so great that the artificially produced form may in the end -differ far more from the original form than do two so-called "good -species" in their natural state. The art of breeding has now made such -progress, that man can often at discretion produce certain peculiarities -in cultivated species of animals and plants. To practised gardeners and -farmers, you may give distinct commissions, and say, for example, I wish -to have this species of plant with this or that colour, and with this or -that shape. Where breeding has reached the perfection which it has -attained in England, gardeners and farmers are frequently able to -furnish to order the desired result within a definite period, that is, -at the end of a number of generations. Sir John Sebright, one of the -most experienced English pigeon-breeders, could assert that in three -years he would produce any form of feather, but that he required six -years to obtain any desired form of the head and beak. In the process of -breeding the merino-sheep of Saxony, the animals are three times placed -on a table beside one another, and most carefully compared and studied. -Each time only the best sheep with the finest wool are selected, so that -in the end, out of a great multitude, there remain only some few -animals, but their wool is exquisitely fine, and only these last are -used in breeding. We see, therefore, that the causes through which, in -artificial breeding, great effects are produced, are unusually simple, -and these great effects are obtained simply by accumulating the -differences which in themselves are very insignificant, and become -surprisingly increased by a continually repeated selection. - -Before we pass on to a comparison of this artificial with natural -breeding, let us see what natural qualities of the organisms are made -use of by the artificial breeder or cultivator. We can trace all the -different qualities which here come into play to physiological -fundamental qualities of the organism, which are common to all animals -and plants, and are most closely connected with the functions of -_propagation_ and _nutrition_. These two fundamental qualities are -_transmissivity_, or the capability of _transmitting by inheritance_, -and _mutability_, or the capability of _adaptation_. The breeder starts -from the fact that all the individuals of one and the same species are -different, though in a very slight degree, a fact which is as true of -organisms in a wild as in a cultivated state. If you look about you in a -forest consisting of only a single species of tree, for example of -beech, you will certainly not find in the whole forest two trees of this -kind which are absolutely identical or perfectly equal in the form of -their branches, the number of their branches and leaves, blossoms and -fruits. Special differences occur everywhere, just as in the case of -men. There are no two men who are absolutely identical, perfectly equal -in size, in the formation of their faces, the number of their hairs, -their temperament, character, etc. The very same is true of individuals -of all the different species of animals and plants. It is true that in -most organisms the differences are very trifling to the eye of the -uninitiated. Everything here essentially depends on the exercise of the -faculty of discovering these often very minute differences of form. The -shepherd, for example, knows every individual of his flock, solely by -accurately observing their features, while the uninitiated are incapable -of distinguishing at all the different individuals of one and the same -flock. This fact of the individual difference is the extremely important -foundation on which the whole of man's power of breeding rests. If -individual differences did not exist everywhere, man would not be able -to produce a number of different varieties or races from one and the -same original stock. We must, at the outset, hold fast the principle -that the phenomenon is quite universal; we must necessarily assume it -even where, with the imperfect capabilities of our senses, we are unable -to discover differences. Among the higher plants (the phanerogams, or -flower-plants), where the individual stocks show such numerous -differences in the number of branches or leaves, and in the formation of -the stem and branches, we can almost always easily perceive these -differences. But this is not the case in the lower plants, such as -mosses, algae, fungi, and in most animals, especially the lower ones. The -distinction of all the individuals of one species is here, for the most -part, extremely difficult or altogether impossible. But there is no -reason for ascribing individual differences only to those organisms in -which we can perceive them at once. We may, on the contrary, with full -certainty assume such individuality as a universal quality of all -organisms, and we can do this all the more surely since we are able to -trace the mutability of individuals to the mechanical conditions of -nutrition. We can show that by influencing nutrition we are able to -produce striking individual differences where they would not exist if -the conditions of nutrition had not been altered. The many complicated -conditions of nutrition are never absolutely identical in two -individuals of a species. - -Now, just as we see that the mutability or capability of adaptation has -a causal connection with the general relations of nutrition in animals -and plants, so too we find the second fundamental phenomenon of life, -with which we are here concerned, namely, the capability of -_transmitting by inheritance_, to have a direct connection with the -phenomenon of _propagation_. The second thing that a farmer or gardener -does in artificial breeding, after he has selected, and has consequently -availed himself of the mutability, is to endeavour to hold fast and -develop the modified forms by Inheritance. He starts from the universal -fact that children resemble their parents, that "the apple does not fall -far from the tree." This phenomenon of Inheritance has hitherto been -scientifically examined only to a very small extent, which may partly -arise from the fact that the phenomenon is of such everyday occurrence. -Every one considers it quite natural that every species should produce -its like; that a horse should not suddenly produce a goose, or a goose a -frog. We are accustomed to look upon these everyday occurrences of -Inheritance as self-evident. But this phenomenon is not so simply -self-evident as it appears at first sight, and in the examination of -Inheritance the fact is very frequently overlooked that the different -descendants, derived from one and the same parents, are in reality -_never_ quite identical, and also never absolutely like the parents, but -are always slightly different. We cannot formulate the principle of -Inheritance, as "Like produces like," but we must limit the expression -to "Similar things produce similar things." The gardener, as well as the -farmer, avails himself of the fact of Inheritance in its widest form, -and indeed with special regard to the fact that not only those qualities -of organisms are transmitted by inheritance which they have inherited -from _their_ parents but those also which they themselves have -_acquired_. This is an important point upon which very much depends. An -organism can transmit to its descendants not only those qualities of -form, colour, and size which it has inherited from its parents, but it -can also transmit changes of these qualities, which it has acquired -during its own life through the influence of outward circumstances, such -as climate, nourishment, training, etc. - -These are the two fundamental qualities of animals and plants of which -the breeder must avail himself in order to produce new forms. The -theoretical principle of breeding is, indeed, extremely simple, but in -detail the practical application of this simple principle is difficult -and immensely complicated. A thoughtful breeder, acting according to a -definite plan, must understand the art of correctly estimating, in every -case, the general interaction between the two fundamental qualities of -heirship and mutability. - -Now, if we examine the real nature of those two important properties of -life, we find that we can trace them, like all physiological functions, -to physical and chemical causes, to the properties and the phenomena of -motion of those substances of which the bodies of animals and plants -consist. As we shall hereafter have to show in the more accurate -consideration of these two functions, the transmission by _Inheritance_, -if we express ourselves quite generally, is essentially dependent upon -the material continuity and partial identity of the matter in the -producing and produced organism, the parents and the child. In every act -of breeding a certain quantity of protoplasm or albuminous matter is -transferred from the parents to the child, and along with it there is -transferred the individually _peculiar molecular motion_. These -molecular phenomena of motion in the protoplasm, which call forth the -phenomena of life, and are their active and true cause, differ more or -less in all living individuals; they are of infinite variety. - -_Adaptation_, or transmutation is, on the other hand, essentially the -consequence of material influences, which the substance of the organism -experiences from the material surrounding it,--in the widest sense of -the word from the _conditions_ of life. The external influences of the -latter are communicated to the individual parts of the body by the -molecular processes of nutrition. In every act of Adaptation the -individual molecular motion of the protoplasm, peculiar to each part, -disturbs and modifies the whole individual, or part of it, by -mechanical, physical, or chemical influences. The innate, inherited -vital actions of the protoplasm--that is, the molecular phenomena of -motion of the smallest albuminous particles--are therefore more or less -modified by it. The phenomenon of Adaptation, or transmutation, depends -therefore upon the material influence which the organism experiences -from its surroundings, or its conditions of existence; while the -transmission by Inheritance is due to the partial identity of the -producing and produced organism. These are the real, simple, mechanical -foundations of the artificial process of breeding. - -Now Darwin asked himself, Does there exist a similar process of -selection in nature, and are there forces in nature which take the place -of man's activity in artificial selection? Is there a natural tendency -among wild animals and plants which acts selectingly, in a similar -manner to the artificial selection practised by the designing will of -man? All here depended upon the discovery of such a relation, and Darwin -succeeded in this so satisfactorily, that we consider his theory of -selection completely sufficient to explain, mechanically, the origin of -the wild species of animals and plants. That relation which in free -nature influences the forms of animals and plants, by selecting and -transforming them, is called by Darwin the "_Struggle for Existence_." - -The "Struggle for Existence" has rapidly become a watchword of the day. -Yet this designation is, perhaps, in many respects not very happily -chosen, and the phenomena might probably have been more accurately -described as "_Competition for the Means of Subsistence_." For under the -name of "Struggle for Life," many relations are comprehended which -properly and strictly speaking do not belong to it. As we have seen from -the letter inserted in the last chapter, Darwin arrived at the idea of -the "Struggle for Existence" from the study of Malthus' book "On the -Conditions and the Consequences of the Increase of Population." It was -proved in that important work, that the number of human beings, on the -average, increases in a geometrical progression, while the amount of -articles of food increase only in an arithmetical progression. This -disproportion gives rise to a number of inconveniences in the human -community, which cause among men a continual competition to obtain the -necessary means of life, which do not suffice for all. - -Darwin's theory of the struggle for life is, to a certain extent, a -general application of Malthus' theory of population to the whole of -organic nature. It starts from the consideration that the number of -_possible_ organic individuals which might arise from the germs -produced, is far greater than the number of _actual_ individuals which, -in fact, do simultaneously live on the earth's surface. The number of -possible or _potential individuals_ is given us by the number of the -eggs and organic germs produced by organisms. The number of these germs, -from each of which, under favourable circumstances, an individual might -arise, is very much larger than the number of real or actual -_individuals_--that is, of those that really arise from these germs, -come into life, and propagate themselves. By far the greater number of -germs perish in the earliest stage of life, and it is only some favoured -organisms which manage to develop, and actually survive the first period -of early youth, and finally succeed in propagating themselves. This -important fact is easily proved by a comparison of the number of eggs in -a given species with the number of individuals which exist of this -species. These numerical relations show the most striking contrast. -There are, for example, species of fowls which lay great numbers of -eggs, and yet are among the rarest of birds; and the bird which is said -to be the commonest (the most widely spread) of all, the stormy petrel -(_Procellaria glacialis_), lays only a single egg. The relation is the -same in other animals. There are many very rare invertebrate animals, -which lay immense quantities of eggs; and others again which produce -only very few eggs, and yet are among the commonest of animals. Take, -for example, the proportion which is observed among the human -tape-worms. Each tape-worm produces within a short period millions of -eggs, while man, in whom these tape-worms are lodged, forms a far -smaller number of eggs, and yet fortunately there are fewer tape-worms -than human beings. In like manner, among plants there are many splendid -orchids, which produce thousands of seeds and yet are very rare, and -some kinds of asters (Compositae), which have but few seeds, are -exceedingly common. - -This important fact might be illustrated by an immense number of -examples. It is evidently, therefore, not the number of actually -existing germs which indicates the number of individuals which -afterwards come into life and maintain themselves in life; but rather -the case is this, that the number of adult individuals is limited by -other circumstances, especially by the relations in which the organism -stands to its organic and inorganic surroundings. Every organism, from -the commencement of its existence, struggles with a number of hostile -influences: it struggles against animals which feed on it, and to which -it is the natural food, against animals of prey and parasites; it -struggles against inorganic influences of the most varied kinds, against -temperature, weather, and other circumstances; but it also struggles -(and this is much the most important!), above all, against organisms -most like and akin to itself. Every individual, of every animal and -vegetable species, is engaged in the fiercest competition with every -other individual of the same species which lives in the same place with -it. In the economy of nature the means of subsistence are nowhere -scattered in abundance, but are very limited, and far from sufficient -for the number of organisms which might develop from the germs produced. -Therefore the young individuals of most species of animals and -vegetables must have hard work in obtaining the means of subsistence; -this necessarily causes a competition among them in order to obtain the -indispensable supplies of life. - -This great competition for the necessaries of life goes on everywhere -and at all times, among human beings and animals as well as among -plants; in the case of the latter this circumstance, at first sight, is -not so clearly apparent. If we examine a field which is richly sown with -wheat, we can see that of the numerous young plants (perhaps some -thousands) which shoot up on a limited space, only a very small -proportion preserve themselves in life. A competition takes place for -the space of ground which each plant requires for fixing its root, a -competition for sunlight and moisture. And in the same manner we find -that, among all animal species, all the individuals of one and the same -species compete with one another to obtain these indispensable means of -life, or the conditions of existence in the wide sense of the word. They -are equally indispensable to all, but really fall to the lot of only a -few--"Many are called, but few are chosen." The fact of the great -competition is quite universal. You need only to cast a glance at human -society, where this competition exists everywhere, and in all the -different branches of human activity. Here, too, a struggle is brought -about by the free competition of the different labourers of one and the -same class. Here too, as everywhere, this competition benefits the -thing, or the work, which is the object of competition. The greater and -more general the competition, the more quickly improvements and -inventions are made in the branch of labour, and the higher is the grade -of perfection of the labourers themselves. - -The position of the different individuals in this struggle for life is -evidently very unequal. Starting from the inequality of individuals, -which is a recognized fact, we must in all cases necessarily suppose -that all the individuals of one and the same species do not have equally -favourable prospects. Even at the beginning they are differently placed -in this competition by their different strengths and abilities, -independently of the fact that the conditions of existence are -different, and act differently at every point of the earth's surface. We -evidently have an infinite combination of influences, which, together -with the original inequality of the individuals during the competition -for the conditions of existence, favour some individuals and prejudice -others. The favoured individuals will gain the victory over the others, -and while the latter perish more or less early, without leaving any -descendants, the former alone will be able to survive and finally to -propagate the species. As, therefore, it is clear that in the struggle -for life the favoured individuals succeed in propagating themselves, we -shall (even as the result of this relation) perceive in the next -generation differences from the preceding one. Some individuals of this -second generation, though perhaps not all of them, will, by inheritance, -receive the individual advantage by which their parents gained the -victory over their rivals. - -But now--and this is a very important law of inheritance--if such a -transmission of a favourable character is continued through a series of -generations, it is not simply transmitted in the original manner, but it -is constantly increased and strengthened, and in a last generation it -attains a strength which distinguishes this generation very essentially -from the original parent. Let us, for example, examine a number of -plants of one and the same species which grow together in a very dry -soil. As the hairs on the leaves of plants are very useful for receiving -moisture from the air, and as the hairs on the leaves are very -changeable, the individuals possessing the thickest hair on their leaves -will have an advantage in this unfavourable locality where the plants -have directly to struggle with the want of water, and in addition to -this have to compete with one another for the possession of what little -water there may be. These alone hold out, while the others possessing -less hairy leaves perish; the more hairy ones will be propagated, and -their descendants will, on the average, be more distinguished by their -thick and strong hairs than the individuals of the first generation. If -this process is continued for several generations in one and the same -locality, there will arise at last such an increase of this -characteristic, such an increase of the hairs on the surface of the -leaf, that an entirely new species seems to present itself. It must here -be observed, that in consequence of the interactions of all the parts of -every organism, generally one individual part cannot be changed without -at the same time producing changes in other parts. If, for instance, in -our imaginary example, the number of the hairs on the leaves is greatly -increased, a certain amount of nourishment is thereby withdrawn from -other parts; the material which might be employed to form flowers or -seeds is diminished, and a smaller size of the flower or seed will then -be the direct or indirect consequence of the struggle for life, which in -the first place only produced a change in the leaves. Thus the struggle -for life, in this instance, acts as a means of selecting and -transforming. The struggle of the different individuals to obtain the -necessary conditions of existence, or, taking it in its widest sense, -the inter-relations of organisms to the whole of their surroundings, -produce mutations of form such as are produced in the cultivated state -by the action of man's selection. - -This agency will perhaps appear at first sight small and insignificant, -and the reader will not be inclined to concede to the action of such -relations the weight which it in reality possesses. I must therefore -find space in a subsequent chapter to put forward further examples of -the immense and far-reaching power of transformation exhibited in -natural selection. For the present I will confine myself to simply -placing side by side the two processes of artificial and natural -selection, and clearly explaining the agreement and the differences of -the two. - -Both natural and artificial selection are quite simple natural, -mechanical relations of life, which depend upon the _interaction_ of two -physiological functions, namely, on _Adaptation_ and _Inheritance_, -functions which, as such, must again be traced to physical and chemical -properties of organic matter. The difference between the two forms of -selection consists in this: in artificial selection the will of man -makes the selection according to a _plan_, whereas in natural selection, -the struggle for life (that universal inter-relation of organisms) acts -_without a plan_, but otherwise produces quite the same result, namely, -a selection of a particular kind of individuals for propagation. The -alterations produced by artificial selection are turned to the advantage -of _those who make the selection_; in natural selection, on the other -hand, to the advantage of the _selected organism_. - -These are the most essential differences and agreements of the two modes -of selection; it must, however, be further observed that there is -another difference, viz., in the duration of time required for the two -processes of selection. Man in his artificial selection can produce very -important changes in a very short time, while in natural selection -similar results are obtained only after a much longer time. This arises -from the fact that man can make his selection with much greater care. -Man is able with the greatest nicety to pick out individuals from a -large number, drop the others, and to employ only the privileged beings -for propagation, which is not the case in natural selection. In natural -conditions, besides the privileged individuals which first succeed in -propagating themselves, some few or many of the less distinguished -individuals will propagate themselves by the side of the former. -Moreover, man can prevent the crossing of the original and the new form, -which in natural selection is often unavoidable. If such a crossing, -that is, a sexual connection, of the new variety with the original forms -takes place, the offspring thereby produced generally returns to the -original character. In natural selection, such a crossing can be avoided -only when the new variety by migration separates from the original and -isolates itself. - -Natural selection therefore acts much more slowly; it requires much -longer periods than the artificial process of selection. But it is an -essential consequence of this difference, that the product of artificial -selection disappears much more easily, and that the new form returns -rapidly to the earlier one, which is not the case in natural selection. -The new species arising from natural selection maintain themselves much -more permanently, and return much less easily to the original form, than -is the case with products of artificial selection, and accordingly -maintain themselves during a much longer time than the artificial races -produced by man. But these are only subordinate differences, which are -explained by the different conditions of natural and artificial -selection, and in reality are connected only with differences in the -duration of time. The nature of the transformation and the means by -which it is produced are entirely the same in both artificial and -natural selection. (Gen. Morph. ii. 248.) - -The thoughtless and narrow-minded opponents of Darwin are never tired of -asserting that his theory of selection is a groundless conjecture, or at -least an hypothesis which has yet to be proved. That this assertion is -completely unfounded, may be perceived even from the outlines of the -doctrine of selection which have just been discussed. Darwin assumes no -kind of unknown forces of nature, nor hypothetical conditions, as the -acting causes for the transformation of organic forms, but solely and -simply the universally recognized vital activities of all organisms, -which we term _Inheritance_ and _Adaptation_. Every naturalist -acquainted with physiology knows that these two phenomena are directly -connected with the functions of propagation and nutrition, and, like all -other phenomena of life, are purely mechanical processes of nature, that -is, they depend upon the molecular phenomena of motion in organic -matter. That the interaction of these two functions effect a continual, -slow transmutation of organic forms, is a necessary result of the -struggle for existence. But this, again, is no more a hypothetical -relation, nor one requiring a proof, than is the interaction of -Inheritance and Adaptation. The struggle for life is a mathematical -necessity, arising from the disproportion between the limited number of -places in nature's household, and the excessive number of organic germs. -The origin of new species is moreover greatly favoured by the active or -passive _migrations_ of animals and plants, which takes place everywhere -and at all times, without being, however, entitled to rank as -_necessary_ agents in the process of natural selection. - -The origin of new species by natural selection, or, what is the same -thing, by the interaction of Inheritance and Adaptation in the struggle -for life, is therefore a _mathematical necessity_ of nature which needs -no further proof. Whoever, in spite of the present state of our -knowledge, still seeks for _proofs_ for the Theory of Selection, only -shows that he either does not thoroughly understand the theory, or is -not sufficiently acquainted with the biological facts--has not the -requisite amount of experimental knowledge in Anthropology, Zoology, and -Botany. - -If, as we maintain, natural selection is the great active cause which -has produced the whole wonderful variety of organic life on the earth, -all the interesting phenomena of _human life_ must also be explicable -from the same cause. For man is after all only a most highly-developed -vertebrate animal, and all aspects of human life have their parallels, -or, more correctly, their lower stages of development in the animal -kingdom. The whole history of nations, or what is called "Universal -History," must therefore be explicable by means of "natural -selection,"--must be a physico-chemical process, depending upon the -interaction of Adaptation and Inheritance in the struggle for life. And -this is actually the case. We shall give further proofs of this later -on. - -It appears of interest here to remark that not only _natural_ selection, -but also _artificial_ selection exercises its influence in many ways in -universal history. A remarkable instance of _artificial selection in -man_, on a great scale, is furnished by the ancient Spartans, among -whom, in obedience to a special law, all newly-born children were -subject to a careful examination and selection. All those that were -weak, sickly, or affected with any bodily infirmity, were killed. Only -the perfectly healthy and strong children were allowed to live, and they -alone afterwards propagated the race. By this means, the Spartan race -was not only continually preserved in excellent strength and vigour, but -the perfection of their bodies increased with every generation. No doubt -the Spartans owed their rare degree of masculine strength and rough -heroic valour (for which they are eminent in ancient history) in a -great measure to this artificial selection. - -Many tribes also among the Red Indians of North America (who at present -are succumbing in the struggle for life to the superior numbers of the -white intruders, in spite of a most heroic and courageous resistance) -owe their rare degree of bodily strength and warlike bravery to a -similar careful selection of the newly-born children. Among them, also, -all children that are weak or affected with any infirmity are -immediately killed, and only the perfectly strong individuals remain in -life, and propagate the race. That the race becomes greatly -strengthened, in the course of very many generations, by this artificial -selection cannot in itself be doubted, and is sufficiently proved by -many well known facts. - -The opposite of this artificial selection of the wild Redskins and the -ancient Spartans is seen in the individual selection which is -universally practised in our modern military states, for the purpose of -maintaining standing armies, and which, under the name of _military -selection_, we may conveniently consider as a special form of selection. -Unfortunately, in our day, militarism is more than ever prominent in our -so-called "civilization"; all the strength and all the wealth of -flourishing civilized states are squandered on its development; whereas -the education of the young, and public instruction, which are the -foundations of the true welfare of nations and the ennobling of -humanity, are neglected and mismanaged in a most pitiable manner. And -this is done in states which believe themselves to be the privileged -leaders of the highest human intelligence, and to stand at the head of -civilization. As is well known, in order to increase the standing army -as much as possible, all healthy and strong young men are annually -selected by a strict system of recruiting. The stronger, healthier, and -more spirited a youth is, the greater is his prospect of being killed by -needle-guns, cannons, and other similar instruments of civilization. All -youths that are unhealthy, weak, or affected with infirmities, on the -other hand, are spared by the "military selection," and remain at home -during the war, marry, and propagate themselves. The more useless, the -weaker, or infirmer the youth is, the greater is his prospect of -escaping the recruiting officer, and of founding a family. While the -healthy flower of youth dies on the battle-field, the feeble remainder -enjoy the satisfaction of reproduction and of transmitting all their -weaknesses and infirmities to their descendants. According to the laws -of transmission by inheritance, there must necessarily follow in each -succeeding generation, not only a further extension, but also a more -deeply-seated development of weakness of body, and what is inseparable -from it, a condition of mental weakness also. This and other forms of -artificial selection practised in our civilized states sufficiently -explain the sad fact that, in reality, weakness of the body and weakness -of character are on the perpetual increase among civilized nations, and -that, together with strong, healthy bodies, free and independent spirits -are becoming more and more scarce. - -To the increasing enervation of modern civilized nations, which is the -necessary consequence of military selection, there is further added -another evil. The progress of modern medical science, although still -little able really to cure diseases, yet possesses and practises more -than it used to do the art of prolonging life during lingering, chronic -diseases for many years. Such ravaging evils as consumption, scrofula, -syphilis, and also many forms of mental disorders, are transmitted by -inheritance to a great extent, and transferred by sickly parents to some -of their children, or even to the whole of their descendants. Now, the -longer the diseased parents, with medical assistance, can drag on their -sickly existence, the more numerous are the descendants who will inherit -incurable evils, and the greater will be the number of individuals, -again, in the succeeding generation, thanks to that artificial "_medical -selection_," who will be infected by their parents with lingering, -hereditary disease. - -If any one were to venture the proposal, after the examples of the -Spartans and Redskins, to kill, immediately upon their birth, all -miserable, crippled children to whom with certainty a sickly life could -be prophesied, instead of keeping them in life injurious to them and to -the race, our so-called "humane civilization" would utter a cry of -indignation. But the same "humane civilization" thinks it quite as it -should be, and accepts without a murmur, that at the outbreak of every -war (and in the present state of civilized life, and in the continual -development of standing armies, wars must naturally become more -frequent) hundreds and thousands of the finest men, full of youthful -vigour, are sacrificed in the hazardous game of battles. The same -"humane civilization" at present praises the abolition of capital -punishment as a "liberal measure!" And yet capital punishment for -incorrigible and degraded criminals is not only just, but also a benefit -to the better portion of mankind; the same benefit is done by destroying -luxuriant weeds, for the prosperity of a well cultivated garden. As by -a careful rooting out of weeds, light, air, and ground is gained for -good and useful plants, in like manner, by the indiscriminate -destruction of all incorrigible criminals, not only would the struggle -for life among the better portion of mankind be made easier, but also an -advantageous artificial process of selection would be set in practice, -since the possibility of transmitting their injurious qualities by -inheritance would be taken from those degenerate outcasts. - -Against the injurious influence of artificial military and medical -selection, we fortunately have a salutary counterpoise, in the -invincible and much more powerful influence of _natural selection_, -which prevails everywhere. For in the life of man, as well as in that of -animals and plants, this influence is the most important transforming -principle, and the strongest lever for progress and amelioration. The -result of the struggle for life is that, in the long run, that which is -better, because more perfect, conquers that which is weaker and -imperfect. In human life, however, this struggle for life will ever -become more and more of an intellectual struggle, not a struggle with -weapons of murder. The organ which, above all others, in man becomes -more perfect by the ennobling influence of natural selection, is the -_brain_. The man with the most perfect understanding, not the man with -the best revolver, will in the long run be victorious; he will transmit -to his descendants the qualities of the brain which assisted him in the -victory. Thus then we may justly hope, in spite of all the efforts of -retrograde forces, that the progress of mankind towards freedom, and -thus to the utmost perfection, will, by the happy influence of natural -selection, become more and more certain. - - - - -CHAPTER VIII. - -TRANSMISSION BY INHERITANCE AND PROPAGATION. - - - Universality of Inheritance and Transmission by - Inheritance.--Special Evidences of the same.--Human - Beings with four, six, or seven Fingers and - Toes.--Porcupine Men.--Transmission of Diseases, - especially Diseases of the Mind.--Original - Sin.--Hereditary Monarchies.--Hereditary - Aristocracy.--Hereditary Talents and Mental - Qualities.--Material Causes of Transmission by - Inheritance.--Connection between Transmission by - Inheritance and Propagation.--Spontaneous Generation and - Propagation.--Non-sexual or Monogonous - Propagation.--Propagation by Self-Division.--Monera and - Amoebae.--Propagation by the formation of Buds, by the - formation of Germ-Buds, by the formation of - Germ-Cells.--Sexual or Amphigonous - Propagation.--Formation of Hermaphrodites.--Distinction - of Sexes, or Gonochorism.--Virginal Breeding, or - Parthenogenesis.--Material Transmission of Peculiarities - of both Parents to the Child by Sexual - Propagation.--Difference between Transmission by - Inheritance in Sexual and in Asexual Propagation. - - -The reader has, in the last chapter, become acquainted with natural -selection according to Darwin's theory, as the constructive force of -nature which produces the different forms of animal and vegetable -species. By natural selection we understand the interaction which takes -place in the struggle for life between the _transmission by inheritance_ -and the _mutability_ of organisms, between two physiological functions -which are innate in all animals and plants, and which may be traced to -other processes of life--the functions of propagation and nutrition. All -the different forms of organisms, which people are usually inclined to -look upon as the products of a creative power, acting for a definite -purpose, we, according to the Theory of Selection, can conceive as the -necessary productions of natural selection, working without a -purpose,--as the unconscious interaction between the two properties of -Mutability and Hereditivity. Considering the importance which -accordingly belongs to these vital properties of organisms, we must -examine them a little more closely, and employ a chapter with the -consideration of Transmission by Inheritance. (Gen. Morph. ii. 170-191.) - -Strictly speaking, we must distinguish between Hereditivity -(Transmissivity) and Inheritance (Transmission). Hereditivity is the -power of transmission, the capability of organisms to transfer their -peculiarities to their descendants by propagation. Transmission by -Inheritance, or Inheritance simply, on the other hand, denotes the -exercise of the capability, the actual transmission. - -Hereditivity and Transmission by Inheritance are such universal, -everyday phenomena, that most people do not heed them, and but few are -inclined to reflect upon the operation and import of these phenomena of -life. It is generally thought quite natural and self-evident that every -organism should produce its like, and that children should more or less -resemble their parents. Heredity is usually only taken notice of and -discussed in cases relating to some special peculiarity, which appears -for the first time in a human individual without having been inherited, -and then is transmitted to his descendants. It shows itself in a -specially striking manner in the case of certain diseases, and in -unusual and irregular (monstrous) deviations from the usual formation of -the body. - -Among these cases of the inheritance of monstrous deviations, those are -specially interesting which consist in an abnormal increase or decrease -of the number five in the fingers or toes of man. It is not unfrequently -observed in families through several generations, that individuals have -six fingers on each hand, or six toes on each foot. Less frequent is the -number of four or seven fingers or toes. The unusual formation arises at -first from a single individual who, from unknown causes, is born with an -excess of the usual number of fingers and toes, and transmits these, by -inheritance, to a portion of his descendants. In one and the same family -it has happened that, throughout three, four, or more generations, -individuals have possessed six fingers and toes. In a Spanish family -there were no less than forty individuals distinguished by this excess. -The transmission of the sixth finger or toe is not permanent or enduring -in all cases, because six-fingered people always intermarry again with -those possessing five fingers. If a six-fingered family were to -propagate by pure in-breeding, if six-fingered men were always to marry -six-fingered women, this characteristic would become permanent, and a -special six-fingered human race would arise. But as six-fingered men -usually marry five-fingered women, and _vice versa_, their descendants -for the most part show a very mixed numerical relation, and finally, -after the course of some generations, revert again to the normal number -of five. Thus, for example, among eight children of a six-fingered -father and a five-fingered mother, two children may have on both hands -and feet six fingers and toes, four children may have a mixed number, -and two children may have the usual number of five on both hands and -feet. In a Spanish family, each child except the youngest had the number -six on both hands and feet; the youngest, only, had the usual number on -both hands and feet, and the six-fingered father of the child refused to -recognize the last one as his own. - -The power of inheritance, moreover, shows itself very strikingly in the -formation and colour of the human skin and hair. It is well known how -exactly the nature of the complexion in many families--for instance, a -peculiar soft or rough skin, a peculiar luxuriance of the hair, a -peculiar colour and largeness of the eyes--is transmitted through many -generations. In like manner, peculiar local growths or spots on the -skin, the so-called moles, freckles, and other accumulations of pigment -which appear in certain places, are frequently transmitted through -several generations so exactly, that in the descendants they appear on -the same spots on which they existed in the parents. The porcupine men -of the Lambert family, who lived in London last century, are especially -celebrated. Edward Lambert, born in 1717, was remarkable for a most -unusual and monstrous formation of the skin. His whole body was covered -with a horny substance, about an inch thick, which rose in the form of -numerous thorn-shaped and scale-like processes, more than an inch long. -This monstrous formation of the outer skin, or epidermis, was -transmitted by Lambert to his sons and grandsons, but not to his -granddaughters. The transmission in this instance remained in the male -line, as is often the case. In like manner, an excessive development of -fat in certain parts of the body is often transmitted only in the -female line. I scarcely need call to mind how exactly the characteristic -formation of the face is transmitted by inheritance; sometimes it -remains within the male, sometimes within the female line; sometimes it -is blended in both. - -The phenomena of transmission by inheritance of pathological conditions, -especially of the different forms of human diseases, are very -instructive and generally known. Diseases of the respiratory organs, the -glands, and of the nervous system, are specially liable to be -transmitted by inheritance. Very frequently there suddenly appears in an -otherwise healthy family a disease until then unknown among them; it is -produced by external causes, by conditions of life causing disease. This -disease, brought about in an individual by external cause, is propagated -and transmitted to his descendants, and some or all of them then suffer -from the same disease. In case of diseases of the lungs, for instance in -consumption, this sad transmission by inheritance is well known, and it -is the same with diseases of the liver, with syphilis, and diseases of -the mind. The latter are specially interesting. Just as peculiar -characteristic features of man--pride, ambition, frivolity, etc.--are -transmitted to the descendants strictly by inheritance, so too are the -peculiar abnormal manifestations of mental activity, which are usually -called fixed ideas, despondency, imbecility, and generally "diseases of -the mind." This distinctly and irrefragably shows that the soul of man, -just as the soul of animals, is a purely mechanical activity, the sum of -the molecular phenomena of motion in the particles of the brain, and -that it is transmitted by inheritance, together with its substratum, -just as every other quality of the body is materially transmitted by -propagation. - -When this exceedingly important and undeniable fact is mentioned, it -generally causes great offence, and yet in reality it is silently and -universally acknowledged. For upon what else do the ideas of "hereditary -sin," "hereditary wisdom," and "hereditary aristocracy," etc., rest than -upon the conviction that the _quality of the human mind_ is transmitted -by propagation--that is, by a purely _material_ process--through the -body, from the parents to the descendants? The recognition of this great -importance of transmission by inheritance is shown in a number of human -institutions, as for example, among many nations in the division into -castes, such as the castes of warriors, castes of priests, and castes of -labourers, etc. It is evident that the institution of such castes -originally arose from the notion of the great importance of hereditary -distinctions possessed by certain families, which it was presumed would -always be transmitted by the parents to the children. The institution of -an hereditary aristocracy and an hereditary monarchy is to be traced to -the notion of such a transmission of special excellencies. However, it -is unfortunately not only virtues, but also vices that are transmitted -and accumulated by inheritance; and if, in the history of the world, we -compare the different individuals of the different dynasties, we shall -everywhere find a great number of proofs of the transmission of -qualities by inheritance, but fewer of transmissions of virtues than of -vices. Look only, for example, at the Roman emperors, at the Julii and -the Claudii, or at the Bourbons in France, Spain, and Italy! - -In fact, scarcely anywhere could we find such a number of striking -examples of the remarkable transmission of bodily and mental features by -inheritance, as in the history of the reigning houses in hereditary -monarchies. This is specially true in regard to the diseases of the mind -previously mentioned. It is in reigning families that mental disorders -are hereditary in an unusual degree. Thus Esquirol, distinguished for -his knowledge of mental diseases, proved that the number of insane -individuals in the reigning houses was, in proportion to the number -among the ordinary population, as 60 to 1; that is, that disorders of -the brain occur 60 times more frequently in the privileged families of -the ruling houses than among ordinary people. If equally accurate -statistics were made of the hereditary nobility, the result would -probably be that here also we should find an incomparably larger -contingent of mental diseases than among the common, ignoble portion of -mankind. This phenomenon can scarcely astonish us if we consider what -injury these privileged castes inflict upon themselves by their -unnatural, one-sided education, and by their artificial separation from -the rest of mankind. By this means many dark sides of human nature are -specially developed and, as it were, artificially bred, and, according -to the laws of transmission by inheritance, are propagated through -series of generations with ever-increasing force and dominance. - -It is sufficiently obvious from the history of nations how in successive -generations of many dynasties, for example, of the princes of Saxon -Thuringia and of the Medici, the noble solicitude for the most perfect -human accomplishments in science and art were retained and transmitted -from father to son; and how, on the other hand, in many other dynasties, -for centuries a special partiality for the profession of war, for the -oppression of human freedom, and for other rude acts of violence, have -been hereditary. In like manner talents for special mental activities -are transmitted in many families for generations, as, for instance, -talent for mathematics, poetry, music, sculpture, the investigation of -nature, philosophy, etc. In the family of Bach there have been no less -than twenty-two eminent musicians. Of course the transmission of such -peculiarities of mind depends upon the material process of reproduction, -as does the transmission of mental qualities in general. In this case -again, the vital phenomenon, the manifestation of force (as everywhere -in nature), is directly connected with definite relations in the -admixture of the material components of the organism. It is this -definite proportion and molecular motion of matter which is transmitted -by generation. - -Now, before we examine the numerous, and in some cases most interesting -and important, laws of transmission by inheritance, let us make -ourselves acquainted with the actual nature of the process. The -phenomena of transmission by inheritance are generally looked upon as -something quite mysterious, as peculiar processes which cannot be -fathomed by natural science, and the causes and actual nature of which -cannot be understood. It is precisely in such a case that people very -generally assume supernatural influences. But even in the present state -of our physiology it can be proved with complete certainty that all the -phenomena of inheritance are entirely natural processes, that they are -produced by mechanical causes, and that they depend on the material -phenomena of motion in the bodies of organisms, which we may consider as -a part of the phenomena of propagation. All the phenomena of Heredity -and the laws of Transmission by Inheritance can be traced to the -material process of _Propagation_. - -Every organism, every living individual, owes its existence _either_ to -an act of unparental or _Spontaneous Generation_ (Generatio Spontanea, -Archigonia), or to an act of Parental Generation or _Propagation_ -(Generatio Parentalis, Tocogonia). In a future chapter we shall have to -consider Spontaneous Generation, or Archigony. At present we must occupy -ourselves with Propagation, or Tocogony, a closer examination of which -is of the utmost importance for understanding transmission by -inheritance. Most of my readers probably only know those phenomena of -Propagation which are seen universally in the higher plants and animals, -the processes of Sexual Propagation, or Amphigony. The processes of -Non-sexual Propagation, or Monogony, are much less generally known. The -latter, however, are far more suited to throw light upon the nature of -transmission by inheritance in connection with propagation. - -For this reason, we shall first consider only the phenomena of -_non-sexual_ or _monogonic propagation_ (Monogonia). This appears in a -variety of different forms, as for example, self-division, formation of -buds, the formation of germ-cells or spores (Gen. Morph. ii. 36-58). It -will be most instructive, first, to examine the propagation of the -simplest organisms known to us, which we shall have to return to later, -when considering the question of spontaneous generation. These very -simplest of all organisms yet known, and which, at the same time, are -the simplest imaginable organisms, are the _Monera_ living in water; -they are very small living corpuscles, which, strictly speaking, do not -at all deserve the name of organism. For the designation "organism," -applied to living creatures, rests upon the idea that every living -natural body is composed of organs, of various parts, which fit into -one another and work together (as do the different parts of an -artificial machine), in order to produce the action of the whole. During -late years we have become acquainted with _Monera_, organisms which are, -in fact, not composed of any organs at all, but consist entirely of -shapeless, simple, homogeneous matter. The entire body of one of these -Monera, during life, is nothing more than a shapeless, mobile, little -lump of mucus or slime, consisting of an albuminous combination of -carbon. Simpler or more imperfect organisms we cannot possibly conceive. - -The first complete observations on the natural history of a Moneron -(Protogenes primordialis) were made by me at Nice, in 1864. Other very -remarkable Monera I examined later (1866) in Lanzarote, one of the -Canary Islands, and in 1867 in the Straits of Gibraltar. The complete -history of one of these Monera, the orange-red _Protomyxa aurantiaca_, -is represented in Plate I, and its explanation is given in the Appendix. -I have found some curious Monera also in the North Sea, off the -Norwegian coast, near Bergen. Cienkowski has described (1865) an -interesting Moneron from fresh waters, under the name of _Vampyrella_. -But perhaps the most remarkable of all Monera was discovered by Huxley, -the celebrated English zoologist, and called _Bathybius Haeckelii_. -"Bathybius" means, living in the deep. This wonderful organism lives in -immense depths of the ocean, which are over 12,000--indeed, in some -parts 24,000 feet below the surface, and which have become known to us -within the last ten years, through the laborious investigations made by -the English. There, among the numerous Polythalamia and Radiolaria -which inhabit the fine calcareous mud of these abysses, the Bathybius is -found in great quantities, sometimes in the shape of roundish, formless -lumps of mucus, sometimes in the form of a network of mucus, covering -fragments of stone and other objects. Small particles of chalk are -frequently embedded in these mucous gelatinous masses, and are, perhaps, -products of their secretion. The entire body of this remarkable -Bathybius consists solely of shapeless plasma, or protoplasm, as in the -case of the other Monera--that is, it consists of the same albuminous -combination of carbon, which in infinite modifications is found in all -organisms, as the essential and never-failing seat of the phenomena of -life. I have given a detailed description and drawing of the Bathybius -and other Monera in my "Monographie der Moneren," 1870,(15) from which -the drawing in Fig. 9 is taken. - -[Illustration: Life history of a simplest organism. Pl. I. - -E. Haeckel del. _Prototmyxa aurantiaca._ Lagesse sc.] - -In a state of rest most Monera appear as small globules of mucus or -slime, invisible, or nearly so, to the naked eye; they are at most as -large as a pin's head. When the Moneron moves itself, there are formed -on the upper surface of the little mucous globule, shapeless, fingerlike -processes, or very fine radiated threads; these are the so-called false -feet, or pseudopodia. The false feet are simple, direct continuations of -the shapeless albuminous mass, of which the whole body consists. We are -unable to perceive different parts in it, and we can give a direct proof -of the absolute simplicity of the semi-fluid mass of albumen, for with -the aid of the microscope we can follow the Moneron as it takes in -nourishment. When small particles suited for its nourishment--for -instance, small particles of decayed organic bodies or microscopic -plants and infusoria--accidentally come into contact with the Moneron, -they remain hanging to the sticky semi-fluid globule of mucus, and here -create an irritation, which is followed by a strong afflux of the mucous -substance, and, in consequence, they become finally completely inclosed -by it, or are drawn into the body of the Moneron by displacement of the -several albuminous particles, and are there digested, being absorbed by -simple diffusion (endosmosis). - -[Illustration: FIG. 1.--Propagation of the simplest organism, a Moneron, -by self-division. _A._ The entire Moneron, a Protamoeba. _B._ It falls -into two halves by a contraction in the middle. _C._ Each of the two -halves has separated from the other, and now represents an independent -individual.] - -Just as simple as the process of nutrition is the _propagation_ of these -primitive creatures, which in reality we can neither call animals nor -plants. All Monera propagate themselves only in an asexual manner by -monogony; and in the simplest case, by that kind of monogony which we -place at the head of the different forms of propagation, that is, by -self-division. When such a little globule, for example a Protamoeba or -a Protogenes, has attained a certain size by the assimilation of foreign -albuminous matter, it falls into two pieces; a pinching in takes place, -contracting the middle of the globule on all sides, and finally leads to -the separation of the two halves (compare Fig. 1). Each half then -becomes rounded off, and now appears as an independent individual, which -commences anew the simple course of the vital phenomena of nutrition and -propagation. In other Monera (Vampyrella), the body in the process of -propagation does not fall into two, but into four equal pieces, and in -others, again (Protomonas, Protomyxa, Myxastrum), at once into a number -of small globules of mucus, each of which again, by simple growth, -becomes like the parent body. Here it is evident that the process of -_propagation is nothing but a growth of the organism beyond its own -individual limit of size_. - -The simple method of propagation of the Moneron by self-division is, in -reality, the most universal and most widely spread of all the different -modes of propagation; for by the same simple process of division, -_cells_ also propagate themselves. Cells are those simple organic -individuals, a large number of which constitute the bodies of most -organisms, the human body not excepted. With the exception of the -organisms of the lowest order, which have not even the perfect form of a -cell (Monera), or during life only represent a single cell (many -Protista and single-celled plants), the body of every organic individual -is composed of a great number of cells. Every organic cell is to a -certain degree an independent organism, a so-called "elementary -organism," or an "individual of the first order." Every higher organism -is, in a measure, a society or a state of such variously shaped -elementary individuals, variously developed by division of labour.(39) -Originally every organic cell is only a single globule of mucus, like a -Moneron, but differing from it in the fact that the homogeneous -albuminous substance has separated itself into two different parts, a -firmer albuminous body, the _cell-kernel_ (nucleus), and an external, -softer albuminous body, the _cell-substance_ or _body_ (protoplasma). -Besides this, many cells later on form a third (frequently absent) -distinct part, inasmuch as they cover themselves with a capsule, by -exuding an outer pellicle or _cell-membrane_ (membrana). All other forms -of cells, besides these, are of subordinate importance, and are of no -further interest to us here. - -Every organism composed of many cells was originally a single cell, and -it becomes many-celled owing to the fact that the original cell -propagates itself by self-division, and that the new individual cells -originating in this manner remain together, and by division of labour -form a community or a state. The forms and vital phenomena of all -many-celled organisms are merely the effect or the expression of all the -forms and vital phenomena of all the individual cells of which they are -composed. The egg, from which most animals and plants are developed, is -a simple cell. - -[Illustration: FIG. 2.--Propagation of a single-celled organism, -Amoeba sphaerococcus, by self-division. _A._ The enclosed Amoeba, a -simple globular cell consisting of a lump of protoplasm (_c_), which -contains a kernel (_b_) and a kernel speck (_a_), and is surrounded by a -cell-membrane or capsule. _B._ The free Amoeba, which has burst and -left the cyst or cell-membrane. _C._ It begins to divide by its kernel -forming two kernels, and by the cell-substance between the two becoming -contracted. _D._ The division is completed by the cell-substance -likewise falling into two halves (_Da_ and _Db_).] - -The single-celled organisms, that is, those which during life retain the -form of a single cell, for example the Amoebae, as a rule propagate -themselves in the simplest way by self-division. This process differs -from the previously described self-division of the Moneron only in the -fact that at the commencement the firmer cell-kernel (nucleus) falls -into two halves, by a pinching in at its middle. The two young kernels -separate from each other and act now as two distinct centres of -attraction upon the surrounding softer albuminous matter, that is, the -cell-substance (protoplasma). By this process finally the latter also -divides into two halves, and there now exist two new cells, which are -like the mother cell. If the cell was surrounded by a membrane, this -either does not divide at all, as in the case of egg-cleavage (Fig. 3, -4), or it passively follows the active pinching in of the protoplasm; -or, lastly, every new cell exudes a new membrane for itself. - -[Illustration: FIG. 3.--Egg of a mammal (a simple cell). _a._ The small -kernel speck or nucleolus (the so-called germ-spot of the egg). _b._ -Kernel or nucleus (the so-called germ-bladder of the egg). _c._ -Cell-substance or protoplasm (the so-called yolk of the egg). _d._ -Cell-capsule or membrane (membrane of the yolk) of the egg; called in -mammals, on account of its transparency, Membrana pellucida.] - -The non-independent cells which remain united in communities or states, -and thus constitute the body of higher organisms, are propagated in the -same manner as are independent single-celled organisms, for example, -Amoeba (Fig. 2). Just as in that case, the cell with which most -animals and plants commence their individual existence, namely, the egg, -multiplies itself by simple division. When an animal, for instance a -mammal (Fig. 3, 4), develops out of an egg, this process of development -always begins by the simple egg-cell (Fig. 3) forming an accumulation of -cells (Fig. 4) by continued self-division. The outer covering, or cell -membrane, of the globular egg remains undivided. First, the cell-kernel -of the egg (the so-called germinal vesicle) divides itself into two -kernels, then follows the cell-substance (the yolk of the egg) (Fig. 4 -_A_). In like manner, the two cells, by continued self-division, -separate into four (Fig. 4 _B_), these into eight (Fig. 4 _C_), into -sixteen, thirty-two, etc., and finally there is produced a globular mass -of very numerous little cells (Fig. 4 _D_). These now, by further -increase and heterogeneous development (division of labour), gradually -build up the compound many-celled organism. Every one of us, at the -commencement of our individual development, has undergone the very same -process as that represented in Fig. 4. The egg of a mammal--represented -in Fig. 3, and its development in Fig. 4--might as well be that of a -man, as of an ape, dog, horse, or any other placental mammal. - -[Illustration: FIG. 4.--First commencement of the development of a -mammal's egg, the so-called "cleavage of the egg" (propagation of the -egg-cell by repeated self-division). _A._ The egg, by the formation of -the first furrow, falls into two cells. _B._ These separate by division -into four cells. _C._ The latter have divided into eight cells. _D._ By -repeated division a globular accumulation of numerous cells has -arisen.] - -Now, when one examines this simplest form of propagation, this -self-division, it surely cannot be considered wonderful that the -products of the division of the original organism should possess the -same qualities as the parental individual. For they are parts or halves -of the parental organism, and the matter or substance in both halves is -the same, and as both the young individuals have received an equal -amount and the same quality of matter from the parent individual, one -can but consider it natural that the vital phenomena, the physiological -qualities should be the same in both children. In fact, in regard to -their form and substance, as well as to their vital phenomena, the two -produced cells can in no respect be distinguished from one another, or -from the mother cell. They have _inherited_ from her the same nature. - -But this same simple propagation by self-division is not only confined -to simple cells--it is the same also in the higher many-celled -organisms; for example, in the coral zoophytes. Many of them which -exhibit a high complexity of composition and organization, nevertheless, -propagate themselves by simple division. In this case the whole -organism, with all its organs, falls into two equal halves as soon as by -growth it has attained a certain size. Each half again develops itself, -by growth, into a complete individual. Here, again, it is surely -self-evident that the two products of division will share the qualities -of the parental organism, as they themselves are in fact halves of that -parent. - -Next to propagation by division we come to propagation by the _formation -of buds_. This kind of monogony is exceedingly widely spread. It occurs -both in the case of simple cells (though not frequently) and in the -higher organisms composed of many cells. The formation of buds is -universal in the vegetable kingdom, less frequent in the animal kingdom. -However, here also it occurs in the tribe of Plant-like Animals, -especially among the Coral Zoophytes, and among the greater portion of -the Hydroid Polyps very frequently, further also among some worms -(Planarian Worms, Ring-Worms, Moss Animals, Tunicates). Most branching -animal-trees or colonies, which are exceedingly like branching plants, -arise like those plants, by the formation of buds. - -Propagation by the _formation of buds_ (Gemmatio) is essentially -distinguished from propagation by division, in the fact that the two -organisms thus produced by budding are not of equal age, and therefore -at first are not of equal value, as they are in the case of division. In -division we cannot clearly distinguish either of the two newly produced -individuals as the parental, that is as the producer, because, in fact, -both have an equal share in the composition of the original parental -individual. If, on the other hand, an organism sends out a bud, then the -latter is the child of the former. The two individuals are of unequal -size and of unequal form. If, for instance, a cell propagates itself by -the formation of buds, we do not see the cell fall into two equal -halves, but there appears at one point of it a protuberance, which -becomes larger and larger, more or less separates itself from the -parental cell, and then grows independently. In like manner we observe -in the budding of a plant or animal, that a small local growth arises on -a part of the mature individual, which growth becomes larger and larger, -and likewise more or less separates itself from the parental organism by -an independence in its growth. The bud, after it has attained a certain -size, may either completely separate itself from the parental -individual, or it may remain connected with it and form a stock or -colony, whilst at the same time its life may be quite independent of -that of its parent. While the growth which starts the propagation, in -the case of self-division, is a total one affecting the whole body, it -is in the formation of buds only partial, affecting merely a portion of -the parental organism. But here, also, the bud--the newly-produced -individual which remains so long most directly connected with the -parental organism, and which proceeds from it--retains the essential -qualities and the original tendency of development of its parent. - -A third mode of non-sexual propagation, that of the _formation of -germ-buds_ (Polysporogonia), is intimately connected with the formation -of buds. In the case of the lower, imperfect organisms, among animals, -especially in the case of the Plant-like animals and Worms, we very -frequently find that in the interior of an individual composed of many -cells, a small group of cells separates itself from those surrounding -it, and that this small isolated group gradually develops itself into -an individual, which, becomes like the parent, and sooner or later comes -out of it. Thus, for example, in the body of the Fluke-worms -(Trematodes) there often arise numerous little bodies consisting of many -cells, that is _germ-buds_, or _polyspores_, which, at an early stage -separate themselves completely from the parent body, and leave it when -they have attained a certain stage of development. - -The formation of germ-buds is evidently but little different from real -budding. But, on the other hand, it is connected with a fourth kind of -non-sexual propagation, which almost forms a transition to sexual -reproduction, namely, the _formation of germ-cells_ (Monosporogonia), -which is often briefly called formation of spores (sporogonia). In this -case it is no longer a group of cells, but a single cell, which -separates itself from the surrounding cells in the interior of the -producing organism, and which only becomes further developed after it -has come out of its parent. After this _germ-cell_, or monospore (or, -briefly, spore), has left the parental individual, it multiplies by -division, and thus forms a many-celled organism, which by growth and -gradual development attains the hereditary qualities of the parental -organism. This occurs very generally among lower plants (Cryptogama). - -Although the formation of germ-cells very much resembles the formation -of germ buds, it evidently and very essentially differs from the latter, -and also from the other forms of non-sexual propagation which have -previously been mentioned, by the fact that only a very small portion of -the producing organism takes part in the propagation and, accordingly, -in the transmission by inheritance. In the case of self-division, where -the whole organism falls into two halves, in the formation of buds, -where a considerable portion of the whole body, already more or less -developed, separates from the producing individual, we easily understand -that the forms and vital phenomena should be the same in the producing -and produced organism. It is much more difficult to understand in the -formation of germ-buds, and more difficult still in the formation of -germ-cells, how this very small, quite undeveloped portion of the body, -this group of cells, or this single cell, not only directly takes with -it certain parental qualities into its independent existence, but also -after its separation from the parental individual develops into a -many-celled body, and in this repeats the forms and vital phenomena of -the original producing organism. This last form of monogonic -propagation--that of the germ cells, or spore-formation--leads us -directly to a form of propagation which is the most difficult of all to -explain, namely, sexual propagation. - -_Sexual or amphigonic propagation_ (Amphigonia) is the usual method of -propagation among all higher animals and plants. It is evident that it -has only developed, at a very late period of the earth's history, from -non-sexual propagation, and apparently in the first instance from the -method of propagation by germ-cells. In the earliest periods of the -organic history of the earth, all organisms propagated themselves in a -non-sexual manner, as numerous lower organisms still do, especially all -those which are at the lowest stage of organization, and which, strictly -speaking, can be considered neither as animals nor as plants, and which -therefore, as primary creatures, or Protista, are best excluded from -both the animal and vegetable kingdoms. In the case of the higher -animals and plants, the increase of individuals, as a rule, is at -present brought about in the majority of cases by sexual propagation. - -In all the chief forms of non-sexual propagation mentioned above--in -fission, in the formation of buds, germ buds, and germ cells--the -separated cell or group of cells was able by itself to develop into a -new individual, but in the case of sexual propagation the cell must -first be fructified by another generative substance. The fructifying -male sperm must first mix with the female germ-cell (the egg) before the -latter can develop into a new individual. These two different -generative substances, the male sperm and the female egg, are either -produced by one and the same individual hermaphrodite -(Hermaphroditismus), or by two different individuals (sexual separation, -Gonochorismus) (Gen. Morph. ii. 58, 59). - -The simpler and more ancient form of sexual propagation is through -double-sexed individuals (Hermaphroditismus). It occurs in the great -majority of plants, but only in a minority of animals, for example, in -the garden snails, leeches, earth-worms, and many other worms. Every -single individual among hermaphrodites produces within itself materials -of both sexes--eggs and sperm. In most of the higher plants every -blossom contains both the male organ (stamens and anther) and the female -organs (style and germ). Every garden snail produces in one part of its -sexual gland eggs, and in another part sperm. Many hermaphrodites can -fructify themselves; in others, however, copulation and reciprocal -fructification of both hermaphrodites is necessary for causing the -development of the eggs. This latter case is evidently a transition to -sexual separation. - -_Sexual separation_ (Gonochorismus,) which characterizes the more -complicated of the two kinds of sexual reproduction, has evidently been -developed from the condition of hermaphroditism at a late period of the -organic history of the world. It is at present the universal method of -propagation of the higher animals, and occurs, on the other hand, only -in the minority of plants (for example, in many aquatic plants, _e.g._ -Hydrocharis, Vallisneria; and in trees, _e.g._ Willows, Poplars). Every -organic individual, as a non-hermaphrodite (Gonochoristus), produces -within itself only one of two generative substances, either the male or -the female. The female individuals, both in animals and plants, produce -eggs or egg-cells. The eggs of plants in the case of flowering plants -(Phanerogama), are commonly called "embryo sacs"; in the case of -flowerless plants (Cryptogama), "fruit spores." In animals, the male -individual secretes the fructifying sperm (sperma); in plants, the -corpuscles, which correspond to the sperm. In the Phanerogama, these are -the pollen grains, or flower-dust; in the Cryptogama, a sperm, which, -like that of most animals, consists of floating vibratile cells actively -moving in a fluid--the zoosperms, spermatozoa, or sperm-cells. - -The so-called _virginal reproduction_ (Parthenogenesis) offers an -interesting form of transition from sexual reproduction to the -non-sexual formation of germ-cells (which most resembles it); it has -been demonstrated to occur in many cases among Insects, especially by -Siebold's excellent investigations. In this case germ-cells, which -otherwise appear and are formed exactly like egg-cells, become capable -of developing themselves into new individuals without requiring the -fructifying seed. The most remarkable and most instructive of the -different partheno-genetic phenomena are furnished by those cases in -which the same germ-cells, according as they are fructified or not, -produce different kinds of individuals. Among our common honey bees, a -male individual (a drone) arises out of the eggs of the queen, if the -egg has not been fructified; a female (a queen, or working bee), if the -egg has been fructified. It is evident from this, that in reality there -exists no wide chasm between sexual and non-sexual reproduction, but -that both modes of reproduction are directly connected. The -parthenogenesis of Insects must probably be regarded as a _relapse_ from -the sexual mode of propagation (possessed by the original parents of the -insects) to the earlier condition of non-sexual propagation. (Gen. -Morph. ii. 86.) In any case, however, sexual reproduction, both in -plants and animals, which seems such a wonderful process, has only -arisen at a later date out of the more ancient process of non-sexual -reproduction. In both cases heredity is a necessary part of the -phenomenon. - -In all the different modes of propagation the essential point of the -process is invariably a detachment of a portion of the parental organism -possessing the capability of leading an individual, independent -existence. We may, therefore, in all cases expect, _a priori_, that the -produced individuals--which are, in fact, as is commonly said, "the -flesh and blood" of the parents--will receive the vital characteristics -and qualities of form which the parental individuals possess. It is -simply a larger or smaller quantity of the parental material, in fact of -its albuminous protoplasm, or cell-substance, which passes to the -produced individual. But together with the material, its vital -properties--that is, the molecular motions of the plasma--are -transmitted, which then manifest themselves in its form. Inheritance by -sexual breeding loses very much of the mysterious and wonderful -character which it at first sight possesses for the uninitiated, if we -consider the above-mentioned series of the different modes of -propagation, and their connection one with another. It at first appears -exceedingly wonderful that in the sexual propagation of man, and of all -higher animals, the small egg, the minute cell, often invisible to the -naked eye, is able to transfer to the produced organism all the -qualities of the maternal organism, and, no less mysterious, that at -the same time the essential qualities of the paternal organism are -transferred to the offspring by means of the male sperm, which -fructifies the egg-cell by means of a viscid substance in which minute -thread-like cells or zoosperms move about. But as soon as we compare the -connected stages of the different kinds of propagation, in which the -produced organism separates itself more and more as a distinct growth -from the parental individual, and more or less early enters upon its -independent career; as soon as we consider, at the same time, that the -growth and development of every higher organism only depends upon the -increase of the cells composing it--that is, upon their simple -propagation by division--it becomes quite evident that all these -remarkable processes belong to one series. - -The life of every organic individual is nothing but a connected chain of -very complicated material phenomena of motion. These motions must be -considered as changes in the position and combination of the molecules, -that is, of the smallest particles of animated matter (of atoms placed -together in the most varied manner). The specific, definite tendency of -these orderly, continuous, and inherent motions of life depends, in -every organism, upon the chemical mingling of the albuminous generative -matter to which it owes its origin. In man, as in the case of the higher -animals which propagate themselves in a sexual manner, the individual -vital motion commences at the moment in which the egg-cell is fructified -by the spermatic filaments of the seed, in which process both generative -substances actually mix; and here the tendency of the vital motion is -determined by the specific, or more accurately, by the individual -nature of the sperm as well as of the egg. There can be no doubt as to -the purely mechanical material nature of this process. But here we stand -full of wonder and astonishment before the infinite and inconceivable -delicacy of this albuminous matter. We are amazed at the undeniable fact -that the simple egg-cell of the maternal organism, and a single paternal -sperm-thread, transfer the molecular individual vital motion of these -two individuals to the child so accurately, that afterwards the minutest -bodily and mental peculiarities of both parents reappear in it. - -Here we stand before a mechanical phenomenon of nature of which Virchow, -whose genius founded the "cellular pathology," says with full justice: -"If the naturalist cared to follow the custom of historians and -preachers, and to clothe phenomena, which are in their way unique, with -the hollow pomp of ponderous and sounding words, this would be the -opportunity for him; for we have now approached one of those great -mysteries of animal nature, which encircle the region of animal life as -opposed to all the rest of the world of phenomena. The question of the -formation of cells, the question of the excitation of a continuous and -equable motion, and, finally, the questions of the independence of the -nervous system and of the soul--these are the great problems on which -the human mind can measure its strength." To comprehend the relation of -the male and female to the egg-cell is almost as much as to solve all -those mysteries. The origin and development of the egg-cell in the -mother's body, the transmission of the bodily and mental peculiarities -of the father to it by his seed, touch upon all the questions which the -human mind has ever raised about man's existence. And, we add, these -most important questions are solved, by means of the Theory of Descent, -in a purely mechanical and purely monistic sense! - -There can then be no further doubt that, in the sexual propagation of -man and all higher organisms, inheritance, which is a purely mechanical -process, is directly dependent upon the material continuity of the -producing and produced organism, just as is the case in the simplest -non-sexual propagation of the lower organisms. However, I must at once -take this opportunity of drawing attention to an important difference -which inheritance presents in sexual and non-sexual propagation. It is a -fact long since acknowledged, that the individual peculiarities of the -producing organism are much more accurately transmitted to the produced -organism by non-sexual than by sexual propagation. Gardeners have for a -long time made use of this fact in many ways. When, for instance, a -single individual of a species of tree with stiff, upright branches -accidentally produces down-hanging branches, a gardener, as a rule, -cannot transmit this peculiarity by sexual, but only by non-sexual -propagation. The twigs cut off such a weeping tree and planted as -cuttings or slips, afterwards produce trees having likewise hanging -branches, as, for example, the weeping willows and beeches. Seedlings, -on the other hand, which have been reared out of the seed of such a -weeping tree, generally have the original stiff and upright form of -branches possessed by their ancestors. The same may be observed in a -very striking manner in the so-called "copper-coloured trees," that is, -varieties of trees which are characterized by a red or reddish brown -colour of the leaves. Off-shoots from such copper-coloured trees (for -example, the copper beech), which have been propagated by cuttings in a -non-sexual manner, show the peculiar colour and nature of the leaves -which distinguished the parental individual, while others reared from -seeds of such a copper-coloured tree return to the green-coloured -condition of leaf. - -This difference in inheritance will seem very natural when we consider -that the material connection between the producing and produced -individuals is much closer and lasts much longer in non-sexual than in -sexual propagation. The special tendency of the molecular motion of life -can therefore fix itself much longer and more thoroughly in the filial -organism, and be more strictly transmitted by non-sexual than by sexual -propagation. All these phenomena, considered in connection, clearly -prove that the transmission of bodily and mental peculiarities is a -purely material and mechanical process. By propagation a greater or -lesser quantity of albuminous particles, and together with them the -individual form of motion inherent in these molecules of protoplasm, are -transmitted from the parental organism to the offspring. As this form of -motion remains continuous, the more delicate peculiarities inherent in -the parental organism must sooner or later reappear in the filial -organism. - - - - -CHAPTER IX. - -LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND NUTRITION. - - - Distinction between Conservative and Progressive - Transmission by Inheritance.--Laws of Conservative - Transmission: Transmission of Inherited - Characters.--Uninterrupted or Continuous - Transmission.--Interrupted or Latent - Transmission.--Alternation of - Generations.--Relapse.--Degeneracy.--Sexual - Transmission.--Secondary Sexual Characters.--Mixed or - Amphigonous Transmission.--Hybrids.--Abridged or - Simplified Transmission.--Laws of Progressive - Inheritance: Transmission of Acquired - Characters.--Adapted or Acquired Transmission.--Fixed or - Established Transmission.--Homochronous Transmission - (Identity in Epoch).--Homotopic Transmission (Identity in - Part).--Adaptation and Mutability.--Connection between - Adaptation and Nutrition.--Distinction between Indirect - and Direct Adaptation. - - -In the last chapter we considered Transmission by Inheritance, one of -the two universal vital activities of organisms, Adaptation and -Inheritance, which by their interaction produce the different species of -organisms, and we have endeavoured to trace this very mysterious vital -activity to a more general physiological function of organisms, namely, -to Propagation. This latter in its turn, like other vital phenomena of -animals and plants, depends on physical and chemical relations. It is -true they appear at times exceedingly complicated, but can nevertheless -in reality be traced to simple mechanical causes--that is, to the -relations of attraction and repulsion in the particles or molecules--in -fact, to the motional phenomena of matter. - -Now, before we turn our attention to the second function, the phenomenon -of Adaptation or Mutability, which counteracts the Transmission by -Inheritance, it seems appropriate first to cast one more glance at the -various manifestations of Heredity, which we may perhaps even now -denominate the "_laws of transmission by inheritance._" Unfortunately, -up to the present time very little has been done for this most important -subject, either in zoology or in botany, and almost all we know of the -different laws of inheritance is confined to the experiences of -gardeners and farmers. It is not therefore to be wondered at, that on -the whole these exceedingly interesting and important phenomena have not -been investigated with desirable scientific accuracy, or reduced to the -form of scientific laws. Accordingly, what I shall relate of the -different laws of transmission are only some preliminary fragments taken -out of the infinitely rich store which lies open to our inquiry. - -We may first divide all the different phenomena of inheritance into two -groups, which we may distinguish as the transmission of _inherited_ -characters, and the transmission of _acquired_ characters; and we may -call the former the _conservative_ transmission, and the latter the -_progressive_ transmission by inheritance. This distinction depends upon -the exceedingly important fact that the individuals of every species of -animals and plants can transmit to their descendants, not only those -qualities which they themselves have inherited from their ancestors, but -also the peculiar, individual qualities which they have acquired during -their own life. The latter are transmitted by progressive, the former -by conservative inheritance. We have now first to examine the phenomena -of _conservative inheritance_, that is, the transmission of such -qualities as the organism has already received from its parents or -ancestors. (Gen. Morph. ii. 180.) - -Among the phenomena of conservative inheritance we are first struck by -that which is its most general law, and which we may term the _law of -uninterrupted or continuous transmission_. It is so universal among the -higher animals and plants, that the uninitiated might overestimate its -action and consider it as the only normal law of transmission by -inheritance. This law simply consists in the fact that among most -species of animals and plants, every generation is, on the whole, like -the preceding--that the parents are as like the grandparents as they are -like the children. "Like produces like," as is commonly said, but more -accurately "similar things produce similar things." For, in reality, the -descendants of every organism are never absolutely equal in all points, -but only similar in a greater or less degree. This law is so generally -known, that I need not give any examples of it. - -The _law of interrupted or latent transmission_ by inheritance, which -might also be termed alternating transmission, is in a measure opposed -to the preceding law. This important law appears principally active -among many lower animals and plants, and manifests itself in contrast to -the former in the fact that the offspring are not like their parents, -but very dissimilar, and that only the third or a later generation -becomes similar to the first. The grandchildren are like the -grandparents, but quite unlike the parents. This is a remarkable -phenomenon, and, as is well known, occurs also very frequently, though -in a less degree, in human families. Every one of my readers doubtless -knows some members of a family who, in this or that peculiarity, much -more resemble the grandfather or grandmother than the father or mother. -Sometimes it lies in bodily peculiarities, for example, features of -face, colour of hair, size of body--sometimes in mental qualities, for -example, temperament, energy, understanding--which are transmitted in -this manner. This fact may be observed in domestic animals as well as in -the case of man. Among the domestic animals most liable to vary--as the -dog, horse, and ox--breeders very frequently find that the product by -breeding resembles the grandparents far more than it does its own -parental organism. If we express this general law and the succession of -generations by the letters of the alphabet, then A = C = E, whilst -B = D = F, and so on. - -This very remarkable fact appears in a more striking way in the lower -animals and plants than in the higher, and especially in the well-known -phenomenon of _alternation of generations_ (metagenesis). Here we very -frequently find--for example, among the Planarian worms, sea-squirts or -Tunicates, Zoophytes, and also among ferns and mosses--that the organic -individual in the first place produces, by propagation, a form -completely different from the parental form, and that only the -descendants of this generation, again, become like the first. This -regular change of generation was discovered by the poet Chamisso, on his -voyage round the world in 1819, among the _Salpae_, cylindrical -tunicates, transparent like glass, which float on the surface of the -sea. Here the larger generation, the individuals of which live isolated -and possess an eye of the form of a horse-shoe, produce in a non-sexual -manner (by the formation of buds) a completely different and smaller -generation. The individuals of this second smaller generation live -united in chains and possess a cone-shaped eye. Every individual of such -a chain produces, in a sexual manner (hermaphrodite) again, a non-sexual -solitary form of the first and larger generation. Among the Salpae, -therefore, it is always the first, third, and fifth generation, and in -like manner the second, fourth, and sixth generations, that are entirely -like one another. However, it is not always only one, but in other cases -a number of generations, which are thus leapt over; so that the first -generation resembles the fourth and seventh, the second resembles the -fifth and eighth, the third resembles the sixth and ninth, and so on. -Three different generations alternate with one another; for example, -among the neat _little sea-buoys_ (Doliolum), small tunicates closely -related to the Salpae. In this case it is A = D = G, further, B = E = H, -and C = F = I. Among the plant-lice (Aphides), each sexual generation is -followed by a succession of from eight to ten or twelve non-sexual -generations, which are like one another, but differ from the sexual -generations. Then, again, a sexual generation reappears like the one -long before vanished. - -If we further follow this remarkable law of latent or interrupted -inheritance, and take into consideration all the phenomena appertaining -to it, we may comprise under it also the well-known phenomena of -_reversion_. By the term "reversion" or "atavism" we understand the -remarkable fact known to all breeders of animals, that occasionally -single and individual animals assume a form which has not existed for -many generations, but belongs to a generation which has long since -disappeared. One of the most remarkable instances of this kind is the -fact that in some horses there sometimes appear singular dark stripes, -similar to those of the zebra, quagga, and other wild species of African -horses. Domestic horses of the most different races and of all colours -sometimes show such dark stripes; for example, a stripe along the back, -a stripe across the shoulders, and the like. The sudden appearance of -these stripes can only be explained by the supposition that it is the -effect of a latent transmission, a relapse into the ancient original -form, which has long since vanished, and was once common to all species -of horses; the original form, undoubtedly, was originally striped like -the zebras, quaggas, etc. In like manner, certain qualities in other -domestic animals sometimes appear quite suddenly, which once marked -their wild ancestors, now long since extinct. In plants, also, such a -relapse can be observed very frequently. All my readers probably know -the wild yellow toad-flax (Linaria vulgaris), a plant very common in our -fields and hedges. Its dragon-mouthed yellow flower contains two long -and two short stamens. But sometimes there appears a single blossom -(Peloria) which is funnel-shaped, and quite regularly composed of five -individual and equal sections, with five corresponding stamens. This -Peloria can only be explained as a relapse into the long since extinct -and very ancient common form of all those plants which, like the -toad-flax, possess dragon-mouthed, two-lipped flowers, with two long and -two short stamens. The original form, like the Peloria, possessed a -regular five-spurred blossom, with five equal stamens, which only later -and by degrees have become unequal (compare p. 17). All such relapses -are to be brought under the law of interrupted or latent transmission, -although the number of intervening generations may be enormous. - -When cultivated plants or domestic animals become wild, when they are -withdrawn from the conditions of cultivated life, they experience -changes which appear not only as adaptations to their new mode of life, -but partially also as relapses into the ancient original form out of -which the cultivated forms have been developed. Thus the different kinds -of cabbage, which are exceedingly different in form, may be led back to -the original form, by allowing them to grow wild. In like manner, dogs, -horses, heifers, etc., when growing wild, often revert more or less to a -long extinct generation. An immensely long succession of generations may -pass away before this power of latent transmission becomes extinguished. - -A third law of conservative transmission may be called the _law of -sexual transmission_, according to which each sex transmits to the -descendants of the same sex peculiarities which are not inherited by the -descendants of the other sex. The so-called secondary sexual characters, -which in many respects are of extraordinary interest, everywhere furnish -numerous examples of this law. Subordinate or secondary sexual -characters are those peculiarities of one of the two sexes which are not -directly connected with the sexual organs themselves; such characters, -which exclusively belong to the male sex, are, for example, the antlers -of the stag, the mane of the lion, and the spur of the cock. The human -beard, an ornament commonly denied to the female sex, belongs to the -same class. Similar characteristics by which the female sex is alone -distinguished are, for example, the developed breasts, with the -lactatory glands of female mammals and the pouch of the female opossum. -The bodily size, also, and complexion, differs in female animals of many -species from that of the male. All these secondary sexual qualities, -like the sexual organs themselves, are transmitted by the male organism -only to the male, not to the female, and _vice versa_. Contrary facts -are rare exceptions to the rule. - -A fourth law of transmission, which has here to be mentioned, in a -certain sense contradicts the last, and limits it, viz., the _law of -mixed or mutual_ (amphigonous) _transmission_. This law tells us that -every organic individual produced in a sexual way receives qualities -from both parents, from the father as well as from the mother. This -fact, that personal qualities of each of the two sexes are transmitted -to both male and female descendants, is very important, Goethe mentions -it of himself, in the beautiful lines-- - - "Von Vater hab ich die Statur, des Lebens ernstes Fuehren - Von Muetterchen die Frohnatur und Lust zu fabuliren." - - "From my father I have my stature and the serious tenour of my life, - From my mother a joyous nature and a turn for poetizing." - -This phenomenon, I suppose, is so well-known to all, that I need not -here enter upon it. It is according to the different portions of their -character which father and mother transmit to their children, that the -individual differences among brothers and sisters are chiefly -determined. - -The very important and interesting phenomenon of _hybridism_ also -belongs to this law of mixed or amphigonous transmission. It alone, -when rightly estimated, is quite sufficient to refute the prevailing -dogma of the constancy of species. Plants, as well as animals, belonging -to quite different species, may sexually mingle with one another and -produce descendants which in many cases can again propagate themselves, -and that indeed either (more frequently) by mingling with one of the two -parental species, or (more rarely) by pure in-breeding, hybrid mixing -with hybrid. The latter is well established, for example, in the hybrids -of hares and rabbits (Lepus Darwinii, p. 147). The hybrids of a horse -and a donkey, two different species of the same genus (Equus), are well -known. These hybrids differ according as the father or the mother -belongs to the one or the other species--the horse or the donkey. The -mule produced by a mare and a he-donkey has qualities quite different -from those of the jinny (Hinnus), the hybrid of a horse and she-donkey. -In both cases the hybrid produced by the crossing of two different -species is a mixed form, which receives qualities from both parents; but -the qualities of the hybrid are different, according to the form of the -crossing. In like manner, mulattoes produced by a European and a negress -show a different mixture of characters from the hybrids produced by a -negro with a European female. In these phenomena of hybrid-breeding, as -well as in the other laws of transmission previously mentioned, we are -as yet unable to show the acting causes in detail; but no naturalist -doubts the fact that the causes are in all cases purely mechanical and -dependent upon the nature of organic matter itself. If we possessed more -delicate means of investigation than our rude organs of sense and -auxilliary instruments, we should be able to discover those causes, and -to trace them to the chemical and physical properties of matter. - -Among the phenomena of conservative transmission, we must now mention, -as the fifth law, the _law of abridged or simplified transmission_. This -law is very important in regard to embryology or ontogeny, that is in -regard to the history of the development of organic individuals. -_Ontogeny_, or the history of the development of individuals, as I have -already mentioned in the first chapter (p. 10), and as I subsequently -shall explain more minutely, is nothing but a short and quick repetition -of _Phylogeny_ dependent on the laws of transmission and -adaptation--that is, a repetition of the palaeontological history of -development of the whole organic tribe, or phylum, to which the organism -belongs. If, for example, we follow the individual development of a man, -an ape, or any other higher mammal within the maternal body from the -egg, we find that the foetus or embryo arising out of the egg passes -through a series of very different forms, which on the whole agrees -with, or at least runs parallel to, a series of forms which is presented -to us by the historical chain of ancestors of the higher mammals. Among -these ancestors we may mention certain fishes, amphibians, marsupials, -etc. But the parallelism or agreement of these two series of development -is never quite complete; on the contrary, in ontogeny there are always -gaps and leaps which indicate the omission of certain stages belonging -to the phylogeny. Fritz Mueller, in his excellent work, "Fuer Darwin,"(16) -has clearly shown in the case of the Crustacea, or crabs, that "the -historical record preserved in the individual history of development is -gradually obscured, in proportion as development takes a more and more -direct route from the egg to the complete animal." This process of -obscuring and shortening is determined by the law of abridged -transmission, and I mention it here specially because it is of great -importance for the understanding of embryology, and because it explains -the fact, at first so strange, that the whole series of forms which our -ancestors have passed through in their gradual development are no longer -visible in the series of forms of our own individual development from -the egg. - -Opposed to the laws of the conservative transmission, hitherto -discussed, are the phenomena of the transmission of the second series, -that is, the _laws of progressive transmission by inheritance_. As -already mentioned, they depend upon the fact that the organism transmits -to its descendants not only those qualities which it has inherited from -its own ancestors, but also a number of those individual qualities which -it has acquired during its own lifetime. Adaptation is here seen to be -connected with transmission by inheritance (Gen. Morph. ii. 186). - -At the head of these important phenomena of progressive transmission, we -may mention the _law of adapted or acquired transmission_. In reality it -asserts nothing more than what I have said above, that in certain -circumstances the organism is capable of transmitting to its descendants -all the qualities which it has acquired during its own life by -adaptation. This phenomenon, of course, shows itself most distinctly -when the newly acquired peculiarity produces any considerable change in -the inherited form. This is the case in the examples I mentioned in the -preceding chapter as to transmission in general, in the case of the men -with six fingers and toes, the porcupine men, copper beeches, weeping -willows, etc. The transmission of acquired diseases, such as -consumption, madness, and albinism, likewise form very striking -examples. Albinoes are those individuals who are distinguished by the -absence of colouring matter, or pigments, in the skin. They are of -frequent occurrence among men, animals, and plants. In the case of -animals of a definite dark colour, individuals are not unfrequently born -which are entirely without colour, and in animals possessing eyes, this -absence of pigment extends even to the eyes, so that the iris of the -eye, which is commonly of a bright or intense colour, is colourless, but -appears red, on account of the blood-vessels being seen through it. -Among many animals, such as rabbits and mice, albinoes with white fur -and red eyes are so much liked that they are propagated in great numbers -as a special race. This would be impossible were it not for the law of -the transmission of adaptations. - -Which of the changes acquired by an organism are transmitted to its -descendants, and which are not, cannot be determined _a priori_, and we -are unfortunately not acquainted with the definite conditions under -which the transmission takes place. We only know in a general way that -certain acquired qualities are much more easily transmitted than others, -for example, more easily than the mutilations caused by accidents. These -latter are generally not transmitted by inheritance, otherwise the -descendants of men who have lost their arms or legs would be born -without the corresponding arm or leg; but here, also, exceptions occur, -and a race of dogs without tails has been produced by consistently -cutting off the tails of both sexes of the dog during several -generations. A few years ago a case occurred on an estate near Jena, in -which by a careless slamming of a stable door the tail of a bull was -wrenched off, and the calves begotten by this bull were all born without -a tail. This is certainly an exception; but it is very important to note -the fact, that under certain unknown conditions such violent changes are -transmitted in the same manner as many diseases. - -In very many cases the change which is transmitted and preserved by -adapted transmission is constitutional or inborn, as in the case of -albinism mentioned before. The change then depends upon that form of -adaptation which we call the indirect or potential. A very striking -instance is furnished by the hornless cattle of Paraguay, in South -America. A special race of oxen is there bred which is entirely without -horns. It is descended from a single bull, which was born in 1770 of an -ordinary pair of parents, and the absence of horns was the result of -some unknown cause. All the descendants of this bull produced with a -horned cow were entirely without horns. This quality was found -advantageous, and by propagating the hornless cattle among one another, -a hornless race was obtained, which at present has almost entirely -supplanted the horned cattle in Paraguay. The case of the otter-sheep of -North America forms a similar example. In the year 1791 a farmer, by -name Seth Wright, lived in Massachusetts, in North America; in his -normally formed flock of sheep a lamb was suddenly born with a -surprisingly long body and very short and crooked legs. It was therefore -unable to take any great leaps, and especially unable to leap across a -hedge into a neighbour's garden--a quality which seemed advantageous to -the owner, as the territories were divided by hedges. It therefore -occurred to him to transmit this quality to other sheep, and by -crossing this ram with normally shaped ewes, he produced a whole race -of sheep, all of which had the qualities of the father, short and -crooked legs and a long body. None of them could leap across the hedges, -and they therefore were much liked and propagated in Massachusetts. - -A second law, which likewise belongs to the series of progressive -transmissions, may be called the _law of established or habitual -transmission_. It manifests itself in this, that qualities acquired by -an organism during its individual life are the more certainly -transmitted to its descendants the longer the causes of that change have -been in action, and that this change becomes the more certainly the -property of all subsequent generations the longer the cause of change -acts upon these latter also. The quality newly acquired by adaptation or -mutation must be established or constituted to a certain degree before -we can calculate with any probability that it will be transmitted at all -to the descendants. In this respect transmission resembles adaptation. -The longer a newly acquired quality has been transmitted by inheritance, -the more certainly will it be preserved in future generations. If, -therefore, for example, a gardener by methodical treatment has produced -a new kind of apple, he may calculate with the greater certainty upon -preserving the desired peculiarity of this sort the longer he has -transmitted the same by inheritance. The same is clearly shown in the -transmission of diseases. The longer consumption or madness has been -hereditary in a family the deeper is the root of the evil, and the more -probable it is that all succeeding generations will suffer from it. - -We may conclude the consideration of the phenomena of inheritance with -the two very important laws of _homotopic_ and _contemporaneous -transmission by inheritance_. We understand by them the fact that -changes acquired by an organism during its life, and transmitted to its -descendants, appear in the same part of the body in which the parental -organism was first affected by them, and that they also appear in the -offspring at the same age as that at which they did so in the parent. - -_The law of contemporaneous or homochronous transmission_, which Darwin -calls the law of "transmission in corresponding periods of life," can -be shown very clearly in the transmission of diseases, especially of -such as are recognized as very destructive, on account of their -hereditary character. They generally appear in the organism of the child -at the time corresponding with that in which the parental organism -contracted the disease. Hereditary diseases of the lungs, liver, teeth, -brain, skin, etc., usually appear in the descendants at the same period, -or a little earlier than they showed themselves in the parental -organism, or were contracted by it. The calf gets its horns at the same -period of life as its parents did. In like manner the young stag -receives its antlers at the same period of life in which they appeared -in its father or grandfather. In every one of the different sorts of -vine the grapes ripen at the same time as they did in the case of their -progenitors. It is well known that the time of ripening varies greatly -in the different sorts; but as all are descended from a single species, -this variation has been acquired by the progenitors of the several -sorts, and has then been transmitted by inheritance. - -The _law of homotopic transmission_, which is most closely connected -with the last mentioned law, and which might be called the law of -transmission in corresponding parts of the body, may also be very -distinctly recognized in pathological cases of inheritance. Large moles, -for example, or accumulations of pigment in several parts of the skin, -tumours also, often appear during many generations, not only at the same -period of life, but also in the same part of the skin. Excessive -development of fat in certain parts of the body is likewise transmitted -by inheritance. Above all, it is to be noted that numerous examples of -this, as well as of the preceding law, may be found everywhere in the -study of embryology. Both the _law of homochronous and homotopic -transmission are fundamental laws of embryology, or ontogeny_. For these -laws explain the remarkable fact that the different successive forms of -individual development in all generations of one and the same species -always appear in the same order of succession, and that the variations -of the body always take place in the same parts. This apparently simple -and self-evident phenomenon is nevertheless exceedingly wonderful and -curious; we cannot explain its real causes, but may confidently assert -that they are due to the direct transmission of the organic matter from -the parental organism to that of the offspring, as we have seen above in -the case of the process of transmission in general, by a consideration -of the details of the various modes of reproduction. - -Having thus, then, considered the most important laws of Inheritance, we -now turn to the second series of phenomena bearing on natural selection, -viz., to those of Adaptation or Variation. These phenomena, taken as a -whole, stand in a certain opposition to the phenomena of Inheritance, -and the difficulty which arises in examining them consists mainly in -the two sets of phenomena being so completely intercrossed and -interwoven. We are but seldom able to say with certainty--of the -variations of form which occur before our eyes--how much is owing to -Inheritance, and how much to Adaptation. All characters of form, by -which organisms are distinguished, are caused _either_ by Inheritance or -by Adaptation; but as both functions are continually interacting with -each other, it is extremely difficult for the systematic inquirer to -recognize the share belonging to each of the two functions in the -special structure of individual forms. This is, at present, all the more -difficult, because we are as yet scarcely aware of the immense -importance of this fact, and because most naturalists have neglected the -theory of Adaptation, as well as that of Inheritance. The laws of -Inheritance, which we have just discussed, as well as the laws of -Adaptation, which we shall consider directly, in reality form only a -small portion of the phenomena existing in this domain, but which have -not as yet been investigated; and since every one of these laws can -interact with every other, it is clear that there is an infinite -complication of physiological actions, which are at work in the -construction of organisms. - -But now, as to the phenomenon of variation or adaptation in general, we -must, as in the case of inheritance, view it as a quite universal, -physiological fundamental quality of all organisms, without -exception--as a manifestation of life which cannot be separated from the -idea of organism. Strictly speaking, we must here also, as in the case -of inheritance, distinguish between Adaptation itself and Adaptability. -By Adaptation (Adaptio), or Variation (Variatio), we understand the fact -that the organism, in consequence of influences of the surrounding -outer world, assumes certain new peculiarities in its vital activity, -composition, and form which it has not inherited from its parents; these -acquired individual qualities are opposed to those which have been -inherited, or, in other words, those which have been transmitted to it -from its parents or ancestors. On the other hand, we call Adaptability -(Adaptabilitas), or Variability (Variabilitas), the capability inherent -in all organisms to acquire such new qualities under the influence of -the outer world. (Gen. Morph. ii. 191.) - -The undeniable fact of organic adaptation or variation is universally -known, and can be observed at every moment in thousands of phenomena -surrounding us. But just because the phenomena of variation by external -influences appear so self-evident, they have hitherto undergone scarcely -any accurate scientific investigation. To them belong all the phenomena -which we look upon as the results of contracting and giving up habits, -of practice and giving up practices, or as the results of training, of -education, of acclimatization, of gymnastics, etc. Many permanent -variations brought about by causes producing disease, that is to say, -many diseases, are nothing but dangerous adaptations of the organism to -injurious conditions of life. In the case of cultivated plants and -domestic animals, variation is so striking and powerful that the breeder -of animals and the gardener found their whole mode of proceeding upon -it, or rather upon the interaction between these phenomena and those of -Inheritance. It is also well known to every one that animals and plants, -in their wild state, are subject to variation. Every systematic treatise -on a group of animals or plants, if it were to be quite complete and -exhaustive, ought to mention in every individual species the number of -variations which differ more or less from the prevailing or typical form -of the species. Indeed, in every careful systematic special treatise one -finds, in the case of most species, mention of a number of such -variations, which are described sometimes as individual deviations, and -sometimes as so-called races, varieties, degenerate species, or -subordinate species, and which often differ exceedingly from the -original species, solely in consequence of the adaptation of the -organism to the external conditions of life. - -If we now endeavour to fathom the general causes of these phenomena of -Adaptation, we arrive at the conclusion that in reality they are as -simple as the causes of the phenomena of Inheritance. We have shown that -the nature of the process of propagation furnishes the real explanation -of the facts of Transmission by Inheritance, that is, the transmission -of parental matter to the body of the offspring; and in like manner we -can show that the physiological function of _nutrition_, or _change of -substance_, affords a general explanation of Adaptation or Variation. -When I here point to "nutrition" as the fundamental cause of variation -and adaptation, I take this word in its widest sense, and I understand -by it the whole of the material changes which the organism undergoes in -all its parts through the influences of the surrounding outer world. -Nutrition thus comprises not only the reception of actual nutritive -substances and the influence of different kinds of food, but also, for -example, the action upon the organism of water and of the atmosphere, -the influence of sunlight, of temperature, and of all those -meteorological phenomena which are implied in the term "climate." The -indirect and direct influence of the nature of the soil and of the -dwelling-place also belong to it; and further, the extremely important -and varied influence which is exercised upon every animal and every -plant by the surrounding organisms, friends and neighbours, enemies and -robbers, parasites, etc. All these and many other very important -influences, all of which more or less modify the organism in its -material composition, must be taken into consideration in studying the -change of substance which goes on in living things. Adaptation, -accordingly, is the consequence of all those material variations which -are produced in the change of substance of the organism by the external -conditions of existence, or by the influences of the surrounding -external world. - -How very much every organism is dependent upon the whole of its external -surroundings, and changed by their alteration, is, in a general way, -well known to every one. Only think how much the human power of action -is dependent upon the temperature of the air, or how much the -disposition of our minds depends upon the colour of the sky. Accordingly -as the sky is cloudless and sunny, or covered with large heavy clouds, -our state of mind is cheerful or dull. How differently do we feel and -think in a forest during a stormy winter night and during a bright -summer day! All the different moods of our soul depend upon purely -material changes of our brain, upon movements of molecular plasma, which -are started through the medium of the senses by the different influences -of light, warmth, moisture, etc. "We are a plaything to every pressure -of the air." No less important and deeply influential are the effects -produced upon our mind and body by the different quality and quantity -of food. Our mental activity, the activity of our understanding and of -our imagination, is quite different accordingly as we have taken tea or -coffee, wine or beer, before or during our work. Our moods, wishes, and -feelings are quite different when we are hungry and when we are -satisfied. The national character of Englishmen and Gauchos, in South -America, who live principally on meat and food rich in nitrogen, is -wholly different from that of the Irish, feeding on potatoes, and that -of the Chinese, living on rice, both of whom take food deficient in -nitrogen. The latter also form much more fat than the former. Here, as -everywhere, the variations of the mind go hand in hand with the -corresponding transformations of the body; both are produced by purely -material causes. But all other organisms, in the same way as man, are -varied and changed by the different influences of nutrition. It is well -known that we can change in an arbitrary way the form, size, colour, -etc., of our cultivated plants and domestic animals, by change of food; -that, for example, we can take from or give to a plant definite -qualities, accordingly as we expose it to a greater or less degree of -sunlight and moisture. As these phenomena are generally widely known, -and as we shall proceed presently to the consideration of the different -laws of adaptation, we will not dwell here any longer on the general -facts of variation. - -As the different laws of transmission may be naturally divided into the -two series of conservative and progressive transmission, so we may also -distinguish between two series of the laws of adaptation, first, the -series of laws of _indirect_, and secondly, the series of laws of -_direct_ adaptation. The latter may also be called the laws of actual, -and the former the laws of potential, adaptation. - -The first series, comprising the phenomena of _indirect_ (potential) -adaptation, has, on the whole, hitherto been little attended to, and -Darwin has the merit of having directed special attention to this series -of changes. It is somewhat difficult to place this subject clearly -before the reader; I will endeavour to make it clear hereafter by -examples. Speaking quite generally, indirect or potential adaptation -consists in the fact that certain changes in the organism, effected by -the influence of nutrition (in its widest sense) and of the external -conditions of existence in general, show themselves not in the -individual form of the respective organism, but in that of its -descendants. Thus, especially in organisms propagating themselves in a -sexual way, the reproductive system, or sexual apparatus, is often -influenced by external causes (which little affect the rest of the -organism), to such a degree that its descendants show a complete -alteration of form. This can be seen very strikingly in artificially -produced monstrosities. Monstrosities can be produced by subjecting the -parental organism to certain extraordinary conditions of life, and, -curiously enough, such an extraordinary condition of life does not -produce a change of the organism itself, but a change in its -descendants. This cannot be called transmission by inheritance, because -it is not a quality existing in the parental organism that is -transmitted by inheritance. It is, on the contrary, a change affecting -the parental organism, but not perceptible in it, that appears in the -peculiar formation of its descendants. It is only the impulse to this -new formation which is transmitted in propagation through the egg of the -mother or the sperm of the father. The new formation exists in the -parental organism only as a possibility (potential); in the descendants -it becomes a reality (actual). - -As this very important and very general phenomenon had hitherto been -entirely neglected, people were inclined to consider all the visible -variations and transformations of organic forms as phenomena of -adaptation of the second series, that is, as phenomena of _direct_ or -actual adaptation. The essence of this latter kind of adaptation -consists in the fact that the change affecting the organism (through -nutrition, etc.) shows itself immediately by some transformation, and -does not only make itself apparent in the descendants. To this class -belong all the well-known phenomena in which we can directly trace the -transforming influence of climate, food, education, training, etc., in -their effects upon the individual itself. - -We have seen how the two series of phenomena of progressive and -conservative transmission, in spite of their difference in principle, in -many ways interfere with and modify each other, and in many ways -co-operate with and cross each other. The same is the case, in a still -higher degree, in the two series of phenomena of indirect and direct -adaptation, which are opposed to each other and yet closely connected. -Some naturalists, especially Darwin and Carl Vogt, ascribe to the -indirect or potential adaptation by far the more important and almost -exclusive influence. But the majority of naturalists have hitherto been -inclined to take the opposite view, and to attribute the principal -influence to direct or actual adaptation. I consider this controversy, -in the mean while, as almost useless. It is but seldom that we are in a -condition, in any individual case of variation, to judge how much of it -belongs to direct and how much to indirect adaptation. We are, on the -whole, still too little acquainted with these exceedingly important and -intricate relations, and can only assert, in a general way, that the -transformation of organic forms is to be ascribed _either_ to direct -adaptation alone, _or_ to indirect adaptation alone, or lastly, to the -co-operation of both direct _and_ indirect adaptation. - - - - -CHAPTER X. - -LAWS OF ADAPTATION. - - - Laws of Indirect or Potential Adaptation.--Individual - Adaptation.--Monstrous or Sudden Adaptation.--Sexual - Adaptation.--Laws of Direct or Actual - Adaptation.--Universal Adaptation.--Cumulative - Adaptation.--Cumulative Influence of External Conditions - of Existence and Cumulative Counter-Influence of the - Organism.--Free Will.--Use and Non-use of - Organs.--Practice and Habit.--Correlative - Adaptation.--Correlation of Development.--Correlation of - Organs.--Explanation of Indirect or Potential Adaptation - by the Correlation of the Sexual Organs and of the other - parts of the Body.--Divergent Adaptation.--Unlimited or - Infinite Adaptation. - - -In the last chapter we reduced into two groups the phenomena of -Adaptation or Variation, which, in connection and interaction with the -phenomena of Heredity, produce all the endless variety of forms in -animals and plants--first, the group of indirect or potential, and -secondly, the group of direct or actual Adaptation. We shall occupy -ourselves with a closer examination of the different laws which we can -discover in these two groups of the phenomena of variation. Let us first -take into consideration the remarkable and very important, although -hitherto much neglected, phenomena of indirect variation. - -_Indirect or potential adaptation_ manifests itself, it will be -remembered, in the striking and exceedingly important fact that organic -individuals experience transformations and assume forms in consequence -of changes of nutrition which have not operated on them themselves, but -upon their parental organism. The transforming influence of the external -conditions of existence, of climate, of nutrition, etc., shows its -effects here not directly in the transformation of the organism itself, -but indirectly in that of its descendants. (Gen. Morph. ii. 202.) - -As the principal and most universal of the laws of indirect variation -must be mentioned _the law of individual adaptation_, or the important -proposition that all organic individuals from the commencement of their -individual existence are unequal, although often very much alike. As a -proof of this proposition, I may at once point to the fact, that in the -human race in general all brothers and sisters, all children of the same -parents, are unequal from their birth. No one will venture to assert -that two children at their birth are perfectly alike; that the size of -the individual parts of their bodies, the number of hairs on their -heads, the number of cells composing their outer skins or epidermis, the -number of blood-cells are the same in both children, or that both -children have come into the world with the same abilities or talents. -But what more specially proves this law of individual difference, is the -fact that in the case of those animals which produce several young ones -at a time,--for instance, dogs and cats,--all the young of each birth -differ from one another more or less strikingly in size and colour of -the individual parts of the body, or in strength, etc. Now this law is -universal. All organic individuals from their beginning are -distinguished by certain, though often extremely minute, differences, -and the cause of these individual differences, though in detail usually -utterly unknown to us, depends partly or entirely on certain influences -which the organs of propagation in the parental organism have undergone. - -A second law of indirect adaptation, which we shall call _the law of -monstrous or sudden adaptation_, is of less importance and less general -than the law of individual adaptation. Here the divergences of the -child-organism from the parental form are so striking that, as a rule, -we may designate them as monstrosities. In many cases they are produced, -as has been proved by experiments, by the parental organism having been -subject to a certain treatment, and placed under peculiar conditions of -nutrition; for example, when air and light are withdrawn from it, or -when other influences powerfully acting upon its nutrition are changed -in a certain way. The new condition of existence causes a strong and -striking modification of form, not directly of the organism itself, but -only of that of its descendants. The mode of this influence in detail we -cannot discover, and we can only in a very general way detect a causal -connection between the abnormal formation of the child and a certain -change in the conditions of existence of its parents exerting a special -influence upon the organs of propagation in the latter. The previously -mentioned phenomenon of albinism probably belongs to this group of -abnormal or sudden variations, also the individual cases of human beings -with six fingers and toes, the case of the hornless cattle, as well as -those of sheep and goats with four or six horns. The abnormal deviation -in all these cases probably owes its origin to a cause which at first -only affected the reproductive system of the parental organism, the egg -of the mother or the sperm of the father. - -A third curious manifestation of indirect adaptation may be termed _the -law of sexual adaptation_. Under this name we indicate the remarkable -fact that certain influences, which act upon the male organs of -propagation only, affect the structure of the male descendants, and in -like manner other influences, which act upon the female organs of -propagation only, manifest their effect only in the change of structure -of the female descendants. This remarkable phenomenon is still very -obscure, and has not as yet been investigated, but is probably of great -importance in regard to the origin of "secondary sexual -characteristics," to which we have already made allusion. - -All the phenomena of sexual, monstrous, and individual adaptation, which -we may comprise under the name of the laws of _indirect or potential -adaptation_, are as yet very little known to us in their real nature and -in their deeper causal connection. Only this much we can at present -maintain with certainty, that numerous and important transformations in -organic forms owe their existence to this process. Many and striking -variations of form solely depend on causes which at first only affect -the nutrition of the parental organism, and specially its organs of -propagation. Evidently the relations in which the sexual organs stand to -other parts of the body are of the greatest importance. We shall have -more to say of these presently, when we speak of the law of correlative -adaptation. How powerfully the variations in the conditions of life and -nutrition affect the propagation of organisms is rendered obvious by the -remarkable fact that numerous wild animals which we keep in our -zoological gardens, and exotic plants which are grown in our botanical -gardens, are no longer able to reproduce themselves. This is the case, -for example, with most birds of prey, parrots, and monkeys. The -elephant, also, and the animals of prey of the bear genus, in captivity -hardly ever produce young ones. In like manner many plants in a -cultivated state become sterile. The two sexes may indeed unite, but no -fructification, or no development of the fructified germ, takes place. -From this it follows with certainty that the changed mode of nutrition -in the cultivated state is able completely to destroy the capability of -reproduction, and therefore to exercise the greatest influence upon the -sexual organs. In like manner other adaptations or variations of -nutrition in the parental organism may cause, not indeed a complete want -of descendants, but still important changes in their form. - -Much better known than the phenomena of indirect or potential adaptation -are those of _direct or actual adaptation_, to the consideration of -which we now turn our attention. To them belong all those changes of -organisms which are generally considered to be the results of practice, -habit, training, education, etc.; also those changes of organic forms -which are effected directly by the influence of nutrition, of climate, -and other external conditions of existence. As has already been remarked -in direct or actual adaptation, the transforming influence of the -external cause affects the form of the organism itself, and does not -only manifest itself in that of the descendants. (Gen. Morph. ii. 207.) - -We may place _the law of universal adaptation_ at the head of the -different laws of direct or actual adaptation, because it is the chief -and most comprehensive among them. It may be briefly explained in the -following proposition: "All organic individuals become unequal to one -another in the course of their life by adaptation to different -conditions of life, although the individuals of one and the same species -remain mostly very much alike." A certain inequality of organic -individuals, as we have seen, was already to be assumed in virtue of the -law of individual (indirect) adaptation. But, beyond this, the original -inequality of individuals is afterwards increased by the fact that every -individual, during its own independent life, subjects and adapts itself -to its own peculiar conditions of existence. All different individuals -of every species, however like they may be in their first stages of -life, become in the further course of their existence less like to one -another. They deviate from one another in more or less important -peculiarities, and this is a natural consequence of the different -conditions under which the individuals live. There are no two single -individuals of any species which can complete their life under exactly -the same external circumstances. The vital conditions of nutrition, of -moisture, air, light; further, the vital conditions of society, the -inter-relations with surrounding individuals of the same or other -species, are different in every individual being; and this difference -first affects the functions, and later changes the form of every -individual organism. If the children of a human family show, even at the -beginning, certain individual inequalities which we may consider as the -consequence of individual (indirect) adaptation, they will appear still -more different at a later period of life, when each child has passed -through different experiences, and has adapted itself to different -conditions of life. The original difference of the individual processes -of development, evidently becomes greater the longer the life lasts and -the more various the external conditions which influence the separate -individuals. This may be demonstrated in the simplest manner in man, as -well as in domestic animals and cultivated plants, in which the vital -conditions may be arbitrarily modified. Two brothers, of whom one is -brought up as a workman and the other as a priest, develop quite -differently in body as well as in mind; in like manner, two dogs of one -and the same birth, of which one is trained as a sporting dog and the -other chained up as a watch dog. The same observation may also readily -be made as to organic individuals in a natural state. If, for instance, -one carefully compares all the trees in a fir or beech forest, which -consists of trees of a single species, one finds that among all the -hundreds or thousands of trees, there are not two individual trees -completely agreeing in size of trunk and other parts, in the number of -branches, leaves, etc. Everywhere we find individual inequalities which, -in part at least, are merely the consequences of the different -conditions of life under which the trees have developed. It is true we -can never say with certainty how much of this dissimilarity in all the -individuals of every species may have originally been caused by indirect -individual adaptation, and how much of it acquired under the influence -of direct or universal adaptation. - -A second series of phenomena of direct adaptation, which we may comprise -under _the law of cumulative adaptation_, is no less important and -general than universal adaptation. Under this name I include a great -number of very important phenomena, which are usually divided into two -quite distinct groups. Naturalists, as a rule, have distinguished, -first, those variations of organisms which are produced directly by the -permanent influence of external conditions (by the constant action of -nutrition, of climate, of surroundings, etc.), and secondly, those -variations which arise from habit and practice, from accustoming -themselves to definite conditions of life, and from the use and non-use -of organs. The latter influences have been set forth especially by -Lamarck as important causes of the change of organic forms, while the -former have for a very long time been recognized as such more generally. - -The sharp distinction usually made between these two groups of -cumulative adaptation, and which even Darwin still maintains, disappears -as soon as we reflect more accurately and deeply upon the real nature -and causal foundation of these two, apparently very different, series of -adaptations. We then arrive at the conviction that in both cases there -are always two different active causes to be dealt with: on the one hand -the _external influence_ or _action_ of adaptative conditions of life, -and on the other hand the _internal reaction of the organism_ which -subjects and adapts itself to that condition of life. If cumulative -adaptation is considered from the first point of view alone, and the -transforming actions of the permanent external conditions of life are -traced to those conditions solely, then the principal stress is laid -unduly upon the external factor, and the necessary internal reaction of -the organism is not taken into proper consideration. If, on the other -hand, cumulative adaptation is unjustly regarded solely in relation to -its second factor, and the transforming action of the organism itself, -its reaction against the external influences, its change by practice, -habit, use, or non-use of organs, is put into the foreground, then we -forget that this reaction is first called into play by the action of -external conditions of existence. Hence it seems that the distinction -made between these two groups lies only in the different manner of -viewing them, and I believe that they can, with full justice, be -considered as one. The most essential fact in these phenomena of -cumulative adaptation is that the change of the organism which manifests -itself first in the functions, and at a later period in the form, is the -result either of long enduring, or of often repeated, influences of an -external cause. The smallest cause, by cumulation of its action, can -attain the greatest results. - -There are innumerable examples of this kind of direct adaptation. In -whatever direction we may examine the life of animals and plants, we -discover on all hands evident and undeniable changes of this kind. Let -me first mention some of those phenomena of adaptation occasioned -directly by nutrition itself. Every one knows that the domestic animals -which are bred for certain purposes can be variously modified, according -to the different quantity and quality of the food given to them. If a -farmer in breeding sheep wishes to produce fine wool, he gives them -different food from what he would give if he wished to obtain good flesh -or an abundance of fat. Choice race and carriage horses receive better -food than dray and cart horses. Even the bodily form of man--for -example, the amount of fat--is quite different according to his -nutrition. Food containing much nitrogen produces little fat, that -containing little nitrogen produces a great deal of fat. People who, by -means of Banting's system, at present so popular, wish to become thin -eat only meat and eggs--no bread, no potatoes. The important variations -that can be produced among cultivated plants, solely by changing the -quantity and quality of nourishment, are well known. The same plant -acquires an altogether different appearance, according as it is placed -in a dry and warm place, exposed to the sunlight or placed in a cool -damp spot in the shade. Many plants, if transferred to the sea shore, -get in a short space of time thick, fleshy leaves, and the same plants -placed in a particularly dry and hot locality get thin hairy leaves. All -these variations arise directly from the cumulative influence of changed -nutrition. - -But it is not only the quantity and quality of the articles of nutrition -which affect and powerfully change and transform the organism, but it is -affected also by all the other external conditions of existence, above -all by its nearest organic surroundings, the society of friendly or -hostile organisms. One and the same kind of tree develops itself quite -differently in an open locality, where it is free on all sides, and in a -forest where it must adapt itself to its surroundings, where it is -pressed on all sides by its nearest neighbours, and is forced to shoot -upwards. In the former case, the branches of the tree spread widely out; -in the latter, the trunk extends upwards, and the top of the tree -remains small and contracted. How powerfully all these circumstances, -and how powerfully the hostile or friendly influence of surrounding -organisms, of parasites, etc., affect every animal and every plant, is -so well known, that it appears superfluous to quote further examples. -The change of form, or transformation which is thereby effected, is -never solely the direct result of the external influence, but must -always be traced to the corresponding reaction, and to the activity of -the organism itself, which consists in contracting a habit, or practice, -and in the use or non-use of organs. The fact that these latter -phenomena, as a rule, have been considered distinct from the former, is -owing first to the one-sided manner of viewing them already mentioned, -and secondly to the wrong notion which has been formed as to the nature -and the influence of the activity of the will in animals. - -The activity of the will, which is the organ of habit, of practice, of -the use or non-use of organs among animals, is, like every other -activity of the animal soul, dependent upon material processes in the -central nervous system, upon peculiar motions which emanate from the -albuminous matter of the ganglion cells, and the nervous fibres -connected with them. The will, as well as the other mental activities, -in higher animals, in this respect is different from that of men only in -quantity, not in quality. The will of the animal, as well as that of -man, is never free. The widely spread dogma of the freedom of the will -is, from a scientific point of view, altogether untenable. Every -physiologist who scientifically investigates the activity of the will in -man and animals, must of necessity arrive at the conviction that _in -reality the will is never free_, but is always determined by external or -internal influences. These influences are for the most part ideas which -have been either formed by Adaptation or by Inheritance, and are -traceable to one or other of these two physiological functions. As soon -as we strictly examine the action of our own will, without the -traditional prejudice about its freedom, we perceive that every -apparently free action of the will is the result of previous ideas, -which are based on notions inherited or otherwise acquired, and are -therefore, in the end, dependent on the laws of Adaptation and -Inheritance. The same also applies to the action of the will in all -animals. As soon as their will is considered in connection with their -mode of life, in its relation to the changes which the mode of life is -subject to from external conditions, we are at once convinced that no -other view is possible. Hence the changes of the will which follow the -changes of nutrition, and which, in the form of practice, habit, etc., -produce variations in structure, must be reckoned among the other -material processes of cumulative adaptation. - -Whilst an animal's will is adapting itself to changed conditions of -existence by the acquisition of new habits, practices, etc., it not -unfrequently effects the most remarkable transformations of the organic -form. Numerous instances of this may be found everywhere in animal life. -Thus, for example, many organs in domestic animals are suppressed, when -in consequence of a changed mode of life they cease to act. Ducks and -fowls in a wild state fly exceedingly well, but lose this facility more -or less in a cultivated state. They accustom themselves to use their -legs more than their wings, and in consequence the muscles and skeleton -used in flying are essentially changed in their development and form. -Darwin has proved this by a very careful comparative measurement and -weighing of the respective parts of the skeleton in the different races -of domestic ducks, which are all descended from the wild duck (_Anas -boschas_). The bones of the wings in tame ducks are weaker, the bones of -the legs, on the other hand, are more strongly developed than in wild -ducks. In ostriches and other running birds which have become completely -unaccustomed to fly, the consequence is that their wings are entirely -crippled and degenerate into mere "rudimentary organs" (p. 12). In many -domestic animals, especially in many races of dogs and rabbits, we find -that in the cultivated state they have acquired pendulous ears. This is -simply a consequence of a diminished use of the auricular muscles. In a -wild state these animals have to exert their ears very much in order to -discover an approaching foe, and this is accompanied by a strong -development of the muscular apparatus, which keeps the outer ears in an -upright position, and by which they can turn them in all directions. In -a domestic state the same animals no longer require to listen so -attentively, they prick up or turn their ears only a little; the -auricular muscles cease to be used, gradually become weakened, and the -ears hang down flabbily, or become rudimentary. - -As in these cases the function, and consequently the form also, of the -organ becomes degenerated through disuse, so, on the other hand, it -becomes more developed by greater use. This is particularly striking if -we compare the brain, and the mental activity belonging to it, in wild -animals and those domestic animals which are descended from them. The -dog and horse, which are so vastly improved by cultivation, show an -extraordinary degree of mental development, in comparison with their -wild original ancestors, and evidently the change in the bulk of the -brain, which is connected with it, is mainly determined by persistent -exercise. It is also well known how quickly and powerfully muscles grow -and change their form by continual practice. Compare, for example, the -arms and legs of a trained gymnast with those of an immovable book-worm. - -How powerfully external influences affect the habits of animals and -their mode of life, and in this way still further change their forms, is -very strikingly shown in many cases among amphibious animals and -reptiles. Our commonest indigenous snake, the ringed snake, lays eggs -which require three weeks' time to develop. But when it is kept in -captivity, and no sand is strewn in the cage, it does not lay its eggs, -but retains them until the young ones are developed. The difference -between animals producing living offspring and those laying eggs is here -effaced simply by the change of the ground upon which the animal lives. - -The water-salamanders, or tritons, which have been artificially made to -retain their original gills, are extremely interesting in this respect. -The tritons are amphibious animals, nearly akin to frogs, and possess, -like the latter, in their youth external organs of -respiration--gills--with which they, while living in water, breathe the -air dissolved in the water. At a later date a metamorphosis takes place -in tritons, as in frogs. They leave the water, lose their gills, and -accustom themselves to breathe with their lungs. But if they are -prevented from doing this by being kept shut up in a tank, they do not -lose their gills. The gills remain, and the water salamander continues -through life in that low stage of development, beyond which its lower -relations, the gilled salamanders, or Sozobranchiata, never pass. The -gilled salamander attains its full size, its sexual development, and -reproduces itself without losing its gills. - -Great interest was caused a short time ago, among zoologists, by the -axolotel (Siredon pisciformis), a gilled salamander from Mexico, nearly -related to the triton; it had already been known for a long time, and -been bred on a large scale in the zoological garden in Paris. This -animal possesses external gills, like the young salamander, but retains -them all its life, like all other Sozobranchiata. This gilled salamander -generally remains in the water, with its aquatic organs of respiration, -and also propagates itself there. But in the Paris garden, unexpectedly -from among hundreds of these animals, a small number crept out of the -water on to the dry land, lost their gills, and changed themselves into -gill-less salamanders, which are not to be distinguished from a -North-American genus of tritons (Amblystoma), and breathe only through -lungs. In this exceedingly curious case we can directly follow the great -stride from water-breathing to air-breathing animals, a stride which can -indeed be observed every spring in the individual history of development -of frogs and salamanders. Just as every separate frog and every separate -salamander transforms itself from an amphibious animal breathing through -gills, at a later period into one breathing through lungs, so the whole -group of frogs and salamanders have arisen from animals breathing -through gills, and akin to the Siredon. The Sozobranchiata have remained -up to the present day in that low stage of development. Ontogeny here -explains phylogeny; the history of the development of individuals -explains that of the whole group (p. 10). - -To the law of accumulative adaptation there closely follows a third law -of direct or actual adaptation, _the law of correlative adaptation_. -According to this important law, actual adaptation not only changes -those parts of the organism which are directly affected by its -influence, but other parts also not directly affected by it. This is the -consequence of organic solidarity, and especially of the unity of the -nutrition existing among all the parts of every organism. If, for -example, the hairiness of the leaves increases in a plant by its being -transferred to a dry locality, then this change reacts upon the -nutrition of other parts, and it may result in a shortening of the parts -of the stalk, and produce a more contracted form of the whole plant. In -some races of pigs and dogs--for example, in the Turkish dog--which by -adaptation to a warmer climate have more or less lost their hair, the -teeth also have degenerated. Whales and Endentata (armadillos), which by -their curious skin-covering are removed from the other mammals, also -show the greatest deviations in the formation of their teeth. Further, -those races of domestic animals (oxen and pigs) which have acquired -short legs have, as a rule, also a short and compact head. Among other -examples, the races of pigeons which have the longest legs are also -characterized by the longest beaks. The same correlation between the -length of the legs and beaks is universal in the order of stilted-birds -(Grallatores), in storks, cranes, snipe, etc. The correlations which -thus exist between different parts of the organism are most remarkable, -but their real cause is unknown to us. In general, we can of course say, -the changes of nutrition affecting an individual part must necessarily -react on the other parts, because the nutrition of every organism is a -connected, centralized activity. But why just this or that part should -exhibit this or that particular correlation is in most cases quite -unknown to us. We know a great number of such correlations in nutrition; -they are especially seen in those changes of animals and plants which -give rise to an absence of pigment (noticed previously)--in albinoes. -The want of the usual colouring matter goes hand in hand with certain -changes in the formation of other parts; for example, of the muscular -and osseous system, consequently of organic systems which are not at all -ultimately connected with the system of the outer skin. Very frequently -albinoes are more feebly developed, and consequently the whole structure -of the body is more delicate and weak than in coloured animals of the -same species. The organs of the senses and nervous system are in like -manner curiously affected when there is this want of pigment. White cats -with blue eyes are nearly always deaf. White horses are distinguished -from coloured horses by their special liability to form sarkomatous -tumours. In man, also, the degree of the development of pigment in the -outer skin greatly influences the susceptibility of the organism for -certain diseases; so that, for instance, Europeans with a dark -complexion, black hair, and brown eyes become more easily acclimatized -to tropical countries, and are less subject to the diseases there -prevalent (inflammation of the liver, yellow fever, etc.) than Europeans -of white complexion, fair hair, and blue eyes. (Compare above, p. 150.) - -Among these correlations in the formation of different organs, those are -specially remarkable which exist between the sexual organs and other -parts of the body. No change of any part reacts so powerfully upon the -other parts of the body as a certain treatment of the sexual organs. -Farmers who wish to obtain an abundant formation of fat in pigs, sheep, -etc., remove the sexual organs by cutting them out (castration), and -this is indeed done to animals of both sexes. The result is an -excessive development of fat. The same is done to the singers in certain -religious corporations. These unfortunates are castrated in early youth, -in order that they may retain their high boyish voices. In consequence -of this mutilation of the genitals, the larynx remains in its youthful -stage of development. The muscular tissues of the body remain at the -same time weakly developed, while below the skin an abundance of fat -accumulates. But this mutilation also powerfully reacts upon the -development of the nervous system, the energy of the will, etc., and it -is well known that human castrates, or eunuchs, as well as castrated -animals, are utterly deficient in the special psychical character which -distinguishes the male sex. Man is a man, both in body and soul, solely -through his male generative glands. - -These most important and influential correlations between the sexual -organs and the other parts of the body, especially the brain, are found -equally in both sexes. This might be expected even _a priori_, because -in most animals the two kinds of organs develop themselves from the same -foundation, and at the beginning are not different. In man, as in the -rest of the vertebrate animals, the male and female organs in the -original state of the germ are entirely the same, and the differences of -the two sexes only gradually arise in the course of embryonic -development (in man, in the ninth week of embryonic life), by one and -the same gland developing in the female as the ovary, and in the male as -the testicle. Every change of the female ovary, therefore, has a no less -important reaction upon the whole female organism than every change of -the testicle has upon the male organism. Virchow has expressed the -importance of this correlation in his admirable essay on "Das Weib und -die Zelle" ("Woman and the Cell"), in the following words:--"Woman is -woman only by her sexual glands; all the peculiarities of her body and -mind, of her nutrition and her nervous activity, the sweet delicacy and -roundness of her limbs, the peculiar formation of the pelvis, the -development of the breasts, the continuance of the high voice, that -beautiful ornament of hair on her head, with the scarcely perceptible -soft down on the rest of the skin--then again, the depth of feeling, the -truth of her direct perceptions, her gentleness, devotion, and -fidelity--in short, all the feminine qualities which we admire and -honour in a true woman are but a dependence of the ovary. Take this -ovary away, and the man-woman stands before us--a loathly abortion." - -The same close correlation between the sexual organs and the other parts -of the body occurs among plants as generally as among animals. If one -wishes to obtain an abundance of fruit from a garden plant, the growth -of the leaves is curtailed by cutting off some of them. If, on the other -hand, an ornamental plant with a luxuriance of large and beautiful -leaves is desired, then the development of the blossoms and fruit is -prevented by cutting off the flower buds. In both cases one system of -organs develops at the cost of the others. Thus, also, most variations -in the formation of leaves in wild plants result in corresponding -transformations of the generative parts or blossoms. The great -importance of this "compensation of development," of this "correlation -of parts," has been already set forth by Goethe, by Geoffroy St. -Hilaire, and other nature-philosophers. It rests mainly upon the fact -that direct or actual adaptation cannot produce an important change in a -single part of the body, without at the same time affecting the whole -organism. - -The correlative adaptation between the reproductive organs and the other -parts of the body deserves a very special consideration, because it is, -above all others, likely to throw light upon the obscure and mysterious -phenomena of indirect or potential adaptation, which have already been -considered. For just as every change of the sexual organs powerfully -reacts upon the rest of the body, so on the other hand every important -change in another part of the body must necessarily more or less react -on the sexual organs. This reaction, however, will only become -perceptible in the formation of the offspring which arise out of the -changed generative parts. It is, in fact, precisely those remarkable and -imperceptible changes of the genital system (in themselves utterly -insignificant changes)--changes of the eggs and the sperm--brought about -by such correlations, which have the greatest influence upon the -formation of the offspring, and all the phenomena of indirect or -potential adaptation previously mentioned may in the end be traced to -correlative adaptation. - -A further series of remarkable examples of correlative adaptation is -furnished by the different animals and plants which become degenerated -through parasitic life or parasitism. No other change in the mode of -life so much affects the shapes of organisms as the adoption of a -parasitical life. Plants thereby lose their green leaves; as, for -instance, our native parasitical plants, Orobanche, Lathraea, Monotropa. -Animals which originally have lived freely and independently, but -afterwards adopt a parasitical mode of life on other animals or plants, -in the first place cease to use their organs of motion and their organs -of sense. The loss of this activity is succeeded by the loss of the -organs themselves, and thus we find, for example, many crabs, or -crustacea, which in their youth possess a tolerably high degree of -organization, viz., legs, antennae, and eyes, in old age completely -degenerate, living as parasites, without eyes, without apparatus of -motion, and without antennae. The lively, active form of youth, has -become a shapeless, motionless lump. Only the most necessary organs of -nutrition and propagation retain their activity; all the rest of the -body has degenerated. Evidently these complete transformations are, to a -large extent, the direct consequences of cumulative adaption, of the -non-use and defective exercise of the organs, but a great portion of -them must certainly be attributed also to correlative adaptation. -(Compare Plate X. and XI.) - -A seventh law of adaptation, the fourth in the group of direct -adaptation, is _the law of divergent adaptation_. By this law we -indicate the fact that parts originally formed alike have developed in -different ways under the influence of external conditions. This law of -adaptation is extremely important for the explanation of the phenomenon -of division of labour, or polymorphism. We can see this very easily in -our own selves; for instance, in the activity of our two hands. We -usually accustom our right hand to quite different work from that which -we give our left, and in consequence of the different occupation there -arises a different formation of the two hands. The right hand, which we -use much more than the left, shows a stronger development of the nerves, -muscles, and bones. The same applies to the whole arm. In most human -beings the bones and flesh of the right arm are, in consequence of their -being more employed, stronger and heavier than those of the left arm. -Now, as the special use of the right arm has been adopted and -transmitted by inheritance for thousands of years among Europeans, the -stronger shape and size of the right arm have already become hereditary. -P. Harting, an excellent Dutch naturalist, has shown by measuring and -weighing newly-born children, that even in them the right arm is more -developed than the left. - -According to the same law of divergent adaptation, both eyes also -frequently develop differently. If, for example, a naturalist accustoms -himself always to use one eye for the microscope (it is better to use -the left), then that eye will acquire a power different from that of the -other, and this division of labour is of great advantage. The one eye -will become more short-sighted, and better suited for seeing things near -at hand; the other eye becomes, on the contrary, more long-sighted, more -acute for looking at an object in the distance. If, on the other hand, -the naturalist alternately uses both eyes for the microscope, he will -not acquire the short-sightedness of the one eye and the compensatory -degree of long-sight in the other, which is attained by a wise -distribution of these different functions of sight between the two eyes. -Here then again the function, that is the activity, of originally -equally-formed organs can become divergent by habit; the function reacts -again upon the form of the organ, and thus we find, after a long -duration of such an influence, a change in the more delicate parts and -the relative growth of the divergent organs, which in the end becomes -apparent even in their coarser outlines. - -Divergent adaptation can very easily be perceived among plants, -especially in creepers. Branches of one and the same creeping plant, -which originally were formed alike, acquire a completely different form -and extent, a completely different degree of curvature and diameter of -spiral winding, according as they twine themselves round a thinner or a -thicker bar. The divergent change of form of parts originally identical -in form, which tending in different directions develop themselves under -different external conditions, can be distinctly demonstrated in many -other examples. As this divergent adaptation interacts with progressive -inheritance, it becomes the cause of a division of labour among the -different organs. - -An eighth and last law of adaptation we may call _the law of unlimited -or infinite adaptation_. By it we simply mean to express that we know of -no limit to the variation of organic forms occasioned by the external -conditions of existence. We can assert of no single part of an organism, -that it is no longer variable, or that if it were subjected to new -external conditions it would not be changed by them. It has never yet -been proved by experience that there is a limit to variation. If, for -example, an organ degenerates from non-use, this degeneration ends -finally in a complete disappearance of the organ, as is the case with -the eyes of many animals. On the other hand, we are able, by continual -practice, habit, and the ever-increasing use of an organ, to bring it to -a degree of perfection which we should at the beginning have considered -to be impossible. If we compare the uncivilized savages with civilized -nations, we find among the former a development of the organs of -sense--sight, smell, and hearing--such as civilized nations can hardly -conceive of. On the other hand, the brain, that is mental activity, -among more civilized nations is developed to a degree of which the wild -savages have no idea. - -There appears indeed to be a limit given to the adaptability of every -organism, by the "type" of its tribe or phylum; that is, by the -essential fundamental qualities of this tribe, which have been inherited -from a common ancestor, and transmitted by conservative inheritance to -all its descendants. Thus, for example, no vertebrate animal can acquire -the ventral nerve-chord of articulate animals, instead of the -characteristic spinal marrow of the vertebrate animals. However, within -this hereditary primary form, within this inalienable type, the degree -of adaptability is unlimited. The elasticity and fluidity of the organic -form manifests itself, within the type, freely in all directions, and to -an unlimited extent. But there are some animals, as, for example, the -parasitically degenerate crabs and worms, which seem to pass even the -limit of type, and have forfeited all the essential characteristics of -their tribe by an astonishing degree of degeneration. As to the -adaptability of man, it is, as in all other animals, also unlimited, and -since it is manifested in him above all other animals, in the -modifications of the brain, there can be absolutely no limit to the -knowledge which man in a further progress of mental cultivation may not -be able to exceed. The human mind, according to the law of unlimited -adaptation, enjoys an infinite perspective of becoming ever more and -more perfect. - -These remarks are sufficient to show the extent of the phenomena of -Adaptation, and the great importance to be attached to them. The laws of -Adaptation, or the facts of Variation caused by the influence of -external conditions, are just as important as the laws of Inheritance. -All phenomena of Adaptation, in the end, can be traced to conditions of -nutrition of the organism, in the same way as the phenomena of -Inheritance are referable to conditions of reproduction; but the latter, -as well as the former, may further be traced to chemical and physical, -that is to mechanical, causes. According to Darwin's Theory of Selection -the new forms of organisms, the transformations which artificial -selection produces in the state of cultivation, and which natural -selection produces in the state of nature, arise solely by the -interaction of such causes. - - - - -CHAPTER XI. - -NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION OF LABOUR AND -PROGRESS. - - - Interaction of the Two Organic Formative Causes, - Inheritance and Adaptation.--Natural and Artificial - Selection.--Struggle for Existence, or Competition for - the Necessaries of Life.--Disproportion between the - Number of Possible or Potential, and the Number of Real - or Actual Individuals.--Complicated Correlations of all - Neighbouring Organisms.--Mode of Action in Natural - Selection.--Homochromic Selection as the Cause of - Sympathetic Colourings.--Sexual Selection as the Cause of - the Secondary Sexual Characters.--Law of Separation or - Division of Labour (Polymorphism, Differentiation, - Divergence of Characters).--Transition of Varieties into - Species.--Idea of Species.--Hybridism.--Law of Progress - or Perfectioning (Progressus, Teleosis). - - -In order to arrive at a right understanding of Darwinism, it is, above -all, necessary that the two organic functions of _Inheritance and -Adaptation_, which we spoke of in our last chapter, should be more -closely examined. If we do not, on the one hand, examine the purely -mechanical nature of these two physiological activities, and the various -action of their different laws, and if, on the other hand, we do not -consider how complicated the interaction of these different laws of -Inheritance and Adaptation must be, we shall not be able to understand -how these two functions, by themselves, have been able to produce all -the variety of animal and vegetable forms, which, in fact, they have. -We have, at least, hitherto been unable to discover any other formative -causes besides these two, and if we rightly understand the necessary and -infinitely complicated interaction of Inheritance and Adaptation, we do -not require to look for other unknown causes for the change of organic -forms. These two fundamental causes are, as far as we can see, -completely sufficient. - -Even long before Darwin had published his Theory of Selection, some -naturalists, and especially Goethe, had assumed the interaction of two -distinct formative tendencies--a conservative or preserving, and a -progressive or changing formative tendency--as the causes of the variety -of organic forms. The former was called by Goethe the centripetal or -specifying tendency, the latter the centrifugal tendency, or the -tendency to metamorphosis (p. 89). These two tendencies completely -correspond with the two processes of Inheritance and Adaptation. -_Inheritance_ is the _centripetal_ or _internal formative tendency_ -which strives to keep the organic form in its species, to form the -descendants like the parents, and always to produce identical things -from generation to generation. _Adaptation_, on the other hand, which -counteracts inheritance, is the _centrifugal_ or _external formative -tendency_, which constantly strives to change the organic forms through -the influence of the varying agencies of the outer world, to create new -forms out of those existing, and entirely to destroy the constancy or -permanency of species. Accordingly as Inheritance or Adaptation -predominates in the struggle, the specific form either remains constant -or changes into a new species. The degree of constancy of form in the -different species of animals and plants, which obtains at any moment, -is simply the necessary result of the momentary predominance which -either of these two formative powers (or physiological activities) has -acquired over the other. - -If we now return to the consideration of the process of selection or -choice, the outlines of which we have already examined, we shall be in a -position to see clearly and distinctly that both artificial and natural -selection rest solely upon the interaction of these two formative -tendencies. If we carefully watch the proceedings of an artificial -selector--a farmer or a gardener--we find that only these two -constructive forces are used by him for the production of new forms. The -whole art of artificial selection rests solely upon a thoughtful and -wise application of the laws of Inheritance and Adaptation, and upon -their being applied and regulated in an artistic and systematic manner. -Here the will of man constitutes the selecting force. - -The case of natural selection is quite similar, for it also employs -merely these two organic constructive forces, these ingrained -physiological properties of Adaptation and Heredity, in order to produce -the different species. But the selecting principle or force, which in -_artificial_ selection is represented by the conscious _will of man_ -acting for a definite purpose, consists in _natural_ selection of the -unconscious _struggle for existence_ acting without a definite plan. -What we mean by "struggle for existence" has already been explained in -the seventh chapter. It is the recognition of this exceedingly important -identity which constitutes one of the greatest of Darwin's merits. But -as this relation is very frequently imperfectly or falsely understood, -it is necessary to examine it now more closely, and to illustrate by a -few examples the operation of the struggle for life, and the operation -of natural selection _by means of_ the struggle for life (Gen. Morph. -ii. 231). - -When considering the struggle for life, we started from the fact that -the number of germs which all animals and plants produce is infinitely -greater than the number of individuals which actually come to life and -remain alive for a longer or shorter time. Most organisms produce during -life thousands or millions of germs, from each of which, under -favourable circumstances, a new individual might arise. In most animals -and plants these germs are eggs, that is cells, which for their -development require sexual fructification. But among the Protista, the -lowest organisms, which are neither animals nor plants, and which -propagate themselves only in a non-sexual manner, the germ-cells, or -spores, require no fructification. Now, in all cases the number of -unsexual, as well as of sexual germs, is out of all proportion to the -number of actually living individuals of every species. - -Taken as a whole, the number of living animals and plants on our earth -remains always about the same. The number of places in the economy of -nature is limited, and in most parts of the earth's surface these places -are always approximately occupied. Certainly there occur everywhere and -in every year fluctuations in the absolute and in the relative number of -individuals of all species. However, taken as a whole, these -fluctuations are of little importance, and it is broadly the fact that -the total number of all individuals remains, on an average, almost -constant. There is a constant fluctuation, which depends on the fact -that in one year or another one or other series of animals and plants -predominates, and that every year the struggle for life somewhat alters -their relations. - -Every single species of animals and plants would have densely peopled -the whole earth's surface in a short time, if it had not had to struggle -against a number of enemies and hostile influences. Even Linnaeus -calculated that if an annual plant only produced two seeds (and there is -not one which produces so few), it would have yielded in twenty years a -million of individuals. Darwin has calculated of elephants, which of all -animals seem the slowest to increase, that in seven hundred and fifty -years the descendants of a single pair would amount to nineteen millions -of individuals; this is supposing that every elephant, during its period -of fertility (from the 30th to the 90th year), produced only three pairs -of young ones, and survived itself to its hundredth year. In like manner -the increase of the number of human beings--if calculated on the average -proportion of births to population, and no hindrances to the natural -increase stood in the way--would be such as to double the total in -twenty-five years. In every century the total number of men would have -increased sixteen-fold; whereas we know that the total number of human -beings increases but slowly, and that the increase of population is very -different in different countries. While European tribes spread over the -whole globe, other tribes or species of men every year draw nearer to -their complete extinction. This is the case especially with the redskins -of America, and with the copper-coloured natives of Australia. Even if -these races were to propagate more abundantly than the white Europeans, -yet they would sooner or later succumb to the latter in the struggle for -life. But of all human individuals, as of all other organisms, by far -the majority perish at the earliest period of their lives. Of the -immense quantity of germs which every species produce, only very few -actually succeed in developing, and of these few it is again only a very -small portion which attain to the age in which they can reproduce -themselves (compare p. 161). - -From the disproportion between the immense excess of organic germs and -the small number of chosen individuals which are actually able to -continue in existence beside one another, there follows of necessity -that universal struggle for life, that constant fight for existence, -that perpetual competition for the necessaries of life, of which I gave -a sketch in my seventh chapter. It is this struggle for life which -brings natural selection into play, which in its turn is made use of by -the interaction of the phenomena of Inheritance and Adaptation as a -sifting agency, and which thus causes a continual change in all organic -forms. In this struggle for acquiring the necessary conditions of -existence, those individuals will always overpower their rivals who -possess any individual privilege, any advantageous quality, of which -their fellow competitors are destitute. It is true we are able only in -the fewest cases (in those animals and plants best known to us) to form -an approximate conception of the infinitely complicated interaction of -the numerous circumstances, all of which here come into combination. -Only think how infinitely varied and complicated are the relations of -every single human being to the rest of mankind, and in general, to the -whole of the surrounding outer world. But similar relations prevail also -among all animals and plants which live together in one place. All -influence one another actively or passively. Every animal and every -plant struggles directly with a number of enemies, beasts of prey, -parasitic animals, etc. Plants standing together struggle with one -another for the space of ground requisite for their roots, for the -necessary amount of light, air, moisture, etc. In like-manner, animals -living together struggle with one another for their food, -dwelling-place, etc. In this most active and complicated struggle, any -personal superiority, however small, any individual advantage, may -possibly decide the issue in favour of the one possessing it. This -privileged individual remains the victor in the struggle, and propagates -itself, while its fellow-competitors perish before they succeed in -propagating themselves. The personal advantage which gave it the victory -is transmitted by inheritance to its descendants, and by a further -development may become so strongly marked as to cause us to consider the -later generations as a new species. - -The infinitely complicated correlations which exist between the -organisms of every district, and which must be looked upon as the real -conditions of the struggle for life, are mostly unknown to us, and are -very difficult to discover. We have hitherto been able to trace them -only to a certain point in individual cases, as in the example given by -Darwin of the relations between cats and red clover in England. The red -clover (_Trifolium pratense_), which in England is among the best fodder -for cattle, requires the visit of humming-bees in order to attain the -formation of seeds. These insects, while sucking the honey from the -bottom of the flower, bring the pollen in contact with the stigma, and -thus cause the fructification of the flower, which never takes place -without it. Darwin has shown by experiments, that red clover which is -not visited by humming-bees does not yield a single seed. The number of -bees is determined by the number of their enemies, the most destructive -of which are the field-mice. The more the field-mice predominate, the -less the clover is fructified. The number of field-mice, again, is -dependent upon the number of their enemies, principally cats. Hence in -the neighbourhood of villages and towns, where many cats are kept, there -are plenty of bees. A great number of cats, therefore, is evidently of -great advantage for the fructification of clover. This example may be -followed still further, as has been done by Carl Vogt, if we consider -that cattle which feed on red clover are one of the most important -foundations of the wealth of England. Englishmen preserve their bodily -and mental powers chiefly by making excellent meat--roast beef and -beefsteak--their principal food. The English owe the superiority of -their brains and minds over those of other nations in a great measure to -their excellent meat. But this is clearly indirectly dependent upon the -cats, which pursue the mice. We may, with Huxley, even trace the chain -of causes to those old maids who cherish and keep cats, and, -consequently, are of the greatest importance to the fructification of -the clover and to the prosperity of England. From this example we can -see that the further it is traced the wider is the circle of action and -of correlation. We can with certainty maintain that there exist a great -number of such correlations in every plant and in every animal, only we -are not always able to point out and survey their concatenation as in -the last instance. - -Another remarkable example of important correlations is the following, -given by Darwin. In Paraguay, there are no wild oxen and horses, as in -the neighbouring parts of South America, both north and south of -Paraguay. This surprising circumstance is explained simply by the fact -that in that country a kind of small fly is very frequent, and is in the -habit of laying its eggs in the navel of newly-born calves and foals. -The newly-born animals die in consequence of this attack, and the small -deadly fly is therefore the cause of oxen and horses never becoming wild -in that district. Supposing that this fly were destroyed by some -insect-eating bird, then these large mammals would grow wild in -Paraguay, as well as in the neighbouring parts of South America; and as -they would eat a quantity of certain species of plants, the whole flora, -and, consequently again, the whole fauna of the country would become -changed. It is hardly necessary to state, that at the same time the -whole economy, and consequently the character, of the human population -would alter. - -Thus the prosperity, nay, even the existence of whole populations can be -indirectly determined by a single small animal or vegetable form in -itself extremely insignificant. There are small coral islands whose -human inhabitants live almost entirely upon the fruit of a species of -palm. The fructification of this palm is principally effected by -insects, which carry the pollen from the male to the female palm trees. -The existence of these useful insects is endangered by insect-eating -birds, which in their turn are pursued by birds of prey. The birds of -prey, however, often succumb to the attack of a small parasitical mite, -which develops itself in millions in their feathers. This small, -dangerous parasite, again, may be killed by parasitical moulds. Moulds, -birds of prey, and insects would in this case favour the prosperity of -the palm, and consequently of man; birds, mites, and insect-eating birds -would, on the other hand, endanger it. - -Interesting examples in relation to the change of correlations in the -struggle for life are furnished also by those isolated oceanic islands, -uninhabited by man, on which at different times goats and pigs have been -placed by navigators. These animals become wild, and having no enemies, -they increase in number so excessively, that the rest of the animal and -vegetable population suffer in consequence, and the island finally may -become almost a waste, because there is insufficient food for the large -mammals which increase too numerously. In some cases on an island thus -overrun with goats and pigs, other navigators have let loose a couple of -dogs, who enjoyed this superabundance of food, and they again increased -so numerously, and made such havoc among the herds, that after several -years the dogs themselves lacked food, and they also almost died out. -The equilibrium of species continually changes in this manner in -nature's economy, accordingly as one or another species increases at the -expense of the rest. In most cases the relations of different species of -animals and plants to one another are much too complicated for us to be -able to follow them, and I leave it to the reader to picture to himself -what an infinitely complicated machinery is at work in every part of the -world in consequence of this struggle. The impulses which started the -struggle, and which altered and modified it in different places, are in -the end seen to be the impulses of self-preservation--in fact, the -instinct leading individuals to preserve themselves (the instinct of -obtaining food), and the instinct leading them to preserve the species -(instinct of propagation). It is these two fundamental instincts of -organic self-preservation of which Schiller, the idealist (not Goethe, -the realist!) says: - - "Meanwhile, until philosophy - Sustains the structure of the world, - Her workings will be carried on - By hunger and by love."[4] - -It is these two powerful fundamental instincts which, by their varying -activity, produce such extraordinary differences in species through the -struggle for life. They are the foundations of the phenomena of -Inheritance and Adaptation. We have, in fact, traced all phenomena of -Inheritance to propagation, all phenomena of Adaptation to nutrition, as -the two wider classes of material phenomena to which they belong. - -The struggle for life in natural selection acts with as much selective -power as does the will of man in artificial selection. The latter, -however, acts according to a plan and consciously, the former without a -plan and unconsciously. This important difference between artificial and -natural selection deserves especial consideration. For we learn by it to -understand how _arrangements serving a purpose can be produced by -mechanical causes acting without an object, as well as by causes acting -for an object_. The products of natural selection are arranged even more -for a purpose than the artificial products of man, and yet they owe -their existence not to a creative power acting for a definite purpose, -but to a mechanical relation acting unconsciously and without a plan. -If we had not thoroughly considered the interaction of Inheritance and -Adaptation under the influence of the struggle for life, we should not -at first be inclined to expect such results from this natural process of -selection as are, in fact, furnished by it. It may therefore be -appropriate here to mention a few especially striking examples of the -activity of natural selection. - -Let us first take _Darwin's homochromic selection_ of animals, or the -so-called "sympathetic selection of colours," into consideration. -Earlier naturalists have remarked that numerous animals are of nearly -the same colour as their dwelling-place, or the surroundings in which -they permanently live. Thus, for example, plant-lice and many other -insects living on leaves are of a green colour. The inhabitants of the -deserts, the jerboa, or leaping mice, foxes of the desert, gazelles, -lions, etc., are mostly of a yellow or yellowish-brown colour, like the -sand of the desert. The polar animals, which live on the ice and snow, -are white or grey, like ice and snow. Many of these animals change their -colour in summer and winter. In summer, when the snow partly vanishes, -the fur of these polar creatures becomes brownish-grey or blackish, like -the naked earth, while in winter it again becomes white. Butterflies and -insects which hover round the gay and bright flowers are like them in -colour. Now, Darwin explains this surprising circumstance quite simply -by the fact that such colours as agree with the colour of the habitation -are of the greatest use to the animals concerned. If these animals are -animals of prey, they will be able to approach the object of their -pursuit more safely and with less likelihood of observation, and, in -like manner, those animals which are pursued will be able to escape -more easily, if their colour is as little different as possible from -that of their surroundings. If therefore originally an animal species -varied so as to present cases of all colours, those individuals whose -colour most resembled the surroundings must have been most favoured in -the struggle for life. They remained more unobserved, maintained and -propagated themselves, while those individuals or varieties differently -coloured died out. - -I have tried to explain, by the same sympathetic selection of colour, -the wonderful fact that the majority of pelagic animals--that is, of -those which live on the surface of the open sea--are bluish, or -completely colourless and transparent, like glass and water itself. Such -colourless, glassy animals are met with in the most different classes. -To them belong, among fish, the Helmicthyidae, through whose crystalline -bodies the words of a book can be read; among the molluscs, the finned -snails (Heteropods) and sea-butterflies, or whales-food (Pteropods); -among worms, the Salpae, Alciope, and Sagitta; further, a great number of -pelagic crabs (Crustacea), and the greater part of the Medusae -Umbrella-jellies, (Discomedusae); Comb-jellies, (Ctenophora). All of -these pelagic animals, which float on the surface of the ocean, are -transparent and colourless, like glass and like the water itself, while -their nearest kin live at the bottom of the ocean, and are coloured and -opaque like the inhabitants of the land. This remarkable fact, like the -sympathetic colouring of the inhabitants of the earth, can be explained -by natural selection. Among the ancestors of the pelagic glass-like -animals which showed a different degree of colourlessness and -transparency, those that were the most colourless and transparent must -have been most favoured in the active struggle for life which takes -place on the surface of the ocean. They were enabled to approach their -prey the most easily unobserved, and were themselves least observed by -their enemies. Hence they could preserve and propagate themselves more -easily than their more coloured and opaque relatives; and finally, by -accumulative adaptation and transmission by inheritance, through natural -selection, in the course of many generations their bodies would attain -that degree of crystal-like transparency and colourlessness which we at -present admire in them. (Gen. Morph. ii. 242.) - -No less interesting and instructive than homochromic selection is that -species of natural selection which Darwin calls "_sexual selection_," -which explains the origin of the so-called "secondary sexual -characters." We have already mentioned these subordinate sexual -characteristics, so instructive in many respects. They comprise those -peculiarities of animals and plants which belong only to one of the two -sexes, and which do not stand in any direct relation to the act of -propagation itself (compare above, p. 244). Such secondary sexual -characters occur in great variety among animals. We all know how -striking is the difference of the two sexes in size and colour in many -birds and butterflies. The male sex is generally the larger and more -beautiful. It often possesses special decorations or weapons; as for -example, the spur and comb of the cock, the antlers of the stag and -deer, etc. All these peculiarities of the two sexes have nothing -directly to do with propagation itself, which is effected by the -"primary sexual characters," or actual sexual organs. - -Now, the origin of these remarkable "secondary sexual characters" is -explained by Darwin simply by a choice or selection which takes place -in the propagation of animals. In most animals the number of individuals -of both sexes is unequal; either the number of the female or the number -of the male individuals is greater, and, as a rule, when the season of -propagation approaches, a struggle takes place between the rivals for -the possession of the animals of the other sex. It is well known with -what vigour and vehemence this struggle is fought out among the higher -animals--among mammals and birds--especially among those of polygamous -habits. Among gallinaceous birds, where for one cock there are several -hens, a severe struggle takes place between the competing cocks for as -large a harem as possible. The same is the case with many ruminating -animals. Among stags and deer, for instance, at the period of rut, -deadly struggles take place between the males for the possession of the -females. The secondary sexual character which here distinguishes the -males--the antlers of stags and deer--not possessed by the female, is, -according to Darwin, the consequence of that struggle. Here the motive -and cause determining the struggle is not, as in the case of the -struggle for individual existence, self-preservation, but the -preservation of the species--propagation. There are numerous passive -weapons of defence, as well as active weapons for attack. The lion's -mane, not possessed by the female, is evidently such a weapon of -defence; it is an excellent means of protection against the bites which -the male lions try to inflict on each other's necks when fighting for -the females; consequently those males with the strongest manes have the -greatest advantage in the sexual struggle. The dewlap of the ox and the -comb of the cock are similar defensive weapons. Active weapons of -attack, on the other hand, are the antlers of the stag, the tusks of -the boar, the spur of the cock, and the hugely developed pair of jaws in -the male stag-beetle; all are instruments employed by the males in the -struggle for the females, for annihilating or chasing away their rivals. - -In the cases just mentioned, it is the bodily "struggle to the death" -which determines the origin of the secondary sexual characters. But, -besides these mortal struggles, there are other important competitions -in sexual selection, which no less influence the structure of the -rivals. These consist principally in the fact that the courting sex -tries to please the other by external finery, by beauty of form, or by a -melodious voice. Darwin thinks that the beautiful voices of singing -birds have principally originated in this way. Many male birds carry on -a regular musical contest when they contend for the possession of the -females. It is known of several singing birds, that in the breeding -season the males assemble in numbers round the females, and let their -songs resound before them, and that then the females choose the singers -who best please them for their mates. Among other songsters, individual -males pour out their songs in the loneliness of the forest in order to -attract the females, and the latter follow the most attractive calls. A -similar musical contest, though certainly less melodious, takes place -among crickets and grasshoppers. The male cricket has on its belly two -instruments like drums, and produces with these the sharp chirping notes -which the ancient Greeks curiously enough thought beautiful music. Male -grasshoppers, partly by using their hind-legs like the bow of a violin -against their wing coverings, and partly by rubbing their wing coverings -together, bring out tones which are, indeed, not melodious to us, but -which please the female grasshoppers so much that they choose the male -who fiddles the best. - -Among other insects and birds it is not song or, in fact, any musical -accomplishment, but finery or beauty of the one sex which attracts the -other. Thus we find that, among most gallinaceous birds, the cocks are -distinguished by combs on their heads, or by a beautiful tail, which -they can spread out like a fan; as for example, in the case of the -peacock and turkey-cock. The magnificent tail of the bird of paradise is -also an exclusive ornament of the male sex. In like manner, among very -many other birds and very many insects, principally among butterflies, -the males are distinguished from the females by special colours or other -decorations. These are evidently the results of sexual selection. As the -females do not possess these attractions and decorations, we must come -to the conclusion that they have been acquired by degrees by the males -in the competition for the females, which takes its origin in the -selective discrimination of the females. - -We may easily picture to ourselves, in detail, the application of this -interesting conclusion to the human community. Here, also, the same -causes have evidently influenced the development of the secondary sexual -characters. The characteristics distinguishing the man, as well as those -distinguishing the woman, owe their origin, certainly for the most part, -to the sexual selection of the other sex. In antiquity and in the Middle -Ages, especially in the romantic age of chivalry, it was the bodily -struggles to the death--the tournaments and duels--which determined the -choice of the bride; the strongest carried home the bride. In more -recent times, however, in our so-called "polished" or "highly -civilized" society, competing rivals prefer to contend indirectly by -means of musical accomplishments, instrumental performances and song, by -bodily charms, natural beauty, or artificial decoration. But by far the -most important of these different forms of sexual selection in man is -that form which is the most exalted, namely, _psychical selection_, in -which the mental excellencies of the one sex influence and determine the -choice of the other. The most highly intellectually developed types of -men have, throughout generations, when choosing a partner in life, been -guided by her excellencies of soul, and have thus transmitted these -qualities to their posterity, and they have in this way, more than by -any other thing, helped to create the deep chasm which at present -separates civilized men from the rudest savages, and from our common -animal ancestors. In fact, both the part played by the prevalence of a -higher standard of sexual selection, and the part played by the due -division of labour between the two sexes, is exceedingly important, and -I believe that here we must seek for the most powerful causes which have -determined the origin and the historical development of the races of -man. (Gen. Morph. ii. 247.) As Darwin, in his exceedingly interesting -work, published in 1871, on "The Origin of Man and Sexual -Selection,"(48) has discussed this subject in the most masterly manner, -and has illustrated it by most remarkable examples, I refer for further -detail to that work. - -But now let us look again at two extremely important organic laws which -can be explained by the theory of selection, as necessary consequences -of natural selection in the struggle for existence. I mean the law of -_division of labour_, or _differentiation_, and the law of _progress_, -or _perfecting_. When the phenomena due to these two laws first became -known, through observation of the historical development, the individual -development, and the comparative anatomy of animals and plants, -naturalists were inclined to trace them to a direct creative influence. -It was supposed to be part of the plan of the Creator, acting for a -definite purpose, in the course of time to develop the forms of animals -and plants more and more variously, and to bring them more and more to a -state of perfection. We shall evidently make a great advance in the -knowledge of nature if we reject this teleological and anthropomorphic -conception, and if we can prove the two laws of Division of Labour and -Perfecting to be the necessary consequences of natural selection in the -struggle for life. - -The first great law which follows directly and of necessity from natural -selection, is that of _separation_, or _differentiation_, which is -frequently called _division of labour_, or _polymorphism_, and which -Darwin speaks of as _divergence of character_. (Gen. Morph. ii. 249.) We -understand by it the general tendency of all organic individuals to -develop themselves more and more diversely, and to deviate from the -common primary type. The cause of this general inclination towards -differentiation and the formation of heterogeneous forms from -homogeneous beginnings is, according to Darwin, simply to be traced to -the circumstance that the struggle for life between every two organisms -rages all the more fiercely the nearer the relation in which they stand -to one another, or the more nearly alike they are. This is an -exceedingly important, and in reality an exceedingly simple relation, -but it is usually not duly considered. - -It must be obvious to every one, that in a field of a certain size, -beside the corn-plants which have been sown, a great number of weeds -can exist, and, moreover, in places which could not have been occupied -by corn-plants. The more dry and sterile places of the ground, in which -no corn-plant would thrive, may still furnish sustenance to weeds of -different kinds; and such species and individuals of weeds will more -readily be able to exist in such conditions, in proportion as they are -suited to adapt themselves to the different parts of the ground. It is -the same with animals. It is evident that a much greater number of -animal individuals can live together in one and the same limited -district, if they are of various and different natures, than if they are -all alike. There are trees (for example, the oak) on which a couple of -hundred of different species of insects live together. Some feed on the -fruits of the tree, others on the leaves, others again on the bark, the -root, etc. It would be quite impossible for an equal number of -individuals to live on this tree if all were of one species; if, for -example, all fed on the bark, or only upon the leaves. Exactly the same -is the case in human society. In one and the same small town, only a -certain number of workmen can exist, even when they follow different -occupations. The division of labour, which is of the greatest use to the -whole community, as well as to the individual workman, is a direct -consequence of the struggle for life, of natural selection; for this -struggle can be sustained more easily the more the activities, and -hence, also, the forms of the different individuals deviate from one -another. The different function naturally produces its reaction in -changing the form, and the physiological division of labour necessarily -determines the morphological differentiation, that is, the "divergence -of character."(37) - -Now, I beg the reader again to remember that all species of animals and -plants are variable, and possess the capability of adapting themselves -to different places or to local relations. The varieties or races of -each species, according to the laws of adaptation, deviate all the more -from the original primary species, the greater the difference of the new -conditions to which they adapt themselves. If we imagine these -varieties--which have proceeded from a common primary form--to be -disposed in the shape of a branching, radiating bunch, then those -varieties will be best able to exist side by side and propagate which -are most distant from one another, which stand at the ends of the -series, or at the opposite sides of the bunch. Those forms, on the other -hand, occupying a middle position--presenting a state of -transition--have the most difficult position in the struggle for life. -The necessaries of life differ most in the two extremes, in the -varieties most distant from one another, and consequently these will get -into the least serious conflict with one another in the general struggle -for life. But the intermediate forms, which have deviated less from the -original primary form, require nearly the same necessaries of life as -the original form, and therefore, in competing for them, they will have -to struggle most with, and be most seriously threatened by, its members. -Consequently, when numerous varieties of a species live side by side on -the same spot of the earth, the extremes, or those forms deviating most -from one another, can much more easily continue to exist beside one -another than the intermediate forms which have to struggle with each of -the different extremes. The intermediate forms will not be able to -resist, for any length of time, the hostile influences which the extreme -forms victoriously overcome. These alone maintain and propagate -themselves, and at length cease to be any longer connected with the -original primary species through intermediate forms of transition. Thus -arise "good species" out of varieties. Thus, then, the struggle for life -necessarily favours the general divergence of organic forms, that is, -the constant tendency of organisms to form new species. This fact does -not rest upon any mystic quality, or upon an unknown formative tendency, -but upon the interaction of Inheritance and Adaptation in the struggle -for life. As the intermediate forms, that is, the individuals in a state -of transition, of the varieties of every species die out and become -extinct, the process of divergence constantly goes further, and from the -extremes forms develop which we distinguish as new species. - -Although all naturalists have been obliged to acknowledge the -variability and mutability of all species of animals and plants, yet -most of them have hitherto denied that the modification or -transformation of the organic form surpasses the original limit of the -characters of the species. Our opponents cling to the -proposition--"However far a species may exhibit deviations from its -usual form in a collection of varieties, yet the varieties of it are -never so distinct from one another as two really good species." This -assertion, which Darwin's opponents usually place at the head of their -arguments, is utterly untenable and unfounded. This will become quite -clear as soon as we critically compare the various attempts to define -the idea of species. No naturalist can answer the question as to what is -in reality a "genuine or good species" ("bona species"); yet every -systematic naturalist uses this expression every day, and whole -libraries have been written on the question as to whether this or that -observed form is a species or a variety, whether it is a really good or -a bad species. The most general answer to this question used to be the -following: "To one species belong all those individuals which agree in -all essential characteristics. Essential characteristics of species are -those which remain permanent or constant, and never become modified or -vary." But as soon as a case occurred in which the characteristic--which -had hitherto been considered essential--did become modified, then it was -said, "This characteristic is not essential to the species, for -essential characteristics never vary." Those who argued thus evidently -moved in a circle, and the naivete with which this circular method of -defining species is laid down in thousands of books as an unassailable -truth, and is still constantly repeated, is truly astonishing. - -All other attempts which have been made to arrive at a definite and -logical determination of the idea of organic "species" have, like the -last, been utterly futile, and led to no results. Considering the nature -of the case, it cannot be otherwise. The idea of species is just as -truly a relative one and not absolute, as is the idea of variety, genus, -family, order, class, etc. I have proved this in detail in the criticism -of the idea of species in my "General Morphology" (Gen. Morph. ii. -323-364). I will waste no more time on this unsatisfactory discussion, -and now only add a few words about the _relation of species to -hybridism_. Formerly it was regarded as a dogma, that two good species -could never produce hybrids which could reproduce themselves as such. -Those who thus dogmatized almost always appealed to the hybrids of a -horse and donkey, the mule and the hinny, which, truly enough, are -seldom able to reproduce themselves. But the truth is that such -unfruitful hybrids are rare examples, and in the majority of cases -hybrids of two totally different species are fruitful and able to -reproduce themselves. They can almost always fruitfully mix with one or -other of the parent species, and sometimes also among themselves; and in -this way completely new forms can originate according to the laws of -"mixed transmission by inheritance." - -Thus, in fact, _hybridism is a source of the origin of new species_, -distinct from the source we have hitherto considered--natural selection. -I have already spoken occasionally of these _hybrid species_ (species -hybridae), especially of the hare-rabbit (Lepus Darwinii), which has -arisen from the crossing of a male hare and a female rabbit; the -goat-sheep (Capra ovina), which has arisen from the pairing of a he-goat -and ewe; also the different species of thistles (Cirsium), brambles -(Rubus), etc. It is possible that many wild species have originated in -this way, as even Linnaeus assumed. At all events, these hybrid species, -which can maintain and propagate themselves as well as pure species, -prove that hybridism cannot serve in any way to give an absolute -definition to the idea of species. - -I have already mentioned (p. 47) that the many vain attempts to define -the idea of species theoretically have nothing whatever to do with the -practical distinction of species. The extensive practical application of -the idea of species, as it is carried out in systematic zoology and -botany, is very instructive as furnishing an example of human folly. -Hitherto, by far the majority of zoologists and botanists, in -distinguishing and describing the different forms of animals and plants, -have endeavoured, above all things, to distinguish accurately kindred -forms as so many "good species." However, it has been found scarcely -possible, in any group, to make an accurate and consistent distinction -of such "genuine or good species." There are no two zoologists, no two -botanists, who agree in all cases as to which of the nearly related -forms of a genus are good species, and which are not. All authors have -different views about them. In the genus _Hieracium_, for example, one -of the commonest genera of European plants, no less than 300 species -have been distinguished in Germany alone. The botanist Fries, however, -only admits 106, Koch only 52, as "good species," and others accept -scarcely 20. The differences in the species of brambles (Rubus) are -equally great. Where one botanist makes more than a hundred species, a -second admits only about one half of that number, a third only five or -six, or even fewer species. The birds of Germany have long been very -accurately known. Bechstein, in his careful "Natural History of German -Birds," has distinguished 367 species, L. Reichenbach 379, Meyer and -Wolff 406, and Brehm, a clergyman learned in ornithology, distinguishes -even more than 900 different species. - -Thus we see that here, and, in fact, in every other domain of systematic -zoology and botany, the most arbitrary proceedings prevail, and, from -the nature of the case, must prevail. For it is quite impossible -accurately to distinguish varieties and races from so-called "good -species." _Varieties are commencing species._ The variability or -adaptability of species, under the influence of the struggle for life, -necessitates the continual and progressive separation or differentiation -of varieties, and the perpetual delimitation of new forms. Whenever -these are maintained throughout a number of generations by inheritance, -whilst the intermediate forms die out, they form independent "new -species." The origin of new species by division of labour, or -separation, divergence, or differentiation of varieties, is therefore a -_necessary consequence of natural selection_.(37) - -The same kind of interest attaches to a second great law which we deduce -from natural selection, and which is, indeed, closely connected with the -law of Divergence, but in no way identical with it; namely, the law of -_Progress_ (progressus), or _Perfecting_ (teleosis). (Gen. Morph. ii. -257.) This great and important law, like the law of differentiation, had -long been empirically established by palaeontological experience, before -Darwin's Theory of Selection gave us the key to the explanation of its -cause. The most distinguished palaeontologists have pointed out the law -of progress as the most general result of their investigations of fossil -organisms. This has been specially done by Bronn, whose investigations -on the laws of construction(18) and the laws of the development(19) of -organisms, although little heeded, are excellent, and deserve most -careful consideration. The general results of the law of differentiation -and the law of progress, at which Bronn arrived by a purely mechanical -hypothesis, and by exceedingly accurate, laborious, and careful -investigations, are brilliant confirmations of the truth of these two -great laws which we deduce as necessary inferences from the theory of -selection. - -The law of progress or of perfecting establishes the exceedingly -important fact, on the ground of palaeontological experience, that in -successive periods of this earth's history, a continual increase in the -perfection of organic formations has taken place. Since that -inconceivably remote period in which life on our planet began with the -spontaneous generation of Monera, organisms of all groups, both -collectively as well as individually, have continually become more -perfectly and highly developed. The steadily increasing variety of -living forms has always been accompanied by progress in organization. -The lower the strata of the earth in which the remains of extinct -animals and plants lie buried, that is, the older the strata are, the -more simple and imperfect are the forms which they contain. This applies -to organisms collectively, as well as to every single large or small -group of them, setting aside, of course, those exceptions which are due -to the process of degeneration, which we shall discuss hereafter. - -As a confirmation of this law I shall mention only the most important of -all animal groups, the tribe of vertebrate animals. The oldest fossil -remains of vertebrate animals known to us belong to the lowest class, -that of Fishes. Upon these there followed later more perfect Amphibious -animals, then Reptiles, and lastly, at a much later period, the most -highly organized classes of vertebrate animals, Birds and Mammals. Of -the latter only the lowest and most imperfect forms, without placenta, -appeared at first, such as are the pouched animals (Marsupials), and -afterwards, at a much later period, the more perfect mammals, with -placenta. Of these, also, at first only the lower kinds appeared, the -higher forms later; and not until the late tertiary period did man -gradually develop out of these last. - -If we follow the historical development of the vegetable kingdom we -shall find the same law operative there. Of plants there existed at -first only the lowest and most imperfect classes, the Algae or tangles. -Later there followed the group of Ferns or Filicinae (ferns, pole-reeds, -scale-plants, etc.). But as yet there existed no flowering plants, or -Phanerogama. These originated later with the Gymnosperms (firs and -cycads), whose whole structure stands far below that of the other -flowering plants (Angiosperms), and forms the transition from the group -of fern-like plants to the Angiosperms. These latter developed at a -still later date, and among them there were at first only flowering -plants without corolla (Monocotyledons and Monochlamyds); only later -were there flowering plants with a corolla (Dichlamyds). Finally, again, -among these the lower polypetalous plants preceded the higher -gamopetalous plants. The whole series thus constitutes an irrefutable -proof of the great law of progressive development. - -Now, if we ask what is the cause of this fact, we again, just as in the -case of differentiation, come back to natural selection in the struggle -for life. If once more we consider the whole process of natural -selection, how it operates through the complicated interaction of the -different laws of Inheritance and Adaptation, we shall recognize not -only divergence of character, but also the perfecting of structure to be -the direct and necessary result of it. We can trace the same thing in -the history of the human race. Here, too, it is natural and necessary -that the progressive division of labour constantly furthers mankind, and -urges every individual branch of human activity into new discoveries and -improvements. This progress itself universally depends on -differentiation, and is consequently, like it, a direct result of -natural selection in the struggle for life. - - - - -CHAPTER XII. - -LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS. PHYLOGENY AND -ONTOGENY. - - - Laws of the Development of Mankind: Differentiation and - Perfecting.--Mechanical Cause of these two Fundamental - Laws.--Progress without Differentiation, and - Differentiation without Progress.--Origin of Rudimentary - Organs by Non-use and Discontinuance of - Habit.--Ontogenesis, or Individual Development of - Organisms.--Its General Importance.--Ontogeny, or the - Individual History of Development of Vertebrate Animals, - including Man.--The Fructification of the Egg.--Formation - of the three Germ Layers.--History of the Development of - the Central Nervous System, of the Extremities, of the - Branchial Arches, and of the Tail of Vertebrate - Animals.--Causal Connection and Parallelism of - Ontogenesis and Phylogenesis, that is of the Development - of Individuals and Tribes.--Causal Connection of the - Parallelism of Phylogenesis and of Systematic - Development.--Parallelism of the three Organic Series of - Development. - - -If man wishes to understand his position in nature, and to comprehend as -natural facts his relations to the phenomena of the world cognisable by -him, it is absolutely necessary that he should compare human with -extra-human phenomena, and, above all, with animal phenomena. We have -already seen that the exceedingly important physiological laws of -Inheritance and Adaptation apply to the human organism in the same -manner as to the animal and vegetable kingdoms, and in both cases -interact with one another. Consequently, natural selection in the -struggle for life acts so as to transform human society, just as it -modifies animals and plants, and in both cases constantly produces new -forms. The comparison of the phenomena of human and animal -transformation is especially interesting in connection with the laws of -divergence and progress, the two fundamental laws which, at the end of -the last chapter, we proved to be direct and necessary consequences of -natural selection in the struggle for life. - -A comparative survey of the history of nations, or what is called -"universal history," will readily yield to us, as the first and most -general result, evidence of a continually _increasing variety_ of human -activities, both in the life of individuals and in that of families and -states. This differentiation or separation, this constantly increasing -divergence of human character and the form of human life, is caused by -the ever advancing and more complete division of labour among -individuals. While the most ancient and lowest stages of human -civilization show us throughout the same rude and simple conditions, we -see in every succeeding period of history, among different nations, a -greater variety of customs, practices, and institutions. The increasing -division of labour necessitates an increasing variety of forms -corresponding to it. This is expressed even in the formation of the -human face. Among the lowest tribes of nations, most of the individuals -resemble one another so much that European travellers often cannot -distinguish them at all. With increasing civilization the physiognomy of -individuals becomes differentiated, and finally, among the most highly -civilized nations, the English and Germans, the divergence in the -characters of the face is so great that we very rarely mistake one face -for another. - -The second great fundamental law which is obvious in the history of -nations is the great law of progress or perfecting. Taken as a whole, -the history of man is the history of his _progressive development_. It -is true that everywhere and at all times we may notice individual -retrogressions, or observe that crooked roads towards progress have been -taken, which lead only towards one-sided and external perfecting, and -thus deviate more and more from the higher goal of internal and enduring -perfecting. However, on the whole, the movement of development of all -mankind is and remains a progressive one, inasmuch as man continually -removes himself further from his ape-like ancestors, and continually -approaches nearer to his own ideal. - -Now, if we wish to know what causes actually determine these two great -laws of development in man, namely, the law of divergence and the law of -progress, we must compare them with the corresponding laws of -development in animals, and on a close examination we shall inevitably -come to the conclusion that the phenomena, as well as their causes, are -exactly the same in the two cases. The course of development in man, -just as in that of animals, being directed by the two fundamental laws -of differentiation and perfecting, is determined solely by purely -mechanical causes, and is solely the necessary consequence of natural -selection in the struggle for life. - -Perhaps in the preceding discussion the question has presented itself to -some--"Are not these two laws identical? Is not progress in all cases -necessarily connected with divergence?" This question has often been -answered in the affirmative, and Carl Ernst Baer, for example, one of the -greatest investigators in the domain of the history of development, has -set forth the following proposition as one of the principal laws in the -ontogenesis of the animal body:--"The degree of development (or -perfecting) depends on the stage of separation (or differentiation) of -the parts."(20) Correct as this proposition may be on the whole, yet it -is not universally true. In many individual cases it can be proved that -divergence and progress by no means always coincide. _Every progress is -not a differentiation, and every differentiation is not a progress._ - -Naturalists, guided by purely anatomical considerations, had already set -forth the law relating to progress in organization, that the perfecting -of an organism certainly depends, for the most part, upon the division -of labour among the individual organs and parts of the body, but that -there are also other organic transformations which determine a progress -in organization. One, in particular, which has been generally -recognized, is the _numerical diminution of identical parts_. If, for -example, we compare the lower articulated animals of the crustacean -group, which possess numerous pairs of legs, with spiders which never -have more than four pairs of legs, and with insects which always possess -only three pairs of legs, we find this law, for which a great number of -examples could be adduced, confirmed. The numerical diminution of pairs -of legs is a progress in the organization of articulated animals. In -like manner the numerical diminution of corresponding vertebral joints -in the trunk of vertebrate animals is a progress in their organization. -Fishes and amphibious animals with a very large number of identical -vertebral joints are, for this very reason, less perfect and lower than -birds and mammals, in which the vertebral joints, as a whole, are not -only very much more differentiated, but in which the number of -corresponding vertebrae is also much smaller. Further, according to the -same law of numerical diminution, flowers with numerous stamens are more -imperfect than the flowers of kindred plants with a smaller number of -stamens, etc. If therefore originally a great number of homogeneous -parts exist in an organic body, and if, in the course of very many -generations, this number be gradually decreased, this transformation -will be an example of perfecting. - -Another law of progress, which is quite independent of differentiation, -nay, even appears to a certain extent opposed to it, is the law of -_centralization_. In general the whole organism is the more perfect the -more it is organized as a unit, the more the parts are subordinate to -the whole, and the more the functions and their organs are centralized. -Thus, for example, the system of blood-vessels is most perfect where a -centralized heart exists. In like manner, the dense mass of marrow which -forms the spinal cord of vertebrate animals, and the ventral cord of the -higher articulated animals, is more perfect than the decentralized chain -of ganglia of the lower articulated animals, and the scattered system of -ganglia in the molluscs. Considering the difficulty of explaining these -complicated laws of progress in detail, I cannot here enter upon a -closer discussion of them, and must refer to Bronn's excellent -"Morphologischen Studien," and to my "General Morphology" (Gen. Morph. -i. 370, 550; ii. 257-266). - -Just as we have become acquainted with phenomena of progress, quite -independent of divergence, so we shall, on the other hand, very often -meet with divergencies which are not perfecting, but which are rather -the contrary, that is retrogressions or degenerations. It is easy to see -that the changes which every species of animal and plant experiences -cannot always be improvements. But rather many phenomena of -differentiation, which are of direct advantage to the organism itself, -are yet, in a wider sense, detrimental, inasmuch as they lessen its -general capabilities. Frequently a relapse to simpler conditions of life -takes place, and by adaptation to them a divergence in a retrograde -direction. If, for instance, organisms which have hitherto lived -independently accustom themselves to a parasitical life, they thereby -degenerate or retrograde. Such animals, which hitherto had possessed a -well-developed nervous system and quick organs of sense, as well as the -power of moving freely, lose these when they accustom themselves to a -parasitical mode of life; they consequently retrograde more or less. -There the differentiation viewed by itself is a degeneration, although -it is advantageous to the parasitical organism. In the struggle for life -such an animal, which has accustomed itself to live at the expense of -others, by retaining its eyes and apparatus of motion, which are of no -more use to it, would only expend so much material uselessly; and when -it loses these organs, then a great quantity of nourishment which was -employed for the maintenance of these parts, benefits other parts. In -the struggle for life between the different parasites, therefore, those -which make least pretensions will have advantage over the others, and -this favours their degeneration. - -Just as this is found to be the case with the whole organism, so it is -also with the parts of the body of an individual organism. A -differentiation of parts, which leads to a partial degeneration, and -finally even to the loss of individual organs, is, when looked at by -itself, a degeneration, but yet may be advantageous to the organism in -the struggle for life. It is easier to fight when useless baggage is -thrown aside. Hence we meet everywhere, in the more highly-developed -animal and vegetable bodies, processes of divergence, the essence of -which is that they cause the degeneration, and finally the loss, of -particular parts. And at this point the most important and instructive -of all the series of phenomena bearing upon the history of organisms -presents itself to us, namely, that of _rudimentary or degenerate -organs_. - -It will be remembered that even in my first chapter I considered this -exceedingly remarkable series of phenomena, from a theoretical point of -view, as one of the most important and most striking proofs of the truth -of the doctrine of descent. We designated as rudimentary organs those -parts of the body which are arranged for a definite purpose and yet are -without function. Let me remind the reader of the eyes of those animals -which live in the dark in caves and underground, and which consequently -never can use them. In these animals we find real eyes hidden under the -skin, frequently developed exactly as are the eyes of animals which -really see; and yet these eyes never perform any function, indeed -cannot, simply for the reason that they are covered by an opaque -membrane, and consequently no ray of light falls upon them (compare -above, p. 13). In the ancestors of these animals, which lived in open -daylight, the eyes were well developed, covered by a transparent horny -capsule (cornea), and actually served the purpose of seeing. But as the -animals gradually accustomed themselves to an underground mode of life, -and withdrew from the daylight and no longer used their eyes, these -became degenerated. - -Very clear examples of rudimentary organs, moreover, are the wings of -animals which cannot fly; for example, the wings of the running birds, -like the ostrich, emeu, cassowary, etc., the legs of which have become -exceedingly developed. These birds having lost the habit of flying, have -consequently lost the use of their wings; however, the wings are still -there, although in a crippled form. We very frequently find such -crippled wings in the class of insects, most members of which can fly. - -From reasons derived from comparative anatomy and other circumstances, -we can with certainty draw the inference that all insects now living -(all dragon-flies, grasshoppers, beetles, bees, bugs, flies, -butterflies, etc.) have originated from a single common parental form, -from a primary insect which possessed two well-developed pairs of wings, -and three pairs of legs. Yet there are very many insects in which either -one or both pairs of wings have become more or less degenerated, and -many in which they have even completely disappeared. For example, in the -whole order of flies, or Diptera, the hinder pair of wings--in the -bee-parasites, or Strepsiptera, on the other hand, the fore pair of -wings--have become degenerated or entirely disappeared. Moreover, in -every order of insects we find individual genera, or species, in which -the wings have more or less degenerated or disappeared. The latter is -the case especially in parasites. The females have frequently no wings, -whereas the males have; for instance, in the case of glow-worms -(Lampyris), Strepsiptera, etc. This partial or complete degeneration of -the wings of insects has evidently arisen from natural selection in the -struggle for life. For we find insects without wings living under -circumstances where flying would be useless, or even decidedly injurious -to them. If, for example, insects living on islands fly about much, it -may easily happen that when flying they are blown into the sea by the -wind, and if (as is always the case) the power of flying is differently -developed in different individuals, then those which fly badly have an -advantage over those which fly well; they are less easily blown into the -sea, and remain longer in life than the individuals of the same species -which fly well. In the course of many generations, by the action of -natural selection, this circumstance must necessarily lead to a complete -suppression of the wings. If this conclusion had been arrived at on -purely theoretical grounds, we might be pleased to find its truth -established by facts. For upon isolated islands the proportion of -wingless insects to those possessing wings is surprisingly large, much -larger than among the insects inhabiting continents. Thus, for example, -according to Wollaston, of the 550 species of beetles which inhabit the -island of Madeira, 220 are wingless, or possess such imperfect wings -that they can no longer fly; and of the 29 genera which belong to that -island exclusively, no less than 23 contain such species only. It is -evident that this remarkable circumstance does not need to be explained -by the special wisdom of the Creator, but is sufficiently accounted for -by natural selection, because in this case the hereditary disuse of the -wings, the discontinuance of flying in the presence of dangerous winds, -has been very advantageous in the struggle for life. In other wingless -insects the want of wings has been advantageous for other reasons. -Viewed by itself, the loss of wings is a degeneration, but in these -special conditions of life it is advantageous to the organism in the -struggle for life. - -Among other rudimentary organs I may here, by way of example, further -mention the lungs of serpents and serpent-like lizards. All vertebrate -animals possessing lungs, such as amphibious animals, reptiles, birds, -and mammals, have a pair of lungs, a right and a left one. But in cases -where the body is exceedingly thin and elongated, as in serpents and -serpent-like lizards, there is no room for the one lung by the side of -the other, and it is an evident advantage to the mechanism of -respiration if only one lung is developed. A single large lung here -accomplishes more than two small ones side by side would do; and -consequently, in these animals, we invariably find only the right or -only the left lung fully developed. The other is completely aborted, -although existing as a useless rudiment. In like manner, in all birds -the right ovary is aborted and without function; only the left one is -developed, and yields all the eggs. - -I mentioned in the first chapter that man also possesses such useless -and superfluous rudimentary organs, and I specified as such the muscles -which move the ears. Another of them is the rudiment of the tail which -man possesses in his 3--5 tail vertebrae, and which, in the human embryo, -stands out prominently during the first two months of its development -(compare Plates II. and III.). It afterwards becomes completely hidden. -The rudimentary little tail of man is an irrefutable proof of the fact -that he is descended from tailed ancestors. In woman the tail is -generally by one vertebra longer than in man. There still exist -rudimentary muscles in the human tail which formerly moved it. - -Another case of human rudimentary organs, only belonging to the male, -and which obtains in like manner in all male mammals, is furnished by -the mammary glands on the breast, which, as a rule, are active only in -the female sex. However, cases of different mammals are known, -especially of men, sheep, and goats, in which the mammary glands were -fully developed in the male sex, and yielded milk as food for their -offspring. I have already mentioned before (p. 12) that the rudimentary -auricular muscles in man can still be employed to move their ears, by -some persons who have perseveringly practised them. In fact, rudimentary -organs are frequently very differently developed in different -individuals of the same species; in some they are tolerably large, in -others very small. This circumstance is very important for their -explanation, as is also the other circumstance that generally in -embryos, or in a very early period of life, they are much larger and -stronger in proportion to the rest of the body than they are in fully -developed and fully grown organisms. This can, in particular, be easily -pointed out in the rudimentary sexual organs of plants (stamens and -pistil), which I have already mentioned. They are proportionately much -larger in the young flower-bud than in the mature flower. - -I have remarked (p. 15) that rudimentary or suppressed organs were the -strongest supports of the monistic or mechanical conception of the -universe. If its opponents, the dualists and teleologists, understood -the immense significance of rudimentary organs, it would put them into a -state of despair. Their ludicrous attempts to explain that rudimentary -organs were given to organisms by the Creator "for the sake of -symmetry," or "as a formal provision," or "in consideration of his -general plan of creation," sufficiently prove the utter impotence of -their perverse conception of the universe. I must here repeat that, even -if we knew absolutely nothing of the other phenomena of development, we -should be obliged to believe in the truth of the Theory of Descent, -solely on the ground of the existence of rudimentary organs. Not one of -its opponents has been able to throw even a feeble glimmer of an -acceptable explanation upon these exceedingly remarkable and important -phenomena. There is scarcely any highly developed animal or vegetable -form which has not some rudimentary organs, and in most cases it can be -shown that they are the products of natural selection, and that they -have become suppressed by disuse. It is the reverse of the process of -formation in which new organs arise from adaptation to certain -conditions of life, and by the use of parts as yet incompletely -developed. It is true our opponents usually maintain that the origin of -altogether new parts is completely inexplicable by the Theory of -Descent. However, I distinctly assert that to those who possess a -knowledge of comparative anatomy and physiology this matter does not -present the slightest difficulty. Every one who is familiar with -comparative anatomy and the history of development will find as little -difficulty about the origin of completely new organs as about the utter -disappearance of rudimentary organs. The disappearance of the latter, -viewed by itself, is the converse of the origin of the former. Both -processes are particular phenomena of differentiation, which, like all -others, can be explained quite simply and mechanically by the action of -natural selection in the struggle for life. - -The infinitely important study of rudimentary organs and their origin, -the comparison of their palaeontological and embryological development, -now naturally leads us to the consideration of one of the most important -and instructive of all biological phenomena, namely, the parallelism -which the phenomena of progress and divergence present to us in three -different series. When, in the last chapter, we spoke of perfecting and -division of labour, we understood by those words progress and -separation, and those changes effected by them, which in the long and -slow course of the earth's history have led to a continual variation of -the flora and fauna, to the origin of new and to the disappearance of -ancient species of animals and plants. Now, if we follow the origin, the -development, and the life of every single organic individual, we meet -with exactly the same phenomena of progress and differentiation. The -individual development, or the _ontogenesis_ of every single organism, -from the egg to the complete form is nothing but a growth attended by a -series of diverging and progressive changes. This applies equally to -animals, plants, and protista. If, for example, we consider the ontogeny -of any mammal, of man, of an ape, or of a pouched animal, or if we -follow the individual development of any other vertebrate animal of -another class, we everywhere find essentially the same phenomena. Every -one of these animals develops itself originally out of a single cell, -the egg. This cell increases by self-division, and forms a number of -cells, and by the growth of this accumulation of cells, by the divergent -development of originally identical cells, by the division of labour -among them, and by their perfecting, there arises the perfect organism, -the complicated composition of which excites our admiration. - -It seems to me here indispensable to draw attention more closely to -those infinitely important and interesting processes which accompany -_ontogenesis, or the individual development of organisms_, and -especially to that of vertebrate animals, man included. I wish -especially to recommend these exceedingly remarkable and instructive -phenomena to the reader's most careful consideration, first, because -they are among the strongest supports of the Theory of Descent, and -secondly, because, considering their immense general importance, they -have hitherto been properly considered only by a few privileged persons. - -We cannot indeed but be astonished when we consider the deep ignorance -which still prevails, in the widest circles, about the facts of the -individual development of man and organisms in general. These facts, the -universal importance of which cannot be estimated too highly, were -established, in their most important outlines, even more than a hundred -years ago, in 1759, by the great German naturalist Caspar Friedriech -Wolff, in his classical "Theoria Generationis." But, just as Lamarck's -Theory of Descent, founded in 1809, lay dormant for half a century, and -was only awakened to new and imperishable life in 1859, by Darwin, in -like manner Wolff's Theory of Epigenesis remained unknown for nearly -half a century; and it was only after Oken, in 1806 had published his -history of the development of the intestinal tube, and after Meckel, in -1812, had translated Wolff's work (written in Latin) on the same subject -into German, that Wolff's theory of epigenesis became more generally -known, and formed the foundation of all subsequent investigations of the -history of individual development. The study of ontogenesis now received -a great stimulus, and soon there appeared the classical investigations -of the two friends, Christian Pander (1817) and Carl Ernst Baer (1819). -Baer, in his remarkable "Entwickelungsgeschichte der Thiere,"(20) worked -out the ontogeny of vertebrate animals in all its important facts. He -carried out a series of such excellent observations, and illustrated -them by such profound philosophical reflections, that his work became -the foundation for a thorough understanding of this important group of -animals, to which, of course, man also belongs. The facts of embryology -alone would be sufficient to solve the question of man's position in -nature, which is the highest of all problems. Look attentively at and -compare the eight figures which are represented on the adjoining Plates -II. and III., and it will be seen that the philosophical importance of -embryology cannot be too highly estimated. - -We may well ask, What do our so-called "educated" circles, who think so -much of the high civilization of the 19th century, know of these most -important biological facts, of these indispensable foundations for -understanding their own organism? How much do our speculative -philosophers and theologians know about them, who fancy they can arrive -at an understanding of the human organism by mere guesswork or divine -inspiration? What indeed do the majority of naturalists, not excepting -the majority of the so-called "zoologists" (including the -entomologists!), know about them? - -The answer to this question tells much to the shame of the persons above -indicated, and we must confess, willingly or unwillingly, that these -invaluable facts of human ontogeny are, even at the present day, utterly -unknown to most people, or are in no way valued as they deserve to be. -It is in the face of such a condition of things as this that we see -clearly upon what a wrong and one-sided road the much vaunted culture of -the 19th century still moves. Ignorance and superstition are the -foundations upon which most men construct their conception of their own -organism and its relation to the totality of things; and these palpable -facts of the history of development, which might throw the light of -truth upon them, are ignored. It is true these facts are not calculated -to excite approval among those who assume a thorough difference between -man and the rest of nature, and who will not acknowledge the animal -origin of the human race. That origin must be a very unpleasant truth to -members of the ruling and privileged castes in those nations among which -there exists an hereditary division of social classes, in consequence of -false ideas about the laws of inheritance. It is well known that, even -in our day, in many civilized countries the idea of hereditary grades of -rank goes so far, that, for example, the aristocracy imagine themselves -to be of a nature totally different from that of ordinary citizens, and -nobles who commit a disgraceful offence are punished by being expelled -from the caste of nobles, and thrust down among the pariahs of "vulgar -citizens." What are these nobles to think of the noble blood which flows -in their privileged veins, when they learn that all human embryos, those -of nobles as well as commoners, during the first two months of -development, are scarcely distinguishable from the tailed embryos of -dogs and other mammals? - -As the object of these pages is solely to further the general knowledge -of natural truths, and to spread, in wider circles, a natural conception -of the relations of man to the rest of nature, I shall be justified if I -do not pay any regard to the widely-spread prejudice in favour of an -exceptional and privileged position for man in creation, and simply give -here the embryological facts from which the reader will be able to draw -conclusions affirming the groundlessness of those prejudices. I wish all -the more to entreat him to reflect carefully upon these facts of -ontogeny, as it is my firm conviction that a general knowledge of them -can only promote the intellectual advance, and thereby the mental -perfecting, of the human race. - -Amidst all the infinitely rich and interesting material which lies -before us in the ontogeny of vertebrate animals, that is, in the history -of their individual development, I shall here confine myself to showing -some of those facts which are of the greatest importance to the Theory -of Descent in general, as well as in its special application to man. Man -is at the beginning of his individual existence a simple egg, a single -little cell, just the same as every animal organism which originates by -sexual generation. The human egg is essentially the same as that of all -other mammals, and cannot be distinguished from the egg of the higher -mammals. The egg represented in Fig. 5 might be that of a man or an ape -as well as of a dog, a horse, or any other mammal. Not only the form and -structure, but even the size of the egg in most mammals is the same as -in man, namely, about the 120th part of an inch in diameter, so that the -egg under favorable circumstances, with the naked eye, can just be -perceived as a small speck. The differences which really exist between -the eggs of different mammals and that of man do not consist in the -form, but in the chemical mixture, in the molecular composition of the -albuminous combination of carbon, of which the egg essentially consists. -These minute individual differences of all eggs, which depend upon -indirect or potential adaptation (and especially upon the law of -individual adaptation), are indeed not directly perceptible to the -exceedingly imperfect senses of man, but are cognisable through indirect -means, as the primary causes of the difference of all individuals. - -[Illustration: FIG. 5.--The human egg a hundred times enlarged. _a._ The -kernel speck, or nucleolus (the so-called germinal spot of the egg). -_b._ Kernel, or nucleus (the so-called germinal vesicle of the egg). -_c._ Cell-substance, or protoplasm (so-called yolk of the egg). _d._ -Cell-membrane (the yolk-membrane of the egg; in mammals, on account of -its transparency, called zona pellucida). The eggs of other mammals are -of the same form.] - -The human egg is, like that of all other mammals, a small globular -bladder, which contains all the constituent parts of a simple organic -cell (Fig. 5). The most essential parts of it are the mucous -cell-substance, or the protoplasma (_c_), which in an egg is called the -"yolk," and the cell-kernel, or nucleus (_b_), surrounded by it, which -is here called by the special name of the "germinal vesicle." The latter -is a delicate, clear, glassy globule of albumen, of about 1-600th part -of an inch in diameter, and surrounds, a still smaller, sharply-marked, -rounded granule (_a_), the kernel-speck, or the nucleolus of the cell -(in the egg it is called the "germinal spot"). The outside of the -globular egg-cell of a mammal is surrounded by a thick pellucid -membrane, the cell-membrane or yolk-membrane, which here bears the -special name of zona pellucida (_d_). The eggs of many lower animals -(for example of many Medusae) differ from this in being _naked_ cells, as -the outer covering, or cell-membrane, is wanting. - -As soon as the egg (ovulum) of the mammal has attained its full -maturity, it leaves the ovary of the female, in which it originates, and -passes into the oviduct, and through this narrow passage into the wider -pouch or womb (uterus). If, meanwhile, the egg is fructified by the male -seed (sperm), it develops itself in this pouch into an embryo, and does -not leave it until perfectly developed and capable of coming into the -world at birth as a young mammal. - -The variations of form and transformations which the fructified egg must -go through within the uterus before it assumes the form of the mammal -are exceedingly remarkable, and proceed from the beginning in man, in -precisely the same way as in the other mammals. At first the fructified -egg of the mammal acts as a single-celled organism, which is about to -propagate independently and increase itself; for example, an Amoeba -(compare Fig. 2, p. 188). In point of fact the simple egg-cell becomes -two, by the process of cell-division which I have previously described. -There arise from the single germinal spot (the small kernel-speck of the -original simple egg-cell) two new kernel-specks, and then in like -manner, out of the germinal vesicle (the nucleus), two new cell-kernels. -Then, and not until then, does the globular protoplasma first separate -itself by an equatorial furrow into two halves, in such a manner that -each half encloses one of the two kernels, together with its -kernel-speck. Thus the simple egg-cell, within the original cellular -membrane, has become two naked cells, each possessing its own kernel -(Fig. 6). - -[Illustration: FIG. 6.--First commencement of the development of a -mammal's egg, the so-called "yolk-cleavage" (propagation of the egg-cell -by repeated self-division). _A._ The egg, by the formation of the first -furrow, falls into two cells. _B._ These by division fall into four -cells. _C._ These latter have fallen into eight cells. _D._ By continued -division a globular mass of numerous cells has arisen.] - -The same process of cell-division now repeats itself several times in -succession. In this way, from two cells (Fig. 6 _A_) there arise four -(Fig. 6 _B_); from four, eight (Fig. 6 _C_); from eight, sixteen; from -these, thirty-two, etc. Each time the division of the kernel-speck -precedes that of the kernel; this, again, precedes that of the -cell-substance, or protoplasma. As the division of the latter always -commences with the formation of a superficial annular _furrow_, or -cleft, the whole process is usually called the _furrowing of the egg_, -or yolk-cleavage, and the products of it, that is, the cells arising -from the continued halving, are called the _cleavage spheres_. However, -the whole process is nothing more than a simple, oft-repeated _division -of cells_, and the products of it are actual, naked _cells_. Finally, -through the continued division or "furrowing" of the mammal's egg there -arises a mulberry-shaped ball, which is composed of a great number of -small spheres, naked cells, containing kernels (Fig. 6 _D_). These cells -are the materials out of which the body of the young mammal is -constructed. Every one of us has once been such a simple mulberry-shaped -ball, composed only of small equi-formal cells. - -The further development of the globular lump of cells, which now -represents the young body of the mammal, consists first in its changing -into a globular bladder, as fluid accumulates within it. This bladder is -called the germ-bladder (vesicula blastodermica). Its wall is at first -composed of merely equi-formal cells. But soon, at one point on the -wall, arises a disc-shaped thickening, as the cells here increase -rapidly, and this thickening is now the foundation of the actual body of -the germ or embryo, while the other parts of the germ-bladder serve only -for its nutrition. The thickened disc, or foundation of the embryo, soon -assumes an oblong, and then a fiddle-shaped form, in consequence of its -right and left walls becoming convex (Fig. 7, p. 304). At this stage of -development in the first form of their germ or embryo, not only all -mammals, including man, but even all vertebrate animals in -general--birds, reptiles, amphibious animals, and fishes--can either not -be distinguished from one another at all, or only by very unessential -differences, such as the arrangement of the egg-coverings. In all the -whole body consists of nothing but a quite simple, oblong, oval, or -violin-shaped thin disc, which is composed of three closely connected -membranes or plates, lying one above another. Each of the three plates -or layers of the germ consists simply of cells all exactly like one -another; but each layer has a different function in the building up of -the vertebrate animal body. Out of the upper or outer germ-layer arises -solely the outer skin (epidermis), together with the central parts of -the nervous system (spinal marrow and brain); out of the lower or inner -layer arises only the inner delicate skin (epithelium) which lines the -whole intestinal tube from the mouth to the anus, together with all the -glands connected with it (lung, liver, salivary glands, etc.); out of -the middle germ-layer lying between the two others arise all the other -organs, muscles, bones, blood-vessels. Now, the processes by which the -various and exceedingly complicated parts of the fully-formed body of -vertebrate animals arise out of such simple material--out of the three -germ-layers composed only of cells--are, in the first place, the -repeated division, and consequently the increase of cells; in the second -place, the division of labour or differentiation of these cells; and -thirdly, the union of the variously developed or differentiated cells, -for the formation of the different organs. Thus arises the gradual -progress or perfecting which can be traced step by step in the -development of the embryonic body. The simple embryonic cells, which are -to constitute the body of the vertebrate animal, stand in the same -relation to each other as citizens who wish to found a state. Some take -to one occupation, others to another, and work together for the good of -the whole. By this division of labour, or differentiation, and the -perfecting (the organic progress) which is connected with it, it becomes -possible for the whole state to accomplish undertakings which would have -been impossible to the single individual. The whole body of the -vertebrate animal, like every other many-celled organism, is a -republican state of cells, and consequently it can accomplish organic -functions which the individual cell, as a solitary individual (for -example, an Amoeba, or a single-celled plant), could never perform. - -No sensible person supposes that carefully devised institutions, which -have been established for the good of the whole, as well as for the -individual, in every human state, are the results of the action of a -personal and supernatural Creator, acting for a definite purpose. On the -contrary, every one knows that these useful institutions of organization -in the state are the consequences of the co-operation of the individual -citizens and their common government, as well as of adaptation to the -conditions of existence of the outer world. Just in the same way we must -judge of the many-celled organism. In it also all the useful -arrangements are solely the natural and necessary result of the -co-operation, differentiation, and perfecting of the individual -citizens--the cells--and by no means the artificial arrangements of a -Creator acting for a definite purpose. If we rightly consider this -comparison, and pursue it further, we can distinctly see the perversity -of that dualistic conception of nature which discovers the action of a -creative plan of construction in the various adaptations of the -organization of living things. - -Let us pursue the individual development of the vertebrate animal body a -few stages further, and see what is next done by the citizens of this -embryonic organism. In the central line of the violin-shaped disc, which -is composed of the three cellular germ-layers, there arises a straight -delicate furrow, the so-called "primitive streak," by which the -violin-shaped body is divided into two equal lateral halves--a right and -a left part or "antimer." On both sides of that streak or furrow, the -upper or external germ-layer rises in the form of a longitudinal fold, -and both folds then grow together over the furrow in the central line, -and thus form a cylindrical tube. This tube is called the marrow-tube, -or medullary canal, because it is the foundation of the central nervous -system, the _spinal marrow_ (medulla spinalis). At first it is pointed -both in front and behind, and it remains so for life in the lowest -vertebrate animal, the brainless, skull-less Lancelet (Amphioxus). But -in all other vertebrate animals, which we distinguish from the latter as -skulled animals, or Craniota, a difference between the fore and hinder -end of the marrow tube soon becomes visible, the fore end becoming -dilated, and changing into a roundish bladder, the foundation of the -_brain_. - -In all Craniota, that is, in all vertebrate animals possessing skull and -brain, the brain, which is at first only the bladder-shaped dilatation -of the anterior end of the spinal marrow, divides into five bladders -lying one behind the other, four superficial, transverse in-nippings -being formed. These _five brain-bladders_, out of which afterwards arise -all the different parts of the intricately constructed brain, can be -seen in their original condition in the embryo represented in Fig. 7. It -is just the same whether we examine the embryo of a dog, a fowl, a -lizard, or any other higher vertebrate animal. For the embryos of the -different skulled animals (at least the three higher classes of them, -the reptiles, birds and mammals) cannot be in any way distinguished at -the stage represented in Fig. 7. The whole form of the body is as yet -exceedingly simple, being merely a thin, leaf-like disc. Face, legs, -intestines, etc., are as yet completely wanting. But the five bladders -are already quite distinct from one another. - -[Illustration: FIG. 7.--Embryo of a mammal or bird, in which the five -brain-bladders have just commenced to develop. _v._ Fore brain. _z._ -Twixt brain. _m._ Mid brain. _h._ Hind brain. _n._ After brain. _p._ -Spinal-marrow. _a._ Eye-bladders. _w._ Primitive vertebrae. _d._ -Spinal-axis or notochord.] - -The _first_ bladder, the _fore brain_ (_a_), is in so far the most -important that it principally forms the hemispheres of the so-called -larger brain (cerebrum), that part which is the seat of the higher -mental activities. The more these activities are developed in the series -of vertebrate animals, the more do the two lateral halves of the fore -brain, or the hemispheres, grow at the expense of the other bladders, -and overlap them in front and from above. In man, where they are most -strongly developed, agreeing with his higher mental activity, they -eventually almost entirely cover the other parts from above (compare -Plates II. and III.) The _second_ bladder, the _twixt brain_ (_z_), -forms that portion of the brain which is called the _centre of sight_, -and stands in the closest relation to the eyes (_a_), which grow right -and left out of the fore brain in the shape of two bladders, and later -lie at the bottom of the twixt brain. The _third_ bladder, the _mid -brain_ (_m_), for the most part vanishes in the formation of the -so-called _four bulbs_, a bossy portion of the brain, which is strongly -developed in reptiles and birds (Fig. _E_, _F_, Plate II.), whereas in -mammals it recedes much more (Fig. _G_, _H_, Plate III.). The _fourth_ -bladder, the _hind brain_ (_h_), forms the so-called _little -hemispheres_, together with the middle part of the _small brain_ -(cerebellum), a part of the brain as to the function of which the most -contradictory conjectures are entertained, but which seems principally -to regulate the co-ordination of movements. Lastly, the _fifth_ bladder, -the _after brain_ (_n_), develops into that very important part of the -central nervous system which is called the _prolonged marrow_ (medulla -oblongata). It is the central organ of the respiratory movements, and of -other important functions, and an injury to it immediately causes death, -whereas the large hemispheres of the fore brain (or the organ of the -"soul," in a restricted sense) can be removed bit by bit, and even -completely destroyed, without causing the death of the vertebrate -animal--only its higher mental activities disappearing in consequence. - -These five brain bladders, in all vertebrate animals which possess a -brain at all, are originally arranged in the same manner and develop -gradually in the different groups so differently, that it is afterwards -very difficult to recognize the corresponding parts in the -fully-developed brains. In the early stage of development which is -represented in Fig. 7, it seems as yet quite impossible to distinguish -the embryos of the different mammals, birds, and reptiles, from one -another. But if we compare the much more developed embryos on Plates II. -and III. with one another, we can clearly see an inequality in their -development, and especially it will be perceived that the brain of the -two mammals (_G_ and _H_) already strongly differ from that of birds -(_F_) and of reptiles (_E_). In the two latter the mid brain -predominates, but in the former the fore brain. Even at this stage the -brain of the bird (_F_) is scarcely distinguishable from that of the -tortoise (_E_), and in like manner the brain of the dog (_G_) is as yet -almost the same as that of man (_H_). If, on the other hand, we compare -the brains of these four vertebrate animals in a fully developed -condition, we find them so very different in all anatomical particulars, -that we cannot doubt for a moment as to which animal each brain belongs. - -I have here explained the original equality, the gradual commencement, -and the ever increasing separation or differentiation of the embryos in -the different vertebrate animals, taking the brain as a special example, -just because this organ of the soul's activity is of special interest. -But I might as well have discussed in its stead the heart, or the liver, -or the limbs, in short, any other part of the body, since the same -wonder of creation is here ever repeated, namely, this, that all parts -are originally the same in the different vertebrate animals, and that -the variations by which the different classes, orders, families, genera, -etc., differ and deviate from one another, are only gradually developed. - -There are certainly few parts of the body which are so differently -constructed as the _limbs or extremities_ of the vertebrate animals. -Now, I wish the reader to compare in Fig. _A-H_ on Plates II. and III., -the four extremities (_bv_) of the embryos with one another, and he will -scarcely be able to perceive any important differences between the human -arm (_H bv_), the wing of a bird (_F bv_), the slim foreleg of a dog (_G -bv_), and the plump foreleg of the tortoise (_E bv_). In comparing the -hinder extremities (_bh_) in these figures he will find it equally -difficult to distinguish the leg of a man (_H bh_), of a bird (_F bh_), -the hind-leg of a dog (_G bh_), and that of a tortoise (_E bh_). The -fore as well as the hinder extremities are as yet short, broad -lumps, at the ends of which the foundations of the five toes are placed, -connected as yet by a membrane. At a still earlier stage (Fig. _A-D_) -the five toes are not marked out at all, and it is quite impossible to -distinguish even the fore and hinder extremities from one another. The -latter, as well as the former, are nothing but simple roundish -processes, which have grown out of the side of the trunk. At the very -early stage represented in Fig. 7 they are completely wanting, and the -whole embryo is a simple trunk without a trace of limbs. - -[Illustration: Pl. II. Germs or Embryos of four Vertebrates. - -_v._ Fore-brain. _z._ Twixt-brain. _m._ Mid-brain. _h._ Hind-brain. _n._ -After-brain. _w._ Spine. _r._ Spinal-cord.] - -[Illustration: Pl. III. Germs or Embryos of four Vertebrates. - -_na._ Nose. _a._ Eyes. _o._ Ear. _k__{1} _k__{2} _k__{3}. Gill-arches. -_s._ Tail. _bv._ Fore-leg. _bh._ Hind-leg.] - -I wish especially to draw attention in Plates II. and III., which -represents embryos in early stages of development (Fig. _A-D_)--and in -which we are not able to recognize a trace of the full-grown animal--to -an exceedingly important formation, which originally is common to all -vertebrate animals, but which at a later period is transformed into the -most different organs. Every one surely knows the _gill-arches_ of fish, -those arched bones which lie behind one another, to the number of three -or four, on each side of the neck, and which support the gills, the -respiratory organs of the fish (double rows of red leaves, which are -popularly called "fishes' ears.") Now, these gill-arches originally -exist exactly the same in man (_D_), in dogs (_C_), in fowls (_B_), and -in tortoises (_A_), as well as in all other vertebrate animals. (In Fig. -_A-D_ the three gill-arches of the right side of the neck are marked -_k__{1} _k__{2} _k__{3}). Now, it is only in fishes that these remain in -their original form, and develop into respiratory organs. In the other -vertebrate animals they are partly employed in the formation of the face -(especially the jaw apparatus), and partly in the formation of the organ -of hearing. - -Finally, when comparing the embryos on Plates II. and III., we must not -fail to give attention again to the _human tail_ (_s_), an organ which, -in the original condition, man shares with all other vertebrate animals. -The discovery of tailed men was long anxiously expected by many monistic -philosophers, in order to establish a closer relationship between man -and the other mammals. And in like manner their dualistic opponents -often maintained with pride that the complete want of a tail formed one -of the most important bodily distinctions between men and animals, -though they did not bear in mind the many tailless animals which really -exist. Now, man in the first months of development possesses a real tail -as well as his nearest kindred, the tailless apes (orang-outang, -chimpanzee, gorilla), and vertebrate animals in general. But whereas, in -most of them--for example, the dog (_C_, _G_)--in the course of -development it always grows longer, in man (Fig. _D_, _H_) and in -tailless mammals, at a certain period of development, it degenerates and -finally completely disappears. However, even in fully developed men, the -remnant of the tail is seen in the three, four, or five tail vertebrae -(vertebrae coccygeae) as an aborted or rudimentary organ, which forms the -hinder or lower end of the vertebral column (p. 289). - -Most persons even now refuse to acknowledge the most important deduction -of the Theory of Descent, that is, the palaeontological development of -man from ape-like, and through them from still lower, mammals, and -consider such a transformation of organic form as impossible. But, I -ask, are the phenomena of the individual development of man, the -fundamental features of which I have here given, in any way less -wonderful? Is it not in the highest degree remarkable that all -vertebrate animals of the most different classes--fishes, amphibious -animals, reptiles, birds, and mammals--in the first periods of their -embryonic development cannot be distinguished at all, and even much -later, at a time when reptiles and birds are already distinctly -different from mammals, that the dog and the man are almost identical? -Verily, if we compare those two series of development with one another, -and ask ourselves which of the two is the more wonderful, it must be -confessed that _ontogeny_, or the short and quick history of development -of the _individual_, is much more mysterious than _phylogeny_, or the -long and slow history of development of the _tribe_. For one and the -same grand change of form is accomplished by the latter in the course of -many thousands of years, and by the former in the course of a few -months. Evidently this most rapid and astonishing transformation of the -individual in ontogenesis, which we can actually point out at any moment -by direct observation, is in itself much more wonderful and astonishing -than the corresponding, but much slower and gradual transformation which -the long chain of ancestors of the same individual has gone through in -phylogenesis. - -The two series of organic development, the ontogenesis of the individual -and the phylogenesis of the tribe to which it belongs, stand in the -closest causal connection with each other. I have endeavoured, in the -second volume of the "General Morphology,"(4) to establish this theory -in detail, as I consider it exceedingly important. As I have there -shown, _ontogenesis, or the development of the individual, is a short -and quick repetition_ (recapitulation) _of phylogenesis, or the -development of the tribe to which it belongs, determined by the laws of -inheritance and adaptation_; by tribe I mean the ancestors which form -the chain of progenitors of the individual concerned. (Gen. Morph. ii. -110-147, 371.) - -In this intimate connection of ontogeny and phylogeny, I see one of the -most important and irrefutable proofs of the Theory of Descent. No one -can explain these phenomena unless he has recourse to the laws of -Inheritance and Adaptation; by these alone are they explicable. These -laws, which we have previously explained, are _the laws of abbreviated, -of homochronic, and of homotopic inheritance_, and here deserve renewed -consideration. As so high and complicated an organism as that of man, or -the organism of every other mammal, rises upwards from a simple cellular -state, and as it progresses in its differentiation and perfecting it -passes through the same series of transformations which its animal -progenitors have passed through, during immense spaces of time, -inconceivable ages ago. I have already pointed out this extremely -important parallelism of the development of individuals and tribes (p. -10). Certain very early and low stages in the development of man, and -the other vertebrate animals in general, correspond completely in many -points of structure with conditions which last for life in the lower -fishes. The next phase which follows upon this presents us with a change -of the fish-like being into a kind of amphibious animal. At a later -period the mammal, with its special characteristics, develops out of the -amphibian, and we can clearly see, in the successive stages of its later -development, a series of steps of progressive transformation which -evidently correspond with the differences of different mammalian orders -and families. Now, it is precisely in the same succession that we also -see the ancestors of man, and of the higher mammals, appear one after -the other in the earth's history; first fishes, then amphibians, later -the lower, and at last the higher mammals. Here, therefore, the -embryonic development of the individual is completely parallel to the -palaeontological development of the whole tribe to which it belongs, and -this exceedingly interesting and important phenomenon can be explained -only by the interaction of the laws of Inheritance and Adaptation. - -The example last mentioned, of the parallelism of the palaeontological -and of the individual developmental series, now directs our attention to -a third developmental series, which stands in the closest relations to -these two, and which likewise runs, on the whole, parallel to them. I -mean that series of development of forms which constitutes the object of -investigation in _comparative anatomy_, and which I will briefly call -the _systematic developmental series of species_. By this we understand -the chain of the different, but related and connected forms, which exist -_side by side_ at any one period of the earth's history; as for example, -at the present moment. While comparative anatomy compares the different -forms of fully-developed organisms with one another, it endeavours to -discover the common prototypes which underlie, as it were, the manifold -forms of kindred genera, classes, etc., and which are more or less -concealed by their particular differentiation. It endeavours to make out -the series of progressive steps which are indicated in the different -degrees of perfection of the divergent branches of the tribe. To make -use again of the same particular instance, comparative anatomy shows us -how the individual organs and systems of organs in the tribe of -vertebrate animals--in the different classes, families, and species of -it--have unequally developed, differentiated, and perfected themselves. -It shows us how far the succession of classes of vertebrate animals, -from the Fishes upwards, through the Amphibia to the Mammals, and here -again, from the lower to the higher orders of Mammals, forms a -progressive series or ladder. This attempt to establish a connected -anatomical developmental series we may discover in the works of the -great comparative anatomists of all ages--in the works of Goethe, -Meckel, Cuvier, Johannes Mueller, Gegenbaur, and Huxley. - -The developmental series of mature forms, which comparative anatomy -points out in the different diverging and ascending steps of the organic -system, and which we call the systematic developmental series, is -parallel to the palaeontological developmental series, because it deals -with the _result_ of palaeontological development, and it is parallel to -the individual developmental series, because this is parallel to the -palaeontological series. If two parallels are parallel to a third, they -must be parallel to one another. - -The varied differentiation, and the unequal degree of perfecting which -comparative anatomy points out in the developmental series of the -System, is chiefly determined by the ever increasing variety of -conditions of existence to which the different groups adapt themselves -in the struggle for life, and by the different degrees of rapidity and -completeness with which this adaptation has been effected. Conservative -groups which have retained their inherited peculiarities most -tenaciously remain, in consequence, at the lowest and rudest stage of -development. Those groups progressing most rapidly and variously, and -which have adapted themselves to changed conditions of existence most -readily have attained the highest degree of perfection. The further the -organic world developed in the course of the earth's history, the -greater must the gap between the lower conservative and the higher -progressive groups have become, as in fact may be seen too in the -history of nations. In this way also is explained the historical fact, -that the most perfect animal and vegetable groups have developed -themselves in a comparatively short time to a considerable height, while -the lowest or most conservative groups have remained stationary -throughout all ages in their original simple stage, or have progressed, -but very slowly and gradually. The series of man's progenitors clearly -shows this state of things. The sharks of the present day are still very -like the primary fish, which are among the most ancient vertebrate -progenitors of man, and the lowest amphibians of the present day (the -gilled salamanders and salamanders) are very like the amphibians which -first developed themselves out of fishes. So, too, the later ancestors -of man, the Monotremata and Marsupials, the most ancient mammals, are at -the same time the most imperfect animals of the class which still exist. - -The laws of inheritance and adaptation known to us are completely -sufficient to explain this exceedingly important and interesting -phenomenon, which may be briefly designated as the _parallelism of -individual, of palaeontological, and of systematic development_. No -opponent of the Theory of Descent has been able to give an explanation -of this extremely wonderful fact, whereas it is perfectly explained, -according to the Theory of Descent, by the laws of Inheritance and -Adaptation. - -If we examine this parallelism of the three organic series of -development more accurately, we have to add the following special -qualifications. _Ontogeny_, or the history of the individual development -of every organism (embryology and metamorphology), presents us with a -simple _unbranching_ or graduated chain of forms; and so it is with that -_portion of phylogeny_ which comprises the palaeontological history of -development of the _direct ancestors only_ of an individual organism. -But _the whole of phylogeny_--which meets us in the _natural system_ of -every organic tribe or phylum, and which is concerned with the -investigation of the palaeontological development _of all_ the branches -of this tribe--forms a _branching_ or tree-shaped developmental series, -a veritable pedigree. If we examine and compare the branches of this -pedigree, and place them together according to the degree of their -differentiation and perfection, we obtain the tree-shaped, branching, -_systematic developmental series of comparative anatomy_. Strictly -speaking, therefore, the latter is parallel to _the whole of phylogeny_, -and consequently is only partially parallel to ontogeny; for ontogeny -itself is parallel only to _a portion_ of phylogeny. - -All the phenomena of organic development above discussed, especially the -threefold genealogical parallelism, and the laws of differentiation and -progress, which are evident in each of these three series of organic -development, and, further, the whole history of rudimentary organs, are -exceedingly important proofs of the truth of the Theory of Descent. For -by it alone can they be explained, whereas its opponents cannot even -offer a shadow of an explanation of them. Without the Doctrine of -Filiation, the fact of organic development in general cannot be -understood. We should therefore, for this reason alone, be forced to -accept Lamarck's Theory of Descent, even if we did not possess Darwin's -Theory of Selection. - - - - -CHAPTER XIII. - -THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE EARTH. SPONTANEOUS -GENERATION. THE CARBON THEORY. THE PLASTID THEORY. - - - History of the Development of the Earth.--Kant's Theory - of the Development of the Universe, or the Cosmological - Gas Theory.--Development of Suns, Planets, and - Moons.--First Origin of Water.--Comparison of Organisms - and Anorgana.--Organic and Inorganic Substances.--Degrees - of Density, or Conditions of Aggregation.--Albuminous - Combinations of Carbon.--Organic and Inorganic - Forms.--Crystals and Formless Organisms without - Organs.--Stereometrical Fundamental Forms of Crystals and - of Organisms.--Organic and Inorganic Forces.--Vital - Force.--Growth and Adaptation in Crystals and in - Organisms.--Formative Tendencies of Crystals.--Unity of - Organic and Inorganic Nature.--Spontaneous Generation, or - Archigony.--Autogony and Plasmogony.--Origin of Monera by - Spontaneous Generation.--Origin of Cells from - Monera.--The Cell Theory.--The Plastid Theory.--Plastids, - or Structural Units.--Cytods and Cells.--Four Different - Kinds of Plastids. - - -In our considerations hitherto we have endeavoured to answer the -question, "By what causes have new species of animals and plants arisen -out of existing species?" We have answered this question according to -Darwin's theory, that natural selection in the struggle for -existence--that is, the interaction of the laws of Inheritance and -Adaptation--is completely sufficient for producing mechanically the -endless variety of the different animals and plants, which have the -appearance of being organized according to a plan for a definite -purpose. Meanwhile the question must have already repeatedly presented -itself to the reader, how did the first organisms, or that one original -and primaeval organism arise, from which we derive all the others? - -This question Lamarck(2) answered by the hypothesis of _spontaneous -generation_, or _archigony_. But Darwin passes over and avoids this -subject, as he expressly remarks that he has "nothing to do with the -origin of the soul, nor with that of life itself." At the conclusion of -his work he expresses himself more distinctly in the following -words:--"I imagine that probably all organic beings which ever lived on -this earth descended from some primitive form, which was first called -into life by the Creator." Moreover, Darwin, for the consolation of -those who see in the Theory of Descent the destruction of the whole -"moral order of the universe," appeals to the celebrated author and -divine who wrote to him, that "he has gradually learnt to see that it is -just as noble a conception of the Deity to believe that he created a few -original forms capable of self-development into other and needful forms, -as to believe that he required a fresh act of creation to supply the -voids caused by the action of his laws." - -Those to whom the belief in a supernatural creation is an emotional -necessity may rest satisfied with this conception. They may reconcile -that belief with the Theory of Descent; for in the creation of a single -original organism possessing the capability to develop all others out of -itself by inheritance and adaptation, they can really find much more -cause for admiring the power and wisdom of the Creator than in the -independent creation of different species. - -If, taking this point of view, we were to explain the origin of the -first terrestrial organisms, from which all the others are descended, as -due to the action of a personal Creator acting according to a definite -plan, we should of course have to renounce all scientific knowledge of -the process, and pass from the domain of true science to the completely -distinct domain of poetical faith. By assuming a supernatural act of -creation we should be taking a leap into the inconceivable. Before we -decide upon this latter step, and thereby renounce all pretension to a -scientific knowledge of the process, we are at all events in duty bound -to endeavour to examine it in the light of a mechanical hypothesis. We -must at least examine whether this process is really so wonderful, and -whether we cannot form a tenable conception of a completely -non-miraculous origin of the first primary organism. We might then be -able entirely to reject miracle in creation. - -It will be necessary for this purpose, first of all, to go back further -into the past, and to examine the history of the creation of the earth. -Going back still further, we shall find it necessary to consider the -history of the creation of the whole universe in its most general -outlines. All my readers undoubtedly know that from the structure of the -earth, as it is at present known to us, the notion has been derived, and -as yet has not been refuted, that its interior is in a fiery fluid -condition, and that the firm crust, composed of different strata, on the -surface of which organisms are living, forms only a very thin pellicle -or shell round the fiery fluid centre. We have arrived at this idea by -different confirmatory experiments and reasonings. In the first place, -the observation that the temperature of the earth's crust continually -increases towards the centre is in favour of this supposition. The -deeper we descend, the greater the warmth of the ground, and in such -proportion, that with every 100 feet the temperature increases about one -degree. At a depth of six miles, therefore, a heat of 1500 deg. would be -attained, sufficient to keep most of the firm substances of our earth's -crust in a molten, fiery, fluid state. This depth, however, is only the -286th part of the whole diameter of the earth (1717 miles). We further -know that springs which rise out of a considerable depth possess a very -high temperature, and sometimes even throw water up to the surface in a -boiling state. Lastly, very important proofs are furnished by volcanic -phenomena, the eruption of fiery fluid masses of stone bursting through -certain parts of the earth's crust. All these phenomena lead us with -great certainty to the important assumption that the firm crust of the -earth forms only quite a small fraction, not nearly the one-thousandth -part of the whole diameter of the terrestrial globe, and that the rest -is still for the most part in a molten or fiery fluid state. - -Now if, starting with this assumption, we reflect on the ancient history -of the development of the globe, we are logically carried back a step -further, namely, to the assumption that at an earlier date the whole -earth was a fiery fluid body, and that the formation of a thin, -stiffened crust on the surface was only a later process. Only gradually, -by radiating its intrinsic heat into the cold space of the universe, has -the surface of the glowing ball become condensed into a thin crust. -That the temperature of the earth in remote times was much higher than -it is now, is proved by many phenomena. Among other things, this is -rendered probable by the equal distribution of organisms in remote times -of the earth's history. While at present, as is well known, the -different populations of animals and plants correspond to the different -zones of the earth and their appropriate temperature, in earlier times -this was distinctly not the case. - -We see from the distribution of fossils in the remoter ages, that it was -only at a very late date, in fact, at a comparatively recent period of -the organic history of the earth (at the beginning of the so-called -caenolithic or tertiary period), that a separation of zones and of the -corresponding organic populations occurred. During the immensely long -primary and secondary periods, tropical plants, which require a very -high degree of temperature, lived not only in the present torrid zone, -under the equator, but also in the present temperate and frigid zones. -Many other phenomena also demonstrate a gradual decrease of the -temperature of the globe as a whole, and especially a late and gradual -cooling of the earth's crust about the poles. Bronn, in his excellent -"Investigations of the Laws of Development of the Organic World," has -collected numerous geological and palaeontological proofs of this fact. - -These phenomena and the mathematico-astronomical knowledge of the -structure of the universe justify the theory that, inconceivable ages -ago, long before the first existence of organisms, the whole earth was a -fiery fluid globe. Now, this theory corresponds with the grand theory of -the origin of the universe, and especially of our planetary system, -which, on the ground of mathematical and astronomical facts, was put -forward in 1755 by our critical philosopher Kant,(22) and was later more -thoroughly established by the celebrated mathematicians, Laplace and -Herschel. This cosmogeny, or theory of the development of the universe, -is now almost universally acknowledged; it has not been replaced by a -better one, and mathematicians, astronomers, and geologists have -continually, by various arguments, strengthened its position. - -Kant's cosmogeny maintains that _the whole universe, inconceivable ages -ago, consisted of a gaseous chaos_. All the substances which are found -at present separated on the earth, and other bodies of the universe, in -different conditions of density--in the solid, semi-fluid, liquid, and -elastic fluid or gaseous states of aggregation--originally constituted -together one single homogeneous mass, equally filling up the space of -the universe, which, in consequence of an extremely high degree of -temperature, was in an exceedingly thin gaseous or nebulous state. The -millions of bodies in the universe which at present form the different -solar systems did not then exist. They originated only in consequence of -a universal rotatory movement, or rotation, during which a number of -masses acquired greater density than the remaining gaseous mass, and -then acted upon the latter as central points of attraction. Thus arose a -separation of the chaotic primary nebula, or gaseous universe, into a -number of rotating nebulous spheres, which became more and more -condensed. Our solar system was such a gigantic gaseous or nebulous -ball, all the particles of which revolved round a common central point, -the solar nucleus. The nebulous ball itself, like all the rest, in -consequence of its rotatory movement, assumed a spheroidal or a -flattened globular form. - -While the centripetal force attracted the rotating particles nearer and -nearer to the firm central point of the nebulous ball, and thus -condensed the latter more and more, the centrifugal force, on the other -hand, always tended to separate the peripheral particles further and -further from it, and to hurl them off. On the equatorial sides of the -ball, which was flattened at both poles, this centrifugal force was -strongest, and as soon as, by increase of density, it attained -predominance over the centripetal force, a circular nebulous ring -separated itself from the rotating ball. This nebulous ring marked the -course of future planets. The nebulous mass of the ring gradually -condensed, and became a planet, which revolved round its own axis, and -at the same time rotated round the central body. In precisely the same -manner, from the equator of the planetary mass, as soon as the -centrifugal force gained predominance over the centripetal force, new -nebulous rings were ejected, which moved round the planets as the latter -moved round the sun. These nebulous rings, too, became condensed into -rotating balls. Thus arose the moons, only one of which moves round our -earth, whilst four move round Jupiter, and six round Uranus. The ring of -Saturn still shows us a moon in its early stage of development. As by -increasing refrigeration these simple processes of condensation and -expulsion repeated themselves over and over again, there arose the -different solar systems, the planets rotating round their central suns, -and the satellites or moons moving round their planets. - -The original gaseous condition of the rotating bodies of the universe -gradually changed, by increasing refrigeration and condensation, into -the fiery fluid or molten state of aggregation. By the process of -condensation, a great quantity of heat was emitted, and the rotating -suns, planets, and moons, soon changed into glowing balls of fire, like -gigantic drops of melted metal, which emitted light and heat. By loss of -heat, the melted mass on the surface of the fiery fluid ball became -further condensed, and thus arose a thin, firm crust, which enclosed a -fiery fluid nucleus. In all essential respects our mother earth probably -did not differ from the other bodies of the universe. - -In view of the object of these pages, it will not be of especial -interest to follow in detail the _history of the natural creation of the -universe_, with its different solar and planetary systems, and to -establish it mathematically by the different astronomical and geological -proofs. The outlines of it, which I have just mentioned, must be -sufficient here, and for further details I refer to Kant's[5] "General -History of Nature and Theory of the Heavens."(22) I will only add that -this wonderful theory, which might be called _the cosmological gas -theory_, harmonizes with all the general series of phenomena at present -known to us, and stands in no irreconcilable contradiction to any one of -them. Moreover, it is purely mechanical or monistic, makes use -exclusively of the inherent forces of eternal matter, and entirely -excludes every supernatural process, every prearranged and conscious -action of a personal Creator. Kant's Cosmological Gas Theory -consequently occupies a similar supreme position in _Anorganology_, -especially in _Geology_, and forms the crown of our knowledge in that -department, in the same way as Lamarck's Theory of Descent does in -_Biology_, and especially in _Anthropology_. Both rest exclusively upon -mechanical or unconscious causes (causae efficientes), in no case upon -prearranged or conscious causes (causae finales). (Compare above, p. -100-106.) Both therefore fulfil all the demands of a scientific theory, -and consequently will remain generally acknowledged until they are -replaced by better ones. - -I will, however, not deny that Kant's grand cosmogeny has some weak -points, which prevent our placing the same unconditional confidence in -it as in Lamarck's Theory of Descent. The notion of an original gaseous -chaos filling the whole universe presents great difficulties of various -kinds. A great and unsolved difficulty lies in the fact that the -Cosmological Gas Theory furnishes no starting-point at all in -explanation of the first impulse which caused the rotary motion in the -gas-filled universe. In seeking for such an impulse, we are -involuntarily led to the mistaken questioning about a "first beginning." -We can as little imagine a _first beginning_ of the eternal phenomena of -the motion of the universe as of its final end. - -The universe is unlimited and immeasurable in both space and time. It is -eternal, and it is infinite. Nor can we imagine a beginning or end to -the uninterrupted and eternal motion in which all particles of the -universe are always engaged. The great laws of the _conservation of -force_(38) and the _conservation of matter_, the foundations of our -whole conception of nature, admit of no other supposition. The universe, -as far as it is cognisable to human capability, appears as a connected -chain of material phenomena of motion, necessitating a continual change -of forms. Every form, as the temporary result of a multiplicity of -phenomena of motion, is as such perishable, and of limited duration. -But, in the continual change of forms, matter and the motion inseparable -from it remain eternal and indestructible. - -Now, although Kant's Cosmological Gas Theory is not able to explain the -development of motion in the whole universe in a satisfactory manner, -beyond that gaseous state of chaos, and although many other weighty -considerations may be brought forward against it, especially by -chemistry and geology, yet we must on the whole acknowledge its great -merit, inasmuch as it explains in an excellent manner, by due -consideration of development, the whole structure of all that is -accessible to our observation, that is, the anatomy of the solar -systems, and especially of our planetary system. It may be that this -development was altogether different from what Kant supposes, and our -earth may have arisen by the aggregation of numberless small meteorides, -scattered in space, or in any other manner, but hitherto no one has as -yet been able to establish any other theory of development, or to offer -one in the place of Kant's cosmogeny. - -After this general glance at the monistic cosmogeny, or the -non-miraculous history of the development of the universe, let us now -return to a minute fraction of it, to our mother earth, which we left as -a ball flattened at both poles and in a fiery fluid state, its surface -having condensed by becoming cooled into a very thin firm crust. The -crust, on first cooling, must have covered the whole surface of the -terrestrial sphere as a continuous smooth and thin shell. But soon it -must have become uneven and hummocky; for, since during the continued -cooling, the fiery fluid nucleus became more and more condensed and -contracted, and consequently the diameter of the earth diminished, the -thin cold crust, which could not closely follow the softer nuclear mass, -must have fallen in, in many places. An empty space would have arisen -between the two, had not the pressure of the outer atmosphere forced -down the fragile crust towards the interior, breaking it in so doing. -Other unevennesses probably arose from the fact that, in different -parts, the cooled crust during the process of refrigeration contracted -also itself, and thus became fissured with cracks and rents. The fiery -fluid nucleus flowed up to the external surface through these cracks, -and again became cooled and stiff. Thus, even at an early period there -arose many elevations and depressions, which were the first foundations -of mountains and valleys. - -After the temperature of the cooled terrestrial ball had fallen to a -certain degree, a very important new process was effected, namely, the -_first origin of water_. Water had until then existed only in the form -of steam in the atmosphere surrounding the globe. The water could -evidently not condense into a state of fluid drops until the temperature -of the atmosphere had considerably decreased. Now, then, there began a -further transformation of the earth's crust by the force of water. It -continually fell in the form of rain, and in that form washed down the -elevations of the earth's crust, filling the depressions with the mud -carried along, and, by depositing it in layers, it caused the extremely -important neptunic transformations of the earth's crust, which have -continued since then uninterruptedly, and which in our next chapter we -shall examine a little more closely. - -It was not till the earth's crust had so far cooled that the water had -condensed into a fluid form, it was not till the hitherto dry crust of -the earth had for the first time become covered with liquid water, that -the origin of the first organisms could take place. For all animals and -all plants--in fact, all organisms--consist in great measure of fluid -water, which combines in a peculiar manner with other substances, and -brings them into a semi-fluid state of aggregation. We can therefore, -from these general outlines of the inorganic history of the earth's -crust, deduce the important fact, that at a certain definite time life -had its beginning on earth, and that terrestrial organisms did not exist -from eternity, but at a certain period came into existence for the first -time. - -Now, how are we to conceive of this origin of the first organisms? This -is the point at which most naturalists, even at the present day, are -inclined to give up the attempt at natural explanation, and take refuge -in the miracle of an inconceivable creation. In doing so, as has already -been remarked, they quit the domain of scientific knowledge, and -renounce all further insight into the eternal laws which have determined -nature's history. But before despondingly taking such a step, and before -we despair of the possibility of any knowledge of this important -process, we may at least make an attempt to understand it. Let us see if -in reality the origin of a first organism out of inorganic matter, the -origin of a living body out of lifeless matter, is so utterly -inconceivable and beyond all experience. In one word, let us examine the -question of _spontaneous generation, or archigony_. In so doing, it is -above all things necessary to form a clear idea of the principal -properties of the two chief groups of natural bodies, the so-called -inanimate or inorganic, and the animate or organic bodies, and then -establish what is common to, and what are the differences between, the -two groups. It is desirable to go somewhat carefully into the -_comparison of organisms and anorgana_, since it is commonly very much -neglected, although it is necessary for a right understanding of nature -from the monistic point of view. It will be most advantageous here to -look separately at the three fundamental properties of every natural -body; these are matter, form, and force. Let us begin with _matter_. -(Gen. Morph. iii.) - -By chemistry we have succeeded in analysing all bodies known to us into -a small number of elements or simple substances, which cannot be further -divided, for example, carbon, oxygen, nitrogen, sulphur, and the -different metals: potassium, sodium, iron, gold, etc. At present we know -about seventy such elements or simple substances. The majority of them -are unimportant and rare; the minority only are widely distributed, and -compose not only most of the anorgana, but also all organisms. If we -compare those elements which constitute the body of organisms with those -which are met with in anorgana, we have first to note the highly -important fact that in animal and vegetable bodies no element occurs but -what can be found outside of them in inanimate nature. There are no -special organic elements or simple organic substances. - -The chemical and physical differences existing between organisms and -anorgana, consequently, do not lie in their material foundation; they do -not arise from the different nature of the _elements_ composing them, -but from the different manner in which the latter are united by -chemical _combination_. This different manner of combination gives rise -to certain physical peculiarities, especially in density of substance, -which at first sight seems to constitute a deep chasm between the two -groups of bodies. Inorganic or inanimate natural bodies, such as -crystals and the amorphous rocks, are in a state of density which we -call the firm or solid state, and which we oppose to the liquid state of -water and to the gaseous state of air. It is familiar to every one that -these three different degrees of density, or states of aggregation of -anorgana, are by no means peculiar to the different elements, but are -the results of a certain degree of temperature. Every inorganic solid -body, by increase of temperature, can be reduced to the liquid or melted -state, and, by further heat, to the gaseous or elastic state. In the -same way most gaseous bodies, by a proper decrease of temperature can -first be converted into a liquid state, and further, into a solid state -of density. - -In opposition to these three states of density of anorgana, the living -body of all organisms--animals as well as plants--is in an altogether -peculiar fourth state of aggregation. It is neither solid like stone, -nor liquid like water, but presents rather a medium between these two -states, which may therefore be designated as the firm-fluid or swollen -state of aggregation (viscid). In all living bodies, without exception, -there is a certain quantity of water combined in a peculiar way with -solid matter, and owing to this characteristic combination of water with -solid matter we have that soft state of aggregation, neither solid nor -liquid, which is of great importance in the mechanical explanation of -the phenomena of life. Its cause lies essentially in the physical and -chemical properties of a simple, indivisible, elementary substance, -namely, _carbon_ (Gen. Morph. i. 122-130). - -Of all elements, carbon is to us by far the most important and -interesting, because this simple substance plays the largest part in all -animal and vegetable bodies known to us. It is that element which, by -its peculiar tendency to form complicated combinations with the other -elements, produces the greatest variety of chemical compounds, and among -them the forms and living substance of animal and vegetable bodies. -Carbon is especially distinguished by the fact that it can unite with -the other elements in infinitely manifold relations of number and -weight. By the combination of carbon with three other elements, with -oxygen, hydrogen, and nitrogen (to which generally sulphur, and -frequently, also, phosphorus is added), there arise those exceedingly -important compounds which we have become acquainted with as the first -and most indispensable substratum of all vital phenomena, the albuminous -combinations, or albuminous bodies (protean matter). - -We have before this (p. 185) become acquainted with the simplest of all -species of organisms in the Monera, whose entire bodies when completely -developed consist of nothing but a semi-fluid albuminous lump; they are -organisms which are of the utmost importance for the theory of the first -origin of life. But most other organisms, also, at a certain period of -their existence--at least, in the first period of their life--in the -shape of egg-cells or germ-cells, are essentially nothing but simple -little lumps of such albuminous formative matter, known as plasma, or -protoplasma. They then differ from the Monera only by the fact that in -the interior of the albuminous corpuscle the cell-kernel, or nucleus, -has separated itself from the surrounding cell-substance (protoplasma). -As we have already pointed out, the cells, with their simple attributes, -are so many citizens, who by co-operation and differentiation build up -the body of even the most perfect organism; this being, as it were, a -cell republic (p. 301). The fully developed form and the vital phenomena -of such an organism are determined solely by the activities of these -small albuminous corpuscles. - -It may be considered as one of the greatest triumphs of recent biology, -especially of the theory of tissues, that we are now able to trace the -wonder of the phenomena of life to these substances, and that we can -demonstrate the _infinitely manifold and complicated physical and -chemical properties of the albuminous bodies to be the real cause of -organic or vital phenomena_. All the different forms of organisms are -simply and directly the result of the combination of the different forms -of cells. The infinitely manifold varieties of form, size, and -combination of the cells have arisen only gradually by the division of -labour, and by the gradual adaptation of the simple homogeneous lumps of -plasma, which originally were the only constituents of the cell-mass. -From this it follows of necessity that the fundamental phenomena of -life--nutrition and generation--in their highest manifestations, as well -as in their simplest expressions, must also be traced to the material -nature of that albuminous formative substance. The other vital -activities are gradually evolved from these two. Thus, then, the general -explanation of life is now no more difficult to us than the explanation -of the physical properties of inorganic bodies. All vital phenomena and -formative processes of organisms are as directly dependent upon the -chemical composition and the physical forces of organic matter as the -vital phenomena of inorganic crystals--that is, the process of _their_ -growth and _their_ specific formation--are the direct results of their -chemical composition and of their physical condition. The _ultimate -causes_, it is true, remain in _both_ cases concealed from us. When gold -and copper crystallize in a cubical, bismuth and antimony in a -hexagonal, iodine and sulphur in a rhombic form of crystal, the -occurrence is in reality neither more nor less mysterious to us than is -every elementary process of organic formation, every self-formation of -the organic cell. In this respect we can no longer draw a fundamental -distinction between organisms and anorgana, a distinction of which, -formerly, naturalists were generally convinced. - -Let us secondly examine the agreements and differences which are -presented to us in the _formation_ of organic and inorganic natural -bodies (Gen. Morph. i. 130). Formerly the simple structure of the latter -and the composite structure of the former were looked upon as the -principal distinction. The body of all organisms was supposed to consist -of dissimilar or heterogeneous parts, of instruments or organs which -worked together for the purposes of life. On the other hand, the most -perfect anorgana, that is to say, crystals, were supposed to consist -entirely of continuous or homogeneous matter. This distinction appears -very essential. But it loses all importance through the fact that in -late years we have become acquainted with the exceedingly remarkable and -important Monera.(15) (Compare above, p. 185.) The whole body of these -most simple of all organisms--a semi-fluid, formless, and simple lump of -albumen--consists, in fact, of only a single chemical combination, and -is as perfectly simple in its structure as any crystal, which consists -of a single inorganic combination, for example, of a metallic salt or of -a silicate of the earths and alkalies. - -As naturalists believed in differences in the inner structure or -composition, so they supposed themselves able to find complete -differences in the external forms of organisms and anorgana, especially -in the mathematically determinable crystalline forms of the latter. -Certainly crystallization is pre-eminently a quality of the so-called -anorgana. Crystals are limited by plane surfaces, which meet in straight -lines and at certain measurable angles. Animal and vegetable forms, on -the contrary, seem at first sight to admit of no such geometrical -determination. They are for the most part limited by curved surfaces and -crooked lines, which meet at variable angles. But in recent times we -have become acquainted, among Radiolaria(23) and among many other -Protista, with a large number of lower organisms, whose body, in the -same way as crystals, may be traced to a mathematically determinable -fundamental form, and whose form in its whole, as well as in its parts, -is bounded by definite geometrically determinable planes and angles. In -my general doctrine of _Fundamental Forms, or Promorphology_, I have -given detailed proofs of this, and at the same time established a -general system of forms, the ideal stereometrical type-forms, which -explain the real forms of inorganic crystals, as well as of organic -individuals (Gen. Morph. i. 375-574). Moreover, there are also perfectly -amorphous organisms, like the Monera, Amoeba, etc., which change their -forms every moment, and in which we are as little able to point out a -definite fundamental form as in the case of the shapeless or amorphous -anorgana, such as non-crystallized stones, deposits, etc. We are -consequently unable to find any essential difference in the external -forms or the inner structure of anorgana and organisms. - -Thirdly, let us turn to the _forces_ or the _phenomena of motion_ of -these two different groups of bodies (Gen. Morph. i. 140). Here we meet -with the greatest difficulties. The vital phenomena, known as a rule -only in the highly developed organisms, in the more perfect animals and -plants, seem there so mysterious, so wonderful, so peculiar, that most -persons are decidedly of opinion that in inorganic nature there occurs -nothing at all similar, or in the least degree comparable to them. -Organisms are for this very reason called animate, and the anorgana, -inanimate natural bodies. Hence, even so late as the commencement of the -present century, the science which investigates the phenomena of life, -namely physiology, retained the erroneous idea that the physical and -chemical properties of matter were not sufficient for explaining these -phenomena. In our own day, especially during the last ten years, this -idea may be regarded as having been completely refuted. In physiology, -at least, it has now no place. It now never occurs to a physiologist to -consider any of the vital phenomena as the result of a mysterious _vital -force_, of an active power working for a definite purpose, standing -outside of matter, and, so to speak, taking only the physico-chemical -forces into its service. Modern physiology has arrived at the strictly -monistic conviction that all of the vital phenomena, and, above all, the -two fundamental phenomena of nutrition and propagation are purely -physico-chemical processes, and directly dependent on the material -nature of the organism, just as all the physical and chemical qualities -of every crystal are determined solely by its material composition. Now, -as the elementary substance which determines the peculiar material -composition of organisms is carbon, we must ultimately reduce all vital -phenomena, and, above all, the two fundamental phenomena of nutrition -and propagation to the properties of the carbon. _The -peculiar-chemico-physical properties, and especially the semi-fluid -state of aggregation, and the easy decomposibility of the exceedingly -composite albuminous combinations of carbon, are the mechanical causes -of those peculiar phenomena of motion which distinguish organisms from -anorgana, and which in a narrow sense are usually called "life."_ - -In order to understand this "_carbon theory_," which I have established -in detail in the second book of my General Morphology, it is necessary, -above all things, closely to examine those phenomena of motion which are -common to both groups of natural bodies. First among them is the -_process of growth_. If we cause any inorganic solution of salt slowly -to evaporate, crystals are formed in it, which slowly increase in size -during the continued evaporation of the water. This process of growth -arises from the fact that new particles continually pass over from the -fluid state of aggregation into the solid, and, according to certain -laws, deposit themselves upon the firm kernel of the crystal already -formed. From such an apposition of particles arise the mathematically -definite crystalline shapes. In like manner the growth of organisms -takes place by the accession of new particles. The only difference is -that in the growth of organisms, in consequence of their semi-fluid -state of aggregation, the newly-added particles penetrate into the -interior of the organism (inter-susception), whereas anorgana receive -homogeneous matter from without only by apposition or an addition of new -particles to the surface. This important difference of growth by -inter-susception and by apposition is obviously only the necessary and -direct result of the different conditions of density or state of -aggregation in organisms and anorgana. - -Unfortunately I cannot here follow in detail the various exceedingly -interesting parallels and analogies which occur between the formation of -the most perfect anorgana, the crystals, and the formation of the -simplest organisms, the Monera and their next kindred forms. For this I -must refer to a minute comparison of organisms and anorgana, which I -have carried out in the fifth chapter of my General Morphology (Gen. -Morph. i. 111-160). I have there shown in detail that there exist no -complete differences between organic and inorganic natural bodies, -neither in respect to form and structure, nor in respect to matter and -force; and that the actually existing differences are dependent upon the -peculiar nature of the _carbon_; and that there exists no insurmountable -chasm between organic and inorganic nature. We can perceive this most -important fact very clearly if we examine and compare the origin of the -forms in crystals and in the simplest organic individuals. In the -formation of crystal individuals, two different counteracting formative -tendencies come into operation. The _inner constructive force_, or the -inner formative tendency, which corresponds to the Heredity of -organisms, in the case of the crystal is the direct result of its -material constitution or of its chemical composition. The form of the -crystal, so far as it is determined by this inner original formative -tendency, is the result of the specific and definite way in which the -smallest particles of the crystallizing matter unite together in -different directions according to law. That independent inner formative -force, which is directly inherent in the matter itself, is directly -counteracted by a second formative force. The _external constructive -force_, or the external formative tendency, may be called Adaptation in -crystals as well as in organisms. Every crystal individual during its -formation, like every organic individual, must submit and adapt itself -to the surrounding influences and conditions of existence of the outer -world. In fact, the form and size of every crystal is dependent upon its -whole surroundings, for example, upon the vessel in which the -crystallization takes place, upon the temperature and the pressure of -the air under which the crystal is formed, upon the presence or absence -of heterogeneous bodies, etc. Consequently, the form of every single -crystal, like the form of every single organism, is the result of the -interaction of two opposing factors--the _inner_ formative tendency, -which is determined by the chemical constitution of the _matter itself_, -and of the _external_ formative tendency, which is dependent upon the -influence of _surrounding_ matter. Both these constructive forces -interact similarly also in the organism, and, just as in the crystal, -are of a purely mechanical nature and directly inherent in the substance -of the body. If we designate the growth and the formation of organisms -as a process of life, we may with equal reason apply the same term to -the developing crystal. The teleological conception of nature, which -looks upon organisms as machines of creation arranged for a definite -purpose, must logically acknowledge the same also in regard to the -forms of crystals. The differences which exist between the simplest -organic individuals and inorganic crystals are determined by the _solid_ -state of aggregation of the latter, and by the _semi-fluid_ state of the -former. Beyond that the causes producing form are exactly the same in -both. This conviction forces itself upon us most clearly, if we compare -the exceedingly remarkable phenomena of growth, adaptation, and the -"correlation of parts" of developing crystals with the corresponding -phenomena of the origin of the simplest organic individuals (Monera and -cells). The analogy between the two is so great that, in reality, no -accurate boundary can be drawn. In my General Morphology I have quoted -in support of this a number of striking facts (Gen. Morph. i. 146, 156, -158.) - -If we vividly picture to ourselves this "_unity of organic and inorganic -nature_" this essential agreement of organisms and anorgana in matter, -form, and force, and if we bear in mind that we are not able to -establish any one fundamental distinction between these two groups of -bodies (as was formerly generally assumed), then the question of -spontaneous generation will lose a great deal of the difficulty which at -first seems to surround it. Then the development of the first organism -out of inorganic matter will appear a much more easily conceivable and -intelligible process than has hitherto been the case, whilst an -artificial absolute barrier between organic or animate, and inorganic or -inanimate nature was maintained. - -In the question of _spontaneous generation, or archigony_, which we can -now answer more definitely, it must be borne in mind that by this -conception we understand generally the _non-parental generation of an -organic individual_, the origin of an organism independent of a -parental or producing organism. It is in this sense that on a former -occasion (p. 183) I mentioned spontaneous generation (archigony) as -opposed to parental generation or propagation (tocogony). In the latter -case the organic individual arises by a greater or less portion of an -already existing organism separating itself and growing independently. -(Gen. Morph. ii. 32.) - -In spontaneous generation, which is often also called original -generation (generatio spontanea, aequivoca, primaria etc.), we must first -distinguish two essentially different kinds, namely, _autogeny_ and -_plasmogeny_. By _autogeny_ we understand the origin of a most simple -organic individual in an _inorganic formative fluid_, that is, in a -fluid which contains the fundamental substances for the composition of -the organism dissolved in simple and loose combinations (for example, -carbonic acid, ammonia, binary salts, etc.). On the other hand, we call -spontaneous generation _plasmogeny_ when the organism arises in an -_organic formative fluid_, that is, in a fluid which contains those -requisite fundamental substances dissolved in the form of complicated -and fluid combinations of carbon (for example, albumen, fat, hydrate of -carbon, etc.). (Gen. Morph. i. 174, ii. 33.) - -Neither the process of autogeny, nor that of plasmogeny, has yet been -directly observed with perfect certainty. In early, and also in more -recent times, numerous and interesting experiments have been made as to -the possibility or reality of spontaneous generation. Almost all these -experiments refer not to autogeny, but to plasmogeny, to the origin of -an organism out of already formed organic matter. It is evident, -however, that this latter process is only of subordinate interest for -our history of creation. It is much more important for us to solve the -question, "Is there such a thing as autogeny? Is it possible that an -organism can arise, not out of pre-existing organic, but out of purely -inorganic, matter?" Hence we can quietly lay aside all the numerous -experiments which refer only to plasmogeny, which have been carried on -very zealously during the last ten years, and which for the most part -have had a negative result. For even supposing that the reality of -plasmogeny were strictly proved, still autogeny would not be explained -by it. - -The experiments on autogeny have likewise as yet furnished no certain -and positive result. Yet we must at the outset most distinctly protest -against the notion that these experiments have proved the impossibility -of spontaneous generation in general. Most naturalists who have -endeavoured to decide this question experimentally, and who, after -having employed all possible precautionary measures, under -well-ascertained conditions, have seen no organisms come into being, -have straightway made the assertion, on the ground of these negative -results: "That it is altogether impossible for organisms to come into -existence by themselves without parental generation." This hasty and -inconsiderate assertion they have supported by the negative results of -their experiments, which, after all, could prove nothing except that, -under these or those highly artificial circumstances created by the -experimenters themselves, no organism was developed. From these -experiments, which have been for the most part made under the most -unnatural conditions, and in a highly artificial manner, we can by no -means draw the conclusion that spontaneous generation in general is -impossible. The impossibility of such a process can, in fact, never be -proved. For how can we know that in remote primaeval times there did not -exist conditions quite different from those at present obtaining, and -which may have rendered spontaneous generation possible? Indeed, we can -even positively and with full assurance maintain that the general -conditions of life in primaeval times must have been entirely different -from those of the present time. Think only of the fact that the enormous -masses of carbon which we now find deposited in the primary coal -mountains were first reduced to a solid form by the action of vegetable -life, and are the compressed and condensed remains of innumerable -vegetable substances, which have accumulated in the course of many -millions of years. But at the time when, after the origin of water in a -liquid state on the cooled crust of the earth, organisms were first -formed by spontaneous generation, those immeasurable quantities of -carbon existed in a totally different form, probably for the most part -dispersed in the atmosphere in the shape of carbonic acid. The whole -composition of the atmosphere was therefore extremely different from the -present. Further, as may be inferred upon chemical, physical, and -geological grounds, the density and the electrical conditions of the -atmosphere were quite different. In like manner the chemical and -physical nature of the primaeval ocean, which then continuously covered -the whole surface of the earth as an uninterrupted watery sheet, was -quite peculiar. The temperature, the density, the amount of salt, etc., -must have been very different from those of the present ocean. In any -case, therefore, even if we do not know anything more about it, there -remains to us the supposition, which can at least not be disputed, that -at that time, under conditions quite different from those of to-day, a -spontaneous generation, which now is perhaps no longer possible, may -have taken place. - -But it is necessary to add here that, by the recent progress of -chemistry and physiology, the mysterious and miraculous character which -at first seems to belong to this much disputed and yet inevitable -process of spontaneous generation, has been to a great extent, or almost -entirely, destroyed. Not fifty years ago, all chemists maintained that -we were unable to produce artificially in our laboratories any -complicated combination of carbon, or so-called "organic combination." -The mystic "vital force" alone was supposed to be able to produce these -combinations. When, therefore, in 1828, Woehler, in Goettingen, for the -first time refuted this dogma, and exhibited pure "organic" urea, -obtained in an artificial manner from a purely inorganic body (cyanate -of ammonium), it caused the greatest surprise and astonishment. In more -recent times, by the progress of synthetic chemistry, we have succeeded -in producing in our laboratories a great variety of similar "organic" -combinations of carbon, by purely artificial means--for example alcohol, -acetic acid, formic acid. Indeed, many exceedingly complicated -combinations of carbon are now artificially produced, so that there is -every likelihood, sooner or later, of our producing artificially the -most complicated, and at the same time the most important of all, -namely, the albuminous combinations, or plasma-bodies. By the -consideration of this probability, the deep chasm which was formerly -and generally believed to exist between organic and inorganic bodies is -almost or entirely removed, and the way is paved for the conception of -spontaneous generation. - -Of still greater, nay, the very greatest importance to the hypothesis of -spontaneous generation are, finally, the exceedingly remarkable -_Monera_, those creatures which we have already so frequently mentioned, -and which are not only the simplest of all observed organisms, but even -the simplest of all imaginable organisms. I have already described these -wonderful "_organisms without organs_," when examining the simplest -phenomena of propagation and inheritance. We already know seven -different genera of these Monera, some of which live in fresh water, -others in the sea (compare above, p. 184; also Plate I. and its -explanation in the Appendix). In a perfectly developed and freely motile -state, they one and all present us with nothing but a simple little lump -of an albuminous combination of carbon. The individual genera and -species differ only a little in the manner of propagation and -development, and in the way of taking nourishment. Through the discovery -of these organisms, which are of the utmost importance, the supposition -of a spontaneous generation loses most of its difficulties. For as all -trace of organization--all distinction of heterogeneous parts--is still -wanting in them, and as all the vital phenomena are performed by one and -the same homogeneous and formless matter, we can easily imagine their -origin by spontaneous generation. If this happens through _plasmogeny_, -and if plasma capable of life already exists, it then only needs to -individualize itself in the same way as the mother liquor of crystals -individualizes itself in crystallization. If, on the other hand, the -spontaneous generation of the Monera takes place by true _autogeny_, -then it is further requisite that that plasma capable of life, that -primaeval mucus, should be formed out of simpler combinations of carbon. -As we are now able artificially to produce, in our laboratories, -combinations of carbon similar to this in the complexity of their -constitution, there is absolutely no reason for supposing that there are -not conditions in free nature also, in which such combinations could -take place. Formerly, when the doctrine of spontaneous generation was -advocated, it failed at once to obtain adherents on account of the -composite structure of the simplest organisms then known. It is only -since we have discovered the exceedingly important Monera, only since we -have become acquainted in them with organisms not in any way built up of -distinct organs, but which consist solely of a single chemical -combination, and yet grow, nourish, and propagate themselves, that this -great difficulty has been removed, and the hypothesis of spontaneous -generation has gained a degree of probability which entitles it to fill -up the gap existing between Kant's cosmogony and Lamarck's Theory of -Descent. Even among the Monera at present known there is a species which -probably, even now, always comes into existence by spontaneous -generation. This is the wonderful _Bathybius Haeckelii_, discovered and -described by Huxley. As I have already mentioned (p. 184), this Moneron -is found in the greatest depths of the sea, at a depth of between 12,000 -and 24,000 feet, where it covers the ground partly as retiform threads -and plaits of plasma, partly in the form of larger or smaller irregular -lumps of the same material.[6] - -Only such homogeneous organisms as are yet not differentiated, and are -similar to inorganic crystals in being homogeneously composed of one -single substance, could arise by spontaneous generation, and could -become the primaeval parents of all other organisms. In their further -development we have pointed out that the most important process is the -formation of a _kernel_ or _nucleus_ in the simple little lump of -albumen. We can conceive this to take place in a purely physical manner, -by the condensation of the innermost central part of the albumen. The -more solid central mass, which at first gradually shaded off into the -peripheral plasma, becomes sharply separated from it, and thus forms an -independent, round, albuminous corpuscle, the kernel; and by this -process the Moneron becomes a _cell_. Now, it must have become evident -from our previous chapters, that the further development of all other -organisms out of such a cell presents no difficulty, for every animal -and every plant, in the beginning of its individual life, is a simple -cell. Man, as well as every other animal, is at first nothing but a -simple egg-cell, a single lump of mucus, containing a kernel (p. 297, -Fig. 5). - -In the same way as the kernel of the organic cell arose in the interior -or central mass of the originally homogeneous lump of plasma, by -separation, so, too, the first _cell-membrane_ was formed on its -surface. This simple, but most important process, as has already been -remarked, can likewise be explained in a purely physical manner, either -as a chemical deposit, or as a physical condensation in the uppermost -stratum of the mass, or as a secretion. One of the first processes of -adaptation effected by the Moneron originating by spontaneous generation -must have been the condensation of an external crust, which as a -protecting covering shut in the softer interior from the hostile -influences of the outer world. As soon as, by condensation of the -homogeneous Moneron, a cell-kernel arose in the interior and a membrane -arose on the surface, all the fundamental parts of the unit were -furnished, out of which, by infinitely manifold repetition and -combination, as attested by actual observation, the body of higher -organisms is constructed. - -As has already been mentioned, our whole understanding of an organism -rests upon the cell theory established thirty years ago by Schleiden and -Schwann. According to it, every organism is either a simple cell or a -cell-community, a republic of closely connected cells. All the forms and -vital phenomena of every organism are the collective result of the forms -and vital phenomena of all the single cells of which it is composed. By -the recent progress of the cell theory it has become necessary to give -the elementary organisms, that is, the "organic" individuals of the -first order, which are usually designated as _cells_, the more general -and more suitable name of _form-units_, or _plastids_. Among these -form-units we distinguish two main groups, namely, the cytods and the -genuine cells. The _cytods_ are, like the Monera, pieces of plasma -without a kernel (p. 186, Fig. 1). _Cells_, on the other hand, are -pieces of plasma containing a kernel or nucleus (p. 188, Fig. 2). Each -of these two main groups of plastids is again divided into two -subordinate groups, according as they possess or do not possess an -external covering (skin, shell, or membrane). We may accordingly -distinguish the following four grades or species of plastids, namely: 1. -_Simple cytods_ (p. 186, Fig. 1 _A_); 2. _Encased cytods_; 3. _Simple -cells_ (p. 188, Fig. 2 _B_); 4. _Encased cells_ (p. 188, Fig. 2 _A_). -(Gen. Morph. i. 269-289.) - -Concerning the relation of these four forms of plastids to spontaneous -generation, the following is the most probable:--1. The _simple cytods_ -(Gymnocytoda), naked particles of plasma without kernel, like the still -living Monera, are the only plastids which directly come into existence -by spontaneous generation. 2. The _enclosed cytods_ (Lepocytoda), -particles of plasma without kernel, which are surrounded by a covering -(membrane or shell), arose out of the simple cytods either by the -condensation of the outer layers of plasma or by the secretion of a -covering. 3. The _simple cells_ (Gymnocyta), or naked cells, particles -of plasma with kernel, but without covering, arose out of the simple -cytods by the condensation of the innermost particles of plasma into a -kernel, or nucleus, by differentiation of a central kernel and -peripheral cell-substance. 4. The _enclosed cells_ (Lepocyta), or -testaceous cells, particles of plasma with kernel and an outer covering -(membrane or shell), arose either out of the enclosed cytods by the -formation of a kernel, or out of the simple cells by the formation of a -membrane. All the other forms of form-units, or plastids, met with, -besides these, have only subsequently arisen out of these four -fundamental forms by natural selection, by descent with adaptation, by -differentiation and transformation. - -By this _theory of plastids_, by deducing all the different forms of -plastids, and hence, also, all organisms composed of them, from the -Monera, we obtain a simple and natural connection in the whole series of -the development of nature. The origin of the first Monera by spontaneous -generation appears to us as a simple and necessary event in the process -of the development of the earth. We admit that this process, as long as -it is not directly observed or repeated by experiment, remains a pure -hypothesis. But I must again say that this hypothesis is indispensable -for the consistent completion of the non-miraculous history of creation, -that it has absolutely nothing forced or miraculous about it, and that -certainly it can never be positively refuted. It must be taken into -consideration that the process of spontaneous generation, even if it -still took place daily and hourly, would in any case be exceedingly -difficult to observe and establish with absolute certainty as such. With -regard to the Monera, we find ourselves placed before the following -alternative: _either_ they are actually directly derived from -pre-existing, or "created," most ancient Monera, and in this case they -would have had to propagate themselves unchanged for many millions of -years, and to have maintained their original form of simple particles of -plasma; _or_, the _present_ Monera have originated much later in the -course of the organic history of the earth, by repeated acts of -spontaneous generation, and in this case spontaneous generation may take -place now as well as then. The latter supposition has evidently much -more probability on its side than the former. - -If we do not accept the hypothesis of spontaneous generation, then at -this one point of the history of development we must have recourse to -the miracle of a _supernatural creation_. The Creator must have created -the first organism, or a few first organisms, from which all others are -derived, and as such he must have created the simplest Monera, or -primaeval cytods, and given them the capability of developing further in -a mechanical way. I leave it to each one of my readers to choose between -this idea and the hypothesis of spontaneous generation. To me the idea -that the Creator should have in this one point arbitrarily interfered -with the regular process of development of matter, which in all other -cases proceeds entirely without his interposition, seems to be just as -unsatisfactory to a believing mind as to a scientific intellect. If, on -the other hand, we assume the hypothesis of spontaneous generation for -the origin of the first organisms, which in consequence of reasons -mentioned above, and especially in consequence of the discovery of the -Monera, has lost its former difficulty, then we arrive at the -establishment of an uninterrupted natural connection between the -development of the earth and the organisms produced on it, and, in this -last remaining lurking-place of obscurity, we can proclaim the _unity of -all Nature, and the unity of her laws of Development_ (Gen. Morph. i. -164). - - - - -CHAPTER XIV. - -MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE ICE-PERIOD OF -THE EARTH. - - - Chorological Facts and Causes.--Origin of most Species in - one Single Locality: "Centres of Creation."--Distribution - by Migration.--Active and Passive Migrations of Animals - and Plants.--Means of Transport.--Transport of Germs by - Water and by Wind.--Continual Change of the Area of - Distribution by Elevations and Depressions of the - Ground.--Chorological Importance of Geological - Processes.--Influence of the Change of Climate.--Ice or - Glacial Period.--Its Importance to Chorology.--Importance - of Migrations for the Origin of New Species.--Isolation - of Colonists.--Wagner's Law of Migration.--Connection - between the Theory of Migration and the Theory of - Selection.--Agreement of its Results with the Theory of - Descent. - - -As I have repeatedly said, but cannot too much emphasize, the actual -value and invincible strength of the Theory of Descent does not lie in -its explaining this or that single phenomenon, but in the fact that it -explains _all_ biological phenomena, that it makes _all_ botanical and -zoological series of phenomena intelligible in their relations to one -another. Hence every thoughtful investigator is the more firmly and -deeply convinced of its truth the more he advances from single -biological observations to a general view of the whole domain of animal -and vegetable life. Let us now, starting from this comprehensive point -of view, survey a biological domain, the varied and complicated -phenomena of which may be explained with remarkable simplicity and -clearness by the theory of selection. I mean _Chorology_, or the theory -of the _local distribution of organisms over the surface of the earth_. -By this I do not only mean the _geographical_ distribution of animal and -vegetable species over the different parts and provinces of the earth, -over continents and islands, seas, and rivers; but also their -_topographical_ distribution in a _vertical_ direction, their ascending -to the heights of mountains, and their descending into the depths of the -ocean. (Gen. Morph. ii. 286.) - -The strange chorological series of phenomena which show the horizontal -distribution of organisms over parts of the earth, and their vertical -distribution in heights and depths, have long since excited general -interest. In recent times Alexander Humboldt(39) and Frederick Schouw -have especially discussed the geography of plants, and Berghaus and -Schmarda the geography of animals, on a large scale. But although these -and several other naturalists have in many ways increased our knowledge -of the distribution of animal and vegetable forms, and laid open to us a -new domain of science, full of wonderful and interesting phenomena, yet -Chorology as a whole remained, as far as their labours were concerned, -only a desultory knowledge of a mass of individual _facts_. It could not -be called a science as long as the _causes_ for the explanation of these -facts were wanting. These causes were first disclosed by the theory of -selection and its doctrine of the _migrations_ of animal and vegetable -species, and it is only since the works of Darwin and Wallace that we -have been able to speak of an independent _science of Chorology_. - -If all the phenomena of the geographical and topographical distribution -of organisms are examined by themselves, without considering the gradual -development of species, and if at the same time, following the customary -superstition, the individual species of animals and plants are -considered as forms independently created and independent of one -another, then there remains nothing for us to do but to gaze at those -phenomena as a confused collection of incomprehensible and inexplicable -miracles. But as soon as we leave this low stand-point, and rise to the -height of the theory of development, by means of the supposition of a -blood-relationship between the different species, then all at once a -clear light falls upon this strange series of miracles, and we see that -all chorological facts can be understood quite simply and clearly by the -supposition of a common descent of the species, and their passive and -active migrations. - -The most important principle from which we must start in chorology, and -of the truth of which we are convinced by due examination of the theory -of selection, is that, as a rule, every animal and vegetable species has -arisen only _once_ in the course of time and only in _one_ place on the -earth--its so-called "centre of creation"--by natural selection. I share -this opinion of Darwin's unconditionally, in respect to the great -majority of higher and perfect organisms, and in respect to most animals -and plants in which the division of labour, or differentiation of the -cells and organs of which they are composed, has attained a certain -stage. For it is quite incredible, or could at best only be an -exceedingly rare accident, that all the manifold and complicated -circumstances--all the different conditions of the struggle for life, -which influence the origin of a new species by natural selection--should -have worked together in exactly the same agreement and combination more -than once in the earth's history, or should have been active at the same -time at several different points of the earth's surface. - -On the other hand, I consider it to be very probable that certain -exceedingly imperfect organisms of the simplest structure, forms of -species of an exceedingly indifferent nature, as, for example, many -single-celled Protista, but especially the Monera, the simplest of them -all, should have several times or simultaneously arisen in their -specific form in several parts of the earth. For the few and very simple -conditions by which their specific form was changed in the struggle for -life may surely have often been repeated, in the course of time, -independently in different parts of the earth. Further, those higher -specific forms also, which have not arisen by natural selection, but by -_hybridism_ (the previously-mentioned hybrid species, pp. 147 and 275), -may have repeatedly arisen anew in different localities. As, however, -this proportionately small number of organisms does not especially -interest us here, we may, in respect of chorology, leave them alone, and -need only take into consideration the distribution of the great majority -of animal and vegetable species in regard to which the _single origin of -every species in a single locality_, in its so-called "central point of -creation," can be considered as tolerably certain. - -Every animal and vegetable species from the beginning of its existence -has possessed the tendency to spread beyond the limited locality of its -origin, beyond the boundary of its "centre of creation," or, in other -words, beyond its _primaeval home_, or its natal place. This is a -necessary consequence of the relations of population and over-population -(pp. 161 and 256). The more an animal or vegetable species increases, -the less is its limited natal place sufficient for its sustenance, and -the fiercer the struggle for life; the more rapid the _over-population_ -of the natal spot, the more it leads to _emigration_. These _migrations_ -are common to all organisms, and are the real cause of the wide -distribution of the different species of organisms over the earth's -surface. Just as men leave over-crowded states, so all animals and -plants migrate from their over-crowded primaeval homes. - -Many distinguished naturalists, especially Lyell(11) and Schleiden, have -before this repeatedly drawn attention to the great importance of these -very interesting migrations of organisms. The means of transport by -which they are effected are extremely varied. Darwin has discussed these -most excellently in the eleventh and twelfth chapters of his work, which -are exclusively devoted to "geographical distribution." The means of -transport are partly active, partly passive; that is to say, the -organism effects its migration partly by free locomotion due to its own -activity, and partly by the movements of other natural bodies in which -it has no active share. - -It is self-evident that _active migrations_ play the chief part in -animals able to move freely. The more freely an animal's organization -permits it to all move in directions, the more easily the animal species -can migrate, and the more rapidly it will spread over the earth. -_Flying_ animals are of course most favoured in this respect, among -vertebrate animals especially birds, and among articulated animals, -insects. These two classes, as soon as they came into existence, can -have more easily spread over the whole earth than any other animal, and -this fact partly explains the extraordinary uniformity of structure -which characterizes these two great classes of animals. For, although -they contain an exceedingly large number of different species, and -although the insect class alone is said to possess more different -species than all other classes of animals together, yet all the -innumerable species of insects, and in like manner, also, the different -species of birds, agree most strikingly in all essential peculiarities -of their organization. Hence, in the class of insects, as well as in -that of birds, we can distinguish only a very small number of large -natural groups or orders, and these few orders differ but very little -from one another in their internal structure. The orders of birds with -their numerous species are not nearly as distinct from one another as -the orders of the mammalian class, containing much fewer species; and -the orders of insects, which are extremely rich in genera and species, -resemble one another much more closely in their internal structure than -do the much smaller orders of the crab class. The general parallelism -between birds and insects is also very interesting in relation to -systematic zoology; and the great importance of their richness in forms, -for scientific morphology, lies in the fact that they show us how, -within the narrowest anatomical sphere, and without profound changes of -the essential internal organization, the greatest variety in external -bodily forms can be attained. The reason of this is evidently their -flying mode of life and their free locomotion. In consequence of this -birds, as well as insects, have spread very rapidly over the whole -surface of the earth, have settled in all possible localities -inaccessible to other animals, and variously modified their specific -form by superficial adaptation to particular local relations. - -Next to the flying animals, those animals, of course, have spread most -quickly and furthest which were next best able to migrate, that is, the -best runners among the inhabitants of the land, and the best swimmers -among the inhabitants of the water. However, the power of such active -migrations is not confined to those animals which throughout life enjoy -free locomotion. For the fixed animals also, such as corals, tubicolous -worms, sea-squirts, lily encrinites, sea-acorns, barnacles, and many -other lower animals which adhere to seaweeds, stones, etc., enjoy, at -least at an early period of life, free locomotion. They all migrate -before they adhere to anything. Their first free locomotive condition of -early life is generally that of a "ciliated" larva, a roundish, cellular -corpuscle, which, by means of a garb of movable "flimmer-hairs," (Latin, -"cilia") swarms about in the water and bears the name of Planula. - -But the power of free locomotion, and hence, also, of active migration, -is not confined to animals alone, but many plants likewise enjoy it. -Many lower aquatic plants, especially the class of the Tangles (Algae), -swim about freely in the water in early life, like the lower animals -just mentioned, by means of a vibratile hairy coat, a vibrating whip, or -a covering of tremulous fringes, and only at a later period adhere to -objects. Even in the case of many higher plants, which we designate as -creepers and climbing plants, we may speak of active migration. Their -elongated stalks and perennial roots creep or climb during their long -process of growth to new positions, and by means of their widespread -branches they acquire new habitations, to which they attach themselves -by buds, and bring forth new colonies of individuals of their species. - -Influential as these active migrations of most animals and many plants -are, yet alone they would by no means be sufficient to explain the -chorology of organisms. _Passive migrations_ have ever been by far the -more important, and of far greater influence, in the case of most plants -and in that of many animals. Such passive changes of locality are -produced by extremely numerous causes. Air and water in their eternal -motion, wind and waves with their manifold currents, play the chief -part. The wind in all places and at all times raises light organisms, -small animals and plants, but especially their young germs, animal eggs -and plant seeds, and carries them far over land and seas. Where they -fall into the water they are seized by currents or waves and carried to -other places. It is well known, from numerous examples, how far in many -cases trunks of trees, hard shelled fruits, and other not readily -perishable portions of plants are carried away from their original home -by the course of rivers and by the currents of the sea. Trunks of palm -trees from the West Indies are brought by the Gulf Stream to the British -and Norwegian coasts. All large rivers bring down driftwood from the -mountains, and frequently alpine plants are carried from their home at -the source of the river into the plains, and even further, down to the -sea. Frequently numerous inhabitants live between the roots of the -plants thus carried down, and between the branches of the trees thus -washed away there are various inhabitants which have to take part in the -passive migration. The bark of the tree is covered with mosses, lichens, -and parasitic insects. Other insects, spiders, etc., even small -reptiles and mammals, are hidden within the hollow trunk or cling to the -branches. In the earth adhering to the fibres of the roots, in the dust -lying in the cracks of the bark, there are innumerable germs of smaller -animals and plants. Now, if the trunk thus washed away lands safely on a -foreign shore or on a distant island, the guests who had to take part in -the involuntary voyage can leave their boat and settle in the new -country. A very remarkable kind of water-transport is formed by the -floating icebergs which annually become loosened from the eternal ice of -the Polar Sea. Although these cold regions are thinly peopled, yet many -of their inhabitants, who were accidentally upon an iceberg while it was -becoming loosened, are carried away with it by the currents, and landed -on warmer shores. In this manner, by means of loosened blocks of ice -from the northern Polar Sea, often whole populations of small animals -and plants have been carried to the northern shores of Europe and -America. Nay, even polar foxes and polar bears have been carried in this -way to Iceland and to the British Isles. - -Transport by air is no less important than transport by water in this -matter of passive migration. The dust covering our streets and roofs, -the earth lying on dry fields and dried-up pools, the light moist soil -of forests, in short, the whole surface of the globe contains millions -of small organisms and their germs. Many of these small animals and -plants can without injury become completely dried up, and awake again to -life as soon as they are moistened. Every gust of wind raises up with -the dust innumerable little creatures of this kind, and often carries -them away to other places miles off. But even larger organisms, and -especially their germs, may often make distant passive journeys through -the air. The seeds of many plants are provided with light feathery -processes, which act as parachutes and facilitate their flight in the -air, and prevent their falling. Spiders make journeys of many miles -through the air on their fine filaments, their so-called gossamer -threads. Young frogs are frequently raised by whirlwinds into the air by -thousands, and fall down in a distant part as a "shower of frogs." -Storms may carry birds and insects across half the earth's -circumference. They drop in the United States, having risen in England. -Starting from California, they only come to rest in China. But, again, -many other organisms may make the journey from one continent to another -together with the birds and insects. Of course all parasites, the number -of which is legion, fleas, lice, mites, moulds, etc., migrate with the -organisms upon which they live. In the earth which often remains -sticking to the claws of birds there are also small animals and plants -or their germs. Thus the voluntary or involuntary migration of a single -larger organism may carry a whole small flora and fauna from one part of -the earth to another. - -Besides the means of transport here mentioned, there are many others -which explain the distribution of animal and vegetable species over the -large tracts of the earth's surface, and especially the general -distribution of the so-called cosmopolitan species. But these alone -would not nearly be sufficient to explain all chorological facts. How is -it, for example, that many inhabitants of fresh water live in various -rivers or lakes far away and quite apart from one another? How is it -that many inhabitants of mountains, which cannot exist in plains, are -found upon entirely separated and far distant chains of mountains? It -is difficult to believe, and in many cases quite inconceivable, that -these inhabitants of fresh water should have in any way, actively or -passively, migrated over the land lying between the lakes, or that the -inhabitants of mountains in any way, actively or passively, crossed the -plains lying between their mountain homes. But here geology comes to our -help, as a mighty ally, and completely solves these difficult problems -for us. - -The history of the earth's development shows us that the distribution of -land and water on its surface is ever and continually changing. In -consequence of geological changes of the earth's crust, _elevations_ and -_depressions_ of the ground take place everywhere, sometimes more -strongly marked in one place, sometimes in another. Even if they happen -so slowly that in the course of centuries the seashore rises or sinks -only a few inches, or even only a few lines, still they nevertheless -effect great results in the course of long periods of time. And -long--immeasurably long--periods of time have not been wanting in the -earth's history. During the course of many millions of years, ever since -organic life existed on the earth, land and water have perpetually -struggled for supremacy. Continents and islands have sunk into the sea, -and new ones have arisen out of its bosom. Lakes and seas have slowly -been raised and dried up, and new water basins have arisen by the -sinking of the ground. Peninsulas have become islands by the narrow neck -of land which connected them with the mainland sinking into the water. -The islands of an archipelago have become the peaks of a continuous -chain of mountains by the whole floor of their sea being considerably -raised. - -Thus the Mediterranean at one time was an inland sea, when, in the place -of the Straits of Gibraltar, an isthmus connected Africa with Spain. -England, even during the more recent history of the earth, when man -already existed, has repeatedly been connected with the European -continent and been repeatedly separated from it. Nay, even Europe and -North America have been directly connected. The South Sea at one time -formed a large Pacific Continent, and the numerous little islands which -now lie scattered in it were simply the highest peaks of the mountains -covering that continent. The Indian Ocean formed a continent which -extended from the Sunda Islands along the southern coast of Asia to the -east coast of Africa. This large continent of former times Sclater, an -Englishman, has called _Lemuria_, from the monkey-like animals which -inhabited it, and it is at the same time of great importance from being -the probable cradle of the human race, which in all likelihood here -first developed out of anthropoid apes. The important proof which Alfred -Wallace has furnished,(36) by the help of chorological facts, that the -present Malayan Archipelago consists in reality of two completely -different divisions, is particularly interesting. The western division, -the Indo-Malayan Archipelago, comprising the large islands of Borneo, -Java, and Sumatra, was formerly connected by Malacca with the Asiatic -continent, and probably also with the Lemurian continent just mentioned. -The eastern division, on the other hand, the Austro-Malayan Archipelago, -comprising Celebes, the Moluccas, New Guinea, Solomon's Islands, etc., -was formerly directly connected with Australia. Both divisions were -formerly two continents separated by a strait, but they have now for -the most part sunk below the level of the sea. Wallace, solely on the -ground of his accurate chorological observations, has been able in the -most acute manner to determine the position of this former strait, the -south end of which passes between Balij and Lombok. - -Thus, ever since liquid water existed on the earth, the boundaries of -water and land have eternally changed, and we may assert that the -outlines of continents and islands have never remained for an hour, nay, -even for a minute, exactly the same. For the waves eternally and -perpetually break on the edge of the coast, and whatever the land in -these places loses in extent, it gains in other places by the -accumulation of mud, which condenses into solid stone and again rises -above the level of the sea as new land. Nothing can be more erroneous -than the idea of a firm and unchangeable outline of our continents, such -as is impressed upon us in early youth by defective lessons on -geography, which are devoid of a geological basis. - -I need hardly draw attention to the fact that these geological changes -of the earth's surface have ever been exceedingly important to the -migrations of organisms, and consequently to their Chorology. From them -we learn to understand how it is that the same or nearly related species -of animals and plants can occur on different islands, although they -could not have passed through the water separating them, and how other -species living in fresh water can inhabit different enclosed -water-basins, although they could not have crossed the land lying -between them. These islands were formerly mountain peaks of a connected -continent, and these lakes were once directly connected with one -another. The former were separated by geological depressions, the latter -by elevations. Now, if we further consider how often and how unequally -these alternating elevations and depressions occur on the different -parts of the earth, and how, in consequence of this, the boundaries of -the geographical tracts of distribution of species become changed, and -if we further consider in what exceedingly various ways the active and -passive migrations of organisms must have been influenced by them, then -we shall be in a position to completely understand the great variety of -the picture which is at present offered to us by the distribution of -animal and vegetable species. - -There is yet another important circumstance to be mentioned here, which -is likewise of great importance for a complete explanation of this -varied geographical picture, and which throws light upon many very -obscure facts, which, without its help, we should not be able to -comprehend. I mean the gradual _change of climate_ which has taken place -during the long course of the organic history of the earth. As we saw in -our last chapter, at the beginning of organic life on the earth a much -higher and more equal temperature must have generally prevailed than at -present. The differences of zones, which in our time are so very -striking, did not exist at all in those times. It is probable that for -many millions of years but one climate prevailed over the whole earth, -which very closely resembled, or even surpassed, the hottest tropical -climate of the present day. The highest north which man has yet reached -was then covered with palms and other tropical plants, the fossil -remains of which are still found there. The temperature of this climate -at a later period gradually decreased; but still the poles remained so -warm that the whole surface of the earth could be inhabited by -organisms. It was only at a comparatively very recent period of the -earth's history, namely, at the beginning of the tertiary period, that -there occurred, as it seems, the first perceptible cooling of the -earth's crust at the poles, and through this the first differentiation -or separation of the different zones of temperature or climatic zones. -But the slow and gradual decrease of temperature continued to extend -more and more within the tertiary period, until at last, at both poles -of the earth, the first permanent ice caps were formed. - -I need scarcely point out in detail how very much this change of climate -must have affected the geographical distribution of organisms, and the -origin of numerous new species. The animal and vegetable species, which, -down to the tertiary period, had found an agreeable tropical climate all -over the earth, even as far as the poles, were now forced either to -adapt themselves to the intruding cold, or to flee from it. Those -species which adapted and accustomed themselves to the decreasing -temperature became new species simply by this very acclimatization, -under the influence of natural selection. The other species, which fled -from the cold, had to emigrate and seek a milder climate in lower -latitudes. The tracts of distribution which had hitherto existed must by -this have been vastly changed. - -However, during the last great period of the earth's history, during the -quaternary period (or diluvial period) succeeding the tertiary one, the -decrease of the heat of the earth from the poles did not by any means -remain stationary. The temperature fell lower and lower, nay, even far -below the present degree. Northern and Central Asia, Europe, and North -America from the north pole, were covered to a great extent by a -connected sheet of ice, which in our part of the earth seems to have -reached the Alps. In a similar manner the cold also advancing from the -south pole covered a large portion of the southern hemisphere, which is -now free from it, with a rigid sheet of ice. Thus, between these vast -lifeless ice continents there remained only a narrow zone to which the -life of the organic world had to withdraw. This period, during which -man, or at least the human ape, already existed, and which forms the -first period of the so-called _diluvial epoch_, is now universally known -as the _ice_ or _glacial period_. - -The ingenious Carl Schimper is the first naturalist who clearly -conceived the idea of the ice period, and proved the great extent of the -former glaciation of Central Europe by the help of the so-called -boulders, or erratic blocks of stone, as also by the "glacier tables." -Louis Agassiz, stimulated by him, and considerably supported by the -independent investigations of the eminent geologist Charpentier, -afterwards undertook the task of carrying out the theory of the ice -period. In England, the geologist Forbes distinguished himself in this -matter, and also was the first to apply it to the theory of migrations -and the geographical distribution of species dependent upon migration. -Agassiz, however, afterwards injured the theory by his one-sided -exaggeration, inasmuch as, from his partiality to Cuvier's theory of -cataclysms, he endeavoured to attribute the destruction of the whole -animate creation then existing, to the sudden coming on of the cold of -the ice period and the "revolution" connected with it. - -It is unnecessary here to enter into detail as to the ice period itself, -and into investigations about its limits, and I may omit this all the -more reasonably since the whole of our recent geological literature is -full of it. It will be found discussed in detail in the works of -Cotta,(31) Lyell,(30) Vogt,(27) Zittel,(32) etc. Its great importance to -us here is that it helps us to explain the most difficult chorological -problems, as Darwin has correctly perceived. - -For there can be no doubt that this glaciation of the present temperate -zones must have exercised an exceedingly important influence on the -geographical and topographical distribution of organisms, and that it -must have entirely changed it. While the cold slowly advanced from the -poles towards the equator, and covered land and sea with a connected -sheet of ice, it must of course have driven the whole living world -before it. Animals and plants had to migrate if they wished to escape -being frozen. But as at that time the temperate and tropical zones were -probably no less densely peopled with animals and plants than at -present, there must have arisen a fearful struggle for life between the -latter and the intruders coming from the poles. During this struggle, -which certainly lasted many thousands of years, many species must have -perished and many become modified and been transformed into new species. -The hitherto existing tracts of distribution of species must have become -completely changed, and the struggle have been continued, nay, indeed, -must have broken out anew and been carried on in new forms, when the ice -period had reached and gone beyond its furthest point, and when in the -post-glacial period the temperature again increased, and organisms began -to migrate back again towards the poles. - -In any case this great change of climate, whether a greater or less -importance be ascribed to it, is one of those occurrences in the history -of the earth which have most powerfully influenced the distribution of -organic forms. But more especially one important and difficult -chorological circumstance is explained by it in the simplest manner, -namely, the specific agreement of many of our Alpine inhabitants with -some of those living in polar regions. There is a great number of -remarkable animal and vegetable forms which are common to these two far -distant parts of the earth, and which are found nowhere in the wide -plains lying between them. Their migration from the polar lands to the -Alpine heights, or _vice versa_, would be inconceivable under the -present climatic circumstances, or could be assumed at least only in a -few rare instances. But such a migration could take place, nay, was -obliged to take place, during the gradual advance and retreat of the -ice-sheet. As the glaciation encroached from Northern Europe towards our -Alpine chains, the polar inhabitants retreating before it--gentian, -saxifrage, polar foxes, and polar hares--must have peopled Germany, in -fact all Central Europe. When the temperature again increased, only a -portion of these Arctic inhabitants returned with the retreating ice to -the Arctic zones. Another portion of them climbed up the mountains of -the Alpine chain instead, and there found the cold climate suited to -them. The problem is thus solved in a most simple manner. - -We have hitherto principally considered the _theory of the migrations_ -of organisms in so far as it explains the radiation of every animal and -vegetable species from a single primaeval home, from a "central point of -creation," and the dispersion of these species over a greater or less -portion of the earth's surface. But these migrations are also of great -importance to the theory of development, because we can perceive in them -a very important means for the _origin of new species_. When animals and -plants migrate they meet in their new home, in the same way as do human -emigrants, with conditions which are more or less different from those -which they have inherited throughout generations, and to which they have -been accustomed. The emigrants must either submit and adapt themselves -to these new conditions of life or they perish. By adaptation their -peculiar specific character becomes the more changed the greater the -difference between the new and the old home. The new climate, the new -food, but above all, new neighbours in the forms of other animals and -plants, influence and tend to modify the inherited character of the -immigrant species, and if it is not hardy enough to resist the -influences, then sooner or later a new species must arise out of it. In -most cases this transformation of an immigrant species takes place so -quickly under the influence of the altered struggle for life, that even -after a few generations a new species arises from it. - -Migration has an especial influence in this way on all organisms with -separate sexes. For in them the origin of new species by natural -selection is always rendered difficult, or delayed, by the fact that the -modified descendants occasionally again mix sexually with the unchanged -original form, and thus by crossing return to the first form. But if -such varieties have migrated, if great distances or barriers to -migration--seas, mountains, etc.--have separated them from the old home, -then the danger of a mingling with the primary form is prevented, and -the isolation of the emigrant form, which becomes a new species by -adaptation, prevents its breeding with the old stock, and hence prevents -its return in this way to the original form. - -The importance of migration for the isolation of newly-originating -species and the prevention of a speedy return to the primary form has -been especially pointed out by the philosophic traveller, Moritz Wagner, -of Munich. In a special treatise on "Darwin's Theory and the Law of the -Migration of Organisms,"(40) Wagner gives from his own rich experience a -great number of striking examples which confirm the theory of migration -set forth by Darwin in the eleventh and twelfth chapters of his book, -where he especially discusses the effect of the complete isolation of -emigrant organisms in the origin of new species. Wagner sets forth the -simple causes which have "locally bounded the form and founded its -typical difference," in the following three propositions:--1. The -greater the total amount of change in the hitherto existing conditions -of life which the emigrating individuals find on entering a new -territory, the more intensely must the innate variability of every -organism manifest itself. 2. The less this increased individual -variability of organisms is disturbed in the peaceful process of -reproduction by the mingling of numerous subsequent immigrants of the -same species, the more frequently will nature succeed, by -intensification and transmission of the new characteristics, in forming -a new variety or race, that is, a commencing species. 3. The more -advantageous the changes experienced by the individual organs are to the -variety, the more readily will it be able to adapt itself to the -surrounding conditions; and the longer the undisturbed breeding of a -commencing variety of colonists in a new territory continues without its -mingling with subsequent immigrants of the same species, the oftener a -new species will arise out of the variety. - -Every one will agree with these three propositions of Moritz Wagner's. -But we must consider his view, that the migration and the subsequent -isolation of the emigrant individuals is a _necessary_ condition for the -origin of new species, to be completely erroneous. Wagner says, "without -a long-enduring separation of colonists from their former species, the -formation of a new race cannot succeed--selection, in fact, cannot take -place. Unlimited crossing, unhindered sexual mingling of all individuals -of a species will always produce uniformity, and drive varieties, whose -characteristics have not been fixed throughout a series of generations, -back to the primary form." - -This sentence, in which Wagner himself comprises the main result of his -investigations, he would be able to defend only if all organisms were of -separate sexes, if every origin of new individuals were possible only by -the mingling of male and female individuals. But this is by no means the -case. Curiously enough, Wagner says nothing of the numerous -hermaphrodites which, possessing both the sexual organs, are capable of -self-fructification, and likewise nothing of the countless organisms -which are not sexually differentiated. - -Now, from the earliest times of the organic history of the earth, there -have existed thousands of organic species (thousands of which still -exist) in which no difference of sex whatever exists, and, in fact, in -which no sexual propagation takes place, and which exclusively reproduce -themselves in a non-sexual manner by division, budding, formation of -spores, etc. All the great mass of Protista, the Monera, Amoebae, -Myxomycetes, Rhizopoda, etc., in short, all the lower organisms which we -shall have to enumerate in the domain of Protista, standing midway -between the animal and vegetable kingdoms, propagate themselves -_exclusively in a non-sexual manner_. And this domain comprises a class -of organisms which is one of the richest in forms, nay, even in a -certain respect the richest of all in forms, as all possible geometrical -fundamental forms are represented in it. I allude to the wonderful class -of the Rhizopoda, or Ray-streamers, to which the lime-shelled Acyttaria -and the flint-shelled Radiolaria belong. (Compare chapter xvi.) - -It is self-evident, therefore, that Wagner's theory is quite -inapplicable to all these non-sexual organisms. Moreover, the same -applies to all those hermaphrodites in which every individual possesses -both male and female organs and is capable of self-fructification. This -is the case, for instance, in the Flat-worms, flukes, and tape-worms, -further in the important Sack-worms (Tunicates), the invertebrate -relatives of the vertebrate animals, and in very many other organisms of -different groups. Many of these species have arisen by natural -selection, without a "crossing" of the originating species with its -primary form having been possible. - -As I have already shown in the eighth chapter, the origin of the two -sexes, and consequently sexual propagation in general, must be -considered as a process which began only in later periods of the organic -history of the earth, being the result of differentiation or _division -of labour_. The most ancient terrestrial organisms can have propagated -themselves only in the simplest non-sexual manner. Even now all -Protista, as well as all the countless forms of cells, which constitute -the body of higher organisms, multiply themselves only by non-sexual -generation. And yet there arise here "new species" by differentiation in -consequence of natural selection. - -But even if we were to take into consideration the animal and vegetable -species with separate sexes, in this case too we should have to oppose -Wagner's chief proposition, that "the _migration_ of organisms and their -formation of colonies is the _necessary condition of natural -selection_." August Weismann, in his treatise on the "Influence of -Isolation upon the Formation of Species,"(24) has already sufficiently -refuted that proposition, and has shown that even in one and the same -district one bi-sexual species may divide itself into several species by -natural selection. In relation to this question, I must again call to -mind the great influence which _division of labour, or differentiation_, -possesses, being one of the necessary results of natural selection. All -the different kinds of cells constituting the body of the higher -organisms, the nerve cells, muscle cells, gland cells, etc., all these -"good species," these "bonae species" of elementary organisms, have -arisen solely by division of labour, in consequence of natural -selection, although they not only never were locally isolated, but ever -since their origin have always existed in the closest local relations -one with another. Now, the same reasoning that applies to these -elementary organisms, or "individuals of the first order," applies also -to the many-celled organisms of a higher order which only at a later -date have arisen as "good species" from among their fellows. - -We are therefore of the same opinion as Darwin and Wallace, that the -migration of organisms and their isolation in their new home is a very -advantageous condition for the origin of new species; but we cannot -admit, as Wagner asserts, that it is a _necessary_ condition, and that -without it no species can arise. Wagner sets up this opinion, "that -migration is a necessary condition for natural selection," as a special -"_law of migration_"; but we consider it sufficiently refuted by the -above-mentioned facts. We have, moreover, already pointed out that in -reality the origin of new species by natural selection is a -_mathematical and logical necessity_ which, without anything else, -follows from the simple combination of three great facts. These three -fundamental facts are--the Struggle for Life, the Adaptability, and the -Hereditivity of organisms. - -We cannot here enter into detail concerning the numerous interesting -phenomena furnished by the geographical and topographical distribution -of organic species, which are all wonderfully explained by the theory of -selection and migration. For these I refer to the writings of Darwin,(1) -Wallace,(36) and Moritz Wagner,(40) in which the important doctrine of -the _limits of distribution_--seas, rivers, and mountains--is -excellently discussed and illustrated by numerous examples. Only three -other phenomena must be mentioned here on account of their special -importance. First, the close relation of forms, that is, the striking -"family likeness" existing between the characteristic local forms of -every part of the globe, and their extinct fossil ancestors in the same -part of the globe; secondly, the no less striking "family likeness" -between the inhabitants of island groups and those of the neighbouring -continent from which the islands were peopled; lastly and thirdly, the -peculiar character presented in general by the flora and fauna of -islands taken as a whole. - -All these chorological facts given by Darwin, Wallace, and -Wagner--especially the remarkable phenomena of the limited local fauna -and flora, the relations of insular to continental inhabitants, the wide -distribution of the so-called "cosmopolitan species," the close -relationship of the local species of the present day with the extinct -species of the same limited territory, the demonstrable radiation of -every species from a single central point of creation--all these, and -all other phenomena furnished to us by the geographical and the -topographical distribution of organisms, are explained in a simple and -thorough manner by the theory of selection and migration, while without -it they are simply incomprehensible. Consequently, in the whole of this -series of phenomena we find a new and weighty proof of the truth of the -Theory of Descent. - - - [1] The world is perfect save where Man - Comes in with his strife. - - [2] Archebiosis (Bastian), Abiogenesis (Huxley). - - [3] Alle Glieder bilden sich aus nach ew'gen Gesetzen, - Und die seltenste Form bewahrt im Geheimniss das Urbild. - Also bestimmt die Gestalt die Lebensweise des Thieres. - Und die Weise zu leben, sie wirkt auf alle Gestalten - Maechtig zurueck. So zeiget sich fest die geordnete Bildung, - Welche zum Wechsel sich neigt durch aeusserlich wirkende Wesen. - - [4] "Einstweilen bis den Bau der Welt - Philosophie zusammenhaelt, - Erhaelt sich ihr Getriebe - Durch Hunger und durch Liebe." - - [5] "Allgemeine Naturgeschichte und Theorie des Himmels." - - [6] We must wait for fuller information on the subject of - Bathybius, at the hands of the naturalists of the _Challenger_ - expedition, before accepting it finally as a distinct - organism.--_Editor._ - - -END OF VOL. I. - - - - -WORKS OF PROFESSOR ERNST HAECKEL. - - - FREEDOM IN SCIENCE AND TEACHING. From the German of ERNST - HAECKEL. With a Prefatory Note by T. H. Huxley, F.R.S. 1 - vol., 12mo. - - THE EVOLUTION OF MAN. A Popular Exposition of the - Principal Points of Human Ontogeny and Phylogeny. From - the German of ERNST HAECKEL, Professor in the University - of Jena, author of "The History of Creation," etc. With - numerous Illustrations. In two vols., 12mo. Cloth. 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