initial commit of ebook 22764HEADmain

515 files changed, 15322 insertions, 0 deletions

diff --git a/old/2007-09-25_22764-8.zip b/old/2007-09-25_22764-8.zip
new file mode 100644
index 0000000..1b34c7c
--- /dev/null
+++ b/old/2007-09-25_22764-8.zip
diff --git a/old/2007-09-25_22764-h.zip b/old/2007-09-25_22764-h.zip
new file mode 100644
index 0000000..f96fac1
--- /dev/null
+++ b/old/2007-09-25_22764-h.zip
diff --git a/old/22764-8.txt b/old/22764-8.txt
new file mode 100644
index 0000000..20feea3
--- /dev/null
+++ b/old/22764-8.txt
@@ -0,0 +1,15322 @@
+The Project Gutenberg EBook of On the Origin of Species by Means of
+Natural Selection, by Charles Darwin
+
+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: On the Origin of Species by Means of Natural Selection
+       or the Preservation of Favoured Races in the Struggle for
+       Life. (2nd edition)
+
+Author: Charles Darwin
+
+Release Date: September 25, 2007 [EBook #22764]
+
+Language: English
+
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ORIGIN OF SPECIES ***
+
+
+
+
+Produced by Steven Gibbs, Keith Edkins and the Online
+Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+Transcriber's note: A few typographical errors have been corrected: they
+are listed at the end of the text.
+
+       *       *       *       *       *
+
+
+ON THE
+
+ORIGIN OF SPECIES.
+
+       *       *       *       *       *
+
+"But with regard to the material world, we can at least go so far as
+this--we can perceive that events are brought about not by insulated
+interpositions of Divine power, exerted in each particular case, but by the
+establishment of general laws."
+
+WHEWELL: _Bridgewater Treatise_.
+
+"The only distinct meaning of the word 'natural' is _stated_, _fixed_, or
+_settled_; since what is natural as much requires and presupposes an
+intelligent agent to render it so, _i.e._ to effect it continually or at
+stated times, as what is supernatural or miraculous does to effect it for
+once."
+
+BUTLER: _Analogy of Revealed Religion_.
+
+"To conclude, therefore, let no man out of a weak conceit of sobriety, or
+an ill-applied moderation, think or maintain, that a man can search too far
+or be too well studied in the book of God's word, or in the book of God's
+works; divinity or philosophy; but rather let men endeavour an endless
+progress or proficience in both."
+
+BACON: _Advancement of Learning_.
+
+       *       *       *       *       *
+
+  _Down, Bromley, Kent,_
+      _October 1st, 1859._ (_1st Thousand_).
+
+       *       *       *       *       *
+
+
+ON
+
+THE ORIGIN OF SPECIES
+
+BY MEANS OF NATURAL SELECTION,
+
+OR THE
+
+PRESERVATION OF FAVOURED RACES IN THE STRUGGLE
+FOR LIFE.
+
+BY CHARLES DARWIN, M.A.,
+
+FELLOW OF THE ROYAL, GEOLOGICAL, LINNEAN, ETC., SOCIETIES;
+
+AUTHOR OF 'JOURNAL OF RESEARCHES DURING H. M. S. BEAGLE'S VOYAGE
+ROUND THE WORLD.'
+
+_FIFTH THOUSAND._
+
+LONDON:
+JOHN MURRAY, ALBEMARLE STREET.
+1860.
+
+_The right of Translation is reserved._
+
+       *       *       *       *       *
+
+LONDON: PRINTED BY W. CLOWES AND SONS, STAMFORD STREET,
+AND CHARING CROSS.
+
+       *       *       *       *       *
+
+
+{v}
+
+CONTENTS.
+
+       *       *       *       *       *
+
+INTRODUCTION
+
+Page 1
+
+CHAPTER I.
+
+VARIATION UNDER DOMESTICATION.
+
+Causes of Variability--Effects of Habit--Correlation of
+Growth--Inheritance--Character of Domestic Varieties--Difficulty of
+distinguishing between Varieties and Species--Origin of Domestic Varieties
+from one or more Species--Domestic Pigeons, their Differences and
+Origin--Principle of Selection anciently followed, its Effects--Methodical
+and Unconscious Selection--Unknown Origin of our Domestic
+Productions--Circumstances favourable to Man's power of Selection
+
+7-43
+
+CHAPTER II.
+
+VARIATION UNDER NATURE.
+
+Variability--Individual differences--Doubtful species--Wide ranging, much
+diffused, and common species vary most--Species of the larger genera in any
+country vary more than the species of the smaller genera--Many of the
+species of the larger genera resemble varieties in being very closely, but
+unequally, related to each other, and in having restricted ranges
+
+44-59
+
+{vi}
+
+CHAPTER III.
+
+STRUGGLE FOR EXISTENCE.
+
+Its bearing on natural selection--The term used in a wide
+sense--Geometrical powers of increase--Rapid increase of naturalised
+animals and plants--Nature of the checks to increase--Competition
+universal--Effects of climate--Protection from the number of
+individuals--Complex relations of all animals and plants throughout
+nature--Struggle for life most severe between individuals and varieties of
+the same species; often severe between species of the same genus--The
+relation of organism to organism the most important of all relations
+
+60-79
+
+CHAPTER IV.
+
+NATURAL SELECTION.
+
+Natural Selection--its power compared with man's selection--its power on
+characters of trifling importance--its power at all ages and on both
+sexes--Sexual Selection--On the generality of intercrosses between
+individuals of the same species--Circumstances favourable and unfavourable
+to Natural Selection, namely, intercrossing, isolation, number of
+individuals--Slow action--Extinction caused by Natural
+Selection--Divergence of Character, related to the diversity of inhabitants
+of any small area, and to naturalisation--Action of Natural Selection,
+through Divergence of Character and Extinction, on the descendants from a
+common parent--Explains the Grouping of all organic beings
+
+80-130
+
+CHAPTER V.
+
+LAWS OF VARIATION.
+
+Effects of external conditions--Use and disuse, combined with natural
+selection; organs of flight and of vision--Acclimatisation--Correlation of
+growth--Compensation and economy of growth--False correlations--Multiple,
+rudimentary, and lowly organised structures variable--Parts developed in an
+unusual manner are highly variable: specific characters more variable than
+generic: secondary sexual characters variable--Species of the same genus
+vary in an analogous manner--Reversions to long-lost characters--Summary
+
+131-170
+
+{vii}
+
+CHAPTER VI.
+
+DIFFICULTIES ON THEORY.
+
+Difficulties on the theory of descent with
+modification--Transitions--Absence or rarity of transitional
+varieties--Transitions in habits of life--Diversified habits in the same
+species--Species with habits widely different from those of their
+allies--Organs of extreme perfection--Means of transition--Cases of
+difficulty--Natura non facit saltum--Organs of small importance--Organs not
+in all cases absolutely perfect--The law of Unity of Type and of the
+Conditions of Existence embraced by the theory of Natural Selection
+
+171-206
+
+CHAPTER VII.
+
+INSTINCT.
+
+Instincts comparable with habits, but different in their origin--Instincts
+graduated--Aphides and ants--Instincts variable--Domestic instincts, their
+origin--Natural instincts of the cuckoo, ostrich, and parasitic
+bees--Slave-making ants--Hive-bee, its cell-making instinct--Difficulties
+on the theory of the Natural Selection of instincts--Neuter or sterile
+insects--Summary
+
+207-244
+
+CHAPTER VIII.
+
+HYBRIDISM.
+
+Distinction between the sterility of first crosses and of
+hybrids--Sterility various in degree, not universal, affected by close
+interbreeding, removed by domestication--Laws governing the sterility of
+hybrids--Sterility not a special endowment, but incidental on other
+differences--Causes of the sterility of first crosses and of
+hybrids--Parallelism between the effects of changed conditions of life and
+crossing--Fertility of varieties when crossed and of their mongrel
+offspring not universal--Hybrids and mongrels compared independently of
+their fertility--Summary
+
+245-278
+
+{viii}
+
+CHAPTER IX.
+
+ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
+
+On the absence of intermediate varieties at the present day--On the nature
+of extinct intermediate varieties; on their number--On the vast lapse of
+time, as inferred from the rate of deposition and of denudation--On the
+poorness of our palæontological collections--On the intermittence of
+geological formations--On the absence of intermediate varieties in any one
+formation--On the sudden appearance of groups of species--On their sudden
+appearance in the lowest known fossiliferous strata
+
+279-311
+
+CHAPTER X.
+
+ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
+
+On the slow and successive appearance of new species--On their different
+rates of change--Species once lost do not reappear--Groups of species
+follow the same general rules in their appearance and disappearance as do
+single species--On Extinction--On simultaneous changes in the forms of life
+throughout the world--On the affinities of extinct species to each other
+and to living species--On the state of development of ancient forms--On the
+succession of the same types within the same areas--Summary of preceding
+and present chapters
+
+312-345
+
+CHAPTER XI.
+
+GEOGRAPHICAL DISTRIBUTION.
+
+Present distribution cannot be accounted for by differences in physical
+conditions--Importance of barriers--Affinity of the productions of the same
+continent--Centres of creation--Means of dispersal, by changes of climate
+and of the level of the land, and by occasional means--Dispersal during the
+Glacial period co-extensive with the world
+
+346-382
+
+CHAPTER XII.
+
+GEOGRAPHICAL DISTRIBUTION--_continued_.
+
+Distribution of fresh-water productions--On the inhabitants of oceanic
+islands--Absence of Batrachians and of terrestrial Mammals--On the relation
+of the inhabitants of islands to those of the nearest mainland--On
+colonisation from the nearest source with subsequent modification--Summary
+of the last and present chapters
+
+383-410
+
+CHAPTER XIII.
+
+MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY: EMBRYOLOGY: RUDIMENTARY
+ORGANS.
+
+CLASSIFICATION, groups subordinate to groups--Natural system--Rules and
+difficulties in classification, explained on the theory of descent with
+modification--Classification of varieties--Descent always used in
+classification--Analogical or adaptive characters--Affinities, general,
+complex and radiating--Extinction separates and defines groups--MORPHOLOGY,
+between members of the same class, between parts of the same
+individual--EMBRYOLOGY, laws of, explained by variations not supervening at
+an early age, and being inherited at a corresponding age--RUDIMENTARY
+ORGANS; their origin explained--Summary
+
+411-458
+
+CHAPTER XIV.
+
+RECAPITULATION AND CONCLUSION.
+
+Recapitulation of the difficulties on the theory of Natural
+Selection--Recapitulation of the general and special circumstances in its
+favour--Causes of the general belief in the immutability of species--How
+far the theory of natural selection may be extended--Effects of its
+adoption on the study of Natural history--Concluding remarks
+
+459-490
+
+       *       *       *       *       *
+
+
+{1}
+
+ON THE ORIGIN OF SPECIES.
+
+       *       *       *       *       *
+
+INTRODUCTION.
+
+When on board H.M.S. 'Beagle,' as naturalist, I was much struck with
+certain facts in the distribution of the inhabitants of South America, and
+in the geological relations of the present to the past inhabitants of that
+continent. These facts seemed to me to throw some light on the origin of
+species--that mystery of mysteries, as it has been called by one of our
+greatest philosophers. On my return home, it occurred to me, in 1837, that
+something might perhaps be made out on this question by patiently
+accumulating and reflecting on all sorts of facts which could possibly have
+any bearing on it. After five years' work I allowed myself to speculate on
+the subject, and drew up some short notes; these I enlarged in 1844 into a
+sketch of the conclusions, which then seemed to me probable: from that
+period to the present day I have steadily pursued the same object. I hope
+that I may be excused for entering on these personal details, as I give
+them to show that I have not been hasty in coming to a decision.
+
+My work is now nearly finished; but as it will take me two or three more
+years to complete it, and as my health is far from strong, I have been
+urged to publish this Abstract. I have more especially been induced to do
+this, as Mr. Wallace, who is now studying the {2} natural history of the
+Malay archipelago, has arrived at almost exactly the same general
+conclusions that I have on the origin of species. Last year he sent me a
+memoir on this subject, with a request that I would forward it to Sir
+Charles Lyell, who sent it to the Linnean Society, and it is published in
+the third volume of the Journal of that Society. Sir C. Lyell and Dr.
+Hooker, who both knew of my work--the latter having read my sketch of
+1844--honoured me by thinking it advisable to publish, with Mr. Wallace's
+excellent memoir, some brief extracts from my manuscripts.
+
+This Abstract, which I now publish, must necessarily be imperfect. I cannot
+here give references and authorities for my several statements; and I must
+trust to the reader reposing some confidence in my accuracy. No doubt
+errors will have crept in, though I hope I have always been cautious in
+trusting to good authorities alone. I can here give only the general
+conclusions at which I have arrived, with a few facts in illustration, but
+which, I hope, in most cases will suffice. No one can feel more sensible
+than I do of the necessity of hereafter publishing in detail all the facts,
+with references, on which my conclusions have been grounded; and I hope in
+a future work to do this. For I am well aware that scarcely a single point
+is discussed in this volume on which facts cannot be adduced, often
+apparently leading to conclusions directly opposite to those at which I
+have arrived. A fair result can be obtained only by fully stating and
+balancing the facts and arguments on both sides of each question; and this
+cannot possibly be here done.
+
+I much regret that want of space prevents my having the satisfaction of
+acknowledging the generous assistance which I have received from very many
+naturalists, some of them personally unknown to me. I cannot, however, {3}
+let this opportunity pass without expressing my deep obligations to Dr.
+Hooker, who for the last fifteen years has aided me in every possible way
+by his large stores of knowledge and his excellent judgment.
+
+In considering the Origin of Species, it is quite conceivable that a
+naturalist, reflecting on the mutual affinities of organic beings, on their
+embryological relations, their geographical distribution, geological
+succession, and other such facts, might come to the conclusion that each
+species had not been independently created, but had descended, like
+varieties, from other species. Nevertheless, such a conclusion, even if
+well founded, would be unsatisfactory, until it could be shown how the
+innumerable species inhabiting this world have been modified, so as to
+acquire that perfection of structure and coadaptation which most justly
+excites our admiration. Naturalists continually refer to external
+conditions, such as climate, food, &c., as the only possible cause of
+variation. In one very limited sense, as we shall hereafter see, this may
+be true; but it is preposterous to attribute to mere external conditions,
+the structure, for instance, of the woodpecker, with its feet, tail, beak,
+and tongue, so admirably adapted to catch insects under the bark of trees.
+In the case of the misseltoe, which draws its nourishment from certain
+trees, which has seeds that must be transported by certain birds, and which
+has flowers with separate sexes absolutely requiring the agency of certain
+insects to bring pollen from one flower to the other, it is equally
+preposterous to account for the structure of this parasite, with its
+relations to several distinct organic beings, by the effects of external
+conditions, or of habit, or of the volition of the plant itself.
+
+The author of the 'Vestiges of Creation' would, I presume, say that, after
+a certain unknown number of {4} generations, some bird had given birth to a
+woodpecker, and some plant to the missletoe, and that these had been
+produced perfect as we now see them; but this assumption seems to me to be
+no explanation, for it leaves the case of the coadaptations of organic
+beings to each other and to their physical conditions of life, untouched
+and unexplained.
+
+It is, therefore, of the highest importance to gain a clear insight into
+the means of modification and coadaptation. At the commencement of my
+observations it seemed to me probable that a careful study of domesticated
+animals and of cultivated plants would offer the best chance of making out
+this obscure problem. Nor have I been disappointed; in this and in all
+other perplexing cases I have invariably found that our knowledge,
+imperfect though it be, of variation under domestication, afforded the best
+and safest clue. I may venture to express my conviction of the high value
+of such studies, although they have been very commonly neglected by
+naturalists.
+
+From these considerations, I shall devote the first chapter of this
+Abstract to Variation under Domestication. We shall thus see that a large
+amount of hereditary modification is at least possible; and, what is
+equally or more important, we shall see how great is the power of man in
+accumulating by his Selection successive slight variations. I will then
+pass on to the variability of species in a state of nature; but I shall,
+unfortunately, be compelled to treat this subject far too briefly, as it
+can be treated properly only by giving long catalogues of facts. We shall,
+however, be enabled to discuss what circumstances are most favourable to
+variation. In the next chapter the Struggle for Existence amongst all
+organic beings throughout the world, which inevitably follows from the high
+geometrical ratio of their {5} increase, will be treated of. This is the
+doctrine of Malthus, applied to the whole animal and vegetable kingdoms. As
+many more individuals of each species are born than can possibly survive;
+and as, consequently, there is a frequently recurring struggle for
+existence, it follows that any being, if it vary however slightly in any
+manner profitable to itself, under the complex and sometimes varying
+conditions of life, will have a better chance of surviving, and thus be
+_naturally selected_. From the strong principle of inheritance, any
+selected variety will tend to propagate its new and modified form.
+
+This fundamental subject of Natural Selection will be treated at some
+length in the fourth chapter; and we shall then see how Natural Selection
+almost inevitably causes much Extinction of the less improved forms of
+life, and leads to what I have called Divergence of Character. In the next
+chapter I shall discuss the complex and little known laws of variation and
+of correlation of growth. In the four succeeding chapters, the most
+apparent and gravest difficulties on the theory will be given: namely,
+first, the difficulties of transitions, or in understanding how a simple
+being or a simple organ can be changed and perfected into a highly
+developed being or elaborately constructed organ; secondly, the subject of
+Instinct, or the mental powers of animals; thirdly, Hybridism, or the
+infertility of species and the fertility of varieties when intercrossed;
+and fourthly, the imperfection of the Geological Record. In the next
+chapter I shall consider the geological succession of organic beings
+throughout time; in the eleventh and twelfth, their geographical
+distribution throughout space; in the thirteenth, their classification or
+mutual affinities, both when mature and in an embryonic condition. In the
+last chapter I shall give a {6} brief recapitulation of the whole work, and
+a few concluding remarks.
+
+No one ought to feel surprise at much remaining as yet unexplained in
+regard to the origin of species and varieties, if he makes due allowance
+for our profound ignorance in regard to the mutual relations of all the
+beings which live around us. Who can explain why one species ranges widely
+and is very numerous, and why another allied species has a narrow range and
+is rare? Yet these relations are of the highest importance, for they
+determine the present welfare, and, as I believe, the future success and
+modification of every inhabitant of this world. Still less do we know of
+the mutual relations of the innumerable inhabitants of the world during the
+many past geological epochs in its history. Although much remains obscure,
+and will long remain obscure, I can entertain no doubt, after the most
+deliberate study and dispassionate judgment of which I am capable, that the
+view which most naturalists entertain, and which I formerly
+entertained--namely, that each species has been independently created--is
+erroneous. I am fully convinced that species are not immutable; but that
+those belonging to what are called the same genera are lineal descendants
+of some other and generally extinct species, in the same manner as the
+acknowledged varieties of any one species are the descendants of that
+species. Furthermore, I am convinced that Natural Selection has been the
+main but not exclusive means of modification.
+
+       *       *       *       *       *
+
+
+{7}
+
+CHAPTER I.
+
+VARIATION UNDER DOMESTICATION.
+
+    Causes of Variability--Effects of Habit--Correlation of
+    Growth--Inheritance--Character of Domestic Varieties--Difficulty of
+    distinguishing between Varieties and Species--Origin of Domestic
+    Varieties from one or more Species--Domestic Pigeons, their Differences
+    and Origin--Principle of Selection anciently followed, its
+    Effects--Methodical and Unconscious Selection--Unknown Origin of our
+    Domestic Productions--Circumstances favourable to Man's power of
+    Selection.
+
+When we look to the individuals of the same variety or sub-variety of our
+older cultivated plants and animals, one of the first points which strikes
+us, is, that they generally differ more from each other than do the
+individuals of any one species or variety in a state of nature. When we
+reflect on the vast diversity of the plants and animals which have been
+cultivated, and which have varied during all ages under the most different
+climates and treatment, I think we are driven to conclude that this great
+variability is simply due to our domestic productions having been raised
+under conditions of life not so uniform as, and somewhat different from,
+those to which the parent-species have been exposed under nature. There is
+also, I think, some probability in the view propounded by Andrew Knight,
+that this variability may be partly connected with excess of food. It seems
+pretty clear that organic beings must be exposed during several generations
+to the new conditions of life to cause any appreciable amount of variation;
+and that when the organisation has once begun to vary, it generally
+continues to vary for many generations. {8} No case is on record of a
+variable being ceasing to be variable under cultivation. Our oldest
+cultivated plants, such as wheat, still often yield new varieties: our
+oldest domesticated animals are still capable of rapid improvement or
+modification.
+
+It has been disputed at what period of life the causes of variability,
+whatever they may be, generally act; whether during the early or late
+period of development of the embryo, or at the instant of conception.
+Geoffroy St. Hilaire's experiments show that unnatural treatment of the
+embryo causes monstrosities; and monstrosities cannot be separated by any
+clear line of distinction from mere variations. But I am strongly inclined
+to suspect that the most frequent cause of variability may be attributed to
+the male and female reproductive elements having been affected prior to the
+act of conception. Several reasons make me believe in this; but the chief
+one is the remarkable effect which confinement or cultivation has on the
+function of the reproductive system; this system appearing to be far more
+susceptible than any other part of the organisation, to the action of any
+change in the conditions of life. Nothing is more easy than to tame an
+animal, and few things more difficult than to get it to breed freely under
+confinement, even in the many cases when the male and female unite. How
+many animals there are which will not breed, though living long under not
+very close confinement in their native country! This is generally
+attributed to vitiated instincts; but how many cultivated plants display
+the utmost vigour, and yet rarely or never seed! In some few such cases it
+has been discovered that very trifling changes, such as a little more or
+less water at some particular period of growth, will determine whether or
+not the plant sets a seed. I cannot here enter on the copious details which
+I have collected on {9} this curious subject; but to show how singular the
+laws are which determine the reproduction of animals under confinement, I
+may just mention that carnivorous animals, even from the tropics, breed in
+this country pretty freely under confinement, with the exception of the
+plantigrades or bear family; whereas carnivorous birds, with the rarest
+exceptions, hardly ever lay fertile eggs. Many exotic plants have pollen
+utterly worthless, in the same exact condition as in the most sterile
+hybrids. When, on the one hand, we see domesticated animals and plants,
+though often weak and sickly, yet breeding quite freely under confinement;
+and when, on the other hand, we see individuals, though taken young from a
+state of nature, perfectly tamed, long-lived, and healthy (of which I could
+give numerous instances), yet having their reproductive system so seriously
+affected by unperceived causes as to fail in acting, we need not be
+surprised at this system, when it does act under confinement, acting not
+quite regularly, and producing offspring not perfectly like their parents.
+
+Sterility has been said to be the bane of horticulture; but on this view we
+owe variability to the same cause which produces sterility; and variability
+is the source of all the choicest productions of the garden. I may add,
+that as some organisms will breed freely under the most unnatural
+conditions (for instance, the rabbit and ferret kept in hutches), showing
+that their reproductive system has not been thus affected; so will some
+animals and plants withstand domestication or cultivation, and vary very
+slightly--perhaps hardly more than in a state of nature.
+
+A long list could easily be given of "sporting plants;" by this term
+gardeners mean a single bud or offset, which suddenly assumes a new and
+sometimes very different character from that of the rest of the plant. {10}
+Such buds can be propagated by grafting, &c., and sometimes by seed. These
+"sports" are extremely rare under nature, but far from rare under
+cultivation; and in this case we see that the treatment of the parent has
+affected a bud or offset, and not the ovules or pollen. But it is the
+opinion of most physiologists that there is no essential difference between
+a bud and an ovule in their earliest stages of formation; so that, in fact,
+"sports" support my view, that variability may be largely attributed to the
+ovules or pollen, or to both, having been affected by the treatment of the
+parent prior to the act of conception. These cases anyhow show that
+variation is not necessarily connected, as some authors have supposed, with
+the act of generation.
+
+Seedlings from the same fruit, and the young of the same litter, sometimes
+differ considerably from each other, though both the young and the parents,
+as Müller has remarked, have apparently been exposed to exactly the same
+conditions of life; and this shows how unimportant the direct effects of
+the conditions of life are in comparison with the laws of reproduction, of
+growth, and of inheritance; for had the action of the conditions been
+direct, if any of the young had varied, all would probably have varied in
+the same manner. To judge how much, in the case of any variation, we should
+attribute to the direct action of heat, moisture, light, food, &c., is most
+difficult: my impression is, that with animals such agencies have produced
+very little direct effect, though apparently more in the case of plants.
+Under this point of view, Mr. Buckman's recent experiments on plants are
+extremely valuable. When all or nearly all the individuals exposed to
+certain conditions are affected in the same way, the change at first
+appears to be directly due to such conditions; but in some cases it can be
+shown that quite opposite conditions produce {11} similar changes of
+structure. Nevertheless some slight amount of change may, I think, be
+attributed to the direct action of the conditions of life--as, in some
+cases, increased size from amount of food, colour from particular kinds of
+food or from light, and perhaps the thickness of fur from climate.
+
+Habit also has a decided influence, as in the period of flowering with
+plants when transported from one climate to another. In animals it has a
+more marked effect; for instance, I find in the domestic duck that the
+bones of the wing weigh less and the bones of the leg more, in proportion
+to the whole skeleton, than do the same bones in the wild-duck; and I
+presume that this change may be safely attributed to the domestic duck
+flying much less, and walking more, than its wild parent. The great and
+inherited development of the udders in cows and goats in countries where
+they are habitually milked, in comparison with the state of these organs in
+other countries, is another instance of the effect of use. Not a single
+domestic animal can be named which has not in some country drooping ears;
+and the view suggested by some authors, that the drooping is due to the
+disuse of the muscles of the ear, from the animals not being much alarmed
+by danger, seems probable.
+
+There are many laws regulating variation, some few of which can be dimly
+seen, and will be hereafter briefly mentioned. I will here only allude to
+what may be called correlation of growth. Any change in the embryo or larva
+will almost certainly entail changes in the mature animal. In
+monstrosities, the correlations between quite distinct parts are very
+curious; and many instances are given in Isidore Geoffroy St. Hilaire's
+great work on this subject. Breeders believe that long limbs are almost
+always accompanied by an elongated head. Some instances of correlation are
+quite whimsical: thus {12} cats with blue eyes are invariably deaf; colour
+and constitutional peculiarities go together, of which many remarkable
+cases could be given amongst animals and plants. From the facts collected
+by Heusinger, it appears that white sheep and pigs are differently affected
+from coloured individuals by certain vegetable poisons. Hairless dogs have
+imperfect teeth: long-haired and coarse-haired animals are apt to have, as
+is asserted, long or many horns; pigeons with feathered feet have skin
+between their outer toes; pigeons with short beaks have small feet, and
+those with long beaks large feet. Hence, if man goes on selecting, and thus
+augmenting, any peculiarity, he will almost certainly unconsciously modify
+other parts of the structure, owing to the mysterious laws of the
+correlation of growth.
+
+The result of the various, quite unknown, or dimly seen laws of variation
+is infinitely complex and diversified. It is well worth while carefully to
+study the several treatises published on some of our old cultivated plants,
+as on the hyacinth, potato, even the dahlia, &c.; and it is really
+surprising to note the endless points in structure and constitution in
+which the varieties and sub-varieties differ slightly from each other. The
+whole organisation seems to have become plastic, and tends to depart in
+some small degree from that of the parental type.
+
+Any variation which is not inherited is unimportant for us. But the number
+and diversity of inheritable deviations of structure, both those of slight
+and those of considerable physiological importance, is endless. Dr. Prosper
+Lucas's treatise, in two large volumes, is the fullest and the best on this
+subject. No breeder doubts how strong is the tendency to inheritance: like
+produces like is his fundamental belief: doubts have been thrown on this
+principle by theoretical writers alone. When any deviation of structure
+often appears, and we see it in the {13} father and child, we cannot tell
+whether it may not be due to the same cause having acted on both; but when
+amongst individuals, apparently exposed to the same conditions, any very
+rare deviation, due to some extraordinary combination of circumstances,
+appears in the parent--say, once amongst several million individuals--and
+it reappears in the child, the mere doctrine of chances almost compels us
+to attribute its reappearance to inheritance. Every one must have heard of
+cases of albinism, prickly skin, hairy bodies, &c., appearing in several
+members of the same family. If strange and rare deviations of structure are
+truly inherited, less strange and commoner deviations may be freely
+admitted to be inheritable. Perhaps the correct way of viewing the whole
+subject, would be, to look at the inheritance of every character whatever
+as the rule, and non-inheritance as the anomaly.
+
+The laws governing inheritance are quite unknown; no one can say why a
+peculiarity in different individuals of the same species, or in individuals
+of different species, is sometimes inherited and sometimes not so; why the
+child often reverts in certain characters to its grandfather or grandmother
+or other more remote ancestor; why a peculiarity is often transmitted from
+one sex to both sexes, or to one sex alone, more commonly but not
+exclusively to the like sex. It is a fact of some little importance to us,
+that peculiarities appearing in the males of our domestic breeds are often
+transmitted either exclusively, or in a much greater degree, to males
+alone. A much more important rule, which I think may be trusted, is that,
+at whatever period of life a peculiarity first appears, it tends to appear
+in the offspring at a corresponding age, though sometimes earlier. In many
+cases this could not be otherwise: thus the inherited peculiarities in the
+horns of cattle could appear only in {14} the offspring when nearly mature;
+peculiarities in the silkworm are known to appear at the corresponding
+caterpillar or cocoon stage. But hereditary diseases and some other facts
+make me believe that the rule has a wider extension, and that when there is
+no apparent reason why a peculiarity should appear at any particular age,
+yet that it does tend to appear in the offspring at the same period at
+which it first appeared in the parent. I believe this rule to be of the
+highest importance in explaining the laws of embryology. These remarks are
+of course confined to the first _appearance_ of the peculiarity, and not to
+its primary cause, which may have acted on the ovules or male element; in
+nearly the same manner as in the crossed offspring from a short-horned cow
+by a long-horned bull, the greater length of horn, though appearing late in
+life, is clearly due to the male element.
+
+Having alluded to the subject of reversion, I may here refer to a statement
+often made by naturalists--namely, that our domestic varieties, when run
+wild, gradually but certainly revert in character to their aboriginal
+stocks. Hence it has been argued that no deductions can be drawn from
+domestic races to species in a state of nature. I have in vain endeavoured
+to discover on what decisive facts the above statement has so often and so
+boldly been made. There would be great difficulty in proving its truth: we
+may safely conclude that very many of the most strongly-marked domestic
+varieties could not possibly live in a wild state. In many cases we do not
+know what the aboriginal stock was, and so could not tell whether or not
+nearly perfect reversion had ensued. It would be quite necessary, in order
+to prevent the effects of intercrossing, that only a single variety should
+be turned loose in its new home. Nevertheless, as our varieties certainly
+do occasionally {15} revert in some of their characters to ancestral forms,
+it seems to me not improbable, that if we could succeed in naturalising, or
+were to cultivate, during many generations, the several races, for
+instance, of the cabbage, in very poor soil (in which case, however, some
+effect would have to be attributed to the direct action of the poor soil),
+that they would to a large extent, or even wholly, revert to the wild
+aboriginal stock. Whether or not the experiment would succeed, is not of
+great importance for our line of argument; for by the experiment itself the
+conditions of life are changed. If it could be shown that our domestic
+varieties manifested a strong tendency to reversion,--that is, to lose
+their acquired characters, whilst kept under the same conditions, and
+whilst kept in a considerable body, so that free intercrossing might check,
+by blending together, any slight deviations in their structure, in such
+case, I grant that we could deduce nothing from domestic varieties in
+regard to species. But there is not a shadow of evidence in favour of this
+view: to assert that we could not breed our cart and race-horses, long and
+short-horned cattle, and poultry of various breeds, and esculent
+vegetables, for an almost infinite number of generations, would be opposed
+to all experience. I may add, that when under nature the conditions of life
+do change, variations and reversions of character probably do occur; but
+natural selection, as will hereafter be explained, will determine how far
+the new characters thus arising shall be preserved.
+
+When we look to the hereditary varieties or races of our domestic animals
+and plants, and compare them with closely allied species, we generally
+perceive in each domestic race, as already remarked, less uniformity of
+character than in true species. Domestic races of the same species, also,
+often have a somewhat monstrous character; by which I mean, that, although
+differing {16} from each other, and from other species of the same genus,
+in several trifling respects, they often differ in an extreme degree in
+some one part, both when compared one with another, and more especially
+when compared with all the species in nature to which they are nearest
+allied. With these exceptions (and with that of the perfect fertility of
+varieties when crossed,--a subject hereafter to be discussed), domestic
+races of the same species differ from each other in the same manner as,
+only in most cases in a lesser degree than, do closely-allied species of
+the same genus in a state of nature. I think this must be admitted, when we
+find that there are hardly any domestic races, either amongst animals or
+plants, which have not been ranked by competent judges as mere varieties,
+and by other competent judges as the descendants of aboriginally distinct
+species. If any marked distinction existed between domestic races and
+species, this source of doubt could not so perpetually recur. It has often
+been stated that domestic races do not differ from each other in characters
+of generic value. I think it could be shown that this statement is hardly
+correct; but naturalists differ widely in determining what characters are
+of generic value; all such valuations being at present empirical. Moreover,
+on the view of the origin of genera which I shall presently give, we have
+no right to expect often to meet with generic differences in our
+domesticated productions.
+
+When we attempt to estimate the amount of structural difference between the
+domestic races of the same species, we are soon involved in doubt, from not
+knowing whether they have descended from one or several parent-species.
+This point, if it could be cleared up, would be interesting; if, for
+instance, it could be shown that the greyhound, bloodhound, terrier,
+spaniel, and bull-dog, which we all know propagate their kind so truly,
+were the {17} offspring of any single species, then such facts would have
+great weight in making us doubt about the immutability of the many very
+closely allied natural species--for instance, of the many foxes--inhabiting
+different quarters of the world. I do not believe, as we shall presently
+see, that the whole amount of difference between the several breeds of the
+dog has been produced under domestication; I believe that some small part
+of the difference is due to their being descended from distinct species. In
+the case of some other domesticated species, there is presumptive, or even
+strong evidence, that all the breeds have descended from a single wild
+stock.
+
+It has often been assumed that man has chosen for domestication animals and
+plants having an extraordinary inherent tendency to vary, and likewise to
+withstand diverse climates. I do not dispute that these capacities have
+added largely to the value of most of our domesticated productions; but how
+could a savage possibly know, when he first tamed an animal, whether it
+would vary in succeeding generations, and whether it would endure other
+climates? Has the little variability of the ass or guinea-fowl, or the
+small power of endurance of warmth by the reindeer, or of cold by the
+common camel, prevented their domestication? I cannot doubt that if other
+animals and plants, equal in number to our domesticated productions, and
+belonging to equally diverse classes and countries, were taken from a state
+of nature, and could be made to breed for an equal number of generations
+under domestication, they would vary on an average as largely as the parent
+species of our existing domesticated productions have varied.
+
+In the case of most of our anciently domesticated animals and plants, I do
+not think it is possible to come to any definite conclusion, whether they
+have descended from one or several wild species. The argument mainly relied
+on by those who believe in the multiple origin {18} of our domestic animals
+is, that we find in the most ancient records, more especially on the
+monuments of Egypt, much diversity in the breeds; and that some of the
+breeds closely resemble, perhaps are identical with, those still existing.
+Even if this latter fact were found more strictly and generally true than
+seems to me to be the case, what does it show, but that some of our breeds
+originated there, four or five thousand years ago? But Mr. Horner's
+researches have rendered it in some degree probable that man sufficiently
+civilized to have manufactured pottery existed in the valley of the Nile
+thirteen or fourteen thousand years ago; and who will pretend to say how
+long before these ancient periods, savages, like those of Tierra del Fuego
+or Australia, who possess a semi-domestic dog, may not have existed in
+Egypt?
+
+The whole subject must, I think, remain vague; nevertheless, I may, without
+here entering on any details, state that, from geographical and other
+considerations, I think it highly probable that our domestic dogs have
+descended from several wild species. Knowing, as we do, that savages are
+very fond of taming animals, it seems to me unlikely, in the case of the
+dog-genus, which is distributed in a wild state throughout the world, that
+since man first appeared one single species alone should have been
+domesticated. In regard to sheep and goats I can form no opinion. I should
+think, from facts communicated to me by Mr. Blyth, on the habits, voice,
+and constitution, &c., of the humped Indian cattle, that these had
+descended from a different aboriginal stock from our European cattle; and
+several competent judges believe that these latter have had more than one
+wild parent. With respect to horses, from reasons which I cannot give here,
+I am doubtfully inclined to believe, in opposition to several authors, that
+all the races have descended from one {19} wild stock. Mr. Blyth, whose
+opinion, from his large and varied stores of knowledge, I should value more
+than that of almost any one, thinks that all the breeds of poultry have
+proceeded from the common wild Indian fowl (Gallus bankiva). In regard to
+ducks and rabbits, the breeds of which differ considerably from each other
+in structure, I do not doubt that they have all descended from the common
+wild duck and rabbit.
+
+The doctrine of the origin of our several domestic races from several
+aboriginal stocks, has been carried to an absurd extreme by some authors.
+They believe that every race which breeds true, let the distinctive
+characters be ever so slight, has had its wild prototype. At this rate
+there must have existed at least a score of species of wild cattle, as many
+sheep, and several goats in Europe alone, and several even within Great
+Britain. One author believes that there formerly existed in Great Britain
+eleven wild species of sheep peculiar to it! When we bear in mind that
+Britain has now hardly one peculiar mammal, and France but few distinct
+from those of Germany and conversely, and so with Hungary, Spain, &c., but
+that each of these kingdoms possesses several peculiar breeds of cattle,
+sheep, &c., we must admit that many domestic breeds have originated in
+Europe; for whence could they have been derived, as these several countries
+do not possess a number of peculiar species as distinct parent-stocks? So
+it is in India. Even in the case of the domestic dogs of the whole world,
+which I fully admit have probably descended from several wild species, I
+cannot doubt that there has been an immense amount of inherited variation.
+Who can believe that animals closely resembling the Italian greyhound, the
+bloodhound, the bull-dog, or Blenheim spaniel, &c.--so unlike all wild
+Canidæ--ever existed freely in a state of nature? It has often been loosely
+said that all our races of dogs have {20} been produced by the crossing of
+a few aboriginal species; but by crossing we can only get forms in some
+degree intermediate between their parents; and if we account for our
+several domestic races by this process, we must admit the former existence
+of the most extreme forms, as the Italian greyhound, bloodhound, bull-dog,
+&c., in the wild state. Moreover, the possibility of making distinct races
+by crossing has been greatly exaggerated. There can be no doubt that a race
+may be modified by occasional crosses, if aided by the careful selection of
+those individual mongrels, which present any desired character; but that a
+race could be obtained nearly intermediate between two extremely different
+races or species, I can hardly believe. Sir J. Sebright expressly
+experimentised for this object, and failed. The offspring from the first
+cross between two pure breeds is tolerably and sometimes (as I have found
+with pigeons) extremely uniform, and everything seems simple enough; but
+when these mongrels are crossed one with another for several generations,
+hardly two of them will be alike, and then the extreme difficulty, or
+rather utter hopelessness, of the task becomes apparent. Certainly, a breed
+intermediate between _two very distinct_ breeds could not be got without
+extreme care and long-continued selection; nor can I find a single case on
+record of a permanent race having been thus formed.
+
+_On the Breeds of the Domestic Pigeon._--Believing that it is always best
+to study some special group, I have, after deliberation, taken up domestic
+pigeons. I have kept every breed which I could purchase or obtain, and have
+been most kindly favoured with skins from several quarters of the world,
+more especially by the Hon. W. Elliot from India, and by the Hon. C. Murray
+from Persia. Many treatises in different languages have been published on
+pigeons, and some of them are very important, as being of {21} considerable
+antiquity. I have associated with several eminent fanciers, and have been
+permitted to join two of the London Pigeon Clubs. The diversity of the
+breeds is something astonishing. Compare the English carrier and the
+short-faced tumbler, and see the wonderful difference in their beaks,
+entailing corresponding differences in their skulls. The carrier, more
+especially the male bird, is also remarkable from the wonderful development
+of the carunculated skin about the head, and this is accompanied by greatly
+elongated eyelids, very large external orifices to the nostrils, and a wide
+gape of mouth. The short-faced tumbler has a beak in outline almost like
+that of a finch; and the common tumbler has the singular inherited habit of
+flying at a great height in a compact flock, and tumbling in the air head
+over heels. The runt is a bird of great size, with long, massive beak and
+large feet; some of the sub-breeds of runts have very long necks, others
+very long wings and tails, others singularly short tails. The barb is
+allied to the carrier, but, instead of a very long beak, has a very short
+and very broad one. The pouter has a much elongated body, wings, and legs;
+and its enormously developed crop, which it glories in inflating, may well
+excite astonishment and even laughter. The turbit has a very short and
+conical beak, with a line of reversed feathers down the breast; and it has
+the habit of continually expanding slightly the upper part of the
+oesophagus. The Jacobin has the feathers so much reversed along the back of
+the neck that they form a hood, and it has, proportionally to its size,
+much elongated wing and tail feathers. The trumpeter and laugher, as their
+names express, utter a very different coo from the other breeds. The
+fantail has thirty or even forty tail feathers, instead of twelve or
+fourteen, the normal number in all members of the great pigeon family; and
+these feathers are kept expanded, and are {22} carried so erect that in
+good birds the head and tail touch; the oil-gland is quite aborted. Several
+other less distinct breeds might be specified.
+
+In the skeletons of the several breeds, the development of the bones of the
+face in length and breadth and curvature differs enormously. The shape, as
+well as the breadth and length of the ramus of the lower jaw, varies in a
+highly remarkable manner. The number of the caudal and sacral vertebræ
+vary; as does the number of the ribs, together with their relative breadth
+and the presence of processes. The size and shape of the apertures in the
+sternum are highly variable; so is the degree of divergence and relative
+size of the two arms of the furcula. The proportional width of the gape of
+mouth, the proportional length of the eyelids, of the orifice of the
+nostrils, of the tongue (not always in strict correlation with the length
+of beak), the size of the crop and of the upper part of the oesophagus; the
+development and abortion of the oil-gland; the number of the primary wing
+and caudal feathers; the relative length of wing and tail to each other and
+to the body; the relative length of leg and of the feet; the number of
+scutellæ on the toes, the development of skin between the toes, are all
+points of structure which are variable. The period at which the perfect
+plumage is acquired varies, as does the state of the down with which the
+nestling birds are clothed when hatched. The shape and size of the eggs
+vary. The manner of flight differs remarkably; as does in some breeds the
+voice and disposition. Lastly, in certain breeds, the males and females
+have come to differ to a slight degree from each other.
+
+Altogether at least a score of pigeons might be chosen, which if shown to
+an ornithologist, and he were told that they were wild birds, would
+certainly, I think, be ranked by him as well-defined species. Moreover, I
+do not believe that any ornithologist would place the {23} English carrier,
+the short-faced tumbler, the runt, the barb, pouter, and fantail in the
+same genus; more especially as in each of these breeds several
+truly-inherited sub-breeds, or species as he might have called them, could
+be shown him.
+
+Great as the differences are between the breeds of pigeons, I am fully
+convinced that the common opinion of naturalists is correct, namely, that
+all have descended from the rock-pigeon (Columba livia), including under
+this term several geographical races or sub-species, which differ from each
+other in the most trifling respects. As several of the reasons which have
+led me to this belief are in some degree applicable in other cases, I will
+here briefly give them. If the several breeds are not varieties, and have
+not proceeded from the rock-pigeon, they must have descended from at least
+seven or eight aboriginal stocks; for it is impossible to make the present
+domestic breeds by the crossing of any lesser number: how, for instance,
+could a pouter be produced by crossing two breeds unless one of the
+parent-stocks possessed the characteristic enormous crop? The supposed
+aboriginal stocks must all have been rock-pigeons, that is, not breeding or
+willingly perching on trees. But besides C. livia, with its geographical
+sub-species, only two or three other species of rock-pigeons are known; and
+these have not any of the characters of the domestic breeds. Hence the
+supposed aboriginal stocks must either still exist in the countries where
+they were originally domesticated, and yet be unknown to ornithologists;
+and this, considering their size, habits, and remarkable characters, seems
+very improbable; or they must have become extinct in the wild state. But
+birds breeding on precipices, and good fliers, are unlikely to be
+exterminated; and the common rock-pigeon, which has the same habits with
+the domestic breeds, has not been exterminated {24} even on several of the
+smaller British islets, or on the shores of the Mediterranean. Hence the
+supposed extermination of so many species having similar habits with the
+rock-pigeon seems to me a very rash assumption. Moreover, the several
+above-named domesticated breeds have been transported to all parts of the
+world, and, therefore, some of them must have been carried back again into
+their native country; but not one has ever become wild or feral, though the
+dovecot-pigeon, which is the rock-pigeon in a very slightly altered state,
+has become feral in several places. Again, all recent experience shows that
+it is most difficult to get any wild animal to breed freely under
+domestication; yet on the hypothesis of the multiple origin of our pigeons,
+it must be assumed that at least seven or eight species were so thoroughly
+domesticated in ancient times by half-civilized man, as to be quite
+prolific under confinement.
+
+An argument, as it seems to me, of great weight, and applicable in several
+other cases, is, that the above-specified breeds, though agreeing generally
+in constitution, habits, voice, colouring, and in most parts of their
+structure, with the wild rock-pigeon, yet are certainly highly abnormal in
+other parts of their structure; we may look in vain throughout the whole
+great family of Columbidæ for a beak like that of the English carrier, or
+that of the short-faced tumbler, or barb; for reversed feathers like those
+of the Jacobin; for a crop like that of the pouter; for tail-feathers like
+those of the fantail. Hence it must be assumed not only that half-civilized
+man succeeded in thoroughly domesticating several species, but that he
+intentionally or by chance picked out extraordinarily abnormal species; and
+further, that these very species have since all become extinct or unknown.
+So many strange contingencies seem to me improbable in the highest degree.
+{25}
+
+Some facts in regard to the colouring of pigeons well deserve
+consideration. The rock-pigeon is of a slaty-blue, and has a white rump
+(the Indian subspecies, C. intermedia of Strickland, having it bluish); the
+tail has a terminal dark bar, with the bases of the outer feathers
+externally edged with white; the wings have two black bars; some
+semi-domestic breeds and some apparently truly wild breeds have, besides
+the two black bars, the wings chequered with black. These several marks do
+not occur together in any other species of the whole family. Now, in every
+one of the domestic breeds, taking thoroughly well-bred birds, all the
+above marks, even to the white edging of the outer tail-feathers, sometimes
+concur perfectly developed. Moreover, when two birds belonging to two
+distinct breeds are crossed, neither of which is blue or has any of the
+above-specified marks, the mongrel offspring are very apt suddenly to
+acquire these characters; for instance, I crossed some uniformly white
+fantails with some uniformly black barbs, and they produced mottled brown
+and black birds; these I again crossed together, and one grandchild of the
+pure white fantail and pure black barb was of as beautiful a blue colour,
+with the white rump, double black wing-bar, and barred and white-edged
+tail-feathers, as any wild rock-pigeon! We can understand these facts, on
+the well-known principle of reversion to ancestral characters, if all the
+domestic breeds have descended from the rock-pigeon. But if we deny this,
+we must make one of the two following highly improbable suppositions.
+Either, firstly, that all the several imagined aboriginal stocks were
+coloured and marked like the rock-pigeon, although no other existing
+species is thus coloured and marked, so that in each separate breed there
+might be a tendency to revert to the very same colours and markings. Or,
+secondly, {26} that each breed, even the purest, has within a dozen or, at
+most, within a score of generations, been crossed by the rock-pigeon: I say
+within a dozen or twenty generations, for we know of no fact countenancing
+the belief that the child ever reverts to some one ancestor, removed by a
+greater number of generations. In a breed which has been crossed only once
+with some distinct breed, the tendency to reversion to any character
+derived from such cross will naturally become less and less, as in each
+succeeding generation there will be less of the foreign blood; but when
+there has been no cross with a distinct breed, and there is a tendency in
+both parents to revert to a character, which has been lost during some
+former generation, this tendency, for all that we can see to the contrary,
+may be transmitted undiminished for an indefinite number of generations.
+These two distinct cases are often confounded in treatises on inheritance.
+
+Lastly, the hybrids or mongrels from between all the domestic breeds of
+pigeons are perfectly fertile. I can state this from my own observations,
+purposely made, on the most distinct breeds. Now, it is difficult, perhaps
+impossible, to bring forward one case of the hybrid offspring of two
+animals _clearly distinct_ being themselves perfectly fertile. Some authors
+believe that long-continued domestication eliminates this strong tendency
+to sterility: from the history of the dog I think there is some probability
+in this hypothesis, if applied to species closely related together, though
+it is unsupported by a single experiment. But to extend the hypothesis so
+far as to suppose that species, aboriginally as distinct as carriers,
+tumblers, pouters, and fantails now are, should yield offspring perfectly
+fertile, _inter se_, seems to me rash in the extreme.
+
+From these several reasons, namely, the improbability of man having
+formerly got seven or eight supposed {27} species of pigeons to breed
+freely under domestication; these supposed species being quite unknown in a
+wild state, and their becoming nowhere feral; these species having very
+abnormal characters in certain respects, as compared with all other
+Columbidæ, though so like in most other respects to the rock-pigeon; the
+blue colour and various marks occasionally appearing in all the breeds,
+both when kept pure and when crossed; the mongrel offspring being perfectly
+fertile;--from these several reasons, taken together, I can feel no doubt
+that all our domestic breeds have descended from the Columba livia with its
+geographical sub-species.
+
+In favour of this view, I may add, firstly, that C. livia, or the
+rock-pigeon, has been found capable of domestication in Europe and in
+India; and that it agrees in habits and in a great number of points of
+structure with all the domestic breeds. Secondly, although an English
+carrier or short-faced tumbler differs immensely in certain characters from
+the rock-pigeon, yet by comparing the several sub-breeds of these
+varieties, more especially those brought from distant countries, we can
+make an almost perfect series between the extremes of structure. Thirdly,
+those characters which are mainly distinctive of each breed, for instance
+the wattle and length of beak of the carrier, the shortness of that of the
+tumbler, and the number of tail-feathers in the fantail, are in each breed
+eminently variable; and the explanation of this fact will be obvious when
+we come to treat of selection. Fourthly, pigeons have been watched, and
+tended with the utmost care, and loved by many people. They have been
+domesticated for thousands of years in several quarters of the world; the
+earliest known record of pigeons is in the fifth Ægyptian dynasty, about
+3000 B.C., as was pointed out to me by Professor Lepsius; but Mr. Birch
+informs me that pigeons are given in a bill {28} of fare in the previous
+dynasty. In the time of the Romans, as we hear from Pliny, immense prices
+were given for pigeons; "nay, they are come to this pass, that they can
+reckon up their pedigree and race." Pigeons were much valued by Akber Khan
+in India, about the year 1600; never less than 20,000 pigeons were taken
+with the court. "The monarchs of Iran and Turan sent him some very rare
+birds;" and, continues the courtly historian, "His Majesty by crossing the
+breeds, which method was never practised before, has improved them
+astonishingly." About this same period the Dutch were as eager about
+pigeons as were the old Romans. The paramount importance of these
+considerations in explaining the immense amount of variation which pigeons
+have undergone, will be obvious when we treat of Selection. We shall then,
+also, see how it is that the breeds so often have a somewhat monstrous
+character. It is also a most favourable circumstance for the production of
+distinct breeds, that male and female pigeons can be easily mated for life;
+and thus different breeds can be kept together in the same aviary.
+
+I have discussed the probable origin of domestic pigeons at some, yet quite
+insufficient, length; because when I first kept pigeons and watched the
+several kinds, knowing well how true they bred, I felt fully as much
+difficulty in believing that they could have descended from a common
+parent, as any naturalist could in coming to a similar conclusion in regard
+to the many species of finches, or other large groups of birds, in nature.
+One circumstance has struck me much; namely, that all the breeders of the
+various domestic animals and the cultivators of plants, with whom I have
+ever conversed, or whose treatises I have read, are firmly convinced that
+the several breeds to which each has attended, are descended from so many
+aboriginally distinct species. {29} Ask, as I have asked, a celebrated
+raiser of Hereford cattle, whether his cattle might not have descended from
+long-horns, and he will laugh you to scorn. I have never met a pigeon, or
+poultry, or duck, or rabbit fancier, who was not fully convinced that each
+main breed was descended from a distinct species. Van Mons, in his treatise
+on pears and apples, shows how utterly he disbelieves that the several
+sorts, for instance a Ribston-pippin or Codlin-apple, could ever have
+proceeded from the seeds of the same tree. Innumerable other examples could
+be given. The explanation, I think, is simple: from long-continued study
+they are strongly impressed with the differences between the several races;
+and though they well know that each race varies slightly, for they win
+their prizes by selecting such slight differences, yet they ignore all
+general arguments, and refuse to sum up in their minds slight differences
+accumulated during many successive generations. May not those naturalists
+who, knowing far less of the laws of inheritance than does the breeder, and
+knowing no more than he does of the intermediate links in the long lines of
+descent, yet admit that many of our domestic races have descended from the
+same parents--may they not learn a lesson of caution, when they deride the
+idea of species in a state of nature being lineal descendants of other
+species?
+
+_Selection._--Let us now briefly consider the steps by which domestic races
+have been produced, either from one or from several allied species. Some
+little effect may, perhaps, be attributed to the direct action of the
+external conditions of life, and some little to habit; but he would be a
+bold man who would account by such agencies for the differences of a dray
+and race horse, a greyhound and bloodhound, a carrier and tumbler pigeon.
+One of the most remarkable features in our domesticated races {30} is that
+we see in them adaptation, not indeed to the animal's or plant's own good,
+but to man's use or fancy. Some variations useful to him have probably
+arisen suddenly, or by one step; many botanists, for instance, believe that
+the fuller's teazle, with its hooks, which cannot be rivalled by any
+mechanical contrivance, is only a variety of the wild Dipsacus; and this
+amount of change may have suddenly arisen in a seedling. So it has probably
+been with the turnspit dog; and this is known to have been the case with
+the ancon sheep. But when we compare the dray-horse and race-horse, the
+dromedary and camel, the various breeds of sheep fitted either for
+cultivated land or mountain pasture, with the wool of one breed good for
+one purpose, and that of another breed for another purpose; when we compare
+the many breeds of dogs, each good for man in very different ways; when we
+compare the game-cock, so pertinacious in battle, with other breeds so
+little quarrelsome, with "everlasting layers" which never desire to sit,
+and with the bantam so small and elegant; when we compare the host of
+agricultural, culinary, orchard, and flower-garden races of plants, most
+useful to man at different seasons and for different purposes, or so
+beautiful in his eyes, we must, I think, look further than to mere
+variability. We cannot suppose that all the breeds were suddenly produced
+as perfect and as useful as we now see them; indeed, in several cases, we
+know that this has not been their history. The key is man's power of
+accumulative selection: nature gives successive variations; man adds them
+up in certain directions useful to him. In this sense he may be said to
+make for himself useful breeds.
+
+The great power of this principle of selection is not hypothetical. It is
+certain that several of our eminent breeders have, even within a single
+lifetime, modified to {31} a large extent some breeds of cattle and sheep.
+In order fully to realise what they have done, it is almost necessary to
+read several of the many treatises devoted to this subject, and to inspect
+the animals. Breeders habitually speak of an animal's organisation as
+something quite plastic, which they can model almost as they please. If I
+had space I could quote numerous passages to this effect from highly
+competent authorities. Youatt, who was probably better acquainted with the
+works of agriculturists than almost any other individual, and who was
+himself a very good judge of an animal, speaks of the principle of
+selection as "that which enables the agriculturist, not only to modify the
+character of his flock, but to change it altogether. It is the magician's
+wand, by means of which he may summon into life whatever form and mould he
+pleases." Lord Somerville, speaking of what breeders have done for sheep,
+says:--"It would seem as if they had chalked out upon a wall a form perfect
+in itself, and then had given it existence." That most skilful breeder, Sir
+John Sebright, used to say, with respect to pigeons, that "he would produce
+any given feather in three years, but it would take him six years to obtain
+head and beak." In Saxony the importance of the principle of selection in
+regard to merino sheep is so fully recognised, that men follow it as a
+trade: the sheep are placed on a table and are studied, like a picture by a
+connoisseur; this is done three times at intervals of months, and the sheep
+are each time marked and classed, so that the very best may ultimately be
+selected for breeding.
+
+What English breeders have actually effected is proved by the enormous
+prices given for animals with a good pedigree; and these have now been
+exported to almost every quarter of the world. The improvement is by no
+means generally due to crossing different breeds; {32} all the best
+breeders are strongly opposed to this practice, except sometimes amongst
+closely allied sub-breeds. And when a cross has been made, the closest
+selection is far more indispensable even than in ordinary cases. If
+selection consisted merely in separating some very distinct variety, and
+breeding from it, the principle would be so obvious as hardly to be worth
+notice; but its importance consists in the great effect produced by the
+accumulation in one direction, during successive generations, of
+differences absolutely inappreciable by an uneducated eye--differences
+which I for one have vainly attempted to appreciate. Not one man in a
+thousand has accuracy of eye and judgment sufficient to become an eminent
+breeder. If gifted with these qualities, and he studies his subject for
+years, and devotes his lifetime to it with indomitable perseverance, he
+will succeed, and may make great improvements; if he wants any of these
+qualities, he will assuredly fail. Few would readily believe in the natural
+capacity and years of practice requisite to become even a skilful
+pigeon-fancier.
+
+The same principles are followed by horticulturists; but the variations are
+here often more abrupt. No one supposes that our choicest productions have
+been produced by a single variation from the aboriginal stock. We have
+proofs that this is not so in some cases, in which exact records have been
+kept; thus, to give a very trifling instance, the steadily-increasing size
+of the common gooseberry may be quoted. We see an astonishing improvement
+in many florists' flowers, when the flowers of the present day are compared
+with drawings made only twenty or thirty years ago. When a race of plants
+is once pretty well established, the seed-raisers do not pick out the best
+plants, but merely go over their seed-beds, and pull up the "rogues," as
+they call the plants that deviate from the proper standard. With animals
+this {33} kind of selection is, in fact, also followed; for hardly any one
+is so careless as to allow his worst animals to breed.
+
+In regard to plants, there is another means of observing the accumulated
+effects of selection--namely, by comparing the diversity of flowers in the
+different varieties of the same species in the flower-garden; the diversity
+of leaves, pods, or tubers, or whatever part is valued, in the
+kitchen-garden, in comparison with the flowers of the same varieties; and
+the diversity of fruit of the same species in the orchard, in comparison
+with the leaves and flowers of the same set of varieties. See how different
+the leaves of the cabbage are, and how extremely alike the flowers; how
+unlike the flowers of the heartsease are, and how alike the leaves; how
+much the fruit of the different kinds of gooseberries differ in size,
+colour, shape, and hairiness, and yet the flowers present very slight
+differences. It is not that the varieties which differ largely in some one
+point do not differ at all in other points; this is hardly ever, perhaps
+never, the case. The laws of correlation of growth, the importance of which
+should never be overlooked, will ensure some differences; but, as a general
+rule, I cannot doubt that the continued selection of slight variations,
+either in the leaves, the flowers, or the fruit, will produce races
+differing from each other chiefly in these characters.
+
+It may be objected that the principle of selection has been reduced to
+methodical practice for scarcely more than three-quarters of a century; it
+has certainly been more attended to of late years, and many treatises have
+been published on the subject; and the result has been, in a corresponding
+degree, rapid and important. But it is very far from true that the
+principle is a modern discovery. I could give several references to the
+full acknowledgment of the importance of the principle in works of high
+antiquity. In rude and barbarous periods {34} of English history choice
+animals were often imported, and laws were passed to prevent their
+exportation: the destruction of horses under a certain size was ordered,
+and this may be compared to the "roguing" of plants by nurserymen. The
+principle of selection I find distinctly given in an ancient Chinese
+encyclopædia. Explicit rules are laid down by some of the Roman classical
+writers. From passages in Genesis, it is clear that the colour of domestic
+animals was at that early period attended to. Savages now sometimes cross
+their dogs with wild canine animals, to improve the breed, and they
+formerly did so, as is attested by passages in Pliny. The savages in South
+Africa match their draught cattle by colour, as do some of the Esquimaux
+their teams of dogs. Livingstone shows how much good domestic breeds are
+valued by the negroes of the interior of Africa who have not associated
+with Europeans. Some of these facts do not show actual selection, but they
+show that the breeding of domestic animals was carefully attended to in
+ancient times, and is now attended to by the lowest savages. It would,
+indeed, have been a strange fact, had attention not been paid to breeding,
+for the inheritance of good and bad qualities is so obvious.
+
+At the present time, eminent breeders try by methodical selection, with a
+distinct object in view, to make a new strain or sub-breed, superior to
+anything existing in the country. But, for our purpose, a kind of
+Selection, which may be called Unconscious, and which results from every
+one trying to possess and breed from the best individual animals, is more
+important. Thus, a man who intends keeping pointers naturally tries to get
+as good dogs as he can, and afterwards breeds from his own best dogs, but
+he has no wish or expectation of permanently altering the breed.
+Nevertheless I cannot doubt that this process, continued during centuries,
+{35} would improve and modify any breed, in the same way as Bakewell,
+Collins, &c., by this very same process, only carried on more methodically,
+did greatly modify, even during their own lifetimes, the forms and
+qualities of their cattle. Slow and insensible changes of this kind could
+never be recognised unless actual measurements or careful drawings of the
+breeds in question had been made long ago, which might serve for
+comparison. In some cases, however, unchanged, or but little changed
+individuals of the same breed may be found in less civilised districts,
+where the breed has been less improved. There is reason to believe that
+King Charles's spaniel has been unconsciously modified to a large extent
+since the time of that monarch. Some highly competent authorities are
+convinced that the setter is directly derived from the spaniel, and has
+probably been slowly altered from it. It is known that the English pointer
+has been greatly changed within the last century, and in this case the
+change has, it is believed, been chiefly effected by crosses with the
+fox-hound; but what concerns us is, that the change has been effected
+unconsciously and gradually, and yet so effectually, that, though the old
+Spanish pointer certainly came from Spain, Mr. Borrow has not seen, as I am
+informed by him, any native dog in Spain like our pointer.
+
+By a similar process of selection, and by careful training, the whole body
+of English racehorses have come to surpass in fleetness and size the parent
+Arab stock, so that the latter, by the regulations for the Goodwood Races,
+are favoured in the weights they carry. Lord Spencer and others have shown
+how the cattle of England have increased in weight and in early maturity,
+compared with the stock formerly kept in this country. By comparing the
+accounts given in old pigeon treatises of carriers and tumblers with these
+breeds as now existing in Britain, {36} India, and Persia, we can, I think,
+clearly trace the stages through which they have insensibly passed, and
+come to differ so greatly from the rock-pigeon.
+
+Youatt gives an excellent illustration of the effects of a course of
+selection, which may be considered as unconsciously followed, in so far
+that the breeders could never have expected or even have wished to have
+produced the result which ensued--namely, the production of two distinct
+strains. The two flocks of Leicester sheep kept by Mr. Buckley and Mr.
+Burgess, as Mr. Youatt remarks, "have been purely bred from the original
+stock of Mr. Bakewell for upwards of fifty years. There is not a suspicion
+existing in the mind of any one at all acquainted with the subject that the
+owner of either of them has deviated in any one instance from the pure
+blood of Mr. Bakewell's flock, and yet the difference between the sheep
+possessed by these two gentlemen is so great that they have the appearance
+of being quite different varieties."
+
+If there exist savages so barbarous as never to think of the inherited
+character of the offspring of their domestic animals, yet any one animal
+particularly useful to them, for any special purpose, would be carefully
+preserved during famines and other accidents, to which savages are so
+liable, and such choice animals would thus generally leave more offspring
+than the inferior ones; so that in this case there would be a kind of
+unconscious selection going on. We see the value set on animals even by the
+barbarians of Tierra del Fuego, by their killing and devouring their old
+women, in times of dearth, as of less value than their dogs.
+
+In plants the same gradual process of improvement, through the occasional
+preservation of the best individuals, whether or not sufficiently distinct
+to be ranked at their first appearance as distinct varieties, and whether
+{37} or not two or more species or races have become blended together by
+crossing, may plainly be recognised in the increased size and beauty which
+we now see in the varieties of the heartsease, rose, pelargonium, dahlia,
+and other plants, when compared with the older varieties or with their
+parent-stocks. No one would ever expect to get a first-rate heartsease or
+dahlia from the seed of a wild plant. No one would expect to raise a
+first-rate melting pear from the seed of the wild pear, though he might
+succeed from a poor seedling growing wild, if it had come from a
+garden-stock. The pear, though cultivated in classical times, appears, from
+Pliny's description, to have been a fruit of very inferior quality. I have
+seen great surprise expressed in horticultural works at the wonderful skill
+of gardeners, in having produced such splendid results from such poor
+materials; but the art, I cannot doubt, has been simple, and, as far as the
+final result is concerned, has been followed almost unconsciously. It has
+consisted in always cultivating the best known variety, sowing its seeds,
+and, when a slightly better variety has chanced to appear, selecting it,
+and so onwards. But the gardeners of the classical period, who cultivated
+the best pear they could procure, never thought what splendid fruit we
+should eat; though we owe our excellent fruit, in some small degree, to
+their having naturally chosen and preserved the best varieties they could
+anywhere find.
+
+A large amount of change in our cultivated plants, thus slowly and
+unconsciously accumulated, explains, as I believe, the well-known fact,
+that in a vast number of cases we cannot recognise, and therefore do not
+know, the wild parent-stocks of the plants which have been longest
+cultivated in our flower and kitchen gardens. If it has taken centuries or
+thousands of years to improve or modify most of our plants up to their
+present {38} standard of usefulness to man, we can understand how it is
+that neither Australia, the Cape of Good Hope, nor any other region
+inhabited by quite uncivilised man, has afforded us a single plant worth
+culture. It is not that these countries, so rich in species, do not by a
+strange chance possess the aboriginal stocks of any useful plants, but that
+the native plants have not been improved by continued selection up to a
+standard of perfection comparable with that given to the plants in
+countries anciently civilised.
+
+In regard to the domestic animals kept by uncivilised man, it should not be
+overlooked that they almost always have to struggle for their own food, at
+least during certain seasons. And in two countries very differently
+circumstanced, individuals of the same species, having slightly different
+constitutions or structure, would often succeed better in the one country
+than in the other; and thus by a process of "natural selection," as will
+hereafter be more fully explained, two sub-breeds might be formed. This,
+perhaps, partly explains what has been remarked by some authors, namely,
+that the varieties kept by savages have more of the character of species
+than the varieties kept in civilised countries.
+
+On the view here given of the all-important part which selection by man has
+played, it becomes at once obvious, how it is that our domestic races show
+adaptation in their structure or in their habits to man's wants or fancies.
+We can, I think, further understand the frequently abnormal character of
+our domestic races, and likewise their differences being so great in
+external characters and relatively so slight in internal parts or organs.
+Man can hardly select, or only with much difficulty, any deviation of
+structure excepting such as is externally visible; and indeed he rarely
+cares for what is internal. He can never act by selection, excepting on
+variations {39} which are first given to him in some slight degree by
+nature. No man would ever try to make a fantail, till he saw a pigeon with
+a tail developed in some slight degree in an unusual manner, or a pouter
+till he saw a pigeon with a crop of somewhat unusual size; and the more
+abnormal or unusual any character was when it first appeared, the more
+likely it would be to catch his attention. But to use such an expression as
+trying to make a fantail, is, I have no doubt, in most cases, utterly
+incorrect. The man who first selected a pigeon with a slightly larger tail,
+never dreamed what the descendants of that pigeon would become through
+long-continued, partly unconscious and partly methodical selection. Perhaps
+the parent bird of all fantails had only fourteen tail-feathers somewhat
+expanded, like the present Java fantail, or like individuals of other and
+distinct breeds, in which as many as seventeen tail-feathers have been
+counted. Perhaps the first pouter-pigeon did not inflate its crop much more
+than the turbit now does the upper part of its oesophagus,--a habit which
+is disregarded by all fanciers, as it is not one of the points of the
+breed.
+
+Nor let it be thought that some great deviation of structure would be
+necessary to catch the fancier's eye: he perceives extremely small
+differences, and it is in human nature to value any novelty, however
+slight, in one's own possession. Nor must the value which would formerly be
+set on any slight differences in the individuals of the same species, be
+judged of by the value which would now be set on them, after several breeds
+have once fairly been established. Many slight differences might, and
+indeed do now, arise amongst pigeons, which are rejected as faults or
+deviations from the standard of perfection of each breed. The common goose
+has not given rise to any marked varieties; hence the Thoulouse and the
+common breed, which differ only in colour, that {40} most fleeting of
+characters, have lately been exhibited as distinct at our poultry-shows.
+
+I think these views further explain what has sometimes been
+noticed--namely, that we know nothing about the origin or history of any of
+our domestic breeds. But, in fact, a breed, like a dialect of a language,
+can hardly be said to have had a definite origin. A man preserves and
+breeds from an individual with some slight deviation of structure, or takes
+more care than usual in matching his best animals and thus improves them,
+and the improved individuals slowly spread in the immediate neighbourhood.
+But as yet they will hardly have a distinct name, and from being only
+slightly valued, their history will be disregarded. When further improved
+by the same slow and gradual process, they will spread more widely, and
+will get recognised as something distinct and valuable, and will then
+probably first receive a provincial name. In semi-civilised countries, with
+little free communication, the spreading and knowledge of any new sub-breed
+will be a slow process. As soon as the points of value of the new sub-breed
+are once fully acknowledged, the principle, as I have called it, of
+unconscious selection will always tend,--perhaps more at one period than at
+another, as the breed rises or falls in fashion,--perhaps more in one
+district than in another, according to the state of civilization of the
+inhabitants,--slowly to add to the characteristic features of the breed,
+whatever they may be. But the chance will be infinitely small of any record
+having been preserved of such slow, varying, and insensible changes.
+
+I must now say a few words on the circumstances, favourable, or the
+reverse, to man's power of selection. A high degree of variability is
+obviously favourable, as freely giving the materials for selection to work
+on; not that mere individual differences are not amply {41} sufficient,
+with extreme care, to allow of the accumulation of a large amount of
+modification in almost any desired direction. But as variations manifestly
+useful or pleasing to man appear only occasionally, the chance of their
+appearance will be much increased by a large number of individuals being
+kept; and hence this comes to be of the highest importance to success. On
+this principle Marshall has remarked, with respect to the sheep of parts of
+Yorkshire, that "as they generally belong to poor people, and are mostly
+_in small lots_, they never can be improved." On the other hand,
+nurserymen, from raising large stocks of the same plants, are generally far
+more successful than amateurs in getting new and valuable varieties. The
+keeping of a large number of individuals of a species in any country
+requires that the species should be placed under favourable conditions of
+life, so as to breed freely in that country. When the individuals of any
+species are scanty, all the individuals, whatever their quality may be,
+will generally be allowed to breed, and this will effectually prevent
+selection. But probably the most important point of all, is, that the
+animal or plant should be so highly useful to man, or so much valued by
+him, that the closest attention should be paid to even the slightest
+deviation in the qualities or structure of each individual. Unless such
+attention be paid nothing can be effected. I have seen it gravely remarked,
+that it was most fortunate that the strawberry began to vary just when
+gardeners began to attend closely to this plant. No doubt the strawberry
+had always varied since it was cultivated, but the slight varieties had
+been neglected. As soon, however, as gardeners picked out individual plants
+with slightly larger, earlier, or better fruit, and raised seedlings from
+them, and again picked out the best seedlings and bred from them, then,
+there appeared (aided by some {42} crossing with distinct species) those
+many admirable varieties of the strawberry which have been raised during
+the last thirty or forty years.
+
+In the case of animals with separate sexes, facility in preventing crosses
+is an important element of success in the formation of new races,--at
+least, in a country which is already stocked with other races. In this
+respect enclosure of the land plays a part. Wandering savages or the
+inhabitants of open plains rarely possess more than one breed of the same
+species. Pigeons can be mated for life, and this is a great convenience to
+the fancier, for thus many races may be kept true, though mingled in the
+same aviary; and this circumstance must have largely favoured the
+improvement and formation of new breeds. Pigeons, I may add, can be
+propagated in great numbers and at a very quick rate, and inferior birds
+may be freely rejected, as when killed they serve for food. On the other
+hand, cats, from their nocturnal rambling habits, cannot be matched, and,
+although so much valued by women and children, we hardly ever see a
+distinct breed kept up; such breeds as we do sometimes see are almost
+always imported from some other country, often from islands. Although I do
+not doubt that some domestic animals vary less than others, yet the rarity
+or absence of distinct breeds of the cat, the donkey, peacock, goose, &c.,
+may be attributed in main part to selection not having been brought into
+play: in cats, from the difficulty in pairing them; in donkeys, from only a
+few being kept by poor people, and little attention paid to their breeding;
+in peacocks, from not being very easily reared and a large stock not kept;
+in geese, from being valuable only for two purposes, food and feathers, and
+more especially from no pleasure having been felt in the display of
+distinct breeds.
+
+To sum up on the origin of our Domestic Races of {43} animals and plants. I
+believe that the conditions of life, from their action on the reproductive
+system, are so far of the highest importance as causing variability. I do
+not believe that variability is an inherent and necessary contingency,
+under all circumstances, with all organic beings, as some authors have
+thought. The effects of variability are modified by various degrees of
+inheritance and of reversion. Variability is governed by many unknown laws,
+more especially by that of correlation of growth. Something may be
+attributed to the direct action of the conditions of life. Something must
+be attributed to use and disuse. The final result is thus rendered
+infinitely complex. In some cases, I do not doubt that the intercrossing of
+species, aboriginally distinct, has played an important part in the origin
+of our domestic productions. When in any country several domestic breeds
+have once been established, their occasional intercrossing, with the aid of
+selection, has, no doubt, largely aided in the formation of new sub-breeds;
+but the importance of the crossing of varieties has, I believe, been
+greatly exaggerated, both in regard to animals and to those plants which
+are propagated by seed. In plants which are temporarily propagated by
+cuttings, buds, &c., the importance of the crossing both of distinct
+species and of varieties is immense; for the cultivator here quite
+disregards the extreme variability both of hybrids and mongrels, and the
+frequent sterility of hybrids; but the cases of plants not propagated by
+seed are of little importance to us, for their endurance is only temporary.
+Over all these causes of Change I am convinced that the accumulative action
+of Selection, whether applied methodically and more quickly, or
+unconsciously and more slowly, but more efficiently, is by far the
+predominant Power.
+
+       *       *       *       *       *
+
+
+{44}
+
+CHAPTER II.
+
+VARIATION UNDER NATURE.
+
+    Variability--Individual differences--Doubtful species--Wide ranging,
+    much diffused, and common species vary most--Species of the larger
+    genera in any country vary more than the species of the smaller
+    genera--Many of the species of the larger genera resemble varieties in
+    being very closely, but unequally, related to each other, and in having
+    restricted ranges.
+
+Before applying the principles arrived at in the last chapter to organic
+beings in a state of nature, we must briefly discuss whether these latter
+are subject to any variation. To treat this subject at all properly, a long
+catalogue of dry facts should be given; but these I shall reserve for my
+future work. Nor shall I here discuss the various definitions which have
+been given of the term species. No one definition has as yet satisfied all
+naturalists; yet every naturalist knows vaguely what he means when he
+speaks of a species. Generally the term includes the unknown element of a
+distinct act of creation. The term "variety" is almost equally difficult to
+define; but here community of descent is almost universally implied, though
+it can rarely be proved. We have also what are called monstrosities; but
+they graduate into varieties. By a monstrosity I presume is meant some
+considerable deviation of structure in one part, either injurious to or not
+useful to the species, and not generally propagated. Some authors use the
+term "variation" in a technical sense, as implying a modification directly
+due to the physical conditions of life; and "variations" in this sense are
+supposed not to be inherited: but who can say that the dwarfed condition of
+shells in the brackish waters of the Baltic, or dwarfed {45} plants on
+Alpine summits, or the thicker fur of an animal from far northwards, would
+not in some cases be inherited for at least some few generations? and in
+this case I presume that the form would be called a variety.
+
+Again, we have many slight differences which may be called individual
+differences, such as are known frequently to appear in the offspring from
+the same parents, or which may be presumed to have thus arisen, from being
+frequently observed in the individuals of the same species inhabiting the
+same confined locality. No one supposes that all the individuals of the
+same species are cast in the very same mould. These individual differences
+are highly important for us, as they afford materials for natural selection
+to accumulate, in the same manner as man can accumulate in any given
+direction individual differences in his domesticated productions. These
+individual differences generally affect what naturalists consider
+unimportant parts; but I could show by a long catalogue of facts, that
+parts which must be called important, whether viewed under a physiological
+or classificatory point of view, sometimes vary in the individuals of the
+same species. I am convinced that the most experienced naturalist would be
+surprised at the number of the cases of variability, even in important
+parts of structure, which he could collect on good authority, as I have
+collected, during a course of years. It should be remembered that
+systematists are far from pleased at finding variability in important
+characters, and that there are not many men who will laboriously examine
+internal and important organs, and compare them in many specimens of the
+same species. I should never have expected that the branching of the main
+nerves close to the great central ganglion of an insect would have been
+variable in the same species; I should have expected that changes of this
+nature could have been effected only {46} by slow degrees: yet quite
+recently Mr. Lubbock has shown a degree of variability in these main nerves
+in Coccus, which may almost be compared to the irregular branching of the
+stem of a tree. This philosophical naturalist, I may add, has also quite
+recently shown that the muscles in the larvæ of certain insects are very
+far from uniform. Authors sometimes argue in a circle when they state that
+important organs never vary; for these same authors practically rank that
+character as important (as some few naturalists have honestly confessed)
+which does not vary; and, under this point of view, no instance of an
+important part varying will ever be found: but under any other point of
+view many instances assuredly can be given.
+
+There is one point connected with individual differences, which seems to me
+extremely perplexing: I refer to those genera which have sometimes been
+called "protean" or "polymorphic," in which the species present an
+inordinate amount of variation; and hardly two naturalists can agree which
+forms to rank as species and which as varieties. We may instance Rubus,
+Rosa, and Hieracium amongst plants, several genera of insects, and several
+genera of Brachiopod shells. In most polymorphic genera some of the species
+have fixed and definite characters. Genera which are polymorphic in one
+country seem to be, with some few exceptions, polymorphic in other
+countries, and likewise, judging from Brachiopod shells, at former periods
+of time. These facts seem to be very perplexing, for they seem to show that
+this kind of variability is independent of the conditions of life. I am
+inclined to suspect that we see in these polymorphic genera variations in
+points of structure which are of no service or disservice to the species,
+and which consequently have not been seized on and rendered definite by
+natural selection, as hereafter will be explained. {47}
+
+Those forms which possess in some considerable degree the character of
+species, but which are so closely similar to some other forms, or are so
+closely linked to them by intermediate gradations, that naturalists do not
+like to rank them as distinct species, are in several respects the most
+important for us. We have every reason to believe that many of these
+doubtful and closely-allied forms have permanently retained their
+characters in their own country for a long time; for as long, as far as we
+know, as have good and true species. Practically, when a naturalist can
+unite two forms together by others having intermediate characters, he
+treats the one as a variety of the other, ranking the most common, but
+sometimes the one first described, as the species, and the other as the
+variety. But cases of great difficulty, which I will not here enumerate,
+sometimes occur in deciding whether or not to rank one form as a variety of
+another, even when they are closely connected by intermediate links; nor
+will the commonly-assumed hybrid nature of the intermediate links always
+remove the difficulty. In very many cases, however, one form is ranked as a
+variety of another, not because the intermediate links have actually been
+found, but because analogy leads the observer to suppose either that they
+do now somewhere exist, or may formerly have existed; and here a wide door
+for the entry of doubt and conjecture is opened.
+
+Hence, in determining whether a form should be ranked as a species or a
+variety, the opinion of naturalists having sound judgment and wide
+experience seems the only guide to follow. We must, however, in many cases,
+decide by a majority of naturalists, for few well-marked and well-known
+varieties can be named which have not been ranked as species by at least
+some competent judges. {48}
+
+That varieties of this doubtful nature are far from uncommon cannot be
+disputed. Compare the several floras of Great Britain, of France or of the
+United States, drawn up by different botanists, and see what a surprising
+number of forms have been ranked by one botanist as good species, and by
+another as mere varieties. Mr. H. C. Watson, to whom I lie under deep
+obligation for assistance of all kinds, has marked for me 182 British
+plants, which are generally considered as varieties, but which have all
+been ranked by botanists as species; and in making this list he has omitted
+many trifling varieties, but which nevertheless have been ranked by some
+botanists as species, and he has entirely omitted several highly
+polymorphic genera. Under genera, including the most polymorphic forms, Mr.
+Babington gives 251 species, whereas Mr. Bentham gives only 112,--a
+difference of 139 doubtful forms! Amongst animals which unite for each
+birth, and which are highly locomotive, doubtful forms, ranked by one
+zoologist as a species and by another as a variety, can rarely be found
+within the same country, but are common in separated areas. How many of
+those birds and insects in North America and Europe, which differ very
+slightly from each other, have been ranked by one eminent naturalist as
+undoubted species, and by another as varieties, or, as they are often
+called, as geographical races! Many years ago, when comparing, and seeing
+others compare, the birds from the separate islands of the Galapagos
+Archipelago, both one with another, and with those from the American
+mainland, I was much struck how entirely vague and arbitrary is the
+distinction between species and varieties. On the islets of the little
+Madeira group there are many insects which are characterized as varieties
+in Mr. Wollaston's admirable work, but which it cannot {49} be doubted
+would be ranked as distinct species by many entomologists. Even Ireland has
+a few animals, now generally regarded as varieties, but which have been
+ranked as species by some zoologists. Several most experienced
+ornithologists consider our British red grouse as only a strongly-marked
+race of a Norwegian species, whereas the greater number rank it as an
+undoubted species peculiar to Great Britain. A wide distance between the
+homes of two doubtful forms leads many naturalists to rank both as distinct
+species; but what distance, it has been well asked, will suffice? if that
+between America and Europe is ample, will that between the Continent and
+the Azores, or Madeira, or the Canaries, or Ireland, be sufficient? It must
+be admitted that many forms, considered by highly-competent judges as
+varieties, have so perfectly the character of species that they are ranked
+by other highly-competent judges as good and true species. But to discuss
+whether they are rightly called species or varieties, before any definition
+of these terms has been generally accepted, is vainly to beat the air.
+
+Many of the cases of strongly-marked varieties or doubtful species well
+deserve consideration; for several interesting lines of argument, from
+geographical distribution, analogical variation, hybridism, &c., have been
+brought to bear on the attempt to determine their rank. I will here give
+only a single instance,--the well-known one of the primrose and cowslip, or
+Primula vulgaris and veris. These plants differ considerably in appearance;
+they have a different flavour, and emit a different odour; they flower at
+slightly different periods; they grow in somewhat different stations; they
+ascend mountains to different heights; they have different geographical
+ranges; and lastly, according to very numerous experiments made during
+several years by {50} that most careful observer Gärtner, they can be
+crossed only with much difficulty. We could hardly wish for better evidence
+of the two forms being specifically distinct. On the other hand, they are
+united by many intermediate links, and it is very doubtful whether these
+links are hybrids; and there is, as it seems to me, an overwhelming amount
+of experimental evidence, showing that they descend from common parents,
+and consequently must be ranked as varieties.
+
+Close investigation, in most cases, will bring naturalists to an agreement
+how to rank doubtful forms. Yet it must be confessed that it is in the
+best-known countries that we find the greatest number of forms of doubtful
+value. I have been struck with the fact, that if any animal or plant in a
+state of nature be highly useful to man, or from any cause closely attract
+his attention, varieties of it will almost universally be found recorded.
+These varieties, moreover, will be often ranked by some authors as species.
+Look at the common oak, how closely it has been studied; yet a German
+author makes more than a dozen species out of forms, which are very
+generally considered as varieties; and in this country the highest
+botanical authorities and practical men can be quoted to show that the
+sessile and pedunculated oaks are either good and distinct species or mere
+varieties.
+
+When a young naturalist commences the study of a group of organisms quite
+unknown to him, he is at first much perplexed to determine what differences
+to consider as specific, and what as varieties; for he knows nothing of the
+amount and kind of variation to which the group is subject; and this shows,
+at least, how very generally there is some variation. But if he confine his
+attention to one class within one country, he will soon make up his mind
+how to rank most of the doubtful forms. His {51} general tendency will be
+to make many species, for he will become impressed, just like the pigeon or
+poultry fancier before alluded to, with the amount of difference in the
+forms which he is continually studying; and he has little general knowledge
+of analogical variation in other groups and in other countries, by which to
+correct his first impressions. As he extends the range of his observations,
+he will meet with more cases of difficulty; for he will encounter a greater
+number of closely-allied forms. But if his observations be widely extended,
+he will in the end generally be enabled to make up his own mind which to
+call varieties and which species; but he will succeed in this at the
+expense of admitting much variation,--and the truth of this admission will
+often be disputed by other naturalists. When, moreover, he comes to study
+allied forms brought from countries not now continuous, in which case he
+can hardly hope to find the intermediate links between his doubtful forms,
+he will have to trust almost entirely to analogy, and his difficulties rise
+to a climax.
+
+Certainly no clear line of demarcation has as yet been drawn between
+species and sub-species--that is, the forms which in the opinion of some
+naturalists come very near to, but do not quite arrive at the rank of
+species; or, again, between sub-species and well-marked varieties, or
+between lesser varieties and individual differences. These differences
+blend into each other in an insensible series; and a series impresses the
+mind with the idea of an actual passage.
+
+Hence I look at individual differences, though of small interest to the
+systematist, as of high importance for us, as being the first step towards
+such slight varieties as are barely thought worth recording in works on
+natural history. And I look at varieties which are in any degree more
+distinct and permanent, as steps leading to more {52} strongly marked and
+more permanent varieties; and at these latter, as leading to sub-species,
+and to species. The passage from one stage of difference to another and
+higher stage may be, in some cases, due merely to the long-continued action
+of different physical conditions in two different regions; but I have not
+much faith in this view; and I attribute the passage of a variety, from a
+state in which it differs very slightly from its parent to one in which it
+differs more, to the action of natural selection in accumulating (as will
+hereafter be more fully explained) differences of structure in certain
+definite directions. Hence I believe a well-marked variety may be called an
+incipient species; but whether this belief be justifiable must be judged of
+by the general weight of the several facts and views given throughout this
+work.
+
+It need not be supposed that all varieties or incipient species necessarily
+attain the rank of species. They may whilst in this incipient state become
+extinct, or they may endure as varieties for very long periods, as has been
+shown to be the case by Mr. Wollaston with the varieties of certain fossil
+land-shells in Madeira. If a variety were to flourish so as to exceed in
+numbers the parent species, it would then rank as the species, and the
+species as the variety; or it might come to supplant and exterminate the
+parent species; or both might co-exist, and both rank as independent
+species. But we shall hereafter have to return to this subject.
+
+From these remarks it will be seen that I look at the term species, as one
+arbitrarily given for the sake of convenience to a set of individuals
+closely resembling each other, and that it does not essentially differ from
+the term variety, which is given to less distinct and more fluctuating
+forms. The term variety, again, in comparison with mere individual
+differences, is also applied arbitrarily, and for mere convenience' sake.
+{53}
+
+Guided by theoretical considerations, I thought that some interesting
+results might be obtained in regard to the nature and relations of the
+species which vary most, by tabulating all the varieties in several
+well-worked floras. At first this seemed a simple task; but Mr. H. C.
+Watson, to whom I am much indebted for valuable advice and assistance on
+this subject, soon convinced me that there were many difficulties, as did
+subsequently Dr. Hooker, even in stronger terms. I shall reserve for my
+future work the discussion of these difficulties, and the tables themselves
+of the proportional numbers of the varying species. Dr. Hooker permits me
+to add, that after having carefully read my manuscript, and examined the
+tables, he thinks that the following statements are fairly well
+established. The whole subject, however, treated as it necessarily here is
+with much brevity, is rather perplexing, and allusions cannot be avoided to
+the "struggle for existence," "divergence of character," and other
+questions, hereafter to be discussed.
+
+Alph. de Candolle and others have shown that plants which have very wide
+ranges generally present varieties; and this might have been expected, as
+they become exposed to diverse physical conditions, and as they come into
+competition (which, as we shall hereafter see, is a far more important
+circumstance) with different sets of organic beings. But my tables further
+show that, in any limited country, the species which are most common, that
+is abound most in individuals, and the species which are most widely
+diffused within their own country (and this is a different consideration
+from wide range, and to a certain extent from commonness), often give rise
+to varieties sufficiently well-marked to have been recorded in botanical
+works. Hence it is the most flourishing, or, as they may be called, the
+dominant species,--those {54} which range widely over the world, are the
+most diffused in their own country, and are the most numerous in
+individuals,--which oftenest produce well-marked varieties, or, as I
+consider them, incipient species. And this, perhaps, might have been
+anticipated; for, as varieties, in order to become in any degree permanent,
+necessarily have to struggle with the other inhabitants of the country, the
+species which are already dominant will be the most likely to yield
+offspring, which, though in some slight degree modified, still inherit
+those advantages that enabled their parents to become dominant over their
+compatriots.
+
+If the plants inhabiting a country and described in any Flora be divided
+into two equal masses, all those in the larger genera being placed on one
+side, and all those in the smaller genera on the other side, a somewhat
+larger number of the very common and much diffused or dominant species will
+be found on the side of the larger genera. This, again, might have been
+anticipated; for the mere fact of many species of the same genus inhabiting
+any country, shows that there is something in the organic or inorganic
+conditions of that country favourable to the genus; and, consequently, we
+might have expected to have found in the larger genera, or those including
+many species, a large proportional number of dominant species. But so many
+causes tend to obscure this result, that I am surprised that my tables show
+even a small majority on the side of the larger genera. I will here allude
+to only two causes of obscurity. Fresh-water and salt-loving plants have
+generally very wide ranges and are much diffused, but this seems to be
+connected with the nature of the stations inhabited by them, and has little
+or no relation to the size of the genera to which the species belong.
+Again, plants low in the scale of organisation are {55} generally much more
+widely diffused than plants higher in the scale; and here again there is no
+close relation to the size of the genera. The cause of lowly-organised
+plants ranging widely will be discussed in our chapter on geographical
+distribution.
+
+From looking at species as only strongly-marked and well-defined varieties,
+I was led to anticipate that the species of the larger genera in each
+country would oftener present varieties, than the species of the smaller
+genera; for wherever many closely related species (_i.e._ species of the
+same genus) have been formed, many varieties or incipient species ought, as
+a general rule, to be now forming. Where many large trees grow, we expect
+to find saplings. Where many species of a genus have been formed through
+variation, circumstances have been favourable for variation; and hence we
+might expect that the circumstances would generally be still favourable to
+variation. On the other hand, if we look at each species as a special act
+of creation, there is no apparent reason why more varieties should occur in
+a group having many species, than in one having few.
+
+To test the truth of this anticipation I have arranged the plants of twelve
+countries, and the coleopterous insects of two districts, into two nearly
+equal masses, the species of the larger genera on one side, and those of
+the smaller genera on the other side, and it has invariably proved to be
+the case that a larger proportion of the species on the side of the larger
+genera present varieties, than on the side of the smaller genera. Moreover,
+the species of the large genera which present any varieties, invariably
+present a larger average number of varieties than do the species of the
+small genera. Both these results follow when another division is made, and
+when all the smallest genera, with from only one to four species, are
+absolutely excluded from the tables. These {56} facts are of plain
+signification on the view that species are only strongly marked and
+permanent varieties; for wherever many species of the same genus have been
+formed, or where, if we may use the expression, the manufactory of species
+has been active, we ought generally to find the manufactory still in
+action, more especially as we have every reason to believe the process of
+manufacturing new species to be a slow one. And this certainly is the case,
+if varieties be looked at as incipient species; for my tables clearly show
+as a general rule that, wherever many species of a genus have been formed,
+the species of that genus present a number of varieties, that is of
+incipient species beyond the average. It is not that all large genera are
+now varying much, and are thus increasing in the number of their species,
+or that no small genera are now varying and increasing; for if this had
+been so, it would have been fatal to my theory; inasmuch as geology plainly
+tells us that small genera have in the lapse of time often increased
+greatly in size; and that large genera have often come to their maxima,
+declined, and disappeared. All that we want to show is, that where many
+species of a genus have been formed, on an average many are still forming;
+and this holds good.
+
+There are other relations between the species of large genera and their
+recorded varieties which deserve notice. We have seen that there is no
+infallible criterion by which to distinguish species and well-marked
+varieties; and in those cases in which intermediate links have not been
+found between doubtful forms, naturalists are compelled to come to a
+determination by the amount of difference between them, judging by analogy
+whether or not the amount suffices to raise one or both to the rank of
+species. Hence the amount of difference is one very important criterion in
+settling whether two forms {57} should be ranked as species or varieties.
+Now Fries has remarked in regard to plants, and Westwood in regard to
+insects, that in large genera the amount of difference between the species
+is often exceedingly small. I have endeavoured to test this numerically by
+averages, and, as far as my imperfect results go, they confirm the view. I
+have also consulted some sagacious and experienced observers, and, after
+deliberation, they concur in this view. In this respect, therefore, the
+species of the larger genera resemble varieties, more than do the species
+of the smaller genera. Or the case may be put in another way, and it may be
+said, that in the larger genera, in which a number of varieties or
+incipient species greater than the average are now manufacturing, many of
+the species already manufactured still to a certain extent resemble
+varieties, for they differ from each other by a less than usual amount of
+difference.
+
+Moreover, the species of the large genera are related to each other, in the
+same manner as the varieties of any one species are related to each other.
+No naturalist pretends that all the species of a genus are equally distinct
+from each other; they may generally be divided into sub-genera, or
+sections, or lesser groups. As Fries has well remarked, little groups of
+species are generally clustered like satellites around certain other
+species. And what are varieties but groups of forms, unequally related to
+each other, and clustered round certain forms--that is, round their
+parent-species? Undoubtedly there is one most important point of difference
+between varieties and species; namely, that the amount of difference
+between varieties, when compared with each other or with their
+parent-species, is much less than that between the species of the same
+genus. But when we come to discuss the principle, as I call it, of
+Divergence of Character, {58} we shall see how this may be explained, and
+how the lesser differences between varieties will tend to increase into the
+greater differences between species.
+
+There is one other point which seems to me worth notice. Varieties
+generally have much restricted ranges: this statement is indeed scarcely
+more than a truism, for if a variety were found to have a wider range than
+that of its supposed parent-species, their denominations ought to be
+reversed. But there is also reason to believe, that those species which are
+very closely allied to other species, and in so far resemble varieties,
+often have much restricted ranges. For instance, Mr. H. C. Watson has
+marked for me in the well-sifted London Catalogue of plants (4th edition)
+63 plants which are therein ranked as species, but which he considers as so
+closely allied to other species as to be of doubtful value: these 63
+reputed species range on an average over 6.9 of the provinces into which
+Mr. Watson has divided Great Britain. Now, in this same catalogue, 53
+acknowledged varieties are recorded, and these range over 7.7 provinces;
+whereas, the species to which these varieties belong range over 14.3
+provinces. So that the acknowledged varieties have very nearly the same
+restricted average range, as have those very closely allied forms, marked
+for me by Mr. Watson as doubtful species, but which are almost universally
+ranked by British botanists as good and true species.
+
+
+
+Finally, then, varieties have the same general characters as species, for
+they cannot be distinguished from species,--except, firstly, by the
+discovery of intermediate linking forms, and the occurrence of such links
+cannot affect the actual characters of the forms which they connect; and
+except, secondly by a certain amount of {59} difference, for two forms, if
+differing very little, are generally ranked as varieties, notwithstanding
+that intermediate linking forms have not been discovered; but the amount of
+difference considered necessary to give to two forms the rank of species is
+quite indefinite. In genera having more than the average number of species
+in any country, the species of these genera have more than the average
+number of varieties. In large genera the species are apt to be closely, but
+unequally allied together, forming little clusters round certain species.
+Species very closely allied to other species apparently have restricted
+ranges. In all these several respects the species of large genera present a
+strong analogy with varieties. And we can clearly understand these
+analogies, if species have once existed as varieties, and have thus
+originated: whereas, these analogies are utterly inexplicable if each
+species has been independently created.
+
+We have, also, seen that it is the most flourishing or dominant species of
+the larger genera which on an average vary most; and varieties, as we shall
+hereafter see, tend to become converted into new and distinct species. The
+larger genera thus tend to become larger; and throughout nature the forms
+of life which are now dominant tend to become still more dominant by
+leaving many modified and dominant descendants. But by steps hereafter to
+be explained, the larger genera also tend to break up into smaller genera.
+And thus, the forms of life throughout the universe become divided into
+groups subordinate to groups.
+
+       *       *       *       *       *
+
+
+{60}
+
+CHAPTER III.
+
+STRUGGLE FOR EXISTENCE.
+
+    Bears on natural selection--The term used in a wide sense--Geometrical
+    powers of increase--Rapid increase of naturalised animals and
+    plants--Nature of the checks to increase--Competition
+    universal--Effects of climate--Protection from the number of
+    individuals--Complex relations of all animals and plants throughout
+    nature--Struggle for life most severe between individuals and varieties
+    of the same species; often severe between species of the same
+    genus--The relation of organism to organism the most important of all
+    relations.
+
+Before entering on the subject of this chapter, I must make a few
+preliminary remarks, to show how the struggle for existence bears on
+Natural Selection. It has been seen in the last chapter that amongst
+organic beings in a state of nature there is some individual variability:
+indeed I am not aware that this has ever been disputed. It is immaterial
+for us whether a multitude of doubtful forms be called species or
+sub-species or varieties; what rank, for instance, the two or three hundred
+doubtful forms of British plants are entitled to hold, if the existence of
+any well-marked varieties be admitted. But the mere existence of individual
+variability and of some few well-marked varieties, though necessary as the
+foundation for the work, helps us but little in understanding how species
+arise in nature. How have all those exquisite adaptations of one part of
+the organisation to another part, and to the conditions of life, and of one
+distinct organic being to another being, been perfected? We see these
+beautiful co-adaptations most {61} plainly in the woodpecker and missletoe;
+and only a little less plainly in the humblest parasite which clings to the
+hairs of a quadruped or feathers of a bird; in the structure of the beetle
+which dives through the water; in the plumed seed which is wafted by the
+gentlest breeze; in short, we see beautiful adaptations everywhere and in
+every part of the organic world.
+
+Again, it may be asked, how is it that varieties, which I have called
+incipient species, become ultimately converted into good and distinct
+species, which in most cases obviously differ from each other far more than
+do the varieties of the same species? How do those groups of species, which
+constitute what are called distinct genera, and which differ from each
+other more than do the species of the same genus, arise? All these results,
+as we shall more fully see in the next chapter, follow from the struggle
+for life. Owing to this struggle for life, any variation, however slight,
+and from whatever cause proceeding, if it be in any degree profitable to an
+individual of any species, in its infinitely complex relations to other
+organic beings and to external nature, will tend to the preservation of
+that individual, and will generally be inherited by its offspring. The
+offspring, also, will thus have a better chance of surviving, for, of the
+many individuals of any species which are periodically born, but a small
+number can survive. I have called this principle, by which each slight
+variation, if useful, is preserved, by the term of Natural Selection, in
+order to mark its relation to man's power of selection. We have seen that
+man by selection can certainly produce great results, and can adapt organic
+beings to his own uses, through the accumulation of slight but useful
+variations, given to him by the hand of Nature. But Natural Selection, as
+we shall hereafter see, is a power incessantly ready for action, and is as
+{62} immeasurably superior to man's feeble efforts, as the works of Nature
+are to those of Art.
+
+We will now discuss in a little more detail the struggle for existence. In
+my future work this subject shall be treated, as it well deserves, at much
+greater length. The elder de Candolle and Lyell have largely and
+philosophically shown that all organic beings are exposed to severe
+competition. In regard to plants, no one has treated this subject with more
+spirit and ability than W. Herbert, Dean of Manchester, evidently the
+result of his great horticultural knowledge. Nothing is easier than to
+admit in words the truth of the universal struggle for life, or more
+difficult--at least I have found it so--than constantly to bear this
+conclusion in mind. Yet unless it be thoroughly engrained in the mind, I am
+convinced that the whole economy of nature, with every fact on
+distribution, rarity, abundance, extinction, and variation, will be dimly
+seen or quite misunderstood. We behold the face of nature bright with
+gladness, we often see superabundance of food; we do not see, or we forget
+that the birds which are idly singing round us mostly live on insects or
+seeds, and are thus constantly destroying life; or we forget how largely
+these songsters, or their eggs, or their nestlings, are destroyed by birds
+and beasts of prey; we do not always bear in mind, that though food may be
+now superabundant, it is not so at all seasons of each recurring year.
+
+I should premise that I use the term Struggle for Existence in a large and
+metaphorical sense, including dependence of one being on another, and
+including (which is more important) not only the life of the individual,
+but success in leaving progeny. Two canine animals in a time of dearth, may
+be truly said to struggle with each other which shall get food and live.
+But a plant on the edge of a desert is said to struggle {63} for life
+against the drought, though more properly it should be said to be dependent
+on the moisture. A plant which annually produces a thousand seeds, of which
+on an average only one comes to maturity, may be more truly said to
+struggle with the plants of the same and other kinds which already clothe
+the ground. The missletoe is dependent on the apple and a few other trees,
+but can only in a far-fetched sense be said to struggle with these trees,
+for if too many of these parasites grow on the same tree, it will languish
+and die. But several seedling missletoes, growing close together on the
+same branch, may more truly be said to struggle with each other. As the
+missletoe is disseminated by birds, its existence depends on birds; and it
+may metaphorically be said to struggle with other fruit-bearing plants, in
+order to tempt birds to devour and thus disseminate its seeds rather than
+those of other plants. In these several senses, which pass into each other,
+I use for convenience' sake the general term of struggle for existence.
+
+A struggle for existence inevitably follows from the high rate at which all
+organic beings tend to increase. Every being, which during its natural
+lifetime produces several eggs or seeds, must suffer destruction during
+some period of its life, and during some season or occasional year,
+otherwise, on the principle of geometrical increase, its numbers would
+quickly become so inordinately great that no country could support the
+product. Hence, as more individuals are produced than can possibly survive,
+there must in every case be a struggle for existence, either one individual
+with another of the same species, or with the individuals of distinct
+species, or with the physical conditions of life. It is the doctrine of
+Malthus applied with manifold force to the whole animal and vegetable
+kingdoms; for in this case there {64} can be no artificial increase of
+food, and no prudential restraint from marriage. Although some species may
+be now increasing, more or less rapidly, in numbers, all cannot do so, for
+the world would not hold them.
+
+There is no exception to the rule that every organic being naturally
+increases at so high a rate, that if not destroyed, the earth would soon be
+covered by the progeny of a single pair. Even slow-breeding man has doubled
+in twenty-five years, and at this rate, in a few thousand years, there
+would literally not be standing room for his progeny. Linnæus has
+calculated that if an annual plant produced only two seeds--and there is no
+plant so unproductive as this--and their seedlings next year produced two,
+and so on, then in twenty years there would be a million plants. The
+elephant is reckoned the slowest breeder of all known animals, and I have
+taken some pains to estimate its probable minimum rate of natural increase:
+it will be under the mark to assume that it breeds when thirty years old,
+and goes on breeding till ninety years old, bringing forth three pair of
+young in this interval; if this be so, at the end of the fifth century
+there would be alive fifteen million elephants, descended from the first
+pair.
+
+But we have better evidence on this subject than mere theoretical
+calculations, namely, the numerous recorded cases of the astonishingly
+rapid increase of various animals in a state of nature, when circumstances
+have been favourable to them during two or three following seasons. Still
+more striking is the evidence from our domestic animals of many kinds which
+have run wild in several parts of the world: if the statements of the rate
+of increase of slow-breeding cattle and horses in South America, and
+latterly in Australia, had not been well authenticated, they would have
+been incredible. So it is with plants: cases could be given of {65}
+introduced plants which have become common throughout whole islands in a
+period of less than ten years. Several of the plants, such as the cardoon
+and a tall thistle, now most numerous over the wide plains of La Plata,
+clothing square leagues of surface almost to the exclusion of all other
+plants, have been introduced from Europe; and there are plants which now
+range in India, as I hear from Dr. Falconer, from Cape Comorin to the
+Himalaya, which have been imported from America since its discovery. In
+such cases, and endless instances could be given, no one supposes that the
+fertility of these animals or plants has been suddenly and temporarily
+increased in any sensible degree. The obvious explanation is that the
+conditions of life have been very favourable, and that there has
+consequently been less destruction of the old and young, and that nearly
+all the young have been enabled to breed. In such cases the geometrical
+ratio of increase, the result of which never fails to be surprising, simply
+explains the extraordinarily rapid increase and wide diffusion of
+naturalised productions in their new homes.
+
+In a state of nature almost every plant produces seed, and amongst animals
+there are very few which do not annually pair. Hence we may confidently
+assert, that all plants and animals are tending to increase at a
+geometrical ratio, that all would most rapidly stock every station in which
+they could any how exist, and that the geometrical tendency to increase
+must be checked by destruction at some period of life. Our familiarity with
+the larger domestic animals tends, I think, to mislead us: we see no great
+destruction falling on them, and we forget that thousands are annually
+slaughtered for food, and that in a state of nature an equal number would
+have somehow to be disposed of.
+
+The only difference between organisms which annually {66} produce eggs or
+seeds by the thousand, and those which produce extremely few, is, that the
+slow-breeders would require a few more years to people, under favourable
+conditions, a whole district, let it be ever so large. The condor lays a
+couple of eggs and the ostrich a score, and yet in the same country the
+condor may be the more numerous of the two: the Fulmar petrel lays but one
+egg, yet it is believed to be the most numerous bird in the world. One fly
+deposits hundreds of eggs, and another, like the hippobosca, a single one;
+but this difference does not determine how many individuals of the two
+species can be supported in a district. A large number of eggs is of some
+importance to those species which depend on a rapidly fluctuating amount of
+food, for it allows them rapidly to increase in number. But the real
+importance of a large number of eggs or seeds is to make up for much
+destruction at some period of life; and this period in the great majority
+of cases is an early one. If an animal can in any way protect its own eggs
+or young, a small number may be produced, and yet the average stock be
+fully kept up; but if many eggs or young are destroyed, many must be
+produced, or the species will become extinct. It would suffice to keep up
+the full number of a tree, which lived on an average for a thousand years,
+if a single seed were produced once in a thousand years, supposing that
+this seed were never destroyed, and could be ensured to germinate in a
+fitting place. So that in all cases, the average number of any animal or
+plant depends only indirectly on the number of its eggs or seeds.
+
+In looking at Nature, it is most necessary to keep the foregoing
+considerations always in mind--never to forget that every single organic
+being around us may be said to be striving to the utmost to increase in
+numbers; that each lives by a struggle at some period of {67} its life;
+that heavy destruction inevitably falls either on the young or old, during
+each generation or at recurrent intervals. Lighten any check, mitigate the
+destruction ever so little, and the number of the species will almost
+instantaneously increase to any amount.
+
+The causes which check the natural tendency of each species to increase in
+number are most obscure. Look at the most vigorous species; by as much as
+it swarms in numbers, by so much will its tendency to increase be still
+further increased. We know not exactly what the checks are in even one
+single instance. Nor will this surprise any one who reflects how ignorant
+we are on this head, even in regard to mankind, so incomparably better
+known than any other animal. This subject has been ably treated by several
+authors, and I shall, in my future work, discuss some of the checks at
+considerable length, more especially in regard to the feral animals of
+South America. Here I will make only a few remarks, just to recall to the
+reader's mind some of the chief points. Eggs or very young animals seem
+generally to suffer most, but this is not invariably the case. With plants
+there is a vast destruction of seeds, but, from some observations which I
+have made, I believe that it is the seedlings which suffer most from
+germinating in ground already thickly stocked with other plants. Seedlings,
+also, are destroyed in vast numbers by various enemies; for instance, on a
+piece of ground three feet long and two wide, dug and cleared, and where
+there could be no choking from other plants, I marked all the seedlings of
+our native weeds as they came up, and out of the 357 no less than 295 were
+destroyed, chiefly by slugs and insects. If turf which has long been mown,
+and the case would be the same with turf closely browsed by quadrupeds, be
+let to grow, the more vigorous plants {68} gradually kill the less
+vigorous, though fully grown, plants: thus out of twenty species growing on
+a little plot of turf (three feet by four) nine species perished from the
+other species being allowed to grow up freely.
+
+The amount of food for each species of course gives the extreme limit to
+which each can increase; but very frequently it is not the obtaining food,
+but the serving as prey to other animals, which determines the average
+numbers of a species. Thus, there seems to be little doubt that the stock
+of partridges, grouse, and hares on any large estate depends chiefly on the
+destruction of vermin. If not one head of game were shot during the next
+twenty years in England, and, at the same time, if no vermin were
+destroyed, there would, in all probability, be less game than at present,
+although hundreds of thousands of game animals are now annually killed. On
+the other hand, in some cases, as with the elephant and rhinoceros, none
+are destroyed by beasts of prey: even the tiger in India most rarely dares
+to attack a young elephant protected by its dam.
+
+Climate plays an important part in determining the average numbers of a
+species, and periodical seasons of extreme cold or drought, I believe to be
+the most effective of all checks. I estimated that the winter of 1854-55
+destroyed four-fifths of the birds in my own grounds; and this is a
+tremendous destruction, when we remember that ten per cent, is an
+extraordinarily severe mortality from epidemics with man. The action of
+climate seems at first sight to be quite independent of the struggle for
+existence; but in so far as climate chiefly acts in reducing food, it
+brings on the most severe struggle between the individuals, whether of the
+same or of distinct species, which subsist on the same kind of food. Even
+when climate, for instance extreme cold, {69} acts directly, it will be the
+least vigorous, or those which have got least food through the advancing
+winter, which will suffer most. When we travel from south to north, or from
+a damp region to a dry, we invariably see some species gradually getting
+rarer and rarer, and finally disappearing; and the change of climate being
+conspicuous, we are tempted to attribute the whole effect to its direct
+action. But this is a false view: we forget that each species, even where
+it most abounds, is constantly suffering enormous destruction at some
+period of its life, from enemies or from competitors for the same place and
+food; and if these enemies or competitors be in the least degree favoured
+by any slight change of climate, they will increase in numbers, and, as
+each area is already fully stocked with inhabitants, the other species will
+decrease. When we travel southward and see a species decreasing in numbers,
+we may feel sure that the cause lies quite as much in other species being
+favoured, as in this one being hurt. So it is when we travel northward, but
+in a somewhat lesser degree, for the number of species of all kinds, and
+therefore of competitors, decreases northwards; hence in going northward,
+or in ascending a mountain, we far oftener meet with stunted forms, due to
+the _directly_ injurious action of climate, than we do in proceeding
+southwards or in descending a mountain. When we reach the Arctic regions,
+or snow-capped summits, or absolute deserts, the struggle for life is
+almost exclusively with the elements.
+
+That climate acts in main part indirectly by favouring other species, we
+may clearly see in the prodigious number of plants in our gardens which can
+perfectly well endure our climate, but which never become naturalised, for
+they cannot compete with our native plants nor resist destruction by our
+native animals. {70}
+
+When a species, owing to highly favourable circumstances, increases
+inordinately in numbers in a small tract, epidemics--at least, this seems
+generally to occur with our game animals--often ensue: and here we have a
+limiting check independent of the struggle for life. But even some of these
+so-called epidemics appear to be due to parasitic worms, which have from
+some cause, possibly in part through facility of diffusion amongst the
+crowded animals, been disproportionably favoured: and here comes in a sort
+of struggle between the parasite and its prey.
+
+On the other hand, in many cases, a large stock of individuals of the same
+species, relatively to the numbers of its enemies, is absolutely necessary
+for its preservation. Thus we can easily raise plenty of corn and
+rape-seed, &c., in our fields, because the seeds are in great excess
+compared with the number of birds which feed on them; nor can the birds,
+though having a superabundance of food at this one season, increase in
+number proportionally to the supply of seed, as their numbers are checked
+during winter: but any one who has tried, knows how troublesome it is to
+get seed from a few wheat or other such plants in a garden: I have in this
+case lost every single seed. This view of the necessity of a large stock of
+the same species for its preservation, explains, I believe, some singular
+facts in nature, such as that of very rare plants being sometimes extremely
+abundant in the few spots where they do occur; and that of some social
+plants being social, that is, abounding in individuals, even on the extreme
+confines of their range. For in such cases, we may believe, that a plant
+could exist only where the conditions of its life were so favourable that
+many could exist together, and thus save the species from utter
+destruction. I should add that the good effects of frequent intercrossing,
+and {71} the ill effects of close interbreeding, probably come into play in
+some of these cases; but on this intricate subject I will not here enlarge.
+
+Many cases are on record showing how complex and unexpected are the checks
+and relations between organic beings, which have to struggle together in
+the same country. I will give only a single instance, which, though a
+simple one, has interested me. In Staffordshire, on the estate of a
+relation, where I had ample means of investigation, there was a large and
+extremely barren heath, which had never been touched by the hand of man;
+but several hundred acres of exactly the same nature had been enclosed
+twenty-five years previously and planted with Scotch fir. The change in the
+native vegetation of the planted part of the heath was most remarkable,
+more than is generally seen in passing from one quite different soil to
+another: not only the proportional numbers of the heath-plants were wholly
+changed, but twelve species of plants (not counting grasses and carices)
+flourished in the plantations, which could not be found on the heath. The
+effect on the insects must have been still greater, for six insectivorous
+birds were very common in the plantations, which were not to be seen on the
+heath; and the heath was frequented by two or three distinct insectivorous
+birds. Here we see how potent has been the effect of the introduction of a
+single tree, nothing whatever else having been done, with the exception
+that the land had been enclosed, so that cattle could not enter. But how
+important an element enclosure is, I plainly saw near Farnham, in Surrey.
+Here there are extensive heaths, with a few clumps of old Scotch firs on
+the distant hill-tops: within the last ten years large spaces have been
+enclosed, and self-sown firs are now springing up in multitudes, so close
+together that all cannot live. {72} When I ascertained that these young
+trees had not been sown or planted, I was so much surprised at their
+numbers that I went to several points of view, whence I could examine
+hundreds of acres of the unenclosed heath, and literally I could not see a
+single Scotch fir, except the old planted clumps. But on looking closely
+between the stems of the heath, I found a multitude of seedlings and little
+trees, which had been perpetually browsed down by the cattle. In one square
+yard, at a point some hundred yards distant from one of the old clumps, I
+counted thirty-two little trees; and one of them, with twenty-six rings of
+growth, had during many years tried to raise its head above the stems of
+the heath, and had failed. No wonder that, as soon as the land was
+enclosed, it became thickly clothed with vigorously growing young firs. Yet
+the heath was so extremely barren and so extensive that no one would ever
+have imagined that cattle would have so closely and effectually searched it
+for food.
+
+Here we see that cattle absolutely determine the existence of the Scotch
+fir; but in several parts of the world insects determine the existence of
+cattle. Perhaps Paraguay offers the most curious instance of this; for here
+neither cattle nor horses nor dogs have ever run wild, though they swarm
+southward and northward in a feral state; and Azara and Rengger have shown
+that this is caused by the greater number in Paraguay of a certain fly,
+which lays its eggs in the navels of these animals when first born. The
+increase of these flies, numerous as they are, must be habitually checked
+by some means, probably by birds. Hence, if certain insectivorous birds
+(whose numbers are probably regulated by hawks or beasts of prey) were to
+increase in Paraguay, the flies would decrease--then cattle and horses
+would became feral, and this would certainly greatly {73} alter (as indeed
+I have observed in parts of South America) the vegetation: this again would
+largely affect the insects; and this, as we just have seen in
+Staffordshire, the insectivorous birds, and so onwards in ever-increasing
+circles of complexity. We began this series by insectivorous birds, and we
+have ended with them, Not that in nature the relations can ever be as
+simple as this. Battle within battle must ever be recurring with varying
+success; and yet in the long-run the forces are so nicely balanced, that
+the face of nature remains uniform for long periods of time, though
+assuredly the merest trifle would often give the victory to one organic
+being over another. Nevertheless so profound is our ignorance, and so high
+our presumption, that we marvel when we hear of the extinction of an
+organic being; and as we do not see the cause, we invoke cataclysms to
+desolate the world, or invent laws on the duration of the forms of life!
+
+I am tempted to give one more instance showing how plants and animals, most
+remote in the scale of nature, are bound together by a web of complex
+relations. I shall hereafter have occasion to show that the exotic Lobelia
+fulgens, in this part of England, is never visited by insects, and
+consequently, from its peculiar structure, never can set a seed. Many of
+our orchidaceous plants absolutely require the visits of moths to remove
+their pollen-masses and thus to fertilise them. I have, also, reason to
+believe that humble-bees are indispensable to the fertilisation of the
+heartsease (Viola tricolor), for other bees do not visit this flower. From
+experiments which I have lately tried, I have found that the visits of bees
+are necessary for the fertilisation of some kinds of clover; but
+humble-bees alone visit the red clover (Trifolium pratense), as other bees
+cannot reach the nectar. Hence I have very little doubt, that if the {74}
+whole genus of humble-bees became extinct or very rare in England, the
+heartsease and red clover would become very rare, or wholly disappear. The
+number of humble-bees in any district depends in a great degree on the
+number of field-mice, which destroy their combs and nests; and Mr. H.
+Newman, who has long attended to the habits of humble-bees, believes that
+"more than two-thirds of them are thus destroyed all over England." Now the
+number of mice is largely dependent, as every one knows, on the number of
+cats; and Mr. Newman says, "Near villages and small towns I have found the
+nests of humble-bees more numerous than elsewhere, which I attribute to the
+number of cats that destroy the mice." Hence it is quite credible that the
+presence of a feline animal in large numbers in a district might determine,
+through the intervention first of mice and then of bees, the frequency of
+certain flowers in that district!
+
+In the case of every species, many different checks, acting at different
+periods of life, and during different seasons or years, probably come into
+play; some one check or some few being generally the most potent, but all
+concur in determining the average number or even the existence of the
+species. In some cases it can be shown that widely-different checks act on
+the same species in different districts. When we look at the plants and
+bushes clothing an entangled bank, we are tempted to attribute their
+proportional numbers and kinds to what we call chance. But how false a view
+is this! Every one has heard that when an American forest is cut down, a
+very different vegetation springs up; but it has been observed that ancient
+Indian ruins in the Southern United States, which must formerly have been
+cleared of trees, now display the same beautiful diversity and proportion
+of kinds as in the surrounding {75} virgin forests. What a struggle between
+the several kinds of trees must here have gone on during long centuries,
+each annually scattering its seeds by the thousand; what war between insect
+and insect--between insects, snails, and other animals with birds and
+beasts of prey--all striving to increase, and all feeding on each other or
+on the trees or their seeds and seedlings, or on the other plants which
+first clothed the ground and thus checked the growth of the trees! Throw up
+a handful of feathers, and all must fall to the ground according to
+definite laws; but how simple is this problem compared to the action and
+reaction of the innumerable plants and animals which have determined, in
+the course of centuries, the proportional numbers and kinds of trees now
+growing on the old Indian ruins!
+
+The dependency of one organic being on another, as of a parasite on its
+prey, lies generally between beings remote in the scale of nature. This is
+often the case with those which may strictly be said to struggle with each
+other for existence, as in the case of locusts and grass-feeding
+quadrupeds. But the struggle almost invariably will be most severe between
+the individuals of the same species, for they frequent the same districts,
+require the same food, and are exposed to the same dangers. In the case of
+varieties of the same species, the struggle will generally be almost
+equally severe, and we sometimes see the contest soon decided; for
+instance, if several varieties of wheat be sown together, and the mixed
+seed be resown, some of the varieties which best suit the soil or climate,
+or are naturally the most fertile, will beat the others and so yield more
+seed, and will consequently in a few years quite supplant the other
+varieties. To keep up a mixed stock of even such extremely close varieties
+as the variously {76} coloured sweet-peas, they must be each year harvested
+separately, and the seed then mixed in due proportion, otherwise the weaker
+kinds will steadily decrease in numbers and disappear. So again with the
+varieties of sheep: it has been asserted that certain mountain-varieties
+will starve out other mountain-varieties, so that they cannot be kept
+together. The same result has followed from keeping together different
+varieties of the medicinal leech. It may even be doubted whether the
+varieties of any one of our domestic plants or animals have so exactly the
+same strength, habits, and constitution, that the original proportions of a
+mixed stock could be kept up for half-a-dozen generations, if they were
+allowed to struggle together, like beings in a state of nature, and if the
+seed or young were not annually sorted.
+
+As species of the same genus have usually, though by no means invariably,
+some similarity in habits and constitution, and always in structure, the
+struggle will generally be more severe between species of the same genus,
+when they come into competition with each other, than between species of
+distinct genera. We see this in the recent extension over parts of the
+United States of one species of swallow having caused the decrease of
+another species. The recent increase of the missel-thrush in parts of
+Scotland has caused the decrease of the song-thrush. How frequently we hear
+of one species of rat taking the place of another species under the most
+different climates! In Russia the small Asiatic cockroach has everywhere
+driven before it its great congener. One species of charlock will supplant
+another, and so in other cases. We can dimly see why the competition should
+be most severe between allied forms, which fill nearly the same place in
+the economy of nature; {77} but probably in no one case could we precisely
+say why one species has been victorious over another in the great battle of
+life.
+
+A corollary of the highest importance may be deduced from the foregoing
+remarks, namely, that the structure of every organic being is related, in
+the most essential yet often hidden manner, to that of all other organic
+beings, with which it comes into competition for food or residence, or from
+which it has to escape, or on which it preys. This is obvious in the
+structure of the teeth and talons of the tiger; and in that of the legs and
+claws of the parasite which clings to the hair on the tiger's body. But in
+the beautifully plumed seed of the dandelion, and in the flattened and
+fringed legs of the water-beetle, the relation seems at first confined to
+the elements of air and water. Yet the advantage of plumed seeds no doubt
+stands in the closest relation to the land being already thickly clothed by
+other plants; so that the seeds may be widely distributed and fall on
+unoccupied ground. In the water-beetle, the structure of its legs, so well
+adapted for diving, allows it to compete with other aquatic insects, to
+hunt for its own prey, and to escape serving as prey to other animals.
+
+The store of nutriment laid up within the seeds of many plants seems at
+first sight to have no sort of relation to other plants. But from the
+strong growth of young plants produced from such seeds (as peas and beans),
+when sown in the midst of long grass, I suspect that the chief use of the
+nutriment in the seed is to favour the growth of the young seedling, whilst
+struggling with other plants growing vigorously all around.
+
+Look at a plant in the midst of its range, why does it not double or
+quadruple its numbers? We know {78} that it can perfectly well withstand a
+little more heat or cold, dampness or dryness, for elsewhere it ranges into
+slightly hotter or colder, damper or drier districts. In this case we can
+clearly see that if we wished in imagination to give the plant the power of
+increasing in number, we should have to give it some advantage over its
+competitors, or over the animals which preyed on it. On the confines of its
+geographical range, a change of constitution with respect to climate would
+clearly be an advantage to our plant; but we have reason to believe that
+only a few plants or animals range so far, that they are destroyed by the
+rigour of the climate alone. Not until we reach the extreme confines of
+life, in the Arctic regions or on the borders of an utter desert, will
+competition cease. The land may be extremely cold or dry, yet there will be
+competition between some few species, or between the individuals of the
+same species, for the warmest or dampest spots.
+
+Hence, also, we can see that when a plant or animal is placed in a new
+country amongst new competitors, though the climate may be exactly the same
+as in its former home, yet the conditions of its life will generally be
+changed in an essential manner. If we wished to increase its average
+numbers in its new home, we should have to modify it in a different way to
+what we should have done in its native country; for we should have to give
+it some advantage over a different set of competitors or enemies.
+
+It is good thus to try in our imagination to give any form some advantage
+over another. Probably in no single instance should we know what to do, so
+as to succeed. It will convince us of our ignorance on the mutual relations
+of all organic beings; a conviction as necessary, as it seems to be
+difficult to acquire. All that we can do, is to keep steadily in mind that
+each {79} organic being is striving to increase at a geometrical ratio;
+that each at some period of its life, during some season of the year,
+during each generation or at intervals, has to struggle for life, and to
+suffer great destruction. When we reflect on this struggle, we may console
+ourselves with the full belief, that the war of nature is not incessant,
+that no fear is felt, that death is generally prompt, and that the
+vigorous, the healthy, and the happy survive and multiply.
+
+       *       *       *       *       *
+
+
+{80}
+
+CHAPTER IV.
+
+NATURAL SELECTION.
+
+    Natural Selection--its power compared with man's selection--its power
+    on characters of trifling importance--its power at all ages and on both
+    sexes--Sexual Selection--On the generality of intercrosses between
+    individuals of the same species--Circumstances favourable and
+    unfavourable to Natural Selection, namely, intercrossing, isolation,
+    number of individuals--Slow action--Extinction caused by Natural
+    Selection--Divergence of Character, related to the diversity of
+    inhabitants of any small area, and to naturalisation--Action of Natural
+    Selection, through Divergence of Character and Extinction, on the
+    descendants from a common parent--Explains the Grouping of all organic
+    beings.
+
+How will the struggle for existence, discussed too briefly in the last
+chapter, act in regard to variation? Can the principle of selection, which
+we have seen is so potent in the hands of man, apply in nature? I think we
+shall see that it can act most effectually. Let it be borne in mind in what
+an endless number of strange peculiarities our domestic productions, and,
+in a lesser degree, those under nature, vary; and how strong the hereditary
+tendency is. Under domestication, it may be truly said that the whole
+organisation becomes in some degree plastic. Let it be borne in mind how
+infinitely complex and close-fitting are the mutual relations of all
+organic beings to each other and to their physical conditions of life. Can
+it, then, be thought improbable, seeing that variations useful to man have
+undoubtedly occurred, that other variations useful in some way to each
+being in the great and complex battle of life, should sometimes occur in
+the course of thousands of generations? If such do occur, can we doubt {81}
+(remembering that many more individuals are born than can possibly survive)
+that individuals having any advantage, however slight, over others, would
+have the best chance of surviving and of procreating their kind? On the
+other hand, we may feel sure that any variation in the least degree
+injurious would be rigidly destroyed. This preservation of favourable
+variations and the rejection of injurious variations, I call Natural
+Selection. Variations neither useful nor injurious would not be affected by
+natural selection, and would be left a fluctuating element, as perhaps we
+see in the species called polymorphic.
+
+We shall best understand the probable course of natural selection by taking
+the case of a country undergoing some physical change, for instance, of
+climate. The proportional numbers of its inhabitants would almost
+immediately undergo a change, and some species might become extinct. We may
+conclude, from what we have seen of the intimate and complex manner in
+which the inhabitants of each country are bound together, that any change
+in the numerical proportions of some of the inhabitants, independently of
+the change of climate itself, would seriously affect many of the others. If
+the country were open on its borders, new forms would certainly immigrate,
+and this also would seriously disturb the relations of some of the former
+inhabitants. Let it be remembered how powerful the influence of a single
+introduced tree or mammal has been shown to be. But in the case of an
+island, or of a country partly surrounded by barriers, into which new and
+better adapted forms could not freely enter, we should then have places in
+the economy of nature which would assuredly be better filled up, if some of
+the original inhabitants were in some manner modified; for, had the area
+been open to immigration, these same {82} places would have been seized on
+by intruders. In such case, every slight modification, which in the course
+of ages chanced to arise, and which in any way favoured the individuals of
+any of the species, by better adapting them to their altered conditions,
+would tend to be preserved; and natural selection would thus have free
+scope for the work of improvement.
+
+We have reason to believe, as stated in the first chapter, that a change in
+the conditions of life, by specially acting on the reproductive system,
+causes or increases variability; and in the foregoing case the conditions
+of life are supposed to have undergone a change, and this would manifestly
+be favourable to natural selection, by giving a better chance of profitable
+variations occurring; and unless profitable variations do occur, natural
+selection can do nothing. Not that, as I believe, any extreme amount of
+variability is necessary; as man can certainly produce great results by
+adding up in any given direction mere individual differences, so could
+Nature, but far more easily, from having incomparably longer time at her
+disposal. Nor do I believe that any great physical change, as of climate,
+or any unusual degree of isolation to check immigration, is actually
+necessary to produce new and unoccupied places for natural selection to
+fill up by modifying and improving some of the varying inhabitants. For as
+all the inhabitants of each country are struggling together with nicely
+balanced forces, extremely slight modifications in the structure or habits
+of one inhabitant would often give it an advantage over others; and still
+further modifications of the same kind would often still further increase
+the advantage. No country can be named in which all the native inhabitants
+are now so perfectly adapted to each other and to the physical conditions
+under which they live, that none of {83} them could anyhow be improved; for
+in all countries, the natives have been so far conquered by naturalised
+productions, that they have allowed foreigners to take firm possession of
+the land. And as foreigners have thus everywhere beaten some of the
+natives, we may safely conclude that the natives might have been modified
+with advantage, so as to have better resisted such intruders.
+
+As man can produce and certainly has produced a great result by his
+methodical and unconscious means of selection, what may not Nature effect?
+Man can act only on external and visible characters: Nature cares nothing
+for appearances, except in so far as they may be useful to any being. She
+can act on every internal organ, on every shade of constitutional
+difference, on the whole machinery of life. Man selects only for his own
+good; Nature only for that of the being which she tends. Every selected
+character is fully exercised by her; and the being is placed under
+well-suited conditions of life. Man keeps the natives of many climates in
+the same country; he seldom exercises each selected character in some
+peculiar and fitting manner; he feeds a long and a short beaked pigeon on
+the same food; he does not exercise a long-backed or long-legged quadruped
+in any peculiar manner; he exposes sheep with long and short wool to the
+same climate. He does not allow the most vigorous males to struggle for the
+females. He does not rigidly destroy all inferior animals, but protects
+during each varying season, as far as lies in his power, all his
+productions. He often begins his selection by some half-monstrous form; or
+at least by some modification prominent enough to catch his eye, or to be
+plainly useful to him. Under nature, the slightest difference of structure
+or constitution may well turn the nicely-balanced scale in the struggle for
+life, and so be {84} preserved. How fleeting are the wishes and efforts of
+man! how short his time! and consequently how poor will his products be,
+compared with those accumulated by Nature during whole geological periods.
+Can we wonder, then, that Nature's productions should be far "truer" in
+character than man's productions; that they should be infinitely better
+adapted to the most complex conditions of life, and should plainly bear the
+stamp of far higher workmanship?
+
+It may metaphorically be said that natural selection is daily and hourly
+scrutinising, throughout the world, every variation, even the slightest;
+rejecting that which is bad, preserving and adding up all that is good;
+silently and insensibly working, whenever and wherever opportunity offers,
+at the improvement of each organic being in relation to its organic and
+inorganic conditions of life. We see nothing of these slow changes in
+progress, until the hand of time has marked the long lapse of ages, and
+then so imperfect is our view into long past geological ages, that we only
+see that the forms of life are now different from what they formerly were.
+
+Although natural selection can act only through and for the good of each
+being, yet characters and structures, which we are apt to consider as of
+very trifling importance, may thus be acted on. When we see leaf-eating
+insects green, and bark-feeders mottled-grey; the alpine ptarmigan white in
+winter, the red-grouse the colour of heather, and the black-grouse that of
+peaty earth, we must believe that these tints are of service to these birds
+and insects in preserving them from danger. Grouse, if not destroyed at
+some period of their lives, would increase in countless numbers; they are
+known to suffer largely from birds of prey; and hawks are guided by
+eyesight to their prey--so much so, that on {85} parts of the Continent
+persons are warned not to keep white pigeons, as being the most liable to
+destruction. Hence I can see no reason to doubt that natural selection
+might be most effective in giving the proper colour to each kind of grouse,
+and in keeping that colour, when once acquired, true and constant. Nor
+ought we to think that the occasional destruction of an animal of any
+particular colour would produce little effect: we should remember how
+essential it is in a flock of white sheep to destroy every lamb with the
+faintest trace of black. In plants the down on the fruit and the colour of
+the flesh are considered by botanists as characters of the most trifling
+importance: yet we hear from an excellent horticulturist, Downing, that in
+the United States smooth-skinned fruits suffer far more from a beetle, a
+curculio, than those with down; that purple plums suffer far more from a
+certain disease than yellow plums; whereas another disease attacks
+yellow-fleshed peaches far more than those with other coloured flesh. If,
+with all the aids of art, these slight differences make a great difference
+in cultivating the several varieties, assuredly, in a state of nature,
+where the trees would have to struggle with other trees and with a host of
+enemies, such differences would effectually settle which variety, whether a
+smooth or downy, a yellow or purple fleshed fruit, should succeed.
+
+In looking at many small points of difference between species, which, as
+far as our ignorance permits us to judge, seem quite unimportant, we must
+not forget that climate, food, &c., probably produce some slight and direct
+effect. It is, however, far more necessary to bear in mind that there are
+many unknown laws of correlation of growth, which, when one part of the
+organisation is modified through variation, and the modifications are
+accumulated by natural selection for {86} the good of the being, will cause
+other modifications, often of the most unexpected nature.
+
+As we see that those variations which under domestication appear at any
+particular period of life, tend to reappear in the offspring at the same
+period;--for instance, in the seeds of the many varieties of our culinary
+and agricultural plants; in the caterpillar and cocoon stages of the
+varieties of the silkworm; in the eggs of poultry, and in the colour of the
+down of their chickens; in the horns of our sheep and cattle when nearly
+adult;--so in a state of nature, natural selection will be enabled to act
+on and modify organic beings at any age, by the accumulation of variations
+profitable at that age, and by their inheritance at a corresponding age. If
+it profit a plant to have its seeds more and more widely disseminated by
+the wind, I can see no greater difficulty in this being effected through
+natural selection, than in the cotton-planter increasing and improving by
+selection the down in the pods on his cotton-trees. Natural selection may
+modify and adapt the larva of an insect to a score of contingencies, wholly
+different from those which concern the mature insect. These modifications
+will no doubt affect, through the laws of correlation, the structure of the
+adult; and probably in the case of those insects which live only for a few
+hours, and which never feed, a large part of their structure is merely the
+correlated result of successive changes in the structure of their larvæ.
+So, conversely, modifications in the adult will probably often affect the
+structure of the larva; but in all cases natural selection will ensure that
+modifications consequent on other modifications at a different period of
+life, shall not be in the least degree injurious: for if they became so,
+they would cause the extinction of the species.
+
+Natural selection will modify the structure of the {87} young in relation
+to the parent, and of the parent in relation to the young. In social
+animals it will adapt the structure of each individual for the benefit of
+the community; if each in consequence profits by the selected change. What
+natural selection cannot do, is to modify the structure of one species,
+without giving it any advantage, for the good of another species; and
+though statements to this effect may be found in works of natural history,
+I cannot find one case which will bear investigation. A structure used only
+once in an animal's whole life, if of high importance to it, might be
+modified to any extent by natural selection; for instance, the great jaws
+possessed by certain insects, used exclusively for opening the cocoon--or
+the hard tip to the beak of nestling birds, used for breaking the egg. It
+has been asserted, that of the best short-beaked tumbler-pigeons more
+perish in the egg than are able to get out of it; so that fanciers assist
+in the act of hatching. Now, if nature had to make the beak of a full-grown
+pigeon very short for the bird's own advantage, the process of modification
+would be very slow, and there would be simultaneously the most rigorous
+selection of the young birds within the egg, which had the most powerful
+and hardest beaks, for all with weak beaks would inevitably perish: or,
+more delicate and more easily broken shells might be selected, the
+thickness of the shell being known to vary like every other structure.
+
+
+
+_Sexual Selection._--Inasmuch as peculiarities often appear under
+domestication in one sex and become hereditarily attached to that sex, the
+same fact probably occurs under nature, and if so, natural selection will
+be able to modify one sex in its functional relations to the other sex, or
+in relation to wholly different habits of life in the two sexes, as is
+sometimes the case {88} with insects. And this leads me to say a few words
+on what I call Sexual Selection. This depends, not on a struggle for
+existence, but on a struggle between the males for possession of the
+females; the result is not death to the unsuccessful competitor, but few or
+no offspring. Sexual selection is, therefore, less rigorous than natural
+selection. Generally, the most vigorous males, those which are best fitted
+for their places in nature, will leave most progeny. But in many cases,
+victory depends not on general vigour, but on having special weapons,
+confined to the male sex. A hornless stag or spurless cock would have a
+poor chance of leaving offspring. Sexual selection by always allowing the
+victor to breed might surely give indomitable courage, length to the spur,
+and strength to the wing to strike in the spurred leg, as well as the
+brutal cock-fighter, who knows well that he can improve his breed by
+careful selection of the best cocks. How low in the scale of nature the law
+of battle descends, I know not; male alligators have been described as
+fighting, bellowing, and whirling round, like Indians in a war-dance, for
+the possession of the females; male salmons have been seen fighting all day
+long; male stag-beetles often bear wounds from the huge mandibles of other
+males. The war is, perhaps, severest between the males of polygamous
+animals, and these seem oftenest provided with special weapons. The males
+of carnivorous animals are already well armed; though to them and to
+others, special means of defence may be given through means of sexual
+selection, as the mane to the lion, the shoulder-pad to the boar, and the
+hooked jaw to the male salmon; for the shield may be as important for
+victory, as the sword or spear.
+
+Amongst birds, the contest is often of a more peaceful character. All those
+who have attended to the subject, {89} believe that there is the severest
+rivalry between the males of many species to attract by singing the
+females. The rock-thrush of Guiana, birds of Paradise, and some others,
+congregate; and successive males display their gorgeous plumage and perform
+strange antics before the females, which, standing by as spectators, at
+last choose the most attractive partner. Those who have closely attended to
+birds in confinement well know that they often take individual preferences
+and dislikes: thus Sir R. Heron has described how one pied peacock was
+eminently attractive to all his hen birds. It may appear childish to
+attribute any effect to such apparently weak means: I cannot here enter on
+the details necessary to support this view; but if man can in a short time
+give elegant carriage and beauty to his bantams, according to his standard
+of beauty, I can see no good reason to doubt that female birds, by
+selecting, during thousands of generations, the most melodious or beautiful
+males, according to their standard of beauty, might produce a marked
+effect. I strongly suspect that some well-known laws, with respect to the
+plumage of male and female birds, in comparison with the plumage of the
+young, can be explained on the view of plumage having been chiefly modified
+by sexual selection, acting when the birds have come to the breeding age or
+during the breeding season; the modifications thus produced being inherited
+at corresponding ages or seasons, either by the males alone, or by the
+males and females; but I have not space here to enter on this subject.
+
+Thus it is, as I believe, that when the males and females of any animal
+have the same general habits of life, but differ in structure, colour, or
+ornament, such differences have been mainly caused by sexual selection;
+that is, individual males have had, in successive generations, some slight
+advantage over other {90} males, in their weapons, means of defence, or
+charms; and have transmitted these advantages to their male offspring. Yet,
+I would not wish to attribute all such sexual differences to this agency:
+for we see peculiarities arising and becoming attached to the male sex in
+our domestic animals (as the wattle in male carriers, horn-like
+protuberances in the cocks of certain fowls, &c.), which we cannot believe
+to be either useful to the males in battle, or attractive to the females.
+We see analogous cases under nature, for instance, the tuft of hair on the
+breast of the turkey-cock, which can hardly be either useful or ornamental
+to this bird;--indeed, had the tuft appeared under domestication, it would
+have been called a monstrosity.
+
+
+
+_Illustrations of the action of Natural Selection._--In order to make it
+clear how, as I believe, natural selection acts, I must beg permission to
+give one or two imaginary illustrations. Let us take the case of a wolf,
+which preys on various animals, securing some by craft, some by strength,
+and some by fleetness; and let us suppose that the fleetest prey, a deer
+for instance, had from any change in the country increased in numbers, or
+that other prey had decreased in numbers, during that season of the year
+when the wolf is hardest pressed for food. I can under such circumstances
+see no reason to doubt that the swiftest and slimmest wolves would have the
+best chance of surviving, and so be preserved or selected,--provided always
+that they retained strength to master their prey at this or at some other
+period of the year, when they might be compelled to prey on other animals.
+I can see no more reason to doubt this, than that man can improve the
+fleetness of his greyhounds by careful and methodical selection, or by that
+unconscious selection which results from each man trying {91} to keep the
+best dogs without any thought of modifying the breed.
+
+Even without any change in the proportional numbers of the animals on which
+our wolf preyed, a cub might be born with an innate tendency to pursue
+certain kinds of prey. Nor can this be thought very improbable; for we
+often observe great differences in the natural tendencies of our domestic
+animals; one cat, for instance, taking to catch rats, another mice; one
+cat, according to Mr. St. John, bringing home winged game, another hares or
+rabbits, and another hunting on marshy ground and almost nightly catching
+woodcocks or snipes. The tendency to catch rats rather than mice is known
+to be inherited. Now, if any slight innate change of habit or of structure
+benefited an individual wolf, it would have the best chance of surviving
+and of leaving offspring. Some of its young would probably inherit the same
+habits or structure, and by the repetition of this process, a new variety
+might be formed which would either supplant or coexist with the parent form
+of wolf. Or, again, the wolves inhabiting a mountainous district, and those
+frequenting the lowlands, would naturally be forced to hunt different prey;
+and from the continued preservation of the individuals best fitted for the
+two sites, two varieties might slowly be formed. These varieties would
+cross and blend where they met; but to this subject of intercrossing we
+shall soon have to return. I may add, that, according to Mr. Pierce, there
+are two varieties of the wolf inhabiting the Catskill Mountains in the
+United States, one with a light greyhound-like form, which pursues deer,
+and the other more bulky, with shorter legs, which more frequently attacks
+the shepherd's flocks.
+
+Let us now take a more complex case. Certain plants excrete a sweet juice,
+apparently for the sake of eliminating something injurious from their sap:
+this is {92} effected by glands at the base of the stipules in some
+Leguminosæ, and at the back of the leaf of the common laurel. This juice,
+though small in quantity, is greedily sought by insects. Let us now suppose
+a little sweet juice or nectar to be excreted by the inner bases of the
+petals of a flower. In this case insects in seeking the nectar would get
+dusted with pollen, and would certainly often transport the pollen from one
+flower to the stigma of another flower. The flowers of two distinct
+individuals of the same species would thus get crossed; and the act of
+crossing, we have good reason to believe (as will hereafter be more fully
+alluded to), would produce very vigorous seedlings, which consequently
+would have the best chance of flourishing and surviving. Some of these
+seedlings would probably inherit the nectar-excreting power. Those
+individual flowers which had the largest glands or nectaries, and which
+excreted most nectar, would be oftenest visited by insects, and would be
+oftenest crossed; and so in the long-run would gain the upper hand. Those
+flowers, also, which had their stamens and pistils placed, in relation to
+the size and habits of the particular insects which visited them, so as to
+favour in any degree the transportal of their pollen from flower to flower,
+would likewise be favoured or selected. We might have taken the case of
+insects visiting flowers for the sake of collecting pollen instead of
+nectar; and as pollen is formed for the sole object of fertilisation, its
+destruction appears a simple loss to the plant; yet if a little pollen were
+carried, at first occasionally and then habitually, by the pollen-devouring
+insects from flower to flower, and a cross thus effected, although
+nine-tenths of the pollen were destroyed, it might still be a great gain to
+the plant; and those individuals which produced more and more pollen, and
+had larger and larger anthers, would be selected. {93}
+
+When our plant, by this process of the continued preservation or natural
+selection of more and more attractive flowers, had been rendered highly
+attractive to insects, they would, unintentionally on their part, regularly
+carry pollen from flower to flower; and that they can most effectually do
+this, I could easily show by many striking instances. I will give only
+one--not as a very striking case, but as likewise illustrating one step in
+the separation of the sexes of plants, presently to be alluded to. Some
+holly-trees bear only male flowers, which have four stamens producing a
+rather small quantity of pollen, and a rudimentary pistil; other
+holly-trees bear only female flowers; these have a full-sized pistil, and
+four stamens with shrivelled anthers, in which not a grain of pollen can be
+detected. Having found a female tree exactly sixty yards from a male tree,
+I put the stigmas of twenty flowers, taken from different branches, under
+the microscope, and on all, without exception, there were pollen-grains,
+and on some a profusion of pollen. As the wind had set for several days
+from the female to the male tree, the pollen could not thus have been
+carried. The weather had been cold and boisterous, and therefore not
+favourable to bees, nevertheless every female flower which I examined had
+been effectually fertilised by the bees, accidentally dusted with pollen,
+having flown from tree to tree in search of nectar. But to return to our
+imaginary case: as soon as the plant had been rendered so highly attractive
+to insects that pollen was regularly carried from flower to flower, another
+process might commence. No naturalist doubts the advantage of what has been
+called the "physiological division of labour;" hence we may believe that it
+would be advantageous to a plant to produce stamens alone in one flower or
+on one whole plant, and pistils alone in {94} another flower or on another
+plant. In plants under culture and placed under new conditions of life,
+sometimes the male organs and sometimes the female organs become more or
+less impotent; now if we suppose this to occur in ever so slight a degree
+under nature, then as pollen is already carried regularly from flower to
+flower, and as a more complete separation of the sexes of our plant would
+be advantageous on the principle of the division of labour, individuals
+with this tendency more and more increased, would be continually favoured
+or selected, until at last a complete separation of the sexes would be
+effected.
+
+Let us now turn to the nectar-feeding insects in our imaginary case: we may
+suppose the plant of which we have been slowly increasing the nectar by
+continued selection, to be a common plant; and that certain insects
+depended in main part on its nectar for food. I could give many facts,
+showing how anxious bees are to save time; for instance, their habit of
+cutting holes and sucking the nectar at the bases of certain flowers, which
+they can, with a very little more trouble, enter by the mouth. Bearing such
+facts in mind, I can see no reason to doubt that an accidental deviation in
+the size and form of the body, or in the curvature and length of the
+proboscis, &c., far too slight to be appreciated by us, might profit a bee
+or other insect, so that an individual so characterised would be able to
+obtain its food more quickly, and so have a better chance of living and
+leaving descendants. Its descendants would probably inherit a tendency to a
+similar slight deviation of structure. The tubes of the corollas of the
+common red and incarnate clovers (Trifolium pratense and incarnatum) do not
+on a hasty glance appear to differ in length; yet the hive-bee can easily
+suck the nectar out of the incarnate clover, but not out of the common red
+{95} clover, which is visited by humble-bees alone; so that whole fields of
+the red clover offer in vain an abundant supply of precious nectar to the
+hive-bee. Thus it might be a great advantage to the hive-bee to have a
+slightly longer or differently constructed proboscis. On the other hand, I
+have found by experiment that the fertility of clover depends on bees
+visiting and moving parts of the corolla, so as to push the pollen on to
+the stigmatic surface. Hence, again, if humble-bees were to become rare in
+any country, it might be a great advantage to the red clover to have a
+shorter or more deeply divided tube to its corolla, so that the hive-bee
+could visit its flowers. Thus I can understand how a flower and a bee might
+slowly become, either simultaneously or one after the other, modified and
+adapted in the most perfect manner to each other, by the continued
+preservation of individuals presenting mutual and slightly favourable
+deviations of structure.
+
+I am well aware that this doctrine of natural selection, exemplified in the
+above imaginary instances, is open to the same objections which were at
+first urged against Sir Charles Lyell's noble views on "the modern changes
+of the earth, as illustrative of geology;" but we now seldom hear the
+action, for instance, of the coast-waves, called a trifling and
+insignificant cause, when applied to the excavation of gigantic valleys or
+to the formation of the longest lines of inland cliffs. Natural selection
+can act only by the preservation and accumulation of infinitesimally small
+inherited modifications, each profitable to the preserved being; and as
+modern geology has almost banished such views as the excavation of a great
+valley by a single diluvial wave, so will natural selection, if it be a
+true principle, banish the belief of the continued creation of new organic
+{96} beings, or of any great and sudden modification in their structure.
+
+
+
+_On the Intercrossing of Individuals._--I must here introduce a short
+digression. In the case of animals and plants with separated sexes, it is
+of course obvious that two individuals must always (with the exception of
+the curious and not well-understood cases of parthenogenesis) unite for
+each birth; but in the case of hermaphrodites this is far from obvious.
+Nevertheless I am strongly inclined to believe that with all hermaphrodites
+two individuals, either occasionally or habitually, concur for the
+reproduction of their kind. This view was first suggested by Andrew Knight.
+We shall presently see its importance; but I must here treat the subject
+with extreme brevity, though I have the materials prepared for an ample
+discussion. All vertebrate animals, all insects, and some other large
+groups of animals, pair for each birth. Modern research has much diminished
+the number of supposed hermaphrodites, and of real hermaphrodites a large
+number pair; that is, two individuals regularly unite for reproduction,
+which is all that concerns us. But still there are many hermaphrodite
+animals which certainly do not habitually pair, and a vast majority of
+plants are hermaphrodites. What reason, it may be asked, is there for
+supposing in these cases that two individuals ever concur in reproduction?
+As it is impossible here to enter on details, I must trust to some general
+considerations alone.
+
+In the first place, I have collected so large a body of facts, showing, in
+accordance with the almost universal belief of breeders, that with animals
+and plants a cross between different varieties, or between individuals of
+the same variety but of another strain, gives vigour and {97} fertility to
+the offspring; and on the other hand, that _close_ interbreeding diminishes
+vigour and fertility; that these facts alone incline me to believe that it
+is a general law of nature (utterly ignorant though we be of the meaning of
+the law) that no organic being self-fertilises itself for an eternity of
+generations; but that a cross with another individual is
+occasionally--perhaps at very long intervals--indispensable.
+
+On the belief that this is a law of nature, we can, I think, understand
+several large classes of facts, such as the following, which on any other
+view are inexplicable. Every hybridizer knows how unfavourable exposure to
+wet is to the fertilisation of a flower, yet what a multitude of flowers
+have their anthers and stigmas fully exposed to the weather! but if an
+occasional cross be indispensable, the fullest freedom for the entrance of
+pollen from another individual will explain this state of exposure, more
+especially as the plant's own anthers and pistil generally stand so close
+together that self-fertilisation seems almost inevitable. Many flowers, on
+the other hand, have their organs of fructification closely enclosed, as in
+the great papilionaceous or pea-family; but in several, perhaps in all,
+such flowers, there is a very curious adaptation between the structure of
+the flower and the manner in which bees suck the nectar; for, in doing
+this, they either push the flower's own pollen on the stigma, or bring
+pollen from another flower. So necessary are the visits of bees to
+papilionaceous flowers, that I have found, by experiments published
+elsewhere, that their fertility is greatly diminished if these visits be
+prevented. Now, it is scarcely possible that bees should fly from flower to
+flower, and not carry pollen from one to the other, to the great good, as I
+believe, of the plant. Bees will act like a camel-hair pencil, and it is
+quite sufficient just to touch the anthers of {98} one flower and then the
+stigma of another with the same brush to ensure fertilisation; but it must
+not be supposed that bees would thus produce a multitude of hybrids between
+distinct species; for if you bring on the same brush a plant's own pollen
+and pollen from another species, the former will have such a prepotent
+effect, that it will invariably and completely destroy, as has been shown
+by Gärtner, any influence from the foreign pollen.
+
+When the stamens of a flower suddenly spring towards the pistil, or slowly
+move one after the other towards it, the contrivance seems adapted solely
+to ensure self-fertilisation; and no doubt it is useful for this end: but,
+the agency of insects is often required to cause the stamens to spring
+forward, as Kölreuter has shown to be the case with the barberry; and in
+this very genus, which seems to have a special contrivance for
+self-fertilisation, it is well known that if closely-allied forms or
+varieties are planted near each other, it is hardly possible to raise pure
+seedlings, so largely do they naturally cross. In many other cases, far
+from there being any aids for self-fertilisation, there are special
+contrivances, as I could show from the writings of C. C. Sprengel and from
+my own observations, which effectually prevent the stigma receiving pollen
+from its own flower: for instance, in Lobelia fulgens, there is a really
+beautiful and elaborate contrivance by which every one of the infinitely
+numerous pollen-granules are swept out of the conjoined anthers of each
+flower, before the stigma of that individual flower is ready to receive
+them; and as this flower is never visited, at least in my garden, by
+insects, it never sets a seed, though by placing pollen from one flower on
+the stigma of another, I raised plenty of seedlings; and whilst another
+species of Lobelia growing close by, which is visited by bees, seeds
+freely. In very many other cases, though there {99} be no special
+mechanical contrivance to prevent the stigma of a flower receiving its own
+pollen, yet, as C. C. Sprengel has shown, and as I can confirm, either the
+anthers burst before the stigma is ready for fertilisation, or the stigma
+is ready before the pollen of that flower is ready, so that these plants
+have in fact separated sexes, and must habitually be crossed. How strange
+are these facts! How strange that the pollen and stigmatic surface of the
+same flower, though placed so close together, as if for the very purpose of
+self-fertilisation, should in so many cases be mutually useless to each
+other! How simply are these facts explained on the view of an occasional
+cross with a distinct individual being advantageous or indispensable!
+
+If several varieties of the cabbage, radish, onion, and of some other
+plants, be allowed to seed near each other, a large majority, as I have
+found, of the seedlings thus raised will turn out mongrels: for instance, I
+raised 233 seedling cabbages from some plants of different varieties
+growing near each other, and of these only 78 were true to their kind, and
+some even of these were not perfectly true. Yet the pistil of each
+cabbage-flower is surrounded not only by its own six stamens, but by those
+of the many other flowers on the same plant. How, then, comes it that such
+a vast number of the seedlings are mongrelized? I suspect that it must
+arise from the pollen of a distinct _variety_ having a prepotent effect
+over a flower's own pollen; and that this is part of the general law of
+good being derived from the intercrossing of distinct individuals of the
+same species. When distinct _species_ are crossed the case is directly the
+reverse, for a plant's own pollen is always prepotent over foreign pollen;
+but to this subject we shall return in a future chapter.
+
+In the case of a gigantic tree covered with {100} innumerable flowers, it
+may be objected that pollen could seldom be carried from tree to tree, and
+at most only from flower to flower on the same tree, and that flowers on
+the same tree can be considered as distinct individuals only in a limited
+sense. I believe this objection to be valid, but that nature has largely
+provided against it by giving to trees a strong tendency to bear flowers
+with separated sexes. When the sexes are separated, although the male and
+female flowers may be produced on the same tree, we can see that pollen
+must be regularly carried from flower to flower; and this will give a
+better chance of pollen being occasionally carried from tree to tree. That
+trees belonging to all Orders have their sexes more often separated than
+other plants, I find to be the case in this country; and at my request Dr.
+Hooker tabulated the trees of New Zealand, and Dr. Asa Gray those of the
+United States, and the result was as I anticipated. On the other hand, Dr.
+Hooker has recently informed me that he finds that the rule does not hold
+in Australia; and I have made these few remarks on the sexes of trees
+simply to call attention to the subject.
+
+Turning for a very brief space to animals: on the land there are some
+hermaphrodites, as land-mollusca and earth-worms; but these all pair. As
+yet I have not found a single case of a terrestrial animal which fertilises
+itself. We can understand this remarkable fact, which offers so strong a
+contrast with terrestrial plants, on the view of an occasional cross being
+indispensable, by considering the medium in which terrestrial animals live,
+and the nature of the fertilising element; for we know of no means,
+analogous to the action of insects and of the wind in the case of plants,
+by which an occasional cross could be effected with terrestrial animals
+without the concurrence of two individuals. Of aquatic animals, there are
+many self-fertilising hermaphrodites; but here {101} currents in the water
+offer an obvious means for an occasional cross. And, as in the case of
+flowers, I have as yet failed, after consultation with one of the highest
+authorities, namely, Professor Huxley, to discover a single case of an
+hermaphrodite animal with the organs of reproduction so perfectly enclosed
+within the body, that access from without and the occasional influence of a
+distinct individual can be shown to be physically impossible. Cirripedes
+long appeared to me to present a case of very great difficulty under this
+point of view; but I have been enabled, by a fortunate chance, elsewhere to
+prove that two individuals, though both are self-fertilising
+hermaphrodites, do sometimes cross.
+
+It must have struck most naturalists as a strange anomaly that, in the case
+of both animals and plants, species of the same family and even of the same
+genus, though agreeing closely with each other in almost their whole
+organisation, yet are not rarely, some of them hermaphrodites, and some of
+them unisexual. But if, in fact, all hermaphrodites do occasionally
+intercross with other individuals, the difference between hermaphrodites
+and unisexual species, as far as function is concerned, becomes very small.
+
+From these several considerations and from the many special facts which I
+have collected, but which I am not here able to give, I am strongly
+inclined to suspect that, both in the vegetable and animal kingdoms, an
+occasional intercross with a distinct individual is a law of nature. I am
+well aware that there are, on this view, many cases of difficulty, some of
+which I am trying to investigate. Finally then, we may conclude that in
+many organic beings, a cross between two individuals is an obvious
+necessity for each birth; in many others it occurs perhaps only at long
+intervals; but in none, as I suspect, can self-fertilisation go on for
+perpetuity. {102}
+
+
+
+_Circumstances favourable to Natural Selection._--This is an extremely
+intricate subject. A large amount of inheritable and diversified
+variability is favourable, but I believe mere individual differences
+suffice for the work. A large number of individuals, by giving a better
+chance for the appearance within any given period of profitable variations,
+will compensate for a lesser amount of variability in each individual, and
+is, I believe, an extremely important element of success. Though nature
+grants vast periods of time for the work of natural selection, she does not
+grant an indefinite period; for as all organic beings are striving, it may
+be said, to seize on each place in the economy of nature, if any one
+species does not become modified and improved in a corresponding degree
+with its competitors, it will soon be exterminated.
+
+In man's methodical selection, a breeder selects for some definite object,
+and free intercrossing will wholly stop his work. But when many men,
+without intending to alter the breed, have a nearly common standard of
+perfection, and all try to get and breed from the best animals, much
+improvement and modification surely but slowly follow from this unconscious
+process of selection, notwithstanding a large amount of crossing with
+inferior animals. Thus it will be in nature; for within a confined area,
+with some place in its polity not so perfectly occupied as might be,
+natural selection will always tend to preserve all the individuals varying
+in the right direction, though in different degrees, so as better to fill
+up the unoccupied place. But if the area be large, its several districts
+will almost certainly present different conditions of life; and then if
+natural selection be modifying and improving a species in the several
+districts, there will be intercrossing with the other individuals of the
+same species on the confines of each. And in {103} this case the effects of
+intercrossing can hardly be counterbalanced by natural selection always
+tending to modify all the individuals in each district in exactly the same
+manner to the conditions of each; for in a continuous area, the physical
+conditions at least will generally graduate away insensibly from one
+district to another. The intercrossing will most affect those animals which
+unite for each birth, which wander much, and which do not breed at a very
+quick rate. Hence in animals of this nature, for instance in birds,
+varieties will generally be confined to separated countries; and this I
+believe to be the case. In hermaphrodite organisms which cross only
+occasionally, and likewise in animals which unite for each birth, but which
+wander little and which can increase at a very rapid rate, a new and
+improved variety might be quickly formed on any one spot, and might there
+maintain itself in a body, so that whatever intercrossing took place would
+be chiefly between the individuals of the same new variety. A local variety
+when once thus formed might subsequently slowly spread to other districts.
+On the above principle, nurserymen always prefer getting seed from a large
+body of plants of the same variety, as the chance of intercrossing with
+other varieties is thus lessened.
+
+Even in the case of slow-breeding animals, which unite for each birth, we
+must not overrate the effects of intercrosses in retarding natural
+selection; for I can bring a considerable catalogue of facts, showing that
+within the same area, varieties of the same animal can long remain
+distinct, from haunting different stations, from breeding at slightly
+different seasons, or from varieties of the same kind preferring to pair
+together.
+
+Intercrossing plays a very important part in nature in keeping the
+individuals of the same species, or of the same variety, true and uniform
+in character. It will {104} obviously thus act far more efficiently with
+those animals which unite for each birth; but I have already attempted to
+show that we have reason to believe that occasional intercrosses take place
+with all animals and with all plants. Even if these take place only at long
+intervals, I am convinced that the young thus produced will gain so much in
+vigour and fertility over the offspring from long-continued
+self-fertilisation, that they will have a better chance of surviving and
+propagating their kind; and thus, in the long run, the influence of
+intercrosses, even at rare intervals, will be great. If there exist organic
+beings which never intercross, uniformity of character can be retained
+amongst them, as long as their conditions of life remain the same, only
+through the principle of inheritance, and through natural selection
+destroying any which depart from the proper type; but if their conditions
+of life change and they undergo modification, uniformity of character can
+be given to their modified offspring, solely by natural selection
+preserving the same favourable variations.
+
+Isolation, also, is an important element in the process of natural
+selection. In a confined or isolated area, if not very large, the organic
+and inorganic conditions of life will generally be in a great degree
+uniform; so that natural selection will tend to modify all the individuals
+of a varying species throughout the area in the same manner in relation to
+the same conditions. Intercrosses, also, with the individuals of the same
+species, which otherwise would have inhabited the surrounding and
+differently circumstanced districts, will be prevented. But isolation
+probably acts more efficiently in checking the immigration of better
+adapted organisms, after any physical change, such as of climate or
+elevation of the land, &c.; and thus new places in the natural economy of
+the country are left open for the old inhabitants to struggle for, and
+become adapted to, through {105} modifications in their structure and
+constitution. Lastly, isolation, by checking immigration and consequently
+competition, will give time for any new variety to be slowly improved; and
+this may sometimes be of importance in the production of new species. If,
+however, an isolated area be very small, either from being surrounded by
+barriers, or from having very peculiar physical conditions, the total
+number of the individuals supported on it will necessarily be very small;
+and fewness of individuals will greatly retard the production of new
+species through natural selection, by decreasing the chance of the
+appearance of favourable variations.
+
+If we turn to nature to test the truth of these remarks, and look at any
+small isolated area, such as an oceanic island, although the total number
+of the species inhabiting it, will be found to be small, as we shall see in
+our chapter on geographical distribution; yet of these species a very large
+proportion are endemic,--that is, have been produced there, and nowhere
+else. Hence an oceanic island at first sight seems to have been highly
+favourable for the production of new species. But we may thus greatly
+deceive ourselves, for to ascertain whether a small isolated area, or a
+large open area like a continent, has been most favourable for the
+production of new organic forms, we ought to make the comparison within
+equal times; and this we are incapable of doing.
+
+Although I do not doubt that isolation is of considerable importance in the
+production of new species, on the whole I am inclined to believe that
+largeness of area is of more importance, more especially in the production
+of species, which will prove capable of enduring for a long period, and of
+spreading widely. Throughout a great and open area, not only will there be
+a better chance of favourable variations arising from the large number of
+individuals of the same species {106} there supported, but the conditions
+of life are infinitely complex from the large number of already existing
+species; and if some of these many species become modified and improved,
+others will have to be improved in a corresponding degree or they will be
+exterminated. Each new form, also, as soon as it has been much improved,
+will be able to spread over the open and continuous area, and will thus
+come into competition with many others. Hence more new places will be
+formed, and the competition to fill them will be more severe, on a large
+than on a small and isolated area. Moreover, great areas, though now
+continuous, owing to oscillations of level, will often have recently
+existed in a broken condition, so that the good effects of isolation will
+generally, to a certain extent, have concurred. Finally, I conclude that,
+although small isolated areas probably have been in some respects highly
+favourable for the production of new species, yet that the course of
+modification will generally have been more rapid on large areas; and what
+is more important, that the new forms produced on large areas, which
+already have been victorious over many competitors, will be those that will
+spread most widely, will give rise to most new varieties and species, and
+will thus play an important part in the changing history of the organic
+world.
+
+We can, perhaps, on these views, understand some facts which will be again
+alluded to in our chapter on geographical distribution; for instance, that
+the productions of the smaller continent of Australia have formerly
+yielded, and apparently are now yielding, before those of the larger
+Europæo-Asiatic area. Thus, also, it is that continental productions have
+everywhere become so largely naturalised on islands. On a small island, the
+race for life will have been less severe, and there will have been less
+modification and less {107} extermination. Hence, perhaps, it comes that
+the flora of Madeira, according to Oswald Heer, resembles the extinct
+tertiary flora of Europe. All fresh-water basins, taken together, make a
+small area compared with that of the sea or of the land; and, consequently,
+the competition between fresh-water productions will have been less severe
+than elsewhere; new forms will have been more slowly formed, and old forms
+more slowly exterminated. And it is in fresh water that we find seven
+genera of Ganoid fishes, remnants of a once preponderant order: and in
+fresh water we find some of the most anomalous forms now known in the
+world, as the Ornithorhynchus and Lepidosiren, which, like fossils, connect
+to a certain extent orders now widely separated in the natural scale. These
+anomalous forms may almost be called living fossils; they have endured to
+the present day, from having inhabited a confined area, and from having
+thus been exposed to less severe competition.
+
+To sum up the circumstances favourable and unfavourable to natural
+selection, as far as the extreme intricacy of the subject permits. I
+conclude, looking to the future, that for terrestrial productions a large
+continental area, which will probably undergo many oscillations of level,
+and which consequently will exist for long periods in a broken condition,
+is the most favourable for the production of many new forms of life, likely
+to endure long and to spread widely. For the area first existed as a
+continent, and the inhabitants, at this period numerous in individuals and
+kinds, will have been subjected to very severe competition. When converted
+by subsidence into large separate islands, there will still exist many
+individuals of the same species on each island: intercrossing on the
+confines of the range of each species will thus be checked: after physical
+changes of any kind, immigration will be {108} prevented, so that new
+places in the polity of each island will have to be filled up by
+modifications of the old inhabitants; and time will be allowed for the
+varieties in each to become well modified and perfected. When, by renewed
+elevation, the islands shall be re-converted into a continental area, there
+will again be severe competition: the most favoured or improved varieties
+will be enabled to spread: there will be much extinction of the less
+improved forms, and the relative proportional numbers of the various
+inhabitants of the renewed continent will again be changed; and again there
+will be a fair field for natural selection to improve still further the
+inhabitants, and thus produce new species.
+
+That natural selection will always act with extreme slowness, I fully
+admit. Its action depends on there being places in the polity of nature,
+which can be better occupied by some of the inhabitants of the country
+undergoing modification of some kind. The existence of such places will
+often depend on physical changes, which are generally very slow, and on the
+immigration of better adapted forms having been checked. But the action of
+natural selection will probably still oftener depend on some of the
+inhabitants becoming slowly modified; the mutual relations of many of the
+other inhabitants being thus disturbed. Nothing can be effected, unless
+favourable variations occur, and variation itself is apparently always a
+very slow process. The process will often be greatly retarded by free
+intercrossing. Many will exclaim that these several causes are amply
+sufficient wholly to stop the action of natural selection. I do not believe
+so. On the other hand, I do believe that natural selection always acts very
+slowly, often only at long intervals of time, and generally on only a very
+few of the inhabitants of the same region at the same time. I further
+believe, that this very slow, {109} intermittent action of natural
+selection accords perfectly well with what geology tells us of the rate and
+manner at which the inhabitants of this world have changed.
+
+Slow though the process of selection may be, if feeble man can do much by
+his powers of artificial selection, I can see no limit to the amount of
+change, to the beauty and infinite complexity of the coadaptations between
+all organic beings, one with another and with their physical conditions of
+life, which may be effected in the long course of time by nature's power of
+selection.
+
+
+
+_Extinction._--This subject will be more fully discussed in our chapter on
+Geology; but it must be here alluded to from being intimately connected
+with natural selection. Natural selection acts solely through the
+preservation of variations in some way advantageous, which consequently
+endure. But as from the high geometrical ratio of increase of all organic
+beings, each area is already fully stocked with inhabitants, it follows
+that as each selected and favoured form increases in number, so will the
+less favoured forms decrease and become rare. Rarity, as geology tells us,
+is the precursor to extinction. We can, also, see that any form represented
+by few individuals will, during fluctuations in the seasons or in the
+number of its enemies, run a good chance of utter extinction. But we may go
+further than this; for as new forms are continually and slowly being
+produced, unless we believe that the number of specific forms goes on
+perpetually and almost indefinitely increasing, numbers inevitably must
+become extinct. That the number of specific forms has not indefinitely
+increased, geology shows us plainly; and indeed we can see reason why they
+should not have thus increased, for the number of places in the polity of
+nature is not indefinitely great,--not that we {110} have any means of
+knowing that any one region has as yet got its maximum of species. Probably
+no region is as yet fully stocked, for at the Cape of Good Hope, where more
+species of plants are crowded together than in any other quarter of the
+world, some foreign plants have become naturalised, without causing, as far
+as we know, the extinction of any natives.
+
+Furthermore, the species which are most numerous in individuals will have
+the best chance of producing within any given period favourable variations.
+We have evidence of this, in the facts given in the second chapter, showing
+that it is the common species which afford the greatest number of recorded
+varieties, or incipient species. Hence, rare species will be less quickly
+modified or improved within any given period, and they will consequently be
+beaten in the race for life by the modified descendants of the commoner
+species.
+
+From these several considerations I think it inevitably follows, that as
+new species in the course of time are formed through natural selection,
+others will become rarer and rarer, and finally extinct. The forms which
+stand in closest competition with those undergoing modification and
+improvement, will naturally suffer most. And we have seen in the chapter on
+the Struggle for Existence that it is the most closely-allied
+forms,--varieties of the same species, and species of the same genus or of
+related genera,--which, from having nearly the same structure,
+constitution, and habits, generally come into the severest competition with
+each other. Consequently, each new variety or species, during the progress
+of its formation, will generally press hardest on its nearest kindred, and
+tend to exterminate them. We see the same process of extermination amongst
+our domesticated productions, through the selection of improved forms by
+man. Many curious {111} instances could be given showing how quickly new
+breeds of cattle, sheep, and other animals, and varieties of flowers, take
+the place of older and inferior kinds. In Yorkshire, it is historically
+known that the ancient black cattle were displaced by the long-horns, and
+that these "were swept away by the short-horns" (I quote the words of an
+agricultural writer) "as if by some murderous pestilence."
+
+
+
+_Divergence of Character._--The principle, which I have designated by this
+term, is of high importance on my theory, and explains, as I believe,
+several important facts. In the first place, varieties, even
+strongly-marked ones, though having somewhat of the character of
+species--as is shown by the hopeless doubts in many cases how to rank
+them--yet certainly differ from each other far less than do good and
+distinct species. Nevertheless, according to my view, varieties are species
+in the process of formation, or are, as I have called them, incipient
+species. How, then, does the lesser difference between varieties become
+augmented into the greater difference between species? That this does
+habitually happen, we must infer from most of the innumerable species
+throughout nature presenting well-marked differences; whereas varieties,
+the supposed prototypes and parents of future well-marked species, present
+slight and ill-defined differences. Mere chance, as we may call it, might
+cause one variety to differ in some character from its parents, and the
+offspring of this variety again to differ from its parent in the very same
+character and in a greater degree; but this alone would never account for
+so habitual and large an amount of difference as that between varieties of
+the same species and species of the same genus.
+
+As has always been my practice, let us seek light on {112} this head from
+our domestic productions. We shall here find something analogous. A fancier
+is struck by a pigeon having a slightly shorter beak; another fancier is
+struck by a pigeon having a rather longer beak; and on the acknowledged
+principle that "fanciers do not and will not admire a medium standard, but
+like extremes," they both go on (as has actually occurred with
+tumbler-pigeons) choosing and breeding from birds with longer and longer
+beaks, or with shorter and shorter beaks. Again, we may suppose that at an
+early period one man preferred swifter horses; another stronger and more
+bulky horses. The early differences would be very slight; in the course of
+time, from the continued selection of swifter horses by some breeders, and
+of stronger ones by others, the differences would become greater, and would
+be noted as forming two sub-breeds; finally, after the lapse of centuries,
+the sub-breeds would become converted into two well-established and
+distinct breeds. As the differences slowly become greater, the inferior
+animals with intermediate characters, being neither very swift nor very
+strong, will have been neglected, and will have tended to disappear. Here,
+then, we see in man's productions the action of what may be called the
+principle of divergence, causing differences, at first barely appreciable,
+steadily to increase, and the breeds to diverge in character both from each
+other and from their common parent.
+
+But how, it may be asked, can any analogous principle apply in nature? I
+believe it can and does apply most efficiently, from the simple
+circumstance that the more diversified the descendants from any one species
+become in structure, constitution, and habits, by so much will they be
+better enabled to seize on many and widely diversified places in the polity
+of nature, and so be enabled to increase in numbers. {113}
+
+We can clearly see this in the case of animals with simple habits. Take the
+case of a carnivorous quadruped, of which the number that can be supported
+in any country has long ago arrived at its full average. If its natural
+powers of increase be allowed to act, it can succeed in increasing (the
+country not undergoing any change in its conditions) only by its varying
+descendants seizing on places at present occupied by other animals: some of
+them, for instance, being enabled to feed on new kinds of prey, either dead
+or alive; some inhabiting new stations, climbing trees, frequenting water,
+and some perhaps becoming less carnivorous. The more diversified in habits
+and structure the descendants of our carnivorous animal became, the more
+places they would be enabled to occupy. What applies to one animal will
+apply throughout all time to all animals--that is, if they vary--for
+otherwise natural selection can do nothing. So it will be with plants. It
+has been experimentally proved, that if a plot of ground be sown with one
+species of grass, and a similar plot be sown with several distinct genera
+of grasses, a greater number of plants and a greater weight of dry herbage
+can thus be raised. The same has been found to hold good when first one
+variety and then several mixed varieties of wheat have been sown on equal
+spaces of ground. Hence, if any one species of grass were to go on varying,
+and those varieties were continually selected which differed from each
+other in at all the same manner as distinct species and genera of grasses
+differ from each other, a greater number of individual plants of this
+species of grass, including its modified descendants, would succeed in
+living on the same piece of ground. And we well know that each species and
+each variety of grass is annually sowing almost countless seeds; and thus,
+as it may be said, is striving its utmost to increase its numbers. {114}
+Consequently, I cannot doubt that in the course of many thousands of
+generations, the most distinct varieties of any one species of grass would
+always have the best chance of succeeding and of increasing in numbers, and
+thus of supplanting the less distinct varieties; and varieties, when
+rendered very distinct from each other, take the rank of species.
+
+The truth of the principle, that the greatest amount of life can be
+supported by great diversification of structure, is seen under many natural
+circumstances. In an extremely small area, especially if freely open to
+immigration, and where the contest between individual and individual must
+be severe, we always find great diversity in its inhabitants. For instance,
+I found that a piece of turf, three feet by four in size, which had been
+exposed for many years to exactly the same conditions, supported twenty
+species of plants, and these belonged to eighteen genera and to eight
+orders, which shows how much these plants differed from each other. So it
+is with the plants and insects on small and uniform islets; and so in small
+ponds of fresh water. Farmers find that they can raise most food by a
+rotation of plants belonging to the most different orders: nature follows
+what may be called a simultaneous rotation. Most of the animals and plants
+which live close round any small piece of ground, could live on it
+(supposing it not to be in any way peculiar in its nature), and may be said
+to be striving to the utmost to live there; but, it is seen, that where
+they come into the closest competition with each other, the advantages of
+diversification of structure, with the accompanying differences of habit
+and constitution, determine that the inhabitants, which thus jostle each
+other most closely, shall, as a general rule, belong to what we call
+different genera and orders.
+
+The same principle is seen in the naturalisation of {115} plants through
+man's agency in foreign lands. It might have been expected that the plants
+which have succeeded in becoming naturalised in any land would generally
+have been closely allied to the indigenes; for these are commonly looked at
+as specially created and adapted for their own country. It might, also,
+perhaps have been expected that naturalised plants would have belonged to a
+few groups more especially adapted to certain stations in their new homes.
+But the case is very different; and Alph. De Candolle has well remarked in
+his great and admirable work, that floras gain by naturalisation,
+proportionally with the number of the native genera and species, far more
+in new genera than in new species. To give a single instance: in the last
+edition of Dr. Asa Gray's 'Manual of the Flora of the Northern United
+States,' 260 naturalised plants are enumerated, and these belong to 162
+genera. We thus see that these naturalised plants are of a highly
+diversified nature. They differ, moreover, to a large extent from the
+indigenes, for out of the 162 genera, no less than 100 genera are not there
+indigenous, and thus a large proportional addition is made to the genera of
+these States.
+
+By considering the nature of the plants or animals which have struggled
+successfully with the indigenes of any country, and have there become
+naturalised, we may gain some crude idea in what manner some of the natives
+would have to be modified, in order to gain an advantage over the other
+natives; and we may at least safely infer that diversification of
+structure, amounting to new generic differences, would be profitable to
+them.
+
+The advantage of diversification in the inhabitants of the same region is,
+in fact, the same as that of the physiological division of labour in the
+organs of the same individual body--a subject so well elucidated by Milne
+{116} Edwards. No physiologist doubts that a stomach adapted to digest
+vegetable matter alone, or flesh alone, draws most nutriment from these
+substances. So in the general economy of any land, the more widely and
+perfectly the animals and plants are diversified for different habits of
+life, so will a greater number of individuals be capable of there
+supporting themselves. A set of animals, with their organisation but little
+diversified, could hardly compete with a set more perfectly diversified in
+structure. It may be doubted, for instance, whether the Australian
+marsupials, which are divided into groups differing but little from each
+other, and feebly representing, as Mr. Waterhouse and others have remarked,
+our carnivorous, ruminant, and rodent mammals, could successfully compete
+with these well-pronounced orders. In the Australian mammals, we see the
+process of diversification in an early and incomplete stage of development.
+
+After the foregoing discussion, which ought to have been much amplified, we
+may, I think, assume that the modified descendants of any one species will
+succeed by so much the better as they become more diversified in structure,
+and are thus enabled to encroach on places occupied by other beings. Now
+let us see how this principle of benefit being derived from divergence of
+character, combined with the principles of natural selection and of
+extinction, will tend to act.
+
+The accompanying diagram will aid us in understanding this rather
+perplexing subject. Let A to L represent the species of a genus large in
+its own country; these species are supposed to resemble each other in
+unequal degrees, as is so generally the case in nature, and as is
+represented in the diagram by the letters standing at unequal distances. I
+have said a large genus, because we have seen in the second chapter, {117}
+that on an average more of the species of large genera vary than of small
+genera; and the varying species of the large genera present a greater
+number of varieties. We have, also, seen that the species, which are the
+commonest and the most widely-diffused, vary more than rare species with
+restricted ranges. Let (A) be a common, widely-diffused, and varying
+species, belonging to a genus large in its own country. The little fan of
+diverging dotted lines of unequal lengths proceeding from (A), may
+represent its varying offspring. The variations are supposed to be
+extremely slight, but of the most diversified nature; they are not supposed
+all to appear simultaneously, but often after long intervals of time; nor
+are they all supposed to endure for equal periods. Only those variations
+which are in some way profitable will be preserved or naturally selected.
+And here the importance of the principle of benefit being derived from
+divergence of character comes in; for this will generally lead to the most
+different or divergent variations (represented by the outer dotted lines)
+being preserved and accumulated by natural selection. When a dotted line
+reaches one of the horizontal lines, and is there marked by a small
+numbered letter, a sufficient amount of variation is supposed to have been
+accumulated to have formed a fairly well-marked variety, such as would be
+thought worthy of record in a systematic work.
+
+[Illustration]
+
+The intervals between the horizontal lines in the diagram, may represent
+each a thousand generations; but it would have been better if each had
+represented ten thousand generations. After a thousand generations, species
+(A) is supposed to have produced two fairly well-marked varieties, namely
+a^1 and m^1. These two varieties will generally continue to be exposed to
+the same conditions which made their parents variable, {118} and the
+tendency to variability is in itself hereditary, consequently they will
+tend to vary, and generally to vary in nearly the same manner as their
+parents varied. Moreover, these two varieties, being only slightly modified
+forms, will tend to inherit those advantages which made their parent (A)
+more numerous than most of the other inhabitants of the same country; they
+will likewise partake of those more general advantages which made the genus
+to which the parent-species belonged, a large genus in its own country. And
+these circumstances we know to be favourable to the production of new
+varieties.
+
+If, then, these two varieties be variable, the most divergent of their
+variations will generally be preserved during the next thousand
+generations. And after this interval, variety a^1 is supposed in the
+diagram to have produced variety a^2, which will, owing to the principle of
+divergence, differ more from (A) than did variety a^1. Variety m^1 is
+supposed to have produced two varieties, namely m^2 and s^2, differing from
+each other, and more considerably from their common parent (A). We may
+continue the process by similar steps for any length of time; some of the
+varieties, after each thousand generations, producing only a single
+variety, but in a more and more modified condition, some producing two or
+three varieties, and some failing to produce any. Thus the varieties or
+modified descendants, proceeding from the common parent (A), will generally
+go on increasing in number and diverging in character. In the diagram the
+process is represented up to the ten-thousandth generation, and under a
+condensed and simplified form up to the fourteen-thousandth generation.
+
+But I must here remark that I do not suppose that the process ever goes on
+so regularly as is represented in the diagram, though in itself made
+somewhat irregular. {119} I am far from thinking that the most divergent
+varieties will invariably prevail and multiply: a medium form may often
+long endure, and may or may not produce more than one modified descendant;
+for natural selection will always act according to the nature of the places
+which are either unoccupied or not perfectly occupied by other beings; and
+this will depend on infinitely complex relations. But as a general rule,
+the more diversified in structure the descendants from any one species can
+be rendered, the more places they will be enabled to seize on, and the more
+their modified progeny will be increased. In our diagram the line of
+succession is broken at regular intervals by small numbered letters marking
+the successive forms which have become sufficiently distinct to be recorded
+as varieties. But these breaks are imaginary, and might have been inserted
+anywhere, after intervals long enough to have allowed the accumulation of a
+considerable amount of divergent variation.
+
+As all the modified descendants from a common and widely-diffused species,
+belonging to a large genus, will tend to partake of the same advantages
+which made their parent successful in life, they will generally go on
+multiplying in number as well as diverging in character: this is
+represented in the diagram by the several divergent branches proceeding
+from (A). The modified offspring from the later and more highly improved
+branches in the lines of descent, will, it is probable, often take the
+place of, and so destroy, the earlier and less improved branches: this is
+represented in the diagram by some of the lower branches not reaching to
+the upper horizontal lines. In some cases I do not doubt that the process
+of modification will be confined to a single line of descent, and the
+number of the descendants will not be increased; although the amount {120}
+of divergent modification may have been increased in the successive
+generations. This case would be represented in the diagram, if all the
+lines proceeding from (A) were removed, excepting that from a^1 to a^{10}.
+In the same way, for instance, the English race-horse and English pointer
+have apparently both gone on slowly diverging in character from their
+original stocks, without either having given off any fresh branches or
+races.
+
+After ten thousand generations, species (A) is supposed to have produced
+three forms, a^{10}, f^{10}, and m^{10}, which, from having diverged in
+character during the successive generations, will have come to differ
+largely, but perhaps unequally, from each other and from their common
+parent. If we suppose the amount of change between each horizontal line in
+our diagram to be excessively small, these three forms may still be only
+well-marked varieties; or they may have arrived at the doubtful category of
+sub-species; but we have only to suppose the steps in the process of
+modification to be more numerous or greater in amount, to convert these
+three forms into well-defined species: thus the diagram illustrates the
+steps by which the small differences distinguishing varieties are increased
+into the larger differences distinguishing species. By continuing the same
+process for a greater number of generations (as shown in the diagram in a
+condensed and simplified manner), we get eight species, marked by the
+letters between a^{14} and m^{14}, all descended from (A). Thus, as I
+believe, species are multiplied and genera are formed.
+
+In a large genus it is probable that more than one species would vary. In
+the diagram I have assumed that a second species (I) has produced, by
+analogous steps, after ten thousand generations, either two well-marked
+varieties (w^{10} and z^{10}) or two species, according to the amount of
+change supposed to be represented {121} between the horizontal lines. After
+fourteen thousand generations, six new species, marked by the letters
+n^{14} to z^{14}, are supposed to have been produced. In each genus, the
+species, which are already extremely different in character, will generally
+tend to produce the greatest number of modified descendants; for these will
+have the best chance of filling new and widely different places in the
+polity of nature: hence in the diagram I have chosen the extreme species
+(A), and the nearly extreme species (I), as those which have largely
+varied, and have given rise to new varieties and species. The other nine
+species (marked by capital letters) of our original genus, may for a long
+period continue to transmit unaltered descendants; and this is shown in the
+diagram by the dotted lines not prolonged far upwards from want of space.
+
+But during the process of modification, represented in the diagram, another
+of our principles, namely that of extinction, will have played an important
+part. As in each fully stocked country natural selection necessarily acts
+by the selected form having some advantage in the struggle for life over
+other forms, there will be a constant tendency in the improved descendants
+of any one species to supplant and exterminate in each stage of descent
+their predecessors and their original parent. For it should be remembered
+that the competition will generally be most severe between those forms
+which are most nearly related to each other in habits, constitution, and
+structure. Hence all the intermediate forms between the earlier and later
+states, that is between the less and more improved state of a species, as
+well as the original parent-species itself, will generally tend to become
+extinct. So it probably will be with many whole collateral lines of
+descent, which will be conquered by later and improved lines of descent.
+If, however, the {122} modified offspring of a species get into some
+distinct country, or become quickly adapted to some quite new station, in
+which child and parent do not come into competition, both may continue to
+exist.
+
+If then our diagram be assumed to represent a considerable amount of
+modification, species (A) and all the earlier varieties will have become
+extinct, having been replaced by eight new species (a^{14} to m^{14}); and
+(I) will have been replaced by six (n^{14} to z^{14}) new species.
+
+But we may go further than this. The original species of our genus were
+supposed to resemble each other in unequal degrees, as is so generally the
+case in nature; species (A) being more nearly related to B, C, and D, than
+to the other species; and species (I) more to G, H, K, L, than to the
+others. These two species (A) and (I), were also supposed to be very common
+and widely diffused species, so that they must originally have had some
+advantage over most of the other species of the genus. Their modified
+descendants, fourteen in number at the fourteen-thousandth generation, will
+probably have inherited some of the same advantages: they have also been
+modified and improved in a diversified manner at each stage of descent, so
+as to have become adapted to many related places in the natural economy of
+their country. It seems, therefore, to me extremely probable that they will
+have taken the places of, and thus exterminated, not only their parents (A)
+and (I), but likewise some of the original species which were most nearly
+related to their parents. Hence very few of the original species will have
+transmitted offspring to the fourteen-thousandth generation. We may suppose
+that only one (F), of the two species which were least closely related to
+the other nine original species, has transmitted descendants to this late
+stage of descent. {123}
+
+The new species in our diagram descended from the original eleven species,
+will now be fifteen in number. Owing to the divergent tendency of natural
+selection, the extreme amount of difference in character between species
+a^{14} and z^{14} will be much greater than that between the most different
+of the original eleven species. The new species, moreover, will be allied
+to each other in a widely different manner. Of the eight descendants from
+(A) the three marked a^{14}, q^{14}, p^{14}, will be nearly related from
+having recently branched off from a^{10}; b^{14} and f^{14}, from having
+diverged at an earlier period from a^5, will be in some degree distinct
+from the three first-named species; and lastly, o^{14}, e^{14} and m^{14},
+will be nearly related one to the other, but from having diverged at the
+first commencement of the process of modification, will be widely different
+from the other five species, and may constitute a sub-genus or even a
+distinct genus.
+
+The six descendants from (I) will form two sub-genera or even genera. But
+as the original species (I) differed largely from (A), standing nearly at
+the extreme points of the original genus, the six descendants from (I)
+will, owing to inheritance alone, differ considerably from the eight
+descendants from (A); the two groups, moreover, are supposed to have gone
+on diverging in different directions. The intermediate species, also (and
+this is a very important consideration), which connected the original
+species (A) and (I), have all become, excepting (F), extinct, and have left
+no descendants. Hence the six new species descended from (I), and the eight
+descended from (A), will have to be ranked as very distinct genera, or even
+as distinct sub-families.
+
+Thus it is, as I believe, that two or more genera are produced by descent
+with modification, from two or more species of the same genus. And the two
+or {124} more parent-species are supposed to have descended from some one
+species of an earlier genus. In our diagram, this is indicated by the
+broken lines, beneath the capital letters, converging in sub-branches
+downwards towards a single point; this point representing a single species,
+the supposed single parent of our several new sub-genera and genera.
+
+It is worth while to reflect for a moment on the character of the new
+species F^{14}, which is supposed not to have diverged much in character,
+but to have retained the form of (F), either unaltered or altered only in a
+slight degree. In this case, its affinities to the other fourteen new
+species will be of a curious and circuitous nature. Having descended from a
+form which stood between the two parent-species (A) and (I), now supposed
+to be extinct and unknown, it will be in some degree intermediate in
+character between the two groups descended from these species. But as these
+two groups have gone on diverging in character from the type of their
+parents, the new species (F^{14}) will not be directly intermediate between
+them, but rather between types of the two groups; and every naturalist will
+be able to bring some such case before his mind.
+
+In the diagram, each horizontal line has hitherto been supposed to
+represent a thousand generations, but each may represent a million or
+hundred million generations, and likewise a section of the successive
+strata of the earth's crust including extinct remains. We shall, when we
+come to our chapter on Geology, have to refer again to this subject, and I
+think we shall then see that the diagram throws light on the affinities of
+extinct beings, which, though generally belonging to the same orders, or
+families, or genera, with those now living, yet are often, in some degree,
+intermediate in character between existing groups; and we can understand
+this fact, for {125} the extinct species lived at very ancient epochs when
+the branching lines of descent had diverged less.
+
+I see no reason to limit the process of modification, as now explained, to
+the formation of genera alone. If, in our diagram, we suppose the amount of
+change represented by each successive group of diverging dotted lines to be
+very great, the forms marked a^{14} to p^{14}, those marked b^{14} and
+f^{14}, and those marked o^{14} to m^{14}, will form three very distinct
+genera. We shall also have two very distinct genera descended from (I); and
+as these latter two genera, both from continued divergence of character and
+from inheritance from a different parent, will differ widely from the three
+genera descended from (A), the two little groups of genera will form two
+distinct families, or even orders, according to the amount of divergent
+modification supposed to be represented in the diagram. And the two new
+families, or orders, will have descended from two species of the original
+genus; and these two species are supposed to have descended from one
+species of a still more ancient and unknown genus.
+
+We have seen that in each country it is the species of the larger genera
+which oftenest present varieties or incipient species. This, indeed, might
+have been expected; for as natural selection acts through one form having
+some advantage over other forms in the struggle for existence, it will
+chiefly act on those which already have some advantage; and the largeness
+of any group shows that its species have inherited from a common ancestor
+some advantage in common. Hence, the struggle for the production of new and
+modified descendants, will mainly lie between the larger groups, which are
+all trying to increase in number. One large group will slowly conquer
+another large group, reduce its numbers, and thus lessen its chance of
+further variation and improvement. Within the same large {126} group, the
+later and more highly perfected sub-groups, from branching out and seizing
+on many new places in the polity of Nature, will constantly tend to
+supplant and destroy the earlier and less improved sub-groups. Small and
+broken groups and sub-groups will finally disappear. Looking to the future,
+we can predict that the groups of organic beings which are now large and
+triumphant, and which are least broken up, that is, which as yet have
+suffered least extinction, will for a long period continue to increase. But
+which groups will ultimately prevail, no man can predict; for we well know
+that many groups, formerly most extensively developed, have now become
+extinct. Looking still more remotely to the future, we may predict that,
+owing to the continued and steady increase of the larger groups, a
+multitude of smaller groups will become utterly extinct, and leave no
+modified descendants; and consequently that of the species living at any
+one period, extremely few will transmit descendants to a remote futurity. I
+shall have to return to this subject in the chapter on Classification, but
+I may add that on this view of extremely few of the more ancient species
+having transmitted descendants, and on the view of all the descendants of
+the same species making a class, we can understand how it is that there
+exist but very few classes in each main division of the animal and
+vegetable kingdoms. Although extremely few of the most ancient species may
+now have living and modified descendants, yet at the most remote geological
+period, the earth may have been as well peopled with many species of many
+genera, families, orders, and classes, as at the present day.
+
+
+
+_Summary of Chapter._--If during the long course of ages and under varying
+conditions of life, organic beings {127} vary at all in the several parts
+of their organisation, and I think this cannot be disputed; if there be,
+owing to the high geometrical ratio of increase of each species, a severe
+struggle for life at some age, season, or year, and this certainly cannot
+be disputed; then, considering the infinite complexity of the relations of
+all organic beings to each other and to their conditions of existence,
+causing an infinite diversity in structure, constitution, and habits, to be
+advantageous to them, I think it would be a most extraordinary fact if no
+variation ever had occurred useful to each being's own welfare, in the same
+manner as so many variations have occurred useful to man. But if variations
+useful to any organic being do occur, assuredly individuals thus
+characterised will have the best chance of being preserved in the struggle
+for life; and from the strong principle of inheritance they will tend to
+produce offspring similarly characterised. This principle of preservation,
+I have called, for the sake of brevity, Natural Selection; and it leads to
+the improvement of each creature in relation to its organic and inorganic
+conditions of life.
+
+Natural selection, on the principle of qualities being inherited at
+corresponding ages, can modify the egg, seed, or young, as easily as the
+adult. Amongst many animals, sexual selection will give its aid to ordinary
+selection, by assuring to the most vigorous and best adapted males the
+greatest number of offspring. Sexual selection will also give characters
+useful to the males alone, in their struggles with other males.
+
+Whether natural selection has really thus acted in nature, in modifying and
+adapting the various forms of life to their several conditions and
+stations, must be judged of by the general tenour and balance of evidence
+given in the following chapters. But we already see how it entails
+extinction; and how largely extinction {128} has acted in the world's
+history, geology plainly declares. Natural selection, also, leads to
+divergence of character; for more living beings can be supported on the
+same area the more they diverge in structure, habits, and constitution, of
+which we see proof by looking to the inhabitants of any small spot or to
+naturalised productions. Therefore during the modification of the
+descendants of any one species, and during the incessant struggle of all
+species to increase in numbers, the more diversified these descendants
+become, the better will be their chance of succeeding in the battle for
+life. Thus the small differences distinguishing varieties of the same
+species, steadily tend to increase till they come to equal the greater
+differences between species of the same genus, or even of distinct genera.
+
+We have seen that it is the common, the widely-diffused, and widely-ranging
+species, belonging to the larger genera, which vary most; and these tend to
+transmit to their modified offspring that superiority which now makes them
+dominant in their own countries. Natural selection, as has just been
+remarked, leads to divergence of character and to much extinction of the
+less improved and intermediate forms of life. On these principles, I
+believe, the nature of the affinities of all organic beings may be
+explained. It is a truly wonderful fact--the wonder of which we are apt to
+overlook from familiarity--that all animals and all plants throughout all
+time and space should be related to each other in group subordinate to
+group, in the manner which we everywhere behold--namely, varieties of the
+same species most closely related together, species of the same genus less
+closely and unequally related together, forming sections and sub-genera,
+species of distinct genera much less closely related, and genera related in
+different degrees, forming {129} sub-families, families, orders,
+sub-classes, and classes. The several subordinate groups in any class
+cannot be ranked in a single file, but seem rather to be clustered round
+points, and these round other points, and so on in almost endless cycles.
+On the view that each species has been independently created, I can see no
+explanation of this great fact in the classification of all organic beings;
+but, to the best of my judgment, it is explained through inheritance and
+the complex action of natural selection, entailing extinction and
+divergence of character, as we have seen illustrated in the diagram.
+
+The affinities of all the beings of the same class have sometimes been
+represented by a great tree. I believe this simile largely speaks the
+truth. The green and budding twigs may represent existing species; and
+those produced during each former year may represent the long succession of
+extinct species. At each period of growth all the growing twigs have tried
+to branch out on all sides, and to overtop and kill the surrounding twigs
+and branches, in the same manner as species and groups of species have
+tried to overmaster other species in the great battle for life. The limbs
+divided into great branches, and these into lesser and lesser branches,
+were themselves once, when the tree was small, budding twigs; and this
+connexion of the former and present buds by ramifying branches may well
+represent the classification of all extinct and living species in groups
+subordinate to groups. Of the many twigs which flourished when the tree was
+a mere bush, only two or three, now grown into great branches, yet survive
+and bear all the other branches; so with the species which lived during
+long-past geological periods, very few now have living and modified
+descendants. From the first growth of the tree, many a limb and branch has
+decayed and dropped off; and these lost branches of various {130} sizes may
+represent those whole orders, families, and genera which have now no living
+representatives, and which are known to us only from having been found in a
+fossil state. As we here and there see a thin straggling branch springing
+from a fork low down in a tree, and which by some chance has been favoured
+and is still alive on its summit, so we occasionally see an animal like the
+Ornithorhynchus or Lepidosiren, which in some small degree connects by its
+affinities two large branches of life, and which has apparently been saved
+from fatal competition by having inhabited a protected station. As buds
+give rise by growth to fresh buds, and these, if vigorous, branch out and
+overtop on all sides many a feebler branch, so by generation I believe it
+has been with the great Tree of Life, which fills with its dead and broken
+branches the crust of the earth, and covers the surface with its ever
+branching and beautiful ramifications.
+
+       *       *       *       *       *
+
+
+{131}
+
+CHAPTER V.
+
+LAWS OF VARIATION.
+
+    Effects of external conditions--Use and disuse, combined with natural
+    selection; organs of flight and of vision--Acclimatisation--Correlation
+    of growth--Compensation and economy of growth--False
+    correlations--Multiple, rudimentary, and lowly organised structures
+    variable--Parts developed in an unusual manner are highly variable:
+    specific characters more variable than generic: secondary sexual
+    characters variable--Species of the same genus vary in an analogous
+    manner--Reversions to long-lost characters--Summary.
+
+I have hitherto sometimes spoken as if the variations--so common and
+multiform in organic beings under domestication, and in a lesser degree in
+those in a state of nature--had been due to chance. This, of course, is a
+wholly incorrect expression, but it serves to acknowledge plainly our
+ignorance of the cause of each particular variation. Some authors believe
+it to be as much the function of the reproductive system to produce
+individual differences, or very slight deviations of structure, as to make
+the child like its parents. But the much greater variability, as well as
+the greater frequency of monstrosities, under domestication or cultivation,
+than under nature, leads me to believe that deviations of structure are in
+some way due to the nature of the conditions of life, to which the parents
+and their more remote ancestors have been exposed during several
+generations. I have remarked in the first chapter--but a long catalogue of
+facts which cannot be here given would be necessary to show the truth of
+the remark--that the reproductive system is eminently susceptible to
+changes in the conditions of life; and to {132} this system being
+functionally disturbed in the parents, I chiefly attribute the varying or
+plastic condition of the offspring. The male and female sexual elements
+seem to be affected before that union takes place which is to form a new
+being. In the case of "sporting" plants, the bud, which in its earliest
+condition does not apparently differ essentially from an ovule, is alone
+affected. But why, because the reproductive system is disturbed, this or
+that part should vary more or less, we are profoundly ignorant.
+Nevertheless, we can here and there dimly catch a faint ray of light, and
+we may feel sure that there must be some cause for each deviation of
+structure, however slight.
+
+How much direct effect difference of climate, food, &c., produces on any
+being is extremely doubtful. My impression is, that the effect is extremely
+small in the case of animals, but perhaps rather more in that of plants. We
+may, at least, safely conclude that such influences cannot have produced
+the many striking and complex co-adaptations of structure between one
+organic being and another, which we see everywhere throughout nature. Some
+little influence may be attributed to climate, food, &c.: thus, E. Forbes
+speaks confidently that shells at their southern limit, and when living in
+shallow water, are more brightly coloured than those of the same species
+further north or from greater depths. Gould believes that birds of the same
+species are more brightly coloured under a clear atmosphere, than when
+living on islands or near the coast. So with insects, Wollaston is
+convinced that residence near the sea affects their colours. Moquin-Tandon
+gives a list of plants which when growing near the sea-shore have their
+leaves in some degree fleshy, though not elsewhere fleshy. Several other
+such cases could be given.
+
+The fact of varieties of one species, when they range {133} into the zone
+of habitation of other species, often acquiring in a very slight degree
+some of the characters of such species, accords with our view that species
+of all kinds are only well-marked and permanent varieties. Thus the species
+of shells which are confined to tropical and shallow seas are generally
+brighter-coloured than those confined to cold and deeper seas. The birds
+which are confined to continents are, according to Mr. Gould,
+brighter-coloured than those of islands. The insect-species confined to
+sea-coasts, as every collector knows, are often brassy or lurid. Plants
+which live exclusively on the sea-side are very apt to have fleshy leaves.
+He who believes in the creation of each species, will have to say that this
+shell, for instance, was created with bright colours for a warm sea; but
+that this other shell became bright-coloured by variation when it ranged
+into warmer or shallower waters.
+
+When a variation is of the slightest use to a being, we cannot tell how
+much of it to attribute to the accumulative action of natural selection,
+and how much to the conditions of life. Thus, it is well known to furriers
+that animals of the same species have thicker and better fur the more
+severe the climate is under which they have lived; but who can tell how
+much of this difference may be due to the warmest-clad individuals having
+been favoured and preserved during many generations, and how much to the
+direct action of the severe climate? for it would appear that climate has
+some direct action on the hair of our domestic quadrupeds.
+
+Instances could be given of the same variety being produced under
+conditions of life as different as can well be conceived; and, on the other
+hand, of different varieties being produced from the same species under the
+same conditions. Such facts show how indirectly {134} the conditions of
+life act. Again, innumerable instances are known to every naturalist of
+species keeping true, or not varying at all, although living under the most
+opposite climates. Such considerations as these incline me to lay very
+little weight on the direct action of the conditions of life. Indirectly,
+as already remarked, they seem to play an important part in affecting the
+reproductive system, and in thus inducing variability; and natural
+selection will then accumulate all profitable variations, however slight,
+until they become plainly developed and appreciable by us.
+
+
+
+_Effects of Use and Disuse._--From the facts alluded to in the first
+chapter, I think there can be little doubt that use in our domestic animals
+strengthens and enlarges certain parts, and disuse diminishes them; and
+that such modifications are inherited. Under free nature, we can have no
+standard of comparison, by which to judge of the effects of long-continued
+use or disuse, for we know not the parent-forms; but many animals have
+structures which can be explained by the effects of disuse. As Professor
+Owen has remarked, there is no greater anomaly in nature than a bird that
+cannot fly; yet there are several in this state. The logger-headed duck of
+South America can only flap along the surface of the water, and has its
+wings in nearly the same condition as the domestic Aylesbury duck. As the
+larger ground-feeding birds seldom take flight except to escape danger, I
+believe that the nearly wingless condition of several birds, which now
+inhabit or have lately inhabited several oceanic islands, tenanted by no
+beast of prey, has been caused by disuse. The ostrich indeed inhabits
+continents and is exposed to danger from which it cannot escape by flight,
+but by kicking it can defend itself from enemies, as well as any of the
+smaller {135} quadrupeds. We may imagine that the early progenitor of the
+ostrich had habits like those of a bustard, and that as natural selection
+increased in successive generations the size and weight of its body, its
+legs were used more, and its wings less, until they became incapable of
+flight.
+
+Kirby has remarked (and I have observed the same fact) that the anterior
+tarsi, or feet, of many male dung-feeding beetles are very often broken
+off; he examined seventeen specimens in his own collection, and not one had
+even a relic left. In the Onites apelles the tarsi are so habitually lost,
+that the insect has been described as not having them. In some other genera
+they are present, but in a rudimentary condition. In the Ateuchus or sacred
+beetle of the Egyptians, they are totally deficient. There is not
+sufficient evidence to induce me to believe that mutilations are ever
+inherited; and I should prefer explaining the entire absence of the
+anterior tarsi in Ateuchus, and their rudimentary condition in some other
+genera, by the long-continued effects of disuse in their progenitors; for
+as the tarsi are almost always lost in many dung-feeding beetles, they must
+be lost early in life, and therefore cannot be much used by these insects.
+
+In some cases we might easily put down to disuse modifications of structure
+which are wholly, or mainly, due to natural selection. Mr. Wollaston has
+discovered the remarkable fact that 200 beetles, out of the 550 species
+inhabiting Madeira, are so far deficient in wings that they cannot fly; and
+that of the twenty-nine endemic genera, no less than twenty-three genera
+have all their species in this condition! Several facts, namely, that
+beetles in many parts of the world are frequently blown to sea and perish;
+that the beetles in Madeira, as observed by Mr. Wollaston, lie much
+concealed, {136} until the wind lulls and the sun shines; that the
+proportion of wingless beetles is larger on the exposed Desertas than in
+Madeira itself; and especially the extraordinary fact, so strongly insisted
+on by Mr. Wollaston, of the almost entire absence of certain large groups
+of beetles, elsewhere excessively numerous, and which groups have habits of
+life almost necessitating frequent flight;--these several considerations
+have made me believe that the wingless condition of so many Madeira beetles
+is mainly due to the action of natural selection, but combined probably
+with disuse. For during thousands of successive generations each individual
+beetle which flew least, either from its wings having been ever so little
+less perfectly developed or from indolent habit, will have had the best
+chance of surviving from not being blown out to sea; and, on the other
+hand, those beetles which most readily took to flight would oftenest have
+been blown to sea and thus have been destroyed.
+
+The insects in Madeira which are not ground-feeders, and which, as the
+flower-feeding coleoptera and lepidoptera, must habitually use their wings
+to gain their subsistence, have, as Mr. Wollaston suspects, their wings not
+at all reduced, but even enlarged. This is quite compatible with the action
+of natural selection. For when a new insect first arrived on the island,
+the tendency of natural selection to enlarge or to reduce the wings, would
+depend on whether a greater number of individuals were saved by
+successfully battling with the winds, or by giving up the attempt and
+rarely or never flying. As with mariners shipwrecked near a coast, it would
+have been better for the good swimmers if they had been able to swim still
+further, whereas it would have been better for the bad swimmers if they had
+not been able to swim at all and had stuck to the wreck. {137}
+
+The eyes of moles and of some burrowing rodents are rudimentary in size,
+and in some cases are quite covered up by skin and fur. This state of the
+eyes is probably due to gradual reduction from disuse, but aided perhaps by
+natural selection. In South America, a burrowing rodent, the tuco-tuco, or
+Ctenomys, is even more subterranean in its habits than the mole; and I was
+assured by a Spaniard, who had often caught them, that they were frequently
+blind; one which I kept alive was certainly in this condition, the cause,
+as appeared on dissection, having been inflammation of the nictitating
+membrane. As frequent inflammation of the eyes must be injurious to any
+animal, and as eyes are certainly not indispensable to animals with
+subterranean habits, a reduction in their size with the adhesion of the
+eyelids and growth of fur over them, might in such case be an advantage;
+and if so, natural selection would constantly aid the effects of disuse.
+
+It is well known that several animals, belonging to the most different
+classes, which inhabit the caves of Styria and of Kentucky, are blind. In
+some of the crabs the foot-stalk for the eye remains, though the eye is
+gone; the stand for the telescope is there, though the telescope with its
+glasses has been lost. As it is difficult to imagine that eyes, though
+useless, could be in any way injurious to animals living in darkness, I
+attribute their loss wholly to disuse. In one of the blind animals, namely,
+the cave-rat, the eyes are of immense size; and Professor Silliman thought
+that it regained, after living some days in the light, some slight power of
+vision. In the same manner as in Madeira the wings of some of the insects
+have been enlarged, and the wings of others have been reduced by natural
+selection aided by use and disuse, so in the case of the cave-rat natural
+selection seems to have struggled with the loss of light and {138} to have
+increased the size of the eyes; whereas with all the other inhabitants of
+the caves, disuse by itself seems to have done its work.
+
+It is difficult to imagine conditions of life more similar than deep
+limestone caverns under a nearly similar climate; so that on the common
+view of the blind animals having been separately created for the American
+and European caverns, close similarity in their organisation and affinities
+might have been expected; but, as Schiödte and others have remarked, this
+is not the case, and the cave-insects of the two continents are not more
+closely allied than might have been anticipated from the general
+resemblance of the other inhabitants of North America and Europe. On my
+view we must suppose that American animals, having ordinary powers of
+vision, slowly migrated by successive generations from the outer world into
+the deeper and deeper recesses of the Kentucky caves, as did European
+animals into the caves of Europe. We have some evidence of this gradation
+of habit; for, as Schiödte remarks, "animals not far remote from ordinary
+forms, prepare the transition from light to darkness. Next follow those
+that are constructed for twilight; and, last of all, those destined for
+total darkness." By the time that an animal had reached, after numberless
+generations, the deepest recesses, disuse will on this view have more or
+less perfectly obliterated its eyes, and natural selection will often have
+effected other changes, such as an increase in the length of the antennæ or
+palpi, as a compensation for blindness. Notwithstanding such modifications,
+we might expect still to see in the cave-animals of America, affinities to
+the other inhabitants of that continent, and in those of Europe, to the
+inhabitants of the European continent. And this is the case with some of
+the American cave-animals, as I hear from {139} Professor Dana; and some of
+the European cave-insects are very closely allied to those of the
+surrounding country. It would be most difficult to give any rational
+explanation of the affinities of the blind cave-animals to the other
+inhabitants of the two continents on the ordinary view of their independent
+creation. That several of the inhabitants of the caves of the Old and New
+Worlds should be closely related, we might expect from the well-known
+relationship of most of their other productions. Far from feeling any
+surprise that some of the cave-animals should be very anomalous, as Agassiz
+has remarked in regard to the blind fish, the Amblyopsis, and as is the
+case with the blind Proteus with reference to the reptiles of Europe, I am
+only surprised that more wrecks of ancient life have not been preserved,
+owing to the less severe competition to which the inhabitants of these dark
+abodes will probably have been exposed.
+
+
+
+_Acclimatisation._--Habit is hereditary with plants, as in the period of
+flowering, in the amount of rain requisite for seeds to germinate, in the
+time of sleep, &c., and this leads me to say a few words on
+acclimatisation. As it is extremely common for species of the same genus to
+inhabit very hot and very cold countries, and as I believe that all the
+species of the same genus have descended from a single parent, if this view
+be correct, acclimatisation must be readily effected during long-continued
+descent. It is notorious that each species is adapted to the climate of its
+own home: species from an arctic or even from a temperate region cannot
+endure a tropical climate, or conversely. So again, many succulent plants
+cannot endure a damp climate. But the degree of adaptation of species to
+the climates under which they live is often overrated. {140} We may infer
+this from our frequent inability to predict whether or not an imported
+plant will endure our climate, and from the number of plants and animals
+brought from warmer countries which here enjoy good health. We have reason
+to believe that species in a state of nature are limited in their ranges by
+the competition of other organic beings quite as much as, or more than, by
+adaptation to particular climates. But whether or not the adaptation be
+generally very close, we have evidence, in the case of some few plants, of
+their becoming, to a certain extent, naturally habituated to different
+temperatures, or becoming acclimatised: thus the pines and rhododendrons,
+raised from seed collected by Dr. Hooker from trees growing at different
+heights on the Himalaya, were found in this country to possess different
+constitutional powers of resisting cold. Mr. Thwaites informs me that he
+has observed similar facts in Ceylon, and analogous observations have been
+made by Mr. H. C. Watson on European species of plants brought from the
+Azores to England. In regard to animals, several authentic cases could be
+given of species within historical times having largely extended their
+range from warmer to cooler latitudes, and conversely; but we do not
+positively know that these animals were strictly adapted to their native
+climate, but in all ordinary cases we assume such to be the case; nor do we
+know that they have subsequently become acclimatised to their new homes.
+
+As I believe that our domestic animals were originally chosen by
+uncivilised man because they were useful and bred readily under
+confinement, and not because they were subsequently found capable of
+far-extended transportation, I think the common and extraordinary capacity
+in our domestic animals of not only withstanding the most different
+climates but of being perfectly {141} fertile (a far severer test) under
+them, may be used as an argument that a large proportion of other animals,
+now in a state of nature, could easily be brought to bear widely different
+climates. We must not, however, push the foregoing argument too far, on
+account of the probable origin of some of our domestic animals from several
+wild stocks: the blood, for instance, of a tropical and arctic wolf or wild
+dog may perhaps be mingled in our domestic breeds. The rat and mouse cannot
+be considered as domestic animals, but they have been transported by man to
+many parts of the world, and now have a far wider range than any other
+rodent, living free under the cold climate of Faroe in the north and of the
+Falklands in the south, and on many islands in the torrid zones. Hence I am
+inclined to look at adaptation to any special climate as a quality readily
+grafted on an innate wide flexibility of constitution, which is common to
+most animals. On this view, the capacity of enduring the most different
+climates by man himself and by his domestic animals, and such facts as that
+former species of the elephant and rhinoceros were capable of enduring a
+glacial climate, whereas the living species are now all tropical or
+sub-tropical in their habits, ought not to be looked at as anomalies, but
+merely as examples of a very common flexibility of constitution, brought,
+under peculiar circumstances, into play.
+
+How much of the acclimatisation of species to any peculiar climate is due
+to mere habit, and how much to the natural selection of varieties having
+different innate constitutions, and how much to both means combined, is a
+very obscure question. That habit or custom has some influence I must
+believe, both from analogy, and from the incessant advice given in
+agricultural works, even in the ancient Encyclopædias of China, to be very
+{142} cautious in transposing animals from one district to another; for it
+is not likely that man should have succeeded in selecting so many breeds
+and sub-breeds with constitutions specially fitted for their own districts:
+the result must, I think, be due to habit. On the other hand, I can see no
+reason to doubt that natural selection will continually tend to preserve
+those individuals which are born with constitutions best adapted to their
+native countries. In treatises on many kinds of cultivated plants, certain
+varieties are said to withstand certain climates better than others: this
+is very strikingly shown in works on fruit trees published in the United
+States, in which certain varieties are habitually recommended for the
+northern, and others for the southern States; and as most of these
+varieties are of recent origin, they cannot owe their constitutional
+differences to habit. The case of the Jerusalem artichoke, which is never
+propagated by seed, and of which consequently new varieties have not been
+produced, has even been advanced--for it is now as tender as ever it
+was--as proving that acclimatisation cannot be effected! The case, also, of
+the kidney-bean has been often cited for a similar purpose, and with much
+greater weight; but until some one will sow, during a score of generations,
+his kidney-beans so early that a very large proportion are destroyed by
+frost, and then collect seed from the few survivors, with care to prevent
+accidental crosses, and then again get seed from these seedlings, with the
+same precautions, the experiment cannot be said to have been even tried.
+Nor let it be supposed that no differences in the constitution of seedling
+kidney-beans ever appear, for an account has been published how much more
+hardy some seedlings appeared to be than others.
+
+On the whole, I think we may conclude that habit, {143} use, and disuse,
+have, in some cases, played a considerable part in the modification of the
+constitution, and of the structure of various organs; but that the effects
+of use and disuse have often been largely combined with, and sometimes
+overmastered by the natural selection of innate variations.
+
+
+
+_Correlation of Growth._--I mean by this expression that the whole
+organisation is so tied together during its growth and development, that
+when slight variations in any one part occur, and are accumulated through
+natural selection, other parts become modified. This is a very important
+subject, most imperfectly understood. The most obvious case is, that
+modifications accumulated solely for the good of the young or larva, will,
+it may safely be concluded, affect the structure of the adult; in the same
+manner as any malconformation affecting the early embryo, seriously affects
+the whole organisation of the adult. The several parts of the body which
+are homologous, and which, at an early embryonic period, are alike, seem
+liable to vary in an allied manner: we see this in the right and left sides
+of the body varying in the same manner; in the front and hind legs, and
+even in the jaws and limbs, varying together, for the lower jaw is believed
+to be homologous with the limbs. These tendencies, I do not doubt, may be
+mastered more or less completely by natural selection: thus a family of
+stags once existed with an antler only on one side; and if this had been of
+any great use to the breed it might probably have been rendered permanent
+by natural selection.
+
+Homologous parts, as has been remarked by some authors, tend to cohere;
+this is often seen in monstrous plants; and nothing is more common than the
+union of homologous parts in normal structures, as the union of {144} the
+petals of the corolla into a tube. Hard parts seem to affect the form of
+adjoining soft parts; it is believed by some authors that the diversity in
+the shape of the pelvis in birds causes the remarkable diversity in the
+shape of their kidneys. Others believe that the shape of the pelvis in the
+human mother influences by pressure the shape of the head of the child. In
+snakes, according to Schlegel, the shape of the body and the manner of
+swallowing determine the position of several of the most important viscera.
+
+The nature of the bond of correlation is very frequently quite obscure. M.
+Is. Geoffroy St. Hilaire has forcibly remarked, that certain
+malconformations very frequently, and that others rarely coexist, without
+our being able to assign any reason. What can be more singular than the
+relation between blue eyes and deafness in cats, and the tortoise-shell
+colour with the female sex; the feathered feet and skin between the outer
+toes in pigeons, and the presence of more or less down on the young birds
+when first hatched, with the future colour of their plumage; or, again, the
+relation between the hair and teeth in the naked Turkish dog, though here
+probably homology comes into play? With respect to this latter case of
+correlation, I think it can hardly be accidental, that if we pick out the
+two orders of mammalia which are most abnormal in their dermal covering,
+viz. Cetacea (whales) and Edentata (armadilloes, scaly anteaters, &c.),
+that these are likewise the most abnormal in their teeth.
+
+I know of no case better adapted to show the importance of the laws of
+correlation in modifying important structures, independently of utility
+and, therefore, of natural selection, than that of the difference between
+the outer and inner flowers in some Compositous and Umbelliferous plants.
+Every one knows the {145} difference in the ray and central florets of, for
+instance, the daisy, and this difference is often accompanied with the
+abortion of parts of the flower. But, in some Compositous plants, the seeds
+also differ in shape and sculpture; and even the ovary itself, with its
+accessory parts, differs, as has been described by Cassini. These
+differences have been attributed by some authors to pressure, and the shape
+of the seeds in the ray-florets in some Compositæ countenances this idea;
+but, in the case of the corolla of the Umbelliferæ, it is by no means, as
+Dr. Hooker informs me, in species with the densest heads that the inner and
+outer flowers most frequently differ. It might have been thought that the
+development of the ray-petals by drawing nourishment from certain other
+parts of the flower had caused their abortion; but in some Compositæ there
+is a difference in the seeds of the outer and inner florets without any
+difference in the corolla. Possibly, these several differences may be
+connected with some difference in the flow of nutriment towards the central
+and external flowers: we know, at least, that in irregular flowers, those
+nearest to the axis are oftenest subject to peloria, and become regular. I
+may add, as an instance of this, and of a striking case of correlation,
+that I have recently observed in some garden pelargoniums, that the central
+flower of the truss often loses the patches of darker colour in the two
+upper petals; and that when this occurs, the adherent nectary is quite
+aborted; when the colour is absent from only one of the two upper petals,
+the nectary is only much shortened.
+
+With respect to the difference in the corolla of the central and exterior
+flowers of a head or umbel, I do not feel at all sure that C. C. Sprengel's
+idea that the ray-florets serve to attract insects, whose agency is highly
+advantageous in the fertilisation of plants of {146} these two orders, is
+so far-fetched, as it may at first appear: and if it be advantageous,
+natural selection may have come into play. But in regard to the differences
+both in the internal and external structure of the seeds, which are not
+always correlated with any differences in the flowers, it seems impossible
+that they can be in any way advantageous to the plant: yet in the
+Umbelliferæ these differences are of such apparent importance--the seeds
+being in some cases, according to Tausch, orthospermous in the exterior
+flowers and coelospermous in the central flowers,--that the elder De
+Candolle founded his main divisions of the order on analogous differences.
+Hence we see that modifications of structure, viewed by systematists as of
+high value, may be wholly due to unknown laws of correlated growth, and
+without being, as far as we can see, of the slightest service to the
+species.
+
+We may often falsely attribute to correlation of growth, structures which
+are common to whole groups of species, and which in truth are simply due to
+inheritance; for an ancient progenitor may have acquired through natural
+selection some one modification in structure, and, after thousands of
+generations, some other and independent modification; and these two
+modifications, having been transmitted to a whole group of descendants with
+diverse habits, would naturally be thought to be correlated in some
+necessary manner. So, again, I do not doubt that some apparent
+correlations, occurring throughout whole orders, are entirely due to the
+manner alone in which natural selection can act. For instance, Alph. De
+Candolle has remarked that winged seeds are never found in fruits which do
+not open: I should explain the rule by the fact that seeds could not
+gradually become winged through natural selection, except in fruits which
+opened; so that the individual plants producing {147} seeds which were a
+little better fitted to be wafted further, might get an advantage over
+those producing seed less fitted for dispersal; and this process could not
+possibly go on in fruit which did not open.
+
+The elder Geoffroy and Goethe propounded, at about the same period, their
+law of compensation or balancement of growth; or, as Goethe expressed it,
+"in order to spend on one side, nature is forced to economise on the other
+side." I think this holds true to a certain extent with our domestic
+productions: if nourishment flows to one part or organ in excess, it rarely
+flows, at least in excess, to another part; thus it is difficult to get a
+cow to give much milk and to fatten readily. The same varieties of the
+cabbage do not yield abundant and nutritious foliage and a copious supply
+of oil-bearing seeds. When the seeds in our fruits become atrophied, the
+fruit itself gains largely in size and quality. In our poultry, a large
+tuft of feathers on the head is generally accompanied by a diminished comb,
+and a large beard by diminished wattles. With species in a state of nature
+it can hardly be maintained that the law is of universal application; but
+many good observers, more especially botanists, believe in its truth. I
+will not, however, here give any instances, for I see hardly any way of
+distinguishing between the effects, on the one hand, of a part being
+largely developed through natural selection and another and adjoining part
+being reduced by this same process or by disuse, and, on the other hand,
+the actual withdrawal of nutriment from one part owing to the excess of
+growth in another and adjoining part.
+
+I suspect, also, that some of the cases of compensation which have been
+advanced, and likewise some other facts, may be merged under a more general
+principle, namely, that natural selection is continually trying to
+economise in every part of the organisation. If under {148} changed
+conditions of life a structure before useful becomes less useful, any
+diminution, however slight, in its development, will be seized on by
+natural selection, for it will profit the individual not to have its
+nutriment wasted in building up an useless structure. I can thus only
+understand a fact with which I was much struck when examining cirripedes,
+and of which many other instances could be given: namely, that when a
+cirripede is parasitic within another and is thus protected, it loses more
+or less completely its own shell or carapace. This is the case with the
+male Ibla, and in a truly extraordinary manner with the Proteolepas: for
+the carapace in all other cirripedes consists of the three highly-important
+anterior segments of the head enormously developed, and furnished with
+great nerves and muscles; but in the parasitic and protected Proteolepas,
+the whole anterior part of the head is reduced to the merest rudiment
+attached to the bases of the prehensile antennæ. Now the saving of a large
+and complex structure, when rendered superfluous by the parasitic habits of
+the Proteolepas, though effected by slow steps, would be a decided
+advantage to each successive individual of the species; for in the struggle
+for life to which every animal is exposed, each individual Proteolepas
+would have a better chance of supporting itself, by less nutriment being
+wasted in developing a structure now become useless.
+
+Thus, as I believe, natural selection will always succeed in the long run
+in reducing and saving every part of the organisation, as soon as it is
+rendered superfluous, without by any means causing some other part to be
+largely developed in a corresponding degree. And, conversely, that natural
+selection may perfectly well succeed in largely developing any organ,
+without requiring as a necessary compensation the reduction of some
+adjoining part. {149}
+
+It seems to be a rule, as remarked by Is. Geoffroy St. Hilaire, both in
+varieties and in species, that when any part or organ is repeated many
+times in the structure of the same individual (as the vertebræ in snakes,
+and the stamens in polyandrous flowers) the number is variable; whereas the
+number of the same part or organ, when it occurs in lesser numbers, is
+constant. The same author and some botanists have further remarked that
+multiple parts are also very liable to variation in structure. Inasmuch as
+this "vegetative repetition," to use Prof. Owen's expression, seems to be a
+sign of low organisation, the foregoing remark seems connected with the
+very general opinion of naturalists, that beings low in the scale of nature
+are more variable than those which are higher. I presume that lowness in
+this case means that the several parts of the organisation have been but
+little specialised for particular functions; and as long as the same part
+has to perform diversified work, we can perhaps see why it should remain
+variable, that is, why natural selection should have preserved or rejected
+each little deviation of form less carefully than when the part has to
+serve for one special purpose alone. In the same way that a knife which has
+to cut all sorts of things may be of almost any shape; whilst a tool for
+some particular object had better be of some particular shape. Natural
+selection, it should never be forgotten, can act on each part of each
+being, solely through and for its advantage.
+
+Rudimentary parts, it has been stated by some authors, and I believe with
+truth, are apt to be highly variable. We shall have to recur to the general
+subject of rudimentary and aborted organs; and I will here only add that
+their variability seems to be owing to their uselessness, and therefore to
+natural selection having no power to check deviations in their structure.
+Thus {150} rudimentary parts are left to the free play of the various laws
+of growth, to the effects of long-continued disuse, and to the tendency to
+reversion.
+
+
+
+_A part developed in any species in an extraordinary degree or manner, in
+comparison with the same part in allied species, tends to be highly
+variable._--Several years ago I was much struck with a remark, nearly to
+the above effect, published by Mr. Waterhouse. I infer also from an
+observation made by Professor Owen, with respect to the length of the arms
+of the ourang-outang, that he has come to a nearly similar conclusion. It
+is hopeless to attempt to convince any one of the truth of this proposition
+without giving the long array of facts which I have collected, and which
+cannot possibly be here introduced. I can only state my conviction that it
+is a rule of high generality. I am aware of several causes of error, but I
+hope that I have made due allowance for them. It should be understood that
+the rule by no means applies to any part, however unusually developed,
+unless it be unusually developed in comparison with the same part in
+closely allied species. Thus, the bat's wing is a most abnormal structure
+in the class mammalia; but the rule would not here apply, because there is
+a whole group of bats having wings; it would apply only if some one species
+of bat had its wings developed in some remarkable manner in comparison with
+the other species of the same genus. The rule applies very strongly in the
+case of secondary sexual characters, when displayed in any unusual manner.
+The term, secondary sexual characters, used by Hunter, applies to
+characters which are attached to one sex, but are not directly connected
+with the act of reproduction. The rule applies to males and females; but as
+females more rarely offer remarkable secondary sexual characters, it
+applies {151} more rarely to them. The rule being so plainly applicable in
+the case of secondary sexual characters, may be due to the great
+variability of these characters, whether or not displayed in any unusual
+manner--of which fact I think there can be little doubt. But that our rule
+is not confined to secondary sexual characters is clearly shown in the case
+of hermaphrodite cirripedes; and I may here add, that I particularly
+attended to Mr. Waterhouse's remark, whilst investigating this Order, and I
+am fully convinced that the rule almost invariably holds good with
+cirripedes. I shall, in my future work, give a list of the more remarkable
+cases; I will here only briefly give one, as it illustrates the rule in its
+largest application. The opercular valves of sessile cirripedes (rock
+barnacles) are, in every sense of the word, very important structures, and
+they differ extremely little even in different genera; but in the several
+species of one genus, Pyrgoma, these valves present a marvellous amount of
+diversification: the homologous valves in the different species being
+sometimes wholly unlike in shape; and the amount of variation in the
+individuals of several of the species is so great, that it is no
+exaggeration to state that the varieties differ more from each other in the
+characters of these important valves than do other species of distinct
+genera.
+
+As birds within the same country vary in a remarkably small degree, I have
+particularly attended to them, and the rule seems to me certainly to hold
+good in this class. I cannot make out that it applies to plants, and this
+would seriously have shaken my belief in its truth, had not the great
+variability in plants made it particularly difficult to compare their
+relative degrees of variability.
+
+When we see any part or organ developed in a remarkable degree or manner in
+any species, the fair {152} presumption is that it is of high importance to
+that species; nevertheless the part in this case is eminently liable to
+variation. Why should this be so? On the view that each species has been
+independently created, with all its parts as we now see them, I can see no
+explanation. But on the view that groups of species have descended from
+other species, and have been modified through natural selection, I think we
+can obtain some light. In our domestic animals, if any part, or the whole
+animal, be neglected and no selection be applied, that part (for instance,
+the comb in the Dorking fowl) or the whole breed will cease to have a
+nearly uniform character. The breed will then be said to have degenerated.
+In rudimentary organs, and in those which have been but little specialised
+for any particular purpose, and perhaps in polymorphic groups, we see a
+nearly parallel natural case; for in such cases natural selection either
+has not or cannot come into full play, and thus the organisation is left in
+a fluctuating condition. But what here more especially concerns us is, that
+in our domestic animals those points, which at the present time are
+undergoing rapid change by continued selection, are also eminently liable
+to variation. Look at the breeds of the pigeon; see what a prodigious
+amount of difference there is in the beak of the different tumblers, in the
+beak and wattle of the different carriers, in the carriage and tail of our
+fantails, &c., these being the points now mainly attended to by English
+fanciers. Even in the sub-breeds, as in the short-faced tumbler, it is
+notoriously difficult to breed them nearly to perfection, and frequently
+individuals are born which depart widely from the standard. There may be
+truly said to be a constant struggle going on between, on the one hand, the
+tendency to reversion to a less modified state, as well as an innate
+tendency to further {153} variability of all kinds, and, on the other hand,
+the power of steady selection to keep the breed true. In the long run
+selection gains the day, and we do not expect to fail so far as to breed a
+bird as coarse as a common tumbler from a good short-faced strain. But as
+long as selection is rapidly going on, there may always be expected to be
+much variability in the structure undergoing modification. It further
+deserves notice that these variable characters, produced by man's
+selection, sometimes become attached, from causes quite unknown to us, more
+to one sex than to the other, generally to the male sex, as with the wattle
+of carriers and the enlarged crop of pouters.
+
+Now let us turn to nature. When a part has been developed in an
+extraordinary manner in any one species, compared with the other species of
+the same genus, we may conclude that this part has undergone an
+extraordinary amount of modification since the period when the species
+branched off from the common progenitor of the genus. This period will
+seldom be remote in any extreme degree, as species very rarely endure for
+more than one geological period. An extraordinary amount of modification
+implies an unusually large and long-continued amount of variability, which
+has continually been accumulated by natural selection for the benefit of
+the species. But as the variability of the extraordinarily-developed part
+or organ has been so great and long-continued within a period not
+excessively remote, we might, as a general rule, expect still to find more
+variability in such parts than in other parts of the organisation which
+have remained for a much longer period nearly constant. And this, I am
+convinced, is the case. That the struggle between natural selection on the
+one hand, and the tendency to reversion and variability on the other hand,
+will in the {154} course of time cease; and that the most abnormally
+developed organs may be made constant, I can see no reason to doubt. Hence
+when an organ, however abnormal it may be, has been transmitted in
+approximately the same condition to many modified descendants, as in the
+case of the wing of the bat, it must have existed, according to my theory,
+for an immense period in nearly the same state; and thus it comes to be no
+more variable than any other structure. It is only in those cases in which
+the modification has been comparatively recent and extraordinarily great
+that we ought to find the _generative variability_, as it may be called,
+still present in a high degree. For in this case the variability will
+seldom as yet have been fixed by the continued selection of the individuals
+varying in the required manner and degree, and by the continued rejection
+of those tending to revert to a former and less modified condition.
+
+The principle included in these remarks may be extended. It is notorious
+that specific characters are more variable than generic. To explain by a
+simple example what is meant. If some species in a large genus of plants
+had blue flowers and some had red, the colour would be only a specific
+character, and no one would be surprised at one of the blue species varying
+into red, or conversely; but if all the species had blue flowers, the
+colour would become a generic character, and its variation would be a more
+unusual circumstance. I have chosen this example because an explanation is
+not in this case applicable, which most naturalists would advance, namely,
+that specific characters are more variable than generic, because they are
+taken from parts of less physiological importance than those commonly used
+for classing genera. I believe this explanation is partly, yet only
+indirectly, true; I shall, however, have to {155} return to this subject in
+our chapter on Classification. It would be almost superfluous to adduce
+evidence in support of the above statement, that specific characters are
+more variable than generic; but I have repeatedly noticed in works on
+natural history, that when an author has remarked with surprise that some
+_important_ organ or part, which is generally very constant throughout
+large groups of species, has _differed_ considerably in closely-allied
+species, that it has, also, been _variable_ in the individuals of some of
+the species. And this fact shows that a character, which is generally of
+generic value, when it sinks in value and becomes only of specific value,
+often becomes variable, though its physiological importance may remain the
+same. Something of the same kind applies to monstrosities: at least Is.
+Geoffroy St. Hilaire seems to entertain no doubt, that the more an organ
+normally differs in the different species of the same group, the more
+subject it is to individual anomalies.
+
+On the ordinary view of each species having been independently created, why
+should that part of the structure, which differs from the same part in
+other independently-created species of the same genus, be more variable
+than those parts which are closely alike in the several species? I do not
+see that any explanation can be given. But on the view of species being
+only strongly marked and fixed varieties, we might surely expect to find
+them still often continuing to vary in those parts of their structure which
+have varied within a moderately recent period, and which have thus come to
+differ. Or to state the case in another manner:--the points in which all
+the species of a genus resemble each other, and in which they differ from
+the species of some other genus, are called generic characters; and these
+characters in common I attribute to {156} inheritance from a common
+progenitor, for it can rarely have happened that natural selection will
+have modified several species, fitted to more or less widely-different
+habits, in exactly the same manner: and as these so-called generic
+characters have been inherited from a remote period, since that period when
+the species first branched off from their common progenitor, and
+subsequently have not varied or come to differ in any degree, or only in a
+slight degree, it is not probable that they should vary at the present day.
+On the other hand, the points in which species differ from other species of
+the same genus, are called specific characters; and as these specific
+characters have varied and come to differ within the period of the
+branching off of the species from a common progenitor, it is probable that
+they should still often be in some degree variable,--at least more variable
+than those parts of the organisation which have for a very long period
+remained constant.
+
+In connexion with the present subject, I will make only two other remarks.
+I think it will be admitted, without my entering on details, that secondary
+sexual characters are very variable; I think it also will be admitted that
+species of the same group differ from each other more widely in their
+secondary sexual characters, than in other parts of their organisation;
+compare, for instance, the amount of difference between the males of
+gallinaceous birds, in which secondary sexual characters are strongly
+displayed, with the amount of difference between their females; and the
+truth of this proposition will be granted. The cause of the original
+variability of secondary sexual characters is not manifest; but we can see
+why these characters should not have been rendered as constant and uniform
+as other parts of the organisation; for secondary sexual characters have
+been accumulated by sexual selection, which {157} is less rigid in its
+action than ordinary selection, as it does not entail death, but only gives
+fewer offspring to the less favoured males. Whatever the cause may be of
+the variability of secondary sexual characters, as they are highly
+variable, sexual selection will have had a wide scope for action, and may
+thus readily have succeeded in giving to the species of the same group a
+greater amount of difference in their sexual characters, than in other
+parts of their structure.
+
+It is a remarkable fact, that the secondary sexual differences between the
+two sexes of the same species are generally displayed in the very same
+parts of the organisation in which the different species of the same genus
+differ from each other. Of this fact I will give in illustration two
+instances, the first which happen to stand on my list; and as the
+differences in these cases are of a very unusual nature, the relation can
+hardly be accidental. The same number of joints in the tarsi is a character
+generally common to very large groups of beetles, but in the Engidæ, as
+Westwood has remarked, the number varies greatly; and the number likewise
+differs in the two sexes of the same species: again in fossorial
+hymenoptera, the manner of neuration of the wings is a character of the
+highest importance, because common to large groups; but in certain genera
+the neuration differs in the different species, and likewise in the two
+sexes of the same species. This relation has a clear meaning on my view of
+the subject: I look at all the species of the same genus as having as
+certainly descended from the same progenitor, as have the two sexes of any
+one of the species. Consequently, whatever part of the structure of the
+common progenitor, or of its early descendants, became variable; variations
+of this part would, it is highly probable, be taken advantage of by natural
+and sexual selection, in order to fit {158} the several species to their
+several places in the economy of nature, and likewise to fit the two sexes
+of the same species to each other, or to fit the males and females to
+different habits of life, or the males to struggle with other males for the
+possession of the females.
+
+Finally, then, I conclude that the greater variability of specific
+characters, or those which distinguish species from species, than of
+generic characters, or those which the species possess in common;--that the
+frequent extreme variability of any part which is developed in a species in
+an extraordinary manner in comparison with the same part in its congeners;
+and the slight degree of variability in a part, however extraordinarily it
+may be developed, if it be common to a whole group of species;--that the
+great variability of secondary sexual characters, and the great amount of
+difference in these same characters between closely allied species;--that
+secondary sexual and ordinary specific differences are generally displayed
+in the same parts of the organisation,--are all principles closely
+connected together. All being mainly due to the species of the same group
+having descended from a common progenitor, from whom they have inherited
+much in common,--to parts which have recently and largely varied being more
+likely still to go on varying than parts which have long been inherited and
+have not varied,--to natural selection having more or less completely,
+according to the lapse of time, overmastered the tendency to reversion and
+to further variability,--to sexual selection being less rigid than ordinary
+selection,--and to variations in the same parts having been accumulated by
+natural and sexual selection, and having been thus adapted for secondary
+sexual, and for ordinary specific purposes. {159}
+
+
+
+_Distinct species present analogous variations; and a variety of one
+species often assumes some of the characters of an allied species, or
+reverts to some of the characters of an early progenitor._--These
+propositions will be most readily understood by looking to our domestic
+races. The most distinct breeds of pigeons, in countries most widely apart,
+present sub-varieties with reversed feathers on the head and feathers on
+the feet,--characters not possessed by the aboriginal rock-pigeon; these
+then are analogous variations in two or more distinct races. The frequent
+presence of fourteen or even sixteen tail-feathers in the pouter, may be
+considered as a variation representing the normal structure of another
+race, the fantail. I presume that no one will doubt that all such analogous
+variations are due to the several races of the pigeon having inherited from
+a common parent the same constitution and tendency to variation, when acted
+on by similar unknown influences. In the vegetable kingdom we have a case
+of analogous variation, in the enlarged stems, or roots as commonly called,
+of the Swedish turnip and Ruta baga, plants which several botanists rank as
+varieties produced by cultivation from a common parent: if this be not so,
+the case will then be one of analogous variation in two so-called distinct
+species; and to these a third may be added, namely, the common turnip.
+According to the ordinary view of each species having been independently
+created, we should have to attribute this similarity in the enlarged stems
+of these three plants, not to the _vera causa_ of community of descent, and
+a consequent tendency to vary in a like manner, but to three separate yet
+closely related acts of creation.
+
+With pigeons, however, we have another case, namely, the occasional
+appearance in all the breeds, of slaty-blue birds with two black bars on
+the wings, a white {160} rump, a bar at the end of the tail, with the outer
+feathers externally edged near their bases with white. As all these marks
+are characteristic of the parent rock-pigeon, I presume that no one will
+doubt that this is a case of reversion, and not of a new yet analogous
+variation appearing in the several breeds. We may I think confidently come
+to this conclusion, because, as we have seen, these coloured marks are
+eminently liable to appear in the crossed offspring of two distinct and
+differently coloured breeds; and in this case there is nothing in the
+external conditions of life to cause the reappearance of the slaty-blue,
+with the several marks, beyond the influence of the mere act of crossing on
+the laws of inheritance.
+
+No doubt it is a very surprising fact that characters should reappear after
+having been lost for many, perhaps for hundreds of generations. But when a
+breed has been crossed only once by some other breed, the offspring
+occasionally show a tendency to revert in character to the foreign breed
+for many generations--some say, for a dozen or even a score of generations.
+After twelve generations, the proportion of blood, to use a common
+expression, of any one ancestor, is only 1 in 2048; and yet, as we see, it
+is generally believed that a tendency to reversion is retained by this very
+small proportion of foreign blood. In a breed which has not been crossed,
+but in which _both_ parents have lost some character which their progenitor
+possessed, the tendency, whether strong or weak, to reproduce the lost
+character might be, as was formerly remarked, for all that we can see to
+the contrary, transmitted for almost any number of generations. When a
+character which has been lost in a breed, reappears after a great number of
+generations, the most probable hypothesis is, not that the offspring
+suddenly takes after an ancestor some hundred generations {161} distant,
+but that in each successive generation there has been a tendency to
+reproduce the character in question, which at last, under unknown
+favourable conditions, gains an ascendancy. For instance, it is probable
+that in each generation of the barb-pigeon, which produces most rarely a
+blue and black-barred bird, there has been a tendency in each generation in
+the plumage to assume this colour. This view is hypothetical, but could be
+supported by some facts; and I can see no more abstract improbability in a
+tendency to produce any character being inherited for an endless number of
+generations, than in quite useless or rudimentary organs being, as we all
+know them to be, thus inherited. Indeed, we may sometimes observe a mere
+tendency to produce a rudiment inherited: for instance, in the common
+snapdragon (Antirrhinum) a rudiment of a fifth stamen so often appears,
+that this plant must have an inherited tendency to produce it.
+
+As all the species of the same genus are supposed, on my theory, to have
+descended from a common parent, it might be expected that they would
+occasionally vary in an analogous manner; so that a variety of one species
+would resemble in some of its characters another species; this other
+species being on my view only a well-marked and permanent variety. But
+characters thus gained would probably be of an unimportant nature, for the
+presence of all important characters will be governed by natural selection,
+in accordance with the diverse habits of the species, and will not be left
+to the mutual action of the conditions of life and of a similar inherited
+constitution. It might further be expected that the species of the same
+genus would occasionally exhibit reversions to lost ancestral characters.
+As, however, we never know the exact character of the common ancestor of a
+group, we could not distinguish these two {162} cases: if, for instance, we
+did not know that the rock-pigeon was not feather-footed or turn-crowned,
+we could not have told, whether these characters in our domestic breeds
+were reversions or only analogous variations; but we might have inferred
+that the blueness was a case of reversion, from the number of the markings,
+which are correlated with the blue tint, and which it does not appear
+probable would all appear together from simple variation. More especially
+we might have inferred this, from the blue colour and marks so often
+appearing when distinct breeds of diverse colours are crossed. Hence,
+though under nature it must generally be left doubtful, what cases are
+reversions to an anciently existing character, and what are new but
+analogous variations, yet we ought, on my theory, sometimes to find the
+varying offspring of a species assuming characters (either from reversion
+or from analogous variation) which already occur in some other members of
+the same group. And this undoubtedly is the case in nature.
+
+A considerable part of the difficulty in recognising a variable species in
+our systematic works, is due to its varieties mocking, as it were, some of
+the other species of the same genus. A considerable catalogue, also, could
+be given of forms intermediate between two other forms, which themselves
+must be doubtfully ranked as either varieties or species; and this shows,
+unless all these forms be considered as independently created species, that
+the one in varying has assumed some of the characters of the other, so as
+to produce the intermediate form. But the best evidence is afforded by
+parts or organs of an important and uniform nature occasionally varying so
+as to acquire, in some degree, the character of the same part or organ in
+an allied species. I have collected a long list of such cases; but {163}
+here, as before, I lie under a great disadvantage in not being able to give
+them. I can only repeat that such cases certainly do occur, and seem to me
+very remarkable.
+
+I will, however, give one curious and complex case, not indeed as affecting
+any important character, but from occurring in several species of the same
+genus, partly under domestication and partly under nature. It is a case
+apparently of reversion. The ass not rarely has very distinct transverse
+bars on its legs, like those on the legs of the zebra: it has been asserted
+that these are plainest in the foal, and from inquiries which I have made,
+I believe this to be true. It has also been asserted that the stripe on
+each shoulder is sometimes double. The shoulder-stripe is certainly very
+variable in length and outline. A white ass, but _not_ an albino, has been
+described without either spinal or shoulder stripe; and these stripes are
+sometimes very obscure, or actually quite lost, in dark-coloured asses. The
+koulan of Pallas is said to have been seen with a double shoulder-stripe.
+The hemionus has no shoulder-stripe; but traces of it, as stated by Mr.
+Blyth and others, occasionally appear: and I have been informed by Colonel
+Poole that the foals of this species are generally striped on the legs, and
+faintly on the shoulder. The quagga, though so plainly barred like a zebra
+over the body, is without bars on the legs; but Dr. Gray has figured one
+specimen with very distinct zebra-like bars on the hocks.
+
+With respect to the horse, I have collected cases in England of the spinal
+stripe in horses of the most distinct breeds, and of _all_ colours;
+transverse bars on the legs are not rare in duns, mouse-duns, and in one
+instance in a chestnut: a faint shoulder-stripe may sometimes be seen in
+duns, and I have seen a trace in a {164} bay horse. My son made a careful
+examination and sketch for me of a dun Belgian cart-horse with a double
+stripe on each shoulder and with leg-stripes; and a man, whom I can
+implicitly trust, has examined for me a small dun Welch pony with _three_
+short parallel stripes on each shoulder.
+
+In the north-west part of India the Kattywar breed of horses is so
+generally striped, that, as I hear from Colonel Poole, who examined the
+breed for the Indian Government, a horse without stripes is not considered
+as purely-bred. The spine is always striped; the legs are generally barred;
+and the shoulder-stripe, which is sometimes double and sometimes treble, is
+common; the side of the face, moreover, is sometimes striped. The stripes
+are plainest in the foal; and sometimes quite disappear in old horses.
+Colonel Poole has seen both gray and bay Kattywar horses striped when first
+foaled. I have, also, reason to suspect, from information given me by Mr.
+W. W. Edwards, that with the English racehorse the spinal stripe is much
+commoner in the foal than in the full-grown animal. Without here entering
+on further details, I may state that I have collected cases of leg and
+shoulder stripes in horses of very different breeds, in various countries
+from Britain to Eastern China; and from Norway in the north to the Malay
+Archipelago in the south. In all parts of the world these stripes occur far
+oftenest in duns and mouse-duns; by the term dun a large range of colour is
+included, from one between brown and black to a close approach to
+cream-colour.
+
+I am aware that Colonel Hamilton Smith, who has written on this subject,
+believes that the several breeds of the horse have descended from several
+aboriginal species--one of which, the dun, was striped; and that the
+above-described appearances are all due to ancient {165} crosses with the
+dun stock. But I am not at all satisfied with this theory, and should be
+loth to apply it to breeds so distinct as the heavy Belgian cart-horse,
+Welch ponies, cobs, the lanky Kattywar race, &c., inhabiting the most
+distant parts of the world.
+
+Now let us turn to the effects of crossing the several species of the
+horse-genus. Rollin asserts, that the common mule from the ass and horse is
+particularly apt to have bars on its legs: according to Mr. Gosse, in
+certain parts of the United States about nine out of ten mules have striped
+legs. I once saw a mule with its legs so much striped that any one would at
+first have thought that it must have been the product of a zebra; and Mr.
+W. C. Martin, in his excellent treatise on the horse, has given a figure of
+a similar mule. In four coloured drawings, which I have seen, of hybrids
+between the ass and zebra, the legs were much more plainly barred than the
+rest of the body; and in one of them there was a double shoulder-stripe. In
+Lord Morton's famous hybrid from a chestnut mare and male quagga, the
+hybrid, and even the pure offspring subsequently produced from the mare by
+a black Arabian sire, were much more plainly barred across the legs than is
+even the pure quagga. Lastly, and this is another most remarkable case, a
+hybrid has been figured by Dr. Gray (and he informs me that he knows of a
+second case) from the ass and the hemionus; and this hybrid, though the ass
+seldom has stripes on his legs and the hemionus has none and has not even a
+shoulder-stripe, nevertheless had all four legs barred, and had three short
+shoulder-stripes, like those on the dun Welch pony, and even had some
+zebra-like stripes on the sides of its face. With respect to this last
+fact, I was so convinced that not even a stripe of colour appears from what
+would commonly be called an {166} accident, that I was led solely from the
+occurrence of the face-stripes on this hybrid from the ass and hemionus to
+ask Colonel Poole whether such face-stripes ever occur in the eminently
+striped Kattywar breed of horses, and was, as we have seen, answered in the
+affirmative.
+
+What now are we to say to these several facts? We see several very distinct
+species of the horse-genus becoming, by simple variation, striped on the
+legs like a zebra, or striped on the shoulders like an ass. In the horse we
+see this tendency strong whenever a dun tint appears--a tint which
+approaches to that of the general colouring of the other species of the
+genus. The appearance of the stripes is not accompanied by any change of
+form or by any other new character. We see this tendency to become striped
+most strongly displayed in hybrids from between several of the most
+distinct species. Now observe the case of the several breeds of pigeons:
+they are descended from a pigeon (including two or three sub-species or
+geographical races) of a bluish colour, with certain bars and other marks;
+and when any breed assumes by simple variation a bluish tint, these bars
+and other marks invariably reappear; but without any other change of form
+or character. When the oldest and truest breeds of various colours are
+crossed, we see a strong tendency for the blue tint and bars and marks to
+reappear in the mongrels. I have stated that the most probable hypothesis
+to account for the reappearance of very ancient characters, is--that there
+is a _tendency_ in the young of each successive generation to produce the
+long-lost character, and that this tendency, from unknown causes, sometimes
+prevails. And we have just seen that in several species of the horse-genus
+the stripes are either plainer or appear more commonly in the young than in
+the old. Call the breeds of pigeons, some of which have bred true for {167}
+centuries, species; and how exactly parallel is the case with that of the
+species of the horse-genus! For myself, I venture confidently to look back
+thousands on thousands of generations, and I see an animal striped like a
+zebra, but perhaps otherwise very differently constructed, the common
+parent of our domestic horse, whether or not it be descended from one or
+more wild stocks, of the ass, the hemionus, quagga, and zebra.
+
+He who believes that each equine species was independently created, will, I
+presume, assert that each species has been created with a tendency to vary,
+both under nature and under domestication, in this particular manner, so as
+often to become striped like other species of the genus; and that each has
+been created with a strong tendency, when crossed with species inhabiting
+distant quarters of the world, to produce hybrids resembling in their
+stripes, not their own parents, but other species of the genus. To admit
+this view is, as it seems to me, to reject a real for an unreal, or at
+least for an unknown, cause. It makes the works of God a mere mockery and
+deception; I would almost as soon believe with the old and ignorant
+cosmogonists, that fossil shells had never lived, but had been created in
+stone so as to mock the shells now living on the sea-shore.
+
+
+
+_Summary._--Our ignorance of the laws of variation is profound. Not in one
+case out of a hundred can we pretend to assign any reason why this or that
+part differs, more or less, from the same part in the parents. But whenever
+we have the means of instituting a comparison, the same laws appear to have
+acted in producing the lesser differences between varieties of the same
+species, and the greater differences between species of the same genus. The
+external conditions of life, as {168} climate and food, &c., seem to have
+induced some slight modifications. Habit in producing constitutional
+differences, and use in strengthening and disuse in weakening and
+diminishing organs, seem to have been more potent in their effects.
+Homologous parts tend to vary in the same way, and homologous parts tend to
+cohere. Modifications in hard parts and in external parts sometimes affect
+softer and internal parts. When one part is largely developed, perhaps it
+tends to draw nourishment from the adjoining parts; and every part of the
+structure which can be saved without detriment to the individual, will be
+saved. Changes of structure at an early age will generally affect parts
+subsequently developed; and there are very many other correlations of
+growth, the nature of which we are utterly unable to understand. Multiple
+parts are variable in number and in structure, perhaps arising from such
+parts not having been closely specialised to any particular function, so
+that their modifications have not been closely checked by natural
+selection. It is probably from this same cause that organic beings low in
+the scale of nature are more variable than those which have their whole
+organisation more specialised, and are higher in the scale. Rudimentary
+organs, from being useless, will be disregarded by natural selection, and
+hence probably are variable. Specific characters--that is, the characters
+which have come to differ since the several species of the same genus
+branched off from a common parent--are more variable than generic
+characters, or those which have long been inherited, and have not differed
+within this same period. In these remarks we have referred to special parts
+or organs being still variable, because they have recently varied and thus
+come to differ; but we have also seen in the second Chapter that the same
+principle applies to the whole individual; {169} for in a district where
+many species of any genus are found--that is, where there has been much
+former variation and differentiation, or where the manufactory of new
+specific forms has been actively at work--there, on an average, we now find
+most varieties or incipient species. Secondary sexual characters are highly
+variable, and such characters differ much in the species of the same group.
+Variability in the same parts of the organisation has generally been taken
+advantage of in giving secondary sexual differences to the sexes of the
+same species, and specific differences to the several species of the same
+genus. Any part or organ developed to an extraordinary size or in an
+extraordinary manner, in comparison with the same part or organ in the
+allied species, must have gone through an extraordinary amount of
+modification since the genus arose; and thus we can understand why it
+should often still be variable in a much higher degree than other parts;
+for variation is a long-continued and slow process, and natural selection
+will in such cases not as yet have had time to overcome the tendency to
+further variability and to reversion to a less modified state. But when a
+species with any extraordinarily-developed organ has become the parent of
+many modified descendants--which on my view must be a very slow process,
+requiring a long lapse of time--in this case, natural selection may readily
+have succeeded in giving a fixed character to the organ, in however
+extraordinary a manner it may be developed. Species inheriting nearly the
+same constitution from a common parent and exposed to similar influences
+will naturally tend to present analogous variations, and these same species
+may occasionally revert to some of the characters of their ancient
+progenitors. Although new and important modifications may not arise from
+reversion and analogous {170} variation, such modifications will add to the
+beautiful and harmonious diversity of nature.
+
+Whatever the cause may be of each slight difference in the offspring from
+their parents--and a cause for each must exist--it is the steady
+accumulation, through natural selection, of such differences, when
+beneficial to the individual, that gives rise to all the more important
+modifications of structure, by which the innumerable beings on the face of
+this earth are enabled to struggle with each other, and the best adapted to
+survive.
+
+       *       *       *       *       *
+
+
+{171}
+
+CHAPTER VI.
+
+DIFFICULTIES ON THEORY.
+
+    Difficulties on the theory of descent with
+    modification--Transitions--Absence or rarity of transitional
+    varieties--Transitions in habits of life--Diversified habits in the
+    same species--Species with habits widely different from those of their
+    allies--Organs of extreme perfection--Means of transition--Cases of
+    difficulty--Natura non facit saltum--Organs of small importance--Organs
+    not in all cases absolutely perfect--The law of Unity of Type and of
+    the Conditions of Existence embraced by the theory of Natural
+    Selection.
+
+Long before having arrived at this part of my work, a crowd of difficulties
+will have occurred to the reader. Some of them are so grave that to this
+day I can never reflect on them without being staggered; but, to the best
+of my judgment, the greater number are only apparent, and those that are
+real are not, I think, fatal to my theory.
+
+These difficulties and objections may be classed under the following
+heads:--Firstly, why, if species have descended from other species by
+insensibly fine gradations, do we not everywhere see innumerable
+transitional forms? Why is not all nature in confusion instead of the
+species being, as we see them, well defined?
+
+Secondly, is it possible that an animal having, for instance, the structure
+and habits of a bat, could have been formed by the modification of some
+animal with wholly different habits? Can we believe that natural selection
+could produce, on the one hand, organs of trifling importance, such as the
+tail of a giraffe, which serves as a fly-flapper, and, on the other hand,
+organs of {172} such wonderful structure, as the eye, of which we hardly as
+yet fully understand the inimitable perfection?
+
+Thirdly, can instincts be acquired and modified through natural selection?
+What shall we say to so marvellous an instinct as that which leads the bee
+to make cells, which has practically anticipated the discoveries of
+profound mathematicians?
+
+Fourthly, how can we account for species, when crossed, being sterile and
+producing sterile offspring, whereas, when varieties are crossed, their
+fertility is unimpaired?
+
+The two first heads shall be here discussed--Instinct and Hybridism in
+separate chapters.
+
+
+
+_On the absence or rarity of transitional varieties._--As natural selection
+acts solely by the preservation of profitable modifications, each new form
+will tend in a fully-stocked country to take the place of, and finally to
+exterminate, its own less improved parent or other less-favoured forms with
+which it comes into competition. Thus extinction and natural selection
+will, as we have seen, go hand in hand. Hence, if we look at each species
+as descended from some other unknown form, both the parent and all the
+transitional varieties will generally have been exterminated by the very
+process of formation and perfection of the new form.
+
+But, as by this theory innumerable transitional forms must have existed,
+why do we not find them embedded in countless numbers in the crust of the
+earth? It will be much more convenient to discuss this question in the
+chapter on the Imperfection of the geological record; and I will here only
+state that I believe the answer mainly lies in the record being
+incomparably less perfect than is generally supposed; the imperfection of
+the record being chiefly due to organic beings not inhabiting {173}
+profound depths of the sea, and to their remains being embedded and
+preserved to a future age only in masses of sediment sufficiently thick and
+extensive to withstand an enormous amount of future degradation; and such
+fossiliferous masses can be accumulated only where much sediment is
+deposited on the shallow bed of the sea, whilst it slowly subsides. These
+contingencies will concur only rarely, and after enormously long intervals.
+Whilst the bed of the sea is stationary or is rising, or when very little
+sediment is being deposited, there will be blanks in our geological
+history. The crust of the earth is a vast museum; but the natural
+collections have been made only at intervals of time immensely remote.
+
+But it may be urged that when several closely-allied species inhabit the
+same territory we surely ought to find at the present time many
+transitional forms. Let us take a simple case: in travelling from north to
+south over a continent, we generally meet at successive intervals with
+closely allied or representative species, evidently filling nearly the same
+place in the natural economy of the land. These representative species
+often meet and interlock; and as the one becomes rarer and rarer, the other
+becomes more and more frequent, till the one replaces the other. But if we
+compare these species where they intermingle, they are generally as
+absolutely distinct from each other in every detail of structure as are
+specimens taken from the metropolis inhabited by each. By my theory these
+allied species have descended from a common parent; and during the process
+of modification, each has become adapted to the conditions of life of its
+own region, and has supplanted and exterminated its original parent and all
+the transitional varieties between its past and present states. Hence we
+ought not to expect at the {174} present time to meet with numerous
+transitional varieties in each region, though they must have existed there,
+and may be embedded there in a fossil condition. But in the intermediate
+region, having intermediate conditions of life, why do we not now find
+closely-linking intermediate varieties? This difficulty for a long time
+quite confounded me. But I think it can be in large part explained.
+
+In the first place we should be extremely cautious in inferring, because an
+area is now continuous, that it has been continuous during a long period.
+Geology would lead us to believe that almost every continent has been
+broken up into islands even during the later tertiary periods; and in such
+islands distinct species might have been separately formed without the
+possibility of intermediate varieties existing in the intermediate zones.
+By changes in the form of the land and of climate, marine areas now
+continuous must often have existed within recent times in a far less
+continuous and uniform condition than at present. But I will pass over this
+way of escaping from the difficulty; for I believe that many perfectly
+defined species have been formed on strictly continuous areas; though I do
+not doubt that the formerly broken condition of areas now continuous has
+played an important part in the formation of new species, more especially
+with freely-crossing and wandering animals.
+
+In looking at species as they are now distributed over a wide area, we
+generally find them tolerably numerous over a large territory, then
+becoming somewhat abruptly rarer and rarer on the confines, and finally
+disappearing. Hence the neutral territory between two representative
+species is generally narrow in comparison with the territory proper to
+each. We see the same fact in ascending mountains, and sometimes {175} it
+is quite remarkable how abruptly, as Alph. de Candolle has observed, a
+common alpine species disappears. The same fact has been noticed by E.
+Forbes in sounding the depths of the sea with the dredge. To those who look
+at climate and the physical conditions of life as the all-important
+elements of distribution, these facts ought to cause surprise, as climate
+and height or depth graduate away insensibly. But when we bear in mind that
+almost every species, even in its metropolis, would increase immensely in
+numbers, were it not for other competing species; that nearly all either
+prey on or serve as prey for others; in short, that each organic being is
+either directly or indirectly related in the most important manner to other
+organic beings, we must see that the range of the inhabitants of any
+country by no means exclusively depends on insensibly changing physical
+conditions, but in large part on the presence of other species, on which it
+depends, or by which it is destroyed, or with which it comes into
+competition; and as these species are already defined objects (however they
+may have become so), not blending one into another by insensible
+gradations, the range of any one species, depending as it does on the range
+of others, will tend to be sharply defined. Moreover, each species on the
+confines of its range, where it exists in lessened numbers, will, during
+fluctuations in the number of its enemies or of its prey, or in the
+seasons, be extremely liable to utter extermination; and thus its
+geographical range will come to be still more sharply defined.
+
+If I am right in believing that allied or representative species, when
+inhabiting a continuous area, are generally so distributed that each has a
+wide range, with a comparatively narrow neutral territory between them, in
+which they become rather suddenly rarer and rarer; then, as varieties do
+not essentially differ from species, {176} the same rule will probably
+apply to both; and if we in imagination adapt a varying species to a very
+large area, we shall have to adapt two varieties to two large areas, and a
+third variety to a narrow intermediate zone. The intermediate variety,
+consequently, will exist in lesser numbers from inhabiting a narrow and
+lesser area; and practically, as far as I can make out, this rule holds
+good with varieties in a state of nature. I have met with striking
+instances of the rule in the case of varieties intermediate between
+well-marked varieties in the genus Balanus. And it would appear from
+information given me by Mr. Watson, Dr. Asa Gray, and Mr. Wollaston, that
+generally when varieties intermediate between two other forms occur, they
+are much rarer numerically than the forms which they connect. Now, if we
+may trust these facts and inferences, and therefore conclude that varieties
+linking two other varieties together have generally existed in lesser
+numbers than the forms which they connect, then, I think, we can understand
+why intermediate varieties should not endure for very long periods;--why as
+a general rule they should be exterminated and disappear, sooner than the
+forms which they originally linked together.
+
+For any form existing in lesser numbers would, as already remarked, run a
+greater chance of being exterminated than one existing in large numbers;
+and in this particular case the intermediate form would be eminently liable
+to the inroads of closely allied forms existing on both sides of it. But a
+far more important consideration, as I believe, is that, during the process
+of further modification, by which two varieties are supposed on my theory
+to be converted and perfected into two distinct species, the two which
+exist in larger numbers from inhabiting larger areas, will have a great
+advantage over the intermediate variety, which exists {177} in smaller
+numbers in a narrow and intermediate zone. For forms existing in larger
+numbers will always have a better chance, within any given period, of
+presenting further favourable variations for natural selection to seize on,
+than will the rarer forms which exist in lesser numbers. Hence, the more
+common forms, in the race for life, will tend to beat and supplant the less
+common forms, for these will be more slowly modified and improved. It is
+the same principle which, as I believe, accounts for the common species in
+each country, as shown in the second chapter, presenting on an average a
+greater number of well-marked varieties than do the rarer species. I may
+illustrate what I mean by supposing three varieties of sheep to be kept,
+one adapted to an extensive mountainous region; a second to a comparatively
+narrow, hilly tract; and a third to wide plains at the base; and that the
+inhabitants are all trying with equal steadiness and skill to improve their
+stocks by selection; the chances in this case will be strongly in favour of
+the great holders on the mountains or on the plains improving their breeds
+more quickly than the small holders on the intermediate narrow, hilly
+tract; and consequently the improved mountain or plain breed will soon take
+the place of the less improved hill breed; and thus the two breeds, which
+originally existed in greater numbers, will come into close contact with
+each other, without the interposition of the supplanted, intermediate
+hill-variety.
+
+To sum up, I believe that species come to be tolerably well-defined
+objects, and do not at any one period present an inextricable chaos of
+varying and intermediate links: firstly, because new varieties are very
+slowly formed, for variation is a very slow process, and natural selection
+can do nothing until favourable {178} variations chance to occur, and until
+a place in the natural polity of the country can be better filled by some
+modification of some one or more of its inhabitants. And such new places
+will depend on slow changes of climate, or on the occasional immigration of
+new inhabitants, and, probably, in a still more important degree, on some
+of the old inhabitants becoming slowly modified, with the new forms thus
+produced and the old ones acting and reacting on each other. So that, in
+any one region and at any one time, we ought only to see a few species
+presenting slight modifications of structure in some degree permanent; and
+this assuredly we do see.
+
+Secondly, areas now continuous must often have existed within the recent
+period in isolated portions, in which many forms, more especially amongst
+the classes which unite for each birth and wander much, may have separately
+been rendered sufficiently distinct to rank as representative species. In
+this case, intermediate varieties between the several representative
+species and their common parent, must formerly have existed in each broken
+portion of the land, but these links will have been supplanted and
+exterminated during the process of natural selection, so that they will no
+longer exist in a living state.
+
+Thirdly, when two or more varieties have been formed in different portions
+of a strictly continuous area, intermediate varieties will, it is probable,
+at first have been formed in the intermediate zones, but they will
+generally have had a short duration. For these intermediate varieties will,
+from reasons already assigned (namely from what we know of the actual
+distribution of closely allied or representative species, and likewise of
+acknowledged varieties), exist in the intermediate zones in lesser numbers
+than the varieties which they {179} tend to connect. From this cause alone
+the intermediate varieties will be liable to accidental extermination; and
+during the process of further modification through natural selection, they
+will almost certainly be beaten and supplanted by the forms which they
+connect; for these from existing in greater numbers will, in the aggregate,
+present more variation, and thus be further improved through natural
+selection and gain further advantages.
+
+Lastly, looking not to any one time, but to all time, if my theory be true,
+numberless intermediate varieties, linking most closely all the species of
+the same group together, must assuredly have existed; but the very process
+of natural selection constantly tends, as has been so often remarked, to
+exterminate the parent-forms and the intermediate links. Consequently
+evidence of their former existence could be found only amongst fossil
+remains, which are preserved, as we shall in a future chapter attempt to
+show, in an extremely imperfect and intermittent record.
+
+
+
+_On the origin and transitions of organic beings with peculiar habits and
+structure._--It has been asked by the opponents of such views as I hold,
+how, for instance, a land carnivorous animal could have been converted into
+one with aquatic habits; for how could the animal in its transitional state
+have subsisted? It would be easy to show that within the same group
+carnivorous animals exist having every intermediate grade between truly
+aquatic and strictly terrestrial habits; and as each exists by a struggle
+for life, it is clear that each is well adapted in its habits to its place
+in nature. Look at the Mustela vison of North America, which has webbed
+feet and which resembles an otter in its fur, short legs, and form of tail;
+during summer this animal {180} dives for and preys on fish, but during the
+long winter it leaves the frozen waters, and preys like other polecats on
+mice and land animals. If a different case had been taken, and it had been
+asked how an insectivorous quadruped could possibly have been converted
+into a flying bat, the question would have been far more difficult, and I
+could have given no answer. Yet I think such difficulties have very little
+weight.
+
+Here, as on other occasions, I lie under a heavy disadvantage, for out of
+the many striking cases which I have collected, I can give only one or two
+instances of transitional habits and structures in closely allied species
+of the same genus; and of diversified habits, either constant or
+occasional, in the same species. And it seems to me that nothing less than
+a long list of such cases is sufficient to lessen the difficulty in any
+particular case like that of the bat.
+
+Look at the family of squirrels; here we have the finest gradation from
+animals with their tails only slightly flattened, and from others, as Sir
+J. Richardson has remarked, with the posterior part of their bodies rather
+wide and with the skin on their flanks rather full, to the so-called flying
+squirrels; and flying squirrels have their limbs and even the base of the
+tail united by a broad expanse of skin, which serves as a parachute and
+allows them to glide through the air to an astonishing distance from tree
+to tree. We cannot doubt that each structure is of use to each kind of
+squirrel in its own country, by enabling it to escape birds or beasts of
+prey, or to collect food more quickly, or, as there is reason to believe,
+by lessening the danger from occasional falls. But it does not follow from
+this fact that the structure of each squirrel is the best that it is
+possible to conceive under all natural conditions. Let the climate and
+vegetation change, let other competing {181} rodents or new beasts of prey
+immigrate, or old ones become modified, and all analogy would lead us to
+believe that some at least of the squirrels would decrease in numbers or
+become exterminated, unless they also became modified and improved in
+structure in a corresponding manner. Therefore, I can see no difficulty,
+more especially under changing conditions of life, in the continued
+preservation of individuals with fuller and fuller flank-membranes, each
+modification being useful, each being propagated, until by the accumulated
+effects of this process of natural selection, a perfect so-called flying
+squirrel was produced.
+
+Now look at the Galeopithecus or flying lemur, which formerly was falsely
+ranked amongst bats. It has an extremely wide flank-membrane, stretching
+from the corners of the jaw to the tail, and including the limbs and the
+elongated fingers: the flank-membrane is, also, furnished with an extensor
+muscle. Although no graduated links of structure, fitted for gliding
+through the air, now connect the Galeopithecus with the other Lemuridæ, yet
+I see no difficulty in supposing that such links formerly existed, and that
+each had been formed by the same steps as in the case of the less perfectly
+gliding squirrels; and that each grade of structure was useful to its
+possessor. Nor can I see any insuperable difficulty in further believing it
+possible that the membrane-connected fingers and forearm of the
+Galeopithecus might be greatly lengthened by natural selection; and this,
+as far as the organs of flight are concerned, would convert it into a bat.
+In bats which have the wing-membrane extended from the top of the shoulder
+to the tail, including the hind-legs, we perhaps see traces of an apparatus
+originally constructed for gliding through the air rather than for flight.
+{182}
+
+If about a dozen genera of birds had become extinct or were unknown, who
+would have ventured to have surmised that birds might have existed which
+used their wings solely as flappers, like the logger-headed duck
+(Micropterus of Eyton); as fins in the water and front legs on the land,
+like the penguin; as sails, like the ostrich; and functionally for no
+purpose, like the Apteryx. Yet the structure of each of these birds is good
+for it, under the conditions of life to which it is exposed, for each has
+to live by a struggle; but it is not necessarily the best possible under
+all possible conditions. It must not be inferred from these remarks that
+any of the grades of wing-structure here alluded to, which perhaps may all
+have resulted from disuse, indicate the natural steps by which birds have
+acquired their perfect power of flight; but they serve, at least, to show
+what diversified means of transition are possible.
+
+Seeing that a few members of such water-breathing classes as the Crustacea
+and Mollusca are adapted to live on the land; and seeing that we have
+flying birds and mammals, flying insects of the most diversified types, and
+formerly had flying reptiles, it is conceivable that flying-fish, which now
+glide far through the air, slightly rising and turning by the aid of their
+fluttering fins, might have been modified into perfectly winged animals. If
+this had been effected, who would have ever imagined that in an early
+transitional state they had been inhabitants of the open ocean, and had
+used their incipient organs of flight exclusively, as far as we know, to
+escape being devoured by other fish?
+
+When we see any structure highly perfected for any particular habit, as the
+wings of a bird for flight, we should bear in mind that animals displaying
+early {183} transitional grades of the structure will seldom continue to
+exist to the present day, for they will have been supplanted by the very
+process of perfection through natural selection. Furthermore, we may
+conclude that transitional grades between structures fitted for very
+different habits of life will rarely have been developed at an early period
+in great numbers and under many subordinate forms. Thus, to return to our
+imaginary illustration of the flying-fish, it does not seem probable that
+fishes capable of true flight would have been developed under many
+subordinate forms, for taking prey of many kinds in many ways, on the land
+and in the water, until their organs of flight had come to a high stage of
+perfection, so as to have given them a decided advantage over other animals
+in the battle for life. Hence the chance of discovering species with
+transitional grades of structure in a fossil condition will always be less,
+from their having existed in lesser numbers, than in the case of species
+with fully developed structures.
+
+I will now give two or three instances of diversified and of changed habits
+in the individuals of the same species. When either case occurs, it would
+be easy for natural selection to fit the animal, by some modification of
+its structure, for its changed habits, or exclusively for one of its
+several different habits. But it is difficult to tell, and immaterial for
+us, whether habits generally change first and structure afterwards; or
+whether slight modifications of structure lead to changed habits; both
+probably often change almost simultaneously. Of cases of changed habits it
+will suffice merely to allude to that of the many British insects which now
+feed on exotic plants, or exclusively on artificial substances. Of
+diversified habits innumerable instances could be given: I have often
+watched a tyrant flycatcher (Saurophagus sulphuratus) in South America,
+hovering over one spot {184} and then proceeding to another, like a
+kestrel, and at other times standing stationary on the margin of water, and
+then dashing like a kingfisher at a fish. In our own country the larger
+titmouse (Parus major) may be seen climbing branches, almost like a
+creeper; it often, like a shrike, kills small birds by blows on the head;
+and I have many times seen and heard it hammering the seeds of the yew on a
+branch, and thus breaking them like a nuthatch. In North America the black
+bear was seen by Hearne swimming for hours with widely open mouth, thus
+catching, almost like a whale, insects in the water.
+
+As we sometimes see individuals of a species following habits widely
+different from those of their own species and of the other species of the
+same genus, we might expect, on my theory, that such individuals would
+occasionally have given rise to new species, having anomalous habits, and
+with their structure either slightly or considerably modified from that of
+their proper type. And such instances do occur in nature. Can a more
+striking instance of adaptation be given than that of a woodpecker for
+climbing trees and for seizing insects in the chinks of the bark? Yet in
+North America there are woodpeckers which feed largely on fruit, and others
+with elongated wings which chase insects on the wing; and on the plains of
+La Plata, where not a tree grows, there is a woodpecker, which in every
+essential part of its organisation, even in its colouring, in the harsh
+tone of its voice, and undulatory flight, told me plainly of its close
+blood-relationship to our common species; yet it is a woodpecker which
+never climbs a tree!
+
+Petrels are the most aërial and oceanic of birds, yet in the quiet Sounds
+of Tierra del Fuego, the Puffinuria berardi, in its general habits, in its
+astonishing power of diving, its manner of swimming, and of flying when
+{185} unwillingly it takes flight, would be mistaken by any one for an auk
+or grebe; nevertheless, it is essentially a petrel, but with many parts of
+its organisation profoundly modified. On the other hand, the acutest
+observer by examining the dead body of the water-ouzel would never have
+suspected its sub-aquatic habits; yet this anomalous member of the strictly
+terrestrial thrush family wholly subsists by diving,--grasping the stones
+with its feet and using its wings under water.
+
+He who believes that each being has been created as we now see it, must
+occasionally have felt surprise when he has met with an animal having
+habits and structure not at all in agreement. What can be plainer than that
+the webbed feet of ducks and geese are formed for swimming? yet there are
+upland geese with webbed feet which rarely or never go near the water; and
+no one except Audubon has seen the frigate-bird, which has all its four
+toes webbed, alight on the surface of the sea. On the other hand grebes and
+coots are eminently aquatic, although their toes are only bordered by
+membrane. What seems plainer than that the long toes of grallatores are
+formed for walking over swamps and floating plants, yet the water-hen is
+nearly as aquatic as the coot; and the landrail nearly as terrestrial as
+the quail or partridge. In such cases, and many others could be given,
+habits have changed without a corresponding change of structure. The webbed
+feet of the upland goose may be said to have become rudimentary in
+function, though not in structure. In the frigate-bird, the deeply-scooped
+membrane between the toes shows that structure has begun to change.
+
+He who believes in separate and innumerable acts of creation will say, that
+in these cases it has pleased the Creator to cause a being of one type to
+take the place of one of another type; but this seems to me only {186}
+restating the fact in dignified language. He who believes in the struggle
+for existence and in the principle of natural selection, will acknowledge
+that every organic being is constantly endeavouring to increase in numbers;
+and that if any one being vary ever so little, either in habits or
+structure, and thus gain an advantage over some other inhabitant of the
+country, it will seize on the place of that inhabitant, however different
+it may be from its own place. Hence it will cause him no surprise that
+there should be geese and frigate-birds with webbed feet, living on the dry
+land or most rarely alighting on the water; that there should be long-toed
+corncrakes living in meadows instead of in swamps; that there should be
+woodpeckers where not a tree grows; that there should be diving thrushes,
+and petrels with the habits of auks.
+
+
+
+_Organs of extreme perfection and complication._--To suppose that the eye,
+with all its inimitable contrivances for adjusting the focus to different
+distances, for admitting different amounts of light, and for the correction
+of spherical and chromatic aberration, could have been formed by natural
+selection, seems, I freely confess, absurd in the highest possible degree.
+Yet reason tells me, that if numerous gradations from a perfect and complex
+eye to one very imperfect and simple, each grade being useful to its
+possessor, can be shown to exist; if further, the eye does vary ever so
+slightly, and the variations be inherited, which is certainly the case; and
+if any variation or modification in the organ be ever useful to an animal
+under changing conditions of life, then the difficulty of believing that a
+perfect and complex eye could be formed by natural selection, though
+insuperable by our imagination, can hardly be considered real. How a nerve
+comes to be sensitive to {187} light, hardly concerns us more than how life
+itself first originated; but I may remark that several facts make me
+suspect that any sensitive nerve may be rendered sensitive to light, and
+likewise to those coarser vibrations of the air which produce sound.
+
+In looking for the gradations by which an organ in any species has been
+perfected, we ought to look exclusively to its lineal ancestors; but this
+is scarcely ever possible, and we are forced in each case to look to
+species of the same group, that is to the collateral descendants from the
+same original parent-form, in order to see what gradations are possible,
+and for the chance of some gradations having been transmitted from the
+earlier stages of descent, in an unaltered or little altered condition.
+Amongst existing Vertebrata, we find but a small amount of gradation in the
+structure of the eye, and from fossil species we can learn nothing on this
+head. In this great class we should probably have to descend far beneath
+the lowest known fossiliferous stratum to discover the earlier stages, by
+which the eye has been perfected.
+
+In the Articulata we can commence a series with an optic nerve merely
+coated with pigment, and without any other mechanism; and from this low
+stage, numerous gradations of structure, branching off in two fundamentally
+different lines, can be shown to exist, until we reach a moderately high
+stage of perfection. In certain crustaceans, for instance, there is a
+double cornea, the inner one divided into facets, within each of which
+there is a lens-shaped swelling. In other crustaceans the transparent cones
+which are coated by pigment, and which properly act only by excluding
+lateral pencils of light, are convex at their upper ends and must act by
+convergence; and at their lower ends there seems to be an imperfect
+vitreous substance. {188} With these facts, here far too briefly and
+imperfectly given, which show that there is much graduated diversity in the
+eyes of living crustaceans, and bearing in mind how small the number of
+living animals is in proportion to those which have become extinct, I can
+see no very great difficulty (not more than in the case of many other
+structures) in believing that natural selection has converted the simple
+apparatus of an optic nerve merely coated with pigment and invested by
+transparent membrane, into an optical instrument as perfect as is possessed
+by any member of the great Articulate class.
+
+He who will go thus far, if he find on finishing this treatise that large
+bodies of facts, otherwise inexplicable, can be explained by the theory of
+descent, ought not to hesitate to go further, and to admit that a structure
+even as perfect as the eye of an eagle might be formed by natural
+selection, although in this case he does not know any of the transitional
+grades. His reason ought to conquer his imagination; though I have felt the
+difficulty far too keenly to be surprised at any degree of hesitation in
+extending the principle of natural selection to such startling lengths.
+
+It is scarcely possible to avoid comparing the eye to a telescope. We know
+that this instrument has been perfected by the long-continued efforts of
+the highest human intellects; and we naturally infer that the eye has been
+formed by a somewhat analogous process. But may not this inference be
+presumptuous? Have we any right to assume that the Creator works by
+intellectual powers like those of man? If we must compare the eye to an
+optical instrument, we ought in imagination to take a thick layer of
+transparent tissue, with a nerve sensitive to light beneath, and then
+suppose every part of this layer to be continually changing {189} slowly in
+density, so as to separate into layers of different densities and
+thicknesses, placed at different distances from each other, and with the
+surfaces of each layer slowly changing in form. Further we must suppose
+that there is a power always intently watching each slight accidental
+alteration in the transparent layers; and carefully selecting each
+alteration which, under varied circumstances, may in any way, or in any
+degree, tend to produce a distincter image. We must suppose each new state
+of the instrument to be multiplied by the million; and each to be preserved
+till a better be produced, and then the old ones to be destroyed. In living
+bodies, variation will cause the slight alterations, generation will
+multiply them almost infinitely, and natural selection will pick out with
+unerring skill each improvement. Let this process go on for millions on
+millions of years; and during each year on millions of individuals of many
+kinds; and may we not believe that a living optical instrument might thus
+be formed as superior to one of glass, as the works of the Creator are to
+those of man?
+
+If it could be demonstrated that any complex organ existed, which could not
+possibly have been formed by numerous, successive, slight modifications, my
+theory would absolutely break down. But I can find out no such case. No
+doubt many organs exist of which we do not know the transitional grades,
+more especially if we look to much-isolated species, round which, according
+to my theory, there has been much extinction. Or again, if we look to an
+organ common to all the members of a large class, for in this latter case
+the organ must have been first formed at an extremely remote period, since
+which all the many members of the class have been developed; and in order
+to discover the early transitional grades through which the organ has {190}
+passed, we should have to look to very ancient ancestral forms, long since
+become extinct.
+
+We should be extremely cautious in concluding that an organ could not have
+been formed by transitional gradations of some kind. Numerous cases could
+be given amongst the lower animals of the same organ performing at the same
+time wholly distinct functions; thus the alimentary canal respires,
+digests, and excretes in the larva of the dragon-fly and in the fish
+Cobites. In the Hydra, the animal may be turned inside out, and the
+exterior surface will then digest and the stomach respire. In such cases
+natural selection might easily specialise, if any advantage were thus
+gained, a part or organ, which had performed two functions, for one
+function alone, and thus wholly change its nature by insensible steps. Two
+distinct organs sometimes perform simultaneously the same function in the
+same individual; to give one instance, there are fish with gills or
+branchiæ that breathe the air dissolved in the water, at the same time that
+they breathe free air in their swimbladders, this latter organ having a
+ductus pneumaticus for its supply, and being divided by highly vascular
+partitions. In these cases one of the two organs might with ease be
+modified and perfected so as to perform all the work by itself, being aided
+during the process of modification by the other organ; and then this other
+organ might be modified for some other and quite distinct purpose, or be
+quite obliterated.
+
+The illustration of the swimbladder in fishes is a good one, because it
+shows us clearly the highly important fact that an organ originally
+constructed for one purpose, namely flotation, may be converted into one
+for a wholly different purpose, namely respiration. The swimbladder has,
+also, been worked in as an accessory to the auditory organs of certain
+fish, or, for I do not know {191} which view is now generally held, a part
+of the auditory apparatus has been worked in as a complement to the
+swimbladder. All physiologists admit that the swimbladder is homologous, or
+"ideally similar" in position and structure with the lungs of the higher
+vertebrate animals: hence there seems to me to be no great difficulty in
+believing that natural selection has actually converted a swimbladder into
+a lung, or organ used exclusively for respiration.
+
+I can, indeed, hardly doubt that all vertebrate animals having true lungs
+have descended by ordinary generation from an ancient prototype, of which
+we know nothing, furnished with a floating apparatus or swimbladder. We can
+thus, as I infer from Professor Owen's interesting description of these
+parts, understand the strange fact that every particle of food and drink
+which we swallow has to pass over the orifice of the trachea, with some
+risk of falling into the lungs, notwithstanding the beautiful contrivance
+by which the glottis is closed. In the higher Vertebrata the branchiæ have
+wholly disappeared--the slits on the sides of the neck and the loop-like
+course of the arteries still marking in the embryo their former position.
+But it is conceivable that the now utterly lost branchiæ might have been
+gradually worked in by natural selection for some quite distinct purpose:
+in the same manner as, on the view entertained by some naturalists that the
+branchiæ and dorsal scales of Annelids are homologous with the wings and
+wing-covers of insects, it is probable that organs which at a very ancient
+period served for respiration have been actually converted into organs of
+flight.
+
+In considering transitions of organs, it is so important to bear in mind
+the probability of conversion from one function to another, that I will
+give one more instance. Pedunculated cirripedes have two minute folds of
+skin, {192} called by me the ovigerous frena, which serve, through the
+means of a sticky secretion, to retain the eggs until they are hatched
+within the sack. These cirripedes have no branchiæ, the whole surface of
+the body and sack, including the small frena, serving for respiration. The
+Balanidæ or sessile cirripedes, on the other hand, have no ovigerous frena,
+the eggs lying loose at the bottom of the sack, in the well-enclosed shell;
+but they have large folded branchiæ. Now I think no one will dispute that
+the ovigerous frena in the one family are strictly homologous with the
+branchiæ of the other family; indeed, they graduate into each other.
+Therefore I do not doubt that little folds of skin, which originally served
+as ovigerous frena, but which, likewise, very slightly aided the act of
+respiration, have been gradually converted by natural selection into
+branchiæ, simply through an increase in their size and the obliteration of
+their adhesive glands. If all pedunculated cirripedes had become extinct,
+and they have already suffered far more extinction than have sessile
+cirripedes, who would ever have imagined that the branchiæ in this latter
+family had originally existed as organs for preventing the ova from being
+washed out of the sack?
+
+Although we must be extremely cautious in concluding that any organ could
+not possibly have been produced by successive transitional gradations, yet,
+undoubtedly, grave cases of difficulty occur, some of which will be
+discussed in my future work.
+
+One of the gravest is that of neuter insects, which are often very
+differently constructed from either the males or fertile females; but this
+case will be treated of in the next chapter. The electric organs of fishes
+offer another case of special difficulty; it is impossible to conceive by
+what steps these wondrous organs have been produced; but, as Owen and
+others have remarked, {193} their intimate structure closely resembles that
+of common muscle; and as it has lately been shown that Rays have an organ
+closely analogous to the electric apparatus, and yet do not, as Matteucci
+asserts, discharge any electricity, we must own that we are far too
+ignorant to argue that no transition of any kind is possible.
+
+The electric organs offer another and even more serious difficulty; for
+they occur in only about a dozen fishes, of which several are widely remote
+in their affinities. Generally when the same organ appears in several
+members of the same class, especially if in members having very different
+habits of life, we may attribute its presence to inheritance from a common
+ancestor; and its absence in some of the members to its loss through disuse
+or natural selection. But if the electric organs had been inherited from
+one ancient progenitor thus provided, we might have expected that all
+electric fishes would have been specially related to each other. Nor does
+geology at all lead to the belief that formerly most fishes had electric
+organs, which most of their modified descendants have lost. The presence of
+luminous organs in a few insects, belonging to different families and
+orders, offers a parallel case of difficulty. Other cases could be given;
+for instance in plants, the very curious contrivance of a mass of
+pollen-grains, borne on a foot-stalk with a sticky gland at the end, is the
+same in Orchis and Asclepias,--genera almost as remote as possible amongst
+flowering plants. In all these cases of two very distinct species furnished
+with apparently the same anomalous organ, it should be observed that,
+although the general appearance and function of the organ may be the same,
+yet some fundamental difference can generally be detected. I am inclined to
+believe that in nearly the same way as two men have sometimes independently
+hit on {194} the very same invention, so natural selection, working for the
+good of each being and taking advantage of analogous variations, has
+sometimes modified in very nearly the same manner two parts in two organic
+beings, which beings owe but little of their structure in common to
+inheritance from the same ancestor.
+
+Although in many cases it is most difficult to conjecture by what
+transitions organs could have arrived at their present state; yet,
+considering that the proportion of living and known forms to the extinct
+and unknown is very small, I have been astonished how rarely an organ can
+be named, towards which no transitional grade is known to lead. The truth
+of this remark is indeed shown by that old but somewhat exaggerated canon
+in natural history of "Natura non facit saltum." We meet with this
+admission in the writings of almost every experienced naturalist; or, as
+Milne Edwards has well expressed it, Nature is prodigal in variety, but
+niggard in innovation. Why, on the theory of Creation, should this be so?
+Why should all the parts and organs of many independent beings, each
+supposed to have been separately created for its proper place in nature, be
+so commonly linked together by graduated steps? Why should not Nature have
+taken a leap from structure to structure? On the theory of natural
+selection, we can clearly understand why she should not; for natural
+selection can act only by taking advantage of slight successive variations;
+she can never take a leap, but must advance by the shortest and slowest
+steps.
+
+
+
+_Organs of little apparent importance._--As natural selection acts by life
+and death,--by the preservation of individuals with any favourable
+variation, and by the destruction of those with any unfavourable deviation
+of structure,--I have sometimes felt much difficulty in {195} understanding
+the origin of simple parts, of which the importance does not seem
+sufficient to cause the preservation of successively varying individuals. I
+have sometimes felt as much difficulty, though of a very different kind, on
+this head, as in the case of an organ as perfect and complex as the eye.
+
+In the first place, we are much too ignorant in regard to the whole economy
+of any one organic being, to say what slight modifications would be of
+importance or not. In a former chapter I have given instances of most
+trifling characters, such as the down on fruit and the colour of its flesh,
+which, from determining the attacks of insects or from being correlated
+with constitutional differences, might assuredly be acted on by natural
+selection. The tail of the giraffe looks like an artificially constructed
+fly-flapper; and it seems at first incredible that this could have been
+adapted for its present purpose by successive slight modifications, each
+better and better, for so trifling an object as driving away flies; yet we
+should pause before being too positive even in this case, for we know that
+the distribution and existence of cattle and other animals in South America
+absolutely depends on their power of resisting the attacks of insects: so
+that individuals which could by any means defend themselves from these
+small enemies, would be able to range into new pastures and thus gain a
+great advantage. It is not that the larger quadrupeds are actually
+destroyed (except in some rare cases) by flies, but they are incessantly
+harassed and their strength reduced, so that they are more subject to
+disease, or not so well enabled in a coming dearth to search for food, or
+to escape from beasts of prey.
+
+Organs now of trifling importance have probably in some cases been of high
+importance to an early progenitor, and, after having been slowly perfected
+at a {196} former period, have been transmitted in nearly the same state,
+although now become of very slight use; and any actually injurious
+deviations in their structure will always have been checked by natural
+selection. Seeing how important an organ of locomotion the tail is in most
+aquatic animals, its general presence and use for many purposes in so many
+land animals, which in their lungs or modified swimbladders betray their
+aquatic origin, may perhaps be thus accounted for. A well-developed tail
+having been formed in an aquatic animal, it might subsequently come to be
+worked in for all sorts of purposes, as a fly-flapper, an organ of
+prehension, or as an aid in turning, as with the dog, though the aid must
+be slight, for the hare, with hardly any tail, can double quickly enough.
+
+In the second place, we may sometimes attribute importance to characters
+which are really of very little importance, and which have originated from
+quite secondary causes, independently of natural selection. We should
+remember that climate, food, &c., probably have some little direct
+influence on the organisation; that characters reappear from the law of
+reversion; that correlation of growth will have had a most important
+influence in modifying various structures; and finally, that sexual
+selection will often have largely modified the external characters of
+animals having a will, to give one male an advantage in fighting with
+another or in charming the females. Moreover when a modification of
+structure has primarily arisen from the above or other unknown causes, it
+may at first have been of no advantage to the species, but may subsequently
+have been taken advantage of by the descendants of the species under new
+conditions of life and with newly acquired habits.
+
+To give a few instances to illustrate these latter {197} remarks. If green
+woodpeckers alone had existed, and we did not know that there were many
+black and pied kinds, I dare say that we should have thought that the green
+colour was a beautiful adaptation to hide this tree-frequenting bird from
+its enemies; and consequently that it was a character of importance and
+might have been acquired through natural selection; as it is, I have no
+doubt that the colour is due to some quite distinct cause, probably to
+sexual selection. A trailing bamboo in the Malay Archipelago climbs the
+loftiest trees by the aid of exquisitely constructed hooks clustered around
+the ends of the branches, and this contrivance, no doubt, is of the highest
+service to the plant; but as we see nearly similar hooks on many trees
+which are not climbers, the hooks on the bamboo may have arisen from
+unknown laws of growth, and have been subsequently taken advantage of by
+the plant undergoing further modification and becoming a climber. The naked
+skin on the head of a vulture is generally looked at as a direct adaptation
+for wallowing in putridity; and so it may be, or it may possibly be due to
+the direct action of putrid matter; but we should be very cautious in
+drawing any such inference, when we see that the skin on the head of the
+clean-feeding male turkey is likewise naked. The sutures in the skulls of
+young mammals have been advanced as a beautiful adaptation for aiding
+parturition, and no doubt they facilitate, or may be indispensable for this
+act; but as sutures occur in the skulls of young birds and reptiles, which
+have only to escape from a broken egg, we may infer that this structure has
+arisen from the laws of growth, and has been taken advantage of in the
+parturition of the higher animals.
+
+We are profoundly ignorant of the causes producing slight and unimportant
+variations; and we are {198} immediately made conscious of this by
+reflecting on the differences in the breeds of our domesticated animals in
+different countries,--more especially in the less civilised countries where
+there has been but little artificial selection. Careful observers are
+convinced that a damp climate affects the growth of the hair, and that with
+the hair the horns are correlated. Mountain breeds always differ from
+lowland breeds; and a mountainous country would probably affect the hind
+limbs from exercising them more, and possibly even the form of the pelvis;
+and then by the law of homologous variation, the front limbs and even the
+head would probably be affected. The shape, also, of the pelvis might
+affect by pressure the shape of the head of the young in the womb. The
+laborious breathing necessary in high regions would, we have some reason to
+believe, increase the size of the chest; and again correlation would come
+into play. Animals kept by savages in different countries often have to
+struggle for their own subsistence, and would be exposed to a certain
+extent to natural selection, and individuals with slightly different
+constitutions would succeed best under different climates; and there is
+reason to believe that constitution and colour are correlated. A good
+observer, also, states that in cattle susceptibility to the attacks of
+flies is correlated with colour, as is the liability to be poisoned by
+certain plants; so that colour would be thus subjected to the action of
+natural selection. But we are far too ignorant to speculate on the relative
+importance of the several known and unknown laws of variation; and I have
+here alluded to them only to show that, if we are unable to account for the
+characteristic differences of our domestic breeds, which nevertheless we
+generally admit to have arisen through ordinary generation, we ought not to
+lay too much stress on our ignorance of the precise cause {199} of the
+slight analogous differences between species. I might have adduced for this
+same purpose the differences between the races of man, which are so
+strongly marked; I may add that some little light can apparently be thrown
+on the origin of these differences, chiefly through sexual selection of a
+particular kind, but without here entering on copious details my reasoning
+would appear frivolous.
+
+The foregoing remarks lead me to say a few words on the protest lately made
+by some naturalists, against the utilitarian doctrine that every detail of
+structure has been produced for the good of its possessor. They believe
+that very many structures have been created for beauty in the eyes of man,
+or for mere variety. This doctrine, if true, would be absolutely fatal to
+my theory. Yet I fully admit that many structures are of no direct use to
+their possessors. Physical conditions probably have had some little effect
+on structure, quite independently of any good thus gained. Correlation of
+growth has no doubt played a most important part, and a useful modification
+of one part will often have entailed on other parts diversified changes of
+no direct use. So again characters which formerly were useful, or which
+formerly had arisen from correlation of growth, or from other unknown
+cause, may reappear from the law of reversion, though now of no direct use.
+The effects of sexual selection, when displayed in beauty to charm the
+females, can be called useful only in rather a forced sense. But by far the
+most important consideration is that the chief part of the organisation of
+every being is simply due to inheritance; and consequently, though each
+being assuredly is well fitted for its place in nature, many structures now
+have no direct relation to the habits of life of each species. Thus, we can
+hardly believe that the webbed feet of the upland {200} goose or of the
+frigate-bird are of special use to these birds; we cannot believe that the
+same bones in the arm of the monkey, in the fore-leg of the horse, in the
+wing of the bat, and in the nipper of the seal, are of special use to these
+animals. We may safely attribute these structures to inheritance. But to
+the progenitor of the upland goose and of the frigate-bird, webbed feet no
+doubt were as useful as they now are to the most aquatic of existing birds.
+So we may believe that the progenitor of the seal had not a nipper, but a
+foot with five toes fitted for walking or grasping; and we may further
+venture to believe that the several bones in the limbs of the monkey,
+horse, and bat, which have been inherited from a common progenitor, were
+formerly of more special use to that progenitor, or its progenitors, than
+they now are to these animals having such widely diversified habits.
+Therefore we may infer that these several bones might have been acquired
+through natural selection, subjected formerly, as now, to the several laws
+of inheritance, reversion, correlation of growth, &c. Hence every detail of
+structure in every living creature (making some little allowance for the
+direct action of physical conditions) may be viewed, either as having been
+of special use to some ancestral form, or as being now of special use to
+the descendants of this form--either directly, or indirectly through the
+complex laws of growth.
+
+Natural selection cannot possibly produce any modification in any one
+species exclusively for the good of another species; though throughout
+nature one species incessantly takes advantage of, and profits by, the
+structure of another. But natural selection can and does often produce
+structures for the direct injury of other species, as we see in the fang of
+the adder, and in the ovipositor of the ichneumon, by which its eggs are
+{201} deposited in the living bodies of other insects. If it could be
+proved that any part of the structure of any one species had been formed
+for the exclusive good of another species, it would annihilate my theory,
+for such could not have been produced through natural selection. Although
+many statements may be found in works on natural history to this effect, I
+cannot find even one which seems to me of any weight. It is admitted that
+the rattlesnake has a poison-fang for its own defence and for the
+destruction of its prey; but some authors suppose that at the same time
+this snake is furnished with a rattle for its own injury, namely, to warn
+its prey to escape. I would almost as soon believe that the cat curls the
+end of its tail when preparing to spring, in order to warn the doomed
+mouse. But I have not space here to enter on this and other such cases.
+
+Natural selection will never produce in a being anything injurious to
+itself, for natural selection acts solely by and for the good of each. No
+organ will be formed, as Paley has remarked, for the purpose of causing
+pain or for doing an injury to its possessor. If a fair balance be struck
+between the good and evil caused by each part, each will be found on the
+whole advantageous. After the lapse of time, under changing conditions of
+life, if any part comes to be injurious, it will be modified; or if it be
+not so, the being will become extinct, as myriads have become extinct.
+
+Natural selection tends only to make each organic being as perfect as, or
+slightly more perfect than, the other inhabitants of the same country with
+which it has to struggle for existence. And we see that this is the degree
+of perfection attained under nature. The endemic productions of New
+Zealand, for instance, are perfect one compared with another; but they are
+now rapidly yielding before the advancing legions of plants {202} and
+animals introduced from Europe. Natural selection will not produce absolute
+perfection, nor do we always meet, as far as we can judge, with this high
+standard under nature. The correction for the aberration of light is said,
+on high authority, not to be perfect even in that most perfect organ, the
+eye. If our reason leads us to admire with enthusiasm a multitude of
+inimitable contrivances in nature, this same reason tells us, though we may
+easily err on both sides, that some other contrivances are less perfect.
+Can we consider the sting of the wasp or of the bee as perfect, which, when
+used against many attacking animals, cannot be withdrawn, owing to the
+backward serratures, and so inevitably causes the death of the insect by
+tearing out its viscera?
+
+If we look at the sting of the bee, as having originally existed in a
+remote progenitor as a boring and serrated instrument, like that in so many
+members of the same great order, and which has been modified but not
+perfected for its present purpose, with the poison originally adapted to
+cause galls subsequently intensified, we can perhaps understand how it is
+that the use of the sting should so often cause the insect's own death: for
+if on the whole the power of stinging be useful to the community, it will
+fulfil all the requirements of natural selection, though it may cause the
+death of some few members. If we admire the truly wonderful power of scent
+by which the males of many insects find their females, can we admire the
+production for this single purpose of thousands of drones, which are
+utterly useless to the community for any other end, and which are
+ultimately slaughtered by their industrious and sterile sisters? It may be
+difficult, but we ought to admire the savage instinctive hatred of the
+queen-bee, which urges her instantly to destroy the {203} young queens her
+daughters as soon as born, or to perish herself in the combat; for
+undoubtedly this is for the good of the community; and maternal love or
+maternal hatred, though the latter fortunately is most rare, is all the
+same to the inexorable principle of natural selection. If we admire the
+several ingenious contrivances, by which the flowers of the orchis and of
+many other plants are fertilised through insect agency, can we consider as
+equally perfect the elaboration by our fir-trees of dense clouds of pollen,
+in order that a few granules may be wafted by a chance breeze on to the
+ovules?
+
+
+
+_Summary of Chapter._--We have in this chapter discussed some of the
+difficulties and objections which may be urged against my theory. Many of
+them are very serious; but I think that in the discussion light has been
+thrown on several facts, which on the theory of independent acts of
+creation are utterly obscure. We have seen that species at any one period
+are not indefinitely variable, and are not linked together by a multitude
+of intermediate gradations, partly because the process of natural selection
+will always be very slow, and will act, at any one time, only on a very few
+forms; and partly because the very process of natural selection almost
+implies the continual supplanting and extinction of preceding and
+intermediate gradations. Closely allied species, now living on a continuous
+area, must often have been formed when the area was not continuous, and
+when the conditions of life did not insensibly graduate away from one part
+to another. When two varieties are formed in two districts of a continuous
+area, an intermediate variety will often be formed, fitted for an
+intermediate zone; but from reasons assigned, the intermediate variety will
+usually exist in lesser numbers than {204} the two forms which it connects;
+consequently the two latter, during the course of further modification,
+from existing in greater numbers, will have a great advantage over the less
+numerous intermediate variety, and will thus generally succeed in
+supplanting and exterminating it.
+
+We have seen in this chapter how cautious we should be in concluding that
+the most different habits of life could not graduate into each other; that
+a bat, for instance, could not have been formed by natural selection from
+an animal which at first could only glide through the air.
+
+We have seen that a species may under new conditions of life change its
+habits, or have diversified habits, with some habits very unlike those of
+its nearest congeners. Hence we can understand, bearing in mind that each
+organic being is trying to live wherever it can live, how it has arisen
+that there are upland geese with webbed feet, ground woodpeckers, diving
+thrushes, and petrels with the habits of auks.
+
+Although the belief that an organ so perfect as the eye could have been
+formed by natural selection, is more than enough to stagger any one; yet in
+the case of any organ, if we know of a long series of gradations in
+complexity, each good for its possessor, then, under changing conditions of
+life there is no logical impossibility in the acquirement of any
+conceivable degree of perfection through natural selection. In the cases in
+which we know of no intermediate or transitional states, we should be very
+cautious in concluding that none could have existed, for the homologies of
+many organs and their intermediate states show that wonderful metamorphoses
+in function are at least possible. For instance, a swim-bladder has
+apparently been converted into an air-breathing lung. The same organ having
+performed {205} simultaneously very different functions, and then having
+been specialised for one function; and two very distinct organs having
+performed at the same time the same function, the one having been perfected
+whilst aided by the other, must often have largely facilitated transitions.
+
+We are far too ignorant, in almost every case, to be enabled to assert that
+any part or organ is so unimportant for the welfare of a species, that
+modifications in its structure could not have been slowly accumulated by
+means of natural selection. But we may confidently believe that many
+modifications, wholly due to the laws of growth, and at first in no way
+advantageous to a species, have been subsequently taken advantage of by the
+still further modified descendants of this species. We may, also, believe
+that a part formerly of high importance has often been retained (as the
+tail of an aquatic animal by its terrestrial descendants), though it has
+become of such small importance that it could not, in its present state,
+have been acquired by natural selection,--a power which acts solely by the
+preservation of profitable variations in the struggle for life.
+
+Natural selection will produce nothing in one species for the exclusive
+good or injury of another; though it may well produce parts, organs, and
+excretions highly useful or even indispensable, or highly injurious to
+another species, but in all cases at the same time useful to the owner.
+Natural selection in each well-stocked country, must act chiefly through
+the competition of the inhabitants one with another, and consequently will
+produce perfection, or strength in the battle for life, only according to
+the standard of that country. Hence the inhabitants of one country,
+generally the smaller one, will often yield, as we see they do yield, to
+the inhabitants of another and generally larger country. For in {206} the
+larger country there will have existed more individuals, and more
+diversified forms, and the competition will have been severer, and thus the
+standard of perfection will have been rendered higher. Natural selection
+will not necessarily produce absolute perfection; nor, as far as we can
+judge by our limited faculties, can absolute perfection be everywhere
+found.
+
+On the theory of natural selection we can clearly understand the full
+meaning of that old canon in natural history, "Natura non facit saltum."
+This canon, if we look only to the present inhabitants of the world, is not
+strictly correct, but if we include all those of past times, it must by my
+theory be strictly true.
+
+It is generally acknowledged that all organic beings have been formed on
+two great laws--Unity of Type, and the Conditions of Existence. By unity of
+type is meant that fundamental agreement in structure, which we see in
+organic beings of the same class, and which is quite independent of their
+habits of life. On my theory, unity of type is explained by unity of
+descent. The expression of conditions of existence, so often insisted on by
+the illustrious Cuvier, is fully embraced by the principle of natural
+selection. For natural selection acts by either now adapting the varying
+parts of each being to its organic and inorganic conditions of life; or by
+having adapted them during long-past periods of time: the adaptations being
+aided in some cases by use and disuse, being slightly affected by the
+direct action of the external conditions of life, and being in all cases
+subjected to the several laws of growth. Hence, in fact, the law of the
+Conditions of Existence is the higher law; as it includes, through the
+inheritance of former adaptations, that of Unity of Type.
+
+       *       *       *       *       *
+
+
+{207}
+
+CHAPTER VII.
+
+INSTINCT.
+
+    Instincts comparable with habits, but different in their
+    origin--Instincts graduated--Aphides and ants--Instincts
+    variable--Domestic instincts, their origin--Natural instincts of the
+    cuckoo, ostrich, and parasitic bees--Slave-making-ants--Hive-bee, its
+    cell-making instinct--Difficulties on the theory of the Natural
+    Selection of instincts--Neuter or sterile insects--Summary.
+
+The subject of instinct might have been worked into the previous chapters;
+but I have thought that it would be more convenient to treat the subject
+separately, especially as so wonderful an instinct as that of the hive-bee
+making its cells will probably have occurred to many readers, as a
+difficulty sufficient to overthrow my whole theory. I must premise, that I
+have nothing to do with the origin of the primary mental powers, any more
+than I have with that of life itself. We are concerned only with the
+diversities of instinct and of the other mental qualities of animals within
+the same class.
+
+I will not attempt any definition of instinct. It would be easy to show
+that several distinct mental actions are commonly embraced by this term;
+but every one understands what is meant, when it is said that instinct
+impels the cuckoo to migrate and to lay her eggs in other birds' nests. An
+action, which we ourselves should require experience to enable us to
+perform, when performed by an animal, more especially by a very young one,
+without any experience, and when performed by many individuals in the same
+way, without their knowing for what purpose it is performed, is usually
+said to be instinctive. {208} But I could show that none of these
+characters of instinct are universal. A little dose, as Pierre Huber
+expresses it, of judgment or reason, often comes into play, even in animals
+very low in the scale of nature.
+
+Frederick Cuvier and several of the older metaphysicians have compared
+instinct with habit. This comparison gives, I think, a remarkably accurate
+notion of the frame of mind under which an instinctive action is performed,
+but not of its origin. How unconsciously many habitual actions are
+performed, indeed not rarely in direct opposition to our conscious will!
+yet they may be modified by the will or reason. Habits easily become
+associated with other habits, and with certain periods of time and states
+of the body. When once acquired, they often remain constant throughout
+life. Several other points of resemblance between instincts and habits
+could be pointed out. As in repeating a well-known song, so in instincts,
+one action follows another by a sort of rhythm; if a person be interrupted
+in a song, or in repeating anything by rote, he is generally forced to go
+back to recover the habitual train of thought: so P. Huber found it was
+with a caterpillar, which makes a very complicated hammock; for if he took
+a caterpillar which had completed its hammock up to, say, the sixth stage
+of construction, and put it into a hammock completed up only to the third
+stage, the caterpillar simply re-performed the fourth, fifth, and sixth
+stages of construction. If, however, a caterpillar were taken out of a
+hammock made up, for instance, to the third stage, and were put into one
+finished up to the sixth stage, so that much of its work, was already done
+for it, far from feeling the benefit of this, it was much embarrassed, and,
+in order to complete its hammock, seemed forced to start from the third
+stage, where it had left off, and thus tried to complete the already
+finished work. {209}
+
+If we suppose any habitual action to become inherited--and I think it can
+be shown that this does sometimes happen--then the resemblance between what
+originally was a habit and an instinct becomes so close as not to be
+distinguished. If Mozart, instead of playing the pianoforte at three years
+old with wonderfully little practice, had played a tune with no practice at
+all, he might truly be said to have done so instinctively. But it would be
+the most serious error to suppose that the greater number of instincts have
+been acquired by habit in one generation, and then transmitted by
+inheritance to succeeding generations. It can be clearly shown that the
+most wonderful instincts with which we are acquainted, namely, those of the
+hive-bee and of many ants, could not possibly have been thus acquired.
+
+It will be universally admitted that instincts are as important as
+corporeal structure for the welfare of each species, under its present
+conditions of life. Under changed conditions of life, it is at least
+possible that slight modifications of instinct might be profitable to a
+species; and if it can be shown that instincts do vary ever so little, then
+I can see no difficulty in natural selection preserving and continually
+accumulating variations of instinct to any extent that may be profitable.
+It is thus, as I believe, that all the most complex and wonderful instincts
+have originated. As modifications of corporeal structure arise from, and
+are increased by, use or habit, and are diminished or lost by disuse, so I
+do not doubt it has been with instincts. But I believe that the effects of
+habit are of quite subordinate importance to the effects of the natural
+selection of what may be called accidental variations of instincts;--that
+is of variations produced by the same unknown causes which produce slight
+deviations of bodily structure.
+
+No complex instinct can possibly be produced through {210} natural
+selection, except by the slow and gradual accumulation of numerous, slight,
+yet profitable, variations. Hence, as in the case of corporeal structures,
+we ought to find in nature, not the actual transitional gradations by which
+each complex instinct has been acquired--for these could be found only in
+the lineal ancestors of each species--but we ought to find in the
+collateral lines of descent some evidence of such gradations; or we ought
+at least to be able to show that gradations of some kind are possible; and
+this we certainly can do. I have been surprised to find, making allowance
+for the instincts of animals having been but little observed except in
+Europe and North America, and for no instinct being known amongst extinct
+species, how very generally gradations, leading to the most complex
+instincts, can be discovered. Changes of instinct may sometimes be
+facilitated by the same species having different instincts at different
+periods of life, or at different seasons of the year, or when placed under
+different circumstances &c.; in which case either one or the other instinct
+might be preserved by natural selection. And such instances of diversity of
+instinct in the same species can be shown to occur in nature.
+
+Again as in the case of corporeal structure, and conformably with my
+theory, the instinct of each species is good for itself, but has never, as
+far as we can judge, been produced for the exclusive good of others. One of
+the strongest instances of an animal apparently performing an action for
+the sole good of another, with which I am acquainted, is that of aphides
+voluntarily yielding their sweet excretion to ants: that they do so
+voluntarily, the following facts show. I removed all the ants from a group
+of about a dozen aphides on a dock-plant, and prevented their attendance
+during several hours. After this interval, I felt sure that the aphides
+{211} would want to excrete. I watched them for some time through a lens,
+but not one excreted; I then tickled and stroked them with a hair in the
+same manner, as well as I could, as the ants do with their antennæ; but not
+one excreted. Afterwards I allowed an ant to visit them, and it immediately
+seemed, by its eager way of running about, to be well aware what a rich
+flock it had discovered; it then began to play with its antennæ on the
+abdomen first of one aphis and then of another; and each aphis, as soon as
+it felt the antennæ, immediately lifted up its abdomen and excreted a
+limpid drop of sweet juice, which was eagerly devoured by the ant. Even the
+quite young aphides behaved in this manner, showing that the action was
+instinctive, and not the result of experience. But as the excretion is
+extremely viscid, it is probably a convenience to the aphides to have it
+removed; and therefore probably the aphides do not instinctively excrete
+for the sole good of the ants. Although I do not believe that any animal in
+the world performs an action for the exclusive good of another of a
+distinct species, yet each species tries to take advantage of the instincts
+of others, as each takes advantage of the weaker bodily structure of
+others. So again, in some few cases, certain instincts cannot be considered
+as absolutely perfect; but as details on this and other such points are not
+indispensable, they may be here passed over.
+
+As some degree of variation in instincts under a state of nature, and the
+inheritance of such variations, are indispensable for the action of natural
+selection, as many instances as possible ought to be here given; but want
+of space prevents me. I can only assert, that instincts certainly do
+vary--for instance, the migratory instinct, both in extent and direction,
+and in its total loss. So it is with the nests of birds, which vary partly
+{212} in dependence on the situations chosen, and on the nature and
+temperature of the country inhabited, but often from causes wholly unknown
+to us: Audubon has given several remarkable cases of differences in the
+nests of the same species in the northern and southern United States. Fear
+of any particular enemy is certainly an instinctive quality, as may be seen
+in nestling birds, though it is strengthened by experience, and by the
+sight of fear of the same enemy in other animals. But fear of man is slowly
+acquired, as I have elsewhere shown, by various animals inhabiting desert
+islands; and we may see an instance of this, even in England, in the
+greater wildness of all our large birds than of our small birds; for the
+large birds have been most persecuted by man. We may safely attribute the
+greater wildness of our large birds to this cause; for in uninhabited
+islands large birds are not more fearful than small; and the magpie, so
+wary in England, is tame in Norway, as is the hooded crow in Egypt.
+
+That the general disposition of individuals of the same species, born in a
+state of nature, is extremely diversified, can be shown by a multitude of
+facts. Several cases also, could be given, of occasional and strange habits
+in certain species, which might, if advantageous to the species, give rise,
+through natural selection, to quite new instincts. But I am well aware that
+these general statements, without facts given in detail, can produce but a
+feeble effect on the reader's mind. I can only repeat my assurance, that I
+do not speak without good evidence.
+
+The possibility, or even probability, of inherited variations of instinct
+in a state of nature will be strengthened by briefly considering a few
+cases under domestication. We shall thus also be enabled to see the
+respective parts which habit and the selection of {213} so-called
+accidental variations have played in modifying the mental qualities of our
+domestic animals. A number of curious and authentic instances could be
+given of the inheritance of all shades of disposition and tastes, and
+likewise of the oddest tricks, associated with certain frames of mind or
+periods of time. But let us look to the familiar case of the several breeds
+of dogs: it cannot be doubted that young pointers (I have myself seen a
+striking instance) will sometimes point and even back other dogs the very
+first time that they are taken out; retrieving is certainly in some degree
+inherited by retrievers; and a tendency to run round, instead of at, a
+flock of sheep, by shepherd-dogs. I cannot see that these actions,
+performed without experience by the young, and in nearly the same manner by
+each individual, performed with eager delight by each breed, and without
+the end being known,--for the young pointer can no more know that he points
+to aid his master, than the white butterfly knows why she lays her eggs on
+the leaf of the cabbage,--I cannot see that these actions differ
+essentially from true instincts. If we were to see one kind of wolf, when
+young and without any training, as soon as it scented its prey, stand
+motionless like a statue, and then slowly crawl forward with a peculiar
+gait; and another kind of wolf rushing round, instead of at, a herd of
+deer, and driving them to a distant point, we should assuredly call these
+actions instinctive. Domestic instincts, as they may be called, are
+certainly far less fixed or invariable than natural instincts; but they
+have been acted on by far less rigorous selection, and have been
+transmitted for an incomparably shorter period, under less fixed conditions
+of life.
+
+How strongly these domestic instincts, habits, and dispositions are
+inherited, and how curiously they become mingled, is well shown when
+different breeds of dogs are {214} crossed. Thus it is known that a cross
+with a bull-dog has affected for many generations the courage and obstinacy
+of greyhounds; and a cross with a greyhound has given to a whole family of
+shepherd-dogs a tendency to hunt hares. These domestic instincts, when thus
+tested by crossing, resemble natural instincts, which in a like manner
+become curiously blended together, and for a long period exhibit traces of
+the instincts of either parent: for example, Le Roy describes a dog, whose
+great-grandfather was a wolf, and this dog showed a trace of its wild
+parentage only in one way, by not coming in a straight line to his master
+when called.
+
+Domestic instincts are sometimes spoken of as actions which have become
+inherited solely from long-continued and compulsory habit, but this, I
+think, is not true. No one would ever have thought of teaching, or probably
+could have taught, the tumbler-pigeon to tumble,--an action which, as I
+have witnessed, is performed by young birds, that have never seen a pigeon
+tumble. We may believe that some one pigeon showed a slight tendency to
+this strange habit, and that the long-continued selection of the best
+individuals in successive generations made tumblers what they now are; and
+near Glasgow there are house-tumblers, as I hear from Mr. Brent, which
+cannot fly eighteen inches high without going head over heels. It may be
+doubted whether any one would have thought of training a dog to point, had
+not some one dog naturally shown a tendency in this line; and this is known
+occasionally to happen, as I once saw in a pure terrier: the act of
+pointing is probably, as many have thought, only the exaggerated pause of
+an animal preparing to spring on its prey. When the first tendency to point
+was once displayed, methodical selection and the inherited effects of
+compulsory training in each successive generation would soon complete the
+{215} work; and unconscious selection is still at work, as each man tries
+to procure, without intending to improve the breed, dogs which will stand
+and hunt best. On the other hand, habit alone in some cases has sufficed;
+no animal is more difficult to tame than the young of the wild rabbit;
+scarcely any animal is tamer than the young of the tame rabbit; but I do
+not suppose that domestic rabbits have ever been selected for tameness; and
+I presume that we must attribute the whole of the inherited change from
+extreme wildness to extreme tameness, simply to habit and long-continued
+close confinement.
+
+Natural instincts are lost under domestication: a remarkable instance of
+this is seen in those breeds of fowls which very rarely or never become
+"broody," that is, never wish to sit on their eggs. Familiarity alone
+prevents our seeing how universally and largely the minds of our domestic
+animals have been modified by domestication. It is scarcely possible to
+doubt that the love of man has become instinctive in the dog. All wolves,
+foxes, jackals, and species of the cat genus, when kept tame, are most
+eager to attack poultry, sheep, and pigs; and this tendency has been found
+incurable in dogs which have been brought home as puppies from countries,
+such as Tierra del Fuego and Australia, where the savages do not keep these
+domestic animals. How rarely, on the other hand, do our civilised dogs,
+even when quite young, require to be taught not to attack poultry, sheep,
+and pigs! No doubt they occasionally do make an attack, and are then
+beaten; and if not cured, they are destroyed; so that habit, with some
+degree of selection, has probably concurred in civilising by inheritance
+our dogs. On the other hand, young chickens have lost, wholly by habit,
+that fear of the dog and cat which no doubt was originally instinctive in
+them, in the same way as it is so plainly instinctive in {216} young
+pheasants, though reared under a hen. It is not that chickens have lost all
+fear, but fear only of dogs and cats, for if the hen gives the
+danger-chuckle, they will run (more especially young turkeys) from under
+her, and conceal themselves in the surrounding grass or thickets; and this
+is evidently done for the instinctive purpose of allowing, as we see in
+wild ground-birds, their mother to fly away. But this instinct retained by
+our chickens has become useless under domestication, for the mother-hen has
+almost lost by disuse the power of flight.
+
+Hence, we may conclude, that domestic instincts have been acquired and
+natural instincts have been lost partly by habit, and partly by man
+selecting and accumulating during successive generations, peculiar mental
+habits and actions, which at first appeared from what we must in our
+ignorance call an accident. In some cases compulsory habit alone has
+sufficed to produce such inherited mental changes; in other cases
+compulsory habit has done nothing, and all has been the result of
+selection, pursued both methodically and unconsciously; but in most cases,
+probably, habit and selection have acted together.
+
+We shall, perhaps, best understand how instincts in a state of nature have
+become modified by selection, by considering a few cases. I will select
+only three, out of the several which I shall have to discuss in my future
+work,--namely, the instinct which leads the cuckoo to lay her eggs in other
+birds' nests; the slave-making instinct of certain ants; and the
+comb-making power of the hive-bee; these two latter instincts have
+generally, and most justly, been ranked by naturalists as the most
+wonderful of all known instincts.
+
+It is now commonly admitted that the more immediate and final cause of the
+cuckoo's instinct is, that {217} she lays her eggs, not daily, but at
+intervals of two or three days; so that, if she were to make her own nest
+and sit on her own eggs, those first laid would have to be left for some
+time unincubated, or there would be eggs and young birds of different ages
+in the same nest. If this were the case, the process of laying and hatching
+might be inconveniently long, more especially as she has to migrate at a
+very early period; and the first hatched young would probably have to be
+fed by the male alone. But the American cuckoo is in this predicament; for
+she makes her own nest and has eggs and young successively hatched, all at
+the same time. It has been asserted that the American cuckoo occasionally
+lays her eggs in other birds' nests; but I hear on the high authority of
+Dr. Brewer, that this is a mistake. Nevertheless, I could give several
+instances of various birds which have been known occasionally to lay their
+eggs in other birds' nests. Now let us suppose that the ancient progenitor
+of our European cuckoo had the habits of the American cuckoo; but that
+occasionally she laid an egg in another bird's nest. If the old bird
+profited by this occasional habit, or if the young were made more vigorous
+by advantage having been taken of the mistaken maternal instinct of another
+bird, than by their own mother's care, encumbered as she can hardly fail to
+be by having eggs and young of different ages at the same time; then the
+old birds or the fostered young would gain an advantage. And analogy would
+lead me to believe, that the young thus reared would be apt to follow by
+inheritance the occasional and aberrant habit of their mother, and in their
+turn would be apt to lay their eggs in other birds' nests, and thus be
+successful in rearing their young. By a continued process of this nature, I
+believe that the strange instinct of our cuckoo could be, and has been,
+{218} generated. I may add that, according to Dr. Gray and to some other
+observers, the European cuckoo has not utterly lost all maternal love and
+care for her own offspring.
+
+The occasional habit of birds laying their eggs in other birds' nests,
+either of the same or of a distinct species, is not very uncommon with the
+Gallinaceæ; and this perhaps explains the origin of a singular instinct in
+the allied group of ostriches. For several hen ostriches, at least in the
+case of the American species, unite and lay first a few eggs in one nest
+and then in another; and these are hatched by the males. This instinct may
+probably be accounted for by the fact of the hens laying a large number of
+eggs; but, as in the case of the cuckoo, at intervals of two or three days.
+This instinct, however, of the American ostrich has not as yet been
+perfected; for a surprising number of eggs lie strewed over the plains, so
+that in one day's hunting I picked up no less than twenty lost and wasted
+eggs.
+
+Many bees are parasitic, and always lay their eggs in the nests of bees of
+other kinds. This case is more remarkable than that of the cuckoo; for
+these bees have not only their instincts but their structure modified in
+accordance with their parasitic habits; for they do not possess the
+pollen-collecting apparatus which would be necessary if they had to store
+food for their own young. Some species, likewise, of Sphegidæ (wasp-like
+insects) are parasitic on other species; and M. Fabre has lately shown good
+reason for believing that although the Tachytes nigra generally makes its
+own burrow and stores it with paralysed prey for its own larvæ to feed on,
+yet that when this insect finds a burrow already made and stored by another
+sphex, it takes advantage of the prize, and becomes for the occasion
+parasitic. In this case, as with the supposed case of the cuckoo, I can
+{219} see no difficulty in natural selection making an occasional habit
+permanent, if of advantage to the species, and if the insect whose nest and
+stored food are thus feloniously appropriated, be not thus exterminated.
+
+
+
+_Slave-making instinct._--This remarkable instinct was first discovered in
+the Formica (Polyerges) rufescens by Pierre Huber, a better observer even
+than his celebrated father. This ant is absolutely dependent on its slaves;
+without their aid, the species would certainly become extinct in a single
+year. The males and fertile females do no work. The workers or sterile
+females, though most energetic and courageous in capturing slaves, do no
+other work. They are incapable of making their own nests, or of feeding
+their own larvæ. When the old nest is found inconvenient, and they have to
+migrate, it is the slaves which determine the migration, and actually carry
+their masters in their jaws. So utterly helpless are the masters, that when
+Huber shut up thirty of them without a slave, but with plenty of the food
+which they like best, and with their larvae and pupæ to stimulate them to
+work, they did nothing; they could not even feed themselves, and many
+perished of hunger. Huber then introduced a single slave (F. fusca), and
+she instantly set to work, fed and saved the survivors; made some cells and
+tended the larvæ, and put all to rights. What can be more extraordinary
+than these well-ascertained facts? If we had not known of any other
+slave-making ant, it would have been hopeless to have speculated how so
+wonderful an instinct could have been perfected.
+
+Another species, Formica sanguinea, was likewise first discovered by P.
+Huber to be a slave-making ant. This species is found in the southern parts
+of England, and its habits have been attended to by Mr. F. Smith, of {220}
+the British Museum, to whom I am much indebted for information on this and
+other subjects. Although fully trusting to the statements of Huber and Mr.
+Smith, I tried to approach the subject in a sceptical frame of mind, as any
+one may well be excused for doubting the truth of so extraordinary and
+odious an instinct as that of making slaves. Hence I will give the
+observations which I have myself made, in some little detail. I opened
+fourteen nests of F. sanguinea, and found a few slaves in all. Males and
+fertile females of the slave-species (F. fusca) are found only in their own
+proper communities, and have never been observed in the nests of F.
+sanguinea. The slaves are black and not above half the size of their red
+masters, so that the contrast in their appearance is very great. When the
+nest is slightly disturbed, the slaves occasionally come out, and like
+their masters are much agitated and defend the nest: when the nest is much
+disturbed and the larvæ and pupæ are exposed, the slaves work energetically
+with their masters in carrying them away to a place of safety. Hence, it is
+clear, that the slaves feel quite at home. During the months of June and
+July, on three successive years, I have watched for many hours several
+nests in Surrey and Sussex, and never saw a slave either leave or enter a
+nest. As, during these months, the slaves are very few in number, I thought
+that they might behave differently when more numerous; but Mr. Smith
+informs me that he has watched the nests at various hours during May, June
+and August, both in Surrey and Hampshire, and has never seen the slaves,
+through present in large numbers in August, either leave or enter the nest.
+Hence he considers them as strictly household slaves. The masters, on the
+other hand, may be constantly seen bringing in materials for the nest, and
+food of all kinds. During the present year, however, in the month {221} of
+July, I came across a community with an unusually large stock of slaves,
+and I observed a few slaves mingled with their masters leaving the nest,
+and marching along the same road to a tall Scotch-fir-tree, twenty-five
+yards distant, which they ascended together, probably in search of aphides
+or cocci. According to Huber, who had ample opportunities for observation,
+in Switzerland the slaves habitually work with their masters in making the
+nest, and they alone open and close the doors in the morning and evening;
+and, as Huber expressly states, their principal office is to search for
+aphides. This difference in the usual habits of the masters and slaves in
+the two countries, probably depends merely on the slaves being captured in
+greater numbers in Switzerland than in England.
+
+One day I fortunately witnessed a migration of F. sanguinea from one nest
+to another, and it was a most interesting spectacle to behold the masters
+carefully carrying (instead of being carried by, as in the case of F.
+rufescens) their slaves in their jaws. Another day my attention was struck
+by about a score of the slave-makers haunting the same spot, and evidently
+not in search of food; they approached and were vigorously repulsed by an
+independent community of the slave-species (F. fusca); sometimes as many as
+three of these ants clinging to the legs of the slave-making F. sanguinea.
+The latter ruthlessly killed their small opponents, and carried their dead
+bodies as food to their nest, twenty-nine yards distant; but they were
+prevented from getting any pupæ to rear as slaves. I then dug up a small
+parcel of the pupæ of F. fusca from another nest, and put them down on a
+bare spot near the place of combat; they were eagerly seized, and carried
+off by the tyrants, who perhaps fancied that, after all, they had been
+victorious in their late combat. {222}
+
+At the same time I laid on the same place a small parcel of the pupæ of
+another species, F. flava, with a few of these little yellow ants still
+clinging to the fragments of the nest. This species is sometimes, though
+rarely, made into slaves, as has been described by Mr. Smith. Although so
+small a species, it is very courageous, and I have seen it ferociously
+attack other ants. In one instance I found to my surprise an independent
+community of F. flava under a stone beneath a nest of the slave-making F.
+sanguinea; and when I had accidentally disturbed both nests, the little
+ants attacked their big neighbours with surprising courage. Now I was
+curious to ascertain whether F. sanguinea could distinguish the pupæ of F.
+fusca, which they habitually make into slaves, from those of the little and
+furious F. flava, which they rarely capture, and it was evident that they
+did at once distinguish them: for we have seen that they eagerly and
+instantly seized the pupæ of F. fusca, whereas they were much terrified
+when they came across the pupæ, or even the earth from the nest of F.
+flava, and quickly ran away; but in about a quarter of an hour, shortly
+after all the little yellow ants had crawled away, they took heart and
+carried off the pupæ.
+
+One evening I visited another community of F. sanguinea, and found a number
+of these ants returning home and entering their nests, carrying the dead
+bodies of F. fusca (showing that it was not a migration) and numerous pupæ.
+I traced a long file of ants burthened with booty, for about forty yards,
+to a very thick clump of heath, whence I saw the last individual of F.
+sanguinea emerge, carrying a pupa; but I was not able to find the desolated
+nest in the thick heath. The nest, however, must have been close at hand,
+for two or three individuals of F. fusca were rushing about in the greatest
+{223} agitation, and one was perched motionless with its own pupa in its
+mouth on the top of a spray of heath, an image of despair, over its ravaged
+home.
+
+Such are the facts, though they did not need confirmation by me, in regard
+to the wonderful instinct of making slaves. Let it be observed what a
+contrast the instinctive habits of F. sanguinea present with those of the
+continental F. rufescens. The latter does not build its own nest, does not
+determine its own migrations, does not collect food for itself or its
+young, and cannot even feed itself: it is absolutely dependent on its
+numerous slaves. Formica sanguinea, on the other hand, possesses much fewer
+slaves, and in the early part of the summer extremely few: the masters
+determine when and where a new nest shall be formed, and when they migrate,
+the masters carry the slaves. Both in Switzerland and England the slaves
+seem to have the exclusive care of the larvæ, and the masters alone go on
+slave-making expeditions. In Switzerland the slaves and masters work
+together, making and bringing materials for the nest: both, but chiefly the
+slaves, tend, and milk as it may be called, their aphides; and thus both
+collect food for the community. In England the masters alone usually leave
+the nest to collect building materials and food for themselves, their
+slaves and larvæ. So that the masters in this country receive much less
+service from their slaves than they do in Switzerland.
+
+By what steps the instinct of F. sanguinea originated I will not pretend to
+conjecture. But as ants, which are not slave-makers, will, as I have seen,
+carry off pupæ of other species, if scattered near their nests, it is
+possible that such pupæ originally stored as food might become developed;
+and the foreign ants thus unintentionally reared would then follow their
+proper instincts, and do {224} what work they could. If their presence
+proved useful to the species which had seized them--if it were more
+advantageous to this species to capture workers than to procreate them--the
+habit of collecting pupae originally for food might by natural selection be
+strengthened and rendered permanent for the very different purpose of
+raising slaves. When the instinct was once acquired, if carried out to a
+much less extent even than in our British F. sanguinea, which, as we have
+seen, is less aided by its slaves than the same species in Switzerland, I
+can see no difficulty in natural selection increasing and modifying the
+instinct--always supposing each modification to be of use to the
+species--until an ant was formed as abjectly dependent on its slaves as is
+the Formica rufescens.
+
+
+
+_Cell-making instinct of the Hive-Bee._--I will not here enter on minute
+details on this subject, but will merely give an outline of the conclusions
+at which I have arrived. He must be a dull man who can examine the
+exquisite structure of a comb, so beautifully adapted to its end, without
+enthusiastic admiration. We hear from mathematicians that bees have
+practically solved a recondite problem, and have made their cells of the
+proper shape to hold the greatest possible amount of honey, with the least
+possible consumption of precious wax in their construction. It has been
+remarked that a skilful workman, with fitting tools and measures, would
+find it very difficult to make cells of wax of the true form, though this
+is perfectly effected by a crowd of bees working in a dark hive. Grant
+whatever instincts you please, and it seems at first quite inconceivable
+how they can make all the necessary angles and planes, or even perceive
+when they are correctly made. But the difficulty is not {225} nearly so
+great as it at first appears: all this beautiful work can be shown, I
+think, to follow from a few very simple instincts.
+
+I was led to investigate this subject by Mr. Waterhouse, who has shown that
+the form of the cell stands in close relation to the presence of adjoining
+cells; and the following view may, perhaps, be considered only as a
+modification of his theory. Let us look to the great principle of
+gradation, and see whether Nature does not reveal to us her method of work.
+At one end of a short series we have humble-bees, which use their old
+cocoons to hold honey, sometimes adding to them short tubes of wax, and
+likewise making separate and very irregular rounded cells of wax. At the
+other end of the series we have the cells of the hive-bee, placed in a
+double layer: each cell, as is well known, is an hexagonal prism, with the
+basal edges of its six sides bevelled so as to fit on to a pyramid, formed
+of three rhombs. These rhombs have certain angles, and the three which form
+the pyramidal base of a single cell on one side of the comb, enter into the
+composition of the bases of three adjoining cells on the opposite side. In
+the series between the extreme perfection of the cells of the hive-bee and
+the simplicity of those of the humble-bee, we have the cells of the Mexican
+Melipona domestica, carefully described and figured by Pierre Huber. The
+Melipona itself is intermediate in structure between the hive and humble
+bee, but more nearly related to the latter: it forms a nearly regular waxen
+comb of cylindrical cells, in which the young are hatched, and, in
+addition, some large cells of wax for holding honey. These latter cells are
+nearly spherical and of nearly equal sizes, and are aggregated into an
+irregular mass. But the important point to notice, is that these cells are
+always made at that degree of nearness to each other, that they would have
+{226} intersected or broken into each other, if the spheres had been
+completed; but this is never permitted, the bees building perfectly flat
+walls of wax between the spheres which thus tend to intersect. Hence each
+cell consists of an outer spherical portion and of two, three, or more
+perfectly flat surfaces, according as the cell adjoins two, three, or more
+other cells. When one cell comes into contact with three other cells,
+which, from the spheres being nearly of the same size, is very frequently
+and necessarily the case, the three flat surfaces are united into a
+pyramid; and this pyramid, as Huber has remarked, is manifestly a gross
+imitation of the three-sided pyramidal bases of the cell of the hive-bee.
+As in the cells of the hive-bee, so here, the three plane surfaces in any
+one cell necessarily enter into the construction of three adjoining cells.
+It is obvious that the Melipona saves wax by this manner of building; for
+the flat walls between the adjoining cells are not double, but are of the
+same thickness as the outer spherical portions, and yet each flat portion
+forms a part of two cells.
+
+Reflecting on this case, it occurred to me that if the Melipona had made
+its spheres at some given distance from each other, and had made them of
+equal sizes and had arranged them symmetrically in a double layer, the
+resulting structure would probably have been as perfect as the comb of the
+hive-bee. Accordingly I wrote to Professor Miller, of Cambridge, and this
+geometer has kindly read over the following statement, drawn up from his
+information, and tells me that it is strictly correct:--
+
+If a number of equal spheres be described with their centres placed in two
+parallel layers; with the centre of each sphere at the distance of radius ×
+[root]2, or radius × 1.41421 (or at some lesser distance), from the centres
+of the six surrounding spheres in the same {227} layer; and at the same
+distance from the centres of the adjoining spheres in the other and
+parallel layer; then, if planes of intersection between the several spheres
+in both layers be formed, there will result a double layer of hexagonal
+prisms united together by pyramidal bases formed of three rhombs; and the
+rhombs and the sides of the hexagonal prisms will have every angle
+identically the same with the best measurements which have been made of the
+cells of the hive-bee.
+
+Hence we may safely conclude that if we could slightly modify the instincts
+already possessed by the Melipona, and in themselves not very wonderful,
+this bee would make a structure as wonderfully perfect as that of the
+hive-bee. We must suppose the Melipona to make her cells truly spherical,
+and of equal sizes; and this would not be very surprising, seeing that she
+already does so to a certain extent, and seeing what perfectly cylindrical
+burrows in wood many insects can make, apparently by turning round on a
+fixed point. We must suppose the Melipona to arrange her cells in level
+layers, as she already does her cylindrical cells; and we must further
+suppose, and this is the greatest difficulty, that she can somehow judge
+accurately at what distance to stand from her fellow-labourers when several
+are making their spheres; but she is already so far enabled to judge of
+distance, that she always describes her spheres so as to intersect largely;
+and then she unites the points of intersection by perfectly flat surfaces.
+We have further to suppose, but this is no difficulty, that after hexagonal
+prisms have been formed by the intersection of adjoining spheres in the
+same layer, she can prolong the hexagon to any length requisite to hold the
+stock of honey; in the same way as the rude humble-bee adds cylinders of
+wax to the circular mouths of her old cocoons. By such {228} modifications
+of instincts in themselves not very wonderful,--hardly more wonderful than
+those which guide a bird to make its nest,--I believe that the hive-bee has
+acquired, through natural selection, her inimitable architectural powers.
+
+But this theory can be tested by experiment. Following the example of Mr.
+Tegetmeier, I separated two combs, and put between them a long, thick,
+square strip of wax: the bees instantly began to excavate minute circular
+pits in it; and as they deepened these little pits, they made them wider
+and wider until they were converted into shallow basins, appearing to the
+eye perfectly true or parts of a sphere, and of about the diameter of a
+cell. It was most interesting to me to observe that wherever several bees
+had begun to excavate these basins near together, they had begun their work
+at such a distance from each other, that by the time the basins had
+acquired the above stated width (_i.e._ about the width of an ordinary
+cell), and were in depth about one sixth of the diameter of the sphere of
+which they formed a part, the rims of the basins intersected or broke into
+each other. As soon as this occurred, the bees ceased to excavate, and
+began to build up flat walls of wax on the lines of intersection between
+the basins, so that each hexagonal prism was built upon the scalloped edge
+of a smooth basin, instead of on the straight edges of a three-sided
+pyramid as in the case of ordinary cells.
+
+I then put into the hive, instead of a thick, square piece of wax, a thin
+and narrow, knife-edged ridge, coloured with vermilion. The bees instantly
+began on both sides to excavate little basins near to each other, in the
+same way as before; but the ridge of wax was so thin, that the bottoms of
+the basins, if they had been excavated to the same depth as in the former
+{229} experiment, would have broken into each other from the opposite
+sides. The bees, however, did not suffer this to happen, and they stopped
+their excavations in due time; so that the basins, as soon as they had been
+a little deepened, came to have flat bottoms; and these flat bottoms,
+formed by thin little plates of the vermilion wax having been left
+ungnawed, were situated, as far as the eye could judge, exactly along the
+planes of imaginary intersection between the basins on the opposite sides
+of the ridge of wax. In parts, only little bits, in other parts, large
+portions of a rhombic plate had been left between the opposed basins, but
+the work, from the unnatural state of things, had not been neatly
+performed. The bees must have worked at very nearly the same rate on the
+opposite sides of the ridge of vermilion wax, as they circularly gnawed
+away and deepened the basins on both sides, in order to have succeeded in
+thus leaving flat plates between the basins, by stopping work along the
+intermediate planes or planes of intersection.
+
+Considering how flexible thin wax is, I do not see that there is any
+difficulty in the bees, whilst at work on the two sides of a strip of wax,
+perceiving when they have gnawed the wax away to the proper thinness, and
+then stopping their work. In ordinary combs it has appeared to me that the
+bees do not always succeed in working at exactly the same rate from the
+opposite sides; for I have noticed half-completed rhombs at the base of a
+just-commenced cell, which were slightly concave on one side, where I
+suppose that the bees had excavated too quickly, and convex on the opposed
+side, where the bees had worked less quickly. In one well-marked instance,
+I put the comb back into the hive, and allowed the bees to go on working
+for a short time, and again examined the cell, and I found that the rhombic
+{230} plate had been completed, and had become _perfectly flat_: it was
+absolutely impossible, from the extreme thinness of the little rhombic
+plate, that they could have effected this by gnawing away the convex side;
+and I suspect that the bees in such cases stand in the opposed cells and
+push and bend the ductile and warm wax (which as I have tried is easily
+done) into its proper intermediate plane, and thus flatten it.
+
+From the experiment of the ridge of vermilion wax, we can clearly see that
+if the bees were to build for themselves a thin wall of wax, they could
+make their cells of the proper shape, by standing at the proper distance
+from each other, by excavating at the same rate, and by endeavouring to
+make equal spherical hollows, but never allowing the spheres to break into
+each other. Now bees, as may be clearly seen by examining the edge of a
+growing comb, do make a rough, circumferential wall or rim all round the
+comb; and they gnaw into this from the opposite sides, always working
+circularly as they deepen each cell. They do not make the whole three-sided
+pyramidal base of any one cell at the same time, but only the one rhombic
+plate which stands on the extreme growing margin, or the two plates, as the
+case may be; and they never complete the upper edges of the rhombic plates,
+until the hexagonal walls are commenced. Some of these statements differ
+from those made by the justly celebrated elder Huber, but I am convinced of
+their accuracy; and if I had space, I could show that they are conformable
+with my theory.
+
+Huber's statement that the very first cell is excavated out of a little
+parallel-sided wall of wax, is not, as far as I have seen, strictly
+correct; the first commencement having always been a little hood of wax;
+but I will not here enter on these details. We see how important {231} a
+part excavation plays in the construction of the cells; but it would be a
+great error to suppose that the bees cannot build up a rough wall of wax in
+the proper position--that is, along the plane of intersection between two
+adjoining spheres. I have several specimens showing clearly that they can
+do this. Even in the rude circumferential rim or wall of wax round a
+growing comb, flexures may sometimes be observed, corresponding in position
+to the planes of the rhombic basal plates of future cells. But the rough
+wall of wax has in every case to be finished off, by being largely gnawed
+away on both sides. The manner in which the bees build is curious; they
+always make the first rough wall from ten to twenty times thicker than the
+excessively thin finished wall of the cell, which will ultimately be left.
+We shall understand how they work, by supposing masons first to pile up a
+broad ridge of cement, and then to begin cutting it away equally on both
+sides near the ground, till a smooth, very thin wall is left in the middle;
+the masons always piling up the cut-away cement, and adding fresh cement,
+on the summit of the ridge. We shall thus have a thin wall steadily growing
+upward; but always crowned by a gigantic coping. From all the cells, both
+those just commenced and those completed, being thus crowned by a strong
+coping of wax, the bees can cluster and crawl over the comb without
+injuring the delicate hexagonal walls, which are only about one
+four-hundredth of an inch in thickness; the plates of the pyramidal basis
+being about twice as thick. By this singular manner of building, strength
+is continually given to the comb, with the utmost ultimate economy of wax.
+
+It seems at first to add to the difficulty of understanding how the cells
+are made, that a multitude of bees all work together; one bee after working
+a short time at one cell going to another, so that, as Huber has stated,
+{232} a score of individuals work even at the commencement of the first
+cell. I was able practically to show this fact, by covering the edges of
+the hexagonal walls of a single cell, or the extreme margin of the
+circumferential rim of a growing comb, with an extremely thin layer of
+melted vermilion wax; and I invariably found that the colour was most
+delicately diffused by the bees--as delicately as a painter could have done
+with his brush--by atoms of the coloured wax having been taken from the
+spot on which it had been placed, and worked into the growing edges of the
+cells all round. The work of construction seems to be a sort of balance
+struck between many bees, all instinctively standing at the same relative
+distance from each other, all trying to sweep equal spheres, and then
+building up, or leaving ungnawed, the planes of intersection between these
+spheres. It was really curious to note in cases of difficulty, as when two
+pieces of comb met at an angle, how often the bees would pull down and
+rebuild in different ways the same cell, sometimes recurring to a shape
+which they had at first rejected.
+
+When bees have a place on which they can stand in their proper positions
+for working,--for instance, on a slip of wood, placed directly under the
+middle of a comb growing downwards so that the comb has to be built over
+one face of the slip--in this case the bees can lay the foundations of one
+wall of a new hexagon, in its strictly proper place, projecting beyond the
+other completed cells. It suffices that the bees should be enabled to stand
+at their proper relative distances from each other and from the walls of
+the last completed cells, and then, by striking imaginary spheres, they can
+build up a wall intermediate between two adjoining spheres; but, as far as
+I have seen, they never gnaw away and finish off the angles of a cell till
+a large part both of that cell and of {233} the adjoining cells has been
+built. This capacity in bees of laying down under certain circumstances a
+rough wall in its proper place between two just-commenced cells, is
+important, as it bears on a fact, which seems at first quite subversive of
+the foregoing theory; namely, that the cells on the extreme margin of
+wasp-combs are sometimes strictly hexagonal; but I have not space here to
+enter on this subject. Nor does there seem to me any great difficulty in a
+single insect (as in the case of a queen-wasp) making hexagonal cells, if
+she work alternately on the inside and outside of two or three cells
+commenced at the same time, always standing at the proper relative distance
+from the parts of the cells just begun, sweeping spheres or cylinders, and
+building up intermediate planes. It is even conceivable that an insect
+might, by fixing on a point at which to commence a cell, and then moving
+outside, first to one point, and then to five other points, at the proper
+relative distances from the central point and from each other, strike the
+planes of intersection, and so make an isolated hexagon: but I am not aware
+that any such case has been observed; nor would any good be derived from a
+single hexagon being built, as in its construction more materials would be
+required than for a cylinder.
+
+As natural selection acts only by the accumulation of slight modifications
+of structure or instinct, each profitable to the individual under its
+conditions of life, it may reasonably be asked, how a long and graduated
+succession of modified architectural instincts, all tending towards the
+present perfect plan of construction, could have profited the progenitors
+of the hive-bee? I think the answer is not difficult: it is known that bees
+are often hard pressed to get sufficient nectar; and I am informed by Mr.
+Tegetmeier that it has been experimentally found that no less than from
+twelve to fifteen pounds of dry sugar {234} are consumed by a hive of bees
+for the secretion of each pound of wax; to that a prodigious quantity of
+fluid nectar must be collected and consumed by the bees in a hive for the
+secretion of the wax necessary for the construction of their combs.
+Moreover, many bees have to remain idle for many days during the process of
+secretion. A large store of honey is indispensable to support a large stock
+of bees during the winter; and the security of the hive is known mainly to
+depend on a large number of bees being supported. Hence the saving of wax
+by largely saving honey must be a most important element of success in any
+family of bees. Of course the success of any species of bee may be
+dependent on the number of its parasites or other enemies, or on quite
+distinct causes, and so be altogether independent of the quantity of honey
+which the bees could collect. But let us suppose that this latter
+circumstance determined, as it probably often does determine, the numbers
+of a humble-bee which could exist in a country; and let us further suppose
+that the community lived throughout the winter, and consequently required a
+store of honey: there can in this case be no doubt that it would be an
+advantage to our humble-bee, if a slight modification of her instinct led
+her to make her waxen cells near together, so as to intersect a little; for
+a wall in common even to two adjoining cells, would save some little wax.
+Hence it would continually be more and more advantageous to our humble-bee,
+if she were to make her cells more and more regular, nearer together, and
+aggregated into a mass, like the cells of the Melipona; for in this case a
+large part of the bounding surface of each cell would serve to bound other
+cells, and much wax would be saved. Again, from the same cause, it would be
+advantageous to the Melipona, if she were to make her cells closer
+together, and more regular in every way {235} than at present; for then, as
+we have seen, the spherical surfaces would wholly disappear, and would all
+be replaced by plane surfaces; and the Melipona would make a comb as
+perfect as that of the hive-bee. Beyond this stage of perfection in
+architecture, natural selection could not lead; for the comb of the
+hive-bee, as far as we can see, is absolutely perfect in economising wax.
+
+Thus, as I believe, the most wonderful of all known instincts, that of the
+hive-bee, can be explained by natural selection having taken advantage of
+numerous, successive, slight modifications of simpler instincts; natural
+selection having by slow degrees, more and more perfectly, led the bees to
+sweep equal spheres at a given distance from each other in a double layer,
+and to build up and excavate the wax along the planes of intersection. The
+bees, of course, no more knowing that they swept their spheres at one
+particular distance from each other, than they know what are the several
+angles of the hexagonal prisms and of the basal rhombic plates. The motive
+power of the process of natural selection having been economy of wax; that
+individual swarm which wasted least honey in the secretion of wax, having
+succeeded best, and having transmitted by inheritance its newly acquired
+economical instinct to new swarms, which in their turn will have had the
+best chance of succeeding in the struggle for existence.
+
+
+
+No doubt many instincts of very difficult explanation could be opposed to
+the theory of natural selection,--cases, in which we cannot see how an
+instinct could possibly have originated; cases, in which no intermediate
+gradations are known to exist; cases of instinct of apparently such
+trifling importance, that they could {236} hardly have been acted on by
+natural selection; cases of instincts almost identically the same in
+animals so remote in the scale of nature, that we cannot account for their
+similarity by inheritance from a common parent, and must therefore believe
+that they have been acquired by independent acts of natural selection. I
+will not here enter on these several cases, but will confine myself to one
+special difficulty, which at first appeared to me insuperable, and actually
+fatal to my whole theory. I allude to the neuters or sterile females in
+insect-communities: for these neuters often differ widely in instinct and
+in structure from both the males and fertile females, and yet, from being
+sterile, they cannot propagate their kind.
+
+The subject well deserves to be discussed at great length, but I will here
+take only a single case, that of working or sterile ants. How the workers
+have been rendered sterile is a difficulty; but not much greater than that
+of any other striking modification of structure; for it can be shown that
+some insects and other articulate animals in a state of nature occasionally
+become sterile; and if such insects had been social, and it had been
+profitable to the community that a number should have been annually born
+capable of work, but incapable of procreation, I can see no very great
+difficulty in this being effected by natural selection. But I must pass
+over this preliminary difficulty. The great difficulty lies in the working
+ants differing widely from both the males and the fertile females in
+structure, as in the shape of the thorax and in being destitute of wings
+and sometimes of eyes, and in instinct. As far as instinct alone is
+concerned, the prodigious difference in this respect between the workers
+and the perfect females, would have been far better exemplified by the
+hive-bee. If a working ant or other neuter insect had been an animal {237}
+in the ordinary state, I should have unhesitatingly assumed that all its
+characters had been slowly acquired through natural selection; namely, by
+an individual having been born with some slight profitable modification of
+structure, this being inherited by its offspring, which again varied and
+were again selected, and so onwards. But with the working ant we have an
+insect differing greatly from its parents, yet absolutely sterile; so that
+it could never have transmitted successively acquired modifications of
+structure or instinct to its progeny. It may well be asked how is it
+possible to reconcile this case with the theory of natural selection?
+
+First, let it be remembered that we have innumerable instances, both in our
+domestic productions and in those in a state of nature, of all sorts of
+differences of structure which have become correlated to certain ages, and
+to either sex. We have differences correlated not only to one sex, but to
+that short period alone when the reproductive system is active, as in the
+nuptial plumage of many birds, and in the hooked jaws of the male salmon.
+We have even slight differences in the horns of different breeds of cattle
+in relation to an artificially imperfect state of the male sex; for oxen of
+certain breeds have longer horns than in other breeds, in comparison with
+the horns of the bulls or cows of these same breeds. Hence I can see no
+real difficulty in any character having become correlated with the sterile
+condition of certain members of insect-communities: the difficulty lies in
+understanding how such correlated modifications of structure could have
+been slowly accumulated by natural selection.
+
+This difficulty, though appearing insuperable, is lessened, or, as I
+believe, disappears, when it is remembered that selection may be applied to
+the family, as well as to the individual, and may thus gain the {238}
+desired end. Thus, a well-flavoured vegetable is cooked, and the individual
+is destroyed; but the horticulturist sows seeds of the same stock, and
+confidently expects to get nearly the same variety: breeders of cattle wish
+the flesh and fat to be well marbled together; the animal has been
+slaughtered, but the breeder goes with confidence to the same family. I
+have such faith in the powers of selection, that I do not doubt that a
+breed of cattle, always yielding oxen with extraordinarily long horns,
+could be slowly formed by carefully watching which individual bulls and
+cows, when matched, produced oxen with the longest horns; and yet no one ox
+could ever have propagated its kind. Thus I believe it has been with social
+insects: a slight modification of structure, or instinct, correlated with
+the sterile condition of certain members of the community, has been
+advantageous to the community: consequently the fertile males and females
+of the same community flourished, and transmitted to their fertile
+offspring a tendency to produce sterile members having the same
+modification. And I believe that this process has been repeated, until that
+prodigious amount of difference between the fertile and sterile females of
+the same species has been produced, which we see in many social insects.
+
+But we have not as yet touched on the climax of the difficulty; namely, the
+fact that the neuters of several ants differ, not only from the fertile
+females and males, but from each other, sometimes to an almost incredible
+degree, and are thus divided into two or even three castes. The castes,
+moreover, do not generally graduate into each other, but are perfectly well
+defined; being as distinct from each other, as are any two species of the
+same genus, or rather as any two genera of the same family. Thus in Eciton,
+there are working and soldier neuters, with jaws and instincts
+extraordinarily {239} different: in Cryptocerus, the workers of one caste
+alone carry a wonderful sort of shield on their heads, the use of which is
+quite unknown: in the Mexican Myrmecocystus, the workers of one caste never
+leave the nest; they are fed by the workers of another caste, and they have
+an enormously developed abdomen which secretes a sort of honey, supplying
+the place of that excreted by the aphides, or the domestic cattle as they
+may be called, which our European ants guard or imprison.
+
+It will indeed be thought that I have an overweening confidence in the
+principle of natural selection, when I do not admit that such wonderful and
+well-established facts at once annihilate my theory. In the simpler case of
+neuter insects all of one caste or of the same kind, which have been
+rendered by natural selection, as I believe to be quite possible, different
+from the fertile males and females,--in this case, we may safely conclude
+from the analogy of ordinary variations, that each successive, slight,
+profitable modification did not probably at first appear in all the
+individual neuters in the same nest, but in a few alone; and that by the
+long-continued selection of the fertile parents which produced most neuters
+with the profitable modification, all the neuters ultimately came to have
+the desired character. On this view we ought occasionally to find
+neuter-insects of the same species, in the same nest, presenting gradations
+of structure; and this we do find, even often, considering how few
+neuter-insects out of Europe have been carefully examined. Mr. F. Smith has
+shown how surprisingly the neuters of several British ants differ from each
+other in size and sometimes in colour; and that the extreme forms can
+sometimes be perfectly linked together by individuals taken out of the same
+nest: I have myself compared perfect gradations of this kind. It often
+happens that the larger or the smaller sized workers {240} are the most
+numerous; or that both large and small are numerous, with those of an
+intermediate size scanty in numbers. Formica flava has larger and smaller
+workers, with some of intermediate size; and, in this species, as Mr. F.
+Smith has observed, the larger workers have simple eyes (ocelli), which
+though small can be plainly distinguished, whereas the smaller workers have
+their ocelli rudimentary. Having carefully dissected several specimens of
+these workers, I can affirm that the eyes are far more rudimentary in the
+smaller workers than can be accounted for merely by their proportionally
+lesser size; and I fully believe, though I dare not assert so positively,
+that the workers of intermediate size have their ocelli in an exactly
+intermediate condition. So that we here have two bodies of sterile workers
+in the same nest, differing not only in size, but in their organs of
+vision, yet connected by some few members in an intermediate condition. I
+may digress by adding, that if the smaller workers had been the most useful
+to the community, and those males and females had been continually
+selected, which produced more and more of the smaller workers, until all
+the workers had come to be in this condition; we should then have had a
+species of ant with neuters very nearly in the same condition with those of
+Myrmica. For the workers of Myrmica have not even rudiments of ocelli,
+though the male and female ants of this genus have well-developed ocelli.
+
+I may give one other case: so confidently did I expect to find gradations
+in important points of structure between the different castes of neuters in
+the same species, that I gladly availed myself of Mr. F. Smith's offer of
+numerous specimens from the same nest of the driver ant (Anomma) of West
+Africa. The reader will perhaps best appreciate the amount of difference in
+these {241} workers, by my giving not the actual measurements, but a
+strictly accurate illustration: the difference was the same as if we were
+to see a set of workmen building a house of whom many were five feet four
+inches high, and many sixteen feet high; but we must suppose that the
+larger workmen had heads four instead of three times as big as those of the
+smaller men, and jaws nearly five times as big. The jaws, moreover, of the
+working ants of the several sizes differed wonderfully in shape, and in the
+form and number of the teeth. But the important fact for us is, that though
+the workers can be grouped into castes of different sizes, yet they
+graduate insensibly into each other, as does the widely-different structure
+of their jaws. I speak confidently on this latter point, as Mr. Lubbock
+made drawings for me with the camera lucida of the jaws which I had
+dissected from the workers of the several sizes.
+
+With these facts before me, I believe that natural selection, by acting on
+the fertile parents, could form a species which should regularly produce
+neuters, either all of large size with one form of jaw, or all of small
+size with jaws having a widely different structure; or lastly, and this is
+our climax of difficulty, one set of workers of one size and structure, and
+simultaneously another set of workers of a different size and structure;--a
+graduated series having been first formed, as in the case of the driver
+ant, and then the extreme forms, from being the most useful to the
+community, having been produced in greater and greater numbers through the
+natural selection of the parents which generated them; until none with an
+intermediate structure were produced.
+
+Thus, as I believe, the wonderful fact of two distinctly defined castes of
+sterile workers existing in the same nest, both widely different from each
+other and from {242} their parents, has originated. We can see how useful
+their production may have been to a social community of insects, on the
+same principle that the division of labour is useful to civilised man. As
+ants work by inherited instincts and by inherited organs or tools, and not
+by acquired knowledge and manufactured instruments, a perfect division of
+labour could be effected with them only by the workers being sterile; for
+had they been fertile, they would have intercrossed, and their instincts
+and structure would have become blended. And nature has, as I believe,
+effected this admirable division of labour in the communities of ants, by
+the means of natural selection. But I am bound to confess, that, with all
+my faith in this principle, I should never have anticipated that natural
+selection could have been efficient in so high a degree, had not the case
+of these neuter insects convinced me of the fact. I have, therefore,
+discussed this case, at some little but wholly insufficient length, in
+order to show the power of natural selection, and likewise because this is
+by far the most serious special difficulty, which my theory has
+encountered. The case, also, is very interesting, as it proves that with
+animals, as with plants, any amount of modification in structure can be
+effected by the accumulation of numerous, slight, and as we must call them
+accidental, variations, which are in any manner profitable, without
+exercise or habit having come into play. For no amount of exercise, or
+habit, or volition, in the utterly sterile members of a community could
+possibly affect the structure or instincts of the fertile members, which
+alone leave descendants. I am surprised that no one has advanced this
+demonstrative case of neuter insects, against the well-known doctrine of
+Lamarck.
+
+
+
+_Summary._--I have endeavoured briefly in this chapter {243} to show that
+the mental qualities of our domestic animals vary, and that the variations
+are inherited. Still more briefly I have attempted to show that instincts
+vary slightly in a state of nature. No one will dispute that instincts are
+of the highest importance to each animal. Therefore I can see no
+difficulty, under changing conditions of life, in natural selection
+accumulating slight modifications of instinct to any extent, in any useful
+direction. In some cases habit or use and disuse have probably come into
+play. I do not pretend that the facts given in this chapter strengthen in
+any great degree my theory; but none of the cases of difficulty, to the
+best of my judgment, annihilate it. On the other hand, the fact that
+instincts are not always absolutely perfect and are liable to
+mistakes;--that no instinct has been produced for the exclusive good of
+other animals, but that each animal takes advantage of the instincts of
+others;--that the canon in natural history, of "Natura non facit saltum,"
+is applicable to instincts as well as to corporeal structure, and is
+plainly explicable on the foregoing views, but is otherwise
+inexplicable,--all tend to corroborate the theory of natural selection.
+
+This theory is, also, strengthened by some few other facts in regard to
+instincts; as by that common case of closely allied, but certainly
+distinct, species, when inhabiting distant parts of the world and living
+under considerably different conditions of life, yet often retaining nearly
+the same instincts. For instance, we can understand on the principle of
+inheritance, how it is that the thrush of South America lines its nest with
+mud, in the same peculiar manner as does our British thrush: how it is that
+the male wrens (Troglodytes) of North America, build "cock-nests," to roost
+in, like the males of our distinct Kitty-wrens,--a habit wholly unlike that
+of {244} any other known bird. Finally, it may not be a logical deduction,
+but to my imagination it is far more satisfactory to look at such instincts
+as the young cuckoo ejecting its foster-brothers,--ants making slaves,--the
+larvae of ichneumonidæ feeding within the live bodies of caterpillars,--not
+as specially endowed or created instincts, but as small consequences of one
+general law, leading to the advancement of all organic beings, namely,
+multiply, vary, let the strongest live and the weakest die.
+
+       *       *       *       *       *
+
+
+{245}
+
+CHAPTER VIII.
+
+HYBRIDISM.
+
+    Distinction between the sterility of first crosses and of
+    hybrids--Sterility various in degree, not universal, affected by close
+    interbreeding, removed by domestication--Laws governing the sterility
+    of hybrids--Sterility not a special endowment, but incidental on other
+    differences--Causes of the sterility of first crosses and of
+    hybrids--Parallelism between the effects of changed conditions of life
+    and crossing--Fertility of varieties when crossed and of their mongrel
+    offspring not universal--Hybrids and mongrels compared independently of
+    their fertility--Summary.
+
+The view generally entertained by naturalists is that species, when
+intercrossed, have been specially endowed with the quality of sterility, in
+order to prevent the confusion of all organic forms. This view certainly
+seems at first probable, for species within the same country could hardly
+have kept distinct had they been capable of crossing freely. The importance
+of the fact that hybrids are very generally sterile, has, I think, been
+much underrated by some late writers. On the theory of natural selection
+the case is especially important, inasmuch as the sterility of hybrids
+could not possibly be of any advantage to them, and therefore could not
+have been acquired by the continued preservation of successive profitable
+degrees of sterility. I hope, however, to be able to show that sterility is
+not a specially acquired or endowed quality, but is incidental on other
+acquired differences.
+
+In treating this subject, two classes of facts, to a large extent
+fundamentally different, have generally been confounded together; namely,
+the sterility of two species {246} when first crossed, and the sterility of
+the hybrids produced from them.
+
+Pure species have of course their organs of reproduction in a perfect
+condition, yet when intercrossed they produce either few or no offspring.
+Hybrids, on the other hand, have their reproductive organs functionally
+impotent, as may be clearly seen in the state of the male element in both
+plants and animals; though the organs themselves are perfect in structure,
+as far as the microscope reveals. In the first case the two sexual elements
+which go to form the embryo are perfect; in the second case they are either
+not at all developed, or are imperfectly developed. This distinction is
+important, when the cause of the sterility, which is common to the two
+cases, has to be considered. The distinction has probably been slurred
+over, owing to the sterility in both cases being looked on as a special
+endowment, beyond the province of our reasoning powers.
+
+The fertility of varieties, that is of the forms known or believed to have
+descended from common parents, when intercrossed, and likewise the
+fertility of their mongrel offspring, is, on my theory, of equal importance
+with the sterility of species; for it seems to make a broad and clear
+distinction between varieties and species.
+
+First, for the sterility of species when crossed and of their hybrid
+offspring. It is impossible to study the several memoirs and works of those
+two conscientious and admirable observers, Kölreuter and Gärtner, who
+almost devoted their lives to this subject, without being deeply impressed
+with the high generality of some degree of sterility. Kölreuter makes the
+rule universal; but then he cuts the knot, for in ten cases in which he
+found two forms, considered by most authors as distinct species, quite
+fertile together, he unhesitatingly ranks {247} them as varieties. Gärtner,
+also, makes the rule equally universal; and he disputes the entire
+fertility of Kölreuter's ten cases. But in these and in many other cases,
+Gärtner is obliged carefully to count the seeds, in order to show that
+there is any degree of sterility. He always compares the maximum number of
+seeds produced by two species when crossed and by their hybrid offspring,
+with the average number produced by both pure parent-species in a state of
+nature. But a serious cause of error seems to me to be here introduced: a
+plant to be hybridised must be castrated, and, what is often more
+important, must be secluded in order to prevent pollen being brought to it
+by insects from other plants. Nearly all the plants experimentised on by
+Gärtner were potted, and apparently were kept in a chamber in his house.
+That these processes are often injurious to the fertility of a plant cannot
+be doubted; for Gärtner gives in his table about a score of cases of plants
+which he castrated, and artificially fertilised with their own pollen, and
+(excluding all cases such as the Leguminosæ, in which there is an
+acknowledged difficulty in the manipulation) half of these twenty plants
+had their fertility in some degree impaired. Moreover, as Gärtner during
+several years repeatedly crossed the primrose and cowslip, which we have
+such good reason to believe to be varieties, and only once or twice
+succeeded in getting fertile seed; as he found the common red and blue
+pimpernels (Anagallis arvensis and coerulea), which the best botanists rank
+as varieties, absolutely sterile together; and as he came to the same
+conclusion in several other analogous cases; it seems to me that we may
+well be permitted to doubt whether many other species are really so
+sterile, when intercrossed, as Gärtner believes. {248}
+
+It is certain, on the one hand, that the sterility of various species when
+crossed is so different in degree and graduates away so insensibly, and, on
+the other hand, that the fertility of pure species is so easily affected by
+various circumstances, that for all practical purposes it is most difficult
+to say where perfect fertility ends and sterility begins. I think no better
+evidence of this can be required than that the two most experienced
+observers who have ever lived, namely, Kölreuter and Gärtner, should have
+arrived at diametrically opposite conclusions in regard to the very same
+species. It is also most instructive to compare--but I have not space here
+to enter on details--the evidence advanced by our best botanists on the
+question whether certain doubtful forms should be ranked as species or
+varieties, with the evidence from fertility adduced by different
+hybridisers, or by the same author, from experiments made during different
+years. It can thus be shown that neither sterility nor fertility affords
+any clear distinction between species and varieties; but that the evidence
+from this source graduates away, and is doubtful in the same degree as is
+the evidence derived from other constitutional and structural differences.
+
+In regard to the sterility of hybrids in successive generations; though
+Gärtner was enabled to rear some hybrids, carefully guarding them from a
+cross with either pure parent, for six or seven, and in one case for ten
+generations, yet he asserts positively that their fertility never
+increased, but generally greatly decreased. I do not doubt that this is
+usually the case, and that the fertility often suddenly decreases in the
+first few generations. Nevertheless I believe that in all these experiments
+the fertility has been diminished by an independent cause, namely, from
+close interbreeding. I have collected so large a body of facts, showing
+{249} that close interbreeding lessens fertility, and, on the other hand,
+that an occasional cross with a distinct individual or variety increases
+fertility, that I cannot doubt the correctness of this almost universal
+belief amongst breeders. Hybrids are seldom raised by experimentalists in
+great numbers; and as the parent-species, or other allied hybrids,
+generally grow in the same garden, the visits of insects must be carefully
+prevented during the flowering season: hence hybrids will generally be
+fertilised during each generation by their own individual pollen; and I am
+convinced that this would be injurious to their fertility, already lessened
+by their hybrid origin. I am strengthened in this conviction by a
+remarkable statement repeatedly made by Gärtner, namely, that if even the
+less fertile hybrids be artificially fertilised with hybrid pollen of the
+same kind, their fertility, notwithstanding the frequent ill effects of
+manipulation, sometimes decidedly increases, and goes on increasing. Now,
+in artificial fertilisation pollen is as often taken by chance (as I know
+from my own experience) from the anthers of another flower, as from the
+anthers of the flower itself which is to be fertilised; so that a cross
+between two flowers, though probably on the same plant, would be thus
+effected. Moreover, whenever complicated experiments are in progress, so
+careful an observer as Gärtner would have castrated his hybrids, and this
+would have insured in each generation a cross with a pollen from a distinct
+flower, either from the same plant or from another plant of the same hybrid
+nature. And thus, the strange fact of the increase of fertility in the
+successive generations of _artificially fertilised_ hybrids may, I believe,
+be accounted for by close interbreeding having been avoided.
+
+Now let us turn to the results arrived at by the third most experienced
+hybridiser, namely, the Hon. and {250} Rev. W. Herbert. He is as emphatic
+in his conclusion that some hybrids are perfectly fertile--as fertile as
+the pure parent-species--as are Kölreuter and Gärtner that some degree of
+sterility between distinct species is a universal law of nature. He
+experimentised on some of the very same species as did Gärtner. The
+difference in their results may, I think, be in part accounted for by
+Herbert's great horticultural skill, and by his having hothouses at his
+command. Of his many important statements I will here give only a single
+one as an example, namely, that "every ovule in a pod of Crinum capense
+fertilised by C. revolutum produced a plant, which (he says) I never saw to
+occur in a case of its natural fecundation." So that we here have perfect,
+or even more than commonly perfect, fertility in a first cross between two
+distinct species.
+
+This case of the Crinum leads me to refer to a most singular fact, namely,
+that there are individual plants of certain species of Lobelia and of some
+other genera, which can be far more easily fertilised by the pollen of
+another and distinct species, than by their own pollen; and all the
+individuals of nearly all the species of Hippeastrum seem to be in this
+predicament. For these plants have been found to yield seed to the pollen
+of a distinct species, though quite sterile with their own pollen,
+notwithstanding that their own pollen was found to be perfectly good, for
+it fertilised distinct species. So that certain individual plants and all
+the individuals of certain species can actually be hybridised much more
+readily than they can be self-fertilised! For instance, a bulb of
+Hippeastrum aulicum produced four flowers; three were fertilised by Herbert
+with their own pollen, and the fourth was subsequently fertilised by the
+pollen of a compound hybrid descended from three other and distinct {251}
+species: the result was that "the ovaries of the three first flowers soon
+ceased to grow, and after a few days perished entirely, whereas the pod
+impregnated by the pollen of the hybrid made vigorous growth and rapid
+progress to maturity, and bore good seed, which vegetated freely." In a
+letter to me, in 1839, Mr. Herbert told me that he had then tried the
+experiment during five years, and he continued to try it during several
+subsequent years, and always with the same result. This result has, also,
+been confirmed by other observers in the case of Hippeastrum with its
+sub-genera, and in the case of some other genera, as Lobelia, Passiflora
+and Verbascum. Although the plants in these experiments appeared perfectly
+healthy, and although both the ovules and pollen of the same flower were
+perfectly good with respect to other species, yet as they were functionally
+imperfect in their mutual self-action, we must infer that the plants were
+in an unnatural state. Nevertheless these facts show on what slight and
+mysterious causes the lesser or greater fertility of species when crossed,
+in comparison with the same species when self-fertilised, sometimes
+depends.
+
+The practical experiments of horticulturists, though not made with
+scientific precision, deserve some notice. It is notorious in how
+complicated a manner the species of Pelargonium, Fuchsia, Calceolaria,
+Petunia, Rhododendron, &c., have been crossed, yet many of these hybrids
+seed freely. For instance, Herbert asserts that a hybrid from Calceolaria
+integrifolia and plantaginea, species most widely dissimilar in general
+habit, "reproduced itself as perfectly as if it had been a natural species
+from the mountains of Chile." I have taken some pains to ascertain the
+degree of fertility of some of the complex crosses of Rhododendrons, and I
+am assured that many of them {252} are perfectly fertile. Mr. C. Noble, for
+instance, informs me that he raises stocks for grafting from a hybrid
+between Rhod. Ponticum and Catawbiense, and that this hybrid "seeds as
+freely as it is possible to imagine." Had hybrids, when fairly treated,
+gone on decreasing in fertility in each successive generation, as Gärtner
+believes to be the case, the fact would have been notorious to nurserymen.
+Horticulturists raise large beds of the same hybrids, and such alone are
+fairly treated, for by insect agency the several individuals of the same
+hybrid variety are allowed to freely cross with each other, and the
+injurious influence of close interbreeding is thus prevented. Any one may
+readily convince himself of the efficiency of insect-agency by examining
+the flowers of the more sterile kinds of hybrid rhododendrons, which
+produce no pollen, for he will find on their stigmas plenty of pollen
+brought from other flowers.
+
+In regard to animals, much fewer experiments have been carefully tried than
+with plants. If our systematic arrangements can be trusted, that is if the
+genera of animals are as distinct from each other, as are the genera of
+plants, then we may infer that animals more widely separated in the scale
+of nature can be more easily crossed than in the case of plants; but the
+hybrids themselves are, I think, more sterile. I doubt whether any case of
+a perfectly fertile hybrid animal can be considered as thoroughly well
+authenticated. It should, however, be borne in mind that, owing to few
+animals breeding freely under confinement, few experiments have been fairly
+tried: for instance, the canary-bird has been crossed with nine other
+finches, but as not one of these nine species breeds freely in confinement,
+we have no right to expect that the first crosses between them and the
+canary, or that their hybrids, {253} should be perfectly fertile. Again,
+with respect to the fertility in successive generations of the more fertile
+hybrid animals, I hardly know of an instance in which two families of the
+same hybrid have been raised at the same time from different parents, so as
+to avoid the ill effects of close interbreeding. On the contrary, brothers
+and sisters have usually been crossed in each successive generation, in
+opposition to the constantly repeated admonition of every breeder. And in
+this case, it is not at all surprising that the inherent sterility in the
+hybrids should have gone on increasing. If we were to act thus, and pair
+brothers and sisters in the case of any pure animal, which from any cause
+had the least tendency to sterility, the breed would assuredly be lost in a
+very few generations.
+
+Although I do not know of any thoroughly well-authenticated cases of
+perfectly fertile hybrid animals, I have some reason to believe that the
+hybrids from Cervulus vaginalis and Reevesii, and from Phasianus colchicus
+with P. torquatus and with P. versicolor are perfectly fertile. There is no
+doubt that these three pheasants, namely, the common, the true ring-necked,
+and the Japan, intercross, and are becoming blended together in the woods
+of several parts of England. The hybrids from the common and Chinese geese
+(A. cygnoides), species which are so different that they are generally
+ranked in distinct genera, have often bred in this country with either pure
+parent, and in one single instance they have bred _inter se_. This was
+effected by Mr. Eyton, who raised two hybrids from the same parents but
+from different hatches; and from these two birds he raised no less than
+eight hybrids (grandchildren of the pure geese) from one nest. In India,
+however, these cross-bred geese must be far more fertile; for I am assured
+by two eminently capable judges, namely {254} Mr. Blyth and Capt. Hutton,
+that whole flocks of these crossed geese are kept in various parts of the
+country; and as they are kept for profit, where neither pure parent-species
+exists, they must certainly be highly fertile.
+
+A doctrine which originated with Pallas, has been largely accepted by
+modern naturalists; namely, that most of our domestic animals have
+descended from two or more wild species, since commingled by intercrossing.
+On this view, the aboriginal species must either at first have produced
+quite fertile hybrids, or the hybrids must have become in subsequent
+generations quite fertile under domestication. This latter alternative
+seems to me the most probable, and I am inclined to believe in its truth,
+although it rests on no direct evidence. I believe, for instance, that our
+dogs have descended from several wild stocks; yet, with perhaps the
+exception of certain indigenous domestic dogs of South America, all are
+quite fertile together; and analogy makes me greatly doubt, whether the
+several aboriginal species would at first have freely bred together and
+have produced quite fertile hybrids. So again there is reason to believe
+that our European and the humped Indian cattle are quite fertile together;
+but from facts communicated to me by Mr. Blyth, I think they must be
+considered as distinct species. On this view of the origin of many of our
+domestic animals, we must either give up the belief of the almost universal
+sterility of distinct species of animals when crossed; or we must look at
+sterility, not as an indelible characteristic, but as one capable of being
+removed by domestication.
+
+Finally, looking to all the ascertained facts on the intercrossing of
+plants and animals, it may be concluded that some degree of sterility, both
+in first crosses {255} and in hybrids, is an extremely general result; but
+that it cannot, under our present state of knowledge, be considered as
+absolutely universal.
+
+
+
+_Laws governing the Sterility of first Crosses and of Hybrids._--We will
+now consider a little more in detail the circumstances and rules governing
+the sterility of first crosses and of hybrids. Our chief object will be to
+see whether or not the rules indicate that species have specially been
+endowed with this quality, in order to prevent their crossing and blending
+together in utter confusion. The following rules and conclusions are
+chiefly drawn up from Gärtner's admirable work on the hybridisation of
+plants. I have taken much pains to ascertain how far the rules apply to
+animals, and considering how scanty our knowledge is in regard to hybrid
+animals, I have been surprised to find how generally the same rules apply
+to both kingdoms.
+
+It has been already remarked, that the degree of fertility, both of first
+crosses and of hybrids, graduates from zero to perfect fertility. It is
+surprising in how many curious ways this gradation can be shown to exist;
+but only the barest outline of the facts can here be given. When pollen
+from a plant of one family is placed on the stigma of a plant of a distinct
+family, it exerts no more influence than so much inorganic dust. From this
+absolute zero of fertility, the pollen of different species of the same
+genus applied to the stigma of some one species, yields a perfect gradation
+in the number of seeds produced, up to nearly complete or even quite
+complete fertility; and, as we have seen, in certain abnormal cases, even
+to an excess of fertility, beyond that which the plant's own pollen will
+produce. So in hybrids themselves, there are some which never have
+produced, and probably never would produce, even {256} with the pollen of
+either pure parent, a single fertile seed: but in some of these cases a
+first trace of fertility may be detected, by the pollen of one of the pure
+parent-species causing the flower of the hybrid to wither earlier than it
+otherwise would have done; and the early withering of the flower is well
+known to be a sign of incipient fertilisation. From this extreme degree of
+sterility we have self-fertilised hybrids producing a greater and greater
+number of seeds up to perfect fertility.
+
+Hybrids from two species which are very difficult to cross, and which
+rarely produce any offspring, are generally very sterile; but the
+parallelism between the difficulty of making a first cross, and the
+sterility of the hybrids thus produced--two classes of facts which are
+generally confounded together--is by no means strict. There are many cases,
+in which two pure species can be united with unusual facility, and produce
+numerous hybrid-offspring, yet these hybrids are remarkably sterile. On the
+other hand, there are species which can be crossed very rarely, or with
+extreme difficulty, but the hybrids, when at last produced, are very
+fertile. Even within the limits of the same genus, for instance in
+Dianthus, these two opposite cases occur.
+
+The fertility, both of first crosses and of hybrids, is more easily
+affected by unfavourable conditions, than is the fertility of pure species.
+But the degree of fertility is likewise innately variable; for it is not
+always the same when the same two species are crossed under the same
+circumstances, but depends in part upon the constitution of the individuals
+which happen to have been chosen for the experiment. So it is with hybrids,
+for their degree of fertility is often found to differ greatly in the
+several individuals raised from seed out of the same capsule and exposed to
+exactly the same conditions. {257}
+
+By the term systematic affinity is meant, the resemblance between species
+in structure and in constitution, more especially in the structure of parts
+which are of high physiological importance and which differ little in the
+allied species. Now the fertility of first crosses between species, and of
+the hybrids produced from them, is largely governed by their systematic
+affinity. This is clearly shown by hybrids never having been raised between
+species ranked by systematists in distinct families; and on the other hand,
+by very closely allied species generally uniting with facility. But the
+correspondence between systematic affinity and the facility of crossing is
+by no means strict. A multitude of cases could be given of very closely
+allied species which will not unite, or only with extreme difficulty; and
+on the other hand of very distinct species which unite with the utmost
+facility. In the same family there may be a genus, as Dianthus, in which
+very many species can most readily be crossed; and another genus, as
+Silene, in which the most persevering efforts have failed to produce
+between extremely close species a single hybrid. Even within the limits of
+the same genus, we meet with this same difference; for instance, the many
+species of Nicotiana have been more largely crossed than the species of
+almost any other genus; but Gärtner found that N. acuminata, which is not a
+particularly distinct species, obstinately failed to fertilise, or to be
+fertilised by, no less than eight other species of Nicotiana. Very many
+analogous facts could be given.
+
+No one has been able to point out what kind, or what amount, of difference
+in any recognisable character is sufficient to prevent two species
+crossing. It can be shown that plants most widely different in habit and
+general appearance, and having strongly marked {258} differences in every
+part of the flower, even in the pollen, in the fruit, and in the
+cotyledons, can be crossed. Annual and perennial plants, deciduous and
+evergreen trees, plants inhabiting different stations and fitted for
+extremely different climates, can often be crossed with ease.
+
+By a reciprocal cross between two species, I mean the case, for instance,
+of a stallion-horse being first crossed with a female-ass, and then a
+male-ass with a mare: these two species may then be said to have been
+reciprocally crossed. There is often the widest possible difference in the
+facility of making reciprocal crosses. Such cases are highly important, for
+they prove that the capacity in any two species to cross is often
+completely independent of their systematic affinity, or of any recognisable
+difference in their whole organisation. On the other hand, these cases
+clearly show that the capacity for crossing is connected with
+constitutional differences imperceptible by us, and confined to the
+reproductive system. This difference in the result of reciprocal crosses
+between the same two species was long ago observed by Kölreuter. To give an
+instance: Mirabilis jalapa can easily be fertilised by the pollen of M.
+longiflora, and the hybrids thus produced are sufficiently fertile; but
+Kölreuter tried more than two hundred times, during eight following years,
+to fertilise reciprocally M. longiflora with the pollen of M. jalapa, and
+utterly failed. Several other equally striking cases could be given. Thuret
+has observed the same fact with certain sea-weeds or Fuci. Gärtner,
+moreover, found that this difference of facility in making reciprocal
+crosses is extremely common in a lesser degree. He has observed it even
+between forms so closely related (as Matthiola annua and glabra) that many
+botanists rank them only as varieties. It is also a remarkable fact, that
+hybrids raised from reciprocal crosses, though {259} of course compounded
+of the very same two species, the one species having first been used as the
+father and then as the mother, generally differ in fertility in a small,
+and occasionally in a high degree.
+
+Several other singular rules could be given from Gärtner: for instance,
+some species have a remarkable power of crossing with other species; other
+species of the same genus have a remarkable power of impressing their
+likeness on their hybrid offspring; but these two powers do not at all
+necessarily go together. There are certain hybrids which instead of having,
+as is usual, an intermediate character between their two parents, always
+closely resemble one of them; and such hybrids, though externally so like
+one of their pure parent-species, are with rare exceptions extremely
+sterile. So again amongst hybrids which are usually intermediate in
+structure between their parents, exceptional and abnormal individuals
+sometimes are born, which closely resemble one of their pure parents; and
+these hybrids are almost always utterly sterile, even when the other
+hybrids raised from seed from the same capsule have a considerable degree
+of fertility. These facts show how completely fertility in the hybrid is
+independent of its external resemblance to either pure parent.
+
+Considering the several rules now given, which govern the fertility of
+first crosses and of hybrids, we see that when forms, which must be
+considered as good and distinct species, are united, their fertility
+graduates from zero to perfect fertility, or even to fertility under
+certain conditions in excess. That their fertility, besides being eminently
+susceptible to favourable and unfavourable conditions, is innately
+variable. That it is by no means always the same in degree in the first
+cross and in the hybrids produced {260} from this cross. That the fertility
+of hybrids is not related to the degree in which they resemble in external
+appearance either parent. And lastly, that the facility of making a first
+cross between any two species is not always governed by their systematic
+affinity or degree of resemblance to each other. This latter statement is
+clearly proved by reciprocal crosses between the same two species, for
+according as the one species or the other is used as the father or the
+mother, there is generally some difference, and occasionally the widest
+possible difference, in the facility of effecting an union. The hybrids,
+moreover, produced from reciprocal crosses often differ in fertility.
+
+Now do these complex and singular rules indicate that species have been
+endowed with sterility simply to prevent their becoming confounded in
+nature? I think not. For why should the sterility be so extremely different
+in degree, when various species are crossed, all of which we must suppose
+it would be equally important to keep from blending together? Why should
+the degree of sterility be innately variable in the individuals of the same
+species? Why should some species cross with facility, and yet produce very
+sterile hybrids; and other species cross with extreme difficulty, and yet
+produce fairly fertile hybrids? Why should there often be so great a
+difference in the result of a reciprocal cross between the same two
+species? Why, it may even be asked, has the production of hybrids been
+permitted? to grant to species the special power of producing hybrids, and
+then to stop their further propagation by different degrees of sterility,
+not strictly related to the facility of the first union between their
+parents, seems to be a strange arrangement.
+
+The foregoing rules and facts, on the other hand, {261} appear to me
+clearly to indicate that the sterility both of first crosses and of hybrids
+is simply incidental or dependent on unknown differences, chiefly in the
+reproductive systems, of the species which are crossed. The differences
+being of so peculiar and limited a nature, that, in reciprocal crosses
+between two species the male sexual element of the one will often freely
+act on the female sexual element of the other, but not in a reversed
+direction. It will be advisable to explain a little more fully by an
+example what I mean by sterility being incidental on other differences, and
+not a specially endowed quality. As the capacity of one plant to be grafted
+or budded on another is so entirely unimportant for its welfare in a state
+of nature, I presume that no one will suppose that this capacity is a
+_specially_ endowed quality, but will admit that it is incidental on
+differences in the laws of growth of the two plants. We can sometimes see
+the reason why one tree will not take on another, from differences in their
+rate of growth, in the hardness of their wood, in the period of the flow or
+nature of their sap, &c.; but in a multitude of cases we can assign no
+reason whatever. Great diversity in the size of two plants, one being woody
+and the other herbaceous, one being evergreen and the other deciduous, and
+adaptation to widely different climates, does not always prevent the two
+grafting together. As in hybridisation, so with grafting, the capacity is
+limited by systematic affinity, for no one has been able to graft trees
+together belonging to quite distinct families; and, on the other hand,
+closely allied species, and varieties of the same species, can usually, but
+not invariably, be grafted with ease. But this capacity, as in
+hybridisation, is by no means absolutely governed by systematic affinity.
+Although many distinct genera within the same family have been grafted
+{262} together, in other cases species of the same genus will not take on
+each other. The pear can be grafted far more readily on the quince, which
+is ranked as a distinct genus, than on the apple, which is a member of the
+same genus. Even different varieties of the pear take with different
+degrees of facility on the quince; so do different varieties of the apricot
+and peach on certain varieties of the plum.
+
+As Gärtner found that there was sometimes an innate difference in different
+_individuals_ of the same two species in crossing; so Sagaret believes this
+to be the case with different individuals of the same two species in being
+grafted together. As in reciprocal crosses, the facility of effecting an
+union is often very far from equal, so it sometimes is in grafting; the
+common gooseberry, for instance, cannot be grafted on the currant, whereas
+the currant will take, though with difficulty, on the gooseberry.
+
+We have seen that the sterility of hybrids, which have their reproductive
+organs in an imperfect condition, is a very different case from the
+difficulty of uniting two pure species, which have their reproductive
+organs perfect; yet these two distinct cases run to a certain extent
+parallel. Something analogous occurs in grafting; for Thouin found that
+three species of Robinia, which seeded freely on their own roots, and which
+could be grafted with no great difficulty on another species, when thus
+grafted were rendered barren. On the other hand, certain species of Sorbus,
+when grafted on other species, yielded twice as much fruit as when on their
+own roots. We are reminded by this latter fact of the extraordinary case of
+Hippeastrum, Lobelia, &c., which seeded much more freely when fertilised
+with the pollen of distinct species, than when self-fertilised with their
+own pollen. {263}
+
+We thus see, that although there is a clear and fundamental difference
+between the mere adhesion of grafted stocks, and the union of the male and
+female elements in the act of reproduction, yet that there is a rude degree
+of parallelism in the results of grafting and of crossing distinct species.
+And as we must look at the curious and complex laws governing the facility
+with which trees can be grafted on each other as incidental on unknown
+differences in their vegetative systems, so I believe that the still more
+complex laws governing the facility of first crosses, are incidental on
+unknown differences, chiefly in their reproductive systems. These
+differences, in both cases, follow to a certain extent, as might have been
+expected, systematic affinity, by which every kind of resemblance and
+dissimilarity between organic beings is attempted to be expressed. The
+facts by no means seem to me to indicate that the greater or lesser
+difficulty of either grafting or crossing together various species has been
+a special endowment; although in the case of crossing, the difficulty is as
+important for the endurance and stability of specific forms, as in the case
+of grafting it is unimportant for their welfare.
+
+
+
+_Causes of the Sterility of first Crosses and of Hybrids._--We may now look
+a little closer at the probable causes of the sterility of first crosses
+and of hybrids. These two cases are fundamentally different, for, as just
+remarked, in the union of two pure species the male and female sexual
+elements are perfect, whereas in hybrids they are imperfect. Even in first
+crosses, the greater or lesser difficulty in effecting a union apparently
+depends on several distinct causes. There must sometimes be a physical
+impossibility in the male element reaching the ovule, as would be the case
+with a plant {264} having a pistil too long for the pollen-tubes to reach
+the ovarium. It has also been observed that when pollen of one species is
+placed on the stigma of a distantly allied species, though the pollen-tubes
+protrude, they do not penetrate the stigmatic surface. Again, the male
+element may reach the female element, but be incapable of causing an embryo
+to be developed, as seems to have been the case with some of Thuret's
+experiments on Fuci. No explanation can be given of these facts, any more
+than why certain trees cannot be grafted on others. Lastly, an embryo may
+be developed, and then perish at an early period. This latter alternative
+has not been sufficiently attended to; but I believe, from observations
+communicated to me by Mr. Hewitt, who has had great experience in
+hybridising gallinaceous birds, that the early death of the embryo is a
+very frequent cause of sterility in first crosses. I was at first very
+unwilling to believe in this view; as hybrids, when once born, are
+generally healthy and long-lived, as we see in the case of the common mule.
+Hybrids, however, are differently circumstanced before and after birth:
+when born and living in a country where their two parents can live, they
+are generally placed under suitable conditions of life. But a hybrid
+partakes of only half of the nature and constitution of its mother, and
+therefore before birth, as long as it is nourished within its mother's womb
+or within the egg or seed produced by the mother, it may be exposed to
+conditions in some degree unsuitable, and consequently be liable to perish
+at an early period; more especially as all very young beings seem eminently
+sensitive to injurious or unnatural conditions of life.
+
+In regard to the sterility of hybrids, in which the sexual elements are
+imperfectly developed, the case is {265} very different. I have more than
+once alluded to a large body of facts, which I have collected, showing that
+when animals and plants are removed from their natural conditions, they are
+extremely liable to have their reproductive systems seriously affected.
+This, in fact, is the great bar to the domestication of animals. Between
+the sterility thus superinduced and that of hybrids, there are many points
+of similarity. In both cases the sterility is independent of general
+health, and is often accompanied by excess of size or great luxuriance. In
+both cases, the sterility occurs in various degrees; in both, the male
+element is the most liable to be affected; but sometimes the female more
+than the male. In both, the tendency goes to a certain extent with
+systematic affinity, for whole groups of animals and plants are rendered
+impotent by the same unnatural conditions; and whole groups of species tend
+to produce sterile hybrids. On the other hand, one species in a group will
+sometimes resist great changes of conditions with unimpaired fertility; and
+certain species in a group will produce unusually fertile hybrids. No one
+can tell, till he tries, whether any particular animal will breed under
+confinement or any exotic plant seed freely under culture; nor can he tell,
+till he tries, whether any two species of a genus will produce more or less
+sterile hybrids. Lastly, when organic beings are placed during several
+generations under conditions not natural to them, they are extremely liable
+to vary, which is due, as I believe, to their reproductive systems having
+been specially affected, though in a lesser degree than when sterility
+ensues. So it is with hybrids, for hybrids in successive generations are
+eminently liable to vary, as every experimentalist has observed.
+
+Thus we see that when organic beings are placed under new and unnatural
+conditions, and when hybrids {266} are produced by the unnatural crossing
+of two species, the reproductive system, independently of the general state
+of health, is affected by sterility in a very similar manner. In the one
+case, the conditions of life have been disturbed, though often in so slight
+a degree as to be inappreciable by us; in the other case, or that of
+hybrids, the external conditions have remained the same, but the
+organisation has been disturbed by two different structures and
+constitutions having been blended into one. For it is scarcely possible
+that two organisations should be compounded into one, without some
+disturbance occurring in the development, or periodical action, or mutual
+relation of the different parts and organs one to another, or to the
+conditions of life. When hybrids are able to breed _inter se_, they
+transmit to their offspring from generation to generation the same
+compounded organisation, and hence we need not be surprised that their
+sterility, though in some degree variable, rarely diminishes.
+
+It must, however, be confessed that we cannot understand, excepting on
+vague hypotheses, several facts with respect to the sterility of hybrids;
+for instance, the unequal fertility of hybrids produced from reciprocal
+crosses; or the increased sterility in those hybrids which occasionally and
+exceptionally resemble closely either pure parent. Nor do I pretend that
+the foregoing remarks go to the root of the matter: no explanation is
+offered why an organism, when placed under unnatural conditions, is
+rendered sterile. All that I have attempted to show, is that in two cases,
+in some respects allied, sterility is the common result,--in the one case
+from the conditions of life having been disturbed, in the other case from
+the organisation having been disturbed by two organisations having been
+compounded into one.
+
+It may seem fanciful, but I suspect that a similar {267} parallelism
+extends to an allied yet very different class of facts. It is an old and
+almost universal belief, founded, I think, on a considerable body of
+evidence, that slight changes in the conditions of life are beneficial to
+all living things. We see this acted on by farmers and gardeners in their
+frequent exchanges of seed, tubers, &c., from one soil or climate to
+another, and back again. During the convalescence of animals, we plainly
+see that great benefit is derived from almost any change in the habits of
+life. Again, both with plants and animals, there is abundant evidence, that
+a cross between very distinct individuals of the same species, that is
+between members of different strains or sub-breeds, gives vigour and
+fertility to the offspring. I believe, indeed, from the facts alluded to in
+our fourth chapter, that a certain amount of crossing is indispensable even
+with hermaphrodites; and that close interbreeding continued during several
+generations between the nearest relations, especially if these be kept
+under the same conditions of life, always induces weakness and sterility in
+the progeny.
+
+Hence it seems that, on the one hand, slight changes in the conditions of
+life benefit all organic beings, and on the other hand, that slight
+crosses, that is crosses between the males and females of the same species
+which have varied and become slightly different, give vigour and fertility
+to the offspring. But we have seen that greater changes, or changes of a
+particular nature, often render organic beings in some degree sterile; and
+that greater crosses, that is crosses between males and females which have
+become widely or specifically different, produce hybrids which are
+generally sterile in some degree. I cannot persuade myself that this
+parallelism is an accident or an illusion. Both series of facts seem to be
+connected together by some {268} common but unknown bond, which is
+essentially related to the principle of life.
+
+
+
+_Fertility of Varieties when crossed, and of their Mongrel offspring._--It
+may be urged, as a most forcible argument, that there must be some
+essential distinction between species and varieties, and that there must be
+some error in all the foregoing remarks, inasmuch as varieties, however
+much they may differ from each other in external appearance, cross with
+perfect facility, and yield perfectly fertile offspring. I fully admit that
+this is almost invariably the case. But if we look to varieties produced
+under nature, we are immediately involved in hopeless difficulties; for if
+two hitherto reputed varieties be found in any degree sterile together,
+they are at once ranked by most naturalists as species. For instance, the
+blue and red pimpernel, the primrose and cowslip, which are considered by
+many of our best botanists as varieties, are said by Gärtner not to be
+quite fertile when crossed, and he consequently ranks them as undoubted
+species. If we thus argue in a circle, the fertility of all varieties
+produced under nature will assuredly have to be granted.
+
+If we turn to varieties, produced, or supposed to have been produced, under
+domestication, we are still involved in doubt. For when it is stated, for
+instance, that the German Spitz dog unites more easily than other dogs with
+foxes, or that certain South American indigenous domestic dogs do not
+readily cross with European dogs, the explanation which will occur to every
+one, and probably the true one, is that these dogs have descended from
+several aboriginally distinct species. Nevertheless the perfect fertility
+of so many domestic varieties, differing widely from each other in
+appearance, for instance of the pigeon or of the cabbage, is {269} a
+remarkable fact; more especially when we reflect how many species there
+are, which, though resembling each other most closely, are utterly sterile
+when intercrossed. Several considerations, however, render the fertility of
+domestic varieties less remarkable than at first appears. It can, in the
+first place, be clearly shown that mere external dissimilarity between two
+species does not determine their greater or lesser degree of sterility when
+crossed; and we may apply the same rule to domestic varieties. In the
+second place, some eminent naturalists believe that a long course of
+domestication tends to eliminate sterility in the successive generations of
+hybrids which were at first only slightly sterile; and if this be so, we
+surely ought not to expect to find sterility both appearing and
+disappearing under nearly the same conditions of life. Lastly, and this
+seems to me by far the most important consideration, new races of animals
+and plants are produced under domestication by man's methodical and
+unconscious power of selection, for his own use and pleasure: he neither
+wishes to select, nor could select, slight differences in the reproductive
+system, or other constitutional differences correlated with the
+reproductive system. He supplies his several varieties with the same food;
+treats them in nearly the same manner, and does not wish to alter their
+general habits of life. Nature acts uniformly and slowly during vast
+periods of time on the whole organisation, in any way which may be for each
+creature's own good; and thus she may, either directly, or more probably
+indirectly, through correlation, modify the reproductive system in the
+several descendants from any one species. Seeing this difference in the
+process of selection, as carried on by man and nature, we need not be
+surprised at some difference in the result.
+
+I have as yet spoken as if the varieties of the same {270} species were
+invariably fertile when intercrossed. But it seems to me impossible to
+resist the evidence of the existence of a certain amount of sterility in
+the few following cases, which I will briefly abstract. The evidence is at
+least as good as that from which we believe in the sterility of a multitude
+of species. The evidence is, also, derived from hostile witnesses, who in
+all other cases consider fertility and sterility as safe criterions of
+specific distinction. Gärtner kept during several years a dwarf kind of
+maize with yellow seeds, and a tall variety with red seeds, growing near
+each other in his garden; and although these plants have separated sexes,
+they never naturally crossed. He then fertilised thirteen flowers of the
+one with the pollen of the other; but only a single head produced any seed,
+and this one head produced only five grains. Manipulation in this case
+could not have been injurious, as the plants have separated sexes. No one,
+I believe, has suspected that these varieties of maize are distinct
+species; and it is important to notice that the hybrid plants thus raised
+were themselves _perfectly_ fertile; so that even Gärtner did not venture
+to consider the two varieties as specifically distinct.
+
+Girou de Buzareingues crossed three varieties of gourd, which like the
+maize has separated sexes, and he asserts that their mutual fertilisation
+is by so much the less easy as their differences are greater. How far these
+experiments may be trusted, I know not; but the forms experimentised on,
+are ranked by Sagaret, who mainly founds his classification by the test of
+infertility, as varieties.
+
+The following case is far more remarkable, and seems at first quite
+incredible; but it is the result of an astonishing number of experiments
+made during many years on nine species of Verbascum, by so good an observer
+{271} and so hostile a witness, as Gärtner: namely, that yellow and white
+varieties of the same species of Verbascum when intercrossed produce less
+seed, than do either coloured varieties when fertilised with pollen from
+their own coloured flowers. Moreover, he asserts that when yellow and white
+varieties of one species are crossed with yellow and white varieties of a
+_distinct_ species, more seed is produced by the crosses between the
+similarly coloured flowers, than between those which are differently
+coloured. Yet these varieties of Verbascum present no other difference
+besides the mere colour of the flower; and one variety can sometimes be
+raised from the seed of the other.
+
+From observations which I have made on certain varieties of hollyhock, I am
+inclined to suspect that they present analogous facts.
+
+Kölreuter, whose accuracy has been confirmed by every subsequent observer,
+has proved the remarkable fact, that one variety of the common tobacco is
+more fertile, when crossed with a widely distinct species, than are the
+other varieties. He experimentised on five forms, which are commonly
+reputed to be varieties, and which he tested by the severest trial, namely,
+by reciprocal crosses, and he found their mongrel offspring perfectly
+fertile. But one of these five varieties, when used either as father or
+mother, and crossed with the Nicotiana glutinosa, always yielded hybrids
+not so sterile as those which were produced from the four other varieties
+when crossed with N. glutinosa. Hence the reproductive system of this one
+variety must have been in some manner and in some degree modified.
+
+From these facts; from the great difficulty of ascertaining the infertility
+of varieties in a state of nature, for a supposed variety if infertile in
+any degree would generally be ranked as species; from man selecting only
+{272} external characters in the production of the most distinct domestic
+varieties, and from not wishing or being able to produce recondite and
+functional differences in the reproductive system; from these several
+considerations and facts, I do not think that the very general fertility of
+varieties can be proved to be of universal occurrence, or to form a
+fundamental distinction between varieties and species. The general
+fertility of varieties does not seem to me sufficient to overthrow the view
+which I have taken with respect to the very general, but not invariable,
+sterility of first crosses and of hybrids, namely, that it is not a special
+endowment, but is incidental on slowly acquired modifications, more
+especially in the reproductive systems of the forms which are crossed.
+
+
+
+_Hybrids and Mongrels compared, independently of their
+fertility._--Independently of the question of fertility, the offspring of
+species when crossed and of varieties when crossed may be compared in
+several other respects. Gärtner, whose strong wish was to draw a marked
+line of distinction between species and varieties, could find very few and,
+as it seems to me, quite unimportant differences between the so-called
+hybrid offspring of species, and the so-called mongrel offspring of
+varieties. And, on the other hand, they agree most closely in very many
+important respects.
+
+I shall here discuss this subject with extreme brevity. The most important
+distinction is, that in the first generation mongrels are more variable
+than hybrids; but Gärtner admits that hybrids from species which have long
+been cultivated are often variable in the first generation; and I have
+myself seen striking instances of this fact. Gärtner further admits that
+hybrids between very closely allied species are more variable {273} than
+those from very distinct species; and this shows that the difference in the
+degree of variability graduates away. When mongrels and the more fertile
+hybrids are propagated for several generations an extreme amount of
+variability in their offspring is notorious; but some few cases both of
+hybrids and mongrels long retaining uniformity of character could be given.
+The variability, however, in the successive generations of mongrels is,
+perhaps, greater than in hybrids.
+
+This greater variability of mongrels than of hybrids does not seem to me at
+all surprising. For the parents of mongrels are varieties, and mostly
+domestic varieties (very few experiments having been tried on natural
+varieties), and this implies in most cases that there has been recent
+variability; and therefore we might expect that such variability would
+often continue and be superadded to that arising from the mere act of
+crossing. The slight degree of variability in hybrids from the first cross
+or in the first generation, in contrast with their extreme variability in
+the succeeding generations, is a curious fact and deserves attention. For
+it bears on and corroborates the view which I have taken on the cause of
+ordinary variability; namely, that it is due to the reproductive system
+being eminently sensitive to any change in the conditions of life, being
+thus often rendered either impotent or at least incapable of its proper
+function of producing offspring identical with the parent-form. Now hybrids
+in the first generation are descended from species (excluding those long
+cultivated) which have not had their reproductive systems in any way
+affected, and they are not variable; but hybrids themselves have their
+reproductive systems seriously affected, and their descendants are highly
+variable.
+
+But to return to our comparison of mongrels and {274} hybrids: Gärtner
+states that mongrels are more liable than hybrids to revert to either
+parent-form; but this, if it be true, is certainly only a difference in
+degree. Gärtner further insists that when any two species, although most
+closely allied to each other, are crossed with a third species, the hybrids
+are widely different from each other; whereas if two very distinct
+varieties of one species are crossed with another species, the hybrids do
+not differ much. But this conclusion, as far as I can make out, is founded
+on a single experiment; and seems directly opposed to the results of
+several experiments made by Kölreuter.
+
+These alone are the unimportant differences, which Gärtner is able to point
+out, between hybrid and mongrel plants. On the other hand, the resemblance
+in mongrels and in hybrids to their respective parents, more especially in
+hybrids produced from nearly related species, follows according to Gärtner
+the same laws. When two species are crossed, one has sometimes a prepotent
+power of impressing its likeness on the hybrid; and so I believe it to be
+with varieties of plants. With animals one variety certainly often has this
+prepotent power over another variety. Hybrid plants produced from a
+reciprocal cross, generally resemble each other closely; and so it is with
+mongrels from a reciprocal cross. Both hybrids and mongrels can be reduced
+to either pure parent-form, by repeated crosses in successive generations
+with either parent.
+
+These several remarks are apparently applicable to animals; but the subject
+is here excessively complicated, partly owing to the existence of secondary
+sexual characters; but more especially owing to prepotency in transmitting
+likeness running more strongly in one sex than in the other, both when one
+species is crossed with another, and when, one variety is crossed with
+{275} another variety. For instance, I think those authors are right, who
+maintain that the ass has a prepotent power over the horse, so that both
+the mule and the hinny more resemble the ass than the horse; but that the
+prepotency runs more strongly in the male-ass than in the female, so that
+the mule, which is the offspring of the male-ass and mare, is more like an
+ass, than is the hinny, which is the offspring of the female-ass and
+stallion.
+
+Much stress has been laid by some authors on the supposed fact, that
+mongrel animals alone are born closely like one of their parents; but it
+can be shown that this does sometimes occur with hybrids; yet I grant much
+less frequently with hybrids than with mongrels. Looking to the cases which
+I have collected of cross-bred animals closely resembling one parent, the
+resemblances seem chiefly confined to characters almost monstrous in their
+nature, and which have suddenly appeared--such as albinism, melanism,
+deficiency of tail or horns, or additional fingers and toes; and do not
+relate to characters which have been slowly acquired by selection.
+Consequently, sudden reversions to the perfect character of either parent
+would be more likely to occur with mongrels, which are descended from
+varieties often suddenly produced and semi-monstrous in character, than
+with hybrids, which are descended from species slowly and naturally
+produced. On the whole I entirely agree with Dr. Prosper Lucas, who, after
+arranging an enormous body of facts with respect to animals, comes to the
+conclusion, that the laws of resemblance of the child to its parents are
+the same, whether the two parents differ much or little from each other,
+namely in the union of individuals of the same variety, or of different
+varieties, or of distinct species.
+
+Laying aside the question of fertility and sterility, {276} in all other
+respects there seems to be a general and close similarity in the offspring
+of crossed species, and of crossed varieties. If we look at species as
+having been specially created, and at varieties as having been produced by
+secondary laws, this similarity would be an astonishing fact. But it
+harmonises perfectly with the view that there is no essential distinction
+between species and varieties.
+
+
+
+_Summary of Chapter._--First crosses between forms sufficiently distinct to
+be ranked as species, and their hybrids, are very generally, but not
+universally, sterile. The sterility is of all degrees, and is often so
+slight that the two most careful experimentalists who have ever lived, have
+come to diametrically opposite conclusions in ranking forms by this test.
+The sterility is innately variable in individuals of the same species, and
+is eminently susceptible of favourable and unfavourable conditions. The
+degree of sterility does not strictly follow systematic affinity, but is
+governed by several curious and complex laws. It is generally different,
+and sometimes widely different, in reciprocal crosses between the same two
+species. It is not always equal in degree in a first cross and in the
+hybrid produced from this cross.
+
+In the same manner as in grafting trees, the capacity of one species or
+variety to take on another, is incidental on generally unknown differences
+in their vegetative systems, so in crossing, the greater or less facility
+of one species to unite with another, is incidental on unknown differences
+in their reproductive systems. There is no more reason to think that
+species have been specially endowed with various degrees of sterility to
+prevent them crossing and blending in nature, than to think that trees have
+been specially endowed with various and {277} somewhat analogous degrees of
+difficulty in being grafted together in order to prevent them becoming
+inarched in our forests.
+
+The sterility of first crosses between pure species, which have their
+reproductive systems perfect, seems to depend on several circumstances; in
+some cases largely on the early death of the embryo. The sterility of
+hybrids, which have their reproductive systems imperfect, and which have
+had this system and their whole organisation disturbed by being compounded
+of two distinct species, seems closely allied to that sterility which so
+frequently affects pure species, when their natural conditions of life have
+been disturbed. This view is supported by a parallelism of another
+kind;--namely, that the crossing of forms only slightly different is
+favourable to the vigour and fertility of their offspring; and that slight
+changes in the conditions of life are apparently favourable to the vigour
+and fertility of all organic beings. It is not surprising that the degree
+of difficulty in uniting two species, and the degree of sterility of their
+hybrid-offspring should generally correspond, though due to distinct
+causes; for both depend on the amount of difference of some kind between
+the species which are crossed. Nor is it surprising that the facility of
+effecting a first cross, the fertility of the hybrids produced from it, and
+the capacity of being grafted together--though this latter capacity
+evidently depends on widely different circumstances--should all run, to a
+certain extent, parallel with the systematic affinity of the forms which
+are subjected to experiment; for systematic affinity attempts to express
+all kinds of resemblance between all species.
+
+First crosses between forms known to be varieties, or sufficiently alike to
+be considered as varieties, and their mongrel offspring, are very
+generally, but not quite {278} universally, fertile. Nor is this nearly
+general and perfect fertility surprising, when we remember how liable we
+are to argue in a circle with respect to varieties in a state of nature;
+and when we remember that the greater number of varieties have been
+produced under domestication by the selection of mere external differences,
+and not of differences in the reproductive system. In all other respects,
+excluding fertility, there is a close general resemblance between hybrids
+and mongrels. Finally, then, the facts briefly given in this chapter do not
+seem to me opposed to, but even rather to support the view, that there is
+no fundamental distinction between species and varieties.
+
+       *       *       *       *       *
+
+
+{279}
+
+CHAPTER IX.
+
+ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
+
+    On the absence of intermediate varieties at the present day--On the
+    nature of extinct intermediate varieties; on their number--On the vast
+    lapse of time, as inferred from the rate of deposition and of
+    denudation--On the poorness of our palæontological collections--On the
+    intermittence of geological formations--On the absence of intermediate
+    varieties in any one formation--On the sudden appearance of groups of
+    species--On their sudden appearance in the lowest known fossiliferous
+    strata.
+
+In the sixth chapter I enumerated the chief objections which might be
+justly urged against the views maintained in this volume. Most of them have
+now been discussed. One, namely the distinctness of specific forms, and
+their not being blended together by innumerable transitional links, is a
+very obvious difficulty. I assigned reasons why such links do not commonly
+occur at the present day, under the circumstances apparently most
+favourable for their presence, namely on an extensive and continuous area
+with graduated physical conditions. I endeavoured to show, that the life of
+each species depends in a more important manner on the presence of other
+already defined organic forms, than on climate; and, therefore, that the
+really governing conditions of life do not graduate away quite insensibly
+like heat or moisture. I endeavoured, also, to show that intermediate
+varieties, from existing in lesser numbers than the forms which they
+connect, will generally be beaten out and exterminated during the course of
+further modification and improvement. The main cause, however, of
+innumerable intermediate links not now occurring everywhere throughout
+nature {280} depends on the very process of natural selection, through
+which new varieties continually take the places of and exterminate their
+parent-forms. But just in proportion as this process of extermination has
+acted on an enormous scale, so must the number of intermediate varieties,
+which have formerly existed on the earth, be truly enormous. Why then is
+not every geological formation and every stratum full of such intermediate
+links? Geology assuredly does not reveal any such finely graduated organic
+chain; and this, perhaps, is the most obvious and gravest objection which
+can be urged against my theory. The explanation lies, as I believe, in the
+extreme imperfection of the geological record.
+
+In the first place it should always be borne in mind what sort of
+intermediate forms must, on my theory, have formerly existed. I have found
+it difficult, when looking at any two species, to avoid picturing to
+myself, forms _directly_ intermediate between them. But this is a wholly
+false view; we should always look for forms intermediate between each
+species and a common but unknown progenitor; and the progenitor will
+generally have differed in some respects from all its modified descendants.
+To give a simple illustration: the fantail and pouter pigeons have both
+descended from the rock-pigeon; if we possessed all the intermediate
+varieties which have ever existed, we should have an extremely close series
+between both and the rock-pigeon; but we should have no varieties directly
+intermediate between the fantail and pouter; none, for instance, combining
+a tail somewhat expanded with a crop somewhat enlarged, the characteristic
+features of these two breeds. These two breeds, moreover, have become so
+much modified, that if we had no historical or indirect evidence regarding
+their origin, it would not have been possible to have {281} determined from
+a mere comparison of their structure with that of the rock-pigeon, whether
+they had descended from this species or from some other allied species,
+such as C. oenas.
+
+So with natural species, if we look to forms very distinct, for instance to
+the horse and tapir, we have no reason to suppose that links ever existed
+directly intermediate between them, but between each and an unknown common
+parent. The common parent will have had in its whole organisation much
+general resemblance to the tapir and to the horse; but in some points of
+structure may have differed considerably from both, even perhaps more than
+they differ from each other. Hence in all such cases, we should be unable
+to recognise the parent-form of any two or more species, even if we closely
+compared the structure of the parent with that of its modified descendants,
+unless at the same time we had a nearly perfect chain of the intermediate
+links.
+
+It is just possible by my theory, that one of two living forms might have
+descended from the other; for instance, a horse from a tapir; and in this
+case _direct_ intermediate links will have existed between them. But such a
+case would imply that one form had remained for a very long period
+unaltered, whilst its descendants had undergone a vast amount of change;
+and the principle of competition between organism and organism, between
+child and parent, will render this a very rare event; for in all cases the
+new and improved forms of life tend to supplant the old and unimproved
+forms.
+
+By the theory of natural selection all living species have been connected
+with the parent-species of each genus, by differences not greater than we
+see between the varieties of the same species at the present {282} day; and
+these parent-species, now generally extinct, have in their turn been
+similarly connected with more ancient species; and so on backwards, always
+converging to the common ancestor of each great class. So that the number
+of intermediate and transitional links, between all living and extinct
+species, must have been inconceivably great. But assuredly, if this theory
+be true, such have lived upon this earth.
+
+
+
+_On the lapse of Time._--Independently of our not finding fossil remains of
+such infinitely numerous connecting links, it may be objected, that time
+will not have sufficed for so great an amount of organic change, all
+changes having been effected very slowly through natural selection. It is
+hardly possible for me even to recall to the reader, who may not be a
+practical geologist, the facts leading the mind feebly to comprehend the
+lapse of time. He who can read Sir Charles Lyell's grand work on the
+Principles of Geology, which the future historian will recognise as having
+produced a revolution in natural science, yet does not admit how
+incomprehensively vast have been the past periods of time, may at once
+close this volume. Not that it suffices to study the Principles of Geology,
+or to read special treatises by different observers on separate formations,
+and to mark how each author attempts to give an inadequate idea of the
+duration of each formation or even each stratum. A man must for years
+examine for himself great piles of superimposed strata, and watch the sea
+at work grinding down old rocks and making fresh sediment, before he can
+hope to comprehend anything of the lapse of time, the monuments of which we
+see around us.
+
+It is good to wander along lines of sea-coast, when formed of moderately
+hard rocks, and mark the {283} process of degradation. The tides in most
+cases reach the cliffs only for a short time twice a day, and the waves eat
+into them only when they are charged with sand or pebbles; for there is
+good evidence that pure water can effect little or nothing in wearing away
+rock. At last the base of the cliff is undermined, huge fragments fall
+down, and these remaining fixed, have to be worn away, atom by atom, until
+reduced in size they can be rolled about by the waves, and then are more
+quickly ground into pebbles, sand, or mud. But how often do we see along
+the bases of retreating cliffs rounded boulders, all thickly clothed by
+marine productions, showing how little they are abraded and how seldom they
+are rolled about! Moreover, if we follow for a few miles any line of rocky
+cliff, which is undergoing degradation, we find that it is only here and
+there, along a short length or round a promontory, that the cliffs are at
+the present time suffering. The appearance of the surface and the
+vegetation show that elsewhere years have elapsed since the waters washed
+their base.
+
+He who most closely studies the action of the sea on our shores, will, I
+believe, be most deeply impressed with the slowness with which rocky coasts
+are worn away. The observations on this head by Hugh Miller, and by that
+excellent observer Mr. Smith of Jordan Hill, are most impressive. With the
+mind thus impressed, let any one examine beds of conglomerate many thousand
+feet in thickness, which, though probably formed at a quicker rate than
+many other deposits, yet, from being formed of worn and rounded pebbles,
+each of which bears the stamp of time, are good to show how slowly the mass
+has been accumulated. In the Cordillera I estimated one pile of
+conglomerate at ten thousand feet in thickness. Let the {284} observer
+remember Lyell's profound remark that the thickness and extent of
+sedimentary formations are the result and measure of the degradation which
+the earth's crust has elsewhere suffered. And what an amount of degradation
+is implied by the sedimentary deposits of many countries! Professor Ramsay
+has given me the maximum thickness, in most cases from actual measurement,
+in a few cases from estimate, of each formation in different parts of Great
+Britain; and this is the result:--
+
+                                                     Feet.
+  Palæozoic strata (not including igneous beds)      57,154
+  Secondary strata                                   13,190
+  Tertiary strata                                     2,240
+
+--making altogether 72,584 feet; that is, very nearly thirteen and
+three-quarters British miles. Some of the formations, which are represented
+in England by thin beds, are thousands of feet in thickness on the
+Continent. Moreover, between each successive formation, we have, in the
+opinion of most geologists, enormously long blank periods. So that the
+lofty pile of sedimentary rocks in Britain, gives but an inadequate idea of
+the time which has elapsed during their accumulation; yet what time this
+must have consumed! Good observers have estimated that sediment is
+deposited by the great Mississippi river at the rate of only 600 feet in a
+hundred thousand years. This estimate has no pretension to strict
+exactness; yet, considering over what wide spaces very fine sediment is
+transported by the currents of the sea, the process of accumulation in any
+one area must be extremely slow.
+
+But the amount of denudation which the strata have in many places suffered,
+independently of the rate of accumulation of the degraded matter, probably
+offers the best evidence of the lapse of time. I remember {285} having been
+much struck with the evidence of denudation, when viewing volcanic islands,
+which have been worn by the waves and pared all round into perpendicular
+cliffs of one or two thousand feet in height; for the gentle slope of the
+lava-streams, due to their formerly liquid state, showed at a glance how
+far the hard, rocky beds had once extended into the open ocean. The same
+story is still more plainly told by faults,--those great cracks along which
+the strata have been upheaved on one side, or thrown down on the other, to
+the height or depth of thousands of feet; for since the crust cracked, the
+surface of the land has been so completely planed down by the action of the
+sea, that no trace of these vast dislocations is externally visible.
+
+The Craven fault, for instance, extends for upwards of 30 miles, and along
+this line the vertical displacement of the strata has varied from 600 to
+3000 feet. Prof. Ramsay has published an account of a downthrow in Anglesea
+of 2300 feet; and he informs me that he fully believes there is one in
+Merionethshire of 12,000 feet; yet in these cases there is nothing on the
+surface to show such prodigious movements; the pile of rocks on the one or
+other side having been smoothly swept away. The consideration of these
+facts impresses my mind almost in the same manner as does the vain
+endeavour to grapple with the idea of eternity.
+
+I am tempted to give one other case, the well-known one of the denudation
+of the Weald. Though it must be admitted that the denudation of the Weald
+has been a mere trifle, in comparison with that which has removed masses of
+our palæozoic strata, in parts ten thousand feet in thickness, as shown in
+Prof. Ramsay's masterly memoir on this subject: yet it is an admirable
+lesson to stand on the intermediate hilly country and look on the one hand
+at the North Downs, and {286} on the other hand at the South Downs; for,
+remembering that at no great distance to the west the northern and southern
+escarpments meet and close, one can safely picture to oneself the great
+dome of rocks which must have covered up the Weald within so limited a
+period as since the latter part of the Chalk formation. The distance from
+the northern to the southern Downs is about 22 miles, and the thickness of
+the several formations is on an average about 1100 feet, as I am informed
+by Prof. Ramsay. But if, as some geologists suppose, a range of older rocks
+underlies the Weald, on the flanks of which the overlying sedimentary
+deposits might have accumulated in thinner masses than elsewhere, the above
+estimate would be erroneous; but this source of doubt probably would not
+greatly affect the estimate as applied to the western extremity of the
+district. If, then, we knew the rate at which the sea commonly wears away a
+line of cliff of any given height, we could measure the time requisite to
+have denuded the Weald. This, of course cannot be done; but we may, in
+order to form some crude notion on the subject, assume that the sea would
+eat into cliffs 500 feet in height at the rate of one inch in a century.
+This will at first appear much too small an allowance; but it is the same
+as if we were to assume a cliff one yard in height to be eaten back along a
+whole line of coast at the rate of one yard in nearly every twenty-two
+years. I doubt whether any rock, even as soft as chalk, would yield at this
+rate excepting on the most exposed coasts; though no doubt the degradation
+of a lofty cliff would be more rapid from the breakage of the fallen
+fragments. On the other hand, I do not believe that any line of coast, ten
+or twenty miles in length, ever suffers degradation at the same time along
+its whole indented length; and we {287} must remember that almost all
+strata contain harder layers or nodules, which from long resisting
+attrition form a breakwater at the base. We may at least confidently
+believe that no rocky coast 500 feet in height commonly yields at the rate
+of a foot per century; for this would be the same in amount as a cliff one
+yard in height retreating twelve yards in twenty-two years; and no one, I
+think, who has carefully observed the shape of old fallen fragments at the
+base of cliffs, will admit any near approach to such rapid wearing away.
+Hence, under ordinary circumstances, I should infer that for a cliff 500
+feet in height, a denudation of one inch per century for the whole length
+would be a sufficient allowance. At this rate, on the above data, the
+denudation of the Weald must have required 306,662,400 years; or say three
+hundred million years. But perhaps it would be safer to allow two or three
+inches per century, and this would reduce the number of years to one
+hundred and fifty or one hundred million years.
+
+The action of fresh water on the gently inclined Wealden district, when
+upraised, could hardly have been great, but it would somewhat reduce the
+above estimate. On the other hand, during oscillations of level, which we
+know this area has undergone, the surface may have existed for millions of
+years as land, and thus have escaped the action of the sea: when deeply
+submerged for perhaps equally long periods, it would, likewise, have
+escaped the action of the coast-waves. So that it is not improbable that a
+longer period than 300 million years has elapsed since the latter part of
+the Secondary period.
+
+I have made these few remarks because it is highly important for us to gain
+some notion, however imperfect, of the lapse of years. During each of these
+years, {288} over the whole world, the land and the water has been peopled
+by hosts of living forms. What an infinite number of generations, which the
+mind cannot grasp, must have succeeded each other in the long roll of
+years! Now turn to our richest geological museums, and what a paltry
+display we behold!
+
+
+
+_On the poorness of our Palæontological collections._--That our
+palæontological collections are very imperfect, is admitted by every one.
+The remark of that admirable palæontologist, the late Edward Forbes, should
+not be forgotten, namely, that numbers of our fossil species are known and
+named from single and often broken specimens, or from a few specimens
+collected on some one spot. Only a small portion of the surface of the
+earth has been geologically explored, and no part with sufficient care, as
+the important discoveries made every year in Europe prove. No organism
+wholly soft can be preserved. Shells and bones will decay and disappear
+when left on the bottom of the sea, where sediment is not accumulating. I
+believe we are continually taking a most erroneous view, when we tacitly
+admit to ourselves that sediment is being deposited over nearly the whole
+bed of the sea, at a rate sufficiently quick to embed and preserve fossil
+remains. Throughout an enormously large proportion of the ocean, the bright
+blue tint of the water bespeaks its purity. The many cases on record of a
+formation conformably covered, after an enormous interval of time, by
+another and later formation, without the underlying bed having suffered in
+the interval any wear and tear, seem explicable only on the view of the
+bottom of the sea not rarely lying for ages in an unaltered condition. The
+remains which do become embedded, if in sand or gravel, will when the beds
+are upraised generally be dissolved {289} by the percolation of rain-water.
+I suspect that but few of the very many animals which live on the beach
+between high and low watermark are preserved. For instance, the several
+species of the Chthamalinæ (a subfamily of sessile cirripedes) coat the
+rocks all over the world in infinite numbers: they are all strictly
+littoral, with the exception of a single Mediterranean species, which
+inhabits deep water and has been found fossil in Sicily, whereas not one
+other species has hitherto been found in any tertiary formation: yet it is
+now known that the genus Chthamalus existed during the chalk period. The
+molluscan genus Chiton offers a partially analogous case.
+
+With respect to the terrestrial productions which lived during the
+Secondary and Palæozoic periods, it is superfluous to state that our
+evidence from fossil remains is fragmentary in an extreme degree. For
+instance, not a land shell is known belonging to either of these vast
+periods, with the exception of one species discovered by Sir C. Lyell and
+Dr. Dawson in the carboniferous strata of North America, of which shell
+several specimens have now been collected. In regard to mammiferous
+remains, a single glance at the historical table published in the
+Supplement to Lyell's Manual, will bring home the truth, how accidental and
+rare is their preservation, far better than pages of detail. Nor is their
+rarity surprising, when we remember how large a proportion of the bones of
+tertiary mammals have been discovered either in caves or in lacustrine
+deposits; and that not a cave or true lacustrine bed is known belonging to
+the age of our secondary or palæozoic formations.
+
+But the imperfection in the geological record mainly results from another
+and more important cause than any of the foregoing; namely, from the
+several formations {290} being separated from each other by wide intervals
+of time. When we see the formations tabulated in written works, or when we
+follow them in nature, it is difficult to avoid believing that they are
+closely consecutive. But we know, for instance, from Sir R. Murchison's
+great work on Russia, what wide gaps there are in that country between the
+superimposed formations; so it is in North America, and in many other parts
+of the world. The most skilful geologist, if his attention had been
+exclusively confined to these large territories, would never have suspected
+that during the periods which were blank and barren in his own country,
+great piles of sediment, charged with new and peculiar forms of life, had
+elsewhere been accumulated. And if in each separate territory, hardly any
+idea can be formed of the length of time which has elapsed between the
+consecutive formations, we may infer that this could nowhere be
+ascertained. The frequent and great changes in the mineralogical
+composition of consecutive formations, generally implying great changes in
+the geography of the surrounding lands, whence the sediment has been
+derived, accords with the belief of vast intervals of time having elapsed
+between each formation.
+
+But we can, I think, see why the geological formations of each region are
+almost invariably intermittent; that is, have not followed each other in
+close sequence. Scarcely any fact struck me more when examining many
+hundred miles of the South American coasts, which have been upraised
+several hundred feet within the recent period, than the absence of any
+recent deposits sufficiently extensive to last for even a short geological
+period. Along the whole west coast, which is inhabited by a peculiar marine
+fauna, tertiary beds are so poorly developed, that no record of several
+{291} successive and peculiar marine faunas will probably be preserved to a
+distant age. A little reflection will explain why along the rising coast of
+the western side of South America, no extensive formations with recent or
+tertiary remains can anywhere be found, though the supply of sediment must
+for ages have been great, from the enormous degradation of the coast-rocks
+and from muddy streams entering the sea. The explanation, no doubt, is,
+that the littoral and sub-littoral deposits are continually worn away, as
+soon as they are brought up by the slow and gradual rising of the land
+within the grinding action of the coast-waves.
+
+We may, I think, safely conclude that sediment must be accumulated in
+extremely thick, solid, or extensive masses, in order to withstand the
+incessant action of the waves, when first upraised and during subsequent
+oscillations of level. Such thick and extensive accumulations of sediment
+may be formed in two ways; either, in profound depths of the sea, in which
+case, judging from the researches of E. Forbes, we may conclude that the
+bottom will be inhabited by extremely few animals, and the mass when
+upraised will give a most imperfect record of the forms of life which then
+existed; or, sediment may be accumulated to any thickness and extent over a
+shallow bottom, if it continue slowly to subside. In this latter case, as
+long as the rate of subsidence and supply of sediment nearly balance each
+other, the sea will remain shallow and favourable for life, and thus a
+fossiliferous formation thick enough, when upraised, to resist any amount
+of degradation, may be formed.
+
+I am convinced that all our ancient formations, which are rich in fossils,
+have thus been formed during subsidence. Since publishing my views on this
+subject in 1845, I have watched the progress of {292} Geology, and have
+been surprised to note how author after author, in treating of this or that
+great formation, has come to the conclusion that it was accumulated during
+subsidence. I may add, that the only ancient tertiary formation on the west
+coast of South America, which has been bulky enough to resist such
+degradation as it has as yet suffered, but which will hardly last to a
+distant geological age, was certainly deposited during a downward
+oscillation of level, and thus gained considerable thickness.
+
+All geological facts tell us plainly that each area has undergone numerous
+slow oscillations of level, and apparently these oscillations have affected
+wide spaces. Consequently formations rich in fossils and sufficiently thick
+and extensive to resist subsequent degradation, may have been formed over
+wide spaces during periods of subsidence, but only where the supply of
+sediment was sufficient to keep the sea shallow and to embed and preserve
+the remains before they had time to decay. On the other hand, as long as
+the bed of the sea remained stationary, _thick_ deposits could not have
+been accumulated in the shallow parts, which are the most favourable to
+life. Still less could this have happened during the alternate periods of
+elevation; or, to speak more accurately, the beds which were then
+accumulated will have been destroyed by being upraised and brought within
+the limits of the coast-action.
+
+Thus the geological record will almost necessarily be rendered
+intermittent. I feel much confidence in the truth of these views, for they
+are in strict accordance with the general principles inculcated by Sir C.
+Lyell; and E. Forbes subsequently but independently arrived at a similar
+conclusion.
+
+One remark is here worth a passing notice. During periods of elevation the
+area of the land and of the {293} adjoining shoal parts of the sea will be
+increased, and new stations will often be formed;--all circumstances most
+favourable, as previously explained, for the formation of new varieties and
+species; but during such periods there will generally be a blank in the
+geological record. On the other hand, during subsidence, the inhabited area
+and number of inhabitants will decrease (excepting the productions on the
+shores of a continent when first broken up into an archipelago), and
+consequently during subsidence, though there will be much extinction, fewer
+new varieties or species will be formed; and it is during these very
+periods of subsidence, that our great deposits rich in fossils have been
+accumulated. Nature may almost be said to have guarded against the frequent
+discovery of her transitional or linking forms.
+
+From the foregoing considerations it cannot be doubted that the geological
+record, viewed as a whole, is extremely imperfect; but if we confine our
+attention to any one formation, it becomes more difficult to understand,
+why we do not therein find closely graduated varieties between the allied
+species which lived at its commencement and at its close. Some cases are on
+record of the same species presenting distinct varieties in the upper and
+lower parts of the same formation, but, as they are rare, they may be here
+passed over. Although each formation has indisputably required a vast
+number of years for its deposition, I can see several reasons why each
+should not include a graduated series of links between the species which
+then lived; but I can by no means pretend to assign due proportional weight
+to the following considerations.
+
+Although each formation may mark a very long lapse of years, each perhaps
+is short compared with the period requisite to change one species into
+another. I am {294} aware that two palæontologists, whose opinions are
+worthy of much deference, namely Bronn and Woodward, have concluded that
+the average duration of each formation is twice or thrice as long as the
+average duration of specific forms. But insuperable difficulties, as it
+seems to me, prevent us coming to any just conclusion on this head. When we
+see a species first appearing in the middle of any formation, it would be
+rash in the extreme to infer that it had not elsewhere previously existed.
+So again when we find a species disappearing before the uppermost layers
+have been deposited, it would be equally rash to suppose that it then
+became wholly extinct. We forget how small the area of Europe is compared
+with the rest of the world; nor have the several stages of the same
+formation throughout Europe been correlated with perfect accuracy.
+
+With marine animals of all kinds, we may safely infer a large amount of
+migration during climatal and other changes; and when we see a species
+first appearing in any formation, the probability is that it only then
+first immigrated into that area. It is well known, for instance, that
+several species appeared somewhat earlier in the palæozoic beds of North
+America than in those of Europe; time having apparently been required for
+their migration from the American to the European seas. In examining the
+latest deposits of various quarters of the world, it has everywhere been
+noted, that some few still existing species are common in the deposit, but
+have become extinct in the immediately surrounding sea; or, conversely,
+that some are now abundant in the neighbouring sea, but are rare or absent
+in this particular deposit. It is an excellent lesson to reflect on the
+ascertained amount of migration of the inhabitants of Europe during the
+Glacial period, which forms only a part of one whole geological period;
+{295} and likewise to reflect on the great changes of level, on the
+inordinately great change of climate, on the prodigious lapse of time, all
+included within this same glacial period. Yet it may be doubted whether in
+any quarter of the world, sedimentary deposits, _including fossil remains_,
+have gone on accumulating within the same area during the whole of this
+period. It is not, for instance, probable that sediment was deposited
+during the whole of the glacial period near the mouth of the Mississippi,
+within that limit of depth at which marine animals can flourish; for we
+know what vast geographical changes occurred in other parts of America
+during this space of time. When such beds as were deposited in shallow
+water near the mouth of the Mississippi during some part of the glacial
+period shall have been upraised, organic remains will probably first appear
+and disappear at different levels, owing to the migration of species and to
+geographical changes. And in the distant future, a geologist examining
+these beds, might be tempted to conclude that the average duration of life
+of the embedded fossils had been less than that of the glacial period,
+instead of having been really far greater, that is extending from before
+the glacial epoch to the present day.
+
+In order to get a perfect gradation between two forms in the upper and
+lower parts of the same formation, the deposit must have gone on
+accumulating for a very long period, in order to have given sufficient time
+for the slow process of variation; hence the deposit will generally have to
+be a very thick one; and the species undergoing modification will have had
+to live on the same area throughout this whole time. But we have seen that
+a thick fossiliferous formation can only be accumulated during a period of
+subsidence; and to keep the depth approximately the same, which is
+necessary in {296} order to enable the same species to live on the same
+space, the supply of sediment must nearly have counterbalanced the amount
+of subsidence. But this same movement of subsidence will often tend to sink
+the area whence the sediment is derived, and thus diminish the supply
+whilst the downward movement continues. In fact, this nearly exact
+balancing between the supply of sediment and the amount of subsidence is
+probably a rare contingency; for it has been observed by more than one
+palæontologist, that very thick deposits are usually barren of organic
+remains, except near their upper or lower limits.
+
+It would seem that each separate formation, like the whole pile of
+formations in any country, has generally been intermittent in its
+accumulation. When we see, as is so often the case, a formation composed of
+beds of different mineralogical composition, we may reasonably suspect that
+the process of deposition has been much interrupted, as a change in the
+currents of the sea and a supply of sediment of a different nature will
+generally have been due to geographical changes requiring much time. Nor
+will the closest inspection of a formation give any idea of the time which
+its deposition has consumed. Many instances could be given of beds only a
+few feet in thickness, representing formations, elsewhere thousands of feet
+in thickness, and which must have required an enormous period for their
+accumulation; yet no one ignorant of this fact would have suspected the
+vast lapse of time represented by the thinner formation. Many cases could
+be given of the lower beds of a formation having been upraised, denuded,
+submerged, and then re-covered by the upper beds of the same
+formation,--facts, showing what wide, yet easily overlooked, intervals have
+occurred in its accumulation. In other cases we have the plainest evidence
+{297} in great fossilised trees, still standing upright as they grew, of
+many long intervals of time and changes of level during the process of
+deposition, which would never even have been suspected, had not the trees
+chanced to have been preserved: thus Messrs. Lyell and Dawson found
+carboniferous beds 1400 feet thick in Nova Scotia, with ancient
+root-bearing strata, one above the other, at no less than sixty-eight
+different levels. Hence, when the same species occur at the bottom, middle,
+and top of a formation, the probability is that they have not lived on the
+same spot during the whole period of deposition, but have disappeared and
+reappeared, perhaps many times, during the same geological period. So that
+if such species were to undergo a considerable amount of modification
+during any one geological period, a section would not probably include all
+the fine intermediate gradations which must on my theory have existed
+between them, but abrupt, though perhaps very slight, changes of form.
+
+It is all-important to remember that naturalists have no golden rule by
+which to distinguish species and varieties; they grant some little
+variability to each species, but when they meet with a somewhat greater
+amount of difference between any two forms, they rank both as species,
+unless they are enabled to connect them together by close intermediate
+gradations. And this from the reasons just assigned we can seldom hope to
+effect in any one geological section. Supposing B and C to be two species,
+and a third, A, to be found in an underlying bed; even if A were strictly
+intermediate between B and C, it would simply be ranked as a third and
+distinct species, unless at the same time it could be most closely
+connected with either one or both forms by intermediate varieties. Nor
+should it be forgotten, as before explained, that A might be the actual
+progenitor {298} of B and C, and yet might not at all necessarily be
+strictly intermediate between them in all points of structure. So that we
+might obtain the parent-species and its several modified descendants from
+the lower and upper beds of a formation, and unless we obtained numerous
+transitional gradations, we should not recognise their relationship, and
+should consequently be compelled to rank them all as distinct species.
+
+It is notorious on what excessively slight differences many palæontologists
+have founded their species; and they do this the more readily if the
+specimens come from different sub-stages of the same formation. Some
+experienced conchologists are now sinking many of the very fine species of
+D'Orbigny and others into the rank of varieties; and on this view we do
+find the kind of evidence of change which on my theory we ought to find.
+Moreover, if we look to rather wider intervals, namely, to distinct but
+consecutive stages of the same great formation, we find that the embedded
+fossils, though almost universally ranked as specifically different, yet
+are far more closely allied to each other than are the species found in
+more widely separated formations; but to this subject I shall have to
+return in the following chapter.
+
+One other consideration is worth notice: with animals and plants that can
+propagate rapidly and are not highly locomotive, there is reason to
+suspect, as we have formerly seen, that their varieties are generally at
+first local; and that such local varieties do not spread widely and
+supplant their parent-forms until they have been modified and perfected in
+some considerable degree. According to this view, the chance of discovering
+in a formation in any one country all the early stages of transition
+between any two forms, is small, for the successive changes are supposed to
+have been local or {299} confined to some one spot. Most marine animals
+have a wide range; and we have seen that with plants it is those which have
+the widest range, that oftenest present varieties; so that with shells and
+other marine animals, it is probably those which have had the widest range,
+far exceeding the limits of the known geological formations of Europe,
+which have oftenest given rise, first to local varieties and ultimately to
+new species; and this again would greatly lessen the chance of our being
+able to trace the stages of transition in any one geological formation.
+
+It should not be forgotten, that at the present day, with perfect specimens
+for examination, two forms can seldom be connected by intermediate
+varieties and thus proved to be the same species, until many specimens have
+been collected from many places; and in the case of fossil species this
+could rarely be effected by palæontologists. We shall, perhaps, best
+perceive the improbability of our being enabled to connect species by
+numerous, fine, intermediate, fossil links, by asking ourselves whether,
+for instance, geologists at some future period will be able to prove, that
+our different breeds of cattle, sheep, horses, and dogs have descended from
+a single stock or from several aboriginal stocks; or, again, whether
+certain sea-shells inhabiting the shores of North America, which are ranked
+by some conchologists as distinct species from their European
+representatives, and by other conchologists as only varieties, are really
+varieties or are, as it is called, specifically distinct. This could be
+effected only by the future geologist discovering in a fossil state
+numerous intermediate gradations; and such success seems to me improbable
+in the highest degree.
+
+Geological research, though it has added numerous species to existing and
+extinct genera, and has made the {300} intervals between some few groups
+less wide than they otherwise would have been, yet has done scarcely
+anything in breaking down the distinction between species, by connecting
+them together by numerous, fine, intermediate varieties; and this not
+having been effected, is probably the gravest and most obvious of all the
+many objections which may be urged against my views. Hence it will be worth
+while to sum up the foregoing remarks, under an imaginary illustration. The
+Malay Archipelago is of about the size of Europe from the North Cape to the
+Mediterranean, and from Britain to Russia; and therefore equals all the
+geological formations which have been examined with any accuracy, excepting
+those of the United States of America. I fully agree with Mr.
+Godwin-Austen, that the present condition of the Malay Archipelago, with
+its numerous large islands separated by wide and shallow seas, probably
+represents the former state of Europe, whilst most of our formations were
+accumulating. The Malay Archipelago is one of the richest regions of the
+whole world in organic beings; yet if all the species were to be collected
+which have ever lived there, how imperfectly would they represent the
+natural history of the world!
+
+But we have every reason to believe that the terrestrial productions of the
+archipelago would be preserved in an excessively imperfect manner in the
+formations which we suppose to be there accumulating. I suspect that not
+many of the strictly littoral animals, or of those which lived on naked
+submarine rocks, would be embedded; and those embedded in gravel or sand,
+would not endure to a distant epoch. Wherever sediment did not accumulate
+on the bed of the sea, or where it did not accumulate at a sufficient rate
+to protect organic bodies from decay, no remains could be preserved.
+
+I believe that fossiliferous formations could be formed {301} in the
+archipelago, of thickness sufficient to last to an age as distant in
+futurity as the secondary formations lie in the past, only during periods
+of subsidence. These periods of subsidence would be separated from each
+other by enormous intervals, during which the area would be either
+stationary or rising; whilst rising, each fossiliferous formation would be
+destroyed, almost as soon as accumulated, by the incessant coast-action, as
+we now see on the shores of South America. During the periods of subsidence
+there would probably be much extinction of life; during the periods of
+elevation, there would be much variation, but the geological record would
+then be least perfect.
+
+It may be doubted whether the duration of any one great period of
+subsidence over the whole or part of the archipelago, together with a
+contemporaneous accumulation of sediment, would _exceed_ the average
+duration of the same specific forms; and these contingencies are
+indispensable for the preservation of all the transitional gradations
+between any two or more species. If such gradations were not fully
+preserved, transitional varieties would merely appear as so many distinct
+species. It is, also, probable that each great period of subsidence would
+be interrupted by oscillations of level, and that slight climatal changes
+would intervene during such lengthy periods; and in these cases the
+inhabitants of the archipelago would have to migrate, and no closely
+consecutive record of their modifications could be preserved in any one
+formation.
+
+Very many of the marine inhabitants of the archipelago now range thousands
+of miles beyond its confines; and analogy leads me to believe that it would
+be chiefly these far-ranging species which would oftenest produce new
+varieties; and the varieties would at first generally be local or confined
+to one place, but if possessed {302} of any decided advantage, or when
+further modified and improved, they would slowly spread and supplant their
+parent-forms. When such varieties returned to their ancient homes, as they
+would differ from their former state, in a nearly uniform, though perhaps
+extremely slight degree, they would, according to the principles followed
+by many palæontologists, be ranked as new and distinct species.
+
+If then, there be some degree of truth in these remarks, we have no right
+to expect to find in our geological formations, an infinite number of those
+fine transitional forms, which on my theory assuredly have connected all
+the past and present species of the same group into one long and branching
+chain of life. We ought only to look for a few links, some more closely,
+some more distantly related to each other; and these links, let them be
+ever so close, if found in different stages of the same formation, would,
+by most palæontologists, be ranked as distinct species. But I do not
+pretend that I should ever have suspected how poor a record of the
+mutations of life, the best preserved geological section presented, had not
+the difficulty of our not discovering innumerable transitional links
+between the species which appeared at the commencement and close of each
+formation, pressed so hardly on my theory.
+
+
+
+_On the sudden appearance of whole groups of Allied Species._--The abrupt
+manner in which whole groups of species suddenly appear in certain
+formations, has been urged by several palæontologists--for instance, by
+Agassiz, Pictet, and by none more forcibly than by Professor Sedgwick--as a
+fatal objection to the belief in the transmutation of species. If numerous
+species, belonging to the same genera or families, have really {303}
+started into life all at once, the fact would be fatal to the theory of
+descent with slow modification through natural selection. For the
+development of a group of forms, all of which have descended from some one
+progenitor, must have been an extremely slow process; and the progenitors
+must have lived long ages before their modified descendants. But we
+continually over-rate the perfection of the geological record, and falsely
+infer, because certain genera or families have not been found beneath a
+certain stage, that they did not exist before that stage. We continually
+forget how large the world is, compared with the area over which our
+geological formations have been carefully examined; we forget that groups
+of species may elsewhere have long existed and have slowly multiplied
+before they invaded the ancient archipelagoes of Europe and of the United
+States. We do not make due allowance for the enormous intervals of time,
+which have probably elapsed between our consecutive formations,--longer
+perhaps in most cases than the time required for the accumulation of each
+formation. These intervals will have given time for the multiplication of
+species from some one or some few parent-forms; and in the succeeding
+formation such species will appear as if suddenly created.
+
+I may here recall a remark formerly made, namely that it might require a
+long succession of ages to adapt an organism to some new and peculiar line
+of life, for instance to fly through the air; but that when this had been
+effected, and a few species had thus acquired a great advantage over other
+organisms, a comparatively short time would be necessary to produce many
+divergent forms, which would be able to spread rapidly and widely
+throughout the world.
+
+I will now give a few examples to illustrate these {304} remarks, and to
+show how liable we are to error in supposing that whole groups of species
+have suddenly been produced. I may recall the well-known fact that in
+geological treatises, published not many years ago, the great class of
+mammals was always spoken of as having abruptly come in at the commencement
+of the tertiary series. And now one of the richest known accumulations of
+fossil mammals, for its thickness, belongs to the middle of the secondary
+series; and one true mammal has been discovered in the new red sandstone at
+nearly the commencement of this great series. Cuvier used to urge that no
+monkey occurred in any tertiary stratum; but now extinct species have been
+discovered in India, South America, and in Europe even as far back as the
+eocene stage. Had it not been for the rare accident of the preservation of
+footsteps in the new red sandstone of the United States, who would have
+ventured to suppose that, besides reptiles, no less than at least thirty
+kinds of birds, some of gigantic size, existed during that period? Not a
+fragment of bone has been discovered in these beds. Notwithstanding that
+the number of joints shown in the fossil impressions correspond with the
+number in the several toes of living birds' feet, some authors doubt
+whether the animals which left the impressions were really birds. Until
+quite recently these authors might have maintained, and some have
+maintained, that the whole class of birds came suddenly into existence
+during an early tertiary period; but now we know, on the authority of
+Professor Owen (as may be seen in Lyell's 'Manual'), that a bird certainly
+lived during the deposition of the upper greensand.
+
+I may give another instance, which from having passed under my own eyes has
+much struck me. In a memoir on Fossil Sessile Cirripedes, I have stated
+that, from the {305} number of existing and extinct tertiary species; from
+the extraordinary abundance of the individuals of many species all over the
+world, from the Arctic regions to the equator, inhabiting various zones of
+depths from the upper tidal limits to 50 fathoms; from the perfect manner
+in which specimens are preserved in the oldest tertiary beds; from the ease
+with which even a fragment of a valve can be recognised; from all these
+circumstances, I inferred that had sessile cirripedes existed during the
+secondary periods, they would certainly have been preserved and discovered;
+and as not one species had then been discovered in beds of this age, I
+concluded that this great group had been suddenly developed at the
+commencement of the tertiary series. This was a sore trouble to me, adding
+as I thought one more instance of the abrupt appearance of a great group of
+species. But my work had hardly been published, when a skilful
+palæontologist, M. Bosquet, sent me a drawing of a perfect specimen of an
+unmistakeable sessile cirripede, which he had himself extracted from the
+chalk of Belgium. And, as if to make the case as striking as possible, this
+sessile cirripede was a Chthamalus, a very common, large, and ubiquitous
+genus, of which not one specimen has as yet been found even in any tertiary
+stratum. Hence we now positively know that sessile cirripedes existed
+during the secondary period; and these cirripedes might have been the
+progenitors of our many tertiary and existing species.
+
+The case most frequently insisted on by palæontologists of the apparently
+sudden appearance of a whole group of species, is that of the teleostean
+fishes, low down in the Chalk period. This group includes the large
+majority of existing species. Lately, Professor Pictet has carried their
+existence one sub-stage further back; and some palæontologists believe that
+certain {306} much older fishes, of which the affinities are as yet
+imperfectly known, are really teleostean. Assuming, however, that the whole
+of them did appear, as Agassiz believes, at the commencement of the chalk
+formation, the fact would certainly be highly remarkable; but I cannot see
+that it would be an insuperable difficulty on my theory, unless it could
+likewise be shown that the species of this group appeared suddenly and
+simultaneously throughout the world at this same period. It is almost
+superfluous to remark that hardly any fossil-fish are known from south of
+the equator; and by running through Pictet's Palæontology it will be seen
+that very few species are known from several formations in Europe. Some few
+families of fish now have a confined range; the teleostean fish might
+formerly have had a similarly confined range, and after having been largely
+developed in some one sea, might have spread widely. Nor have we any right
+to suppose that the seas of the world have always been so freely open from
+south to north as they are at present. Even at this day, if the Malay
+Archipelago were converted into land, the tropical parts of the Indian
+Ocean would form a large and perfectly enclosed basin, in which any great
+group of marine animals might be multiplied; and here they would remain
+confined, until some of the species became adapted to a cooler climate, and
+were enabled to double the southern capes of Africa or Australia, and thus
+reach other and distant seas.
+
+From these and similar considerations, but chiefly from our ignorance of
+the geology of other countries beyond the confines of Europe and the United
+States; and from the revolution in our palæontological ideas on many
+points, which the discoveries of even the last dozen years have effected,
+it seems to me to be about as rash in us to dogmatize on the succession of
+organic {307} beings throughout the world, as it would be for a naturalist
+to land for five minutes on some one barren point in Australia, and then to
+discuss the number and range of its productions.
+
+
+
+_On the sudden appearance of groups of Allied Species in the lowest known
+fossiliferous strata._--There is another and allied difficulty, which is
+much graver. I allude to the manner in which numbers of species of the same
+group, suddenly appear in the lowest known fossiliferous rocks. Most of the
+arguments which have convinced me that all the existing species of the same
+group have descended from one progenitor, apply with nearly equal force to
+the earliest known species. For instance, I cannot doubt that all the
+Silurian trilobites have descended from some one crustacean, which must
+have lived long before the Silurian age, and which probably differed
+greatly from any known animal. Some of the most ancient Silurian animals,
+as the Nautilus, Lingula, &c., do not differ much from living species; and
+it cannot on my theory be supposed, that these old species were the
+progenitors of all the species of the orders to which they belong, for they
+do not present characters in any degree intermediate between them. If,
+moreover, they had been the progenitors of these orders, they would almost
+certainly have been long ago supplanted and exterminated by their numerous
+and improved descendants.
+
+Consequently, if my theory be true, it is indisputable that before the
+lowest Silurian stratum was deposited, long periods elapsed, as long as, or
+probably far longer than, the whole interval from the Silurian age to the
+present day; and that during these vast, yet quite unknown, periods of
+time, the world swarmed with living creatures. {308}
+
+To the question why we do not find records of these vast primordial
+periods, I can give no satisfactory answer. Several of the most eminent
+geologists, with Sir E. Murchison at their head, are convinced that we see
+in the organic remains of the lowest Silurian stratum the dawn of life on
+this planet. Other highly competent judges, as Lyell and the late E.
+Forbes, dispute this conclusion. We should not forget that only a small
+portion of the world is known with accuracy. M. Barrande has lately added
+another and lower stage to the Silurian system, abounding with new and
+peculiar species. Traces of life have been detected in the Longmynd beds,
+beneath Barrande's so-called primordial zone. The presence of phosphatic
+nodules and bituminous matter in some of the lowest azoic rocks, probably
+indicates the former existence of life at these periods. But the difficulty
+of understanding the absence of vast piles of fossiliferous strata, which
+on my theory no doubt were somewhere accumulated before the Silurian epoch,
+is very great. If these most ancient beds had been wholly worn away by
+denudation, or obliterated by metamorphic action, we ought to find only
+small remnants of the formations next succeeding them in age, and these
+ought to be very generally in a metamorphosed condition. But the
+descriptions which we now possess of the Silurian deposits over immense
+territories in Russia and in North America, do not support the view, that
+the older a formation is, the more it has always suffered the extremity of
+denudation and metamorphism.
+
+The case at present must remain inexplicable; and may be truly urged as a
+valid argument against the views here entertained. To show that it may
+hereafter receive some explanation, I will give the following hypothesis.
+From the nature of the organic remains which {309} do not appear to have
+inhabited profound depths, in the several formations of Europe and of the
+United States; and from the amount of sediment, miles in thickness, of
+which the formations are composed, we may infer that from first to last
+large islands or tracts of land, whence the sediment was derived, occurred
+in the neighbourhood of the existing continents of Europe and North
+America. But we do not know what was the state of things in the intervals
+between the successive formations; whether Europe and the United States
+during these intervals existed as dry land, or as a submarine surface near
+land, on which sediment was not deposited, or as the bed of an open and
+unfathomable sea.
+
+Looking to the existing oceans, which are thrice as extensive as the land,
+we see them studded with many islands; but not one oceanic island is as yet
+known to afford even a remnant of any palæozoic or secondary formation.
+Hence we may perhaps infer, that during the palæozoic and secondary
+periods, neither continents nor continental islands existed where our
+oceans now extend; for had they existed there, palæozoic and secondary
+formations would in all probability have been accumulated from sediment
+derived from their wear and tear; and would have been at least partially
+upheaved by the oscillations of level, which we may fairly conclude must
+have intervened during these enormously long periods. If then we may infer
+anything from these facts, we may infer that where our oceans now extend,
+oceans have extended from the remotest period of which we have any record;
+and on the other hand, that where continents now exist, large tracts of
+land have existed, subjected no doubt to great oscillations of level, since
+the earliest silurian period. The coloured map appended to my volume on
+Coral Reefs, led me to conclude that the great oceans are still mainly
+areas of {310} subsidence, the great archipelagoes still areas of
+oscillations of level, and the continents areas of elevation. But have we
+any right to assume that things have thus remained from the beginning of
+this world? Our continents seem to have been formed by a preponderance,
+during many oscillations of level, of the force of elevation; but may not
+the areas of preponderant movement have changed in the lapse of ages? At a
+period immeasurably antecedent to the silurian epoch, continents may have
+existed where oceans are now spread out; and clear and open oceans may have
+existed where our continents now stand. Nor should we be justified in
+assuming that if, for instance, the bed of the Pacific Ocean were now
+converted into a continent, we should there find formations older than the
+silurian strata, supposing such to have been formerly deposited; for it
+might well happen that strata which had subsided some miles nearer to the
+centre of the earth, and which had been pressed on by an enormous weight of
+superincumbent water, might have undergone far more metamorphic action than
+strata which have always remained nearer to the surface. The immense areas
+in some parts of the world, for instance in South America, of bare
+metamorphic rocks, which must have been heated under great pressure, have
+always seemed to me to require some special explanation; and we may perhaps
+believe that we see in these large areas, the many formations long anterior
+to the silurian epoch in a completely metamorphosed condition.
+
+
+
+The several difficulties here discussed, namely our not finding in the
+successive formations infinitely numerous transitional links between the
+many species which now exist or have existed; the sudden manner {311} in
+which whole groups of species appear in our European formations; the almost
+entire absence, as at present known, of fossiliferous formations beneath
+the Silurian strata, are all undoubtedly of the gravest nature. We see this
+in the plainest manner by the fact that all the most eminent
+palæontologists, namely Cuvier, Agassiz, Barrande, Falconer, E. Forbes,
+&c., and all our greatest geologists, as Lyell, Murchison, Sedgwick, &c.,
+have unanimously, often vehemently, maintained the immutability of species.
+But I have reason to believe that one great authority, Sir Charles Lyell,
+from further reflexion entertains grave doubts on this subject. I feel how
+rash it is to differ from these authorities, to whom, with others, we owe
+all our knowledge. Those who think the natural geological record in any
+degree perfect, and who do not attach much weight to the facts and
+arguments of other kinds given in this volume, will undoubtedly at once
+reject my theory. For my part, following out Lyell's metaphor, I look at
+the natural geological record, as a history of the world imperfectly kept,
+and written in a changing dialect; of this history we possess the last
+volume alone, relating only to two or three countries. Of this volume, only
+here and there a short chapter has been preserved; and of each page, only
+here and there a few lines. Each word of the slowly-changing language, in
+which the history is supposed to be written, being more or less different
+in the interrupted succession of chapters, may represent the apparently
+abruptly changed forms of life, entombed in our consecutive, but widely
+separated, formations. On this view, the difficulties above discussed are
+greatly diminished, or even disappear.
+
+       *       *       *       *       *
+
+
+{312}
+
+CHAPTER X.
+
+ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
+
+    On the slow and successive appearance of new species--On their
+    different rates of change--Species once lost do not reappear--Groups of
+    species follow the same general rules in their appearance and
+    disappearance as do single species--On Extinction--On simultaneous
+    changes in the forms of life throughout the world--On the affinities of
+    extinct species to each other and to living species--On the state of
+    development of ancient forms--On the succession of the same types
+    within the same areas--Summary of preceding and present chapters.
+
+Let us now see whether the several facts and rules relating to the
+geological succession of organic beings, better accord with the common view
+of the immutability of species, or with that of their slow and gradual
+modification, through descent and natural selection.
+
+New species have appeared very slowly, one after another, both on the land
+and in the waters. Lyell has shown that it is hardly possible to resist the
+evidence on this head in the case of the several tertiary stages; and every
+year tends to fill up the blanks between them, and to make the percentage
+system of lost and new forms more gradual. In some of the most recent beds,
+though undoubtedly of high antiquity if measured by years, only one or two
+species are lost forms, and only one or two are new forms, having here
+appeared for the first time, either locally, or, as far as we know, on the
+face of the earth. If we may trust the observations of Philippi in Sicily,
+the successive changes in the marine inhabitants of that island have been
+many and most gradual. The secondary formations are more broken; but, as
+Bronn has remarked, neither the appearance {313} nor disappearance of their
+many now extinct species has been simultaneous in each separate formation.
+
+Species of different genera and classes have not changed at the same rate,
+or in the same degree. In the oldest tertiary beds a few living shells may
+still be found in the midst of a multitude of extinct forms. Falconer has
+given a striking instance of a similar fact, in an existing crocodile
+associated with many strange and lost mammals and reptiles in the
+sub-Himalayan deposits. The Silurian Lingula differs but little from the
+living species of this genus; whereas most of the other Silurian Molluscs
+and all the Crustaceans have changed greatly. The productions of the land
+seem to change at a quicker rate than those of the sea, of which a striking
+instance has lately been observed in Switzerland. There is some reason to
+believe that organisms, considered high in the scale of nature, change more
+quickly than those that are low: though there are exceptions to this rule.
+The amount of organic change, as Pictet has remarked, does not strictly
+correspond with the succession of our geological formations; so that
+between each two consecutive formations, the forms of life have seldom
+changed in exactly the same degree. Yet if we compare any but the most
+closely related formations, all the species will be found to have undergone
+some change. When a species has once disappeared from the face of the
+earth, we have reason to believe that the same identical form never
+reappears. The strongest apparent exception to this latter rule, is that of
+the so-called "colonies" of M. Barrande, which intrude for a period in the
+midst of an older formation, and then allow the pre-existing fauna to
+reappear; but Lyell's explanation, namely, that it is a case of temporary
+migration from a distinct geographical province, seems to me satisfactory.
+{314}
+
+These several facts accord well with my theory. I believe in no fixed law
+of development, causing all the inhabitants of a country to change
+abruptly, or simultaneously, or to an equal degree. The process of
+modification must be extremely slow. The variability of each species is
+quite independent of that of all others. Whether such variability be taken
+advantage of by natural selection, and whether the variations be
+accumulated to a greater or lesser amount, thus causing a greater or lesser
+amount of modification in the varying species, depends on many complex
+contingencies,--on the variability being of a beneficial nature, on the
+power of intercrossing, on the rate of breeding, on the slowly changing
+physical conditions of the country, and more especially on the nature of
+the other inhabitants with which the varying species comes into
+competition. Hence it is by no means surprising that one species should
+retain the same identical form much longer than others; or, if changing,
+that it should change less. We see the same fact in geographical
+distribution; for instance, in the land-shells and coleopterous insects of
+Madeira having come to differ considerably from their nearest allies on the
+continent of Europe, whereas the marine shells and birds have remained
+unaltered. We can perhaps understand the apparently quicker rate of change
+in terrestrial and in more highly organised productions compared with
+marine and lower productions, by the more complex relations of the higher
+beings to their organic and inorganic conditions of life, as explained in a
+former chapter. When many of the inhabitants of a country have become
+modified and improved, we can understand, on the principle of competition,
+and on that of the many all-important relations of organism to organism,
+that any form which does not become in some degree modified and improved,
+{315} will be liable to be exterminated. Hence we can see why all the
+species in the same region do at last, if we look to wide enough intervals
+of time, become modified; for those which do not change will become
+extinct.
+
+In members of the same class the average amount of change, during long and
+equal periods of time, may, perhaps, be nearly the same; but as the
+accumulation of long-enduring fossiliferous formations depends on great
+masses of sediment having been deposited on areas whilst subsiding, our
+formations have been almost necessarily accumulated at wide and irregularly
+intermittent intervals; consequently the amount of organic change exhibited
+by the fossils embedded in consecutive formations is not equal. Each
+formation, on this view, does not mark a new and complete act of creation,
+but only an occasional scene, taken almost at hazard, in a slowly changing
+drama.
+
+We can clearly understand why a species when once lost should never
+reappear, even if the very same conditions of life, organic and inorganic,
+should recur. For though the offspring of one species might be adapted (and
+no doubt this has occurred in innumerable instances) to fill the exact
+place of another species in the economy of nature, and thus supplant it;
+yet the two forms--the old and the new--would not be identically the same;
+for both would almost certainly inherit different characters from their
+distinct progenitors. For instance, it is just possible, if our
+fantail-pigeons were all destroyed, that fanciers, by striving during long
+ages for the same object, might make a new breed hardly distinguishable
+from our present fantail; but if the parent rock-pigeon were also
+destroyed, and in nature we have every reason to believe that the
+parent-form will generally be supplanted and exterminated by its improved
+offspring, it is quite {316} incredible that a fantail, identical with the
+existing breed, could be raised from any other species of pigeon, or even
+from the other well-established races of the domestic pigeon, for the
+newly-formed fantail would be almost sure to inherit from its new
+progenitor some slight characteristic differences.
+
+Groups of species, that is, genera and families, follow the same general
+rules in their appearance and disappearance as do single species, changing
+more or less quickly, and in a greater or lesser degree. A group does not
+reappear after it has once disappeared; or its existence, as long as it
+lasts, is continuous. I am aware that there are some apparent exceptions to
+this rule, but the exceptions are surprisingly few, so few that E. Forbes,
+Pictet, and Woodward (though all strongly opposed to such views as I
+maintain) admit its truth; and the rule strictly accords with my theory.
+For as all the species of the same group have descended from some one
+species, it is clear that as long as any species of the group have appeared
+in the long succession of ages, so long must its members have continuously
+existed, in order to have generated either new and modified or the same old
+and unmodified forms. Species of the genus Lingula, for instance, must have
+continuously existed by an unbroken succession of generations, from the
+lowest Silurian stratum to the present day.
+
+We have seen in the last chapter that the species of a group sometimes
+falsely appear to have come in abruptly; and I have attempted to give an
+explanation of this fact, which if true would have been fatal to my views.
+But such cases are certainly exceptional; the general rule being a gradual
+increase in number, till the group reaches its maximum, and then, sooner or
+later, it gradually decreases. If the number of the species of a genus, or
+the number of {317} the genera of a family, be represented by a vertical
+line of varying thickness, crossing the successive geological formations in
+which the species are found, the line will sometimes falsely appear to
+begin at its lower end, not in a sharp point, but abruptly; it then
+gradually thickens upwards, sometimes keeping for a space of equal
+thickness, and ultimately thins out in the upper beds, marking the decrease
+and final extinction of the species. This gradual increase in number of the
+species of a group is strictly conformable with my theory; as the species
+of the same genus, and the genera of the same family, can increase only
+slowly and progressively; for the process of modification and the
+production of a number of allied forms must be slow and gradual,--one
+species giving rise first to two or three varieties, these being slowly
+converted into species, which in their turn produce by equally slow steps
+other species, and so on, like the branching of a great tree from a single
+stem, till the group becomes large.
+
+
+
+_On Extinction._--We have as yet spoken only incidentally of the
+disappearance of species and of groups of species. On the theory of natural
+selection the extinction of old forms and the production of new and
+improved forms are intimately connected together. The old notion of all the
+inhabitants of the earth having been swept away at successive periods by
+catastrophes, is very generally given up, even by those geologists, as Elie
+de Beaumont, Murchison, Barrande, &c., whose general views would naturally
+lead them to this conclusion. On the contrary, we have every reason to
+believe, from the study of the tertiary formations, that species and groups
+of species gradually disappear, one after another, first from one spot,
+then from another, and finally from the world. Both single species and
+whole {318} groups of species last for very unequal periods; some groups,
+as we have seen, having endured from the earliest known dawn of life to the
+present day; some having disappeared before the close of the palæozoic
+period. No fixed law seems to determine the length of time during which any
+single species or any single genus endures. There is reason to believe that
+the complete extinction of the species of a group is generally a slower
+process than their production: if the appearance and disappearance of a
+group of species be represented, as before, by a vertical line of varying
+thickness, the line is found to taper more gradually at its upper end,
+which marks the progress of extermination, than at its lower end, which
+marks the first appearance and increase in numbers of the species. In some
+cases, however, the extermination of whole groups of beings, as of
+ammonites towards the close of the secondary period, has been wonderfully
+sudden.
+
+The whole subject of the extinction of species has been involved in the
+most gratuitous mystery. Some authors have even supposed that as the
+individual has a definite length of life, so have species a definite
+duration. No one I think can have marvelled more at the extinction of
+species, than I have done. When I found in La Plata the tooth of a horse
+embedded with the remains of Mastodon, Megatherium, Toxodon, and other
+extinct monsters, which all co-existed with still living shells at a very
+late geological period, I was filled with astonishment; for seeing that the
+horse, since its introduction by the Spaniards into South America, has run
+wild over the whole country and has increased in numbers at an unparalleled
+rate, I asked myself what could so recently have exterminated the former
+horse under conditions of life apparently so favourable. But how utterly
+groundless was my astonishment! {319} Professor Owen soon perceived that
+the tooth, though so like that of the existing horse, belonged to an
+extinct species. Had this horse been still living, but in some degree rare,
+no naturalist would have felt the least surprise at its rarity; for rarity
+is the attribute of a vast number of species of all classes, in all
+countries. If we ask ourselves why this or that species is rare, we answer
+that something is unfavourable in its conditions of life; but what that
+something is, we can hardly ever tell. On the supposition of the fossil
+horse still existing as a rare species, we might have felt certain from the
+analogy of all other mammals, even of the slow-breeding elephant, and from
+the history of the naturalisation of the domestic horse in South America,
+that under more favourable conditions it would in a very few years have
+stocked the whole continent. But we could not have told what the
+unfavourable conditions were which checked its increase, whether some one
+or several contingencies, and at what period of the horse's life, and in
+what degree, they severally acted. If the conditions had gone on, however
+slowly, becoming less and less favourable, we assuredly should not have
+perceived the fact, yet the fossil horse would certainly have become rarer
+and rarer, and finally extinct;--its place being seized on by some more
+successful competitor.
+
+It is most difficult always to remember that the increase of every living
+being is constantly being checked by unperceived injurious agencies; and
+that these same unperceived agencies are amply sufficient to cause rarity,
+and finally extinction. We see in many cases in the more recent tertiary
+formations, that rarity precedes extinction; and we know that this has been
+the progress of events with those animals which have been exterminated,
+either locally or wholly, through {320} man's agency. I may repeat what I
+published in 1845, namely, that to admit that species generally become rare
+before they become extinct--to feel no surprise at the rarity of a species,
+and yet to marvel greatly when it ceases to exist, is much the same as to
+admit that sickness in the individual is the forerunner of death--to feel
+no surprise at sickness, but when the sick man dies, to wonder and to
+suspect that he died by some unknown deed of violence.
+
+The theory of natural selection is grounded on the belief that each new
+variety, and ultimately each new species, is produced and maintained by
+having some advantage over those with which it comes into competition; and
+the consequent extinction of less-favoured forms almost inevitably follows.
+It is the same with our domestic productions: when a new and slightly
+improved variety has been raised, it at first supplants the less improved
+varieties in the same neighbourhood; when much improved it is transported
+far and near, like our short-horn cattle, and takes the place of other
+breeds in other countries. Thus the appearance of new forms and the
+disappearance of old forms, both natural and artificial, are bound
+together. In certain flourishing groups, the number of new specific forms
+which have been produced within a given time is probably greater than that
+of the old specific forms which have been exterminated; but we know that
+the number of species has not gone on indefinitely increasing, at least
+during the later geological periods, so that looking to later times we may
+believe that the production of new forms has caused the extinction of about
+the same number of old forms.
+
+The competition will generally be most severe, as formerly explained and
+illustrated by examples, between the forms which are most like each other
+in all respects. {321} Hence the improved and modified descendants of a
+species will generally cause the extermination of the parent-species; and
+if many new forms have been developed from any one species, the nearest
+allies of that species, _i.e._ the species of the same genus, will be the
+most liable to extermination. Thus, as I believe, a number of new species
+descended from one species, that is a new genus, comes to supplant an old
+genus, belonging to the same family. But it must often have happened that a
+new species belonging to some one group will have seized on the place
+occupied by a species belonging to a distinct group, and thus caused its
+extermination; and if many allied forms be developed from the successful
+intruder, many will have to yield their places; and it will generally be
+allied forms, which will suffer from some inherited inferiority in common.
+But whether it be species belonging to the same or to a distinct class,
+which yield their places to other species which have been modified and
+improved, a few of the sufferers may often long be preserved, from being
+fitted to some peculiar line of life, or from inhabiting some distant and
+isolated station, where they have escaped severe competition. For instance,
+a single species of Trigonia, a great genus of shells in the secondary
+formations, survives in the Australian seas; and a few members of the great
+and almost extinct group of Ganoid fishes still inhabit our fresh waters.
+Therefore the utter extinction of a group is generally, as we have seen, a
+slower process than its production.
+
+With respect to the apparently sudden extermination of whole families or
+orders, as of Trilobites at the close of the palæozoic period and of
+Ammonites at the close of the secondary period, we must remember what has
+been already said on the probable wide intervals of time {322} between our
+consecutive formations; and in these intervals there may have been much
+slow extermination. Moreover, when by sudden immigration or by unusually
+rapid development, many species of a new group have taken possession of a
+new area, they will have exterminated in a correspondingly rapid manner
+many of the old inhabitants; and the forms which thus yield their places
+will commonly be allied, for they will partake of some inferiority in
+common.
+
+Thus, as it seems to me, the manner in which single species and whole
+groups of species become extinct, accords well with the theory of natural
+selection. We need not marvel at extinction; if we must marvel, let it be
+at our presumption in imagining for a moment that we understand the many
+complex contingencies, on which the existence of each species depends. If
+we forget for an instant, that each species tends to increase inordinately,
+and that some check is always in action, yet seldom perceived by us, the
+whole economy of nature will be utterly obscured. Whenever we can precisely
+say why this species is more abundant in individuals than that; why this
+species and not another can be naturalised in a given country; then, and
+not till then, we may justly feel surprise why we cannot account for the
+extinction of this particular species or group of species.
+
+
+
+_On the Forms of Life changing almost simultaneously throughout the
+World._--Scarcely any palæontological discovery is more striking than the
+fact, that the forms of life change almost simultaneously throughout the
+world. Thus our European Chalk formation can be recognised in many distant
+parts of the world, under the most different climates, where not a fragment
+of the mineral chalk itself can be found; namely, in North {323} America,
+in equatorial South America, in Tierra del Fuego, at the Cape of Good Hope,
+and in the peninsula of India. For at these distant points, the organic
+remains in certain beds present an unmistakeable degree of resemblance to
+those of the Chalk. It is not that the same species are met with; for in
+some cases not one species is identically the same, but they belong to the
+same families, genera, and sections of genera, and sometimes are similarly
+characterised in such trifling points as mere superficial sculpture.
+Moreover other forms, which are not found in the Chalk of Europe, but which
+occur in the formations either above or below, are similarly absent at
+these distant points of the world. In the several successive palæozoic
+formations of Russia, Western Europe and North America, a similar
+parallelism in the forms of life has been observed by several authors: so
+it is, according to Lyell, with the several European and North American
+tertiary deposits. Even if the few fossil species which are common to the
+Old and New Worlds be kept wholly out of view, the general parallelism in
+the successive forms of life, in the stages of the widely separated
+palæozoic and tertiary periods, would still be manifest, and the several
+formations could be easily correlated.
+
+These observations, however, relate to the marine inhabitants of distant
+parts of the world: we have not sufficient data to judge whether the
+productions of the land and of fresh water change at distant points in the
+same parallel manner. We may doubt whether they have thus changed: if the
+Megatherium, Mylodon, Macrauchenia, and Toxodon had been brought to Europe
+from La Plata, without any information in regard to their geological
+position, no one would have suspected that they had co-existed with still
+living sea-shells; but as these anomalous monsters co-existed with the
+{324} Mastodon and Horse, it might at least have been inferred that they
+had lived during one of the later tertiary stages.
+
+When the marine forms of life are spoken of as having changed
+simultaneously throughout the world, it must not be supposed that this
+expression relates to the same thousandth or hundred-thousandth year, or
+even that it has a very strict geological sense; for if all the marine
+animals which live at the present day in Europe, and all those that lived
+in Europe during the pleistocene period (an enormously remote period as
+measured by years, including the whole glacial epoch), were to be compared
+with those now living in South America or in Australia, the most skilful
+naturalist would hardly be able to say whether the existing or the
+pleistocene inhabitants of Europe resembled most closely those of the
+southern hemisphere. So, again, several highly competent observers believe
+that the existing productions of the United States are more closely related
+to those which lived in Europe during certain later tertiary stages, than
+to those which now live here; and if this be so, it is evident that
+fossiliferous beds deposited at the present day on the shores of North
+America would hereafter be liable to be classed with somewhat older
+European beds. Nevertheless, looking to a remotely future epoch, there can,
+I think, be little doubt that all the more modern _marine_ formations,
+namely, the upper pliocene, the pleistocene and strictly modern beds, of
+Europe, North and South America, and Australia, from containing fossil
+remains in some degree allied, and from not including those forms which are
+only found in the older underlying deposits, would be correctly ranked as
+simultaneous in a geological sense.
+
+The fact of the forms of life changing simultaneously, in the above large
+sense, at distant parts of the world, has greatly struck those admirable
+observers, MM. {325} de Verneuil and d'Archiac. After referring to the
+parallelism of the palæozoic forms of life in various parts of Europe, they
+add, "If struck by this strange sequence, we turn our attention to North
+America, and there discover a series of analogous phenomena, it will appear
+certain that all these modifications of species, their extinction, and the
+introduction of new ones, cannot be owing to mere changes in marine
+currents or other causes more or less local and temporary, but depend on
+general laws which govern the whole animal kingdom." M. Barrande has made
+forcible remarks to precisely the same effect. It is, indeed, quite futile
+to look to changes of currents, climate, or other physical conditions, as
+the cause of these great mutations in the forms of life throughout the
+world, under the most different climates. We must, as Barrande has
+remarked, look to some special law. We shall see this more clearly when we
+treat of the present distribution of organic beings, and find how slight is
+the relation between the physical conditions of various countries, and the
+nature of their inhabitants.
+
+This great fact of the parallel succession of the forms of life throughout
+the world, is explicable on the theory of natural selection. New species
+are formed by new varieties arising, which have some advantage over older
+forms; and those forms, which are already dominant, or have some advantage
+over the other forms in their own country, would naturally oftenest give
+rise to new varieties or incipient species; for these latter must be
+victorious in a still higher degree in order to be preserved and to
+survive. We have distinct evidence on this head, in the plants which are
+dominant, that is, which are commonest in their own homes, and are most
+widely diffused, having produced the greatest number of new varieties. It
+is also natural that the {326} dominant, varying, and far-spreading
+species, which already have invaded to a certain extent the territories of
+other species, should be those which would have the best chance of
+spreading still further, and of giving rise in new countries to new
+varieties and species. The process of diffusion may often be very slow,
+being dependent on climatal and geographical changes, or on strange
+accidents, but in the long run the dominant forms will generally succeed in
+spreading. The diffusion would, it is probable, be slower with the
+terrestrial inhabitants of distinct continents than with the marine
+inhabitants of the continuous sea. We might therefore expect to find, as we
+apparently do find, a less strict degree of parallel succession in the
+productions of the land than of the sea.
+
+Dominant species spreading from any region might encounter still more
+dominant species, and then their triumphant course, or even their
+existence, would cease. We know not at all precisely what are all the
+conditions most favourable for the multiplication of new and dominant
+species; but we can, I think, clearly see that a number of individuals,
+from giving a better chance of the appearance of favourable variations, and
+that severe competition with many already existing forms, would be highly
+favourable, as would be the power of spreading into new territories. A
+certain amount of isolation, recurring at long intervals of time, would
+probably be also favourable, as before explained. One quarter of the world
+may have been most favourable for the production of new and dominant
+species on the land, and another for those in the waters of the sea. If two
+great regions had been for a long period favourably circumstanced in an
+equal degree, whenever their inhabitants met, the battle would be prolonged
+and severe; and some from one birthplace and some from the other might be
+victorious. But in the course of time, the {327} forms dominant in the
+highest degree, wherever produced, would tend everywhere to prevail. As
+they prevailed, they would cause the extinction of other and inferior
+forms; and as these inferior forms would be allied in groups by
+inheritance, whole groups would tend slowly to disappear; though here and
+there a single member might long be enabled to survive.
+
+Thus, as it seems to me, the parallel, and, taken in a large sense,
+simultaneous, succession of the same forms of life throughout the world,
+accords well with the principle of new species having been formed by
+dominant species spreading widely and varying; the new species thus
+produced being themselves dominant owing to inheritance, and to having
+already had some advantage over their parents or over other species; these
+again spreading, varying, and producing new species. The forms which are
+beaten and which yield their places to the new and victorious forms, will
+generally be allied in groups, from inheriting some inferiority in common;
+and therefore as new and improved groups spread throughout the world, old
+groups will disappear from the world; and the succession of forms in both
+ways will everywhere tend to correspond.
+
+There is one other remark connected with this subject worth making. I have
+given my reasons for believing that all our greater fossiliferous
+formations were deposited during periods of subsidence; and that blank
+intervals of vast duration occurred during the periods when the bed of the
+sea was either stationary or rising, and likewise when sediment was not
+thrown down quickly enough to embed and preserve organic remains. During
+these long and blank intervals I suppose that the inhabitants of each
+region underwent a considerable amount of modification and extinction, and
+that there was much migration from {328} other parts of the world. As we
+have reason to believe that large areas are affected by the same movement,
+it is probable that strictly contemporaneous formations have often been
+accumulated over very wide spaces in the same quarter of the world; but we
+are far from having any right to conclude that this has invariably been the
+case, and that large areas have invariably been affected by the same
+movements. When two formations have been deposited in two regions during
+nearly, but not exactly the same period, we should find in both, from the
+causes explained in the foregoing paragraphs, the same general succession
+in the forms of life; but the species would not exactly correspond; for
+there will have been a little more time in the one region than in the other
+for modification, extinction, and immigration.
+
+I suspect that cases of this nature occur in Europe. Mr. Prestwich, in his
+admirable Memoirs on the eocene deposits of England and France, is able to
+draw a close general parallelism between the successive stages in the two
+countries; but when he compares certain stages in England with those in
+France, although he finds in both a curious accordance in the numbers of
+the species belonging to the same genera, yet the species themselves differ
+in a manner very difficult to account for, considering the proximity of the
+two areas,--unless, indeed, it be assumed that an isthmus separated two
+seas inhabited by distinct, but contemporaneous, faunas. Lyell has made
+similar observations on some of the later tertiary formations. Barrande,
+also, shows that there is a striking general parallelism in the successive
+Silurian deposits of Bohemia and Scandinavia; nevertheless he finds a
+surprising amount of difference in the species. If the several formations
+in these regions have not been deposited during the same exact {329}
+periods,--a formation in one region often corresponding with a blank
+interval in the other,--and if in both regions the species have gone on
+slowly changing during the accumulation of the several formations and
+during the long intervals of time between them; in this case, the several
+formations in the two regions could be arranged in the same order, in
+accordance with the general succession of the form of life, and the order
+would falsely appear to be strictly parallel; nevertheless the species
+would not all be the same in the apparently corresponding stages in the two
+regions.
+
+
+
+_On the Affinities of extinct Species to each other, and to living
+forms._--Let us now look to the mutual affinities of extinct and living
+species. They all fall into one grand natural system; and this fact is at
+once explained on the principle of descent. The more ancient any form is,
+the more, as a general rule, it differs from living forms. But, as Buckland
+long ago remarked, all fossils can be classed either in still existing
+groups, or between them. That the extinct forms of life help to fill up the
+wide intervals between existing genera, families, and orders, cannot be
+disputed. For if we confine our attention either to the living or to the
+extinct alone, the series is far less perfect than if we combine both into
+one general system. With respect to the Vertebrata, whole pages could be
+filled with striking illustrations from our great palaeontologist, Owen,
+showing how extinct animals fall in between existing groups. Cuvier ranked
+the Ruminants and Pachyderms, as the two most distinct orders of mammals;
+but Owen has discovered so many fossil links, that he has had to alter the
+whole classification of these two orders; and has placed certain pachyderms
+in the same sub-order with ruminants: for example, he dissolves by fine
+gradations the apparently {330} wide difference between the pig and the
+camel. In regard to the Invertebrata, Barrande, and a higher authority
+could not be named, asserts that he is every day taught that Palaeozoic
+animals, though belonging to the same orders, families, or genera with
+those living at the present day, were not at this early epoch limited in
+such distinct groups as they now are.
+
+Some writers have objected to any extinct species or group of species being
+considered as intermediate between living species or groups. If by this
+term it is meant that an extinct form is directly intermediate in all its
+characters between two living forms, the objection is probably valid. But I
+apprehend that in a perfectly natural classification many fossil species
+would have to stand between living species, and some extinct genera between
+living genera, even between genera belonging to distinct families. The most
+common case, especially with respect to very distinct groups, such as fish
+and reptiles, seems to be, that supposing them to be distinguished at the
+present day from each other by a dozen characters, the ancient members of
+the same two groups would be distinguished by a somewhat lesser number of
+characters, so that the two groups, though formerly quite distinct, at that
+period made some small approach to each other.
+
+It is a common belief that the more ancient a form is, by so much the more
+it tends to connect by some of its characters groups now widely separated
+from each other. This remark no doubt must be restricted to those groups
+which have undergone much change in the course of geological ages; and it
+would be difficult to prove the truth of the proposition, for every now and
+then even a living animal, as the Lepidosiren, is discovered having
+affinities directed towards very distinct groups. Yet if we compare the
+older Reptiles and {331} Batrachians, the older Fish, the older
+Cephalopods, and the eocene Mammals, with the more recent members of the
+same classes, we must admit that there is some truth in the remark.
+
+Let us see how far these several facts and inferences accord with the
+theory of descent with modification. As the subject is somewhat complex, I
+must request the reader to turn to the diagram in the fourth chapter. We
+may suppose that the numbered letters represent genera, and the dotted
+lines diverging from them the species in each genus. The diagram is much
+too simple, too few genera and too few species being given, but this is
+unimportant for us. The horizontal lines may represent successive
+geological formations, and all the forms beneath the uppermost line may be
+considered as extinct. The three existing genera, a^{14}, q^{14}, p^{14},
+will form a small family; b^{14} and f^{14} a closely allied family or
+sub-family; and o^{14}, e^{14}, m^{14}, a third family. These three
+families, together with the many extinct genera on the several lines of
+descent diverging from the parent-form (A), will form an order; for all
+will have inherited something in common from their ancient and common
+progenitor. On the principle of the continued tendency to divergence of
+character, which was formerly illustrated by this diagram, the more recent
+any form is, the more it will generally differ from its ancient progenitor.
+Hence we can understand the rule that the most ancient fossils differ most
+from existing forms. We must not, however, assume that divergence of
+character is a necessary contingency; it depends solely on the descendants
+from a species being thus enabled to seize on many and different places in
+the economy of nature. Therefore it is quite possible, as we have seen in
+the case of some Silurian forms, that a species might go on being slightly
+modified in relation to its slightly altered conditions of {332} life, and
+yet retain throughout a vast period the same general characteristics. This
+is represented in the diagram by the letter F^{14}.
+
+All the many forms, extinct and recent, descended from (A), make, as before
+remarked, one order; and this order, from the continued effects of
+extinction and divergence of character, has become divided into several
+sub-families and families, some of which are supposed to have perished at
+different periods, and some to have endured to the present day.
+
+By looking at the diagram we can see that if many of the extinct forms,
+supposed to be embedded in the successive formations, were discovered at
+several points low down in the series, the three existing families on the
+uppermost line would be rendered less distinct from each other. If, for
+instance, the genera a^1, a^5, a^{10}, f^8, m^3, m^6, m^9, were
+disinterred, these three families would be so closely linked together that
+they probably would have to be united into one great family, in nearly the
+same manner as has occurred with ruminants and pachyderms. Yet he who
+objected to call the extinct genera, which thus linked the living genera of
+three families together, intermediate in character, would be justified, as
+they are intermediate, not directly, but only by a long and circuitous
+course through many widely different forms. If many extinct forms were to
+be discovered above one of the middle horizontal lines or geological
+formations --for instance, above No. VI.--but none from beneath this line,
+then only the two families on the left hand (namely, a^{14}, &c., and
+b^{14}, &c.) would have to be united into one family; and the two other
+families (namely, a^{14} to f^{14} now including five genera, and o^{14} to
+m^{14}) would yet remain distinct. These two families, however, would be
+less distinct from each other than they were before the discovery of the
+fossils. If, for instance, we suppose the existing genera of the two
+families to differ from each {333} other by a dozen characters, in this
+case the genera, at the early period marked VI., would differ by a lesser
+number of characters; for at this early stage of descent they have not
+diverged in character from the common progenitor of the order, nearly so
+much as they subsequently diverged. Thus it comes that ancient and extinct
+genera are often in some slight degree intermediate in character between
+their modified descendants, or between their collateral relations.
+
+In nature the case will be far more complicated than is represented in the
+diagram; for the groups will have been more numerous, they will have
+endured for extremely unequal lengths of time, and will have been modified
+in various degrees. As we possess only the last volume of the geological
+record, and that in a very broken condition, we have no right to expect,
+except in very rare cases, to fill up wide intervals in the natural system,
+and thus unite distinct families or orders. All that we have a right to
+expect, is that those groups, which have within known geological periods
+undergone much modification, should in the older formations make some
+slight approach to each other; so that the older members should differ less
+from each other in some of their characters than do the existing members of
+the same groups; and this by the concurrent evidence of our best
+palæontologists seems frequently to be the case.
+
+Thus, on the theory of descent with modification, the main facts with
+respect to the mutual affinities of the extinct forms of life to each other
+and to living forms, seem to me explained in a satisfactory manner. And
+they are wholly inexplicable on any other view.
+
+On this same theory, it is evident that the fauna of any great period in
+the earth's history will be intermediate in general character between that
+which preceded and that which succeeded it. Thus, the species which lived
+at the sixth great stage of descent in the {334} diagram are the modified
+offspring of those which lived at the fifth stage, and are the parents of
+those which became still more modified at the seventh stage; hence they
+could hardly fail to be nearly intermediate in character between the forms
+of life above and below. We must, however, allow for the entire extinction
+of some preceding forms, and in any one region for the immigration of new
+forms from other regions, and for a large amount of modification, during
+the long and blank intervals between the successive formations. Subject to
+these allowances, the fauna of each geological period undoubtedly is
+intermediate in character, between the preceding and succeeding faunas. I
+need give only one instance, namely, the manner in which the fossils of the
+Devonian system, when this system was first discovered, were at once
+recognised by palæontologists as intermediate in character between those of
+the overlying carboniferous, and underlying Silurian system. But each fauna
+is not necessarily exactly intermediate, as unequal intervals of time have
+elapsed between consecutive formations.
+
+It is no real objection to the truth of the statement, that the fauna of
+each period as a whole is nearly intermediate in character between the
+preceding and succeeding faunas, that certain genera offer exceptions to
+the rule. For instance, mastodons and elephants, when arranged by Dr.
+Falconer in two series, first according to their mutual affinities and then
+according to their periods of existence, do not accord in arrangement. The
+species extreme in character are not the oldest, or the most recent; nor
+are those which are intermediate in character, intermediate in age. But
+supposing for an instant, in this and other such cases, that the record of
+the first appearance and disappearance of the species was perfect, we have
+no reason to believe that forms successively produced necessarily endure
+for {335} corresponding lengths of time: a very ancient form might
+occasionally last much longer than a form elsewhere subsequently produced,
+especially in the case of terrestrial productions inhabiting separated
+districts. To compare small things with great: if the principal living and
+extinct races of the domestic pigeon were arranged as well as they could be
+in serial affinity, this arrangement would not closely accord with the
+order in time of their production, and still less with the order of their
+disappearance; for the parent rock-pigeon now lives; and many varieties
+between the rock-pigeon and the carrier have become extinct; and carriers
+which are extreme in the important character of length of beak originated
+earlier than short-beaked tumblers, which are at the opposite end of the
+series in this same respect.
+
+Closely connected with the statement, that the organic remains from an
+intermediate formation are in some degree intermediate in character, is the
+fact, insisted on by all palæontologists, that fossils from two consecutive
+formations are far more closely related to each other, than are the fossils
+from two remote formations. Pictet gives as a well-known instance, the
+general resemblance of the organic remains from the several stages of the
+Chalk formation, though the species are distinct in each stage. This fact
+alone, from its generality, seems to have shaken Professor Pictet in his
+firm belief in the immutability of species. He who is acquainted with the
+distribution of existing species over the globe, will not attempt to
+account for the close resemblance of the distinct species in closely
+consecutive formations, by the physical conditions of the ancient areas
+having remained nearly the same. Let it be remembered that the forms of
+life, at least those inhabiting the sea, have changed almost simultaneously
+throughout the world, and therefore under the most different climates and
+conditions. Consider the {336} prodigious vicissitudes of climate during
+the pleistocene period, which includes the whole glacial period, and note
+how little the specific forms of the inhabitants of the sea have been
+affected.
+
+On the theory of descent, the full meaning of the fact of fossil remains
+from closely consecutive formations, though ranked as distinct species,
+being closely related, is obvious. As the accumulation of each formation
+has often been interrupted, and as long blank intervals have intervened
+between successive formations, we ought not to expect to find, as I
+attempted to show in the last chapter, in any one or two formations all the
+intermediate varieties between the species which appeared at the
+commencement and close of these periods; but we ought to find after
+intervals, very long as measured by years, but only moderately long as
+measured geologically, closely allied forms, or, as they have been called
+by some authors, representative species; and these we assuredly do find. We
+find, in short, such evidence of the slow and scarcely sensible mutation of
+specific forms, as we have a just right to expect to find.
+
+
+
+_On the state of Development of Ancient Forms._--There has been much
+discussion whether recent forms are more highly developed than ancient. I
+will not here enter on this subject, for naturalists have not as yet
+defined to each other's satisfaction what is meant by high and low forms.
+The best definition probably is, that the higher forms have their organs
+more distinctly specialised for different functions; and as such division
+of physiological labour seems to be an advantage to each being, natural
+selection will constantly tend in so far to make the later and more
+modified forms higher than their early progenitors, or than the slightly
+modified descendants of such progenitors. In a more general sense the {337}
+more recent forms must, on my theory, be higher than the more ancient; for
+each new species is formed by having had some advantage in the struggle for
+life over other and preceding forms. If under a nearly similar climate, the
+eocene inhabitants of one quarter of the world were put into competition
+with the existing inhabitants of the same or some other quarter, the eocene
+fauna or flora would certainly be beaten and exterminated; as would a
+secondary fauna by an eocene, and a palæozoic fauna by a secondary fauna. I
+do not doubt that this process of improvement has affected in a marked and
+sensible manner the organisation of the more recent and victorious forms of
+life, in comparison with the ancient and beaten forms; but I can see no way
+of testing this sort of progress. Crustaceans, for instance, not the
+highest in their own class, may have beaten the highest molluscs. From the
+extraordinary manner in which European productions have recently spread
+over New Zealand, and have seized on places which must have been previously
+occupied, we may believe, if all the animals and plants of Great Britain
+were set free in New Zealand, that in the course of time a multitude of
+British forms would become thoroughly naturalized there, and would
+exterminate many of the natives. On the other hand, from what we see now
+occurring in New Zealand, and from hardly a single inhabitant of the
+southern hemisphere having become wild in any part of Europe, we may doubt,
+if all the productions of New Zealand were set free in Great Britain,
+whether any considerable number would be enabled to seize on places now
+occupied by our native plants and animals. Under this point of view, the
+productions of Great Britain may be said to be higher than those of New
+Zealand. Yet the most skilful naturalist from an examination of the {338}
+species of the two countries could not have foreseen this result.
+
+Agassiz insists that ancient animals resemble to a certain extent the
+embryos of recent animals of the same classes; or that the geological
+succession of extinct forms is in some degree parallel to the embryological
+development of recent forms. I must follow Pictet and Huxley in thinking
+that the truth of this doctrine is very far from proved. Yet I fully expect
+to see it hereafter confirmed, at least in regard to subordinate groups,
+which have branched off from each other within comparatively recent times.
+For this doctrine of Agassiz accords well with the theory of natural
+selection. In a future chapter I shall attempt to show that the adult
+differs from its embryo, owing to variations supervening at a not early
+age, and being inherited at a corresponding age. This process, whilst it
+leaves the embryo almost unaltered, continually adds, in the course of
+successive generations, more and more difference to the adult.
+
+Thus the embryo comes to be left as a sort of picture, preserved by nature,
+of the ancient and less modified condition of each animal. This view may be
+true, and yet it may never be capable of full proof. Seeing, for instance,
+that the oldest known mammals, reptiles, and fish strictly belong to their
+own proper classes, though some of these old forms are in a slight degree
+less distinct from each other than are the typical members of the same
+groups at the present day, it would be vain to look for animals having the
+common embryological character of the Vertebrata, until beds far beneath
+the lowest Silurian strata are discovered--a discovery of which the chance
+is very small.
+
+
+
+_On the Succession of the same Types within the same {339} areas, during
+the later tertiary periods._--Mr. Clift many years ago showed that the
+fossil mammals from the Australian caves were closely allied to the living
+marsupials of that continent. In South America, a similar relationship is
+manifest, even to an uneducated eye, in the gigantic pieces of armour like
+those of the armadillo, found in several parts of La Plata; and Professor
+Owen has shown in the most striking manner that most of the fossil mammals,
+buried there in such numbers, are related to South American types. This
+relationship is even more clearly seen in the wonderful collection of
+fossil bones made by MM. Lund and Clausen in the caves of Brazil. I was so
+much impressed with these facts that I strongly insisted, in 1839 and 1845,
+on this "law of the succession of types,"--on "this wonderful relationship
+in the same continent between the dead and the living." Professor Owen has
+subsequently extended the same generalisation to the mammals of the Old
+World. We see the same law in this author's restorations of the extinct and
+gigantic birds of New Zealand. We see it also in the birds of the caves of
+Brazil. Mr. Woodward has shown that the same law holds good with
+sea-shells, but from the wide distribution of most genera of molluscs, it
+is not well displayed by them. Other cases could be added, as the relation
+between the extinct and living land-shells of Madeira; and between the
+extinct and living brackish-water shells of the Aralo-Caspian Sea.
+
+Now what does this remarkable law of the succession of the same types
+within the same areas mean? He would be a bold man, who after comparing the
+present climate of Australia and of parts of South America under the same
+latitude, would attempt to account, on the one hand, by dissimilar physical
+conditions for the dissimilarity of the inhabitants of these two
+continents, {340} and, on the other hand, by similarity of conditions, for
+the uniformity of the same types in each during the later tertiary periods.
+Nor can it be pretended that it is an immutable law that marsupials should
+have been chiefly or solely produced in Australia; or that Edentata and
+other American types should have been solely produced in South America. For
+we know that Europe in ancient times was peopled by numerous marsupials;
+and I have shown in the publications above alluded to, that in America the
+law of distribution of terrestrial mammals was formerly different from what
+it now is. North America formerly partook strongly of the present character
+of the southern half of the continent; and the southern half was formerly
+more closely allied, than it is at present, to the northern half. In a
+similar manner we know from Falconer and Cautley's discoveries, that
+northern India was formerly more closely related in its mammals to Africa
+than it is at the present time. Analogous facts could be given in relation
+to the distribution of marine animals.
+
+On the theory of descent with modification, the great law of the long
+enduring, but not immutable, succession of the same types within the same
+areas, is at once explained; for the inhabitants of each quarter of the
+world will obviously tend to leave in that quarter, during the next
+succeeding period of time, closely allied though in some degree modified
+descendants. If the inhabitants of one continent formerly differed greatly
+from those of another continent, so will their modified descendants still
+differ in nearly the same manner and degree. But after very long intervals
+of time and after great geographical changes, permitting much
+inter-migration, the feebler will yield to the more dominant forms, and
+there will be nothing immutable in the laws of past and present
+distribution. {341}
+
+It may be asked in ridicule, whether I suppose that the megatherium and
+other allied huge monsters have left behind them in South America, the
+sloth, armadillo, and anteater, as their degenerate descendants. This
+cannot for an instant be admitted. These huge animals have become wholly
+extinct, and have left no progeny. But in the caves of Brazil, there are
+many extinct species which are closely allied in size and in other
+characters to the species still living in South America; and some of these
+fossils may be the actual progenitors of living species. It must not be
+forgotten that, on my theory, all the species of the same genus have
+descended from some one species; so that if six genera, each having eight
+species, be found in one geological formation, and in the next succeeding
+formation there be six other allied or representative genera with the same
+number of species, then we may conclude that only one species of each of
+the six older genera has left modified descendants, constituting the six
+new genera. The other seven species of the old genera have all died out and
+have left no progeny. Or, which would probably be a far commoner case, two
+or three species of two or three alone of the six older genera will have
+been the parents of the six new genera; the other old species and the other
+whole old genera having become utterly extinct. In failing orders, with the
+genera and species decreasing in numbers, as apparently is the case of the
+Edentata of South America, still fewer genera and species will have left
+modified blood-descendants.
+
+
+
+_Summary of the preceding and present Chapters._--I have attempted to show
+that the geological record is extremely imperfect; that only a small
+portion of the globe has been geologically explored with care; that {342}
+only certain classes of organic beings have been largely preserved in a
+fossil state; that the number both of specimens and of species, preserved
+in our museums, is absolutely as nothing compared with the incalculable
+number of generations which must have passed away even during a single
+formation; that, owing to subsidence being necessary for the accumulation
+of fossiliferous deposits thick enough to resist future degradation,
+enormous intervals of time have elapsed between the successive formations;
+that there has probably been more extinction during the periods of
+subsidence, and more variation during the periods of elevation, and during
+the latter the record will have been least perfectly kept; that each single
+formation has not been continuously deposited; that the duration of each
+formation is, perhaps, short compared with the average duration of specific
+forms; that migration has played an important part in the first appearance
+of new forms in any one area and formation; that widely ranging species are
+those which have varied most, and have oftenest given rise to new species;
+and that varieties have at first often been local. All these causes taken
+conjointly, must have tended to make the geological record extremely
+imperfect, and will to a large extent explain why we do not find
+interminable varieties, connecting together all the extinct and existing
+forms of life by the finest graduated steps.
+
+He who rejects these views on the nature of the geological record, will
+rightly reject my whole theory. For he may ask in vain where are the
+numberless transitional links which must formerly have connected the
+closely allied or representative species, found in the several stages of
+the same great formation. He may disbelieve in the enormous intervals of
+time which have elapsed between our consecutive formations; he {343} may
+overlook how important a part migration must have played, when the
+formations of any one great region alone, as that of Europe, are
+considered; he may urge the apparent, but often falsely apparent, sudden
+coming in of whole groups of species. He may ask where are the remains of
+those infinitely numerous organisms which must have existed long before the
+first bed of the Silurian system was deposited: I can answer this latter
+question only hypothetically, by saying that as far as we can see, where
+our oceans now extend they have for an enormous period extended, and where
+our oscillating continents now stand they have stood ever since the
+Silurian epoch; but that long before that period, the world may have
+presented a wholly different aspect; and that the older continents, formed
+of formations older than any known to us, may now all be in a metamorphosed
+condition, or may lie buried under the ocean.
+
+Passing from these difficulties, all the other great leading facts in
+palæontology seem to me simply to follow on the theory of descent with
+modification through natural selection. We can thus understand how it is
+that new species come in slowly and successively; how species of different
+classes do not necessarily change together, or at the same rate, or in the
+same degree; yet in the long run that all undergo modification to some
+extent. The extinction of old forms is the almost inevitable consequence of
+the production of new forms. We can understand why when a species has once
+disappeared it never reappears. Groups of species increase in numbers
+slowly, and endure for unequal periods of time; for the process of
+modification is necessarily slow, and depends on many complex
+contingencies. The dominant species of the larger dominant groups tend to
+leave many modified {344} descendants, and thus new sub-groups and groups
+are formed. As these are formed, the species of the less vigorous groups,
+from their inferiority inherited from a common progenitor, tend to become
+extinct together, and to leave no modified offspring on the face of the
+earth. But the utter extinction of a whole group of species may often be a
+very slow process, from the survival of a few descendants, lingering in
+protected and isolated situations. When a group has once wholly
+disappeared, it does not reappear; for the link of generation has been
+broken.
+
+We can understand how the spreading of the dominant forms of life, which
+are those that oftenest vary, will in the long run tend to people the world
+with allied, but modified, descendants; and these will generally succeed in
+taking the places of those groups of species which are their inferiors in
+the struggle for existence. Hence, after long intervals of time, the
+productions of the world will appear to have changed simultaneously.
+
+We can understand how it is that all the forms of life, ancient and recent,
+make together one grand system; for all are connected by generation. We can
+understand, from the continued tendency to divergence of character, why the
+more ancient a form is, the more it generally differs from those now
+living. Why ancient and extinct forms often tend to fill up gaps between
+existing forms, sometimes blending two groups previously classed as
+distinct into one; but more commonly only bringing them a little closer
+together. The more ancient a form is, the more often, apparently, it
+displays characters in some degree intermediate between groups now
+distinct; for the more ancient a form is, the more nearly it will be
+related to, and consequently resemble, the common progenitor of groups,
+since {345} become widely divergent. Extinct forms are seldom directly
+intermediate between existing forms; but are intermediate only by a long
+and circuitous course through many extinct and very different forms. We can
+clearly see why the organic remains of closely consecutive formations are
+more closely allied to each other, than are those of remote formations; for
+the forms are more closely linked together by generation: we can clearly
+see why the remains of an intermediate formation are intermediate in
+character.
+
+The inhabitants of each successive period in the world's history have
+beaten their predecessors in the race for life, and are, in so far, higher
+in the scale of nature; and this may account for that vague yet ill-defined
+sentiment, felt by many palæontologists, that organisation on the whole has
+progressed. If it should hereafter be proved that ancient animals resemble
+to a certain extent the embryos of more recent animals of the same class,
+the fact will be intelligible. The succession of the same types of
+structure within the same areas during the later geological periods ceases
+to be mysterious, and is simply explained by inheritance.
+
+If then the geological record be as imperfect as I believe it to be, and it
+may at least be asserted that the record cannot be proved to be much more
+perfect, the main objections to the theory of natural selection are greatly
+diminished or disappear. On the other hand, all the chief laws of
+palæontology plainly proclaim, as it seems to me, that species have been
+produced by ordinary generation: old forms having been supplanted by new
+and improved forms of life, produced by the laws of variation still acting
+round us, and preserved by Natural Selection.
+
+       *       *       *       *       *
+
+
+{346}
+
+CHAPTER XI.
+
+GEOGRAPHICAL DISTRIBUTION.
+
+    Present distribution cannot be accounted for by differences in physical
+    conditions--Importance of barriers--Affinity of the productions of the
+    same continent--Centres of creation--Means of dispersal, by changes of
+    climate and of the level of the land, and by occasional
+    means--Dispersal during the Glacial period co-extensive with the world.
+
+In considering the distribution of organic beings over the face of the
+globe, the first great fact which strikes us is, that neither the
+similarity nor the dissimilarity of the inhabitants of various regions can
+be accounted for by their climatal and other physical conditions. Of late,
+almost every author who has studied the subject has come to this
+conclusion. The case of America alone would almost suffice to prove its
+truth: for if we exclude the northern parts where the circumpolar land is
+almost continuous, all authors agree that one of the most fundamental
+divisions in geographical distribution is that between the New and Old
+Worlds; yet if we travel over the vast American continent, from the central
+parts of the United States to its extreme southern point, we meet with the
+most diversified conditions; the most humid districts, arid deserts, lofty
+mountains, grassy plains, forests, marshes, lakes, and great rivers, under
+almost every temperature. There is hardly a climate or condition in the Old
+World which cannot be paralleled in the New--at least as closely as the
+same species generally require; for it is a most rare case to find a group
+of organisms confined to any small spot, having conditions peculiar in only
+a slight {347} degree; for instance, small areas in the Old World could be
+pointed out hotter than any in the New World, yet these are not inhabited
+by a peculiar fauna or flora. Notwithstanding this parallelism in the
+conditions of the Old and New Worlds, how widely different are their living
+productions!
+
+In the southern hemisphere, if we compare large tracts of land in
+Australia, South Africa, and western South America, between latitudes 25°
+and 35°, we shall find parts extremely similar in all their conditions, yet
+it would not be possible to point out three faunas and floras more utterly
+dissimilar. Or again we may compare the productions of South America south
+of lat. 35° with those north of 25°, which consequently inhabit a
+considerably different climate, and they will be found incomparably more
+closely related to each other, than they are to the productions of
+Australia or Africa under nearly the same climate. Analogous facts could be
+given with respect to the inhabitants of the sea.
+
+A second great fact which strikes us in our general review is, that
+barriers of any kind, or obstacles to free migration, are related in a
+close and important manner to the differences between the productions of
+various regions. We see this in the great difference of nearly all the
+terrestrial productions of the New and Old Worlds, excepting in the
+northern parts, where the land almost joins, and where, under a slightly
+different climate, there might have been free migration for the northern
+temperate forms, as there now is for the strictly arctic productions. We
+see the same fact in the great difference between the inhabitants of
+Australia, Africa, and South America under the same latitude: for these
+countries are almost as much isolated from each other as is possible. On
+each continent, also, we see the same fact; for on the opposite sides of
+{348} lofty and continuous mountain-ranges, and of great deserts, and
+sometimes even of large rivers, we find different productions; though as
+mountain-chains, deserts, &c., are not as impassable, or likely to have
+endured so long as the oceans separating continents, the differences are
+very inferior in degree to those characteristic of distinct continents.
+
+Turning to the sea, we find the same law. No two marine faunas are more
+distinct, with hardly a fish, shell, or crab in common, than those of the
+eastern and western shores of South and Central America; yet these great
+faunas are separated only by the narrow, but impassable, isthmus of Panama.
+Westward of the shores of America, a wide space of open ocean extends, with
+not an island as a halting-place for emigrants; here we have a barrier of
+another kind, and as soon as this is passed we meet in the eastern islands
+of the Pacific, with another and totally distinct fauna. So that here three
+marine faunas range far northward and southward, in parallel lines not far
+from each other, under corresponding climates; but from being separated
+from each other by impassable barriers, either of land or open sea, they
+are wholly distinct. On the other hand, proceeding still further westward
+from the eastern islands of the tropical parts of the Pacific, we encounter
+no impassable barriers, and we have innumerable islands as halting-places,
+or continuous coasts, until after travelling over a hemisphere we come to
+the shores of Africa; and over this vast space we meet with no well-defined
+and distinct marine faunas. Although hardly one shell, crab or fish is
+common to the above-named three approximate faunas of Eastern and Western
+America and the eastern Pacific islands, yet many fish range from the
+Pacific into the Indian Ocean, and many shells are common to the eastern
+islands of the Pacific {349} and the eastern shores of Africa, on almost
+exactly opposite meridians of longitude.
+
+A third great fact, partly included in the foregoing statements, is the
+affinity of the productions of the same continent or sea, though the
+species themselves are distinct at different points and stations. It is a
+law of the widest generality, and every continent offers innumerable
+instances. Nevertheless the naturalist in travelling, for instance, from
+north to south never fails to be struck by the manner in which successive
+groups of beings, specifically distinct, yet clearly related, replace each
+other. He hears from closely allied, yet distinct kinds of birds, notes
+nearly similar, and sees their nests similarly constructed, but not quite
+alike, with eggs coloured in nearly the same manner. The plains near the
+Straits of Magellan are inhabited by one species of Rhea (American
+ostrich), and northward the plains of La Plata by another species of the
+same genus; and not by a true ostrich or emu, like those found in Africa
+and Australia under the same latitude. On these same plains of La Plata, we
+see the agouti and bizcacha, animals having nearly the same habits as our
+hares and rabbits and belonging to the same order of Rodents, but they
+plainly display an American type of structure. We ascend the lofty peaks of
+the Cordillera and we find an alpine species of bizcacha; we look to the
+waters, and we do not find the beaver or musk-rat, but the coypu and
+capybara, rodents of the American type. Innumerable other instances could
+be given. If we look to the islands off the American shore, however much
+they may differ in geological structure, the inhabitants, though they may
+be all peculiar species, are essentially American. We may look back to past
+ages, as shown in the last chapter, and we find American types then
+prevalent on {350} the American continent and in the American seas. We see
+in these facts some deep organic bond, prevailing throughout space and
+time, over the same areas of land and water, and independent of their
+physical conditions. The naturalist must feel little curiosity, who is not
+led to inquire what this bond is.
+
+This bond, on my theory, is simply inheritance, that cause which alone, as
+far as we positively know, produces organisms quite like, or, as we see in
+the case of varieties, nearly like each other. The dissimilarity of the
+inhabitants of different regions may be attributed to modification through
+natural selection, and in a quite subordinate degree to the direct
+influence of different physical conditions. The degree of dissimilarity
+will depend on the migration of the more dominant forms of life from one
+region into another having been effected with more or less ease, at periods
+more or less remote;--on the nature and number of the former
+immigrants;--and on their action and reaction, in their mutual struggles
+for life;--the relation of organism to organism being, as I have already
+often remarked, the most important of all relations. Thus the high
+importance of barriers comes into play by checking migration; as does time
+for the slow process of modification through natural selection.
+Widely-ranging species, abounding in individuals, which have already
+triumphed over many competitors in their own widely-extended homes will
+have the best chance of seizing on new places, when they spread into new
+countries. In their new homes they will be exposed to new conditions, and
+will frequently undergo further modification and improvement; and thus they
+will become still further victorious, and will produce groups of modified
+descendants. On this principle of inheritance with modification, we can
+understand how it is that sections of genera, whole genera, {351} and even
+families are confined to the same areas, as is so commonly and notoriously
+the case.
+
+I believe, as was remarked in the last chapter, in no law of necessary
+development. As the variability of each species is an independent property,
+and will be taken advantage of by natural selection, only so far as it
+profits the individual in its complex struggle for life, so the degree of
+modification in different species will be no uniform quantity. If, for
+instance, a number of species, which stand in direct competition with each
+other, migrate in a body into a new and afterwards isolated country, they
+will be little liable to modification; for neither migration nor isolation
+in themselves can do anything. These principles come into play only by
+bringing organisms into new relations with each other, and in a lesser
+degree with the surrounding physical conditions. As we have seen in the
+last chapter that some forms have retained nearly the same character from
+an enormously remote geological period, so certain species have migrated
+over vast spaces, and have not become greatly modified.
+
+On these views, it is obvious, that the several species of the same genus,
+though inhabiting the most distant quarters of the world, must originally
+have proceeded from the same source, as they have descended from the same
+progenitor. In the case of those species, which have undergone during whole
+geological periods but little modification, there is not much difficulty in
+believing that they may have migrated from the same region; for during the
+vast geographical and climatal changes which will have supervened since
+ancient times, almost any amount of migration is possible. But in many
+other cases, in which we have reason to believe that the species of a genus
+have been produced within comparatively recent times, there is great
+difficulty on this head. It {352} is also obvious that the individuals of
+the same species, though now inhabiting distant and isolated regions, must
+have proceeded from one spot, where their parents were first produced: for,
+as explained in the last chapter, it is incredible that individuals
+identically the same should ever have been produced through natural
+selection from parents specifically distinct.
+
+We are thus brought to the question which has been largely discussed by
+naturalists, namely, whether species have been created at one or more
+points of the earth's surface. Undoubtedly there are very many cases of
+extreme difficulty, in understanding how the same species could possibly
+have migrated from some one point to the several distant and isolated
+points, where now found. Nevertheless the simplicity of the view that each
+species was first produced within a single region captivates the mind. He
+who rejects it, rejects the _vera causa_ of ordinary generation with
+subsequent migration, and calls in the agency of a miracle. It is
+universally admitted, that in most cases the area inhabited by a species is
+continuous; and when a plant or animal inhabits two points so distant from
+each other, or with an interval of such a nature, that the space could not
+be easily passed over by migration, the fact is given as something
+remarkable and exceptional. The capacity of migrating across the sea is
+more distinctly limited in terrestrial mammals, than perhaps in any other
+organic beings; and, accordingly, we find no inexplicable cases of the same
+mammal inhabiting distant points of the world. No geologist will feel any
+difficulty in such cases as Great Britain having been formerly united to
+Europe, and consequently possessing the same quadrupeds. But if the same
+species can be produced at two separate points, why do we not find a single
+mammal common to Europe and {353} Australia or South America? The
+conditions of life are nearly the same, so that a multitude of European
+animals and plants have become naturalised in America and Australia; and
+some of the aboriginal plants are identically the same at these distant
+points of the northern and southern hemispheres? The answer, as I believe,
+is, that mammals have not been able to migrate, whereas some plants, from
+their varied means of dispersal, have migrated across the vast and broken
+interspace. The great and striking influence which barriers of every kind
+have had on distribution, is intelligible only on the view that the great
+majority of species have been produced on one side alone, and have not been
+able to migrate to the other side. Some few families, many sub-families,
+very many genera, and a still greater number of sections of genera are
+confined to a single region; and it has been observed by several
+naturalists, that the most natural genera, or those genera in which the
+species are most closely related to each other, are generally local, or
+confined to one area. What a strange anomaly it would be, if, when coming
+one step lower in the series, to the individuals of the same species, a
+directly opposite rule prevailed; and species were not local, but had been
+produced in two or more distinct areas!
+
+Hence it seems to me, as it has to many other naturalists, that the view of
+each species having been produced in one area alone, and having
+subsequently migrated from that area as far as its powers of migration and
+subsistence under past and present conditions permitted, is the most
+probable. Undoubtedly many cases occur, in which we cannot explain how the
+same species could have passed from one point to the other. But the
+geographical and climatal changes, which have certainly occurred within
+recent geological times, must have interrupted or rendered discontinuous
+the {354} formerly continuous range of many species. So that we are reduced
+to consider whether the exceptions to continuity of range are so numerous
+and of so grave a nature, that we ought to give up the belief, rendered
+probable by general considerations, that each species has been produced
+within one area, and has migrated thence as far as it could. It would be
+hopelessly tedious to discuss all the exceptional cases of the same
+species, now living at distant and separated points; nor do I for a moment
+pretend that any explanation could be offered of many such cases. But after
+some preliminary remarks, I will discuss a few of the most striking classes
+of facts; namely, the existence of the same species on the summits of
+distant mountain-ranges, and at distant points in the arctic and antarctic
+regions; and secondly (in the following chapter), the wide distribution of
+freshwater productions; and thirdly, the occurrence of the same terrestrial
+species on islands and on the mainland, though separated by hundreds of
+miles of open sea. If the existence of the same species at distant and
+isolated points of the earth's surface, can in many instances be explained
+on the view of each species having migrated from a single birthplace; then,
+considering our ignorance with respect to former climatal and geographical
+changes and various occasional means of transport, the belief that this has
+been the universal law, seems to me incomparably the safest.
+
+In discussing this subject, we shall be enabled at the same time to
+consider a point equally important for us, namely, whether the several
+distinct species of a genus, which on my theory have all descended from a
+common progenitor, can have migrated (undergoing modification during some
+part of their migration) from the area inhabited by their progenitor. If it
+can be shown to be almost invariably the case, that a region, of which
+{355} most of its inhabitants are closely related to, or belong to the same
+genera with the species of a second region, has probably received at some
+former period immigrants from this other region, my theory will be
+strengthened; for we can clearly understand, on the principle of
+modification, why the inhabitants of a region should be related to those of
+another region, whence it has been stocked. A volcanic island, for
+instance, upheaved and formed at the distance of a few hundreds of miles
+from a continent, would probably receive from it in the course of time a
+few colonists, and their descendants, though modified, would still be
+plainly related by inheritance to the inhabitants of the continent. Cases
+of this nature are common, and are, as we shall hereafter more fully see,
+inexplicable on the theory of independent creation. This view of the
+relation of species in one region to those in another, does not differ much
+(by substituting the word variety for species) from that lately advanced in
+an ingenious paper by Mr. Wallace, in which he concludes, that "every
+species has come into existence coincident both in space and time with a
+pre-existing closely allied species." And I now know from correspondence,
+that this coincidence he attributes to generation with modification.
+
+The previous remarks on "single and multiple centres of creation" do not
+directly bear on another allied question,--namely whether all the
+individuals of the same species have descended from a single pair, or
+single hermaphrodite, or whether, as some authors suppose, from many
+individuals simultaneously created. With those organic beings which never
+intercross (if such exist), the species, on my theory, must have descended
+from a succession of improved varieties, which will never have blended with
+other individuals or varieties, but will have supplanted each other; so
+that, at each {356} successive stage of modification and improvement, all
+the individuals of each variety will have descended from a single parent.
+But in the majority of cases, namely, with all organisms which habitually
+unite for each birth, or which often intercross, I believe that during the
+slow process of modification the individuals of the species will have been
+kept nearly uniform by intercrossing; so that many individuals will have
+gone on simultaneously changing, and the whole amount of modification will
+not have been due, at each stage, to descent from a single parent. To
+illustrate what I mean: our English racehorses differ slightly from the
+horses of every other breed; but they do not owe their difference and
+superiority to descent from any single pair, but to continued care in
+selecting and training many individuals during many generations.
+
+Before discussing the three classes of facts, which I have selected as
+presenting the greatest amount of difficulty on the theory of "single
+centres of creation," I must say a few words on the means of dispersal.
+
+
+
+_Means of Dispersal._--Sir C. Lyell and other authors have ably treated
+this subject. I can give here only the briefest abstract of the more
+important facts. Change of climate must have had a powerful influence on
+migration: a region when its climate was different may have been a high
+road for migration, but now be impassable; I shall, however, presently have
+to discuss this branch of the subject in some detail. Changes of level in
+the land must also have been highly influential: a narrow isthmus now
+separates two marine faunas; submerge it, or let it formerly have been
+submerged, and the two faunas will now blend or may formerly have blended:
+where the sea now extends, land may at a former period have connected
+islands or {357} possibly even continents together, and thus have allowed
+terrestrial productions to pass from one to the other. No geologist will
+dispute that great mutations of level have occurred within the period of
+existing organisms. Edward Forbes insisted that all the islands in the
+Atlantic must recently have been connected with Europe or Africa, and
+Europe likewise with America. Other authors have thus hypothetically
+bridged over every ocean, and have united almost every island to some
+mainland. If indeed the arguments used by Forbes are to be trusted, it must
+be admitted that scarcely a single island exists which has not recently
+been united to some continent. This view cuts the Gordian knot of the
+dispersal of the same species to the most distant points, and removes many
+a difficulty: but to the best of my judgment we are not authorized in
+admitting such enormous geographical changes within the period of existing
+species. It seems to me that we have abundant evidence of great
+oscillations of level in our continents; but not of such vast changes in
+their position and extension, as to have united them within the recent
+period to each other and to the several intervening oceanic islands. I
+freely admit the former existence of many islands, now buried beneath the
+sea, which may have served as halting places for plants and for many
+animals during their migration. In the coral-producing oceans such sunken
+islands are now marked, as I believe, by rings of coral or atolls standing
+over them. Whenever it is fully admitted, as I believe it will some day be,
+that each species has proceeded from a single birthplace, and when in the
+course of time we know something definite about the means of distribution,
+we shall be enabled to speculate with security on the former extension of
+the land. But I do not believe that it will ever be proved that within the
+{358} recent period continents which are now quite separate, have been
+continuously, or almost continuously, united with each other, and with the
+many existing oceanic islands. Several facts in distribution,--such as the
+great difference in the marine faunas on the opposite sides of almost every
+continent,--the close relation of the tertiary inhabitants of several lands
+and even seas to their present inhabitants,--a certain degree of relation
+(as we shall hereafter see) between the distribution of mammals and the
+depth of the sea,--these and other such facts seem to me opposed to the
+admission of such prodigious geographical revolutions within the recent
+period, as are necessitated on the view advanced by Forbes and admitted by
+his many followers. The nature and relative proportions of the inhabitants
+of oceanic islands likewise seem to me opposed to the belief of their
+former continuity with continents. Nor does their almost universally
+volcanic composition favour the admission that they are the wrecks of
+sunken continents;--if they had originally existed as mountain-ranges on
+the land, some at least of the islands would have been formed, like other
+mountain-summits, of granite, metamorphic schists, old fossiliferous or
+other such rocks, instead of consisting of mere piles of volcanic matter.
+
+I must now say a few words on what are called accidental means, but which
+more properly might be called occasional means of distribution. I shall
+here confine myself to plants. In botanical works, this or that plant is
+stated to be ill adapted for wide dissemination; but for transport across
+the sea, the greater or less facilities may be said to be almost wholly
+unknown. Until I tried, with Mr. Berkeley's aid, a few experiments, it was
+not even known how far seeds could resist the injurious action of
+sea-water. To my surprise I found that {359} out of 87 kinds, 64 germinated
+after an immersion of 28 days, and a few survived an immersion of 137 days.
+For convenience' sake I chiefly tried small seeds, without the capsule or
+fruit; and as all of these sank in a few days, they could not be floated
+across wide spaces of the sea, whether or not they were injured by the
+salt-water. Afterwards I tried some larger fruits, capsules, &c., and some
+of these floated for a long time. It is well known what a difference there
+is in the buoyancy of green and seasoned timber; and it occurred to me that
+floods might wash down plants or branches, and that these might be dried on
+the banks, and then by a fresh rise in the stream be washed into the sea.
+Hence I was led to dry stems and branches of 94 plants with ripe fruit, and
+to place them on sea-water. The majority sank quickly, but some which
+whilst green floated for a very short time, when dried floated much longer;
+for instance, ripe hazel-nuts sank immediately, but when dried they floated
+for 90 days, and afterwards when planted they germinated; an asparagus
+plant with ripe berries floated for 23 days, when dried it floated for 85
+days, and the seeds afterwards germinated; the ripe seeds of Helosciadium
+sank in two days, when dried they floated for above 90 days, and afterwards
+germinated. Altogether out of the 94 dried plants, 18 floated for above 28
+days, and some of the 18 floated for a very much longer period. So that as
+64/87 seeds germinated after an immersion of 28 days; and as 18/94 plants
+with ripe fruit (but not all the same species as in the foregoing
+experiment) floated, after being dried, for above 28 days, as far as we may
+infer anything from these scanty facts, we may conclude that the seeds of
+14/100 plants of any country might be floated by sea-currents during 28
+days, and would retain their power of germination. In Johnston's Physical
+Atlas, the average {360} rate of the several Atlantic currents is 33 miles
+per diem (some currents running at the rate of 60 miles per diem); on this
+average, the seeds of 14/100 plants belonging to one country might be
+floated across 924 miles of sea to another country; and when stranded, if
+blown to a favourable spot by an inland gale, they would germinate.
+
+Subsequently to my experiments, M. Martens tried similar ones, but in a
+much better manner, for he placed the seeds in a box in the actual sea, so
+that they were alternately wet and exposed to the air like really floating
+plants. He tried 98 seeds, mostly different from mine; but he chose many
+large fruits and likewise seeds from plants which live near the sea; and
+this would have favoured the average length of their flotation and of their
+resistance to the injurious action of the salt-water. On the other hand he
+did not previously dry the plants or branches with the fruit; and this, as
+we have seen, would have caused some of them to have floated much longer.
+The result was that 18/98 of his seeds floated for 42 days, and were then
+capable of germination. But I do not doubt that plants exposed to the waves
+would float for a less time than those protected from violent movement as
+in our experiments. Therefore it would perhaps be safer to assume that the
+seeds of about 10/100 plants of a flora, after having been dried, could be
+floated across a space of sea 900 miles in width, and would then germinate.
+The fact of the larger fruits often floating longer than the small, is
+interesting; as plants with large seeds or fruit could hardly be
+transported by any other means; and Alph. de Candolle has shown that such
+plants generally have restricted ranges.
+
+But seeds may be occasionally transported in another manner. Drift timber
+is thrown up on most islands, {361} even on those in the midst of the
+widest oceans; and the natives of the coral-islands in the Pacific, procure
+stones for their tools, solely from the roots of drifted trees, these
+stones being a valuable royal tax. I find on examination, that when
+irregularly shaped stones are embedded in the roots of trees, small parcels
+of earth are very frequently enclosed in their interstices and behind
+them,--so perfectly that not a particle could be washed away in the longest
+transport: out of one small portion of earth thus _completely_ enclosed by
+wood in an oak about 50 years old, three dicotyledonous plants germinated:
+I am certain of the accuracy of this observation. Again, I can show that
+the carcasses of birds, when floating on the sea, sometimes escape being
+immediately devoured; and seeds of many kinds in the crops of floating
+birds long retain their vitality: peas and vetches, for instance, are
+killed by even a few days' immersion in sea-water; but some taken out of
+the crop of a pigeon, which had floated on artificial salt-water for 30
+days, to my surprise nearly all germinated.
+
+Living birds can hardly fail to be highly effective agents in the
+transportation of seeds. I could give many facts showing how frequently
+birds of many kinds are blown by gales to vast distances across the ocean.
+We may I think safely assume that under such circumstances their rate of
+flight would often be 35 miles an hour; and some authors have given a far
+higher estimate. I have never seen an instance of nutritious seeds passing
+through the intestines of a bird; but hard seeds of fruit pass uninjured
+through even the digestive organs of a turkey. In the course of two months,
+I picked up in my garden 12 kinds of seeds, out of the excrement of small
+birds, and these seemed perfect, and some of them, which I tried,
+germinated. {362} But the following fact is more important: the crops of
+birds do not secrete gastric juice, and do not in the least injure, as I
+know by trial, the germination of seeds; now after a bird has found and
+devoured a large supply of food, it is positively asserted that all the
+grains do not pass into the gizzard for 12 or even 18 hours. A bird in this
+interval might easily be blown to the distance of 500 miles, and hawks are
+known to look out for tired birds, and the contents of their torn crops
+might thus readily get scattered. Mr. Brent informs me that a friend of his
+had to give up flying carrier-pigeons from France to England, as the hawks
+on the English coast destroyed so many on their arrival. Some hawks and
+owls bolt their prey whole, and after an interval of from twelve to twenty
+hours, disgorge pellets, which, as I know from experiments made in the
+Zoological Gardens, include seeds capable of germination. Some seeds of the
+oat, wheat, millet, canary, hemp, clover, and beet germinated after having
+been from twelve to twenty-one hours in the stomachs of different birds of
+prey; and two seeds of beet grew after having been thus retained for two
+days and fourteen hours. Freshwater fish, I find, eat seeds of many land
+and water plants: fish are frequently devoured by birds, and thus the seeds
+might be transported from place to place. I forced many kinds of seeds into
+the stomachs of dead fish, and then gave their bodies to fishing-eagles,
+storks, and pelicans; these birds after an interval of many hours, either
+rejected the seeds in pellets or passed them in their excrement; and
+several of these seeds retained their power of germination. Certain seeds,
+however, were always killed by this process.
+
+Although the beaks and feet of birds are generally quite clean, I can show
+that earth sometimes adheres to them: in one instance I removed twenty-two
+grains {363} of dry argillaceous earth from one foot of a partridge, and in
+this earth there was a pebble quite as large as the seed of a vetch. Thus
+seeds might occasionally be transported to great distances; for many facts
+could be given showing that soil almost everywhere is charged with seeds.
+Reflect for a moment on the millions of quails which annually cross the
+Mediterranean; and can we doubt that the earth adhering to their feet would
+sometimes include a few minute seeds? But I shall presently have to recur
+to this subject.
+
+As icebergs are known to be sometimes loaded with earth and stones, and
+have even carried brushwood, bones, and the nest of a land-bird, I can
+hardly doubt that they must occasionally have transported seeds from one
+part to another of the arctic and antarctic regions, as suggested by Lyell;
+and during the Glacial period from one part of the now temperate regions to
+another. In the Azores, from the large number of the species of plants
+common to Europe, in comparison with the plants of other oceanic islands
+nearer to the mainland, and (as remarked by Mr. H. C. Watson) from the
+somewhat northern character of the flora in comparison with the latitude, I
+suspected that these islands had been partly stocked by ice-borne seeds,
+during the Glacial epoch. At my request Sir C. Lyell wrote to M. Hartung to
+inquire whether he had observed erratic boulders on these islands, and he
+answered that he had found large fragments of granite and other rocks,
+which do not occur in the archipelago. Hence we may safely infer that
+icebergs formerly landed their rocky burthens on the shores of these
+mid-ocean islands, and it is at least possible that they may have brought
+thither the seeds of northern plants.
+
+Considering that the several above means of transport, and that several
+other means, which without {364} doubt remain to be discovered, have been
+in action year after year, for centuries and tens of thousands of years, it
+would I think be a marvellous fact if many plants had not thus become
+widely transported. These means of transport are sometimes called
+accidental, but this is not strictly correct: the currents of the sea are
+not accidental, nor is the direction of prevalent gales of wind. It should
+be observed that scarcely any means of transport would carry seeds for very
+great distances; for seeds do not retain their vitality when exposed for a
+great length of time to the action of sea-water; nor could they be long
+carried in the crops or intestines of birds. These means, however, would
+suffice for occasional transport across tracts of sea some hundred miles in
+breadth, or from island to island, or from a continent to a neighbouring
+island, but not from one distant continent to another. The floras of
+distant continents would not by such means become mingled in any great
+degree; but would remain as distinct as we now see them to be. The
+currents, from their course, would never bring seeds from North America to
+Britain, though they might and do bring seeds from the West Indies to our
+western shores, where, if not killed by so long an immersion in salt-water,
+they could not endure our climate. Almost every year, one or two land-birds
+are blown across the whole Atlantic Ocean, from North America to the
+western shores of Ireland and England; but seeds could be transported by
+these wanderers only by one means, namely, in dirt sticking to their feet,
+which is in itself a rare accident. Even in this case, how small would the
+chance be of a seed falling on favourable soil, and coming to maturity! But
+it would be a great error to argue that because a well-stocked island, like
+Great Britain, has not, as far as is known {365} (and it would be very
+difficult to prove this), received within the last few centuries, through
+occasional means of transport, immigrants from Europe or any other
+continent, that a poorly-stocked island, though standing more remote from
+the mainland, would not receive colonists by similar means. I do not doubt
+that out of twenty seeds or animals transported to an island, even if far
+less well-stocked than Britain, scarcely more than one would be so well
+fitted to its new home, as to become naturalised. But this, as it seems to
+me, is no valid argument against what would be effected by occasional means
+of transport, during the long lapse of geological time, whilst an island
+was being upheaved and formed, and before it had become fully stocked with
+inhabitants. On almost bare land, with few or no destructive insects or
+birds living there, nearly every seed, which chanced to arrive, if fitted
+for the climate, would be sure to germinate and survive.
+
+
+
+_Dispersal during the Glacial period._--The identity of many plants and
+animals, on mountain-summits, separated from each other by hundreds of
+miles of lowlands, where the Alpine species could not possibly exist, is
+one of the most striking cases known of the same species living at distant
+points, without the apparent possibility of their having migrated from one
+to the other. It is indeed a remarkable fact to see so many of the same
+plants living on the snowy regions of the Alps or Pyrenees, and in the
+extreme northern parts of Europe; but it is far more remarkable, that the
+plants on the White Mountains, in the United States of America, are all the
+same with those of Labrador, and nearly all the same, as we hear from Asa
+Gray, with those on the loftiest mountains of Europe. Even as long ago as
+1747, such facts led Gmelin to conclude that the {366} same species must
+have been independently created at several distinct points; and we might
+have remained in this same belief, had not Agassiz and others called vivid
+attention to the Glacial period, which, as we shall immediately see,
+affords a simple explanation of these facts. We have evidence of almost
+every conceivable kind, organic and inorganic, that within a very recent
+geological period, central Europe and North America suffered under an
+Arctic climate. The ruins of a house burnt by fire do not tell their tale
+more plainly, than do the mountains of Scotland and Wales, with their
+scored flanks, polished surfaces, and perched boulders, of the icy streams
+with which their valleys were lately filled. So greatly has the climate of
+Europe changed, that in Northern Italy, gigantic moraines, left by old
+glaciers, are now clothed by the vine and maize. Throughout a large part of
+the United States, erratic boulders, and rocks scored by drifted icebergs
+and coast-ice, plainly reveal a former cold period.
+
+The former influence of the glacial climate on the distribution of the
+inhabitants of Europe, as explained with remarkable clearness by Edward
+Forbes, is substantially as follows. But we shall follow the changes more
+readily, by supposing a new glacial period to come slowly on, and then pass
+away, as formerly occurred. As the cold came on, and as each more southern
+zone became fitted for arctic beings and ill-fitted for their former more
+temperate inhabitants, the latter would be supplanted and arctic
+productions would take their places. The inhabitants of the more temperate
+regions would at the same time travel southward, unless they were stopped
+by barriers, in which case they would perish. The mountains would become
+covered with snow and ice, and their former Alpine inhabitants would
+descend to the plains. By the time that the cold had reached {367} its
+maximum, we should have a uniform arctic fauna and flora, covering the
+central parts of Europe, as far south as the Alps and Pyrenees, and even
+stretching into Spain. The now temperate regions of the United States would
+likewise be covered by arctic plants and animals, and these would be nearly
+the same with those of Europe; for the present circumpolar inhabitants,
+which we suppose to have everywhere travelled southward, are remarkably
+uniform round the world. We may suppose that the Glacial period came on a
+little earlier or later in North America than in Europe, so will the
+southern migration there have been a little earlier or later; but this will
+make no difference in the final result.
+
+As the warmth returned, the arctic forms would retreat northward, closely
+followed up in their retreat by the productions of the more temperate
+regions. And as the snow melted from the bases of the mountains, the arctic
+forms would seize on the cleared and thawed ground, always ascending higher
+and higher, as the warmth increased, whilst their brethren were pursuing
+their northern journey. Hence, when the warmth had fully returned, the same
+arctic species, which had lately lived in a body together on the lowlands
+of the Old and New Worlds, would be left isolated on distant
+mountain-summits (having been exterminated on all lesser heights) and in
+the arctic regions of both hemispheres.
+
+Thus we can understand the identity of many plants at points so immensely
+remote as on the mountains of the United States and of Europe. We can thus
+also understand the fact that the Alpine plants of each mountain-range are
+more especially related to the arctic forms living due north or nearly due
+north of them: for the migration as the cold came on, and the re-migration
+on the returning warmth, will generally {368} have been due south and
+north. The Alpine plants, for example, of Scotland, as remarked by Mr.
+H. C. Watson, and those of the Pyrenees, as remarked by Ramond, are more
+especially allied to the plants of northern Scandinavia; those of the
+United States to Labrador; those of the mountains of Siberia to the arctic
+regions of that country. These views, grounded as they are on the perfectly
+well-ascertained occurrence of a former Glacial period, seem to me to
+explain in so satisfactory a manner the present distribution of the Alpine
+and Arctic productions of Europe and America, that when in other regions we
+find the same species on distant mountain-summits, we may almost conclude
+without other evidence, that a colder climate permitted their former
+migration across the low intervening tracts, since become too warm for
+their existence.
+
+If the climate, since the Glacial period, has ever been in any degree
+warmer than at present (as some geologists in the United States believe to
+have been the case, chiefly from the distribution of the fossil Gnathodon),
+then the arctic and temperate productions will at a very late period have
+marched a little further north, and subsequently have retreated to their
+present homes; but I have met with no satisfactory evidence with respect to
+this intercalated slightly warmer period, since the Glacial period.
+
+The arctic forms, during their long southern migration and re-migration
+northward, will have been exposed to nearly the same climate, and, as is
+especially to be noticed, they will have kept in a body together;
+consequently their mutual relations will not have been much disturbed, and,
+in accordance with the principles inculcated in this volume, they will not
+have been liable to much modification. But with our Alpine productions,
+left isolated from the moment of the returning warmth, {369} first at the
+bases and ultimately on the summits of the mountains, the case will have
+been somewhat different; for it is not likely that all the same arctic
+species will have been left on mountain ranges distant from each other, and
+have survived there ever since; they will, also, in all probability have
+become mingled with ancient Alpine species, which must have existed on the
+mountains before the commencement of the Glacial epoch, and which during
+its coldest period will have been temporarily driven down to the plains;
+they will, also, have been exposed to somewhat different climatal
+influences. Their mutual relations will thus have been in some degree
+disturbed; consequently they will have been liable to modification; and
+this we find has been the case; for if we compare the present Alpine plants
+and animals of the several great European mountain-ranges, though very many
+of the species are identically the same, some present varieties, some are
+ranked as doubtful forms, and some few are distinct yet closely allied or
+representative species.
+
+In illustrating what, as I believe, actually took place during the Glacial
+period, I assumed that at its commencement the arctic productions were as
+uniform round the polar regions as they are at the present day. But the
+foregoing remarks on distribution apply not only to strictly arctic forms,
+but also to many sub-arctic and to some few northern temperate forms, for
+some of these are the same on the lower mountains and on the plains of
+North America and Europe; and it may be reasonably asked how I account for
+the necessary degree of uniformity of the sub-arctic and northern temperate
+forms round the world, at the commencement of the Glacial period. At the
+present day, the sub-arctic and northern temperate productions of the Old
+and New Worlds are separated from each other by the {370} Atlantic Ocean
+and by the extreme northern part of the Pacific. During the Glacial period,
+when the inhabitants of the Old and New Worlds lived further southwards
+than at present, they must have been still more completely separated by
+wider spaces of ocean. I believe the above difficulty may be surmounted by
+looking to still earlier changes of climate of an opposite nature. We have
+good reason to believe that during the newer Pliocene period, before the
+Glacial epoch, and whilst the majority of the inhabitants of the world were
+specifically the same as now, the climate was warmer than at the present
+day. Hence we may suppose that the organisms now living under the climate
+of latitude 60°, during the Pliocene period lived further north under the
+Polar Circle, in latitude 66°-67°; and that the strictly arctic productions
+then lived on the broken land still nearer to the pole. Now if we look at a
+globe, we shall see that under the Polar Circle there is almost continuous
+land from western Europe, through Siberia, to eastern America. And to this
+continuity of the circumpolar land, and to the consequent freedom for
+intermigration under a more favourable climate, I attribute the necessary
+amount of uniformity in the sub-arctic and northern temperate productions
+of the Old and New Worlds, at a period anterior to the Glacial epoch.
+
+Believing, from reasons before alluded to, that our continents have long
+remained in nearly the same relative position, though subjected to large,
+but partial oscillations of level, I am strongly inclined to extend the
+above view, and to infer that during some earlier and still warmer period,
+such as the older Pliocene period, a large number of the same plants and
+animals inhabited the almost continuous circumpolar land; and that these
+plants and animals, both in the Old and {371} New Worlds, began slowly to
+migrate southwards as the climate became less warm, long before the
+commencement of the Glacial period. We now see, as I believe, their
+descendants, mostly in a modified condition, in the central parts of Europe
+and the United States. On this view we can understand the relationship,
+with very little identity, between the productions of North America and
+Europe,--a relationship which is most remarkable, considering the distance
+of the two areas, and their separation by the Atlantic Ocean. We can
+further understand the singular fact remarked on by several observers, that
+the productions of Europe and America during the later tertiary stages were
+more closely related to each other than they are at the present time; for
+during these warmer periods the northern parts of the Old and New Worlds
+will have been almost continuously united by land, serving as a bridge,
+since rendered impassable by cold, for the intermigration of their
+inhabitants.
+
+During the slowly decreasing warmth of the Pliocene period, as soon as the
+species in common, which inhabited the New and Old Worlds, migrated south
+of the Polar Circle, they must have been completely cut off from each
+other. This separation, as far as the more temperate productions are
+concerned, took place long ages ago. And as the plants and animals migrated
+southward, they will have become mingled in the one great region with the
+native American productions, and have had to compete with them; and in the
+other great region, with those of the Old World. Consequently we have here
+everything favourable for much modification,--for far more modification
+than with the Alpine productions, left isolated, within a much more recent
+period, on the several mountain-ranges and on the arctic lands of the two
+Worlds. Hence it has come, that when we compare {372} the now living
+productions of the temperate regions of the New and Old Worlds, we find
+very few identical species (though Asa Gray has lately shown that more
+plants are identical than was formerly supposed), but we find in every
+great class many forms, which some naturalists rank as geographical races,
+and others as distinct species; and a host of closely allied or
+representative forms which are ranked by all naturalists as specifically
+distinct.
+
+As on the land, so in the waters of the sea, a slow southern migration of a
+marine fauna, which during the Pliocene or even a somewhat earlier period,
+was nearly uniform along the continuous shores of the Polar Circle, will
+account, on the theory of modification, for many closely allied forms now
+living in areas completely sundered. Thus, I think, we can understand the
+presence of many existing and tertiary representative forms on the eastern
+and western shores of temperate North America; and the still more striking
+case of many closely allied crustaceans (as described in Dana's admirable
+work), of some fish and other marine animals, in the Mediterranean and in
+the seas of Japan,--areas now separated by a continent and by nearly a
+hemisphere of equatorial ocean.
+
+These cases of relationship, without identity, of the inhabitants of seas
+now disjoined, and likewise of the past and present inhabitants of the
+temperate lands of North America and Europe, are inexplicable on the theory
+of creation. We cannot say that they have been created alike, in
+correspondence with the nearly similar physical conditions of the areas;
+for if we compare, for instance, certain parts of South America with the
+southern continents of the Old World, we see countries closely
+corresponding in all their physical conditions, but with their inhabitants
+utterly dissimilar. {373}
+
+But we must return to our more immediate subject, the Glacial period. I am
+convinced that Forbes's view may be largely extended. In Europe we have the
+plainest evidence of the cold period, from the western shores of Britain to
+the Oural range, and southward to the Pyrenees. We may infer from the
+frozen mammals and nature of the mountain vegetation, that Siberia was
+similarly affected. Along the Himalaya, at points 900 miles apart, glaciers
+have left the marks of their former low descent; and in Sikkim, Dr. Hooker
+saw maize growing on gigantic ancient moraines. South of the equator, we
+have some direct evidence of former glacial action in New Zealand; and the
+same plants, found on widely separated mountains in that island, tell the
+same story. If one account which has been published can be trusted, we have
+direct evidence of glacial action in the south-eastern corner of Australia.
+
+Looking to America; in the northern half, ice-borne fragments of rock have
+been observed on the eastern side as far south as lat. 36°-37°, and on the
+shores of the Pacific, where the climate is now so different, as far south
+as lat. 46°; erratic boulders have, also, been noticed on the Rocky
+Mountains. In the Cordillera of Equatorial South America, glaciers once
+extended far below their present level. In central Chili I was astonished
+at the structure of a vast mound of detritus, about 800 feet in height,
+crossing a valley of the Andes; and this I now feel convinced was a
+gigantic moraine, left far below any existing glacier. Further south on
+both sides of the continent, from lat. 41° to the southernmost extremity,
+we have the clearest evidence of former glacial action, in huge boulders
+transported far from their parent source.
+
+We do not know that the Glacial epoch was strictly simultaneous at these
+several far distant points on {374} opposite sides of the world. But we
+have good evidence in almost every case, that the epoch was included within
+the latest geological period. We have, also, excellent evidence, that it
+endured for an enormous time, as measured by years, at each point. The cold
+may have come on, or have ceased, earlier at one point of the globe than at
+another, but seeing that it endured for long at each, and that it was
+contemporaneous in a geological sense, it seems to me probable that it was,
+during a part at least of the period, actually simultaneous throughout the
+world. Without some distinct evidence to the contrary, we may at least
+admit as probable that the glacial action was simultaneous on the eastern
+and western sides of North America, in the Cordillera under the equator and
+under the warmer temperate zones, and on both sides of the southern
+extremity of the continent. If this be admitted, it is difficult to avoid
+believing that the temperature of the whole world was at this period
+simultaneously cooler. But it would suffice for my purpose, if the
+temperature was at the same time lower along certain broad belts of
+longitude.
+
+On this view of the whole world, or at least of broad longitudinal belts,
+having been simultaneously colder from pole to pole, much light can be
+thrown on the present distribution of identical and allied species. In
+America, Dr. Hooker has shown that between forty and fifty of the flowering
+plants of Tierra del Fuego, forming no inconsiderable part of its scanty
+flora, are common to Europe, enormously remote as these two points are; and
+there are many closely allied species. On the lofty mountains of equatorial
+America a host of peculiar species belonging to European genera occur. On
+the highest mountains of Brazil, some few European genera were found by
+Gardner, which do not exist in the wide {375} intervening hot countries. So
+on the Silla of Caraccas the illustrious Humboldt long ago found species
+belonging to genera characteristic of the Cordillera. On the mountains of
+Abyssinia, several European forms and some few representatives of the
+peculiar flora of the Cape of Good Hope occur. At the Cape of Good Hope a
+very few European species, believed not to have been introduced by man, and
+on the mountains, some few representative European forms are found, which
+have not been discovered in the intertropical parts of Africa. On the
+Himalaya, and on the isolated mountain-ranges of the peninsula of India, on
+the heights of Ceylon, and on the volcanic cones of Java, many plants
+occur, either identically the same or representing each other, and at the
+same time representing plants of Europe, not found in the intervening hot
+lowlands. A list of the genera collected on the loftier peaks of Java
+raises a picture of a collection made on a hill in Europe! Still more
+striking is the fact that southern Australian forms are clearly represented
+by plants growing on the summits of the mountains of Borneo. Some of these
+Australian forms, as I hear from Dr. Hooker, extend along the heights of
+the peninsula of Malacca, and are thinly scattered, on the one hand over
+India and on the other as far north as Japan.
+
+On the southern mountains of Australia, Dr. F. Müller has discovered
+several European species; other species, not introduced by man, occur on
+the lowlands; and a long list can be given, as I am informed by Dr. Hooker,
+of European genera, found in Australia, but not in the intermediate torrid
+regions. In the admirable 'Introduction to the Flora of New Zealand,' by
+Dr. Hooker, analogous and striking facts are given in regard to the plants
+of that large island. Hence we see that throughout the world, the plants
+growing on the {376} more lofty mountains, and on the temperate lowlands of
+the northern and southern hemispheres, are sometimes identically the same;
+but they are much oftener specifically distinct, though related to each
+other in a most remarkable manner.
+
+This brief abstract applies to plants alone: some strictly analogous facts
+could be given on the distribution of terrestrial animals. In marine
+productions, similar cases occur; as an example, I may quote a remark by
+the highest authority, Prof. Dana, that "it is certainly a wonderful fact
+that New Zealand should have a closer resemblance in its Crustacea to Great
+Britain, its antipode, than to any other part of the world." Sir J.
+Richardson, also, speaks of the reappearance on the shores of New Zealand,
+Tasmania, &c., of northern forms of fish. Dr. Hooker informs me that
+twenty-five species of Algæ are common to New Zealand and to Europe, but
+have not been found in the intermediate tropical seas.
+
+It should be observed that the northern species and forms found in the
+southern parts of the southern hemisphere, and on the mountain-ranges of
+the intertropical regions, are not arctic, but belong to the northern
+temperate zones. As Mr. H. C. Watson has recently remarked, "In receding
+from polar towards equatorial latitudes, the Alpine or mountain floras
+really become less and less arctic." Many of the forms living on the
+mountains of the warmer regions of the earth and in the southern hemisphere
+are of doubtful value, being ranked by some naturalists as specifically
+distinct, by others as varieties; but some are certainly identical, and
+many, though closely related to northern forms, must be ranked as distinct
+species.
+
+Now let us see what light can be thrown on the foregoing facts, on the
+belief, supported as it is by a large {377} body of geological evidence,
+that the whole world, or a large part of it, was during the Glacial period
+simultaneously much colder than at present. The Glacial period, as measured
+by years, must have been very long; and when we remember over what vast
+spaces some naturalised plants and animals have spread within a few
+centuries, this period will have been ample for any amount of migration. As
+the cold came slowly on, all the tropical plants and other productions will
+have retreated from both sides towards the equator, followed in the rear by
+the temperate productions, and these by the arctic; but with the latter we
+are not now concerned. The tropical plants probably suffered much
+extinction; how much no one can say; perhaps formerly the tropics supported
+as many species as we see at the present day crowded together at the Cape
+of Good Hope, and in parts of temperate Australia. As we know that many
+tropical plants and animals can withstand a considerable amount of cold,
+many might have escaped extermination during a moderate fall of
+temperature, more especially by escaping into the lowest, most protected,
+and warmest districts. But the great fact to bear in mind is, that all
+tropical productions will have suffered to a certain extent. On the other
+hand, the temperate productions, after migrating nearer to the equator,
+though they will have been placed under somewhat new conditions, will have
+suffered less. And it is certain that many temperate plants, if protected
+from the inroads of competitors, can withstand a much warmer climate than
+their own. Hence, it seems to me possible, bearing in mind that the
+tropical productions were in a suffering state and could not have presented
+a firm front against intruders, that a certain number of the more vigorous
+and dominant temperate forms might have penetrated the native ranks and
+have reached or {378} even crossed the equator. The invasion would, of
+course, have been greatly favoured by high land, and perhaps by a dry
+climate; for Dr. Falconer informs me that it is the damp with the heat of
+the tropics which is so destructive to perennial plants from a temperate
+climate. On the other hand, the most humid and hottest districts will have
+afforded an asylum to the tropical natives. The mountain-ranges north-west
+of the Himalaya, and the long line of the Cordillera, seem to have afforded
+two great lines of invasion: and it is a striking fact, lately communicated
+to me by Dr. Hooker, that all the flowering plants, about forty-six in
+number, common to Tierra del Fuego and to Europe still exist in North
+America, which must have lain on the line of march. But I do not doubt that
+some temperate productions entered and crossed even the _lowlands_ of the
+tropics at the period when the cold was most intense,--when arctic forms
+had migrated some twenty-five degrees of latitude from their native country
+and covered the land at the foot of the Pyrenees. At this period of extreme
+cold, I believe that the climate under the equator at the level of the sea
+was about the same with that now felt there at the height of six or seven
+thousand feet. During this the coldest period, I suppose that large spaces
+of the tropical lowlands were clothed with a mingled tropical and temperate
+vegetation, like that now growing with strange luxuriance at the base of
+the Himalaya, as graphically described by Hooker.
+
+Thus, as I believe, a considerable number of plants, a few terrestrial
+animals, and some marine productions, migrated during the Glacial period
+from the northern and southern temperate zones into the intertropical
+regions, and some even crossed the equator. As the warmth returned, these
+temperate forms would naturally ascend the higher mountains, being
+exterminated on the {379} lowlands; those which had not reached the equator
+would re-migrate northward or southward towards their former homes; but the
+forms, chiefly northern, which had crossed the equator, would travel still
+further from their homes into the more temperate latitudes of the opposite
+hemisphere. Although we have reason to believe from geological evidence
+that the whole body of arctic shells underwent scarcely any modification
+during their long southern migration and re-migration northward, the case
+may have been wholly different with those intruding forms which settled
+themselves on the intertropical mountains, and in the southern hemisphere.
+These being surrounded by strangers will have had to compete with many new
+forms of life; and it is probable that selected modifications in their
+structure, habits, and constitutions will have profited them. Thus many of
+these wanderers, though still plainly related by inheritance to their
+brethren of the northern or southern hemispheres, now exist in their new
+homes as well-marked varieties or as distinct species.
+
+It is a remarkable fact, strongly insisted on by Hooker in regard to
+America, and by Alph. de Candolle in regard to Australia, that many more
+identical plants and allied forms have apparently migrated from the north
+to the south, than in a reversed direction. We see, however, a few southern
+vegetable forms on the mountains of Borneo and Abyssinia. I suspect that
+this preponderant migration from north to south is due to the greater
+extent of land in the north, and to the northern forms having existed in
+their own homes in greater numbers, and having consequently been advanced
+through natural selection and competition to a higher stage of perfection
+or dominating power, than the southern forms. And thus, when they became
+commingled during the Glacial period, the northern forms {380} were enabled
+to beat the less powerful southern forms. Just in the same manner as we see
+at the present day, that very many European productions cover the ground in
+La Plata, and in a lesser degree in Australia, and have to a certain extent
+beaten the natives; whereas extremely few southern forms have become
+naturalised in any part of Europe, though hides, wool, and other objects
+likely to carry seeds have been largely imported into Europe during the
+last two or three centuries from La Plata, and during the last thirty or
+forty years from Australia. Something of the same kind must have occurred
+on the intertropical mountains: no doubt before the Glacial period they
+were stocked with endemic Alpine forms; but these have almost everywhere
+largely yielded to the more dominant forms, generated in the larger areas
+and more efficient workshops of the north. In many islands the native
+productions are nearly equalled or even outnumbered by the naturalised; and
+if the natives have not been actually exterminated, their numbers have been
+greatly reduced, and this is the first stage towards extinction. A mountain
+is an island on the land; and the intertropical mountains before the
+Glacial period must have been completely isolated; and I believe that the
+productions of these islands on the land yielded to those produced within
+the larger areas of the north, just in the same way as the productions of
+real islands have everywhere lately yielded to continental forms,
+naturalised by man's agency.
+
+I am far from supposing that all difficulties are removed on the view here
+given in regard to the range and affinities of the allied species which
+live in the northern and southern temperate zones and on the mountains of
+the intertropical regions. Very many difficulties remain to be solved. I do
+not pretend to {381} indicate the exact lines and means of migration, or
+the reason why certain species and not others have migrated; why certain
+species have been modified and have given rise to new groups of forms, and
+others have remained unaltered. We cannot hope to explain such facts, until
+we can say why one species and not another becomes naturalised by man's
+agency in a foreign land; why one ranges twice or thrice as far, and is
+twice or thrice as common, as another species within their own homes.
+
+I have said that many difficulties remain to be solved: some of the most
+remarkable are stated with admirable clearness by Dr. Hooker in his
+botanical works on the antarctic regions. These cannot be here discussed. I
+will only say that as far as regards the occurrence of identical species at
+points so enormously remote as Kerguelen Land, New Zealand, and Fuegia, I
+believe that towards the close of the Glacial period, icebergs, as
+suggested by Lyell, have been largely concerned in their dispersal. But the
+existence of several quite distinct species, belonging to genera
+exclusively confined to the south, at these and other distant points of the
+southern hemisphere, is, on my theory of descent with modification, a far
+more remarkable case of difficulty. For some of these species are so
+distinct, that we cannot suppose that there has been time since the
+commencement of the Glacial period for their migration, and for their
+subsequent modification to the necessary degree. The facts seem to me to
+indicate that peculiar and very distinct species have migrated in radiating
+lines from some common centre; and I am inclined to look in the southern,
+as in the northern hemisphere, to a former and warmer period, before the
+commencement of the Glacial period, when the antarctic lands, now covered
+with ice, supported a highly peculiar {382} and isolated flora. I suspect
+that before this flora was exterminated by the Glacial epoch, a few forms
+were widely dispersed to various points of the southern hemisphere by
+occasional means of transport, and by the aid, as halting-places, of
+existing and now sunken islands: By these means, as I believe, the southern
+shores of America, Australia, New Zealand, have become slightly tinted by
+the same peculiar forms of vegetable life.
+
+Sir C. Lyell in a striking passage has speculated, in language almost
+identical with mine, on the effects of great alternations of climate on
+geographical distribution. I believe that the world has recently felt one
+of his great cycles of change; and that on this view, combined with
+modification through natural selection, a multitude of facts in the present
+distribution both of the same and of allied forms of life can be explained.
+The living waters may be said to have flowed during one short period from
+the north and from the south, and to have crossed at the equator; but to
+have flowed with greater force from the north so as to have freely
+inundated the south. As the tide leaves its drift in horizontal lines,
+though rising higher on the shores where the tide rises highest, so have
+the living waters left their living drift on our mountain-summits, in a
+line gently rising from the arctic lowlands to a great height under the
+equator. The various beings thus left stranded may be compared with savage
+races of man, driven up and surviving in the mountain-fastnesses of almost
+every land, which serve as a record, full of interest to us, of the former
+inhabitants of the surrounding lowlands.
+
+       *       *       *       *       *
+
+
+{383}
+
+CHAPTER XII.
+
+GEOGRAPHICAL DISTRIBUTION--_continued_.
+
+    Distribution of fresh-water productions--On the inhabitants of oceanic
+    islands--Absence of Batrachians and of terrestrial Mammals--On the
+    relation of the inhabitants of islands to those of the nearest
+    mainland--On colonisation from the nearest source with subsequent
+    modification--Summary of the last and present chapters.
+
+As lakes and river-systems are separated from each other by barriers of
+land, it might have been thought that fresh-water productions would not
+have ranged widely within the same country, and as the sea is apparently a
+still more impassable barrier, that they never would have extended to
+distant countries. But the case is exactly the reverse. Not only have many
+fresh-water species, belonging to quite different classes, an enormous
+range, but allied species prevail in a remarkable manner throughout the
+world. I well remember, when first collecting in the fresh waters of
+Brazil, feeling much surprise at the similarity of the fresh-water insects,
+shells, &c., and at the dissimilarity of the surrounding terrestrial
+beings, compared with those of Britain.
+
+But this power in fresh-water productions of ranging widely, though so
+unexpected, can, I think, in most cases be explained by their having become
+fitted, in a manner highly useful to them, for short and frequent
+migrations from pond to pond, or from stream to stream; and liability to
+wide dispersal would follow from this capacity as an almost necessary
+consequence. We can here consider only a few cases. In regard to {384}
+fish, I believe that the same species never occur in the fresh waters of
+distant continents. But on the same continent the species often range
+widely and almost capriciously; for two river-systems will have some fish
+in common and some different. A few facts seem to favour the possibility of
+their occasional transport by accidental means; like that of the live fish
+not rarely dropped by whirlwinds in India, and the vitality of their ova
+when removed from the water. But I am inclined to attribute the dispersal
+of fresh-water fish mainly to slight changes within the recent period in
+the level of the land, having caused rivers to flow into each other.
+Instances, also, could be given of this having occurred during floods,
+without any change of level. We have evidence in the loess of the Rhine of
+considerable changes of level in the land within a very recent geological
+period, and when the surface was peopled by existing land and fresh-water
+shells. The wide difference of the fish on opposite sides of continuous
+mountain-ranges, which from an early period must have parted river-systems
+and completely prevented their inosculation, seems to lead to this same
+conclusion. With respect to allied fresh-water fish occurring at very
+distant points of the world, no doubt there are many cases which cannot at
+present be explained: but some fresh-water fish belong to very ancient
+forms, and in such cases there will have been ample time for great
+geographical changes, and consequently time and means for much migration.
+In the second place, salt-water fish can with care be slowly accustomed to
+live in fresh water; and, according to Valenciennes, there is hardly a
+single group of fishes confined exclusively to fresh water, so that we may
+imagine that a marine member of a fresh-water group might travel far along
+the shores of the sea, and {385} subsequently become modified and adapted
+to the fresh waters of a distant land.
+
+Some species of fresh-water shells have a very wide range, and allied
+species, which, on my theory, are descended from a common parent and must
+have proceeded from a single source, prevail throughout the world. Their
+distribution at first perplexed me much, as their ova are not likely to be
+transported by birds, and they are immediately killed by sea-water, as are
+the adults. I could not even understand how some naturalised species have
+rapidly spread throughout the same country. But two facts, which I have
+observed--and no doubt many others remain to be observed--throw some light
+on this subject. When a duck suddenly emerges from a pond covered with
+duck-weed, I have twice seen these little plants adhering to its back; and
+it has happened to me, in removing a little duckweed from one aquarium to
+another, that I have quite unintentionally stocked the one with fresh-water
+shells from the other. But another agency is perhaps more effectual: I
+suspended a duck's feet, which might represent those of a bird sleeping in
+a natural pond, in an aquarium, where many ova of fresh-water shells were
+hatching; and I found that numbers of the extremely minute and just-hatched
+shells crawled on the feet, and clung to them so firmly that when taken out
+of the water they could not be jarred off, though at a somewhat more
+advanced age they would voluntarily drop off. These just hatched molluscs,
+though aquatic in their nature, survived on the duck's feet, in damp air,
+from twelve to twenty hours; and in this length of time a duck or heron
+might fly at least six or seven hundred miles, and would be sure to alight
+on a pool or rivulet, if blown across sea to an oceanic island or to any
+other distant point. Sir Charles Lyell also {386} informs me that a Dyticus
+has been caught with an Ancylus (a fresh-water shell like a limpet) firmly
+adhering to it; and a water-beetle of the same family, a Colymbetes, once
+flew on board the 'Beagle,' when forty-five miles distant from the nearest
+land: how much farther it might have flown with a favouring gale no one can
+tell.
+
+With respect to plants, it has long been known what enormous ranges many
+fresh-water and even marsh-species have, both over continents and to the
+most remote oceanic islands. This is strikingly shown, as remarked by Alph.
+de Candolle, in large groups of terrestrial plants, which have only a very
+few aquatic members; for these latter seem immediately to acquire, as if in
+consequence, a very wide range. I think favourable means of dispersal
+explain this fact. I have before mentioned that earth occasionally, though
+rarely, adheres in some quantity to the feet and beaks of birds. Wading
+birds, which frequent the muddy edges of ponds, if suddenly flushed, would
+be the most likely to have muddy feet. Birds of this order I can show are
+the greatest wanderers, and are occasionally found on the most remote and
+barren islands in the open ocean; they would not be likely to alight on the
+surface of the sea, so that the dirt would not be washed off their feet;
+when making land, they would be sure to fly to their natural fresh-water
+haunts. I do not believe that botanists are aware how charged the mud of
+ponds is with seeds: I have tried several little experiments, but will here
+give only the most striking case: I took in February three table-spoonfuls
+of mud from three different points, beneath water, on the edge of a little
+pond; this mud when dry weighed only 6¾ ounces; I kept it covered up in my
+study for six months, pulling up and counting each plant as it grew; the
+plants were {387} of many kinds, and were altogether 537 in number; and yet
+the viscid mud was all contained in a breakfast cup! Considering these
+facts, I think it would be an inexplicable circumstance if water-birds did
+not transport the seeds of fresh-water plants to vast distances, and if
+consequently the range of these plants was not very great. The same agency
+may have come into play with the eggs of some of the smaller fresh-water
+animals.
+
+Other and unknown agencies probably have also played a part. I have stated
+that fresh-water fish eat some kinds of seeds, though they reject many
+other kinds after having swallowed them; even small fish swallow seeds of
+moderate size, as of the yellow water-lily and Potamogeton. Herons and
+other birds, century after century, have gone on daily devouring fish; they
+then take flight and go to other waters, or are blown across the sea; and
+we have seen that seeds retain their power of germination, when rejected in
+pellets or in excrement, many hours afterwards. When I saw the great size
+of the seeds of that fine water-lily, the Nelumbium, and remembered Alph.
+de Candolle's remarks on this plant, I thought that its distribution must
+remain quite inexplicable; but Audubon states that he found the seeds of
+the great southern water-lily (probably, according to Dr. Hooker, the
+Nelumbium luteum) in a heron's stomach; although I do not know the fact,
+yet analogy makes me believe that a heron flying to another pond and
+getting a hearty meal of fish, would probably reject from its stomach a
+pellet containing the seeds of the Nelumbium undigested; or the seeds might
+be dropped by the bird whilst feeding its young, in the same way as fish
+are known sometimes to be dropped.
+
+In considering these several means of distribution, {388} it should be
+remembered that when a pond or stream is first formed, for instance, on a
+rising islet, it will be unoccupied; and a single seed or egg will have a
+good chance of succeeding. Although there will always be a struggle for
+life between the individuals of the species, however few, already occupying
+any pond, yet as the number of kinds is small, compared with those on the
+land, the competition will probably be less severe between aquatic than
+between terrestrial species; consequently an intruder from the waters of a
+foreign country, would have a better chance of seizing on a place, than in
+the case of terrestrial colonists. We should, also, remember that some,
+perhaps many, freshwater productions are low in the scale of nature, and
+that we have reason to believe that such low beings change or become
+modified less quickly than the high; and this will give longer time than
+the average for the migration of the same aquatic species. We should not
+forget the probability of many species having formerly ranged as
+continuously as fresh-water productions ever can range, over immense areas,
+and having subsequently become extinct in intermediate regions. But the
+wide distribution of fresh-water plants and of the lower animals, whether
+retaining the same identical form or in some degree modified, I believe
+mainly depends on the wide dispersal of their seeds and eggs by animals,
+more especially by fresh-water birds, which have large powers of flight,
+and naturally travel from one to another and often distant piece of water.
+Nature, like a careful gardener, thus takes her seeds from a bed of a
+particular nature, and drops them in another equally well fitted for them.
+
+
+
+_On the Inhabitants of Oceanic Islands._--We now come to the last of the
+three classes of facts, which I {389} have selected as presenting the
+greatest amount of difficulty, on the view that all the individuals both of
+the same and of allied species have descended from a single parent; and
+therefore have all proceeded from a common birthplace, notwithstanding that
+in the course of time they have come to inhabit distant points of the
+globe. I have already stated that I cannot honestly admit Forbes's view on
+continental extensions, which, if legitimately followed out, would lead to
+the belief that within the recent period all existing islands have been
+nearly or quite joined to some continent. This view would remove many
+difficulties, but it would not, I think, explain all the facts in regard to
+insular productions. In the following remarks I shall not confine myself to
+the mere question of dispersal; but shall consider some other facts, which
+bear on the truth of the two theories of independent creation and of
+descent with modification.
+
+The species of all kinds which inhabit oceanic islands are few in number
+compared with those on equal continental areas: Alph. de Candolle admits
+this for plants, and Wollaston for insects. If we look to the large size
+and varied stations of New Zealand, extending over 780 miles of latitude,
+and compare its flowering plants, only 750 in number, with those on an
+equal area at the Cape of Good Hope or in Australia, we must, I think,
+admit that something quite independently of any difference in physical
+conditions has caused so great a difference in number. Even the uniform
+county of Cambridge has 847 plants, and the little island of Anglesea 764,
+but a few ferns and a few introduced plants are included in these numbers,
+and the comparison in some other respects is not quite fair. We have
+evidence that the barren island of Ascension aboriginally possessed under
+half-a-dozen flowering plants; {390} yet many have become naturalised on
+it, as they have on New Zealand and on every other oceanic island which can
+be named. In St. Helena there is reason to believe that the naturalised
+plants and animals have nearly or quite exterminated many native
+productions. He who admits the doctrine of the creation of each separate
+species, will have to admit, that a sufficient number of the best adapted
+plants and animals have not been created on oceanic islands; for man has
+unintentionally stocked them from various sources far more fully and
+perfectly than has nature.
+
+Although in oceanic islands the number of kinds of inhabitants is scanty,
+the proportion of endemic species (_i.e._ those found nowhere else in the
+world) is often extremely large. If we compare, for instance, the number of
+the endemic land-shells in Madeira, or of the endemic birds in the
+Galapagos Archipelago, with the number found on any continent, and then
+compare the area of the islands with that of the continent, we shall see
+that this is true. This fact might have been expected on my theory, for, as
+already explained, species occasionally arriving after long intervals in a
+new and isolated district, and having to compete with new associates, will
+be eminently liable to modification, and will often produce groups of
+modified descendants. But it by no means follows, that, because in an
+island nearly all the species of one class are peculiar, those of another
+class, or of another section of the same class, are peculiar; and this
+difference seems to depend partly on the species which do not become
+modified having immigrated with facility and in a body, so that their
+mutual relations have not been much disturbed; and partly on the frequent
+arrival of unmodified immigrants from the mother-country, and the
+consequent intercrossing with them. With respect to the effects of this
+intercrossing, {391} it should be remembered that the offspring of such
+crosses would almost certainly gain in vigour; so that even an occasional
+cross would produce more effect than might at first have been anticipated.
+To give a few examples: in the Galapagos Islands nearly every land-bird,
+but only two out of the eleven marine birds, are peculiar; and it is
+obvious that marine birds could arrive at these islands more easily than
+land-birds. Bermuda, on the other hand, which lies at about the same
+distance from North America as the Galapagos Islands do from South America,
+and which has a very peculiar soil, does not possess one endemic land-bird;
+and we know from Mr. J. M. Jones's admirable account of Bermuda, that very
+many North American birds, during their great annual migrations, visit
+either periodically or occasionally this island. Madeira does not possess
+one peculiar bird, and many European and African birds are almost every
+year blown there, as I am informed by Mr. E. V. Harcourt. So that these two
+islands of Bermuda and Madeira have been stocked by birds, which for long
+ages have struggled together in their former homes, and have become
+mutually adapted to each other; and when settled in their new homes, each
+kind will have been kept by the others to their proper places and habits,
+and will consequently have been little liable to modification. Any tendency
+to modification will, also, have been checked by intercrossing with the
+unmodified immigrants from the mother-country. Madeira, again, is inhabited
+by a wonderful number of peculiar land-shells, whereas not one species of
+sea-shell is confined to its shores: now, though we do not know how
+sea-shells are dispersed, yet we can see that their eggs or larvae, perhaps
+attached to seaweed or floating timber, or to the feet of wading-birds,
+might be transported far more easily than {392} land-shells, across three
+or four hundred miles of open sea. The different orders of insects in
+Madeira apparently present analogous facts.
+
+Oceanic islands are sometimes deficient in certain classes, and their
+places are apparently occupied by the other inhabitants; in the Galapagos
+Islands reptiles, and in New Zealand gigantic wingless birds, take the
+place of mammals. In the plants of the Galapagos Islands, Dr. Hooker has
+shown that the proportional numbers of the different orders are very
+different from what they are elsewhere. Such cases are generally accounted
+for by the physical conditions of the islands; but this explanation seems
+to me not a little doubtful. Facility of immigration, I believe, has been
+at least as important as the nature of the conditions.
+
+Many remarkable little facts could be given with respect to the inhabitants
+of remote islands. For instance, in certain islands not tenanted by
+mammals, some of the endemic plants have beautifully hooked seeds; yet few
+relations are more striking than the adaptation of hooked seeds for
+transportal by the wool and fur of quadrupeds. This case presents no
+difficulty on my view, for a hooked seed might be transported to an island
+by some other means; and the plant then becoming slightly modified, but
+still retaining its hooked seeds, would form an endemic species, having as
+useless an appendage as any rudimentary organ,--for instance, as the
+shrivelled wings under the soldered elytra of many insular beetles. Again,
+islands often possess trees or bushes belonging to orders which elsewhere
+include only herbaceous species; now trees, as Alph. de Candolle has shown,
+generally have, whatever the cause may be, confined ranges. Hence trees
+would be little likely to reach distant oceanic islands; and an herbaceous
+plant, though it would have no chance of {393} successfully competing in
+stature with a fully developed tree, when established on an island and
+having to compete with herbaceous plants alone, might readily gain an
+advantage by growing taller and taller and overtopping the other plants. If
+so, natural selection would often tend to add to the stature of herbaceous
+plants when growing on an oceanic island, to whatever order they belonged,
+and thus convert them first into bushes and ultimately into trees.
+
+With respect to the absence of whole orders on oceanic islands, Bory St.
+Vincent long ago remarked that Batrachians (frogs, toads, newts) have never
+been found on any of the many islands with which the great oceans are
+studded. I have taken pains to verify this assertion, and I have found it
+strictly true. I have, however, been assured that a frog exists on the
+mountains of the great island of New Zealand; but I suspect that this
+exception (if the information be correct) may be explained through glacial
+agency. This general absence of frogs, toads, and newts on so many oceanic
+islands cannot be accounted for by their physical conditions; indeed it
+seems that islands are peculiarly well fitted for these animals; for frogs
+have been introduced into Madeira, the Azores, and Mauritius, and have
+multiplied so as to become a nuisance. But as these animals and their spawn
+are known to be immediately killed by sea-water, on my view we can see that
+there would be great difficulty in their transportal across the sea, and
+therefore why they do not exist on any oceanic island. But why, on the
+theory of creation, they should not have been created there, it would be
+very difficult to explain.
+
+Mammals offer another and similar case. I have carefully searched the
+oldest voyages, but have not finished my search; as yet I have not found a
+single {394} instance, free from doubt, of a terrestrial mammal (excluding
+domesticated animals kept by the natives) inhabiting an island situated
+above 300 miles from a continent or great continental island; and many
+islands situated at a much less distance are equally barren. The Falkland
+Islands, which are inhabited by a wolf-like fox, come nearest to an
+exception; but this group cannot be considered as oceanic, as it lies on a
+bank connected with the mainland; moreover, icebergs formerly brought
+boulders to its western shores, and they may have formerly transported
+foxes, as so frequently now happens in the arctic regions. Yet it cannot be
+said that small islands will not support small mammals, for they occur in
+many parts of the world on very small islands, if close to a continent; and
+hardly an island can be named on which our smaller quadrupeds have not
+become naturalised and greatly multiplied. It cannot be said, on the
+ordinary view of creation, that there has not been time for the creation of
+mammals; many volcanic islands are sufficiently ancient, as shown by the
+stupendous degradation which they have suffered and by their tertiary
+strata: there has also been time for the production of endemic species
+belonging to other classes; and on continents it is thought that mammals
+appear and disappear at a quicker rate than other and lower animals. Though
+terrestrial mammals do not occur on oceanic islands, aërial mammals do
+occur on almost every island. New Zealand possesses two bats found nowhere
+else in the world: Norfolk Island, the Viti Archipelago, the Bonin Islands,
+the Caroline and Marianne Archipelagoes, and Mauritius, all possess their
+peculiar bats. Why, it may be asked, has the supposed creative force
+produced bats and no other mammals on remote islands? On my view this
+question can easily be answered; for no {395} terrestrial mammal can be
+transported across a wide space of sea, but bats can fly across. Bats have
+been seen wandering by day far over the Atlantic Ocean; and two North
+American species either regularly or occasionally visit Bermuda, at the
+distance of 600 miles from the mainland. I hear from Mr. Tomes, who has
+specially studied this family, that many of the same species have enormous
+ranges, and are found on continents and on far distant islands. Hence we
+have only to suppose that such wandering species have been modified through
+natural selection in their new homes in relation to their new position, and
+we can understand the presence of endemic bats on islands, with the absence
+of all terrestrial mammals.
+
+Besides the absence of terrestrial mammals in relation to the remoteness of
+islands from continents, there is also a relation, to a certain extent
+independent of distance, between the depth of the sea separating an island
+from the neighbouring mainland, and the presence in both of the same
+mammiferous species or of allied species in a more or less modified
+condition. Mr. Windsor Earl has made some striking observations on this
+head in regard to the great Malay Archipelago, which is traversed near
+Celebes by a space of deep ocean; and this space separates two widely
+distinct mammalian faunas. On either side the islands are situated on
+moderately deep submarine banks, and they are inhabited by closely allied
+or identical quadrupeds. No doubt some few anomalies occur in this great
+archipelago, and there is much difficulty in forming a judgment in some
+cases owing to the probable naturalisation of certain mammals through man's
+agency; but we shall soon have much light thrown on the natural history of
+this archipelago by the admirable zeal and researches of Mr. Wallace. I
+have not as yet had time to {396} follow up this subject in all other
+quarters of the world; but as far as I have gone, the relation generally
+holds good. We see Britain separated by a shallow channel from Europe, and
+the mammals are the same on both sides; we meet with analogous facts on
+many islands separated by similar channels from Australia. The West Indian
+Islands stand on a deeply submerged bank, nearly 1000 fathoms in depth, and
+here we find American forms, but the species and even the genera are
+distinct. As the amount of modification in all cases depends to a certain
+degree on the lapse of time, and as during changes of level it is obvious
+that islands separated by shallow channels are more likely to have been
+continuously united within a recent period to the mainland than islands
+separated by deeper channels, we can understand the frequent relation
+between the depth of the sea and the degree of affinity of the mammalian
+inhabitants of islands with those of a neighbouring continent,--an
+inexplicable relation on the view of independent acts of creation.
+
+All the foregoing remarks on the inhabitants of oceanic islands,--namely,
+the scarcity of kinds--the richness in endemic forms in particular classes
+or sections of classes,--the absence of whole groups, as of batrachians,
+and of terrestrial mammals notwithstanding the presence of aërial
+bats,--the singular proportions of certain orders of plants,--herbaceous
+forms having been developed into trees, &c.,--seem to me to accord better
+with the view of occasional means of transport having been largely
+efficient in the long course of time, than with the view of all our oceanic
+islands having been formerly connected by continuous land with the nearest
+continent; for on this latter view the migration would probably have been
+more complete; and if modification be admitted, all the forms of life would
+have been more {397} equally modified, in accordance with the paramount
+importance of the relation of organism to organism.
+
+I do not deny that there are many and grave difficulties in understanding
+how several of the inhabitants of the more remote islands, whether still
+retaining the same specific form or modified since their arrival, could
+have reached their present homes. But the probability of many islands
+having existed as halting-places, of which not a wreck now remains, must
+not be overlooked. I will here give a single instance of one of the cases
+of difficulty. Almost all oceanic islands, even the most isolated and
+smallest, are inhabited by land-shells, generally by endemic species, but
+sometimes by species found elsewhere. Dr. Aug. A. Gould has given several
+interesting cases in regard to the land-shells of the islands of the
+Pacific. Now it is notorious that land-shells are very easily killed by
+salt; their eggs, at least such as I have tried, sink in sea-water and are
+killed by it. Yet there must be, on my view, some unknown, but highly
+efficient means for their transportal. Would the just-hatched young
+occasionally crawl on and adhere to the feet of birds roosting on the
+ground, and thus get transported? It occurred to me that land-shells, when
+hybernating and having a membranous diaphragm over the mouth of the shell,
+might be floated in chinks of drifted timber across moderately wide arms of
+the sea. And I found that several species did in this state withstand
+uninjured an immersion in sea-water during seven days: one of these shells
+was the Helix pomatia, and after it had again hybernated I put it in
+sea-water for twenty days, and it perfectly recovered. As this species has
+a thick calcareous operculum, I removed it, and when it had formed a new
+membranous one, I immersed it for fourteen days in sea-water, and it
+recovered and crawled away: but more experiments are wanted on this head.
+{398}
+
+The most striking and important fact for us in regard to the inhabitants of
+islands, is their affinity to those of the nearest mainland, without being
+actually the same species. Numerous instances could be given of this fact.
+I will give only one, that of the Galapagos Archipelago, situated under the
+equator, between 500 and 600 miles from the shores of South America. Here
+almost every product of the land and water bears the unmistakeable stamp of
+the American continent. There are twenty-six land-birds, and twenty-five of
+these are ranked by Mr. Gould as distinct species, supposed to have been
+created here; yet the close affinity of most of these birds to American
+species in every character, in their habits, gestures, and tones of voice,
+was manifest. So it is with the other animals, and with nearly all the
+plants, as shown by Dr. Hooker in his admirable memoir on the Flora of this
+archipelago. The naturalist, looking at the inhabitants of these volcanic
+islands in the Pacific, distant several hundred miles from the continent,
+yet feels that he is standing on American land. Why should this be so? why
+should the species which are supposed to have been created in the Galapagos
+Archipelago, and nowhere else, bear so plain a stamp of affinity to those
+created in America? There is nothing in the conditions of life, in the
+geological nature of the islands, in their height or climate, or in the
+proportions in which the several classes are associated together, which
+resembles closely the conditions of the South American coast: in fact there
+is a considerable dissimilarity in all these respects. On the other hand,
+there is a considerable degree of resemblance in the volcanic nature of the
+soil, in climate, height, and size of the islands, between the Galapagos
+and Cape de Verde Archipelagos: but what an entire and absolute difference
+in their inhabitants! The inhabitants of the Cape de Verde Islands are
+related to {399} those of Africa, like those of the Galapagos to America. I
+believe this grand fact can receive no sort of explanation on the ordinary
+view of independent creation; whereas on the view here maintained, it is
+obvious that the Galapagos Islands would be likely to receive colonists,
+whether by occasional means of transport or by formerly continuous land,
+from America; and the Cape de Verde Islands from Africa; and that such
+colonists would be liable to modification;--the principle of inheritance
+still betraying their original birthplace.
+
+Many analogous facts could be given: indeed it is an almost universal rule
+that the endemic productions of islands are related to those of the nearest
+continent, or of other near islands. The exceptions are few, and most of
+them can be explained. Thus the plants of Kerguelen Land, though standing
+nearer to Africa than to America, are related, and that very closely, as we
+know from Dr. Hooker's account, to those of America: but on the view that
+this island has been mainly stocked by seeds brought with earth and stones
+on icebergs, drifted by the prevailing currents, this anomaly disappears.
+New Zealand in its endemic plants is much more closely related to
+Australia, the nearest mainland, than to any other region: and this is what
+might have been expected; but it is also plainly related to South America,
+which, although the next nearest continent, is so enormously remote, that
+the fact becomes an anomaly. But this difficulty almost disappears on the
+view that both New Zealand, South America, and other southern lands were
+long ago partially stocked from a nearly intermediate though distant point,
+namely from the antarctic islands, when they were clothed with vegetation,
+before the commencement of the Glacial period. The affinity, which, though
+feeble, I am assured by Dr. Hooker is real, between the flora of the
+south-western corner of Australia and of the Cape of Good {400} Hope, is a
+far more remarkable case, and is at present inexplicable: but this affinity
+is confined to the plants, and will, I do not doubt, be some day explained.
+
+The law which causes the inhabitants of an archipelago, though specifically
+distinct, to be closely allied to those of the nearest continent, we
+sometimes see displayed on a small scale, yet in a most interesting manner,
+within the limits of the same archipelago. Thus the several islands of the
+Galapagos Archipelago are tenanted, as I have elsewhere shown, in a quite
+marvellous manner, by very closely related species; so that the inhabitants
+of each separate island, though mostly distinct, are related in an
+incomparably closer degree to each other than to the inhabitants of any
+other part of the world. And this is just what might have been expected on
+my view, for the islands are situated so near each other that they would
+almost certainly receive immigrants from the same original source, or from
+each other. But this dissimilarity between the endemic inhabitants of the
+islands may be used as an argument against my views; for it may be asked,
+how has it happened in the several islands situated within sight of each
+other, having the same geological nature, the same height, climate, &c.,
+that many of the immigrants should have been differently modified, though
+only in a small degree. This long appeared to me a great difficulty: but it
+arises in chief part from the deeply-seated error of considering the
+physical conditions of a country as the most important for its inhabitants;
+whereas it cannot, I think, be disputed that the nature of the other
+inhabitants, with which each has to compete, is as least as important, and
+generally a far more important element of success. Now if we look to those
+inhabitants of the Galapagos Archipelago which are found in other parts of
+the world (laying on one side for the moment the {401} endemic species,
+which cannot be here fairly included, as we are considering how they have
+come to be modified since their arrival), we find a considerable amount of
+difference in the several islands. This difference might indeed have been
+expected on the view of the islands having been stocked by occasional means
+of transport--a seed, for instance, of one plant having been brought to one
+island, and that of another plant to another island. Hence when in former
+times an immigrant settled on any one or more of the islands, or when it
+subsequently spread from one island to another, it would undoubtedly be
+exposed to different conditions of life in the different islands, for it
+would have to compete with different sets of organisms: a plant for
+instance, would find the best-fitted ground more perfectly occupied by
+distinct plants in one island than in another, and it would be exposed to
+the attacks of somewhat different enemies. If then it varied, natural
+selection would probably favour different varieties in the different
+islands. Some species, however, might spread and yet retain the same
+character throughout the group, just as we see on continents some species
+spreading widely and remaining the same.
+
+The really surprising fact in this case of the Galapagos Archipelago, and
+in a lesser degree in some analogous instances, is that the new species
+formed in the separate islands have not quickly spread to the other
+islands. But the islands, though in sight of each other, are separated by
+deep arms of the sea, in most cases wider than the British Channel, and
+there is no reason to suppose that they have at any former period been
+continuously united. The currents of the sea are rapid and sweep across the
+archipelago, and gales of wind are extraordinarily rare; so that the
+islands are far more effectually separated from each other than they appear
+to be on a map. Nevertheless a good many {402} species, both those found in
+other parts of the world and those confined to the archipelago, are common
+to the several islands, and we may infer from certain facts that these have
+probably spread from some one island to the others. But we often take, I
+think, an erroneous view of the probability of closely-allied species
+invading each other's territory, when put into free intercommunication.
+Undoubtedly if one species has any advantage whatever over another, it will
+in a very brief time wholly or in part supplant it; but if both are equally
+well fitted for their own places in nature, both probably will hold their
+own places and keep separate for almost any length of time. Being familiar
+with the fact that many species, naturalised through man's agency, have
+spread with astonishing rapidity over new countries, we are apt to infer
+that most species would thus spread; but we should remember that the forms
+which become naturalised in new countries are not generally closely allied
+to the aboriginal inhabitants, but are very distinct species, belonging in
+a large proportion of cases, as shown by Alph. de Candolle, to distinct
+genera. In the Galapagos Archipelago, many even of the birds, though so
+well adapted for flying from island to island, are distinct on each; thus
+there are three closely-allied species of mocking-thrush, each confined to
+its own island. Now let us suppose the mocking-thrush of Chatham Island to
+be blown to Charles Island, which has its own mocking-thrush: why should it
+succeed in establishing itself there? We may safely infer that Charles
+Island is well stocked with its own species, for annually more eggs are
+laid there than can possibly be reared; and we may infer that the
+mocking-thrush peculiar to Charles Island is at least as well fitted for
+its home as is the species peculiar to Chatham Island. Sir C. Lyell and Mr.
+Wollaston have communicated to me a remarkable fact bearing on this {403}
+subject; namely, that Madeira and the adjoining islet of Porto Santo
+possess many distinct but representative land-shells, some of which live in
+crevices of stone; and although large quantities of stone are annually
+transported from Porto Santo to Madeira, yet this latter island has not
+become colonised by the Porto Santo species: nevertheless both islands have
+been colonised by some European land-shells, which no doubt had some
+advantage over the indigenous species. From these considerations I think we
+need not greatly marvel at the endemic and representative species, which
+inhabit the several islands of the Galapagos Archipelago, not having
+universally spread from island to island. In many other instances, as in
+the several districts of the same continent, pre-occupation has probably
+played an important part in checking the commingling of species under the
+same conditions of life. Thus, the south-east and south-west corners of
+Australia have nearly the same physical conditions, and are united by
+continuous land, yet they are inhabited by a vast number of distinct
+mammals, birds, and plants.
+
+The principle which determines the general character of the fauna and flora
+of oceanic islands, namely, that the inhabitants, when not identically the
+same, yet are plainly related to the inhabitants of that region whence
+colonists could most readily have been derived,--the colonists having been
+subsequently modified and better fitted to their new homes,--is of the
+widest application throughout nature. We see this on every mountain, in
+every lake and marsh. For Alpine species, excepting in so far as the same
+forms, chiefly of plants, have spread widely throughout the world during
+the recent Glacial epoch, are related to those of the surrounding
+lowlands;--thus we have in South America, Alpine humming-birds, Alpine
+rodents, Alpine plants, {404} &c., all of strictly American forms, and it
+is obvious that a mountain, as it became slowly upheaved, would naturally
+be colonised from the surrounding lowlands. So it is with the inhabitants
+of lakes and marshes, excepting in so far as great facility of transport
+has given the same general forms to the whole world. We see this same
+principle in the blind animals inhabiting the caves of America and of
+Europe. Other analogous facts could be given. And it will, I believe, be
+universally found to be true, that wherever in two regions, let them be
+ever so distant, many closely-allied or representative species occur, there
+will likewise be found some identical species, showing, in accordance with
+the foregoing view, that at some former period there has been
+intercommunication or migration between the two regions. And wherever many
+closely-allied species occur, there will be found many forms which some
+naturalists rank as distinct species, and some as varieties; these doubtful
+forms showing us the steps in the process of modification.
+
+This relation between the power and extent of migration of a species,
+either at the present time or at some former period under different
+physical conditions, and the existence at remote points of the world of
+other species allied to it, is shown in another and more general way. Mr.
+Gould remarked to me long ago, that in those genera of birds which range
+over the world, many of the species have very wide ranges. I can hardly
+doubt that this rule is generally true, though it would be difficult to
+prove it. Amongst mammals, we see it strikingly displayed in Bats, and in a
+lesser degree in the Felidæ and Canidæ. We see it, if we compare the
+distribution of butterflies and beetles. So it is with most fresh-water
+productions, in which so many genera range over the world, and many
+individual species have {405} enormous ranges. It is not meant that in
+world-ranging genera all the species have a wide range, or even that they
+have on an _average_ a wide range; but only that some of the species range
+very widely; for the facility with which widely-ranging species vary and
+give rise to new forms will largely determine their average range. For
+instance, two varieties of the same species inhabit America and Europe, and
+the species thus has an immense range; but, if the variation had been a
+little greater, the two varieties would have been ranked as distinct
+species, and the common range would have been greatly reduced. Still less
+is it meant, that a species which apparently has the capacity of crossing
+barriers and ranging widely, as in the case of certain powerfully-winged
+birds, will necessarily range widely; for we should never forget that to
+range widely implies not only the power of crossing barriers, but the more
+important power of being victorious in distant lands in the struggle for
+life with foreign associates. But on the view of all the species of a genus
+having descended from a single parent, though now distributed to the most
+remote points of the world, we ought to find, and I believe as a general
+rule we do find, that some at least of the species range very widely; for
+it is necessary that the unmodified parent should range widely, undergoing
+modification during its diffusion, and should place itself under diverse
+conditions favourable for the conversion of its offspring, firstly into new
+varieties and ultimately into new species.
+
+In considering the wide distribution of certain genera, we should bear in
+mind that some are extremely ancient, and must have branched off from a
+common parent at a remote epoch; so that in such cases there will have been
+ample time for great climatal and geographical changes and for accidents of
+transport; and consequently for the migration of some of the species into
+all {406} quarters of the world, where they may have become slightly
+modified in relation to their new conditions. There is, also, some reason
+to believe from geological evidence that organisms low in the scale within
+each great class, generally change at a slower rate than the higher forms;
+and consequently the lower forms will have had a better chance of ranging
+widely and of still retaining the same specific character. This fact,
+together with the seeds and eggs of many low forms being very minute and
+better fitted for distant transportation, probably accounts for a law which
+has long been observed, and which has lately been admirably discussed by
+Alph. de Candolle in regard to plants, namely, that the lower any group of
+organisms is, the more widely it is apt to range.
+
+The relations just discussed,--namely, low and slowly-changing organisms
+ranging more widely than the high,--some of the species of widely-ranging
+genera themselves ranging widely,--such facts, as alpine, lacustrine, and
+marsh productions being related (with the exceptions before specified) to
+those on the surrounding low lands and dry lands, though these stations are
+so different,--the very close relation of the distinct species which
+inhabit the islets of the same archipelago,--and especially the striking
+relation of the inhabitants of each whole archipelago or island to those of
+the nearest mainland,--are, I think, utterly inexplicable on the ordinary
+view of the independent creation of each species, but are explicable on the
+view of colonisation from the nearest or readiest source, together with the
+subsequent modification and better adaptation of the colonists to their new
+homes.
+
+
+
+_Summary of last and present Chapters._--In these chapters I have
+endeavoured to show, that if we make due allowance for our ignorance of the
+full effects of all {407} the changes of climate and of the level of the
+land, which have certainly occurred within the recent period, and of other
+similar changes which may have occurred within the same period; if we
+remember how profoundly ignorant we are with respect to the many and
+curious means of occasional transport,--a subject which has hardly ever
+been properly experimentised on; if we bear in mind how often a species may
+have ranged continuously over a wide area, and then have become extinct in
+the intermediate tracts, I think the difficulties in believing that all the
+individuals of the same species, wherever located, have descended from the
+same parents, are not insuperable. And we are led to this conclusion, which
+has been arrived at by many naturalists under the designation of single
+centres of creation, by some general considerations, more especially from
+the importance of barriers and from the analogical distribution of
+sub-genera, genera, and families.
+
+With respect to the distinct species of the same genus, which on my theory
+must have spread from one parent-source; if we make the same allowances as
+before for our ignorance, and remember that some forms of life change most
+slowly, enormous periods of time being thus granted for their migration, I
+do not think that the difficulties are insuperable; though they often are
+in this case, and in that of the individuals of the same species, extremely
+great.
+
+As exemplifying the effects of climatal changes on distribution, I have
+attempted to show how important has been the influence of the modern
+Glacial period, which I am fully convinced simultaneously affected the
+whole world, or at least great meridional belts. As showing how diversified
+are the means of occasional transport, I have discussed at some little
+length the means of dispersal of fresh-water productions. {408}
+
+If the difficulties be not insuperable in admitting that in the long course
+of time the individuals of the same species, and likewise of allied
+species, have proceeded from some one source; then I think all the grand
+leading facts of geographical distribution are explicable on the theory of
+migration (generally of the more dominant forms of life), together with
+subsequent modification and the multiplication of new forms. We can thus
+understand the high importance of barriers, whether of land or water, which
+separate our several zoological and botanical provinces. We can thus
+understand the localisation of sub-genera, genera, and families; and how it
+is that under different latitudes, for instance in South America, the
+inhabitants of the plains and mountains, of the forests, marshes, and
+deserts, are in so mysterious a manner linked together by affinity, and are
+likewise linked to the extinct beings which formerly inhabited the same
+continent. Bearing in mind that the mutual relation of organism to organism
+is of the highest importance, we can see why two areas having nearly the
+same physical conditions should often be inhabited by very different forms
+of life; for according to the length of time which has elapsed since new
+inhabitants entered one region; according to the nature of the
+communication which allowed certain forms and not others to enter, either
+in greater or lesser numbers; according or not, as those which entered
+happened to come in more or less direct competition with each other and
+with the aborigines; and according as the immigrants were capable of
+varying more or less rapidly, there would ensue in different regions,
+independently of their physical conditions, infinitely diversified
+conditions of life,--there would be an almost endless amount of organic
+action and reaction,--and we should find, as we do find, some groups of
+beings greatly, and some only slightly modified,--some {409} developed in
+great force, some existing in scanty numbers--in the different great
+geographical provinces of the world.
+
+On these same principles, we can understand, as I have endeavoured to show,
+why oceanic islands should have few inhabitants, but of these a great
+number should be endemic or peculiar; and why, in relation to the means of
+migration, one group of beings, even within the same class, should have all
+its species endemic, and another group should have all its species common
+to other quarters of the world. We can see why whole groups of organisms,
+as batrachians and terrestrial mammals, should be absent from oceanic
+islands, whilst the most isolated islands possess their own peculiar
+species of aërial mammals or bats. We can see why there should be some
+relation between the presence of mammals, in a more or less modified
+condition, and the depth of the sea between an island and the mainland. We
+can clearly see why all the inhabitants of an archipelago, though
+specifically distinct on the several islets, should be closely related to
+each other, and likewise be related, but less closely, to those of the
+nearest continent or other source whence immigrants were probably derived.
+We can see why in two areas, however distant from each other, there should
+be a correlation, in the presence of identical species, of varieties, of
+doubtful species, and of distinct but representative species.
+
+As the late Edward Forbes often insisted, there is a striking parallelism
+in the laws of life throughout time and space: the laws governing the
+succession of forms in past times being nearly the same with those
+governing at the present time the differences in different areas. We see
+this in many facts. The endurance of each species and group of species is
+continuous in time; for the exceptions to the rule are so few, that they
+may {410} fairly be attributed to our not having as yet discovered in an
+intermediate deposit the forms which are therein absent, but which occur
+above and below: so in space, it certainly is the general rule that the
+area inhabited by a single species, or by a group of species, is
+continuous; and the exceptions, which are not rare, may, as I have
+attempted to show, be accounted for by migration at some former period
+under different conditions or by occasional means of transport, and by the
+species having become extinct in the intermediate tracts. Both in time and
+space, species and groups of species have their points of maximum
+development. Groups of species, belonging either to a certain period of
+time, or to a certain area, are often characterised by trifling characters
+in common, as of sculpture or colour. In looking to the long succession of
+ages, as in now looking to distant provinces throughout the world, we find
+that some organisms differ little, whilst others belonging to a different
+class, or to a different order, or even only to a different family of the
+same order, differ greatly. In both time and space the lower members of
+each class generally change less than the higher; but there are in both
+cases marked exceptions to the rule. On my theory these several relations
+throughout time and space are intelligible; for whether we look to the
+forms of life which have changed during successive ages within the same
+quarter of the world, or to those which have changed after having migrated
+into distant quarters, in both cases the forms within each class have been
+connected by the same bond of ordinary generation; and the more nearly any
+two forms are related in blood, the nearer they will generally stand to
+each other in time and space; in both cases the laws of variation have been
+the same, and modifications have been accumulated by the same power of
+natural selection.
+
+       *       *       *       *       *
+
+
+{411}
+
+CHAPTER XIII.
+
+MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY: EMBRYOLOGY: RUDIMENTARY
+ORGANS.
+
+    CLASSIFICATION, groups subordinate to groups--Natural system--Rules and
+    difficulties in classification, explained on the theory of descent with
+    modification--Classification of varieties--Descent always used in
+    classification--Analogical or adaptive characters--Affinities, general,
+    complex and radiating--Extinction separates and defines
+    groups--MORPHOLOGY, between members of the same class, between parts of
+    the same individual--EMBRYOLOGY, laws of, explained by variations not
+    supervening at an early age, and being inherited at a corresponding
+    age--RUDIMENTARY ORGANS; their origin explained--Summary.
+
+From the first dawn of life, all organic beings are found to resemble each
+other in descending degrees, so that they can be classed in groups under
+groups. This classification is evidently not arbitrary like the grouping of
+the stars in constellations. The existence of groups would have been of
+simple signification, if one group had been exclusively fitted to inhabit
+the land, and another the water; one to feed on flesh, another on vegetable
+matter, and so on; but the case is widely different in nature; for it is
+notorious how commonly members of even the same sub-group have different
+habits. In our second and fourth chapters, on Variation and on Natural
+Selection, I have attempted to show that it is the widely ranging, the much
+diffused and common, that is the dominant species belonging to the larger
+genera, which vary most. The varieties, or incipient species, thus produced
+ultimately become converted, as I believe, into new and distinct species;
+and these, on the principle of inheritance, tend to produce other new and
+dominant {412} species. Consequently the groups which are now large, and
+which generally include many dominant species, tend to go on increasing
+indefinitely in size. I further attempted to show that from the varying
+descendants of each species trying to occupy as many and as different
+places as possible in the economy of nature, there is a constant tendency
+in their characters to diverge. This conclusion was supported by looking at
+the great diversity of the forms of life which, in any small area, come
+into the closest competition, and by looking to certain facts in
+naturalisation.
+
+I attempted also to show that there is a constant tendency in the forms
+which are increasing in number and diverging in character, to supplant and
+exterminate the less divergent, the less improved, and preceding forms. I
+request the reader to turn to the diagram illustrating the action, as
+formerly explained, of these several principles; and he will see that the
+inevitable result is that the modified descendants proceeding from one
+progenitor become broken up into groups subordinate to groups. In the
+diagram each letter on the uppermost line may represent a genus including
+several species; and all the genera on this line form together one class,
+for all have descended from one ancient but unseen parent, and,
+consequently, have inherited something in common. But the three genera on
+the left hand have, on this same principle, much in common, and form a
+sub-family, distinct from that including the next two genera on the right
+hand, which diverged from a common parent at the fifth stage of descent.
+These five genera have also much, though less, in common; and they form a
+family distinct from that including the three genera still further to the
+right hand, which diverged at a still earlier period. And all these genera,
+descended from (A), form an order distinct from the {413} genera descended
+from (I). So that we here have many species descended from a single
+progenitor grouped into genera; and the genera are included in, or
+subordinate to, sub-families, families, and orders, all united into one
+class. Thus, the grand fact in natural history of the subordination of
+group under group, which, from its familiarity, does not always
+sufficiently strike us, is in my judgment explained.
+
+Naturalists try to arrange the species, genera, and families in each class,
+on what is called the Natural System. But what is meant by this system?
+Some authors look at it merely as a scheme for arranging together those
+living objects which are most alike, and for separating those which are
+most unlike; or as an artificial means for enunciating, as briefly as
+possible, general propositions,--that is, by one sentence to give the
+characters common, for instance, to all mammals, by another those common to
+all carnivora, by another those common to the dog-genus, and then by adding
+a single sentence, a full description is given of each kind of dog. The
+ingenuity and utility of this system are indisputable. But many naturalists
+think that something more is meant by the Natural System; they believe that
+it reveals the plan of the Creator; but unless it be specified whether
+order in time or space, or what else is meant by the plan of the Creator,
+it seems to me that nothing is thus added to our knowledge. Such
+expressions as that famous one of Linnæus, and which we often meet with in
+a more or less concealed form, that the characters do not make the genus,
+but that the genus gives the characters, seem to imply that something more
+is included in our classification, than mere resemblance. I believe that
+something more is included; and that propinquity of descent,--the only
+known cause of the similarity of organic beings,--is the bond, hidden as it
+is by various degrees of {414} modification, which is partially revealed to
+us by our classifications.
+
+Let us now consider the rules followed in classification, and the
+difficulties which are encountered on the view that classification either
+gives some unknown plan of creation, or is simply a scheme for enunciating
+general propositions and of placing together the forms most like each
+other. It might have been thought (and was in ancient times thought) that
+those parts of the structure which determined the habits of life, and the
+general place of each being in the economy of nature, would be of very high
+importance in classification. Nothing can be more false. No one regards the
+external similarity of a mouse to a shrew, of a dugong to a whale, of a
+whale to a fish, as of any importance. These resemblances, though so
+intimately connected with the whole life of the being, are ranked as merely
+"adaptive or analogical characters;" but to the consideration of these
+resemblances we shall have to recur. It may even be given as a general
+rule, that the less any part of the organisation is concerned with special
+habits, the more important it becomes for classification. As an instance:
+Owen, in speaking of the dugong, says, "The generative organs being those
+which are most remotely related to the habits and food of an animal, I have
+always regarded as affording very clear indications of its true affinities.
+We are least likely in the modifications of these organs to mistake a
+merely adaptive for an essential character." So with plants, how remarkable
+it is that the organs of vegetation, on which their whole life depends, are
+of little signification, excepting in the first main divisions; whereas the
+organs of reproduction, with their product the seed, are of paramount
+importance!
+
+We must not, therefore, in classifying, trust to resemblances in parts of
+the organisation, however important {415} they may be for the welfare of
+the being in relation to the outer world. Perhaps from this cause it has
+partly arisen, that almost all naturalists lay the greatest stress on
+resemblances in organs of high vital or physiological importance. No doubt
+this view of the classificatory importance of organs which are important is
+generally, but by no means always, true. But their importance for
+classification, I believe, depends on their greater constancy throughout
+large groups of species; and this constancy depends on such organs having
+generally been subjected to less change in the adaptation of the species to
+their conditions of life. That the mere physiological importance of an
+organ does not determine its classificatory value, is almost shown by the
+one fact, that in allied groups, in which the same organ, as we have every
+reason to suppose, has nearly the same physiological value, its
+classificatory value is widely different. No naturalist can have worked at
+any group without being struck with this fact; and it has been fully
+acknowledged in the writings of almost every author. It will suffice to
+quote the highest authority, Robert Brown, who in speaking of certain
+organs in the Proteaceæ, says their generic importance, "like that of all
+their parts, not only in this but, as I apprehend, in every natural family,
+is very unequal, and in some cases seems to be entirely lost." Again in
+another work he says, the genera of the Connaraceæ "differ in having one or
+more ovaria, in the existence or absence of albumen, in the imbricate or
+valvular æstivation. Any one of these characters singly is frequently of
+more than generic importance, though here even when all taken together they
+appear insufficient to separate Cnestis from Connarus." To give an example
+amongst insects, in one great division of the Hymenoptera, the antennæ, as
+Westwood has remarked, are most constant in structure; {416} in another
+division they differ much, and the differences are of quite subordinate
+value in classification; yet no one probably will say that the antennae in
+these two divisions of the same order are of unequal physiological
+importance. Any number of instances could be given of the varying
+importance for classification of the same important organ within the same
+group of beings.
+
+Again, no one will say that rudimentary or atrophied organs are of high
+physiological or vital importance; yet, undoubtedly, organs in this
+condition are often of high value in classification. No one will dispute
+that the rudimentary teeth in the upper jaws of young ruminants, and
+certain rudimentary bones of the leg, are highly serviceable in exhibiting
+the close affinity between Ruminants and Pachyderms. Robert Brown has
+strongly insisted on the fact that the rudimentary florets are of the
+highest importance in the classification of the Grasses.
+
+Numerous instances could be given of characters derived from parts which
+must be considered of very trifling physiological importance, but which are
+universally admitted as highly serviceable in the definition of whole
+groups. For instance, whether or not there is an open passage from the
+nostrils to the mouth, the only character, according to Owen, which
+absolutely distinguishes fishes and reptiles--the inflection of the angle
+of the jaws in Marsupials--the manner in which the wings of insects are
+folded--mere colour in certain Algæ--mere pubescence on parts of the flower
+in grasses--the nature of the dermal covering, as hair or feathers, in the
+Vertebrata. If the Ornithorhynchus had been covered with feathers instead
+of hair, this external and trifling character would, I think, have been
+considered by naturalists as important an aid in determining the degree of
+affinity of this strange creature to {417} birds and reptiles, as an
+approach in structure in any one internal and important organ.
+
+The importance, for classification, of trifling characters, mainly depends
+on their being correlated with several other characters of more or less
+importance. The value indeed of an aggregate of characters is very evident
+in natural history. Hence, as has often been remarked, a species may depart
+from its allies in several characters, both of high physiological
+importance and of almost universal prevalence, and yet leave us in no doubt
+where it should be ranked. Hence, also, it has been found, that a
+classification founded on any single character, however important that may
+be, has always failed; for no part of the organisation is universally
+constant. The importance of an aggregate of characters, even when none are
+important, alone explains, I think, that saying of Linnæus, that the
+characters do not give the genus, but the genus gives the characters; for
+this saying seems founded on an appreciation of many trifling points of
+resemblance, too slight to be defined. Certain plants, belonging to the
+Malpighiaceæ, bear perfect and degraded flowers; in the latter, as A. de
+Jussieu has remarked, "the greater number of the characters proper to the
+species, to the genus, to the family, to the class, disappear, and thus
+laugh at our classification." But when Aspicarpa produced in France, during
+several years, only degraded flowers, departing so wonderfully in a number
+of the most important points of structure from the proper type of the
+order, yet M. Richard sagaciously saw, as Jussieu observes, that this genus
+should still be retained amongst the Malpighiaceæ. This case seems to me
+well to illustrate the spirit with which our classifications are sometimes
+necessarily founded.
+
+Practically when naturalists are at work, they do {418} not trouble
+themselves about the physiological value of the characters which they use
+in defining a group, or in allocating any particular species. If they find
+a character nearly uniform, and common to a great number of forms, and not
+common to others, they use it as one of high value; if common to some
+lesser number, they use it as of subordinate value. This principle has been
+broadly confessed by some naturalists to be the true one; and by none more
+clearly than by that excellent botanist, Aug. St. Hilaire. If certain
+characters are always found correlated with others, though no apparent bond
+of connexion can be discovered between them, especial value is set on them.
+As in most groups of animals, important organs, such as those for
+propelling the blood, or for aërating it, or those for propagating the
+race, are found nearly uniform, they are considered as highly serviceable
+in classification; but in some groups of animals all these, the most
+important vital organs, are found to offer characters of quite subordinate
+value.
+
+We can see why characters derived from the embryo should be of equal
+importance with those derived from the adult, for our classifications of
+course include all ages of each species. But it is by no means obvious, on
+the ordinary view, why the structure of the embryo should be more important
+for this purpose than that of the adult, which alone plays its full part in
+the economy of nature. Yet it has been strongly urged by those great
+naturalists, Milne Edwards and Agassiz, that embryonic characters are the
+most important of any in the classification of animals; and this doctrine
+has very generally been admitted as true. The same fact holds good with
+flowering plants, of which the two main divisions have been founded on
+characters derived from the embryo,--on the number and position of the
+{419} embryonic leaves or cotyledons, and on the mode of development of the
+plumule and radicle. In our discussion on embryology, we shall see why such
+characters are so valuable, on the view of classification tacitly including
+the idea of descent.
+
+Our classifications are often plainly influenced by chains of affinities.
+Nothing can be easier than to define a number of characters common to all
+birds; but in the case of crustaceans, such definition has hitherto been
+found impossible. There are crustaceans at the opposite ends of the series,
+which have hardly a character in common; yet the species at both ends, from
+being plainly allied to others, and these to others, and so onwards, can be
+recognised as unequivocally belonging to this, and to no other class of the
+Articulata.
+
+Geographical distribution has often been used, though perhaps not quite
+logically, in classification, more especially in very large groups of
+closely allied forms. Temminck insists on the utility or even necessity of
+this practice in certain groups of birds; and it has been followed by
+several entomologists and botanists.
+
+Finally, with respect to the comparative value of the various groups of
+species, such as orders, sub-orders, families, sub-families, and genera,
+they seem to be, at least at present, almost arbitrary. Several of the best
+botanists, such as Mr. Bentham and others, have strongly insisted on their
+arbitrary value. Instances could be given amongst plants and insects, of a
+group of forms, first ranked by practised naturalists as only a genus, and
+then raised to the rank of a sub-family or family; and this has been done,
+not because further research has detected important structural differences,
+at first overlooked, but because numerous allied species, with slightly
+different grades of difference, have been subsequently discovered. {420}
+
+All the foregoing rules and aids and difficulties in classification are
+explained, if I do not greatly deceive myself, on the view that the natural
+system is founded on descent with modification; that the characters which
+naturalists consider as showing true affinity between any two or more
+species, are those which have been inherited from a common parent, and, in
+so far, all true classification is genealogical; that community of descent
+is the hidden bond which naturalists have been unconsciously seeking, and
+not some unknown plan of creation, or the enunciation of general
+propositions, and the mere putting together and separating objects more or
+less alike.
+
+But I must explain my meaning more fully. I believe that the _arrangement_
+of the groups within each class, in due subordination and relation to the
+other groups, must be strictly genealogical in order to be natural; but
+that the _amount_ of difference in the several branches or groups, though
+allied in the same degree in blood to their common progenitor, may differ
+greatly, being due to the different degrees of modification which they have
+undergone; and this is expressed by the forms being ranked under different
+genera, families, sections, or orders. The reader will best understand what
+is meant, if he will take the trouble of referring to the diagram in the
+fourth chapter. We will suppose the letters A to L to represent allied
+genera, which lived during the Silurian epoch, and these have descended
+from a species which existed at an unknown anterior period. Species of
+three of these genera (A, F, and I) have transmitted modified descendants
+to the present day, represented by the fifteen genera (a^{14} to z^{14}) on
+the uppermost horizontal line. Now all these modified descendants from a
+single species, are represented as related in blood or descent to the same
+{421} degree; they may metaphorically be called cousins to the same
+millionth degree; yet they differ widely and in different degrees from each
+other. The forms descended from A, now broken up into two or three
+families, constitute a distinct order from those descended from I, also
+broken up into two families. Nor can the existing species, descended from
+A, be ranked in the same genus with the parent A; or those from I, with the
+parent I. But the existing genus F^{14} may be supposed to have been but
+slightly modified; and it will then rank with the parent-genus F; just as
+some few still living organic beings belong to Silurian genera. So that the
+amount or value of the differences between organic beings all related to
+each other in the same degree in blood, has come to be widely different.
+Nevertheless their genealogical _arrangement_ remains strictly true, not
+only at the present time, but at each successive period of descent. All the
+modified descendants from A will have inherited something in common from
+their common parent, as will all the descendants from I; so will it be with
+each subordinate branch of descendants, at each successive period. If,
+however, we choose to suppose that any of the descendants of A or of I have
+been so much modified as to have more or less completely lost traces of
+their parentage, in this case, their places in a natural classification
+will have been more or less completely lost,--as sometimes seems to have
+occurred with existing organisms. All the descendants of the genus F, along
+its whole line of descent, are supposed to have been but little modified,
+and they yet form a single genus. But this genus, though much isolated,
+will still occupy its proper intermediate position; for F originally was
+intermediate in character between A and I, and the several genera descended
+from these two genera will {422} have inherited to a certain extent their
+characters. This natural arrangement is shown, as far as is possible on
+paper, in the diagram, but in much too simple a manner. If a branching
+diagram had not been used, and only the names of the groups had been
+written in a linear series, it would have been still less possible to have
+given a natural arrangement; and it is notoriously not possible to
+represent in a series, on a flat surface, the affinities which we discover
+in nature amongst the beings of the same group. Thus, on the view which I
+hold, the natural system is genealogical in its arrangement, like a
+pedigree; but the degrees of modification which the different groups have
+undergone, have to be expressed by ranking them under different so-called
+genera, sub-families, families, sections, orders, and classes.
+
+It may be worth while to illustrate this view of classification, by taking
+the case of languages. If we possessed a perfect pedigree of mankind, a
+genealogical arrangement of the races of man would afford the best
+classification of the various languages now spoken throughout the world;
+and if all extinct languages, and all intermediate and slowly changing
+dialects, had to be included, such an arrangement would, I think, be the
+only possible one. Yet it might be that some very ancient language had
+altered little, and had given rise to few new languages, whilst others
+(owing to the spreading and subsequent isolation and states of civilisation
+of the several races, descended from a common race) had altered much, and
+had given rise to many new languages and dialects. The various degrees of
+difference in the languages from the same stock, would have to be expressed
+by groups subordinate to groups; but the proper or even only possible
+arrangement would still be genealogical; and this would be strictly
+natural, as {423} it would connect together all languages, extinct and
+modern, by the closest affinities, and would give the filiation and origin
+of each tongue.
+
+In confirmation of this view, let us glance at the classification of
+varieties, which are believed or known to have descended from one species.
+These are grouped under species, with sub-varieties under varieties; and
+with our domestic productions, several other grades of difference are
+requisite, as we have seen with pigeons. The origin of the existence of
+groups subordinate to groups, is the same with varieties as with species,
+namely, closeness of descent with various degrees of modification. Nearly
+the same rules are followed in classifying varieties, as with species.
+Authors have insisted on the necessity of classing varieties on a natural
+instead of an artificial system; we are cautioned, for instance, not to
+class two varieties of the pine-apple together, merely because their fruit,
+though the most important part, happens to be nearly identical; no one puts
+the swedish and common turnips together, though the esculent and thickened
+stems are so similar. Whatever part is found to be most constant, is used
+in classing varieties: thus the great agriculturist Marshall says the horns
+are very useful for this purpose with cattle, because they are less
+variable than the shape or colour of the body, &c.; whereas with sheep the
+horns are much less serviceable, because less constant. In classing
+varieties, I apprehend if we had a real pedigree, a genealogical
+classification would be universally preferred; and it has been attempted by
+some authors. For we might feel sure, whether there had been more or less
+modification, the principle of inheritance would keep the forms together
+which were allied in the greatest number of points. In tumbler pigeons,
+though some sub-varieties differ from the others {424} in the important
+character of having a longer beak, yet all are kept together from having
+the common habit of tumbling; but the short-faced breed has nearly or quite
+lost this habit; nevertheless, without any reasoning or thinking on the
+subject, these tumblers are kept in the same group, because allied in blood
+and alike in some other respects. If it could be proved that the Hottentot
+had descended from the Negro, I think he would be classed under the Negro
+group, however much he might differ in colour and other important
+characters from negroes.
+
+With species in a state of nature, every naturalist has in fact brought
+descent into his classification; for he includes in his lowest grade, or
+that of a species, the two sexes; and how enormously these sometimes differ
+in the most important characters, is known to every naturalist: scarcely a
+single fact can be predicated in common of the males and hermaphrodites of
+certain cirripedes, when adult, and yet no one dreams of separating them.
+The naturalist includes as one species the several larval stages of the
+same individual, however much they may differ from each other and from the
+adult; as he likewise includes the so-called alternate generations of
+Steenstrup, which can only in a technical sense be considered as the same
+individual. He includes monsters; he includes varieties, not solely because
+they closely resemble the parent-form, but because they are descended from
+it. He who believes that the cowslip is descended from the primrose, or
+conversely, ranks them together as a single species, and gives a single
+definition. As soon as three Orchidean forms (Monochanthus, Myanthus, and
+Catasetum), which had previously been ranked as three distinct genera, were
+known to be sometimes produced on the same spike, they were immediately
+included as a single species. {425}
+
+As descent has universally been used in classing together the individuals
+of the same species, though the males and females and larvæ are sometimes
+extremely different; and as it has been used in classing varieties which
+have undergone a certain, and sometimes a considerable amount of
+modification, may not this same element of descent have been unconsciously
+used in grouping species under genera, and genera under higher groups,
+though in these cases the modification has been greater in degree, and has
+taken a longer time to complete? I believe it has thus been unconsciously
+used; and only thus can I understand the several rules and guides which
+have been followed by our best systematists. We have no written pedigrees;
+we have to make out community of descent by resemblances of any kind.
+Therefore we choose those characters which, as far as we can judge, are the
+least likely to have been modified in relation to the conditions of life to
+which each species has been recently exposed. Rudimentary structures on
+this view are as good as, or even sometimes better than, other parts of the
+organisation. We care not how trifling a character may be--let it be the
+mere inflection of the angle of the jaw, the manner in which an insect's
+wing is folded, whether the skin be covered by hair or feathers--if it
+prevail throughout many and different species, especially those having very
+different habits of life, it assumes high value; for we can account for its
+presence in so many forms with such different habits, only by its
+inheritance from a common parent. We may err in this respect in regard to
+single points of structure, but when several characters, let them be ever
+so trifling, occur together throughout a large group of beings having
+different habits, we may feel almost sure, on the theory of descent, that
+these characters have been inherited from a common ancestor. {426} And we
+know that such correlated or aggregated characters have especial value in
+classification.
+
+We can understand why a species or a group of species may depart, in
+several of its most important characteristics, from its allies, and yet be
+safely classed with them. This may be safely done, and is often done, as
+long as a sufficient number of characters, let them be ever so unimportant,
+betrays the hidden bond of community of descent. Let two forms have not a
+single character in common, yet if these extreme forms are connected
+together by a chain of intermediate groups, we may at once infer their
+community of descent, and we put them all into the same class. As we find
+organs of high physiological importance--those which serve to preserve life
+under the most diverse conditions of existence--are generally the most
+constant, we attach especial value to them; but if these same organs, in
+another group or section of a group, are found to differ much, we at once
+value them less in our classification. We shall hereafter, I think, clearly
+see why embryological characters are of such high classificatory
+importance. Geographical distribution may sometimes be brought usefully
+into play in classing large and widely-distributed genera, because all the
+species of the same genus, inhabiting any distinct and isolated region,
+have in all probability descended from the same parents.
+
+We can understand, on these views, the very important distinction between
+real affinities and analogical or adaptive resemblances. Lamarck first
+called attention to this distinction, and he has been ably followed by
+Macleay and others. The resemblance, in the shape of the body and in the
+fin-like anterior limbs, between the dugong, which is a pachydermatous
+animal, and the whale, and between both these mammals and fishes, is
+analogical. Amongst insects there are innumerable {427} instances: thus
+Linnæus, misled by external appearances, actually classed an homopterous
+insect as a moth. We see something of the same kind even in our domestic
+varieties, as in the thickened stems of the common and swedish turnip. The
+resemblance of the greyhound and racehorse is hardly more fanciful than the
+analogies which have been drawn by some authors between very distinct
+animals. On my view of characters being of real importance for
+classification, only in so far as they reveal descent, we can clearly
+understand why analogical or adaptive character, although of the utmost
+importance to the welfare of the being, are almost valueless to the
+systematist. For animals, belonging to two most distinct lines of descent,
+may readily become adapted to similar conditions, and thus assume a close
+external resemblance; but such resemblances will not reveal--will rather
+tend to conceal their blood-relationship to their proper lines of descent.
+We can also understand the apparent paradox, that the very same characters
+are analogical when one class or order is compared with another, but give
+true affinities when the members of the same class or order are compared
+one with another: thus the shape of the body and fin-like limbs are only
+analogical when whales are compared with fishes, being adaptations in both
+classes for swimming through the water; but the shape of the body and
+fin-like limbs serve as characters exhibiting true affinity between the
+several members of the whale family; for these cetaceans agree in so many
+characters, great and small, that we cannot doubt that they have inherited
+their general shape of body and structure of limbs from a common ancestor.
+So it is with fishes.
+
+As members of distinct classes have often been adapted by successive slight
+modifications to live under nearly similar circumstances,--to inhabit for
+instance {428} the three elements of land, air, and water,--we can perhaps
+understand how it is that a numerical parallelism has sometimes been
+observed between the sub-groups in distinct classes. A naturalist, struck
+by a parallelism of this nature in any one class, by arbitrarily raising or
+sinking the value of the groups in other classes (and all our experience
+shows that this valuation has hitherto been arbitrary), could easily extend
+the parallelism over a wide range; and thus the septenary, quinary,
+quaternary, and ternary classifications have probably arisen.
+
+As the modified descendants of dominant species, belonging to the larger
+genera, tend to inherit the advantages, which made the groups to which they
+belong large and their parents dominant, they are almost sure to spread
+widely, and to seize on more and more places in the economy of nature. The
+larger and more dominant groups thus tend to go on increasing in size; and
+they consequently supplant many smaller and feebler groups. Thus we can
+account for the fact that all organisms, recent and extinct, are included
+under a few great orders, under still fewer classes, and all in one great
+natural system. As showing how few the higher groups are in number, and how
+widely spread they are throughout the world, the fact is striking, that the
+discovery of Australia has not added a single insect belonging to a new
+class; and that in the vegetable kingdom, as I learn from Dr. Hooker, it
+has added only two or three orders of small size.
+
+In the chapter on geological succession I attempted to show, on the
+principle of each group having generally diverged much in character during
+the long-continued process of modification, how it is that the more ancient
+forms of life often present characters in some slight degree intermediate
+between existing groups. A few {429} old and intermediate parent-forms
+having occasionally transmitted to the present day descendants but little
+modified, will give to us our so-called osculant or aberrant groups. The
+more aberrant any form is, the greater must be the number of connecting
+forms which on my theory have been exterminated and utterly lost. And we
+have some evidence of aberrant forms having suffered severely from
+extinction, for they are generally represented by extremely few species;
+and such species as do occur are generally very distinct from each other,
+which again implies extinction. The genera Ornithorhynchus and Lepidosiren,
+for example, would not have been less aberrant had each been represented by
+a dozen species instead of by a single one; but such richness in species,
+as I find after some investigation, does not commonly fall to the lot of
+aberrant genera. We can, I think, account for this fact only by looking at
+aberrant forms as failing groups conquered by more successful competitors,
+with a few members preserved by some unusual coincidence of favourable
+circumstances.
+
+Mr. Waterhouse has remarked that, when a member belonging to one group of
+animals exhibits an affinity to a quite distinct group, this affinity in
+most cases is general and not special: thus, according to Mr. Waterhouse,
+of all Rodents, the bizcacha is most nearly related to Marsupials; but in
+the points in which it approaches this order, its relations are general,
+and not to any one marsupial species more than to another. As the points of
+affinity of the bizcacha to Marsupials are believed to be real and not
+merely adaptive, they are due on my theory to inheritance in common.
+Therefore we must suppose either that all Rodents, including the bizcacha,
+branched off from some very ancient Marsupial, which will have had a
+character in some degree intermediate with respect to all existing
+Marsupials; or {430} that both Rodents and Marsupials branched off from a
+common progenitor, and that both groups have since undergone much
+modification in divergent directions. On either view we may suppose that
+the bizcacha has retained, by inheritance, more of the character of its
+ancient progenitor than have other Rodents; and therefore it will not be
+specially related to any one existing Marsupial, but indirectly to all or
+nearly all Marsupials, from having partially retained the character of
+their common progenitor, or of an early member of the group. On the other
+hand, of all Marsupials, as Mr. Waterhouse has remarked, the phascolomys
+resembles most nearly, not any one species, but the general order of
+Rodents. In this case, however, it may be strongly suspected that the
+resemblance is only analogical, owing to the phascolomys having become
+adapted to habits like those of a Rodent. The elder De Candolle has made
+nearly similar observations on the general nature of the affinities of
+distinct orders of plants.
+
+On the principle of the multiplication and gradual divergence in character
+of the species descended from a common parent, together with their
+retention by inheritance of some characters in common, we can understand
+the excessively complex and radiating affinities by which all the members
+of the same family or higher group are connected together. For the common
+parent of a whole family of species, now broken up by extinction into
+distinct groups and sub-groups, will have transmitted some of its
+characters, modified in various ways and degrees, to all; and the several
+species will consequently be related to each other by circuitous lines of
+affinity of various lengths (as may be seen in the diagram so often
+referred to), mounting up through many predecessors. As it is difficult to
+show the blood-relationship between the numerous kindred {431} of any
+ancient and noble family, even by the aid of a genealogical tree, and
+almost impossible to do this without this aid, we can understand the
+extraordinary difficulty which naturalists have experienced in describing,
+without the aid of a diagram, the various affinities which they perceive
+between the many living and extinct members of the same great natural
+class.
+
+Extinction, as we have seen in the fourth chapter, has played an important
+part in defining and widening the intervals between the several groups in
+each class. We may thus account even for the distinctness of whole classes
+from each other--for instance, of birds from all other vertebrate
+animals--by the belief that many ancient forms of life have been utterly
+lost, through which the early progenitors of birds were formerly connected
+with the early progenitors of the other vertebrate classes. There has been
+less entire extinction of the forms of life which once connected fishes
+with batrachians. There has been still less in some other classes, as in
+that of the Crustacea, for here the most wonderfully diverse forms are
+still tied together by a long, but broken, chain of affinities. Extinction
+has only separated groups: it has by no means made them; for if every form
+which has ever lived on this earth were suddenly to reappear, though it
+would be quite impossible to give definitions by which each group could be
+distinguished from other groups, as all would blend together by steps as
+fine as those between the finest existing varieties, nevertheless a natural
+classification, or at least a natural arrangement, would be possible. We
+shall see this by turning to the diagram: the letters, A to L, may
+represent eleven Silurian genera, some of which have produced large groups
+of modified descendants. Every intermediate link between these eleven
+genera and their primordial parent, and every {432} intermediate link in
+each branch and sub-branch of their descendants, may be supposed to be
+still alive; and the links to be as fine as those between the finest
+varieties. In this case it would be quite impossible to give any definition
+by which the several members of the several groups could be distinguished
+from their more immediate parents; or these parents from their ancient and
+unknown progenitor. Yet the natural arrangement in the diagram would still
+hold good; and, on the principle of inheritance, all the forms descended
+from A, or from I, would have something in common. In a tree we can specify
+this or that branch, though at the actual fork the two unite and blend
+together. We could not, as I have said, define the several groups; but we
+could pick out types, or forms, representing most of the characters of each
+group, whether large or small, and thus give a general idea of the value of
+the differences between them. This is what we should be driven to, if we
+were ever to succeed in collecting all the forms in any class which have
+lived throughout all time and space. We shall certainly never succeed in
+making so perfect a collection: nevertheless, in certain classes, we are
+tending in this direction; and Milne Edwards has lately insisted, in an
+able paper, on the high importance of looking to types, whether or not we
+can separate and define the groups to which such types belong.
+
+Finally, we have seen that natural selection, which results from the
+struggle for existence, and which almost inevitably induces extinction and
+divergence of character in the many descendants from one dominant
+parent-species, explains that great and universal feature in the affinities
+of all organic beings, namely, their subordination in group under group. We
+use the element of descent in classing the individuals of both sexes and of
+all ages, although having few characters in common, {433} under one
+species; we use descent in classing acknowledged varieties, however
+different they may be from their parent; and I believe this element of
+descent is the hidden bond of connexion which naturalists have sought under
+the term of the Natural System. On this idea of the natural system being,
+in so far as it has been perfected, genealogical in its arrangement, with
+the grades of difference between the descendants from a common parent,
+expressed by the terms genera, families, orders, &c., we can understand the
+rules which we are compelled to follow in our classification. We can
+understand why we value certain resemblances far more than others; why we
+are permitted to use rudimentary and useless organs, or others of trifling
+physiological importance; why, in comparing one group with a distinct
+group, we summarily reject analogical or adaptive characters, and yet use
+these same characters within the limits of the same group. We can clearly
+see how it is that all living and extinct forms can be grouped together in
+one great system; and how the several members of each class are connected
+together by the most complex and radiating lines of affinities. We shall
+never, probably, disentangle the inextricable web of affinities between the
+members of any one class; but when we have a distinct object in view, and
+do not look to some unknown plan of creation, we may hope to make sure but
+slow progress.
+
+
+
+_Morphology._--We have seen that the members of the same class,
+independently of their habits of life, resemble each other in the general
+plan of their organisation. This resemblance is often expressed by the term
+"unity of type;" or by saying that the several parts and organs in the
+different species of the class are homologous. The whole subject is
+included under {434} the general name of Morphology. This is the most
+interesting department of natural history, and may be said to be its very
+soul. What can be more curious than that the hand of a man, formed for
+grasping, that of a mole for digging, the leg of the horse, the paddle of
+the porpoise, and the wing of the bat, should all be constructed on the
+same pattern, and should include similar bones, in the same relative
+positions? Geoffroy St. Hilaire has insisted strongly on the high
+importance of relative connexion in homologous organs: the parts may change
+to almost any extent in form and size, and yet they always remain connected
+together in the same order. We never find, for instance, the bones of the
+arm and forearm, or of the thigh and leg, transposed. Hence the same names
+can be given to the homologous bones in widely different animals. We see
+the same great law in the construction of the mouths of insects: what can
+be more different than the immensely long spiral proboscis of a
+sphinx-moth, the curious folded one of a bee or bug, and the great jaws of
+a beetle?--yet all these organs, serving for such different purposes, are
+formed by infinitely numerous modifications of an upper lip, mandibles, and
+two pairs of maxillæ. Analogous laws govern the construction of the mouths
+and limbs of crustaceans. So it is with the flowers of plants.
+
+Nothing can be more hopeless than to attempt to explain this similarity of
+pattern in members of the same class, by utility or by the doctrine of
+final causes. The hopelessness of the attempt has been expressly admitted
+by Owen in his most interesting work on the 'Nature of Limbs.' On the
+ordinary view of the independent creation of each being, we can only say
+that so it is;--that it has so pleased the Creator to construct each animal
+and plant.
+
+The explanation is manifest on the theory of the {435} natural selection of
+successive slight modifications,--each modification being profitable in
+some way to the modified form, but often affecting by correlation of growth
+other parts of the organisation. In changes of this nature, there will be
+little or no tendency to modify the original pattern, or to transpose
+parts. The bones of a limb might be shortened and widened to any extent,
+and become gradually enveloped in thick membrane, so as to serve as a fin;
+or a webbed foot might have all its bones, or certain bones, lengthened to
+any extent, and the membrane connecting them increased to any extent, so as
+to serve as a wing: yet in all this great amount of modification there will
+be no tendency to alter the framework of bones or the relative connexion of
+the several parts. If we suppose that the ancient progenitor, the archetype
+as it may be called, of all mammals, had its limbs constructed on the
+existing general pattern, for whatever purpose they served, we can at once
+perceive the plain signification of the homologous construction of the
+limbs throughout the whole class. So with the mouths of insects, we have
+only to suppose that their common progenitor had an upper lip, mandibles,
+and two pair of maxillæ, these parts being perhaps very simple in form; and
+then natural selection, acting on some originally created form, will
+account for the infinite diversity in structure and function of the mouths
+of insects. Nevertheless, it is conceivable that the general pattern of an
+organ might become so much obscured as to be finally lost, by the atrophy
+and ultimately by the complete abortion of certain parts, by the soldering
+together of other parts, and by the doubling or multiplication of
+others,--variations which we know to be within the limits of possibility.
+In the paddles of the extinct gigantic sea-lizards, and in the mouths of
+certain suctorial crustaceans, the {436} general pattern seems to have been
+thus to a certain extent obscured.
+
+There is another and equally curious branch of the present subject; namely,
+the comparison not of the same part in different members of a class, but of
+the different parts or organs in the same individual. Most physiologists
+believe that the bones of the skull are homologous with--that is correspond
+in number and in relative connexion with--the elemental parts of a certain
+number of vertebræ. The anterior and posterior limbs in each member of the
+vertebrate and articulate classes are plainly homologous. We see the same
+law in comparing the wonderfully complex jaws and legs in crustaceans. It
+is familiar to almost every one, that in a flower the relative position of
+the sepals, petals, stamens, and pistils, as well as their intimate
+structure, are intelligible on the view that they consist of metamorphosed
+leaves, arranged in a spire. In monstrous plants, we often get direct
+evidence of the possibility of one organ being transformed into another;
+and we can actually see in embryonic crustaceans and in many other animals,
+and in flowers, that organs, which when mature become extremely different,
+are at an early stage of growth exactly alike.
+
+How inexplicable are these facts on the ordinary view of creation! Why
+should the brain be enclosed in a box composed of such numerous and such
+extraordinary shaped pieces of bone? As Owen has remarked, the benefit
+derived from the yielding of the separate pieces in the act of parturition
+of mammals, will by no means explain the same construction in the skulls of
+birds. Why should similar bones have been created in the formation of the
+wing and leg of a bat, used as they are for such totally different
+purposes? Why should one crustacean, which has an extremely complex {437}
+mouth formed of many parts, consequently always have fewer legs; or
+conversely, those with many legs have simpler mouths? Why should the
+sepals, petals, stamens, and pistils in any individual flower, though
+fitted for such widely different purposes, be all constructed on the same
+pattern?
+
+On the theory of natural selection, we can satisfactorily answer these
+questions. In the vertebrata, we see a series of internal vertebræ bearing
+certain processes and appendages; in the articulata, we see the body
+divided into a series of segments, bearing external appendages; and in
+flowering plants, we see a series of successive spiral whorls of leaves. An
+indefinite repetition of the same part or organ is the common
+characteristic (as Owen has observed) of all low or little-modified forms;
+therefore we may readily believe that the unknown progenitor of the
+vertebrata possessed many vertebræ; the unknown progenitor of the
+articulata, many segments; and the unknown progenitor of flowering plants,
+many spiral whorls of leaves. We have formerly seen that parts many times
+repeated are eminently liable to vary in number and structure; consequently
+it is quite probable that natural selection, during a long-continued course
+of modification, should have seized on a certain number of the primordially
+similar elements, many times repeated, and have adapted them to the most
+diverse purposes. And as the whole amount of modification will have been
+effected by slight successive steps, we need not wonder at discovering in
+such parts or organs, a certain degree of fundamental resemblance, retained
+by the strong principle of inheritance.
+
+In the great class of molluscs, though we can homologise the parts of one
+species with those of other and distinct species, we can indicate but few
+serial homologies; that is, we are seldom enabled to say that one {438}
+part or organ is homologous with another in the same individual. And we can
+understand this fact; for in molluscs, even in the lowest members of the
+class, we do not find nearly so much indefinite repetition of any one part,
+as we find in the other great classes of the animal and vegetable kingdoms.
+
+Naturalists frequently speak of the skull as formed of metamorphosed
+vertebræ: the jaws of crabs as metamorphosed legs; the stamens and pistils
+of flowers as metamorphosed leaves; but it would in these cases probably be
+more correct, as Professor Huxley has remarked, to speak of both skull and
+vertebræ, both jaws and legs, &c.,--as having been metamorphosed, not one
+from the other, but from some common element. Naturalists, however, use
+such language only in a metaphorical sense: they are far from meaning that
+during a long course of descent, primordial organs of any kind--vertebræ in
+the one case and legs in the other--have actually been modified into skulls
+or jaws. Yet so strong is the appearance of a modification of this nature
+having occurred, that naturalists can hardly avoid employing language
+having this plain signification. On my view these terms may be used
+literally; and the wonderful fact of the jaws, for instance, of a crab
+retaining numerous characters, which they would probably have retained
+through inheritance, if they had really been metamorphosed during a long
+course of descent from true legs, or from some simple appendage, is
+explained.
+
+
+
+_Embryology._--It has already been casually remarked that certain organs in
+the individual, which when mature become widely different and serve for
+different purposes, are in the embryo exactly alike. The embryos, also, of
+distinct animals within the same class are often strikingly similar: a
+better proof of this cannot be given, than a {439} circumstance mentioned
+by Agassiz, namely, that having forgotten to ticket the embryo of some
+vertebrate animal, he cannot now tell whether it be that of a mammal, bird,
+or reptile. The vermiform larvæ of moths, flies, beetles, &c., resemble
+each other much more closely than do the mature insects; but in the case of
+larvæ, the embryos are active, and have been adapted for special lines of
+life. A trace of the law of embryonic resemblance, sometimes lasts till a
+rather late age: thus birds of the same genus, and of closely allied
+genera, often resemble each other in their first and second plumage; as we
+see in the spotted feathers in the thrush group. In the cat tribe, most of
+the species are striped or spotted in lines; and stripes can be plainly
+distinguished in the whelp of the lion. We occasionally though rarely see
+something of this kind in plants: thus the embryonic leaves of the ulex or
+furze, and the first leaves of the phyllodineous acaceas, are pinnate or
+divided like the ordinary leaves of the leguminosæ.
+
+The points of structure, in which the embryos of widely different animals
+of the same class resemble each other, often have no direct relation to
+their conditions of existence. We cannot, for instance, suppose that in the
+embryos of the vertebrata the peculiar loop-like course of the arteries
+near the branchial slits are related to similar conditions,--in the young
+mammal which is nourished in the womb of its mother, in the egg of the bird
+which is hatched in a nest, and in the spawn of a frog under water. We have
+no more reason to believe in such a relation, than we have to believe that
+the same bones in the hand of a man, wing of a bat, and fin of a porpoise,
+are related to similar conditions of life. No one will suppose that the
+stripes on the whelp of a lion, or the spots on the young blackbird, {440}
+are of any use to these animals, or are related to the conditions to which
+they are exposed.
+
+The case, however, is different when an animal during any part of its
+embryonic career is active, and has to provide for itself. The period of
+activity may come on earlier or later in life; but whenever it comes on,
+the adaptation of the larva to its conditions of life is just as perfect
+and as beautiful as in the adult animal. From such special adaptations, the
+similarity of the larvæ or active embryos of allied animals is sometimes
+much obscured; and cases could be given of the larvæ of two species, or of
+two groups of species, differing quite as much, or even more, from each
+other than do their adult parents. In most cases, however, the larvæ,
+though active, still obey, more or less closely, the law of common
+embryonic resemblance. Cirripedes afford a good instance of this: even the
+illustrious Cuvier did not perceive that a barnacle was, as it certainly
+is, a crustacean; but a glance at the larva shows this to be the case in an
+unmistakeable manner. So again the two main divisions of cirripedes, the
+pedunculated and sessile, which differ widely in external appearance, have
+larvæ in all their stages barely distinguishable.
+
+The embryo in the course of development generally rises in organisation: I
+use this expression, though I am aware that it is hardly possible to define
+clearly what is meant by the organisation being higher or lower. But no one
+probably will dispute that the butterfly is higher than the caterpillar. In
+some cases, however, the mature animal is generally considered as lower in
+the scale than the larva, as with certain parasitic crustaceans. To refer
+once again to cirripedes: the larvæ in the first stage have three pairs of
+legs, a very simple single eye, and a probosciformed mouth, with which they
+feed largely, for they increase much in {441} size. In the second stage,
+answering to the chrysalis stage of butterflies, they have six pairs of
+beautifully constructed natatory legs, a pair of magnificent compound eyes,
+and extremely complex antennæ; but they have a closed and imperfect mouth,
+and cannot feed: their function at this stage is, to search by their
+well-developed organs of sense, and to reach by their active powers of
+swimming, a proper place on which to become attached and to undergo their
+final metamorphosis. When this is completed they are fixed for life: their
+legs are now converted into prehensile organs; they again obtain a
+well-constructed mouth; but they have no antennæ, and their two eyes are
+now reconverted into a minute, single, and very simple eye-spot. In this
+last and complete state, cirripedes may be considered as either more highly
+or more lowly organised than they were in the larval condition. But in some
+genera the larvæ become developed either into hermaphrodites having the
+ordinary structure, or into what I have called complemental males: and in
+the latter, the development has assuredly been retrograde; for the male is
+a mere sack, which lives for a short time, and is destitute of mouth,
+stomach, or other organ of importance, excepting for reproduction.
+
+We are so much accustomed to see differences in structure between the
+embryo and the adult, and likewise a close similarity in the embryos of
+widely different animals within the same class, that we might be led to
+look at these facts as necessarily contingent in some manner on growth. But
+there is no obvious reason why, for instance, the wing of a bat, or the fin
+of a porpoise, should not have been sketched out with all the parts in
+proper proportion, as soon as any structure became visible in the embryo.
+And in some whole groups of animals and in certain members of other groups,
+the embryo does not at any period differ widely from the {442} adult: thus
+Owen has remarked in regard to cuttle-fish, "there is no metamorphosis; the
+cephalopodic character is manifested long before the parts of the embryo
+are completed;" and again in spiders, "there is nothing worthy to be called
+a metamorphosis." The larvæ of insects, whether adapted to the most diverse
+and active habits, or quite inactive, being fed by their parents or placed
+in the midst of proper nutriment, yet nearly all pass through a similar
+worm-like stage of development; but in some few cases, as in that of Aphis,
+if we look to the admirable drawings by Professor Huxley of the development
+of this insect, we see no trace of the vermiform stage.
+
+How, then, can we explain these several facts in embryology,--namely the
+very general, but not universal difference in structure between the embryo
+and the adult;--of parts in the same individual embryo, which ultimately
+become very unlike and serve for diverse purposes, being at this early
+period of growth alike;--of embryos of different species within the same
+class, generally, but not universally, resembling each other;--of the
+structure of the embryo not being closely related to its conditions of
+existence, except when the embryo becomes at any period of life active and
+has to provide for itself;--of the embryo apparently having sometimes a
+higher organisation than the mature animal, into which it is developed? I
+believe that all these facts can be explained, as follows, on the view of
+descent with modification.
+
+It is commonly assumed, perhaps from monstrosities often affecting the
+embryos at a very early period, that slight variations necessarily appear
+at an equally early period. But we have little evidence on this
+head--indeed the evidence rather points the other way; for it is notorious
+that breeders of cattle, horses, and various {443} fancy animals, cannot
+positively tell, until some time after the animal has been born, what its
+merits or form will ultimately turn out. We see this plainly in our own
+children; we cannot always tell whether the child will be tall or short, or
+what its precise features will be. The question is not, at what period of
+life any variation has been caused, but at what period it is fully
+displayed. The cause may have acted, and I believe generally has acted,
+even before the embryo is formed; and the variation may be due to the male
+and female sexual elements having been affected by the conditions to which
+either parent, or their ancestors, have been exposed. Nevertheless an
+effect thus caused at a very early period, even before the formation of the
+embryo, may appear late in life; as when an hereditary disease, which
+appears in old age alone, has been communicated to the offspring from the
+reproductive element of one parent. Or again, as when the horns of
+cross-bred cattle have been affected by the shape of the horns of either
+parent. For the welfare of a very young animal, as long as it remains in
+its mother's womb, or in the egg, or as long as it is nourished and
+protected by its parent, it must be quite unimportant whether most of its
+characters are fully acquired a little earlier or later in life. It would
+not signify, for instance, to a bird which obtained its food best by having
+a long beak, whether or not it assumed a beak of this particular length, as
+long as it was fed by its parents. Hence, I conclude, that it is quite
+possible, that each of the many successive modifications, by which each
+species has acquired its present structure, may have supervened at a not
+very early period of life; and some direct evidence from our domestic
+animals supports this view. But in other cases it is quite possible that
+each successive modification, or {444} most of them, may have appeared at
+an extremely early period.
+
+I have stated in the first chapter, that there is some evidence to render
+it probable, that at whatever age any variation first appears in the
+parent, it tends to reappear at a corresponding age in the offspring.
+Certain variations can only appear at corresponding ages, for instance,
+peculiarities in the caterpillar, cocoon, or imago states of the silk-moth;
+or, again, in the horns of almost full-grown cattle. But further than this,
+variations which, for all that we can see, might have appeared earlier or
+later in life, tend to appear at a corresponding age in the offspring and
+parent. I am far from meaning that this is invariably the case; and I could
+give a good many cases of variations (taking the word in the largest sense)
+which have supervened at an earlier age in the child than in the parent.
+
+These two principles, if their truth be admitted, will, I believe, explain
+all the above specified leading facts in embryology. But first let us look
+at a few analogous cases in domestic varieties. Some authors who have
+written on Dogs, maintain that the greyhound and bulldog, though appearing
+so different, are really varieties most closely allied, and have probably
+descended from the same wild stock; hence I was curious to see how far
+their puppies differed from each other: I was told by breeders that they
+differed just as much as their parents, and this, judging by the eye,
+seemed almost to be the case; but on actually measuring the old dogs and
+their six-days old puppies, I found that the puppies had not nearly
+acquired their full amount of proportional difference. So, again, I was
+told that the foals of cart and race-horses differed as much as the
+full-grown animals; and this surprised me greatly, as I think it probable
+that the difference between these two breeds has been wholly {445} caused
+by selection under domestication; but having had careful measurements made
+of the dam and of a three-days old colt of a race and heavy cart-horse, I
+find that the colts have by no means acquired their full amount of
+proportional difference.
+
+As the evidence appears to me conclusive, that the several domestic breeds
+of Pigeon have descended from one wild species, I compared young pigeons of
+various breeds, within twelve hours after being hatched; I carefully
+measured the proportions (but will not here give details) of the beak,
+width of mouth, length of nostril and of eyelid, size of feet and length of
+leg, in the wild stock, in pouters, fantails, runts, barbs, dragons,
+carriers, and tumblers. Now some of these birds, when mature, differ so
+extraordinarily in length and form of beak, that they would, I cannot
+doubt, be ranked in distinct genera, had they been natural productions. But
+when the nestling birds of these several breeds were placed in a row,
+though most of them could be distinguished from each other, yet their
+proportional differences in the above specified several points were
+incomparably less than in the full-grown birds. Some characteristic points
+of difference--for instance, that of the width of mouth--could hardly be
+detected in the young. But there was one remarkable exception to this rule,
+for the young of the short-faced tumbler differed from the young of the
+wild rock-pigeon and of the other breeds, in all its proportions, almost
+exactly as much as in the adult state.
+
+The two principles above given seem to me to explain these facts in regard
+to the later embryonic stages of our domestic varieties. Fanciers select
+their horses, dogs, and pigeons, for breeding, when they are nearly grown
+up: they are indifferent whether the desired qualities and structures have
+been acquired earlier or {446} later in life, if the full-grown animal
+possesses them. And the cases just given, more especially that of pigeons,
+seem to show that the characteristic differences which give value to each
+breed, and which have been accumulated by man's selection, have not
+generally first appeared at an early period of life, and have been
+inherited by the offspring at a corresponding not early period. But the
+case of the short-faced tumbler, which when twelve hours old had acquired
+its proper proportions, proves that this is not the universal rule; for
+here the characteristic differences must either have appeared at an earlier
+period than usual, or, if not so, the differences must have been inherited,
+not at the corresponding, but at an earlier age.
+
+Now let us apply these facts and the above two principles--which latter,
+though not proved true, can be shown to be in some degree probable--to
+species in a state of nature. Let us take a genus of birds, descended on my
+theory from some one parent-species, and of which the several new species
+have become modified through natural selection in accordance with their
+diverse habits. Then, from the many slight successive steps of variation
+having supervened at a rather late age, and having been inherited at a
+corresponding age, the young of the new species of our supposed genus will
+manifestly tend to resemble each other much more closely than do the
+adults, just as we have seen in the case of pigeons. We may extend this
+view to whole families or even classes. The fore-limbs, for instance, which
+served as legs in the parent-species, may have become, by a long course of
+modification, adapted in one descendant to act as hands, in another as
+paddles, in another as wings; and on the above two principles--namely of
+each successive modification supervening at a rather late age, and being
+inherited at a {447} corresponding late age--the fore-limbs in the embryos
+of the several descendants of the parent-species will still resemble each
+other closely, for they will not have been modified. But in each of our new
+species, the embryonic fore-limbs will differ greatly from the fore-limbs
+in the mature animal; the limbs in the latter having undergone much
+modification at a rather late period of life, and having thus been
+converted into hands, or paddles, or wings. Whatever influence
+long-continued exercise or use on the one hand, and disuse on the other,
+may have in modifying an organ, such influence will mainly affect the
+mature animal, which has come to its full powers of activity and has to
+gain its own living; and the effects thus produced will be inherited at a
+corresponding mature age. Whereas the young will remain unmodified, or be
+modified in a lesser degree, by the effects of use and disuse.
+
+In certain cases the successive steps of variation might supervene, from
+causes of which we are wholly ignorant, at a very early period of life, or
+each step might be inherited at an earlier period than that at which it
+first appeared. In either case (as with the short-faced tumbler) the young
+or embryo would closely resemble the mature parent-form. We have seen that
+this is the rule of development in certain whole groups of animals, as with
+cuttle-fish and spiders, and with a few members of the great class of
+insects, as with Aphis. With respect to the final cause of the young in
+these cases not undergoing any metamorphosis, or closely resembling their
+parents from their earliest age, we can see that this would result from the
+two following contingencies: firstly, from the young, during a course of
+modification carried on for many generations, having to provide for their
+own wants at a very early stage {448} of development, and secondly, from
+their following exactly the same habits of life with their parents; for in
+this case, it would be indispensable for the existence of the species, that
+the child should be modified at a very early age in the same manner with
+its parents, in accordance with their similar habits. Some further
+explanation, however, of the embryo not undergoing any metamorphosis is
+perhaps requisite. If, on the other hand, it profited the young to follow
+habits of life in any degree different from those of their parent, and
+consequently to be constructed in a slightly different manner, then, on the
+principle of inheritance at corresponding ages, the active young or larvæ
+might easily be rendered by natural selection different to any conceivable
+extent from their parents. Such differences might, also, become correlated
+with successive stages of development; so that the larvæ, in the first
+stage, might differ greatly from the larvæ in the second stage, as we have
+seen to be the case with cirripedes. The adult might become fitted for
+sites or habits, in which organs of locomotion or of the senses, &c., would
+be useless; and in this case the final metamorphosis would be said to be
+retrograde.
+
+As all the organic beings, extinct and recent, which have ever lived on
+this earth have to be classed together, and as all have been connected by
+the finest gradations, the best, or indeed, if our collections were nearly
+perfect, the only possible arrangement, would be genealogical. Descent
+being on my view the hidden bond of connexion which naturalists have been
+seeking under the term of the natural system. On this view we can
+understand how it is that, in the eyes of most naturalists, the structure
+of the embryo is even more important for classification than that of the
+adult. For the embryo is the animal in its less modified state; {449} and
+in so far it reveals the structure of its progenitor. In two groups of
+animals, however much they may at present differ from each other in
+structure and habits, if they pass through the same or similar embryonic
+stages, we may feel assured that they have both descended from the same or
+nearly similar parents, and are therefore in that degree closely related.
+Thus, community in embryonic structure reveals community of descent. It
+will reveal this community of descent, however much the structure of the
+adult may have been modified and obscured; we have seen, for instance, that
+cirripedes can at once be recognised by their larvæ as belonging to the
+great class of crustaceans. As the embryonic state of each species and
+group of species partially shows us the structure of their less modified
+ancient progenitors, we can clearly see why ancient and extinct forms of
+life should resemble the embryos of their descendants,--our existing
+species. Agassiz believes this to be a law of nature; but I am bound to
+confess that I only hope to see the law hereafter proved true. It can be
+proved true in those cases alone in which the ancient state, now supposed
+to be represented in existing embryos, has not been obliterated, either by
+the successive variations in a long course of modification having
+supervened at a very early age, or by the variations having been inherited
+at an earlier period than that at which they first appeared. It should also
+be borne in mind, that the supposed law of resemblance of ancient forms of
+life to the embryonic stages of recent forms, may be true, but yet, owing
+to the geological record not extending far enough back in time, may remain
+for a long period, or for ever, incapable of demonstration.
+
+Thus, as it seems to me, the leading facts in embryology, which are second
+in importance to none in natural history, are explained on the principle of
+slight {450} modifications not appearing, in the many descendants from some
+one ancient progenitor, at a very early period in the life of each, though
+perhaps caused at the earliest, and being inherited at a corresponding not
+early period. Embryology rises greatly in interest, when we thus look at
+the embryo as a picture, more or less obscured, of the common parent-form
+of each great class of animals.
+
+
+
+_Rudimentary, atrophied, or aborted Organs._--Organs or parts in this
+strange condition, bearing the stamp of inutility, are extremely common
+throughout nature. For instance, rudimentary mammæ are very general in the
+males of mammals: I presume that the "bastard-wing" in birds may be safely
+considered as a digit in a rudimentary state: in very many snakes one lobe
+of the lungs is rudimentary; in other snakes there are rudiments of the
+pelvis and hind limbs. Some of the cases of rudimentary organs are
+extremely curious; for instance, the presence of teeth in foetal whales,
+which when grown up have not a tooth in their heads; and the presence of
+teeth, which never cut through the gums, in the upper jaws of our unborn
+calves. It has even been stated on good authority that rudiments of teeth
+can be detected in the beaks of certain embryonic birds. Nothing can be
+plainer than that wings are formed for flight, yet in how many insects do
+we see wings so reduced in size as to be utterly incapable of flight, and
+not rarely lying under wing-cases, firmly soldered together!
+
+The meaning of rudimentary organs is often quite unmistakeable: for
+instance there are beetles of the same genus (and even of the same species)
+resembling each other most closely in all respects, one of which will have
+full-sized wings, and another mere rudiments of membrane; and here it is
+impossible to doubt, that the {451} rudiments represent wings. Rudimentary
+organs sometimes retain their potentiality, and are merely not developed:
+this seems to be the case with the mammæ of male mammals, for many
+instances are on record of these organs having become well developed in
+full-grown males, and having secreted milk. So again there are normally
+four developed and two rudimentary teats in the udders of the genus Bos,
+but in our domestic cows the two sometimes become developed and give milk.
+In plants of the same species the petals sometimes occur as mere rudiments,
+and sometimes in a well-developed state. In plants with separated sexes,
+the male flowers often have a rudiment of a pistil; and Kölreuter found
+that by crossing such male plants with an hermaphrodite species, the
+rudiment of the pistil in the hybrid offspring was much increased in size;
+and this shows that the rudiment and the perfect pistil are essentially
+alike in nature.
+
+An organ serving for two purposes, may become rudimentary or utterly
+aborted for one, even the more important purpose; and remain perfectly
+efficient for the other. Thus in plants, the office of the pistil is to
+allow the pollen-tubes to reach the ovules protected in the ovarium at its
+base. The pistil consists of a stigma supported on the style; but in some
+Compositæ, the male florets, which of course cannot be fecundated, have a
+pistil, which is in a rudimentary state, for it is not crowned with a
+stigma; but the style remains well developed, and is clothed with hairs as
+in other compositæ, for the purpose of brushing the pollen out of the
+surrounding anthers. Again, an organ may become rudimentary for its proper
+purpose, and be used for a distinct object: in certain fish the
+swim-bladder seems to be nearly rudimentary for its proper function of
+giving buoyancy, but has become converted into a {452} nascent breathing
+organ or lung. Other similar instances could be given.
+
+Organs, however little developed, if of use, should not be called
+rudimentary; they cannot properly be said to be in an atrophied condition;
+they may be called nascent, and may hereafter be developed to any extent by
+natural selection. Rudimentary organs, on the other hand, are essentially
+useless, as teeth which never cut through the gums; in a still less
+developed condition, they would be of still less use. They cannot,
+therefore, under their present condition, have been formed by natural
+selection, which acts solely by the preservation of useful modifications;
+they have been retained, as we shall see, by inheritance, and relate to a
+former condition of their possessor. It is difficult to know what are
+nascent organs; looking to the future, we cannot of course tell how any
+part will be developed, and whether it is now nascent; looking to the past,
+creatures with an organ in a nascent condition will generally have been
+supplanted and exterminated by their successors with the organ in a more
+perfect and developed condition. The wing of the penguin is of high
+service, and acts as a fin; it may, therefore, represent the nascent state
+of the wings of birds; not that I believe this to be the case, it is more
+probably a reduced organ, modified for a new function: the wing of the
+Apteryx is useless, and is truly rudimentary. The mammary glands of the
+Ornithorhynchus may, perhaps, be considered, in comparison with the udder
+of a cow, as in a nascent state. The ovigerous frena of certain cirripedes,
+which are only slightly developed and which have ceased to give attachment
+to the ova, are nascent branchiæ.
+
+Rudimentary organs in the individuals of the same species are very liable
+to vary in degree of development {453} and in other respects. Moreover, in
+closely allied species, the degree to which the same organ has been
+rendered rudimentary occasionally differs much. This latter fact is well
+exemplified in the state of the wings of the female moths in certain
+groups. Rudimentary organs may be utterly aborted; and this implies, that
+we find in an animal or plant no trace of an organ, which analogy would
+lead us to expect to find, and which is occasionally found in monstrous
+individuals of the species. Thus in the snapdragon (antirrhinum) we
+generally do not find a rudiment of a fifth stamen; but this may sometimes
+be seen. In tracing the homologies of the same part in different members of
+a class, nothing is more common, or more necessary, than the use and
+discovery of rudiments. This is well shown in the drawings given by Owen of
+the bones of the leg of the horse, ox, and rhinoceros.
+
+It is an important fact that rudimentary organs, such as teeth in the upper
+jaws of whales and ruminants, can often be detected in the embryo, but
+afterwards wholly disappear. It is also, I believe, a universal rule, that
+a rudimentary part or organ is of greater size relatively to the adjoining
+parts in the embryo, than in the adult; so that the organ at this early age
+is less rudimentary, or even cannot be said to be in any degree
+rudimentary. Hence, also, a rudimentary organ in the adult is often said to
+have retained its embryonic condition.
+
+I have now given the leading facts with respect to rudimentary organs. In
+reflecting on them, every one must be struck with astonishment: for the
+same reasoning power which tells us plainly that most parts and organs are
+exquisitely adapted for certain purposes, tells us with equal plainness
+that these rudimentary or atrophied organs, are imperfect and useless. In
+works {454} on natural history rudimentary organs are generally said to
+have been created "for the sake of symmetry," or in order "to complete the
+scheme of nature;" but this seems to me no explanation, merely a
+re-statement of the fact. Would it be thought sufficient to say that
+because planets revolve in elliptic courses round the sun, satellites
+follow the same course round the planets, for the sake of symmetry, and to
+complete the scheme of nature? An eminent physiologist accounts for the
+presence of rudimentary organs, by supposing that they serve to excrete
+matter in excess, or injurious to the system; but can we suppose that the
+minute papilla, which often represents the pistil in male flowers, and
+which is formed merely of cellular tissue, can thus act? Can we suppose
+that the formation of rudimentary teeth, which are subsequently absorbed,
+can be of any service to the rapidly growing embryonic calf by the
+excretion of precious phosphate of lime? When a man's fingers have been
+amputated, imperfect nails sometimes appear on the stumps: I could as soon
+believe that these vestiges of nails have appeared, not from unknown laws
+of growth, but in order to excrete horny matter, as that the rudimentary
+nails on the fin of the manatee were formed for this purpose.
+
+On my view of descent with modification, the origin of rudimentary organs
+is simple. We have plenty of cases of rudimentary organs in our domestic
+productions,--as the stump of a tail in tailless breeds,--the vestige of an
+ear in earless breeds,--the reappearance of minute dangling horns in
+hornless breeds of cattle, more especially, according to Youatt, in young
+animals,--and the state of the whole flower in the cauliflower. We often
+see rudiments of various parts in monsters. But I doubt whether any of
+these cases throw light on the origin of rudimentary organs in a state of
+nature, {455} further than by showing that rudiments can be produced; for I
+doubt whether species under nature ever undergo abrupt changes. I believe
+that disuse has been the main agency; that it has led in successive
+generations to the gradual reduction of various organs, until they have
+become rudimentary,--as in the case of the eyes of animals inhabiting dark
+caverns, and of the wings of birds inhabiting oceanic islands, which have
+seldom been forced to take flight, and have ultimately lost the power of
+flying. Again, an organ useful under certain conditions, might become
+injurious under others, as with the wings of beetles living on small and
+exposed islands; and in this case natural selection would continue slowly
+to reduce the organ, until it was rendered harmless and rudimentary.
+
+Any change in function, which can be effected by insensibly small steps, is
+within the power of natural selection; so that an organ rendered, during
+changed habits of life, useless or injurious for one purpose, might be
+modified and used for another purpose. Or an organ might be retained for
+one alone of its former functions. An organ, when rendered useless, may
+well be variable, for its variations cannot be checked by natural
+selection. At whatever period of life disuse or selection reduces an organ,
+and this will generally be when the being has come to maturity and to its
+full powers of action, the principle of inheritance at corresponding ages
+will reproduce the organ in its reduced state at the same age, and
+consequently will seldom affect or reduce it in the embryo. Thus we can
+understand the greater relative size of rudimentary organs in the embryo,
+and their lesser relative size in the adult. But if each step of the
+process of reduction were to be inherited, not at the corresponding age,
+but at an extremely early period of life (as we have good {456} reason to
+believe to be possible), the rudimentary part would tend to be wholly lost,
+and we should have a case of complete abortion. The principle, also, of
+economy, explained in a former chapter, by which the materials forming any
+part or structure, if not useful to the possessor, will be saved as far as
+is possible, will probably often come into play; and this will tend to
+cause the entire obliteration of a rudimentary organ.
+
+As the presence of rudimentary organs is thus due to the tendency in every
+part of the organisation, which has long existed, to be inherited--we can
+understand, on the genealogical view of classification, how it is that
+systematists have found rudimentary parts as useful as, or even sometimes
+more useful than, parts of high physiological importance. Rudimentary
+organs may be compared with the letters in a word, still retained in the
+spelling, but become useless in the pronunciation, but which serve as a
+clue in seeking for its derivation. On the view of descent with
+modification, we may conclude that the existence of organs in a
+rudimentary, imperfect, and useless condition, or quite aborted, far from
+presenting a strange difficulty, as they assuredly do on the ordinary
+doctrine of creation, might even have been anticipated, and can be
+accounted for by the laws of inheritance.
+
+
+
+_Summary._--In this chapter I have attempted to show, that the
+subordination of group to group in all organisms throughout all time; that
+the nature of the relationship, by which all living and extinct beings are
+united by complex, radiating, and circuitous lines of affinities into one
+grand system; the rules followed and the difficulties encountered by
+naturalists in their classifications; the value set upon characters, if
+constant and prevalent, whether of high vital importance, or of the most
+trifling {457} importance, or, as in rudimentary organs, of no importance;
+the wide opposition in value between analogical or adaptive characters, and
+characters of true affinity; and other such rules;--all naturally follow on
+the view of the common parentage of those forms which are considered by
+naturalists as allied, together with their modification through natural
+selection, with its contingencies of extinction and divergence of
+character. In considering this view of classification, it should be borne
+in mind that the element of descent has been universally used in ranking
+together the sexes, ages, and acknowledged varieties of the same species,
+however different they may be in structure. If we extend the use of this
+element of descent,--the only certainly known cause of similarity in
+organic beings,--we shall understand what is meant by the natural system:
+it is genealogical in its attempted arrangement, with the grades of
+acquired difference marked by the terms varieties, species, genera,
+families, orders, and classes.
+
+On this same view of descent with modification, all the great facts in
+Morphology become intelligible,--whether we look to the same pattern
+displayed in the homologous organs, to whatever purpose applied, of the
+different species of a class; or to the homologous parts constructed on the
+same pattern in each individual animal and plant.
+
+On the principle of successive slight variations, not necessarily or
+generally supervening at a very early period of life, and being inherited
+at a corresponding period, we can understand the great leading facts in
+Embryology; namely, the resemblance in an individual embryo of the
+homologous parts, which when matured will become widely different from each
+other in structure and function; and the resemblance in different species
+of a class of the homologous parts or {458} organs, though fitted in the
+adult members for purposes as different as possible. Larvæ are active
+embryos, which have become specially modified in relation to their habits
+of life, through the principle of modifications being inherited at
+corresponding ages. On this same principle--and bearing in mind, that when
+organs are reduced in size, either from disuse or selection, it will
+generally be at that period of life when the being has to provide for its
+own wants, and bearing in mind how strong is the principle of
+inheritance--the occurrence of rudimentary organs and their final abortion,
+present to us no inexplicable difficulties; on the contrary, their presence
+might have been even anticipated. The importance of embryological
+characters and of rudimentary organs in classification is intelligible, on
+the view that an arrangement is only so far natural as it is genealogical.
+
+Finally, the several classes of facts which have been considered in this
+chapter, seem to me to proclaim so plainly, that the innumerable species,
+genera, and families of organic beings, with which this world is peopled,
+have all descended, each within its own class or group, from common
+parents, and have all been modified in the course of descent, that I should
+without hesitation adopt this view, even if it were unsupported by other
+facts or arguments.
+
+       *       *       *       *       *
+
+
+{459}
+
+CHAPTER XIV.
+
+RECAPITULATION AND CONCLUSION.
+
+    Recapitulation of the difficulties on the theory of Natural
+    Selection--Recapitulation of the general and special circumstances in
+    its favour--Causes of the general belief in the immutability of
+    species--How far the theory of natural selection may be
+    extended--Effects of its adoption on the study of Natural
+    history--Concluding remarks.
+
+As this whole volume is one long argument, it may be convenient to the
+reader to have the leading facts and inferences briefly recapitulated.
+
+That many and serious objections may be advanced against the theory of
+descent with modification through natural selection, I do not deny. I have
+endeavoured to give to them their full force. Nothing at first can appear
+more difficult to believe than that the more complex organs and instincts
+should have been perfected, not by means superior to, though analogous
+with, human reason, but by the accumulation of innumerable slight
+variations, each good for the individual possessor. Nevertheless, this
+difficulty, though appearing to our imagination insuperably great, cannot
+be considered real if we admit the following propositions, namely,--that
+gradations in the perfection of any organ or instinct which we may
+consider, either do now exist or could have existed, each good of its
+kind,--that all organs and instincts are, in ever so slight a degree,
+variable,--and, lastly, that there is a struggle for existence leading to
+the preservation of each profitable deviation of structure or instinct. The
+truth of these propositions cannot, I think, be disputed. {460}
+
+It is, no doubt, extremely difficult even to conjecture by what gradations
+many structures have been perfected, more especially amongst broken and
+failing groups of organic beings; but we see so many strange gradations in
+nature, that we ought to be extremely cautious in saying that any organ or
+instinct, or any whole being, could not have arrived at its present state
+by many graduated steps. There are, it must be admitted, cases of special
+difficulty on the theory of natural selection; and one of the most curious
+of these is the existence of two or three defined castes of workers or
+sterile females in the same community of ants; but I have attempted to show
+how this difficulty can be mastered.
+
+With respect to the almost universal sterility of species when first
+crossed, which forms so remarkable a contrast with the almost universal
+fertility of varieties when crossed, I must refer the reader to the
+recapitulation of the facts given at the end of the eighth chapter, which
+seem to me conclusively to show that this sterility is no more a special
+endowment than is the incapacity of two trees to be grafted together; but
+that it is incidental on constitutional differences in the reproductive
+systems of the intercrossed species. We see the truth of this conclusion in
+the vast difference in the result, when the same two species are crossed
+reciprocally; that is, when one species is first used as the father and
+then as the mother.
+
+The fertility of varieties when intercrossed and of their mongrel offspring
+cannot be considered as universal; nor is their very general fertility
+surprising when we remember that it is not likely that either their
+constitutions or their reproductive systems should have been profoundly
+modified. Moreover, most of the varieties which have been experimentised on
+have been {461} produced under domestication; and as domestication (I do
+not mean mere confinement) apparently tends to eliminate sterility, we
+ought not to expect it also to produce sterility.
+
+The sterility of hybrids is a very different case from that of first
+crosses, for their reproductive organs are more or less functionally
+impotent; whereas in first crosses the organs on both sides are in a
+perfect condition. As we continually see that organisms of all kinds are
+rendered in some degree sterile from their constitutions having been
+disturbed by slightly different and new conditions of life, we need not
+feel surprise at hybrids being in some degree sterile, for their
+constitutions can hardly fail to have been disturbed from being compounded
+of two distinct organisations. This parallelism is supported by another
+parallel, but directly opposite, class of facts; namely, that the vigour
+and fertility of all organic beings are increased by slight changes in
+their conditions of life, and that the offspring of slightly modified forms
+or varieties acquire from being crossed increased vigour and fertility. So
+that, on the one hand, considerable changes in the conditions of life and
+crosses between greatly modified forms, lessen fertility; and on the other
+hand, lesser changes in the conditions of life and crosses between less
+modified forms, increase fertility.
+
+Turning to geographical distribution, the difficulties encountered on the
+theory of descent with modification are grave enough. All the individuals
+of the same species, and all the species of the same genus, or even higher
+group, must have descended from common parents; and therefore, in however
+distant and isolated parts of the world they are now found, they must in
+the course of successive generations have passed from some one part to the
+others. We are often wholly unable {462} even to conjecture how this could
+have been effected. Yet, as we have reason to believe that some species
+have retained the same specific form for very long periods, enormously long
+as measured by years, too much stress ought not to be laid on the
+occasional wide diffusion of the same species; for during very long periods
+of time there will always have been a good chance for wide migration by
+many means. A broken or interrupted range may often be accounted for by the
+extinction of the species in the intermediate regions. It cannot be denied
+that we are as yet very ignorant of the full extent of the various climatal
+and geographical changes which have affected the earth during modern
+periods; and such changes will obviously have greatly facilitated
+migration. As an example, I have attempted to show how potent has been the
+influence of the Glacial period on the distribution both of the same and of
+representative species throughout the world. We are as yet profoundly
+ignorant of the many occasional means of transport. With respect to
+distinct species of the same genus inhabiting very distant and isolated
+regions, as the process of modification has necessarily been slow, all the
+means of migration will have been possible during a very long period; and
+consequently the difficulty of the wide diffusion of species of the same
+genus is in some degree lessened.
+
+As on the theory of natural selection an interminable number of
+intermediate forms must have existed, linking together all the species in
+each group by gradations as fine as our present varieties, it may be asked,
+Why do we not see these linking forms all around us? Why are not all
+organic beings blended together in an inextricable chaos? With respect to
+existing forms, we should remember that we have no right to expect
+(excepting in rare cases) to discover _directly_ connecting {463} links
+between them, but only between each and some extinct and supplanted form.
+Even on a wide area, which has during a long period remained continuous,
+and of which the climate and other conditions of life change insensibly in
+going from a district occupied by one species into another district
+occupied by a closely allied species, we have no just right to expect often
+to find intermediate varieties in the intermediate zone. For we have reason
+to believe that only a few species are undergoing change at any one period;
+and all changes are slowly effected. I have also shown that the
+intermediate varieties which will at first probably exist in the
+intermediate zones, will be liable to be supplanted by the allied forms on
+either hand; and the latter, from existing in greater numbers, will
+generally be modified and improved at a quicker rate than the intermediate
+varieties, which exist in lesser numbers; so that the intermediate
+varieties will, in the long run, be supplanted and exterminated.
+
+On this doctrine of the extermination of an infinitude of connecting links,
+between the living and extinct inhabitants of the world, and at each
+successive period between the extinct and still older species, why is not
+every geological formation charged with such links? Why does not every
+collection of fossil remains afford plain evidence of the gradation and
+mutation of the forms of life? We meet with no such evidence, and this is
+the most obvious and forcible of the many objections which may be urged
+against my theory. Why, again, do whole groups of allied species appear,
+though certainly they often falsely appear, to have come in suddenly on the
+several geological stages? Why do we not find great piles of strata beneath
+the Silurian system, stored with the remains of the progenitors of the
+Silurian groups of fossils? For certainly on my theory such {464} strata
+must somewhere have been deposited at these ancient and utterly unknown
+epochs in the world's history.
+
+I can answer these questions and grave objections only on the supposition
+that the geological record is far more imperfect than most geologists
+believe. It cannot be objected that there has not been time sufficient for
+any amount of organic change; for the lapse of time has been so great as to
+be utterly inappreciable by the human intellect. The number of specimens in
+all our museums is absolutely as nothing compared with the countless
+generations of countless species which certainly have existed. We should
+not be able to recognise a species as the parent of any one or more species
+if we were to examine them ever so closely, unless we likewise possessed
+many of the intermediate links between their past or parent and present
+states; and these many links we could hardly ever expect to discover, owing
+to the imperfection of the geological record. Numerous existing doubtful
+forms could be named which are probably varieties; but who will pretend
+that in future ages so many fossil links will be discovered, that
+naturalists will be able to decide, on the common view, whether or not
+these doubtful forms are varieties? As long as most of the links between
+any two species are unknown, if any one link or intermediate variety be
+discovered, it will simply be classed as another and distinct species. Only
+a small portion of the world has been geologically explored. Only organic
+beings of certain classes can be preserved in a fossil condition, at least
+in any great number. Widely ranging species vary most, and varieties are
+often at first local,--both causes rendering the discovery of intermediate
+links less likely. Local varieties will not spread into other and distant
+regions until they are considerably modified and {465} improved; and when
+they do spread, if discovered in a geological formation, they will appear
+as if suddenly created there, and will be simply classed as new species.
+Most formations have been intermittent in their accumulation; and their
+duration, I am inclined to believe, has been shorter than the average
+duration of specific forms. Successive formations are separated from each
+other by enormous blank intervals of time; for fossiliferous formations,
+thick enough to resist future degradation, can be accumulated only where
+much sediment is deposited on the subsiding bed of the sea. During the
+alternate periods of elevation and of stationary level the record will be
+blank. During these latter periods there will probably be more variability
+in the forms of life; during periods of subsidence, more extinction.
+
+With respect to the absence of fossiliferous formations beneath the lowest
+Silurian strata, I can only recur to the hypothesis given in the ninth
+chapter. That the geological record is imperfect all will admit; but that
+it is imperfect to the degree which I require, few will be inclined to
+admit. If we look to long enough intervals of time, geology plainly
+declares that all species have changed; and they have changed in the manner
+which my theory requires, for they have changed slowly and in a graduated
+manner. We clearly see this in the fossil remains from consecutive
+formations invariably being much more closely related to each other, than
+are the fossils from formations distant from each other in time.
+
+Such is the sum of the several chief objections and difficulties which may
+justly be urged against my theory; and I have now briefly recapitulated the
+answers and explanations which can be given to them. I have felt these
+difficulties far too heavily during many years to {466} doubt their weight.
+But it deserves especial notice that the more important objections relate
+to questions on which we are confessedly ignorant; nor do we know how
+ignorant we are. We do not know all the possible transitional gradations
+between the simplest and the most perfect organs; it cannot be pretended
+that we know all the varied means of Distribution during the long lapse of
+years, or that we know how imperfect the Geological Record is. Grave as
+these several difficulties are, in my judgment they do not overthrow the
+theory of descent from a few created forms with subsequent modification.
+
+
+
+Now let us turn to the other side of the argument. Under domestication we
+see much variability. This seems to be mainly due to the reproductive
+system being eminently susceptible to changes in the conditions of life; so
+that this system, when not rendered impotent, fails to reproduce offspring
+exactly like the parent-form. Variability is governed by many complex
+laws,--by correlation of growth, by use and disuse, and by the direct
+action of the physical conditions of life. There is much difficulty in
+ascertaining how much modification our domestic productions have undergone;
+but we may safely infer that the amount has been large, and that
+modifications can be inherited for long periods. As long as the conditions
+of life remain the same, we have reason to believe that a modification,
+which has already been inherited for many generations, may continue to be
+inherited for an almost infinite number of generations. On the other hand
+we have evidence that variability, when it has once come into play, does
+not wholly cease; for new varieties are still occasionally produced by our
+most anciently domesticated productions. {467}
+
+Man does not actually produce variability; he only unintentionally exposes
+organic beings to new conditions of life, and then nature acts on the
+organisation, and causes variability. But man can and does select the
+variations given to him by nature, and thus accumulate them in any desired
+manner. He thus adapts animals and plants for his own benefit or pleasure.
+He may do this methodically, or he may do it unconsciously by preserving
+the individuals most useful to him at the time, without any thought of
+altering the breed. It is certain that he can largely influence the
+character of a breed by selecting, in each successive generation,
+individual differences so slight as to be quite inappreciable by an
+uneducated eye. This process of selection has been the great agency in the
+production of the most distinct and useful domestic breeds. That many of
+the breeds produced by man have to a large extent the character of natural
+species, is shown by the inextricable doubts whether very many of them are
+varieties or aboriginal species.
+
+There is no obvious reason why the principles which have acted so
+efficiently under domestication should not have acted under nature. In the
+preservation of favoured individuals and races, during the
+constantly-recurrent Struggle for Existence, we see the most powerful and
+ever-acting means of selection. The struggle for existence inevitably
+follows from the high geometrical ratio of increase which is common to all
+organic beings. This high rate of increase is proved by calculation,--by
+the rapid increase of many animals and plants during a succession of
+peculiar seasons, or when naturalised in a new country. More individuals
+are born than can possibly survive. A grain in the balance will determine
+which individual shall live and which shall die,--which variety or species
+shall increase in number, and which {468} shall decrease, or finally become
+extinct. As the individuals of the same species come in all respects into
+the closest competition with each other, the struggle will generally be
+most severe between them; it will be almost equally severe between the
+varieties of the same species, and next in severity between the species of
+the same genus. But the struggle will often be very severe between beings
+most remote in the scale of nature. The slightest advantage in one being,
+at any age or during any season, over those with which it comes into
+competition, or better adaptation in however slight a degree to the
+surrounding physical conditions, will turn the balance.
+
+With animals having separated sexes there will in most cases be a struggle
+between the males for possession of the females. The most vigorous
+individuals, or those which have most successfully struggled with their
+conditions of life, will generally leave most progeny. But success will
+often depend on having special weapons or means of defence, or on the
+charms of the males; and the slightest advantage will lead to victory.
+
+As geology plainly proclaims that each land has undergone great physical
+changes, we might have expected that organic beings would have varied under
+nature, in the same way as they generally have varied under the changed
+conditions of domestication. And if there be any variability under nature,
+it would be an unaccountable fact if natural selection had not come into
+play. It has often been asserted, but the assertion is quite incapable of
+proof, that the amount of variation under nature is a strictly limited
+quantity. Man, though acting on external characters alone and often
+capriciously, can produce within a short period a great result by adding up
+mere individual differences in his domestic productions; and every one
+admits that there are at least individual differences in species under
+{469} nature. But, besides such differences, all naturalists have admitted
+the existence of varieties, which they think sufficiently distinct to be
+worthy of record in systematic works. No one can draw any clear distinction
+between individual differences and slight varieties; or between more
+plainly marked varieties and sub-species, and species. Let it be observed
+how naturalists differ in the rank which they assign to the many
+representative forms in Europe and North America.
+
+If then we have under nature variability and a powerful agent always ready
+to act and select, why should we doubt that variations in any way useful to
+beings, under their excessively complex relations of life, would be
+preserved, accumulated, and inherited? Why, if man can by patience select
+variations most useful to himself, should nature fail in selecting
+variations useful, under changing conditions of life, to her living
+products? What limit can be put to this power, acting during long ages and
+rigidly scrutinising the whole constitution, structure, and habits of each
+creature,--favouring the good and rejecting the bad? I can see no limit to
+this power, in slowly and beautifully adapting each form to the most
+complex relations of life. The theory of natural selection, even if we
+looked no further than this, seems to me to be in itself probable. I have
+already recapitulated, as fairly as I could, the opposed difficulties and
+objections: now let us turn to the special facts and arguments in favour of
+the theory.
+
+On the view that species are only strongly marked and permanent varieties,
+and that each species first existed as a variety, we can see why it is that
+no line of demarcation can be drawn between species, commonly supposed to
+have been produced by special acts of creation, and varieties which are
+acknowledged to have been produced by secondary laws. On this same {470}
+view we can understand how it is that in each region where many species of
+a genus have been produced, and where they now flourish, these same species
+should present many varieties; for where the manufactory of species has
+been active, we might expect, as a general rule, to find it still in
+action; and this is the case if varieties be incipient species. Moreover,
+the species of the larger genera, which afford the greater number of
+varieties or incipient species, retain to a certain degree the character of
+varieties; for they differ from each other by a less amount of difference
+than do the species of smaller genera. The closely allied species also of
+the larger genera apparently have restricted ranges, and in their
+affinities they are clustered in little groups round other species--in
+which respects they resemble varieties. These are strange relations on the
+view of each species having been independently created, but are
+intelligible if all species first existed as varieties.
+
+As each species tends by its geometrical ratio of reproduction to increase
+inordinately in number; and as the modified descendants of each species
+will be enabled to increase by so much the more as they become diversified
+in habits and structure, so as to be enabled to seize on many and widely
+different places in the economy of nature, there will be a constant
+tendency in natural selection to preserve the most divergent offspring of
+any one species. Hence during a long-continued course of modification, the
+slight differences, characteristic of varieties of the same species, tend
+to be augmented into the greater differences characteristic of species of
+the same genus. New and improved varieties will inevitably supplant and
+exterminate the older, less improved and intermediate varieties; and thus
+species are rendered to a large extent defined and distinct objects.
+Dominant species belonging to the {471} larger groups tend to give birth to
+new and dominant forms; so that each large group tends to become still
+larger, and at the same time more divergent in character. But as all groups
+cannot thus succeed in increasing in size, for the world would not hold
+them, the more dominant groups beat the less dominant. This tendency in the
+large groups to go on increasing in size and diverging in character,
+together with the almost inevitable contingency of much extinction,
+explains the arrangement of all the forms of life, in groups subordinate to
+groups, all within a few great classes, which we now see everywhere around
+us, and which has prevailed throughout all time. This grand fact of the
+grouping of all organic beings seems to me utterly inexplicable on the
+theory of creation.
+
+As natural selection acts solely by accumulating slight, successive,
+favourable variations, it can produce no great or sudden modification; it
+can act only by very short and slow steps. Hence the canon of "Natura non
+facit saltum," which every fresh addition to our knowledge tends to make
+truer, is on this theory simply intelligible. We can plainly see why nature
+is prodigal in variety, though niggard in innovation. But why this should
+be a law of nature if each species has been independently created, no man
+can explain.
+
+Many other facts are, as it seems to me, explicable on this theory. How
+strange it is that a bird, under the form of woodpecker, should have been
+created to prey on insects on the ground; that upland geese, which never or
+rarely swim, should have been created with webbed feet; that a thrush
+should have been created to dive and feed on sub-aquatic insects; and that
+a petrel should have been created with habits and structure fitting it for
+the life of an auk or grebe! and so on in endless other cases. But on the
+view of each {472} species constantly trying to increase in number, with
+natural selection always ready to adapt the slowly varying descendants of
+each to any unoccupied or ill-occupied place in nature, these facts cease
+to be strange, or perhaps might even have been anticipated.
+
+As natural selection acts by competition, it adapts the inhabitants of each
+country only in relation to the degree of perfection of their associates;
+so that we need feel no surprise at the inhabitants of any one country,
+although on the ordinary view supposed to have been specially created and
+adapted for that country, being beaten and supplanted by the naturalised
+productions from another land. Nor ought we to marvel if all the
+contrivances in nature be not, as far as we can judge, absolutely perfect;
+and if some of them be abhorrent to our ideas of fitness. We need not
+marvel at the sting of the bee causing the bee's own death; at drones being
+produced in such vast numbers for one single act, with the great majority
+slaughtered by their sterile sisters; at the astonishing waste of pollen by
+our fir-trees; at the instinctive hatred of the queen bee for her own
+fertile daughters; at ichneumonidæ feeding within the live bodies of
+caterpillars; and at other such cases. The wonder indeed is, on the theory
+of natural selection, that more cases of the want of absolute perfection
+have not been observed.
+
+The complex and little known laws governing variation are the same, as far
+as we can see, with the laws which have governed the production of
+so-called specific forms. In both cases physical conditions seem to have
+produced but little direct effect; yet when varieties enter any zone, they
+occasionally assume some of the characters of the species proper to that
+zone. In both varieties and species, use and disuse seem to have produced
+some effect; for it is difficult to resist this {473} conclusion when we
+look, for instance, at the logger-headed duck, which has wings incapable of
+flight, in nearly the same condition as in the domestic duck; or when we
+look at the burrowing tucutucu, which is occasionally blind, and then at
+certain moles, which are habitually blind and have their eyes covered with
+skin; or when we look at the blind animals inhabiting the dark caves of
+America and Europe. In both varieties and species correlation of growth
+seems to have played a most important part, so that when one part has been
+modified other parts are necessarily modified. In both varieties and
+species reversions to long-lost characters occur. How inexplicable on the
+theory of creation is the occasional appearance of stripes on the shoulder
+and legs of the several species of the horse-genus and in their hybrids!
+How simply is this fact explained if we believe that these species have
+descended from a striped progenitor, in the same manner as the several
+domestic breeds of pigeon have descended from the blue and barred
+rock-pigeon!
+
+On the ordinary view of each species having been independently created, why
+should the specific characters, or those by which the species of the same
+genus differ from each other, be more variable than the generic characters
+in which they all agree? Why, for instance, should the colour of a flower
+be more likely to vary in any one species of a genus, if the other species,
+supposed to have been created independently, have differently coloured
+flowers, than if all the species of the genus have the same coloured
+flowers? If species are only well-marked varieties, of which the characters
+have become in a high degree permanent, we can understand this fact; for
+they have already varied since they branched off from a common progenitor
+in certain characters, by which they have come to be specifically distinct
+from each other; {474} and therefore these same characters would be more
+likely still to be variable than the generic characters which have been
+inherited without change for an enormous period. It is inexplicable on the
+theory of creation why a part developed in a very unusual manner in any one
+species of a genus, and therefore, as we may naturally infer, of great
+importance to the species, should be eminently liable to variation; but, on
+my view, this part has undergone, since the several species branched off
+from a common progenitor, an unusual amount of variability and
+modification, and therefore we might expect this part generally to be still
+variable. But a part may be developed in the most unusual manner, like the
+wing of a bat, and yet not be more variable than any other structure, if
+the part be common to many subordinate forms, that is, if it has been
+inherited for a very long period; for in this case it will have been
+rendered constant by long-continued natural selection.
+
+Glancing at instincts, marvellous as some are, they offer no greater
+difficulty than does corporeal structure on the theory of the natural
+selection of successive, slight, but profitable modifications. We can thus
+understand why nature moves by graduated steps in endowing different
+animals of the same class with their several instincts. I have attempted to
+show how much light the principle of gradation throws on the admirable
+architectural powers of the hive-bee. Habit no doubt sometimes comes into
+play in modifying instincts; but it certainly is not indispensable, as we
+see, in the case of neuter insects, which leave no progeny to inherit the
+effects of long-continued habit. On the view of all the species of the same
+genus having descended from a common parent, and having inherited much in
+common, we can understand how it is that allied species, when placed under
+considerably different conditions of life, {475} yet should follow nearly
+the same instincts; why the thrush of South America, for instance, lines
+her nest with mud like our British species. On the view of instincts having
+been slowly acquired through natural selection we need not marvel at some
+instincts being apparently not perfect and liable to mistakes, and at many
+instincts causing other animals to suffer.
+
+If species be only well-marked and permanent varieties, we can at once see
+why their crossed offspring should follow the same complex laws in their
+degrees and kinds of resemblance to their parents,--in being absorbed into
+each other by successive crosses, and in other such points,--as do the
+crossed offspring of acknowledged varieties. On the other hand, these would
+be strange facts if species have been independently created, and varieties
+have been produced by secondary laws.
+
+If we admit that the geological record is imperfect in an extreme degree,
+then such facts as the record gives, support the theory of descent with
+modification. New species have come on the stage slowly and at successive
+intervals; and the amount of change, after equal intervals of time, is
+widely different in different groups. The extinction of species and of
+whole groups of species, which has played so conspicuous a part in the
+history of the organic world, almost inevitably follows on the principle of
+natural selection; for old forms will be supplanted by new and improved
+forms. Neither single species nor groups of species reappear when the chain
+of ordinary generation has once been broken. The gradual diffusion of
+dominant forms, with the slow modification of their descendants, causes the
+forms of life, after long intervals of time, to appear as if they had
+changed simultaneously throughout the world. The fact of the fossil remains
+of each formation being in some degree intermediate in character between
+the {476} fossils in the formations above and below, is simply explained by
+their intermediate position in the chain of descent. The grand fact that
+all extinct organic beings belong to the same system with recent beings,
+falling either into the same or into intermediate groups, follows from the
+living and the extinct being the offspring of common parents. As the groups
+which have descended from an ancient progenitor have generally diverged in
+character, the progenitor with its early descendants will often be
+intermediate in character in comparison with its later descendants; and
+thus we can see why the more ancient a fossil is, the oftener it stands in
+some degree intermediate between existing and allied groups. Recent forms
+are generally looked at as being, in some vague sense, higher than ancient
+and extinct forms; and they are in so far higher as the later and more
+improved forms have conquered the older and less improved organic beings in
+the struggle for life. Lastly, the law of the long endurance of allied
+forms on the same continent,--of marsupials in Australia, of edentata in
+America, and other such cases,--is intelligible, for within a confined
+country, the recent and the extinct will naturally be allied by descent.
+
+Looking to geographical distribution, if we admit that there has been
+during the long course of ages much migration from one part of the world to
+another, owing to former climatal and geographical changes and to the many
+occasional and unknown means of dispersal, then we can understand, on the
+theory of descent with modification, most of the great leading facts in
+Distribution. We can see why there should be so striking a parallelism in
+the distribution of organic beings throughout space, and in their
+geological succession throughout time; for in both cases the beings have
+been connected by the bond of ordinary generation, and the means of {477}
+modification have been the same. We see the full meaning of the wonderful
+fact, which must have struck every traveller, namely, that on the same
+continent, under the most diverse conditions, under heat and cold, on
+mountain and lowland, on deserts and marshes, most of the inhabitants
+within each great class are plainly related; for they will generally be
+descendants of the same progenitors and early colonists. On this same
+principle of former migration, combined in most cases with modification, we
+can understand, by the aid of the Glacial period, the identity of some few
+plants, and the close alliance of many others, on the most distant
+mountains, under the most different climates; and likewise the close
+alliance of some of the inhabitants of the sea in the northern and southern
+temperate zones, though separated by the whole intertropical ocean.
+Although two areas may present the same physical conditions of life, we
+need feel no surprise at their inhabitants being widely different, if they
+have been for a long period completely separated from each other; for as
+the relation of organism to organism is the most important of all
+relations, and as the two areas will have received colonists from some
+third source or from each other, at various periods and in different
+proportions, the course of modification in the two areas will inevitably be
+different.
+
+On this view of migration, with subsequent modification, we can see why
+oceanic islands should be inhabited by few species, but of these, that many
+should be peculiar. We can clearly see why those animals which cannot cross
+wide spaces of ocean, as frogs and terrestrial mammals, should not inhabit
+oceanic islands; and why, on the other hand, new and peculiar species of
+bats, which can traverse the ocean, should so often be found on islands far
+distant from any continent. Such facts {478} as the presence of peculiar
+species of bats, and the absence of all other mammals, on oceanic islands,
+are utterly inexplicable on the theory of independent acts of creation.
+
+The existence of closely allied or representative species in any two areas,
+implies, on the theory of descent with modification, that the same parents
+formerly inhabited both areas; and we almost invariably find that wherever
+many closely allied species inhabit two areas, some identical species
+common to both still exist. Wherever many closely allied yet distinct
+species occur, many doubtful forms and varieties of the same species
+likewise occur. It is a rule of high generality that the inhabitants of
+each area are related to the inhabitants of the nearest source whence
+immigrants might have been derived. We see this in nearly all the plants
+and animals of the Galapagos archipelago, of Juan Fernandez, and of the
+other American islands being related in the most striking manner to the
+plants and animals of the neighbouring American mainland; and those of the
+Cape de Verde archipelago and other African islands to the African
+mainland. It must be admitted that these facts receive no explanation on
+the theory of creation.
+
+The fact, as we have seen, that all past and present organic beings
+constitute one grand natural system, with group subordinate to group, and
+with extinct groups often falling in between recent groups, is intelligible
+on the theory of natural selection with its contingencies of extinction and
+divergence of character. On these same principles we see how it is, that
+the mutual affinities of the species and genera within each class are so
+complex and circuitous. We see why certain characters are far more
+serviceable than others for classification;--why adaptive characters,
+though of paramount importance to the being, are of hardly any {479}
+importance in classification; why characters derived from rudimentary
+parts, though of no service to the being, are often of high classificatory
+value; and why embryological characters are the most valuable of all. The
+real affinities of all organic beings are due to inheritance or community
+of descent. The natural system is a genealogical arrangement, in which we
+have to discover the lines of descent by the most permanent characters,
+however slight their vital importance may be.
+
+The framework of bones being the same in the hand of a man, wing of a bat,
+fin of the porpoise, and leg of the horse,--the same number of vertebræ
+forming the neck of the giraffe and of the elephant,--and innumerable other
+such facts, at once explain themselves on the theory of descent with slow
+and slight successive modifications. The similarity of pattern in the wing
+and leg of a bat, though used for such different purpose,--in the jaws and
+legs of a crab,--in the petals, stamens, and pistils of a flower, is
+likewise intelligible on the view of the gradual modification of parts or
+organs, which were alike in the early progenitor of each class. On the
+principle of successive variations not always supervening at an early age,
+and being inherited at a corresponding not early period of life, we can
+clearly see why the embryos of mammals, birds, reptiles, and fishes should
+be so closely alike, and should be so unlike the adult forms. We may cease
+marvelling at the embryo of an air-breathing mammal or bird having
+branchial slits and arteries running in loops, like those in a fish which
+has to breathe the air dissolved in water, by the aid of well-developed
+branchiæ.
+
+Disuse, aided sometimes by natural selection, will often tend to reduce an
+organ, when it has become useless by changed habits or under changed
+conditions {480} of life; and we can clearly understand on this view the
+meaning of rudimentary organs. But disuse and selection will generally act
+on each creature, when it has come to maturity and has to play its full
+part in the struggle for existence, and will thus have little power of
+acting on an organ during early life; hence the organ will not be much
+reduced or rendered rudimentary at this early age. The calf, for instance,
+has inherited teeth, which never cut through the gums of the upper jaw,
+from an early progenitor having well-developed teeth; and we may believe,
+that the teeth in the mature animal were reduced, during successive
+generations, by disuse or by the tongue and palate having been better
+fitted by natural selection to browse without their aid; whereas in the
+calf, the teeth have been left untouched by selection or disuse, and on the
+principle of inheritance at corresponding ages have been inherited from a
+remote period to the present day. On the view of each organic being and
+each separate organ having been specially created, how utterly inexplicable
+it is that parts, like the teeth in the embryonic calf or like the
+shrivelled wings under the soldered wing-covers of some beetles, should
+thus so frequently bear the plain stamp of inutility! Nature may be said to
+have taken pains to reveal, by rudimentary organs and by homologous
+structures, her scheme of modification, which it seems that we wilfully
+will not understand.
+
+
+
+I have now recapitulated the chief facts and considerations which have
+thoroughly convinced me that species have been modified, during a long
+course of descent, by the preservation or the natural selection of many
+successive slight favourable variations. I cannot believe that a false
+theory would explain, as it seems to me that the theory of natural
+selection does explain, {481} the several large classes of facts above
+specified. I see no good reason why the views given in this volume should
+shock the religious feelings of any one. A celebrated author and divine has
+written to me that "he has gradually learnt to see that it is just as noble
+a conception of the Deity to believe that He created a few original forms
+capable of self-development into other and needful forms, as to believe
+that He required a fresh act of creation to supply the voids caused by the
+action of His laws."
+
+Why, it may be asked, have all the most eminent living naturalists and
+geologists rejected this view of the mutability of species? It cannot be
+asserted that organic beings in a state of nature are subject to no
+variation; it cannot be proved that the amount of variation in the course
+of long ages is a limited quantity; no clear distinction has been, or can
+be, drawn between species and well-marked varieties. It cannot be
+maintained that species when intercrossed are invariably sterile, and
+varieties invariably fertile; or that sterility is a special endowment and
+sign of creation. The belief that species were immutable productions was
+almost unavoidable as long as the history of the world was thought to be of
+short duration; and now that we have acquired some idea of the lapse of
+time, we are too apt to assume, without proof, that the geological record
+is so perfect that it would have afforded us plain evidence of the mutation
+of species, if they had undergone mutation.
+
+But the chief cause of our natural unwillingness to admit that one species
+has given birth to other and distinct species, is that we are always slow
+in admitting any great change of which we do not see the intermediate
+steps. The difficulty is the same as that felt by so many geologists, when
+Lyell first insisted that long {482} lines of inland cliffs had been
+formed, and great valleys excavated, by the slow action of the coast-waves.
+The mind cannot possibly grasp the full meaning of the term of a hundred
+million years; it cannot add up and perceive the full effects of many
+slight variations, accumulated during an almost infinite number of
+generations.
+
+Although I am fully convinced of the truth of the views given in this
+volume under the form of an abstract, I by no means expect to convince
+experienced naturalists whose minds are stocked with a multitude of facts
+all viewed, during a long course of years, from a point of view directly
+opposite to mine. It is so easy to hide our ignorance under such
+expressions as the "plan of creation," "unity of design," &c., and to think
+that we give an explanation when we only restate a fact. Any one whose
+disposition leads him to attach more weight to unexplained difficulties
+than to the explanation of a certain number of facts will certainly reject
+my theory. A few naturalists, endowed with much flexibility of mind, and
+who have already begun to doubt on the immutability of species, may be
+influenced by this volume; but I look with confidence to the future, to
+young and rising naturalists, who will be able to view both sides of the
+question with impartiality. Whoever is led to believe that species are
+mutable will do good service by conscientiously expressing his conviction;
+for only thus can the load of prejudice by which this subject is
+overwhelmed be removed.
+
+Several eminent naturalists have of late published their belief that a
+multitude of reputed species in each genus are not real species; but that
+other species are real, that is, have been independently created. This
+seems to me a strange conclusion to arrive at. They admit that a multitude
+of forms, which till lately {483} they themselves thought were special
+creations, and which are still thus looked at by the majority of
+naturalists, and which consequently have every external characteristic
+feature of true species,--they admit that these have been produced by
+variation, but they refuse to extend the same view to other and very
+slightly different forms. Nevertheless they do not pretend that they can
+define, or even conjecture, which are the created forms of life, and which
+are those produced by secondary laws. They admit variation as a _vera
+causa_ in one case, they arbitrarily reject it in another, without
+assigning any distinction in the two cases. The day will come when this
+will be given as a curious illustration of the blindness of preconceived
+opinion. These authors seem no more startled at a miraculous act of
+creation than at an ordinary birth. But do they really believe that at
+innumerable periods in the earth's history certain elemental atoms have
+been commanded suddenly to flash into living tissues? Do they believe that
+at each supposed act of creation one individual or many were produced? Were
+all the infinitely numerous kinds of animals and plants created as eggs or
+seed, or as full grown? and in the case of mammals, were they created
+bearing the false marks of nourishment from the mother's womb? Although
+naturalists very properly demand a full explanation of every difficulty
+from those who believe in the mutability of species, on their own side they
+ignore the whole subject of the first appearance of species in what they
+consider reverent silence.
+
+It may be asked how far I extend the doctrine of the modification of
+species. The question is difficult to answer, because the more distinct the
+forms are which we may consider, by so much the arguments fall away in
+force. But some arguments of the greatest weight {484} extend very far. All
+the members of whole classes can be connected together by chains of
+affinities, and all can be classified on the same principle, in groups
+subordinate to groups. Fossil remains sometimes tend to fill up very wide
+intervals between existing orders. Organs in a rudimentary condition
+plainly show that an early progenitor had the organ in a fully developed
+state; and this in some instances necessarily implies an enormous amount of
+modification in the descendants. Throughout whole classes various
+structures are formed on the same pattern, and at an embryonic age the
+species closely resemble each other. Therefore I cannot doubt that the
+theory of descent with modification embraces all the members of the same
+class. I believe that animals have descended from at most only four or five
+progenitors, and plants from an equal or lesser number.
+
+Analogy would lead me one step further, namely, to the belief that all
+animals and plants have descended from some one prototype. But analogy may
+be a deceitful guide. Nevertheless all living things have much in common,
+in their chemical composition, their germinal vesicles, their cellular
+structure, and their laws of growth and reproduction. We see this even in
+so trifling a circumstance as that the same poison often similarly affects
+plants and animals; or that the poison secreted by the gall-fly produces
+monstrous growths on the wild rose or oak-tree. Therefore I should infer
+from analogy that probably all the organic beings which have ever lived on
+this earth have descended from some one primordial form, into which life
+was first breathed by the Creator.
+
+
+
+When the views advanced by me in this volume, and by Mr. Wallace in the
+Linnean Journal, or when analogous views on the origin of species are
+generally {485} admitted, we can dimly foresee that there will be a
+considerable revolution in natural history. Systematists will be able to
+pursue their labours as at present; but they will not be incessantly
+haunted by the shadowy doubt whether this or that form be in essence a
+species. This I feel sure, and I speak after experience, will be no slight
+relief. The endless disputes whether or not some fifty species of British
+brambles are true species will cease. Systematists will have only to decide
+(not that this will be easy) whether any form be sufficiently constant and
+distinct from other forms, to be capable of definition; and if definable,
+whether the differences be sufficiently important to deserve a specific
+name. This latter point will become a far more essential consideration than
+it is at present; for differences, however slight, between any two forms,
+if not blended by intermediate gradations, are looked at by most
+naturalists as sufficient to raise both forms to the rank of species.
+Hereafter we shall be compelled to acknowledge that the only distinction
+between species and well-marked varieties is, that the latter are known, or
+believed, to be connected at the present day by intermediate gradations,
+whereas species were formerly thus connected. Hence, without rejecting the
+consideration of the present existence of intermediate gradations between
+any two forms, we shall be led to weigh more carefully and to value higher
+the actual amount of difference between them. It is quite possible that
+forms now generally acknowledged to be merely varieties may hereafter be
+thought worthy of specific names, as with the primrose and cowslip; and in
+this case scientific and common language will come into accordance. In
+short, we shall have to treat species in the same manner as those
+naturalists treat genera, who admit that genera are merely artificial
+combinations {486} made for convenience. This may not be a cheering
+prospect; but we shall at least be freed from the vain search for the
+undiscovered and undiscoverable essence of the term species.
+
+The other and more general departments of natural history will rise greatly
+in interest. The terms used by naturalists of affinity, relationship,
+community of type, paternity, morphology, adaptive characters, rudimentary
+and aborted organs, &c., will cease to be metaphorical, and will have a
+plain signification. When we no longer look at an organic being as a savage
+looks at a ship, as at something wholly beyond his comprehension; when we
+regard every production of nature as one which has had a history; when we
+contemplate every complex structure and instinct as the summing up of many
+contrivances, each useful to the possessor, nearly in the same way as when
+we look at any great mechanical invention as the summing up of the labour,
+the experience, the reason, and even the blunders of numerous workmen; when
+we thus view each organic being, how far more interesting, I speak from
+experience, will the study of natural history become!
+
+A grand and almost untrodden field of inquiry will be opened, on the causes
+and laws of variation, on correlation of growth, on the effects of use and
+disuse, on the direct action of external conditions, and so forth. The
+study of domestic productions will rise immensely in value. A new variety
+raised by man will be a more important and interesting subject for study
+than one more species added to the infinitude of already recorded species.
+Our classifications will come to be, as far as they can be so made,
+genealogies; and will then truly give what may be called the plan of
+creation. The rules for classifying will no doubt become simpler when we
+have a definite object in view. We possess no {487} pedigrees or armorial
+bearings; and we have to discover and trace the many diverging lines of
+descent in our natural genealogies, by characters of any kind which have
+long been inherited. Rudimentary organs will speak infallibly with respect
+to the nature of long-lost structures. Species and groups of species, which
+are called aberrant, and which may fancifully be called living fossils,
+will aid us in forming a picture of the ancient forms of life. Embryology
+will reveal to us the structure, in some degree obscured, of the prototypes
+of each great class.
+
+When we can feel assured that all the individuals of the same species, and
+all the closely allied species of most genera, have within a not very
+remote period descended from one parent, and have migrated from some one
+birthplace; and when we better know the many means of migration, then, by
+the light which geology now throws, and will continue to throw, on former
+changes of climate and of the level of the land, we shall surely be enabled
+to trace in an admirable manner the former migrations of the inhabitants of
+the whole world. Even at present, by comparing the differences of the
+inhabitants of the sea on the opposite sides of a continent, and the nature
+of the various inhabitants of that continent in relation to their apparent
+means of immigration, some light can be thrown on ancient geography.
+
+The noble science of Geology loses glory from the extreme imperfection of
+the record. The crust of the earth with its embedded remains must not be
+looked at as a well-filled museum, but as a poor collection made at hazard
+and at rare intervals. The accumulation of each great fossiliferous
+formation will be recognised as having depended on an unusual concurrence
+of circumstances, and the blank intervals between the successive stages as
+having been of vast duration. But we shall {488} be able to gauge with some
+security the duration of these intervals by a comparison of the preceding
+and succeeding organic forms. We must be cautious in attempting to
+correlate as strictly contemporaneous two formations, which include few
+identical species, by the general succession of their forms of life. As
+species are produced and exterminated by slowly acting and still existing
+causes, and not by miraculous acts of creation and by catastrophes; and as
+the most important of all causes of organic change is one which is almost
+independent of altered and perhaps suddenly altered physical conditions,
+namely, the mutual relation of organism to organism,--the improvement of
+one being entailing the improvement or the extermination of others; it
+follows, that the amount of organic change in the fossils of consecutive
+formations probably serves as a fair measure of the lapse of actual time. A
+number of species, however, keeping in a body might remain for a long
+period unchanged, whilst within this same period, several of these species,
+by migrating into new countries and coming into competition with foreign
+associates, might become modified; so that we must not overrate the
+accuracy of organic change as a measure of time. During early periods of
+the earth's history, when the forms of life were probably fewer and
+simpler, the rate of change was probably slower; and at the first dawn of
+life, when very few forms of the simplest structure existed, the rate of
+change may have been slow in an extreme degree. The whole history of the
+world, as at present known, although of a length quite incomprehensible by
+us, will hereafter be recognised as a mere fragment of time, compared with
+the ages which have elapsed since the first creature, the progenitor of
+innumerable extinct and living descendants, was created.
+
+In the distant future I see open fields for far more {489} important
+researches. Psychology will be based on a new foundation, that of the
+necessary acquirement of each mental power and capacity by gradation. Light
+will be thrown on the origin of man and his history.
+
+Authors of the highest eminence seem to be fully satisfied with the view
+that each species has been independently created. To my mind it accords
+better with what we know of the laws impressed on matter by the Creator,
+that the production and extinction of the past and present inhabitants of
+the world should have been due to secondary causes, like those determining
+the birth and death of the individual. When I view all beings not as
+special creations, but as the lineal descendants of some few beings which
+lived long before the first bed of the Silurian system was deposited, they
+seem to me to become ennobled. Judging from the past, we may safely infer
+that not one living species will transmit its unaltered likeness to a
+distant futurity. And of the species now living very few will transmit
+progeny of any kind to a far distant futurity; for the manner in which all
+organic beings are grouped, shows that the greater number of species of
+each genus, and all the species of many genera, have left no descendants,
+but have become utterly extinct. We can so far take a prophetic glance into
+futurity as to foretel that it will be the common and widely-spread
+species, belonging to the larger and dominant groups, which will ultimately
+prevail and procreate new and dominant species. As all the living forms of
+life are the lineal descendants of those which lived long before the
+Silurian epoch, we may feel certain that the ordinary succession by
+generation has never once been broken, and that no cataclysm has desolated
+the whole world. Hence we may look with some confidence to a secure future
+of equally inappreciable length. And as natural selection works {490}
+solely by and for the good of each being, all corporeal and mental
+endowments will tend to progress towards perfection.
+
+It is interesting to contemplate an entangled bank, clothed with many
+plants of many kinds, with birds singing on the bushes, with various
+insects flitting about, and with worms crawling through the damp earth, and
+to reflect that these elaborately constructed forms, so different from each
+other, and dependent on each other in so complex a manner, have all been
+produced by laws acting around us. These laws, taken in the largest sense,
+being Growth with Reproduction; Inheritance which is almost implied by
+reproduction; Variability from the indirect and direct action of the
+external conditions of life, and from use and disuse; a Ratio of Increase
+so high as to lead to a Struggle for Life, and as a consequence to Natural
+Selection, entailing Divergence of Character and the Extinction of
+less-improved forms. Thus, from the war of nature, from famine and death,
+the most exalted object which we are capable of conceiving, namely, the
+production of the higher animals, directly follows. There is grandeur in
+this view of life, with its several powers, having been originally breathed
+by the Creator into a few forms or into one; and that, whilst this planet
+has gone cycling on according to the fixed law of gravity, from so simple a
+beginning endless forms most beautiful and most wonderful have been, and
+are being, evolved.
+
+       *       *       *       *       *
+
+
+{491}
+
+INDEX.
+
+          A.
+
+  Aberrant groups, 429.
+  Abyssinia, plants of, 375.
+  Acclimatisation, 139.
+  Affinities of extinct species, 329.
+  ---- of organic beings, 411.
+  Agassiz on Amblyopsis, 139.
+  ---- on groups of species suddenly appearing, 302, 305.
+  ---- on embryological succession, 338.
+  ---- on the glacial period, 366.
+  ---- on embryological characters, 418.
+  ---- on the embryos of vertebrata, 439.
+  ---- on parallelism of embryological development and geological
+      succession, 449.
+  Algæ of New Zealand, 376.
+  Alligators, males, fighting, 88.
+  Amblyopsis, blind fish, 139.
+  America, North, productions allied to those of Europe, 371.
+  --------, boulders and glaciers of, 373.
+  ----, South, no modern formations on west coast, 290.
+  Ammonites, sudden extinction of, 321.
+  Anagallis, sterility of, 247.
+  Analogy of variations, 159.
+  Ancylus, 386.
+  Animals, not domesticated from being variable, 17.
+  ----, domestic, descended from several stocks, 19.
+  --------, acclimatisation of, 141.
+  ---- of Australia, 116.
+  ---- with thicker fur in cold climates, 133.
+  ----, blind, in caves, 137.
+  ----, extinct, of Australia, 339.
+  Anomma, 240.
+  Antarctic islands, ancient flora of, 399.
+  Antirrhinum, 161.
+  Ants attending aphides, 210.
+  ----, slave-making instinct, 219.
+  ----, neuter, structure of, 236.
+  Aphides, attended by ants, 210.
+  Aphis, development of, 442.
+  Apteryx, 182.
+  Arab horses, 35.
+  Aralo-Caspian Sea, 339.
+  Archaic, M. de, on the succession of species, 325.
+  Artichoke, Jerusalem, 142.
+  Ascension, plants of, 389.
+  Asclepias, pollen of, 193.
+  Asparagus, 359.
+  Aspicarpa, 417.
+  Asses, striped, 163.
+  Ateuchus, 135.
+  Audubon on habits of frigate-bird, 185.
+  ---- on variation in birds'-nests, 212.
+  ---- on heron eating seeds, 387.
+  Australia, animals of, 116.
+  ----. dogs of, 215.
+  ----, extinct animals of, 339.
+  ----, European plants in, 375.
+  Azara on flies destroying cattle, 72.
+  Azores, flora of, 363.
+
+          B.
+
+  Babington, Mr., on British plants, 48.
+  Balancement of growth, 147.
+  Bamboo with hooks, 197.
+  Barberry, flowers of, 98.
+  Barrande, M., on Silurian colonies, 313.
+  ---- on the succession of species, 325.
+  ---- on parallelism of palæozoic formations, 328.
+  ---- on affinities of ancient species, 330.
+  Barriers, importance of, 347.
+  Batrachians on islands, 393.
+  Bats, how structure acquired, 180.
+  ----, distribution of, 394.
+  Bear, catching water-insects, 184.
+  Bee, sting of, 202.
+  ----, queen, killing rivals, 202.
+  Bees fertilising flowers, 73.
+  ----, hive, not sucking the red clover, 95.
+  {492}
+  --------, cell-making instinct, 224.
+  ----, humble, cells of, 225.
+  ----, parasitic, 218.
+  Beetles, wingless, in Madeira, 135.
+  ---- with deficient tarsi, 135.
+  Bentham, Mr., on British plants, 48.
+  ----, on classification, 419.
+  Berkeley, Mr., on seeds in salt-water, 358.
+  Bermuda, birds of, 391.
+  Birds acquiring fear, 212.
+  ---- annually cross the Atlantic, 364.
+  ----, colour of, on continents, 132.
+  ----, footsteps and remains of, in secondary rocks, 304.
+  ----, fossil, in caves of Brazil, 339.
+  ---- of Madeira, Bermuda, and Galapagos, 391.
+  ----, song of males, 89.
+  ---- transporting seeds, 361.
+  ----, waders, 385.
+  ----, wingless, 134, 182.
+  ----, with traces of embryonic teeth, 450.
+  Bizcacha, 349.
+  ----, affinities of, 429.
+  Bladder for swimming in fish, 190.
+  Blindness of cave animals, 137.
+  Blyth, Mr., on distinctness of Indian cattle, 18.
+  ----, on striped Hemionus, 163.
+  ----, on crossed geese, 254.
+  Boar, shoulder-pad of, 88.
+  Borrow, Mr., on the Spanish pointer, 35.
+  Bory St. Vincent on Batrachians, 393.
+  Bosquet, M., on fossil Chthamalus, 305.
+  Boulders, erratic, on the Azores, 363.
+  Branchiæ, 190.
+  Brent, Mr., on house-tumblers, 214.
+  ----, on hawks killing pigeons, 362.
+  Brewer, Dr., on American cuckoo, 217.
+  Britain, mammals of, 396.
+  Bronn on duration of specific forms, 294.
+  Brown, Robert, on classification, 415.
+  Buckman on variation in plants, 10.
+  Buzareingues on sterility of varieties, 270.
+
+          C.
+
+  Cabbage, varieties of, crossed, 99.
+  Calceolaria, 251.
+  Canary-birds, sterility of hybrids, 252.
+  Cape de Verde islands, 398.
+  Cape of Good Hope, plants of, 110, 375.
+  Carrier-pigeons killed by hawks, 362.
+  Cassini on flowers of compositæ, 145.
+  Catasetum, 424.
+  Cats, with blue eyes, deaf, 12.
+  ----, variation in habits of, 91.
+  ---- curling tail when going to spring, 201.
+  Cattle destroying fir-trees, 72.
+  ---- destroyed by flies in La Plata, 72.
+  ----, breeds of, locally extinct, 111.
+  ----, fertility of Indian and European breeds, 254.
+  Cave, inhabitants of, blind, 137.
+  Centres of creation, 352.
+  Cephalopodæ, development of, 442.
+  Cervulus, 253.
+  Cetacea, teeth and hair, 144.
+  Ceylon, plants of, 375.
+  Chalk formation, 322.
+  Characters, divergence of, 111.
+  ----, sexual, variable, 156.
+  ----, adaptive or analogical, 426.
+  Charlock, 76.
+  Checks to increase, 67.
+  ---- ----, mutual, 71.
+  Chickens, instinctive tameness of, 216.
+  Chthamalinæ, 289.
+  Chthamalus, cretacean species of, 305.
+  Circumstances favourable to selection of domestic products, 40.
+  ---- ---- to natural selection, 102.
+  Cirripedes capable of crossing, 101.
+  ----, carapace aborted, 148.
+  ----, their ovigerous frena, 192.
+  ----, fossil, 304.
+  ----, larvæ of, 440.
+  Classification, 413.
+  Clift, Mr., on the succession of types, 339.
+  Climate, effects of, in checking increase of beings, 68.
+  ----, adaptation of, to organisms, 139.
+  {493}
+  Cobites, intestine of, 190.
+  Cockroach, 76.
+  Collections, palæontological, poor, 288.
+  Colour, influenced by climate, 132.
+  ----, in relation to attacks by flies, 198.
+  Columba livia, parent of domestic pigeons, 23.
+  Colymbetes, 386.
+  Compensation of growth, 147.
+  Compositæ, outer and inner florets of, 144.
+  ----, male flowers of, 451.
+  Conclusion, general, 480.
+  Conditions, slight changes in, favourable to fertility, 267.
+  Coot, 185.
+  Coral-islands, seeds drifted to, 361.
+  ---- reefs, indicating movements of earth, 310.
+  Corn-crake, 186.
+  Correlation of growth in domestic productions, 11.
+  ---- of growth, 143, 198.
+  Cowslip, 49.
+  Creation, single centres of, 352.
+  Crinum, 250.
+  Crosses, reciprocal, 258.
+  Crossing of domestic animals, importance in altering breeds, 20.
+  ----, advantages of, 96.
+  ---- unfavourable to selection, 102.
+  Crustacea of New Zealand, 376.
+  Crustacean, blind, 137.
+  Cryptocerus, 239.
+  Ctenomys, blind, 137.
+  Cuckoo, instinct of, 216.
+  Currants, grafts of, 262.
+  Currents of sea, rate of, 360.
+  Cuvier on conditions of existence, 206.
+  ---- on fossil monkeys, 304.
+  ----, Fred., on instinct, 208.
+
+          D.
+
+  Dana, Prof., on blind cave-animals, 139.
+  ----, on relations of crustaceans of Japan, 372.
+  ----, on crustaceans of New Zealand, 376.
+  De Candolle on struggle for existence, 62.
+  ---- on umbelliferæ, 146.
+  ---- on general affinities, 430.
+  ----, Alph., on low plants, widely dispersed, 406.
+  ----, ----, on widely-ranging plants being variable, 53.
+  ----, ----, on naturalisation, 115.
+  ----, ----, on winged seeds, 146.
+  ----, ----, on Alpine species suddenly becoming rare, 175.
+  ----, ----, on distribution of plants with large seeds, 360.
+  ----, ----, on vegetation of Australia, 379.
+  ----, ----, on fresh-water plants, 386.
+  ----, ----, on insular plants, 389.
+  Degradation of coast-rocks, 282.
+  Denudation, rate of, 285.
+  ---- of oldest rocks, 308.
+  Development of ancient forms, 336.
+  Devonian system, 334.
+  Dianthus, fertility of crosses, 256.
+  Dirt on feet of birds, 362.
+  Dispersal, means of, 356.
+  ---- during glacial period, 365.
+  Distribution, geographical, 346.
+  ----, means of, 356.
+  Disuse, effects of, under nature, 134.
+  Divergence of character, 111.
+  Division, physiological, of labour, 115.
+  Dogs, hairless, with imperfect teeth, 12.
+  ---- descended from several wild stocks, 18.
+  ----, domestic instincts of, 213.
+  ----, inherited civilisation of, 215.
+  ----, fertility of breeds together, 254.
+  ----, ---- of crosses, 268.
+  ----, proportions of, when young, 444.
+  Domestication, variation under, 7.
+  Downing, Mr., on fruit-trees in America, 85.
+  Downs, North and South, 286.
+  Dragon-flies, intestines of, 190.
+  Drift-timber, 360.
+  Driver-ant, 240.
+  Drones killed by other bees, 202.
+  Duck, domestic, wings of, reduced, 11.
+  ----, logger-headed, 182.
+  {494}
+  Duckweed, 385.
+  Dugong, affinities of, 414.
+  Dung-beetles with deficient tarsi, 135.
+  Dyticus, 386.
+
+          E.
+
+  Earl, Mr. W., on the Malay Archipelago, 395.
+  Ears, drooping, in domestic animals, 11.
+  ----, rudimentary, 454.
+  Earth, seeds in roots of trees, 361.
+  Eciton, 238.
+  Economy of organisation, 147.
+  Edentata, teeth and hair, 144.
+  ----, fossil species of, 339.
+  Edwards, Milne, on physiological divisions of labour, 115.
+  ----, on gradations of structure, 194.
+  ----, on embryonical characters, 418.
+  Eggs, young birds escaping from, 87.
+  Electric organs, 192.
+  Elephant, rate of increase, 64.
+  ---- of glacial period, 141.
+  Embryology, 438.
+  Existence, struggle for, 60.
+  ----, conditions of, 206.
+  Extinction, as bearing on natural selection, 109.
+  ---- of domestic varieties, 111,
+  ----, 317.
+  Eye, structure of, 187.
+  ----, correction for aberration, 202.
+  Eyes reduced in moles, 137.
+
+          F.
+
+  Fabre, M. on parasitic sphex, 218.
+  Falconer, Dr., on naturalisation of plants in India, 65.
+  ---- on fossil crocodile, 313.
+  ---- on elephants and mastodons, 334.
+  ---- and Cautley on mammals of sub-Himalayan beds, 340.
+  Falkland Island, wolf of, 394.
+  Faults, 285.
+  Faunas, marine, 348.
+  Fear, instinctive, in birds, 212.
+  Feet of bird, young molluscs adhering to, 385.
+  Fertility of hybrids, 249.
+  ---- from slight changes in conditions, 267.
+  ---- of crossed varieties, 268.
+  Fir-trees destroyed by cattle, 72.
+  ---- ----, pollen of, 203.
+  Fish, flying, 182.
+  ----, teleostean, sudden appearance of, 305.
+  ---- eating seeds, 362, 387.
+  ----, fresh-water, distribution of, 384.
+  Fishes, ganoid, now confined to fresh water, 107.
+  ----, electric organs of, 192.
+  ----, ganoid, living in fresh water, 321.
+  ---- of southern hemisphere, 376.
+  Flight, powers of, how acquired, 182.
+  Flowers, structure of, in relation to crossing, 97.
+  ---- of compositæ and umbelliferæ, 144.
+  Forbes, E., on colours of shells, 132.
+  ---- on abrupt range of shells in depth, 175.
+  ---- on poorness of palæontological collections, 288.
+  ---- on continuous succession of genera, 316.
+  ---- on continental extensions, 357.
+  ---- on distribution during glacial period, 366.
+  ---- on parallelism in time and space, 409.
+  Forests, changes in, in America, 74.
+  Formation, Devonian, 334.
+  Formations, thickness of, in Britain, 284.
+  ----, intermittent, 290.
+  Formica rufescens, 219.
+  ---- sanguinea, 219.
+  ---- flava, neuter of, 240.
+  Frena, ovigerous, of cirripedes, 192.
+  Fresh-water productions, dispersal of, 383.
+  Fries on species in large genera being closely allied to other species,
+      57.
+  Frigate-bird, 185.
+  Frogs on islands, 393.
+  Fruit-trees, gradual improvement of, 37.
+  ---- ---- in United States, 85.
+  ---- ----, varieties of, acclimatised in United States, 142.
+  {495}
+  Fuci, crossed, 258.
+  Fur, thicker in cold climates, 133.
+  Furze, 439.
+
+          G.
+
+  Galapagos Archipelago, birds of, 390.
+  ----, productions of, 398, 400.
+  Galeopithecus, 181.
+  Game, increase of, checked by vermin, 68.
+  Gärtner on sterility of hybrids, 247, 255.
+  ----, on reciprocal crosses, 258.
+  ----, on crossed maize and verbascum, 270.
+  ----, on comparison of hybrids and mongrels, 272.
+  Geese, fertility when crossed, 253.
+  ----, upland, 185.
+  Genealogy important in classification, 425.
+  Geoffroy St. Hilaire on balancement, 147.
+  ---- ---- on homologous organs, 434.
+  ---- ----, Isidore, on variability of repeated parts, 149.
+  ---- ----, on correlation in monstrosities, 11.
+  ---- ----, on correlation, 144.
+  ---- ----, on variable parts being often monstrous, 155.
+  Geographical distribution, 346.
+  Geography, ancient, 487.
+  Geology, future progress of, 487.
+  ----, imperfection of the record, 279.
+  Giraffe, tail of, 195.
+  Glacial period, 365.
+  Gmelin on distribution, 365.
+  Gnathodon, fossil, 368.
+  Godwin-Austen, Mr., on the Malay Archipelago, 300.
+  Goethe on compensation of growth, 147.
+  Gooseberry, grafts of, 262.
+  Gould, Dr. A., on land-shells, 397.
+  ----, Mr., on colours of birds, 132.
+  ----, on birds of the Galapagos, 398.
+  ----, on distribution of genera of birds, 404.
+  Gourds, crossed, 270.
+  Grafts, capacity of, 261.
+  Grasses, varieties of, 113.
+  Gray, Dr. Asa, on trees of United States, 100.
+  ----, on naturalised plants in the United States, 115.
+  ----, on rarity of intermediate varieties, 176.
+  ----, on Alpine plants, 365.
+  ----, Dr. J. E., on striped mule, 165.
+  Grebe, 185.
+  Groups, aberrant, 429.
+  Grouse, colours of, 84.
+  ----, red, a doubtful species, 49.
+  Growth, compensation of, 147.
+  ----, correlation of, in domestic products, 11.
+  ----, correlation of, 143.
+
+          H.
+
+  Habit, effect of, under domestication, 11.
+  ----, effect of, under nature, 134.
+  ----, diversified, of same species, 183.
+  Hair and teeth, correlated, 144.
+  Harcourt, Mr. E. V., on the birds of Madeira, 391.
+  Hartung, M. on boulders in the Azores, 363.
+  Hazel-nuts, 359.
+  Hearne on habits of bears, 184.
+  Heath, changes in vegetation, 72.
+  Heer, O., on plants of Madeira, 107.
+  Helix pomatia, 397.
+  Helosciadium, 359.
+  Hemionus, striped, 163.
+  Herbert, W., on struggle for existence, 62.
+  ----, on sterility of hybrids, 249.
+  Hermaphrodites crossing, 96.
+  Heron eating seed, 387.
+  Heron, Sir R., on peacocks, 89.
+  Heusinger on white animals not poisoned by certain plants, 12.
+  Hewitt, Mr., on sterility of first crosses, 264.
+  Himalaya, glaciers of, 373.
+  ----, plants of, 375.
+  Hippeastrum, 250.
+  Holly-trees, sexes of, 93.
+  Hollyhock, varieties of, crossed, 271.
+  Hooker, Dr., on trees of New Zealand, 100.
+  {496}
+  ----, on acclimatisation of Himalayan trees, 140.
+  ----, on flowers of umbelliferæ, 145.
+  ----, on glaciers of Himalaya, 373.
+  ----, on algæ of New Zealand, 376.
+  ----, on vegetation at the base of the Himalaya, 378.
+  ----, on plants of Tierra del Fuego, 374, 378.
+  ----, on Australian plants, 375, 399.
+  ----, on relations of flora of South America, 379.
+  ----, on flora of the Antarctic lands, 381, 399.
+  ----, on the plants of the Galapagos, 392, 398.
+  Hooks on bamboos, 197.
+  ---- to seeds on islands, 392.
+  Horner, Mr., on the antiquity of Egyptians, 18.
+  Horns, rudimentary, 454.
+  Horse, fossil, in La Plata, 318.
+  Horses destroyed by flies in La Plata, 72.
+  ----, striped, 163.
+  ----, proportions of, when young, 444.
+  Horticulturists, selection applied by, 32.
+  Huber on cells of bees, 230.
+  ----, P., on reason blended with instinct, 208.
+  ----, on habitual nature of instincts, 208.
+  ----, on slave-making ants, 219.
+  ----, on Melipona domestica, 225.
+  Humble-bees, cells of, 225.
+  Hunter, J., on secondary sexual characters, 150.
+  Hutton, Captain, on crossed geese, 254.
+  Huxley, Prof., on structure of hermaphrodites, 101.
+  ----, on embryological succession, 338.
+  ----, on homologous organs, 438.
+  ----, on the development of aphis, 442.
+  Hybrids and mongrels compared, 272.
+  Hybridism, 245.
+  Hydra, structure of, 190.
+
+          I.
+
+  Ibla, 148.
+  Icebergs transporting seeds, 363.
+  Increase, rate of, 63.
+  Individuals, numbers favourable to selection, 102.
+  ----, many, whether simultaneously created, 355.
+  Inheritance, laws of, 12.
+  ---- at corresponding ages, 14, 86.
+  Insects, colour of, fitted for habitations, 84.
+  ----, sea-side, colours of, 132.
+  ----, blind, in caves, 138.
+  ----, luminous, 193.
+  ----, neuter, 236.
+  Instinct, 207.
+  Instincts, domestic, 213.
+  Intercrossing, advantages of, 96.
+  Islands, oceanic, 388.
+  Isolation favourable to selection, 104.
+
+          J.
+
+  Japan, productions of, 372.
+  Java, plants of, 375.
+  Jones, Mr. J. M., on the birds of Bermuda, 391.
+  Jussieu on classification, 417.
+
+          K.
+
+  Kentucky, caves of, 137.
+  Kerguelen-land, flora of, 381, 399.
+  Kidney-bean, acclimatisation of, 142.
+  Kidneys of birds, 144.
+  Kirby on tarsi deficient in beetles, 135.
+  Knight, Andrew, on cause of variation, 7.
+  Kölreuter on the barberry, 98.
+  ---- on sterility of hybrids, 246.
+  ---- on reciprocal crosses, 258.
+  ---- on crossed varieties of nicotiana, 271.
+  ---- on crossing male and hermaphrodite flowers, 451.
+
+          L.
+
+  Lamarck on adaptive characters, 426.
+  Land-shells, distribution of, 397.
+  ---- of Madeira, naturalised, 403.
+  Languages, classification of, 422.
+  Lapse, great, of time, 282.
+  {497}
+  Larvæ, 440.
+  Laurel, nectar secreted by the leaves,
+  Laws of variation, 131.
+  Leech, varieties of, 76.
+  Leguminosæ, nectar secreted by glands, 92.
+  Lepidosiren, 107, 330.
+  Life, struggle for, 60.
+  Lingula, Silurian, 307.
+  Linnæus, aphorism of, 413.
+  Lion, mane of, 88.
+  ----, young of, striped, 439.
+  Lobelia fulgens, 73, 98.
+  Lobelia, sterility of crosses, 250.
+  Loess of the Rhine, 384.
+  Lowness of structure connected with variability, 149.
+  Lowness, related to wide distribution, 406.
+  Lubbock, Mr., on the nerves of coccus, 46.
+  Lucas, Dr. P., on inheritance, 12.
+  ----, on resemblance of child to parent, 275.
+  Lund and Clausen on fossils of Brazil, 339.
+  Lyell, Sir C, on the struggle for existence, 62.
+  ----, on modern changes of the earth, 95.
+  ----, on measure of denudation, 284.
+  ----, on a carboniferous land-shell, 289.
+  ----, on strata beneath Silurian system, 308.
+  ----, on the imperfection of the geological record, 311.
+  ----, on the appearance of species, 312.
+  ----, on Barrande's colonies, 313.
+  ----, on tertiary formations of Europe and North America, 323.
+  ----, on parallelism of tertiary formations, 328.
+  ----, on transport of seeds by icebergs, 363.
+  ----, on great alternations of climate, 382.
+  ----, on the distribution of fresh-water shells, 385.
+  ----, on land-shells of Madeira, 402.
+  Lyell and Dawson on fossilized trees in Nova Scotia, 297.
+
+          M.
+
+  Macleay on analogical characters, 426.
+  Madeira, plants of, 107.
+  ----, beetles of, wingless, 135.
+  ----, fossil land-shells of, 339.
+  ----, birds of, 390.
+  Magpie tame in Norway, 212.
+  Maize, crossed, 270.
+  Malay Archipelago compared with Europe, 300.
+  ----, mammals of, 395.
+  Malpighiaceæ, 417.
+  Mammæ, rudimentary, 451.
+  Mammals, fossil, in secondary formation, 304.
+  ----, insular, 394.
+  Man, origin of races of, 199.
+  Manatee, rudimentary nails of, 454.
+  Marsupials of Australia, 116.
+  ----, fossil species of, 339.
+  Martens, M., experiment on seeds, 360.
+  Martin, Mr. W. C., on striped mules, 165.
+  Matteucci on the electric organs of rays, 193.
+  Matthiola, reciprocal crosses of, 258.
+  Means of dispersal, 356.
+  Melipona domestica, 225.
+  Metamorphism of oldest rocks, 308.
+  Mice destroying bees, 74.
+  ----, acclimatisation of, 141.
+  Migration, bears on first appearance of fossils, 297.
+  Miller, Prof., on the cells of bees, 226.
+  Mirabilis, crosses of, 258.
+  Missel-thrush, 76.
+  Misseltoe, complex relations of, 3.
+  Mississippi, rate of deposition at mouth, 284.
+  Mocking-thrush of the Galapagos, 402.
+  Modification of species, how far applicable, 483.
+  Moles, blind, 137.
+  Mongrels, fertility and sterility of, 268.
+  ---- and hybrids compared, 272.
+  {498}
+  Monkeys, fossil, 304.
+  Monocanthus, 424.
+  Mons, Van, on the origin of fruit-trees, 29.
+  Moquin-Tandon on sea-side plants, 132.
+  Morphology, 433.
+  Mozart, musical powers of, 209.
+  Mud, seeds in, 386.
+  Mules, striped, 165.
+  Müller, Dr. F., on Alpine Australian plants, 375.
+  Murchison, Sir R., on the formations of Russia, 290.
+  ----, on azoic formations, 308.
+  ----, on extinction, 317.
+  Mustela vison, 179.
+  Myanthus, 424.
+  Myrmecocystus, 239.
+  Myrmica, eyes of, 240.
+
+          N.
+
+  Nails, rudimentary, 454.
+  Natural history, future progress of, 485.
+  ---- selection, 80.
+  ---- system, 413.
+  Naturalisation of forms distinct from the indigenous species, 115.
+  ---- in New Zealand, 201.
+  Nautilus, Silurian, 307.
+  Nectar of plants, 92.
+  Nectaries, how formed, 92.
+  Nelumbium luteum, 387.
+  Nests, variation in, 211.
+  Neuter insects, 236.
+  Newman, Mr., on humble-bees, 74.
+  New Zealand, productions of, not perfect, 201.
+  ----, naturalised products of, 337.
+  ----, fossil birds of, 339.
+  ----, glacial action in, 373.
+  ----, crustaceans of, 376.
+  ----, algæ of, 376.
+  ----, number of plants of, 389.
+  ----, flora of, 399.
+  Nicotiana, crossed varieties of, 271.
+  ----, certain species very sterile, 257.
+  Noble, Mr., on fertility of Rhododendron, 252.
+  Nodules, phosphatic, in azoic rocks, 308.
+
+          O.
+
+  Oak, varieties of, 50.
+  Onites apelles, 135.
+  Orchis, pollen of, 193.
+  Organs of extreme perfection, 186.
+  ----, electric, of fishes, 192.
+  ---- of little importance, 194.
+  ----, homologous, 434.
+  ----, rudiments of, and nascent, 450.
+  Ornithorhynchus, 107, 416.
+  Ostrich not capable of flight, 134.
+  ----, habit of laying eggs together, 218.
+  ----, American, two species of, 349.
+  Otter, habits of, how acquired, 179.
+  Ouzel, water, 185.
+  Owen, Prof., on birds not flying, 134.
+  ----, on vegetative repetition, 149.
+  ----, on variable length of arms in ourang-outang, 150.
+  ----, on the swim-bladder of fishes, 191.
+  ----, on electric organs, 192.
+  ----, on fossil horse of La Plata, 319.
+  ----, on relations of ruminants and pachyderms, 329.
+  ----, on fossil birds of New Zealand, 339.
+  ----, on succession of types, 339.
+  ----, on affinities of the dugong, 414.
+  ----, on homologous organs, 434.
+  ----, on the metamorphosis of cephalopods and spiders, 442.
+
+          P.
+
+  Pacific Ocean, faunas of, 348.
+  Paley on no organ formed to give pain, 201.
+  Pallas on the fertility of the wild stocks of domestic animals, 254.
+  Paraguay, cattle destroyed by flies, 72.
+  Parasites, 217.
+  Partridge, dirt on feet, 363.
+  Parts greatly developed, variable, 150.
+  ----, degrees of utility of, 201.
+  Parus major, 184.
+  Passiflora, 251.
+  Peaches in United States, 85.
+  Pear, grafts of, 262.
+  {499}
+  Pelargonium, flowers of, 145.
+  ----, sterility of, 251.
+  Pelvis of women, 144.
+  Peloria, 145.
+  Period, glacial, 365.
+  Petrels, habits of, 184.
+  Phasianus, fertility of hybrids, 253.
+  Pheasant, young, wild, 216.
+  Philippi on tertiary species in Sicily, 312.
+  Pictet, Prof., on groups of species suddenly appearing, 302, 305.
+  ----, on rate of organic change, 313.
+  ----, on continuous succession of genera, 316.
+  ----, on close alliance of fossils in consecutive formations, 335.
+  ----, on embryological succession, 338.
+  Pierce, Mr., on varieties of wolves, 91.
+  Pigeons with feathered feet and skin between toes, 12.
+  ----, breeds described, and origin of, 20.
+  ----, breeds of, how produced, 39, 42.
+  ----, tumbler, not being able to get out of egg, 87.
+  ----, reverting to blue colour, 160.
+  ----, instinct of tumbling, 214.
+  ----, carriers, killed by hawks, 362.
+  ----, young of, 445.
+  Pistil, rudimentary, 451.
+  Plants, poisonous, not affecting certain coloured animals, 12.
+  ----, selection applied to, 32.
+  ----, gradual improvement of, 37.
+  ---- not improved in barbarous countries, 38.
+  ---- destroyed by insects, 67.
+  ----, in midst of range, have to struggle with other plants, 77.
+  ----, nectar of, 92.
+  ----, fleshy, on sea-shores, 132.
+  ----, fresh-water, distribution of, 386.
+  ----, low in scale, widely distributed, 406.
+  Plumage, laws of change in sexes of birds, 89.
+  Plums in the United States, 85.
+  Pointer dog, origin of, 35.
+  ----, habits of, 213.
+  Poison not affecting certain coloured animals, 12.
+  ----, similar effect of, on animals and plants, 484.
+  Pollen of fir-trees, 203.
+  Poole, Col., on striped hemionus, 163.
+  Potamogeton, 387.
+  Prestwich, Mr., on English and French eocene formations, 328.
+  Primrose, 49.
+  ----, sterility of, 247.
+  Primula, varieties of, 49.
+  Proteolepas, 148.
+  Proteus, 139.
+  Psychology, future progress of, 489.
+
+          Q.
+
+  Quagga, striped, 165.
+  Quince, grafts of, 262.
+
+          R.
+
+  Rabbit, disposition of young, 215.
+  Races, domestic, characters of, 16.
+  Race-horses, Arab, 35.
+  ----, English, 356.
+  Ramond on plants of Pyrenees, 368.
+  Ramsay, Prof., on thickness of the British formations, 284.
+  ----, on faults, 285.
+  Ratio of increase, 63.
+  Rats, supplanting each other, 76.
+  ----, acclimatisation of, 141.
+  ----, blind in cave, 137.
+  Rattle-snake, 201.
+  Reason and instinct, 208.
+  Recapitulation, general, 459.
+  Reciprocity of crosses, 258.
+  Record, geological, imperfect, 279.
+  Rengger on flies destroying cattle, 72.
+  Reproduction, rate of, 63.
+  Resemblance to parents in mongrels and hybrids, 273.
+  Reversion, law of inheritance, 14.
+  ---- in pigeons to blue colour, 160.
+  Rhododendron, sterility of, 251.
+  Richard, Prof., on Aspicarpa, 417.
+  Richardson, Sir J., on structure of squirrels, 180.
+  ----, on fishes of the southern hemisphere, 376.
+  Robinia, grafts of, 262.
+  {500}
+  Rodents, blind, 137.
+  Rudimentary organs, 450.
+  Rudiments important for classification, 416.
+
+          S.
+
+  Sagaret on grafts, 262.
+  Salmons, males fighting, and hooked jaws of, 88.
+  Salt-water, how far injurious to seeds, 358.
+  Saurophagus sulphuratus, 183.
+  Schiödte on blind insects, 138.
+  Schlegel on snakes, 144.
+  Sea-water, how far injurious to seeds, 358.
+  Sebright, Sir J., on crossed animals, 20.
+  ----, on selection of pigeons, 31.
+  Sedgwick, Prof., on groups of species suddenly appearing, 302.
+  Seedlings destroyed by insects, 67.
+  Seeds, nutriment in, 77.
+  ----, winged, 146.
+  ----, power of resisting salt-water, 358.
+  ---- in crops and intestines of birds, 361.
+  ---- eaten by fish, 362, 387.
+  ---- in mud, 386.
+  ----, hooked, on islands, 392.
+  Selection of domestic products, 29.
+  ----, principle not of recent origin, 33.
+  ----, unconscious, 34.
+  ----, natural, 80.
+  ----, sexual, 87.
+  ----, natural, circumstances favourable to, 102.
+  Sexes, relations of, 87.
+  Sexual characters variable, 156.
+  ---- selection, 87.
+  Sheep, Merino, their selection, 31.
+  ----, two sub-breeds unintentionally produced, 36.
+  ----, mountain, varieties of, 76.
+  Shells, colours of, 132.
+  ----, littoral, seldom embedded, 288.
+  ----, fresh-water, dispersal of, 385
+  ---- of Madeira, 391.
+  ----, land, distribution of, 397.
+  Silene, fertility of crosses, 257.
+  Silliman, Prof., on blind rat, 137.
+  Skulls of young mammals, 197, 436.
+  Slave-making instinct, 219.
+  Smith, Col. Hamilton, on striped horses, 164.
+  ----, Mr. Fred., on slave-making ants, 219.
+  ----, on neuter ants, 239.
+  ----, Mr., of Jordan Hill, on the degradation of coast-rocks, 283.
+  Snap-dragon, 161.
+  Somerville, Lord, on selection of sheep, 31.
+  Sorbus, grafts of, 262.
+  Spaniel, King Charles's breed, 35.
+  Species, polymorphic, 46.
+  ----, common, variable, 53.
+  ---- in large genera variable, 54.
+  ----, groups of, suddenly appearing, 302, 307.
+  ---- beneath Silurian formations, 307.
+  ---- successively appearing, 312.
+  ---- changing simultaneously throughout the world, 322.
+  Spencer, Lord, on increase in size of cattle, 35.
+  Sphex, parasitic, 218.
+  Spiders, development of, 442.
+  Spitz-dog crossed with fox, 268.
+  Sports in plants, 9.
+  Sprengel, C. C, on crossing, 98.
+  ----, on ray-florets, 145.
+  Squirrels, gradations in structure, 180.
+  Staffordshire, heath, changes in, 71.
+  Stag-beetles, fighting, 88.
+  Sterility from changed conditions of life, 9.
+  ---- of hybrids, 246.
+  ---- ----, laws of, 255.
+  ---- ----, causes of, 263.
+  ---- from unfavourable conditions, 265.
+  ---- of certain varieties, 269.
+  St. Helena, productions of, 390.
+  St. Hilaire, Aug., on classification, 418.
+  St. John, Mr., on habits of cats, 91.
+  Sting of bee, 202.
+  Stocks, aboriginal, of domestic animals, 18.
+  Strata, thickness of, in Britain, 284.
+  Stripes on horses, 163.
+  {501}
+  Structure, degrees of utility of, 201.
+  Struggle for existence, 60.
+  Succession, geological, 312.
+  Succession of types in same areas, 338.
+  Swallow, one species supplanting another, 76.
+  Swim-bladder, 190.
+  System, natural, 413.
+
+          T.
+
+  Tail of giraffe, 195.
+  ---- of aquatic animals, 196.
+  ----, rudimentary, 454.
+  Tarsi deficient, 135.
+  Tausch on umbelliferous flowers, 146.
+  Teeth and hair correlated, 144.
+  ----, embryonic, traces of, in birds, 450.
+  ----, rudimentary, in embryonic calf, 450, 480.
+  Tegetmeier, Mr., on cells of bees, 228, 233.
+  Temminck on distribution aiding classification, 419.
+  Thouin on grafts, 262.
+  Thrush, aquatic species of, 185.
+  ----, mocking, of the Galapagos, 402.
+  ----, young of, spotted, 439.
+  ----, nest of, 243.
+  Thuret, M., on crossed fuci, 258.
+  Thwaites, Mr., on acclimatisation, 140.
+  Tierra del Fuego, dogs of, 215.
+  ----, plants of, 374, 378.
+  Timber-drift, 360.
+  Time, lapse of, 282.
+  Titmouse, 184.
+  Toads on islands, 393.
+  Tobacco, crossed varieties of, 271.
+  Tomes, Mr., on the distribution of bats, 395.
+  Transitions in varieties rare, 172.
+  Trees on islands belong to peculiar orders, 392.
+  ---- with separated sexes, 99.
+  Trifolium pratense, 73, 94.
+  ---- incarnatum, 94.
+  Trigonia, 321.
+  Trilobites, 307.
+  ----, sudden extinction of, 321.
+  Troglodytes, 243.
+  Tucutucu, blind, 137.
+  Tumbler pigeons, habits of, hereditary, 214.
+  ----, young of, 446.
+  Turkey-cock, brush of hair on breast, 90.
+  Turkey, naked skin on head, 197.
+  ----, young, wild, 216.
+  Turnip and cabbage, analogous variations of, 159.
+  Type, unity of, 206.
+  Types, succession of, in same areas, 339.
+
+          U.
+
+  Udders enlarged by use, 11.
+  ----, rudimentary, 451.
+  Ulex, young leaves of, 439.
+  Umbelliferæ, outer and inner florets of, 144.
+  Unity of type, 206.
+  Use, effects of, under domestication, 11.
+  ----, effects of, in a state of nature, 134.
+  Utility, how far important in the construction of each part, 199.
+
+          V.
+
+  Valenciennes on fresh-water fish, 384.
+  Variability of mongrels and hybrids, 274.
+  Variation under domestication, 7.
+  ---- caused by reproductive system being affected by conditions of life,
+      8.
+  ---- under nature, 44.
+  ----, laws of, 131.
+  Variations appear at corresponding ages, 14, 86.
+  ----, analogous in distinct species, 159.
+  Varieties, natural, 44.
+  ----, struggle between, 75.
+  ----, domestic, extinction of, 111.
+  ----, transitional, rarity of, 172.
+  ----, when crossed, fertile, 268.
+  ----, when crossed, sterile, 269.
+  ----, classification of, 423.
+  Verbascum, sterility of, 251.
+  ----, varieties of, crossed, 271.
+  Verneuil, M. de, on the succession of species, 325.
+  Viola tricolor, 73.
+  {502}
+  Volcanic islands, denudation of, 285.
+  Vulture, naked skin on head, 197.
+
+          W.
+
+  Wading-birds, 386.
+  Wallace, Mr., on origin of species, 2.
+  ----, on law of geographical distribution, 355.
+  ----, on the Malay Archipelago, 395.
+  Wasp, sting of, 202.
+  Water, fresh, productions of, 383.
+  Water-hen, 185.
+  Waterhouse, Mr., on Australian marsupials, 116.
+  ----, on greatly developed parts being variable, 150.
+  ----, on the cells of bees, 225.
+  ----, on general affinities, 429.
+  Water-ouzel, 185.
+  Watson, Mr. H. C, on range of varieties of British plants, 58.
+  ----, on acclimatisation, 140.
+  ----, on flora of Azores, 363.
+  ----, on Alpine plants, 368, 376.
+  ----, on rarity of intermediate varieties, 176.
+  Weald, denudation of, 285.
+  Web of feet in water-birds, 185.
+  West Indian islands, mammals of, 396.
+  Westwood on species in large genera being closely allied to others, 57.
+  ---- on the tarsi of Engidæ, 157.
+  ---- on the antennæ of hymenopterous insects, 415.
+  Wheat, varieties of, 113.
+  White Mountains, flora of, 365.
+  Wings, reduction of size, 134.
+  ---- of insects homologous with branchiæ, 191.
+  ----, rudimentary, in insects, 450.
+  Wolf crossed with dog, 214.
+  ---- of Falkland Isles, 394.
+  Wollaston, Mr., on varieties of insects, 48.
+  ----, on fossil varieties of land-shells in Madeira, 52.
+  ----, on colours of insects on sea-shore, 132.
+  ----, on wingless beetles, 135.
+  ----, on rarity of intermediate varieties, 176.
+  ----, on insular insects, 389.
+  ----, on land-shells of Madeira, naturalised, 402.
+  Wolves, varieties of, 90.
+  Woodpecker, habits of, 184.
+  ----, green colour of, 197.
+  Woodward, Mr., on the duration of specific forms, 294.
+  ----, on the continuous succession of genera, 316.
+  ----, on the succession of types, 339.
+  World, species changing simultaneously throughout, 322.
+  Wrens, nest of, 243.
+
+          Y.
+
+  Youatt, Mr., on selection, 31.
+  ----, on sub-breeds of sheep, 36.
+  ----, on rudimentary horns in young cattle, 454.
+
+          Z.
+
+  Zebra, stripes on, 163.
+
+THE END.
+
+       *       *       *       *       *
+
+LONDON: PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET, AND CHARING
+CROSS.
+
+       *       *       *       *       *
+
+
+Corrections made to printed original.
+
+p. 133. "the slightest use to a being": 'slighest' in original.
+
+p. 193. "as Matteucci asserts": 'Matteucei' in original (the index
+correctly has Matteucci).
+
+p. 201. "deposited in the living bodies of other insects": 'depo-sisted'
+(across page break) in original.
+
+p. 315. "the newly-formed fantail": 'faintail' in original.
+
+p. 398. "the volcanic nature of the soil": 'volanic' in original.
+
+p. 403. "Madeira and the adjoining islet": 'Maderia' in original; and so in
+"from Porto Santo to Madeira".
+
+p. 442. "the same individual embryo": 'indivividual' in original.
+
+p. 458. "innumerable species, genera, and families": 'inumerable' in
+original.
+
+p. 490. "Inheritance which is almost implied by reproduction":
+'Inheritrnce' in original.
+
+
+
+
+
+
+End of the Project Gutenberg EBook of On the Origin of Species by Means of
+Natural Selection, by Charles Darwin
+
+*** END OF THIS PROJECT GUTENBERG EBOOK ORIGIN OF SPECIES ***
+
+***** This file should be named 22764-8.txt or 22764-8.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/2/2/7/6/22764/
+
+Produced by Steven Gibbs, Keith Edkins and the Online
+Distributed Proofreading Team at http://www.pgdp.net
+
+
+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.  Special rules,
+set forth in the General Terms of Use part of this license, apply to
+copying and distributing Project Gutenberg-tm electronic works to
+protect the PROJECT GUTENBERG-tm concept and trademark.  Project
+Gutenberg is a registered trademark, and may not be used if you
+charge for the eBooks, unless you receive specific permission.  If you
+do not charge anything for copies of this eBook, complying with the
+rules is very easy.  You may use this eBook for nearly any purpose
+such as creation of derivative works, reports, performances and
+research.  They may be modified and printed and given away--you may do
+practically ANYTHING with public domain eBooks.  Redistribution is
+subject to the trademark license, especially commercial
+redistribution.
+
+
+
+*** START: FULL LICENSE ***
+
+THE FULL PROJECT GUTENBERG LICENSE
+PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
+
+To protect the Project Gutenberg-tm mission of promoting the free
+distribution of electronic works, by using or distributing this work
+(or any other work associated in any way with the phrase "Project
+Gutenberg"), you agree to comply with all the terms of the Full Project
+Gutenberg-tm License (available with this file or online at
+http://gutenberg.org/license).
+
+
+Section 1.  General Terms of Use and Redistributing Project Gutenberg-tm
+electronic works
+
+1.A.  By reading or using any part of this Project Gutenberg-tm
+electronic work, you indicate that you have read, understand, agree to
+and accept all the terms of this license and intellectual property
+(trademark/copyright) agreement.  If you do not agree to abide by all
+the terms of this agreement, you must cease using and return or destroy
+all copies of Project Gutenberg-tm electronic works in your possession.
+If you paid a fee for obtaining a copy of or access to a Project
+Gutenberg-tm electronic work and you do not agree to be bound by the
+terms of this agreement, you may obtain a refund from the person or
+entity to whom you paid the fee as set forth in paragraph 1.E.8.
+
+1.B.  "Project Gutenberg" is a registered trademark.  It may only be
+used on or associated in any way with an electronic work by people who
+agree to be bound by the terms of this agreement.  There are a few
+things that you can do with most Project Gutenberg-tm electronic works
+even without complying with the full terms of this agreement.  See
+paragraph 1.C below.  There are a lot of things you can do with Project
+Gutenberg-tm electronic works if you follow the terms of this agreement
+and help preserve free future access to Project Gutenberg-tm electronic
+works.  See paragraph 1.E below.
+
+1.C.  The Project Gutenberg Literary Archive Foundation ("the Foundation"
+or PGLAF), owns a compilation copyright in the collection of Project
+Gutenberg-tm electronic works.  Nearly all the individual works in the
+collection are in the public domain in the United States.  If an
+individual work is in the public domain in the United States and you are
+located in the United States, we do not claim a right to prevent you from
+copying, distributing, performing, displaying or creating derivative
+works based on the work as long as all references to Project Gutenberg
+are removed.  Of course, we hope that you will support the Project
+Gutenberg-tm mission of promoting free access to electronic works by
+freely sharing Project Gutenberg-tm works in compliance with the terms of
+this agreement for keeping the Project Gutenberg-tm name associated with
+the work.  You can easily comply with the terms of this agreement by
+keeping this work in the same format with its attached full Project
+Gutenberg-tm License when you share it without charge with others.
+
+1.D.  The copyright laws of the place where you are located also govern
+what you can do with this work.  Copyright laws in most countries are in
+a constant state of change.  If you are outside the United States, check
+the laws of your country in addition to the terms of this agreement
+before downloading, copying, displaying, performing, distributing or
+creating derivative works based on this work or any other Project
+Gutenberg-tm work.  The Foundation makes no representations concerning
+the copyright status of any work in any country outside the United
+States.
+
+1.E.  Unless you have removed all references to Project Gutenberg:
+
+1.E.1.  The following sentence, with active links to, or other immediate
+access to, the full Project Gutenberg-tm License must appear prominently
+whenever any copy of a Project Gutenberg-tm work (any work on which the
+phrase "Project Gutenberg" appears, or with which the phrase "Project
+Gutenberg" is associated) is accessed, displayed, performed, viewed,
+copied or distributed:
+
+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
+
+1.E.2.  If an individual Project Gutenberg-tm electronic work is derived
+from the public domain (does not contain a notice indicating that it is
+posted with permission of the copyright holder), the work can be copied
+and distributed to anyone in the United States without paying any fees
+or charges.  If you are redistributing or providing access to a work
+with the phrase "Project Gutenberg" associated with or appearing on the
+work, you must comply either with the requirements of paragraphs 1.E.1
+through 1.E.7 or obtain permission for the use of the work and the
+Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
+1.E.9.
+
+1.E.3.  If an individual Project Gutenberg-tm electronic work is posted
+with the permission of the copyright holder, your use and distribution
+must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
+terms imposed by the copyright holder.  Additional terms will be linked
+to the Project Gutenberg-tm License for all works posted with the
+permission of the copyright holder found at the beginning of this work.
+
+1.E.4.  Do not unlink or detach or remove the full Project Gutenberg-tm
+License terms from this work, or any files containing a part of this
+work or any other work associated with Project Gutenberg-tm.
+
+1.E.5.  Do not copy, display, perform, distribute or redistribute this
+electronic work, or any part of this electronic work, without
+prominently displaying the sentence set forth in paragraph 1.E.1 with
+active links or immediate access to the full terms of the Project
+Gutenberg-tm License.
+
+1.E.6.  You may convert to and distribute this work in any binary,
+compressed, marked up, nonproprietary or proprietary form, including any
+word processing or hypertext form.  However, if you provide access to or
+distribute copies of a Project Gutenberg-tm work in a format other than
+"Plain Vanilla ASCII" or other format used in the official version
+posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
+you must, at no additional cost, fee or expense to the user, provide a
+copy, a means of exporting a copy, or a means of obtaining a copy upon
+request, of the work in its original "Plain Vanilla ASCII" or other
+form.  Any alternate format must include the full Project Gutenberg-tm
+License as specified in paragraph 1.E.1.
+
+1.E.7.  Do not charge a fee for access to, viewing, displaying,
+performing, copying or distributing any Project Gutenberg-tm works
+unless you comply with paragraph 1.E.8 or 1.E.9.
+
+1.E.8.  You may charge a reasonable fee for copies of or providing
+access to or distributing Project Gutenberg-tm electronic works provided
+that
+
+- You pay a royalty fee of 20% of the gross profits you derive from
+     the use of Project Gutenberg-tm works calculated using the method
+     you already use to calculate your applicable taxes.  The fee is
+     owed to the owner of the Project Gutenberg-tm trademark, but he
+     has agreed to donate royalties under this paragraph to the
+     Project Gutenberg Literary Archive Foundation.  Royalty payments
+     must be paid within 60 days following each date on which you
+     prepare (or are legally required to prepare) your periodic tax
+     returns.  Royalty payments should be clearly marked as such and
+     sent to the Project Gutenberg Literary Archive Foundation at the
+     address specified in Section 4, "Information about donations to
+     the Project Gutenberg Literary Archive Foundation."
+
+- You provide a full refund of any money paid by a user who notifies
+     you in writing (or by e-mail) within 30 days of receipt that s/he
+     does not agree to the terms of the full Project Gutenberg-tm
+     License.  You must require such a user to return or
+     destroy all copies of the works possessed in a physical medium
+     and discontinue all use of and all access to other copies of
+     Project Gutenberg-tm works.
+
+- You provide, in accordance with paragraph 1.F.3, a full refund of any
+     money paid for a work or a replacement copy, if a defect in the
+     electronic work is discovered and reported to you within 90 days
+     of receipt of the work.
+
+- You comply with all other terms of this agreement for free
+     distribution of Project Gutenberg-tm works.
+
+1.E.9.  If you wish to charge a fee or distribute a Project Gutenberg-tm
+electronic work or group of works on different terms than are set
+forth in this agreement, you must obtain permission in writing from
+both the Project Gutenberg Literary Archive Foundation and Michael
+Hart, the owner of the Project Gutenberg-tm trademark.  Contact the
+Foundation as set forth in Section 3 below.
+
+1.F.
+
+1.F.1.  Project Gutenberg volunteers and employees expend considerable
+effort to identify, do copyright research on, transcribe and proofread
+public domain works in creating the Project Gutenberg-tm
+collection.  Despite these efforts, Project Gutenberg-tm electronic
+works, and the medium on which they may be stored, may contain
+"Defects," such as, but not limited to, incomplete, inaccurate or
+corrupt data, transcription errors, a copyright or other intellectual
+property infringement, a defective or damaged disk or other medium, a
+computer virus, or computer codes that damage or cannot be read by
+your equipment.
+
+1.F.2.  LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
+of Replacement or Refund" described in paragraph 1.F.3, the Project
+Gutenberg Literary Archive Foundation, the owner of the Project
+Gutenberg-tm trademark, and any other party distributing a Project
+Gutenberg-tm electronic work under this agreement, disclaim all
+liability to you for damages, costs and expenses, including legal
+fees.  YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
+LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
+PROVIDED IN PARAGRAPH F3.  YOU AGREE THAT THE FOUNDATION, THE
+TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
+LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
+INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
+DAMAGE.
+
+1.F.3.  LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
+defect in this electronic work within 90 days of receiving it, you can
+receive a refund of the money (if any) you paid for it by sending a
+written explanation to the person you received the work from.  If you
+received the work on a physical medium, you must return the medium with
+your written explanation.  The person or entity that provided you with
+the defective work may elect to provide a replacement copy in lieu of a
+refund.  If you received the work electronically, the person or entity
+providing it to you may choose to give you a second opportunity to
+receive the work electronically in lieu of a refund.  If the second copy
+is also defective, you may demand a refund in writing without further
+opportunities to fix the problem.
+
+1.F.4.  Except for the limited right of replacement or refund set forth
+in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER
+WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE.
+
+1.F.5.  Some states do not allow disclaimers of certain implied
+warranties or the exclusion or limitation of certain types of damages.
+If any disclaimer or limitation set forth in this agreement violates the
+law of the state applicable to this agreement, the agreement shall be
+interpreted to make the maximum disclaimer or limitation permitted by
+the applicable state law.  The invalidity or unenforceability of any
+provision of this agreement shall not void the remaining provisions.
+
+1.F.6.  INDEMNITY - You agree to indemnify and hold the Foundation, the
+trademark owner, any agent or employee of the Foundation, anyone
+providing copies of Project Gutenberg-tm electronic works in accordance
+with this agreement, and any volunteers associated with the production,
+promotion and distribution of Project Gutenberg-tm electronic works,
+harmless from all liability, costs and expenses, including legal fees,
+that arise directly or indirectly from any of the following which you do
+or cause to occur: (a) distribution of this or any Project Gutenberg-tm
+work, (b) alteration, modification, or additions or deletions to any
+Project Gutenberg-tm work, and (c) any Defect you cause.
+
+
+Section  2.  Information about the Mission of Project Gutenberg-tm
+
+Project Gutenberg-tm is synonymous with the free distribution of
+electronic works in formats readable by the widest variety of computers
+including obsolete, old, middle-aged and new computers.  It exists
+because of the efforts of hundreds of volunteers and donations from
+people in all walks of life.
+
+Volunteers and financial support to provide volunteers with the
+assistance they need, is critical to reaching Project Gutenberg-tm's
+goals and ensuring that the Project Gutenberg-tm collection will
+remain freely available for generations to come.  In 2001, the Project
+Gutenberg Literary Archive Foundation was created to provide a secure
+and permanent future for Project Gutenberg-tm and future generations.
+To learn more about the Project Gutenberg Literary Archive Foundation
+and how your efforts and donations can help, see Sections 3 and 4
+and the Foundation web page at http://www.pglaf.org.
+
+
+Section 3.  Information about the Project Gutenberg Literary Archive
+Foundation
+
+The Project Gutenberg Literary Archive Foundation is a non profit
+501(c)(3) educational corporation organized under the laws of the
+state of Mississippi and granted tax exempt status by the Internal
+Revenue Service.  The Foundation's EIN or federal tax identification
+number is 64-6221541.  Its 501(c)(3) letter is posted at
+http://pglaf.org/fundraising.  Contributions to the Project Gutenberg
+Literary Archive Foundation are tax deductible to the full extent
+permitted by U.S. federal laws and your state's laws.
+
+The Foundation's principal office is located at 4557 Melan Dr. S.
+Fairbanks, AK, 99712., but its volunteers and employees are scattered
+throughout numerous locations.  Its business office is located at
+809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email
+business@pglaf.org.  Email contact links and up to date contact
+information can be found at the Foundation's web site and official
+page at http://pglaf.org
+
+For additional contact information:
+     Dr. Gregory B. Newby
+     Chief Executive and Director
+     gbnewby@pglaf.org
+
+
+Section 4.  Information about Donations to the Project Gutenberg
+Literary Archive Foundation
+
+Project Gutenberg-tm depends upon and cannot survive without wide
+spread public support and donations to carry out its mission of
+increasing the number of public domain and licensed works that can be
+freely distributed in machine readable form accessible by the widest
+array of equipment including outdated equipment.  Many small donations
+($1 to $5,000) are particularly important to maintaining tax exempt
+status with the IRS.
+
+The Foundation is committed to complying with the laws regulating
+charities and charitable donations in all 50 states of the United
+States.  Compliance requirements are not uniform and it takes a
+considerable effort, much paperwork and many fees to meet and keep up
+with these requirements.  We do not solicit donations in locations
+where we have not received written confirmation of compliance.  To
+SEND DONATIONS or determine the status of compliance for any
+particular state visit http://pglaf.org
+
+While we cannot and do not solicit contributions from states where we
+have not met the solicitation requirements, we know of no prohibition
+against accepting unsolicited donations from donors in such states who
+approach us with offers to donate.
+
+International donations are gratefully accepted, but we cannot make
+any statements concerning tax treatment of donations received from
+outside the United States.  U.S. laws alone swamp our small staff.
+
+Please check the Project Gutenberg Web pages for current donation
+methods and addresses.  Donations are accepted in a number of other
+ways including checks, online payments and credit card donations.
+To donate, please visit: http://pglaf.org/donate
+
+
+Section 5.  General Information About Project Gutenberg-tm electronic
+works.
+
+Professor Michael S. Hart is the originator of the Project Gutenberg-tm
+concept of a library of electronic works that could be freely shared
+with anyone.  For thirty years, he produced and distributed Project
+Gutenberg-tm eBooks with only a loose network of volunteer support.
+
+
+Project Gutenberg-tm eBooks are often created from several printed
+editions, all of which are confirmed as Public Domain in the U.S.
+unless a copyright notice is included.  Thus, we do not necessarily
+keep eBooks in compliance with any particular paper edition.
+
+
+Most people start at our Web site which has the main PG search facility:
+
+     http://www.gutenberg.org
+
+This Web site includes information about Project Gutenberg-tm,
+including how to make donations to the Project Gutenberg Literary
+Archive Foundation, how to help produce our new eBooks, and how to
+subscribe to our email newsletter to hear about new eBooks.
diff --git a/old/22764-8.zip b/old/22764-8.zip
new file mode 100644
index 0000000..a721196
--- /dev/null
+++ b/old/22764-8.zip
diff --git a/old/22764-page-images/f001.png b/old/22764-page-images/f001.png
new file mode 100644
index 0000000..924a983
--- /dev/null
+++ b/old/22764-page-images/f001.png
diff --git a/old/22764-page-images/f002.png b/old/22764-page-images/f002.png
new file mode 100644
index 0000000..c3069eb
--- /dev/null
+++ b/old/22764-page-images/f002.png
diff --git a/old/22764-page-images/f003.png b/old/22764-page-images/f003.png
new file mode 100644
index 0000000..74c80d6
--- /dev/null
+++ b/old/22764-page-images/f003.png
diff --git a/old/22764-page-images/f004.png b/old/22764-page-images/f004.png
new file mode 100644
index 0000000..cb2c3f1
--- /dev/null
+++ b/old/22764-page-images/f004.png
diff --git a/old/22764-page-images/f005.png b/old/22764-page-images/f005.png
new file mode 100644
index 0000000..1837b2f
--- /dev/null
+++ b/old/22764-page-images/f005.png
diff --git a/old/22764-page-images/f006.png b/old/22764-page-images/f006.png
new file mode 100644
index 0000000..24c49a3
--- /dev/null
+++ b/old/22764-page-images/f006.png
diff --git a/old/22764-page-images/f007.png b/old/22764-page-images/f007.png
new file mode 100644
index 0000000..0a51f09
--- /dev/null
+++ b/old/22764-page-images/f007.png
diff --git a/old/22764-page-images/f008.png b/old/22764-page-images/f008.png
new file mode 100644
index 0000000..8a62b2f
--- /dev/null
+++ b/old/22764-page-images/f008.png
diff --git a/old/22764-page-images/f009.png b/old/22764-page-images/f009.png
new file mode 100644
index 0000000..a7c101f
--- /dev/null
+++ b/old/22764-page-images/f009.png
diff --git a/old/22764-page-images/f010.png b/old/22764-page-images/f010.png
new file mode 100644
index 0000000..6dd1dea
--- /dev/null
+++ b/old/22764-page-images/f010.png
diff --git a/old/22764-page-images/f011.png b/old/22764-page-images/f011.png
new file mode 100644
index 0000000..f255474
--- /dev/null
+++ b/old/22764-page-images/f011.png
diff --git a/old/22764-page-images/f012.png b/old/22764-page-images/f012.png
new file mode 100644
index 0000000..d422a4f
--- /dev/null
+++ b/old/22764-page-images/f012.png
diff --git a/old/22764-page-images/f013.png b/old/22764-page-images/f013.png
new file mode 100644
index 0000000..646a8bf
--- /dev/null
+++ b/old/22764-page-images/f013.png
diff --git a/old/22764-page-images/f014.png b/old/22764-page-images/f014.png
new file mode 100644
index 0000000..62049f9
--- /dev/null
+++ b/old/22764-page-images/f014.png
diff --git a/old/22764-page-images/p007.png b/old/22764-page-images/p007.png
new file mode 100644
index 0000000..7672b62
--- /dev/null
+++ b/old/22764-page-images/p007.png
diff --git a/old/22764-page-images/p008.png b/old/22764-page-images/p008.png
new file mode 100644
index 0000000..27a1b06
--- /dev/null
+++ b/old/22764-page-images/p008.png
diff --git a/old/22764-page-images/p009.png b/old/22764-page-images/p009.png
new file mode 100644
index 0000000..f4c43c0
--- /dev/null
+++ b/old/22764-page-images/p009.png
diff --git a/old/22764-page-images/p010.png b/old/22764-page-images/p010.png
new file mode 100644
index 0000000..219f3c4
--- /dev/null
+++ b/old/22764-page-images/p010.png
diff --git a/old/22764-page-images/p011.png b/old/22764-page-images/p011.png
new file mode 100644
index 0000000..a808ea3
--- /dev/null
+++ b/old/22764-page-images/p011.png
diff --git a/old/22764-page-images/p012.png b/old/22764-page-images/p012.png
new file mode 100644
index 0000000..fa1028f
--- /dev/null
+++ b/old/22764-page-images/p012.png
diff --git a/old/22764-page-images/p013.png b/old/22764-page-images/p013.png
new file mode 100644
index 0000000..c8e11d2
--- /dev/null
+++ b/old/22764-page-images/p013.png
diff --git a/old/22764-page-images/p014.png b/old/22764-page-images/p014.png
new file mode 100644
index 0000000..3c1029a
--- /dev/null
+++ b/old/22764-page-images/p014.png
diff --git a/old/22764-page-images/p015.png b/old/22764-page-images/p015.png
new file mode 100644
index 0000000..b5c173b
--- /dev/null
+++ b/old/22764-page-images/p015.png
diff --git a/old/22764-page-images/p016.png b/old/22764-page-images/p016.png
new file mode 100644
index 0000000..73e9613
--- /dev/null
+++ b/old/22764-page-images/p016.png
diff --git a/old/22764-page-images/p017.png b/old/22764-page-images/p017.png
new file mode 100644
index 0000000..9e26e44
--- /dev/null
+++ b/old/22764-page-images/p017.png
diff --git a/old/22764-page-images/p018.png b/old/22764-page-images/p018.png
new file mode 100644
index 0000000..ddc8890
--- /dev/null
+++ b/old/22764-page-images/p018.png
diff --git a/old/22764-page-images/p019.png b/old/22764-page-images/p019.png
new file mode 100644
index 0000000..aafefc2
--- /dev/null
+++ b/old/22764-page-images/p019.png
diff --git a/old/22764-page-images/p020.png b/old/22764-page-images/p020.png
new file mode 100644
index 0000000..94a8f9b
--- /dev/null
+++ b/old/22764-page-images/p020.png
diff --git a/old/22764-page-images/p021.png b/old/22764-page-images/p021.png
new file mode 100644
index 0000000..11f0324
--- /dev/null
+++ b/old/22764-page-images/p021.png
diff --git a/old/22764-page-images/p022.png b/old/22764-page-images/p022.png
new file mode 100644
index 0000000..24d309f
--- /dev/null
+++ b/old/22764-page-images/p022.png
diff --git a/old/22764-page-images/p023.png b/old/22764-page-images/p023.png
new file mode 100644
index 0000000..f78f95f
--- /dev/null
+++ b/old/22764-page-images/p023.png
diff --git a/old/22764-page-images/p024.png b/old/22764-page-images/p024.png
new file mode 100644
index 0000000..c856956
--- /dev/null
+++ b/old/22764-page-images/p024.png
diff --git a/old/22764-page-images/p025.png b/old/22764-page-images/p025.png
new file mode 100644
index 0000000..fbee1cc
--- /dev/null
+++ b/old/22764-page-images/p025.png
diff --git a/old/22764-page-images/p026.png b/old/22764-page-images/p026.png
new file mode 100644
index 0000000..a3360f8
--- /dev/null
+++ b/old/22764-page-images/p026.png
diff --git a/old/22764-page-images/p027.png b/old/22764-page-images/p027.png
new file mode 100644
index 0000000..96ebe82
--- /dev/null
+++ b/old/22764-page-images/p027.png
diff --git a/old/22764-page-images/p028.png b/old/22764-page-images/p028.png
new file mode 100644
index 0000000..6460712
--- /dev/null
+++ b/old/22764-page-images/p028.png
diff --git a/old/22764-page-images/p029.png b/old/22764-page-images/p029.png
new file mode 100644
index 0000000..9732286
--- /dev/null
+++ b/old/22764-page-images/p029.png
diff --git a/old/22764-page-images/p030.png b/old/22764-page-images/p030.png
new file mode 100644
index 0000000..99e3fbd
--- /dev/null
+++ b/old/22764-page-images/p030.png
diff --git a/old/22764-page-images/p031.png b/old/22764-page-images/p031.png
new file mode 100644
index 0000000..b443b1a
--- /dev/null
+++ b/old/22764-page-images/p031.png
diff --git a/old/22764-page-images/p032.png b/old/22764-page-images/p032.png
new file mode 100644
index 0000000..b9f7511
--- /dev/null
+++ b/old/22764-page-images/p032.png
diff --git a/old/22764-page-images/p033.png b/old/22764-page-images/p033.png
new file mode 100644
index 0000000..8ddc2ff
--- /dev/null
+++ b/old/22764-page-images/p033.png
diff --git a/old/22764-page-images/p034.png b/old/22764-page-images/p034.png
new file mode 100644
index 0000000..b249ed4
--- /dev/null
+++ b/old/22764-page-images/p034.png
diff --git a/old/22764-page-images/p035.png b/old/22764-page-images/p035.png
new file mode 100644
index 0000000..fdcc545
--- /dev/null
+++ b/old/22764-page-images/p035.png
diff --git a/old/22764-page-images/p036.png b/old/22764-page-images/p036.png
new file mode 100644
index 0000000..898a0b1
--- /dev/null
+++ b/old/22764-page-images/p036.png
diff --git a/old/22764-page-images/p037.png b/old/22764-page-images/p037.png
new file mode 100644
index 0000000..99ed602
--- /dev/null
+++ b/old/22764-page-images/p037.png
diff --git a/old/22764-page-images/p038.png b/old/22764-page-images/p038.png
new file mode 100644
index 0000000..f54bf0e
--- /dev/null
+++ b/old/22764-page-images/p038.png
diff --git a/old/22764-page-images/p039.png b/old/22764-page-images/p039.png
new file mode 100644
index 0000000..e725594
--- /dev/null
+++ b/old/22764-page-images/p039.png
diff --git a/old/22764-page-images/p040.png b/old/22764-page-images/p040.png
new file mode 100644
index 0000000..c61746d
--- /dev/null
+++ b/old/22764-page-images/p040.png
diff --git a/old/22764-page-images/p041.png b/old/22764-page-images/p041.png
new file mode 100644
index 0000000..b582574
--- /dev/null
+++ b/old/22764-page-images/p041.png
diff --git a/old/22764-page-images/p042.png b/old/22764-page-images/p042.png
new file mode 100644
index 0000000..c385e30
--- /dev/null
+++ b/old/22764-page-images/p042.png
diff --git a/old/22764-page-images/p043.png b/old/22764-page-images/p043.png
new file mode 100644
index 0000000..1860877
--- /dev/null
+++ b/old/22764-page-images/p043.png
diff --git a/old/22764-page-images/p044.png b/old/22764-page-images/p044.png
new file mode 100644
index 0000000..9987fa2
--- /dev/null
+++ b/old/22764-page-images/p044.png
diff --git a/old/22764-page-images/p045.png b/old/22764-page-images/p045.png
new file mode 100644
index 0000000..7dc60e6
--- /dev/null
+++ b/old/22764-page-images/p045.png
diff --git a/old/22764-page-images/p046.png b/old/22764-page-images/p046.png
new file mode 100644
index 0000000..73fea0d
--- /dev/null
+++ b/old/22764-page-images/p046.png
diff --git a/old/22764-page-images/p047.png b/old/22764-page-images/p047.png
new file mode 100644
index 0000000..96540e9
--- /dev/null
+++ b/old/22764-page-images/p047.png
diff --git a/old/22764-page-images/p048.png b/old/22764-page-images/p048.png
new file mode 100644
index 0000000..26abd63
--- /dev/null
+++ b/old/22764-page-images/p048.png
diff --git a/old/22764-page-images/p049.png b/old/22764-page-images/p049.png
new file mode 100644
index 0000000..5b2d7b3
--- /dev/null
+++ b/old/22764-page-images/p049.png
diff --git a/old/22764-page-images/p050.png b/old/22764-page-images/p050.png
new file mode 100644
index 0000000..692770f
--- /dev/null
+++ b/old/22764-page-images/p050.png
diff --git a/old/22764-page-images/p051.png b/old/22764-page-images/p051.png
new file mode 100644
index 0000000..9aca595
--- /dev/null
+++ b/old/22764-page-images/p051.png
diff --git a/old/22764-page-images/p052.png b/old/22764-page-images/p052.png
new file mode 100644
index 0000000..b433562
--- /dev/null
+++ b/old/22764-page-images/p052.png
diff --git a/old/22764-page-images/p053.png b/old/22764-page-images/p053.png
new file mode 100644
index 0000000..63d5db4
--- /dev/null
+++ b/old/22764-page-images/p053.png
diff --git a/old/22764-page-images/p054.png b/old/22764-page-images/p054.png
new file mode 100644
index 0000000..09817c2
--- /dev/null
+++ b/old/22764-page-images/p054.png
diff --git a/old/22764-page-images/p055.png b/old/22764-page-images/p055.png
new file mode 100644
index 0000000..1c27be5
--- /dev/null
+++ b/old/22764-page-images/p055.png
diff --git a/old/22764-page-images/p056.png b/old/22764-page-images/p056.png
new file mode 100644
index 0000000..75a7204
--- /dev/null
+++ b/old/22764-page-images/p056.png
diff --git a/old/22764-page-images/p057.png b/old/22764-page-images/p057.png
new file mode 100644
index 0000000..1502ccd
--- /dev/null
+++ b/old/22764-page-images/p057.png
diff --git a/old/22764-page-images/p058.png b/old/22764-page-images/p058.png
new file mode 100644
index 0000000..945a2e4
--- /dev/null
+++ b/old/22764-page-images/p058.png
diff --git a/old/22764-page-images/p059.png b/old/22764-page-images/p059.png
new file mode 100644
index 0000000..79dfff1
--- /dev/null
+++ b/old/22764-page-images/p059.png
diff --git a/old/22764-page-images/p060.png b/old/22764-page-images/p060.png
new file mode 100644
index 0000000..c3dfe63
--- /dev/null
+++ b/old/22764-page-images/p060.png
diff --git a/old/22764-page-images/p061.png b/old/22764-page-images/p061.png
new file mode 100644
index 0000000..4c6d2fe
--- /dev/null
+++ b/old/22764-page-images/p061.png
diff --git a/old/22764-page-images/p062.png b/old/22764-page-images/p062.png
new file mode 100644
index 0000000..1501bf7
--- /dev/null
+++ b/old/22764-page-images/p062.png
diff --git a/old/22764-page-images/p063.png b/old/22764-page-images/p063.png
new file mode 100644
index 0000000..612e466
--- /dev/null
+++ b/old/22764-page-images/p063.png
diff --git a/old/22764-page-images/p064.png b/old/22764-page-images/p064.png
new file mode 100644
index 0000000..4f7bed6
--- /dev/null
+++ b/old/22764-page-images/p064.png
diff --git a/old/22764-page-images/p065.png b/old/22764-page-images/p065.png
new file mode 100644
index 0000000..e3cdf5e
--- /dev/null
+++ b/old/22764-page-images/p065.png
diff --git a/old/22764-page-images/p066.png b/old/22764-page-images/p066.png
new file mode 100644
index 0000000..5c6b714
--- /dev/null
+++ b/old/22764-page-images/p066.png
diff --git a/old/22764-page-images/p067.png b/old/22764-page-images/p067.png
new file mode 100644
index 0000000..3364984
--- /dev/null
+++ b/old/22764-page-images/p067.png
diff --git a/old/22764-page-images/p068.png b/old/22764-page-images/p068.png
new file mode 100644
index 0000000..51c6e9b
--- /dev/null
+++ b/old/22764-page-images/p068.png
diff --git a/old/22764-page-images/p069.png b/old/22764-page-images/p069.png
new file mode 100644
index 0000000..1bf4f2a
--- /dev/null
+++ b/old/22764-page-images/p069.png
diff --git a/old/22764-page-images/p070.png b/old/22764-page-images/p070.png
new file mode 100644
index 0000000..90eefd7
--- /dev/null
+++ b/old/22764-page-images/p070.png
diff --git a/old/22764-page-images/p071.png b/old/22764-page-images/p071.png
new file mode 100644
index 0000000..7780124
--- /dev/null
+++ b/old/22764-page-images/p071.png
diff --git a/old/22764-page-images/p072.png b/old/22764-page-images/p072.png
new file mode 100644
index 0000000..613a9f2
--- /dev/null
+++ b/old/22764-page-images/p072.png
diff --git a/old/22764-page-images/p073.png b/old/22764-page-images/p073.png
new file mode 100644
index 0000000..389028a
--- /dev/null
+++ b/old/22764-page-images/p073.png
diff --git a/old/22764-page-images/p074.png b/old/22764-page-images/p074.png
new file mode 100644
index 0000000..836d9aa
--- /dev/null
+++ b/old/22764-page-images/p074.png
diff --git a/old/22764-page-images/p075.png b/old/22764-page-images/p075.png
new file mode 100644
index 0000000..c1b2f23
--- /dev/null
+++ b/old/22764-page-images/p075.png
diff --git a/old/22764-page-images/p076.png b/old/22764-page-images/p076.png
new file mode 100644
index 0000000..2a7b11a
--- /dev/null
+++ b/old/22764-page-images/p076.png
diff --git a/old/22764-page-images/p077.png b/old/22764-page-images/p077.png
new file mode 100644
index 0000000..6be7444
--- /dev/null
+++ b/old/22764-page-images/p077.png
diff --git a/old/22764-page-images/p078.png b/old/22764-page-images/p078.png
new file mode 100644
index 0000000..b9fa0dc
--- /dev/null
+++ b/old/22764-page-images/p078.png
diff --git a/old/22764-page-images/p079.png b/old/22764-page-images/p079.png
new file mode 100644
index 0000000..f332025
--- /dev/null
+++ b/old/22764-page-images/p079.png
diff --git a/old/22764-page-images/p080.png b/old/22764-page-images/p080.png
new file mode 100644
index 0000000..77153c3
--- /dev/null
+++ b/old/22764-page-images/p080.png
diff --git a/old/22764-page-images/p081.png b/old/22764-page-images/p081.png
new file mode 100644
index 0000000..a0a0bb9
--- /dev/null
+++ b/old/22764-page-images/p081.png
diff --git a/old/22764-page-images/p082.png b/old/22764-page-images/p082.png
new file mode 100644
index 0000000..56710e5
--- /dev/null
+++ b/old/22764-page-images/p082.png
diff --git a/old/22764-page-images/p083.png b/old/22764-page-images/p083.png
new file mode 100644
index 0000000..e5c5578
--- /dev/null
+++ b/old/22764-page-images/p083.png
diff --git a/old/22764-page-images/p084.png b/old/22764-page-images/p084.png
new file mode 100644
index 0000000..4b593de
--- /dev/null
+++ b/old/22764-page-images/p084.png
diff --git a/old/22764-page-images/p085.png b/old/22764-page-images/p085.png
new file mode 100644
index 0000000..5022a52
--- /dev/null
+++ b/old/22764-page-images/p085.png
diff --git a/old/22764-page-images/p086.png b/old/22764-page-images/p086.png
new file mode 100644
index 0000000..f500932
--- /dev/null
+++ b/old/22764-page-images/p086.png
diff --git a/old/22764-page-images/p087.png b/old/22764-page-images/p087.png
new file mode 100644
index 0000000..503f693
--- /dev/null
+++ b/old/22764-page-images/p087.png
diff --git a/old/22764-page-images/p088.png b/old/22764-page-images/p088.png
new file mode 100644
index 0000000..50e4727
--- /dev/null
+++ b/old/22764-page-images/p088.png
diff --git a/old/22764-page-images/p089.png b/old/22764-page-images/p089.png
new file mode 100644
index 0000000..e76103f
--- /dev/null
+++ b/old/22764-page-images/p089.png
diff --git a/old/22764-page-images/p090.png b/old/22764-page-images/p090.png
new file mode 100644
index 0000000..bda2812
--- /dev/null
+++ b/old/22764-page-images/p090.png
diff --git a/old/22764-page-images/p091.png b/old/22764-page-images/p091.png
new file mode 100644
index 0000000..094ac96
--- /dev/null
+++ b/old/22764-page-images/p091.png
diff --git a/old/22764-page-images/p092.png b/old/22764-page-images/p092.png
new file mode 100644
index 0000000..cc3cf6d
--- /dev/null
+++ b/old/22764-page-images/p092.png
diff --git a/old/22764-page-images/p093.png b/old/22764-page-images/p093.png
new file mode 100644
index 0000000..6504770
--- /dev/null
+++ b/old/22764-page-images/p093.png
diff --git a/old/22764-page-images/p094.png b/old/22764-page-images/p094.png
new file mode 100644
index 0000000..81c2f62
--- /dev/null
+++ b/old/22764-page-images/p094.png
diff --git a/old/22764-page-images/p095.png b/old/22764-page-images/p095.png
new file mode 100644
index 0000000..1ed7834
--- /dev/null
+++ b/old/22764-page-images/p095.png
diff --git a/old/22764-page-images/p096.png b/old/22764-page-images/p096.png
new file mode 100644
index 0000000..35b11a6
--- /dev/null
+++ b/old/22764-page-images/p096.png
diff --git a/old/22764-page-images/p097.png b/old/22764-page-images/p097.png
new file mode 100644
index 0000000..be66048
--- /dev/null
+++ b/old/22764-page-images/p097.png
diff --git a/old/22764-page-images/p098.png b/old/22764-page-images/p098.png
new file mode 100644
index 0000000..0923856
--- /dev/null
+++ b/old/22764-page-images/p098.png
diff --git a/old/22764-page-images/p099.png b/old/22764-page-images/p099.png
new file mode 100644
index 0000000..a5f17f8
--- /dev/null
+++ b/old/22764-page-images/p099.png
diff --git a/old/22764-page-images/p100.png b/old/22764-page-images/p100.png
new file mode 100644
index 0000000..dd4f16a
--- /dev/null
+++ b/old/22764-page-images/p100.png
diff --git a/old/22764-page-images/p101.png b/old/22764-page-images/p101.png
new file mode 100644
index 0000000..e0079b3
--- /dev/null
+++ b/old/22764-page-images/p101.png
diff --git a/old/22764-page-images/p102.png b/old/22764-page-images/p102.png
new file mode 100644
index 0000000..a2dc56a
--- /dev/null
+++ b/old/22764-page-images/p102.png
diff --git a/old/22764-page-images/p103.png b/old/22764-page-images/p103.png
new file mode 100644
index 0000000..43c7b01
--- /dev/null
+++ b/old/22764-page-images/p103.png
diff --git a/old/22764-page-images/p104.png b/old/22764-page-images/p104.png
new file mode 100644
index 0000000..42b7f71
--- /dev/null
+++ b/old/22764-page-images/p104.png
diff --git a/old/22764-page-images/p105.png b/old/22764-page-images/p105.png
new file mode 100644
index 0000000..c114108
--- /dev/null
+++ b/old/22764-page-images/p105.png
diff --git a/old/22764-page-images/p106.png b/old/22764-page-images/p106.png
new file mode 100644
index 0000000..ac94220
--- /dev/null
+++ b/old/22764-page-images/p106.png
diff --git a/old/22764-page-images/p107.png b/old/22764-page-images/p107.png
new file mode 100644
index 0000000..82bf142
--- /dev/null
+++ b/old/22764-page-images/p107.png
diff --git a/old/22764-page-images/p108.png b/old/22764-page-images/p108.png
new file mode 100644
index 0000000..13ce473
--- /dev/null
+++ b/old/22764-page-images/p108.png
diff --git a/old/22764-page-images/p109.png b/old/22764-page-images/p109.png
new file mode 100644
index 0000000..952c660
--- /dev/null
+++ b/old/22764-page-images/p109.png
diff --git a/old/22764-page-images/p110.png b/old/22764-page-images/p110.png
new file mode 100644
index 0000000..681bcc4
--- /dev/null
+++ b/old/22764-page-images/p110.png
diff --git a/old/22764-page-images/p111.png b/old/22764-page-images/p111.png
new file mode 100644
index 0000000..91ba268
--- /dev/null
+++ b/old/22764-page-images/p111.png
diff --git a/old/22764-page-images/p112.png b/old/22764-page-images/p112.png
new file mode 100644
index 0000000..2304854
--- /dev/null
+++ b/old/22764-page-images/p112.png
diff --git a/old/22764-page-images/p113.png b/old/22764-page-images/p113.png
new file mode 100644
index 0000000..3f2182b
--- /dev/null
+++ b/old/22764-page-images/p113.png
diff --git a/old/22764-page-images/p114.png b/old/22764-page-images/p114.png
new file mode 100644
index 0000000..ed7c7b4
--- /dev/null
+++ b/old/22764-page-images/p114.png
diff --git a/old/22764-page-images/p115.png b/old/22764-page-images/p115.png
new file mode 100644
index 0000000..8db5934
--- /dev/null
+++ b/old/22764-page-images/p115.png
diff --git a/old/22764-page-images/p116.png b/old/22764-page-images/p116.png
new file mode 100644
index 0000000..09f461c
--- /dev/null
+++ b/old/22764-page-images/p116.png
diff --git a/old/22764-page-images/p117-insert.png b/old/22764-page-images/p117-insert.png
new file mode 100644
index 0000000..7512280
--- /dev/null
+++ b/old/22764-page-images/p117-insert.png
diff --git a/old/22764-page-images/p117.png b/old/22764-page-images/p117.png
new file mode 100644
index 0000000..f65ceeb
--- /dev/null
+++ b/old/22764-page-images/p117.png
diff --git a/old/22764-page-images/p118.png b/old/22764-page-images/p118.png
new file mode 100644
index 0000000..f2bf3cb
--- /dev/null
+++ b/old/22764-page-images/p118.png
diff --git a/old/22764-page-images/p119.png b/old/22764-page-images/p119.png
new file mode 100644
index 0000000..13b747c
--- /dev/null
+++ b/old/22764-page-images/p119.png
diff --git a/old/22764-page-images/p120.png b/old/22764-page-images/p120.png
new file mode 100644
index 0000000..052ba3b
--- /dev/null
+++ b/old/22764-page-images/p120.png
diff --git a/old/22764-page-images/p121.png b/old/22764-page-images/p121.png
new file mode 100644
index 0000000..880197b
--- /dev/null
+++ b/old/22764-page-images/p121.png
diff --git a/old/22764-page-images/p122.png b/old/22764-page-images/p122.png
new file mode 100644
index 0000000..c7c0658
--- /dev/null
+++ b/old/22764-page-images/p122.png
diff --git a/old/22764-page-images/p123.png b/old/22764-page-images/p123.png
new file mode 100644
index 0000000..80896b6
--- /dev/null
+++ b/old/22764-page-images/p123.png
diff --git a/old/22764-page-images/p124.png b/old/22764-page-images/p124.png
new file mode 100644
index 0000000..044a636
--- /dev/null
+++ b/old/22764-page-images/p124.png
diff --git a/old/22764-page-images/p125.png b/old/22764-page-images/p125.png
new file mode 100644
index 0000000..bc1579e
--- /dev/null
+++ b/old/22764-page-images/p125.png
diff --git a/old/22764-page-images/p126.png b/old/22764-page-images/p126.png
new file mode 100644
index 0000000..24efd78
--- /dev/null
+++ b/old/22764-page-images/p126.png
diff --git a/old/22764-page-images/p127.png b/old/22764-page-images/p127.png
new file mode 100644
index 0000000..bf564ff
--- /dev/null
+++ b/old/22764-page-images/p127.png
diff --git a/old/22764-page-images/p128.png b/old/22764-page-images/p128.png
new file mode 100644
index 0000000..2f8ad1c
--- /dev/null
+++ b/old/22764-page-images/p128.png
diff --git a/old/22764-page-images/p129.png b/old/22764-page-images/p129.png
new file mode 100644
index 0000000..9c7c9ef
--- /dev/null
+++ b/old/22764-page-images/p129.png
diff --git a/old/22764-page-images/p130.png b/old/22764-page-images/p130.png
new file mode 100644
index 0000000..5e2246a
--- /dev/null
+++ b/old/22764-page-images/p130.png
diff --git a/old/22764-page-images/p131.png b/old/22764-page-images/p131.png
new file mode 100644
index 0000000..4675ada
--- /dev/null
+++ b/old/22764-page-images/p131.png
diff --git a/old/22764-page-images/p132.png b/old/22764-page-images/p132.png
new file mode 100644
index 0000000..b3f1536
--- /dev/null
+++ b/old/22764-page-images/p132.png
diff --git a/old/22764-page-images/p133.png b/old/22764-page-images/p133.png
new file mode 100644
index 0000000..82db5fc
--- /dev/null
+++ b/old/22764-page-images/p133.png
diff --git a/old/22764-page-images/p134.png b/old/22764-page-images/p134.png
new file mode 100644
index 0000000..688b515
--- /dev/null
+++ b/old/22764-page-images/p134.png
diff --git a/old/22764-page-images/p135.png b/old/22764-page-images/p135.png
new file mode 100644
index 0000000..3fe553f
--- /dev/null
+++ b/old/22764-page-images/p135.png
diff --git a/old/22764-page-images/p136.png b/old/22764-page-images/p136.png
new file mode 100644
index 0000000..375f74d
--- /dev/null
+++ b/old/22764-page-images/p136.png
diff --git a/old/22764-page-images/p137.png b/old/22764-page-images/p137.png
new file mode 100644
index 0000000..87d51fa
--- /dev/null
+++ b/old/22764-page-images/p137.png
diff --git a/old/22764-page-images/p138.png b/old/22764-page-images/p138.png
new file mode 100644
index 0000000..d7b8797
--- /dev/null
+++ b/old/22764-page-images/p138.png
diff --git a/old/22764-page-images/p139.png b/old/22764-page-images/p139.png
new file mode 100644
index 0000000..f9bfac6
--- /dev/null
+++ b/old/22764-page-images/p139.png
diff --git a/old/22764-page-images/p140.png b/old/22764-page-images/p140.png
new file mode 100644
index 0000000..c4989cf
--- /dev/null
+++ b/old/22764-page-images/p140.png
diff --git a/old/22764-page-images/p141.png b/old/22764-page-images/p141.png
new file mode 100644
index 0000000..8e0bfa4
--- /dev/null
+++ b/old/22764-page-images/p141.png
diff --git a/old/22764-page-images/p142.png b/old/22764-page-images/p142.png
new file mode 100644
index 0000000..7bcd70f
--- /dev/null
+++ b/old/22764-page-images/p142.png
diff --git a/old/22764-page-images/p143.png b/old/22764-page-images/p143.png
new file mode 100644
index 0000000..81144ff
--- /dev/null
+++ b/old/22764-page-images/p143.png
diff --git a/old/22764-page-images/p144.png b/old/22764-page-images/p144.png
new file mode 100644
index 0000000..e6005d3
--- /dev/null
+++ b/old/22764-page-images/p144.png
diff --git a/old/22764-page-images/p145.png b/old/22764-page-images/p145.png
new file mode 100644
index 0000000..641b2c4
--- /dev/null
+++ b/old/22764-page-images/p145.png
diff --git a/old/22764-page-images/p146.png b/old/22764-page-images/p146.png
new file mode 100644
index 0000000..c2c6e3f
--- /dev/null
+++ b/old/22764-page-images/p146.png
diff --git a/old/22764-page-images/p147.png b/old/22764-page-images/p147.png
new file mode 100644
index 0000000..a13fd46
--- /dev/null
+++ b/old/22764-page-images/p147.png
diff --git a/old/22764-page-images/p148.png b/old/22764-page-images/p148.png
new file mode 100644
index 0000000..b966901
--- /dev/null
+++ b/old/22764-page-images/p148.png
diff --git a/old/22764-page-images/p149.png b/old/22764-page-images/p149.png
new file mode 100644
index 0000000..bd3e413
--- /dev/null
+++ b/old/22764-page-images/p149.png
diff --git a/old/22764-page-images/p150.png b/old/22764-page-images/p150.png
new file mode 100644
index 0000000..4e22506
--- /dev/null
+++ b/old/22764-page-images/p150.png
diff --git a/old/22764-page-images/p151.png b/old/22764-page-images/p151.png
new file mode 100644
index 0000000..7c644c1
--- /dev/null
+++ b/old/22764-page-images/p151.png
diff --git a/old/22764-page-images/p152.png b/old/22764-page-images/p152.png
new file mode 100644
index 0000000..f030d42
--- /dev/null
+++ b/old/22764-page-images/p152.png
diff --git a/old/22764-page-images/p153.png b/old/22764-page-images/p153.png
new file mode 100644
index 0000000..a20a531
--- /dev/null
+++ b/old/22764-page-images/p153.png
diff --git a/old/22764-page-images/p154.png b/old/22764-page-images/p154.png
new file mode 100644
index 0000000..1f6df4c
--- /dev/null
+++ b/old/22764-page-images/p154.png
diff --git a/old/22764-page-images/p155.png b/old/22764-page-images/p155.png
new file mode 100644
index 0000000..60b1f09
--- /dev/null
+++ b/old/22764-page-images/p155.png
diff --git a/old/22764-page-images/p156.png b/old/22764-page-images/p156.png
new file mode 100644
index 0000000..6299545
--- /dev/null
+++ b/old/22764-page-images/p156.png
diff --git a/old/22764-page-images/p157.png b/old/22764-page-images/p157.png
new file mode 100644
index 0000000..1bd0fde
--- /dev/null
+++ b/old/22764-page-images/p157.png
diff --git a/old/22764-page-images/p158.png b/old/22764-page-images/p158.png
new file mode 100644
index 0000000..50fe6e0
--- /dev/null
+++ b/old/22764-page-images/p158.png
diff --git a/old/22764-page-images/p159.png b/old/22764-page-images/p159.png
new file mode 100644
index 0000000..52883b9
--- /dev/null
+++ b/old/22764-page-images/p159.png
diff --git a/old/22764-page-images/p160.png b/old/22764-page-images/p160.png
new file mode 100644
index 0000000..6981a27
--- /dev/null
+++ b/old/22764-page-images/p160.png
diff --git a/old/22764-page-images/p161.png b/old/22764-page-images/p161.png
new file mode 100644
index 0000000..51e8d17
--- /dev/null
+++ b/old/22764-page-images/p161.png
diff --git a/old/22764-page-images/p162.png b/old/22764-page-images/p162.png
new file mode 100644
index 0000000..b28faa3
--- /dev/null
+++ b/old/22764-page-images/p162.png
diff --git a/old/22764-page-images/p163.png b/old/22764-page-images/p163.png
new file mode 100644
index 0000000..2b180d6
--- /dev/null
+++ b/old/22764-page-images/p163.png
diff --git a/old/22764-page-images/p164.png b/old/22764-page-images/p164.png
new file mode 100644
index 0000000..9623ef2
--- /dev/null
+++ b/old/22764-page-images/p164.png
diff --git a/old/22764-page-images/p165.png b/old/22764-page-images/p165.png
new file mode 100644
index 0000000..792b016
--- /dev/null
+++ b/old/22764-page-images/p165.png
diff --git a/old/22764-page-images/p166.png b/old/22764-page-images/p166.png
new file mode 100644
index 0000000..ac25d6b
--- /dev/null
+++ b/old/22764-page-images/p166.png
diff --git a/old/22764-page-images/p167.png b/old/22764-page-images/p167.png
new file mode 100644
index 0000000..8191e56
--- /dev/null
+++ b/old/22764-page-images/p167.png
diff --git a/old/22764-page-images/p168.png b/old/22764-page-images/p168.png
new file mode 100644
index 0000000..500df9e
--- /dev/null
+++ b/old/22764-page-images/p168.png
diff --git a/old/22764-page-images/p169.png b/old/22764-page-images/p169.png
new file mode 100644
index 0000000..c302654
--- /dev/null
+++ b/old/22764-page-images/p169.png
diff --git a/old/22764-page-images/p170.png b/old/22764-page-images/p170.png
new file mode 100644
index 0000000..a14d630
--- /dev/null
+++ b/old/22764-page-images/p170.png
diff --git a/old/22764-page-images/p171.png b/old/22764-page-images/p171.png
new file mode 100644
index 0000000..9a00ede
--- /dev/null
+++ b/old/22764-page-images/p171.png
diff --git a/old/22764-page-images/p172.png b/old/22764-page-images/p172.png
new file mode 100644
index 0000000..810f492
--- /dev/null
+++ b/old/22764-page-images/p172.png
diff --git a/old/22764-page-images/p173.png b/old/22764-page-images/p173.png
new file mode 100644
index 0000000..4633a41
--- /dev/null
+++ b/old/22764-page-images/p173.png
diff --git a/old/22764-page-images/p174.png b/old/22764-page-images/p174.png
new file mode 100644
index 0000000..470b73f
--- /dev/null
+++ b/old/22764-page-images/p174.png
diff --git a/old/22764-page-images/p175.png b/old/22764-page-images/p175.png
new file mode 100644
index 0000000..ef2592f
--- /dev/null
+++ b/old/22764-page-images/p175.png
diff --git a/old/22764-page-images/p176.png b/old/22764-page-images/p176.png
new file mode 100644
index 0000000..a399247
--- /dev/null
+++ b/old/22764-page-images/p176.png
diff --git a/old/22764-page-images/p177.png b/old/22764-page-images/p177.png
new file mode 100644
index 0000000..30c1e66
--- /dev/null
+++ b/old/22764-page-images/p177.png
diff --git a/old/22764-page-images/p178.png b/old/22764-page-images/p178.png
new file mode 100644
index 0000000..0f3fbbf
--- /dev/null
+++ b/old/22764-page-images/p178.png
diff --git a/old/22764-page-images/p179.png b/old/22764-page-images/p179.png
new file mode 100644
index 0000000..5487363
--- /dev/null
+++ b/old/22764-page-images/p179.png
diff --git a/old/22764-page-images/p180.png b/old/22764-page-images/p180.png
new file mode 100644
index 0000000..c67979f
--- /dev/null
+++ b/old/22764-page-images/p180.png
diff --git a/old/22764-page-images/p181.png b/old/22764-page-images/p181.png
new file mode 100644
index 0000000..3f712a6
--- /dev/null
+++ b/old/22764-page-images/p181.png
diff --git a/old/22764-page-images/p182.png b/old/22764-page-images/p182.png
new file mode 100644
index 0000000..6835f95
--- /dev/null
+++ b/old/22764-page-images/p182.png
diff --git a/old/22764-page-images/p183.png b/old/22764-page-images/p183.png
new file mode 100644
index 0000000..957b9a9
--- /dev/null
+++ b/old/22764-page-images/p183.png
diff --git a/old/22764-page-images/p184.png b/old/22764-page-images/p184.png
new file mode 100644
index 0000000..cce9bb7
--- /dev/null
+++ b/old/22764-page-images/p184.png
diff --git a/old/22764-page-images/p185.png b/old/22764-page-images/p185.png
new file mode 100644
index 0000000..749896f
--- /dev/null
+++ b/old/22764-page-images/p185.png
diff --git a/old/22764-page-images/p186.png b/old/22764-page-images/p186.png
new file mode 100644
index 0000000..47190a1
--- /dev/null
+++ b/old/22764-page-images/p186.png
diff --git a/old/22764-page-images/p187.png b/old/22764-page-images/p187.png
new file mode 100644
index 0000000..65692b7
--- /dev/null
+++ b/old/22764-page-images/p187.png
diff --git a/old/22764-page-images/p188.png b/old/22764-page-images/p188.png
new file mode 100644
index 0000000..0adc2f7
--- /dev/null
+++ b/old/22764-page-images/p188.png
diff --git a/old/22764-page-images/p189.png b/old/22764-page-images/p189.png
new file mode 100644
index 0000000..0b41bab
--- /dev/null
+++ b/old/22764-page-images/p189.png
diff --git a/old/22764-page-images/p190.png b/old/22764-page-images/p190.png
new file mode 100644
index 0000000..e809e19
--- /dev/null
+++ b/old/22764-page-images/p190.png
diff --git a/old/22764-page-images/p191.png b/old/22764-page-images/p191.png
new file mode 100644
index 0000000..f5bb21a
--- /dev/null
+++ b/old/22764-page-images/p191.png
diff --git a/old/22764-page-images/p192.png b/old/22764-page-images/p192.png
new file mode 100644
index 0000000..6df37dc
--- /dev/null
+++ b/old/22764-page-images/p192.png
diff --git a/old/22764-page-images/p193.png b/old/22764-page-images/p193.png
new file mode 100644
index 0000000..add8a22
--- /dev/null
+++ b/old/22764-page-images/p193.png
diff --git a/old/22764-page-images/p194.png b/old/22764-page-images/p194.png
new file mode 100644
index 0000000..762a880
--- /dev/null
+++ b/old/22764-page-images/p194.png
diff --git a/old/22764-page-images/p195.png b/old/22764-page-images/p195.png
new file mode 100644
index 0000000..5e6ecf3
--- /dev/null
+++ b/old/22764-page-images/p195.png
diff --git a/old/22764-page-images/p196.png b/old/22764-page-images/p196.png
new file mode 100644
index 0000000..0faa2f3
--- /dev/null
+++ b/old/22764-page-images/p196.png
diff --git a/old/22764-page-images/p197.png b/old/22764-page-images/p197.png
new file mode 100644
index 0000000..6b9e612
--- /dev/null
+++ b/old/22764-page-images/p197.png
diff --git a/old/22764-page-images/p198.png b/old/22764-page-images/p198.png
new file mode 100644
index 0000000..0cd2647
--- /dev/null
+++ b/old/22764-page-images/p198.png
diff --git a/old/22764-page-images/p199.png b/old/22764-page-images/p199.png
new file mode 100644
index 0000000..a9c50c0
--- /dev/null
+++ b/old/22764-page-images/p199.png
diff --git a/old/22764-page-images/p200.png b/old/22764-page-images/p200.png
new file mode 100644
index 0000000..9c17b86
--- /dev/null
+++ b/old/22764-page-images/p200.png
diff --git a/old/22764-page-images/p201.png b/old/22764-page-images/p201.png
new file mode 100644
index 0000000..12a8bf7
--- /dev/null
+++ b/old/22764-page-images/p201.png
diff --git a/old/22764-page-images/p202.png b/old/22764-page-images/p202.png
new file mode 100644
index 0000000..d848829
--- /dev/null
+++ b/old/22764-page-images/p202.png
diff --git a/old/22764-page-images/p203.png b/old/22764-page-images/p203.png
new file mode 100644
index 0000000..8720822
--- /dev/null
+++ b/old/22764-page-images/p203.png
diff --git a/old/22764-page-images/p204.png b/old/22764-page-images/p204.png
new file mode 100644
index 0000000..f38ca06
--- /dev/null
+++ b/old/22764-page-images/p204.png
diff --git a/old/22764-page-images/p205.png b/old/22764-page-images/p205.png
new file mode 100644
index 0000000..d5679e6
--- /dev/null
+++ b/old/22764-page-images/p205.png
diff --git a/old/22764-page-images/p206.png b/old/22764-page-images/p206.png
new file mode 100644
index 0000000..7f81eaf
--- /dev/null
+++ b/old/22764-page-images/p206.png
diff --git a/old/22764-page-images/p207.png b/old/22764-page-images/p207.png
new file mode 100644
index 0000000..208425c
--- /dev/null
+++ b/old/22764-page-images/p207.png
diff --git a/old/22764-page-images/p208.png b/old/22764-page-images/p208.png
new file mode 100644
index 0000000..dba2137
--- /dev/null
+++ b/old/22764-page-images/p208.png
diff --git a/old/22764-page-images/p209.png b/old/22764-page-images/p209.png
new file mode 100644
index 0000000..27be6e3
--- /dev/null
+++ b/old/22764-page-images/p209.png
diff --git a/old/22764-page-images/p210.png b/old/22764-page-images/p210.png
new file mode 100644
index 0000000..41532bf
--- /dev/null
+++ b/old/22764-page-images/p210.png
diff --git a/old/22764-page-images/p211.png b/old/22764-page-images/p211.png
new file mode 100644
index 0000000..e25a9ed
--- /dev/null
+++ b/old/22764-page-images/p211.png
diff --git a/old/22764-page-images/p212.png b/old/22764-page-images/p212.png
new file mode 100644
index 0000000..6cb741c
--- /dev/null
+++ b/old/22764-page-images/p212.png
diff --git a/old/22764-page-images/p213.png b/old/22764-page-images/p213.png
new file mode 100644
index 0000000..71b079e
--- /dev/null
+++ b/old/22764-page-images/p213.png
diff --git a/old/22764-page-images/p214.png b/old/22764-page-images/p214.png
new file mode 100644
index 0000000..8a72b29
--- /dev/null
+++ b/old/22764-page-images/p214.png
diff --git a/old/22764-page-images/p215.png b/old/22764-page-images/p215.png
new file mode 100644
index 0000000..d3581fc
--- /dev/null
+++ b/old/22764-page-images/p215.png
diff --git a/old/22764-page-images/p216.png b/old/22764-page-images/p216.png
new file mode 100644
index 0000000..2d55edf
--- /dev/null
+++ b/old/22764-page-images/p216.png
diff --git a/old/22764-page-images/p217.png b/old/22764-page-images/p217.png
new file mode 100644
index 0000000..9fa2dfa
--- /dev/null
+++ b/old/22764-page-images/p217.png
diff --git a/old/22764-page-images/p218.png b/old/22764-page-images/p218.png
new file mode 100644
index 0000000..8cc32bf
--- /dev/null
+++ b/old/22764-page-images/p218.png
diff --git a/old/22764-page-images/p219.png b/old/22764-page-images/p219.png
new file mode 100644
index 0000000..5c50b81
--- /dev/null
+++ b/old/22764-page-images/p219.png
diff --git a/old/22764-page-images/p220.png b/old/22764-page-images/p220.png
new file mode 100644
index 0000000..fa43c80
--- /dev/null
+++ b/old/22764-page-images/p220.png
diff --git a/old/22764-page-images/p221.png b/old/22764-page-images/p221.png
new file mode 100644
index 0000000..b6a6fbe
--- /dev/null
+++ b/old/22764-page-images/p221.png
diff --git a/old/22764-page-images/p222.png b/old/22764-page-images/p222.png
new file mode 100644
index 0000000..5e1ab50
--- /dev/null
+++ b/old/22764-page-images/p222.png
diff --git a/old/22764-page-images/p223.png b/old/22764-page-images/p223.png
new file mode 100644
index 0000000..b7a49c1
--- /dev/null
+++ b/old/22764-page-images/p223.png
diff --git a/old/22764-page-images/p224.png b/old/22764-page-images/p224.png
new file mode 100644
index 0000000..a1ff519
--- /dev/null
+++ b/old/22764-page-images/p224.png
diff --git a/old/22764-page-images/p225.png b/old/22764-page-images/p225.png
new file mode 100644
index 0000000..4de1757
--- /dev/null
+++ b/old/22764-page-images/p225.png
diff --git a/old/22764-page-images/p226.png b/old/22764-page-images/p226.png
new file mode 100644
index 0000000..0ad196f
--- /dev/null
+++ b/old/22764-page-images/p226.png
diff --git a/old/22764-page-images/p227.png b/old/22764-page-images/p227.png
new file mode 100644
index 0000000..376f061
--- /dev/null
+++ b/old/22764-page-images/p227.png
diff --git a/old/22764-page-images/p228.png b/old/22764-page-images/p228.png
new file mode 100644
index 0000000..ecc4aa0
--- /dev/null
+++ b/old/22764-page-images/p228.png
diff --git a/old/22764-page-images/p229.png b/old/22764-page-images/p229.png
new file mode 100644
index 0000000..3eba8ef
--- /dev/null
+++ b/old/22764-page-images/p229.png
diff --git a/old/22764-page-images/p230.png b/old/22764-page-images/p230.png
new file mode 100644
index 0000000..d374679
--- /dev/null
+++ b/old/22764-page-images/p230.png
diff --git a/old/22764-page-images/p231.png b/old/22764-page-images/p231.png
new file mode 100644
index 0000000..6a8abb0
--- /dev/null
+++ b/old/22764-page-images/p231.png
diff --git a/old/22764-page-images/p232.png b/old/22764-page-images/p232.png
new file mode 100644
index 0000000..139a0e4
--- /dev/null
+++ b/old/22764-page-images/p232.png
diff --git a/old/22764-page-images/p233.png b/old/22764-page-images/p233.png
new file mode 100644
index 0000000..56ebc10
--- /dev/null
+++ b/old/22764-page-images/p233.png
diff --git a/old/22764-page-images/p234.png b/old/22764-page-images/p234.png
new file mode 100644
index 0000000..8287992
--- /dev/null
+++ b/old/22764-page-images/p234.png
diff --git a/old/22764-page-images/p235.png b/old/22764-page-images/p235.png
new file mode 100644
index 0000000..64421c4
--- /dev/null
+++ b/old/22764-page-images/p235.png
diff --git a/old/22764-page-images/p236.png b/old/22764-page-images/p236.png
new file mode 100644
index 0000000..c419c72
--- /dev/null
+++ b/old/22764-page-images/p236.png
diff --git a/old/22764-page-images/p237.png b/old/22764-page-images/p237.png
new file mode 100644
index 0000000..970e55a
--- /dev/null
+++ b/old/22764-page-images/p237.png
diff --git a/old/22764-page-images/p238.png b/old/22764-page-images/p238.png
new file mode 100644
index 0000000..673603f
--- /dev/null
+++ b/old/22764-page-images/p238.png
diff --git a/old/22764-page-images/p239.png b/old/22764-page-images/p239.png
new file mode 100644
index 0000000..66de652
--- /dev/null
+++ b/old/22764-page-images/p239.png
diff --git a/old/22764-page-images/p240.png b/old/22764-page-images/p240.png
new file mode 100644
index 0000000..53dda16
--- /dev/null
+++ b/old/22764-page-images/p240.png
diff --git a/old/22764-page-images/p241.png b/old/22764-page-images/p241.png
new file mode 100644
index 0000000..96a9b3a
--- /dev/null
+++ b/old/22764-page-images/p241.png
diff --git a/old/22764-page-images/p242.png b/old/22764-page-images/p242.png
new file mode 100644
index 0000000..ab321ff
--- /dev/null
+++ b/old/22764-page-images/p242.png
diff --git a/old/22764-page-images/p243.png b/old/22764-page-images/p243.png
new file mode 100644
index 0000000..cd70610
--- /dev/null
+++ b/old/22764-page-images/p243.png
diff --git a/old/22764-page-images/p244.png b/old/22764-page-images/p244.png
new file mode 100644
index 0000000..3e36b76
--- /dev/null
+++ b/old/22764-page-images/p244.png
diff --git a/old/22764-page-images/p245.png b/old/22764-page-images/p245.png
new file mode 100644
index 0000000..c6ba347
--- /dev/null
+++ b/old/22764-page-images/p245.png
diff --git a/old/22764-page-images/p246.png b/old/22764-page-images/p246.png
new file mode 100644
index 0000000..9774858
--- /dev/null
+++ b/old/22764-page-images/p246.png
diff --git a/old/22764-page-images/p247.png b/old/22764-page-images/p247.png
new file mode 100644
index 0000000..21716b2
--- /dev/null
+++ b/old/22764-page-images/p247.png
diff --git a/old/22764-page-images/p248.png b/old/22764-page-images/p248.png
new file mode 100644
index 0000000..32662ce
--- /dev/null
+++ b/old/22764-page-images/p248.png
diff --git a/old/22764-page-images/p249.png b/old/22764-page-images/p249.png
new file mode 100644
index 0000000..5e07f84
--- /dev/null
+++ b/old/22764-page-images/p249.png
diff --git a/old/22764-page-images/p250.png b/old/22764-page-images/p250.png
new file mode 100644
index 0000000..1d1feed
--- /dev/null
+++ b/old/22764-page-images/p250.png
diff --git a/old/22764-page-images/p251.png b/old/22764-page-images/p251.png
new file mode 100644
index 0000000..1f5625a
--- /dev/null
+++ b/old/22764-page-images/p251.png
diff --git a/old/22764-page-images/p252.png b/old/22764-page-images/p252.png
new file mode 100644
index 0000000..a549a76
--- /dev/null
+++ b/old/22764-page-images/p252.png
diff --git a/old/22764-page-images/p253.png b/old/22764-page-images/p253.png
new file mode 100644
index 0000000..d01355d
--- /dev/null
+++ b/old/22764-page-images/p253.png
diff --git a/old/22764-page-images/p254.png b/old/22764-page-images/p254.png
new file mode 100644
index 0000000..55a0392
--- /dev/null
+++ b/old/22764-page-images/p254.png
diff --git a/old/22764-page-images/p255.png b/old/22764-page-images/p255.png
new file mode 100644
index 0000000..ee43f25
--- /dev/null
+++ b/old/22764-page-images/p255.png
diff --git a/old/22764-page-images/p256.png b/old/22764-page-images/p256.png
new file mode 100644
index 0000000..a1c8778
--- /dev/null
+++ b/old/22764-page-images/p256.png
diff --git a/old/22764-page-images/p257.png b/old/22764-page-images/p257.png
new file mode 100644
index 0000000..8ce333e
--- /dev/null
+++ b/old/22764-page-images/p257.png
diff --git a/old/22764-page-images/p258.png b/old/22764-page-images/p258.png
new file mode 100644
index 0000000..7dc2162
--- /dev/null
+++ b/old/22764-page-images/p258.png
diff --git a/old/22764-page-images/p259.png b/old/22764-page-images/p259.png
new file mode 100644
index 0000000..de26ff3
--- /dev/null
+++ b/old/22764-page-images/p259.png
diff --git a/old/22764-page-images/p260.png b/old/22764-page-images/p260.png
new file mode 100644
index 0000000..e5bab41
--- /dev/null
+++ b/old/22764-page-images/p260.png
diff --git a/old/22764-page-images/p261.png b/old/22764-page-images/p261.png
new file mode 100644
index 0000000..f3a32a5
--- /dev/null
+++ b/old/22764-page-images/p261.png
diff --git a/old/22764-page-images/p262.png b/old/22764-page-images/p262.png
new file mode 100644
index 0000000..e76317c
--- /dev/null
+++ b/old/22764-page-images/p262.png
diff --git a/old/22764-page-images/p263.png b/old/22764-page-images/p263.png
new file mode 100644
index 0000000..a9f81e9
--- /dev/null
+++ b/old/22764-page-images/p263.png
diff --git a/old/22764-page-images/p264.png b/old/22764-page-images/p264.png
new file mode 100644
index 0000000..9327e72
--- /dev/null
+++ b/old/22764-page-images/p264.png
diff --git a/old/22764-page-images/p265.png b/old/22764-page-images/p265.png
new file mode 100644
index 0000000..aaee3d6
--- /dev/null
+++ b/old/22764-page-images/p265.png
diff --git a/old/22764-page-images/p266.png b/old/22764-page-images/p266.png
new file mode 100644
index 0000000..66094ad
--- /dev/null
+++ b/old/22764-page-images/p266.png
diff --git a/old/22764-page-images/p267.png b/old/22764-page-images/p267.png
new file mode 100644
index 0000000..ee4c13a
--- /dev/null
+++ b/old/22764-page-images/p267.png
diff --git a/old/22764-page-images/p268.png b/old/22764-page-images/p268.png
new file mode 100644
index 0000000..eb627dd
--- /dev/null
+++ b/old/22764-page-images/p268.png
diff --git a/old/22764-page-images/p269.png b/old/22764-page-images/p269.png
new file mode 100644
index 0000000..636cc65
--- /dev/null
+++ b/old/22764-page-images/p269.png
diff --git a/old/22764-page-images/p270.png b/old/22764-page-images/p270.png
new file mode 100644
index 0000000..f40063a
--- /dev/null
+++ b/old/22764-page-images/p270.png
diff --git a/old/22764-page-images/p271.png b/old/22764-page-images/p271.png
new file mode 100644
index 0000000..6ae6d66
--- /dev/null
+++ b/old/22764-page-images/p271.png
diff --git a/old/22764-page-images/p272.png b/old/22764-page-images/p272.png
new file mode 100644
index 0000000..e420752
--- /dev/null
+++ b/old/22764-page-images/p272.png
diff --git a/old/22764-page-images/p273.png b/old/22764-page-images/p273.png
new file mode 100644
index 0000000..ba52988
--- /dev/null
+++ b/old/22764-page-images/p273.png
diff --git a/old/22764-page-images/p274.png b/old/22764-page-images/p274.png
new file mode 100644
index 0000000..902e0dd
--- /dev/null
+++ b/old/22764-page-images/p274.png
diff --git a/old/22764-page-images/p275.png b/old/22764-page-images/p275.png
new file mode 100644
index 0000000..97a6d52
--- /dev/null
+++ b/old/22764-page-images/p275.png
diff --git a/old/22764-page-images/p276.png b/old/22764-page-images/p276.png
new file mode 100644
index 0000000..0c472e7
--- /dev/null
+++ b/old/22764-page-images/p276.png
diff --git a/old/22764-page-images/p277.png b/old/22764-page-images/p277.png
new file mode 100644
index 0000000..3dc4630
--- /dev/null
+++ b/old/22764-page-images/p277.png
diff --git a/old/22764-page-images/p278.png b/old/22764-page-images/p278.png
new file mode 100644
index 0000000..4ff0a99
--- /dev/null
+++ b/old/22764-page-images/p278.png
diff --git a/old/22764-page-images/p279.png b/old/22764-page-images/p279.png
new file mode 100644
index 0000000..8e94718
--- /dev/null
+++ b/old/22764-page-images/p279.png
diff --git a/old/22764-page-images/p280.png b/old/22764-page-images/p280.png
new file mode 100644
index 0000000..9f70fd1
--- /dev/null
+++ b/old/22764-page-images/p280.png
diff --git a/old/22764-page-images/p281.png b/old/22764-page-images/p281.png
new file mode 100644
index 0000000..435e068
--- /dev/null
+++ b/old/22764-page-images/p281.png
diff --git a/old/22764-page-images/p282.png b/old/22764-page-images/p282.png
new file mode 100644
index 0000000..77e3230
--- /dev/null
+++ b/old/22764-page-images/p282.png
diff --git a/old/22764-page-images/p283.png b/old/22764-page-images/p283.png
new file mode 100644
index 0000000..66d80c7
--- /dev/null
+++ b/old/22764-page-images/p283.png
diff --git a/old/22764-page-images/p284.png b/old/22764-page-images/p284.png
new file mode 100644
index 0000000..36058ae
--- /dev/null
+++ b/old/22764-page-images/p284.png
diff --git a/old/22764-page-images/p285.png b/old/22764-page-images/p285.png
new file mode 100644
index 0000000..c2ef202
--- /dev/null
+++ b/old/22764-page-images/p285.png
diff --git a/old/22764-page-images/p286.png b/old/22764-page-images/p286.png
new file mode 100644
index 0000000..c07c0cb
--- /dev/null
+++ b/old/22764-page-images/p286.png
diff --git a/old/22764-page-images/p287.png b/old/22764-page-images/p287.png
new file mode 100644
index 0000000..910350d
--- /dev/null
+++ b/old/22764-page-images/p287.png
diff --git a/old/22764-page-images/p288.png b/old/22764-page-images/p288.png
new file mode 100644
index 0000000..f7c31f5
--- /dev/null
+++ b/old/22764-page-images/p288.png
diff --git a/old/22764-page-images/p289.png b/old/22764-page-images/p289.png
new file mode 100644
index 0000000..a208475
--- /dev/null
+++ b/old/22764-page-images/p289.png
diff --git a/old/22764-page-images/p290.png b/old/22764-page-images/p290.png
new file mode 100644
index 0000000..0f130e4
--- /dev/null
+++ b/old/22764-page-images/p290.png
diff --git a/old/22764-page-images/p291.png b/old/22764-page-images/p291.png
new file mode 100644
index 0000000..8cc348c
--- /dev/null
+++ b/old/22764-page-images/p291.png
diff --git a/old/22764-page-images/p292.png b/old/22764-page-images/p292.png
new file mode 100644
index 0000000..fcf68c8
--- /dev/null
+++ b/old/22764-page-images/p292.png
diff --git a/old/22764-page-images/p293.png b/old/22764-page-images/p293.png
new file mode 100644
index 0000000..f694186
--- /dev/null
+++ b/old/22764-page-images/p293.png
diff --git a/old/22764-page-images/p294.png b/old/22764-page-images/p294.png
new file mode 100644
index 0000000..4933ac7
--- /dev/null
+++ b/old/22764-page-images/p294.png
diff --git a/old/22764-page-images/p295.png b/old/22764-page-images/p295.png
new file mode 100644
index 0000000..db5f62b
--- /dev/null
+++ b/old/22764-page-images/p295.png
diff --git a/old/22764-page-images/p296.png b/old/22764-page-images/p296.png
new file mode 100644
index 0000000..5f0fb32
--- /dev/null
+++ b/old/22764-page-images/p296.png
diff --git a/old/22764-page-images/p297.png b/old/22764-page-images/p297.png
new file mode 100644
index 0000000..ffcf215
--- /dev/null
+++ b/old/22764-page-images/p297.png
diff --git a/old/22764-page-images/p298.png b/old/22764-page-images/p298.png
new file mode 100644
index 0000000..9cb703a
--- /dev/null
+++ b/old/22764-page-images/p298.png
diff --git a/old/22764-page-images/p299.png b/old/22764-page-images/p299.png
new file mode 100644
index 0000000..3ff6120
--- /dev/null
+++ b/old/22764-page-images/p299.png
diff --git a/old/22764-page-images/p300.png b/old/22764-page-images/p300.png
new file mode 100644
index 0000000..a512615
--- /dev/null
+++ b/old/22764-page-images/p300.png
diff --git a/old/22764-page-images/p301.png b/old/22764-page-images/p301.png
new file mode 100644
index 0000000..7ffda5f
--- /dev/null
+++ b/old/22764-page-images/p301.png
diff --git a/old/22764-page-images/p302.png b/old/22764-page-images/p302.png
new file mode 100644
index 0000000..27b5bc6
--- /dev/null
+++ b/old/22764-page-images/p302.png
diff --git a/old/22764-page-images/p303.png b/old/22764-page-images/p303.png
new file mode 100644
index 0000000..f479f41
--- /dev/null
+++ b/old/22764-page-images/p303.png
diff --git a/old/22764-page-images/p304.png b/old/22764-page-images/p304.png
new file mode 100644
index 0000000..af13f32
--- /dev/null
+++ b/old/22764-page-images/p304.png
diff --git a/old/22764-page-images/p305.png b/old/22764-page-images/p305.png
new file mode 100644
index 0000000..ec4d0cd
--- /dev/null
+++ b/old/22764-page-images/p305.png
diff --git a/old/22764-page-images/p306.png b/old/22764-page-images/p306.png
new file mode 100644
index 0000000..d7a72f8
--- /dev/null
+++ b/old/22764-page-images/p306.png
diff --git a/old/22764-page-images/p307.png b/old/22764-page-images/p307.png
new file mode 100644
index 0000000..01726d7
--- /dev/null
+++ b/old/22764-page-images/p307.png
diff --git a/old/22764-page-images/p308.png b/old/22764-page-images/p308.png
new file mode 100644
index 0000000..74b779f
--- /dev/null
+++ b/old/22764-page-images/p308.png
diff --git a/old/22764-page-images/p309.png b/old/22764-page-images/p309.png
new file mode 100644
index 0000000..1eedf75
--- /dev/null
+++ b/old/22764-page-images/p309.png
diff --git a/old/22764-page-images/p310.png b/old/22764-page-images/p310.png
new file mode 100644
index 0000000..bc1da5d
--- /dev/null
+++ b/old/22764-page-images/p310.png
diff --git a/old/22764-page-images/p311.png b/old/22764-page-images/p311.png
new file mode 100644
index 0000000..c93a5b7
--- /dev/null
+++ b/old/22764-page-images/p311.png
diff --git a/old/22764-page-images/p312.png b/old/22764-page-images/p312.png
new file mode 100644
index 0000000..a4fd34f
--- /dev/null
+++ b/old/22764-page-images/p312.png
diff --git a/old/22764-page-images/p313.png b/old/22764-page-images/p313.png
new file mode 100644
index 0000000..0964037
--- /dev/null
+++ b/old/22764-page-images/p313.png
diff --git a/old/22764-page-images/p314.png b/old/22764-page-images/p314.png
new file mode 100644
index 0000000..2552f10
--- /dev/null
+++ b/old/22764-page-images/p314.png
diff --git a/old/22764-page-images/p315.png b/old/22764-page-images/p315.png
new file mode 100644
index 0000000..e131615
--- /dev/null
+++ b/old/22764-page-images/p315.png
diff --git a/old/22764-page-images/p316.png b/old/22764-page-images/p316.png
new file mode 100644
index 0000000..dd9e556
--- /dev/null
+++ b/old/22764-page-images/p316.png
diff --git a/old/22764-page-images/p317.png b/old/22764-page-images/p317.png
new file mode 100644
index 0000000..bcd6f47
--- /dev/null
+++ b/old/22764-page-images/p317.png
diff --git a/old/22764-page-images/p318.png b/old/22764-page-images/p318.png
new file mode 100644
index 0000000..1c26a82
--- /dev/null
+++ b/old/22764-page-images/p318.png
diff --git a/old/22764-page-images/p319.png b/old/22764-page-images/p319.png
new file mode 100644
index 0000000..25aacb2
--- /dev/null
+++ b/old/22764-page-images/p319.png
diff --git a/old/22764-page-images/p320.png b/old/22764-page-images/p320.png
new file mode 100644
index 0000000..9955208
--- /dev/null
+++ b/old/22764-page-images/p320.png
diff --git a/old/22764-page-images/p321.png b/old/22764-page-images/p321.png
new file mode 100644
index 0000000..fd46b52
--- /dev/null
+++ b/old/22764-page-images/p321.png
diff --git a/old/22764-page-images/p322.png b/old/22764-page-images/p322.png
new file mode 100644
index 0000000..8e61fb8
--- /dev/null
+++ b/old/22764-page-images/p322.png
diff --git a/old/22764-page-images/p323.png b/old/22764-page-images/p323.png
new file mode 100644
index 0000000..a01b1a1
--- /dev/null
+++ b/old/22764-page-images/p323.png
diff --git a/old/22764-page-images/p324.png b/old/22764-page-images/p324.png
new file mode 100644
index 0000000..7bf51b0
--- /dev/null
+++ b/old/22764-page-images/p324.png
diff --git a/old/22764-page-images/p325.png b/old/22764-page-images/p325.png
new file mode 100644
index 0000000..2ace20f
--- /dev/null
+++ b/old/22764-page-images/p325.png
diff --git a/old/22764-page-images/p326.png b/old/22764-page-images/p326.png
new file mode 100644
index 0000000..c3ca278
--- /dev/null
+++ b/old/22764-page-images/p326.png
diff --git a/old/22764-page-images/p327.png b/old/22764-page-images/p327.png
new file mode 100644
index 0000000..3a23dff
--- /dev/null
+++ b/old/22764-page-images/p327.png
diff --git a/old/22764-page-images/p328.png b/old/22764-page-images/p328.png
new file mode 100644
index 0000000..fb9d3f1
--- /dev/null
+++ b/old/22764-page-images/p328.png
diff --git a/old/22764-page-images/p329.png b/old/22764-page-images/p329.png
new file mode 100644
index 0000000..6097c4b
--- /dev/null
+++ b/old/22764-page-images/p329.png
diff --git a/old/22764-page-images/p330.png b/old/22764-page-images/p330.png
new file mode 100644
index 0000000..3fed108
--- /dev/null
+++ b/old/22764-page-images/p330.png
diff --git a/old/22764-page-images/p331.png b/old/22764-page-images/p331.png
new file mode 100644
index 0000000..9f91a87
--- /dev/null
+++ b/old/22764-page-images/p331.png
diff --git a/old/22764-page-images/p332.png b/old/22764-page-images/p332.png
new file mode 100644
index 0000000..7b8c2dc
--- /dev/null
+++ b/old/22764-page-images/p332.png
diff --git a/old/22764-page-images/p333.png b/old/22764-page-images/p333.png
new file mode 100644
index 0000000..d6fd390
--- /dev/null
+++ b/old/22764-page-images/p333.png
diff --git a/old/22764-page-images/p334.png b/old/22764-page-images/p334.png
new file mode 100644
index 0000000..d5668bc
--- /dev/null
+++ b/old/22764-page-images/p334.png
diff --git a/old/22764-page-images/p335.png b/old/22764-page-images/p335.png
new file mode 100644
index 0000000..9a01de4
--- /dev/null
+++ b/old/22764-page-images/p335.png
diff --git a/old/22764-page-images/p336.png b/old/22764-page-images/p336.png
new file mode 100644
index 0000000..5c797af
--- /dev/null
+++ b/old/22764-page-images/p336.png
diff --git a/old/22764-page-images/p337.png b/old/22764-page-images/p337.png
new file mode 100644
index 0000000..e08630c
--- /dev/null
+++ b/old/22764-page-images/p337.png
diff --git a/old/22764-page-images/p338.png b/old/22764-page-images/p338.png
new file mode 100644
index 0000000..e6e6cb9
--- /dev/null
+++ b/old/22764-page-images/p338.png
diff --git a/old/22764-page-images/p339.png b/old/22764-page-images/p339.png
new file mode 100644
index 0000000..957f578
--- /dev/null
+++ b/old/22764-page-images/p339.png
diff --git a/old/22764-page-images/p340.png b/old/22764-page-images/p340.png
new file mode 100644
index 0000000..7319b0f
--- /dev/null
+++ b/old/22764-page-images/p340.png
diff --git a/old/22764-page-images/p341.png b/old/22764-page-images/p341.png
new file mode 100644
index 0000000..501979c
--- /dev/null
+++ b/old/22764-page-images/p341.png
diff --git a/old/22764-page-images/p342.png b/old/22764-page-images/p342.png
new file mode 100644
index 0000000..60de1aa
--- /dev/null
+++ b/old/22764-page-images/p342.png
diff --git a/old/22764-page-images/p343.png b/old/22764-page-images/p343.png
new file mode 100644
index 0000000..d9be741
--- /dev/null
+++ b/old/22764-page-images/p343.png
diff --git a/old/22764-page-images/p344.png b/old/22764-page-images/p344.png
new file mode 100644
index 0000000..92a69a7
--- /dev/null
+++ b/old/22764-page-images/p344.png
diff --git a/old/22764-page-images/p345.png b/old/22764-page-images/p345.png
new file mode 100644
index 0000000..23e84a4
--- /dev/null
+++ b/old/22764-page-images/p345.png
diff --git a/old/22764-page-images/p346.png b/old/22764-page-images/p346.png
new file mode 100644
index 0000000..042981a
--- /dev/null
+++ b/old/22764-page-images/p346.png
diff --git a/old/22764-page-images/p347.png b/old/22764-page-images/p347.png
new file mode 100644
index 0000000..f06e05f
--- /dev/null
+++ b/old/22764-page-images/p347.png
diff --git a/old/22764-page-images/p348.png b/old/22764-page-images/p348.png
new file mode 100644
index 0000000..1429927
--- /dev/null
+++ b/old/22764-page-images/p348.png
diff --git a/old/22764-page-images/p349.png b/old/22764-page-images/p349.png
new file mode 100644
index 0000000..8eeba3e
--- /dev/null
+++ b/old/22764-page-images/p349.png
diff --git a/old/22764-page-images/p350.png b/old/22764-page-images/p350.png
new file mode 100644
index 0000000..3dbf2d7
--- /dev/null
+++ b/old/22764-page-images/p350.png
diff --git a/old/22764-page-images/p351.png b/old/22764-page-images/p351.png
new file mode 100644
index 0000000..bec316a
--- /dev/null
+++ b/old/22764-page-images/p351.png
diff --git a/old/22764-page-images/p352.png b/old/22764-page-images/p352.png
new file mode 100644
index 0000000..6f07683
--- /dev/null
+++ b/old/22764-page-images/p352.png
diff --git a/old/22764-page-images/p353.png b/old/22764-page-images/p353.png
new file mode 100644
index 0000000..91b037d
--- /dev/null
+++ b/old/22764-page-images/p353.png
diff --git a/old/22764-page-images/p354.png b/old/22764-page-images/p354.png
new file mode 100644
index 0000000..c29a025
--- /dev/null
+++ b/old/22764-page-images/p354.png
diff --git a/old/22764-page-images/p355.png b/old/22764-page-images/p355.png
new file mode 100644
index 0000000..a5422a3
--- /dev/null
+++ b/old/22764-page-images/p355.png
diff --git a/old/22764-page-images/p356.png b/old/22764-page-images/p356.png
new file mode 100644
index 0000000..372485e
--- /dev/null
+++ b/old/22764-page-images/p356.png
diff --git a/old/22764-page-images/p357.png b/old/22764-page-images/p357.png
new file mode 100644
index 0000000..cb5ae8c
--- /dev/null
+++ b/old/22764-page-images/p357.png
diff --git a/old/22764-page-images/p358.png b/old/22764-page-images/p358.png
new file mode 100644
index 0000000..bfbf0f8
--- /dev/null
+++ b/old/22764-page-images/p358.png
diff --git a/old/22764-page-images/p359.png b/old/22764-page-images/p359.png
new file mode 100644
index 0000000..8b0edee
--- /dev/null
+++ b/old/22764-page-images/p359.png
diff --git a/old/22764-page-images/p360.png b/old/22764-page-images/p360.png
new file mode 100644
index 0000000..9af760a
--- /dev/null
+++ b/old/22764-page-images/p360.png
diff --git a/old/22764-page-images/p361.png b/old/22764-page-images/p361.png
new file mode 100644
index 0000000..15db3e6
--- /dev/null
+++ b/old/22764-page-images/p361.png
diff --git a/old/22764-page-images/p362.png b/old/22764-page-images/p362.png
new file mode 100644
index 0000000..f72da9f
--- /dev/null
+++ b/old/22764-page-images/p362.png
diff --git a/old/22764-page-images/p363.png b/old/22764-page-images/p363.png
new file mode 100644
index 0000000..fade5a4
--- /dev/null
+++ b/old/22764-page-images/p363.png
diff --git a/old/22764-page-images/p364.png b/old/22764-page-images/p364.png
new file mode 100644
index 0000000..aca850b
--- /dev/null
+++ b/old/22764-page-images/p364.png
diff --git a/old/22764-page-images/p365.png b/old/22764-page-images/p365.png
new file mode 100644
index 0000000..3f421dd
--- /dev/null
+++ b/old/22764-page-images/p365.png
diff --git a/old/22764-page-images/p366.png b/old/22764-page-images/p366.png
new file mode 100644
index 0000000..744e419
--- /dev/null
+++ b/old/22764-page-images/p366.png
diff --git a/old/22764-page-images/p367.png b/old/22764-page-images/p367.png
new file mode 100644
index 0000000..cf39d07
--- /dev/null
+++ b/old/22764-page-images/p367.png
diff --git a/old/22764-page-images/p368.png b/old/22764-page-images/p368.png
new file mode 100644
index 0000000..64fd9a5
--- /dev/null
+++ b/old/22764-page-images/p368.png
diff --git a/old/22764-page-images/p369.png b/old/22764-page-images/p369.png
new file mode 100644
index 0000000..068216f
--- /dev/null
+++ b/old/22764-page-images/p369.png
diff --git a/old/22764-page-images/p370.png b/old/22764-page-images/p370.png
new file mode 100644
index 0000000..f8c9244
--- /dev/null
+++ b/old/22764-page-images/p370.png
diff --git a/old/22764-page-images/p371.png b/old/22764-page-images/p371.png
new file mode 100644
index 0000000..c93b36d
--- /dev/null
+++ b/old/22764-page-images/p371.png
diff --git a/old/22764-page-images/p372.png b/old/22764-page-images/p372.png
new file mode 100644
index 0000000..5ecf515
--- /dev/null
+++ b/old/22764-page-images/p372.png
diff --git a/old/22764-page-images/p373.png b/old/22764-page-images/p373.png
new file mode 100644
index 0000000..ae0fef5
--- /dev/null
+++ b/old/22764-page-images/p373.png
diff --git a/old/22764-page-images/p374.png b/old/22764-page-images/p374.png
new file mode 100644
index 0000000..726f92a
--- /dev/null
+++ b/old/22764-page-images/p374.png
diff --git a/old/22764-page-images/p375.png b/old/22764-page-images/p375.png
new file mode 100644
index 0000000..f000258
--- /dev/null
+++ b/old/22764-page-images/p375.png
diff --git a/old/22764-page-images/p376.png b/old/22764-page-images/p376.png
new file mode 100644
index 0000000..a5534a6
--- /dev/null
+++ b/old/22764-page-images/p376.png
diff --git a/old/22764-page-images/p377.png b/old/22764-page-images/p377.png
new file mode 100644
index 0000000..fc09553
--- /dev/null
+++ b/old/22764-page-images/p377.png
diff --git a/old/22764-page-images/p378.png b/old/22764-page-images/p378.png
new file mode 100644
index 0000000..97854dd
--- /dev/null
+++ b/old/22764-page-images/p378.png
diff --git a/old/22764-page-images/p379.png b/old/22764-page-images/p379.png
new file mode 100644
index 0000000..25c54d5
--- /dev/null
+++ b/old/22764-page-images/p379.png
diff --git a/old/22764-page-images/p380.png b/old/22764-page-images/p380.png
new file mode 100644
index 0000000..34aa9dd
--- /dev/null
+++ b/old/22764-page-images/p380.png
diff --git a/old/22764-page-images/p381.png b/old/22764-page-images/p381.png
new file mode 100644
index 0000000..db39160
--- /dev/null
+++ b/old/22764-page-images/p381.png
diff --git a/old/22764-page-images/p382.png b/old/22764-page-images/p382.png
new file mode 100644
index 0000000..5176b8b
--- /dev/null
+++ b/old/22764-page-images/p382.png
diff --git a/old/22764-page-images/p383.png b/old/22764-page-images/p383.png
new file mode 100644
index 0000000..0d914e1
--- /dev/null
+++ b/old/22764-page-images/p383.png
diff --git a/old/22764-page-images/p384.png b/old/22764-page-images/p384.png
new file mode 100644
index 0000000..5272dba
--- /dev/null
+++ b/old/22764-page-images/p384.png
diff --git a/old/22764-page-images/p385.png b/old/22764-page-images/p385.png
new file mode 100644
index 0000000..042b639
--- /dev/null
+++ b/old/22764-page-images/p385.png
diff --git a/old/22764-page-images/p386.png b/old/22764-page-images/p386.png
new file mode 100644
index 0000000..be15c65
--- /dev/null
+++ b/old/22764-page-images/p386.png
diff --git a/old/22764-page-images/p387.png b/old/22764-page-images/p387.png
new file mode 100644
index 0000000..eb039f2
--- /dev/null
+++ b/old/22764-page-images/p387.png
diff --git a/old/22764-page-images/p388.png b/old/22764-page-images/p388.png
new file mode 100644
index 0000000..54c2299
--- /dev/null
+++ b/old/22764-page-images/p388.png
diff --git a/old/22764-page-images/p389.png b/old/22764-page-images/p389.png
new file mode 100644
index 0000000..4e46e22
--- /dev/null
+++ b/old/22764-page-images/p389.png
diff --git a/old/22764-page-images/p390.png b/old/22764-page-images/p390.png
new file mode 100644
index 0000000..3b09000
--- /dev/null
+++ b/old/22764-page-images/p390.png
diff --git a/old/22764-page-images/p391.png b/old/22764-page-images/p391.png
new file mode 100644
index 0000000..9fecdfa
--- /dev/null
+++ b/old/22764-page-images/p391.png
diff --git a/old/22764-page-images/p392.png b/old/22764-page-images/p392.png
new file mode 100644
index 0000000..b0b3660
--- /dev/null
+++ b/old/22764-page-images/p392.png
diff --git a/old/22764-page-images/p393.png b/old/22764-page-images/p393.png
new file mode 100644
index 0000000..804671d
--- /dev/null
+++ b/old/22764-page-images/p393.png
diff --git a/old/22764-page-images/p394.png b/old/22764-page-images/p394.png
new file mode 100644
index 0000000..a17fe0f
--- /dev/null
+++ b/old/22764-page-images/p394.png
diff --git a/old/22764-page-images/p395.png b/old/22764-page-images/p395.png
new file mode 100644
index 0000000..aaf7aba
--- /dev/null
+++ b/old/22764-page-images/p395.png
diff --git a/old/22764-page-images/p396.png b/old/22764-page-images/p396.png
new file mode 100644
index 0000000..02ef09d
--- /dev/null
+++ b/old/22764-page-images/p396.png
diff --git a/old/22764-page-images/p397.png b/old/22764-page-images/p397.png
new file mode 100644
index 0000000..ff0c630
--- /dev/null
+++ b/old/22764-page-images/p397.png
diff --git a/old/22764-page-images/p398.png b/old/22764-page-images/p398.png
new file mode 100644
index 0000000..09c9056
--- /dev/null
+++ b/old/22764-page-images/p398.png
diff --git a/old/22764-page-images/p399.png b/old/22764-page-images/p399.png
new file mode 100644
index 0000000..ab7511c
--- /dev/null
+++ b/old/22764-page-images/p399.png
diff --git a/old/22764-page-images/p400.png b/old/22764-page-images/p400.png
new file mode 100644
index 0000000..c7f69e4
--- /dev/null
+++ b/old/22764-page-images/p400.png
diff --git a/old/22764-page-images/p401.png b/old/22764-page-images/p401.png
new file mode 100644
index 0000000..8f127c6
--- /dev/null
+++ b/old/22764-page-images/p401.png
diff --git a/old/22764-page-images/p402.png b/old/22764-page-images/p402.png
new file mode 100644
index 0000000..b0a4d27
--- /dev/null
+++ b/old/22764-page-images/p402.png
diff --git a/old/22764-page-images/p403.png b/old/22764-page-images/p403.png
new file mode 100644
index 0000000..bfdffa7
--- /dev/null
+++ b/old/22764-page-images/p403.png
diff --git a/old/22764-page-images/p404.png b/old/22764-page-images/p404.png
new file mode 100644
index 0000000..5bf2a77
--- /dev/null
+++ b/old/22764-page-images/p404.png
diff --git a/old/22764-page-images/p405.png b/old/22764-page-images/p405.png
new file mode 100644
index 0000000..733b5a0
--- /dev/null
+++ b/old/22764-page-images/p405.png
diff --git a/old/22764-page-images/p406.png b/old/22764-page-images/p406.png
new file mode 100644
index 0000000..147226f
--- /dev/null
+++ b/old/22764-page-images/p406.png
diff --git a/old/22764-page-images/p407.png b/old/22764-page-images/p407.png
new file mode 100644
index 0000000..4488ad9
--- /dev/null
+++ b/old/22764-page-images/p407.png
diff --git a/old/22764-page-images/p408.png b/old/22764-page-images/p408.png
new file mode 100644
index 0000000..6ad3438
--- /dev/null
+++ b/old/22764-page-images/p408.png
diff --git a/old/22764-page-images/p409.png b/old/22764-page-images/p409.png
new file mode 100644
index 0000000..9456345
--- /dev/null
+++ b/old/22764-page-images/p409.png
diff --git a/old/22764-page-images/p410.png b/old/22764-page-images/p410.png
new file mode 100644
index 0000000..cd7c8a5
--- /dev/null
+++ b/old/22764-page-images/p410.png
diff --git a/old/22764-page-images/p411.png b/old/22764-page-images/p411.png
new file mode 100644
index 0000000..366d84d
--- /dev/null
+++ b/old/22764-page-images/p411.png
diff --git a/old/22764-page-images/p412.png b/old/22764-page-images/p412.png
new file mode 100644
index 0000000..8e5c4e2
--- /dev/null
+++ b/old/22764-page-images/p412.png
diff --git a/old/22764-page-images/p413.png b/old/22764-page-images/p413.png
new file mode 100644
index 0000000..fc5f68b
--- /dev/null
+++ b/old/22764-page-images/p413.png
diff --git a/old/22764-page-images/p414.png b/old/22764-page-images/p414.png
new file mode 100644
index 0000000..c9c013a
--- /dev/null
+++ b/old/22764-page-images/p414.png
diff --git a/old/22764-page-images/p415.png b/old/22764-page-images/p415.png
new file mode 100644
index 0000000..ed9b919
--- /dev/null
+++ b/old/22764-page-images/p415.png
diff --git a/old/22764-page-images/p416.png b/old/22764-page-images/p416.png
new file mode 100644
index 0000000..096cc26
--- /dev/null
+++ b/old/22764-page-images/p416.png
diff --git a/old/22764-page-images/p417.png b/old/22764-page-images/p417.png
new file mode 100644
index 0000000..a8c4ee8
--- /dev/null
+++ b/old/22764-page-images/p417.png
diff --git a/old/22764-page-images/p418.png b/old/22764-page-images/p418.png
new file mode 100644
index 0000000..2fa4002
--- /dev/null
+++ b/old/22764-page-images/p418.png
diff --git a/old/22764-page-images/p419.png b/old/22764-page-images/p419.png
new file mode 100644
index 0000000..18f463e
--- /dev/null
+++ b/old/22764-page-images/p419.png
diff --git a/old/22764-page-images/p420.png b/old/22764-page-images/p420.png
new file mode 100644
index 0000000..3d0e4c4
--- /dev/null
+++ b/old/22764-page-images/p420.png
diff --git a/old/22764-page-images/p421.png b/old/22764-page-images/p421.png
new file mode 100644
index 0000000..cc53ef9
--- /dev/null
+++ b/old/22764-page-images/p421.png
diff --git a/old/22764-page-images/p422.png b/old/22764-page-images/p422.png
new file mode 100644
index 0000000..bd70fa4
--- /dev/null
+++ b/old/22764-page-images/p422.png
diff --git a/old/22764-page-images/p423.png b/old/22764-page-images/p423.png
new file mode 100644
index 0000000..68feaaa
--- /dev/null
+++ b/old/22764-page-images/p423.png
diff --git a/old/22764-page-images/p424.png b/old/22764-page-images/p424.png
new file mode 100644
index 0000000..44b47ba
--- /dev/null
+++ b/old/22764-page-images/p424.png
diff --git a/old/22764-page-images/p425.png b/old/22764-page-images/p425.png
new file mode 100644
index 0000000..2b53334
--- /dev/null
+++ b/old/22764-page-images/p425.png
diff --git a/old/22764-page-images/p426.png b/old/22764-page-images/p426.png
new file mode 100644
index 0000000..6813550
--- /dev/null
+++ b/old/22764-page-images/p426.png
diff --git a/old/22764-page-images/p427.png b/old/22764-page-images/p427.png
new file mode 100644
index 0000000..8c76040
--- /dev/null
+++ b/old/22764-page-images/p427.png
diff --git a/old/22764-page-images/p428.png b/old/22764-page-images/p428.png
new file mode 100644
index 0000000..9803800
--- /dev/null
+++ b/old/22764-page-images/p428.png
diff --git a/old/22764-page-images/p429.png b/old/22764-page-images/p429.png
new file mode 100644
index 0000000..6c4ba75
--- /dev/null
+++ b/old/22764-page-images/p429.png
diff --git a/old/22764-page-images/p430.png b/old/22764-page-images/p430.png
new file mode 100644
index 0000000..ab0439b
--- /dev/null
+++ b/old/22764-page-images/p430.png
diff --git a/old/22764-page-images/p431.png b/old/22764-page-images/p431.png
new file mode 100644
index 0000000..ee5c376
--- /dev/null
+++ b/old/22764-page-images/p431.png
diff --git a/old/22764-page-images/p432.png b/old/22764-page-images/p432.png
new file mode 100644
index 0000000..680dbfa
--- /dev/null
+++ b/old/22764-page-images/p432.png
diff --git a/old/22764-page-images/p433.png b/old/22764-page-images/p433.png
new file mode 100644
index 0000000..b527f2c
--- /dev/null
+++ b/old/22764-page-images/p433.png
diff --git a/old/22764-page-images/p434.png b/old/22764-page-images/p434.png
new file mode 100644
index 0000000..5d5ff05
--- /dev/null
+++ b/old/22764-page-images/p434.png
diff --git a/old/22764-page-images/p435.png b/old/22764-page-images/p435.png
new file mode 100644
index 0000000..6710558
--- /dev/null
+++ b/old/22764-page-images/p435.png
diff --git a/old/22764-page-images/p436.png b/old/22764-page-images/p436.png
new file mode 100644
index 0000000..bc652b7
--- /dev/null
+++ b/old/22764-page-images/p436.png
diff --git a/old/22764-page-images/p437.png b/old/22764-page-images/p437.png
new file mode 100644
index 0000000..3d7e5f7
--- /dev/null
+++ b/old/22764-page-images/p437.png
diff --git a/old/22764-page-images/p438.png b/old/22764-page-images/p438.png
new file mode 100644
index 0000000..b23e537
--- /dev/null
+++ b/old/22764-page-images/p438.png
diff --git a/old/22764-page-images/p439.png b/old/22764-page-images/p439.png
new file mode 100644
index 0000000..72666d3
--- /dev/null
+++ b/old/22764-page-images/p439.png
diff --git a/old/22764-page-images/p440.png b/old/22764-page-images/p440.png
new file mode 100644
index 0000000..c9a8d81
--- /dev/null
+++ b/old/22764-page-images/p440.png
diff --git a/old/22764-page-images/p441.png b/old/22764-page-images/p441.png
new file mode 100644
index 0000000..d8c7cc3
--- /dev/null
+++ b/old/22764-page-images/p441.png
diff --git a/old/22764-page-images/p442.png b/old/22764-page-images/p442.png
new file mode 100644
index 0000000..aa54f17
--- /dev/null
+++ b/old/22764-page-images/p442.png
diff --git a/old/22764-page-images/p443.png b/old/22764-page-images/p443.png
new file mode 100644
index 0000000..aded1a7
--- /dev/null
+++ b/old/22764-page-images/p443.png
diff --git a/old/22764-page-images/p444.png b/old/22764-page-images/p444.png
new file mode 100644
index 0000000..19ba2e2
--- /dev/null
+++ b/old/22764-page-images/p444.png
diff --git a/old/22764-page-images/p445.png b/old/22764-page-images/p445.png
new file mode 100644
index 0000000..07512cd
--- /dev/null
+++ b/old/22764-page-images/p445.png
diff --git a/old/22764-page-images/p446.png b/old/22764-page-images/p446.png
new file mode 100644
index 0000000..b9895f4
--- /dev/null
+++ b/old/22764-page-images/p446.png
diff --git a/old/22764-page-images/p447.png b/old/22764-page-images/p447.png
new file mode 100644
index 0000000..c94e2b5
--- /dev/null
+++ b/old/22764-page-images/p447.png
diff --git a/old/22764-page-images/p448.png b/old/22764-page-images/p448.png
new file mode 100644
index 0000000..df9a560
--- /dev/null
+++ b/old/22764-page-images/p448.png
diff --git a/old/22764-page-images/p449.png b/old/22764-page-images/p449.png
new file mode 100644
index 0000000..8704891
--- /dev/null
+++ b/old/22764-page-images/p449.png
diff --git a/old/22764-page-images/p450.png b/old/22764-page-images/p450.png
new file mode 100644
index 0000000..e7615bd
--- /dev/null
+++ b/old/22764-page-images/p450.png
diff --git a/old/22764-page-images/p451.png b/old/22764-page-images/p451.png
new file mode 100644
index 0000000..110b318
--- /dev/null
+++ b/old/22764-page-images/p451.png
diff --git a/old/22764-page-images/p452.png b/old/22764-page-images/p452.png
new file mode 100644
index 0000000..344656f
--- /dev/null
+++ b/old/22764-page-images/p452.png
diff --git a/old/22764-page-images/p453.png b/old/22764-page-images/p453.png
new file mode 100644
index 0000000..da9daf3
--- /dev/null
+++ b/old/22764-page-images/p453.png
diff --git a/old/22764-page-images/p454.png b/old/22764-page-images/p454.png
new file mode 100644
index 0000000..916e770
--- /dev/null
+++ b/old/22764-page-images/p454.png
diff --git a/old/22764-page-images/p455.png b/old/22764-page-images/p455.png
new file mode 100644
index 0000000..127b83f
--- /dev/null
+++ b/old/22764-page-images/p455.png
diff --git a/old/22764-page-images/p456.png b/old/22764-page-images/p456.png
new file mode 100644
index 0000000..36b6768
--- /dev/null
+++ b/old/22764-page-images/p456.png
diff --git a/old/22764-page-images/p457.png b/old/22764-page-images/p457.png
new file mode 100644
index 0000000..e70d1ea
--- /dev/null
+++ b/old/22764-page-images/p457.png
diff --git a/old/22764-page-images/p458.png b/old/22764-page-images/p458.png
new file mode 100644
index 0000000..1a734b8
--- /dev/null
+++ b/old/22764-page-images/p458.png
diff --git a/old/22764-page-images/p459.png b/old/22764-page-images/p459.png
new file mode 100644
index 0000000..32e8c40
--- /dev/null
+++ b/old/22764-page-images/p459.png
diff --git a/old/22764-page-images/p460.png b/old/22764-page-images/p460.png
new file mode 100644
index 0000000..83fd53a
--- /dev/null
+++ b/old/22764-page-images/p460.png
diff --git a/old/22764-page-images/p461.png b/old/22764-page-images/p461.png
new file mode 100644
index 0000000..e20acba
--- /dev/null
+++ b/old/22764-page-images/p461.png
diff --git a/old/22764-page-images/p462.png b/old/22764-page-images/p462.png
new file mode 100644
index 0000000..d8ab2de
--- /dev/null
+++ b/old/22764-page-images/p462.png
diff --git a/old/22764-page-images/p463.png b/old/22764-page-images/p463.png
new file mode 100644
index 0000000..ec04056
--- /dev/null
+++ b/old/22764-page-images/p463.png
diff --git a/old/22764-page-images/p464.png b/old/22764-page-images/p464.png
new file mode 100644
index 0000000..508ef0e
--- /dev/null
+++ b/old/22764-page-images/p464.png
diff --git a/old/22764-page-images/p465.png b/old/22764-page-images/p465.png
new file mode 100644
index 0000000..0e7ad33
--- /dev/null
+++ b/old/22764-page-images/p465.png
diff --git a/old/22764-page-images/p466.png b/old/22764-page-images/p466.png
new file mode 100644
index 0000000..f422f0f
--- /dev/null
+++ b/old/22764-page-images/p466.png
diff --git a/old/22764-page-images/p467.png b/old/22764-page-images/p467.png
new file mode 100644
index 0000000..351942d
--- /dev/null
+++ b/old/22764-page-images/p467.png
diff --git a/old/22764-page-images/p468.png b/old/22764-page-images/p468.png
new file mode 100644
index 0000000..a5629e8
--- /dev/null
+++ b/old/22764-page-images/p468.png
diff --git a/old/22764-page-images/p469.png b/old/22764-page-images/p469.png
new file mode 100644
index 0000000..bd5830a
--- /dev/null
+++ b/old/22764-page-images/p469.png
diff --git a/old/22764-page-images/p470.png b/old/22764-page-images/p470.png
new file mode 100644
index 0000000..86649b9
--- /dev/null
+++ b/old/22764-page-images/p470.png
diff --git a/old/22764-page-images/p471.png b/old/22764-page-images/p471.png
new file mode 100644
index 0000000..ed2a8e7
--- /dev/null
+++ b/old/22764-page-images/p471.png
diff --git a/old/22764-page-images/p472.png b/old/22764-page-images/p472.png
new file mode 100644
index 0000000..c042db2
--- /dev/null
+++ b/old/22764-page-images/p472.png
diff --git a/old/22764-page-images/p473.png b/old/22764-page-images/p473.png
new file mode 100644
index 0000000..a7d3705
--- /dev/null
+++ b/old/22764-page-images/p473.png
diff --git a/old/22764-page-images/p474.png b/old/22764-page-images/p474.png
new file mode 100644
index 0000000..3a0ca20
--- /dev/null
+++ b/old/22764-page-images/p474.png
diff --git a/old/22764-page-images/p475.png b/old/22764-page-images/p475.png
new file mode 100644
index 0000000..fe220af
--- /dev/null
+++ b/old/22764-page-images/p475.png
diff --git a/old/22764-page-images/p476.png b/old/22764-page-images/p476.png
new file mode 100644
index 0000000..7ade7a2
--- /dev/null
+++ b/old/22764-page-images/p476.png
diff --git a/old/22764-page-images/p477.png b/old/22764-page-images/p477.png
new file mode 100644
index 0000000..505abfd
--- /dev/null
+++ b/old/22764-page-images/p477.png
diff --git a/old/22764-page-images/p478.png b/old/22764-page-images/p478.png
new file mode 100644
index 0000000..487b7b0
--- /dev/null
+++ b/old/22764-page-images/p478.png
diff --git a/old/22764-page-images/p479.png b/old/22764-page-images/p479.png
new file mode 100644
index 0000000..0649acc
--- /dev/null
+++ b/old/22764-page-images/p479.png
diff --git a/old/22764-page-images/p480.png b/old/22764-page-images/p480.png
new file mode 100644
index 0000000..49afec7
--- /dev/null
+++ b/old/22764-page-images/p480.png
diff --git a/old/22764-page-images/p481.png b/old/22764-page-images/p481.png
new file mode 100644
index 0000000..344428a
--- /dev/null
+++ b/old/22764-page-images/p481.png
diff --git a/old/22764-page-images/p482.png b/old/22764-page-images/p482.png
new file mode 100644
index 0000000..20c41ca
--- /dev/null
+++ b/old/22764-page-images/p482.png
diff --git a/old/22764-page-images/p483.png b/old/22764-page-images/p483.png
new file mode 100644
index 0000000..8003180
--- /dev/null
+++ b/old/22764-page-images/p483.png
diff --git a/old/22764-page-images/p484.png b/old/22764-page-images/p484.png
new file mode 100644
index 0000000..3047d48
--- /dev/null
+++ b/old/22764-page-images/p484.png
diff --git a/old/22764-page-images/p485.png b/old/22764-page-images/p485.png
new file mode 100644
index 0000000..403e69b
--- /dev/null
+++ b/old/22764-page-images/p485.png
diff --git a/old/22764-page-images/p486.png b/old/22764-page-images/p486.png
new file mode 100644
index 0000000..c756f45
--- /dev/null
+++ b/old/22764-page-images/p486.png
diff --git a/old/22764-page-images/p487.png b/old/22764-page-images/p487.png
new file mode 100644
index 0000000..9427b2b
--- /dev/null
+++ b/old/22764-page-images/p487.png
diff --git a/old/22764-page-images/p488.png b/old/22764-page-images/p488.png
new file mode 100644
index 0000000..ff3acee
--- /dev/null
+++ b/old/22764-page-images/p488.png
diff --git a/old/22764-page-images/p489.png b/old/22764-page-images/p489.png
new file mode 100644
index 0000000..fdc1a03
--- /dev/null
+++ b/old/22764-page-images/p489.png
diff --git a/old/22764-page-images/p490.png b/old/22764-page-images/p490.png
new file mode 100644
index 0000000..21ab868
--- /dev/null
+++ b/old/22764-page-images/p490.png
diff --git a/old/22764-page-images/p491.png b/old/22764-page-images/p491.png
new file mode 100644
index 0000000..84b0d17
--- /dev/null
+++ b/old/22764-page-images/p491.png
diff --git a/old/22764-page-images/p492.png b/old/22764-page-images/p492.png
new file mode 100644
index 0000000..2ce4554
--- /dev/null
+++ b/old/22764-page-images/p492.png
diff --git a/old/22764-page-images/p493.png b/old/22764-page-images/p493.png
new file mode 100644
index 0000000..902c467
--- /dev/null
+++ b/old/22764-page-images/p493.png
diff --git a/old/22764-page-images/p494.png b/old/22764-page-images/p494.png
new file mode 100644
index 0000000..96aa4f4
--- /dev/null
+++ b/old/22764-page-images/p494.png
diff --git a/old/22764-page-images/p495.png b/old/22764-page-images/p495.png
new file mode 100644
index 0000000..a5a0ffd
--- /dev/null
+++ b/old/22764-page-images/p495.png
diff --git a/old/22764-page-images/p496.png b/old/22764-page-images/p496.png
new file mode 100644
index 0000000..e7b0722
--- /dev/null
+++ b/old/22764-page-images/p496.png
diff --git a/old/22764-page-images/p497.png b/old/22764-page-images/p497.png
new file mode 100644
index 0000000..cb56af1
--- /dev/null
+++ b/old/22764-page-images/p497.png
diff --git a/old/22764-page-images/p498.png b/old/22764-page-images/p498.png
new file mode 100644
index 0000000..8c1ef5a
--- /dev/null
+++ b/old/22764-page-images/p498.png
diff --git a/old/22764-page-images/p499.png b/old/22764-page-images/p499.png
new file mode 100644
index 0000000..232bb1f
--- /dev/null
+++ b/old/22764-page-images/p499.png
diff --git a/old/22764-page-images/p500.png b/old/22764-page-images/p500.png
new file mode 100644
index 0000000..fb90e45
--- /dev/null
+++ b/old/22764-page-images/p500.png
diff --git a/old/22764-page-images/p501.png b/old/22764-page-images/p501.png
new file mode 100644
index 0000000..d7e697d
--- /dev/null
+++ b/old/22764-page-images/p501.png
diff --git a/old/22764-page-images/p502.png b/old/22764-page-images/p502.png
new file mode 100644
index 0000000..ea53223
--- /dev/null
+++ b/old/22764-page-images/p502.png