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diff --git a/old/44541.txt b/old/44541.txt new file mode 100644 index 0000000..dca43af --- /dev/null +++ b/old/44541.txt @@ -0,0 +1,3418 @@ +The Project Gutenberg EBook of The Last Link, 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 Last Link + Our Present Knowledge of the Descent of Man + +Author: Ernst Haeckel + +Commentator: Hans Gadow + +Release Date: December 29, 2013 [EBook #44541] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE LAST LINK *** + + + + +Produced by Chris Curnow, Les Galloway and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + + + + + + THE LAST LINK + + OUR PRESENT KNOWLEDGE OF THE + DESCENT OF MAN + + BY + + ERNST HAECKEL + (JENA) + + WITH NOTES AND BIOGRAPHICAL SKETCHES + + BY + + HANS GADOW, F.R.S. + (CAMBRIDGE) + + + LONDON + ADAM AND CHARLES BLACK + 1898 + + + +CONTENTS + + + PAGE + THE LAST LINK + + INTRODUCTORY 1 + + COMPARATIVE ANATOMY 8 + + PALAEONTOLOGY 20 + + OTHER EVIDENCE 42 + + STAGES RECAPITULATED 47 + + BIOGRAPHICAL SKETCHES: + + LAMARCK, SAINT-HILAIRE, CUVIER, BAER, + MUELLER, VIRCHOW, COPE, KOELLIKER, GEGENBAUR, + HAECKEL 80 + + THEORY OF CELLS 115 + + FACTORS OF EVOLUTION 117 + + GEOLOGICAL TIME AND EVOLUTION 135 + + + + NOTE + + +The address I delivered on August 26 at the Fourth International +Congress of Zoology at Cambridge, 'On our Present Knowledge of the +Descent of Man,' has, I find, from the high significance of the theme +and the general importance of the questions connected with it, excited +much interest, and has led to requests for its publication. Hence this +volume, edited by my friend Dr. H. Gadow, my pupil in earlier days, +who has not only revised the text, but has also enriched it by many +valuable additions and notes. + + ERNST HAECKEL. + +_Jena, December, 1898._ + + + + + THE LAST LINK + + +At the end of the nineteenth century, the age of 'natural science,' the +department of knowledge that has made most progress is zoology. From +zoology has arisen the study of transformism, which now dominates the +whole of biology. Lamarck[1] laid its foundation in 1809, and forty +years ago Charles Darwin obtained for it a recognition which is now +universal. It is not my task to repeat the well-known principles of +Darwinism. I am not concerned to explain the scientific value of the +whole theory of descent. The whole of our biological study is pervaded +by it. No general problem in zoology and botany, in anatomy and +physiology, can be discussed without the question arising, How has this +problem originated? What are the real causes of its development? + + [1] See note, p. 80. + +This question was almost unknown seventy years ago, when Charles +Darwin, the great reformer of biology, began his academical career at +Cambridge as a student of theology. In the same year, 1828, Carl Ernst +von Baer[2] published in Germany his classical work on the embryology +of animals, the first successful attempt to elucidate by 'observation +and reflection' the mysterious origin of the animal body from the +egg, and to explain in every respect the 'history of the growing +individuality.' Darwin at that time had no knowledge of this great +advance, and he could not divine that forty years later embryology +would be one of the strongest supports of his own life's work--of that +very theory of transformism which, founded by Lamarck in the year of +Darwin's birth, was accepted with enthusiasm by Charles's grandfather +Erasmus. There is no doubt that of all the celebrated naturalists of +the nineteenth century Darwin achieved the greatest success, and we +should be justified in designating the last forty years as the Age of +Darwin. + + [2] See note, p. 89. + +In searching for the causes of this unexampled success, we must clearly +separate three sets of considerations: first, the comprehensive reform +of Lamarck's transformism, and its firm establishment by the many +arguments drawn from modern biology; secondly, the construction of the +new theory of selection, as established by Darwin, and independently +by Alfred Wallace (a theory called Darwinism in the proper sense); +thirdly, the deduction of anthropogeny, that most important conclusion +of the theory of descent, the value of which far surpasses all the +other truths in evolution. + +It is the third point of Darwin's theory that I shall discuss here; and +I shall discuss it chiefly with the intention of examining critically +the evidence and the different conclusions which at present represent +our scientific knowledge of the descent of man and of the different +stages of his animal pedigree. + +It is now generally admitted that this problem is the most important +of all biological questions. Huxley was right when in 1863 he called +it the question of questions for mankind. The problem which underlies +all others, and is more deeply interesting than any other, is as +to the place which man occupies in nature and his relations to the +universe of things. 'Whence our race has come; what are the limits of +our power over nature, and of nature's power over us; to what goal are +we tending--these are the problems which present themselves anew and +with undiminished interest to every man born into the world.' This +impressive view was explained by Huxley thirty-five years ago in his +three celebrated essays on 'Evidence as to Man's Place in Nature.' The +first is entitled 'On the Natural History of the Man-like Apes'; the +second, 'On the Relations of Man to the Lower Animals'; the third, 'On +some Fossil Remains of Man.' Darwin himself felt the burden of these +problems as much as Huxley; but in his chief work, 'On the Origin of +Species,' in 1859, he had purposely only just touched them, suggesting +that the theory of descent would shed light upon the origin of man and +his history. Twelve years later, in his celebrated work on 'The Descent +of Man, and Selection in Relation to Sex,' Darwin discussed fully and +ingeniously all the different sides of this 'question of questions' +from the morphological, historical, physiological, and psychological +points of view. As early as 1866 I myself had applied in the _Generelle +Morphologie der Organismen_ the theory of transformism to anthropology, +and had shown that the fundamental law of biogeny claims the same +value for man as for all the other animals. The intimate causal +connection between ontogeny and phylogeny, between the development of +the individual and the history of its ancestors, enables us to gain +a safe and certain knowledge of our ancestral series. I had at that +time distinguished in this series ten chief degrees of vertebrate +organization. I attributed the highest importance to the logical +connection of anthropogeny with transformism. If the latter be true, +the truth of the former is absolute. 'Our theory that man is descended +from lower vertebrates, and immediately from apes or primates, is a +case of special _deduction_ which follows with absolute certainty from +the general _induction_ of the theory of descent.' The full proof and +detailed explanation of this view was afterwards given in my 'History +of Natural Creation,' and especially in my 'Anthropogeny.'[3] Lastly, +it has received an ample scientific and critical foundation in the +third part of my 'Systematic Phylogeny.'[3] + + [3] See notes, pp. 102, 106 + +During the forty years which have elapsed since Darwin's first +publication of his theories an enormous literature, discussing the +_general problems_ of transformism as well as its special application +to man, has been published. In spite of the wide divergence of the +different views, all agree in one main point: the natural development +of man cannot be separated from general transformism. There are only +two possibilities. Either all the various species of animals and +plants have been created independently by supernatural forces (and +in this case the creation of man also is a miracle); or the species +have been produced in a natural way by transmutation, by adaptation +and progressive heredity (and in this case man also is descended from +other vertebrates, and immediately from a series of primates). We are +absolutely convinced that only the latter theory is fully scientific. +To prove its truth, we have to examine critically the strength of the +different arguments claimed for it. + + + + + I. + + +First, we have to consider the relative place which comparative +anatomy concedes to man in the 'natural system' of animals, for the +true value of our 'natural classification' is based upon its meaning +as a pedigree. All the minor and major groups of the system--the +classes, legions, orders, families, genera, and species--are only +different branches of the same pedigree. For man himself, his place +in the pedigree has been fixed since Lamarck,[4] in 1801, defined the +group of vertebrates. The most perfect[5] of these are the Mammalia; +and at the head of this class stands the order of Primates, in which +Linnaeus, in 1735, united four 'genera'--Homo, Simia, Lemur, and +Vespertilio. If we exclude the last-named, the Chiroptera of modern +zoology, there remain three natural groups of Primates--the Lemures, +the Simiae, and the Anthropi or Hominidae. This is the classification of +the majority of zoologists; but if we compare man with the two chief +groups of monkeys--the Eastern monkeys (or Catarrhinae) and the Western +or American monkeys (Platyrrhinae)--there can be no doubt that the +former group is much more closely related to man than is the latter. +In the natural order of the Catarrhinae we find united a long series +of lower and higher forms. The lowest, the Cynopitheci, appear still +closely related to the Platyrrhinae and to the Lemures; while, on the +other hand, the tailless apes (Anthropomorphae) approach man through +their higher organization. Hence one of our best authorities on the +Primates, Robert Hartmann,[6] proposed to subdivide the whole order of +the Simiae into three groups: (1) Primarii, man together with the other +Anthropomorphae, or tailless apes; (2) Simiae, all the other monkeys; (3) +Prosimiae, or Lemurs. This arrangement has received strong support from +the interesting discovery by Selenka that the peculiar placentation +of the human embryo is the same as in the great apes, and different +from that of all the other monkeys. Our choice between these different +classifications of Primates is best determined by the important thesis +of Huxley, in which, in 1863, he carried out a most careful and +critical comparison of all the anatomical gradations within this order. +In my opinion, this ingenious thesis--which I have called the Huxleyan +Law, or the 'Pithecometra-thesis of Huxley'--is of the utmost value. +It runs as follows: 'Thus, whatever system of organs be studied, the +comparison of their modifications in the ape-series leads to one and +the same result--that the structural differences which separate man +from the gorilla and the chimpanzee are not so great as those which +separate the gorilla from the lower apes.' If we accept the Huxleyan +law without prejudice, and apply it to the natural classification of +the Primates, we must concede that man's place is within the order +of the Simiae. On examining this relation with care, and judging +with logical persistence, we may even go a step further. Instead of +the wider conception of 'Simiae,' we must use the restricted term of +Catarrhinae, and our Pithecometra-thesis has then to be formulated +as follows: _The comparative anatomy of all organs of the group of +Catarrhine Simiae leads to the result that the morphological differences +between man and the great apes are not so great as are those between +the man-like apes and the lowest Catarrhinae_. In fact, it is very +difficult to show why man should not be classed with the large apes in +the same zoological family. We all know a man from an ape; but it is +quite another thing to find differences which are absolute and not of +degree only. Speaking generally, we may say that man alone combines the +four following features: (1) Erect walk; (2) extremities differentiated +accordingly; (3) articulate speech; (4) higher reasoning power. Speech +and reason are obviously relative distinctions only--the direct result +of more brains and more brain-power, the so-called mental faculties. +The erect walk is not an absolutely distinguishing characteristic: the +large apes likewise walk on their feet only, supporting their bodies +by touching the ground with the backs of their hands--in fact, with +their knuckles--and this is a mode of progression very different from +that of the tailed monkeys, which walk upon the palms of their hands. +There are, however, two obvious differences in the development of the +muscles. In man alone the gastrocnemius and the soleus muscle are thick +enough to form the calf of the leg, and the glutaeus maximus is enlarged +into the buttocks. A fourth glutaeal muscle occurs occasionally in +man, while it is constantly present in apes as the so-called musculus +scansorius. Concerning the muscles of the whole body, we cannot do +better than quote Testut's summary: 'The mass of recorded observations +upon the muscular anomalies in man is so great, and the agreement of +many of these with the condition normal in apes is so marked, that the +gap which usually separates the muscular system of man from that of the +apes appears to be completely bridged over.' + + [4] See note, p. 80. + + [5] _Perfect_, in the sense of highest stage of evolution, may seem a + _petitio principii_. Leaving aside the consideration that no living + creature is absolutely perfect, in the sense that its organization + cannot become more efficient or proficient, we have here to deal with + relative perfection of the whole organization. A fish or a snake is in + its way more specialized than a mammal; but specialization does not + necessarily mean height of development: it generally means life in a + comparatively narrow groove. The acts of giving birth and nourishing + the young with the mother's milk is a much higher stage than the act + of laying eggs and letting them run their chance. The development of + a hairy coat goes along with heightened temperature of the blood, + subsequent greater independence of the surrounding temperature, and + increased steady activity of the brain and other nerve-centres. The + brain of the Mammalia, in its minute structure, is much more complex. + This rule applies to some of the principal sense organs, chiefly the + nose and the ear. The skeleton, not so much as a whole as in the + various bones and joints, is more neatly finished, and built up more + in conformity with 'scientific principles,' than is the case even with + birds, in spite of their marvellous specialization. The same is the + case with the vascular system, notably the heart and the veins, and + with the excretory organs. In all of these many imperfections, still + to be found in the other classes, have been corrected in Mammalia. The + Primates take an easy first by their hands, and among them the apes and + man himself by their brains. + + [6] 'Die menschenaehnlichen Affen und ihre Organisation im Vergleich zur + menschlichen.' 1883. + +There are, for example, the muscles of the ear. In most people the +majority, or even all of them, are no longer movable at will, while in +the apes they are still in use. The important point, however, is that +these muscles are still present in man, although often in a reduced +condition. They are the following: (1) Musculus auricularis anterior +or attrahens auris, which is frequently much reduced and no longer +reaches the ear at all, being then absolutely useless; (2) Musculus +auricularis superior or attollens auris, more constant than the former; +(3) Musculus auricularis posterior or retrahens auris, likewise often +functional. Occasionally smaller slips differentiated from these +three muscles are present, and as so-called intrinsic muscles are +restricted to the ear itself; their function is, or was, that of +curling up or opening the external ear. + +[Illustration: OUTLINES OF THE LEFT EAR OF-- + +1. _Lemur macaco_; 2. _Macacus rhesus_, the Rhesus monkey; 3. +Cercopithecus, a macaque; 4. human embryo of six months; 5. man, with +Darwin's point well retained: the dotted outline is that of the ear of +a baboon; 6. orang-utan (after G. Schwalbe):[7] ^x the original tip of +the ear; 7. human ear with the principal muscles. + + [7] G. Schwalbe, 'In wiefern ist die menschliche Ohrmuschel ein + rudimentaeres Organ?'--In what Respects is the Human Outer Ear a + Rudimentary Organ? (_Archiv f. Anatomie und Physiologie_, 1889).] + +In connection with the ear, I may touch upon another interesting +and most suggestive little feature which is present in many +individuals--namely, 'Darwin's point.' This is the last remnant of the +original tip of the ear, before the outer, upper, and hinder rim became +doubled up or folded in. It is a feature quite useless, and absolutely +impossible of interpretation, excepting as the vestige of such previous +ancestral conditions as are normal in the monkeys. + +In some cases the reduction of muscles has proceeded further in apes +than in man--for example, the muscles of the little toe. Another +instance is afforded by the coccyx or vestige of the tail; this is +still furnished with muscles which are now in man, as well as in +the apes, quite useless, and vary considerably with every sign of +degeneration, most so in the orang-utan. + +Darwin has mentioned the frequent action of the 'snarling muscle,' by +which, in sneering, our upper canine teeth are exposed, like those of a +dog prepared to fight. + +Monkeys and apes possess vocal sacs, especially large in the +orang-utan; survivals of them, although no longer used, persist in man +in the shape of a pair of small diverticula, the pouches of Morgagni, +between the true and the false vocal cords. + +'In the native Australians, the dental formula appears least removed +from the hypothetical original type, for in it are still found complete +rows of splendid teeth, with powerfully-developed canines and molars, +the latter being either uniform, or even increasing in size, as we +proceed backwards, in such a way that the wisdom tooth is the largest +of the series. This is decidedly a pithecoid characteristic which is +always found in apes. The upper incisors of the Malay, apart from their +prognathous disposition, have occasionally a distinctly pithecoid +form, their anterior surface being convex, and their lingual surface +slightly concave. The ancestors of Europeans seem to have had the same +form of teeth, for the oldest existing fragments of skulls from the +Mammoth age (_e.g._, the jaws from La Naulette, in Belgium) reveal +tooth-forms which must be classed with those of the lowest races of +to-day.'[8] + + [8] Wiedersheim, 'Der Bau des Menschen als Zeugniss fuer seine + Vergangenheit.' Freiburg, 1888. Translated: 'The Structure of Man an + Index to his Past History.' London, 1895. + +Now we are able to apply this fundamental Pithecometra-thesis directly +to the classification of the Primates and to the phylogeny of man, +which is intimately connected with it, because in this order, as in +all the other groups of animals, the natural system is the clear +expression of true phylogenetic affinity. Four results follow from our +thesis: (1) The Primates, as the highest legion or order of mammals, +form one natural, monophyletic group. All the Lemures, Simiae, and +Homines descend from one common ancestral form, from a hypothetical +'Archiprimas.' (2) The Lemures are the older and lower of the natural +groups of the Primates; they stand between the oldest Placentalia +(Prochoriata) and the true Simiae. (3) All the Catarrhinae, or Eastern +Simiae, form one natural monophyletic group. Their hypothetical +common ancestor, the Archipithecus, may have descended directly or +indirectly from a branch of the Lemures. (4) Man is descended directly +from one series of extinct Catarrhine ancestors. The more recent +ancestors of this series were tailless anthropoids (similar to the +Anthropopithecus), with five sacral vertebrae. The more remote ancestors +were tailed Cercopitheci, with three or four sacral vertebrae. + +These four theses possess, in my opinion, absolute certainty. +They are independent of all future anatomical, embryological, and +palaeontological discoveries which may possibly throw more light upon +the details of our phyletic anthropogenesis. + + + + + II. + + +The next question is, how the facts of palaeontology agree with these +most important results of comparative anatomy and ontogeny. The fossils +are the true historical 'medals of creation,' the palpable evidence of +the historical succession of all those innumerable organic forms which +have peopled the globe for many millions of years. Here the question +arises, If the known fossil specimens of Mammalia, and particularly +of Primates, give proof of these Pithecometra-theses, do they confirm +directly the descent of man from ape-like creatures? The answer to this +question is, in my opinion, affirmative. + +It is true that the gaps in the palaeontological evidence, here as +elsewhere, are many and keenly felt. In the order of the Primates +they are greater than in many other orders, chiefly because of the +arboreal life of our ancestors. The explanation is very simple. It is +really due to a long chain of favourable coincidences if the skeleton +of a vertebrate, covered as it was with flesh and skin, and containing +still more perishable viscera, is petrified at all. The body may be +devoured by other creatures, and its bones scattered about; or it rots +away and crumbles to pieces. Many animals hide in thick undergrowth +when death approaches them; and, leading an almost entirely arboreal +life, the Primates are especially likely to disappear without being +fossilized. It is only when the body is quickly covered with sand, or +is embedded in suitable lime or silica containing mud, that the process +of petrifaction can come to pass. Even then it is only by great good +luck that we come across such a fossil. Very few countries have been +searched systematically, and the areas that have been searched amount +to little in comparison with the whole surface of the land, even if we +leave out of account the fact that more than two-thirds of the globe +are covered by water. + +These deplorable deficiencies of empirical palaeontology are balanced +on the other side by a growing number of positive facts, which possess +an inestimable value in human phylogeny. The most interesting and most +important of these is the celebrated fossil _Pithecanthropus erectus_, +discovered in Java in 1894 by Dr. Eugene Dubois.[9] Three years ago +this now famous ape-like man provoked an animated discussion at the +third International Zoological Congress at Leyden. I may therefore +be allowed to say a few words as to its scientific significance. +Unfortunately, the fossil remains of this creature are very scanty: the +skull-cap, a femur, and two teeth. It is obviously impossible to form +from these scanty remains a complete and satisfactory reconstruction of +this remarkable Pliocene Primate. + +[9] _Pithecanthropus erectus._ 'Eine menschenaehnliche Uebergangsform +aus Java' ('A Human-like Transitional Form'). Batavia, 1894. + +The more important points are the following: The remains in question +rested upon a conglomerate which lies upon a bed of marine marl and +sand of Pliocene age. Together with the bones of Pithecanthropus were +found those of Stegodon, Leptobos, Rhinoceros, Sus, Felis, Hyaena, +Hippopotamus, Tapir, Elephas, and a gigantic Pangolin. It is remarkable +that the first two of these genera are now extinct, and that neither +hippopotamus nor hyaena exists any longer in the Oriental region. If we +may judge from these fossil remains, the bones of Pithecanthropus are +not younger than the oldest Pleistocene, and probably belong to the +upper Pliocene. The teeth are like those of man. The femur, also, is +very human, but shows some resemblances to that of the gibbons. Its +size, however, indicates an animal which stood when erect not less +than 5 feet 6 inches high. The skull-cap also is very human, but with +very prominent eyebrow ridges, like those of the famous Neanderthal +cranium. It is certainly not that of an idiot. It had an estimated +cranial capacity of about 1,000 cubic centimetres--that is to say, much +more than that of the largest ape, which possesses not more than 600 +c.c. The crania of female Australians and Veddahs measure not more than +1,100, some even less than 1,000 c.c.; but, as these Veddah women stand +only about 4 feet 9 inches high, the computed cranial capacity of the +much taller Pithecanthropus is comparatively very low indeed.[10] + + [10] On the day after the delivery of this address Dr. Dubois exhibited + the cranium of Pithecanthropus, from which he had removed the stony + matrix which filled the inside, in order to examine the impression left + by the cerebral convolutions. He was able to show that they also are + very human, and more highly developed than those of the recent apes. [ + Illustration: The upper figure represents the outlines + of the skull of Pithecanthropus, as restored by Manouvier.[11] The + lower figure shows the comparative size and shape of Pithecanthropus, + the Neanderthal skull, a specimen of the Cro-Magnon race of neolithic + France, and a Young Chimpanzee before the full development of the + supraorbital crests.] + + [11] L. Manouvier: 'Deuxieme etude sur le Pithecanthropus erectus comme + precurseur presume de l'homme.' (_Bulletins de la Soc. d'Anthropologie + de Paris_, 1895.) + +The final result of the long discussion at Leyden was that, of twelve +experts present, three held that the fossil remains belonged to a low +race of man; three declared them to be those of a man-like ape of great +size; the rest maintained that they belonged to an intermediate +form, which directly connected primitive man with the anthropoid +apes. This last view is the right one, and accords with the laws of +logical inference. _Pithecanthropus erectus_ of Dubois is truly a +Pliocene remainder of that famous group of highest Catarrhines which +were the immediate pithecoid ancestors of man. He is, indeed, the +long-searched-for 'missing link,' for which, in 1866, I myself had +proposed the hypothetical genus Pithecanthropus, species Alalus. + +It must, however, be admitted that this opinion is still strongly +combated by some distinguished authorities. At the Leyden Congress it +was attacked by the illustrious pathologist Rudolf Virchow.[12] He, +however, is one of the minority of leading men of science who set +themselves to refute the theory of Evolution in every possible way. For +thirty years he has defended the thesis: 'It is quite certain that man +is not a descendant of apes.' He declares any intermediate form to be +unimaginable save in a dream. + + [12] See Notes, p. 93. + +Virchow went to the Leyden Congress with the set purpose of disproving +that the bones found by Dubois belonged to a creature which linked +together apes and man. First, he maintained that the skull was that +of an ape, while the thigh belonged to man. This insinuation was at +once refuted by the expert palaeontologists, who declared that without +the slightest doubt the bones belonged to one and the same individual. +Next, Virchow explained that certain exostoses or growths observable on +the thigh proved its human nature, since only under careful treatment +the patient could have healed the original injury. Thereupon Professor +Marsh, the celebrated palaeontologist, exhibited a number of thigh-bones +of wild monkeys which showed similar exostoses and had healed without +hospital treatment. As a last argument the Berlin pathologist declared +that the deep constriction behind the upper margin of the orbits +proved that the skull was that of an ape, as such never occurred in +man. It so happened that a few weeks later Professor Nehring of Berlin +demonstrated exactly the same formation on a human prehistoric skull +received by him from Santos, in Brazil. + +Virchow was, in fact, just as unlucky in Leyden in his fight with our +pliocene ancestor as he had been unfortunate in his opinion on the +famous skulls of Neanderthal, Spy, La Naulette, etc., every one of which +he explained as a pathological abnormality. It would be a very curious +coincidence indeed if all these and other fossil human remains were +those of idiots or otherwise abnormal individuals, provided they are +old and low enough in their organization to be of phylogenetic value to +the unbiassed zoologist. + +As the sworn adversary of Evolution, transformism, and Darwinism in +particular, but a believer in the constancy of species, the great and +renowned pathologist has been driven to the incredible contention that +all variations of organic forms are pathological. + +Four years ago, as honorary president of the Anthropological Congress +at Vienna, he attacked Darwinism in the severest manner, and declared +that 'man may be as well descended from the elephant or from the sheep +as from the ape.' Such attacks on the theory of transformism indicate a +failure to understand the principles of the theory of Evolution and to +appreciate the significance of palaeontology, comparative anatomy, and +ontogeny. + +The thousands of other objections which have been made during the last +forty years (chiefly by outsiders) may be passed over in silence. They +do not require serious refutation. In spite of, or perhaps because of, +these attacks, the theory of Evolution stands established more firmly +than ever. + +It is easy for the outsider to exult over the difficulties which our +problem implies--difficulties which we who have given our lives to the +study understand likewise, and try our best not only to bridge over, +but also to point out. Anyhow, we do not conceal them; while those who +reject the explanation offered by Evolution make the most of the gaps, +and pass silently over the far more numerous points favourable to our +theory. + +How fruitful during the last thirty years the astonishing progress in +our palaeontological knowledge has been for our Pithecometra-thesis is +best shown by a short glance at the growth of our knowledge of fossil +Primates. Cuvier,[13] the founder of palaeontology, continued up to the +time of his death, in 1832, to assert that fossil remains of monkeys +and lemurs did not exist. The only skull of a fossil lemuroid which +he described (namely, Adapis) he declared to be that of an ungulate. +Not until 1836 were the first fragments of extinct monkeys found in +India; it was two years later, near Athens, that the skeleton of +_Mesopithecus penthelicus_ was discovered. Other remains of lemurs were +found in 1862. But during the last twenty years the number of fossil +Primates has been augmented by the remarkable discoveries of Gaudry, +Filhol, Milne Edwards, Seeley, Schlosser, and others in Europe; of +Marsh, Cope, Osborn, Leidy, Ameghino, in South America; and Forsyth +Major in Madagascar.[14] These tertiary remains, chiefly of Eocene and +Miocene date, fill many gaps between existing genera of Primates, and +afford us quite a clear insight into the phyletic development of this +order during the millions of years of the Caenozoic age. + + [13] See notes, p. 87. + + [14] + F. AMEGHINO: 'Contribucion al conocimiento de los mamiferos + de la republica Argentina.' In _Actas de la Academia nacional de + Sciencias en Cordoba_, 1889.--Another article in _Revista Argentina de + Historia natural_. Buenos Aires, 1891. + + A. GAUDRY: 'Animaux fossiles et geologie de l'Attique.' + 1862.--'Le Dryopitheque.' _Mem. Soc. geol. de France_: + 'Paleontologie.' 1890. + + O. MARSH: 'Introduction and Succession of Vertebrate Life in + America.' Address, Amer. Assoc. Adv. Sci., Nashville, 1887. + + H. F. OSBORN: 'The Rise of the Mammalia in North America.' + Address, Amer. Assoc. Adv. Sci., Madison, 1893. + + L. RUETIMEYER: 'Ueber die Herkunft unserer Thierwelt,' Basel, + 1867. + + C. S. FORSYTH MAJOR: 'Fossil Monkeys from Madagascar.' + _Geological Magazine_, 1896. + + M. SCHLOSSER: 'Ueber die Beziehungen der ausgestorbenen + Saeugethierfaunen und ihr Verhaeltniss zur Saeugethierfauna der + Gegenwart.' Biolog. Centralblatt, 1888. + +The most important difference between the two groups of existing +monkeys is indicated by their dentition. Adult man possesses, like +all the other Catarrhine Simiae, thirty-two teeth, whilst the American +monkeys (the Platyrrhinae) have thirty-six teeth--namely, one pair of +premolars more in the upper and lower jaws. Comparative odontology +leads us to the phylogenetic conclusion that this number has been +produced by reduction from a still older form with forty-four teeth. +This typical dental formula (three incisors, one canine, four +premolars, and three molars, in each half-jaw) is common to all those +most important older mammals which in the beginning of the Eocene +period constituted the four large groups of Lemuravida, Condylarthra, +Esthonychida, and Ictopsida. These are the four ancestral groups +of the four main orders of Placentalia--namely, of the Primates, +Ungulata, Rodentia, and Carnassia. They seem to be so closely related +by their primitive organization that they may be united in one common +super-order, Prochoriata. + +With a considerable degree of probability, we are led to formulate +the further hypothesis that all the orders of Placentalia--from the +lowest Prochoriata upwards to man--have descended from some unknown +common ancestor living in the Cretaceous period, and that this oldest +placental form originated from some Jurassic group of marsupials. + +Among these numerous fossil Lemures which have been discovered within +the last twenty years, there exist, indeed, all the connecting forms +of the older series of Primates, all the 'missing links' sought for by +comparative odontology. + +The oldest Lemures of the tertiary age are the Eocene Pachylemures, +or Hyopsodina. They possess the complete dentition of the +Prochoriata--namely, forty-four teeth (3.1.4.3/3.1.4.3). Then follow +the Eocene Palaeolemures, or Adapida, with forty teeth, they having lost +one pair of incisors in each jaw. To these are attached the younger +Autolemures, or Stenopida, with thirty-six teeth, they thus possessing +already the same dentition as the Platyrrhinae. The characteristic +dentition of the Catarrhinae is derived from this formula by the loss of +another premolar. + +These relations are so clear and so closely connected with a +gradual transformation of the whole skull, and with the progressive +differentiation of the Primate-form, that we are justified in saying +that the pedigree of the Primates, from the oldest Eocene Lemures +upwards to man, is now so well known, its principal features so firmly +fixed within the Tertiary age, that there is no missing link whatever. + +Quite different, and much more incomplete, is the palaeontological +evidence, if we go further back into the Secondary or Mesozoic age, +and look there for the older ancestors of the mammalian series. There +we meet everywhere with wide gaps, and the scarce fragments of fossil +Mesozoic mammals (excessively rare in the Cretaceous formation) are too +poor to permit definite conclusions as to their systematic position. +Indeed, comparative anatomy and ontogeny lead us to the hypothesis +that the oldest Cretaceous Mammalia--the Prochoriata--are descended +from Jurassic marsupials, and these again from Monotremes. We may +also suppose with high probability that among the unknown Cretaceous +Prochoriata there have been Lemuravida and forms intermediate between +these and the Jurassic Amphitheriidae, and that these marsupials in +their turn are descendants of Pantotheria or similar monotreme-like +creatures of the Triassic age. Any certain evidence for these +hypotheses is at present still wanting. One important fact, however, +is established--namely, that these interesting and oldest Mammalia--the +Pantotheria of Marsh, the Triassic Dromatheriidae, and the Jurassic +Triconodontidae of Osborn--were small insectivorous mammals with a very +primitive organization. Probably they were Monotremes, and may be +derived directly from Permian Sauromammalia, an ill-defined mixture of +Mammalia and Reptilia. + +This generalized characteristic supports our view that _the whole +class of Mammalia is monophyletic_, and that all its members, from +the oldest Monotremes upwards to man, have descended from one common +ancestor living in the older Triassic, or perhaps in the Permian, +age. To acquire full conviction of this important conception, we have +only to think of the hair and the glands of our human skin, of our +diaphragm, the heart and the blood corpuscles without a nucleus, our +skull with its squamoso-mandibular articulation. All these singular +and striking modifications of the vertebrate organization are common +to mammals, and distinguish them clearly from the other Craniota. This +characteristic combination and correlation proves that they have been +developed only _once_ in the history of the vertebrate stem, and that +they have been transferred by heredity from one common ancestor to all +the members of the class of Mammalia. + +The next step, as we trace our human phylogeny to its origin, leads us +further back into the lower Vertebrata, into that obscure Palaeozoic +age the immeasurable length of which (much greater than that of the +Mesozoic) may, according to one of the newest geological calculations, +have comprised about one thousand millions of years.[15] + + [15] See note, 'Geological Time and Evolution' p. 134. + +The first important fact we have to face here is the complete absence +of mammalian remains. Instead of these we find in the later Palaeozoic +period, the Permian, air-breathing _reptiles_ as the earliest +representatives of Amniota. They belong to the most primitive order +of that class, the Tocosauria; and besides them there were the +Theromorpha, which approach the Mammalia in a remarkable manner. These +reptiles in turn were preceded, in the Carboniferous period, by true +Amphibia, most of them belonging to the armour-clad Stegocephali. +These interesting Progonamphibia were the oldest Tetrapoda, the first +vertebrates which had adapted themselves to the terrestrial mode of +life; in them the swimming fin of fishes and Dipneusta was transformed +into the pentadactyle extremities characteristic of quadrupeds. + +To appreciate the high importance of this metamorphosis, we need only +compare the skeleton of our own human limbs with that of the living +Amphibia. We find in the latter the same characteristic composition as +in man: the same shoulder and pelvic girdle; the same single bone, the +humerus or the femur, followed by the same pair of bones in the forearm +and leg; then the same skeletal elements composing the wrist and the +ankle regions; and, lastly, the same five fingers and toes. + +The arrangement of these bones, peculiar and often complicated, but +everywhere essentially the same in all the Tetrapoda, is a striking +evidence that man is a descendant from the oldest pentadactyle Amphibia +of the Carboniferous period. In man the pentadactyle type has been +better preserved by constant heredity than in many other Mammalia, +notably the Ungulata. + +The oldest Carboniferous Amphibia, the armour-clad Stegocephali, and +especially the remarkable Branchiosauri discovered by Credner, are +now regarded by all competent zoologists as the indubitable common +ancestral group of all Tetrapoda, comprising both Amphibia and Amniota. +But whence this most remote group of Tetrapoda? That difficult question +is answered by the marvellous progress of modern palaeontology, and +the answer is in complete harmony with the older results arrived +at by comparative anatomy and ontogeny. Thirty-four years ago Carl +Gegenbaur,[16] the great living master of comparative anatomy, had +demonstrated in a series of works how the skeletal parts of the various +classes of Vertebrata, especially the skull and the limbs, still +represent a continuous scale of phyletic gradations. Apart from the +Cyclostomes, there are the fishes, and among them the Elasmobranchi +(sharks and rays), which have best preserved the original structure in +all its essential parts of organization. Closely connected with the +Elasmobranchi are the Crossopterygii, and with these the Dipneusta or +Dipnoi. Among the latter the highest importance attaches to the ancient +Australian Ceratodus. Its organization and development is now, at last, +becoming well known. This transitional group of Dipnoi, 'fishes with +lungs' but without pentadactyle limbs, is the morphological bridge +which joins the Ganoids and the oldest Amphibia. With this chain +of successive groups of Vertebrata, constructed anatomically, the +palaeontological facts agree most satisfactorily. Selachians and Ganoids +existed in the Silurian times, Dipnoi in the Devonian, Amphibia in the +Carboniferous, Reptilia in the Permian, Mammalia in the Trias. These +are historical facts of first rank. They connote in the most convincing +manner that remarkable ascending scale in the series of vertebrates +for our knowledge of which we are indebted to the works of Cuvier and +Blainville, Meckel, Johannes Mueller and Gegenbaur, Owen and Huxley. +The historical succession of the classes and orders of the Vertebrata +in the course of untold millions of years is definitely fixed by the +concordance of those leading works, and this invaluable acquisition is +much more important for the foundation of our human pedigree than would +be a complete series of all possible skeletons of Primates. + + [16] See note, p. 97. + +Greater and more frequent difficulties arise if we penetrate further +into the most remote part of the human phylogeny, and attempt to derive +the vertebrate stem from an older stem of invertebrate ancestors. None +of those had a skeleton which could be petrified; and the same remark +applies to the lowest classes of Vertebrata--to the Cyclostomes and +the Acrania. Palaeontology, therefore, can tell us nothing about them; +and we are limited to the other two great documents of phylogeny--the +results of comparative anatomy and ontogeny. The value of their +evidence is, however, so great that every competent zoologist can +perceive the most important features of the most remote portion of our +phylogeny. + +Here the first place belongs to the invaluable results which modern +comparative ontogeny has gained by the aid of the biogenetic law or +the theory of recapitulation. The foundation-stones of vertebrate +embryology had been laid by the works of Von Baer, Bischoff,[17] Remak, +and Koelliker;[18] but the clearest light was thrown upon it by the +famous discoveries of Kowalevsky[19] in 1866. He proved the identity +of the first developmental stages of Amphioxus and the Ascidians, and +thereby confirmed the divination of Goodsir, who had already announced +the close affinity of Vertebrates and Tunicates. The acknowledgment of +this affinity has proved of increasing importance, and has abolished +the erroneous hypothesis that the Vertebrata may have arisen from +Annelids or from other Articulata. Meanwhile, from 1860 to 1872, I +myself had been studying the development of the Spongiae, Medusae, +Siphonophora, and other Coelenterata. Their comparison led me to the +statements embodied in the 'Gastraeatheorie,' the first abstract of +which was published in 1872 in my monograph of the Calcispongiae. + + [17] Wilhelm Bischoff of Munich: works on the history of the + development of the rabbit, dog, guinea-pig, roe-deer. 1840-1854. + + [18] See note, p. 96. + + [19] 'Ueber die Entwicklung der einfachen Ascidien,' Mem. Acad. St. + Petersbourg, vii. ser., tome x. (1866). Other papers in 'Archiv f. + Mikroskop. Anatomie,' vii. (1871); xiii. (1877). + +These ideas were carried on and expanded during the subsequent ten +years by the help of many excellent embryologists--first of all by E. +Ray Lankester and Francis Balfour. The most fruitful result of these +widely extended researches was the conclusion that the first stages of +embryonic development are essentially the same in all the different +Metazoa, and that we may derive from these facts certain views on +the common descent of all from one ancestral form. The unicellular +egg[20] repeats the stage of our Protozoan ancestors; the Blastula +is equivalent to an ancestral coenobium of Magosphaera or Volvox; +the Gastrula is the hereditary repetition of the Gastraea, the common +ancestor of all the Metazoa. + + [20] See note, p. 115--Theory of cells. + +Man agrees in all these respects with the other vertebrates, and must +have descended with them from the same common root. + +Particularly obscure is that part of our phylogeny which extends from +the Gastraea to Amphioxus. The morphological importance of this last +small creature had been perceived by Johannes Mueller, who in 1842 +gave the first accurate description of it. It would not, of course, be +correct to proclaim the modern Amphioxus the common ancestor of all the +vertebrates; but he must be regarded as closely related to them, and +as the only survivor of the whole class of Acrania. If the Amphioxidae +had through some unfortunate accident become extinct, we should not +have been able to gain anything like a positive glimpse at our most +remote vertebrate ancestor. On the one hand, Amphioxus is closely +connected with the early larva of the Cyclostomes, which are the +oldest Craniota, and the pre-Silurian ancestors of the fishes. On the +other hand, the ontogeny of Amphioxus is in harmony with that of the +Ascidians, and if this agreement is not merely coincidental, but due to +relationship, we are justified in reconstructing for both Ascidians +and Amphioxus one common ancestral group of chordate animals, the +hypothetical _Prochordonia_. The modern Copelata give us a remote idea +of their structure. The curious Balanoglossus, the only living form of +Enteropneusta, seems to connect these Prochordonia with the Nemertina +and other Vermalia, which we unite in one large class--Frontonia. + +No doubt these pre-Cambrian Vermalia, and the common root of all +Metazoa, the Gastraeades, were connected during the Laurentian period +by a long chain of intermediate forms, and probably among these +were some older forms of Rotatoria and Turbellaria; but at present +it is not possible to fill this wide gap with hypotheses that are +satisfactory, and we have to admit that here indeed are many missing +links in the older history of the Invertebrata. Still, every zoologist +who is convinced of the truth of transformism, and is accustomed to +phylogenetic speculations, knows very well that their results are most +unequal, often incomplete. + + + + +III. + + +Let us now recapitulate the ancestral chain of man, as it is set forth +in the accompanying diagram (p. 55), which represents our present +knowledge of our descent. For simplicity's sake the many side-issues +or branches which lead to groups not in the main line of our descent +have been left out, or have been indicated merely. Many of the stages +are of course hypothetical, arrived at by the study of comparative +anatomy and ontogeny; but an example for each of them has been taken +from those living or fossil creatures which seem to be their nearest +representatives. + +1. The most remote ancestors of all living organisms were living beings +of the simplest imaginable kind, organisms without organs, like +the still existing _Monera_. Each consisted of a simple granule of +protoplasm, a structureless mass of albuminous matter or plasson, like +the recent Chromaceae and Bacteriae. The morphological value of these +beings is not yet that of a cell, but that of a cytode, or cell without +a nucleus. Cytoplasm and nucleus were still undifferentiated. + +I assume that the first Monera owe their existence to spontaneous +creation out of so-called anorganic combinations, consisting of carbon, +hydrogen, oxygen, and nitrogen. An explanation of this hypothesis I +have given in my 'Generelle Morphologie.' + +The Monera probably arose early in the Laurentian period. The oldest +are the Phytomonera, with vegetable metabolism. They possessed the +power (characteristic of plants) of forming albumin by synthesis from +carbon, water, and ammonia. From some of these plasma-forming Monera +arose the plasmophagous Zoomonera with animal metabolism, living +directly upon the produce of their plasmodomous or plasma-forming +sisters. This is the first instance of the great principle of division +of labour. + +2. The second stage is that of the _simple and single cell_, a bit +of protoplasm with a nucleus. Such unicellular organisms are still +very common. The _Amoebae_ are their simplest representatives. The +morphological value of such beings is the same as that of the egg +of any animal. The naked egg cells of the sponges creep about in an +amoeboid fashion, scarcely distinguishable from Amoeba. The same +remark applies to the egg-cell of man himself in its early stages +before it is enclosed in a membrane. The first unicellular organisms +arose from Monera through differentiation of the inner nucleus from the +outer protoplasm. + +3. Repeated division of the unicellular organism produces the +_Synamoebium_, or community of Amoebae, provided the divisional +products, or new generations of the original cell, do not scatter, +but remain together. The existence of such a _Coenobium_, a number +of equal and only loosely-connected cells, as a separate stage in the +ancestral history of animals, is made highly probable by the fact that +the eggs of all animals undergo after fertilization such a process of +repeated self-division, or 'cleavage,' until the single egg cell is +transformed into a heap of cells closely packed together, not unlike a +mulberry (_morula_)--hence _morula_ stage in ontogeny. + +4. The morula of most animals further changes into a _Blastula_, a +hollow ball filled with fluid, the wall being formed by a single layer +of cells, the blastoderm or germinal layer. This modification is +brought about by the action of the cells--they conveying nourishing +fluid into the interior of the whole cell colony and thereby +being themselves forced towards the surface. The Blastula of most +Invertebrata, and even that of Amphioxus, is possessed of fine ciliae, +or hair-like processes, the vibrating motion of which causes the whole +organism to rotate and advance in the water. Living representatives of +such Blastaeads, namely, globular gelatinous colonies of cells enclosing +a cavity, are Volvox and Magosphaera. + +5. The Blastula of most animals assumes a new larval form called +_Gastrula_, in which the essential characteristics are that a portion +of the blastoderm by invagination converts the Blastula into a cup +with double walls, enclosing a new cavity, the primitive gut. This +invagination or bulging-in obliterates the original inner cavity of +the Blastula. The outer layer of the Gastrula is the ectoderm, the +inner the endoderm; both pass into each other at the blastoporus, or +opening of the gut cavity. The Gastrula is a stage in the embryonic +development of the various great groups of animals, and some such +primitive form as ancestral to all Metazoa is thus indicated. This +hypothetical _Gastraea_ is still very essentially represented by the +lower Coelenterates--_e.g._, Olynthus, Hydra. + +6. The sixth stage--that of the _Platodes_, or flat-worms--is very +hypothetical. They are bilateral gastraeads, with a flattened oblong +body, furnished with ciliae, with a primitive nervous system, simple +sensory and reproductive organs, but still without appendages, body +cavity, vent, and blood-vessels. The nearest living representatives of +such creatures are the acoelous Turbellarians--_e.g._, Convoluta, a +free-swimming, ciliated creature. + +7. The next higher stage is represented by such low animals as the +_Gastrotricha_--_e.g._, Chaetonotus among the Rotatoria, which differ +from the rhabdocoelous Turbellarians chiefly by the formation of +a vent and the beginnings of a coelom, or cavity, between gut and +body wall. The addition of a primitive vascular system and a pair of +nephridia, or excretory organs, is first met with in the _Nemertines_. + +8. These, together with the _Enteropneusta_ (Balanoglossus), are +comprised under the name of Frontonia, or Rhynchelminthes, and form the +highest group of the Vermalia. + +The Enteropneusta especially fix our attention, because they alone, +although essentially 'worms,' exhibit certain characteristics which +make it possible to bridge over the gulf which still separates the +Invertebrata from the vertebrate phylum. The anterior portion of the +gut is transformed into a breathing apparatus--hence Gegenbaur's +term of Enteropneusta, or Gut-breathers. Moreover, Balanoglossus and +Cephalodiscus possess another modification of the gut--namely, a +peculiar diverticulum, which, in the present state of our knowledge, +may be looked upon as the forerunner of the chorda dorsalis. + +9. Stage of _Prochordonia_, as indicated by the larval form, called +Chordula, which is common to the Tunicata and all the Vertebrata. +These two groups possess three most important features: (_a_) A chorda +dorsalis, a stiff rod lying in the long axis of the body, dorsally from +the gut and below the central nervous system. This latter, for the +first time in the animal kingdom, appears in the shape of a spinal +cord. (_b_) The use of the anterior portion of the gut for respiratory +purposes. (_c_) The larval development of the Tunicata is essentially +the same as that of the Vertebrata in its early stages. Only the +free-swimming Copelata or Appendicularia among the Tunicates retain +most of these features. The others, which become sessile--namely, the +Ascidiae, or sea-squirts--degenerate and specialize away from the main +line. + +10. Stage of the _Acrania_, represented by Amphioxus. The early +development of this little marine creature agrees closely with +that of the Tunicates; but one important feature is added to its +organization--namely, metamerism, segmentally arranged mesoderm. +Amphioxus still possesses neither skull nor vertebrae, neither ribs +nor jaws, and no limbs. But it is a member of the Vertebrata if we +define these as follows: Bilateral symmetrical animals with segmentally +arranged mesoderm, with a chorda dorsalis between the tubular nervous +system and the gut, and with respiratory organs which arise from the +anterior portion of the gut. We do not assume that Amphioxus stands +in the direct ancestral line; it is probably much specialized, partly +degenerated, and represents a side-branch; but it is, nevertheless, +the only creature, hitherto known, which satisfactorily connects the +Vertebrata with their invertebrate ancestors. Many other efforts have +been made to solve the mystery of the origin of the Vertebrata--all +less satisfactory than the present suggestion, or even absolutely +futile. This remark applies especially to the attempts to derive them +from either Articulata or Echinoderms. The other great and highly +developed phylum, the Mollusca, is quite out of the question. We have +to go back to a level at which all these principal phyla meet, and +there we find the Vermalia, the lower of which alone permit connection +in an upward direction with the higher phyla. + + ANCESTRAL TREE OF THE VERTEBRATA. + + _Abridged from 'Systemat. Phylogenie,' Sec. 15._ + + Names underlined refer to hypothetical groups. + + _Mammalia_ + _Aves_ | + | _Reptilia_ | + | | | + +----------------+ | + | | + +--------------+ + | + _Proreptilia_ + | _Amphibia_ + _Pisces_ | | + | | +----------+ + | | | + | | | _Dipnoi_ + | _Stegocephali_ | + | | | + | +---------------+ + | | + +---------------+ + | _Cyclostomata_ + _Proselachii_ | + | | + _Tunicata_ | +--------+ + | | | + | *_Archicrania_* + | | _Acrania_ + | | | + | *_Prospondylia_*------+ + | | + +----------+ | + | | + *_Prochordonia_* + + +11. Stage of _Cyclostomata_. This now small group of Lampreys and +Hagfishes represents the lowest Craniota; and although much specialized +as a side-branch of the main-stem from which the other Craniota have +sprung, they give us an idea of what the direct ancestors of the latter +must have been like:--still without visceral arches, without jaws and +without paired limbs; with a persistent pronephros; the ear with one +semicircular canal only; mouth suctorial; cranium very primitive; +and the metamerism of the vertebral column indicated only by little +blocks of cartilage in the perichordal sheath. Such creatures must +have existed at least as early as the Lower Silurian epoch; but until +1890 fossil Cyclostomes were unknown. Their life in the mud, or as +endoparasites of fishes, coupled with their soft structure, makes them +very unfit for preservation. This gives all the greater importance to +Traquair's discovery, in 1890, of many little creatures, called by him +_Palaeospondylus gunni_, in the Old Red Sandstone of Caithness, which +seem to be very closely allied to Cyclostomata. + +12. The _Elasmobranchi_ (sharks and skates), with their immediate +forerunners, the Acanthodi of the Devonian and Carboniferous age, +are the first typical fishes. That they existed as far back as the +Silurian age is proved by many enamelled spines of the dermal armour, +chiefly from the dorsal fins. This higher stage is characterized by the +possession of typical jaws, by visceral or gill-bearing arches, and by +two pairs of limbs. None of the Elasmobranchs, fossil or recent, stands +in the direct ancestral line; but they are the lowest Gnathostomata, +jaw-and-limb-possessing creatures, known. + +13. Closely connected with the Elasmobranchs in a wider sense are the +_Crossopterygii_, which begin in the Devonian age as a large group, but +have left only two survivals, the African Polypterus and Calamoichthys. +They are possessed of dermal bones and other ossifications, and are +characterized by their lobate paired fins, which have a thick axis +beset with biserial fin rays. Their gill-clefts are covered by an +operculum, and they have a well-developed air-bladder. Whilst they +are in many respects more highly developed than the Elasmobranchs, +and are intimately connected with the typical Ganoids and other +bony fishes (all of which form a great, manifold side-branch of the +general vertebrate stem), they stand in many other respects (notably, +the structure of the paired fins, the vertebral column, and the +air-bladder) nearer the main-stem of our own ancestral line. + +14. This is shown by their intimate relation to the _Dipnoi_, which +are still represented by the Australian, African, and South American +mud-fishes: Ceratodus, Protopterus, and Lepidosiren. The genus +Ceratodus existed in the Upper Trias, whence various other unmistakably +dipnoous forms lead down through the Carboniferous (_e.g._, Ctenodus) +to the Devonian strata--_e.g._, Dipterus. They are characterized as +follows: The paired fins still retain the archipterygial form (namely, +one axis with biserial rays); the heart is already trilocular, and +receives blood which is mixed arterial and venous, owing to the gills +being retained, while the air-bladder has been modified into a lung. In +fact, the generalized Dipnoi form the actual link between fishes and +_Amphibia_. + +15. _Amphibia._ The earliest amphibian fossils occur in +the Carboniferous strata. They alone--the Stegocephali or +Phractamphibia--stand in the ancestral line, while the Lissamphibia, to +which all the recent forms belong, are side-branches. The Stegocephali +are the earliest Tetrapoda, the archipterygial paired fins having been +transformed into the pentadactyle fore and hind limbs, which are so +characteristic of all the higher Vertebrata. The cranium is roofed +over by dermal bones, of which, besides others, supra-occipitals, +supra-orbitals, and supra-temporals are always present. The lowest +members (Branchiosauri) still retained gills besides the lungs, while +others (Microsauri) have lost the gills. Be it remembered that all +the recent Amphibia still undergo the same metamorphosis during their +ontogenetic development. + +In the very important Temnospondyli, a subgroup of the +Stegocephali--_e.g._, Trimerorhachis of the Lower Red Sandstone or +Lower Permian--the component cartilaginous or bony units which compose +the vertebrae still remained in a separate, unfused state, showing at +the same time an arrangement whence has arisen that which is typical +of the Amniota. The same applies to the limbs and their girdles. In +fact, the Stegocephali, taken as a whole, lead imperceptibly to the +_Proreptilia_. + +16. _Proreptilia_ are represented by the Permian genera Eryops and +Cricotus. Until quite recently these and many other fossils from +the Carboniferous strata were looked upon as Amphibia, while many +undoubted fossil Amphibia were mistaken for reptiles, as indicated by +the frequent termination '-saurus' in their names. + +The nearest living representative of these extinct Proreptilia is +the New Zealand reptile Hatteria, or Sphenodon, close relations +of which are known from the Upper Trias; while others--_e.g._, +Palaeohatteria--have been discovered in the Permian. Anyhow, Sphenodon +is the reptile which stands nearest to the main stem of our ancestry. + +The most important characteristics of the Reptilia, which mark a higher +stage or level, are (1) The entire suppression of the gills--although +during the embryonic development the gill-clefts still appear in all +reptiles, birds, and mammals; (2) The development of an amnion and an +allantois, both for the embryonic life only, but so characteristic +that all these animals are comprised under the name of Amniota; +(3) The articulation of the skull with the first neck vertebrae by +well-developed condyles, either single (really triple) or double (such +a condylar arrangement begins with the Amphibia, but only the two +lateral condyles are developed, while the middle portion, belonging to +the basi-occipital element, remains rudimentary[21]); (4) The formation +of centra, or bodies of the vertebrae, mainly by a ventral pair of the +original quadruple constituents, or arcualia. + + [21] Similar conditions seem to have prevailed among the Proreptilia; + but in those of their descendants which have specialized into Reptiles + and Birds the basi-occipital element becomes more and more predominant + in that formation which ultimately leads to the apparently single + condyle. Hence it is misleading to divide the Tetrapoda into the two + main groups of Amphi-and Mono-condylia, and therefrom to conclude that + the two-condyled Mammalia are more closely related to the likewise + amphicondylous Amphibia than to the so-called monocondylous Reptiles. + +17. Between the Proreptilia and the Mammalia, which latter occur in +the Upper Triassic epoch, we have necessarily to intercalate a group +of very low reptiles, which are still so generalized that their +descendants could branch off either into the Reptilia proper or into +the Mammalia. The changes concerned chiefly the brain and the heart; +of the skeleton, the skull and the pelvis; and, of the tegumentary +structures, the formation of a hairy covering. Many such creatures +existed in the Triassic epoch--namely, the _Theromorpha_--some of which +indeed possess so many characteristics which otherwise occur in the +Mammalia only, that these creatures have been termed _Sauro-Mammalia_. +However, it has to be emphasized that none of the Theromorpha hitherto +discovered fulfils all the requirements which would entitle them to +this important linking position. They only give us an approximate idea +of what this link was like. + +18. Stage of the _Promammalia_, or _Prototheria_. The only surviving +members are the famous duck-bill, Ornithorhynchus, and the spiny +ant-eaters, Echidna and Proechidna, of the Australian region. These +few genera, however, differ so much from one another in various +important respects that they cannot but be remnants of an originally +much larger group. Indeed, many fossils from the Upper Triassic and +from the Jurassic strata have without much doubt to be referred to the +Prototheria. The Prototheria are typical mammals, because they possess +the following characteristics: The heart is completely quadrilocular; +the blood is warm, and its red corpuscles have, owing to the loss +of their nucleus, been modified from biconvex into biconcave discs; +they have a hairy coat and sweat glands, and two occipital condyles; +the ilio-sacral connection is preacetabular; the ankle-joint is +cruro-tarsal; the quadrate bone of the Reptilia has ceased to carry the +under jaw, which now articulates directly with the squamosal portion +of the skull. Their low position is shown by the retention of the +following reptilian features: Complete coracoid bones and a T-shaped +interclavicle; a cloaca, or common chamber for the passage of the +faeces, the genital and the urinary products; they are still oviparous; +the embryo develops without a chorion, and is therefore not nourished +through a placenta. Even the milk glands, which are absolutely +peculiar to the Mammalia, are still in a very primitive stage, and do +not yet produce milk proper; and there is only a temporary shallow +marsupium. + +19. Stage of _Metatheria_, or _Marsupialia_, are direct descendants of +Prototheria; but they show higher development by the reduction of the +coracoid bones and the interclavicle. The original cloaca is divided +into a rectal chamber and a uro-genital sinus, completely separated, +at least in the males; they are viviparous; the young are received +into a permanent marsupium, in the walls of which are formed typical +milk glands and nipples, but the embryo is still devoid of a placenta, +although some recent marsupials show indications of such an organ. The +corpus callosum in the brain is still very weak. + +Most of the marsupials are extinct. They occur from the Upper Trias +onwards, and had in the Jurassic epoch attained a wide distribution +both in Europe and in America. Since the Tertiary epoch they have +been restricted to America and to the Australian region, and are now +represented by about 150 species. + +20. Stage of _Prochoriata_, or early _Placentalia_: a further +development of the Metatheria by the development of a placenta, loss +of the marsupium and the marsupial bones, complete division by the +perineum of the anal and uro-genital chambers, stronger development of +the corpus callosum, or chief commissure of the two hemispheres of the +brain. + +Placentalia must have come into existence during the Cretaceous +epoch. Up to that time all the Mammalia seem to have belonged to +either Prototheria or to Metatheria; but in the early Eocene we can +distinguish the main groups of Placentalia--namely, (1) Trogontia, now +represented by the rodents; (2) Edentata, or sloths, armadilloes, etc.; +(3) Carnassia, or Insectivora and Carnivora; (4) Chiroptera, or bats; +(5) Cetomorpha, or whales and dugongs; (6) Ungulata; (7) Primates. +Of these groups, the first and second, third and fourth, fifth and +sixth, can perhaps, to judge from palaeontological evidence, be combined +into three greater groups, as indicated by the fossil Esthonychida, +Ictopsida, and Condylarthra, in addition to the ancestral Primates, +or Lemuravida, as the fourth large branch of the ancestral-tree where +this has reached the placental level. Among none of the first three +branches can we look for the ancestors of the Primates. The Lemuravida, +therefore, represent a branch equivalent to the three other branches. + +21. Stage of _Lemures_, or _Prosimiae_, comprising the older members of +the Primates, consequently approaching most nearly to the Lemuravida. +The limbs are modified into pentadactyle hands and feet of the arboreal +type, and are protected by nails. The dentition is of the frugivorous +or omnivorous type, with an originally complete series of teeth, with +milk teeth and with permanent. The orbit is surrounded by a complete +bony ring, posteriorly by a fronto-jugal arch, but still widely +communicating with the temporal fossa. The placenta is diffuse and +non-deciduous. + + ANCESTRAL TREE OF THE MAMMALIA. + + _'Systematische Phylogenie,' Sec. 386._ + + _Perissodactyla_ _Homo_ _Carnivora_ + | (_Litopterna_) | | _Pinnipedia_ + | | | | | + +-------+ _Anthropoidae_ +------+ + _Artiodactyla_ | | | + | | | _Carnassia_ + +----------+ _Catarhinae_ | + | | _Chiroptera_ | + _Proboscidea_ | | | _Insectivora_ | + | | _Platyrhinae_ | | | + (_Amblypoda_) | | | | +-------+ + | | | | | | _Rodentia_ + +-------+ | _Simiae_ +-------+ | + | | | | (_Tillodontia_) + +--+ | | | + _Cetacea_ | | | _Trogontia_ + | _Sirenia_ | _Lemures_ _*Ictopsales*_ | _Edentata_ + | | | | | | | + _Cetomorpha_ | _Hyracoidea_ | | _*Esthonychales*_ + | | | | | | + +---_?_---+------+ | | | + | _*Lemuravidae*_ | | + _*Condylarthrales*_ | +-------+ | + | | | | + +--------Eutheria s. Placentalia------------------+ + | + | _Marsupialia polyprotodontia_ + _Marsupialia diprotodontia_ | | + | | | + +-------------Metatheria--------------+ + | + | _Monotremata_ + | | (_Allotheria_) + | | | + | +-----------------+ + | | + Prototheria-----+ + | + | + _*Hypotheria s.*_ _*Promammalia*_ + + _Names in brackets indicate extinct groups. + Names *underlined* indicate hypothetical groups or combinations._ + +22. Stage of _Simiae_. Orbit completely separated from the temporal +fossa by an inward extension of the frontal and malar bones meeting the +alisphenoid. Placenta consolidated into a disc, and with a maternal +deciduous portion. Mammae pectoral only. The dental formula is 2.1.3.3. +All the fingers and toes are protected by flat nails. The tail is long. +The American prehensile-tailed monkeys are a lower side-branch. + +23. Stage of _Catarrhinae Cercopithecidae_. The dental formula is +2.1.2.3, owing to the loss of one pair of premolars in each jaw. +The frontal and alisphenoid bones are in contact, separating the +parietal from the malar bone; this feature is correlated with the +enlarged brain. The internarial septum is narrow, and the nostrils +look forwards and downwards instead of sidewards--hence the term +'Catarrhinae.' The external auditory meatus is long and bony. The tail +is long, with the exception of _Macacus inuus_. The body is covered +with a thick coat of furry hair. Catarrhine monkeys have existed, we +know with certainty, since the Miocene. + +24. Stage of _Catarrhinae Anthropoidae_, or _Apes_. Now represented by +the large apes--namely, the Hylobates or gibbon of South-Eastern Asia, +_Simia satyrus_, the orang-utan of Sumatra and Borneo, _Troglodytes +gorilla_, _T. niger_ and _T. calvus_, the gorilla and the chimpanzees +from Western Equatorial Africa. Of fossils are to be mentioned +Pliopithecus and Dryopithecus from European Miocene, and _Troglodytes +sivalensis_ from the Pliocene of the Punjaub. The tail is reduced +to a few caudal vertebrae, which are transformed into a coccyx, not +visible externally; but in the embryos of apes and man the tail is +still a conspicuous feature. The walk is semierect; in adaptation +to the prevailing arboreal life, the arms are longer than the legs. +The hair of the body is considerably more scanty than in the tailed +monkeys. _Troglodytes calvus_, a species or variety of chimpanzee, is +bald-headed. None of the recent genera of apes can lay claim to a place +in the ancestry of mankind. + +25. Stage of _Pithecanthropi_. Hitherto the only known representative +is _Pithecanthropus erectus_, from the Upper Pliocene of Java. In +adaptation to a more erect gait, the legs have become stronger and the +hind-hand has been turned into a flat-soled walking 'foot.' The brain +is considerably enlarged. Presumably it is still devoid of so-called +articulate speech; this is indicated by the fact that children have +to learn the language of their parents, and by the circumstance that +comparative philology declares it impossible to reduce the chief human +languages to anything like one common origin. + +26. _Man._ Known with certainty to have existed as an implement-using +creature in the last Glacial epoch. His probable origin cannot, +therefore, have been later than the beginning of the Plistocene. The +place of origin was probably somewhere in Southern Asia. + +Whilst we have to admit that there are great defects in the older +(invertebrate) portion of our pedigree, we have all the more reason to +be satisfied with the positive results of our investigation of the more +recent (vertebrate) part of it. All modern researches have confirmed +the views of Lamarck, Darwin, and Huxley, and they allow of no doubt +that the nearest vertebrate ancestors of mankind were a series of +Tertiary Primates. + +Particularly valuable are the admirable attempts of the two zoologists, +Paul and Fritz Sarasin,[22] to throw light upon the human phylogeny by +painstaking comparison of all the skeletal parts of man with those of +the anthropoid apes. They have shown that among the lower races of man +the primitive Veddahs of Ceylon approach the apes most nearly, and that +among the latter the chimpanzee stands nearest to man. + + [22] 'Ergebnisse naturwissenschaftlicher Forschungen auf Ceylon,' vols. + 4 and 5. (With an atlas of 84 plates; 1893.) + +The direct descent of man from some extinct ape-like form is now beyond +doubt, and admits of being traced much more clearly than the origin +of many another mammalian order. The pedigrees of the Elephants, the +Sirenia, the Cetacea, and, above all, of the Edentata, for example, +are much more obscure and difficult to explain. In many parts of their +organization--for example, in the number and structure of his five +digits and toes--man and monkeys have remained much more primitive than +most of the Ungulata. + +The immense significance of this positive knowledge of the origin of +man from some Primate does not require to be enforced. Its bearing +upon the highest questions of philosophy cannot be exaggerated. Among +modern philosophers no one has perceived this more deeply than Herbert +Spencer.[23] He is one of those older thinkers who before Darwin were +convinced that the theory of development is the only way to solve +the 'enigma of the world.' Spencer is also the champion of those +evolutionists who lay the greatest weight upon _progressive heredity_, +or the much combated _heredity of acquired characters_. From the first +he has severely attacked and criticised the theories of Weismann, who +denies this most important factor of phylogeny, and would explain +the whole of transformism by the 'all-sufficiency of selection.' In +England the theories of Weismann were received with enthusiastic +acclamation, much more so than on the Continent, and they were called +'Neo-Darwinism,' in opposition to the older conception of Evolution, +or 'Neo-Lamarckism.' Neither of those expressions is correct. Darwin +himself was convinced of the fundamental importance of progressive +heredity quite as much as his great predecessor Lamarck; as were also +Huxley and Spencer. + + [23] 'Principles of Biology': 'The Factors of Organic Evolution'; 'The + Inadequacy of Natural Selection.' + +Three times I had the good fortune to visit Darwin at Down, and on each +occasion we discussed this fundamental question in complete harmony. +I agree with Spencer in the conviction that progressive heredity is +an indispensable factor in every true monistic theory of Evolution, +and that it is one of its most important elements. If one denies with +Weismann the heredity of acquired characters, then it becomes necessary +to have recourse to purely mystical qualities of germ-plasm. I am of +the opinion of Spencer, that in that case it would be better to accept +a mysterious creation of all the various species as described in the +Mosaic account. + +If we look at the results of modern anthropogeny from the highest point +of view, and compare all its empirical arguments, we are justified in +affirming that _the descent of man from an extinct Tertiary series of +Primates is not a vague hypothesis, but an historical fact_. + +Of course, this fact cannot be proved _exactly_. We cannot explain all +the innumerable physical and chemical processes, all the physiological +mutations, which have led during untold millions of years from the +simplest Monera and from the unicellular Protista upwards to the +chimpanzee and to man. But the same consideration applies to all +historical facts. We all believe that Aristotle, Caesar, and King Alfred +did live; but it is impossible to give a proof within the meaning of +modern exact science. We believe firmly in the former existence of +these and other great heroes of thought, because we know well the works +they have left behind them, and we see their effects in the history +of human culture. These indirect arguments do not furnish stronger +evidence than those of our history as vertebrates. We know of many +Jurassic mammals only a single bone, the under jaw. We all believe that +these mammals possessed also an upper jaw, a skull, and other bones. +But the so-called 'exact school,' which regards the transformation of +species as a hypothesis not proven, must suppose that the mandibula was +the only bone in the body of these curious animals. + +Looking forward to the twentieth century, I am convinced that it will +universally accept our theory of descent, and that future science +will regard it as the greatest advance made in our time. I have no +doubt that the influence of the study of anthropogeny upon all other +branches of science will be fruitful and auspicious. The work done in +the present century by Lamarck and Darwin will in all future times be +considered one of the greatest conquests made by thinking man. + + EVOLUTIONARY STAGES OF THE PRINCIPAL GROUPS OF VERTEBRATA.[24] + + STAGES OF THE CLASSES. STAGES OF THE HEART. + PAIRED LIMBS. + + { 1. _Acrania._ I. _Leptocardia._ + I. _Adactylia_ { Cold-blooded; heart + s. _Impinnata_. { with one chamber; + Without jaws { without lungs. + and limbs. { + { 2. _Cyclostomata._ } II. _Ichthyocardia._ + } Cold-blooded; heart + } two-chambered, with + } one atrium and one + } ventricle; heart + } containing venous + } blood only; without + II. _Polydactylia_ { 3. _Pisces._ } lungs. + s. _Pinnata_. { + With two { } III. _Amphicardia._ + pairs of fins. { 4. _Dipnoi._ } Cold-blooded; heart + } with three complete + } chambers, namely, with + } two atria and one + } ventricle, or (Reptilia) + { 5. _Amphibia._ } two ventricles with still + { } incomplete septum; heart + { } containing mixed venous + { } and arterialized + III. _Pentadactylia_ { 6. _Reptilia._ } blood; with lungs. + s. _Tetrapoda_. { + With two pairs { { IV. _Thermocardia._ + of pentadactyle { { Warm-blooded; heart + limbs (unless { 7. _Aves._ { with four complete + they have { { chambers, namely, two + been lost by { { auricles and two + reduction). { { ventricles; right half + { { of the heart with venous, + { { left half with + { { arterialized, blood; with + { 8. _Mammalia._ { lungs. + + + [24] Abridged from Haeckel's 'Systematische Phylogenie der + Vertebraten,' Sec. 14. + + + + + BIOGRAPHICAL SKETCHES + + +JEAN BAPTISTE DE MONET, CHEVALIER DE LAMARCK, was born on +August 1, 1744, in Picardy, where his father owned land. Originally +educated for the Church, he soon enlisted, and distinguished himself +in active service. Owing to an accident affecting his health, the +young Lieutenant gave up the military career, and, without means, +studied medicine and natural sciences at Paris. In 1778 appeared his +'Flore francaise.' In 1793 he was appointed to a Chair of Zoology at +the newly-formed Musee d'Histoire Naturelle. He had the misfortune to +become gradually blind, and the last years of his life were spent amid +straitened circumstances. He died in 1829. + +In 1794 Lamarck divided the whole animal kingdom into vertebrate and +invertebrate animals, and founded successively the groups of Crustacea, +Arachnida, Annelida, and Radiata. Between 1816 and 1822 he published +his celebrated 'Histoire naturelle des Animaux sans Vertebres.' + +His most famous work is the 'Philosophie zoologique,' 1809. + +Assuming the spontaneous origin of life, he propounded the doctrine +that all animals and plants have arisen from low forms through +incessant modifications and changes. In this respect he was in absolute +opposition to Cuvier, who upheld the immutability of species, and did +his best by absolute silence to suppress the spread of the new doctrine. + +Lamarck has explained his views of transformism chiefly in the seventh +chapter of the first volume of his 'Philosophie zoologique.' + +Organisms strive to accommodate or adapt themselves to new +circumstances, or to satisfy new requirements--_e.g._, climate, mode +of procuring food, escape from enemies. The continued function of +parts of an organism changes the old and produces new organs. The +acquirements are inherited by the offspring, and thus are produced the +more complicated from simpler organisms. Continued disuse brings about +degeneration and ultimate loss of an organ. + +Lamarck consequently sees in the adaptability, or power of adaptation, +which he assumes for all living matter the ultimate cause of variation; +and, as he was certainly the first to point out that acquired +characters are inherited by the progeny, he has given a working +explanation of Evolution. + +But his doctrine did not spread--partly because he was misunderstood. +His theory, that a new want, by making itself felt, exacts from the +animal new exertions, perhaps from parts hitherto not used, until the +want is satisfied--this way of putting it sounds too teleological +to explain the yearned-for change in a mechanical or natural way. +Moreover, many of his examples lacked the exact basis of experiment +and observation necessary for their acceptance. Witness that of the +neck of the giraffe,--a never-failing source of ridicule to men who +cannot see the deeper purpose underlying the well-meant attempt at +an explanation, which failed from want of complete knowledge of the +intricate circumstances. + +However, the theory of transformism was, so to speak, in the air; +and various authors have written on the subject, filling the gap +between Lamarck and Darwin, especially Goethe, Treviranus, Leopold +von Buch, and Herbert Spencer. But it is Darwin's immortal merit to +have opened our eyes by his theory of natural selection, which is, at +least, the first attempt to explain some of the causes and incidents +of organic Evolution in a natural mechanical way. Moreover, he was +the first clearly to express the fundamental principles of the theory +of descent, to elaborate what had been at best a general sketch of an +ill-defined problem, and to enter into detail, supported by a host +of painstaking observations, the making of which had taken him half a +lifetime. Darwin, without going further than cursorily into the causes +of variation, argued as follows: We know that variations do occur +in every kind of living creatures. Some of these variations lead to +something, while others do not. An enormously greater number of animals +and plants are born than reach maturity and can in their turn continue +the race. What is the regulating factor? His answer is, The struggle +for existence--in other words, the weeding out of the less fit, or +rather of the owners of those variations which are not so well adapted +to their surroundings. + +For 'adapted' we had better read 'adaptable,' because a variation which +does not answer, which cannot be made use of, or, still more notably, +is a hindrance or disadvantage, does not become an adapted feature. +There is often a confusion between adaptation as an accomplished +fact, a feature, or resultant condition, and adaptation as the mode +of fitting the organism to, or making the best of, the prevailing +surroundings or circumstances. + +ETIENNE GEOFFROY SAINT-HILAIRE was born in 1772 at Etampes, +Seine-et-Oise. He was originally brought up for the Church; but when +already ordained he attended lectures on natural science and medicine +in Paris. He managed to get the place of assistant in the Musee +d'Histoire Naturelle; he became Professor of Zoology in 1793, and took +the opportunity of encouraging young Cuvier. Later he became Professor +of Zoology of the Faculte des Sciences, and in 1818 he published his +remarkable 'Philosophie anatomique.' He died in 1844. + +He had conceived the 'unity of organic composition,' meaning that there +is only one plan of construction,--the same principle, but varied in +its accessory parts. In 1830, when Geoffroy proceeded to apply to the +Invertebrata his views as to the uniformity of animal composition, +he found a vigorous opponent in Cuvier. Geoffroy, like Goethe, held +that there is in Nature a law of compensation, or balancing of growth, +so that if one organ take on an excess of development, it is at the +expense of another part; and he maintained that, since Nature takes no +sudden leaps, even organs which are superfluous in any given species, +if they have played an important part in other species of the same +family, are retained as rudiments, which testify to the permanence +of the general plan of creation. It was his conviction that, owing +to the conditions of life, the same forms had _not_ been perpetuated +since the origin of all things, although it was not his belief that +existing species were becoming modified. Cuvier, on the other hand, +maintained the absolute invariability of species, which, he declared, +had been created with regard to the circumstances in which they were +placed, each organ contrived with a view to the function it had +to fulfil,--thus putting the effect for the cause ('Encyclopaedia +Britannica,' 9th edition, vol. xxi., p. 171). + +GEORGE CUVIER was born in 1769 at Montbeliard, in the department of +Doubs, which at that time belonged to Wuerttemberg. He was educated at +Stuttgart, and studied political economy. While acting as private tutor +to a French family in France he followed his favourite pursuit, the +study of natural sciences. Geoffroy Saint-Hilaire heard of him, and +appointed him assistant in the department of comparative anatomy in the +Musee d'Histoire Naturelle. In 1799 he was elected Professor of Natural +History at the College de France, and soon after he became Perpetual +Secretary of the Institut National. In 1831, a year before his death, +Louis Philippe raised him to the rank of a peer of France. + +Cuvier was the first to indicate the true principle upon which the +natural classification of animals should be based--namely, their +structure. It is the study of the anatomy of the creatures and their +comparison which affords the only sound basis of a classification. +The work which had the greatest influence upon the scientific public +is his 'Regne animal distribue d'apres son Organisation,' 1817. The +system which he propounded in this book gradually came to have almost +world-wide fame, and, in spite of its many obvious deficiencies, still +lingers in some of our most recent text-books. + +A standard work is his 'Lecons d'Anatomie comparee,' and, in truth, he +is the founder of that kind of comparative anatomy which was brought +to such a high state by his pupil, the late Sir Richard Owen. Cuvier +discovered the law of 'correlation of growth,' and was the first to +apply this law to the reconstruction of animals from fragments: see his +monumental work entitled 'Recherches sur les Ossemens fossiles,' 1812. + +Cuvier, however, as a strict matter-of-fact man, was incapable of +appreciating the speculative conclusions which were drawn by his +contemporaries Saint-Hilaire and Lamarck. On the contrary, he firmly +stuck to the doctrine of the immutability of species; and, in order to +account for the existence of animals whose kind exists no longer, he +invented the famous doctrine of successive cataclysms. + +KARL ERNST VON BAER was born in 1792 in Esthonia, studied at Dorpat +and then at Wuerzburg, where Doellinger introduced him to comparative +anatomy. For a few years he was a _Privat-docent_ at Berlin; then he +went to Koenigsberg as Professor of Zoology and Embryology. In 1834 +he became an Academician at St. Petersburg, where for many years he +was occupied with the most varied studies, chiefly geographical and +ethnological. The last years of his long, active life he spent in +contemplative retirement on his paternal estate, and he died at Dorpat +in 1876. + +While still at Wuerzburg he induced his friend Pander, a young man +of means, to study the development of the chick; and Pander was the +first to start the theory of the germinal layers from which all the +organs arise. Baer, however, continued these researches in Koenigsberg, +and after nine years' labour produced his epoch-making work, 'Ueber +Entwicklungsgeschichte der Thiere: Beobachtung und Reflexion,' +Koenigsberg, 1828. Nine years later he completed the second volume. +He established upon a firm basis the theory of the germinal layers, +and by further 'reflexions' arrived at the elucidation of some of the +most fundamental laws of biology. For example, in the first volume +he made the following prophetic statement: 'Perhaps all animals are +alike, and nothing but hollow globes at their earliest developmental +beginning. The farther back we trace their development, the more +resemblance we find in the most different creatures. And this leads to +the question whether at the beginning of their development all animals +are essentially alike, and referable to one common ancestral form. +Considering that the "germ" (which at a certain stage appears in the +shape of a hollow globe or bag) is the undeveloped animal itself, we +are not without reason for assuming that the common fundamental form is +that of a simple vesicle, from which every animal is evolved, not only +theoretically, but historically.' + +This statement is all the more wonderful when we consider that the +cells, the all-composing individual units, were not discovered until +ten years later. + +In 1829 Baer discovered the human egg, and later the chorda dorsalis. +In an address delivered in 1834, entitled 'The Most Universal Law +of Nature in all Development,' he explained that only from a most +superficial point of view can the various species be looked upon as +permanent and immutable types; that, on the contrary, they can be +nothing but passing stages, or series of stages, of development, which +have been evolved by transformation out of common ancestral forms. + +JOHANNES MUELLER, born at Coblenz in 1801, established himself +as _Privat-docent_ at Bonn, where in 1830 he became Professor of +Physiology. In 1833 he accepted the Chair of Anatomy and Physiology at +Berlin, where he died in 1858. + +He was one of the most distinguished physiologists and comparative +anatomists. By summarizing the labours and discoveries already made in +the field of physiology, by reducing them to order, and abstracting the +general principles, he became the founder of modern physiology. But +he was scarcely less distinguished by his researches in comparative +anatomy. His 'Vergleichende Anatomie der Myxinoiden,' in _Abhandlungen +der Berliner Akademie_, 1835-45, and 'Ueber die Grenzen der Ganoiden' +(_ibid._, 1846), are standard works of lasting value. + +Mueller exercised a stimulative influence as a teacher. Many well-known +men--such as Helmholtz, Gegenbaur, Bruecke the physiologist, Guenther +the zoologist, Virchow the pathologist, Koelliker and Haeckel--have +been his pupils. + +RUDOLPH VIRCHOW was born in 1821 at Schievelbein, a small +town in Eastern Pomerania. He studied medicine in Berlin as a pupil +of Johannes Mueller, and went in 1849 to Wuerzburg, where, under the +influence of Koelliker, and Leydig the pathologist, he laid the +foundation of an entirely new branch of medical science--that of +'cellular pathology.' Since 1856 he has filled the principal Chair of +Pathology at Berlin. In 1892 he received the Copley medal of the Royal +Society. + +'His contributions to the study of morbid anatomy have thrown light +upon the diseases of every part of the body; but the broad and +philosophical view he has taken of the processes of pathology has +done more than his most brilliant observations to make the science of +disease. + +'In pathology, strictly so called, his two great achievements--the +detection of the cellular activity which lies at the bottom of +all morbid as well as normal physiological processes, and the +classification of the important group of new growths on a natural +histological basis--have each of them not only made an epoch in +medicine, but have also been the occasion of fresh extension of science +by other labourers' (Proc. Royal Soc., 1892). + +Virchow has not confined himself to medicine. He takes the keenest +interest in anthropology and ethnology, on which subjects he has +contributed many papers. Together with his colleagues Helmholtz the +physicist, and Du Bois Reymond the physiologist, he has taken a leading +place in the spreading of natural science; but, unfortunately, he +did not take to the doctrine of Evolution, and for the last thirty +years has been its declared antagonist, rarely missing an opportunity +of denouncing everything but descriptive anatomy and zoology as the +unsound speculations of dreamers. This has on more than one occasion +brought him into sharp conflict with Haeckel. His activity is +astonishing, especially if it be remembered that Virchow has for many +years been one of the most conspicuous leaders of the Progressists and +Radicals in the German Parliament and Berlin town-council. + +EDWARD DRINKER COPE was born at Philadelphia, Pa. After studying at +several Continental Universities, especially at Heidelberg, he became +first Professor of Natural Science at Haverford College, and later +Professor of Geology and Mineralogy. He died at an early age in 1897. +As a member of various geological expeditions and other surveys, he +explored chiefly Kansas, Wyoming, and Colorado; and he published many +most suggestive papers on the fossil vertebrate fauna of North America, +and on classification especially of Amphibia and Reptiles. + +Among works of a more general philosophical scope may be mentioned 'The +Origin of the Fittest,' 1887, and his latest work, 'The Primary Factors +of Organic Evolution,' 1896. + +ALBERT VON KOELLIKER, born in 1817, became Professor of Anatomy at +Wuerzburg. His earlier studies and discoveries contributed considerably +to the systematic development of the cell theory. In 1844 he observed +the division and further multiplication of the original egg cell. Next +year he showed the continuity between nerve cells and nerve fibres in +the Vertebrata; later, that the non-striped or smooth muscular tissue +is composed of cellular elements. He demonstrated that the Gregarinae +are unicellular creatures. In 1852 he went with his younger friend +Gegenbaur to Messina, where he studied especially the development +of the Cephalopoda (cuttlefishes and allies); and he produced a +magnificent work on Alcyonaria, Medusae, and other allied forms. He +elucidated the development of the vertebral column, especially with +reference to the notochord. + +In 1848 he founded, together with Th. von Siebold, the famous +_Zeitschrift fuer wissenschaftliche Zoologie_. + +A standard work on mammalian embryology is his 'Entwicklungsgeschichte +des Menschen und der hoeheren Thiere,' a text-book of which the second +edition appeared in 1879. + +At the anniversary meeting of 1897 he received the Copley medal, the +highest honour which the Royal Society can bestow. + +CARL GEGENBAUR was born on August 21, 1826, in Bavaria. He studied +medicine and kindred subjects in Wuerzburg, and as a pupil of Johannes +Mueller in Berlin. + +In 1852 he went with Koelliker to Messina to study the structure and +development of the marine fauna. Important papers on Siphonophora, +Echinoderms, Pteropoda, and, later, Hydrozoa and Mollusca, were the +result. Soon after his return he was offered the chair of Anatomy at +Jena, and at this retired spot he produced his most important works, +devoting himself more and more to the study of the Vertebrata. Since +1875 he has held the Chair of Anatomy at Heidelberg. + +In 1859 he published his 'Principles of Comparative Anatomy'; but in +1870 he remodelled it completely, the theory of descent being the +guiding principle. These 'Grundzuege' were followed by a somewhat more +condensed 'Grundriss,' the second edition of which was published +in 1878, and has been translated into French and English. In the +meantime he had broken new ground by the development and treatment of +certain problems concerning the composition and origin of the limbs, +the shoulder-girdle and the skull, researches which are embodied in +his 'Untersuchungen zur vergleichenden Anatomie der Wirbelthiere,' +1864-65-72. + +In 1883 he brought out a text-book on human anatomy. This also marked +a new epoch, because for the first time, not only the nomenclature, +but also the general treatment of human anatomy, was put upon a firm +comparative anatomical basis. The success of this work is indicated by +the fact that it reached the sixth edition in 1897. + +Lastly, in 1898, appeared the first volume of what may be called his +crowning work, 'Vergleichende Anatomie der Wirbelthiere.' + +Gegenbaur is universally recognised, not only as the greatest living +comparative anatomist, but also as the founder of the modern side of +this science, by having based it on the theory of descent. + +In 1896 he received from the Royal Society the Copley medal 'for +his pre-eminence in the science of comparative anatomy or animal +morphology.' + +His marvellously powerful influence as a teacher and investigator has +made Heidelberg a centre whence many pupils have spread his teaching, +and above all his method of research. + +ERNST HEINRICH HAECKEL was born on February 16, 1834, at Potsdam. He +carried out his academical studies alternately at Berlin and Wuerzburg, +attracted by such men as Johannes Mueller, Koelliker, and Virchow. +For years he was undecided what his career should be, whether that +of botanist, collector, or geographical traveller. Certainly that of +medicine attracted him least, although in deference to his father's +wishes he qualified and settled down for a year's practice in Berlin. +As he himself has told us, he might perhaps have proved rather +successful as a physician, to judge from the fact that he did not lose +a single patient. But 'I had only three patients all told, and the +reason of this is perhaps that I had given on my plate the hours of +consultation as from 5 to 6 _a.m._' + +During the year 1859 he travelled as medical man and artist in Sicily. +In 1861 he was induced by Gegenbaur, whose acquaintance he had made in +Wuerzburg, to establish himself as a _Privat-docent_ for comparative +anatomy in Jena. And there he has remained ever since, filling the +Chair of Zoology, and having declined several much more tempting offers +from the Universities of Wuerzburg, Vienna, Strassburg, and Bonn. + +Within one year, 1865, he wrote the two volumes of his 'Generelle +Morphologie der Organismen,' as he himself relates, in order to master +his sorrow over the loss of his first wife. But he broke down, and went +to the Canaries to recruit health and strength. The 'Morphologie,' +which has long been out of print,[25] made scarcely any impression. It +was ignored, probably because he had placed the old-fashioned study of +zoology and morphology upon a thoroughly Darwinistic basis. + +[25] That this great work is now comparatively rare, although still +in the second-hand market, may perhaps be urged in excuse of the +fact of so many attempts made by many authors, both professional and +amateur, to find fault with or to explain the principles of adaptation, +variation, heredity, caenogenesis, phylogeny, etc., in complete +ignorance that all these and many more fundamental questions were fully +discussed more than thirty years ago in the 'Generelle Morphologie.' + +On the advice of his friend Gegenbaur, he gave a more popularly +written abstract of his 'Generelle Morphologie'--in fact, the +substance of a series of his lectures--in the shape of his 'Natuerliche +Schoepfungsgeschichte.' This 'History of Natural Creation,' which +in 1898 has reached the ninth edition (first edition translated +into English in 1873), had the desired effect. So also had his +'Anthropogenie oder Entwicklungsgeschichte des Menschen,' the fourth +edition of which appeared in 1891. + +It was a lucky coincidence that Haeckel had just finished his +preliminary academical studies, was entirely at leisure, and +undetermined to which branch of natural science he should devote his +genius, when Darwin's great work was given to the world. Haeckel +embraced the new doctrine fervently, and, as Huxley was doing in +England, he spread it and fought for it with ever-increasing vigour in +Germany. + +With marvellous vigour and quickness of perception he applied the +principles of Evolution or the theory of descent to the whole organic +world, and not only opened entirely new vistas for the study of +morphology, but also worked them out and fixed them. He was the first +to draw up pedigrees of the various larger groups of animals and +plants, filling the gaps by fossils or with hypothetical forms (the +necessary existence of which he arrived at by logical deductions); +and thus he reconstructed the first universal pedigree, a gigantic +ancestral tree, from the simple unicellular Amoeba to Man. Of course +these pedigrees were entirely provisional, as he himself has over and +over again avowed; but they are, nevertheless, the ideal which all +systematists and morphologists working upon the basis of Evolution have +since been seeking to establish. + +Naturally he was vigorously attacked, not only by anti-Darwinians, +or rather anti-Evolutionists, but also by many of those who, having +accepted the principle of transformism, ought to have known better. +Perhaps they thought they did know better. Imperfections or mistakes in +details of the grand attempt,--and these, naturally, were many,--were +singled out as samples of the whole, which was ridiculed as the romance +of a dreamer. + +In the end, however, this hostility, narrow-minded and unfair in +many respects, has done good to the cause. There has arisen an +ever-increasing school of workers in favour of the new doctrine. Owing +to renewed research, criticism, corrections in all directions, we +now know considerably more about natural classification (and this is +pedigree) than when Haeckel first opened out the whole problem. + +Owing to his fearless mode of exposition, regardless of the indignant +wrath which the new doctrine aroused in certain ecclesiastical +quarters, Haeckel bore the brunt of almost endless attacks, and had to +write polemical essays. The result has been that friend and foe alike +are now working on the lines which he has laid down; most of the ideas +which he was the first to conceive, and to formulate by inventing a +scientific terminology for them, have become important branches, or +even disciplines, of the science. + +Most morphologists of the younger generations now take these terms +for granted, without remembering the name of their founder. It is, +therefore, perhaps not quite superfluous to mention some of them: + +_Phylum_, or stem, the sum total of all those organisms which have +probably descended from one common lower form. He distinguished eight +such phyla--Protozoa, Coelenterata, Helminthes or Vermes, Tunicata, +Mollusca, Articulata, and Vertebrata. The phyla are more or less +analogous to 'super-classes,' large branches or 'circles,' or principal +groups of other zoologists. + +_Phylogeny_, the history of the development of these various phyla, +classes, orders, families, and species. + +_Ontogeny_, the history or study of the development of the individual, +generally called embryology. In reality the scope of embryology +is the ontogenetic study of the various species, and this branch +of developmental study alone can be checked by direct, 'exact' +observation, for the simple reason that the individuals alone are +entities, while the species, genera, families, etc., are abstract ideas. + +The _ontogenesis of any given living organism is a short, condensed +recapitulation of its ancestral history or of its phylogenesis_. This +is Haeckel's 'fundamental biogenetic law.' + +A complete proof of the phylogeny of any creature would be given by +the preservation of an unbroken series of all its fossil ancestors. +Such a series will in most cases, for obvious reasons, always remain a +desideratum. In a few cases, however, the desideratum is nearly met: +for example, the ancestral line of the one-toed digitigrade horse from +a four-or five-toed plantigrade and still very generalized Ungulate is +approaching completion. + +Phylogenetic study has to rely upon other help. This is afforded by +comparative anatomy and by the study of ontogeny. If the latter were +a faithful, unbroken recapitulation of all the stages through which +the ancestors have passed, the whole matter would be very simple; but +we know for certain that in the individual development many stages +are left out (or, rather, are hurried through, and are so condensed +by short-cuts being taken that we cannot observe them), while other +features which have been introduced obscure, and occasionally modify +beyond recognition, the original course. + +Again, the sequence of the appearance of the various organs is +frequently upset (_heterochronism_). Some organs are accelerated in +their development, while others, which we know to be phylogenetically +older, are retarded in making their reappearance in the embryo. + +These disturbing or distorting newly introduced features or factors +show themselves chiefly in connection with the embryonic conditions of +growth--for example, yolk-sac, placenta, amnion. They all come within +the category of _caenogenesis_: they are caenogenetic, while the true, +undisturbed recapitulation is _palingenetic_. + +Lastly, some features, so-called rudimentary or vestigial organs, +instead of disappearing, are most tenacious in their recurrence, +while others of originally fundamental importance scarcely leave +recognisable traces, and are, so to speak, only hinted at during the +embryonic growth of the creature we happen to study. Hence arises the +philosophical study of 'Dysteleology.' + +Among other terms invented by Haeckel, and now in general use, are +_Metamere_, _Metamerism_, _Coelom_, _Gonochorism_, _Gastrula_, +_Metazoa_, _Gnathostomata_, _Acrania_, _Craniota_, and _Amniota_. + +Hitherto we have dealt with his general work only, a resume of which +he gave for many years in a course of thirty lectures before an +audience composed of 'all sorts and conditions of men.' Students of +biology and of medicine side by side with theologians, incipient and +ordained, jurists, political economists, and philosophers, crowded his +lecture-room during the 'seventies to hear the master explaining the +'natural history of creation' or the mysteries of anthropogenesis. +Another course of eighty lectures during the winter semester was, and +still is, devoted to a systematic treatment of zoology, while practical +classes are reserved for the more select. + +His winning personality and fascinating eloquence, combined with a +clear and concise delivery, have gained the enthusiastic admiration of +many a student who went to the quiet University town in order to learn +with his own ears and eyes. + +_List of Separate Publications by Professor Haeckel._ + +'Biologische Studien. I.: Studien ueber die Moneren und andere +Protisten.' Leipzig, 1870 (out of print). He was the first to +make observations on the natural history of the Monera, living +bits of protoplasm, devoid even of a nucleus--_e.g._, _Protogenes +primordialis_, _Protomyxa aurantiaca_. + +'Monographie der Radiolarien.' Berlin, 1862-88. With 171 plates. + +'Entwicklungsgeschichte der Siphonophoren.' Utrecht, 1869. + +'Plankton-Studien. Vergleichende Untersuchungen ueber die Bedeutung und +Zusammensetzung der pelagischen Fauna und Flora.' Jena, 1880. + +'Metagenesis und Hypogenesis von Aurelia aurita.' Jena, 1881. + +'Monographie der Geryoniden oder Ruesselquallen.' Leipzig, 1865. + +'Generelle Morphologie der Organismen.' 2 vols. Berlin, 1866. + +'Anthropogenie oder Entwicklungsgeschichte des Menschen,' 1874; 4th +edition, 1891. + +'Natuerliche Schoepfungs-Geschichte.' 2 vols. Berlin, 1st edition, +1868; 9th edition, 1898. This work has been translated into most +European languages (the first edition in English, under the title +'Natural History of Creation' in 1873; the eighth in 1892). + +'Monographie der Kalkschwaemme.' 3 vols. Berlin, 1872 (out of print). +With the subtitle, 'An Attempt to solve analytically the Problem of +the Origin of Species.' In this work, illustrated by sixty plates, he +showed that the Calcispongia are individually so yielding, so adaptive +to external influences, that it is practically impossible to break up +the whole group into anything like satisfactory species or genera. +According to predilection, we can distinguish either 1 genus with only +3 species, or 3, 21, 43 genera, with 21, 111, 181, or 289 species +respectively. + +In this work, in 1872, Haeckel established the homology of the two +primary layers, ecto- and endoderm, throughout the Metazoa. The attempt +to do the same for the four secondary layers, as made in the second +part of his 'Gastraea-theory,' failed. It caused an enormous amount of +research, hitherto without a satisfactory solution of the problem. + +'Studien zur Gastraea-Theorie.' Jena, 1874. The transformation of +the single primitive egg-cell by cleavage into a globular mass of +cells (Morula)--which latter, becoming hollow (and then known as the +Blastula), turns ultimately by invagination or by delamination into +the Gastrula--is a series of processes which applies to all Metazoa. +The Gastrula is, therefore, the ancestral form of the Metazoa; and the +Gastraea-theory, founded by Haeckel, throws light, on the one hand, upon +the mystery of the phyletic connection of the various animal groups, +while, on the other hand, it connects the Metazoa, or multicellular +organisms, with the lowest Protozoa. We come to this conclusion +becaues the Gastrula arises from and passes through stages which exist as +independent, permanent organisms among the Protozoa. + +Needless to say this Gastraea-theory has been violently attacked in +detail, with the result that various modifications of the Gastrula, +until then undreamed of, have become known. + +'Monographie der Medusen.' Jena, 1879-81. With 72 coloured plates. + +'Reports on the Scientific Results of the Voyage of H.M.S. +_Challenger_.' With 230 plates: + + 1. Deep-sea Medusae. 1881. + 2. Radiolaria. 1887. + 3. Siphonophorae. 1888. + 4. Deep-sea Keratosa. 1889. + +A short holiday spent on the coasts of the Red Sea produced the volume +'Arabische Korallen' (Berlin, 1876); and a longer trip to Ceylon has +been described in 'Indische Reisebriefe,' of which the third edition +appeared in 1893. The English translation (1883) is entitled 'A Visit +to Ceylon.' + +'Monism as connecting Religion and Science: the Confession of Faith of +a Man of Science.' 1894. + +Haeckels latest work is the 'Systematische Phylogenie' (Berlin, 1896), +three volumes dealing with Protistae and Plants, Invertebrata and +Vertebrata. They contain the author's views on the natural system of +the organic world, both living and extinct. Notable in the work are +the many reconstructions of ancestral forms which, provided Evolution +is true, must have existed--hypothetical until they, or something like +them, are found in a fossil state. Everybody who works systematically, +and upon the basis of Evolution, does, sometimes unconsciously, +reconstruct such links, although he may perhaps not see the necessity, +or have the courage to fix his vision, by assigning to it all those +attributes or characters which are indicated by deductions from +comparative anatomy, palaeontology, and embryology. + + + + + THEORY OF CELLS. + + +The vegetable cell was discovered by _Schleiden_, Professor of Botany +at Jena, in 1838. Next year _Schwann_ found the animal cell. + +In 1844 _Koelliker_ discovered that the egg cell, by division and +multiplication, becomes an aggregation--a heap of new cells. + +In 1849 _Huxley_ found the two primary layers (observed long before +by _Pander_ and _Baer_ in the chick) also in certain Invertebrata, +the Medusae; and he called these layers 'ectoderm' and 'endoderm' +respectively. + +In 1851 _Remak_, in his 'Untersuchungen ueber die Entwicklung der +Thiere,' showed the egg to be a simple cell, and that from it, by +repeated division or multiplication, arise the germinal layers, and +that by differentiation of the cells of these layers are formed all the +tissues of the body. + +_Kowalevsky_, of St. Petersburg, found the two primary germinal layers +also in Worms, Echinoderms, Articulata, and other animals. + +_Haeckel_, in 1872, found the same in the Sponges. He stated that these +two germinal layers occur in all animals, except in the Protozoa; +and that they are homologous, or equivalent, in all the groups of +animals, from the Sponges up to Man. In 1873, in his 'Gastraea-theorie,' +he explained the phylogenetic significance, and tried to show the +homology, of the four secondary germinal layers. + + + + + FACTORS OF EVOLUTION. + + +An organism, as living matter, does not stand in opposition to, +or outside of, the rest of the world. It is part of the world. It +receives matter from its surroundings, and gives some back; therefore +it is influenced by its surroundings. It is acted upon, and it reacts +upon the latter, and if these change (and they are nowhere and never +strictly the same) the organism also _varies_. It _adapts_ itself, and +if it does not, or, rather, cannot, do so, it dies, because it is unfit +to live in the world, or, rather, in those particular surroundings +and conditions in which it happens to be. That organism which yields +most easily, accommodates itself most quickly, has the best chance of +existence--_survival of the fittest_. 'Fitness' in this case does not +mean fitness to live, but rather a particular condition which happens +to fit into the new circumstances. + +Adaptation and variation are simultaneous: they are fundamentally the +same. If there were no adaptability and no variability, those simplest +of organisms which we suppose to have sprung into existence in the +pre-Cambrian period would long ago have ceased to exist. + +It is the physiological momentum which models the organism, and, by +causing its adaptations, has produced its organs by change of function. +Gegenbaur illustrates this most important fundamental truth by an +excellent example. Suppose that, in an absolutely simple organism, all +the parts of its exterior are under the same functional conditions, +so that each part of the surface can take in food, and that this is +digested, assimilated, in the interior. There is, in this condition, +not yet any definite organ. If this organism sinks to the bottom and +becomes sessile, this part is excluded from taking in nourishing +matter, while the opposite surface alone remains, or becomes more, fit +for this function. Thus, a simple variation and adaptation has been +produced, and if the same organism continues in this position, its +bottom cells will estrange themselves from their original function, +while those on the top will convey the food into the interior, where +a cavity will be formed, ultimately with a permanent opening, the +primitive gut and mouth, both very different from the 'foot.' + +Thus, by adaptation and variation the organism acquires new functions, +organs, features, and it gives up and eventually loses others. Its +offspring is like it. Like produces like. This is the principle of +_heredity_. Adaptation, when going on generation after generation on +the same lines in the same direction, becomes continuous, and has an +intensifying, _cumulative_ effect. By always weeding out from a flock +of pigeons those birds which possess more dark feathers than the rest, +we ultimately produce an entirely white race. We hurry on what Nature +does slowly. + +The inheritance of acquired characters becomes very obvious in the +following example: The Monera are the lowest living organisms known; +they consist of a mass of protoplasm, and are still devoid of even +a nucleus. They multiply simply by division; each half is like the +other, and like the parent (which by this process has ceased to exist), +except that each is smaller and has to grow. A certain Moneron, +_Protomyxa aurantiaca_, is orange-coloured, and its offspring is from +the beginning of the same colour, and this colour has been acquired +by that kind of Monera-like protoplasm which thereby has become the +species called Aurantiaca. We have no reason for assuming that there +existed from the beginning of life not only colourless, but also red, +orange, and other kinds of protoplasm. In these simplest of organisms +the whole process of heredity seems very obvious; but in the higher +ones, in those which propagate by eggs, the problem is infinitely +more complicated. It is true that the egg is, strictly, nothing but +a small part of the parental organism, and we know from everyday +experience that this single egg-cell has in it all the attributes and +characteristics of the parent; but these attributes and characteristics +make their appearance successively, just as the egg cell of a chick has +neither wings nor feathers, not even a backbone, but develops these +organs because its parents have them. + +The theory that acquired characters are hereditary has often been +vigorously attacked; but the champions of the negative position have +not given us anything satisfactory instead. They question, also, the +principle of adaptation as a factor in Evolution, and substitute +'variation,' coupled with 'natural selection.' + +They point to Darwin's argument: (1) It is a fact that animals and +plants produce a much greater number of young than in their turn grow +up to propagate the race; (2) no two of the frequently many individuals +of the same breed are exactly alike, although the differences may be +hidden to our perception (this is quite true, because no two entities +can live in absolutely the same place and conditions); (3) through +heredity the offspring takes over the faculties and features of the +parents; (4) what decides which of the many individuals (each one +possessing some aberration or variation) are to live and to propagate +the race?--obviously those individual variations which happen to make +the lucky possessors most fit for the struggle for life. + +So far, well; but the 'Neo-Darwinians' imagine that 'adaptation' +is not the cause, but the result, the effect, of the formation of +species. According to them, the species are neither adapted by, nor do +they adapt themselves to, their surroundings. Adaptation is to them +an accomplished fact, a condition which a species happens to be in +because its particular variation is the one which, to the exclusion of +others, suits or fits into its surroundings. Such a view simply takes +variation for granted, and stipulates it as a something _a priori_, +without raising the further necessary question, why there should be +any variations at all. Why, indeed, unless they are caused by external +influences? Haeckel elucidated this by the conception of adaptation as +explained in the foregoing pages. + +These and kindred speculations have produced some rather curious +discussions, which not infrequently end in conundrums. If we speak of +a case of adaptation as a condition, a fact, we easily run the risk +of getting into confusion about cause and effect. For example: Is the +stag swift because he has long and slender legs, or are his legs long +because he is swift? In reality, swiftness and length of legs are cause +and effect in one. His legs have been so modified as to make him swift, +because he has put them continuously to whatever was his full speed, +which in his thick-footed ancestors was probably a very slow one. The +above question reads, therefore, more sensibly as follows: Has the stag +become swift because his legs have become long and slender, or have his +legs become long and slender because he has attained swiftness? Now, we +see that both halves of the double question are practically the same +and instantly suggest the answer. + +A fundamental difference between artificial machines and living +organisms is that the former are worn out by use, while the latter not +only repair the loss caused by use, but are also stimulated to further +increase. On the other hand, organs which are not put into function, +or are not used, _degenerate_. The various cells of the organ react +upon external stimuli by increased activity. Why this should be so is +another question--perhaps because those which do not would soon be not +fit to survive. Each cell has a function; the more specialized the more +intense it is. Every external stimulus, every contact with the outer +surroundings, is an insult, necessarily of detrimental effect, as it +disturbs the equilibrium of the cell body. It must, therefore, be of +advantage to the cells' well-being to return as soon as possible to the +_status quo ante_, and this can only be done by increased activity. + +In the present state of our knowledge, we can approach only the +simplest cases of acquisition of characteristics. Mostly they are +so complicated, subject to so many unthought-of conditions, that we +do not know from which end to approach the problem. Frequently the +supposed use of certain obvious features is the merest guesswork. This +applies especially to features to which we are not accustomed (although +wrongly so) to assign a function--for example, coloration. A green +tree-frog will with predilection rest on green leaves. The advantages +of concealment are obvious, and in this case he 'adapts himself' to the +surroundings by making for green localities: if he did not he would +be eaten up sooner than his more circumspect comrades. But this making +for, and sitting in, the green has not _necessarily_ made him of that +colour. Extreme advocates of one view would argue as follows: Once upon +a time there were among the offspring of ancestral tree-frogs some +which, among other colours, exhibited green, not much, perhaps not even +perceptible to our eyes. The occurrence of this colour, according to +them, was spontaneous, a freak--as if in reality there were anything +spontaneous in the sense of being causeless. The descendants of these +more greenish creatures, provided they did not pair with frogs of the +ordinary set, became still greener (by accumulative inheritance), and +so on, until the green was pronounced sufficient to be of advantage +when competition could set in. + +With this view there is always the difficulty of understanding how the +initial very small changes can be useful, unless we have to deal with +extremely simple organisms. Is it likely in the case of our frogs that +an almost imperceptible variation in colour makes them more fit to +live? We have to assume that 'luck' or chance kept them for generations +out of harm's reach, until the accumulation of green, hitherto quite +ineffective, neither harmful nor useful, became strong enough to be +effective. Such cases undoubtedly happen. + +But we can also argue out this problem in a somewhat different way, +which goes nearer to the root of the whole process. The original +slight, imperceptible change in pigmentation is not a spontaneous +freak; it was caused by the direct influence of the surroundings in +which the particular frogs happened to live, be this factor light or +temperature or food. Thus it stands to reason that the offspring, +living under similar conditions, will be acted upon in the same way. +That factor which has added green to the parents will add green to the +children, until by accumulative inheritance a more decidedly green +race is produced. + +The offspring of green plants do not become green when grown in the +dark; the young plants inherit not the green, but the capacity of +becoming green when acted upon by sunlight. This as an instance of +direct influence of the surroundings on a substance (chlorophyll), +which has not yet performed a function. But the kittens of a pair of +black cats produce black hair before they are born, and we have no +reason to doubt that the black pigment in their tegumentary structures +is ultimately referable to the action of the sunlight. In many +instances creatures living for generations in darkness become white, +pigmentless, and they regain it when exposed to light. For example, the +white, colourless Proteus from the caves of Adelsberg becomes clouded +grey, and ultimately jet black, when kept in a tank whence light is not +strictly excluded. + +Blindness is a very general characteristic of creatures which dwell in +darkness. There are all stages between total blindness and weak eyes. +Now, do these blind creatures live in darkness because they are blind, +or have they become first weak-eyed and then blind because of the +continuous disuse of their eyes? The former explanation has actually +been suggested! Individuals not smitten, but spontaneously, as a freak, +born with sore eyes, have crept into the darkness for relief and have +produced a blind race! To carry such a notion to the bitter end leads +to absurdities. Anyhow, it is not understandable where the benefit +of losing the eyesight arises. It can be explained only by continued +disuse: witness _Spalax typhlus_, the blind mole, and, above all, the +Endoparasites. + +Let us now take an example to explain the influence of a tangible +external stimulus. Repeated pressure produces callosities. Although +they are not exactly beneficial in the shape of corns on our toes, +they are so on our hands. At any rate, the morphologist can trace the +development of the footpads, nails, hoofs, and horns, step by step from +small beginnings. The cells of the Malpighian stratum, of the inner, +active portion of our epidermis, are excited to extra activity, and +by continually producing more horn cells than peel off the surface of +the skin in the normal process of wear and tear cause the formation +of the pad. It need scarcely be mentioned that hypertrophic growths +are not necessarily useful; they are often harmful, and in that case +pathological. + +Lastly, a few words about the very difficult question of _teleology_. +In trying to explain Evolution in a mechanical--sometimes called +monistic, but in reality natural--way, we exclude anything like a +set purpose, a goal, or ideal, a final condition which the organism +strives to attain. Unknown, however, to many morphologists, especially +embryologists, their writings are full of this teleological notion. +Indeed, there are many cases in which an organism becomes changed, and +quickly, too, in a way which cannot but be called reasonable. It starts +modifications, be they outgrowths, alterations in shape or colour, or +the making good of injuries received, which by 'short-cuts' produce +the only advantageous result that can reasonably satisfy the new +requirement or altered circumstances. + +Trees growing in precarious positions, after part of the supporting +rock has slipped away, throw out new roots, and rearrange some of +the old ones in the only way which could save the tree. In animals +which have lost part of a limb the wound closes up, and what is left +is turned into a serviceable stump--for example, in water-tortoises +(creatures in which reproduction of lost limbs does not happen). In +frogs and newts the lost part is reproduced, not correctly, but in a +good semblance. Tortoises which have had their shell smashed can throw +off an astonishingly large portion and renew the bone as well as the +overlapping scutes; but this mending is not neatly done. It serves the +requirement, but it is patchwork; the new shell is such as no tortoise +ever possessed before. + +Mammals transported into colder countries, or subjected to continued +exposure, grow a thicker coat; and the same kind of tree which in a +sheltered valley is tall, large-leaved, and soft-wooded, assumes a very +different aspect, although perhaps growing into a healthy specimen, +when planted on a wind-exposed hill. + +There is no room, or, rather, no time, to apply to these cases the +principle of many variations or the long-continued accumulation of +infinitely small changes. The thing is to be done quickly, or not +at all. Nor can we explain the mending of a wound, which implies an +activity of countless cells, simply as a case of, or similar to, the +reproduction of a lost part; against such an explanation militates the +almost absolute unlikelihood of that precise injury having happened +before to any of the creature's ancestors. + +Still, I think we are brought near the solution of the mystery by +such considerations. We see no difficulty in the regeneration of a +few cells, or in the making good of the disturbance suffered by one +of the most simple organisms; but we become suspicious when we see +that countless cells, not of one kind, but of the most varied tissues +and parts of the body, make common cause in remedying a defect in a +serviceable way. + +We must assume that since the beginning of life organisms have been +subjected to countless insults. We can scarcely speak of a wound in +an Amaeba; but these insults have always been made good, and whenever +this was not the case, that particular organism came to an end. As +these organisms developed into more complicated ones, the possible +insults became more serious, more complicated; and the organisms took +adaptive measures so as to be superior to them. This action, I have +no hesitation in declaring, became by heredity a habit. The whole +creature became so thoroughly 'imbued' (for want of a better word) with +the finding of ways and means for meeting sudden, serious conditions, +that it now acts directly, and produces by a short-cut, with the least +amount of time and with the smallest possible waste of material, that +which meets the occasion, thereby saving the life of the individual +and that of the race. This we cannot but call reasonable and to the +purpose, although it is all carried out by _causae efficientes_ without +there being any _causae finales_. + + + + + GEOLOGICAL TIME AND EVOLUTION. + + +One million years is a stretch of time beyond our conception. We can +arrive at a more or less adequate understanding of what a million +individuals or concrete things means. Several Continental nations +can put more than a million men into the field. We can gaze at a +building which contains as many bricks; and we know that our own body +is composed of millions of millions of cells. No such help applies to +time, because that itself is an entirely relative, abstract conception. +We can imagine what one hundred years are like--a span of time +seemingly short to the hale and hearty octogenarian, enormous to the +child, totally inapplicable to certain animals whose whole life is +crowded into one single day. + +Astronomers have long ceased to reckon distances by miles or any +other understandable unit. They express the distances between us and +the stars and nebulae by 'years of light.' Try to imagine a unit of +length equal to that which is passed through by light (186,000 miles +per second) in one year. Not so very long ago the enormous distances +resulting from astronomical calculations were looked upon as the most +serious objection to the correctness of the astronomers' views as to +the distances which separate our globe from the nearest fixed stars. +We have not yet accustomed ourselves to reckoning time by some similar +broadly-conceived standard--say aeons of so many thousand years each. + +Unfortunately, we possess no data whatever for calculating the age +of the successive geological strata. Thanks to Lyell, the theory of +violent universal cataclysms has been done away with. It is more +probable that the same agencies have acted which are now changing +the aspect of the globe; and these changes are slow, as far as we +know them--at least, as far as the formation of sedimentary strata is +concerned, and these alone we have to deal with. Various calculations +have been made, based upon the denudation of the mountains, the +filling up of the valleys by the debris, the formation of deltas, +etc. The results give enormous stretches of time, but all of them +unsatisfactory, because the methods are so very local in their +application. + +The least objectionable attempt is that which, based upon astronomical +calculations, tried to fix the height of the last Glacial epoch[26] at +about 200,000 years ago, and asserted that since its beginning in the +Pliocene epoch as many as 270,000 years have elapsed. The duration +of the whole Tertiary period has by the same authorities been fixed +approximately at 3,000,000 to 4,000,000 years. Beyond this we cannot +venture without the wildest speculation; but we know to a certain +extent the thickness of the various sedimentary strata, which amount +in all to from 100,000 to 175,000 feet--on the average perhaps 130,000 +feet, or about twenty miles. + + [26] James Croll: 'On Geological Time, and the Probable Date of the + Glacial and Upper Miocene Period,' _Philos. Magazine_, xxxv., 1868, pp. + 363-384; xxxvi., pp. 141-154; 362-386. + +Unless we prefer giving up all attempt at calculation as absolutely +hopeless, and thus resign the whole problem, we must at least try to +arrive at some results, and then see if these cannot reasonably be made +use of. + +Neither geologist nor physicist, and no zoologist, would accept the +suggestion that these 130,000 feet of stratified rocks have been +deposited within only as many years, although the average rate of +deposit would in that case be not more than 1 foot per year. On the +other hand, an indignant protest is raised against the assumption of +1,000,000,000 years. + +Lord Kelvin[27] has come to the conclusion (from data which various +other authorities regard as very unsatisfactory) that not much more +than 100,000,000 years can have elapsed since the molten globe acquired +a consolidated crust. Further time must have passed before the surface +had become stable and cool enough to allow the temperature of the +collecting oceans to fall below boiling-point, and it is obvious that +life cannot possibly have begun until after this had happened. + + [27] William Thomson: 'On the Secular Cooling of the Earth,' _Transact. + R. S. Edinb._, xxiii., 1864, pp. 157-169. + +Wallace, in his 'Island Life,' by making use of Professor A. Geikie's +results as to the rate of denudation of matter by rivers from the +area of their basins, and estimating the average rate of deposition, +concludes that 'the time required to produce this thickness of rock +[Professor Haughton's maximum of 177,000 feet] at the present rate +of denudation and deposition is only 28,000,000 years.' Our lower +assumption of 130,000 feet thickness would give only 20,000,000 +years--a rate of 1 foot in 154 years. + +Again, if we prefer round numbers to start with, we have only to +assume that the age of the whole Tertiary period, with its 3,000 feet +thickness, is 3,000,000 years (_i.e._, 1,000 feet in 1,000,000 years, +or 1 foot in 1,000 years, surely an excessively slow rate); then +130,000,000 years would bring us to the bottom of the Laurentian or +pre-Cambrian deposits. Of course, it is a pure assumption that the +same rate of destruction and sedimentation applies to the whole of the +strata; but we know nothing to the contrary, especially if we consider +the average periods, the quick periods of extra activity, taken with +the slow periods or those of standstill. + +Dana estimated the length of the whole Tertiary period at one-fifteenth +of the Mesozoic and Palaeozoic combined. If we take the duration of the +Tertiary period, as before, as 3,000,000 to 4,000,000 years, the total +will amount to from 45,000,000 to 60,000,000 years. + +Lastly, Walcott[28] has estimated the duration of the Palaeozoic, +Mesozoic, and Caenozoic or Tertiary epochs at about 17,000,000, +7,000,000 and 3,000,000 years respectively, giving 27,700,000 years +from the beginning of the Cambrian; and Williams[29] has calculated the +relative duration of the smaller epochs. See the table on p. 149. + +The results of all these calculations fall surprisingly well within +the limits of Lord Kelvin's allowance. Of course they are based upon +assumptions, but none of them is inherently unreasonable; and it +was my purpose to draw attention to the surprising coincidence in +the closeness of these results, perhaps too good to be true. Such +calculations are considered close enough if they range within a few +multiples of each other. + + [28] 'Geological Time as indicated by the Sedimentary Rocks of North + America.' _Proc. Amer. Assoc. Adv. Sci._, xlii., 1893, pp. 129-169. + + [29] Henry Shaler Williams, 'Geological Biology.' New York, 1895. + +Zoologists have fallen into the habit of requiring enormous lengths of +time for the evolution of the animal kingdom. We know that Evolution is +at best a slow process, and the conception of the changes necessary to +evolve man from monkey-like creatures, these from the lowest imaginary +mammals, these from some reptilian stock, thence descending to Dipnoan +fish-like creatures, and so on back into Invertebrata, down to the +simple Monera--this conception is indeed gigantic. Innumerable, almost +endless, slow changes require seemingly unlimited time, and as time is +endless, why not draw upon it _ad libitum_? + +Huxley pointed out that it took nearly the whole of the Tertiary epoch +to produce the horse out of the four-toed Eohippos, and that, if we +apply this rate to the rest of its pedigree, enormous times would +be required. This is, however, a very misleading statement, which +necessitates considerable reduction, in conformity with our increased +palaeontological knowledge. Animals of the genus Equus--namely, +Ungulata, with one toe, and with a certain tooth pattern--from the +Upper Miocene of India are now known. Moreover, it is not simply a +question of the gradual loss of the side-toes. The change from the +fox-sized little Eohippos and Hyracotherium, so far as skull, teeth, +vertebral column, and limbs are concerned (about the soft parts we know +next to nothing), is a very great one indeed. + +Elephants and mammoths seem to have developed very rapidly. None are +known from Eocene strata; but towards the end of the Miocene they had +spread over Asia, Europe, and North America, and that in great numbers. +The Eocene Amblypoda are still so different that we hesitate to connect +them ancestrally with the elephants. + +The Pinnipedia (seals and walruses) are strongly modified fissiped +Carnivora, and have existed since at least the Upper Miocene; the +transformation must have been accomplished within the Miocene period. + +We cannot shut our eyes to the fact that various groups have from the +time of their first appearance burst out into an exuberant growth of +modifications in form, size, and numbers, into all possible--and one +might almost say impossible--shapes; and they have done this within +comparatively short periods, after which they have died out not less +rapidly. It seems almost as if these go-ahead creatures had, by +accepting every possible modification and carrying the same to the +extreme, too quickly exhausted their plasticity--which, after all, +must have limits--thereby becoming unable to meet successfully the +requirements of further changes in their surroundings. The slowly +developing groups, keeping within main lines of Evolution, and not +being tempted into aberrant side-issues, had, after all, a much better +chance of onward evolution. + +A good example of the former are the Dinosaurs. We do not know +their ancestors; but we have here to deal only with their range of +transformation. The oldest known forms occur in the Upper Trias; they +attain their most stupendous development in the Upper Jurassic and in +the Wealden; and they have died out with the Cretaceous epoch. But +already some of their earliest forms had assumed bipedal gait, and the +Oolitic Compsognathus had developed almost bird-like hind-limbs. + +On the other hand, there are many instances of extremely slow +development--facts which raise the difficult question of 'persistent +types.' Are these due to a state of perfection which cannot be improved +upon? Or are they due to a kind of morphological consolidation (not +necessarily specialization) which can no longer yield easily, so that +therefore through changes in their surroundings they may come to an end +sooner than more plastic groups? + +Struthio, the ostrich; Orycteropus, the Cape ant-eater; Tapirus, and +many others, existed in the Miocene age practically as they are +now; but pre-Pliocene dolphins, cats, monkeys, stags, all belong to +closely-allied and well-defined 'genera,' but different from the living +forms. + +Alligators and crocodiles are known from the Upper Chalk; Tomistoma +since the Miocene; Gavialis since the Pliocene. + +The oldest surviving reptile is Sphenodon, the Hatteria of New Zealand, +a fair representative of what generalized reptiles of the later +Triassic period seem to have been like; and to the same period belongs +Ceratodus, the Australian mud-fish, hitherto the oldest known surviving +genus of a very ancient and low type so far as Vertebrata are concerned. + +Now let us see if the above estimates of geological time are so utterly +inapplicable to animal evolution. On purpose we take one of the lowest +estimates, about 28,000,000 years, and apportion them equally to the +various strata or epochs. + +The original owner of the famous Trinil skull, a _Pithecanthropus +erectus_, lived, according to some, in the Late Pliocene, according +to others in the Early Plistocene, period--that is to say, somewhere +about the beginning of our last Glacial epoch, some 270,000 years ago. +Assuming that he and his like reached puberty at sixteen to twenty +years of age, about 17,000 generations would lie between him and +ourselves, or, to put it more forcibly, between him and the lowest +living human races--say the Ceylonese Veddahs. Only 250 generations, +at twenty years, carry us back to 3000 B.C. (_i.e._, beyond +the ken of history); and if it be objected that the differences between +the oldest inhabitants of Egypt, the Naquada, and the present Fellahin +are very slight, we are welcome to multiply these differences sixty +or seventy fold, in order to arrive at the Pithecanthropus level. +But these Naquada had no metal implements, and there cannot be the +slightest doubt that the development of the human race went on by leaps +and bounds after certain discoveries had been made--to wit, the use +of implements and that of fire. That creature which first took up a +stone or a branch and wielded it thereby got such an enormous advantage +over his fellow-creatures that his mental and bodily development went +on apace. The same applies to the improvement of speech. We assume the +single, monophyletic origin of mankind at one place, in one district; +and the differences between some of the races of man are great enough +to constitute what we might call species. Compare the Venus of Milo, +that noble expression of the ancient Greeks' notion of female beauty, +with the 'products of art' of the Veddahs or the dwarfs of Central +Africa, or think of the beau-ideal which a Michael Angelo could +possibly have evolved if he had never seen any but such people. + + _TIME AND EVOLUTION_ + + ====================================================================== + I. |II.| III. | IV. | V. |VI.| VII. + | | | | | |Generations. + -----------+---+-----------+----------+--------------+---+------------ + |} |} |} |Adam and Eve | | 250 + Recent |} 5|} |} |Man, contem- | | 3,500 + Plistocene |} |} |} 270,000| porary with | | + | |} |} | Reindeer | | + | |} |} | in France | | + Pliocene -|} |} 3,000,000| |_Pithecanthro-| 16| 17,000 + |} |} |} 600,000| pus erectus_| | + Miocene -|}10|} |} |Anthropoid | 10| 60,000 + |} |} |}2,100,000| Apes | | + Eocene -|} |} |} |Lemures | 5| 420,000 + | | | | | | + Cretaceous | 10|} | 3,600,000| | | + Jurassic - | 5|} | 1,800,000| | | + Rhaetic -|} |} |} |Prototheria, | 3| 1,800,000 + |} |} |} | or first | | + |} |} 7,200,000|} | Mammalia | | + Keuper -|} |} |}1,800,000| | | + Muschel- |} 5|} |} | | | + kalk |} |} |} | | | + New Red |} |} |} |Theromorpha | 4| 425,000 + Sandstone| | | | | | + Magnesian |} |} |} | | | + Limestone|} |} |} | | | + Lower Red |} |} |} |Proreptilia | 4| 250,000 + Sandstone|} |} |}4,000,000| | | + Coal- |}15|} |} |Eotetrapoda | 4| 500,000 + measures |} |} |} | | | + Mountain |} |}17,500,000|} | | | + Limestone | |} | | | | + Devonian -| 15|} | 4,000,000|Dipnoi and | 5| 1,000,000 + | |} | |Crossopterygii| | + Silurian -| 10|} | 2,700,000|First fishlike| 3| 900,000 + | |} | | creatures | | + Ordovician | 10|} | 2,700,000| | | + Cambrian -| 15|} | 4,000,000| Sum total of| | + Laurentian | | | | generations| | --------- + Archaean | | | | (about) | | 5,375,000 + or Meta- | | | | | | + morphic | | | | | | + ====================================================================== + +EXPLANATION OF THE TABLE ON P. 149. + + Column I. contains the names of the successive sedimentary strata. + + " II. contains the percentage of the duration of the various epochs, + according to _Williams_, the time from the Cambrian until recent times + being taken as 100. + + " III. gives the estimated duration in years of the Palaeozoic, + Mesozoic, and Caenozoic periods, according to _Walcott_. + + " IV. gives in years the duration of the various smaller epochs, as + computed from Walcott and Williams' statements. + + " V. Representatives of stages of the ancestral line of man. The + names stand in the level of the stratum in which they have made their + first appearance. + + " VI. contains the number of years which, in the present + calculation, have been assumed necessary for the animal to reach + puberty. + + " VII. contains the number of generations which can have elapsed + from stage to stage. For example, 60,000 generations separate the + earliest known anthropoid apes from Pithecanthropus. + +Let us follow the descent of man further back. The next stage, +reckoning backwards, is that from Pithecanthropus to _bona-fide_ +anthropoid apes. They are represented in the Miocene by various +genera--_e.g._, Pliopithecus and Dryopithecus. According to Croll and +Wallace, 850,000 years ago carry us into the Miocene epoch. Assuming +that these apes lived about 600,000 years before Pithecanthropus, +namely, in the later half of the Miocene, and taking puberty at ten +years of age, a high estimate, we get not less than 60,000 generations. + +2. From Apes back to lowest Lemurs in the lowest Eocene. The date of +Eocene being fixed at 3,000,000, we have about 2,100,000 years for this +stage; assuming as much as five years for puberty, this results in +420,000 generations. + +3. From Lemures to Prototheria. The earliest known mammalian remains +come from the Rhaetic, or top formation of the Triassic epoch; allowing +for the Rhaetic only 100,000 years, we have to add the whole of the +Jurassic and Cretaceous, in all about 5,500,000 years. Assuming three +years for a generation, we get 1,800,000 generations. + +4. From Prototheria to something like the Theromorpha at the bottom of +the Triassic strata. A duration of 1,700,000 years divided by four +gives 425,000 generations. + +5. From Theromorpha to Proreptilia, represented by Eryops and Cricotus +from the Lower Permian of Texas. Allowing 1,000,000 years, each +generation at four years, we obtain 250,000 generations. + +6. From Proreptilia to Eotetrapoda, the first terrestrial Vertebrata, +represented by something like the Stegocephali, the earliest of which +are known from the Coal-measures. Assuming them to have come into +existence at the bottom of the Coal-measures, for the duration of which +we may guess 2,000,000 years, we get, with four years' allowance for +puberty, 500,000 generations. + +7. From Eotetrapoda to a not yet separated or differentiated group +of Crossopterygian and Dipnoan fishes, both of which are known from +Devonian strata. The duration of the latter has been computed at +4,000,000 years, which, with 1,000,000 for the Mountain Limestone +formation, gives us 5,000,000 for this stage. Assuming, for the sake +of round numbers, as much as five years for a generation, we get +1,000,000 generations. + +8. Earliest stage, down to the first fish-like creatures. Teeth and +spines indicating the existence of fishes are known from the Upper +Silurian. By carrying the earliest fishes down to the bottom of the +Silurian, with 2,700,000 years' duration, and allowing three years for +attaining puberty, the calculation results in 900,000 generations. + +Further back we cannot go. We do not know of any Vertebrate remains +from the Ordovician and Cambrian, which together represent 6,700,000 +years, enough for at least half as many generations of Prochordate +creatures. The pre-Cambrian or Laurentian epoch lies quite beyond the +reach of calculation, nor have we any trustworthy fossil remains of +living matter from these strata, to which, however, Haeckel and others +refer the first beginnings of life. + +All the above calculations are, of course, only approximate. What we +do know is the existence of representatives of the stages, our proofs +being the fossils; but when we refer the origin of the Eotetrapoda, +for example, to the bottom and not somewhere to the middle of the +Coal-measures, we are guessing merely. Alterations in the levels +assumed for the various stage-representatives will, of course, alter +the result of the number of generations; but the leading idea, as +a whole, is not thereby upset. The fact remains that in the Upper +Silurian we have fishes; from the Coal-measures onwards, fishes and +Amphibia; since the Permian, fishes, Amphibia, and reptiles; since the +end of the Trias these three classes and the Mammalia; and lastly, at +least since the Plistocene, man himself. If Evolution is true at all, +the transformation from early fish-like creatures to man has come about +within these epochs. Being able to assign a time of duration to each +of them, with an approximate total of 21,000,000 years, we are also +able to put the whole ancestral series to a test by expressing each +great stage in generations. The result is very satisfactory. The whole +enormous stretch from the lowest fish-like creatures to man has been +resolved into more than 5,000,000 successive generations, and each of +these means a little step forwards in onward Evolution. + +Nothing is to be gained for the understanding of our problem of +Evolution if we multiply this enormous number of generations by ten +or any other multiple. We are not able to conceive changes so small +as those which necessarily have existed between Pithecanthropus and +man if the whole striking difference is analysed into 17,000 steps. +Every one of these stages in the modifications of the muscles, the +skeletal framework, increase of brain, shortening of the trunk, +lengthening of the legs, improvement of the hands, loss of the hairy +coat, etc., is truly microscopical, imperceptible, just as the +Evolutionist imagines the whole process to have been. Again, where is +the difficulty implied by the change from an air-breathing, in many +structural points half-amphibian, fish into a primitive land-crawling +four-footed creature, if we are allowed to resolve the transformation +into 1,000,000 stages? So far from there being any difficulty, rather +does it appear questionable if so many infinitely small changes have +been necessary to bring about this result. + +One thousand years make apparently no difference in the evolution of +animals, nor does one second change the aspect of the hands on the +face of a clock, nor did Julius Caesar's commission of scientific men +appreciate the error of about eleven minutes in the length of the year +beyond its real value; but now the Russians are, owing to this neglect, +nearly two weeks behind the civilized nations. + + + THE END. + + + BILLING AND SONS, PRINTERS, GUILDFORD. + + + By PROFESSOR ERNST HAECKEL + + + MONISM; + OR, + The Confession of Faith of a Man of Science. + + Translated from the German by J. D. F. GILCHRIST. + + _Crown 8vo., cloth. Price 1s. 6d. net._ + +'We may readily admit that Professor Haeckel has stated his case with +the clearness and courage which we should expect of him, and that +his lecture may be regarded as a fair and authoritative statement +of the views now held by a large number of scientifically educated +people.'--_Times._ + +'The Monism, which is the substance of his faith, is thus defined by +him: "Our conviction that there lives one spirit in all things, and +that the whole cognizable world is constituted, and has been developed, +in accordance with one common fundamental law." As the confession +of a distinguished man of science, this little work deserves to be +read.'--_North British Daily Mail._ + +'This "Confession of Faith" was delivered by the great German +scientist, its author, as an extemporaneous address at Altenburg +rather more than two years ago. There are, no doubt, a large number of +English readers who will welcome a translation, for this "connecting of +religion and science" has long troubled many earnest students of modern +science.'--_Publisher's Circular._ + +'This is a little book of great daring, an example of the wild +speculative flights of one of the very ablest and greatest of our +contemporary men of science.'--_Aberdeen Free Press._ + +'The address, whatever we may think of its conclusions, is, however, +most interesting reading, and is admirably done into English by the +translator.'--_Literary World._ + + + LONDON: ADAM & CHARLES BLACK, SOHO SQUARE. + + + _Demy 8vo., price 7s. 6d. net._ + + SOURCES OF THE APOSTOLIC + CANONS. + + _With a Treatise on the Origin of the Readership and other Lower Orders._ + + By Professor ADOLF HARNACK. + + Translated by LEONARD A. WHEATLEY. + + _With an Introductory Essay on the Organization of the Early Church + and the Evolution of the Reader._ + + By the Rev. JOHN OWEN, Author of 'Evenings with the Skeptics.' + +'Dr. Adolf Harnack is at the present time undoubtedly the leading +liberal authority in Germany on matters connected with early Christian +history.'--_The Times._ + +'Those who are interested in early Church history know how to prize +anything from the pen of Prof. Harnack. They will not be disappointed +with the present paper, in which, with his accustomed learning and +acute criticism, he annotates and comments upon the fragments of +primitive church law which partly form the basis of the Apostolic +Canons.'--_British Weekly._ + +'The wide circulation of this volume would be of the happiest augury +for a more scientific and worthy conception of the organization of the +primitive Church.'--Dr. MARCUS DODS in _The Bookman_. + + + + _Crown 8vo., cloth, price 1s. 6d. net._ + + CHRISTIANITY AND HISTORY. + + By ADOLF HARNACK. + + Translated, with the Author's sanction, by THOMAS BAILEY + SAUNDERS, with an Introductory Note. + +'It is highly interesting and full of thought. The short introductory +note with which Mr. Saunders prefaces it is valuable for its +information and excellent in its tone.'--_Athenaeum._ + +'A singularly able exposition and defence of Christianity, as seen in +the newer light, by one of the most learned and acute "evangelical" +critics of Germany. The essay is a masterly one.'--_Glasgow Herald._ + +' ... We hope the lecture will be widely read.'--_Primitive Methodist +Quarterly Review._ + +'The lecture itself is weighty in its every word, and should be read +and re-read by those desiring to have in a nutshell the central +positions of modern Christianity.'--_Christian World._ + + + LONDON: ADAM & CHARLES BLACK, SOHO SQUARE. + + + _Third Edition. Crown 8vo., cloth, price 5s._ + + SKETCH OF THE HISTORY OF + ISRAEL AND JUDAH. + + By J. WELLHAUSEN, + PROFESSOR AT MARBURG. + +'This work is now issued for the third time as an independent treatise. +It admirably epitomizes the subject, and exhibits on almost every page +evidences of Professor Wellhausen's profound study.'--_Publishers' +Circular._ + +'We would only say that those who differ from his critical views will +yet do well to study them, and to read this history in which he applies +them. Its separate publication, in a handy form and at a moderate +price, makes it generally accessible.'--_North British Daily Mail._ + +'The publication in a separate form of Professor Wellhausen's article +in the "Encyclopaedia Britannica" on "Israel" will be very warmly +welcomed by many readers.'--_Manchester Guardian._ + +'We are very glad to welcome an edition of Professor Wellhausen's +"Sketch of the History of Israel and Judah" in a convenient and handy +form. This is the first time it has appeared in a separate form. It is +already known to students; it ought now to become popular. It is based +on the learned author's studies in Hebrew literature and history, and, +though not controversial in form, it differs totally from orthodox +presentations of the subject.'--_Westminster Review._ + +'A sketch which has created such widespread and profound interest as +this could not be kept in the pages of a voluminous encyclopaedia. +Wellhausen's words necessarily have exceptional importance, even in +the esteem of those who differ from him _toto coelo_.'--_Baptist +Magazine._ + +'The profound scholarship of the author does not elevate his writing +above the interest of the general reader, and a vivid idea of the +involved Jewish history is obtainable from this volume.'--_Christian +Advocate._ + + + LONDON: ADAM & CHARLES BLACK, SOHO SQUARE. + + + _Demy 8vo., boards, price 3s. 6d. net._ + + A CLASSIFICATION OF + VERTEBRATA, + RECENT AND EXTINCT. + + With Diagnoses and Definitions, a Chapter on Geographical + Distribution, and an Etymological Index. + + By HANS GADOW, M.A., PH.D., F.R.S., + + STRICKLAND CURATOR AND LECTURER ON ZOOLOGY TO THE UNIVERSITY, + CAMBRIDGE. + +'At the end of his work Dr. Gadow adds a useful chapter on the +geographical distribution of the Vertebrata, with a table showing +the approximate number of the known recent species. He also gives +a fanciful though striking calculation to show how some groups are +still in the ascendant, while others are distinctly declining. The +little volume is indeed a welcome addition to the biological student's +library, and it deserves the wide circulation which its author's +eminence is likely to ensure for it.'--_Natural Science._ + +'It is a book, it need hardly be said, for the student; it is simply +a list of the principal sub-divisions of backboned animals, with just +as much definition as is needed. It may be regarded as an exceedingly +concentrated extract of a full text-book of the vertebrates.'--_Daily +Chronicle._ + + + + _Demy 8vo., cloth, price 21s._ + + IN NORTHERN SPAIN. + + By Dr. HANS GADOW, M.A., PH.D., F.R.S. + + _Containing Map and 89 Illustrations._ + +'Some years back "Wild Spain," one of the best books of its kind, +made you desirous of knowing more of the country. And Hans Gadow has +deepened this feeling in his excellent volume "In Northern Spain," +and that to an enormous extent. Dwelling at inn or farm, or in their +own tent, they saw the country as it has been seen but rarely, and +they came to know the inhabitants as they can be known in no other +fashion.'--_Black and White._ + +'To persons visiting the provinces with which the author deals, this +book will be invaluable, and will do more to point their attention to +objects of interest than existing guide-books of Spain, most of which +are out of date.'--_The Field._ + +'About the best book of European travel that has appeared these many +years.'--_Literary World._ + + + LONDON: ADAM & CHARLES BLACK, SOHO SQUARE. + + +Transcriber's Notes + + Variations in spelling, punctuation and hyphenation have been retained + except in obvious cases of typographical errors. + Inconsistent hyphenation and spelling are as in the oringinal. + Italics are shown thus _italic_ and underline thus *underline*. + + + + + +End of the Project Gutenberg EBook of The Last Link, by Ernst Haeckel + +*** END OF THIS PROJECT GUTENBERG EBOOK THE LAST LINK *** + +***** This file should be named 44541.txt or 44541.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/4/4/5/4/44541/ + +Produced by Chris Curnow, Les Galloway and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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