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+The Project Gutenberg EBook of Darwin, and After Darwin (Vol. 1 and 3, of
+3), by George John Romanes
+
+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: Darwin, and After Darwin (Vol. 1 and 3, of 3)
+ An Exposition of the Darwinian Theory and a Discussion of
+ Post-Darwinian Questions
+
+Author: George John Romanes
+
+Release Date: March 11, 2008 [EBook #24800]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK DARWIN ***
+
+
+
+
+Produced by Marilynda Fraser-Cunliffe, LN Yaddanapudi and
+the Online Distributed Proofreading Team at
+http://www.pgdp.net
+
+
+
+
+
+[Illustration: Frontispiece-Charles Darwin]
+
+
+
+
+DARWIN, AND AFTER DARWIN
+
+_AN EXPOSITION OF THE DARWINIAN THEORY
+AND A DISCUSSION OF
+POST-DARWINIAN QUESTIONS_
+
+BY
+
+GEORGE JOHN ROMANES, M.A., LL.D., F.R.S.
+_Honorary Fellow of Gonville and Caius College, Cambridge_
+
+I
+THE DARWINIAN THEORY
+
+FOURTH EDITION
+
+Chicago
+THE OPEN COURT PUBLISHING COMPANY
+1910
+
+
+The Illustrations of this book (with the exception of the Frontispiece
+and the colored plate facing page 332) are copyrighted under the title
+"Darwinism Illustrated."
+
+THE OPEN COURT PUBLISHING CO.
+
+
+PRESS OF THE
+BLAKELY-OSWALD PRINTING CO.
+CHICAGO
+
+ [Illustration: Letter to Mr. Hegeler
+
+ Transcription:
+
+ Ch. Ch. Oxford:
+ March 15th 1892.
+
+ My dear Sir,
+
+ As we have now agreed that
+ the Open Court Publishing Company is to
+ undertake the American edition of my
+ work entitled "Darwin and after
+ Darwin," I have much pleasure
+ in transferring to you the copyright
+ thereof, with all that this
+ includes.
+
+ Thanking you very much for
+ the kindness and liberality which
+ have marked your conduct of these
+ negotiations,
+
+ I remain,
+
+ Yours very faithfully,
+
+ George J. Romanes
+
+ To
+ Edward C. Hegeler Esq.
+ La Salle, Ill. U. S.]
+
+
+
+
+PREFACE
+
+
+Several years ago Lord Rosebery founded, in the University of Edinburgh,
+a lectureship on "The Philosophy of Natural History," and I was invited
+by the Senatus to deliver the lectures. This invitation I accepted, and
+subsequently constituted the material of my lectures the foundation of
+another course, which was given in the Royal Institution, under the
+title "Before and after Darwin." Here the course extended over three
+years--namely from 1888 to 1890. The lectures for 1888 were devoted to
+the history of biology from the earliest recorded times till the
+publication of the "Origin of Species" in 1859; the lectures for 1889
+dealt with the theory of organic evolution up to the date of Mr.
+Darwin's death, in 1882; while those of the third year discussed the
+further developments of this theory from that date till the close of the
+course in 1890.
+
+It is from these two courses--which resembled each other in comprising
+between thirty and forty lectures, but differed largely in other
+respects--that the present treatise has grown. Seeing, however, that it
+has grown much beyond the bulk of the original lectures, I have thought
+it desirable to publish the whole in the form of three separate works.
+Of these the first--or that which deals with the purely historical side
+of biological science--may be allowed to stand over for an indefinite
+time. The second is the one which is now brought out and which, as its
+sub-title signifies, is devoted to the general theory of organic
+evolution as this was left by the stupendous labours of Darwin. As soon
+as the translations shall have been completed, the third portion will
+follow (probably in the Autumn season), under the sub-title,
+"Post-Darwinian Questions."
+
+As the present volume is thus intended to be merely a systematic
+exposition of what may be termed the Darwinism of Darwin, and as on this
+account it is likely to prove of more service to general readers than to
+professed naturalists, I have been everywhere careful to avoid assuming
+even the most elementary knowledge of natural science on the part of
+those to whom the exposition is addressed. The case, however, will be
+different as regards the next volume, where I shall have to deal with
+the important questions touching Heredity, Utility, Isolation, &c.,
+which have been raised since the death of Mr. Darwin, and which are now
+being debated with such salutary vehemence by the best naturalists of
+our time.
+
+My obligations to the Senatus of the University of Edinburgh, and to the
+Board of Management of the Royal Institution, have already been
+virtually expressed; but I should like to take this opportunity of also
+expressing my obligations to the students who attended the lectures in
+the University of Edinburgh. For alike in respect of their large
+numbers, their keen intelligence, and their generous sympathy, the
+members of that voluntary class yielded a degree of stimulating
+encouragement, without which the labour of preparing the original
+lectures could not have been attended with the interest and the
+satisfaction that I found in it. My thanks are also due to Mr. R. E.
+Holding for the painstaking manner in which he has assisted me in
+executing most of the original drawings with which this volume is
+illustrated; and likewise to Messrs. Macmillan and Co. for kindly
+allowing me to reprint--without special acknowledgment in every
+case--certain passages from an essay which they published for me many
+years ago, under the title "Scientific Evidences of Organic Evolution."
+Lastly, I must mention that I am indebted to the same firm for
+permission to reproduce an excellent portrait of Mr. Darwin, which
+constitutes the frontispiece.
+
+G. J. R.
+
+CHRIST CHURCH, OXFORD,
+_April 19th, 1892._
+
+
+
+
+CONTENTS
+
+
+ PAGE
+
+CHAPTER I.
+INTRODUCTORY 1
+
+CHAPTER II.
+CLASSIFICATION 23
+
+CHAPTER III.
+MORPHOLOGY 50
+
+CHAPTER IV.
+EMBRYOLOGY 98
+
+CHAPTER V.
+PALÆONTOLOGY 156
+
+CHAPTER VI.
+GEOGRAPHICAL DISTRIBUTION 204
+
+CHAPTER VII.
+THE THEORY OF NATURAL SELECTION 251
+
+CHAPTER VIII.
+EVIDENCES OF THE THEORY OF NATURAL SELECTION 285
+
+CHAPTER IX.
+CRITICISMS OF THE THEORY OF NATURAL SELECTION 333
+
+CHAPTER X.
+THE THEORY OF SEXUAL SELECTION, AND CONCLUDING REMARKS 379
+
+ * * * * *
+
+APPENDIX TO CHAPTER V. 421
+
+NOTE A TO PAGE 257 443
+
+NOTE B TO PAGE 295 445
+
+NOTE C TO PAGE 394 448
+
+INDEX 451
+
+
+
+
+LIST OF ILLUSTRATIONS
+
+
+ FIG. PAGE
+
+ 1. Successive forms of Paludina, from the Tertiary deposits of
+ Slavonia 19
+
+ 2. Skeleton of Seal 52
+
+ 3. Skeleton of Greenland Whale 53
+
+ 4. Paddle of Whale compared with Hand of Man 54
+
+ 5. Wing of Reptile, Mammal, and Bird 56
+
+ 6. Skeleton of _Dinornis gravis_ 61
+
+ 7. Hermit crabs compared with the cocoa-nut crab 64
+
+ 8. Rudimentary or vestigial hind-limbs of Python 67
+
+ 9. _Apteryx Australis_ 69
+
+ 10. Illustrations of the nictitating membrane in various animals
+ named 75
+
+ 11. Rudimentary, or vestigial and useless, muscles of the human
+ ear 76
+
+ 12. Portrait of a young male gorilla 78
+
+ 13. Portrait of a young male child 79
+
+ 14. An infant, three weeks old, supporting its own weight 81
+
+ 15. Sacrum of Gorilla compared with that of Man, showing the
+ rudimentary tail-bones of each 82
+
+ 16. Diagrammatic outline of the human embryo when about seven
+ weeks old 83
+
+ 17. Front and back view of adult human sacrum 84
+
+ 18. _Appendix vermiformis_ in Orang and in Man 85
+
+ 19. The same, showing variation in the Orang 85
+
+ 20. Human ear 86
+
+ 21. Foetus of an Orang 87
+
+ 22. Vestigial characters of human ears 88
+
+ 23. Hair-tracts on the arms and hands of Man, as compared with
+ those on the arms and hands of Chimpanzee 90
+
+ 24. Molar teeth of lower jaw in Gorilla, Orang, and Man 93
+
+ 25. Perforation of the humerus (supra-condyloid foramen) in three
+ species of Quadrumana where it normally occurs, and in Man,
+ where it does not normally occur 95
+
+ 26. Antlers of stag, showing successive addition of branches in
+ successive years 100
+
+ 27. Fission of a Protozoön 107
+
+ 28. _Hydra viridis_, partly in section 111
+
+ 29. Successive stages in the division of the ovum, or egg-cell,
+ of a worm 113
+
+ 30. Ovarian ovum of a Mammal 121
+
+ 31. Amoeboid movements of young egg-cells 122
+
+ 32. Human ovum, mature and greatly magnified 123
+
+ 33. Stages in the formation of the polar bodies in the ovum of a
+ star-fish 125
+
+ 34. Fertilization of the ovum of an echinoderm 126
+
+ 35. Fertilization of the ovum of a star-fish 127
+
+ 36. Karyokinesis of a typical tissue-cell (epithelium of
+ Salamander) 129
+
+ 37. Study of successive changes taking place in the nucleus of an
+ epithelium-cell, preparatory to division of the cell 131
+
+ 38. Formation and conjugation of the pronuclei in _Ascaris
+ megalocephala_ 132, 133
+
+ 39. Segmentation of ovum 135
+
+ 40. The contents of an ovum in an advanced stage of segmentation,
+ drawn in perspective 135
+
+ 41. Formation of the gastrula of _Amphioxus_ 137
+
+ 42. Gastrulation 138
+
+ 43. Gastrula of a Chalk Sponge 139
+
+ 44. _Prophysema primordiale_, an extant gastræa-form 140
+
+ 45. Ideal primitive vertebrate, seen from the left side 143
+
+ 46. The same in transverse section through the ovaries 144
+
+ 47. _Amphioxus lanceolatus_ 145
+
+ 48. _Balanoglossus_ 148
+
+ 49. A large Sea-lamprey (_Petromyzon marinus_) 148
+
+ 50. Adult Shark (_Carcharias melanopterus_) 149
+
+ 51. Diagram of heart and gill-arches of a fish 150
+
+ 52. One gill-arch, with branchial fringe attached 150
+
+ 53. Diagram of heart and gill-arches in a lizard 150
+
+ 54. Ideal diagram of primitive gill-or aortic-arches 151
+
+ 55. The same, modified for a bird 151
+
+ 56. The same, modified for a mammal 151
+
+ 57. A series of embryos at three comparable and progressive
+ stages of development, representing each of the classes of
+ vertebrated animals below the Mammalia 152
+
+ 58. Another series of embryos, also at three comparable and
+ progressive stages of development, representing four different
+ divisions of the class Mammalia 153
+
+ 59. Diagram of geological succession of the classes of the Animal
+ Kingdom 165
+
+ 60. Skull of _Oreodon Culbertsoni_ 167
+
+ 61,62. Horns of _Cervus dicrocerus_ 168
+
+ 63. Horns of _C. matheronis_ 168
+
+ 64. Horns of _C. pardinensis_ 168
+
+ 65. Horns of _C. issiodorensis_ 168
+
+ 66. Horns of _C. Sedgwickii_ 168
+
+ 67. Successive stages in the development of an existing Deer's
+ Antlers 169
+
+ 68. Homocercal tail 169
+
+ 69. Heterocercal tail 170
+
+ 70. Vertebrated but symmetrical fin (diphycercal) 170
+
+ 71. Tail of _Archæopteryx_ 171
+
+ 72. Tail of modern Bird 171
+
+ 73. _Archæopteryx macura_, restored 172
+
+ 74. Skeleton of Polar Bear 174
+
+ 75. Skeleton of Lion 175
+
+ 76. Anterior limb of Man, Dog, Hog, Sheep, and Horse 176
+
+ 77. Posterior limb of Man, Monkey, Dog, Sheep, and Horse 177
+
+ 78. Posterior limb of _Baptanodon discus_, and anterior limb of
+ _Chelydra serpentina_ 179
+
+ 79. Paddle of a Whale 180
+
+ 80. Fossil skeleton of _Phenacodus primævus_ 184
+
+ 81. Bones of the foot of four different forms of the perissodactyl
+ type 186
+
+ 82. Bones of the foot of four different forms of the artiodactyl
+ type 187
+
+ 83. Feet and teeth In fossil pedigree of the Horse 189
+
+ 84. _Palæotherium_. (Lower Tertiary of Paris Basin) 190
+
+ 85. _Hipparion_. (New World Pliocene) 192
+
+ 86. Comparative series of Brains 194
+
+ 87. Ideal section through all the above stages 195
+
+ 88. Skulls of Canadian Stag, _Cervalces Americanus_, and Elk 198
+
+ 89. Transmutations of _Planorbis_ 200
+
+ 90. Transformation of _Strombus_ 202
+
+ 91. Pigeons. Drawn from life 298
+
+ 92. Pigeons (_continued_). Drawn from life 299
+
+ 93. Fowls. Drawn from life 300
+
+ 94. Fowls (_continued_). Drawn from life 301
+
+ 95. Pair of Japanese Fowls, long-tailed breed 302
+
+ 96. Canaries. Drawn from life 303
+
+ 97. Sebastopol, or Frizzled Goose 304
+
+ 98. The Dingo, or wild dog of Australia 304
+
+ 99. Dogs. Drawn from life 305
+
+ 100. Dogs (_continued_). Drawn from life 306
+
+ 101. The Hairless Dog of Japan 307
+
+ 102. The skull of a Bull-dog compared with that of a Deer-hound 307
+
+ 103. Rabbits. Drawn from life 308
+
+ 104. Horses. Drawn from life 309
+
+ 105. Sheep. Drawn from life 310
+
+ 106. Cattle. Drawn from life 311
+
+ 107. Wild Boar contrasted with a modern Domesticated Pig 312
+
+ 108. Seasonal changes of colour in Ptarmigan (_Lagopus mutus_) 317
+
+ 109. _Oedicneus crepitans_, showing the instinctive attitude of
+ concealment 320
+
+ 110. Imitative forms and colours in insects 322
+
+ 111. The larva of Puss Moth (_Cerura vinula_) 325
+
+ 112. The larva of Puss Moth in disturbed attitude 326
+
+ 113. Three cases of mimicry 328
+
+ 114. Two further cases of mimicry; flies resembling a wasp in the
+ one and a bee in the other 329
+
+ 115. A case of mimicry where a non-venomous species of snake
+ resembles a venomous one 330
+
+ 116. A case of mimicry where a homopterous resembles a leaf-cutting
+ ant 332
+
+ 117. Feather-footed pigeon 359
+
+ 118. _Raia radiata_ 368
+
+ 119. Electric organ of the Skate 369
+
+ 120. Electric cells of _Raia radiata_ 370
+
+ 121. The Garden Bower-bird (_Amblyornis inornata_) 382
+
+ 122. Courtship of Spiders 388
+
+ 123. Courtship of Spiders (_continued_) 389
+
+ 124. The Bell-bird (_Chasmorhynchus niveus_) 396
+
+ 125. _C. tricarunculatus_ 397
+
+
+
+
+SECTION I
+
+_EVOLUTION_
+
+
+
+
+CHAPTER I.
+
+INTRODUCTORY.
+
+
+Among the many and unprecedented changes that have been wrought by Mr.
+Darwin's work on the _Origin of Species_, there is one which, although
+second in importance to no other, has not received the attention which
+it deserves. I allude to the profound modification which that work has
+produced on the ideas of naturalists with regard to method.
+
+Having had occasion of late years somewhat closely to follow the history
+of biological science, I have everywhere observed that progress is not
+so much marked by the march of discovery _per se_, as by the altered
+views of method which the march has involved. If we except what
+Aristotle called "the first start" in himself, I think one may fairly
+say that from the rejuvenescence of biology in the sixteenth century to
+the stage of growth which it has now reached in the nineteenth, there is
+a direct proportion to be found between the value of work done and the
+degree in which the worker has thereby advanced the true conception of
+scientific working. Of course, up to a certain point, it is notorious
+that the revolt against the purely "subjective methods" in the sixteenth
+century revived the spirit of _inductive_ research as this had been left
+by the Greeks; but even with regard to this revolt there are two things
+which I should like to observe.
+
+In the first place, it seems to me, an altogether disproportionate value
+has been assigned to Bacon's share in the movement. At most, I think, he
+deserves to be regarded but as a literary exponent of the _Zeitgeist_ of
+his century. Himself a philosopher, as distinguished from a man of
+science, whatever influence his preaching may have had upon the general
+public, it seems little short of absurd to suppose that it could have
+produced any considerable effect upon men who were engaged in the
+practical work of research. And those who read the _Novum Organon_ with
+a first-hand knowledge of what is required for such research can
+scarcely fail to agree with his great contemporary Harvey, that he wrote
+upon science like a Lord Chancellor.
+
+The second thing I should like to observe is, that as the revolt against
+the purely subjective methods grew in extent and influence it passed to
+the opposite extreme, which eventually became only less deleterious to
+the interests of science than was the bondage of authority, and
+addiction to _a priori_ methods, from which the revolt had set her free.
+For, without here waiting to trace the history of this matter in detail,
+I think it ought now to be manifest to everyone who studies it, that up
+to the commencement of the present century the progress of science in
+general, and of natural history in particular, was seriously retarded by
+what may be termed the Bugbear of Speculation. Fully awakened to the
+dangers of web-spinning from the ever-fertile resources of their own
+inner consciousness, naturalists became more and more abandoned to the
+idea that their science ought to consist in a mere observation of facts,
+or tabulation of phenomena, without attempt at theorizing upon their
+philosophical import. If the facts and phenomena presented any such
+import, that was an affair for men of letters to deal with; but, as men
+of science, it was _their_ duty to avoid the seductive temptations of
+the world, the flesh, and the devil, in the form of speculation,
+deduction, and generalization.
+
+I do not allege that this ideal of natural history was either absolute
+or universal; but there can be no question that it was both orthodox and
+general. Even Linnæus was express in his limitations of true scientific
+work in natural history to the collecting and arranging of species of
+plants and animals. In accordance with this view, the _status_ of a
+botanist or a zoologist was estimated by the number of specific names,
+natural habitats, &c., which he could retain in his memory, rather than
+by any evidences which he might give of intellectual powers in the way
+of constructive thought. At the most these powers might legitimately
+exercise themselves only in the direction of taxonomic work; and if a
+Hales, a Haller, or a Hunter obtained any brilliant results in the way
+of observation and experiment, their merit was taken to consist in the
+discovery of facts _per se_: not in any endeavours they might make in
+the way of combining their facts under general principles. Even as late
+in the day as Cuvier this ideal was upheld as the strictly legitimate
+one for a naturalist to follow; and although Cuvier himself was far from
+being always loyal to it, he leaves no doubt regarding the estimate in
+which he held the still greater deviations of his colleagues, St.
+Hilaire and Lamarck.
+
+Now, these traditional notions touching the severance between the facts
+of natural history and the philosophy of it, continued more or less to
+dominate the minds of naturalists until the publication of the _Origin
+of Species_, in 1859. Then it was that an epoch was marked in this
+respect, as in so many other respects where natural history is
+concerned. For, looking to the enormous results which followed from a
+deliberate disregard of such traditional canons by Darwin, it has long
+since become impossible for naturalists, even of the strictest sect, not
+to perceive that their previous bondage to the law of a mere ritual has
+been for ever superseded by what verily deserves to be regarded as a new
+dispensation. Yet it cannot be said, or even so much as suspected, that
+Darwin's method in any way resembled that of pre-scientific days, the
+revolt against which led to the straight-laced--and for a long time most
+salutary--conceptions of method that we have just been noticing. Where,
+then, is the difference? To me it seems that the difference is as
+follows; and, if so, that not the least of our many obligations to
+Darwin as the great organizer of biological science arises from his
+having clearly displayed the true principle which ought to govern
+biological research.
+
+To begin with, he nowhere loses sight of the primary distinction between
+fact and theory; so that, thus far, he loyally follows the spirit of
+revolt against subjective methods. But, while always holding this
+distinction clearly in view, his idea of the scientific use of facts is
+plainly that of furnishing legitimate material for the construction of
+theories. Natural history is not to him an affair of the herbarium or
+the cabinet. The collectors and the species-framers are, as it were, his
+diggers of clay and makers of bricks: even the skilled observers and the
+trained experimentalists are his mechanics. Valuable as the work of all
+these men is in itself, its principal value, as he has finally
+demonstrated, is that which it acquires in rendering possible the work
+of the architect. Therefore, although he has toiled in all the trades
+with his own hands, and in each has accomplished some of the best work
+that has ever been done, the great difference between him and most of
+his predecessors consists in this,--that while to them the discovery or
+accumulation of facts was an end, to him it is the means. In their eyes
+it was enough that the facts should be discovered and recorded. In his
+eyes the value of facts is due to their power of guiding the mind to a
+further discovery of principles. And the extraordinary success which
+attended his work in this respect of _generalization_ immediately
+brought natural history into line with the other inductive sciences,
+behind which, in this most important of all respects, she has so
+seriously fallen. For it was the _Origin of Species_ which first clearly
+revealed to naturalists as a class, that it was the duty of their
+science to take as its motto, what is really the motto of natural
+science in general,
+
+ Felix qui potuit rerum cognoscere causas.
+
+Not facts, then, or phenomena, but causes or principles, are the
+ultimate objects of scientific quest. It remains to ask, How ought this
+quest to be prosecuted?
+
+Well, in the second place, Darwin has shown that next only to the
+importance of clearly distinguishing between facts and theories on the
+one hand, and of clearly recognising the relation between them on the
+other, is the importance of not being scared by the Bugbear of
+Speculation. The spirit of speculation is the same as the spirit of
+science, namely, as we have just seen, a desire to know the causes of
+things. The _hypotheses non fingo_ of Newton, if taken to mean what it
+is often understood as meaning, would express precisely the opposite
+spirit from that in which all scientific research must necessarily take
+its origin. For if it be causes or principles, as distinguished from
+facts or phenomena, that constitute the final aim of scientific
+research, obviously the advancement of such research can be attained
+only by the framing of hypotheses. And to frame hypotheses is to
+speculate.
+
+Therefore, the difference between science and speculation is not a
+difference of spirit; nor, thus far, is it a difference of method. The
+only difference between them is in the subsequent process of verifying
+hypotheses. For while speculation, in its purest form, is satisfied to
+test her explanations only by the degree in which they accord with our
+subjective ideas of probability--or with the "Illative Sense" of
+Cardinal Newman,--science is not satisfied to rest in any explanation as
+final until it shall have been fully verified by an appeal to objective
+proof. This distinction is now so well and so generally appreciated that
+I need not dwell upon it. Nor need I wait to go into any details with
+regard to the so-called canons of verification. My only object is to
+make perfectly clear, first, that in order to have any question to put
+to the test of objective verification, science must already have so far
+employed the method of speculation as to have framed a question to be
+tested; and, secondly, that the point where science parts company with
+speculation is the point where this testing process begins.
+
+Now, if these things are so, there can be no doubt that Darwin was
+following the truest method of inductive research in allowing any amount
+of latitude to his speculative thought in the direction of scientific
+theorizing. For it follows from the above distinctions that the danger
+of speculation does not reside in the width of its range, or even in the
+impetuosity of its vehemence. Indeed, the wider its reach, and the
+greater its energy, the better will it be for the interests of science.
+The only danger of speculation consists in its momentum being apt to
+carry away the mind from the more laborious work of adequate
+verification; and therefore a true scientific judgment consists in
+giving a free rein to speculation on the one hand, while holding ready
+the break of verification with the other. Now, it is just because Darwin
+did both these things with so admirable a judgment, that he gave the
+world of natural history so good a lesson as to the most effectual way
+of driving the chariot of science.
+
+This lesson we have now all more or less learnt to profit by. Yet no
+other naturalist has proved himself so proficient in holding the balance
+true. For the most part, indeed, they have now all ceased to confound
+the process of speculation _per se_ with the danger of inadequate
+verification; and therefore the old ideal of natural history as
+concerned merely with collecting species, classifying affinities, and,
+in general, tabulating facts, has been well-nigh universally
+superseded. But this great gain has been attended by some measure of
+loss. For while not a few naturalists have since erred on the side of
+insufficiently distinguishing between fully verified principles of
+evolution and merely speculative deductions therefrom, a still larger
+number have formed for themselves a Darwinian creed, and regard any
+further theorizing on the subject of evolution as _ipso facto_
+unorthodox.
+
+Having occupied the best years of my life in closely studying the
+literature of Darwinism, I shall endeavour throughout the following
+pages to avoid both these extremes. No one in this generation is able to
+imitate Darwin, either as an observer or a generalizer. But this does
+not hinder that we should all so far endeavour to follow his _method_,
+as always to draw a clear distinction, not merely between observation
+and deduction, but also between degrees of verification. At all events,
+my own aim will everywhere be to avoid dogmatism on the one hand, and
+undue timidity as regards general reasoning on the other. For everything
+that is said justification will be given; and, as far as prolonged
+deliberation has enabled me to do so, the exact value of such
+justification will be rendered by a statement of at least the main
+grounds on which it rests. The somewhat extensive range of the present
+treatise, however, will not admit of my rendering more than a small
+percentage of the facts which in each case go to corroborate the
+conclusion. But although a great deal must thus be necessarily lost on
+the one side, I am disposed to think that more will be gained on the
+other, by presenting, in a terser form than would otherwise be
+possible, the whole theory of organic evolution as I believe that it
+will eventually stand. My endeavour, therefore, will be to exhibit the
+general structure of this theory in what I take to be its strictly
+logical form, rather than to encumber any of its parts by a lengthy
+citation of facts. Following this method, I shall in each case give only
+what I consider the main facts for and against the positions which have
+to be argued; and in most cases I shall arrange the facts in two
+divisions, namely, first those of largest generality, and next a few of
+the most special character that can be found.
+
+As explained in the Preface, the present instalment of the treatise is
+concerned with the theory of evolution, from the appearance of the
+_Origin of Species_ in 1859, to the death of its author in 1882; while
+the second part will be devoted to the sundry post-Darwinian questions
+which have arisen in the subsequent decade. To the possible criticism
+that a disproportionate amount of space will thus be allotted to a
+consideration of these post-Darwinian questions, I may furnish in
+advance the following reply.
+
+In the first place, besides the works of Darwin himself, there are a
+number of others which have already and very admirably expounded the
+evidences, both of organic evolution as a fact, and of natural selection
+as a cause. Therefore, in the present treatise it seemed needless to go
+beyond the ground which was covered by my original lectures, namely, a
+condensed and connected, while at the same time a critical statement of
+the main evidences, and the main objections, which have thus far been
+published with reference to the distinctively Darwinian theory. Indeed
+while re-casting this portion of my lectures for the present
+publication, I have felt that criticism might be more justly urged from
+the side of impatience at a reiteration of facts and arguments already
+so well known. But while endeavouring, as much as possible, to avoid
+overlapping the previous expositions, I have not carried this attempt to
+the extent of damaging my own, by omitting any of the more important
+heads of evidence; and I have sought to invest the latter with some
+measure of novelty by making good what appears to me a deficiency which
+has hitherto obtained in the matter of pictorial illustration. In
+particular, there will be found a tolerably extensive series of
+woodcuts, serving to represent the more important products of artificial
+selection. These, like all the other original illustrations, have been
+drawn either direct from nature or from a comparative study of the best
+authorities. Nevertheless, I desire it to be understood that the first
+part of this treatise is intended to retain its original character, as a
+merely educational exposition of Darwinian teaching--an exposition,
+therefore, which, in its present form, may be regarded as a compendium,
+or hand-book, adapted to the requirements of a general reader, or
+biological student as distinguished from those of a professed
+naturalist.
+
+The case, however, is different with the second instalment, which will
+be published at no very distant date. Here I have not followed with
+nearly so much closeness the material of my original lectures. On the
+contrary, I have had in view a special class of readers; and, although I
+have tried not altogether to sacrifice the more general class, I shall
+desire it to be understood that I am there appealing to naturalists who
+are specialists in Darwinism. One must say advisedly, naturalists who
+are specialists in Darwinism, because, while the literature of Darwinism
+has become a department of science in itself, there are nowadays many
+naturalists who, without having paid any close attention to the subject,
+deem themselves entitled to hold authoritative opinions with regard to
+it. These men may have done admirable work in other departments of
+natural history, and yet their opinions on such matters as we shall
+hereafter have to consider may be destitute of value. As there is no
+necessary relation between erudition in one department of science and
+soundness of judgment in another, the mere fact that a man is
+distinguished as a botanist or zoologist does not in itself qualify him
+as a critic where specially Darwinian questions are concerned. Thus it
+happens now, as it happened thirty years ago, that highly distinguished
+botanists and zoologists prove themselves incapable as judges of general
+reasoning. It was Darwin's complaint that for many years nearly all his
+scientific critics either could not, or would not, understand what he
+had written--and this even as regarded the fundamental principles of his
+theory, which with the utmost clearness he had over and over again
+repeated. Now the only difference between such naturalists and their
+successors of the present day is, that the latter have grown up in a
+Darwinian environment, and so, as already remarked, have more or less
+thoughtlessly adopted some form of Darwinian creed. But this scientific
+creed is not a whit less dogmatic and intolerant than was the more
+theological one which it has supplanted; and while it usually
+incorporates the main elements of Darwin's teaching, it still more
+usually comprises gross perversions of their consequences. All this I
+shall have occasion more fully to show in subsequent parts of the
+present work; and allusion is made to the matter here merely for the
+sake of observing that in future I shall not pay attention to
+unsupported expressions of opinion from any quarter: I shall consider
+only such as are accompanied with some statement of the grounds upon
+which the opinion is held. And, even as thus limited, I do not think it
+will be found that the following exposition devotes any disproportional
+amount of attention to the contemporary movements of Darwinian thought,
+seeing, as we shall see, how active scientific speculation has been in
+the field of Darwinism since the death of Mr. Darwin.
+
+ * * * * *
+
+Leaving, then, these post-Darwinian questions to be dealt with
+subsequently, I shall now begin a systematic _résumé_ of the evidences
+in favour of the Darwinian theory, as this was left to the world by
+Darwin himself.
+
+There is a great distinction to be drawn between the fact of evolution
+and the manner of it, or between the evidence of evolution as having
+taken place somehow, and the evidence of the causes which have been
+concerned in the process. This most important distinction is frequently
+disregarded by popular writers on Darwinism; and, therefore, in order to
+mark it as strongly as possible, I will effect a complete separation
+between the evidence which we have of evolution as a fact, and the
+evidence which we have as to its method. In other words, not until I
+shall have fully considered the evidence of organic evolution as a
+process which somehow or another _has_ taken place, will I proceed to
+consider _how_ it has taken place, or the causes which Darwin and others
+have suggested as having probably been concerned in this process.
+
+Confining, then, our attention in the first instance to a proof of
+evolution considered as a fact, without any reference at all to its
+method, let us begin by considering the antecedent standing of the
+matter.
+
+ * * * * *
+
+First of all we must clearly recognise that there are only two
+hypotheses in the field whereby it is possible so much as to suggest an
+explanation of the origin of species. Either all the species of plants
+and animals must have been supernaturally created, or else they must
+have been naturally evolved. There is no third hypothesis possible; for
+no one can rationally suggest that species have been eternal.
+
+Next, be it observed, that the theory of a continuous transmutation of
+species is not logically bound to furnish a full explanation of _all_
+the natural causes which it may suppose to have been at work. The
+radical distinction between the two theories consists in the one
+assuming an immediate action of some supernatural or inscrutable cause,
+while the other assumes the immediate action of natural--and therefore
+of possibly discoverable--causes. But in order to sustain this latter
+assumption, the theory of descent is under no logical necessity to
+furnish a full proof of _all_ the natural causes which may have been
+concerned in working out the observed results. We do not know the
+natural causes of many diseases; but yet no one nowadays thinks of
+reverting to any hypothesis of a supernatural cause, in order to explain
+the occurrence of any disease the natural causation of which is obscure.
+The science of medicine being in so many cases able to explain the
+occurrence of disease by its hypothesis of natural causes, medical men
+now feel that they are entitled to assume, on the basis of a wide
+analogy, and therefore on the basis of a strong antecedent presumption,
+that all diseases are due to natural causes, whether or not in
+particular cases such causes happen to have been discovered. And from
+this position it follows that medical men are not logically bound to
+entertain any supernatural theory of an obscure disease, merely because
+as yet they have failed to find a natural theory. And so it is with
+biologists and their theory of descent. Even if it be fully proved to
+them that the causes which they have hitherto discovered, or suggested,
+are inadequate to account for all the facts of organic nature, this
+would in no wise logically compel them to vacate their theory of
+evolution, in favour of the theory of creation. All that it would so
+compel them to do would be to search with yet greater diligence for the
+natural causes still undiscovered, but in the existence of which they
+are, by their independent evidence in favour of the theory, bound to
+believe.
+
+In short, the issue is not between the theory of a supernatural cause
+and the theory of any one particular natural cause, or set of
+causes--such as natural selection, use, disuse, and so forth. The issue
+thus far--or where only the _fact_ of evolution is concerned--is between
+the theory of a supernatural cause as operating immediately in
+numberless acts of special creation, and the theory of natural causes as
+a whole, whether these happen, or do not happen, to have been hitherto
+discovered.
+
+This much by way of preliminaries being understood, we have next to
+notice that whichever of the two rival theories we choose to entertain,
+we are not here concerned with any question touching the origin of life.
+We are concerned only with the origin of particular forms of life--that
+is to say, with the origin of species. The theory of descent starts from
+life as a _datum_ already granted. How life itself came to be, the
+theory of descent, as such, is not concerned to show. Therefore, in the
+present discussion, I will take the existence of life as a fact which
+does not fall within the range of our present discussion. No doubt the
+question as to the origin of life is in itself a deeply interesting
+question, and although in the opinion of most biologists it is a
+question which we may well hope will some day fall within the range of
+science to answer, at present, it must be confessed, science is not in a
+position to furnish so much as any suggestion upon the subject; and
+therefore our wisdom as men of science is frankly to acknowledge that
+such is the case.
+
+ * * * * *
+
+We are now in a position to observe that the theory of organic evolution
+is strongly recommended to our acceptance on merely antecedent grounds,
+by the fact that it is in full accordance with what is known as the
+principle of continuity. By the principle of continuity is meant the
+uniformity of nature, in virtue of which the many and varied processes
+going on in nature are due to the same kind of method, i. e. the method
+of natural causation. This conception of the uniformity of nature is
+one that has only been arrived at step by step through a long and
+arduous course of human experience in the explanation of natural
+phenomena. The explanations of such phenomena which are first given are
+always of the supernatural kind; it is not until investigation has
+revealed the natural causes which are concerned that the hypotheses of
+superstition give way to those of science. Thus it follows that the
+hypotheses of superstition which are the latest in yielding to the
+explanations of science, are those which refer to the more recondite
+cases of natural causation; for here it is that methodical investigation
+is longest in discovering the natural causes. Thus it is only by degrees
+that fetishism is superseded by what now appears a common-sense
+interpretation of physical phenomena; that exorcism gives place to
+medicine; alchemy to chemistry; astrology to astronomy; and so forth.
+Everywhere the miraculous is progressively banished from the field of
+explanation by the advance of scientific discovery; and the places where
+it is left longest in occupation are those where the natural causes are
+most intricate or obscure, and thus present the greatest difficulty to
+the advancing explanations of science. Now, in our own day there are but
+very few of these strongholds of the miraculous left. Nearly the whole
+field of explanation is occupied by naturalism, so that no one ever
+thinks of resorting to supernaturalism except in the comparatively few
+cases where science has not yet been able to explore the most obscure
+regions of causation. One of these cases is the origin of life; and,
+until quite recently, another of these cases was the origin of species.
+But now that a very reasonable explanation of the origin of species has
+been offered by science, it is but in accordance with all previous
+historical analogies that many minds should prove themselves unable all
+at once to adjust themselves to the new ideas, and thus still linger
+about the more venerable ideas of supernaturalism. But we are now in
+possession of so many of these historical analogies, that all minds with
+any instincts of science in their composition have grown to distrust, on
+merely antecedent grounds, any explanation which embodies a miraculous
+element. Such minds have grown to regard all these explanations as mere
+expressions of our own ignorance of natural causation; or, in other
+words, they have come to regard it as an _a priori_ truth that nature is
+everywhere uniform in respect of method or causation; that the reign of
+law universal; the principle of continuity ubiquitous.
+
+Now, it must be obvious to any mind which has adopted this attitude of
+thought, that the scientific theory of natural descent is recommended by
+an overwhelming weight of antecedent presumption, as against the
+dogmatic theory of supernatural design.
+
+To begin with, we must remember that the fact of evolution--or, which is
+the same thing, the fact of continuity in natural causation--has now
+been unquestionably proved in so many other and analogous departments of
+nature, that to suppose any interruption of this method as between
+species and species becomes, on grounds of such analogy alone, well-nigh
+incredible. For example, it is now a matter of demonstrated fact that
+throughout the range of _inorganic_ nature the principles of evolution
+have obtained. It is no longer possible for any one to believe with our
+forefathers that the earth's surface has always existed as it now
+exists. For the science of geology has proved to demonstration that seas
+and lands are perpetually undergoing gradual changes of relative
+positions--continents and oceans supplanting each other in the course of
+ages, mountain-chains being slowly uplifted, again as slowly denuded,
+and so forth. Moreover, and as a closer analogy, within the limits of
+animate nature we know it is the universal law that every individual
+life undergoes a process of gradual development; and that breeds, races,
+or strains, may be brought into existence by the intentional use of
+natural processes--the results bearing an unmistakeable resemblance to
+what we know as natural species. Again, even in the case of natural
+species themselves, there are two considerations which present enormous
+force from an antecedent point of view. The first is that organic forms
+are only then recognised as species when intermediate forms are absent.
+If the intermediate forms are actually living, or admit of being found
+in the fossil state, naturalists forthwith regard the whole series as
+varieties, and name all the members of it as belonging to the same
+species. Consequently it becomes obvious that naturalists, in their work
+of naming species, may only have been marking out the cases where
+intermediate or connecting forms have been lost to observation. For
+example, here we have a diagram representing a very unusually complete
+series of fossil shells, which within the last few years has been
+unearthed from the Tertiary lake basins of Slavonia. Before the series
+was completed, some six or eight of the then disconnected forms were
+described as distinct species; but as soon as the connecting forms were
+found--showing a progressive modification from the older to the newer
+beds,--the whole were included as varieties of one species.
+
+ [Illustration: FIG. 1.--Successive forms of Paludina, from the
+ Tertiary deposits of Slavonia (after Neumayr).]
+
+Of course, other cases of the same kind might be adduced, and therefore,
+as just remarked, in their work of naming species naturalists may only
+have been marking out the cases where intermediate forms have been lost
+to observation. And this possibility becomes little less than a
+certainty when we note the next consideration which I have to adduce,
+namely, that in all their systematic divisions of plants and animals in
+groups higher than species--such as genera, families, orders, and the
+rest--naturalists have at all times recognised the fact that the one
+shades off into the other by such imperceptible gradations, that it is
+impossible to regard such divisions as other than conventional. It is
+important to remember that this fact was fully recognised before the
+days of Darwin. In those days the scientifically orthodox doctrine was,
+that although species were to be regarded as fixed units, bearing the
+stamp of a special creation, all the higher taxonomic divisions were
+to be considered as what may be termed the artificial creation of
+naturalists themselves. In other words, it was believed, and in many
+cases known, that if we could go far enough back in the history of the
+earth, we should everywhere find a tendency to mutual approximation
+between allied _groups of species_; so that, for instance, birds and
+reptiles would be found to be drawing nearer and nearer together, until
+eventually they would seem to become fused in a single type; that the
+existing distinctions between herbivorous and carnivorous mammals
+would be found to do likewise; and so on with all the larger
+group-distinctions, at any rate within the limits of the same
+sub-kingdoms. But although naturalists recognised this even in the
+pre-Darwinian days, they stoutly believed that a great exception was to
+be made in the case of species. These, the lowest or initial members of
+their taxonomic series, they supposed to be permanent--the miraculously
+created units of organic nature. Now, all that I have at present to
+remark is, that this pre-Darwinian exception which was made in favour of
+species to the otherwise recognised principle of gradual change, was an
+exception which can at no time have been recommended by any antecedent
+considerations. At all times it stood out of analogy with the principle
+of continuity; and, as we shall fully find in subsequent chapters, it is
+now directly contradicted by all the facts of biological science.
+
+There remains one other fact of high generality to which prominent
+attention should be drawn from the present, or merely antecedent, point
+of view. On the theory of special creation no reason can be assigned why
+distinct specific types should present any correlation, either in time
+or in space, with their nearest allies; for there is evidently no
+conceivable reason why any given species, A, should have been specially
+created on the same area and at about the same time as its nearest
+representative, B,--still less, of course, that such should be a general
+rule throughout all the thousands and millions of species which have
+ever inhabited the earth. But, equally of course, on the theory of a
+natural evolution this is so necessary a consequence, that if no
+correlation of such a two-fold kind were observable, the theory would be
+negatived. Thus the question whether there be any indication of such a
+two-fold correlation may be regarded as a test-question as between the
+two theories; for although the vast majority of extinct species have
+been lost to science, there are a countless number of existing species
+which furnish ample material for answering the question. And the answer
+is so unequivocal that Mr. Wallace, who is one of our greatest
+authorities on geographical distribution, has laid it down as a general
+law, applicable to all the departments of organic nature, that, so far
+as observation can extend, "every species has come into existence
+coincident both in space and time with a pre-existing and closely allied
+species." As it appears to me that the significance of these words
+cannot be increased by any comment upon them, I will here bring this
+introductory chapter to a close.
+
+
+
+
+CHAPTER II.
+
+CLASSIFICATION.
+
+
+The first line of direct evidence in favour of organic evolution which I
+shall open is that which may be termed the argument from Classification.
+
+It is a matter of observable fact that different forms of plants and
+animals present among themselves more or less pronounced resemblances.
+From the earliest times, therefore, it has been the aim of philosophical
+naturalists to classify plants and animals in accordance with these
+resemblances. Of course the earliest attempts at such classification
+were extremely crude. The oldest of these attempts with which we are
+acquainted--namely, that which is presented in the books of Genesis and
+Leviticus--arranges the whole vegetable kingdom in three simple
+divisions of Grass, Herbs, and Trees; while the animal kingdom is
+arranged with almost equal simplicity with reference, first to habitats
+in water, earth, or air, and next as to modes of progression. These, of
+course, were what may be termed common-sense classifications, having
+reference merely to external appearances and habits of life. But when
+Aristotle laboriously investigated the comparative anatomy of animals,
+he could not fail to perceive that their entire structures had to be
+taken into account in order to classify them scientifically; and, also,
+that for this purpose the internal parts were of quite as much
+importance as the external. Indeed, he perceived that they were of
+greatly more importance in this respect, inasmuch as they presented so
+many more points for comparison; and, in the result, he furnished an
+astonishingly comprehensive, as well as an astonishingly accurate
+classification of the larger groups of the animal kingdom. On the other
+hand, classification of the vegetable kingdom continued pretty much as
+it had been left by the book of Genesis--all plants being divided into
+three groups, Herbs, Shrubs, and Trees. Nor was this primitive state of
+matters improved upon till the sixteenth century, when Gesner
+(1516-1565), and still more Cæsalpino (1519-1603), laid the foundations
+of systematic botany.
+
+But the more that naturalists prosecuted their studies on the anatomy of
+plants and animals, the more enormously complex did they find the
+problem of classification become. Therefore they began by forming what
+are called artificial systems, in contradistinction to natural systems.
+An artificial system of classification is a system based on the more or
+less arbitrary selection of some one part, or set of parts; while a
+natural classification is one that is based upon a complete knowledge of
+all the structures of all the organisms which are classified.
+
+Thus, the object of classification has been that of arranging organisms
+in accordance with their natural affinities, by comparing organism with
+organism, for the purpose of ascertaining which of the constituent
+organs are of the most invariable occurrence, and therefore of the most
+typical signification. A porpoise, for instance, has a large number of
+teeth, and in this feature resembles most fish, while it differs from
+all mammals. But it also gives suck to its young. Now, looking to these
+two features alone, should we say that a porpoise ought to be classed as
+a fish or as a mammal? Assuredly as a mammal; because the number of
+teeth is a very variable feature both in fish and mammals, whereas the
+giving of suck is an invariable feature among mammals, and occurs
+nowhere else in the animal kingdom. This, of course, is chosen as a very
+simple illustration. Were all cases as obvious, there would be but
+little distinction between natural and artificial systems of
+classification. But it is because the lines of natural affinity are, as
+it were, so interwoven throughout the organic world, and because there
+is, in consequence, so much difficulty in following them, that
+artificial systems have to be made in the first instance as feelers
+towards eventual discovery of the natural system. In other words, while
+forming their artificial systems of classification, it has always been
+the aim of naturalists--whether consciously or unconsciously--to admit
+as the bases of their systems those characters which, in the then state
+of their knowledge, seemed most calculated to play an important part in
+the eventual construction of the natural system. If we were dealing with
+the history of classification, it would here be interesting to note how
+the course of it has been marked by gradual change in the principles
+which naturalists adopted as guides to the selection of characters on
+which to found their attempts at a natural classification. Some of these
+changes, indeed, I shall have to mention later on; but at present what
+has to be specially noted is, that through all these changes of theory
+or principle, and through all the ever-advancing construction of their
+taxonomic science, naturalists themselves were unable to give any
+intelligible reason for the faith that was in them--or the faith that
+over and above the artificial classifications which were made for the
+mere purpose of cataloguing the living library of organic nature, there
+was deeply hidden in nature itself a truly natural classification, for
+the eventual discovery of which artificial systems might prove to be of
+more or less assistance.
+
+Linnæus, for example, expressly says--"You ask me for the characters of
+the natural orders; I confess that I cannot give them." Yet he maintains
+that, although he cannot define the characters, he knows, by a sort of
+naturalist's instinct, what in a general way will subsequently be found
+to be the organs of most importance in the eventual grouping of plants
+under a natural system. "I will not give my reasons for the distribution
+of the natural orders which I have published," he said: "you, or some
+other person, after twenty or after fifty years, will discover them, and
+see that I was right."
+
+Thus we perceive that in forming their provisional or artificial
+classifications, naturalists have been guided by an instinctive belief
+in some general principle of natural affinity, the character of which
+they have not been able to define; and that the structures which they
+selected as the bases of their classifications when these were
+consciously artificial, were selected because it seemed that they were
+the structures most likely to prove of use in subsequent attempts at
+working out the natural system.
+
+This general principle of natural affinity, of which all naturalists
+have seen more or less well-marked evidence in organic nature, and after
+which they have all been feeling, has sometimes been regarded as
+natural, but more often as supernatural. Those who regarded it as
+supernatural took it to consist in a divine ideal of creation according
+to types, so that the structural affinities of organisms were to them
+expressions of an archetypal plan, which might be revealed in its
+entirety when all organisms on the face of the earth should have been
+examined. Those, on the other hand, who regarded the general principle
+of affinity as depending on some natural causes, for the most part
+concluded that these must have been utilitarian causes; or, in other
+words, that the fundamental affinities of structure must have depended
+upon fundamental requirements of function. According to this view, the
+natural classification would eventually be found to stand upon a basis
+of physiology. Therefore all the systems of classification up to the
+earlier part of the present century went upon the apparent axiom, that
+characters which are of most importance to the organisms presenting them
+must be characters most indicative of natural affinities. But the truth
+of the matter was eventually found to be otherwise. For it was
+eventually found that there is absolutely no correlation between these
+two things; that, therefore, it is a mere chance whether or not organs
+which are of importance to organisms are likewise of importance as
+guides to classification; and, in point of fact, that the general
+tendency in this matter is towards an inverse instead of a direct
+proportion. More often than not, the greater the value of a structure
+for the purpose of indicating natural affinities, the less is its value
+to the creatures presenting it.
+
+Enough has now been said to show three things. First, that long before
+the theory of descent was entertained by naturalists, naturalists
+perceived the fact of natural affinities, and did their best to
+construct a natural system of classification for the purpose of
+expressing such affinities. Second, that naturalists had a kind of
+instinctive belief in some one principle running through the whole
+organic world, which thus served to bind together organisms in groups
+subordinate to groups--that is, into species, genera, orders, families,
+classes, sub-kingdoms, and kingdoms. Third, that they were not able to
+give any very intelligible reason for this faith that was in them;
+sometimes supposing the principle in question to be that of a
+supernatural plan of organization, sometimes regarding it as dependent
+on conditions of physiology, and sometimes not attempting to account for
+it at all.
+
+Of course it is obvious that the theory of descent furnishes the
+explanation which is required. For it is now evident to evolutionists,
+that although these older naturalists did not know what they were doing
+when they were tracing these lines of natural affinity, and thus helping
+to construct a natural classification--I say it is now evident to
+evolutionists that these naturalists were simply tracing the lines of
+genetic relationship. The great principle pervading organic nature,
+which was seen so mysteriously to bind the whole creation together as in
+a nexus of organic affinity, is now easily understood as nothing more or
+less than the principle of Heredity. Let us, therefore, look a little
+more closely at the character of this network, in order to see how far
+it lends itself to this new interpretation.
+
+The first thing that we have to observe about the nexus is, that it is a
+nexus--not a single line, or even a series of parallel lines. In other
+words, some time before the theory of descent was seriously entertained,
+naturalists for the most part had fully recognised that it was
+impossible to arrange either plants or animals, with respect to their
+mutual affinities, in a ladder-like series (as was supposed to be the
+type of classification by the earlier systematists), or even in map-like
+groups (as was supposed to be the type by Linnæus). And similarly, also,
+with respect to grades of organization. In the case of the larger
+groups, indeed, it is usually possible to say that the members of this
+group as a whole are more highly organized than the members of that
+group as a whole; so that, for instance, we have no hesitation in
+regarding the Vertebrata as more highly organized than the Invertebrata,
+Birds than Reptiles, and so on. But when we proceed to smaller
+subdivisions, such as genera and species, it is usually impossible to
+say that the one type is more highly organized than another type. A
+horse, for instance, cannot be said to be more highly organized than a
+zebra or an ass; although the entire horse-genus is clearly a more
+highly organized type than any genus of animal which is not a mammal.
+
+In view of these facts, therefore, the system of classification which
+was eventually arrived at before the days of Darwin, was the system
+which naturalists likened to a tree; and this is the system which all
+naturalists now agreed upon as the true one. According to this system, a
+short trunk may be taken to represent the lowest organisms which cannot
+properly be termed either plants or animals. This short trunk soon
+separates into two large trunks, one of which represents the vegetable
+and the other the animal kingdom. Each of these trunks then gives off
+large branches signifying classes, and these give off smaller, but more
+numerous branches, signifying families, which ramify again into orders,
+genera, and finally into the leaves, which may be taken to represent
+species. Now, in such a representative tree of life, the height of any
+branch from the ground may be taken to indicate the grade of
+organization which the leaves, or species, present; so that, if we
+picture to ourselves such a tree, we may understand that while there is
+a general advance of organization from below upwards, there are many
+deviations in this respect. Sometimes leaves growing on the same branch
+are growing at a different level--especially, of course, if the branch
+be a large one, corresponding to a class or sub-kingdom. And sometimes
+leaves growing on different branches are growing at the same level: that
+is to say, although they represent species belonging to widely divergent
+families, orders, or even classes, it cannot be said that the one
+species is more highly organized than the other.
+
+Now, this tree-like arrangement of species in nature is an arrangement
+for which Darwin is not responsible. For, as we have seen, the detecting
+of it has been due to the progressive work of naturalists for centuries
+past; and even when it was detected, at about the commencement of the
+present century, naturalists were confessedly unable to explain the
+reason of it, or what was the underlying principle that they were
+engaged in tracing when they proceeded ever more and more accurately to
+define these ramifications of natural affinity. But now, as just
+remarked, we can clearly perceive that this underlying principle was
+none other than Heredity as expressed in family likeness,--likeness,
+therefore, growing progressively more unlike with remoteness of
+ancestral relationship. For thus only can we obtain any explanation of
+the sundry puzzles and apparent paradoxes, which a working out of their
+natural classifications revealed to botanists and zoologists during the
+first half of the present century. It will now be my endeavour to show
+how these puzzles and paradoxes are all explained by the theory that
+natural affinities are merely the expression of genetic affinities.
+
+First of all, and from the most general point of view, it is obvious
+that the tree-like system of classification, which Darwin found already
+and empirically worked out by the labours of his predecessors, is as
+suggestive as anything could well be of the fact of genetic
+relationship. For this is the form that every tabulation of family
+pedigree must assume; and therefore the mere fact that a scientific
+tabulation of natural affinities was eventually found to take the form
+of a tree, is in itself highly suggestive of the inference that such a
+tabulation represents a _family_ tree. If all species were separately
+created, there can be no assignable reason why the ideas of earlier
+naturalists touching the form which a natural classification would
+eventually assume should not have represented the truth--why, for
+example, it should not have assumed the form of a ladder (as was
+anticipated in the seventeenth century), or of a map (as was anticipated
+in the eighteenth), or, again, of a number of wholly unrelated lines,
+circles, &c. (as certain speculative writers of the present century have
+imagined). But, on the other hand, if all species were separately and
+independently created, it becomes virtually incredible that we should
+everywhere observe this progressive arborescence of characters common to
+larger groups into more and more numerous, and more and more delicate,
+ramifications of characters distinctive only of smaller and smaller
+groups. A man would be deemed insane if he were to attribute the origin
+of every branch and every twig of a real tree to a separate act of
+special creation; and although we have not been able to witness the
+growth of what we may term in a new sense the Tree of Life, the
+structural relations which are now apparent between its innumerable
+ramifications bear quite as strong a testimony to the fact of their
+having been due to an organic growth, as is the testimony furnished by
+the branches of an actual tree.
+
+Or, to take another illustration. Classification of organic forms, as
+Darwin, Lyell, and Häckel have pointed out, strongly resembles the
+classification of languages. In the case of languages, as in the case of
+species, we have genetic affinities strongly marked; so that it is
+possible to some extent to construct a Language-tree, the branches of
+which shall indicate, in a diagrammatic form, the progressive divergence
+of a large group of languages from a common stock. For instance, Latin
+may be regarded as a fossil language, which has given rise to a group of
+living languages--Italian, Spanish, French, and, to a large extent,
+English. Now what would be thought of a philologist who should maintain
+that English, French, Spanish, and Italian were all specially created
+languages--or languages separately constructed by the Deity, and by as
+many separate acts of inspiration communicated to the nations which now
+speak them--and that their resemblance to the fossil form, Latin, must
+be attributed to special design? Yet the evidence of the natural
+transmutation of species is in one respect much stronger than that of
+the natural transmutation of languages--in respect, namely, of there
+being a vastly greater number of cases all bearing testimony to the fact
+of genetic relationship.
+
+But, quitting now this most general point of view--or the suggestive
+fact that what we have before us is a _tree_--let us next approach this
+tree for the purpose of examining its structure more in detail. When we
+do this, the fact of next greatest generality which we find is as
+follows.
+
+In cases where a very old form of life has continued to exist
+unmodified, so that by investigation of its anatomy we are brought back
+to a more primitive type of structure than that of the newer forms
+growing higher up _upon the same branch_, two things are observable. In
+the first place, the old form is less differentiated than the newer
+ones; and, in the next place, it is seen much more closely to resemble
+types of structure belonging to some of the other and larger branches of
+the tree. The organization of the older form is not only _simpler_; but
+it is, as naturalists say, more _generalized_. It comprises within
+itself characters belonging to its own branch, and also characters
+belonging to neighbouring branches, or to the trunk from which allied
+branches spring. Hence it becomes a general rule of classification, that
+it is by the lowest, or by the oldest, forms of any two natural groups
+that the affinities between the two groups admit of being best detected.
+And it is obvious that this is just what ought to be the case on the
+theory of descent with divergent modification; while, upon the
+alternative theory of special creation, no reason can be assigned why
+the lowest or the oldest types should thus combine the characters which
+afterwards become severally distinctive of higher or newer types.
+
+Again, I have already alluded to the remarkable fact that there is no
+correlation between the value of structures to the organisms which
+present them, and their value to the naturalist for the purpose of
+tracing natural affinity; and I have remarked that up to the close of
+the last century it was regarded as an axiom of taxonomic science, that
+structures which are of most importance to the animals or plants
+possessing them must likewise prove of most importance in any natural
+system of classification. On this account, all attempts to discover the
+natural classification went upon the supposition that such a direct
+proportion must obtain--with the result that organs of most
+physiological importance were chosen as the bases of systematic work.
+And when, in the earlier part of the present century, De Candolle found
+that instead of a direct there was usually an inverse proportion between
+the functional and the taxonomic value of a structure, he was unable to
+suggest any reason for this apparently paradoxical fact. For, upon the
+theory of special creation, no reason can be assigned why organs of
+least importance to organisms should prove of most importance as marks
+of natural affinity. But on the theory of descent with progressive
+modification the apparent paradox is at once explained. For it is
+evident that organs of functional importance are, other things equal,
+the organs which are most likely to undergo different modifications in
+different lines of family descent, and therefore in time to have their
+genetic relationships in these different lines obscured. On the other
+hand, organs or structures which are of no functional importance are
+never called upon to change in response to any change of habit, or to
+any change in the conditions of life. They may, therefore, continue to
+be inherited through many different lines of family descent, and thus
+afford evidence of genetic relationship where such evidence fails to be
+given by any of the structures of vital importance, which in the course
+of many generations have been required to change in many ways according
+to the varied experiences of different branches of the same family.
+Here, then, we have an empirically discovered rule in the science of
+classification, the _raison d'être_ of which we are at once able to
+appreciate upon the theory of evolution, whereas no possible explanation
+of why it should ever have become a rule could be furnished upon the
+theory of special creation.
+
+Here, again, is another empirically determined rule. The larger the
+_number_, as distinguished from the _importance_, of structures which
+are found common to different groups, the greater becomes their value as
+guides to the determination of natural affinity. Or, as Darwin puts it,
+"the value of an aggregate of characters, even when none are important,
+alone explains the aphorism enunciated by Linnæus, namely, that the
+characters do not give the genus, but the genus gives the characters;
+for this seems founded on the appreciation of many trifling points of
+resemblance, too slight to be defined[1]."
+
+ [1] _Origin of Species_, p. 367.
+
+Now it is evident, without comment, of how much value aggregates of
+characters ought to be in classification, if the ultimate meaning of
+classification be that of tracing lines of pedigree; whereas, if this
+ultimate meaning were that of tracing divine ideals manifested in
+special creation, we can see no reason why single characters are not
+such sure tokens of a natural arrangement as are aggregates of
+characters, even though the latter be in every other respect
+unimportant. For, on the special creation theory, we cannot explain why
+an assemblage, say of four or five trifling characters, should have been
+chosen to mark some unity of plan, rather than some one character of
+functional importance, which would have served at least equally well any
+such hypothetical purpose. On the other hand, as Darwin remarks, "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 with 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
+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, concur 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; and
+we know that such aggregated characters have especial value in
+classification[2]."
+
+ [2] _Origin of Species_, p. 372.
+
+It is true that even a single character, if found common to a large
+number of forms, while uniformly absent from others, is also regarded by
+naturalists as of importance for purposes of classification, although
+they recognise it as of a value subordinate to that of aggregates of
+characters. But this also is what we should expect on the theory of
+descent. If even any one structure be found to run through a number of
+animals presenting different habits of life, the readiest explanation of
+the fact is to be found in the theory of descent; but this does not
+hinder that if several such characters always occur together, the
+inference of genetic relationship is correspondingly confirmed. And the
+fact that before this inference was ever drawn, naturalists recognised
+the value of single characters in proportion to their constancy, and the
+yet higher value of aggregates of characters in proportion to their
+number--this fact shows that in their work of classification naturalists
+empirically observed the effects of a cause which we have now
+discovered, to wit, hereditary transmission of characters through
+ever-widening groups of changing species.
+
+There is another argument which appears to tell strongly in favour of
+the theory of descent. We have just seen that non-adaptive structures,
+not being required to change in response to change of habits or
+conditions of life, are allowed to persist unchanged through many
+generations, and thus furnish exceptionally good guides in the science
+of classification--or, according to our theory, in the work of tracing
+lines of pedigree. But now, the converse of this statement holds equally
+true. For it often happens that adaptive structures are required to
+change in different lines of descent in analogous ways, in order to meet
+analogous needs; and, when such is the case, the structures concerned
+have to assume more or less close resemblances to one another, even
+though they have severally descended from quite different ancestors. The
+paddles of a whale, for instance, most strikingly resemble the fins of a
+fish as to their outward form and movements; yet, on the theory of
+descent, they must be held to have had a widely different parentage.
+Now, in all such cases where there is thus what is called an analogous
+(or adaptive) resemblance, as distinguished from what is called an
+homologous (or anatomical) resemblance--in all such cases it is
+observable that the similarities do not extend further into the
+structure of the parts than it is necessary that they should extend, in
+order that the structures should both perform the same functions. The
+whole anatomy of the paddles of a whale is quite unlike that of the fins
+of a fish--being, in fact, that of the fore-limb of a mammal. The
+change, therefore, which the fore-limb has here undergone to suit it to
+the aquatic habits of this mammal, is no greater than was required for
+that purpose: the change has not extended to any one feature of
+_anatomical_ significance. This, of course, is what we should expect on
+the theory of descent with modification of ancestral characters; but on
+the theory of special creation it is not intelligible why there should
+always be so marked a distinction between resemblances as analogical or
+adaptive, and resemblances as homological or of meaning in reference to
+a natural classification. To take another and more detailed instance,
+the Tasmanian wolf is an animal separated from true wolves in a natural
+system of classification. Yet its jaws and teeth bear a strong general
+resemblance to those of all the dog tribe, although there are
+differences of anatomical detail. In particular, while the dogs all have
+on each side of the upper jaw four pre-molars and two molars, the
+Tasmanian wolf has three pre-molars and four molars. Now there is no
+reason, so far as their common function of dealing with flesh is
+concerned, why the teeth of the Tasmanian wolf should not have resembled
+homologically as well as analogically the teeth of a true wolf; and
+therefore we cannot assign any intelligible reason why, if all the
+species of the dog genus were separately created with one pattern of
+teeth, the unallied Tasmanian wolf should have been furnished with what
+is practically the same pattern from a functional point of view, while
+differing from a structural point of view. But, of course, on the theory
+of descent with modification, we can well understand why similarities of
+habit should have led to similarities of structural appearance of an
+adaptive kind in different lines of descent, without there being any
+trace of such real or anatomical similarities as could possibly point to
+genetic relationship.
+
+Lastly, to adduce the only remaining argument from classification which
+I regard as of any considerable weight, naturalists have found it
+necessary, while constructing their natural classifications, to set
+great store on what Mr. Darwin calls "chains of affinities." Thus, for
+instance, "nothing can be easier than to define a number of characters
+common to all birds; but with crustaceans any 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[3]." Now it is evident
+that this progressive modification of specific types--where it cannot be
+said that the continuity of resemblance is anywhere broken, and yet
+terminates in modification so great that but for the connecting links no
+one could divine a natural relationship between the extreme members of
+the series,--it is evident that such chains of affinity speak most
+strongly in favour of a transmutation of the species concerned, while it
+is impossible to suggest any explanation of the fact in terms of the
+rival theory. For if all the links of such a chain were separately
+forged by as many acts of special creation, we can see no reason why B
+should resemble A, C resemble B, and so on, but with ever slight though
+accumulating differences, until there is no resemblance at all between A
+and Z.
+
+ [3] _Origin of Species_, pp. 368-9.
+
+ * * * * *
+
+I hope enough has now been said to show that all the general principles
+and particular facts appertaining to the natural classification of
+plants and animals, are precisely what they ought to be according to the
+theory of genetic descent; while no one of them is such as might
+be--and, indeed, used to be--expected upon the theory of special
+creation. Therefore, the only possible way in which all this uniform
+body of direct evidence can be met by a supporter of the latter theory,
+is by falling back upon the argument from ignorance. We do not know, it
+may be said, what hidden reasons there may have been for following all
+these general principles in the separate creation of specific types.
+Now, it is evident that this is a form of argument which admits of being
+brought against all the actual--and even all the possible--lines of
+evidence in favour of evolution. Therefore I deem it desirable thus
+early in our proceedings to place this argument from ignorance on its
+proper logical footing.
+
+If there were any independent evidence in favour of special creation as
+a _fact_, then indeed the argument from ignorance might be fairly used
+against any sceptical cavils regarding the _method_. In this way, for
+example, Bishop Butler made a legitimate use of the argument from
+ignorance when he urged that it is no reasonable objection against a
+revelation, _otherwise accredited_, to show that it has been rendered in
+a form, or after a method, which we should not have antecedently
+expected. But he could not have legitimately employed this argument,
+except on the supposition that he had some independent evidence in
+favour of the revelation; for, in the absence of any such independent
+evidence, appeal to the argument from ignorance would have become a mere
+begging of the question, by simply assuming that a revelation had been
+made. And thus it is in the present case. A man, of course, may quite
+legitimately say, _Assuming that the theory of special creation is
+true_, it is not for us to anticipate the form or method of the
+process. But where the question is as to whether or not the theory _is_
+true, it becomes a mere begging of this question to take refuge in the
+argument from ignorance, or to represent in effect that there is no
+question to be discussed. And if, when the form or method is
+investigated, it be found everywhere charged with evidence in favour of
+the theory of descent, the case becomes the same as that of a supposed
+revelation, which has been discredited by finding that all available
+evidence points to a natural growth. In short, the argument from
+ignorance is in any case available only as a negative foil against
+destructive criticism: in no case has it any positive value, or value of
+a constructive kind. Therefore, if a theory on any subject is destitute
+of positive evidence, while some alternative theory is in possession of
+such evidence, the argument from ignorance can be of no logical use to
+the former, even though it maybe of such use to the latter. For it is
+only the possession of positive evidence which can furnish a logical
+justification of the argument from ignorance: in the absence of such
+evidence, even the negative value of the argument disappears, and it
+then implies nothing more than the gratuitous assumption of a theory.
+
+ * * * * *
+
+I will now sum up the various considerations which have occupied us
+during the present chapter.
+
+First of all we must take note that the classification of plants and
+animals in groups subordinate to groups is not merely arbitrary, or
+undertaken only for a matter of convenience and nomenclature--such, for
+instance, as the classification of stars in constellations. On the
+contrary, the classification of a naturalist differs from that of an
+astronomer, in that the objects which he has to classify present
+structural resemblances and structural differences in numberless
+degrees; and it is the object of his classification to present a tabular
+statement of these facts. Now, long before the theory of evolution was
+entertained, naturalists became fully aware that these facts of
+structural resemblances running through groups subordinate to groups
+were really facts of nature, and not merely poetic imaginations of the
+mind. No one could dissect a number of fishes without perceiving that
+they were all constructed on one anatomical pattern, which differed
+considerably from the equally uniform pattern on which all mammals were
+constructed, even although some mammals bore an extraordinary
+resemblance to fish in external form and habits of life. And similarly
+with all the smaller divisions of the animal and vegetable kingdoms.
+Everywhere investigation revealed the bonds of close structural
+resemblances between species of the same genus, resemblance less close
+between genera of the same family, resemblance still less close between
+families of the same order, resemblance yet more remote between orders
+of the same class, and resemblance only in fundamental features between
+classes of the same sub-kingdom, beyond which limit all anatomical
+resemblance was found to disappear--the different sub-kingdoms being
+formed on wholly different patterns. Furthermore, in tracing all these
+grades of structural relationship, naturalists were slowly led to
+recognise that the form which a natural classification must eventually
+assume would be that of a tree, wherein the constituent branches would
+display a progressive advance of organization from below upwards.
+
+Now we have seen that although this tree-like arrangement of natural
+groups was as suggestive as anything could well be of all the forms o£
+life being bound together by the ties of genetic relationship, such was
+not the inference which was drawn from it. Dominated by the theory of
+special creation, naturalists either regarded the resemblance of type
+subordinate to type as expressive of divine ideals manifested in such
+creation, or else contented themselves with investigating the facts
+without venturing to speculate upon their philosophical import. But even
+those naturalists who abstained from committing themselves to any theory
+of archetypal plans, did not doubt that facts so innumerable and so
+universal must have been due to some one co-ordinating principle--that,
+even though they were not able to suggest what it was, there must have
+been some hidden bond of connexion running through the whole of organic
+nature. Now, as we have seen, it is manifest to evolutionists that this
+hidden bond can be nothing else than heredity; and, therefore, that
+these earlier naturalists, although they did not know what they were
+doing, were really tracing the lines of genetic descent as revealed by
+degrees of structural resemblance,--that the arborescent grouping of
+organic forms which their labours led them to begin, and in large
+measure to execute, was in fact a family tree of life.
+
+Here, then, is the substance of the argument from classification. The
+mere fact that all organic nature thus incontestably lends itself to a
+natural arrangement of group subordinate to group, when due regard is
+paid to degrees of anatomical resemblance--this mere fact of itself
+tells so weightily in favour of descent with progressive modification in
+different lines, that even if it stood alone it would be entitled to
+rank as one of our strongest pieces of evidence. But, as we have seen,
+it does not stand alone. When we look beyond this large and general fact
+of all the innumerable forms of life being thus united in a tree-like
+system by an unquestionable relationship of some kind, to those smaller
+details in the science of classification which have been found most
+useful as guides for this kind of research, then we find that all these
+details, or empirically discovered rules, are exactly what we should
+have expected them to be, supposing the real meaning of classification
+to have been that of tracing lines of pedigree.
+
+In particular, we have seen that the most archaic types are both simpler
+in their organization and more generalized in their characters than are
+the more recent types--a fact of which no explanation can be given on
+the theory of special creation. But, upon the theory of natural
+evolution, we can without difficulty understand why the earlier forms
+should have been the simpler forms, and also why they should have been
+the most generalized. For it is out of the older forms that the newer
+must have grown; and, as they multiplied, they must have become more and
+more differentiated.
+
+Again, we have seen that there is no correlation between the importance
+of any structure from a classificatory point of view, and the importance
+of that structure to the organism which presents it. On the contrary,
+it is a general rule that "the less any part of the organization is
+concerned with special habits, the more important it becomes for
+classification." Now, from the point of view of special creation it is
+unintelligible why unity of ideal should be most manifested by least
+important structures, whereas from the point of view of evolution it is
+to be expected that these life-serving structures should have been most
+liable to divergent modification in divergent lines of descent, or in
+adaptation to different conditions of life, while the trivial or less
+important characters should have been allowed to remain unmodified. Thus
+we can now understand why all primitive classifications were wrong in
+principle when they went upon the assumption that divine ideals were
+best exhibited by resemblances between life-serving (and therefore
+adaptive) structures, with the result that whales were classed with
+fishes, birds with bats, and so on. Nevertheless, these primitive
+naturalists were quite logical; for, from the premises furnished by the
+theory of special creation, it is much more reasonable to expect that
+unity of ideal should be shown in plainly adaptive characters than in
+trivial and more or less hidden anatomical characters. Moreover, long
+after biological science had ceased consciously to follow any
+theological theory, the apparent axiom continued to be entertained, that
+structures of most importance to organisms must also be structures of
+most importance to systematists. And when at last, in the present
+century, this was found not to be the case, no reason could be suggested
+why it was not the case. But now we are able fully to explain this
+apparent anomaly.
+
+Once more, we have seen that aggregates of characters presenting
+resemblances to one another have always been found to be of special
+importance as guides to classification. This, of course, is what we
+should have expected, if the real meaning of classification be that of
+tracing lines of pedigree; but on the theory of special creation no
+reason can be assigned why single characters are not such sure tokens of
+a natural arrangement as are aggregates of characters, however trivial
+the latter may be. For it is obvious that unity of ideal might have been
+even better displayed by everywhere maintaining the pattern of some one
+important structure, than by doing so in the case of several unimportant
+structures. Take an analogous instance from human contrivances. Unity of
+ideal in the case of gun-making would be shown by the same principles of
+mechanism running through all the different sizes and shapes of
+gun-locks, rather than by the ornamental patterns engraved upon the
+outside. Yet it must be supposed that in the mechanisms assumed to have
+been constructed by special creation, it was the trivial details rather
+than the fundamental principles of these mechanisms which were chosen by
+the Divinity to display his ideals.
+
+And this leads us to the next consideration--namely, that when in two
+different lines of descent animals happen to adopt similar habits of
+life, the modifications which they undergo in order to fit them for
+these habits often induces striking resemblances of structure between
+the two animals, as in the case of whales and fish. But in all such
+instances it is invariably found that the resemblance is only
+superficial and apparent: not anatomical or real. In other words, the
+resemblance does not extend further than it is necessary that it
+should, if both sets of organs are to be adapted to perform the same
+functions. Now this, again, is just what one would expect to find as the
+universal rule on the theory of descent, with modification of ancestral
+characters. But, on the opposite theory of special creation, I know not
+how it is to be explained that among so many instances of close
+superficial resemblance between creatures belonging to different
+branches of the tree of life, there are no instances of any real or
+anatomical resemblance. So far as their structures are adapted to
+perform a common function, there is in all such cases what may be termed
+a deceptive appearance of some unity of ideal; but, when carefully
+examined, it is always found that two apparently identical structures
+occurring on different branches of the classificatory tree are in fact
+fundamentally different in respect of their structural plan.
+
+Lastly, we have seen that one of the guiding principles of
+classification has been empirically found to consist in setting a high
+value on "chains of affinities." That is to say, naturalists not
+unfrequently meet with a long series of progressive modifications of
+type, which, although it cannot be said that the continuity is anywhere
+broken, at last leads to so much divergence of character that, but for
+the intermediate links, the members at each end of the chain could not
+be suspected of being in any way related. Well, such cases of chains of
+affinity obviously tell most strongly in favour of descent with
+continuous modification; while it is impossible to suggest why, if all
+the links were separately forged by as many acts of special creation,
+there should have been this gradual transmutation of characters carried
+to the point where the original creative ideal has been so completely
+transformed that, but for the accident of the chain being still
+complete, no one of nature's interpreters could possibly have discovered
+the connexion. For, as we have seen, this is not a case in which any
+appeal can be logically made to the argument from ignorance of divine
+method, unless some independent evidence could be adduced in favour of
+special creation. And that no such independent evidence exists, it will
+be the object of future chapters to show.
+
+
+
+
+CHAPTER III.
+
+MORPHOLOGY.
+
+
+The theory of evolution supposes that hereditary characters admit of
+being slowly modified wherever their modification will render an
+organism better suited to a change in its conditions of life. Let us,
+then, observe the evidence which we have of such adaptive modifications
+of structure, in cases where the need of such modification is apparent.
+We may begin by again taking the case of the whales and porpoises. The
+theory of evolution infers, from the whole structure of these animals,
+that their progenitors must have been terrestrial quadrupeds of some
+kind, which gradually became more and more aquatic in their habits. Now
+the change in the conditions of their life thus brought about would have
+rendered desirable great modifications of structure. These changes would
+have begun by affecting the least typical--that is, the least strongly
+inherited--structures, such as the skin, claws, and teeth. But, as time
+went on, the adaptation would have extended to more typical structures,
+until the shape of the body would have become affected by the bones and
+muscles required for terrestrial locomotion becoming better adapted for
+aquatic locomotion, and the whole outline of the animal more fish-like
+in shape. This is the stage which we actually observe in the seals,
+where the hind legs, although retaining all their typical bones, have
+become shortened up almost to rudiments, and directed backwards, so as
+to be of no use for walking, while serving to complete the fish-like
+taper of the body. (Fig. 2.) But in the whales the modification has gone
+further than this so that the hind legs have ceased to be apparent
+externally, and are only represented internally--and even this only in
+some species--by remnants so rudimentary that it is difficult to make
+out with certainty the homologies of the bones; moreover, the head and
+the whole body have become completely fish-like in shape. (Fig. 3.) But
+profound as are these alterations, they affect only those parts of the
+organism which it was for the benefit of the organism to have altered,
+so that it might be adapted to an aquatic mode of existence. Thus the
+arm, which is used as a fin, still retains the bones of the shoulder,
+fore-arm, wrist, and fingers, although they are all enclosed in a
+fin-shaped sack, so as to render them useless for any purpose other than
+swimming (Fig. 4.) Similarly, the head, although it so closely resembles
+the head of a fish in shape, still retains the bones of the mammalian
+skull in their proper anatomical relations to one another; but modified
+in form so as to offer the least possible resistance to the water. In
+short, it may be said that all the modifications have been effected with
+the least possible divergence from the typical mammalian type, which is
+compatible with securing so perfect an adaptation to a purely aquatic
+mode of life.
+
+ [Illustration: FIG. 2.--Skeleton of Seal, 1/8 nat. size. Drawn from
+ nature (_R. Coll. Surg. Mus._).]
+
+ [Illustration: FIG. 3.--Skeleton of Greenland Whale, 1/100 nat.
+ size. The rudimentary bones of the pelvis are shown on a larger
+ scale in the upper drawing. (From Prof. Flower.)]
+
+ [Illustration: FIG. 4.--Paddle of Whale compared with Hand of Man.
+ Drawn from nature (_R. Coll. Surg. Mus._).]
+
+Now I have chosen the case of the whale and porpoise group, because they
+offer so extreme an example of profound modification of structure in
+adaptation to changed conditions of life. But the same thing may be seen
+in hundreds and hundreds of other cases. For instance, to confine our
+attention to the arm, not only is the limb modified in the whale for
+swimming, but in another mammal--the bat--it is modified for flying, by
+having the fingers enormously elongated and overspread with a membranous
+web.
+
+In birds, again, the arm is modified for flight in a wholly different
+way--the fingers here being very short and all run together, while the
+chief expanse of the wing is composed of the shoulder and fore-arm. In
+frogs and lizards, again, we find hands more like our own; but in an
+extinct species of flying reptile the modification was extreme, the wing
+having been formed by a prodigious elongation of the fifth finger, and a
+membrane spread over it and the rest of the hand. (Fig. 5.) Lastly, in
+serpents the hand and arm have disappeared altogether.
+
+ [Illustration: FIG. 5.--Wing of Reptile, Mammal, and Bird. Drawn
+ from nature (_Brit. Mus._).]
+
+Thus, even if we confine our attention to a single organ, how wonderful
+are the modifications which it is seen to undergo, although never losing
+its typical character. Everywhere we find the distinction between
+homology and analogy which was explained in the last chapter--the
+distinction, that is, between correspondence of structure and
+correspondence of function. On the one hand, we meet with structures
+which are perfectly homologous and yet in no way analogous: the
+structural elements remain, but are profoundly modified so as to perform
+wholly different functions. On the other hand, we meet with structures
+which are perfectly analogous, and yet in no way homologous: totally
+different structures are modified to perform the same functions. How,
+then, are we to explain these things? By design manifested in special
+creation, or by descent with adaptive modification? If it is said by
+design manifested in special creation, we must suppose that the Deity
+formed an archetypal plan of certain structures, and that he determined
+to adhere to this plan through all the modifications which those
+structures exhibit. But, if so, why is it that some structures are
+selected as typical and not others? Why should the vertebral skeleton,
+for instance, be tortured into every conceivable variety of modification
+in order to subserve as great a variety of functions; while another
+structure, such as the eye, is made in different sub-kingdoms on
+fundamentally different plans, notwithstanding that it has throughout to
+perform the same function? Will any one have the hardihood to assert
+that in the case of the skeleton the Deity has endeavoured to show his
+_ingenuity_, by the manifold functions to which he has made the same
+structure subservient; while in the case of the eye he has endeavoured
+to show his _resources_, by the manifold structures which he has adapted
+to serve the same function? If so, it becomes a most unfortunate
+circumstance that, throughout both the vegetable and animal kingdoms,
+all cases which can be pointed to as showing ingenious adaptation of the
+same typical structure to the performance of widely different
+functions--or cases of homology without analogy,--are cases which come
+within the limits of the same natural group of plants and animals, and
+therefore admit of being equally well explained by descent from a common
+ancestry; while all cases of widely different structures performing the
+same function--or cases of analogy without homology,--are to be found in
+different groups of plants or animals, and are therefore suggestive of
+independent variations arising in the different lines of hereditary
+descent.
+
+To take a specific illustration. The octopus, or devil-fish, belongs to
+a widely different class of animals from a true fish; and yet its eye,
+in general appearance, looks wonderfully like the eye of a true fish.
+Now, Mr. Mivart pointed to this fact as a great difficulty in the way of
+the theory of evolution by natural selection, because it must clearly be
+a most improbable thing that so complicated a structure as the eye of a
+fish should happen to be arrived at through each of two totally
+different lines of descent. And this difficulty would, indeed, be a
+formidable one to the theory of evolution, if the similarity were not
+only analogical but homological. Unfortunately for the objection,
+however, Darwin clearly showed in his reply that in no one anatomical or
+homologous feature do the two structures resemble one another; so that,
+in point of fact, the two organs do not resemble one another in any
+particular further than it is necessary that they should, if both are to
+be analogous, or to serve the same function as organs of sight. But now,
+suppose that this had not been the case, and that the two structures,
+besides presenting the necessary superficial or analogical resemblance,
+had also presented an anatomical or homologous resemblance, with what
+force might it have then been urged,--Your hypothesis of hereditary
+descent with progressive modification being here excluded by the fact
+that the animals compared belong to two widely different branches of the
+tree of life, how are we to explain the identity of type manifested by
+these two complicated organs of vision? The only hypothesis open to us
+is intelligent adherence to an ideal plan or mechanism. But as this
+cannot now be urged in any comparable case throughout the whole organic
+world, we may on the other hand present it as a most significant fact,
+that while within the limits of the same large branch of the tree of
+life we constantly find the same typical structures modified so as to
+perform very different functions, we never find any of these particular
+types of structure in other large branches of the tree. That is to say,
+we never find typical structures appearing except in cases where their
+presence may be explained by the hypothesis of hereditary descent; while
+in thousands of such cases we find these structures undergoing every
+conceivable variety of adaptive modification.
+
+Consequently, special creationists must fall back upon another position
+and say,--Well, but it may have pleased the Deity to form a certain
+number of ideal types, and never to have allowed the structures
+occurring in one type to appear in any of the others. We
+answer,--Undoubtedly such may have been the case; but, if so, it is a
+most unfortunate thing for your theory, because the fact implies that
+the Deity has planned his types in such a way as to suggest the
+counter-theory of descent. For instance, it would seem most capricious
+on the part of the Deity to have made the eyes of an innumerable number
+of fish on exactly the same ideal type, and then to have made the eye of
+the octopus so exactly like these other eyes in superficial appearance
+as to deceive so accomplished a naturalist as Mr. Mivart, and yet to
+have taken scrupulous care that in no one ideal particular should the
+one type resemble the other. However, adopting for the sake of argument
+this great assumption, let us suppose that God did lay down these
+arbitrary rules for his own guidance in creation, and then let us see to
+what the assumption leads. If the Deity formed a certain number of ideal
+types, and determined that on no account should he allow any part of one
+type to appear in any part of another, surely we should expect that
+within the limits of the same type the same typical structures should
+always be present. Thus, remember what efforts, so to speak, have been
+made to maintain the uniformity of type in the case of the fore-limb as
+previously explained, and should we not expect that in other and similar
+cases a similar method should have been followed? Yet we repeatedly find
+that this is not the case. Even in the whale, as we have seen, the
+hind-limbs are either altogether absent or dwindled almost to nothing;
+and it is impossible to see in what respect the hind-limbs are of any
+less ideal value than the fore-limbs--which are carefully preserved in
+all vertebrated animals except the snakes, and the extinct _Dinornis_,
+where again we meet in this particular with a sudden and sublime
+indifference to the maintenance of a typical structure. (Fig. 6.)[4] Now
+I say that if the theory of ideal types is true, we have in these facts
+evidence of a most unreasonable inconsistency. But the theory of descent
+with continued adaptive modification fully explains all the known cases;
+for in every case the degree of divergence from the typical structure
+which an organism presents corresponds, in a general way, with the
+length of time during which the divergence has been going on. Thus we
+scarcely ever meet with any great departure from the typical form with
+respect to one of the organs, without some of the other organs being so
+far modified as of themselves to indicate, on the supposition of
+descent with modification, that the animal or plant must have been
+subject to the modifying influences for an enormously long series of
+generations. And this combined testimony of a number of organs in the
+same organism is what the theory of descent would lead us to expect,
+while the rival theory of design can offer no explanation of the fact,
+that when one organ shows a conspicuous departure from the supposed
+ideal type, some of the other organs in the same organism should tend to
+keep it company by doing likewise.
+
+ [4] It is, however, probable that all species of the genus retained
+ a tiny rudiment of wings in greatly dwindled scapulo-coracoid bones.
+ And Mr. H. O. Forbes has detected, in a recently exhumed specimen of
+ the latter, an indication of the glenoid cavity, for the
+ articulation of an extremely aborted humerus. (See _Nature_, Jan.
+ 14th, 1892.)
+
+ [Illustration: FIG. 6.--Skeleton of _Dinornis gravis_, 1/16 nat.
+ size. Drawn from nature (_Brit. Mus._). As separate cuts on a larger
+ scale are shown, 1st, the sternum, as this appears in mounted
+ skeletons, and, 2nd, the same in profile, with its (hypothetical)
+ scapulo-coracoid attached.]
+
+As an illustration both of this and of other points which have been
+mentioned, I may draw attention to what seems to me a particularly
+suggestive case. So-called soldier-or hermit-crabs, are crabs which have
+adopted the habit of appropriating the empty shells of mollusks. In
+association with this peculiar habit, the structure of these animals
+differs very greatly from that of all other crabs. In particular, the
+hinder part of the body, which occupies the mollusk-shell, and which
+therefore has ceased to require any hard covering of its own, has been
+suffered to lose its calcareous integument, and presents a soft fleshy
+character, quite unlike that of the more exposed parts of the animal.
+Moreover, this soft fleshy part of the creature is specially adapted to
+the particular requirements of the creature by having its lateral
+appendages--i. e. appendages which in other crustacea perform the
+function of legs--modified so as to act as claspers to the inside of the
+mollusk-shell; while the tail-end of the part in question is twisted
+into the form of a spiral, which fits into the spiral of the
+mollusk-shell. Now, in Keeling Island there is a large kind of crab
+called _Birgus latro_, which lives upon land and there feeds upon
+cocoa-nuts. The whole structure of this crab, it seems to me,
+unmistakeably resembles the structure of a hermit-crab (see drawings on
+the next page, Fig. 7). Yet this crab neither lives in the shell of a
+mollusk, nor is the hinder part of its body in the soft and fleshy
+condition just described: on the contrary, it is covered with a hard
+integument like all the other parts of the animal. Consequently, I think
+we may infer that the ancestors of _Birgus_ were hermit-crabs living in
+mollusk-shells; but that their descendants gradually relinquished this
+habit as they gradually became more and more terrestrial, while,
+concurrently with these changes in habit, the originally soft posterior
+parts acquired a hard protective covering to take the place of that
+which was formerly supplied by the mollusk-shell. So that, if so, we now
+have, within the limits of a single organism, evidence of a whole series
+of morphological changes in the past history of its species. First,
+there must have been the great change from an ordinary crab to a
+hermit-crab in all the respects previously pointed out. Next, there must
+have been the change back again from a hermit-crab to an ordinary crab,
+so far as living without the necessity of a mollusk-shell is concerned.
+From an evolutionary point of view, therefore, we appear to have in the
+existing structure of _Birgus_ a morphological record of all these
+changes, and one which gives us a reasonable explanation of why the
+animal presents the extraordinary appearance which it does. But, on the
+theory of special creation, it is inexplicable why this land-crab should
+have been formed on the pattern of a hermit-crab, when it never has need
+to enter the shell of a mollusk. In other words, its peculiar
+structure is not specially in keeping with its present habits, although
+so curiously allied to the similar structure of certain other crabs of
+totally different habits, in relation to which the peculiarities are of
+plain and obvious significance.
+
+ [Illustration: FIG. 7.--Hermit-crabs compared with the cocoa-nut
+ crab. On the left of the illustration one hermit-crab is represented
+ as occupying a mollusk-shell, and another (larger specimen) as it
+ appears when withdrawn from such a shell. On the right of the
+ illustration the cocoa-nut crab is represented in its natural
+ habitat on land. When full-grown, however, it is much larger than
+ our hermit-crabs. The latter are drawn from life, natural size, the
+ former from a specimen in the British Museum, 1/6 natural size.]
+
+ * * * * *
+
+I will devote the remainder of this chapter to considering another
+branch of the argument from morphology, to which the case of _Birgus_
+serves as a suitable introduction: I mean the argument from rudimentary
+structures.
+
+Throughout both the animal and vegetable kingdoms we constantly meet
+with dwarfed and useless representatives of organs, which in other and
+allied kinds of animals and plants are of large size and functional
+utility. Thus, for instance, the unborn whale has rudimentary teeth,
+which are never destined to cut the gums; and throughout its life this
+animal retains, in a similarly rudimentary condition, a number of organs
+which never could have been of use to any kind of creature save a
+terrestrial quadruped. The whole anatomy of its internal ear, for
+example, has reference to hearing in air--or, as Hunter long ago
+remarked, "is constructed upon the same principle as in the quadruped";
+yet, as Owen says, "the outer opening and passage leading therefrom to
+the tympanum can rarely be affected by sonorous vibrations of the
+atmosphere, and indeed they are reduced, or have degenerated, to a
+degree which makes it difficult to conceive how such vibrations can be
+propagated to the ear-drum during the brief moments in which the opening
+may be raised above the water."
+
+ [Illustration: FIG. 8.--Rudimentary or vestigial hind-limbs of
+ Python, as exhibited in the skeleton and on the external surface of
+ the animal. Drawn from nature, 1/4 nat. size (_Zoological
+ Gardens_).]
+
+Now, rudimentary organs of this kind are of such frequent occurrence,
+that almost every species presents one or more of them--usually, indeed,
+a considerable number. How, then, are they to be accounted for? of
+course the theory of descent with adaptive modification has a simple
+answer to supply--namely, that when, from changed conditions of life, an
+organ which was previously useful becomes useless, it will be suffered
+to dwindle away in successive generations, under the influence of
+certain natural causes which we shall have to consider in future
+chapters. On the other hand, the theory of special creation can only
+maintain that these rudiments are formed for the sake of adhering to an
+ideal type. Now, here again the former theory appears to be triumphant
+over the latter; for, without waiting to dispute the wisdom of making
+dwarfed and useless structures merely for the whimsical motive assigned,
+surely if such a method were adopted in so many cases, we should expect
+that in consistency it would be adopted in all cases. This reasonable
+expectation, however, is far from being realized. We have already seen
+that in numberless cases, such as that of the fore-limbs of serpents, no
+vestige of a rudiment is present. But the vacillating policy in the
+matter of rudiments does not end here; for it is shown in a still more
+aggravated form where within the limits of the same natural group of
+organisms a rudiment is sometimes present and sometimes absent. For
+instance, although in nearly all the numerous species of snakes there
+are no vestiges of limbs, in the python we find very tiny rudiments of
+the hind-limbs. (Fig. 8.) Now, is it a worthy conception of deity that,
+while neglecting to maintain his unity of ideal in the case of nearly
+all the numerous species of snakes, he should have added a tiny rudiment
+in the case of the python--and even in that case should have maintained
+his ideal very inefficiently, inasmuch as only two limbs, instead of
+four, are represented? how much more reasonable is the naturalistic
+interpretation; for here the very irregularity of their appearance in
+different species, which constitutes rudimentary structures one of the
+crowning difficulties to the theory of special design, furnishes the
+best possible evidence in favour of hereditary descent; seeing that this
+irregularity then becomes what may be termed the anticipated expression
+of progressive dwindling due to inutility. Thus, for example, to return
+to the case of wings, we have already seen that in an extinct genus of
+bird, _dinornis_, these organs were reduced to such an extent as to
+leave it still doubtful whether so much as the tiny rudiment
+hypothetically supplied to fig. 6 (p. 61) was present in all the
+species. And here is another well-known case of another genus of still
+existing bird, which, as was the case with _dinornis_, occurs only in
+new zealand. (Fig. 9.) Upon this island there are no four-footed
+enemies--either existing or extinct--to escape from which the wings of
+birds would be of any service. Consequently we can understand why on
+this island we should meet with such a remarkable dwindling away of
+wings.
+
+ [Illustration: FIG. 9.--_Apteryx Australis._ Drawn from life in the
+ Zoological Gardens, 1/8 nat. size. The external wing is drawn to a
+ scale in the upper part of the cut. The surroundings are supplied
+ from the most recent descriptions.]
+
+Similarly, the logger-headed duck of South America can only flap along
+the surface of the water, having its wings considerably reduced though
+less so than the _Apteryx_ of New Zealand. But here the interesting fact
+is that the young birds are able to fly perfectly well. Now, in
+accordance with a general law to be considered in a future chapter, the
+life-history of an individual organism is a kind of condensed
+recapitulation of the life-history of its species. Consequently, we can
+understand why the little chickens of the logger-headed duck are able to
+fly like all other ducks, while their parents are only able to flap
+along the surface of the water.
+
+Facts analogous to this reduction of wings in birds which have no
+further use for them, are to be met with also in insects under similar
+circumstances. Thus, there are on the island of Madeira somewhere
+between 500 and 600 species of beetles, which are in large part
+peculiar to that island, though related to other--and therefore
+presumably parent--species on the neighbouring continent. Now, no less
+than 200 species--or nearly half the whole number--are so far deficient
+in wings that they cannot fly. And, if we disregard the species which
+are not peculiar to the island--that is to say, all the species which
+likewise occur on the neighbouring continent, and therefore, as
+evolutionists conclude, have but _recently_ migrated to the island,--we
+find this very remarkable proportion. There are altogether 29 peculiar
+genera, and out of these no less than 23 have _all_ their species in
+this condition.
+
+Similar facts have been recently observed by the Rev. A. E. Eaton with
+respect to insects inhabiting Kerguelen Island. All the species which he
+found on the island--viz. a moth, several flies, and numerous
+beetles--he found to be incapable of flight; and therefore, as Wallace
+observes, "as these insects could hardly have reached the islands in a
+wingless state, even if there were any other known land inhabited by
+them, which there is not, we must assume that, like the Madeiran
+insects, they were originally winged, and lost their power of flight
+because its possession was injurious to them"--Kerguelen Island being
+"one of the stormiest places on the globe," and therefore a place where
+insects could rarely afford to fly without incurring the danger of being
+blown out to sea.
+
+Here is another and perhaps an even more suggestive class of facts.
+
+It is now many years ago since the editors of _Silliman's Journal_
+requested the late Professor Agassiz to give them his opinion on the
+following question. In a certain dark subterranean cave, called the
+Mammoth cave, there are found some peculiar species of blind fishes. Now
+the editors of _Silliman's Journal_ wished to know whether Prof. Agassiz
+would hold that these fish had been specially created in these caves,
+and purposely devoided of eyes which could never be of any use to them;
+or whether he would allow that these fish had probably descended from
+other species, but, having got into the dark cave, gradually lost their
+eyes through disuse. Prof. Agassiz, who was a believer in special
+creation, allowed that this ought to constitute a crucial test as
+between the two theories of special design and hereditary descent. "If
+physical circumstances," he said, "ever modified organized beings, it
+should be easily ascertained here." And eventually he gave it as his
+opinion, that these fish "were created under the circumstances in which
+they now live, within the limits over which they now range, and with the
+structural peculiarities which now characterise them."
+
+Since then a great deal of attention has been paid to the fauna of this
+Mammoth cave, and also to the faunas of other dark caverns, not only in
+the New, but also in the Old World. In the result, the following general
+facts have been fully established.
+
+(1) Not only fish, but many representatives of other classes, have been
+found in dark caves.
+
+(2) Wherever the caves are totally dark, all the animals are blind.
+
+(3) If the animals live near enough to the entrance to receive some
+degree of light, they may have large and lustrous eyes.
+
+(4) In all cases the species of blind animals are closely allied to
+species inhabiting the district where the caves occur; so that the blind
+species inhabiting American caves are closely allied to American
+species, while those inhabiting European caves are closely allied to
+European species.
+
+(5) In nearly all cases structural remnants of eyes admit of being
+detected, in various degrees of obsolescence. In the case of some of the
+crustaceans of the Mammoth cave the foot-stalks of the eyes are present,
+although the eyes themselves are entirely absent.
+
+Now, it is evident that all these general facts are in full agreement
+with the theory of evolution, while they offer serious difficulties to
+the theory of special creation. As Darwin remarks, it is hard to imagine
+conditions of life more similar than those furnished by deep limestone
+caverns under nearly the same climate in the two continents of America
+and Europe; so that, in accordance with the theory of special creation,
+very close similarity in the organizations of the two sets of faunas
+might have been expected. But, instead of this, the affinities of these
+two sets of faunas are with those of their respective continents--as of
+course they ought to be on the theory of evolution. Again, what would
+have been the sense of creating useless foot-stalks for the imaginary
+support of absent eyes, not to mention all the other various grades of
+degeneration in other cases? So that, upon the whole, if we agree with
+the late Prof. Agassiz in regarding these cave animals as furnishing a
+crucial test between the rival theories of creation and evolution, we
+must further conclude that the whole body of evidence which they now
+furnish is weighing on the side of evolution.
+
+So much, then, for a few special instances of what Darwin called
+rudimentary structures, but what may be more descriptively
+designated--in accordance with the theory of descent--obsolescent or
+vestigial structures. It is, however, of great importance to add that
+these structures are of such general occurrence throughout both the
+vegetable and animal kingdoms, that, as Darwin has observed, it is
+almost impossible to point to a single species which does not present
+one or more of them. In other words, it is almost impossible to find a
+single species which does not in this way bear some record of its own
+descent from other species; and the more closely the structure of any
+species is examined anatomically, the more numerous are such records
+found to be. Thus, for example, of all organisms that of man has been
+most minutely investigated by anatomists; and therefore I think it will
+be instructive to conclude this chapter by giving a list of the more
+noteworthy vestigial structures which are known to occur in the human
+body. I will take only those which are found in adult man, reserving for
+the next chapter those which occur in a transitory manner during earlier
+periods of his life. But, even as thus restricted, the number of
+obsolescent structures which we all present in our own persons is so
+remarkable, that their combined testimony to our descent from a
+quadrumanous ancestry appears to me in itself conclusive. I mean, that
+even if these structures stood alone, or apart from any more general
+evidences of our family relationships, they would be sufficient to prove
+our parentage. Nevertheless, it is desirable to remark that of course
+these special evidences which I am about to detail do not stand alone.
+Not only is there the general analogy furnished by the general proof of
+evolution elsewhere, but there is likewise the more special
+correspondence between the whole of our anatomy and that of our nearest
+zoological allies. Now the force of this latter consideration is so
+enormous, that no one who has not studied human anatomy can be in a
+position to appreciate it. For without special study it is impossible to
+form any adequate idea of the intricacy of structure which is presented
+by the human form. Yet it is found that this enormously intricate
+organization is repeated in all its details in the bodies of the higher
+apes. There is no bone, muscle, nerve, or vessel of any importance in
+the one which is not answered to by the other. Hence there are hundreds
+of thousands of instances of the most detailed correspondence, without
+there being any instances to the contrary, if we pay due regard to
+vestigial characters. The entire corporeal structure of man is an exact
+anatomical copy of that which we find in the ape.
+
+My object, then, here is to limit attention to those features of our
+corporeal structure which, having become useless on account of our
+change in attitude and habits, are in process of becoming obsolete, and
+therefore occur as mere vestigial records of a former state of things.
+For example, throughout the vertebrated series, from fish to mammals,
+there occurs in the inner corner of the eye a semi-transparent eye-lid,
+which is called the nictitating membrane. The object of this structure
+is to sweep rapidly, every now and then, over the external surface of
+the eye, apparently in order to keep the surface clean. But although the
+membrane occurs in all classes of the sub-kingdom, it is more prevalent
+in some than in others--e.g. in birds than in mammals. Even, however,
+where it does not occur of a size and mobility to be of any use, it is
+usually represented, in animals above fishes, by a functionless
+rudiment, as here depicted in the case of man. (Fig. 10.)
+
+ [Illustration: FIG. 10.--Illustrations of the nictitating membrane
+ in the various animals named drawn from nature. The letter N
+ indicates the membrane in each case. In man it is called the _plica
+ semilunaris_, and is represented in the two lower drawings under
+ this name. In the case of the shark (_Galeus_) the muscular
+ mechanism is shown as dissected.]
+
+Now the organization of man presents so many vestigial structures thus
+referring to various stages of his long ancestral history, that it would
+be tedious so much as to enumerate them. Therefore I will yet further
+limit the list of vestigial structures to be given as examples, by not
+only restricting these to cases which occur in our own organization; but
+of them I shall mention only such as refer us to the very last stage of
+our ancestral history--viz. structures which have become obsolescent
+since the time when our distinctively human branch of the family tree
+diverged from that of our immediate forefathers, the Quadrumana.
+
+(1) _Muscles of the external ear._--These, which are of large size and
+functional use in quadrupeds, we retain in a dwindled and useless
+condition (Fig. 11). This is likewise the case in anthropoid apes; but
+in not a few other Quadrumana (e.g. baboons, macacus, magots, &c.)
+degeneration has not proceeded so far, and the ears are voluntarily
+moveable.
+
+ [Illustration: FIG. 11.--Rudimentary, or vestigial and useless,
+ muscles of the human ear. (From _Gray's Anatomy_.)]
+
+(2) _Panniculus carnosis._--A large number of the mammalia are able to
+move their skin by means of sub-cutaneous muscle--as we see, for
+instance, in a horse, when thus protecting himself against the sucking
+of flies. We, in common with the Quadrumana, possess an active remnant
+of such a muscle in the skin of the forehead, whereby we draw up the
+eyebrows; but we are no longer able to use other considerable remnants
+of it, in the scalp and elsewhere,--or, more correctly, it is rarely
+that we meet with persons who can. But most of the Quadrumana (including
+the anthropoids) are still able to do so. There are also many other
+vestigial muscles, which occur only in a small percentage of human
+beings, but which, when they do occur, present unmistakeable homologies
+with normal muscles in some of the Quadrumana and still lower
+animals[5].
+
+ [5] See especially Mr. John Wood's papers, _Proc. R. S._, xiii to
+ xvi, and xviii; also _Journ. Anat._, i and iii. In this connexion
+ Darwin refers to M. Richard, _Annls. d. Sc. Nat. Zoolg._, tom.
+ xviii, p. 13, 1852.
+
+(3) _Feet._--It is observable that in the infant the feet have a strong
+deflection inwards, so that the soles in considerable measure face one
+another. This peculiarity, which is even more marked in the embryo than
+in the infant (see p. 153), and which becomes gradually less and less
+conspicuous even before the child begins to walk, appears to me a highly
+suggestive peculiarity. For it plainly refers to the condition of
+things in the Quadrumana, seeing that in all these animals the feet are
+similarly curved inwards, to facilitate the grasping of branches. And
+even when walking on the ground apes and monkeys employ to a great
+extent the outside edges of their feet, as does also a child when
+learning to walk. The feet of a young child are also extraordinarily
+mobile in all directions, as are those of apes. In order to show these
+points, I here introduce comparative drawings of a young ape and the
+portrait of a young male child. These drawings, moreover, serve at the
+same time to illustrate two other vestigial characters, which have
+often been previously noticed with regard to the infant's foot. I allude
+to the incurved form of the legs, and the lateral extension of the great
+toe, whereby it approaches the thumb-like character of this organ in the
+Quadrumana. As in the case of the incurved position of the legs and
+feet, so in this case of the lateral extensibility of the great toe, the
+peculiarity is even more marked in embryonic than in infant life. For,
+as Prof. Wyman has remarked with regard to the foetus when about an inch
+in length, "The great toe is shorter than the others; and, instead of
+being parallel to them, is projected at an angle from the side of the
+foot, thus corresponding with the permanent condition of this part in
+the Quadrumana[6]." So that this organ, which, according to Owen, "is
+perhaps the most characteristic peculiarity in the human structure,"
+when traced back to the early stages of its development, is found to
+present a notably less degree of peculiarity.
+
+ [6] _Proc. Nat. Hist. Soc._, Boston, 1863.
+
+ [Illustration: FIG. 12.--Portrait of a young male gorilla (after
+ Hartmann).]
+
+ [Illustration: FIG. 13.--Portrait of a young male child.
+ Photographed from life, when the mobile feet were for a short time
+ at rest in a position of extreme inflection.]
+
+(4) _Hands._--Dr. Louis Robinson has recently observed that the grasping
+power of the whole human hand is so surprisingly great at birth, and
+during the first few weeks of infancy, as to be far in excess of present
+requirements on the part of a young child. Hence he concludes that it
+refers us to our quadrumanous ancestry--the young of anthropoid apes
+being endowed with similar powers of grasping, in order to hold on to
+the hair of the mother when she is using her arms for the purposes of
+locomotion. This inference appears to me justifiable, inasmuch as no
+other explanation can be given of the comparatively inordinate muscular
+force of an infant's grip. For experiments showed that very young babies
+are able to support their own weight, by holding on to a horizontal bar,
+for a period varying from one half to more than two minutes[7]. With his
+kind permission I here reproduce one of Dr. Robinson's instantaneous,
+and hitherto unpublished, photographs of a very young infant. This
+photograph was taken after the above paragraph (3) was written, and I
+introduce it here because it serves to show incidentally--and perhaps
+even better than the preceding figure--the points there mentioned with
+regard to the feet and great toes. Again, as Dr. Robinson observes, the
+attitude, and the disproportionately large development of the arms as
+compared with the legs, give all the photographs a striking resemblance
+to a picture of the chimpanzee "Sally" at the Zoological Gardens. For
+"invariably the thighs are bent nearly at right angles to the body, and
+in no case did the lower limbs hang down and take the attitude of the
+erect position." He adds, "In many cases no sign of distress is evinced,
+and no cry uttered, until the grasp begins to give way."
+
+ [7] _Nineteenth Century_, November, 1891.
+
+ [Illustration: FIG. 14.--An infant, three weeks old, supporting its
+ own weight for over two minutes. The attitude of the lower limbs,
+ feet, and toes, is strikingly simian. Reproduced from an
+ instantaneous photograph, kindly given for the purpose by Dr. L.
+ Robinson.]
+
+(5) _Tail._--The absence of a tail in man is popularly supposed to
+constitute a difficulty against the doctrine of his quadrumanous
+descent. As a matter of fact, however, the absence of an external tail
+in man is precisely what this doctrine would expect, seeing that the
+nearest allies of man in the quadrumanous series are likewise destitute
+of an external tail. Far, then, from this deficiency in man constituting
+any difficulty to be accounted for, if the case were not so--i. e. if
+man _did_ possess an external tail,--the difficulty would be to
+understand how he had managed to retain an organ which had been
+renounced by his most recent ancestors. Nevertheless, as the anthropoid
+apes continue to present the rudimentary vestiges of a tail in a few
+caudal vertebræ below the integuments, we might well expect to find a
+similar state of matters in the case of man. And this is just what we do
+find, as a glance at these two comparative illustrations will show.
+(Fig. 15.) Moreover, during embryonic life, both of the anthropoid apes
+and of man, the tail much more closely resembles that of the lower kinds
+of quadrumanous animals from which these higher representatives of the
+group have descended. For at a certain stage of embryonic life the tail,
+both of apes and of human beings, is actually longer than the legs (see
+Fig. 16). And at this stage of development, also, the tail admits of
+being moved by muscles which later on dwindle away. Occasionally,
+however, these muscles persist, and are then described by anatomists as
+abnormalities. The following illustrations serve to show the muscles in
+question, when thus found in adult man.
+
+ [Illustration: FIG. 15.--Sacrum of Gorilla compared with that of
+ Man, showing the rudimentary tail-bones of each. Drawn from nature
+ (_R. Coll. Surg. Mus._).]
+
+ [Illustration: FIG. 16.--Diagrammatic outline of the human embryo
+ when about seven weeks old, showing the relations of the limbs and
+ tail to the trunk (after Allen Thomson), _r_, the radial, and _u_,
+ the ulnar, border of the hand and fore-arm; _t_, the tibial, and
+ _f_, the fibular, border of the foot and lower leg; _au_, ear; _s_,
+ spinal cord; _v_, umbilical cord; _b_, branchial gill-slits; _c_,
+ tail.]
+
+ [Illustration: FIG. 17.--Front and back view of adult human sacrum,
+ showing abnormal persistence of vestigial tail-muscles. (The first
+ drawing is copied from Prof. Watson's paper in _Journl. Anat. and
+ Physiol._, vol. 79: the second is compiled from different
+ specimens.)]
+
+(6) _Vermiform Appendix of the Cæcum._--This is of large size and
+functional use in the process of digestion among many herbivorous
+animals; while in man it is not only too small to serve any such
+purpose, but is even a source of danger to life--many persons dying
+every year from inflammation set up by the lodgement in this blind tube
+of fruit-stones, &c.
+
+In the orang it is longer than in man (Fig. 18), as it is also in the
+human foetus proportionally compared with the adult. (Fig. 19.) In
+some of the lower herbivorous animals it is longer than the entire body.
+
+Like vestigial structures in general, however, this one is highly
+variable. Thus the above cut (Fig. 19) serves to show that it may
+sometimes be almost as short in the orang as it normally is in man--both
+the human subjects of this illustration having been normal.
+
+ [Illustration: FIG. 18.--_Appendix vermiformis_ in Orang and in Man.
+ Drawn from dried inflated specimens in the Cambridge Museum by Mr.
+ J. J. Lister. _Il_, ilium; _Co_, colon; _C_, cæcum; W, a window cut
+ in the wall of the cæcum; X X X, the appendix.]
+
+ [Illustration: FIG. 19.--The same, showing variation in the Orang.
+ Drawn from a specimen in the Museum of the Royal College of
+ Surgeons.]
+
+(7) _Ear._--Mr. Darwin writes:--
+
+ The celebrated sculptor, Mr. Woolner, informs me of one little
+ peculiarity in the external ear, which he has often observed both
+ in men and women.... The peculiarity consists in a little blunt
+ point, projecting from the inwardly folded margin, or helix. When
+ present, it is developed at birth, and, according to Prof. Ludwig
+ Meyer, more frequently in man than in woman. Mr. Woolner made an
+ exact model of one such case, and sent me the accompanying
+ drawing.... The helix obviously consists of the extreme margin of
+ the ear folded inwards; and the folding appears to be in some
+ manner connected with the whole external ear being permanently
+ pressed backwards. In many monkeys, which do not stand high in the
+ order, as baboons and some species of macacus, the upper portion of
+ the ear is slightly pointed, and the margin is not at all folded
+ inwards; but if the margin were to be thus folded, a slight point
+ would necessarily project towards the centre.... The following
+ wood-cut is an accurate copy of a photograph of the foetus of an
+ orang (kindly sent me by Dr. Nitsche), in which it may be seen how
+ different the pointed outline of the ear is at this period from its
+ adult condition, when it bears a close general resemblance to that
+ of man [including even the occasional appearance of the projecting
+ point shown in the preceding woodcut]. It is evident that the
+ folding over of the tip of such an ear, unless it changed greatly
+ during its further development, would give rise to a point
+ projecting inwards[8].
+
+ [8] _Descent of Man_, 2nd ed., pp. 15-16.
+
+ [Illustration: FIG. 20.--Human ear, modelled and drawn by Mr.
+ Woolner. _a_, the projecting point.]
+
+ [Illustration: FIG. 21.--Foetus of an Orang. Exact copy of a
+ photograph, showing the form of the ear at this early stage.]
+
+The following woodcut serves still further to show vestigial
+resemblances between the human ear and that of apes. The last two
+figures illustrate the general resemblance between the normal ear of
+foetal man and the ear of an adult orang-outang. The other two figures
+on the lower line are intended to exhibit occasional modifications of
+the adult human ear, which approximate simian characters somewhat more
+closely than does the normal type. It will be observed that in their
+comparatively small lobes these ears resemble those of all the apes; and
+that while the outer margin of one is not unlike that of the Barbary
+ape, the outer margin of the other follows those of the chimpanzee and
+orang. Of course it would be easy to select individual human ears which
+present either of these characters in a more pronounced degree; but
+these ears have been chosen as models because they present both
+characters in conjunction. The upper row of figures likewise shows the
+close similarity of hair-tracts, and the direction of growth on the part
+of the hair itself, in cases where the human ear happens to be of an
+abnormally hirsute character. But this particular instance (which I do
+not think has been previously noticed) introduces us to the subject of
+hair, and hair-growth, in general.
+
+ [Illustration: FIG. 22.--Vestigial characters of human ears. Drawn
+ from nature.]
+
+(8) _Hair._--Adult man presents rudimentary hair over most parts of the
+body. Wallace has sought to draw a refined distinction between this
+vestigial coating and the useful coating of quadrumanous animals, in the
+absence of the former from the human back. But even this refined
+distinction does not hold. On the one hand, the comparatively hairless
+chimpanzee which died last year in the Zoological Gardens (_T. calvus_)
+was remarkably denuded over the back; and, on the other hand, men who
+present a considerable development of hair over the rest of their bodies
+present it also on their backs and shoulders. Again, in all men the
+rudimentary hair on the upper and lower arm is directed towards the
+elbow--a peculiarity which occurs nowhere else in the animal kingdom,
+with the exception of the anthropoid apes and a few American monkeys,
+where it presumably has to do with arboreal habits. For, when sitting in
+trees, the orang, as observed by Mr. Wallace, places its hands above its
+head with its elbows pointing downwards: the disposition of hair on
+the arms and fore-arms then has the effect of thatch in turning the
+rain. Again, I find that in all species of apes, monkeys, and baboons
+which I have examined (and they have been numerous), the hair on the
+backs of the hands and feet is continued as far as the first row of
+phalanges; but becomes scanty, or disappears altogether, on the second
+row; while it is invariably absent on the terminal row. I also find that
+the same peculiarity occurs in man. We all have rudimentary hair on the
+first row of phalanges, both of hands and feet: when present at all, it
+is more scanty on the second row; and in no case have I been able to
+find any on the terminal row. In all cases these peculiarities are
+congenital, and the total absence or partial presence of hair on the
+second phalanges is constant in different species of Quadrumana. For
+instance, it is entirely absent in all the chimpanzees, which I have
+examined, while scantily present in all the orangs. As in man, it occurs
+in a patch midway between the joints.
+
+ [Illustration: FIG. 23.--Hair-tracts on the arms and hands of Man,
+ as compared with those on the arms and hands of Chimpanzee. Drawn
+ from life.]
+
+Besides showing these two features with regard to the disposition of
+hair on the human arm and hand, the above woodcut illustrates a third.
+By looking closely at the arm of the very hairy man from whom the
+drawing was taken, it could be seen that there was a strong tendency
+towards a whorled arrangement of the hairs on the backs of the wrists.
+This is likewise, as a general rule, a marked feature in the arrangement
+of hair on the same places in the gorilla, orang, and chimpanzee. In the
+specimen of the latter, however, from which the drawing was taken, this
+characteristic was not well marked. The downward direction of the hair
+on the backs of the hands is exactly the same in man as it is in all
+the anthropoid apes. Again, with regard to hair, Darwin notices that
+occasionally there appears in man a few hairs in the eyebrows much
+longer than the others; and that they seem to be representative of
+similarly long and scattered hairs which occur in the chimpanzee,
+macacus, and baboons.
+
+Lastly, it may be here more conveniently observed than in the next
+chapter on Embryology, that at about the sixth month the human foetus
+is often thickly coated with somewhat long dark hair over the entire
+body, except the soles of the feet and palms of the hands, which are
+likewise bare in all quadrumanous animals. This covering, which is
+called the lanugo, and sometimes extends even to the whole forehead,
+ears, and face, is shed before birth. So that it appears to be useless
+for any purpose other than that of emphatically declaring man a child of
+the monkey.
+
+(9) _Teeth._--Darwin writes:--
+
+ It appears as if the posterior molar or wisdom-teeth were tending
+ to become rudimentary in the more civilized races of man. These
+ teeth are rather smaller than the other molars, as is likewise the
+ case with the corresponding teeth in the chimpanzee and orang; and
+ they have only two separate fangs.... They are also much more
+ liable to vary, both in structure and in the period of their
+ development, than the other teeth. In the Melanian races, on the
+ other hand, the wisdom-teeth are usually furnished with three
+ separate fangs, and are usually sound [i. e. not specially liable
+ to decay]; they also differ from the other molars in size, less
+ than in the Caucasian races.
+
+Now, in addition to these there are other respects in which the
+dwindling condition of wisdom-teeth is manifested--particularly with
+regard to the pattern of their crowns. Indeed, in this respect it would
+seem that even in the anthropoid apes there is the beginning of a
+tendency to degeneration of the molar teeth from behind forwards. For if
+we compare the three molars in the lower jaw of the gorilla, orang, and
+chimpanzee, we find that the gorilla has five well-marked cusps on all
+three of them; but that in the orang the cusps are not so pronounced,
+while in the chimpanzee there are only four of them on the third molar.
+Now in man it is only the first of these three teeth which normally
+presents five cusps, both the others presenting only four. So that,
+comparing all these genera together, it appears that the number of
+cusps is being reduced from behind forwards; the chimpanzee having lost
+one of them from the third molar, while man has not only lost this, but
+also one from the second molar,--and, it may be added, likewise
+partially (or even totally) from the first molar, as a frequent
+variation among civilized races. But, on the other hand, variations are
+often met with in the opposite direction, where the second or the third
+molar of man presents five cusps--in the one case following the
+chimpanzee, in the other the gorilla. These latter variations,
+therefore, may fairly be regarded as reversionary. For these facts I am
+indebted to the kindness of Mr. C. S. Tomes.
+
+ [Illustration: FIG. 24.--Molar teeth of lower jaw in Gorilla, Orang,
+ and Man. Drawn from nature, nat. size (_R. Mus. Coll. Surg._).]
+
+(10) _Perforations of the humerus._--The peculiarities which we have to
+notice under this heading are two in number. First, the supra condyloid
+foramen is a normal feature in some of the lower Quadrumana (Fig. 25),
+where it gives passage to the great nerve of the fore-arm, and often
+also to the great artery. In man, however, it is not a normal feature.
+Yet it occurs in a small percentage of cases--viz., according to Sir W.
+Turner, in about one per cent., and therefore is regarded by Darwin as a
+vestigial character. Secondly, there is inter-condyloid foramen, which
+is also situated near the lower end of the humerus, but more in the
+middle of the bone. This occurs, but not constantly, in apes, and also
+in the human species. From the fact that it does so much more frequently
+in the bones of ancient--and also of some savage--races of mankind (viz.
+in 20 to 30 per cent. of cases), Darwin is disposed to regard it also as
+a vestigial feature. On the other hand, Prof. Flower tells me that in
+his opinion it is but an expression of impoverished nutrition during
+the growth of the bone.
+
+ [Illustration: FIG. 25.--Perforation of the humerus (supra-condyloid
+ foramen) in three species of Quadrumana where it normally occurs,
+ and in Man, where it does not normally occur. Drawn from nature (_R.
+ Coll. Surg. Mus._).]
+
+(11) _Flattening of tibia._--In some very ancient human skeletons, there
+has also been found a lateral flattening of the tibia, which rarely
+occurs in any existing human beings, but which appears to have been
+usual among the earliest races of mankind hitherto discovered. According
+to Broca, the measurements of these fossil human tibiæ resemble those of
+apes. Moreover, the bone is bent and strongly convex forwards, while its
+angles are so rounded as to present the nearly oval section seen in
+apes. It is in association with these ape-like human tibiæ that
+perforated humeri of man are found in greatest abundance.
+
+On the other hand, however, there is reason to doubt whether this form
+of tibia in man is really a survival from his quadrumanous ancestry.
+For, as Boyd-Dawkins and Hartmann have pointed out, the degree of
+flattening presented by some of these ancient human bones is _greater_
+than that which occurs in any existing species of anthropoid ape. Of
+course the possibility remains that the unknown species of ape from
+which man descended may have had its tibia more flattened than is now
+observable in any of the existing species. Nevertheless, as some doubt
+attaches to this particular case, I do not press it--and, indeed, only
+mention it at all in order that the doubt may be expressed.
+
+Similarly, I will conclude by remarking that several other instances of
+the survival of vestigial structures in man have been alleged, which are
+of a still more doubtful character. Of such, for example, are the
+supposed absence of the genial tubercle in the case of a very ancient
+jaw-bone of man, and the disposition of valves in human veins. From the
+former it was argued that the possessor of this very ancient jaw-bone
+was probably speechless, inasmuch as the tubercle in existing man gives
+attachment to muscles of the tongue. From the latter it has been argued
+that all the valves in the veins of the human body have reference, in
+their disposition, to the incidence of blood-pressure when the attitude
+of the body is horizontal, or quadrupedal. Now, the former case has
+already broken down, and I find that the latter does not hold. But we
+can well afford to lose such doubtful and spurious cases, in view of all
+the foregoing unquestionable and genuine cases of vestigial structures
+which are to be met with even within the limits of our own
+organization--and even when these limits are still further limited by
+selecting only those instances which refer to the very latest chapter of
+our long ancestral history.
+
+
+
+
+CHAPTER IV.
+
+EMBRYOLOGY.
+
+
+We will next consider what of late years has become the most important
+of the lines of evidence, not only in favour of the general fact of
+evolution, but also of its history: I mean the evidence which has been
+yielded by the newest of the sciences, the science of Embryology. But
+here, as in the analogous case of adult morphology, in order to do
+justice to the mass of evidence which has now been accumulated, a whole
+volume would be necessary. As in that previous case, therefore, I must
+restrict myself to giving an outline sketch of the main facts.
+
+First I will display what in the language of Paley we may call "the
+state of the argument."
+
+It is an observable fact that there is often a close correspondence
+between developmental changes as revealed by any chronological series of
+fossils which may happen to have been preserved, and developmental
+changes which may be observed during the life-history of now existing
+individuals belonging to the same group of animals. For instance, the
+successive development of prongs in the horns of deer-like animals,
+which is so clearly shown in the geological history of this tribe, is
+closely reproduced in the life-history of existing deer. Or, in other
+words, the antlers of an existing deer furnish in their development a
+kind of _résumé_, or recapitulation, of the successive phases whereby
+the primitive horn was gradually superseded by horns presenting a
+greater and greater number of prongs in successive species of extinct
+deer (Fig. 26). Now it must be obvious that such a recapitulation in the
+life-history of an existing animal of developmental changes successively
+distinctive of sundry allied, though now extinct species, speaks
+strongly in favour of evolution. For as it is of the essence of this
+theory that new forms arise from older forms by way of _hereditary_
+descent, we should antecedently expect, if the theory is true, that the
+phases of development presented by the individual organism would follow,
+in their main outlines, those phases of development through which their
+long line of ancestors had passed. The only alternative view is that as
+species of deer, for instance, were separately created, additional
+prongs were successively added to their antlers; and yet that, in order
+to be so added to successive species every individual deer belonging to
+later species was required to repeat in his own lifetime the process of
+successive additions which had previously taken place in a remote series
+of extinct species. Now I do not deny that this view is a possible view;
+but I do deny that it is a probable one. According to the evolutionary
+interpretation of such facts, we can see a very good _reason_ why the
+life-history of the individual is thus a condensed _résumé_ of the
+life-history of its ancestral species. But according to the opposite
+view no reason can be assigned why such should be the case. In a
+previous chapter--the chapter on Classification--we have seen that if
+each species were created separately, no reason can be assigned why they
+should all have been turned out upon structural patterns so strongly
+suggestive of hereditary descent with gradual modifications, or slow
+divergence--the result being group subordinated to group, with the most
+generalized (or least developed) forms at the bottom, and the highest
+products of organization at the top. And now we see--or shall
+immediately see--that this consideration admits of being greatly
+fortified by a study of the developmental history of every individual
+organism. If it would be an unaccountable fact that every separately
+created species should have been created with close structural
+resemblances to a certain limited number of other species, less close
+resemblances to certain further species, and so backwards; assuredly it
+would be a still more unaccountable fact that every individual of every
+species should exhibit in its own person a history of developmental
+change, every term of which corresponds with the structural
+peculiarities of its now extinct predecessors--and this in the exact
+historical order of their succession in geological time. The more that
+we think about this antithesis between the naturalistic and the
+non-naturalistic interpretations, the greater must we feel the contrast
+in respect of rationality to become; and, therefore, I need not spend
+time by saying anything further upon the antecedent standing of the two
+theories in this respect. The evidence, then, which I am about to adduce
+from the study of development in the life-histories of individual
+organisms, will be regarded by me as so much unquestionable evidence in
+favour of similar processes of development in the life-histories of
+their respective species--in so far, I mean, as the two sets of changes
+admit of being proved parallel.
+
+ [Illustration: FIG. 26.--Antlers of Stag, showing successive
+ addition of branches in successive years. Drawn from nature (_Brit.
+ Mus._).]
+
+In the only illustration hitherto adduced--viz. that of deers'
+horns--the series of changes from a one-pronged horn to a fully
+developed arborescent antler, is a series which takes place during the
+adult life of the animal; for it is only when the breeding age has been
+attained that horns are required to appear. But seeing that every animal
+passes through most of the phases of its development, not only before
+the breeding age has been attained, but even before the time of its own
+birth, clearly the largest field for the study of individual development
+is furnished by embryology. For instance, there is a salamander which
+differs from most other salamanders in being exclusively terrestrial in
+its habits. Now, the young of this salamander before their birth are
+found to be furnished with gills, which, however, they are never
+destined to use. Yet these gills are so perfectly formed, that if the
+young salamanders be removed from the body of their mother shortly
+before birth, and be then immediately placed in water, the little
+animals show themselves quite capable of aquatic respiration, and will
+merrily swim about in a medium which would quickly drown their own
+parent. Here, then, we have both morphological and physiological
+evidence pointing to the possession of gills by the ancestors of the
+land salamander.
+
+It would be easy to devote the whole of the present chapter to an
+enumeration of special instances of the kinds thus chosen for purposes
+of illustration; but as it is desirable to take a deeper, and therefore
+a more general view of the whole subject, I will begin at the
+foundation, and gradually work up from the earliest stages of
+development to the latest. Before starting, however, I ask the reader to
+bear in mind one consideration, which must reasonably prevent our
+anticipating that in _every case_ the life-history of an individual
+organism should present a _full_ recapitulation of the life-history of
+its ancestral line of species. Supposing the theory of evolution to be
+true, it must follow that in many cases it would have been more or less
+disadvantageous to a developing type that it should have been obliged to
+reproduce in its individual representatives all the phases of
+development previously undergone by its ancestry--even within the limits
+of the same family. We can easily understand, for example, that the
+waste of material required for building up the useless gills of the
+embryonic salamanders is a waste which, sooner or later, is likely to be
+done away with; so that the fact of its occurring at all is in itself
+enough to show that the change from aquatic to terrestrial habits on the
+part of this species must have been one of comparatively recent
+occurrence. Now, in as far as it is detrimental to a developing type
+that it should pass through any particular ancestral phases of
+development, we may be sure that natural selection--or whatever other
+adjustive causes we may suppose to have been at work in the adaptation
+of organisms to their surroundings--will constantly seek to get rid of
+this necessity, with the result, when successful, of dropping out the
+detrimental phases. Thus the foreshortening of developmental history
+which takes place in the individual lifetime may be expected often to
+take place, not only in the way of condensation, but also in the way of
+excision. Many pages of ancestral history may be recapitulated in the
+paragraphs of embryonic development, while others may not be so much as
+mentioned. And that this is the true explanation of what embryologists
+term "direct" development--or of a more or less sudden leap from one
+phase to another, without any appearance of intermediate phases--is
+proved by the fact that in some cases both direct and indirect
+development occur within the same group of organisms, some genera or
+families having dropped out the intermediate phases which other genera
+or families retain.
+
+ * * * * *
+
+The argument from embryology must be taken to begin with the first
+beginning of individual life in the ovum. And, in order to understand
+the bearings of the argument in this its first stage, we must consider
+the phenomena of reproduction in the simplest form which these phenomena
+are known to present.
+
+The whole of the animal kingdom is divided into two great groups, which
+are called the Protozoa and the Metazoa. Similarly, the whole of the
+vegetable kingdom is divided into the Protophyta and the Metaphyta. The
+characteristic feature of all the Protozoa and Protophyta is that the
+organism consists of a single physiological cell, while the
+characteristic of all the Metazoa and Metaphyta is that the organism
+consists of a plurality of physiological cells, variously modified to
+subserve different functions in the economy of the animal or plant, as
+the case may be. For the sake of brevity, I shall hereafter deal only
+with the case of animals (Protozoa and Metazoa); but it may throughout
+be understood that everything which is said applies also to the case of
+plants (Protophyta and Metaphyta).
+
+A Protozoön (like a Protophyton) is a solitary cell, or a "unicellular
+organism," while a Metazoön (like a Metaphyton) is a society of cells,
+or a "multicellular organism." Now, it is only in the multicellular
+organisms that there is any observable distinction of sex. In all the
+unicellular organisms the phenomena of reproduction appear to be more or
+less identical with those of growth. Nevertheless, as these phenomena
+are here in some cases suggestively peculiar, I will consider them more
+in detail.
+
+A Protozoön is a single corpuscle of protoplasm which in different
+species of Protozoa varies in size from more than one inch to less than
+1/1000 of an inch in diameter. In some species there is an enveloping
+cortical substance; in other species no such substance can be detected.
+Again, in most species there is a nucleus, while in other species no
+such differentiation of structure has hitherto been observed.
+Nevertheless, from the fact that the nucleus occurs in the majority of
+Protozoa, coupled with the fact that the demonstration of this body is
+often a matter of extreme difficulty, not only in some of the Protozoa
+where it has been but recently detected, but also in the case of certain
+physiological cells elsewhere,--from these facts it is not unreasonable
+to suppose that all the Protozoa possess a nucleus, whether or not it
+admits of being rendered visible by histological methods thus far at our
+disposal. If this is the case, we should be justified in saying, as I
+have said, that a Protozoön is an isolated physiological cell, and, like
+cells in general, multiplies by means of what Spencer and Häckel have
+aptly called a process of discontinuous growth. That is to say, when a
+cell reaches maturity, further growth takes place in the direction of a
+severance of its substance--the separated portion thus starting anew as
+a distinct physiological unit. But, notwithstanding the complex changes
+which have been more recently observed to take place in the nucleus of
+some Protozoa prior to their division, the process of multiplication by
+division may still be regarded as a process of growth, which differs
+from the previous growth of the individual cell in being attended by a
+severance of continuity. If we take a suspended drop of gum, and
+gradually add to its size by allowing more and more gum to flow into it,
+a point will eventually be reached at which the force of gravity will
+overcome that of cohesion, and a portion of the drop will fall away from
+the remainder. Here we have a rough physical simile, although of course
+no true analogy. In virtue of a continuous assimilation of nutriment,
+the protoplasm of a cell increases in mass, until it reaches the size at
+which the forces of disruption overcome those of cohesion--or, in other
+words, the point at which increase of size is no longer compatible with
+continuity of substance. Nevertheless, it must not be supposed that the
+process is thus merely a physical one. The phenomena which occur even in
+the simplest--or so-called "direct"--cell-division, are of themselves
+enough to prove that the process is vital, or physiological; and this in
+a high degree of specialization. But so, likewise, are all processes of
+growth in organic structures; and therefore the simile of the drop of
+gum is not to be regarded as a true analogy: it serves only to indicate
+the fact that when cell-growth proceeds beyond a certain point
+cell-division ensues. The size to which cells may grow before they thus
+divide is very variable in different kinds of cells; for while some may
+normally attain a length of ten or twelve inches, others divide before
+they measure 1/1000 of an inch. This, however, is a matter of detail,
+and does not affect the general physiological principles on which we are
+at present engaged.
+
+Now, as we have seen, a Protozoön is a single cell; for even although in
+some of the higher forms of protozoal life a colony of cells may be
+bound together in organic connexion, each of these cells is in itself an
+"individual," capable of self-nourishment, reproduction, and, generally,
+of independent existence. Consequently, when the growth of a Protozoön
+ends in a division of its substance, the two parts wander away from each
+other as separate organisms. (Fig. 27.)
+
+ [Illustration: FIG. 27.--Fission of a Protozoön. In the left-hand
+ drawing the process is represented as having advanced sufficiently
+ far to have caused a division and segregation both of the nucleus
+ and the vesicle. In the right-hand drawing the process is
+ represented as complete. _n_, N, severed nucleus; _vc_, severed
+ vesicle; _ps_, pseudopodia; _f_, ingested food.]
+
+The next point we have to observe is, that in all cases where a cell or
+a Protozoön multiplies by way of fissiparous division, the process
+begins in the nucleus. If the nucleus divides into two parts, the whole
+cell will eventually divide into two parts, each of which retains a
+portion of the original nucleus, as represented in the above figure. If
+the nucleus divides into three, four, or even, as happens in the
+development of some embryonic tissues, into as many as six parts, the
+cell will subdivide into a corresponding number, each retaining a
+portion of the nucleus. Therefore, in all cases of fissiparous division,
+the seat or origin of the process is the nucleus.
+
+Thus far, then, the phenomena of multiplication are identical in all the
+lowest or unicellular organisms, and in the constituent cells of all the
+higher or multicellular. And this is the first point which I desire to
+make apparent. For where the object is to prove a continuity between the
+phenomena of growth and reproduction, it is of primary importance to
+show--1st, that there is such a continuity in the case of all the
+unicellular organisms, and, 2nd, that there are all the above points of
+resemblance between the multiplication of cells in the unicellular and
+in the multicellular organisms.
+
+It remains to consider the points of difference, and, if possible, to
+show that these do not go to disprove the doctrine of continuity which
+the points of resemblance so forcibly indicate.
+
+The first point of difference obviously is, that in the case of all the
+multicellular organisms the two or more "daughter-cells," which are
+produced by division of the "mother-cell," do not wander away from one
+another; but, as a rule, they continue to be held in more or less close
+apposition by means of other cells and binding membranes,--with the
+result of giving rise to those various "tissues," which in turn go to
+constitute the material of "organs." I cannot suppose, however, that any
+advocate of discontinuity will care to take his stand at this point.
+But, if any one were so foolish as to do so, it would be easy to
+dislodge him by describing the state of matters in some of the Protozoa
+where a number of unicellular "individuals" are organically united so as
+to form a "colony." These cases serve to bridge this distinction between
+Protozoa and Metazoa, of which therefore we may now take leave.
+
+In the second place, there is the no less obvious distinction that the
+result of cell-division in the Metazoa is not merely to multiply cells
+all of the same kind: on the contrary, the process here gives rise to as
+many different kinds of cells as there are different kinds of tissue
+composing the adult organism. But no one, I should think, is likely to
+oppose the doctrine of continuity on the ground of this distinction. For
+the distinction is clearly one which must necessarily arise, if the
+doctrine of continuity between unicellular and multicellular organisms
+be true. In other words, it is a distinction which the theory of
+evolution itself must necessarily pre-suppose, and therefore it is no
+objection to the theory that its pre-supposition is realized. Moreover,
+as we shall see better presently, there is no difficulty in
+understanding why this distinction should have arisen, so soon as it
+became necessary (or desirable) that individual cells, when composing a
+"colony," should conform to the economic principle of the division of
+labour--a principle, indeed, which is already foreshadowed in the
+constituent parts of a single cell, since the nucleus has one set of
+functions and its surrounding protoplasm another.
+
+But now, in the third place, we arrive at a more important distinction,
+and one which lies at the root of the others still remaining to be
+considered. I refer to sexual propagation. For it is a peculiarity of
+the multicellular organisms that, although many of them may likewise
+propagate themselves by other means (Fig. 28), they all propagate
+themselves by means of sexual congress. Now, in its essence, sexual
+congress consists in the fusion of two specialized cells (or, as now
+seems almost certain, of the nuclei thereof), so that it is out of such
+a combination that the new individual arises by means of successive
+cell-divisions, which, beginning in the fertilized ovum, eventually
+build up all the tissues and organs of the body.
+
+ [Illustration: FIG. 28.--_Hydra viridis_, partly in section. M,
+ mouth; O, ovary, or bud containing female reproductive cells; T,
+ testis, or bud containing male reproductive cells. In addition to
+ these buds containing germinal elements alone, there is another
+ which illustrates the process of "gemmation"--i. e. the direct
+ out-growth of a fully formed offspring.]
+
+This process clearly indicates very high specialization on the part of
+germ-cells. For we see by it that although these cells when young
+resemble all other cells in being capable of self-multiplication by
+binary division (thus reproducing cells exactly like themselves), when
+older they lose this power; but, at the same time, they acquire an
+entirely new and very remarkable power of giving rise to a vast
+succession of many different kinds of cells, all of which are mutually
+correlated as to their several functions, so as to constitute a
+hierarchy of cells--or, to speak literally, a multicellular
+_co-organization_. Here it is that we touch the really important
+distinction between the Protozoa and the Metazoa; for although I have
+said that some of the higher Protozoa foreshadow this state of matters
+in forming cell-colonies, it must now be noted that the cells composing
+such colonies are all of the same kind; and, therefore, that the
+principle of producing different kinds of cells which, by mutual
+co-adaptation of functions, shall be capable of constructing a
+multicellular Metazoön,--this great principle of _co-organization_ is
+but dimly nascent in the cell-colonies of Protozoa. And its marvellous
+development in the Metazoa appears ultimately to depend upon the highly
+specialized character of germ-cells. Even in cases where multicellular
+organisms are capable of reproducing their kind without the need of any
+preceding process of fertilization (parthenogenesis), and even in the
+still more numerous cases where complete organisms are budded forth from
+any part of their parent organism (gemmation, Fig. 28), there is now
+very good reason to conclude that these powers of a-sexual reproduction
+on the part of multicellular organisms are all ultimately due to the
+specialized character of their germ-cells. For in all these cases the
+tissues of the parent, from which the budding takes place, were
+ultimately derived from germ-cells--no matter how many generations of
+budded organisms may have intervened. And that propagation by budding,
+&c, in multicellular organisms is thus ultimately due to their
+propagation by sexual methods, seems to be further shown by certain
+facts which will have to be discussed at some length in my next volume.
+Here, therefore, I will mention only one of them--and this because it
+furnishes what appears to be another important distinction between the
+Protozoa and the Metazoa.
+
+In nearly all cases where a Protozoön multiplies itself by fission, the
+process begins by a simple division of the nucleus. But when a Metazoön
+is developed from a germ-cell, although the process likewise begins by a
+division of the nucleus, this division is not a simple or direct one; on
+the contrary, it is inaugurated by a series of processes going on within
+the nucleus, which are so enormously complex, and withal so beautifully
+ordered, that to my mind they constitute the most wonderful--if not also
+the most suggestive--which have ever been revealed by microscopical
+research. It is needless to say that I refer to the phenomena of
+karyokinesis. A few pages further on they will be described more fully.
+For our present purposes it is sufficient to give merely a pictorial
+illustration of their successive phases; for a glance at such a
+representation serves to reveal the only point to which attention has
+now to be drawn--namely, the immense complexity of the processes in
+question, and therefore the contrast which they furnish to the simple
+(or "direct") division of the nucleus preparatory to cell-division in
+the unicellular organisms. Here, then (Fig. 29), we see the complex
+processes of karyokinesis in the first two stages of egg-cell division.
+But similar processes continue to repeat themselves in subsequent
+stages; and this, there is now good reason to believe, throughout _all_
+the stages of cell-division, whereby the original egg-cell eventually
+constructs an entire organism. In other words, all the cells composing
+all the tissues of a multicellular organism, at all stages of its
+development, are probably originated by these complex processes, which
+differ so much from the simple process of direct division in the
+unicellular organisms[9]. In this important respect, therefore, it does
+at first sight appear that we have a distinction between the Protozoa
+and the Metazoa of so pronounced a character, as fairly to raise the
+question whether cell-division is fundamentally identical in unicellular
+and in multicellular organisms.
+
+ [9] I say "probably," because analogy points in this direction. As a
+ matter of fact, in many cases of tissue-formation karyokinesis has
+ not hitherto been detected. But even if in such cases it does not
+ occur--i. e. if failure to detect its occurrence be not due merely
+ to still remaining imperfections of our histological methods,--the
+ large number of cases in which it has been seen to occur in the
+ formation of sundry tissues are of themselves sufficient to indicate
+ some important difference between cells derived from ova (metazoal),
+ and cells which have not been so derived (protozoal). Which is the
+ point now under discussion.
+
+ [Illustration: FIG. 29.--Successive stages in the division of the
+ ovum, or egg-cell, of a worm. (After Strasburger.) _a_ to _d_ show
+ the changes taking place in the nucleus and surrounding
+ cell-contents, which result in the first segmentation of the ovum at
+ _e_; _f_ and _g_ show a repetition of these changes in each of the
+ two resulting cells, leading to the second segmentation stage at
+ _h_.]
+
+Lastly, the only other distinction of a physiologically significant kind
+between a single cell when it occurs as a Protozoön and when it does so
+as the unfertilized ovum of a Metazoön is, that in the latter case the
+nucleus discharges from its own substance two minute protoplasmic masses
+("polar bodies"), which are then eliminated from the cell altogether.
+This process, which will be more fully described later on, appears to be
+of invariable occurrence in the case of all egg-cells, while nothing
+resembling it has ever been observed in any of the Protozoa.
+
+We must now consider these several points of difference _seriatim_.
+
+First, with regard to sexual propagation, we have already seen that this
+is by no means the only method of propagation among the multicellular
+organisms; and it now remains to add that, on the other hand, there is,
+to say the least, a suggestive foreshadowing of sexual propagation among
+the unicellular organisms. For although simple binary fission is here
+the more usual mode of multiplication, very frequently two (rarely three
+or more) Protozoa of the same species come together, fuse into a single
+mass, and thus become very literally "one flesh." This process of
+"conjugation" is usually (though by no means invariably) followed by a
+period of quiescent "encystation"; after which the contents of the cyst
+escape in the form of a number of minute particles, or "spores," and
+these severally develope into the parent type. Obviously this process of
+conjugation, when it is thus a preliminary to multiplication, appears to
+be in its essence the same as fertilization. And if it be objected that
+encystation and spore-formation in the Protozoa are not always preceded
+by conjugation, the answer would be that neither is oviparous
+propagation in the Metazoa invariably preceded by fertilization.
+
+Nevertheless, that there are great distinctions between true sexual
+propagation and this foreshadowing of it in conjugation I do not deny.
+The question, however, is whether they be so great as to justify any
+argument against an historical continuity between them. What, then, are
+these remaining distinctions? Briefly, as we have seen, they are the
+extrusion from egg-cells of polar bodies, and the occurrence, both in
+egg-cells and their products (tissue-cells), of the process of
+karyokinesis. But, as regards the polar bodies, it is surely not
+difficult to suppose that, whatever their significance may be, it is
+probably in some way or another connected with the high specialization
+of the functions which an egg-cell has to discharge. Nor is there any
+difficulty in further supposing that, whatever purpose is served by
+getting rid of polar bodies, the process whereby they are got rid of was
+originally one of utilitarian development--i. e. a process which at its
+commencement did not betoken any difference of kind, or breach of
+continuity, between egg-cells and cells of simpler constitution.
+
+Lastly, with respect to karyokinesis, although it is true that the
+microscope has in comparatively recent years displayed this apparently
+important distinction between unicellular and multicellular organisms,
+two considerations have here to be supplied. The first is, that in some
+of the Protozoa processes very much resembling those of karyokinesis
+have already been observed taking place in the nucleus preparatory to
+its division. And although such processes do not present quite the same
+appearances as are to be met with in egg-cells, neither do the
+karyokinetic processes in tissue-cells, which in their sundry kinds
+exhibit great variations in this respect. Moreover, even if such were
+not the case, the bare fact that nuclear division is not invariably of
+the simple or direct character in the case of all Protozoa, is
+sufficient to show that the distinction now before us--like the one last
+dealt with--is by no means absolute. As in the case of sexual
+propagation, so in that of karyokinesis, processes which are common to
+all the Metazoa are not wholly without their foreshadowings in the
+Protozoa. And seeing how greatly exalted is the office of egg-cells--and
+even of tissue-cells--as compared with that of their supposed ancestry
+in protozoal cells, it seems to me scarcely to be wondered at if their
+specializations of function should be associated with corresponding
+peculiarities of structure--a general fact which would in no way
+militate against the doctrine of evolution. Could we know the whole
+truth, we should probably find that in order to endow the most primitive
+of egg-cells with its powers of marshalling its products into a living
+army of cell-battalions, such an egg-cell must have been passed through
+a course of developmental specialization of so elaborate a kind, that
+even the complex processes of karyokinesis are but a very inadequate
+expression thereof.
+
+Probably I have now said enough to show that, remarkable and altogether
+exceptional as the properties of germ-cells of the multicellular
+organisms unquestionably show themselves to be, yet when these
+properties are traced back to their simplest beginnings in the
+unicellular organisms, they may fairly be regarded as fundamentally
+identical with the properties of living cells in general. Thus viewed,
+no line of real demarcation can be drawn between growth and
+reproduction, even of the sexual kind. The one process is, so to speak,
+physiologically continuous with the other; and hence, so far as the
+pre-embryonic stage of life-history is concerned, the facts cannot
+fairly be regarded as out of keeping with the theory of evolution.
+
+I will now pass on to consider the embryogeny of the Metazoa, beginning
+at its earliest stage in the fertilization of the ovum. And here it is
+that the constructive argument in favour of evolution which is derived
+from embryology may be said properly to commence. For it is surely in
+itself a most suggestive fact that all the Metazoa begin their life in
+the same way, or under the same form and conditions. _Omne vivum ex
+ovo._ This is a formula which has now been found to apply throughout the
+whole range of the multicellular organisms. And seeing, as we have just
+seen, that the ovum is everywhere a single cell, the formula amounts to
+saying that, physiologically speaking, every Metazoön begins its life as
+a Protozoön, and every Metaphyton as a Protophyton[10].
+
+ [10] Even when propagated by budding, a multicellular organism has
+ been ultimately derived from a germ-cell.
+
+Now, if the theory of evolution is true, what should we expect to happen
+when these germ-cells are fertilized, and so enter upon their severally
+distinct processes of development? Assuredly we should expect to find
+that the higher organisms pass through the same phases of development as
+the lower organisms, up to the time when their higher characters begin
+to become apparent. If in the life-history of species these higher
+characters were gained by gradual improvement upon lower characters, and
+if the development of the higher individual is now a general
+recapitulation of that of its ancestral species, in studying this
+recapitulation we should expect to find the higher organism successively
+unfolding its higher characters from the lower ones through which its
+ancestral species had previously passed. And this is just what we do
+find. Take, for example, the case of the highest organism, Man. Like
+that of all other organisms, unicellular or multicellular, his
+development starts from the nucleus of a single cell. Again, like that
+of all the Metazoa and Metaphyta, his development starts from the
+specially elaborated nucleus of an egg-cell, or a nucleus which has been
+formed by the fusion of a male with a female element[11]. When his
+animality becomes established, he exhibits the fundamental anatomical
+qualities which characterize such lowly animals as polyps and
+jelly-fish. And even when he is marked off as a Vertebrate, it cannot be
+said whether he is to be a fish, a reptile, a bird, or a beast. Later on
+it becomes evident that he is to be a Mammal; but not till later still
+can it be said to which order of mammals he belongs.
+
+ [11] It has already been stated that both parthenogenesis and
+ gemmation are ultimately derived from sexual reproduction. It may
+ now be added, on the other hand, that the earlier stages of
+ parthenogenesis have been observed to occur sporadically in all
+ sub-kingdoms of the Metaxoa, including the Vertebrata, and even the
+ highest class, Mammalia. These earlier stages consist in
+ _spontaneous_ segmentations of the ovum; so that even if a virgin
+ has ever conceived and borne a son, and even if such a fact in the
+ human species has been unique, still it would not betoken any breach
+ of physiological continuity. Indeed, according to Weismann's not
+ improbable hypothesis touching the physiological meaning of polar
+ bodies, such a fact need betoken nothing more than a slight
+ disturbance of the complex machinery of ovulation, on account of
+ which the ovum failed to eliminate from its substance an almost
+ inconceivably minute portion of its nucleus.
+
+Here, however, we must guard against an error which is frequently met
+with in popular expositions of this subject. It is not true that the
+embryonic phases in the development of a higher form always resemble so
+many adult stages of lower forms. This may or may not be the case; but
+what always is the case is, that the embryonic phases of the higher
+form resemble the corresponding phases of the lower forms. Thus, for
+example, it would be wrong to suppose that at any stage of his
+development a man resembles a jelly-fish. What he does resemble at an
+early stage of his development is the essential or groundplan of the
+jelly-fish, which that animal presents in _its_ embryonic condition, or
+before it begins to assume its more specialized characters fitting it
+for its own particular sphere of life. The similarities, therefore,
+which it is the function of comparative embryology to reveal are the
+similarities of type or morphological plan: not similarities of specific
+detail. Specific details may have been added to this, that, and the
+other species for their own special requirements, after they had
+severally branched off from the common ancestral stem; and so could not
+be expected to recur in the life-history of an independent specific
+branch. The comparison therefore must be a comparison of embryo with
+embryo; not of embryos with adult forms.
+
+ * * * * *
+
+In order to give a general idea of the results thus far yielded by a
+study of comparative embryology in the present connexion, I will devote
+the rest of this chapter to giving an outline sketch of the most
+important and best established of these results.
+
+Histologically the ovum, or egg-cell, is nearly identical in all
+animals, whether vertebrate or invertebrate. Considered as a cell it is
+of large size, but actually it is not more than 1/100, and may be less
+than 1/200 of an inch in diameter. In man, as in most mammals, it is
+about 1/120. It is a more or less spherical body, presenting a thin
+transparent envelope, called the _zona pellucida_, which
+contains--first, the protoplasmic cell-substance or "yolk," within which
+lies, second, the nucleus or germinal vesicle, within which again lies,
+third, the nucleolus or germinal spot. This description is true of the
+egg-cells of all animals, if we add that in the case of the lowest
+animals--such as sponges, &c.--there is no enveloping membrane: the
+egg-cell is here a naked cell, and its constituent protoplasm, being
+thus unconfined, is free to perform protoplasmic movements, which it
+does after the manner, and with all the activity, of an amoeba. But
+even with respect to this matter of an enveloping membrane, there is no
+essential difference between an ovum of the lowest and an ovum of the
+highest animals. For in their early stages of development within the
+ovary the ova of the highest animals are likewise in the condition of
+naked cells, exhibiting amoebiform movements; the enveloping membrane
+of an ovum being the product of a later development. Moreover this
+membrane, when present, is usually provided with one or more minute
+apertures, through which the spermatozoön passes when fertilizing the
+ovum. It is remarkable that the spermatozoa know, so to speak, of the
+existence of these gate-ways,--their snake-like movements being directed
+towards them, presumably by a stimulus due to some emanation
+therefrom[12]. In the mammalian ovum, however, these apertures are
+exceedingly minute, and distributed all round the circumference of the
+pellucid envelope, as represented in this illustration (Fig. 32).
+
+ [12] The spermatozooids of certain plants can be strongly attracted
+ towards a pipette which is filled with malic acid--crowding around
+ and into it with avidity.
+
+ [Illustration: FIG. 30.--Ovarian ovum of a Mammal, (_a_) magnified
+ and viewed under pressure, (_b_) burst by increased pressure, with
+ yolk and nucleus escaping: (_c_) the nucleus more freed from
+ yolk-substance. (From _Quain's Anatomy_, after Allen Thomson.)]
+
+ [Illustration: FIG. 31.--Amoeboid movements of young egg-cells, _a_,
+ Amoeboid ovum of _Hydra_ (from Balfour, after Kleitnenberg); _b_,
+ early ovum of _Toxopneustes variegatus_, with pseudopodia-like
+ processes (from Balfour, after Selenka); _c_, ovum of _Toxopneustes
+ lividus_, more nearly ripe (from Balfour, Hertwig). A1 to A4, the
+ primitive egg-cell of a Chalk-Sponge (_Leuculmis echinus_), in four
+ successive conditions of motion. B1 to B8, ditto of a Hermit-Crab
+ (_Chondracanthus cornutus_), in eight successive stages (after E.
+ von Beneden). C1 to C5, ditto of a Cat, in five successive stages
+ (after Pflüger). D, ditto of Trout; E, of a Hen; F, of Man. The
+ first series is taken from the _Encycl. Brit._; the second from
+ Häckel's _Evolution of Man_.]
+
+ [Illustration: FIG. 32.--Human ovum, mature and greatly magnified.
+ (After Häckel.)]
+
+In thus saying that the ova of all animals are, so far as microscopes
+can reveal, _substantially_ similar, I am of course speaking of the
+egg-cell proper, and not of what is popularly known as the egg. The egg
+of a bird, for example, is the egg-cell, _plus_ an enormous aggregation
+of nutritive material, an egg-shell, and sundry other structures suited
+to the subsequent development of the egg-cell when separated from the
+parent's body. But all these accessories are, from our present point of
+view, accidental or adventitious. What we have now to understand by the
+ovum, the egg, or the egg-cell, is the microscopical germ which I have
+just described. So far then as this germ is concerned, we find that all
+multicellular organisms begin their existence in the same kind of
+structure, and that this structure is anatomically indistinguishable
+from that of the permanent form presented by the lowest, or unicellular
+organisms. But although anatomically indistinguishable, physiologically
+they present the sundry peculiarities already mentioned.
+
+Now I have endeavoured to show that none of these peculiarities are such
+as to exclude--or even so much as to invalidate--the supposition of
+developmental continuity between the lowest egg-cells and the highest
+protozoal cells. It remains to show in this place, and on the other
+hand, that there is no breach of continuity between the lowest and the
+highest egg-cells; but, on the contrary, that the remarkable uniformity
+of the complex processes whereby their peculiar characters are exhibited
+to the histologist, is such as of itself to sustain the doctrine of
+continuity in a singularly forcible manner. On this account, therefore,
+and also because the facts will again have to be considered in another
+connexion when we come to deal with Weismann's theory of heredity, I
+will here briefly describe the processes in question.
+
+We have already seen that the young egg-cell multiplies itself by simple
+binary division, after the manner of unicellular organisms in
+general--thereby indicating, as also by its amoebiform movements, its
+fundamental identity with such organisms in kind. But, as we have
+likewise seen, when the ovum ceases to resemble these organisms, by
+taking on its higher degree of functional capacity, it is no longer able
+to multiply itself in this manner. On the contrary, its cell-divisions
+are now of an endogenous character, and result in the formation of many
+different kinds of cells, in the order required for constructing the
+multicellular organism to which the whole series of processes eventually
+give rise. We have now to consider these processes _seriatim_.
+
+ [Illustration: FIG. 33.--Stages in the formation of the polar bodies
+ in the ovum of a star-fish. (After Hertwig.) _g.v._, germinal
+ vesicle transformed into a spindle-shaped system of fibres; _p.'_,
+ the first polar body becoming extruded; _p._, _p._, both polar
+ bodies fully extruded; _f. pn._, female pronucleus, or residue of
+ the germinal vesicle.]
+
+First of all the nucleus discharges its polar bodies, as previously
+mentioned, and in the manner here depicted on the previous page. (Fig.
+33.) It will be observed that the nucleus of the ovum, or the germinal
+vesicle as it is called, gets rid first of one and afterwards of the
+other polar body by an "indirect," or karyokinetic, process of division.
+(Fig. 33.) Extrusion of these bodies from the ovum (or it may be only
+from the nucleus) having been accomplished, what remains of the nucleus
+retires from the circumference of the ovum, and is called the female
+pronucleus. (Fig. 33. _f. pn._) The ovum is now ready for fertilization.
+A similar emission of nuclear substance is said by some good observers
+to take place also from the male germ-cell, or spermatozoön, at or about
+the close of _its_ development. The theories to which these facts have
+given rise will be considered in future chapters on Heredity.
+
+Turning now to the mechanism of fertilization, the diagrams (Figs. 34,
+35) represent what happens in the case of star-fish.
+
+ [Illustration: FIG. 34.--Fertilization of the ovum of an echinoderm.
+ (From _Quain's Anatomy_, after Selenka.) S, spermatozoön; _m. pr._,
+ male pronucleus; _f. pr._, female pronucleus. 1 to 4 correspond to D
+ to G in the next figure.]
+
+ [Illustration: FIG. 35.--Fertilization of the ovum of a star-fish.
+ (From the _Encycl. Brit._ after Fol.) A, spermatozoa in the
+ mucilaginous coat of the ovum; a prominence is rising from the
+ surface of the ovum towards a spermatozoön; B, they have almost met;
+ C, they have met; D, the spermatozoön enters the ovum through a
+ distinct opening; H, the entire ovum, showing extruded polar bodies
+ on its upper surface, and the moving together of the male and female
+ pronuclei; E, F, G, meeting and coalescence of the pronuclei.]
+
+The sperm-cell, or spermatozoön, is seen in the act of penetrating the
+ovum. In the first figure it has already pierced the mucilaginous coat
+of the ovum, the limit of which is represented by a line through which
+the tail of the spermatozoön is passing: the head of the spermatozoön is
+just entering the ovum proper. It may be noted that, in the case of many
+animals, the general protoplasm of the ovum becomes aware, so to speak,
+of the approach of a spermatozoön, and sends up a process to meet it.
+(Fig. 35, A, B, C.) Several--or even many--spermatozoa may thus enter
+the coat of the ovum; but normally only one proceeds further, or right
+into the substance of the ovum, for the purpose of effecting
+fertilization. This spermatozoön, as soon as it enters the periphery of
+the yolk, or cell-substance proper, sets up a series of remarkable
+phenomena. First, its own head rapidly increases in size, and takes on
+the appearance of a cell-nucleus: this is called the male pronucleus. At
+the same time its tail begins to disappear, and the enlarged head
+proceeds to make its way directly towards the nucleus of the ovum which,
+as before stated, is now called the female pronucleus. The latter in its
+turn moves towards the former, and when the two meet they fuse into one
+mass, forming a new nucleus. Before the two actually meet, the
+spermatozoön has lost its tail altogether; and it is noteworthy that
+during its passage through the protoplasmic cell-contents of the ovum,
+it appears to exercise upon this protoplasm an attractive influence; for
+the granules of the latter in its vicinity dispose themselves around it
+in radiating lines. All these various phenomena are depicted in the
+above wood-cuts. (Figs. 34, 35.)
+
+Fertilization having been thus effected by fusion of the male and female
+pronuclei into a single (or new) nucleus, this latter body proceeds to
+exhibit complicated processes of karyokinesis, which, as before shown,
+are preliminary to nuclear division in the case of egg-cells. Indeed the
+karyokinetic process may begin in both the pronuclei before their
+junction is effected; and, even when their junction is effected, it does
+not appear that complete fusion of the so-called chromatin elements of
+the two pronuclei takes place. For the purpose of explaining what this
+means, and still more for the purpose of giving a general idea of the
+karyokinetic processes as a whole, I will quote the following
+description of them, because, for terseness combined with lucidity, it
+is unsurpassable.
+
+ [Illustration: FIG. 36.--Karyokinesis of a typical tissue-cell
+ (epithelium of Salamander). (After Flemming and Klein.) The series
+ from A to I represents the successive stages in the movement of the
+ chromatin fibres during division, excepting G, which represents the
+ "nucleus-spindle" of an egg-cell. A, resting nucleus; D,
+ wreath-form; E, single star, the loops of the wreath being broken;
+ F, separation of the star into two groups of U-shaped fibres; H,
+ diaster or double star; I, completion of the cell-division and
+ formation of two resting nuclei. In G the chromatin fibres are
+ marked _a_, and correspond to the "equatorial plate"; _b_,
+ achromatin fibres forming the nucleus-spindle; _c_, granules of the
+ cell-protoplasm forming a "polar star." Such a polar star is seen at
+ each end of the nucleus-spindle, and is not to be confused with the
+ diaster H, the two ends of which are composed of _chromatin_.]
+
+ Researches, chiefly due to Flemming, have shown that the nucleus in
+ very many tissues of higher plants and animals consists of a
+ capsule containing a plasma of "achromatin," not deeply stained by
+ re-agents, ramifying in which is a reticulum of "chromatin"
+ consisting of fibres which readily take a deep stain. (Fig. 36, A).
+ Further it is demonstrated that, when the cell is about to divide
+ into two, definite and very remarkable movements take place in the
+ nucleus, resulting in the disappearance of the capsule and in the
+ arrangement of its fibres first in the form of a wreath (D), and
+ subsequently (by the breaking of the loops formed by the fibres) in
+ the form of a star (E). A further movement within the nucleus leads
+ to an arrangement of the broken loops in two groups (F), the
+ position of the open ends of the broken loops being reversed as
+ compared with what previously obtained. Now the two groups diverge,
+ and in many cases a striated appearance of the achromatin substance
+ between the two groups of chromatin loops is observable (H). In
+ some cases (especially egg-cells) this striated arrangement of the
+ achromatin is then termed a "nucleus-spindle," and the group of
+ chromatin loops (G, _a_) is known as "the equatorial plate." At
+ each end of the nucleus-spindle in these cases there is often seen
+ a star consisting of granules belonging to the general protoplasm
+ of the cell (G, _c_). These are known as "polar stars." After the
+ separation of the two sets of loops (H) the protoplasm of the
+ general substance of the cell becomes constricted, and division
+ occurs, so as to include a group of chromatin loops in each of the
+ two fission products. Each of these then rearranges itself together
+ with the associated chromatin into a nucleus such as was present in
+ the mother cell to commence with (I)[13].
+
+ [13] Ray Lankester, _Encyclop. Brit._, 9th ed., Vol. XIX, pp. 832-3.
+
+Since the above was published, however, further progress has been made.
+In particular it has been found that the chromatin fibres pass from
+phase D to phase F by a process of longitudinal splitting (Fig. 37 _g_,
+_h_; Fig. 38, VI, VII)--which is a point of great importance for
+Weismann's theory of heredity,--and that the protoplasm outside the
+nucleus seems to take as important a part in the karyokinetic process as
+does the nuclear substance. For the so-called "attraction-spheres" (Fig.
+38 II _a_, III, III _a_, VIII to XII), which were at first supposed to
+be of subordinate importance in the process as a whole, are now known to
+take an exceedingly active part in it (see especially IX to XI). Lastly,
+it may be added that there is a growing consensus of authoritative
+opinion, that the chromatin fibres are the seats of the material of
+heredity, or, in other words, that they contain those essential elements
+of the cell which endow the daughter-cells with their distinctive
+characters. Therefore, where the parent-cell is an ovum, it follows from
+this view that all hereditary qualities of the future organism are
+potentially present in the ultra-microscopical structure of the
+chromatin fibres.
+
+ [Illustration: FIG. 37.--Study of successive changes taking place in
+ the nucleus of an epithelium cell, preparatory to division of the
+ cell. (From _Quain's Anatomy_, after Flemming.) _a_, resting cell,
+ showing the nuclear network; _b_, first stage of division, the
+ chromatoplasm transformed into a skein of closely contorted
+ filaments; _c_ to _f_, further stages in the growth and looping
+ arrangement of the filaments; _g_, stellate phase, or aster; _h_,
+ completion of the splitting of the filaments, already begun in _f_
+ and _g_; _i_, _j_, _k_, successive stages in separation of the
+ filaments into two groups; _l_, the final result of this (diaster);
+ _m_ to _q_, stages in the division of the whole cell into two,
+ showing increasing contortion of the filaments, until they reach the
+ resting stage at _q_].
+
+ [Illustration: FIG. 38.--Formation and conjugation of the pronuclei
+ in _Ascaris megalocephala_. (From _Quain's Anatomy_, after E. von
+ Beneden.) _f_, female pronucleus; _m_, male pronucleus; _p_, one of
+ the polar bodies.
+
+ I. The second polar body has just been extruded; both male and
+ female pronuclei contain two chromatin particles; those of the male
+ pronucleus are becoming transformed into a skein. II. The chromatin
+ in both pronuclei now forms into a skein.
+
+ II _a_. The skeins are more distinct. Two attraction (or
+ protoplasmic) spheres, each with a central particle united with a
+ small spindle of achromatic fibres, have made their appearance in
+ the general substance of the egg close to the mutually approaching
+ pronuclei. The male pronucleus has the remains of the body of the
+ spermatozoön adhering to it.
+
+ III. Only the female pronucleus is shown in this figure. The skein
+ is contracted and thickened. The attraction-spheres are near one
+ side of the ovum, and are connected with its periphery by a cone of
+ fibres forming a polar circle, _p.c._; _e.c._, equatorial circle.
+
+ III _a_. The pronuclei have come into contact, and the
+ spindle-system is now arranged across their common axis.
+
+ IV. Contraction of the skein, and formation of two U-or V-shaped
+ chromatin fibres in each pronucleus.
+
+ V. The V-shaped chromatin filaments are now quite distinct: the male
+ and female pronuclei are in close contact.]
+
+ [Illustration: (38 continued)
+
+ VI., VII. The V-shaped filaments are splitting longitudinally; their
+ structure of fine granules of chromatin is apparent in VII., which
+ is more highly magnified. The conjugation of the pronuclei is
+ apparently complete in VII. The attraction-spheres and achromatic
+ spindle, although present, are not depicted in IV., V., VI., and
+ VII.
+
+ VIII. Equatorial arrangement of the four chromatin loops in the
+ middle of the now segmenting ovum: the achromatic substance forming
+ a spindle-shaped system of granules with fibres radiating from the
+ poles of the spindle (attraction-spheres); the chromatin forms an
+ equatorial plate. (Compare Fig. 36 G.)
+
+ IX. Shows diagrammatically the commencing separation of the
+ chromatin fibres of the conjugated nuclei, and the system of fibres
+ radiating from the attraction-spheres. (Compare again Fig. 36 G.)
+ _p.c._, polar circle; _e.c._, equatorial circle; _c.c._, central
+ particle.
+
+ X. Further separation of the chromatin filaments. Each of the
+ central particles of the attraction-spheres has divided into two.
+
+ XI. The chromatin fibres are becoming developed into the skeins of
+ the two daughter-nuclei. These are still united by fibres of
+ achromatin. The general protoplasm of the ovum is becoming divided.
+
+ XII. The two daughter-nuclei exhibit a chromatin network. Each of
+ the attraction-spheres has divided into two, which are joined by
+ fibres of achromatin, and connected with the periphery of the cell
+ in the same way as in the original or parent sphere, III.]
+
+As I shall have more to say about these processes in the next volume,
+when we shall see the important part which they bear in Weismann's
+theory of heredity, it is with a double purpose that I here introduce
+these yet further illustrations of them upon a somewhat larger scale.
+The present purpose is merely that of showing, more clearly than
+hitherto, the great complexity of these processes on the one hand, and,
+on the other, the general similarity which they display in egg-cells and
+in tissue-cells. But as in relation to this purpose the illustrations
+speak for themselves, I may now pass on at once to the history of
+embryonic development, which follows fertilization of the ovum.
+
+ * * * * *
+
+We have seen that when the new nucleus of the fertilized ovum (which is
+formed by a coalescence of the male pronucleus with the female) has
+completed its karyokinetic processes, it is divided into two equal
+parts; that these are disposed at opposite poles of the ovum; and that
+the whole contents of the ovum are thereupon likewise divided into two
+equal parts, with the result that there are now two nucleated cells
+within the spherical wall of the ovum where before there had only been
+one. Moreover, we have also seen that a precisely similar series of
+events repeat themselves in each of these two cells, thus giving rise to
+four cells (see Fig. 29). It must now be added that such duplication is
+continued time after time, as shown in the accompanying illustrations
+(Figs. 39, 40).
+
+ [Illustration: FIG. 39.--Segmentation of ovum. (After Häckel.)
+ Successive stages are marked by the letters A, B, C. D represents
+ several stages in advance of C.]
+
+ [Illustration: FIG. 40.--The contents of an ovum in an advanced
+ stage of segmentation, drawn in perspective. (After Häckel.)]
+
+All this, it will be noticed, is a case of cell-multiplication, which
+differs from that which takes place in the unicellular organisms only in
+its being _invariably_ preceded (as far as we know) by karyokinesis, and
+in the resulting cells being all confined within a common envelope, and
+so in not being free to separate. Nevertheless, from what has already
+been said, it will also be noticed that this feature makes all the
+difference between a Metazoön and a Protozoön; so that already the ovum
+presents the distinguishing character of a Metazoön.
+
+I have dealt thus at considerable length upon the processes whereby the
+originally unicellular ovum and spermatozoön become converted into the
+multicellular germ, because I do not know of any other exposition of the
+argument from Embryology where this, the first stage of the argument,
+has been adequately treated. Yet it is evident that the fact of all the
+processes above described being so similar in the case of sexual (or
+metazoal) reproduction among the innumerable organisms where it occurs,
+constitutes in itself a strong argument in favour of evolution. For the
+mechanism of fertilization, and all the processes which even thus far we
+have seen to follow therefrom, are hereby shown to be not only highly
+complex, but likewise highly specialized. Therefore, the remarkable
+similarity which they present throughout the whole animal kingdom--not
+to speak of the vegetable--is expressive of organic continuity, rather
+than of absolute discontinuity in every case, as the theory of special
+creation must necessarily suppose. And it is evident that this argument
+is strong in proportion to the uniformity, the specialization, and the
+complexity of the processes in question.
+
+Having occupied so much space with supplying what appear to me the
+deficiencies in previous expositions of the argument from Embryology, I
+can now afford to take only a very general view of the more important
+features of this argument as they are successively furnished by all the
+later stages of individual development. But this is of little
+consequence, seeing that from the point at which we have now arrived
+previous expositions of the argument are both good and numerous. The
+following then is to be regarded as a mere sketch of the evidences of
+phyletic (or ancestral) evolution, which are so abundantly furnished by
+all the subsequent phases of ontogenetic (or individual) evolution.
+
+The multicellular body which is formed by the series of segmentations
+above described is at first a sphere of cells (Fig. 40). Soon, however,
+a watery fluid gathers in the centre, and progressively pushes the cells
+towards the circumference, until they there constitute a single layer.
+The ovum, therefore, is now in the form of a hollow sphere containing
+fluid, confined within a continuous wall of cells (Fig. 41 A). The next
+thing that happens is a pitting in of one portion of the sphere (B). The
+pit becomes deeper and deeper, until there is a complete invagination of
+this part of the sphere--the cells which constitute it being
+progressively pushed inwards until they come into contact with those at
+the opposite pole of the ovum. Consequently, instead of a hollow sphere
+of cells, the ovum now becomes an open sac, the walls of which are
+composed of a double layer of cells (C). The ovum is now what has been
+called a gastrula; and it is of importance to observe that probably all
+the Metazoa pass through this stage. At any rate it has been found to
+occur in all the main divisions of the animal kingdom, as a glance at
+the accompanying figures will serve to show (Fig. 42)[14]. Moreover many
+of the lower kinds of Metazoa never pass beyond it; but are all their
+lives nothing else than gastrulæ, wherein the orifice becomes the mouth
+of the animal, the internal or invaginated layer of cells the stomach,
+and the outer layer the skin. So that if we take a child's india-rubber
+ball, of the hollow kind with a hole in it, and push in one side with
+our fingers till internal contact is established all round, by then
+holding the indented side downwards we should get a very fair anatomical
+model of a gastræa form, such as is presented by the adult condition of
+many of the most primitive Metazoa--especially the lower
+_Coelenterata_. The preceding figures represent two other such forms
+in nature, the first locomotive and transitory, the second fixed and
+permanent (Figs. 43, 44).
+
+ [14] In most vertebrated animals this process of gastrulation has
+ been more or less superseded by another, which is called
+ delamination; but it scarcely seems necessary for our present
+ purposes to describe the latter. For not only does it eventually
+ lead to the same result as gastrulation--i. e. the converting of the
+ ovum into a double-walled sac,--but there is good evidence among the
+ lower Vertebrata of its being preceded by gastrulation; so that,
+ even as to the higher Vertebrata, embryologists are pretty well
+ agreed that delamination has been but a later development of, or
+ possibly improvement upon, gastrulation.
+
+ [Illustration: FIG. 41.--Formation of the gastrula of _Amphioxus_.
+ (After Kowalevsky.) A, wall of the ovum, composed of a single layer
+ of cells; B, a stage in the process of gastrulation; C, completion
+ of the process; S, original or segmentation cavity of ovum; _al_,
+ alimentary cavity of gastrula; _ect_, outer layer of cells; _ent_,
+ inner layer of cells; _b_, orifice, constituting the mouth in
+ permanent forms.]
+
+ [Illustration: FIG. 42.--Gastrulation. A, Gastrula of a Zoophyte
+ (_Gastrophysema_). (After Häckel.) B, Gastrula of a Worm
+ (_Sagitta_). (After Kowalevsky.) C, Gastrula of an Echinoderm
+ (_Uraster_). (After A. Agassiz.) D, Gastrula of an Arthropod
+ (_Nauplius_). (After Häckel.) E, Gastrula of a Mollusk (_Limnæus_).
+ (After Rabl.) F, Gastrula of a Vertebrate (_Amphioxus_). (After
+ Kowalevsky.) In all, _d_, indicates the intestinal cavity; _o_, the
+ primitive mouth; _s_, the cleavage-cavity; _i_, the endoderm, or
+ intestinal layer; _e_, the ectoderm or skin-layer.]
+
+ [Illustration: FIG. 43.--Gastrula of a Chalk Sponge. (After Häckel.)
+ A, External view. B, Longitudinal section. _g_, digestive cavities;
+ _o_, mouth; _i_, endoderm; _e_, ectoderm.]
+
+ [Illustration: FIG. 44.--_Prophysema primordiale_, an extant
+ gastræa-form. (After Häckel.) (A). External view of the whole
+ animal, attached by its foot to seaweed. (B). Longitudinal section
+ of the same. The digestive cavity (_d_) opens at its upper end in
+ the mouth (_m_). Among the cells of the endoderm (_g_) lie amoeboid
+ egg-cells of large size (_e_). The ectoderm (_h_) is encrusted with
+ grains of sand, above the sponge spicules.]
+
+Here, then, we leave the lower forms of Metazoa in their condition of
+permanent gastrulæ. They differ from the transitory stage of other
+Metazoa only in being enormously larger (owing to greatly further
+_growth_, without any further _development_ as to matters of fundamental
+importance), and in having sundry tentacles and other organs added later
+on to meet their special requirements. The point to remember is, that in
+all cases a gastrula is an open sac composed of two layers of cells--the
+outer layer being called the ectoderm, and the inner the endoderm. They
+have also been called the animal layer and the vegetative layer, because
+it is the outer layer (ectoderm) that gives rise to all the organs of
+sensation and movement--viz. the skin, the nervous system, and the
+muscular system; while it is the inner layer (endoderm) that gives rise
+to all the organs of nutrition and reproduction. It is desirable only
+further to explain that gastrulation does not take place in all the
+Metazoa after exactly the same plan. In different lines of descent
+various and often considerable modifications of the original and most
+simple plan have been introduced; but I will not burden the present
+exposition by describing these modifications[15]. It is enough for us
+that they always end in the formation of the two primary layers of
+ectoderm and endoderm.
+
+ [15] The most extreme of them is that which is mentioned in the last
+ foot-note.
+
+The next stage of differentiation is common to all the Metazoa, except
+those lowest forms which, as we have just seen, remain permanently as
+large gastrulæ, with sundry specialized additions in the way of
+tentacles, &c. This stage of differentiation consists in the formation
+of either a pouch or an additional layer between the ectoderm and the
+endoderm, which is called the mesoderm. It is probably in most cases
+derived from the endoderm, but the exact mode of its derivation is still
+somewhat obscure. Sometimes it has the appearance of itself constituting
+two layers; but it is needless to go into these details; for in any case
+the ultimate result is the same--viz. that of converting the Metazoön
+into the form of a tube, the walls of which are composed of concentric
+layers of cells. The outermost layer afterwards gives rise to the
+epidermis with its various appendages, and also to the central nervous
+system with its organs of special sense. The median layer gives rise to
+the voluntary muscles, bones, cartilages, &c., the nutritive systems of
+the blood, the chyle, the lymph, and the muscular tube of the intestine.
+Lastly, the innermost layer developes into the epithelium lining of the
+intestine, with its various appendages of liver, lungs, intestinal
+glands, &c.
+
+I have just said that this three or four layered stage is shared by all
+the Metazoa, except those very lowest forms--such as sponges and
+jelly-fish--which do not pass on to it. But from this point the
+developmental histories of all the main branches of the Metazoa
+diverge--the Vermes, the Echinodermata, the Mollusca, the Articulata,
+and the Vertebrata, each taking a different road in their subsequent
+evolution. I will therefore confine attention to only one of these
+several roads or methods, namely, that which is followed by the
+Vertebrata--observing merely that, if space permitted, the same
+principles of progressive though diverging histories of evolution would
+equally well admit of being traced in all the other sub-kingdoms which
+have just been named.
+
+In order to trace these principles in the case of the Vertebrata, it is
+desirable first of all to obtain an idea of the anatomical features
+which most essentially distinguish the sub-kingdom as a whole. The
+following, then, is what may be termed the ideal plan of vertebrate
+organization, as given by Prof. Häckel. First, occupying the major axis
+of body we perceive the primitive vertebral column. The parts lying
+above this axis are those which have been developed from the ectoderm
+and mesoderm--viz. voluntary muscles, central nervous system, and organs
+of special sense. The parts lying below this axis are for the most part
+those which have been developed from the endoderm--namely, the
+digestive tract with its glandular appendages, the circulating system
+and the respiratory system. In transverse section, therefore, the ideal
+vertebrate consists of a solid axis, with a small tube occupied by the
+nervous system above, and a large tube, or body-cavity, below. This
+body-cavity contains the viscera, breathing organs, and heart, with its
+prolongations into the main blood-vessels of the organism. Lastly, on
+either side of the central axis are to be found large masses of
+muscle--two on the dorsal and two on the ventral. As yet, however, there
+are no limbs, nor even any bony skeleton, for the primitive vertebral
+column is hitherto unossified cartilage. This ideal animal, therefore,
+is to all appearance as much like a worm as a fish, and swims by means
+of a lateral undulation of its whole body, assisted, perhaps, by a
+dorsal fin formed out of skin.
+
+ [Illustration: FIG. 45.--Ideal primitive vertebrate, seen from the
+ left side. (After Häckel.) _na_, nose; _au_, eye; _g_, ear; _md_,
+ mouth; _ks_, gill-openings; _x_, notochord; _mr_, spinal tube; _kg_,
+ gill-vessels; _k_, gill-intestine; _hz_, heart; _ms_, muscles; _ma_,
+ stomach; _v_, intestinal vein; _c_, body-cavity; _a_, aorta; _l_,
+ liver; _d_, small intestine; _e_, ovary; _h_, testes; _n_, kidney
+ canal; _af_, anus; _lh_, true or leather-skin; _oh_, outer-skin
+ (epidermis); _f_, skin-fold, acting as a fin.]
+
+ [Illustration: FIG. 46.--The same in transverse section through the
+ ovaries; lettering as in the preceding Fig.]
+
+ [Illustration: FIG. 47.--_Amphioxus lanceolatus_. (After Häckel.)
+ _a_, anus; _au_, eye; _b_, ventral muscles; _c_, body-cavity; _ch_,
+ notochord; _d_, intestine; _do_ and _du_, dorsal and ventral walls
+ of intestine; _f_, fin-seam; _h_, skin; _k_, gills; _ka_,
+ gill-artery; _lb_, liver; _lv_, liver-vein; _m 1_, brain-bladder; _m
+ 2_, spinal marrow; _mg_, stomach; _o_, mouth; _p_, ventral pore;
+ _r_, dorsal muscle; _s_, tail-fin; _t_, aorta; _v_, intestinal vein;
+ _x_, boundary between gill-intestine and stomach-intestine; _y_,
+ hypobranchial groove.]
+
+Now I should not have presented this ideal representation of a primitive
+vertebrate--for I have very little faith in the "scientific use of the
+imagination" where it aspires to discharge the functions of a Creator in
+the manufacture of archetypal forms--I say I should not have presented
+this ideal representative of a primitive vertebrate, were it not that
+the ideal is actually realized in a still existing animal. For there
+still survives what must be an immensely archaic form of vertebrate,
+whose anatomy is almost identical with that of the imaginary type which
+has just been described. I allude, of course, to _Amphioxus_, which is
+by far the most primitive or generalized type of vertebrated animal
+hitherto discovered. Indeed, we may say that this remarkable creature is
+almost as nearly allied to a worm as it is to a fish. For it has no
+specialized head, and therefore no skull, brain, or jaws: it is
+destitute alike of limbs, of a centralized heart, of developed liver,
+kidneys, and, in short, of most of the organs which belong to the other
+Vertebrata. It presents, however, a rudimentary backbone, in the form of
+what is called a notochord. Now a primitive dorsal axis of this kind
+occurs at a very early period of embryonic life in all vertebrated
+animals; but, with the exception of _Amphioxus_, in all other existing
+Vertebrata this structure is not itself destined to become the permanent
+or bony vertebral column. On the contrary, it gives way to, or is
+replaced by, this permanent bony structure at a later stage of
+development. Consequently, it is very suggestive that so distinctively
+embryonic a structure as this temporary cartilaginous axis of all the
+other known Vertebrata should be found actually persisting to the
+present day as the permanent axis of _Amphioxus_. In many other
+respects, likewise, the early embryonic history of other Vertebrata
+refers us to the permanent condition of _Amphioxus_. In particular, we
+must notice that the wall of the neck is always perforated by what in
+_Amphioxus_ are the gill-openings, and that the blood-vessels as they
+proceed from the heart are always distributed in the form of what are
+called gill-arches, adapted to convey the blood round or through the
+gills for the purpose of aeration. In all existing fish and other
+gill-breathing Vertebrata, this arrangement is permanent. It is
+likewise met with in a peculiar kind of worm, called _Balanoglossus_--a
+creature so peculiar, indeed, that it has been constituted by Gegenbaur
+a class all by itself. We can see by the wood-cuts that it presents a
+series of gill-slits, like the homologous parts of the fishes with which
+it is compared--i. e. fishes of a comparatively low type of
+organization, which dates from a time before the development of external
+gills. (Figs. 48, 49, 50.) Now, as I have already said, these
+gill-_slits_ are supported internally by the gill-_arches_, or the
+blood-vessels which convey the blood to be oxygenized in the branchial
+apparatus (see below, Figs. 51, 52, 53); and the whole arrangement is
+developed from the anterior part of the intestine--as is likewise the
+respiratory mechanism of all the gill-breathing Vertebrata. That so
+close a parallel to this peculiar mechanism should be met with in a
+worm, is a strong additional piece of evidence pointing to the
+derivation of the Vertebrata from the Vermes.
+
+ [Illustration: FIG. 48.--_Balanoglossus_. (After A. Agassiz.) _r_,
+ proboscis; _h_, collar; _k_, gill-slits; _d_, digestive posterior
+ intestine; _v_, intestinal vessel; _a_, anus.]
+
+ [Illustration: FIG. 49.--A large Sea-lamprey (_Petromyzon marinus_),
+ much reduced in size. (After Cuvier and Häckel.) A series of seven
+ gill-slits are visible.]
+
+ [Illustration: FIG. 50--Adult Shark (_Carcharias melanopterus_).
+ (After Cuvier and Häckel.)]
+
+ [Illustration: FIG. 51.--Diagram of heart and gill-arches of a fish.
+ (After Owen.)]
+
+ [Illustration: FIG. 52.--One gill-arch, with branchial fringe
+ attached. (After Owen.) H, Heart.]
+
+ [Illustration: FIG. 53.--Diagram of heart and gill-arches in a
+ lizard. (After Owen.) The gill-arches, _a a' a''_, and _b b' b''_,
+ are called aortic arches in air-breathing vertebrata.]
+
+Well, I have just said that in all the gill-breathing Vertebrata, this
+mechanism of gill-slits and vascular gill-arches in the front part of
+the intestinal tract is permanent. But in the air-breathing Vertebrata
+such an arrangement would obviously be of no use. Consequently, the
+gill-slits in the sides of the neck (see Figs. 16 and 57, 58), and the
+gill-arches of the large blood-vessels (Figs. 54, 55, 56), are here
+exhibited only as transitory phases of development. But as such they
+occur in all air-breathing Vertebrata. And, as if to make the homologies
+as striking as possible, at the time when the gill-slits and the
+gill-arches are developed in the embryonic young of air-breathing
+Vertebrata, the heart is constructed upon the fish-like type. That is to
+say, it is placed far forwards, and, from having been a simple tube as
+in Worms, is now divided into two chambers, as in Fish. Later on it
+becomes progressively pushed further back between the developing lungs,
+while it progressively acquires the three cavities distinctive of
+Amphibia, and finally the four cavities belonging only to the complete
+double circulation of Birds and Mammals. Moreover, it has now been
+satisfactorily shown that the lungs of air-breathing Vertebrata, which
+are thus destined to supersede the function of gills, are themselves the
+modified swim-bladder or float, which belongs to Fish. Consequently, all
+these progressive modifications in the important organs of circulation
+and respiration in the air-breathing Vertebrata, together make up as
+complete a history of their aquatic pedigree as it would be possible for
+the most exacting critic to require.
+
+ [Illustration: FIG. 54.--Ideal diagram, of primitive gill-or
+ aortic-arches. (After Rathke.) H, outline of heart. The arrows show
+ the course of the blood.]
+
+ [Illustration: FIG. 55.--The same, modified for a bird. (After Le
+ Conte.) The dark lines show the aortic arches which persist. A,
+ aorta; _p_, pulmonary arches; SC, S'C', sub-clavian; C, C',
+ carotids.]
+
+ [Illustration: FIG. 56.--The same, modified for a mammal. (After Le
+ Conte.)]
+
+ [Illustration: FIG. 57.--A series of embryos at three comparable and
+ progressive stages of development (marked I, II, III), representing
+ each of the classes of vertebrated animals below the Mammalia (After
+ Häckel.)]
+
+ [Illustration: FIG. 58.--Another series of embryos, also at three
+ comparable and progressive stages of development (marked I, II,
+ III), representing four different divisions of the class Mammalia.
+ (After Häckel.)]
+
+If space permitted, it would be easy to present abundance of additional
+evidence to the same effect from the development of the skeleton, the
+skull, the brain, the sense-organs, and, in short, of every constituent
+part of the vertebrate organization. Even without any anatomical
+dissection, the similarity of all vertebrated embryos at comparable
+stages of development admits of being strikingly shown, if we merely
+place the embryos one beside the other. Here, for instance, are the
+embryos of a fish, a salamander, a tortoise, a bird, and four different
+mammals. In each case three comparable stages of development are
+represented. Now, if we read the series horizontally, we can see that
+there is very little difference between the eight animals at the
+earliest of the three stages represented--all having fish-like tails,
+gill-slits, and so on. In the next stage further differentiation has
+taken place, but it will be observed that the limbs are still so
+rudimentary that even in the case of Man they are considerably shorter
+than the tail. But in the third stage the distinctive characters are
+well marked.
+
+ * * * * *
+
+So much then for an outline sketch of the main features in the embryonic
+history of the Vertebrata. But it must be remembered that the science of
+comparative embryology extends to each of the other three great branches
+of the tree of life, where these take their origin, through the worms,
+from the still lower, or gastræa, forms. And in each of these three
+great branches--namely, the Echinodermata, the Mollusca, and the
+Arthropoda--we have a repetition of just the same kind of evidence in
+favour of continuous descent, with adaptive modification in sundry
+lines, as that which I have thus briefly sketched in the case of the
+Vertebrata. The roads are different, but the method of travelling is the
+same. Moreover, when the embryology of the Worms is closely studied, the
+origin of these different roads admits of being clearly traced. So that
+when all this mass of evidence is taken together, we cannot wonder that
+evolutionists should now regard the science of comparative embryology as
+the principal witness to their theory.
+
+
+
+
+CHAPTER V.
+
+PALÆONTOLOGY.
+
+
+The present Chapter will be devoted to a consideration of the evidence
+of organic evolution which has been furnished by the researches of
+geologists. On account of its direct or historical nature, this branch
+of evidence is popularly regarded as the most important--so much so,
+indeed, that in the opinion of most educated persons the whole doctrine
+of organic evolution must stand or fall according to the so-called
+"testimony of the rocks." Now, without at all denying the peculiar
+importance of this line of evidence, I must begin by remarking that it
+does not present the denominating importance which popular judgment
+assigns to it. For although popular judgment is right in regarding the
+testimony of the rocks as of the nature of a history, this judgment, as
+a rule, is very inadequately acquainted with the great imperfections of
+that history. Knowing in a general way what magnificent advances the
+science of geology has made during the present century, the public mind
+is more or less imbued with the notion, that because we now possess a
+tolerably complete record of the chronological succession of geological
+formations, we must therefore possess a correspondingly complete record
+of the chronological succession of the forms of life which from time to
+time have peopled the globe. Now in one sense this notion is partly
+true, but in another sense it is profoundly false. It is partly true if
+we have regard only to those larger divisions of the vegetable or animal
+kingdoms which naturalists designate by the terms classes and orders.
+But the notion becomes progressively more untrue when it is applied to
+families and genera, while it is most of all untrue when applied to
+species. That this must be so may be rendered apparent by two
+considerations.
+
+In the first place, it does not follow that because we have a tolerably
+complete record of the succession of geological formations, we have
+therefore any correspondingly complete record of their fossiliferous
+contents. The work of determining the relative ages of the rocks does
+not require that every cubic mile of the earth's surface should be
+separately examined, in order to find all the different fossils which it
+may contain. Were this the case, we should hitherto have made but very
+small progress in our reading of the testimony of the rocks. The
+relative ages of the rocks are determined by broad comparative surveys
+over extensive areas; and although the identification of widely
+separated deposits is often greatly assisted by a study of their
+fossiliferous contents, the mere pricking of a continent here and there
+is all that is required for this purpose. Hence, the accuracy of our
+information touching the relative ages of geological strata does not
+depend upon--and, therefore, does not betoken--any equivalent accuracy
+of knowledge touching the fossiliferous material which these strata may
+at the present time actually contain. And, as we well know, the
+opportunities which the geologist has of discovering fossils are
+extremely limited, if we consider these opportunities in relation to the
+area of geological formations. The larger portion of the earth's surface
+is buried beneath the sea; and much the larger portion of the
+fossiliferous deposits on shore are no less hopelessly buried beneath
+the land. Therefore it is only upon the fractional portion of the
+earth's surface which at the present time happens to be actually exposed
+to his view that the geologist is able to prosecute his search for
+fossils. But even here how miserably inadequate this search has hitherto
+been! With the exception of a scratch or two in the continents of Asia
+and America, together with a somewhat larger number of similar scratches
+over the continent of Europe, even that comparatively small portion of
+the earth's surface which is available for the purpose has been hitherto
+quite unexplored by the palæontologist. How enormously rich a store of
+material remains to be unearthed by the future scratchings of this
+surface, we may dimly surmise from the astonishing world of bygone life
+which is now being revealed in the newly discovered fossiliferous
+deposits on the continent of America.
+
+But, besides all this, we must remember, in the second place, that all
+the fossiliferous deposits in the world, even if they could be
+thoroughly explored, would still prove highly imperfect, considered as a
+history of extinct forms of life. In order that many of these forms
+should have been preserved as fossils, it is necessary that they should
+have died upon a surface neither too hard nor too soft to admit of their
+leaving an impression; that this surface should afterwards have
+hardened sufficiently to retain the impression; that it should then have
+been protected from the erosion of water, as well as from the
+disintegrating influence of the air; and yet that it should not have
+sunk far enough beneath the surface to have come within the no less
+disintegrating influence of subterranean heat. Remembering thus, as a
+general rule, how many conditions require to have met before a fossil
+can have been both formed and preserved, we must conclude that the
+geological record is probably as imperfect in itself as are our
+opportunities of reading even the little that has been recorded. If we
+speak of it as a history of the succession of life upon the planet, we
+must allow, on the one hand, that it is a history which merits the name
+of a "chapter of accidents"; and, on the other hand, that during the
+whole course of its compilation pages were being destroyed as fast as
+others were being formed, while even of those that remain it is only a
+word, a line, or at most a short paragraph here and there, that we are
+permitted to see. With so fragmentary a record as this to study, I do
+not think it is too much to say that no conclusions can be fairly based
+upon it, merely from the absence of testimony. Only if the testimony
+were positively opposed to the theory of descent, could any argument be
+fairly raised against that theory on the grounds of this testimony. In
+other words, if any of the fossils hitherto discovered prove the order
+of succession to have been incompatible with the theory of genetic
+descent, then the record may fairly be adduced in argument, because we
+should then be in possession of definite information of a positive
+kind, instead of a mere absence of information of any kind. But if the
+adverse argument reaches only to the extent of maintaining that the
+geological record does not furnish us with so complete a series of
+"connecting links" as we might have expected, then, I think, the
+argument is futile. Even in the case of human histories, written with
+the intentional purpose of conveying information, it is an unsafe thing
+to infer the non-occurrence of an event from a mere silence of the
+historian--and this especially in matters of comparatively small detail,
+such as would correspond (in the present analogy) to the occurrence of
+_species_ and _genera_ as connecting links. And, of course, if the
+history had only come down to us in fragments, no one would attach any
+importance at all to what might have been only the _apparent_ silence of
+the historian.
+
+In view, then, of the unfortunate imperfection of the geological record
+_per se_, as well as of the no less unfortunate limitation of our means
+of reading even so much of the record as has come down to us, I conclude
+that this record can only be fairly used in two ways. It may fairly be
+examined for positive testimony against the theory of descent, or for
+proof of the presence of organic remains of a high order of development
+in a low level of strata. And it may be fairly examined for negative
+testimony, or for the absence of connecting links, if the search be
+confined to the larger taxonomic divisions of the fauna and flora of the
+world. The more minute these divisions, the more restricted must have
+been the areas of their origin, and hence the less likelihood of their
+having been preserved in the fossil state, or of our finding them even
+if they have been. Therefore, if the theory of evolution is true, we
+ought not to expect from the geological record a full history of
+_specific_ changes in any but at most a comparatively small number of
+instances, where local circumstances happen to have been favourable for
+the writing and preservation of such a history. But we might reasonably
+expect to find a general concurrence of geological testimony to the
+larger fact--namely, of there having been throughout all geological time
+a uniform progression as regards the larger taxonomic divisions. And, as
+I will next proceed to show, this is, in a general way, what we do find,
+although not altogether without some important exceptions, with which I
+shall deal in an Appendix.
+
+There is no _positive_ proof _against_ the theory of descent to be drawn
+from a study of palæontology, or proof of the presence of any kind of
+fossils in strata where the fact of their presence is incompatible with
+the theory of evolution. On the other hand, there is an enormous body of
+uniform evidence to prove two general facts of the highest importance in
+the present connexion. The first of these general facts is, that an
+increase in the diversity of types both of plants and animals has been
+constant and progressive from the earliest to the latest times, as we
+should anticipate that it must have been on the theory of descent in
+ever-ramifying lines of pedigree. And the second general fact is, that
+through all these branching lines of ever-multiplying types, from the
+first appearance of each of them to their latest known conditions, there
+is overwhelming evidence of one great law of organic nature--the law of
+gradual advance from the general to the special, from the low to the
+high, from the simple to the complex.
+
+Now, the importance of these large and general facts in the present
+connexion must be at once apparent; but it may perhaps be rendered more
+so if we try to imagine how the case would have stood supposing
+geological investigation to have yielded in this matter an opposite
+result, or even so much as an equivocal result. If it had yielded an
+opposite result, if the lower geological formations were found to
+contain as many, as diverse, and as highly organized types as the later
+geological formations, clearly there would have been no room at all for
+any theory of progressive evolution. And, by parity of reasoning, in
+whatever degree such a state of matters were found to prevail, in that
+degree would the theory in question have been discredited. But seeing
+that these opposite principles do not prevail in any (relatively
+speaking) considerable degree[16], we have so far positive testimony of
+the largest and most massive character in favour of this theory. For
+while all these large and general facts are very much what they ought to
+be according to this theory, they cannot be held to lend any support at
+all to the rival theory. In other words, it is clearly no essential part
+of the theory of special creation that species should everywhere exhibit
+this gradual multiplication as to number, coupled with a gradual
+diversification and general elevation of types, in all the growing
+branches of the tree of life. No one could adopt seriously the jocular
+lines of Burns, to the effect that the Creator required to practise his
+prentice hand on lower types before advancing to the formation of
+higher. Yet, without some such assumption, it would be impossible to
+explain, on the theory of independent creations, why there should have
+been this gradual advance from the few to the many, from the general to
+the special, from the low to the high.
+
+ [16] For objections which may be brought against this and similar
+ statements, see the Appendix.
+
+ +---+--------------------------+---------------------------------------
+ | |_Epochs and Formations._ |_Faunal Characters._
+ |C | |
+ |a |--------------------------+---------------------------------------
+ |i |POST-PLIOCENE. |Man. Mammalia principally of living
+ |n | Glacial Period. | species. Mollusca exclusively recent.
+ |o | +---------------------------------------
+ |z |PLIOCENE, 3,000 feet. |Mammalia principally of recent genera
+ |o | | --living species rare. Mollusca very
+ |i | | modern.
+ |c | +---------------------------------------
+ | |MIOCENE, 4,000 ft. |Mammalia principally of living
+ |o | | families; extinct genera numerous;
+ |r | | species all extinct. Mollusca largely
+ | |OLIGOCENE, 8,000 ft. | of recent species.
+ |T | +---------------------------------------
+ |e |EOCENE, 10,000 ft. |Mammalia with numerous extinct families
+ |r | | and orders; all the species and
+ |i | | most of the genera extinct. Modern
+ |a | | type Shell-Fish.
+ |r | |
+ |y | |
+ +---|--------------------------+---------------------------------------
+ | |LARAMIE, 4,000 ft. |Passage beds.
+ | |--------------------------+---------------------------------------
+ |M |CRETACEOUS, 12,000 ft. |Dinosaurian (bird-like) Reptiles;
+ |e | Chalk. | Pterodactyls (flying Reptiles);
+ |s | | toothed Birds; earliest Snake; bony
+ |o | | Fishes; Crocodiles; Turtles;
+ |z | | Ammonites.
+ |o | +---------------------------------------
+ |i |JURASSIC, 6,000 ft. |Earliest Birds; giant Reptiles
+ |c | Oolite. | (Ichthyosaurs, Dinosaurs,
+ | | Lias. | Pterodactyls); Ammonites; Clam- and
+ |o | | Snail-Shells very abundant; decline
+ |r | | of Brachiopods; Butterfly.
+ | | +---------------------------------------
+ |S |TRIAS, 5,000 ft. |First Mammalian (Marsupial); 2-gilled
+ |e | New Red Sandstone. | Cephalopods (Cuttle-Fishes,
+ |c | | Belemnites); reptilian Foot-Prints.
+ |o | |
+ |n | |
+ |d | |
+ |a | |
+ |r | |
+ |y | |
+ |---|--------------------------+---------------------------------------
+ |P |PERMIAN, 5,000 ft. |Earliest true Reptiles.
+ |a | +---------------------------------------
+ |l |CARBONIFEROUS, 26,000 ft. |Earliest Amphibian (Labyrinthodont);
+ |e | | extinction of Trilobites; first
+ |o | Coal. | Cray-fish; Beetles; Cockroaches;
+ |z | | Centipedes; Spiders.
+ |o | +---------------------------------------
+ |i |DEVONIAN, 18,000 ft. |Cartilaginous and Ganoid Fishes;
+ |c | Old Red Sandstone. | earliest and (snail) and freshwater
+ | | | Shells; Shell-Fish abundant; decline
+ |o | | of Trilobites; May-flies; Crab.
+ |r | +---------------------------------------
+ | |SILURIAN, 33,000 ft. |Earliest Fish; the first Air-Breathers
+ |P | | (Insect, Scorpion); Brachiopods and
+ |r | | 4-gilled Cephalopods very abundant;
+ |i | | Trilobites; Corals; Graptolites.
+ |m | +---------------------------------------
+ |a |CAMBRIAN, 24,000 ft. |Trilobites; Brachiopod Mollusks.
+ |r | |
+ |y | |
+ |---|--------------------------+---------------------------------------
+ |A |ARCHÆEAN, 30,000 ft. |
+ |z | Huronian. |Eozoön, (probably not a fossil).
+ |o | Laurentian. |
+ |i |--------------------------+---------------------------------------
+ |c |PRIMEVAL. |Non-sedimentary.
+ +------------------------------+--------------------------------------+
+
+I submit, then, that so far as the largest and most general principles
+in the matter of palæontology are concerned, we have about as strong and
+massive a body of evidence as we could reasonably expect this branch of
+science to yield; for it is at once enormous in amount and positive in
+character. Therefore, if I do not further enlarge upon the evidence
+which we here have, as it were _en masse_, it is only because I do not
+feel that any words could add to its obvious significance. It may best
+be allowed to speak for itself in the millions of facts which are
+condensed in this tabular statement of the order of succession of all
+the known forms of animal life, as presented by the eminent
+palæontologist, Professor Cope[17].
+
+ [17] For difficulties and objections, see Appendix.
+
+Or, taking a still more general survey, this tabular statement may be
+still further condensed, and presented in a diagrammatic form, as it has
+been by another eminent American palæontologist, Prof. Le Conte, in his
+excellent little treatise on _Evolution and its Relations to Religious
+Thought_. The following is his diagrammatic representation, with his
+remarks thereon.
+
+ When each ruling class declined in importance, it did not perish,
+ but continued in a subordinate position. Thus, the whole organic
+ kingdom became not only higher and higher in its highest forms, but
+ also more and more complex in its structure and in the interaction
+ of its correlated parts. The whole process and its result is
+ roughly represented in the accompanying diagram, in which A B
+ represents the course of geological time, and the curve, the rise,
+ culmination, and decline of successive dominate classes.
+
+ [Illustration: FIG. 59.--Diagram of Geological Succession of the
+ Classes of the Animal Kingdom. (After Le Conte.)]
+
+I will here leave the evidence which is thus yielded by the most general
+principles that have been established by the science of palæontology;
+and I will devote the rest of this chapter to a detailed consideration
+of a few highly special lines of evidence. By thus suddenly passing from
+one extreme to the other, I hope to convey the best idea that can be
+conveyed within a brief compass of the minuteness, as well as the
+extent, of the testimony which is furnished by the rocks.
+
+ * * * * *
+
+When Darwin first published his _Origin of Species_, adverse critics
+fastened upon the "missing-link" argument as the strongest that they
+could bring against the theory of descent. Although Darwin had himself
+strongly insisted on the imperfection of the geological record, and the
+consequent precariousness of any negative conclusions raised upon it,
+these critics maintained that he was making too great a demand upon the
+argument from ignorance--that, even allowing for the imperfection of the
+record, they would certainly have expected at least a few cases of
+testimony to _specific_ transmutation. For, they urged in effect,
+looking to the enormous profusion of the extinct species on the one
+hand, and to the immense number of known fossils on the other, it was
+incredible that no satisfactory instances of specific transmutation
+should ever have been brought to light, if such transmutation had ever
+occurred in the universal manner which the theory was bound to suppose.
+But since Darwin first published his great work palæontologists have
+been very active in discovering and exploring fossiliferous beds in
+sundry parts of the world; and the result of their labours has been to
+supply so many of the previously missing links that the voice of
+competent criticism in this matter has now been well-nigh silenced.
+Indeed, the material thus furnished to an advocate of evolution at the
+present time is so abundant that his principal difficulty is to select
+his samples. I think, however, that the most satisfactory result will be
+gained if I restrict my exposition to a minute account of some few
+series of connecting links, rather than if I were to take a more general
+survey of a larger number. I will, therefore, confine the survey to the
+animal kingdom, and there mention only some of the cases which have
+yielded well-detailed proof of continuous differentiation.
+
+It is obvious that the parts of animals most likely to have been
+preserved in such a continuous series of fossils as the present line of
+evidence requires, would have been the hard parts. These are horns,
+bones, teeth, and shells. Therefore I will consider each of these four
+classes of structures separately.
+
+ * * * * *
+
+Horns wherever they occur, are found to be of high importance for
+purposes of classification. They are restricted to the Ruminants, and
+appear under three different forms or types--namely solid, as in
+antelopes; hollow, as in sheep; and deciduous, as in deer. Now, in each
+of these divisions we have a tolerably complete palæontological history
+of the evolution of horns. The early ruminants were altogether hornless
+(Fig. 60). Then, in the middle Miocene, the first antelopes appeared
+with tiny horns, which progressively increased in size among the
+ever-multiplying species of antelopes until the present day. But it is
+in the deer tribe that we meet with even better evidence touching the
+progressive evolution of horns; because here not only size, but shape,
+is concerned. For deer's horns, or antlers, are arborescent; and hence
+in their case we have an opportunity of reading the history, not only of
+a progressive growth in size, but also of an increasing development of
+form. Among the older members of the tribe, in the lower Miocene, there
+are no horns at all. In the mid-Miocene we meet with two-pronged horns
+(_Cervus dicrocerus_, Figs. 61, 62, 1/5 nat. size). Next, in the upper
+Miocene (_C. matheronis_, Fig. 63, 1/8 nat. size), and extending into
+the Pliocene (_C. pardinensis_, Fig. 64, 1/18 nat. size), we meet with
+three-pronged horns. Then, in the Pliocene we find also four-pronged
+horns (_C. issiodorensis_, Fig. 65, 1/16 nat. size), leading us to
+five-pronged (_C. tetraceros_). Lastly, in the Forest-bed of Norfolk we
+meet with arborescent horns (_C. Sedgwickii_, Fig. 66, 1/35 nat. size).
+The life-history of existing stags furnishes a parallel development
+(Fig. 67), beginning with a single horn (which has not yet been found
+palæontologically), going on to two prongs, three prongs, four prongs,
+and afterwards branching.
+
+ [Illustration: FIG. 60.--Skull of _Oreodon Culbertsoni_. (After
+ Leidy.)]
+
+ [Illustration: FIGS. 61-66. The series is reduced from Gaudry's
+ illustrations, after Farge, Croizet, Jobert and Boyd Dawkins.]
+
+ [Illustration: FIG. 67.--Successive stages in the development of an
+ existing Deer's Antlers. (After Gaudry, but a better illustration
+ has already been given on p. 100.)]
+
+ * * * * *
+
+Coming now to bones, we have a singularly complete record of transition
+from one type or pattern of structure to another in the phylogenetic
+history of tails. This has been so clearly and so tersely conveyed by
+Prof. Le Conte, that I cannot do better than quote his statement.
+
+ It has long been noticed that there are among fishes two styles of
+ tail-fins. These are the even-lobed, or homocercal (Fig. 68), and
+ the uneven-lobed, or heterocercal (Fig. 69). The one is
+ characteristic of ordinary fishes (teleosts), the other of sharks
+ and some other orders. In structure the difference is even more
+ fundamental than in form. In the former style the backbone stops
+ abruptly in a series of short, enlarged joints, and thence sends
+ off rays to form the tail-fin (Fig. 68); in the latter the
+ backbone runs through the fin to its very point, growing slenderer
+ by degrees, and giving off rays above and below from each joint,
+ but the rays on the lower side are much longer (Fig. 69). This type
+ of fin is, therefore, _vertebrated_, the other _non-vertebrated_.
+ Figs. 68 and 69 show these two types in form and structure. But
+ there is still another type found only in the lowest and most
+ generalized forms of fishes. In these the tail-fin is vertebrated
+ and yet symmetrical. This type is shown in Fig. 70.
+
+ [Illustration: FIG. 68.--Homocercal Tail, showing (A) external form
+ and (B) internal structure.]
+
+ [Illustration: FIG. 69.--Heterocercal Tail, showing (A) external
+ form and (B) internal structure.]
+
+ [Illustration: FIG. 70.--Vertebrated but symmetrical fin
+ (diphycercal), showing (A) external form and (B) internal
+ structure.]
+
+ Now, in the development of a teleost fish (Fig. 68), as has been
+ shown by Alexander Agassiz, the tail-fin is first like Fig. 70;
+ then becomes heterocercal, like Fig. 69; and, finally, becomes
+ homocercal like Fig. 68. Why so? Not because there is any special
+ advantage in this succession of forms; for the changes take place
+ either in the egg or else in very early embryonic states. The
+ answer is found in the fact that _this is the order of change in
+ the phylogenetic series_. The earliest fish-tails were either like
+ Fig. 69 or Fig. 70; never like Fig. 68. The earliest of all were
+ almost certainly like Fig. 70; then they became like Fig. 69; and,
+ finally, only much later in geological history (Jurassic or
+ Cretaceous), they became like Fig. 68. This order of change is
+ still retained in the embryonic development of the last introduced
+ and most specialized order of existing fishes. The family history
+ is repeated in the individual history.
+
+ Similar changes have taken place in the form and structure of
+ birds' tails. The earliest bird known--the Jurassic
+ _Archæopteryx_--had a long reptilian tail of twenty-one joints,
+ each joint bearing a feather on each side, right and left (Fig.
+ 71): [see also Fig. 73]. In the typical modern bird, on the
+ contrary, the tail-joints are diminished in number, shortened up,
+ and enlarged, and give out long feathers, fan-like, to form the
+ so-called tail (Fig. 72). The _Archæopteryx'_ tail is
+ _vertebrated_, the typical bird's _non-vertebrated_. This
+ shortening up of the tail did not take place at once, but
+ gradually. The Cretaceous birds, intermediate in time, had tails
+ intermediate in structure. The _Hesperornis_ of Marsh had twelve
+ joints. At first--in Jurassic strata--the tail is fully a half of
+ the whole vertebral column. It then gradually shortens up until it
+ becomes the aborted organ of typical modern birds. Now, in
+ embryonic development, the tail of the modern typical bird _passes
+ through all these stages_. At first the tail is nearly one half the
+ whole vertebral column; then, as development goes on, while the
+ rest of the body grows, the growth of the tail stops, and thus
+ finally becomes the aborted organ we now find. The ontogeny still
+ passes through the stages of the phylogeny. The same is true of all
+ tailless animals.
+
+ [Illustration: FIG. 71.--Tail of _Archæopteryx_. A indicates origin
+ of simply-jointed tail.]
+
+ [Illustration: FIG. 72.--Tail of modern Bird. The numerals indicate
+ the foreshortened, enlarged, and consolidated joints; _f_, terminal
+ segment of the vertebral column; D, shafts of feathers.]
+
+ [Illustration: FIG. 73.--_Archæopteryx macura_, restored, 1/2 nat.
+ size. (After Flower.) The section of the tail is copied from Owen,
+ nat. size.]
+
+The extinct _Archæopteryx_ above alluded to presents throughout its
+whole organization a most interesting assemblage of "generalized
+characters." For example, its teeth, and its still unreduced digits of
+the wings (which, like those of the feet, are covered with scales),
+refer us, with almost as much force as does the vertebrated tail, to the
+Sauropsidian type--or the trunk from which birds and reptiles have
+diverged.
+
+We will next consider the palæontological evidence which we now
+possess of the evolution of mammalian limbs, with special reference to
+the hoofed animals, where this line of evidence happens to be most
+complete.
+
+I may best begin by describing the bones as these occur in the sundry
+branches of the mammalian type now living. As we shall presently see,
+the modifications which the limbs have undergone in these sundry
+branches chiefly consist in the suppression of some parts and the
+exaggerated development of others. But, by comparing all mammalian limbs
+together, it is easy to obtain a generalized type of mammalian limb,
+which in actual life is perhaps most nearly conformed to in the case of
+bears. I will therefore choose the bear for the purpose of briefly
+expounding the bones of mammalian limbs in general--merely asking it to
+be understood, that although in the case of many other mammalia some of
+these bones may be dwindled or altogether absent, while others may be
+greatly exaggerated as to relative size, in no case do any _additional_
+bones appear.
+
+On looking, then, at the skeleton of a bear (Fig. 74), the first thing
+to observe is that there is a perfect serial homology between the bones
+of the hind legs and of the fore legs. The thigh-bone, or femur,
+corresponds to the shoulder-bone, or humerus; the two shank bones (tibia
+and fibula) correspond to the two arm-bones (radius and ulna); the many
+little ankle-bones (tarsals) correspond to the many little wrist-bones
+(carpals); the foot-bones (meta-tarsals) correspond to the hand-bones
+(meta-carpals); and, lastly, the bones of each of the toes correspond to
+those of each of the fingers.
+
+ [Illustration: FIG. 74.--Skeleton of Polar Bear, drawn from nature
+ (_Brit. Mus._).]
+
+The next thing to observe is, that the disposition of bones in the case
+of the bear is such that the animal walks in the way that has been
+called plantigrade. That is to say, all the bones of the fingers, as
+well as those of the toes, feet, and ankles, rest upon the ground, or
+help to constitute the "soles." Our own feet are constructed on a
+closely similar pattern. But in the majority of living mammalian forms
+this is not the case. For the majority of mammals are what has been
+called digitigrade. That is to say, the bones of the limb are so
+disposed that both the foot and hand bones, and therefore also the ankle
+and wrist, are removed from the ground altogether, so that the animal
+walks exclusively upon its toes and fingers--as in the case of this
+skeleton (Fig. 75), which is the skeleton of a lion. The next figures
+display a series of limbs, showing the progressive passage of a
+completely plantigrade into a highly digitigrade type--the curved lines
+of connexion serving to indicate the homologous bones (Figs. 76, 77).
+
+ [Illustration: _Fig_. 75.--Skeleton of Lion. (After Huxley.)]
+
+ [Illustration: FIG. 76.--Anterior limb of Man, Dog, Hog, Sheep, and
+ Horse. (After Le Conte.) _Sc_, shoulder-blade; _c_, coracoid; _a_,
+ _b_, bones of fore-arm; 5, bones of the wrist; 6, bones of the hand;
+ 7, bones of the fingers.]
+
+ [Illustration: FIG. 77.--Posterior limb of Man, Monkey, Dog, Sheep
+ and Horse. (After Le Conte.) 1, Hip-joint; 2, thigh-bone; 3,
+ knee-joint; 4, bones of leg; 5, ankle-joint; 6, bones of foot; 7,
+ bones of toes.]
+
+I will now proceed to detail the history of mammalian limbs, as this has
+been recorded for us in fossil remains.
+
+The most generalized or primitive types of limb hitherto discovered in
+any vertebrated animal above the class of fishes, are those which are
+met with in some of the extinct aquatic reptiles. Here, for instance, is
+a diagram of the left hind limb of _Baptanodon discus_ (Fig. 78). It has
+six rows of little symmetrical bones springing from a leg-like origin.
+But the whole structure resembles the fin of a fish about as nearly as
+it does the leg of a mammal. For not only are there six rows of bones,
+instead of five, suggestive of the numerous rays which characterise the
+fin of a fish; but the structure as a whole, having been covered over
+with blubber and skin, was throughout flexible and unjointed--thus in
+function, even more than in structure, resembling a fin. In this
+respect, also, it must have resembled the paddle of a whale (see Fig.
+79); but of course the great difference will be noted, that the paddle
+of a whale reveals the dwindled though still clearly typical bones of a
+true mammalian limb; so that although in outward form and function these
+two paddles are alike, their inward structure clearly shows that while
+the one testifies to the absence of evolution, the other testifies to
+the presence of degeneration. If the paddle of _Baptanodon_ had occurred
+in a whale, or the paddle of a whale had occurred in _Baptanodon_,
+either fact would in itself have been well-nigh destructive of the whole
+theory of evolution.
+
+ [Illustration: FIG. 78.--A, posterior limb of _Baptanodon discus_.
+ (After Marsh.) F, thigh-bone; I to VI, undifferentiated bones of the
+ leg and foot. B, anterior limb of _Chelydra serpentina_. (After
+ Gegenbaur.) U and R, bones of the fore-arm; I to V, fully
+ differentiated bones of the hand, following those of the wrist.]
+
+ [Illustration: FIG. 79.--Paddle of a Whale.]
+
+Such, then, is the most generalized as it is the most ancient type of
+vertebrate limb above the class of fishes. Obviously it is a type
+suited only to aquatic life. Consequently, when aquatic Vertebrata began
+to become terrestrial, the type would have needed modification in order
+to serve for terrestrial locomotion. In particular, it would have needed
+to gain in consolidation and in firmness, which means that it would have
+needed also to become jointed. Accordingly, we find that this archaic
+type gave place in land-reptiles to the exigencies of these
+requirements. Here for example is a diagram, copied from Gegenbaur, of
+the right fore-foot of _Chelydra serpentina_ (Fig. 78). As compared with
+the homologous limb of its purely aquatic predecessor, there is to be
+noticed the disappearance of one of the six rows of small bones, a
+confluence of some of the remainder in the other five rows, a
+duplication of the arm-bone into a radius and ulna, in order to admit of
+jointed rotation of the hand, and a general disposition of the small
+bones below these arm-bones, which clearly foreshadows the joint of the
+wrist. Indeed, in this fore-foot of _Chelydra_, a child could trace all
+the principal homologies of the mammalian counterpart, growing, like the
+next stage in a dissolving view, out of the primitive paddle of
+_Baptanodon_--namely, first the radius and ulna, next the carpals, then
+the meta-carpals, and, lastly, the three phalanges in each of the five
+digits.
+
+Such a type of foot no doubt admirably meets the requirements of slow
+reptilian locomotion over swampy ground. But for anything like rapid
+locomotion over hard and uneven ground, greater modifications would be
+needed. Such modifications, however, need not be other in kind: it is
+enough that they should continue in the same line of advance, so as to
+reach a higher degree of firmness, combined with better joints.
+Accordingly we find that this took place, not indeed among reptiles,
+whose habits of cold-blooded life have not changed, but among their
+warm-blooded descendants, the mammals. Moreover, when we examine the
+whole mammalian series, we find that the required modifications must
+have taken place in slightly different ways in three lines of descent
+simultaneously. We have first the plantigrade and digitigrade
+modifications already mentioned (pp. 178, 179) Of these the plantigrade
+walking entailed least change, because most resembling the ancestral or
+lizard-like mode of progression. All that was here needed was a general
+improvement as to relative lengths of bones, with greater consolidation
+and greater flexibility of joints. Therefore I need not say anything
+more about the plantigrade division. But the digitigrade modification
+necessitated a change of structural plan, to the extent of raising the
+wrist and ankle joints off the ground, so as to make the quadruped walk
+on its fingers and toes. We meet with an interesting case of this
+transition in the existing hare, which while at rest supports itself on
+the whole hind foot after the manner of a plantigrade animal, but when
+running does so upon the ends of its toes, after the manner of a
+digitigrade animal.
+
+It is of importance for us to note that this transition from the
+original plantigrade to the more recent digitigrade type, has been
+carried out on two slightly different plans in two different lines of
+mammalian descent. The hoofed mammals--which are all digitigrade--are
+sub-classified as artiodactyls and perissodactyls, i. e. even-toed and
+odd-toed. Now, whether an animal has an even or an odd number of toes
+may seem a curiously artificial distinction on which to found so
+important a classification of the mammalian group. But if we look at the
+matter from a less empirical and more intelligent point of view, we
+shall see that the alternative of having an even or an odd number of
+toes carries with it alternative consequences of a practically important
+kind to any animal of the digitigrade type. For suppose an aboriginal
+five-toed animal, walking on the ends of its five toes, to be called
+upon to resign some of his toes. If he is left with an even number, it
+must be two or four; and in either case the animal would gain the
+firmest support by so disposing his toes as to admit of the axis of his
+foot passing between an equal number of them--whether it be one or two
+toes on each side. On the other hand, if our early mammal were called
+upon to retain an odd number of toes, he would gain best support by
+adjusting matters so that the axis of his foot should be coincident with
+his middle toe, whether this were his only toe, or whether he had one on
+either side of it. This consideration shows that the classification into
+even-toed and odd-toed is not so artificial as it no doubt at first
+sight appears. Let us, then, consider the stages in the evolution of
+both these types of feet.
+
+Going back to the reptile _Chelydra_, it will be observed that the axis
+of the foot passes down the middle toe, which is therefore supported by
+two toes on either side (Fig. 78). It may also be noticed that the wrist
+or ankle bones do not interlock, either with one another or with the
+bones of the hand or foot below them. This, of course, would give a
+weak foot, suited to slow progression over marshy ground--which, as we
+have seen, was no doubt the origin of the mammalian plantigrade foot.
+Here, for instance, to all intents and purposes, is a similar type of
+foot, which belonged to a very early mammal, antecedent to the elephant
+series, the horse series, the rhinoceros, the hog, and, in short, all
+the known hoofed mammalia (Fig. 80). It was presumably an inhabitant of
+swampy ground, slow in its movements, and low in its intelligence.
+
+ [Illustration: FIG. 80.--Fossil skeleton of _Phenacodus primavus_.
+ (After Cope.)]
+
+But now, as we have seen, for more rapid progression on hard uneven
+ground, a stronger and better jointed foot would be needed. Therefore we
+find the bones of the wrist and ankle beginning to interlock, both among
+themselves and also with those of the foot and hand immediately below
+them. Such a stage of evolution is still apparent in the now existing
+elephant. (See Fig. 81.)
+
+ [Illustration: FIG. 81.--Bones of the foot of four different forms
+ of the perissodactyl type, showing gradual reduction in the number
+ of digits, coupled with a greater consolidation of the bones above
+ the digits. The series reads from right to left. Drawn from nature
+ (_Brit. Mus._).]
+
+Next, however, a still stronger foot was made by the still further
+interlocking of the wrist and ankle bones, so that both the first and
+second rows of them were thus fitted into each other, as well as into
+the bones of the hand and foot beneath. This further modification is
+clearly traceable in some of the earlier perissodactyls, and occurs in
+the majority at the present time. Compare, for example, the greater
+interlocking and consolidation of these small bones in the Rhinoceros as
+contrasted with the Elephant (Fig. 81). Moreover, simultaneously with
+these consolidating improvements in the mechanism of the wrist and ankle
+joints, or possibly at a somewhat later period, a reduction in the
+number of digits began to take place. This was a continuation of the
+policy of consolidating the foot, analogous to the dropping out of the
+sixth row of small bones in the paddle of _Baptanodon_. (Fig. 78.) In
+the pentadactyl plantigrade foot of the early mammals, the first digit,
+being the shortest, was the first to leave the ground, to dwindle,
+and finally to disappear. More work being thus thrown on the remaining
+four, they were strengthened by interlocking with the wrist (or ankle)
+bones above them, as just mentioned; and also by being brought closer
+together.
+
+ [Illustration: FIG. 82.--Bones of the foot of four different forms
+ of the artiodactyl type, showing gradual reduction of the number of
+ digits, coupled with a greater consolidation of the bones above the
+ digits. The series reads from right to left. Drawn from nature
+ (_Brit. Mus._).]
+
+The changes which followed I will render in the words of Professor
+Marsh.
+
+ Two kinds of reduction began. One leading to the existing
+ perissodactyl foot, and the other, apparently later, resulting in
+ the artiodactyl type. In the former the axis of the foot remained
+ in the middle of the third digit, as in the pentadactyl foot. [See
+ Fig. 81.] In the latter, it shifted to the outer side of this
+ digit, or between the third and fourth toe. [See Fig. 82.]
+
+ In the further reduction of the perissodactyl foot, the fifth
+ digit, being shorter than the remaining three, next left the
+ ground, and gradually disappeared. [Fig. 81 B.] Of the three
+ remaining toes, the middle or axial one was the longest, and
+ retaining its supremacy as greater strength and speed were
+ required, finally assumed the chief support of the foot [Fig. 81
+ C], while the outer digits left the ground, ceased to be of use,
+ and were lost, except as splint-bones [Fig. 81 D]. The feet of the
+ existing horse shows the best example of this reduction in the
+ Perissodactyls, as it is the most specialized known in the
+ Ungulates [Fig. 81 D].
+
+ In the artiodactyl foot, the reduction resulted in the gradual
+ diminution of the two outer of the four remaining toes, the third
+ and fourth doing all the work, and thus increasing in size and
+ power. The fifth digit, for the same reasons as in the
+ perissodactyl foot, first left the ground and became smaller. Next,
+ the second soon followed, and these two gradually ceased to be
+ functional, [and eventually disappeared altogether, as shown in the
+ accompanying drawing of the feet of still existing animals, Fig. 82
+ B, C, D].
+
+ The limb of the modern race-horse is a nearly perfect piece of
+ machinery, especially adapted to great speed on dry, level ground.
+ The limb of an antelope, or deer, is likewise well fitted for
+ rapid motion on a plain, but the foot itself is adapted to rough
+ mountain work as well, and it is to this advantage, in part, that
+ the Artiodactyls owe their present supremacy. The plantigrade
+ pentadactyl foot of the primitive Ungulate--and even the
+ perissodactyl foot that succeeded it--both belong to the past humid
+ period of the world's history. As the surface of the earth slowly
+ dried up, in the gradual desiccation still in progress, new types
+ of feet became a necessity, and the horse, antelope, and camel were
+ gradually developed, to meet the altered conditions.
+
+The best instance of such progressive modifications in the case of
+perissodactyl feet is furnished by the fossil pedigree of the existing
+horse, because here, within the limits of the same continuous family
+line, we have presented the entire series of modifications.
+
+There are now known over thirty species of horse-like creatures,
+beginning from the size of a fox, then progressively increasing in bulk,
+and all standing in linear series in structure as in time. Confining
+attention to the teeth and feet, it will be seen from the wood-cut on
+page 189 that the former grow progressively longer in their sockets, and
+also more complex in the patterns of their crowns. On the other hand,
+the latter exhibit a gradual diminution of their lateral toes, together
+with a gradual strengthening of the middle one. (See Fig. 83.) So that
+in the particular case of the horse-ancestry we have a practically
+complete chain of what only a few years ago were "missing links." And
+this now practically completed chain shows us the entire history of what
+happens to be the most peculiar, or highly specialized, limb in the
+whole mammalian class--namely, that of the existing horse. Of the other
+two wood-cuts, the former (Fig. 84) shows the skeleton of a very early
+and highly generalized ancestor, while the other is a partial
+restoration of a much more recent and specialized one. (Fig. 85.)
+
+ [Illustration: FIG. 83.--Feet and teeth in fossil pedigree of the
+ Horse. (After Marsh.) _a_, bones of the fore-foot; _b_, bones of the
+ hind-foot; _c_, radius and ulna; _d_, tibia and fibula; _e_, roots
+ of a tooth; _f_ and _g_, crowns of upper and lower molar teeth.]
+
+ [Illustration: FIG. 84.--_Palæotherium_. (Lower Tertiary of Paris
+ Basin.)]
+
+ [Illustration: FIG. 85.--_Hipparion_. (New World Pliocene.)]
+
+On the other hand, progressive modifications of the artiodactyl feet may
+be traced geologically up to the different stages presented by living
+ruminants, in some of which it has proceeded further than in others. For
+instance, if we compare the pig, the deer, and the camel (Fig. 82), we
+immediately perceive that the dwindling of the two rudimentary digits
+has proceeded much further in the case of the deer than in that of the
+pig, and yet not so far as in that of the camel, seeing that here they
+have wholly disappeared. Moreover, complementary differences are to be
+observed in the degree of consolidation presented by the two useful
+digits. For while in the pig the two foot-bones are still clearly
+distinguishable throughout their entire length, in the deer, and still
+more in the camel, their union is more complete, so that they go to
+constitute a single bone, whose double or compound character is
+indicated externally only by a slight bifurcation at the base.
+Nevertheless, if we examine the state of matters in the unborn young of
+these animals, we find that the two bones in question are still
+separated throughout their length, and thus precisely resemble what used
+to be their permanent condition in some of the now fossil species of
+hoofed mammalia.
+
+Turning next from bones of the limb to other parts of the mammalian
+skeleton, let us briefly consider the evidence of evolution that is here
+likewise presented by the vertebral column, the skull, and the teeth.
+
+As regards the vertebral column, if we examine this structure in any of
+the existing hoofed animals, we find that the bony processes called
+zygapophyses, which belong to each of the constituent vertebræ, are so
+arranged that the anterior pair belonging to each vertebra interlocks
+with the posterior pair belonging to the next vertebra. In this way the
+whole series of vertebræ are connected together in the form of a chain,
+which, while admitting of considerable movement laterally, is everywhere
+guarded against dislocation. But if we examine the skeletons of any
+ungulates from the lower Eocene deposits, we find that in no case is
+there any such arrangement to secure interlocking. In all the hoofed
+mammals of this period the zygapophyses are flat. Now, from this flat
+condition to the present condition of full interlocking we obtain a
+complete series of connecting links. In the middle Miocene period we
+find a group of hoofed animals in which the articulation begins by a
+slight rounding of the previously flat surfaces: later on this rounding
+progressively increases, until eventually we get the complete
+interlocking of the present time.
+
+As regards teeth, and still confining attention to the hoofed mammals,
+we find that low down in the geological series the teeth present on
+their grinding surfaces only three simple tubercles. Later on a fourth
+tubercle is added, and later still there is developed that complicated
+system of ridges and furrows which is characteristic of these teeth at
+the present time, and which was produced by manifold and various
+involutions of the three or four simple tubercles of Eocene and lower
+Miocene times. In other words, the principle of gradual improvement in
+the construction of teeth, which has already been depicted as regards
+the particular case of the Horse-family (Fig. 83), is no less apparent
+in the pedigree of all the other mammalia, wherever the palæontological
+history is sufficiently intact to serve as a record at all.
+
+Lastly, as regards the skull, casts of the interior show that all the
+earlier mammals had small brains with comparatively smooth or
+unconvoluted surfaces; and that as time went on the mammalian brain
+gradually advanced in size and complexity. Indeed so small were the
+cerebral hemispheres of the primitive mammals that they did not overlap
+the cerebellum, while their smoothness must have been such as in this
+respect to have resembled the brain of a bird or reptile. This, of
+course, is just as it ought to be, if the brain, which the skull has to
+accommodate, has been gradually evolved into larger and larger
+proportions in respect of its cerebral hemispheres, or the upper masses
+of it which constitute the seat of intelligence. Thus, if we look at the
+above series of wood-cuts, which represents the comparative structure of
+the brain in the existing classes of the Vertebrata, we can immediately
+understand why the fossil skulls of Mammalia should present a gradual
+increase in size and furrowing, so as to accommodate the general
+increase of the brain in both these respects between the level marked
+"maml" and that marked "man," in the last of the diagrams. (Fig. 87.)
+
+ [Illustration: FIG. 86.--Comparative series of Brains. (After Le
+ Conte.) The series reads from above downwards, and represents
+ diagrammatically the brain of a Fish, a Reptile, a Bird, a Mammal,
+ and a Man. In each case the letter A marks a side view, and the
+ letter B a top view. The small italics throughout signify the
+ following homologous parts: _m_, medulla; _cb_, cerebellum; _op_,
+ optic lobes; _cr_, cerebrum and thalamus; _ol_, olfactory lobes. The
+ series shows a progressive consolidation and enlargement of the
+ brain in general, and of the cerebrum and cerebellum in particular,
+ which likewise exhibit continually advancing structure in respect of
+ convolution. In the case of Man, these two parts of the brain have
+ grown to so great a size that they conceal all the other parts from
+ the superficial points of view represented in the diagram.]
+
+ [Illustration: FIG. 87.--Ideal section through all the above stages.
+ (After Le Conte.])
+
+The tabular statement on the following diagram, which I borrow from
+Prof. Cope, will serve at a glance to reveal the combined significance
+of so many lines of evidence, united within the limits of the same group
+of animals.
+
+To give only one special illustration of the principle of evolution as
+regards the skull, here is one of the most recent instances that has
+occurred of the discovery of a missing link, or connecting form (see
+Fig. 88). The fossil (B), which was found in New Jersey, stands in an
+intermediate position between the stag and the elk. In the stag (A) the
+skull is high, showing but little of that anterior attenuation which is
+such a distinctive feature of the skull of the elk (C). The nasal bones
+(N) of the former, again, are remarkably long when compared with the
+similar bones of the latter, and the premaxillaries (PMX), instead of
+being projected forward along the horizontal plane of the base of the
+skull, are deflected sharply downward. In all these points, it will be
+seen, the newly discovered form (_Cervalces_) holds an intermediate
+position (B). "The skull exhibits a partial attenuation anteriorly,
+the premaxillaries are directed about equally downward and forward, and
+the nasal bones are measurably contracted in size. The horns likewise
+furnish characters which further serve to establish this dual
+relationship[18]."
+
+ [18] Heilprin, _Geological Evidences of Evolution_, pp. 73-4 (1888).
+
+ [Illustration: FIG. 88.--Skulls of--A, Canadian Stag; B, _Cervalces
+ Americanus_; and C, Elk. (After Heilprin.)]
+
+ Formation.
+ |No. of toes
+ | |Feet
+ | | |Astragalus.
+ | | | |Carpus and tarsus.
+ | | | | |Ulno-radius.
+ | | | | | |Superior molars.
+ | | | | | | |Zygapophyses.
+ | | | | | | | |Brain.
+ | | | | | | | |
+ Pliocene.
+ |1-1, 2-2
+ | |Digitigrade. (Plantigrade.)
+ | | |Grooved. (Flat.)
+ | | | |Interlocking. (Opposite.)
+ | | | | |Faceted.
+ | | | | | |4-tubercles, crested and cemented.
+ | | | | | | |Doubly involute. Singly involute.
+ | | | | | | | |Hemispheres larger, convoluted.
+ | | | | | | | |
+ Upper Miocene. (Loup Fork.)
+ |3-3, 4-4, (5-5)
+ | |
+ | | |
+ | | | |
+ | | | | |
+ | | | | | |
+ | | | | | | |
+ | | | | | | | |
+ | | | | | | | |
+ Middle. (John Day.)
+ |2-2, 3-3, 4-4
+ | |Digitigrade.
+ | | |Grooved.
+ | | | |Interlocking.
+ | | | | |Faceted. Smooth
+ | | | | | |4-tubercles, and crested
+ | | | | | | |Singly involute. Double involute.
+ | | | | | | | |Hemispheres larger, convoluted.
+ | | | | | | | |
+ Lower (White River.)
+ |3-3, 4-3
+ | |Digitigrade. Plantigrade.
+ | | |Grooved.
+ | | | |Interlocking.
+ | | | | |Smooth. Faceted.
+ | | | | | |4-tubercles, and crested
+ | | | | | | |? Singly involute.
+ | | | | | | | |Hemispheres small, and largeer.
+ | | | | | | | |
+ Eocene. Upper (Bridger.)
+ |3-3, 4-3, 4-5
+ | |(Digitigrade.) Plantigrade.
+ | | |Grooved. (Flat.)
+ | | | |Opposite. Interlocking.
+ | | | | |Smooth.
+ | | | | | |4-tubercles. 3-tubercles, and crested.
+ | | | | | | |Singly involute. Plane
+ | | | | | | | |Hemispheres small.
+ | | | | | | | |
+ Middle. (Wasatch.)
+ |4-3, 4-5, 5-5
+ | |Plantigrade. (Digitigrade.)
+ | | |Flat. (Grooved.)
+ | | | |Opposite. Interlocking.
+ | | | | |Smooth.
+ | | | | | |4-tubercles. 3-tubercles, a few crested.
+ | | | | | | |Plane. Singly involute.
+ | | | | | | | |Hemispheres small;
+ | | | | | | | |mesencephalon sometimes exposed
+ | | | | | | | |
+ Lower (Puerco.)
+ |5-5
+ | |Plantigrade.
+ | | |Flat.
+ | | | |Opposite.
+ | | | | |Smooth.
+ | | | | | |3-tubercles. (4-tubercles), none crested.
+ | | | | | | |Plane.
+ | | | | | | | |Mesencephalon exposed;
+ | | | | | | | |hemisphere small and smoother.
+ | | | | | | | |
+
+The evidence, then, which is furnished by all parts of the vertebral
+skeleton--whether we have regard to Fishes, Reptiles, Birds, or
+Mammals--is cumulative and consistent. Nowhere do we meet with any
+deviation or ambiguity, while everywhere we encounter similar proofs of
+continuous transformation--proofs which vary only with the varying
+amount of material which happens to be at our disposal, being most
+numerous and detailed in those cases where the greatest number of fossil
+forms has been preserved by the geological record. Here, therefore, we
+may leave the vertebral skeleton; and, having presented a sample of the
+evidence as yielded by horns and bones, I will conclude by glancing with
+similar brevity at the case of shells--which, as before remarked,
+constitute the only other sufficiently hard or permanent material to
+yield unbroken evidence touching the fossil ancestry of animals.
+
+Of course it will be understood that I am everywhere giving merely
+samples of the now superabundant evidence which is yielded by
+palæontology; and, as this chapter is already a long one, I must content
+myself with citing only the case of mollusk-shells, although shells of
+other classes might be made to yield highly important additions to the
+testimony. Moreover, even as regards the one division of mollusk-shells,
+I can afford to quote only a very few cases. These, however, are in my
+opinion the strongest single pieces of evidence in favour of
+transmutation which have thus far been brought to light.
+
+Near the village of Steinheim, in Würtemberg, there is an ancient
+lake-basin, dating from Tertiary times. The lake has long ago dried up;
+but its aqueous deposits are extraordinarily rich in fossil shells,
+especially of different species of the genus _Planorbis_. The following
+is an authoritative _résumé_ of the facts.
+
+ As the deposits seem to have been continuous for ages, and the
+ fossil shells very abundant, this seemed to be an excellent
+ opportunity to test the theory of derivation. With this end in
+ view, they have been made the subject of exhaustive study by
+ Hilgendorf in 1866, and by Hyatt in 1880. In passing from the
+ lowest to the highest strata the species change greatly and many
+ times, the extreme forms being so different that, were it not for
+ the intermediate forms, they would be called not only different
+ species, but different genera. And yet the gradations are so
+ insensible that the whole series is nothing less than a
+ demonstration, in this case at least, of origin of species by
+ derivation with modifications. The accompanying plate of successive
+ forms (Fig. 89), which we take from Prof. Hyatt's admirable memoir,
+ will show this better than any mere verbal explanation. It will be
+ observed that, commencing with four slight varieties--probably
+ sexually isolated varieties--of one species, each series shows a
+ gradual transformation as we go upward in the strata--i. e. onward
+ in time. Series I branches into three sub-series, in two of which
+ the change of form is extreme. Series IV is remarkable for great
+ increase in size as well as change in form. In the plate we give
+ only selected stages, but in the fuller plates of the memoir, and
+ still more in the shells themselves, the subtilest gradations are
+ found[19].
+
+ [19] Le Conte, _loc. cit._, pp. 236-7.
+
+ [Illustration: FIG. 89.--Transmutations of _Planorbis_. (After
+ Hyatt.)]
+
+Here is another and more recently observed case of transmutation in the
+case of mollusks.
+
+The recent species, _Strombus accipitrinus_, still inhabits the coasts
+of Florida. Its extinct prototype, _S. Leidy_, was discovered a few
+years ago by Prof. Heilprin in the Pliocene formations of the interior
+of Florida. The peculiar shape of the wing, and tuberculation of the
+whorl, are thus proved to have grown but of a previously more conical
+form of shell.
+
+ [Illustration: FIG. 90.--Transformation of _Strombus_. (After
+ Heilprin.) 1, 1_a_, _Strombus Leidy_ (1, typical), Pliocene; 2,
+ 2_a_, _Strombus accipitrinus_ (2_a_ typical) Recent.]
+
+Lastly, attention may here again be directed to the very instructive
+series of shells which has already been shown in a previous chapter, and
+which serves to illustrate the successive geological forms of _Paludina_
+from the Tertiary beds of Slavonia, as depicted by Prof. Neumayr of
+Vienna. (Fig. 1, p. 19.)
+
+
+
+
+CHAPTER VI.
+
+GEOGRAPHICAL DISTRIBUTION.
+
+
+The argument from geology is the argument from the distribution of
+species in time. I will next take the argument from the distribution of
+species in space--that is, the present geographical distribution of
+plants and animals.
+
+Seeing that the theory of descent with adaptive modification implies
+slow and gradual change of one species into another, and progressively
+still more slow and gradual changes of one genus, family, or order into
+another genus, family, or order, we should expect on this theory that
+the organic types living on any given geographical area would be found
+to resemble or to differ from organic types living elsewhere, according
+as the area is connected with or disconnected from other geographical
+areas. For instance, the large continental islands of Australia and New
+Zealand are widely disconnected from all other lands of the world, and
+deep sea soundings show that they have probably been thus disconnected,
+either since the time of their origin, or, at the least, through immense
+geological epochs. The theory of evolution, therefore, would expect to
+find two general facts with regard to the inhabitants of these islands.
+First, that the inhabitants should form, as it were, little worlds of
+their own, more or less unlike the inhabitants of any other parts of the
+globe. And next, that some of these inhabitants should present us with
+independent information touching archaic forms of life. For it is
+manifestly most improbable that the course of evolutionary history
+should have run exactly parallel in the case of these isolated oceanic
+continents and in continents elsewhere. Australia and New Zealand,
+therefore, ought to present a very large number, not only of peculiar
+species and genera, but even of families, and possibly of orders. Now
+this is just what Australia and New Zealand do present. The case of the
+dog being doubtful, there is an absence of all mammalian life, except
+that of one of the oldest and least highly developed orders, the
+Marsupials. There even occurs a unique order, still lower in the scale
+of organization--so low, in fact, that it deserves to be regarded as but
+nascent mammalian: I mean, of course, the Monotremata. As regards Birds,
+we have the peculiar wingless forms alluded to in a previous chapter
+(viz. that on Morphology); and, without waiting to go into details, it
+is notorious that the faunas of Australia and New Zealand are not only
+highly peculiar, but also suggestively archaic. Therefore, in both the
+respects above mentioned, the anticipations of our theory are fully
+borne out. But as it would take too long to consider, even cursorily,
+the faunas and floras of these immense islands, I here allude to them
+only for the sake of illustration. In order to present the argument from
+geographical distribution within reasonable limits, I think it is best
+to restrict our examination to smaller areas; for these will better
+admit of brief and yet adequate consideration. But of course it will be
+understood that the less isolated the region, and the shorter the time
+that it has been isolated, the smaller amount of peculiarity should we
+expect to meet with on the part of its present inhabitants. Or,
+conversely stated, the longer and the greater the isolation, the more
+peculiarity of species would our theory expect to find. The object of
+the present chapter will be to show that these, and other cognate
+expectations, are fully realized by facts; but, before proceeding to do
+this, I must say a few words on the antecedent standing of the argument.
+
+Where the question is, as at present, between the rival theories of
+special creation and gradual transmutation, it may at first sight well
+appear that no test can be at once so crucial and so easily applied as
+this of comparing the species of one geographical area with those of
+another, in order to see whether there is any constant correlation
+between differences of type and degrees of separation. But a little
+further thought is enough to show that the test is not quite so simple
+or so absolute--that it is a test to be applied in a large and general
+way over the surface of the whole earth, rather than one to be relied
+upon as exclusively rigid in every special case.
+
+In the first place, there is the obvious consideration that lands or
+seas which are discontinuous now may not always have been so, or not for
+long enough to admit of the effects of separation having been exerted to
+any considerable extent upon their inhabitants. Next, there is the
+scarcely less important consideration, that although land areas may long
+have been separated from one another by extensive tracts of ocean,
+birds and insects may more or less easily have been able to fly from
+one to the other; while even non-flying animals and plants may often
+have been transported by floating ice or timber, wind or water currents,
+and sundry other means of dispersal. Again, there is the important
+influence of climate to be taken into account. We know from geological
+evidence that in the course of geological time the self-same continents
+have been submitted to enormous changes of temperature--varying in fact
+from polar cold to almost tropical heat; and as it is manifestly
+impossible that forms of life suited to one of these climates could have
+survived during the other, we can here perceive a further and most
+potent cause interfering with the test of geographical distribution as
+indiscriminately applied in all cases. When the elephant and
+hippopotamus were flourishing in England amid the luxuriant vegetation
+which these large animals require, it is evident that scarcely any one
+species of either the fauna or the flora of this country can have been
+the same as it was when its African climate gave place to that of
+Greenland. Therefore, as Mr. Wallace observes, "If glacial epochs in
+temperate lands and mild climates near the poles have, as now believed
+by men of eminence, occurred several times over in the past history of
+the earth, the effects of such great and repeated changes both on
+migration, modification, and extinction of species, must have been of
+overwhelming importance--of more importance perhaps than even the
+geological changes of sea and land."
+
+But although for these, and certain other less important reasons which I
+need not wait to detail, we must conclude that the evidence from
+geographical distribution is not to be regarded as a crucial test
+between the rival theories of creation and evolution in all cases
+indiscriminately, I must next remark that it is undoubtedly one of the
+strongest lines of evidence which we possess. When we once remember
+that, according to the general theory of evolution itself, the present
+geographical distribution of plants and animals is "the visible outcome
+or residual product of the whole past history of the earth," and,
+therefore, that of the conditions determining the characters of life
+inhabiting this and that particular area continuity or discontinuity
+with other areas is but one,--when we remember this, we find that no
+further reservation has to be made: all the facts of geographical
+distribution speak with one consent in favour of the naturalistic
+theory.
+
+ * * * * *
+
+The first of these facts which I shall adduce is, that although the
+geographical range of any given species is, as a rule, continuous, such
+is far from being always the case. Very many species have more or less
+discontinuous ranges--the mountain-hare, for instance, extending from
+the Arctic regions over the greater portion of Europe to the Ural
+Mountains and the Caucasus, and yet over all this enormous tract
+appearing only in isolated or discontinuous patches, where there happen
+to be either mountain ranges or climates cold enough to suit its nature.
+Now, in all such cases of discontinuity in the range of a species the
+theory of evolution has a simple explanation to offer--namely, either
+that some representatives of the species have at some former period been
+able to migrate from one region to the other, or else that at one time
+the species occupied the whole of the range in question, but afterwards
+became broken up as geographical, climatic, or other changes rendered
+parts of the area unfit for the species to inhabit. Thus, for instance,
+it is easy to understand that during the last cold epoch the
+mountain-hare would have had a continuous range; but that as the Arctic
+climate gradually receded to polar regions, the species would be able to
+survive in southern latitudes only on mountain ranges, and thus would
+become broken up into many discontinuous patches, corresponding with
+these ranges. In the same way we can explain the occurrence of Arctic
+vegetation on the Alps and Pyrenees--namely, as left behind by the
+retreat of the Arctic climate at the close of the glacial period.
+
+But now, on the other hand, the theory of special creation cannot so
+well afford to render this obvious explanation of discontinuity. In the
+case of the Arctic flora of the Alps, for instance, although it is true
+that much of this vegetation is of an Arctic type, it is not true that
+the species are all identical with those which occur in the Arctic
+regions. Therefore the theory of special creation would here have to
+assume that, although the now common species were left behind on the
+Alps by the retreat of glaciation northwards, the peculiar Alpine
+species were afterwards created separately upon the Alps, and yet
+created with such close affinities to the pre-existing species as to be
+included with them under the same genera. Looking to the absurdity of
+this supposition, as well as of others which I need not wait to mention,
+certain advocates of special creation have sought to take refuge in
+another hypothesis--namely, that species which present a markedly
+discontinuous range may have had a corresponding number of different
+centres of creation, the same specific type having been turned down, so
+to speak, on widely separated areas. But to me it seems that this
+explanation presents even greater difficulty than the other. If it is
+difficult to say why the Divinity should have chosen to create new
+species of plants on the Alps on so precisely the same pattern as the
+old, much more would it be difficult to say why, in addition to these
+new species, he should also have created again the old species which he
+had already placed in the Arctic regions.
+
+ * * * * *
+
+So much, then, for discontinuity of distribution. The next general fact
+to be adduced is, that there is no constant correlation between habitats
+and animals or plants suited to live upon them. Of course all the
+animals and plants living upon any given area are well suited to live
+upon that area; for otherwise they could not be there. But the point now
+is, that besides the area on which they do live, there are usually many
+other areas in different parts of the globe where they might have lived
+equally well--as is proved by the fact that when transported by man they
+thrive as well, or even better, than in their native country. Therefore,
+upon the supposition that all species were separately created in the
+countries where they are respectively found, we must conclude that they
+were created in only some of the places where they might equally well
+have lived. Probably there is at most but a small percentage either of
+plants or animals which would not thrive in some place, or places, on
+the earth's surface other than that in which they occur; and hence we
+must say that one of the objects of special creation--if this be the
+true theory--was that of depositing species in only some among the
+several parts of the earth's surface equally well suited to support
+them.
+
+Now, I do not contend that this fact in itself raises any difficulty
+against the theory of special creation. But I do think that a very
+serious difficulty is raised when to this fact we add another--namely,
+that on every biological region we encounter species related to other
+species in genera, and usually also genera related to other genera in
+families. For if each of all the constituent species of a genus, and
+even of a family, were separately created, we must hence conclude that
+in depositing them there was an unaccountable design manifested to make
+areas of distribution correspond to the natural affinities of their
+inhabitants. For example, the humming-birds are geographically
+restricted to America, and number 120 genera, comprising over 400
+species. Hence, if this betokens 400 separate acts of creation, it
+cannot possibly have been due to chance that they were all performed on
+the same continent: it must have been design which led to every species
+of this large family of birds having been deposited in one geographical
+area. Or, to take a case where only the species of a single genus are
+concerned. The rats and mice proper constitute a genus which comprises
+altogether more than 100 species, and they are all exclusively
+restricted to the Old World. In the New World they are represented by
+another genus comprising about 70 species, which resemble their Old
+World cousins in form and habits; but differ from them in dentition and
+other such minor points. Now, the question is,--Why should all the 100
+species have been separately created on one side of the Atlantic with
+one pattern of dentition, and all the 70 species on the other side with
+another pattern? What has the Atlantic Ocean got to do with any
+"archetypal plan" of rats' teeth?
+
+Or again, to recur to Australia, why should all the mammalian forms of
+life be restricted to the one group of Marsupials, when we know that not
+only the Rodents, such as the rabbit, but all other orders of mammals,
+would thrive there equally well. And similarly, of course, in countless
+other instances. Everywhere we meet with this same correlation between
+areas of distribution and affinities of classification.
+
+Now, it is at once manifest how completely this general fact harmonizes
+with the theory of evolution. If the 400 species of humming-birds, for
+instance, are all modified descendants of common ancestors, and if none
+of their constituent individuals have ever been large enough to make
+their way across the oceans which practically isolate their territory
+from all other tropical and sub-tropical regions of the globe, then we
+can understand why it is that all the 400 species occupy the same
+continent. But on the special-creation theory we can see no reason why
+the 400 species should all have been deposited in America. And, as
+already observed, we must remember that this correlation between a
+geographically restricted habitat and the zoological or botanical
+affinities of its inhabitants, is repeated over and over and over again
+in the faunas and floras of the world, so that merely to enumerate the
+instances would require a separate chapter.
+
+Furthermore, the general argument thus presented in favour of descent
+with continuous modification admits of being enormously strengthened by
+three different classes of additional facts.
+
+The first is, that the correlation in question--namely, that between a
+geographically restricted habitat and the zoological or botanical
+affinities of its inhabitants--is not limited to the now existing
+species, but extends also to the extinct. That is to say, the dead
+species are allied to the living species, as we should expect that they
+must be, if the latter are modified descendants of the former. On the
+alternative theory, however, we have to suppose that the policy of
+maintaining a correlation between geographical restriction and natural
+affinity extends very much further back than even the existing species
+of plants and animals; indeed we must suppose that a practically
+infinite number of additional acts of separate creation were governed by
+the same policy, in the case of long lines of species long since
+extinct.
+
+Thus far, then, the only answer which an advocate of special creation
+can adduce is, that for some reason unknown to us such a policy may have
+been more wise than it appears: it may have served some inscrutable
+purpose that allied products of distinct acts of creation should all be
+kept together on the same areas. Well, in answer to this unjustifiable
+appeal to the argument from ignorance, I will adduce the second of the
+three considerations. This is, that in cases where the geographical
+areas are not restricted the policy in question fails. In other words,
+where the inhabitants of an area are free to migrate to other areas, the
+policy of correlating affinity with distribution is most significantly
+forgotten. In this case species wander away from their native homes, and
+the course of their wanderings is marked by the origination of new
+species springing up en route. Now, is it reasonable to suppose that the
+mere circumstance of some members of a species being able to leave their
+native home should furnish any occasion for creating new and allied
+species upon the tracts over which they travel, or the territories to
+which they go? When the 400 existing species of humming-birds have all
+been created on the same continent for some reason supposed to be
+unknown, why should this reason give way before the accident of any
+means of migration being furnished to humming-birds, so that they should
+be able to visit, say the continents of Africa and Asia, there gain a
+footing beside the sun-birds, and henceforth determine a new centre for
+the separate creation of additional species of humming-birds peculiar to
+the Old World--as has happened in the case of the majority of species
+which, unlike the humming-birds, have been at any time free to migrate
+from their original homes?
+
+Lastly, my third consideration is, that the supposed policy in question
+does not extend to affinities which are wider than those between species
+and genera--more rarely to families, scarcely ever to orders, and never
+to classes. In other words, nature shows a double correlation in her
+geographical distribution of organic types:--first, that which we have
+already considered between geographical restriction and natural
+affinity among inhabitants of the same areas; second, another of a more
+detailed character between _degrees_ of geographical restriction and
+_degrees_ of natural affinity. The more distant the affinity, the more
+general is the extension. This, of course, is what we should expect on
+the theory of descent with modification, because the more distant the
+affinity, and therefore, _ex hypothesi_, the larger and the older the
+original group of organisms, the greater must be the chance of
+dispersal. The 400 species of humming-birds may well be unable to
+migrate from their native continent; but it would indeed have been an
+unaccountable fact if no other species of all the class of birds had
+ever been able to have crossed the Atlantic Ocean. Thus, on the theory
+of evolution, we can well understand the second correlation now before
+us--namely, between remoteness of affinity and generality of
+dispersal,--so that there is no considerable portion of the habitable
+globe without representatives of all the classes of animals, few
+portions without representatives of all the orders, but many portions
+without many of the families, innumerable portions without innumerable
+genera, and, of course, all portions without the great majority of
+species. Now, while this general correlation thus obviously supports the
+theory of natural descent with progressive modification, it makes
+directly against the opposite theory of special creation. For we have
+recently seen that when we restrict our view to the case of species and
+genera, the theory of special creation is obliged to suppose that for
+some inscrutable reason the Deity had regard to systematic affinity
+while determining on what large areas to create his species[20]. But
+now we see that he must be held to have neglected this inscrutable
+reason (whatever it was) when he passed beyond the range of genera--and
+this always in proportion to the remoteness of systematic affinity on
+the part of the species concerned.
+
+ [20] I say "_large_ areas" for the sake of argument; but the same
+ correlation between distribution and affinity extends likewise to
+ _small_ areas where only _small_ differences of affinity are
+ concerned. Thus, for instance, speaking of smaller areas, Moritz
+ Wagner says:--"The broader and more rapid the river, the higher and
+ more regular the mountain-chain, the calmer and more extensive the
+ sea, the more considerable, as a general rule, will be the taxonomic
+ separation between the populations"; and he shows that, in
+ correlation with such differences in the _degrees_ of separation,
+ are the _degrees_ of diversification--i. e., the _numbers_ of
+ species, and even of varieties, which these topographical barriers
+ determine.
+
+I cannot well conceive a _reductio ad absurdum_ more complete than this.
+But, having now presented these most general facts of geographical
+distribution in their relation to the issue before us, we may next
+proceed to consider a few illustrations of them in detail, for in this
+way I think that their overwhelming weight may become yet more
+abundantly apparent.
+
+ * * * * *
+
+It will assist us in dealing with these detailed illustrations if we
+begin by considering the means of dispersal of organisms from one place
+to another. Of course the most ordinary means is that of continuous
+wandering, or emigration; but where geographical barriers of any kind
+have to be surmounted, organisms may only be able to pass them by more
+exceptional and accidental means. The principal barriers of a
+geographical kind are oceans, rivers, mountain-chains, and
+desert-tracts, in the case of terrestrial organisms; and, in the case
+of aquatic organisms, the presence of land. But it is to be observed
+that, as regards marine organisms, any considerable difference in the
+temperature of the water may constitute a barrier as effectual as the
+presence of land; and also that, in the case of all shallow-water
+faunas, a tract of deep ocean constitutes almost as complete a barrier
+as it does to terrestrial faunas.
+
+Now, the means whereby barriers admit of being accidentally or
+occasionally surmounted are, of course, various; and they differ in the
+case of different organisms. Birds, bats, and insects, on account of
+their powers of flight, are particularly apt to be blown out great
+distances to sea, and hence of all animals are most likely to become the
+involuntary colonists of distant shores. Floating timber serves to
+convey seeds and eggs of small animals over great distances; and Darwin
+has shown that many kinds of seeds are able of themselves to float for
+more than a month in sea-water without losing their powers of
+germination. For instance, out of 87 kinds, 64 germinated after an
+immersion of 28 days, and a few survived an immersion of 137 days. As a
+result of all his experiments he concludes, that the seeds of at least
+ten per cent. of the species of plants of any country might be floated
+by sea-currents during 28 days, without losing their powers of
+germination; and this, at the average rate of flow of several Atlantic
+currents, would serve to transport the seeds to a distance of at least
+900 miles. Again, he proved that even seeds which are quickly destroyed
+by contact with sea-water admit of being successfully transported during
+30 days, if they be contained within the crop of a dead bird. He also
+proved that living birds are most active agents in the work of
+dissemination, and this not only by taking seeds into their crops
+(where, so long as they remain, the seeds are uninjured), but likewise
+by carrying seeds (and even young mollusks) attached to their feet and
+feathers. In the course of these experiments he found that a small
+cup-full of mud, which he gathered from the edges of three ponds in
+February, was so charged with seeds that when sown in the ground these
+few ounces of mud yielded no less than 537 plants, belonging to many
+different species. It is therefore evident what opportunities are thus
+afforded for the transportation of seeds on the feet and bills of
+wading-birds. Lastly, floating ice is well known to act as a carrier of
+any kind of life which may prove able to survive this mode of transit.
+
+Such being the nature of geographical barriers, and the means that
+organisms of various kinds may occasionally have of overcoming them, I
+will now give a few detailed illustrations of the argument from
+geographical distribution, as previously presented in its general form.
+
+To begin with aquatic animals. As Darwin remarks, "the marine
+inhabitants of the Eastern and Western shores of South America are very
+distinct; with extremely few shells, crustacea, or echinodermata in
+common." Again, westward of the shores of America, a wide space of open
+ocean extends, which, as we have seen, furnishes as effectual a barrier
+as does the land to any emigration of shallow-water animals. Now, as
+soon as this reach of deep water is passed, we meet in the eastern
+islands of the Pacific with another and totally distinct fauna. "So that
+three marine faunas range northward and southward in parallel lines not
+far from each other, under corresponding climates": they are, however,
+"separated from each other by impassable barriers, either of land or
+open sea": and it is in exact coincidence with the course of these
+barriers that we find so remarkable a differentiation of the faunas[21].
+Obviously, therefore, it is impossible to suggest that this correlation
+is accidental. Altogether many thousands of species are involved, and
+within this comparatively limited area they are sharply marked off into
+three groups as to their natural affinities, and into three groups as to
+their several basins. Hence, if all these species were separately
+created, there is no escape from the conclusion that for some reason or
+another the act of creation was governed by the presence of these
+barriers, so that species deposited on the Eastern shores of South
+America were formed with one set of natural affinities, while species
+deposited on the Western shore were formed with another set; and
+similarly with regard to the third set of species in the third basin,
+which, extending over a whole hemisphere to the coast of Africa without
+any further barrier, nowhere presents, over this vast area, any other
+case of a distinct marine fauna. But what conceivable reason can there
+have been thus to consult these geographical barriers in the original
+creation of specific types? Even if such a case stood alone, it would
+be strongly suggestive of error on the part of the special creation
+theory. But let us take another case, this time from fresh-water faunas.
+
+ [21] The only exception is in the case of the fish on each side of
+ the isthmus of panama, where about 30 per cent, of the species are
+ identical. But it is possible enough that at some previous time this
+ narrow isthmus may have been even narrower than at present, if not
+ actually open. At all events, the fact that this partial exception
+ occurs just where the land-barrier is so narrow, is more suggestive
+ of migration than of independent creation.
+
+Although the geographical distribution of fresh-water fish and
+fresh-water shells is often surprisingly extensive and apparently
+capricious, this may be explained by the means of dispersal being here
+so varied--not only aquatic birds, floods, and whirlwinds, but also
+geographical changes of water-shed having all assisted in the process.
+Moreover, in some cases it is possible that the habits of more widely
+distributed fresh-water fish may have originally been wholly or partly
+marine--which, of course, would explain the existing discontinuity of
+their existing fresh-water distribution. But, be this as it may (and it
+is not a question that affects the issue between special creation and
+gradual evolution, since it is only a question as to how a given species
+has been dispersed from its original home, whether or not in that home
+it was specially created), the point I desire to bring forward is, that
+where we find a barrier to the emigration of fresh-water forms which is
+more formidable than a thousand miles of ocean--a barrier over which
+neither water-fowl nor whirlwinds are likely to pass, and which is above
+the reach of any geological changes of water-shed,--where we find such a
+barrier, we always find a marked difference in the fresh-water faunas on
+either side of it. The kind of barrier to which I allude is a high
+mountain-chain. It may be only a few miles wide; yet it exercises a
+greater influence on the diversification of specific types, where
+fresh-water faunas are concerned, than almost any other. But why should
+this be the case on any intelligible theory of special creation? Why, in
+the depositing of species of newly created fresh-water fish, should the
+presence of an impassable mountain-chain have determined so uniformly a
+difference of specific affinity on either side of it? The question, so
+far as I can see, does not admit of an answer from any reasonable
+opponent.
+
+ * * * * *
+
+Turning now from aquatic organisms to terrestrial, the body of facts
+from which to draw is so large, that I think the space at my disposal
+may be best utilized by confining attention to a single division of
+them--that, namely, which is furnished by the zoological study of
+oceanic islands.
+
+In the comparatively limited--but in itself extensive--class of facts
+thus presented, we have a particularly fair and cogent test as between
+the alternative theories of evolution and creation. For where we meet
+with a volcanic island, hundreds of miles from any other land, and
+rising abruptly from an ocean of enormous depth, we may be quite sure
+that such an island can never have formed part of a now submerged
+continent. In other words, we may be quite sure that it always has been
+what it now is--an oceanic peak, separated from all other land by
+hundreds of miles of sea, and therefore an area supplied by nature for
+the purpose, as it were, of testing the rival theories of creation and
+evolution. For, let us ask, upon these tiny insular specks of land what
+kind of life should we expect to find? To this question the theories of
+special creation and of gradual evolution would agree in giving the
+same answer up to a certain point. For both theories would agree in
+supposing that these islands would, at all events in large part, derive
+their inhabitants from accidental or occasional arrivals of wind-blown
+or water-floated organisms from other countries--especially, of course,
+from the countries least remote. But, after agreeing upon this point,
+the two theories must part company in their anticipations. The
+special-creation theory can have no reason to suppose that a small
+volcanic island in the midst of a great ocean should be chosen as the
+theatre of any extraordinary creative activity, or for any particularly
+rich manufacture of peculiar species to be found nowhere else in the
+world. On the other hand, the evolution theory would expect to find that
+such habitats are stocked with more or less peculiar species. For it
+would expect that when any organisms chanced to reach a wholly isolated
+refuge of this kind, their descendants should forthwith have started
+upon an independent course of evolutionary history. Protected from
+intercrossing with any members of their parent species elsewhere, and
+exposed to considerable changes in their conditions of life, it would
+indeed be fatal to the general theory of evolution if these descendants,
+during the course of many generations, were not to undergo appreciable
+change. It has happened on two or three occasions that European rats
+have been accidentally imported by ships upon some of these islands, and
+even already it is observed that their descendants have undergone a
+slight change of appearance, so as to constitute them what naturalists
+call local varieties. The change, of course, is but slight, because the
+time allowed for it has been so short. But the longer the time that a
+colony of a species is thus completely isolated under changed conditions
+of life the greater, according to the evolution theory, should we expect
+the change to become. Therefore, in all cases where we happen to know,
+from independent evidence of a geological kind, that an oceanic island
+is of very ancient formation, the evolution theory would expect to
+encounter a great wealth of peculiar species. On the other hand, as I
+have just observed, the special-creation theory can have no reason to
+suppose that there should be any correlation between the age of an
+oceanic island and the number of peculiar species which it may be found
+to contain.
+
+Therefore, having considered the principles of geographical distribution
+from the widest or most general point of view, we shall pass to the
+opposite extreme, and consider exhaustively, or in the utmost possible
+detail, the facts of such distribution where the conditions are best
+suited to this purpose--that is, as I have already said, upon oceanic
+islands, which may be metaphorically regarded as having been formed by
+nature for the particular purpose of supplying naturalists with a
+crucial test between the theories of creation and evolution. The
+material upon which my analysis is to be based will be derived from the
+most recent works upon geographical distribution--especially from the
+magnificent contributions to this department of science which we owe to
+the labours of Mr. Wallace. Indeed, all that follows may be regarded as
+a condensed filtrate of the facts which he has collected. Even as thus
+restricted, however, our subject-matter would be too extensive to be
+dealt with on the present occasion, were we to attempt an exhaustive
+analysis of the floras and faunas of all oceanic islands upon the face
+of the globe. Therefore, what I propose to do is to select for such
+exhaustive analysis a few of what may be termed the most oceanic of
+oceanic islands--that is to say, those oceanic islands which are most
+widely separated from mainlands, and which, therefore, furnish the most
+unquestionable of test cases as between the theories of special creation
+and genetic descent.
+
+ * * * * *
+
+_Azores._--A group of volcanic islands, nine in number, about 900 miles
+from the coast of Portugal, and surrounded by ocean depths of 1,800 to
+2,500 fathoms. There is geological evidence that the origin of the group
+dates back at least as far as Miocene times. There is a total absence of
+all terrestrial Vertebrata, other than those which are known to have
+been introduced by man. Flying animals, on the other hand, are abundant;
+namely, 53 species of birds, one species of bat, a few species of
+butterflies, moths, and hymenoptera, with 74 species of indigenous
+beetles. All these animals are unmodified European species, with the
+exception of one bird and many of the beetles. Of the 74 indigenous
+species of the latter, 36 are not found in Europe; but 19 are natives of
+Madeira or the Canaries, and 3 are American, doubtless transplanted by
+drift-wood. The remaining 14 species occur nowhere else in the world,
+though for the most part they are allied to other European species.
+There are 69 known species of land-shells, of which 37 are European, and
+32 peculiar, though all allied to European forms. Lastly, there are 480
+known species of plants, of which 40 are peculiar, though allied to
+European species.
+
+_Bermudas._--A small volcanic group of islands, 700 miles from North
+Carolina. Although there are about 100 islands in the group, their total
+area does not exceed 50 square miles. The group is surrounded by water
+varying in depth from 2,500 to 3,800 fathoms. The only terrestrial
+Vertebrate (unless the rats and mice are indigenous) is a lizard allied
+to an American form, but specifically distinct from it, and therefore a
+solitary species which does not occur anywhere else in the world. None
+of the birds or bats are peculiar, any more than in the case of the
+Azores; but, as in that case, a large percentage of the land-shells are
+so--namely, at least one quarter of the whole. Neither the botany nor
+the entomology of this group has been worked out; but I have said enough
+to show how remarkably parallel are the cases of these two volcanic
+groups of islands situated in different hemispheres, but at about the
+same distance from large continents. In both there is an extraordinary
+paucity of terrestrial vertebrata, and of any peculiar species of bird
+or beast. On the other hand, there is in both a marvellous wealth of
+peculiar species of insects and land-shells. Now these correlations are
+all abundantly intelligible. It is a difficult matter for any
+terrestrial animal to cross 900, or even 700, miles of ocean: therefore
+only one lizard has succeeded in doing so in one of the two parallel
+cases; and, living cut off from intercrossing with its parent form, the
+descendants of that lizard have become modified so as to constitute a
+peculiar species. But it is more easy for large flying animals to cross
+those distances of ocean: consequently, there is only one instance of a
+peculiar species of bird or bat--namely, a bull-finch in the Azores,
+which, being a small land-bird, is not likely ever to have had any other
+visitors from its original parent species coming over from Europe to
+keep up the original breed. Lastly, it is very much more easy for
+insects and land-mollusca to be conveyed to such islands by wind and
+floating timber than it is for terrestrial mammals, or even than it is
+for small birds and bats; but yet such means of transit are not
+sufficiently sure to admit of much recruiting from the mainland for the
+purpose of keeping up the specific types. Consequently, the insects and
+the land-shells present a much greater proportion of peculiar
+species--namely, one half and one fourth of the land-shells in the one
+case, and one eighth of the beetles in the other. All these
+correlations, I say, are abundantly intelligible on the theory of
+evolution; but who shall explain, on the opposite theory, why orders of
+beetles and land-mollusca should have been chosen from among all other
+animals for such superabundant creation on oceanic islands, so that in
+the Azores alone we find no less than 32 of the one and 14 of the other?
+And, in this connexion, I may again allude to the peculiar species of
+beetles in the island of Madeira. Here there are an enormous number of
+peculiar species, though they are nearly all related to, or included
+under the same genera as, beetles on the neighbouring continent. Now, as
+we have previously seen, no less than 200 of these species have lost the
+use of their wings. Evolutionists explain this remarkable fact by their
+general laws of degeneration under disuse, and the operation of natural
+selection, as will be shown later on; but it is not so easy for special
+creationists to explain why this enormous number of peculiar species of
+beetles should have been deposited on Madeira, all allied to beetles on
+the nearest continent, and nearly all deprived of the use of their
+wings. And similarly, of course, with all the peculiar species of the
+Bermudas and the Azores. For who will explain, on the theory of
+independent creation, why all the peculiar species, both of animals and
+plants, which occur on the Bermudas should so unmistakably present
+American affinities, while those which occur on the Azores no less
+unmistakably present European affinities? But to proceed to other, and
+still more remarkable, cases.
+
+_The Galapagos Islands._--This archipelago is of volcanic origin,
+situated under the equator between 500 and 600 miles from the West Coast
+of South America. The depth of the ocean around them varies from 2,000
+to 3,000 fathoms or more. This group is of particular interest, from the
+fact that it was the study of its fauna which first suggested to
+Darwin's mind the theory of evolution. I will, therefore, begin by
+quoting a short passage from his writings upon the zoological relations
+of this particular fauna.
+
+ Here almost every product of the land and of the water bears the
+ unmistakeable stamp of the American continent. There are twenty-six
+ land birds; of these, twenty-one, or perhaps twenty-three, are
+ ranked as distinct species, and would commonly be assumed to have
+ been here created; yet the close affinity of most of these birds to
+ American species is manifest in every character, in their habits,
+ gestures, and tones of voice. So it is with the other animals, and
+ with a large proportion of the plants, as shown by Dr. Hooker in
+ his admirable Flora of this archipelago. The naturalist, looking at
+ the inhabitants of these volcanic islands in the Pacific, distant
+ several hundred miles from the continent, 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 plainly the 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 closely resembles 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 the climate, height, and size of the
+ islands, between the Galapagos and Cape de Verde Archipelagoes; but
+ what an entire and absolute difference in their inhabitants! The
+ inhabitants of the Cape de Verde Islands are related to those of
+ Africa, like those of the Galapagos to America. Facts such as these
+ admit of 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 from
+ America, and the Cape de Verde Islands from Africa; such colonists
+ would be liable to modification--the principle of inheritance still
+ betraying their original birthplace[22].
+
+ [22] _origin of species_, pp. 353-4.
+
+The following is a synopsis of the fauna and flora of this archipelago,
+so far as at present known. The only terrestrial vertebrates are two
+peculiar species of land-tortoise, and one extinct species; five species
+of lizards, all peculiar--two of them so much so as to constitute a
+peculiar genus;--and two species of snakes, both closely allied to South
+American forms. Of birds there are 57 species, of which no less than 38
+are peculiar; and all the non-peculiar species, except one, belong to
+aquatic tribes. The true land birds are represented by 31 species, of
+which all, except one, are peculiar; while more than half of them go to
+constitute peculiar genera. Moreover, while they are all unquestionably
+allied to South American forms, they present a beautiful series of
+gradations, "from perfect identity with the continental species, to
+genera so distinct that it is difficult to determine with what forms
+they are most nearly allied; and it is interesting to note that this
+diversity bears a distinct relation to the probabilities of, and
+facilities for, migration to the islands. The excessively abundant
+rice-bird, which breeds in Canada, and swarms over the whole United
+States, migrating to the West Indies and South America, visiting the
+distant Bermudas almost every year, and extending its range as far as
+Paraquay, is the only species of land-bird which remains completely
+unchanged in the Galapagos; and we may therefore conclude that some
+stragglers of the migrating host reach the islands sufficiently often to
+keep up the purity of the breed[23]." Again, of the thirty peculiar
+land-birds, it is observable that the more they differ from any other
+species or genera on the South American continent, the more certainly
+are they found to have their nearest relations among those South
+American forms which have the more restricted range, and are therefore
+the least likely to have found their way to the islands with any
+frequency.
+
+ [23] Wallace, _Island Life_, pp. 271-2.
+
+The insect fauna of the Galapagos islands is scanty, and chiefly
+composed of beetles. These number 35 species, which are nearly all
+peculiar, and in some cases go to constitute peculiar genera. The same
+remarks apply to the twenty species of land-shells. Lastly, of the total
+number of flowering plants (332 species) more than one half (174
+species) are peculiar. It is observable in the case of these peculiar
+species of plants--as also of the peculiar species of birds--that many
+of them are restricted to single islands. It is also observable that,
+with regard both to the fauna and flora, the Galapagos Islands as a
+whole are very much richer in peculiar species than either the Azores or
+Bermudas, notwithstanding that both the latter are considerably more
+remote from their nearest continents. This difference, which at first
+sight appears to make against the evolutionary interpretation, really
+tends to confirm it. For the Galapagos Islands are situated in a calm
+region of the globe, unvisited by those periodic storms and hurricanes
+which sweep over the North Atlantic, and which every year convey some
+straggling birds, insects, seeds, &c., to the Azores and Bermudas.
+Notwithstanding their somewhat greater isolation geographically,
+therefore, the Azores and Bermudas are really less isolated biologically
+than are the Galapagos Islands; and hence the less degree of peculiarity
+on the part of their endemic species. But, on the theory of special
+creation, it is impossible to understand why there should be any such
+correlation between the prevalence of gales and a comparative inertness
+of creative activity. And, as we have seen, it is equally impossible on
+this theory to understand why there should be a further correlation
+between the _degree_ of peculiarity on the part of the isolated
+species, and the degree in which their nearest allies on the mainland
+are there confined to narrow ranges, and therefore less likely to keep
+up any biological communication with the islands.
+
+_St. Helena._--A small volcanic island, ten miles long by eight wide,
+situated in mid-ocean, 1100 miles from Africa, and 1800 from South
+America. It is very mountainous and rugged, bounded for the most part by
+precipices, rising from ocean depths of 17,000 feet, to a height above
+the sea-level of nearly 3,000. When first discovered it was richly
+clothed with forests; but these were all destroyed by human agency
+during the 16th, 17th and 18th centuries. The records of civilization
+present no more lamentable instance of this kind of destruction. From a
+merely pecuniary point of view the abolition of these primeval forests
+has proved an irreparable loss; but from a scientific point of view the
+loss is incalculable. These forests served to harbour countless forms of
+life, which extended at least from the Miocene age, and which, having
+found there an ocean refuge, survived as the last remnants of a remote
+geological epoch. In those days, as Mr. Wallace observes, St. Helena
+must have formed a kind of natural museum or vivarium of archaic species
+of all classes, the interest of which we can now only surmise from the
+few remnants of those remnants, which are still left among the more
+inaccessible portions of the mountain peaks and crater edges. These
+remnants of remnants are as follows.
+
+There is a total absence of all indigenous mammals, reptiles,
+fresh-water fish, and true land-birds. There is, however, a species of
+plover, allied to one in South Africa; but it is specifically distinct,
+and therefore peculiar to the island. The insect life, on the other
+hand, is abundant. Of beetles no less than 129 species are believed to
+be aboriginal, and, with one single exception, the whole number are
+peculiar to the island. "But in addition to this large amount of
+specific peculiarity (perhaps unequalled anywhere else in the world),
+the beetles of this island are remarkable for their generic isolation,
+and for the altogether exceptional proportion in which the great
+divisions of the order are represented. The species belong to 39 genera,
+of which no less than 25 are peculiar to the island; and many of these
+are such isolated forms that it is impossible to find their allies in
+any particular country[24]." More than two-thirds of all the species
+belong to the group of weevils--a circumstance which serves to explain
+the great wealth of beetle-population, the weevils being beetles which
+live in wood, and St. Helena having been originally a densely wooded
+island. This circumstance is also in accordance with the view that the
+peculiar insect fauna has been in large part evolved from ancestors
+which reached the island by means of floating timber; for, of course, no
+explanation can be suggested why special creation of this highly
+peculiar insect fauna should have run so disproportionately into the
+production of weevils. About two-thirds of the whole number of beetles,
+or over 80 species, show no close affinity with any existing insects,
+while the remaining third have some relations, though often very remote,
+with European and African forms. That this high degree of peculiarity
+is due to high antiquity is further indicated, according to our theory,
+by the large number of species which some of the types comprise. Thus,
+the 54 species of _Cossonidæ_ may be referred to three types; the 11
+species of _Bembidium_ form a group by themselves; and the _Heteromera_
+form two groups. "Now, each of these types may well be descended from a
+single species, which originally reached the island from some other
+land; and the great variety of generic and specific forms into which
+some of them have diverged is an indication, and to some extent a
+measure, of the remoteness of their origin[25]." But, on the
+counter-supposition that all these 128 peculiar species were separately
+created to occupy this particular island, it is surely unaccountable
+that they should thus present such an arborescence of natural affinities
+amongst themselves.
+
+ [24] Wallace, _Island Life_, p. 287.
+
+ [25] Wallace, _Island Life_, p. 287.
+
+Passing over the rest of the insect fauna, which has not yet been
+sufficiently worked out, we next find that there are only 20 species of
+indigenous land-shells--which is not surprising when we remember by what
+enormous reaches of ocean the island is surrounded. Of these 20 species
+no less than 13 have become extinct, three are allied to European
+species, while the rest are so highly peculiar as to have no near allies
+in any other part of the globe. So that the land-shells tell exactly the
+same story as the insects.
+
+Lastly, the plants likewise tell the same story. The truly indigenous
+flowering plants are about 50 in number, besides 26 ferns. Forty of the
+former and ten of the latter are peculiar to the island, and, as Sir
+Joseph Hooker tells us, "cannot be regarded as very close specific
+allies of any other plants at all" Seventeen of them belong to peculiar
+genera, and the others all differ so markedly as species from their
+congeners, that not one comes under the category of being an insular
+form of a continental species. So that with respect to its plants no
+less than with respect to its animals, we find that the island of St.
+Helena constitutes a little world of unique species, allied among
+themselves, but diverging so much from all other known forms that in
+many cases they constitute unique genera.
+
+_Sandwich Islands._--These are an extensive group of islands, larger
+than any we have hitherto considered--the largest of the group being
+about the size of Devonshire. The entire archipelago is volcanic, with
+mountains rising to a height of nearly 14,000 feet. The group is
+situated in the middle of the North Pacific, at a distance of
+considerably over 2,000 miles from any other land, and surrounded by
+enormous ocean depths. The only terrestrial vertebrata are two lizards,
+one of which constitutes a peculiar genus. There are 24 aquatic birds,
+five of which are peculiar; four birds of prey, two of which are
+peculiar; and 16 land-birds, all of which are peculiar. Moreover, these
+16 land-birds constitute no less than 10 peculiar genera, and even one
+peculiar family of five genera. This is an amount of peculiarity far
+exceeding that of any other islands, and, of course, corresponds with
+the great isolation of this archipelago. The only other animals which
+have here been carefully studied are the land-shells, and these tell the
+same story as the birds. For there are no less than 400 species which
+are all, without any exception, peculiar; while about three-quarters of
+them go to constitute peculiar genera. Again, of the plants, 620 species
+are believed to be endemic; and of these 377 are peculiar, yielding no
+less than 39 peculiar genera.
+
+ * * * * *
+
+Prejudice apart, I think we must all now agree that it is needless to
+continue further this line of proof. I have chosen the smallest and most
+isolated islands for the purposes of our present argument, first because
+these furnish the most crucial kind of test, and next because they best
+admit of being dealt with in a short space. But, if necessary, a vast
+amount of additional material could be furnished, not only from other
+small oceanic islands, but still more from the largest islands of the
+world, such as Australia and New Zealand. However, after the detailed
+inventories which have now been given in the case of some of the smaller
+islands most remote from mainlands, we may well be prepared to accept it
+as a general law, that _wherever_ there is evidence of land-areas having
+been for a long time separated from other land-areas, there we meet with
+a more or less extraordinary profusion of unique species, often running
+up into unique genera. And, in point of fact, so far as naturalists have
+hitherto been able to ascertain, _there is no exception to this general
+law in any region of the globe_. Moreover, there is everywhere a
+constant correlation between the _degree_ of this peculiarity on the
+part of the fauna and flora, and the _time_ during which they have been
+isolated. Thus, for instance, among the islands which I have called
+into evidence, those that are at once the most isolated and give
+independent proofs of the highest antiquity, are the Galapagos Islands,
+the Sandwich Islands, and St. Helena. Now, if we apply the method of
+tabular analysis to these three cases, we obtain the following most
+astonishing results. For the sake of simplicity I will omit the
+enumeration of peculiar genera, and confine attention to peculiar
+species. Moreover, I will consider only terrestrial animals; for, as we
+have already seen, aquatic animals are so much more likely to reach
+oceanic islands that they do not furnish nearly so fair a test of the
+evolutionary hypothesis.
+
+ PECULIAR SPECIES.
+
+ +------------+---------+----------+-----------+----------+----------+
+ | | Shells. | Insects. | Reptiles. | Birds. | Mammals. |
+ | +---------+----------+-----------+----------+----------+
+ | Sandwich. | 400 | ? | 2 | 16 | 0 |
+ | Galapagos | 15 | 35 | 10 | 30 | 0 |
+ | St. Helena | 20 | 128 | 0 | 1 | 0 |
+ +------------+---------+----------+-----------+----------+----------+
+ | Totals. | 435 | 163 | 12 | 47 | 0 |
+ +------------+---------+----------+-----------+----------+----------+
+
+ NON-PECULIAR SPECIES.
+
+ +------------+---------+----------+-----------+----------+----------+
+ | | Shells. | Insects. | Reptiles. | Birds. | Mammals. |
+ | +---------+----------+-----------+----------+----------+
+ | Sandwich. | 0 | ? | 0 | 0 | 0 |
+ | Galapagos | ? | ? | 0 | 1 | 0 |
+ | St. Helena | 0 | ? | 0 | 0 | 0 |
+ +------------+---------+----------+-----------+----------+----------+
+ | Totals. | 0 | ? | 0 | 1 | 0 |
+ +------------+---------+----------+-----------+----------+----------+
+
+From this synopsis we perceive that out of a total of 658 species of
+terrestrial animals known to inhabit these three oceanic territories,
+all are peculiar, with the exception of a single land-bird which is
+found in the Galapagos Islands. This is the rice-bird, so very abundant
+on the American continent that its representatives must not unfrequently
+become the involuntary colonists of the Archipelago. There are, however,
+a few species of non-peculiar insects inhabiting the Sandwich and
+Galapagos Islands, the exact number of which is doubtful, and on this
+account are not here quoted. But at most they would be represented by
+units, and therefore do not affect the general result. Lastly, the
+remarkable fact will be noted, that there is no single representative of
+the mammalian class in any of these islands.
+
+If we turn next to consider the case of plants, we obtain the following
+result:--
+
+ +-----------+-----------+--------------+
+ | |_Peculiar |_Non-peculiar |
+ | | Species._ | Species._ |
+ +-----------|-----------|--------------+
+ |Sandwich | 377 | 243 |
+ |Galapagos | 174 | 158 |
+ |St. Helena | 50 | 26 |
+ | | ---- | ---- |
+ | Totals | 601 | 427 |
+ +-----------+-----------+--------------+
+
+So that by adding together peculiar species both of land-animals and
+plants, we find that on these three limited areas alone there are 1258
+forms of life which occur nowhere else upon the globe--not to speak of
+the peculiar aquatic species, nor of the presumably large number of
+peculiar species of all kinds not hitherto discovered in these
+imperfectly explored regions.
+
+Now let us compare these facts with those which are presented by the
+faunas and floras of islands less remote from continents, and known
+from independent geological evidence to be of comparatively recent
+origin--that is, to have been separated from their adjacent mainlands in
+comparatively recent times, and therefore as islands to be comparatively
+young. The British Isles furnish as good an instance as could be chosen,
+for they together comprise over 1000 islands of various sizes, which are
+nowhere separated from one another by deep seas, and in the opinion of
+geologists were all continuous with the European continent since the
+glacial period.
+
+ BRITISH ISLES.
+
+ NON-PECULIAR SPECIES.
+
+ +---------+---------+----------+-----------+---------+---------+
+ | | Land | | Reptiles | Land | Land |
+ | Plants. | Shells. | Insects. | and | Birds. | Mammals.|
+ | | | | Amphibia. | | |
+ +---------+---------+----------+-----------+---------+---------+
+ | 1462 | 83 | 12,551 | 13 | 130 | 40 |
+ +---------+---------+----------+-----------+---------+---------+
+
+ PECULIAR SPECIES.
+ +---------+---------+----------+-----------+---------+---------+
+ | | Land | | Reptiles | Land | Land |
+ | Plants. | Shells. | Insects. | and | Birds. | Mammals.|
+ | | | | Amphibia. | | |
+ +---------+---------+----------+-----------+---------+---------+
+ | 46 | 4 | 149 | 0 | 1 | 0 |
+ +---------+---------+----------+-----------+---------+---------+
+
+ Total Peculiar Plants 46
+ Total Peculiar Animals 154
+ ----
+ Grand Total 200
+
+I have drawn up this table in the most liberal manner possible,
+including as peculiar species forms which many naturalists regard as
+merely local varieties. But, even as thus interpreted, how wonderful is
+the contrast between the 1000 islands of Great Britain and the single
+volcanic rock of St. Helena, where almost all the animals and about half
+the plants are peculiar, instead of about 1/80 of the animals, and 1/30
+of the plants. Of course, if no peculiar species of any kind had
+occurred in the British Isles, advocates of special creation might have
+argued that it was, so to speak, needless for the Divinity to have added
+any new species to those European forms which fully populated the
+islands at the time when they were separated from the continent. But, as
+the matter stands, advocates of special creation must face the fact that
+a certain small number of new and peculiar species have been formed on
+the British Isles; and, therefore, that creative activity has not been
+wholly suspended in their case. Why, then, has it been so meagre in this
+case of a thousand islands, when it has proved so profuse in the case of
+all single islands more remote from mainlands, and presenting a higher
+antiquity? Or why should the Divinity have thus appeared so uniformly to
+consult these merely accidental circumstances of space and time in the
+depositing of his unique specific types? Do not such facts rather speak
+with irresistible force in favour of the view, that while all ancient
+and solitary islands have had time enough, and separation enough, to
+admit of distinct histories of evolution having been written in their
+living inhabitants, no one of the thousand islands of Great Britain has
+had either time enough, or separation enough, to have admitted of more
+than some of the first pages of such a history having been commenced?
+
+But this allusion to Great Britain introduces us to another point. It
+will have been observed that, unlike oceanic islands remote from
+mainlands, Great Britain is well furnished both with reptiles (including
+amphibia) and mammals. For there is no instance of any oceanic island
+situated at more than 300 miles from a continent where any single
+species of the whole class of mammals is to be found, excepting species
+of the only order which is able to fly--namely, the bats. And the same
+has to be said of frogs, toads, and newts, whose spawn is quickly killed
+by contact with sea-water, and therefore could never have reached remote
+islands in a living state. Hence, on evolutionary principles; it is
+quite intelligible why oceanic islands should not present any species of
+mammals or batrachians--peculiar or otherwise,--save such species of
+mammals as are able to fly. But on the theory of special creation we can
+assign no reason why, notwithstanding the extraordinary profusion of
+unique types of other kinds which we have seen to occur on oceanic
+islands, the Deity should have made this curious exception to the
+detriment of all frogs, toads, newts, and mammals, save only such as are
+able to fly. Or, if any one should go so far to save a desperate
+hypothesis as to maintain that there must have been some hidden reason
+why batrachians and quadrupeds were not specially created on oceanic
+islands, I may mention another small--but in this relation a most
+significant--fact. This is that on some of these islands there occur
+certain peculiar species of plants, the seeds of which are provided with
+numerous tiny hooks, obviously and beautifully adapted--like those on
+the seeds of allied plants elsewhere--to catch the wool or hair of
+moving quadrupeds, and so to further their own dissemination. But, as we
+have just seen, there are no quadrupeds in the islands to meet these
+beautiful adaptations on the part of the plants; so that special
+creationists must resort to the almost impious supposition that in these
+cases the Deity has only carried out half his plan, in that while he
+made an elaborate provision for these uniquely created species of
+plants, which depended for its efficiency on the presence of quadrupeds,
+he nevertheless neglected to place any quadrupeds on the islands where
+he had placed the plants. Such one-sided attempts at adaptation surely
+resolve the thesis of special creation to a _reductio ad absurdum_; and
+hence the only reasonable interpretation of them is, that while the
+seeds of allied or ancestral plants were able to float to the islands,
+no quadrupeds were ever able over so great a distance to swim.
+
+ * * * * *
+
+Although much more evidence might still be given under the head of
+geographical distribution, I must now close with a brief summary of the
+main points that have been adduced.
+
+After certain preliminary considerations, I began by noticing that the
+theory of evolution has a much more intelligible account to give than
+has its rival of the facts of discontinuous distribution--the Alpine
+flora, for instance, being allied to the Arctic, not because the same
+species were separately created in both places, but because during the
+glacial period these species extended all over Europe, and were left
+behind on the Alps as the Arctic flora receded northwards--which was
+sufficiently long ago to explain why some of the Alpine species are
+unique, though closely allied to Arctic forms.
+
+Next we saw that, although living things are always adapted to the
+climates under which they live (since otherwise they could not live
+there at all), it is equally true that, as a rule, besides the area on
+which they do live, there are many other areas in different parts of the
+globe where they might have lived equally well. Consequently we must
+conclude that, if all species were separately created, many species were
+severally created on only one among a number of areas where they might
+equally well have thrived. Now, although this conclusion in itself may
+not seem opposed to the theory of special creation, a most serious
+difficulty is raised when it is taken in connexion with another fact of
+an equally general kind. This is, that on every biological region we
+encounter chains of allied species constituting allied genera, families,
+and so on; while we scarcely ever meet with allied species in different
+biological regions, notwithstanding that their climates may be similar,
+and, consequently, just as well suited to maintain some of the allied
+species. Hence we must further conclude, if all species were separately
+created, that in the work of creation some unaccountable regard was paid
+to making areas of distribution correspond to degrees of structural
+affinity. A great many species of the rat genus were created in the Old
+World, and a great many species of another, though allied, genus were
+created in the New World: yet no reason can be assigned why no one
+species of the Old World series should not just as well have been
+deposited in the New World, and _vice versa_. On the other hand, the
+theory of evolution may claim as direct evidence in its support all the
+innumerable cases such as these--cases, indeed, so innumerable that, as
+Mr. Wallace remarks, it may be taken as a law of nature that "every
+species has come into existence coincident both in space and time with a
+pre-existing and closely allied species." A general law which, while in
+itself most strongly suggestive of evolution, is surely impossible to
+reconcile with any reasonable theory of special creation. Furthermore,
+this law extends backwards through all geological time, with the result
+that the extinct species which now occur only as fossils on any given
+geological area, resemble the species still living upon that area, as we
+should expect that they must, if the former were the natural progenitors
+of the latter. On the other hand, if they were not the natural
+progenitors, but all the species, both living and extinct, were the
+supernatural and therefore independent creations which the rival theory
+would suppose, then no reason can be given why the extinct species
+should thus resemble the living--any more than why the living species
+should resemble one another. For, as we have seen, there are almost
+always many other habitats on other parts of the globe, where any
+members of any given group of species might equally well have been
+deposited; and this, of course, applies to geological no less than to
+historical time. Yet throughout all time we meet with this most
+suggestive correlation between continuity of a geographical area and
+structural affinity between the forms of life which have lived, or are
+still living, upon that area.
+
+Similarly, we find the further, and no less suggestive, correlation
+between the birth of new species and the immediate pre-existence of
+closely allied species on the same area--or, at most, on closely
+contiguous areas.
+
+Where a continuous area has long been circumscribed by barriers of any
+kind, which prevent the animals from wandering beyond it, then we find
+that all the species, both extinct and living, constitute more or less a
+world of their own; while, on the other hand, where the animals are free
+to migrate from one area to another, the course of their migrations is
+marked by the origination of new species springing up _en route_, and
+serving to connect the older, or metropolitan, forms with the younger,
+or colonising, forms in the way of a graduated series. This principle,
+however, admits of being traced only in certain cases of species
+belonging to the same genus, of genera belonging to the same family, or,
+at most, of families belonging to the same order. In other words, the
+more general the structural affinity, the more general is the
+geographical extension--as we should expect to be the case on the theory
+of descent with branching modifications, seeing that the larger, the
+older, and the more diverse the group of organisms compared, the greater
+must be their chances of dispersal.
+
+These general considerations led us to contemplate more in detail the
+correlation between structural affinity and barriers to free migration.
+Such barriers, of course, differ in the cases of different organisms.
+Marine organisms are stopped by land, unsuitable temperature, or
+unsuitable depths; fresh-water organisms by sea and by mountain-chains;
+terrestrial organisms chiefly by water. Now it is a matter of fact
+which admits of no dispute, that in each of these cases we meet with a
+direct correlation between the kind of barrier and the kind of organisms
+whose structural affinities are affected thereby. Where we have to do
+with marine organisms, barriers such as the Isthmus of Panama and the
+varying depth of the Western Pacific determine three very distinct
+faunas, ranging north and south in closely parallel lines, and under
+corresponding climates. Where we have to do with fresh-water organisms,
+we find that a mountain-chain only a few miles wide has more influence
+in determining differences of organic type on either side of it than is
+exercised by even thousands of miles of a continuous land-area, if this
+be uninterrupted by any mountains high enough to prevent water-fowl,
+whirlwinds, &c., from dispersing the ova. Again, where we have to do
+with terrestrial organisms, the most effectual barriers are wide reaches
+of ocean; and, accordingly, we find that these exercise an enormous
+influence on the modification of terrestrial types. Moreover, we find
+that the _more_ terrestrial an organism, or the _greater_ the difficulty
+it has in traversing a wide reach of ocean, the _greater_ is the
+modifying influence of such a barrier upon that type. In oceanic
+islands, for example, many of the plants and aquatic birds usually
+belong to the same species as those which occur on the nearest
+mainlands, and where there are any specific differences, these but
+rarely run up to generic differences. But the land-birds, insects, and
+reptiles which are found on such islands are nearly always specifically,
+and very often generically, distinct from those on the nearest
+mainland--although invariably allied with sufficient closeness to leave
+no manner of doubt as to their affinities with the fauna of that
+mainland. Lastly, no amphibians and no mammals (except bats) are ever
+found on any oceanic islands. Yet, as we have seen, on the theory of
+special creation, these islands must all be taken to have been the
+theatres of the most extraordinary creative activity, so that on only
+three of them we found no less than 1258 unique species, whereof 657
+were unique species of land animals, to be set against one single
+species known to occur elsewhere. Nevertheless, notwithstanding this
+prodigious expenditure of creative energy in the case of land-birds,
+land-shells, insects, and reptiles, no single new amphibian, or no
+single new mammal, has been created on any single oceanic island, if we
+except the only kind of mammal that is able to fly, and the ancestors of
+which, like those of the land-birds and insects, might therefore have
+reached the islands ages ago. Moreover, with regard to mammals, even in
+cases where allied forms occur on either side of a sea-channel, it is
+found to be a general rule that if the channel is shallow, the species
+on either side of it are much more closely related than if it be
+deep--and this irrespective of its width. Therefore we can only
+conclude, in the words of Darwin--"As the amount of modification which
+animals of all kinds undergo partly depends on lapse of time, and as the
+islands which are separated from each other or from the mainland by
+shallow channels are more likely to have been continuously united within
+a recent period than islands separated by deeper channels, we can
+understand how it is that a relation exists between the depth of the sea
+separating two mammalian faunas, and the degree of their affinity--a
+relation which is quite inexplicable on the theory of independent acts
+of creation."
+
+ * * * * *
+
+Looking to all these general principles of geographical distribution,
+and remembering the sundry points of smaller detail relating to oceanic
+islands which I will not wait to recapitulate, to my mind it seems that
+there is no escape from the following conclusion, with which I will
+bring my brief epitome of the evidence to a close. The conclusion to
+which, I submit, all the evidence leads is, that if the doctrine of
+special creation is taken to be true, then it must be further taken that
+the one and only principle which has been consistently followed in the
+geographical deposition of species, is that of so depositing them as to
+make it everywhere appear that they were not thus deposited at all, but
+came into existence where they now occur by way of genetic descent with
+perpetual migration and correlative modification. On no other principle,
+so far as I can see, would it be possible to account for the fact that
+"every species has come into existence coincident both in space and time
+with a pre-existing and closely allied species," together with the
+carefully graduated regard to physical barriers which the Creator must
+have displayed while depositing his newly formed species on either sides
+of them--everywhere making _degrees_ of structural affinity correspond
+to _degrees_ of geographical continuity, and _degrees_ of structural
+difference correspond to _degrees_ of geographical separation, whether
+by mountain-chains in the case of fresh-water faunas, by land and by
+deep sea in the case of marine faunas, or by reaches of ocean in the
+case of terrestrial faunas--stocking oceanic islands with an enormous
+profusion of peculiar species all allied to those on the nearest
+mainlands, yet everywhere avoiding the creation upon them of any
+amphibian or mammal, except an occasional bat. We are familiar with the
+doctrine that God is a God who hideth himself; here, however, it seems
+to me, we should have but a thinly-veiled insinuation, not merely that
+in his works he is hidden, but that in these works he is untrue. Than
+which I cannot conceive a stronger condemnation of the theory which it
+has been my object fairly to represent and dispassionately to
+criticise.
+
+
+
+
+SECTION II
+
+_SELECTION_
+
+
+
+
+CHAPTER VII.
+
+THE THEORY OF NATURAL SELECTION.
+
+
+Thus far we have been considering the main evidences of organic
+evolution considered as a fact. We now enter a new field, namely, the
+evidences which thus far have been brought to light touching the causes
+of organic evolution considered as a process.
+
+As was pointed out in the opening chapter, this is obviously the
+methodical course to follow: we must have some reasonable assurance that
+a fact is a fact before we endeavour to explain it. Nevertheless, it is
+not necessary that we should actually demonstrate a fact to be a fact
+before we endeavour to explain it. Even if we have but a reasonable
+presumption as to its probability, we may find it well worth while to
+consider its explanation; for by so doing we may obtain additional
+evidence of the fact itself. And this because, if it really is a fact,
+and if we hit upon the right explanation of it, by proving the
+explanation probable, we may thereby greatly increase our evidence of
+the fact. In the very case before us, for example, the evidence of
+evolution as a fact has from the first been largely derived from testing
+Darwin's theory concerning its method. It was this theoretical
+explanation of its method which first set him seriously to enquire into
+the evidences of evolution as a fact; and ever since he published his
+results, the evidences which he adduced in favour of natural selection
+as a method have constituted some of the strongest reasons which
+scientific men have felt for accepting evolution as a fact. Of course
+the evidence in favour of this fact has gone on steadily growing, quite
+independently of the assistance which was thus so largely lent to it by
+the distinctively Darwinian theory of its method; and, indeed, so much
+has this been the case, that in the present treatise we have been able
+to consider such direct evidence of the fact itself, without any
+reference at all to the indirect or accessory evidence which is derived
+from that of natural selection as a method. From which it follows that
+in most of what I am about to say in subsequent chapters on the
+evidences of natural selection as a method, there will be furnished a
+large addition to the evidences which have already been detailed of
+evolution as a fact. But, as a matter of systematic treatment, I have
+thought it desirable to keep these two branches of our subject separate.
+Which means that I have made the evidences of evolution as a fact to
+stand independently on their own feet--feet which in my opinion are
+amply strong enough to bear any weight of adverse criticism that can be
+placed upon them.
+
+Our position, then, is this. On the foundation of the previous chapters,
+I will henceforth assume that we all accept organic evolution as a fact,
+without requiring any of the accessory evidence which is gained by
+independent proof of natural selection as a method. But in making this
+assumption--namely, that we are all now firmly persuaded of the fact of
+evolution--I do not imagine that such is really the case. I make the
+assumption for the purposes of systematic exposition, and in order that
+different parts of the subject may be kept distinct. I confess it does
+appear to me remarkable that there should still be a doubt in any
+educated mind touching the general fact of evolution; while it becomes
+to me unaccountable that such should be the case with a few still living
+men of science, who cannot be accused of being ignorant of the evidences
+which have now been accumulated. But in whatever measure we may
+severally have been convinced--or remained unconvinced--on this matter,
+for the purposes of exposition I must hereafter assume that we are all
+agreed to the extent of regarding the process of evolution as, at least,
+sufficiently probable to justify enquiry touching its causes on
+supposition of its truth.
+
+Now, the causes of evolution have been set forth in a variety of
+different hypotheses, only the chief of which need be mentioned here.
+Historically speaking the first of these was that which was put forward
+by Erasmus Darwin, Lamarck, and Herbert Spencer. It consists in putting
+together the following facts and inferences.
+
+We know that, in the lifetime of the individual, increased use of
+structures leads to an increase of their functional efficiency; while,
+on the other hand, disuse leads to atrophy. The arms of a blacksmith,
+and the legs of a mountaineer, are familiar illustrations of the first
+principle: our hospital wards are full of illustrations of the second.
+Again, we know that the characters of parents are transmitted to their
+progeny by means of heredity. Now the hypothesis in question consists
+in supposing that if any particular organs in a species are habitually
+used for performing any particular action, they must undergo a
+structural improvement which would more and more adapt them to the
+performance of that action; for in each generation constant use would
+better and better adapt the structures to the discharge of their
+functions, and they would then be bequeathed to the next generation in
+this their improved form by heredity. So that, for instance, if there
+had been a thousand generations of blacksmiths, we might expect the sons
+of the last of them to inherit unusually strong arms, even if these
+young men had themselves taken to some other trade not requiring any
+special use of their arms. Similarly, if there had been a thousand
+generations of men who used their arms but slightly, we should expect
+their descendants to show but a puny development of the upper
+extremities. Now let us apply all this to the animal kingdom in general.
+The giraffe, for instance, is a ruminant whose entire frame has been
+adapted to support an enormously long neck, which is of use to the
+animal in reaching the foliage of trees. The ancestors of the giraffe,
+having had ordinary necks, were supposed by Lamarck to have gradually
+increased the length of them, through many successive generations, by
+constantly stretching to reach high foliage; and he further supposed
+that, when the neck became so long as to require for its support special
+changes in the general form of the animal as a whole, these special
+changes would have brought about the dwindling of other parts from which
+so much activity was no longer required--the general result being that
+the whole organization of the animal became more and more adapted to
+browsing on high foliage. And so in the cases of other animals, Lamarck
+believed that the adaptation of their forms to their habits could be
+explained by this simple hypothesis that the habits created the forms,
+through the effects of use and disuse, coupled with heredity.
+
+Such is what is ordinarily known as Lamarck's theory of evolution. We
+may as well remember, however, that it really constitutes only one part
+of his theory; for besides this hypothesis of the cumulative inheritance
+of functionally-produced modifications--to which we may add the
+inherited effects of any direct action exercised by surrounding
+conditions of life,--Lamarck believed in some transcendental principle
+tending to produce gradual improvement in pre-determined lines of
+advance. Therefore it would really be more correct to designate the
+former hypothesis by the name either of Erasmus Darwin, or, still
+better, of Herbert Spencer. Nevertheless, in order to avoid confusion, I
+will follow established custom, and subsequently speak of this
+hypothesis as the Lamarckian hypothesis--understanding, however, that in
+employing this designation I am not referring to any part or factor of
+Lamarck's general theory of evolution other than the one which has just
+been described--namely, the hypothesis of the cumulative transmission of
+functionally-produced, or otherwise "acquired," modifications.
+
+This, then, was the earliest hypothesis touching the causes of organic
+evolution. But we may at once perceive that it is insufficient to
+explain all that stands to be explained. In the first place, it refers
+in chief part only to the higher animals, which are actuated to effort
+by intelligence. Its explanatory power in the case of most
+invertebrata--as well as in that of all plants--is extremely limited,
+inasmuch as these organisms can never be moved to a greater or less use
+of their several parts by any discriminating volition, such as that
+which leads to the continued straining of a giraffe's neck for the
+purpose of reaching foliage. In the second place, even among the higher
+animals there are numberless tissues and organs which unquestionably
+present a high degree of adaptive evolution, but which nevertheless
+cannot be supposed to have fallen within the influence of Lamarckian
+principles. Of such are the shells of crustacea, tortoises, &c., which
+although undoubtedly of great use to the animals presenting them, cannot
+ever have been _used_ in the sense required by Lamarck's hypothesis, i.
+e. actively exercised, so as to increase a flow of nutrition to the
+part. Lastly, in the third place, the validity of Lamarck's hypothesis
+in any case whatsoever has of late years become a matter of serious
+question, as will be fully shown and discussed in the next volume.
+Meanwhile it is enough to observe that, on account of all these reasons,
+the theory of Lamarck, even if it be supposed to present any truth at
+all, is clearly insufficient as a full or complete theory of organic
+evolution.
+
+ * * * * *
+
+In historical order the next theory that was arrived at was the theory
+of natural selection, simultaneously published by Darwin and Wallace on
+July 1st, 1858.
+
+If we may estimate the importance of an idea by the change of thought
+which it effects, this idea of natural selection is unquestionably the
+most important idea that has ever been conceived by the mind of man.
+Yet the wonder is that it should not have been hit upon long before. Or
+rather, I should say, the wonder is that its immense and immeasurable
+importance should not have been previously recognised. For, since the
+publication of this idea by Darwin and Wallace, it has been found that
+its main features had already occurred to at least two other
+minds--namely, Dr. Wells in 1813, and Mr. Patrick Matthew in 1831. But
+neither of these writers perceived that in the few scattered sentences
+which they had written upon the subject they had struck the key-note of
+organic nature, and resolved one of the principal chords of the
+universe. Still more remarkable is the fact that Mr. Herbert
+Spencer--notwithstanding his great powers of abstract thought and his
+great devotion of those powers to the theory of evolution, when as yet
+this theory was scorned by science--still more remarkable, I say, is the
+fact that Mr. Herbert Spencer should have missed what now appears so
+obvious an idea. But most remarkable of all is the fact that Dr.
+Whewell, with all his stores of information on the history of the
+inductive sciences, and with all his acumen on the matter of scientific
+method, should not only have conceived the idea of natural selection,
+but expressly stated it as a logically possible explanation of the
+origin of species, and yet have so stated it merely for the purpose of
+dismissing it with contempt[26]. This, I think, is most remarkable,
+because it serves to prove how very far men's minds at that time must
+have been from entertaining, as in any way antecedently probable, the
+doctrine of transmutation. In order to show this I will here quote one
+passage from the writings of Whewell, and another from a distinguished
+French naturalist referred to by him.
+
+ [26] For quotations, see Note A.
+
+In 1846 Whewell wrote:--
+
+ Not only is the doctrine of the transmutation of species in itself
+ disproved by the best physiological reasonings, but the additional
+ assumptions which are requisite to enable its advocates to apply it
+ to the explanation of the geological and other phenomena of the
+ earth, are altogether gratuitous and fantastical[27].
+
+ [27] whewell, _indications of the creator_, 2nd ed., 1846.
+
+Then he quotes with approval the following opinion:--
+
+ Against this hypothesis, which, up to the present time, I regard as
+ purely gratuitous, and likely to turn geologists out of the sound
+ and excellent road in which they now are, I willingly raise my
+ voice, with the most absolute conviction of being in the right[28].
+
+ [28] de blainville, _compte rendu_, 1837.
+
+And, after displaying the proof rendered by Lyell of uniformitarianism
+in geology, and cordially subscribing thereto, Whewell adds:--
+
+ We are led by our reasonings to this view, that the present order
+ of things was commenced by an act of creative power entirely
+ different to any agency which has been exerted since. None of the
+ influences which have modified the present races of animals and
+ plants since they were placed in their habitations on the earth's
+ surface can have had any efficacy in producing them at first. We
+ are necessarily driven to assume, as the beginning of the present
+ cycle of organic nature, an event not included in the course of
+ nature[29].
+
+ [29] Whewell, _ibid._, p. 162.
+
+So much, then, for the state of the most enlightened and representative
+opinions on the question of evolution before the publication of
+Darwin's work; and so much, likewise, for the only reasonable
+suggestions as to the causes of evolution which up to that time had been
+put forward, even by those few individuals who entertained any belief in
+evolution as a fact. It was the theory of natural selection that changed
+all this, and created a revolution in the thought of our time, the
+magnitude of which in many of its far-reaching consequences we are not
+even yet in a position to appreciate; but the action of which has
+already wrought a transformation in general philosophy, as well as in
+the more special science of biology, that is without a parallel in the
+history of mankind.
+
+ * * * * *
+
+Although every one is now more or less well acquainted with the theory
+of natural selection, it is necessary, for the sake of completeness,
+that I should state the theory; and I will do so in full detail.
+
+It is a matter of observable fact that all plants and animals are
+perpetually engaged in what Darwin calls a "struggle for existence."
+That is to say, in every generation of every species a great many more
+individuals are born than can possibly survive; so that there is in
+consequence a perpetual battle for life going on among all the
+constituent individuals of any given generation. Now, in this struggle
+for existence, which individuals will be victorious and live? Assuredly
+those which are best fitted to live, in whatever respect, or respects,
+their superiority of fitness may consist. Hence it follows that Nature,
+so to speak, _selects_ the best individuals out of each generation to
+live. And not only so; but as these favoured individuals transmit their
+favourable qualities to their offspring, according to the fixed laws of
+heredity, it further follows that the individuals composing each
+successive generation have a general tendency to be better suited to
+their surroundings than were their forefathers. And this follows, not
+merely because in every generation it is only the "flower of the flock"
+that is allowed to breed, but also because, if in any generation some
+new and beneficial qualities happen to arise as slight variations from
+the ancestral type, they will (other things permitting) be seized upon
+by natural selection, and, being transmitted by heredity to subsequent
+generations, will be added to the previously existing type. Thus the
+best idea of the whole process will be gained by comparing it with the
+closely analogous process whereby gardeners, fanciers, and
+cattle-breeders create their wonderful productions; for just as these
+men, by always "_selecting_" their best individuals to breed from,
+slowly but continuously improve their stock, so Nature, by a similar
+process of "_selection_" slowly but continuously makes the various
+species of plants and animals better and better suited to the conditions
+of their life.
+
+Now, if this process of continuously adapting organisms to their
+environment takes place in nature at all, there is no reason why we
+should set any limits on the extent to which it is able to go, up to the
+point at which a complete and perfect adaptation is achieved. Therefore
+we might suppose that all species would eventually reach this condition
+of perfect harmony with their environment, and then remain fixed. And
+so, according to the theory, they would, if the environment were itself
+unchanging. But forasmuch as the environment (i. e. the sum total of the
+external conditions of life) of almost every organic type alters more
+or less from century to century--whether from astronomical, geological,
+and geographical changes, or from the immigrations and emigrations of
+other species living on contiguous areas, and so on--it follows that the
+process of natural selection need never reach a terminal phase. And
+forasmuch as natural selection may thus continue, _ad infinitum_, slowly
+to alter a specific type in adaptation to a gradually changing
+environment, if in any case the alteration thus effected is sufficient
+in amount to lead naturalists to name the result as a distinct species,
+it follows that natural selection has transmuted one specific type into
+another. Similarly, by a continuation of the process, specific types
+would become transmuted into generic, generic into family types, and so
+on. Thus the process is supposed to go on throughout all the countless
+forms of life continuously and simultaneously--the world of organic
+types being thus regarded as in a state of perpetual, though gradual,
+flux.
+
+ * * * * *
+
+Now, the first thing we have to notice about this theory is, that in all
+its main elements it is merely a statement of observable facts. It is an
+observable fact that in all species of plants and animals a very much
+larger number of individuals are born than can possibly survive. Thus,
+for example, it has been calculated that if the progeny of a single pair
+of elephants--which are the slowest breeding of animals--were all
+allowed to reach maturity and propagate, in 750 years there would be
+living 19,000,000 descendants. Again, in the case of vegetables, if a
+species of annual plant produces only two seeds a year, if these in
+successive years were all allowed to reproduce their kind, in twenty
+years there would be 11,000,000 plants from a single ancestor. Yet we
+know that nearly all animals and plants produce many more young at a
+time than in either of these two supposed cases. Indeed, as individuals
+of many kinds of plants, and not a few kinds of animals, produce every
+year several thousand young, we may make a rough estimate and say, that
+over organic nature as a whole probably not one in a thousand young are
+allowed to survive to the age of reproduction. How tremendous,
+therefore, must be the struggle for existence! It is thought a terrible
+thing in battle when one half the whole number of combatants perish. But
+what are we to think of a battle for life where only one in a thousand
+survives?
+
+This, then, is the first fact. The second is the fact so long ago
+recognised, that the battle is to the strong, the race to the swift. The
+thousandth individual which does survive in the battle for
+existence--which does win the race for life--is, without question, one
+of the individuals best fitted to do so; that is to say, best fitted to
+the conditions of its existence considered as a whole. Nature is,
+therefore, always picking out, or selecting, such individuals to live
+and to breed.
+
+The third fact is, that the individuals so selected transmit their
+favourable qualities to their offspring by heredity. There is no doubt
+about this fact, so far as we are concerned with it. For although, as I
+have already hinted, considerable doubt has of late years been cast upon
+Lamarck's doctrine of the hereditary transmission of _acquired_
+characters, it remains as impossible as ever it was to question the
+hereditary transmission of what are called _congenital_ characters. And
+this is all that Darwin's theory necessarily requires.
+
+The fourth fact is, that although heredity as a whole produces a
+wonderfully exact copy of the parent in the child, there is never a
+precise reduplication. Of all the millions of human beings upon the face
+of the earth, no one is so like another that we cannot see some
+difference; the resemblance is everywhere specific, nowhere individual.
+Now this same remark applies to all specific types. The only reason why
+we notice individual differences in the case of the human type more than
+we do in the case of any other types, is because our attention is here
+more incessantly focussed upon these differences. We are compelled to
+notice them in the case of our own species, however small they may
+appear to a naturalist, because, unless we do so, we should not
+recognise the members of our own family, or be able to distinguish
+between a man whom we know is ready to do us an important service, and
+another man whom we know is ready to cut our throats. But our common
+mother Nature is able thus to distinguish between all her children. Her
+eyes are much more ready to detect small individual peculiarities than
+are the eyes of any naturalist. No slight variations in the cast of
+feature or disposition of parts, no minute difference in the arrangement
+of microscopical cells, can escape her ever vigilant attention. And,
+consequently, when among all the innumerable multitudes of individual
+variations any one arises which--no matter in how slight a degree--gives
+to that individual a better chance of success in the struggle for life,
+Nature chooses that individual to survive, and so to perpetuate the
+improvement in his or her progeny.
+
+Now I say that all these several component parts of Darwinian doctrine
+are not matters of theory, but matters of fact. The only element of
+theory in his doctrine of evolution by natural selection has reference
+to the degree in which these observable facts, when thus brought
+together, are adequate to account for the process of evolution.
+
+ * * * * *
+
+So much, then, as a statement of the theory of natural selection. But
+from this statement--i. e. from the theory of natural selection
+itself--there follow certain matters of general principle which it is
+important to bear in mind. These, therefore, I shall here proceed to
+mention.
+
+First of all, it is evident that the theory is applicable as an
+explanation of organic changes in specific types only in so far as these
+changes are of _use_, or so far as such changes endow the species with
+better chances of success in the general struggle for existence. This is
+the only sense in which I shall always employ the terms use, utility,
+service, benefit, and so forth--that is to say, in the sense of
+life-preserving.
+
+ * * * * *
+
+Next, it must be clearly understood that the life which it is the
+object, so to speak, of natural selection to preserve, is primarily the
+life of the _species_; not that of the _individual_. Natural selection
+preserves the life of the individual only in so far as this is conducive
+to that of the species. Wherever the life-interests of the individual
+clash with those of the species, that individual is sacrificed in favour
+of others who happen better to subserve the interests of the species.
+For example, in all organisms a greater or less amount of vigour is
+wasted, so far as individual interests are concerned, in the formation
+and the nourishment of progeny. In the great majority of plants and
+animals an enormous amount of physiological energy is thus expended.
+Look at the roe or the milt of a herring, for instance, and see what a
+huge drain has been made upon the individual for the sake of its
+species. Again, all unselfish instincts have been developed for the sake
+of the species, and usually against the interests of the individual. An
+ant which will allow her head to be slowly drawn from her body rather
+than relinquish her hold upon a pupa, is clearly acting in response to
+an instinct which has been developed for the benefit of the hive, though
+fatal to the individual. And, in a lesser degree, the parental
+instincts, wherever they occur, are more or less detrimental to the
+interests of the individual, though correspondingly essential to those
+of the race.
+
+These illustrations will serve to show that natural selection always
+works primarily for the life-interests of the species--and, indeed, only
+works for those of the individual at all in so far as the latter happen
+to coincide with the former. Or, otherwise stated, the object of natural
+selection is always that of producing and maintaining specific types in
+the highest degree of efficiency, no matter what may become of the
+constituent individuals. Which is a striking republication by Science of
+a general truth previously stated by Poetry:--
+
+ So careful of the type she seems,
+ So careless of the single life.
+
+Tennyson thus noted the fact, and a few years later Darwin supplied the
+explanation.
+
+But of course in many, if not in the majority of cases, anything that
+adds to the life-sustaining power of the single life thereby ministers
+also to the life-sustaining power of the type; and thus we can
+understand why all mechanisms and instincts which minister to the single
+life have been developed--namely, because the life of the species is
+made up of the lives of all its constituent individuals. It is only
+where the interests of the one clash with those of the other that
+natural selection works against the individual. So long as the interests
+are coincident, it works in favour of both.
+
+Natural selection, then, is a theory which seeks to explain by natural
+causes the occurrence of every kind of adaptation which is to be met
+with in organic nature, on the assumption that adaptations of every kind
+have primary reference to the preservation of species, and therefore
+also, as a general rule, to the preservation of their constituent
+individuals. And from this it follows that where it is for the benefit
+of a species to change its type, natural selection will effect that
+change, thus leading to a specific transmutation, or the evolution of a
+new species. In such cases the old species may or may not become
+extinct. If the transmutation affects the species as a whole, or
+throughout its entire range, of course _that_ particular type becomes
+extinct, although it does so by becoming changed into a still more
+suitable type in the course of successive generations. If, on the other
+hand, the transmutation affects only a part of the original species, or
+not throughout its entire range, then the other parts of that species
+may survive for any number of ages as they originally were. In the one
+case there is a ladder-like transmutation of species in time; in the
+other case a possibly tree-like multiplication of species in space. But
+whether the evolution of species be thus serial in time or divergent in
+space, the object of natural selection, so to speak, is in either case
+the same--namely, that of preserving all types which prove best suited
+to the conditions of their existence.
+
+ * * * * *
+
+Once more, the term "struggle for existence" must be understood to
+comprehend, not only a competition for life among contemporary
+individuals of the same species, but likewise a struggle by all such
+individuals taken collectively for the continuance of their own specific
+type. Thus, on the one hand, while there is a perpetual civil war being
+waged between members of the same species, on the other hand there is a
+foreign war being waged by the species as a whole against its world as a
+whole. Hence it follows that natural selection does not secure survival
+of the fittest as regards individuals only, but also survival of the
+fittest as regards types. This is a most important point to remember,
+because, as a general rule, these two different causes produce exactly
+opposite effects. Success in the civil war, where each is fighting
+against all, is determined by _individual_ fitness and _self-reliance_.
+But success in the foreign war is determined by what may be termed
+_tribal_ fitness and _mutual dependence_. For example, among social
+insects the struggle for existence is quite as great between different
+tribes or communities, as it is between different individuals of the
+same community; and thus we can understand the extraordinary degree in
+which not only co-operative instincts, but also largely intelligent
+social habits, have here been developed[30]. Similarly, in the case of
+mankind, we can understand the still more extraordinary development of
+these things--culminating in the moral sense. I have heard a sermon,
+preached at one of the meetings of the British Association, entirely
+devoted to arguing that the moral sense could not have been evolved by
+natural selection, seeing that the altruism which this sense involves is
+the very opposite of selfishness, which alone ought to have been the
+product of survival of the fittest in a struggle for life. And, of
+course, this argument would have been perfectly sound had Darwin limited
+the struggle for existence to individuals, without extending it to
+communities. But if the preacher had ever read Darwin's works he would
+have found that, when thus extended, the principle of natural selection
+is bound to work in favour of the co-operative instincts in the case of
+so highly social an animal as man; and that of these instincts
+conscience is the highest imaginable exhibition.
+
+ [30] For cases, see _Animal Intelligence_, in the chapters on Ants
+ and Bees; and, for discussion of principles, _Mental Evolution in
+ Animals_, in the chapters on Instinct.
+
+What I have called tribal fitness--in contradistinction to individual
+fitness--begins with the family, developes in the community (herd, hive,
+clan, &c.), and usually ends with the limits of the species. On the one
+hand, however, it is but seldom that it extends so far as to embrace the
+entire species; while, on the other hand, it may in some cases, and as
+it were sporadically, extend beyond the species. In these latter cases
+members of different species mutually assist one another, whether in the
+way of what is called symbiosis, or in a variety of other ways which I
+need not wait to mention. For the only point which I now desire to make
+clear is, that all cases of mutual aid or co-operation, whether within
+or beyond the limits of species, are cases which fall under the
+explanatory sweep of the Darwinian theory[31].
+
+ [31] Prince Kropotkin in the _Nineteenth Century_ (Feb. 1888, Apr.
+ 1891) has adduced a large and interesting body of facts, showing the
+ great prevalence of the principle of co-operation in organic
+ nature.
+
+ * * * * *
+
+Another important point to notice is, that it constitutes no part of the
+theory of natural selection to suppose that survival of the fittest must
+invariably lead to _improvement_ of type, in the sense of superior
+organization. On the contrary, if from change of habits or conditions of
+life an organic type ceases to have any use for previously useful
+organs, natural selection will not only allow these organs in successive
+generations to deteriorate--by no longer placing any selective premium
+upon their maintenance--but may even proceed to assist the agencies
+engaged in their destruction. For, being now useless, they may become
+even deleterious, by absorbing nutriment, causing weight, occupying
+space, &c., without conferring any compensating benefit. Thus we can
+understand why it is that parasites, for example, present the phenomena
+of what is called _degeneration_, i. e. showing by their whole structure
+that they have descended from a possibly very much higher type of
+organization than that which they now exhibit. Having for innumerable
+generations ceased to require their legs, their eyes, and so forth, all
+such organs of high elaboration have either disappeared or become
+vestigial, leaving the parasite as a more or less effete representative
+of its ancestry.
+
+These facts of degeneration, as we have previously seen, are of very
+general occurrence, and it is evident that their importance in the field
+of organic evolution as a whole has been very great. Moreover, it ought
+to be particularly observed that, as just indicated, the facts may be
+due either to a passive _cessation_ of selection, or to an active
+_reversal_ of it. Or, more correctly, these facts are probably _always_
+due to the cessation of selection, although in most cases where species
+in a state of nature are concerned, the process of degeneration has been
+both hastened and intensified by the super-added influence of the
+reversal of selection. In the next volume I shall have occasion to recur
+to this distinction, when it will be seen that it is one of no small
+importance to the general theory of descent.
+
+ * * * * *
+
+We may now proceed to consider certain misconceptions of the Darwinian
+theory which are largely, not to say generally, prevalent among
+supporters of the theory. These misconceptions, therefore, differ from
+those which fall to be considered in the next chapter, i. e.
+misconceptions which constitute grounds of objection to the theory.
+
+ * * * * *
+
+Of all the errors connected with the theory of natural selection,
+perhaps the one most frequently met with--especially among supporters of
+the theory--is that of employing the theory to explain all cases of
+phyletic modification (or inherited change of type) indiscriminately,
+without waiting to consider whether in particular cases its application
+is so much as logically possible. The term "natural selection" thus
+becomes a magic word, or Sesame, at the utterance of which every closed
+door is supposed to be immediately opened. Be it observed, I am not here
+alluding to that merely blind faith in natural selection, which of late
+years has begun dogmatically to force this principle as the sole cause
+of organic evolution in every case where it is _logically possible_ that
+the principle can have come into play. Such a blind faith, indeed, I
+hold to be highly inimical, not only to the progress of biological
+science, but even to the true interests of the natural selection theory
+itself. As to this I shall have a good deal to say in the next volume.
+Here, however, the point is, that the theory in question is often
+invoked in cases where it is not even logically possible that it can
+apply, and therefore in cases where its application betokens, not merely
+an error of judgment or extravagance of dogmatism, but a fallacy of
+reasoning in the nature of a logical contradiction. Almost any number of
+examples might be given; but one will suffice to illustrate what is
+meant. And I choose it from the writings of one of the authors of the
+selection theory itself, in order to show how easy it is to be cheated
+by this mere juggling with a phrase--for of course I do not doubt that a
+moment's thought would have shown the writer the untenability of his
+statement.
+
+In his most recent work Mr. Wallace advances an interesting hypothesis
+to the effect that differences of colour between allied species, which
+are apparently too slight to serve any other purpose, may act as
+"recognition marks," whereby the opposite sexes are enabled at once to
+distinguish between members of their own and of closely resembling
+species. Of course this hypothesis can only apply to the higher animals;
+but the point here is that, supposing it to hold for them, Mr. Wallace
+proceeds to argue thus:--Recognition marks "have in all probability been
+acquired in the process of differentiation for the purpose of checking
+the intercrossing of allied forms," because "one of the first needs of a
+new species would be to keep separate from its nearest allies, and this
+could be more readily done by some easily seen external mark[32]."
+Now, it is clearly not so much as logically possible that these
+recognition-marks (supposing them to be such) can have been acquired
+by natural selection, "for the purpose of checking intercrossing of
+allied forms." For the theory of natural selection, from its own
+essential nature as a theory, is logically exclusive of the supposition
+that survival of the fittest ever provides changes in anticipation of
+future uses. Or, otherwise stated, it involves a contradiction of the
+theory itself to say that the colour-changes in question were originated
+by natural selection, in order to meet "one of the _first_ needs of a
+_new_ species," or for the purpose of _subsequently_ preventing
+intercrossing with allied forms. If it had been said that these
+colour-differentiations were originated by some cause other than natural
+selection (or, if by natural selection, still with regard to some
+_previous_, instead of _prophetic_, "purpose"), and, when so "acquired,"
+_then_ began to serve the "purpose" assigned, the argument would not
+have involved the fallacy which we are now considering. But, as it
+stands, the argument reverts to the teleology of pre-Darwinian days--or
+the hypothesis of a "purpose" in the literal sense which sees the end
+from the beginning, instead of a "purpose" in the metaphorical sense of
+an adaptation that is evolved by the very modifications which subserve
+it[33].
+
+ [32] _Darwinism_, pp. 218 and 227.
+
+ [33] Since the above was written Prof. Lloyd Morgan has published a
+ closely similar notice of the passage in question. "This language,"
+ he says, "seems to savour of teleology (that pitfall of the
+ evolutionist). The cart is put before the horse. The
+ recognition-marks were, I believe, not produced to prevent
+ intercrossing, but intercrossing has been prevented because of
+ preferential mating between individuals possessing special
+ recognition-marks. To miss this point is to miss an important
+ segregation-factor."--(_Animal Life and Intelligence_, p. 103.)
+ Again, on pp. 184-9, he furnishes an excellent discussion on the
+ whole subject of the fallacy alluded to in the text, and gives
+ illustrative quotations from other prominent Darwinians. I should
+ like to add that Darwin himself has nowhere fallen into this, or any
+ of the other fallacies, which are mentioned in the text.
+
+ * * * * *
+
+Another very prevalent, and more deliberate, fallacy connected with the
+theory of natural selection is, _that it follows deductively from the
+theory itself_ that the principle of natural selection must be the sole
+means of modification in all cases where modification is of an
+_adaptive_ kind,--with the consequence that no other principle can ever
+have been concerned in the production of structures or instincts which
+are of any use to their possessors. Whether or not natural selection
+actually has been the sole means of adaptive modification in the race,
+as distinguished from the individual, is a question of biological
+fact[34]; but it involves a grave error of reasoning to suppose that
+this question can be answered deductively from the theory of natural
+selection itself, as I shall show at some length in the next volume.
+
+ [34] Of course adaptive modifications produced in the individual
+ lifetime, and not _inherited_, do not concern the question at all.
+ In this and the following paragraphs, therefore, "adaptations,"
+ "adaptive modifications," &c., refer exclusively to such as are
+ hereditary, i. e. phyletic.
+
+ * * * * *
+
+A still more extravagant, and a still more unaccountable fallacy is the
+one which represents it as following deductively from the theory of
+natural selection itself, that all _hereditary_ characters are
+"necessarily" due to natural selection. In other words, not only all
+adaptive, but likewise all non-adaptive hereditary characters, it is
+said, _must_ be due to natural selection. For non-adaptive characters
+are taken to be due to "correlation of growth," in connexion with some
+of the adaptive ones--natural selection being thus the _indirect_ means
+of producing the former _wherever_ they may occur, on account of its
+being the _direct_ and the _only_ means of producing the latter. Thus it
+is deduced from the theory of natural selection itself,--1st, that the
+principle of natural selection is the only possible cause of adaptive
+modification: 2nd, that non-adaptive modifications can only occur in the
+race as correlated appendages to the adaptive: 3rd, that, consequently,
+natural selection is the only possible cause of modification, whether
+adaptive or non-adaptive. Here again, therefore, we must observe that
+none of these sweeping generalizations can possibly be justified by
+deductive reasoning from the theory of natural selection itself. Any
+attempt at such deductive reasoning must necessarily end in circular
+reasoning, as I shall likewise show in the second volume, where this
+whole "question of utility" will be thoroughly dealt with.
+
+ * * * * *
+
+Once more, there is an important oversight very generally committed by
+the followers of Darwin. For even those who avoid the fallacies above
+mentioned often fail to perceive, that natural selection can only begin
+to operate if the _degree_ of adaptation is already given as
+sufficiently high to count for something in the struggle for
+_existence_. Any adaptations which fall below this level of importance
+cannot possibly have been produced by survival of the fittest. Yet the
+followers of Darwin habitually speak of adaptative characters, which _in
+their own opinion_ are subservient merely to comfort or convenience, as
+having been produced by such means. Clearly this is illogical; for it
+belongs to the essence of Darwin's theory to suppose, that natural
+selection can have no jurisdiction beyond the line where structures or
+instincts already present a sufficient degree of adaptational value to
+increase, in some measure, the expectation of life on the part of their
+possessors. We cannot speak of adaptations as due to natural selection,
+without thereby affirming that they present what I have elsewhere termed
+a "selection value."
+
+ * * * * *
+
+Lastly, as a mere matter of logical definition, it is well-nigh
+self-evident that the theory of natural selection is a theory of the
+origin, and cumulative development, of _adaptations_, whether these be
+distinctive of species, or of genera, orders, families, classes, and
+sub-kingdoms. It is only when the adaptations happen to be distinctive
+of the first (or lowest) of these taxonomic divisions, that the theory
+which accounts for _these_ adaptations accounts also for the forms which
+present them,--i. e. becomes _also_ a theory of the origin of species.
+This, however, is clearly but an accident of particular cases; and,
+therefore, even in them the theory is _primarily_ a theory of
+adaptations, while it is but secondarily a theory of the species which
+present them. Or, otherwise stated, the theory is no more a theory of
+the origin of species than it is of the origin of genera, families, and
+the rest; while, on the other hand, it is _everywhere_ a theory of the
+adaptive modifications whereby each of these taxonomic divisions has
+been differentiated as such. Yet, sufficiently obvious as the accuracy
+of this definition must appear to any one who dispassionately considers
+it, several naturalists of high standing have denounced it in violent
+terms. I shall therefore have to recur to the subject at somewhat
+greater length hereafter. At present it is enough merely to mention the
+matter, as furnishing another and a curious illustration of the not
+infrequent weakness of logical perception on the part of minds well
+gifted with the faculty of observation. It may be added, however, that
+the definition in question is in no way hostile to the one which is
+virtually given by Darwin in the title of his great work. _The Origin of
+Species by means of Natural Selection_ is beyond doubt the best title
+that could have been given, because at the time when the work was
+published the _fact_, no less than the _method_, of organic evolution
+had to be established; and hence the most important thing to be done at
+that time was to prove the transmutation of species. But now that this
+has been done to the satisfaction of naturalists in general, it is as I
+have said, curious to find some of them denouncing a wider definition of
+the principle of natural selection, merely because the narrower (or
+included) definition is invested with the charm of verbal
+associations[35].
+
+ [35] The question as to whether natural selection has been the only
+ principle concerned in the origination of species, is quite distinct
+ from that as to the accuracy of the above definition.
+
+ * * * * *
+
+So much for fallacies and misconceptions touching Darwin's theory, which
+are but too frequently met with in the writings of its supporters. We
+must now pass on to mention some of the still greater fallacies and
+misconceptions which are prevalent in the writings of its opponents.
+And, in order to do this thoroughly, I shall begin by devoting the
+remainder of the present chapter to a consideration of the antecedent
+standing of the two theories of natural selection and supernatural
+design. This having been done, in the succeeding chapters I shall deal
+with the evidences for, and the objections against, the former theory.
+
+ * * * * *
+
+Beginning, then, with the antecedent standing of these alternative
+theories, the first thing to be noticed is, that they are both concerned
+with the same subject-matter, which it is their common object to
+explain. Moreover, this subject-matter is clearly and sharply divisible
+into two great classes of facts in organic nature--namely, those of
+Adaptation and those of Beauty. Darwin's theory of descent explains the
+former by his doctrine of natural selection, and the latter by his
+doctrine of sexual selection. In the first instance, therefore, I shall
+have to deal only with the facts of adaptation, leaving for subsequent
+consideration the facts of beauty.
+
+Innumerable cases of the adaptation of organisms to their surroundings
+being the facts which now stand before us to be explained either by
+natural selection or by supernatural intention, we may first consider a
+statement which is frequently met with--namely, that even if all such
+cases of adaptation were proved to be fully explicable by the theory of
+descent, this would constitute no disproof of the theory of design: all
+the cases of adaptation, it is argued, might still be due to design,
+even though they admit of being hypothetically accounted for by the
+theory of descent. I have heard an eminent Professor tell his class that
+the many instances of mechanical adaptation discovered and described by
+Darwin as occurring in orchids, seemed to him to furnish better proof of
+supernatural contrivance than of natural causes; and another eminent
+Professor has informed me that, although he had read the _Origin of
+Species_ with care, he could see in it no evidence of natural selection
+which might not equally well have been adduced in favour of intelligent
+design. But here we meet with a radical misconception of the whole
+logical attitude of science. For, be it observed, this exception _in
+limine_ to the evidence which we are about to consider does not question
+that natural selection _may_ be able to do all that Darwin ascribes to
+it. The objection is urged against his interpretation of the facts
+merely on the ground that these facts might _equally well_ be ascribed
+to intelligent design. And so undoubtedly they might, if we were all
+simple enough to adopt a supernatural explanation whenever a natural one
+is found sufficient to account for the facts. Once admit the irrational
+principle that we may assume the operation of higher causes where the
+operation of lower ones is sufficient to explain the observed phenomena,
+and all our science and all our philosophy are scattered to the winds.
+For the law of logic which Sir William Hamilton called the law of
+parsimony--or the law which forbids us to assume the operation of higher
+causes when lower ones are found sufficient to explain the observed
+effects--this law constitutes the only barrier between science and
+superstition. It is always possible to give a hypothetical explanation
+of any phenomenon whatsoever, by referring it immediately to the
+intelligence of some supernatural agent; so that the only difference
+between the logic of science and the logic of superstition consists in
+science recognising a validity in the law of parsimony which
+superstition disregards. Therefore one can have no hesitation in saying
+that this way of looking at the evidence in favour of natural selection
+is not a scientific or a reasonable way of looking at it, but a purely
+superstitious way. Let us take, as an illustration, a perfectly parallel
+case. When Kepler was unable to explain by any known causes the paths
+described by the planets, he resorted to a supernatural explanation, and
+supposed that every planet was guided in its movements by some presiding
+angel. But when Newton supplied a beautifully simple physical
+explanation, all persons with a scientific habit of mind at once
+abandoned the metaphysical one. Now, to be consistent, the
+above-mentioned Professors, and all who think with them, ought still to
+adhere to Kepler's hypothesis in preference to Newton's explanation;
+for, excepting the law of parsimony, there is certainly no other
+logical objection to the statement, that the movements of the planets
+afford as good evidence of the influence of guiding angels as they do of
+the influence of gravitation.
+
+So much, then, for the illogical position that, granting the evidence in
+favour of natural descent and supernatural design to be equal and
+parallel, we should hesitate in our choice between the two theories.
+But, of course, if the evidence is supposed _not_ to be equal and
+parallel--i. e. if it is supposed that the theory of natural selection
+is not so good a theory whereby to explain the facts of adaptation as is
+that of supernatural design,--then the objection is no longer the one
+which we are considering. It is quite another objection, and one which
+is not _prima facie_ absurd. Therefore let us state clearly the distinct
+question which thus arises.
+
+Innumerable cases of adaptation of organisms to their environments are
+the observed facts for which an explanation is required. To supply this
+explanation, two, and only two, hypotheses are in the field. Of these
+two hypotheses one is intelligent design manifested directly in special
+creation; the other is natural causation operating through countless
+ages of the past. Now, the adaptations in question involve an
+innumerable multitude of special mechanisms, in most cases even within
+the limits of any one given species; but when we consider the sum of all
+these mechanisms presented by organic nature as a whole, the mind must
+indeed be dull which does not feel astounded. For, be it further
+observed, these mechanical contrivances[36] are, for the most part, no
+merely simple arrangements, which might reasonably be supposed due,
+like the phenomena of crystallization, to comparatively simple physical
+causes. On the contrary, they everywhere and habitually exhibit so
+deep-laid, so intricate, and often so remote an adaptation of means to
+ends, that no machinery of human contrivance can properly be said to
+equal their perfection from a mechanical point of view. Therefore,
+without question, the hypothesis which first of all they suggest--or
+suggest most readily--is the hypothesis of design. And this hypothesis
+becomes virtually the only hypothesis possible, if it be assumed--as it
+generally was assumed by natural theologians of the past,--that all
+species of plants and animals were introduced into the world _suddenly_.
+For it is quite inconceivable that any known cause, other than
+intelligent design, could be competent to turn out instantaneously any
+one of these intricate pieces of machinery, already adapted to the
+performance of its special function. But, on the other hand, if there is
+any evidence to show that one species becomes slowly transformed into
+another--or that one set of adaptations becomes slowly changed into
+another set as changing circumstances require,--then it becomes quite
+possible to imagine that a strictly natural causation may have had
+something to do with the matter. And this suggestion becomes greatly
+more probable when we discover, from geological evidence and
+embryological research, that in the history both of races and of
+individuals the various mechanisms in question have themselves had a
+history--beginning in the forms of most uniformity and simplicity,
+gradually advancing to forms more varied and complex, nowhere exhibiting
+any interruptions in their upward progress, until the world of organic
+machinery as we now have it is seen to have been but the last phase of a
+long and gradual growth, the ultimate roots of which are to be found in
+the soil of undifferentiated protoplasm.
+
+ [36] It is often objected to Darwin's terminology, that it embraces
+ such words as "contrivance," "purpose," &c., which are strictly
+ applicable only to the processes or the products of thought. But
+ when it is understood that they are used in a neutral or
+ metaphorical sense, I cannot see that any harm arises from their
+ use.
+
+Lastly, when there is supplied to us the suggestion of natural selection
+as a cause presumably adequate to account for this continuous growth in
+the number, the intricacy, and the perfection of such mechanisms, it is
+only the most unphilosophical mind that can refuse to pause as between
+the older hypothesis of design and the newer hypothesis of descent.
+
+Thus it is clear that the _a priori_ standing of the rival hypotheses of
+naturalism and supernaturalism in the case of all these pieces of
+organic machinery, is profoundly affected by the question whether they
+came into existence suddenly, or whether they did so gradually. For, if
+they all came into existence suddenly, the fact would constitute
+well-nigh positive proof in favour of supernaturalism, or creation by
+design; whereas, if they all came into existence gradually, this fact
+would in itself constitute presumptive evidence in favour of naturalism,
+or of development by natural causes. And, as shown in the previous
+chapters, the proof that all species of plants and animals came into
+existence gradually--or the proof of evolution as a fact--is simply
+overwhelming.
+
+From a still more general point of view I may state the case in another
+way, by borrowing and somewhat expanding an illustration which, I
+believe, was first used by Professor Huxley. If, when the tide is out,
+we see lying upon the shore a long line of detached sea-weed, marking
+the level which is reached by full tide, we should be free to conclude
+that the separation of the sea-weed from the sand and the stones was due
+to the intelligent work of some one who intended to collect the sea-weed
+for manure, or for any other purpose. But, on the other hand, we might
+explain the fact by a purely physical cause--namely, the separation by
+the sea-waves of the sea-weed from the sand and stones, in virtue of its
+lower specific gravity. Now, thus far the fact would be explained
+equally well by either hypothesis; and this fact would be the fact of
+_selection_. But whether we yielded our assent to the one explanation or
+to the other would depend upon a due consideration of all collateral
+circumstances. The sea-weed might not be of a kind that is of any use to
+man; there might be too great a quantity of it to admit of our supposing
+that it had been collected by man; the fact that it was all deposited on
+the high-water-mark would in itself be highly suggestive of the agency
+of the sea; and so forth. Thus, in such a case any reasonable observer
+would decide in favour of the physical explanation, or against the
+teleological one.
+
+Now the question whether organic evolution has been caused by physical
+agencies or by intelligent design is in precisely the same predicament.
+There can be no logical doubt that, theoretically at all events, the
+physical agencies which the present chapter is concerned with, and which
+are conveniently summed up in the term natural selection, are as
+competent to produce these so-called mechanical contrivances, and the
+other cases of adaptation which are to be met with in organic nature,
+as intelligent design could be. Hence, our choice as between these two
+hypotheses must be governed by a study of all collateral circumstances;
+that is to say, by a study of the evidences in favour of the physical
+explanation. To this study, therefore, we shall now address ourselves,
+in the course of the following chapters.
+
+
+
+
+CHAPTER VIII.
+
+EVIDENCES OF THE THEORY OF NATURAL SELECTION.
+
+
+I will now proceed to state the main arguments in favour of the theory
+of natural selection, and then, in the following chapter, the main
+objections which have been urged against it.
+
+In my opinion, the main arguments in favour of the theory are three in
+number.
+
+First, it is a matter of observation that the struggle for existence in
+nature does lead to the extermination of forms less fitted for the
+struggle, and thus makes room for forms more fitted. This general fact
+may be best observed in cases where an exotic species proves itself
+better fitted to inhabit a new country than is some endemic species
+which it exterminates. In Great Britain, for example, the so-called
+common rat is a comparatively recent importation from Norway, and it has
+so completely supplanted the original British rat, that it is now
+extremely difficult to procure a single specimen of the latter: the
+native black rat has been all but exterminated by the foreign brown rat.
+The same thing is constantly found in the case of imported species of
+plants. I have seen the river at Cambridge so choked with the inordinate
+propagation of a species of water-weed which had been introduced from
+America, that considerable expense had to be incurred in order to clear
+the river for traffic. In New Zealand the same thing has happened with
+the European water-cress, and in Australia with the common rabbit. So it
+is doubtless true, as one of the natives is said to have philosophically
+remarked, "the white man's rat has driven away our rat, the European fly
+drives away our fly, his clover kills our grass, and so will the Maoris
+disappear before the white man himself." Innumerable other cases to the
+same effect might be quoted; and they all go to establish the fact that
+forms less fitted to survive succumb in their competition with forms
+better fitted.
+
+ * * * * *
+
+Secondly, there is a general consideration of the largest possible
+significance in the present connexion--namely, that among all the
+millions of structures and instincts which are so invariably, and for
+the most part so wonderfully, adapted to the needs of the species
+presenting them, we cannot find a single instance, either in the
+vegetable or animal kingdom, of a structure or an instinct which is
+developed for the exclusive benefit of another species. Now this great
+and general fact is to my mind a fact of the most enormous, not to say
+overwhelming, significance. The theory of natural selection has now been
+before the world for more than thirty years, and during that time it had
+stood a fire of criticism such as was never encountered by any
+scientific theory before. From the first Darwin invited this criticism
+to adduce any single instance, either in the vegetable or animal
+kingdom, of a structure or an instinct which should unquestionably be
+proved to be of exclusive use to any species other than the one
+presenting it. He even went so far as to say that if any one such
+instance could be shown he would surrender his whole theory on the
+strength of it--so assured had he become, by his own prolonged
+researches, that natural selection was the true agent in the production
+of adaptive structures, and, as such, could never have permitted such a
+structure to occur in one species for the benefit of another. Now, as
+this invitation has been before the world for so many years, and has not
+yet been answered by any naturalist, we may by this time be pretty
+confident that it never will be answered. How tremendous, then, is the
+significance of this fact in its testimony to Darwin's theory! The
+number of animal and vegetable species, both living and extinct, is to
+be reckoned by millions, and every one of these species presents on an
+average hundreds of adaptive structures,--at least one of which in many,
+possibly in most, if not actually in all cases, is peculiar to the
+species that presents it. In other words, there are millions of adaptive
+structures (not to speak of instincts) which are peculiar to the species
+presenting them, and also many more which are the common property of
+allied species: yet, notwithstanding this inconceivable profusion of
+adaptive structures in organic nature, there is no single instance that
+has been pointed out of the occurrence of such a structure save for the
+benefit of the species that presents it. Therefore, I say that this
+immensely large and general fact speaks with literally immeasurable
+force in favour of natural selection, as at all events one of the main
+causes of organic evolution. For the fact is precisely what we should
+expect if this theory is true, while upon no other theory can its
+universality and invariability be rendered intelligible. On the
+beneficent design theory, for instance, it is inexplicable that no
+species should ever be found to present a structure or an instinct
+having primary reference to the welfare of another species, when, _ex
+hypothesi_, such an endless amount of thought has been displayed in the
+creation of structures and instincts having primary reference to the
+species which present them. For how magnificent a display of divine
+beneficence would organic nature have afforded, if all--or even
+some--species had been so inter-related as to have ministered to each
+others wants. Organic species might then have been likened to a
+countless multitude of voices, all singing in one great harmonious
+psalm. But, as it is, we see absolutely no vestige of such
+co-ordination: every species is for itself, and for itself alone--an
+outcome of the always and everywhere fiercely raging struggle for life.
+
+In order that the force of this argument may not be misapprehended, it
+is necessary to bear in mind that it is in no way affected by cases
+where a structure or an instinct is of primary benefit to its possessor,
+and then becomes of secondary benefit to some other species on account
+of the latter being able in some way or another to utilise its action.
+Of course organic nature is full of cases of this kind; but they only go
+to show the readiness which all species display to utilise for
+themselves everything that can be turned to good account in their own
+environments, and so, among other things, the structures and instincts
+of other animals. For instance, it would be no answer to Darwin's
+challenge if any one were to point to a hermit-crab inhabiting the
+cast-off shell of a mollusk; because the shell was primarily of use to
+the mollusk itself, and, so far as the mollusk is concerned, the fact of
+its shell being afterwards of a secondary use to the crab is quite
+immaterial. What Darwin's challenge requires is, that some structure or
+instinct should be shown which is not merely of such secondary or
+accidental benefit to another species, but clearly adapted to the needs
+of that other species in the first instance--such, for example, as would
+be the case if the tail of a rattle-snake were of no use to its
+possessor, while serving to warn other animals of the proximity of a
+dangerous creature; or, in the case of instincts, if it were true that a
+pilot-fish accompanies a shark for the purpose of helping the shark to
+discover food. Both these instances have been alleged; but both have
+been shown untenable. And so it has proved of all the other cases which
+thus far have been put forward.
+
+Perhaps the most remarkable of all the allegations which ever have been
+put forward in this connexion are those that were current with regard to
+instincts before the publication of Darwin's work. These allegations are
+the most remarkable, because they serve to show, in a degree which I do
+not believe could be shown anywhere else, the warping power of
+preconceived ideas. A short time ago I happened to come across the 8th
+edition of the _Encyclopædia Britannica_, and turned up the article on
+"Instinct" there, in order to see what amount of change had been wrought
+with regard to our views on this subject by the work of Darwin--the 8th
+edition of the _Encyclopædia Britannica_ having been published shortly
+before _The Origin of Species by means of Natural Selection_. I cannot
+wait to give any lengthy quotations from this representative exponent of
+scientific opinion upon the subject at that time; but its general drift
+may be appreciated if I transcribe merely the short concluding
+paragraph, wherein he sums up his general results. Here he says:--
+
+ It thus only remains for us to regard instinct as a mental faculty,
+ _sui generis_, the gift of God to the lower animals, that man in
+ his own person, and by them, might be relieved from the meanest
+ drudgery of nature.
+
+Now, here we have the most extraordinary illustration that is imaginable
+of the obscuring influence of a preconceived idea. Because he started
+with the belief that instincts _must_ have been implanted in animals for
+the benefit of man, this writer, even when writing a purely scientific
+essay, was completely blinded to the largest, the most obvious, and the
+most important of the facts which the phenomena of instinct display.
+For, as a matter of fact, among all the many thousands of instincts
+which are known to occur in animals, there is no single one that can be
+pointed to as having any special reference to man; while, on the other
+hand, it is equally impossible to point to one which does not refer to
+the welfare of the animal presenting it. Indeed, when the point is
+suggested, it seems to me surprising how few in number are the instincts
+of animals which have proved to be so much as of secondary or accidental
+benefit to man, in the same way as skins, furs, and a whole host of
+other animal products are thus of secondary use to him. Therefore, this
+writer not only failed to perceive the most obvious truth that every
+instinct, without any single exception, has reference to the animal
+which presents it; but he also conceived a purely fictitious inversion
+of this truth, and wrote an essay to prove a statement which all the
+instincts in the animal kingdom unite in contradicting.
+
+This example will serve to show, in a striking manner, not only the
+distance that we have travelled in our interpretation of organic nature
+between two successive editions of the _Encyclopædia Britannica_, but
+also the amount of verification which this fact furnishes to the theory
+of natural selection. For, inasmuch as it belongs to the very essence of
+this theory that all adaptive characters (whether instinctive or
+structural) must have reference to their own possessors, we find
+overpowering verification furnished to the theory by the fact now before
+us--namely, that immediately prior to the enunciation of this theory,
+the truth that all adaptive characters have reference only to the
+species which present them was not perceived. In other words, it was the
+testing of this theory by the facts of nature that _revealed_ to
+naturalists the general law which the theory, as it were, predicted--the
+general law that all adaptive characters have primary reference to the
+species which present them. And when we remember that this is a kind of
+verification which is furnished by millions of separate cases, the whole
+mass of it taken together is, as I have before said, overwhelming.
+
+It is somewhat remarkable that the enormous importance of this argument
+in favour of natural selection as a prime factor of organic evolution
+has not received the attention which it deserves. Even Darwin himself,
+with his characteristic reserve, has not presented its incalculable
+significance; nor do I know any of his followers who have made any
+approach to an adequate use of it in their advocacy of his views. In
+preparing the present chapter, therefore, I have been particularly
+careful not to pitch too high my own estimate of its evidential value.
+That is to say, I have considered, both in the domain of structures and
+of instincts, what instances admit of being possibly adduced _per
+contra_, or as standing outside the general law that adaptive structures
+and instincts are of primary use only to their possessors. In the result
+I can only think of two such instances. These, therefore, I will now
+dispose of.
+
+The first was pointed out, and has been fully discussed, by Darwin
+himself. Certain species of ants are fond of a sweet fluid that is
+secreted by aphides, and they even keep the aphides as we keep cows for
+the purpose of profiting by their "milk." Now the point is, that the use
+of this sweet secretion to the aphis itself has not yet been made out.
+Of course, if it is of no use to the aphis, it would furnish a case
+which completely meets Darwin's own challenge. But, even if this
+supposition did not stand out of analogy with all the other facts of
+organic nature, most of us would probably deem it prudent to hold that
+the secretion must primarily be of some use to the aphis itself,
+although the matter has not been sufficiently investigated to inform us
+of what this use is. For, in any case, the secretion is not of any vital
+importance to the ants which feed upon it: and I think but few impartial
+minds would go so far to save an hypothesis as to maintain, that the
+Divinity had imposed this drain upon the internal resources of one
+species of insect for the sole purpose of supplying a luxury to
+another. On the whole, it seems most probable that the fluid is of the
+nature of an excretion, serving to carry off waste products. Such, at
+all events, was the opinion at which Darwin himself arrived, as a result
+of observing the facts anew, and in relation to his theory.
+
+ * * * * *
+
+The other instance to which I have alluded as seeming at first sight
+likely to answer Darwin's challenge is the formation of vegetable galls.
+The great number and variety of galls agree in presenting a more or less
+elaborate structure, which is not only foreign to any of the uses of
+plant-life, but singularly and specially adapted to those of the
+insect-life which they shelter. Yet they are produced by a growth of the
+plant itself, when suitably stimulated by the insects' inoculation--or,
+according to recent observations, by emanations from the bodies of the
+larvæ which develop from the eggs deposited in the plant by the insect.
+Now, without question, this is a most remarkable fact; and if there were
+many more of the like kind to be met with in organic nature, we might
+seriously consider whether the formation of galls should not be held to
+make against the ubiquitous agency of natural selection. But inasmuch as
+the formation of galls stands out as an exception to the otherwise
+universal rule of every species for itself, and for itself alone, we are
+justified in regarding this one apparent exception with extreme
+suspicion. Indeed, I think we are justified in regarding the peculiar
+pathological effect produced in the plant by the secretions of the
+insect as having been in the first instance accidentally beneficial to
+the insects. Thus, if any other effect than that of a growing tumour had
+been produced in the first instance, or if the needs of the insect
+progeny had not been such as to have derived profit from being enclosed
+in such a tumour, then, of course, the inoculating instinct of these
+animals could not have been developed by natural selection. But, given
+these two conditions, and it appears to me there is nothing very much
+more remarkable about an accidental correlation between the effects of a
+parasitic larva on a plant and the needs of that parasite, than there is
+between the similarly accidental correlation between a hydated parasite
+and the nutrition furnished to it by the tissues of a warm-blooded
+animal. Doubtless the case of galls is somewhat more remarkable,
+inasmuch as the morbid growth of the plant has more concern in the
+correlation--being, in many instances, a more specialized structure on
+the part of a host than occurs anywhere else, either in the animal or
+vegetable world. But here I may suggest that although natural selection
+cannot have acted upon the plant directly, so as to have produced galls
+ever better and better adapted to the needs of the insect, it may have
+so acted upon the plants indirectly _though the insects_. For it may
+very well have been that natural selection would ever tend to preserve
+those individual insects, the quality of whose emanations tended to
+produce the form of galls best suited to nourish the insect progeny; and
+thus the character of these pathological growths may have become ever
+better and better adapted to the needs of the insects. Lastly, looking
+to the enormous number of relations and inter-relations between all
+organic species, it is scarcely to be wondered at that even so
+extraordinary an instance of correlation as this should have arisen thus
+by accident, and then have been perfected by such an _indirect_ agency
+of natural selection as is here suggested[37].
+
+ [37] Note B.
+
+ * * * * *
+
+The third general class of facts which tell so immensely in favour of
+natural selection as an important cause of organic evolution, are those
+of domestication. The art of the horticulturist, the fancier, the
+cattle-breeder, &c., consists in producing greater and greater
+deviations from a given wild type of plant or animal, in any particular
+direction that may be desired for purposes either of use or of beauty.
+Cultivated cereals, fruits, and flowers are known to have been all
+derived from wild species; and, of course, the same applies to all our
+domesticated varieties of animals. Yet if we compare a cabbage rose with
+a wild rose, a golden pippin apple with a crab, a toy terrier with any
+species of wild dog, not to mention any number of other instances, there
+can be no question that, if such differences had appeared in nature, the
+organisms presenting them would have been entitled to rank as distinct
+species--or even, in many cases, as distinct genera. Yet we know, as a
+matter of fact, that all these differences have been produced by a
+process of artificial selection, or pairing, which has been continuously
+practised by horticulturists and breeders through a number of
+generations. It is the business of these men to note the individual
+organisms which show most variation in the directions required, and then
+to propagate from these individuals, in order that the progeny shall
+inherit the qualities desired. The results thus become cumulative from
+generation to generation, until we now have an astonishing manifestation
+of useful qualities on the one hand, and of beautiful qualities on the
+other, according as the organisms have been thus bred for purposes of
+use or for those of beauty.
+
+Now it is immediately obvious that in these cases the process of
+artificial selection is precisely analogous to that of natural selection
+(and of sexual selection which will be considered later on), in all
+respects save one: the utility or the beauty which it is the aim of
+artificial selection continually to enhance, is utility or beauty in
+relation to the requirements or to the tastes of man; whereas the
+utility or the beauty which is produced by natural selection and sexual
+selection has reference only to the requirements or the tastes of the
+organisms themselves. But, with the exception of this one point of
+difference, the processes and the products are identical in kind.
+Persevering selection by man is thus proved to be capable of creating
+what are virtually new specific types, and this in any required
+direction. Hence, when we remember how severe is the struggle for
+existence in nature, it becomes impossible to doubt that selection by
+nature is able to do at least as much as artificial selection in the way
+of thus creating new types out of old ones. Artificial selection,
+indeed, notwithstanding the many and marvellous results which it has
+accomplished, can only be regarded as but a feeble imitation of natural
+selection, which must act with so much greater vigilance and through
+such immensely greater periods of time. In a word, the proved
+capabilities of artificial selection furnish, in its best conceivable
+form, what is called an argument _a fortiori_ in favour of natural
+selection.
+
+Or, to put it in another way, it may be said that for thousands of years
+mankind has been engaged in making a gigantic experiment to test, as it
+were by anticipation, the theory of natural selection. For, although
+this prolonged experiment has been carried on without any such intention
+on the part of the experimenters, it is none the less an experiment in
+the sense that its results now furnish an overwhelming verification of
+Mr. Darwin's theory. That is to say, they furnish overwhelming proof of
+the efficacy of the selective principle in the modification of organic
+types, when once this principle is brought steadily and continuously to
+bear upon a sufficiently long series of generations.
+
+In order to furnish ocular evidence of the value of this line of
+verification, I have had the following series of drawings prepared.
+Another and equally striking series might be made of the products of
+artificial selection in the case of plants; but it seems to me that the
+case of animals is more than sufficient for the purpose just stated.
+Perhaps it is desirable to add that considerable care has been bestowed
+upon the execution of these portraits; and that in every case the latter
+have been taken from the most typical specimens of the artificial
+variety depicted. Those of them which have not been drawn directly from
+life are taken from the most authoritative sources; and, before being
+submitted to the engraver, they were all examined by the best judges in
+each department. In none of the groups, however, have I aimed at an
+exhaustive representation of all the varieties: I have merely introduced
+representatives of as many as the page would in each case accommodate.
+
+ [Illustration: FIG. 91.--Pigeons. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 92.--Pigeons, continued. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 93.--Fowls. Drawn from life (prize specimens).]
+
+ [Illustration: FIG. 94.--Fowls, continued. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 95.--Pair of Japanese Fowls, long-tailed breed.
+ Drawn from stuffed specimens in the British Museum.]
+
+ [Illustration: FIG. 96.--Canaries. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 97.--Sebastopol, or Frizzled Goose. Drawn from a
+ photograph.]
+
+ [Illustration: FIG. 98.--The Dingo, or wild dog of Australia, 1/10
+ nat. size. Drawn from life (_Zoological Gardens_).]
+
+ [Illustration: FIG. 99.--Dogs. Drawn from life (prize specimens).]
+
+ [Illustration: FIG. 100.--Dogs, continued. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 101.--The Hairless Dog of Japan, 1/10 nat. size.
+ Drawn from a photograph kindly lent for the purpose by the
+ proprietor.]
+
+ [Illustration: FIG. 102.--The skull of a Bull-dog compared with that
+ of a Deerhound. Drawn from nature.]
+
+ [Illustration: FIG. 103. Rabbits. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 104.--Horses. Drawn from life (prize
+ specimens).]
+
+ [Illustration: FIG. 105.--Sheep. The illustrations are confined to
+ British breeds. Drawn from life (prize specimens).]
+
+ [Illustration: FIG. 106.--Cattle. The illustrations are confined to
+ British breeds. Drawn from life (prize specimens).]
+
+ [Illustration: FIG. 107.--Wild Boar contrasted with a modern
+ Domesticated Pig. Drawn from life (_Zoological Gardens_, and prize
+ specimen).]
+
+The exigencies of space have prevented, in some of the groups, strict
+adherence to a uniform scale--with the result that contrasts between
+different breeds in respect of size are not adequately rendered. This
+remark applies especially to the dogs; for although the artist has
+endeavoured to draw them in perspective, unless the distance between
+those in the foreground and those in the background is understood to be
+more considerable than it appears, an inadequate idea is given of the
+relative differences of size. The most instructive of the groups, I
+think, is that of the Canaries; because the many and great changes in
+different directions must in this case have been produced by artificial
+selection in so comparatively short a time--the first mention of this
+bird that I can find being by Gesner, in the sixteenth century.
+
+ * * * * *
+
+Now, it is surely unquestionable that in these typical proofs of the
+efficacy of artificial selection in the modification of specific types,
+we have the strongest conceivable testimony to the power of natural
+selection in the same direction. For it thus appears that wherever
+mankind has had occasion to operate by selection for a sufficiently long
+time--that is to say, on whatever species of plant or animal he chooses
+thus to operate for the purpose of modifying the type in any required
+direction,--the results are always more or less the same: he finds that
+all specific types lend themselves to continuous deflection in any
+particulars of structure, colour, &c., that he may desire to modify.
+
+Nevertheless, to this parallel between the known effects of artificial
+selection, and the inferred effects of natural selection, two objections
+have been urged. The first is, that in the case of artificial selection
+the selecting agent is a voluntary intelligence, while in the case of
+natural selection the selecting agent is Nature herself; and whether or
+not there is any counterpart of man's voluntary intelligence in nature
+is a question with which Darwinism has nothing to do. Therefore, it is
+alleged, the analogy between natural selection and artificial selection
+fails _ab initio_, or at the fountain-head of the causes which are taken
+by the analogy to be respectively involved.
+
+The second objection to the analogy is, that the products of artificial
+selection, closely as they may resemble natural species in all other
+respects, nevertheless present one conspicuous and highly important
+point of difference: they rarely, if ever, present the physiological
+character of mutual infertility, which is a character of extremely
+general occurrence in the case of natural species, even when these are
+most nearly allied.
+
+I will deal with these two objections in the next chapter, where I shall
+be concerned with the meeting of all the objections which have ever been
+urged against the theory of natural selection. Meanwhile I am engaged
+only in presenting the general arguments which support the theory, and
+therefore mention these objections to one of them merely _en passant_.
+And I do so in order to pledge myself effectually to dispose of them
+later on, so that for the purposes of my present argument both these
+objections may be provisionally regarded as non-existent; which means,
+in other words, that we may provisionally regard the analogy between
+artificial selection and natural selection as everywhere logically
+intact.
+
+ * * * * *
+
+To sum up, then, the results of the foregoing exposition thus far, what
+I hold to be the three principal, or most general, arguments in favour
+of the theory of natural selection, are as follows.
+
+First, there is the _a priori_ consideration that, if on independent
+grounds we believe in the theory of evolution at all, it becomes obvious
+that natural selection _must_ have had _some_ part in the process. For
+no one can deny the potent facts of heredity, variability, the struggle
+for existence, and survival of the fittest. But to admit these facts is
+to admit natural selection as a principle which must be, at any rate,
+one of the factors of organic evolution, supposing such evolution to
+have taken place. Next, when we turn from these _a priori_
+considerations, which thus show that natural selection _must_ have been
+concerned to some extent in the process of evolution, we find in organic
+nature evidence _a posteriori_ of the extent to which this principle
+_has_ been thus concerned. For we find that among all the countless
+millions of adaptive structures which are to be met with in organic
+nature, it is an invariable rule that they exist in relation to the
+needs of the particular species which present them: they never have any
+primary reference to the needs of other species. And as this
+extraordinarily large and general fact is exactly what the theory of
+natural selection would expect, the theory is verified by the fact in an
+extraordinarily cogent manner. In other words, the fact goes to prove
+that in _all_ cases where adaptive structures or instincts are
+concerned, natural selection must have been either the sole cause at
+work, or, at the least, an influence controlling the operation of all
+other causes.
+
+Lastly, an actually experimental verification of the theory has been
+furnished on a gigantic scale by the operations of breeders, fanciers,
+and horticulturists. For these men, by their process of selective
+accumulation, have empirically proved what immense changes of type may
+thus be brought about; and so have verified by anticipation, and in a
+most striking manner, the theory of natural selection--which, as now so
+fully explained, is nothing more than a theory of cumulative
+modifications by means of selective breeding.
+
+So much, then, by way of generalities. But perhaps the proof of natural
+selection as an agency of the first importance in the transmutation of
+species may be best brought home to us by considering a few of its
+applications in detail. I will therefore devote the rest of the present
+chapter to considering a few cases of this kind.
+
+There are so many large fields from which such special illustrations may
+be supplied, that it is difficult to decide which of them to draw upon.
+For instance, the innumerable, always interesting, and often astonishing
+adaptations on the part of flowers to the fertilising agency of insects,
+has alone given rise to an extensive literature since the time when
+Darwin himself was led to investigate the subject by the guidance of his
+own theory. The same may be said of the structures and movements of
+climbing plants, and in short, of all the other departments of natural
+history where the theory of natural selection has led to the study of
+the phenomena of adaptation. For in all these cases the theory of
+natural selection, which first led to their discovery, still remains the
+only scientific theory by which they can be explained. But among all the
+possible fields from which evidences of this kind may be drawn, I think
+the best is that which may be generically termed defensive colouring. To
+this field, therefore, I will restrict myself. But, even so, the cases
+to be mentioned are but mere samples taken from different divisions of
+this field; and therefore it must be understood at the outset that they
+could easily be multiplied a hundred-fold.
+
+
+_Protective Colouring._
+
+A vast number of animals are rendered more or less inconspicuous by
+resembling the colours of the surfaces on which they habitually rest.
+Such, for example, are grouse, partridges, rabbits, &c. Moreover, there
+are many cases in which, if the needs of the creature be such that it
+must habitually frequent surfaces of different colours, it has acquired
+the power of changing its colour accordingly--e. g. cuttle-fish,
+flat-fish, frogs, chameleons, &c. The physiological mechanism whereby
+these adaptive changes of colour are produced differs in different
+animals; but it is needless for our purposes to go into this part of the
+subject. Again, there are yet other cases where protective colouring
+which is admirably suited to conceal an animal through one part of the
+year, would become highly conspicuous during another part of it--namely,
+when the ground is covered with snow. Accordingly, in these cases the
+animals change their colour in the winter months to a snowy white:
+witness stoats, mountain hares, ptarmigan, &c. (Fig. 108.)
+
+ [Illustration: FIG. 108.--Seasonal changes of colour in Ptarmigan
+ (_Lagopus mutus_). Drawn from stuffed specimens in the British
+ Museum, 1/6 nat. size, with appropriate surroundings supplied.]
+
+Now, it is sufficiently obvious that in all these classes of cases the
+concealment from enemies or prey which is thus secured is of advantage
+to the animals concerned; and, therefore, that in the theory of natural
+selection we have a satisfactory theory whereby to explain it. And this
+cannot be said of any other theory of adaptive mechanisms in nature that
+has ever been propounded. The so-called Lamarckian theory, for instance,
+cannot be brought to bear upon the facts at all; and on the theory of
+special creation it is unintelligible why the phenomena of protective
+colouring should be of such general occurrence. For, in as far as
+protective colouring is of advantage to the species which present it, it
+is of corresponding disadvantage to those other species against the
+predatory nature of which it acts as a defence. And, of course, the
+same applies to yet other species, if they serve as prey. Moreover,
+the more minutely this subject is investigated in all its details,
+the more exactly is it found to harmonise with the naturalistic
+interpretation[38].
+
+ [38] Were it not that some of Darwin's critics have overlooked the
+ very point wherein the great value of protective colouring as
+ evidence of natural selection consists, it would be needless to
+ observe that it does so in the _minuteness_ of the protective
+ resemblance which in so many cases is presented. Of course where the
+ resemblance is only very general, the phenomena might be ascribed to
+ mere coincidence, of which the instincts of the animal have taken
+ advantage. But in the measure that the resemblance becomes minutely
+ detailed, the supposition of mere coincidence is excluded, and the
+ agency of some specially adaptive cause demonstrated. Again, it is
+ almost needless to say, no real difficulty is presented (as has been
+ alleged) by the cases above quoted of seasonal imitations, on the
+ ground that natural selection could not act alternately on the same
+ individual. Natural selection is not supposed to act alternately on
+ the same individual. It is supposed to act always in the same
+ manner, and if, as in the case of a regularly recurring change in
+ the colours of the environment, correspondingly recurrent changes
+ are required to appear in the colours of the animals, natural
+ selection sets its premium upon those individuals the constitutions
+ of which best lend themselves to seasonal changes of the needful
+ kind--probably under the influence of stimuli supplied by the
+ changes of external conditions (temperature, moisture, &c.).
+
+In the first place, we always find a complete correspondence between
+imitative colouring and instinctive endowment. If a caterpillar exactly
+resembles the colour of a twig, it also presents the instinct of
+habitually reposing in the attitude which makes it most resemble a
+twig--standing out from the branch on which it rests at the same angle
+as is presented by the real twigs of the tree on which it lives.
+
+Here, again, is a bird protectively coloured so as to resemble stones
+upon the rough ground where it habitually lives; and the drawing shows
+the attitude in which the bird instinctively reposes, so as still
+further to increase its resemblance to a stone. (Fig. 109.)
+
+ [Illustration: FIG. 109.--_Oedicnemus crepitans_, showing the
+ instinctive attitude of concealment. Drawn from a stuffed specimen
+ in the British Museum, 1/6 nat. size, with appropriate surroundings
+ supplied.
+
+To take only one other instance, hares and rabbits, like grouse and
+partridges--or like the plover just alluded to,--instinctively crouch
+upon those surfaces the colours of which they resemble; and I have often
+remarked that if, on account of any individual peculiarity of
+coloration, the animal is not able thus to secure concealment, it
+nevertheless exhibits the instinct of crouching which is of benefit to
+all its kind, although, from the accident of its own abnormal colouring,
+this instinct is then actually detrimental to the animal itself. For
+example, every sportsman must have noticed that the somewhat rare
+melanic variety of the common rabbit will crouch as steadily as the
+normal brownish-gray type, notwithstanding that, owing to its abnormal
+colour, a "nigger-rabbit" thus renders itself the most conspicuous
+object in the landscape. In all such cases, of course, there has been a
+deviation from the normal type in respect of colour, with the result
+that the inherited instinct is no longer in tune with the other
+endowments of the animal. Such a variation of colour, therefore, will
+tend to be suppressed by natural selection; while any variations which
+may bring the animal still more closely to resemble its habitual
+surroundings will be preserved. Thus we can understand the truly
+wonderful extent to which this principle of protective colouring has
+been carried in many cases where the need of it has been most urgent.
+
+Not only colour, but structure, may be profoundly modified for the
+purposes of protective concealment. Thus, caterpillars which resemble
+twigs do so not only in respect of colour, but also of shape; and this
+even down to the most minute details in cases where the adaptation is
+most complete: certain butterflies and leaf-insects so precisely
+resemble the leaves upon which, or among which, they live, that it is
+almost impossible to detect them in the foliage--not only the colour,
+the shape, and the venation being all exactly imitated, but in some
+cases even the defects to which the leaves are liable, in the way of
+fungoid growths, &c. There are other insects which with similar
+exactness resemble moss, lichens, and so forth. A species of fish
+secures a complete resemblance to bunches of sea-weed by a frond-like
+modification of all its appendages, and so on through many other
+instances. Now, in all such cases where there is so precise an
+imitation, both in colour and structure, it seems impossible to suggest
+any other explanation of the facts than the one which is supplied by
+Mr. Darwin's theory--namely, that the more perfect the resemblance is
+caused to become through the continuous influence of natural selection
+always picking out the best imitations, the more highly discriminative
+becomes the perception of those enemies against the depredations of
+which this peculiar kind of protection is developed; so that, in virtue
+of this action and re-action, eventually we have a degree of imitation
+which renders it almost impossible for a naturalist to detect the animal
+when living in its natural environment.
+
+ [Illustration: FIG. 110.--Imitative forms and colours in insects.
+ Drawn from nature (_R. Coll. Surg. Mus._).]
+
+
+_Warning Colours._
+
+In strange and glaring contrast to all these cases of protective
+colouring, stand other cases of conspicuous colouring. Thus, for
+example, although there are numberless species of caterpillars which
+present in an astonishing degree the phenomena of protective colouring,
+there are numberless other species which not only fail to present these
+phenomena in any degree, but actually go to the opposite extreme of
+presenting colours which appear to have been developed for the sake of
+their conspicuousness. At all events, these caterpillars are usually the
+most conspicuous objects in their surroundings, and therefore in the
+early days of Darwinism they were regarded by Darwin himself as
+presenting a formidable difficulty in the way of his theory. To Mr.
+Wallace belongs the merit of having cleared up this difficulty in an
+extraordinarily successful manner. He virtually reasoned thus. If the
+_raison d'être_ of protective colouring be that of concealing agreeably
+flavoured caterpillars from the eye-sight of birds, may not the _raison
+d'être_ of conspicuous colouring be that of protecting disagreeably
+flavoured caterpillars from any possibility of being mistaken by birds?
+Should this be the case, of course the more conspicuous the colouring
+the better would it be for the caterpillars presenting it. Now as soon
+as this suggestion was acted upon experimentally, it was found to be
+borne out by facts. Birds could not be induced to eat caterpillars of
+the kinds in question; and there is now no longer any doubt that their
+conspicuous colouring is correlated with their distastefulness to birds,
+in the same way as the inconspicuous or imitative colouring of other
+caterpillars is correlated with their tastefulness to birds. Here then
+is yet another instance, added to those already given, of the
+verification yielded to the theory of natural selection by its proved
+competency as a guide to facts in nature; for assuredly this particular
+class of facts would never have been suspected but for its suggestive
+agency.
+
+As in the case of protective imitation, so in this case of warning
+conspicuousness, not only colour, but structure may be greatly modified
+for the purpose of securing immunity from attack. Here, of course, the
+object is to assume, as far as possible, a touch-me-not appearance; so
+that, although destitute of any real means of offence, the creatures in
+question present a fictitiously dangerous aspect. As the
+Devil's-coach-horse turns up his stingless tail when threatened by an
+enemy, so in numberless ways do many harmless animals of all classes
+pretend to be formidable. But the point now is that these instincts of
+self-defence are often helped out by structural modifications,
+expressly and exclusively adapted to this end. For example, what a
+remarkable series of protective adjustments occurs in the life-history
+of the Puss Moth--culminating with so comical an instance of the
+particular device now under consideration as the following. I quote the
+facts from Mr. E. B. Poulton's admirable book on _The Colours of
+Animals_ (pp. 269-271).
+
+ [Illustration: FIG. 111.--The larva of Puss Moth (_C. vinula_)
+ when undisturbed; full-fed; natural size.]
+
+ The larva of the Puss Moth (Cerura vinula) is very common upon
+ poplar and willow. The circular dome-like eggs are laid, either
+ singly or in little groups of two or three, upon the upper side of
+ the leaf, and being of a reddish colour strongly suggest the
+ appearance of little galls, or the results of some other injury to
+ the leaf. The youngest larvæ are black, and also rest upon the
+ upper surface of the leaf, resembling the dark patches which are
+ commonly seen in this position. As the larva grows, the apparent
+ black patch would cover too large a space, and would lead to
+ detection if it still occupied the whole surface of the body. The
+ latter gains a green ground-colour which harmonises with the leaf,
+ while the dark marking is chiefly confined to the back. As growth
+ proceeds the relative amount of green increases, and the dark mark
+ is thus prevented from attaining a size which would render it too
+ conspicuous. In the last stage of growth the green larva becomes
+ very large, and usually rests on the twigs of its food-plant (Fig.
+ 111). The dark colour is still present on the back but is softened
+ to a purplish tint, which tends to be replaced by a combination of
+ white and green in many of the largest larvæ. Such a larva is well
+ concealed by General Protective Resemblance, and one may search a
+ long time before finding it, although assured of its presence from
+ the stripped branches of the food-plant and the fæces on the ground
+ beneath.
+
+ [Illustration: FIG. 112.--The larva of Puss Moth in its terrifying
+ attitude after being disturbed; full-fed; natural size.]
+
+ As soon as a large larva is discovered and disturbed it withdraws
+ its head into the first body-ring, inflating the margin, which is
+ of a bright red colour. There are two intensely black spots on this
+ margin in the appropriate position for eyes, and the whole
+ appearance is that of a large flat face extending to the outer edge
+ of the red margin (see Fig. 112). The effect is an intensely
+ exaggerated caricature of a vertebrate face, which is probably
+ alarming to the vertebrate enemies of the caterpillar. The
+ terrifying effect is therefore mimetic. The movements entirely
+ depend on tactile impressions: when touched ever so lightly a
+ healthy larva immediately assumes the terrifying attitude, and
+ turns so as to present its full face towards the enemy; if touched
+ on the other side or on the back it instantly turns its face in the
+ appropriate direction. The effect is also greatly strengthened by
+ two pink whips which are swiftly protruded from the prongs of the
+ fork in which the body terminates. The prongs represent the last
+ pair of larval legs which have been greatly modified from their
+ ordinary shape and use. The end of the body is at the same time
+ curved forward over the back (generally much further than in Fig.
+ 112), so that the pink filaments are brandished above the head.
+
+
+_Mimicry._
+
+Lastly, these facts as to imitative and conspicuous colouring lead on to
+the yet more remarkable facts of what is called mimicry. By mimicry is
+meant the imitation in form and colour of one species by another, in
+order that the imitating species may be mistaken for the imitated, and
+thus participate in some advantage which the latter enjoys. For
+instance, if, as in the case of the conspicuously-coloured caterpillars,
+it is of advantage to an ill-savoured species that it should hold out a
+warning to enemies, clearly it may be of no less advantage to a
+well-savoured species that it should borrow this flag, and thus be
+mistaken for its ill-savoured neighbour. Now, the extent to which this
+device of mimicry is carried is highly remarkable, not only in respect
+of the number of its cases, but also in respect of the astonishing
+accuracy which in most of these cases is exhibited by the imitation.
+There need be little or virtually no zoological affinity between the
+imitating and the imitated forms; that is to say, in some cases the
+zoological affinity is not closer than ordinal, and therefore cannot
+possibly be ascribed to kinship. Like all the other branches of the
+general subject of protective resemblance in form or colouring, this
+branch has already been so largely illustrated by previous writers,
+that, as in the previous cases, I need only give one or two examples.
+Those which I choose are chosen on account of the colours concerned not
+being highly varied or brilliant, and therefore lending themselves to
+less ineffectual treatment by wood-engraving than is the case where
+attempts are made to render by this means even more remarkable
+instances. (Figs. 113, 114, 115.)
+
+ [Illustration: FIG. 113.--Three cases of mimicry. Drawn from nature:
+ first two pairs nat. size, last pair 2/3 (_R. Coll. Surg. Mus._).]
+
+ [Illustration: FIG. 114.--Two further cases of mimicry; flies
+ resembling a wasp in the one and a bee in the other. Drawn from
+ nature: nat. size (_R. Coll. Surg. Mus._).]
+
+ [Illustration: FIG. 115.--A case of mimicry where a non-venomous
+ species of snake resembles a venomous one. Drawn from nature: 1/3
+ nat. size (_R. Coll. Surg. Mus._).]
+
+It is surely apparent, without further comment, that it is impossible to
+imagine stronger evidence in favour of natural selection as a true cause
+in nature, than is furnished by this culminating fact in the matter of
+protective resemblance, whereby it is shown that a species of one
+genus, family, or even order, will accurately mimic the appearance of a
+species belonging to another genus, family, or order, so as to deceive
+its natural enemies into mistaking it for a creature of so totally
+different a kind. And it must be added that while this fact of mimicry
+is of extraordinarily frequent occurrence, there can be no possibility
+of our mistaking its purpose. For the fact is never observable except in
+the case of species which occupy the same area or district.
+
+Such being what appears to me the only reasonable view of the matter, I
+will now conclude this chapter on the evidences of natural selection as
+at all events the main factor of organic evolution, by simply adding
+illustrations of two further cases of mimicry, which are perhaps even
+more remarkable than any of the foregoing examples. The first of the two
+(Fig. 115) speaks for itself. The second will be rendered intelligible
+by the following few words of explanation.
+
+There are certain ants of the Amazons which present the curious instinct
+of cutting off leaves from trees, and carrying them like banners over
+their heads to the hive, as represented in Fig. 116, B, where one ant is
+shown without a leaf, and the others each with a leaf. Their object in
+thus collecting leaves is probably that of growing a fungus upon the
+"soil" which is furnished by the leaves when decomposing. But, be this
+as it may[39], the only point we are now concerned with is the
+appearance which these ants present when engaged in their habitual
+operation of carrying leaves. For it has been recently observed by Mr.
+W. L. Sclater, that in the localities where these hymenopterous insects
+occur, there occurs also a _homopterous_ insect which mimics the ant,
+leaf and all, in a wonderfully deceptive manner. The leaf is imitated by
+the thin flattened body of the insect, "which in its dorsal aspect is so
+compressed laterally that it is no thicker than a leaf, and terminates
+in a sharp jagged edge." The colour is exactly the same as that of a
+leaf, and the brown legs show themselves beneath the green body in just
+the same way as those of the ant show themselves beneath the leaf. So
+that both the form and the colouring of the homopterous insect has been
+brought to resemble, with singular exactness, those belonging to a
+different order of insect, when the latter is engaged in its peculiar
+avocation. A glance at the figure is enough to show the means employed
+and the result attained. In A, an ant and its mimic are represented as
+about 2-1/2 times their natural size, and both proceeding in the same
+direction. It ought to be mentioned, however, that in reality the margin
+of the leaf is seldom allowed to retain its natural serrations as here
+depicted: the ants usually gnaw the edge of the real leaf, so that the
+margin of the false one bears an even closer resemblance to it than the
+illustration represents. B is a drawing from life of a group of five
+ants carrying leaves, and their mimic walking beside them[40].
+
+ [39] For a full account of this instinct and its probable purpose,
+ see _Animal Intelligence_, pp. 93-6.
+
+ [40] Both drawings are reproduced from Mr. Poulton's paper upon the
+ subject (_Proc. Zool. Soc._, June 16, 1891).
+
+ [Illustration: FIG. 116 PROTECTIVE MIMICRY]
+
+
+
+
+CHAPTER IX.
+
+CRITICISMS OF THE THEORY OF NATURAL SELECTION.
+
+
+I will now proceed to consider the various objections and difficulties
+which have hitherto been advanced against the theory of natural
+selection.
+
+Very early in the day Owen hurled the weight of his authority against
+the new theory, and this with a strength of onslaught which was only
+equalled by its want of judgment. Indeed, it is painfully apparent that
+he failed to apprehend the fundamental principles of the Darwinian
+theory. For he says:--
+
+ Natural Selection is an explanation of the process [of
+ transmutation] of the same kind and value as that which has been
+ proffered of the mystery of "secretion." For example, a particular
+ mass of matter in a living animal takes certain elements out of the
+ blood, and rejects them as "bile." Attributes were given to the
+ liver which can only be predicated of the whole animal; the
+ "appetency" of the liver, it was said, was for the elements of
+ bile, and "biliosity," or the "hepatic sensation," guided the gland
+ to their secretion. Such figurative language, I need not say,
+ explains absolutely nothing of the nature of bilification[41].
+
+ [41] _Anatomy of Vertebrates_, vol. iii. p. 794.
+
+Assuredly, it was needless for Owen to say that figurative language of
+this kind explains nothing; but it was little less than puerile in him
+to see no more in the theory of natural selection than such a mere
+figure of speech. To say that the liver selects the elements of bile, or
+that nature selects specific types, may both be equally unmeaning
+re-statements of facts; but when it is explained that the term natural
+selection, unlike that of "hepatic sensation," is used as a shorthand
+expression for a whole group of well-known natural causes--struggle,
+variation, survival, heredity,--then it becomes evidence of an almost
+childish want of thought to affirm that the expression is figurative and
+nothing more. The doctrine of natural selection may be a huge mistake;
+but, if so, this is not because it consists of any unmeaning metaphor:
+it can only be because the combination of natural causes which it
+suggests is not of the same adequacy in fact as it is taken to be in
+theory.
+
+Owen further objected that the struggle for existence could only act as
+a cause of the extinction of species, not of their origination--a view
+of the case which again shows on his part a complete failure to grasp
+the conception of Darwinism. Acting alone, the struggle for existence
+could only cause extermination; but acting together with variation,
+survival, and heredity, it may very well--for anything that Owen, or
+others who followed in this line of criticism, show to the
+contrary--have produced every species of plant and animal that has ever
+appeared upon the face of the earth.
+
+Another and closely allied objection is, that the theory of natural
+selection "personifies an abstraction." Or, as the Duke of Argyll states
+it, the theory is "essentially the image of mechanical necessity
+concealed under the clothes, and parading in the mask, of mental
+purpose. The word 'natural' suggests Matter, and the physical forces.
+The word 'selection' suggests Mind, and the powers of choice." This,
+however, is a mere quarrelling about words. Darwin called the principle
+which he had discovered by the name natural selection in order to mark
+the analogy between it and artificial selection. No doubt in this
+analogy there is not necessarily supposed to be in nature any
+counterpart to the mind of the breeder, nor, therefore, to his powers of
+intelligent choice. But there is no need to limit the term _selection_
+(_se_ and _lego_, Gr. [Greek: legô]) to powers of intelligent choice. As
+previously remarked, a bank of sea-weed on the sea-shore may be said to
+have been selected by the waves from all the surrounding sand and
+stones. Similarly, we may say that grain is selected from chaff by the
+wind in the process of winnowing corn. Or, if it be thought that there
+is any ambiguity involved in such a use of the term in the case of
+"Natural Selection," there is no objection to employing the phrase which
+has been coined by Mr. Spencer as its equivalent--namely, "Survival of
+the Fittest." The point of the theory is, that those organisms which are
+best suited to their surroundings are allowed to live and to propagate,
+while those which are less suited are eliminated; and whether we call
+this process a process of selection, or call it by any other name, is
+clearly immaterial.
+
+A material question is raised only when it is asked whether the process
+is one that can be ascribed to causation strictly natural. It is often
+denied that such is the case, on the ground that natural selection does
+not originate the variations which it favours, but depends upon the
+variations being supplied by some other means. For, it is said, all that
+natural selection does is to preserve the suitable variations _after
+they have arisen_. Natural selection does not _cause_ these suitable
+variations; and therefore, it is argued, Darwin and his followers are
+profoundly mistaken in representing the principle as one which
+_produces_ adaptations. Now, although this objection has been put
+forward by some of the most intelligent minds in our generation, it
+appears to me to betoken some extraordinary failure to appreciate the
+very essence of Darwinian doctrine. No doubt it is perfectly true that
+natural selection does not produce variations of any kind, whether
+beneficial or otherwise. But if it be granted that variations of many
+kinds are occurring in every generation, and that natural selection is
+competent to preserve the more favourable among them, then it appears to
+me unquestionable that this principle of selection deserves to be
+regarded as, in the full sense of the word, a natural cause. The
+variations being expressly regarded by the theory as more or less
+promiscuous[42], survival of the fittest becomes the winnowing fan,
+whose function it is to eliminate all the less fit in each generation,
+in order to preserve the good grain, out of which to constitute the next
+generation. And as this process is supposed to be continuous through
+successive generations, its action is supposed to be cumulative, till
+from the eye of a worm there is gradually developed the eye of an eagle.
+Therefore it follows from these suppositions (which are not disputed by
+the present objection), that if it had not been for the process of
+selection, such development would never have been begun; and that in the
+exact measure of its efficiency will the development proceed. But any
+agency without the operation of which a result cannot take place may
+properly be designated the cause of that result: it is the agency which,
+in co-operation with all the other agencies in the cosmos, produces that
+result.
+
+ [42] The degree in which variability is indefinite, or, on the
+ contrary, determinate, is a question which is not yet ripe for
+ decision--nor even, in my opinion, for discussion. But I may here
+ state the following general principles with regard to it.
+
+ (1) It is evident that up to some point or another variations _must_
+ be pre-determined in definite lines. Men do not gather grapes from
+ thorns, figs from thistles, nor even moss-roses from sweet-briars.
+ In other words, "the nature of the organism" in all cases
+ necessitates the limiting of variations within certain bounds.
+
+ (2) But when the question is as to what these bounds may be, we can
+ only answer in a general way that, according to the general theory
+ of evolution, they must be such as are imposed by heredity, coupled
+ with the degree to which external conditions of life (and possibly
+ also use-inheritance) are capable, in given cases, of modifying
+ congenital characters. These are the only causes which the theory of
+ descent can consistently recognise as producing variations in
+ determinate directions.
+
+ (3) Inasmuch as variation presupposes the existence of parts that
+ vary, and inasmuch as the variation of parts can only be in the
+ alternative directions of increase or decrease around an average, it
+ follows that, in the first instance at all events, every variation,
+ if determinate, must be so only in one or other of these two
+ opposite directions.
+
+ (4) In as far as variations are summated in successive generations,
+ so as eventually to give rise to new structures, organs, mechanisms,
+ &c., natural selection is theoretically competent to explain the
+ facts, without our having to postulate the operation of unknown
+ causes producing variations in determinate lines,--or not further
+ than is stated in paragraphs 1 and 2.
+
+ (5) Nevertheless, it does not follow that there are not such other
+ unknown causes; and, if there are, of course the importance of
+ natural selection as a cause of adaptive modification would be
+ limited in proportion to their number and the extent of their
+ operation. But it is for those who, like the late Professors Asa
+ Gray and Nägeli, maintain the existence of such causes, to
+ substantiate their belief by indicating them.
+
+Take any analogous case. The selective agency of specific gravity which
+is utilised in gold-washing does not create the original differences
+between gold-dust and dust of all other kinds. But these differences
+being presented by as many different bodies in nature, the gold-washer
+takes advantage of the selective agency in question, and, by using it as
+a cause of segregation, is enabled to separate the gold from all the
+earths with which it may happen to be mixed. So far as the objects of
+the gold-washer are concerned, it is immaterial with what other earths
+the gold-dust may happen to be mixed. For although gold-dust may occur
+in intimate association with earths of various kinds in various
+proportions, and although in each case the particular admixture which
+occurs must have been due to definite causes, these things, in relation
+to the selective process of the washer, are what is called accidental:
+that is to say, they have nothing to do with the causative action of the
+selective process. Now, in precisely the same sense Darwin calls the
+multitudinous variations of plants and animals accidental. By so calling
+them he expressly says he does not suppose them to be accidental in the
+sense of not all being due to definite causes. But they are accidental
+in relation to the sifting process of natural selection: all that they
+have to do is to furnish the promiscuous material on which this sifting
+process acts.
+
+Or let us take an even closer analogy. The power of selective breeding
+by man is so wonderful, that in the course of successive generations all
+kinds of peculiarities as to size, shape, colour, special appendages or
+abortions, &c., can be produced at pleasure, as we saw in the last
+chapter. Now all the promiscuous variations which are supplied to the
+breeder, and out of which, by selecting only those that are suited to
+his purpose, he is able to produce the required result--all those
+promiscuous variations, in relation to that purpose, are accidental.
+Therefore the selective agency of the breeder deserves to be regarded as
+the cause of that which it produces, or of that which could not have
+been produced but for the operation of such agency. But where is the
+difference between artificial and natural selection in this respect?
+And, if there is no difference, is not natural selection as much
+entitled to be regarded as a true cause of the origin of natural
+species, as artificial selection is to be regarded as a true cause of
+our domesticated races? Here, as in the case of the previous
+illustration, if there be any ambiguity in speaking of variations as
+accidental, it arises from the incorrect or undefined manner in which
+the term "accidental" is used by Darwin's critics. In its original and
+philosophically-correct usage, the term "accident" signifies a property
+or quality not essential to our conception of a substance: hence, it has
+come to mean anything that happens as a result of unforeseen causes--or,
+lastly, that which is causeless. But, as we know that nothing can happen
+without causes of some kind, the term "accident" is divested of real
+meaning when it is used in the last of these senses. Yet this is the
+sense that is sought to be placed upon it by the objection which we are
+considering. If the objectors will but understand the term in its
+correct philosophical sense--or in the only sense in which it presents
+any meaning at all,--they will see that Darwinians are both logically
+and historically justified in employing the word "accidental" as the
+word which serves most properly to convey the meaning that they
+intend--namely, variations due to causes accidental to the struggle for
+existence. Similarly, when it is said that variations are "spontaneous,"
+or even "fortuitous," nothing further is meant than that we do not know
+the causes which lead to them, and that, so far as the principle of
+selection is concerned, it is immaterial what these causes may be. Or,
+to revert to our former illustration, the various weights of different
+kinds of earths are no doubt all due to definite causes; but, in
+relation to the selective action of the gold-washer, all the different
+weights of whatever kinds of earth he may happen to include in his
+washing-apparatus are, _strictly speaking_, accidental. And as at
+different washings he meets with different proportions of heavy earths
+with light ones, and as these "variations" are immaterial to him, he may
+colloquially speak of them as "fortuitous," or due to "chance," even
+though he knows that at each washing they must have been determined by
+definite causes.
+
+More adequately to deal with this merely formal objection, however,
+would involve more logic-chopping than is desirable on the present
+occasion. But I have already dealt with it fully elsewhere,--viz. in
+_The Contemporary Review_ for June, 1888, to which therefore I may refer
+any one who is interested in dialectics of this kind[43].
+
+ [43] Within the last few months this objection has been presented
+ anew by Mr. D. Syme, whose book _On the Modification of Organisms_
+ exhibits a curious combination of shrewd criticisms with almost
+ ludicrous misunderstandings. One of the latter it is necessary to
+ state, because it pervades the quotation which I am about to supply.
+ He everywhere compares "natural selection" with "the struggle for
+ existence," uses them as convertible terms, and while absurdly
+ stating that "Darwin defines natural selection as the struggle for
+ existence," complains of "the liability of error, both on his own
+ part and on the part of his readers," which arises from his not
+ having everywhere adhered to this definition! (p. 8).
+
+ "Darwin has put forth two distinct and contradictory theories of the
+ functions of natural selection. According to the one theory natural
+ selection is selective or preservative, and nothing more. According
+ to the other theory natural selection creates the variations(!) ...
+ It certainly seems absurd to speak of natural selection, or the
+ struggle for existence, as selective or preservative, for the
+ struggle for existence does not preserve at all, not even the fit
+ variations, as both the fit and the unfit struggle for existence,
+ the unfit naturally more than the fit, and the fit are preserved,
+ not in consequence of the struggle, but in consequence of their
+ fitness. Suppose two varieties of the same species are driven, by an
+ increase of their numbers, to seek for subsistence in a colder
+ region than they have been accustomed to, and that one of these
+ varieties had a hardier constitution than the other; and let us
+ suppose that the former withstood the severe climate better than the
+ latter, and consequently survived, while the other perished. In this
+ case the hardier survived, not because of the struggle, but because
+ it had a constitution better adapted to the climate. I wish to
+ ascertain if a certain metal in my possession is gold or some baser
+ metal, and I apply the usual test; but the mere fact of my testing
+ this metal would not make it gold or any other kind of metal."
+
+ I have thought it worth while to quote this passage for the sake of
+ showing the extraordinary confusion of mind which still prevails on
+ the part of Darwin's critics, even with reference to the very
+ fundamental parts of his theory. For, as I have said, the writer of
+ this passage shows himself a shrewd critic in some other parts of
+ his essay, where he is not engaged especially on the theory of
+ natural selection.
+
+I will now pass on to consider another misconception of the Darwinian
+theory, which is very prevalent in the public mind. It is virtually
+asked, If some species are supposed to have been improved by natural
+selection, why have not all species been similarly improved? Why should
+not all invertebrated animals have risen into vertebrated? Or why
+should not all monkeys have become men?
+
+The answers are manifold. In the first place, it by no means follows
+that because an advance in organization has proved itself of benefit in
+the case of one form of life, therefore any or every other form would
+have been similarly benefited by a similar advance. The business of
+natural selection is to bring this and that form of life into the
+closest harmony with its environment that all the conditions of the case
+permit. Sometimes it will happen that the harmony will admit of being
+improved by an improvement of organization. But just as often it will
+happen that it will be best secured by leaving matters as they are. If,
+therefore, an organism has already been brought into a tolerably full
+degree of harmony with its environment, natural selection will not try
+to change it so long as the environment remains unchanged; and this, no
+doubt, is the reason why some species have survived through enormous
+periods of geological time without having undergone any change. Again,
+as we saw in a previous chapter, there are yet other cases where, on
+account of some change in the environment or even in the habits of the
+organisms themselves, adaption will be best secured by an active
+_reversal_ of natural selection, with the result of causing
+_degeneration_.
+
+But, it is sometimes further urged, there are cases where we cannot
+doubt that improvement of organization would have been of benefit to
+species; and yet such improvement has not taken place--as, for instance,
+in the case all monkeys not turning into men. Here, however, we must
+remember that the operation of natural selection in any case depends
+upon a variety of highly complex conditions; and, therefore, that the
+fact of all those conditions having been satisfied in one instance is no
+reason for concluding that they must also have been satisfied in other
+instances. Take, for example, the case of monkeys passing into men. The
+wonder to me appears to be that this improvement should have taken place
+in even one line of descent; not that, having taken place in one line,
+it should not also have taken place in other lines. For how enormously
+complex must have been the conditions--physical, anatomical,
+physiological, psychological, sociological--which by their happy
+conjunction first began to raise the inarticulate cries of an ape into
+the rational speech of a man. Therefore, the more that we appreciate the
+superiority of a man to an ape, the less ought we to countenance this
+supposed objection to Darwin's theory--namely, that natural selection
+has not effected the change in more than one line of descent.
+
+Even in the case of two races of mankind where one has risen higher in
+the scale of civilization than another, it is now generally impossible
+to assign the particular causes of the difference; much more, then, must
+this be impossible in the case of still more remote conditions which
+have led to the divergence of species. The requisite variations may not
+have arisen in the one line of descent which did arise in the other; or
+if they did arise in both, some counterbalancing disadvantages may have
+attended their initial development in the one case which did not obtain
+in the other. In short, where so exceedingly complex a play of
+conditions are concerned, the only wonder would be if two different
+lines of descent _had_ happened to present two independent and yet
+perfectly parallel lines of history.
+
+These general considerations would apply equally to the great majority
+of other cases where some types have made great advances upon others,
+notwithstanding that we can see no reason why the latter should not in
+this respect have imitated the former. But there is yet a further
+consideration which must be taken into account. The struggle for
+existence is always most keen between closely allied species, because,
+from the similarity of their forms, habits, needs, &c., they are in
+closest competition. Therefore it often happens that the mere fact of
+one species having made an advance upon others of itself precludes the
+others from making any similar advance: the field, so to speak, has
+already been occupied as regards that particular improvement, and where
+the struggle for existence is concerned possession is emphatically nine
+points of the law. For example, to return to the case of apes becoming
+men, the fact of one rational species having been already evolved (even
+if the rational faculty were at first but dimly nascent) must make an
+enormous change in the conditions as regards the possibility of any
+other such species being subsequently evolved--unless, of course, it be
+by way of descent from the rational one. Or, as Sir Charles Lyell has
+well put it, two rational species can never _coexist_ on the globe,
+although the descendants of one rational species may in time become
+_transformed_ into another single rational species[44].
+
+ [44] _Principles of Geology_, vol. ii. p. 487 (11th ed.).
+
+In view of such considerations, another and exactly opposite objection
+has sometimes been urged--viz. that we ought never to find inferior
+forms of organization in company with superior, because in the struggle
+for existence the latter ought to have exterminated the former. Or, to
+quote the most recent expression of this view, "in every locality there
+would only be one species, and that the most highly organized; and thus
+a few superior races would partition the earth amongst them to the
+entire exclusion of the innumerable varieties, species, genera, and
+orders which now inhabit it[45]." Of course to this statement it would
+be sufficient to enquire, On what would these few supremely organized
+species subsist? Unless manna fell from heaven for their especial
+benefit, it would appear that such forms could under no circumstances be
+the most improved forms; in exterminating others on such a scale as
+this, they would themselves be quickly, and very literally, improved off
+the face of the earth. But even when the statement is not made in so
+extravagant a form as this, it must necessarily be futile as an
+objection unless it has first been shown that we know exactly all the
+conditions of the complex struggle for existence between the higher and
+lower forms in question. And this it is impossible that we ever can
+know. The mere fact that one form has been changed in virtue of this
+struggle must in many cases of itself determine a change in the
+conditions of the struggle. Again, the other and closely allied forms
+(and these furnish the best grounds for the objection) may also have
+undergone defensive changes, although these may be less conspicuous to
+our observation, or perhaps less suggestive of "improvement" to our
+imperfect means of judging. Lastly, not to continue citing an endless
+number of such considerations, there is the broad fact that it is only
+to those cases where, for some reason or another, the lower forms have
+not been exposed to a struggle of fatal intensity, that the objection
+applies. But we know that in millions of other cases the lower (i. e.
+less fitted) forms _have_ succumbed, and therefore I do not see that the
+objection has any ground to stand upon. That there is a general tendency
+for lower forms to yield their places to higher is shown by the gradual
+advance of organization throughout geological time; for if _all_ the
+inferior forms had survived, the earth could not have contained them,
+unless she had been continually growing into something like the size of
+Jupiter. And if it be asked why any of the inferior forms have survived,
+the answer has already been given, as above.
+
+ [45] Syme, on the _Modification of Organisms_, p. 46.
+
+There is only one other remark to be made in this connexion. Mr. Syme
+chooses two cases as illustrations of the supposed difficulty. These are
+sufficiently diverse--viz. Foraminifera and Man. Touching the former,
+there is nothing that need be added to the general answer just given.
+But with regard to the latter it must be observed that the dominion of
+natural selection as between different races of mankind is greatly
+restricted by the presence of rationality. Competition in the human
+species is more concerned with wits and ideas than with nails and teeth;
+and therefore the "struggle" between man and man is not so much for
+actual _being_, as for _well-being_. Consequently, in regard to the
+present objection, the human species furnishes the worst example that
+could have been chosen.
+
+ * * * * *
+
+Hitherto I have been considering objections which arise from
+misapprehensions of Darwin's theory. I will now go on to consider a
+logically sound objection, which nevertheless is equally futile,
+because, although it does not depend on any misapprehension of the
+theory, it is not itself supported by fact.
+
+The objection is the same as that which we have already considered in
+relation to the general theory of descent--namely, that similar organs
+or structures are to be met with in widely different branches of the
+tree of life. Now this would be an objection fatal to the theory of
+natural selection, supposing these organs or structures in the cases
+compared are not merely analogous, but also homologous. For it would be
+incredible that in two totally different lines of descent one and the
+same structure should have been built up independently by two parallel
+series of variations, and that in these two lines of descent it should
+always and independently have ministered to the same function. On the
+other hand, there would be nothing against the theory of natural
+selection in the fact that two structures, _not_ homologous, should come
+by independent variation in two different lines of descent to be adapted
+to perform the same function. For it belongs to the very essence of the
+theory of natural selection that a useful function should be secured by
+favourable variations of whatever structural material may happen to be
+presented by different organic types. Flying, for instance, is a very
+useful function, and it has been developed independently in at least
+four different lines of descent--namely, the insects, reptiles, birds,
+and mammals. Now if in all, or indeed in any, of these four cases the
+wings had been developed on the same anatomical pattern, so as not only
+to present the analogical resemblance which it is necessary that they
+should present in order to discharge their common function of flying,
+but likewise an homologous or structural resemblance, showing that they
+had been formed on the same anatomical "plan,"--if such has been the
+case, I say, the theory of natural selection would certainly be
+destroyed.
+
+Now it has been alleged by competent naturalists that there are several
+such cases in organic nature. We have already noticed in a previous
+chapter (pp. 58, 59), that Mr. Mivart has instanced the eye of the
+cuttle-fish as not only analogous to, but also homologous with, the eye
+of a true fish--that is to say, the eye of a mollusk with the eye of a
+vertebrate. And he has also instanced the remarkable resemblance of a
+shrew to a mouse--that is, of an insectivorous mammal to a rodent--not
+to mention other cases. In the chapter alluded to these instances of
+homology, alleged to occur in different branches of the tree of life,
+were considered with reference to the process of organic evolution as a
+fact: they are now being considered with reference to the agency of
+natural selection as a method. And just as in the former case it was
+shown, that if any such alleged instances could be proved, the proof
+would be fatal to the general theory of organic evolution by physical
+causes, so in the present case, if this could be proved, it would be
+equally fatal to the more special theory of natural selection. But, as
+we have before seen, no single case of this kind has ever been made
+out; and, therefore, not only does this supposed objection fall to the
+ground, but in so doing it furnishes an additional argument in favour of
+natural selection. For in the earlier chapter just alluded to I showed
+that this great and general fact of our nowhere being able to find two
+homologous structures in different branches of the tree of life, was the
+strongest possible testimony in favour of the theory of evolution. And,
+by parity of reasoning, I now adduce it as equally strong evidence of
+natural selection having been the cause of _adaptive_ structures,
+independently developed in all the different lines of descent. For the
+alternative is between adaptations having been caused by natural
+selection or by supernatural design. Now, if adaptations were caused by
+natural selection, we can very well understand why they should never be
+homologous in different lines of descent, even in cases where they have
+been brought to be so closely analogous as to have deceived so good a
+naturalist as Mr. Mivart. Indeed, as I have already observed, so well
+can we understand this, that any single instance to the contrary would
+be sufficient to destroy the theory of natural selection _in toto_,
+unless the structure be one of a very simple type. But on the other
+hand, it is impossible to suggest any rational explanation why, if all
+adaptations are due to supernatural design, such scrupulous care should
+have been taken never to allow homologous adaptations to occur in
+different divisions of the animal or vegetable kingdoms. Why, for
+instance, should the eye of a cuttle-fish _not_ have been constructed on
+the same ideal pattern as that of vertebrate? Or why, among the
+thousands of vertebrated species, should no one of their eyes be
+constructed on the ideal pattern that was devised for the cuttle-fish?
+Of course it may be answered that perhaps there was some hidden reason
+why the design should never have allowed an adaptation which it had
+devised for one division of organic nature to appear in another--even in
+cases where the new design necessitated the closest possible resemblance
+in everything else, save in the matter of anatomical homology.
+Undoubtedly such may have been the case--or rather such _must_ have been
+the case--if the theory of special design is true. But where the
+question is as to the truth of this theory, I think there can be no
+doubt that its rival gains an enormous advantage by being able to
+_explain_ why the facts are such as they are instead of being obliged to
+take refuge in hypothetical possibilities of a confessedly
+unsubstantiated and apparently unsubstantial kind.
+
+Therefore, as far as this objection to the theory of natural selection
+is concerned--or the allegation that homologous structures occur in
+different divisions of organic nature--not only does it fall to the
+ground, but positively becomes itself converted into one of the
+strongest arguments in favour of the theory. As soon as the allegation
+is found to be baseless, the very fact that it cannot be brought to bear
+upon any one of all the millions of adaptive structures in organic
+nature becomes a fact of vast significance on the opposite side.
+
+ * * * * *
+
+The next difficulty to which I shall allude is that of explaining by the
+theory of natural selection the preservation of the first beginnings of
+structures which are then useless, though afterwards, when more fully
+developed, they become useful. For it belongs to the very essence of the
+theory of natural selection, that a structure must be supposed already
+useful before it can come under the influence of natural selection:
+therefore the theory seems incapable of explaining the origin and
+conservation of _incipient_ organs, or organs which are not yet
+sufficiently developed to be of any service to the organisms presenting
+them.
+
+This objection is one that has been advanced by all the critics of
+Darwinism; but has been presented with most ability and force by the
+Duke of Argyll. I will therefore state it in his words.
+
+ If the doctrine of evolution be true--that is to say, if all
+ organic creatures have been developed by ordinary generation from
+ parents--then it follows of necessity that the primæval germs must
+ have contained potentially the whole succeeding series. Moreover,
+ if that series has been developed gradually and very slowly, it
+ follows, also as a matter of necessity, that every modification of
+ structure must have been functionless at first, when it began to
+ appear.... Things cannot be selected until they have first been
+ produced. Nor can any structure be selected by utility in the
+ struggle for existence until it has not only been produced, but has
+ been so far perfected as to actually be used.
+
+The Duke proceeds to argue that all adaptive structures must therefore
+originally have been due to special design: in the earlier stages of
+their development they must all have been what he calls "prophetic
+germs." Not yet themselves of any use, and therefore not yet capable of
+being improved by natural selection, both in their origin and in the
+first stages (at all events) of their development, they must be
+regarded as intentionally preparatory to the various uses which they
+subsequently acquire.
+
+Now this argument, forcible as it appears at first sight, is really at
+fault both in its premiss and in its conclusion. By which I mean that,
+in the first place the premiss is not true, and, in the next place, that
+even if it were, the conclusion would not necessarily follow. The
+premiss is, "that every modification of structure must have been
+functionless at first, when it began to appear;" and the conclusion is,
+that, _quâ_ functionless, such a modification cannot have been caused by
+natural selection. I will consider these two points separately.
+
+First as to the premiss, it is not true that every modification of
+structure must necessarily be functionless when it first begins to
+appear. There are two very good reasons why such should not be the case
+in all instances, even if it should be the case in some. For, as a
+matter of observable fact, a very large proportional number of incipient
+organs are useful from the very moment of their inception. Take, for
+example, what is perhaps the most wonderful instance of refined
+mechanism in nature--the eye of a vertebrated animal. Comparative
+anatomy and embryology combine to testify that this organ had its origin
+in modifications of the endings of the ordinary nerves of the skin. Now
+it is evident that from the very first any modification of a cutaneous
+nerve whereby it was rendered able, in however small a degree, to be
+differently affected by light and by darkness would be of benefit to the
+creature presenting it; for the creature would thus be able to seek the
+one and shun the other according to the requirements of its life. And
+being thus useful from the very moment of its inception, it would
+afterwards be gradually improved as variations of more and more utility
+presented themselves, until not only would finer and finer degrees of
+difference between light and shade become perceptible, but even the
+outlines of solid bodies would begin to be appreciated. And so on, stage
+by stage, till from an ordinary nerve-ending in the skin is evolved the
+eye of an eagle.
+
+Moreover, in this particular instance there is very good reason to
+suppose that the modification of the cutaneous nerves in question began
+by a progressive increase in their sensitiveness to temperature.
+Wherever dark pigment happened to be deposited in the skin--and we know
+that in all animals it is apt to be deposited in points and patches, as
+it were by accident, or without any "prophecy" as to future uses,--the
+cutaneous nerves in its vicinity would be better able to appreciate the
+difference between sun and shade in respect of temperature, even though
+as yet there were no change at all in these cutaneous nerves tending to
+make them responsive to light. Now it is easy to see how, from such a
+purely accidental beginning, natural selection would have had from the
+first sufficient material to act upon. It being of advantage to a lowly
+creature that it should distinguish with more and more delicacy, or with
+more and more rapidity, between light and darkness by means of its
+thermal sensations, the pigment spots in the skin would be rendered
+permanent by natural selection, while the nerves in that region would by
+the same agency be rendered more and more specialized as organs adapted
+to perceive changes of temperature, until from the stage of responding
+to the thermal rays of the non-luminous spectrum alone, they become
+capable of responding also to luminous.
+
+So much, then, for the first consideration which serves to invalidate
+the Duke's premiss. The second consideration is, that very often an
+organ which began by being useful for the performance of one function,
+after having been fully developed for the performance of that function,
+finds itself, so to speak, accidentally fitted to the performance of
+some other and even more important function, which it thereupon begins
+to discharge, and so to undergo a new course of adaptive development. In
+such cases, and so far as the new function is concerned, the difficulty
+touching the first inception of an organ does not apply; for here the
+organ has already been built up by natural selection for one purpose,
+before it begins to discharge the other. As an example of such a case we
+may take the lung of an air-breathing animal. Originally the lung was a
+swim-bladder, or float, and as such it was of use to the aquatic
+ancestors of terrestrial animals. But as these ancestors gradually
+became more and more amphibious in their habits, the swim-bladder began
+more and more to discharge the function of a lung, and so to take a
+wholly new point of departure as regards its developmental history. But
+clearly there is here no difficulty with regard to the inception of its
+new function, because the organ was already well developed for one
+purpose before it began to serve another. Or, to take only one
+additional example, there are few structures in the animal kingdom so
+remarkable in respect of adaptation as is the wing of a bird or a bat;
+and at first sight it might well appear that a wing could be of no
+conceivable use until it had already acquired enormous proportional
+dimensions, as well as an immense amount of special elaboration as to
+its general form, size of muscle, amount of blood-supply, and so on.
+For, obviously, not until it had attained all these things could it even
+begin to raise the animal in the air. But observe how fallacious is this
+argument. Although it is perfectly true that a wing could be of no use
+_as a wing_ until sufficiently developed to serve the purpose of flight,
+this is merely to say that until it has become a wing it is no use as a
+wing. It does not, however, follow that on this account it was of no
+prior use for any other purpose. The first modifications of the
+fore-limb which ended in its becoming an organ of flight may very well
+have been due to adapting it as an organ for increased rapidity of
+locomotion of other kinds--whether on land as in the case of its now
+degenerated form in the ostrich, or in water as in the case of the
+expanded fins of fish. Indeed, we may see the actual process of
+transition from the one function to the other in the case of
+"flying-fish." Here the progressive expansion of the pectoral fins must
+certainly have been always of use for continuously promoting rapidity of
+locomotion through water; and thus natural selection may have
+continuously increased their development until they now begin to serve
+also as wings for carrying the animal a short distance through air.
+Again, in the case of the so-called flying squirrels we find the limbs
+united to the body by means of large extensions of the skin, so-that
+when jumping from one tree to another the animal is able to sustain
+itself through a long distance in the air by merely spreading out its
+limbs, and thus allowing the skin-extensions to act after the manner of
+a parachute. Here, of course, we have not yet got a wing, any more than
+we have in the case of the flying-fish; but we have the foundations laid
+for the possible development of a future wing, upon a somewhat similar
+plan as that which has been so wonderfully perfected in the case of
+bats. And through all the stages of progressive expansion which the skin
+of the squirrel has undergone, the expansion has been of use, even
+though it has not yet so much as begun to acquire the distinctive
+functions of a wing. Here, then, there is obviously nothing "prophetic"
+in the matter, any more than there was in the case of the swim-bladder
+and the lung, or in that of the nerve-ending and the eye. In short, it
+is the business of natural selection to secure the highest available
+degree of adaptation for the time being; and, in doing this, it not
+unfrequently happens that an extreme development of a structure in one
+direction (produced by natural selection for the sake of better and
+better adapting the structure to perform some particular function) ends
+by beginning to adapt it to the performance of some other function. And,
+whenever this happens to be the case, natural selection forthwith begins
+to act upon the structure, so to speak, from a new point of departure.
+
+So much, then, for the Duke's premiss--namely, that "every modification
+of structure _must_ have been functionless _at first_, when it began to
+appear." This premiss is clearly opposed to observable fact. But now,
+the second position is that, even if this were not so, the Duke's
+conclusion would not follow. This conclusion, it will be remembered, is,
+that if incipient structures are useless, it necessarily follows that
+natural selection can have had no part whatever in their inception. Now,
+this is a conclusion which does not "necessarily" follow. Even if it be
+granted that there are structures which in their first beginnings are
+not of any use at all for any purpose, it is still possible that they
+may owe their origin to natural selection--not indeed directly, but
+indirectly. This possibility arises from the occurrence in nature of a
+principle which has been called the Correlation of Growth.
+
+Mr. Darwin, who has paid more attention to this matter than any other
+writer, has shown, in considerable detail, that all the parts of any
+given organism are so intimately bound together, or so mutually
+dependent upon each other, that when one part is caused to change by
+means of natural selection, some other parts are very likely to undergo
+modification as a consequence. For example, there are several kinds of
+domesticated pigeons and fowls, which grow peculiar wing-like feathers
+on the feet. These are quite unlike all the other feathers in the
+animal, except those of the wing, to which they bear a very remarkable
+resemblance. Mr. Darwin records the case of a bantam where these
+wing-like feathers were nine inches in length, and I have myself seen a
+pigeon where they reproduced upon the feet a close imitation of the
+different kinds of feathers which occupy homologous positions in the
+wing--primaries, secondaries, and tertiaries all being distinctly
+repeated in their proper anatomical relations. Furthermore, in this
+case, as in most cases where such wing-feathers occur upon the feet, the
+third and fourth toes were partly united by skin; and, as is well known,
+in the wing of a bird the third and fourth digits are completely united
+by skin; "so that in feather-footed pigeons, not only does the exterior
+surface support a row of long feathers, like wing-feathers [which, as
+just stated, may in some cases be obviously differentiated into
+primaries, secondaries and tertiaries], but the very same digits which
+in the wing are completely united by skin become partially united by
+skin in the feet; and thus by the law of correlated variation of
+homologous parts, we can understand the curious connexion of feathered
+legs and membrane between the two outer toes[46]." The illustration is
+drawn from the specimen to which I have referred.
+
+ [46] _Variation of Plants and Animals_, vol. ii. p. 315.
+
+ [Illustration: FIG. 117.--Feather-footed pigeon. Drawn from nature.]
+
+Many similar instances of the same law are to be met with throughout
+organic nature; and it is evident that in this principle we find a
+conceivable explanation of the origin of such adaptive structures as
+could not have been originated by natural selection acting directly upon
+themselves: they may have been originated by natural selection
+developing other adaptive structures elsewhere in the organism, the
+gradual evolution of which has entailed the production of these by
+correlation of growth. And, if so, when once started in this way, these
+structures, because thus accidentally useful, will now themselves come
+under the _direct_ action of natural selection, and so have their
+further evolution determined with or without the correlated association
+which first led to their inception.
+
+Of course it must be understood that in thus applying the principle of
+correlated growth, to explain the origin of adaptive structures where it
+is impossible to explain such origin by natural selection having from
+the first acted directly upon these structures themselves, Darwinists
+do not suppose that in all--or even in most--cases of correlated growth
+the correlated structures are of use. On the contrary, it is well known
+that structures due to correlated growth are, as a rule, useless. Being
+only the by-products of adaptive changes going on elsewhere, in any
+given case the chances are against these correlated effects being
+themselves of any utilitarian significance; and, therefore, as a matter
+of fact, correlated growths appear to be usually meaningless from the
+point of view of adaptation. Still, on the doctrine of chances, it is
+to be expected that sometimes a change of structure which has thus been
+indirectly produced by correlation of growth might happen to prove
+useful for some purpose or another; and in as many cases as such
+indirectly produced structures do prove useful, they will straightway
+begin to be improved by the direct action of natural selection. In all
+such cases, therefore, we should have an explanation of the _origin_ of
+such a structure, which is the only point that we are now considering.
+
+I think, then, that all this effectually disposes of the doctrine of
+"prophetic germs." But, before leaving the subject, I should like to
+make one further statement of greater generality than any which I have
+hitherto advanced. This statement is, that we must remember how large a
+stock of meaningless structures are always being produced in the course
+of specific transmutations, not only by correlation of growth, which we
+have just been considering, but also by the direct action of external
+conditions, together with the constant play of all the many and complex
+forces internal to organisms themselves. In other words, important as
+the principle of correlation undoubtedly is, we must remember that even
+this is very far from being the only principle which is concerned in the
+origination of structures that may or may not chance to be useful.
+Therefore, it is not only natural selection when operating indirectly
+through the correlation of growth that is competent to produce new
+structures without reference to utility. In all the complex action and
+reaction of internal and external forces, new variations are perpetually
+arising without any reference to utility, either present or future.
+Among all this multitude of promiscuous variations, the chances must be
+that some percentage will prove of some service, either from the first
+moment of their appearance, or else after they have undergone some
+amount of development. Such development prior to utility may be due,
+either to correlation of growth, to the structure having previously
+performed some other function, as already explained, or else to a
+continued operation of the causes which were concerned in the first
+appearance of originally useless characters. In a series of chapters
+which will be devoted to the whole question of utility in the next
+volume, I shall hope to give very good reasons for concluding that
+useless characters are not only of highly frequent occurrence, but are
+due to a variety of other causes besides correlation of growth. And, if
+so, the possibility of originally useless characters happening in some
+cases to become, by increased development, useful characters, is
+correspondingly increased. Among a hundred varietal or specific
+characters which are directly produced in as many different species by a
+change of climate, for example, some five or six may be _potentially_
+useful: that is to say, characters thus adventitiously produced in an
+incipient form may only require to be further developed by a continuance
+of the same causes as first originated them, in order that some
+percentage of the whole number shall become of some degree of use. Those
+professed followers of Darwin, therefore, who without any reason--or, as
+it appears to me, against all reason--deny the possibility of useless
+specific characters in any case or in any degree (unless correlated with
+useful characters), are playing into the hands of Darwin's critics by
+indirectly countenancing the difficulty which we are now considering.
+For, if correlation of growth is unreasonably supposed to be the only
+possible cause of the origin of incipient structures which are not
+useful from the first moment of their inception, clearly the field is
+greatly narrowed as regards the occurrence of incipient characters
+sufficient in amount--and, still more, in constancy of appearance and
+persistency of transmission--to admit of furnishing material for the
+working of natural selection. But in the measure that incipient
+characters--whether varietal or specific--are recognised as not always
+or "necessarily" useful from the moment of their inception, and yet
+capable of being developed to a certain extent by the causes which first
+led to their occurrence, in that measure is this line of criticism
+closed. For of all the variations which thus occur, it is only those
+which afterwards prove of any use that are laid hold upon and wrought up
+by natural selection into adaptive structures, or working organs. And,
+therefore, what we see in organic nature is the net outcome of the
+development of all the happy chances. So it comes that the appearance
+presented by organic nature as a whole is that of a continual fulfilment
+of structural prophecies, when, in point of fact, if we had a similar
+record of all the other variations it would be seen that possibly not
+one such prophecy in a thousand is ever destined to be fulfilled.
+
+ * * * * *
+
+Here, then, I feel justified in finally taking leave of the difficulty
+from the uselessness of incipient organs, as this difficulty has been
+presented, in varying degrees of emphasis, by the Duke of Argyll, Mr.
+Mivart, Professors Nägeli, Bronn, Broca, Eimer, and, indeed, by all
+other writers who have hitherto advanced it. For, as thus presented, I
+think I have shown that it admits of being adequately met. But now, I
+must confess, to me individually it does appear that behind this
+erroneous presentation of the difficulty there lies another question,
+which is deserving of much more serious attention. For although it
+admits of being easily shown--as I have just shown--that the difficulty
+as ordinarily presented fails on account of its extravagance, the
+question remains whether, if stated with more moderation, a real
+difficulty might not be found to remain.
+
+My quarrel with the conclusion, like my quarrel with the premiss, is due
+to its universality. By saying in the premiss that _all_ incipient
+organs are _necessarily_ useless at the time of their inception, these
+writers admit of being controverted by fact; and by saying in the
+conclusion that, _if_ all incipient organs are useless, it necessarily
+follows that in _no_ case can natural selection have been the cause of
+building up an organ until it becomes useful, they admit of being
+controverted by logic. For, even if the premiss were true in
+fact--namely, that all incipient organs are useless at the time of their
+inception,--it would not necessarily follow that in no case could
+natural selection build up a useless structure into a useful one;
+because, although it is true that in no case can natural selection do
+this by acting on a useless structure _directly_, it may do so by acting
+on the useless structure _indirectly_, through its direct action on some
+other part of the organism with which the useless structure happens to
+be correlated. Moreover, as I believe, and will subsequently endeavour
+to prove, there is abundant evidence to show that incipient characters
+are often developed to a large extent by causes other than natural
+selection (or apart from any reference to utility), with the result that
+some of them thus happen to become of use, when, of course, the supposed
+difficulty is at an end.
+
+But although it is thus easy to dispose of both the propositions in
+question, on account of their universality, stated more carefully they
+would require, as I have said, more careful consideration. Thus, if it
+had been said that some incipient organs are _presumably_ useless at the
+time of their inception, and that in _some of these cases_ it is
+difficult, or impossible, to conceive how the principle of correlation,
+or any other principle hitherto suggested, can apply--then the question
+would have been raised from the sphere of logical discussion to that of
+biological fact. And the new question thus raised would have to be
+debated, no longer on the ground of general or abstract principles, but
+on that of special or concrete cases. Now until within the last year or
+two it has not been easy to find such a special or concrete case--that
+is to say, a case which can be pointed to as apparently excluding the
+possibility of natural selection having had anything to do with the
+genesis of an unquestionably adaptive structure. But eventually such a
+case has arisen, and the Duke of Argyll has not been slow in perceiving
+its importance. This case is the electric organ in the tail of the
+skate. No sooner had Professor Cossar Ewart published an abstract of his
+first paper on this subject, than the Duke seized upon it as a case for
+which, as he said, he had long been waiting--namely, the case of an
+_adaptive_ organ the genesis of which _could not possibly_ be attributed
+to natural selection, and must therefore be attributed to supernatural
+design. Now, I do not deny that he is here in possession of an admirable
+case--a case, indeed, so admirable that it almost seems to have been
+specially designed for the discomfiture of Darwinians. Therefore, in
+order to do it full justice, I will show that it is even more formidable
+than the Duke of Argyll has represented.
+
+Electric organs are known to occur in several widely different kinds of
+fish--such as the _Gymnotus_ and _Torpedo_. Wherever these organs do
+occur, they perform the function of electric batteries in storing and
+discharging electricity in the form of more or less powerful shocks.
+Here, then, we have a function which is of obvious use to the fish for
+purposes both of offence and defence. These organs are everywhere
+composed of a transformation of muscular, together with an enormous
+development of nervous tissue; but inasmuch as they occupy different
+positions, and are also in other respects dissimilar in the different
+zoological groups of fishes where they occur, no difficulty can be
+alleged as to these analogous organs being likewise homologous in
+different divisions of the aquatic vertebrata.
+
+Now, in the particular case of the skate, the organ is situated in the
+tail, where it is of a spindle-like form, measuring, in a large fish,
+about two feet in length by about an inch in diameter at the middle of
+the spindle. Although its structure is throughout as complex and perfect
+as that of the electric organ in _Gymnotus_ or _Torpedo_, its smaller
+size does not admit of its generating a sufficient amount of
+electricity to yield a discharge that can be felt by the hand.
+Nevertheless, that it does discharge under suitable stimulation has been
+proved by Professor Burdon Sanderson by means of a telephone; for he
+found that every time he stimulated the animal its electrical discharge
+was rendered audible by the telephone. Here, then, the difficulty
+arises. For of what conceivable use is such an organ to its possessor?
+We can scarcely suppose that any aquatic animal is more sensitive to
+electric shocks than is the human hand; and even if such were the case,
+a discharge of so feeble a kind taking place in water would be
+short-circuited in the immediate vicinity of the skate itself. So there
+can be no doubt that such weak discharges as the skate is able to
+deliver must be wholly imperceptible alike to prey and to enemies. Yet
+for the delivery of such discharges there is provided an organ of such
+high peculiarity and huge complexity, that, regarded as a piece of
+living mechanism, it deserves to rank as at once the most extremely
+specialized and the most highly elaborated structure in the whole animal
+kingdom. Thousands of separately formed elements are ranged in row after
+row, all electrically insulated one from another, and packed away into
+the smallest possible space, with the obvious end, or purpose, of
+conspiring together for the simultaneous delivery of an electric shock.
+Nevertheless, the shock when delivered is, as we have just seen, too
+slight to be of any conceivable use to the skate. Therefore it appears
+impossible to suggest how this astonishing structure--much more
+astonishing, in my opinion, than the human eye or the human hand--can
+ever have been begun, or afterwards developed, by means of natural
+selection. For if it be not even yet of any conceivable use to its
+possessor, clearly thus far survival of the fittest can have had nothing
+to do with its formation. On the other hand, seeing that electric organs
+when of larger size, as in the _Gymnotus_ and _Torpedo_, are of obvious
+use to their possessors, the facts of the case, so far as the skate is
+concerned, assuredly do appear to sanction the doctrine of "prophetic
+germs." The organ in the skate seems to be on its way towards becoming
+such an organ as we meet with in these other animals; and, therefore,
+unless we can show that it is now, and in all previous stages of its
+evolution has throughout been, of use to the skate, the facts do present
+a serious difficulty to the theory of natural selection, while they
+readily lend themselves to the interpretation of a disposing or
+fore-ordaining mind, which knows how to construct an electric battery by
+thus transforming muscular tissue into electric tissue, and is now
+actually in process of constructing such an apparatus for the
+prospective benefit of future creatures.
+
+Should it be suggested that possibly the electric organ of the skate may
+be in process of degeneration, and therefore that it is now the
+practically functionless remnant of an organ which in the ancestors of
+the skate was of larger size and functional use--against so obvious a
+suggestion there lie the whole results of Professor Ewart's
+investigations, which go to indicate that the organ is here not in a
+stage of degeneration, but of evolution. For instance, in _Raia
+radiata_, it does not begin to be formed out of the muscular tissue
+until some time after the animal has left the egg-capsule, and assumed
+all the normal proportions (though not yet the size) of the adult
+creature. The organ, therefore, is one of the very latest to appear in
+the ontogeny of _R. radiata_; and, moreover, it does not attain its full
+_development_ (i. e. not merely _growth_, but transforming of muscular
+fibres into electrical elements) till the fish attains maturity. Read in
+the light of embryology, these facts prove, (1) that the electric organ
+of _R. radiata_ must be one of the very latest products of the
+animal's phylogeny; and, (2) that as yet, at all events, it has not
+begun to degenerate. But, if not, it must either be at a stand-still, or
+it must be in course of further evolution; and, whichever of these
+alternatives we adopt, the difficulty of accounting for its present
+condition remains. In this connexion also it is worth while to remark
+that the electric organ, even after it has attained its full
+_development_, continues its _growth_ with the growth of the fish, and
+this in a much higher ratio, either than the tail alone, or the whole
+animal. Lastly, Prof. Burdon Sanderson finds that _section for section_
+the organ in the skate is as efficient as it is in _Torpedo_. It is
+evident that these facts also point to the skate's organ being in course
+of phylogenetic evolution.
+
+ [Illustration: Fig. 118.--_Raia radiata_, representing the life size
+ of the youngest individual in which muscle fibres have been found
+ developing into electric cells].
+
+ [Illustration: Fig. 119.--Electric organ of the skate. The left-hand
+ drawing (i) represents the entire organ (natural size) of a
+ full-grown _r. radiata_. This is a small skate, which rarely exceeds
+ 50 centms. in length; but in the large _r. batis_, the organ may
+ exceed two feet in length. The other drawings represent single
+ muscle-fibres in successive stages of transition. In the first of
+ the series (ii) the motor plate, and the nerves connected with it,
+ have already been considerably enlarged. In the other three
+ specimens, the fibre becomes more and more club-like, and eventually
+ cup-like. These changes of shape are expressive of great changes of
+ structure, as may be seen in the last of the series (v), where the
+ shallow cup is seen in partial section. The electric plate lines the
+ concavity of the cup, and is richly supplied with nerves (only a few
+ of which are represented in the last drawing); the thick walls of
+ the cup are composed of muscular fibres, the striation of which is
+ distinctly visible.]
+
+ [Illustration: Fig. 120.--Electric cells of _raia radiata_. The
+ drawing on the left represents one of the clubs magnified, as in the
+ preceding wood-cut. The drawing on the right represents a number of
+ these clubs, less highly magnified, _in situ_.]
+
+Again, it cannot be answered that the principle of correlation may be
+drawn upon in mitigation of the difficulty. The structure of the
+electric organ is far too elaborate, far too specialized, and far too
+obviously directed to a particular end, to admit of our conceivably
+supposing it due to any accidental correlation with structural changes
+going on elsewhere. Even as regards the initial changes of
+muscle-elements into electrical-elements, I do not think the principle
+of correlation can be reasonably adduced by way of explanation; for, as
+shown in the illustrations, even this initial change is most
+extraordinarily peculiar, elaborate, and specialized. But, be this as it
+may, I am perfectly certain that the principle of correlation cannot
+possibly be adduced to explain the subsequent _association of these
+electrical elements into an electric battery_, actuated by a special
+nervous mechanism of enormous size and elaboration--unless of course,
+the progress of such a structure were assumed to have been throughout of
+some utility. Under this supposition, however, the principle of
+correlation would be forsaken in favour of that of natural selection;
+and we should again be in the presence of the same difficulty as that
+with which we started.
+
+But now, and further, if we do thus abandon correlation in favour of
+natural selection, and therefore if for the sake of saving an hypothesis
+we assume that the organ as it now stands _must_ be of some use to the
+existing skate, we should still have to face the question--Of what
+conceivable use can those initial stages of its formation have been,
+when first the muscle-elements began to be changed into the very
+different electrical-elements, and when therefore they became useless as
+muscles while not yet capable of performing even so much of the
+electrical function as they now perform?
+
+Lastly, we must remember that not only have we here the most highly
+specialized, the most complex, and altogether the most elaboratively
+adaptive organ in the animal kingdom; but also that in the formation of
+this structure there has been needed an altogether unparalleled
+expenditure of the most physiologically expensive of all
+materials--namely, nervous tissue. Whether estimated by volume or by
+weight, the quantity of nervous tissue which is consumed in the electric
+organ of the skate is in excess of all the rest of the nervous system
+put together. It is needless to say that nowhere else in the animal
+kingdom--except, of course, in other electric fishes--is there any
+approach to so enormous a development of nervous tissue for the
+discharge of a special function. Therefore, as nervous tissue is,
+physiologically speaking, the most valuable of all materials, we are
+forced to conclude that natural selection ought strongly to have
+_opposed_ the evolution of such organs, unless from the first moment of
+their inception, and throughout the whole course of their development,
+they were of some such paramount importance as biologically to justify
+so unexampled an expenditure. Yet this paramount importance does not
+admit of being so much as surmised, even where the organ has already
+attained the size and degree of elaboration which it presents in the
+skate.
+
+In view of all these considerations taken together, I freely confess
+that the difficulty presented by this case appears to me of a magnitude
+and importance altogether unequalled by that of any other single
+case--or any series of cases--which has hitherto been encountered by the
+theory of natural selection. So that, if there were many other cases of
+the like kind to be met with in nature, I should myself at once allow
+that the theory of natural selection would have to be discarded. But
+inasmuch as this particular case stands so far entirely by itself, and
+therefore out of analogy with thousands, or even millions, of other
+cases throughout the whole range of organic nature, I am constrained to
+feel it more probable that the electric organ of the skate will some day
+admit of being marshalled under the general law of natural selection--in
+just the same way as proved to be the case with the conspicuous
+colouring of those caterpillars, which, as explained in the last
+chapter, at one time seemed to constitute a serious difficulty to the
+theory, and yet, through a better knowledge of all the relations
+involved, has now come to constitute one of the strongest witnesses in
+its favour.
+
+ * * * * *
+
+I have now stated all the objections of any importance which have
+hitherto been brought against the theory of natural selection, excepting
+three, which I left to be dealt with together because they form a
+logically connected group. With a brief consideration of these,
+therefore, I will bring this chapter to a close.
+
+The three objections to which I allude are, (1) that a large
+proportional number of specific, as well as of higher taxonomic
+characters, are seemingly useless characters, and therefore do not lend
+themselves to explanation by the Darwinian theory; (2) that the most
+general of all specific characters--viz. cross-infertility between
+allied species--cannot possibly be due to natural selection, as is
+demonstrated by Darwin himself; (3) that the swamping effects of free
+intercrossing must always render impossible by natural selection alone
+any evolution of species in divergent (as distinguished from serial)
+lines of change.
+
+These three objections have been urged from time to time by not a few of
+the most eminent botanists and zoologists of our century; and from one
+point of view I cannot myself have the smallest doubt that the
+objections thus advanced are not only valid in themselves, but also by
+far the most formidable objections which the theory of natural selection
+has encountered. From another point of view, however, I am equally
+convinced that they all admit of absolute annihilation. This strong
+antithesis arises, as I have said, from differences of standpoint, or
+from differences in the view which we take of the theory of natural
+selection itself. If we understand this theory to set forth natural
+selection as the sole cause of organic evolution, then all the above
+objections to the theory are not merely, as already stated, valid and
+formidable, but as I will now add, logically insurmountable. On the
+other hand, if we take theory to consist merely in setting forth natural
+selection as a factor of organic evolution, even although we believe it
+to have been the chief factor or principal cause, all the three
+objections in question necessarily vanish. For in this case, even if it
+be satisfactorily proved that the theory of natural selection is unable
+to explain the three classes of facts above mentioned, the theory is not
+thereby affected: facts of each and all of these classes may be
+consistently left by the theory to be explained by causes other than
+natural selection--whether these be so far capable or incapable of
+hypothetical formulation. Thus it is evident that whether the three
+objections above named are to be regarded as logically insurmountable by
+the theory, or as logically non-existent in respect to it, depends
+simply upon the manner in which the theory itself is stated.
+
+In the next volume a great deal more will have to be said upon these
+matters--especially with regard to the causes other than natural
+selection which in my opinion are capable of explaining these so-called
+"difficulties." In the present connexion, however, all I have attempted
+to show is, that, whatever may be thought touching the supplementary
+theories whereby I shall endeavour to explain the facts of inutility,
+cross-sterility, and non-occurrence of free intercrossing, no one of
+these facts is entitled to rank as an objection against the theory of
+natural selection, unless we understand this theory to claim an
+exclusive prerogative in the field of organic evolution. This, as we
+have previously seen, is what Mr. Wallace does claim for it; while on
+the other hand, Mr. Darwin expressly--and even vehemently--repudiates
+the claim: from which it follows that all the three main objections
+against the theory of natural selection are objections which vitally
+affect the theory only as it has been stated and upheld by Wallace. As
+the theory has been stated and upheld by Darwin, all these objections
+are irrelevant. This is a fact which I had not myself perceived at the
+time when I mentioned these objections in a paper entitled
+_Physiological Selection_, which was published in 1886. The discussions
+to which that paper gave rise, however, led me to consider these matters
+more closely; and further study of Darwin's writings, with these matters
+specially in view, has led me to see that none of the objections in
+question are relevant to his theory, as distinguished from that of Mr.
+Wallace. This, I acknowledge, I ought to have perceived before I
+published the paper just alluded to; but in those days I had had no
+occasion to follow out the differences between Darwin and Wallace to all
+their consequences, and therefore adopted the prevalent view that their
+theories of evolution were virtually identical. Now, however, I have
+endeavoured to make it clear that the points wherein they differ involve
+the important consequences above set forth. All these the most
+formidable objections against the theory of natural selection arise
+simply and solely from what I conceive to be the erroneous manner in
+which the theory has been presented by Darwin's distinguished colleague.
+
+ * * * * *
+
+I have now considered, as impartially as I can, all the main criticisms
+and objections which have been brought against the theory of natural
+selection; and the result is to show that, neither singly nor
+collectively, are they entitled to much weight. On the other hand, as
+we have seen in the preceding chapter, there is a vast accumulation of
+evidence in favour of the theory. Hence, it is no wonder that the theory
+has now been accepted by all naturalists, with scarcely any one notable
+exception, as at any rate the best working hypothesis which has ever
+been propounded whereby to explain the facts of organic evolution.
+Moreover, in the opinion of those most competent to judge, the theory is
+entitled to be regarded as something very much more than a working
+hypothesis: it is held to be virtually a completed induction, or, in
+other words, the proved exhibition of a general law, whereby the
+causation of organic evolution admits of being in large part--if not
+altogether--explained.
+
+Now, whether or not we subscribe to this latter conclusion ought, I
+think, to depend upon what we mean by an explanation in the case which
+is before us. If we mean only that, given the large class of known facts
+and unknown causes which are conveniently summarized under the terms
+Heredity and Variability, then the further facts of Struggle and
+Survival serve, in some considerable degree or another, to account for
+the phenomena of adaptive evolution, I cannot see any room to question
+that the evidence is sufficient to prove the statement. But it is clear
+that by taking for granted these great facts of Heredity and
+Variability, we have assumed the larger part of the problem as a whole.
+Or, more correctly, by thus generalizing, in a merely verbal form, all
+the unknown causes which are concerned in these two great factors of the
+process in question, we are not so much as attempting to explain the
+precedent causation which serves as a condition to the process. Much
+more than half the battle would already have been won, had Darwin's
+predecessors been able to explain the causes of Heredity and Variation;
+hence it is but a very partial victory which we have hitherto gained in
+our recent discovery of the effects of Struggle and Survival.
+
+Yet partial though it be in relation to the whole battle, in itself, or
+considered absolutely, there can be no reasonable doubt that it
+constitutes the greatest single victory which has ever been gained by
+the science of Biology. For this very reason, however, it behoves us to
+consider all the more carefully the extent to which it goes. But my
+discussion of this matter must be relegated to the next volume, where I
+hope to give abundant proof of the soundness of Darwin's judgment as
+conveyed in the words:--"I am convinced that natural selection has been
+the main, but not the exclusive, means of modification."
+
+
+
+
+CHAPTER X.
+
+THE THEORY OF SEXUAL SELECTION, AND CONCLUDING REMARKS.
+
+
+Although the explanatory value of the Darwinian theory of natural
+selection is, as we have now seen, incalculably great, it nevertheless
+does not meet those phenomena of organic nature which perhaps more than
+any other attract the general attention, as well as the general
+admiration, of mankind: I mean all that class of phenomena which go to
+constitute the Beautiful. Whatever value beauty as such may have, it
+clearly has not a life-preserving value. The gorgeous plumage of a
+peacock, for instance, is of no advantage to the peacock in his struggle
+for life, and therefore cannot be attributed to the agency of natural
+selection. Now this fact of beauty in organic structures is a fact of
+wide generality--almost as wide, indeed, as is the fact of their
+utility. Mr. Darwin, therefore, suggested another hypothesis whereby to
+render a scientific explanation of this fact. Just as by his theory of
+natural selection he sought to explain the major fact of utility, so did
+he endeavour to explain the minor fact of beauty by a theory of what he
+termed Sexual Selection.
+
+It is a matter of observation that the higher animals do not pair
+indiscriminately; but that the members of either sex prefer those
+individuals of the opposite sex which are to them most attractive. It is
+important to understand _in limine_ that nobody has ever attempted to
+challenge this statement. In other words, it is an unquestionable fact
+that among many of the higher animals there literally and habitually
+occurs a _sexual selection_; and this fact is not a matter of inference,
+but, as I have said, a matter of observation. The inference only begins
+where, from this observable fact, it is argued,--1st, that the sexual
+selection has reference to an æsthetic taste on the part of the animals
+themselves; and 2nd, that, supposing the selection to be determined by
+such a taste, the cause thus given is adequate to explain the phenomena
+of beauty which are presented by these animals. I will consider these
+two points separately.
+
+From the evidence which Darwin has collected, it appears to me
+impossible to doubt that an æsthetic sense is displayed by many birds,
+and not a few mammals. This of course does not necessarily imply that
+the _standards_ of such a sense are the same as our own; nor does it
+necessarily imply that there is any constant relation between such a
+sense and high levels of intelligence in other respects. In point of
+fact, such is certainly not the case, because the best evidence that we
+have of an æsthetic sense in animals is derived from birds, and not from
+mammals. The most cogent cases to quote in this connexion are those of
+the numerous species of birds which habitually adorn their nests with
+gaily coloured feathers, wool, cotton, or any other gaudy materials
+which they may find lying about the woods and fields. In many cases a
+marked preference is shown for particular objects--as, for instance, in
+the case of the Syrian nut-hatch, which chooses the iridescent wings of
+insects, or that of the great crested fly-catcher, which similarly
+chooses the cast-off skins of snakes. But no doubt the most remarkable
+of these cases is that of the baya-bird of Asia, which after having
+completed its bottle-shaped and chambered nest[47], studs it over with
+small lumps of clay, both inside and out, upon which the cock-bird
+sticks fire-flies, apparently for the sole purpose of securing a
+brilliantly decorative effect. Other birds, such as the hammer-head of
+Africa, adorn the surroundings of their nests (which are built upon the
+ground) with shells, bones, pieces of broken glass and earthenware, or
+any objects of a bright and conspicuous character which they may happen
+to find. The most consummate artists in this respect are, however, the
+bower-birds; for the species of this family construct elaborate
+play-houses in the form of arched tunnels, built of twigs upon the
+ground. Through and around such a tunnel they chase one another; and it
+is always observable that not only is the floor paved with a great
+collection of shells, bones, coloured stones, and any other brilliant
+objects which they are able to carry in their beaks, but also that the
+walls are decorated with the most gaudy articles which the birds can
+find. There is one genus, in Papua, which even goes so far as to provide
+the theatre with a surrounding garden. A level piece of ground is
+selected as a site for the building. The latter is about two feet high,
+and constructed round the growing stalk of a shrub, which therefore
+serves as a central pillar to which the frame-work of the roof is
+attached. Twigs are woven into this frame-work until the whole is
+rendered rain-proof. The tent thus erected is about nine feet in
+circumference at its base, and presents a large arch as an entrance. The
+central pillar is banked up with moss at its base, and a gallery is
+built round the interior of the edifice. This gallery is decorated with
+flowers, fruits, fungi, &c. These are also spread over the garden, which
+covers about the same area as the play-house. The flowers are said to
+be removed when they fade, while fresh ones are gathered to supply their
+places. Thus the garden is always kept bright with flowers, as well as
+with the brilliant green of mosses, which are collected and distributed
+in patches, resembling tiny lawns.
+
+ [47] The chambers are three in number. The two upper ones are
+ occupied respectively by the male and the sitting female. The lower
+ one serves as a general living room when the young are hatched.
+
+ [Illustration: FIG. 121.--The Garden Bower-bird (_Amblyornis
+ inornata_). Reduced from _Gould's Birds of New Guinea_ to 1/4 nat.
+ size.]
+
+Now these sundry cases alone seem to prove a high degree of the æsthetic
+sense as occurring among birds; for, it is needless to say, none of the
+facts just mentioned can be due to natural selection, seeing that they
+have no reference to utility, or the preservation of life. But if an
+æsthetic sense occurs in birds, we should expect, on _a priori_ grounds,
+that it would probably be exercised with reference to the personal
+appearance of the sexes. And this expectation is fully realized. For it
+is an observable fact that in most species of birds where the males are
+remarkable for the brilliancy of their plumage, not only is this
+brilliancy most remarkable during the pairing season, but at this season
+also the male birds take elaborate pains to display their charms before
+the females. Then it is that the peacock erects his tail to strut round
+and round the hens, taking care always to present to them a front view,
+where the coloration is most gorgeous. And the same is true of all other
+gaily coloured male birds. During the pairing season they actively
+compete with one another in exhibiting their attractiveness to the
+females; and in many cases there are added all sorts of extraordinary
+antics in the way of dancings and crowings. Again, in the case of all
+song-birds, the object of the singing is to please the females; and for
+this purpose the males rival one another to the best of their musical
+ability.
+
+Thus there can be no question that the courtship of birds is a highly
+elaborate business, in which the males do their best to surpass one
+another in charming the females. Obviously the inference is that the
+males do not take all this trouble for nothing; but that the females
+give their consent to pair with the males whose personal appearance, or
+whose voice, proves to be the most attractive. But, if so, the young of
+the male bird who is thus _selected_ will inherit his superior beauty;
+and thus, in successive generations, a continuous advance will be made
+in the beauty of plumage or of song, as the case may be,--both the
+origin and development of beauty in the animal world being thus supposed
+due to the æsthetic taste of animals themselves.
+
+Such is the theory of sexual selection in its main outlines; and with
+regard to it we must begin by noting two things which are of most
+importance. In the first place, it is a theory wholly and completely
+distinct from the theory of natural selection; so that any truth or
+error in the one does not in the least affect the other. The second
+point is, that there is not so great a wealth of evidence in favour of
+sexual selection as there is in favour of natural selection; and,
+therefore, that while all naturalists nowadays accept natural selection
+as _a_ (whether or not _the_) cause of adaptive, useful, or
+life-preserving structures, there is no such universal--but only a very
+general--agreement with reference to sexual selection as a cause of
+decorative, beautiful, or life-embellishing structures. Nevertheless,
+the evidence in favour of sexual selection is both large in amount and
+massive in weight.
+
+Our consideration of this evidence will bring us to the second division
+of our subject, as previously marked out for discussion--namely,
+granting that an æsthetic sense occurs in certain large divisions of the
+animal kingdom, what is the proof that such a sense is a cause of the
+beauty which is presented by the animals in question?
+
+Before proceeding to state this proof, however, it is desirable to
+observe that under the theory of sexual selection Darwin has included
+two essentially different classes of facts. For besides the large class
+of facts to which I have thus far been alluding,--i. e. the cases where
+two sexes of the same species differ from one another in respect of
+ornamentation,--there is another class of facts equally important,
+namely, the cases where the two sexes of the same species differ from
+one another in respect of size, strength, and the possession of natural
+weapons, such as spurs, horns, &c. In most of these cases it is the
+males which are thus superiorly endowed; and it is a matter of
+observation that in all cases where they are so endowed they use their
+superior strength and natural weapons for fighting together, in order to
+secure possession of the females. Hence results what Mr. Darwin has
+called the Law of Battle between males of the same species; and this law
+of battle he includes under his theory of sexual selection. But it is
+evident that the principle which is operative in the law of battle
+differs from the principle which is concerned in the form of sexual
+selection that has to do with embellishment, and consequent charm. The
+law of battle, in fact, more nearly approaches the law of natural
+selection; seeing that it expresses the natural advantages of brute
+force in the struggling of rival animals, and so frequently results in
+_death of the less fitted_, as distinguished from a mere failure to
+propagate. Now against this doctrine of the law of battle, and the
+consequences to which it leads in the superior fighting powers of male
+animals, no objection has been raised in any quarter. It is only with
+regard to the other aspect of the theory of sexual selection--or that
+which is concerned with the superior embellishment of male animals--that
+any difference of opinion obtains. I will now proceed to give the main
+arguments on both sides of this question, beginning with a _résumé_ of
+the evidences in favour of sexual selection.
+
+In the first place, the fact that secondary sexual characters of the
+embellishing kind are so generally restricted to the male sex in itself
+seems to constitute very cogent proof that, in some way or another, such
+characters are connected with the part which is played by the male in
+the act of propagation. Moreover, secondary sexual characters of this
+kind are of quite as general occurrence as are those of the other kind
+which have to do with rivalry in battle; and the former are usually of
+the more elaborate description. Therefore, as there is no doubt that
+secondary sexual characters of the one order have an immediate purpose
+to serve in the act of propagation, we are by this close analogy
+confirmed in our surmise that secondary sexual characters of the other,
+and still more elaborate, order are likewise so concerned. Moreover,
+this view of their meaning becomes still further strengthened when we
+take into consideration the following facts. Namely, (_a_) secondary
+sexual characters of the embellishing kind are, as a rule, developed
+only at maturity; and most frequently during only a part of the year,
+which is invariably the breeding season: (_b_) they are always more or
+less seriously affected by emasculation: (_c_) they are always, and
+only, displayed in perfection during the act of courtship: (_d_) then,
+however, they are displayed with the most elaborate pains; yet always,
+and only, before the females: (_e_) they appear, at all events in many
+cases, to have the effect of charming the females into a performance of
+the sexual act; while it is certain that in many cases, both among
+quadrupeds and birds, individuals of the one sex are capable of feeling
+a strong antipathy against, or a strong preference for, certain
+individuals of the opposite sex.
+
+Such are the main lines of evidence in favour of the theory of sexual
+selection. And although it is enough that some of them should be merely
+stated as above in order that their immense significance should become
+apparent, in the case of others a bare statement is not sufficient for
+this purpose. More especially is this the case as regards the enormous
+profusion, variety, and elaboration of sexually-embellishing characters
+which occur in birds and mammals--not to mention several divisions of
+Arthropoda; together with the extraordinary amount of trouble which, in
+a no less extraordinary number of different ways, is taken by the male
+animals to display their embellishments before the females. And even in
+many cases where to our eyes there is no particular embellishment to
+display, the process of courtship consists in such an elaborate
+performance of dancings, struttings, and attitudinizings that it is
+scarcely possible to doubt their object is to incite the opposite sex.
+Here, for instance, is a series of drawings illustrating the courtship
+of spiders. I choose this case as an example, partly because it is the
+one which has been published most recently, and partly because it is of
+particular interest as occurring so low down in the zoological scale. I
+am indebted to the kindness of Mr. and Mrs. Peckham for permission to
+reproduce these few selected drawings from their very admirable work,
+which is published by the Natural History Society of Wisconsin, U.S. It
+is evident at a glance that all these elaborate, and to our eyes
+ludicrous, performances are more suggestive of incitation than of any
+other imaginable purpose. And this view of the matter is strongly
+corroborated by the fact that it is the most brightly coloured parts of
+the male spiders which are most obtruded upon the notice of the female
+by these peculiar attitudes--in just the same way as is invariably the
+case in the analogous phenomena of courtship among birds, insects, &c.
+
+ [Illustration: FIG. 122.--Courtship of Spiders. A few examples of
+ some of the attitudes adopted by different species of males when
+ approaching their females. (After Peckham.)]
+
+ [Illustration: FIG. 123.--Courtship of Spiders. Continued from Fig.
+ 122, similarly showing some of the attitudes of approach adopted by
+ males of yet other different species. (After Peckham.)]
+
+But so great is the mass of material which Darwin has collected in proof
+of all the points mentioned in the foregoing paragraph, that to attempt
+anything in the way of an epitome would really be to damage its
+evidential force. Therefore I deem it best simply to refer to it as it
+stands in his _Descent of Man_, concluding, as he concludes,--"This
+surprising uniformity in the laws regulating the differences between the
+sexes in so many and such widely separated classes is intelligible if we
+admit the action throughout all the higher divisions of the animal
+kingdom of one common cause, namely, sexual selection"; while, as he
+might well have added, it is difficult to imagine that all the large
+classes of facts which an admission of this common cause serves to
+explain, can ever admit of being rendered intelligible by any other
+theory.
+
+We may next proceed to consider the objections which have been brought
+against the theory of sexual selection. And this is virtually the same
+thing as saying that we may now consider Mr. Wallace's views upon the
+subject.
+
+Reserving for subsequent consideration the most general of these
+objections--namely, that at best the theory can only apply to the more
+intelligent animals, and so must necessarily fail to explain the
+phenomena of beauty in the less intelligent, or in the non-intelligent,
+as well as in all species of plants--we may take _seriatim_ the other
+objections which, in the opinion of Mr. Wallace, are sufficient to
+dispose of the theory even as regards the higher animals.
+
+In the first place, he argues that the principal cause of the greater
+brilliancy of male animals in general, and of male birds in particular,
+is that they do not so much stand in need of protection arising from
+concealment as is the case with their respective females. Consequently
+natural selection is not so active in repressing brilliancy of colour in
+the males, or, which amounts to the same thing, is more active in
+"repressing in the female those bright colours which are normally
+produced in both sexes by general laws."
+
+Next, he argues that not only does natural selection thus exercise a
+negative influence in passively permitting more heightened colour to
+appear in the males, but even exercises a positive influence in actively
+promoting its development in the males, while, at the same time,
+actively repressing its appearance in the females. For heightened
+colour, he says, is correlated with health and vigour; and as there can
+be no doubt that healthy and vigorous birds best provide for their
+young, natural selection, by always placing its premium on health and
+vigour in the males, thus also incidentally promotes, through correlated
+growth, their superior coloration.
+
+Again, with regard to the display which is practised by male birds, and
+which constitutes the strongest of all Mr. Darwin's arguments in favour
+of sexual selection, Mr. Wallace points out that there is no evidence of
+the females being in any way affected thereby. On the other hand, he
+argues that this display may be due merely to general excitement; and he
+lays stress upon the more special fact that moveable feathers are
+habitually erected under the influence of anger and rivalry, in order to
+make the bird look more formidable in the eyes of antagonists.
+
+Furthermore, he adduces the consideration that, even if the females are
+in any way affected by colour and its display on the part of the males,
+and if, therefore, sexual selection be conceded a true principle in
+theory, still we must remember that, as a matter of fact, it can only
+operate in so far as it is allowed to operate by natural selection. Now,
+according to Mr. Wallace, natural selection must wholly neutralize any
+such supposed influence of sexual selection. For, unless the survivors
+in the general struggle for existence happen to be those which are also
+the most highly ornamented, natural selection must neutralize and
+destroy any influence that may be exerted by female selection. But
+obviously the chances against the otherwise best fitted males happening
+to be likewise the most highly ornamented must be many to one, unless,
+as Wallace supposes, there is some correlation between embellishment and
+general perfection, in which case, as he points out, the theory of
+sexual selection lapses altogether, and becomes but a special case of
+natural selection.
+
+Once more, Mr. Wallace argues that the evidence collected by Mr. Darwin
+himself proves that each bird finds a mate under any circumstances--a
+general fact which in itself must quite neutralize any effect of sexual
+selection of colour or ornament, since the less highly coloured birds
+would be at no disadvantage as regards the leaving of healthy progeny.
+
+Lastly, he urges the high improbability that through thousands of
+generations all the females of any particular species--possibly spread
+over an enormous area--should uniformly and always have displayed
+exactly the same taste with respect to every detail of colour to be
+presented by the males.
+
+Now, without any question, we have here a most powerful array of
+objections against the theory of sexual selection. Each of them is ably
+developed by Mr. Wallace himself in his work on _Tropical Nature_; and
+although I have here space only to state them in the most abbreviated of
+possible forms, I think it will be apparent how formidable these
+objections appear. Unfortunately the work in which they are mainly
+presented was published several years after the second edition of the
+_Descent of Man_, so that Mr. Darwin never had a suitable opportunity of
+replying. But, if he had had such an opportunity, as far as I can judge
+it seems that his reply would have been more or less as follows.
+
+In the first place, Mr. Wallace fails to distinguish between brilliancy
+and ornamentation--or between colour as merely "heightened," and as
+distinctively decorative. Yet there is obviously the greatest possible
+difference between these two things. We may readily enough admit that a
+mere heightening of already existing coloration is likely enough--at all
+events in many cases--to accompany a general increase of vigour, and
+therefore that natural selection, by promoting the latter, may also
+incidentally promote the former, in cases where brilliancy is not a
+source of danger. But clearly this is a widely different thing from
+showing that not only a _general brilliancy of colour_, but also _the
+particular disposition of colours_, in the form of ornamental patterns,
+can thus be accounted for by natural selection. Indeed, it is expressly
+in order to account for the occurrence of such ornamental patterns that
+Mr. Darwin constructed his theory of sexual selection; and therefore, by
+thus virtually ignoring the only facts which that theory endeavours to
+explain, Mr. Wallace is not really criticizing the theory at all. By
+representing that the theory has to do only with brilliancy of colour,
+as distinguished from disposition of colours, he is going off upon a
+false issue which has never really been raised[48]. Look, for example,
+at a peacock's tail. No doubt it is sufficiently brilliant; but far more
+remarkable than its brilliancy is its elaborate pattern on the one hand,
+and its enormous size on the other. There is no conceivable reason why
+mere _brilliancy of colour_, as an accidental concomitant of general
+vigour, should have run into so extraordinary, so elaborate, and so
+beautiful a _design of colours_. Moreover, this design is only unfolded
+when the tail is erected, and the tail is not erected in battle (as Mr.
+Wallace's theory of the erectile function in feathers would require),
+but in courtship; obviously, therefore, the purpose of the pattern, so
+to speak, is correlated with the act of courtship--it being only then,
+in fact, that the general purpose of the whole structure, as well as the
+more special purpose of the pattern, becomes revealed. Lastly, the fact
+of this whole structure being so large, entailing not only a great
+amount of physiological material in its production, but also of
+physiological energy in carrying about such a weight, as well as of
+increased danger from impeding locomotion and inviting capture--all this
+is obviously incompatible with the supposition of the peacock's tail
+having been produced by natural selection. And such a case does not
+stand alone. There are multitudes of other instances of ornamental
+structures imposing a drain upon the vital energies of their possessors,
+without conferring any compensating benefit from a utilitarian point of
+view. Now, in all these cases, without any exception, such structures
+are ornamental structures which present a plain and obvious reference to
+the relationship of the sexes. Therefore it becomes almost impossible to
+doubt--first, that they exist for the sake of ornament; and next, that
+the ornament exists on account of that relationship. If such structures
+were due merely to a superabundance of energy, as Mr. Wallace supposes,
+not only ought they to have been kept down by the economizing influence
+of natural selection; but we can see no reason, either why they should
+be so highly ornamental on the one hand, or so exclusively related to
+the sexual relationship on the other.
+
+ [48] Note C.
+
+Finally, we must take notice of the fact that where peculiar
+_structures_ are concerned for purposes of display in courtship, the
+_elaboration_ of these structures is often no less remarkable than that
+of patterns where colours are thus concerned. Take, for example, the
+case of the Bell-bird, which I select from an innumerable number of
+instances that might be mentioned because, while giving a verbal
+description of this animal, Darwin does not supply a pictorial
+representation thereof. The bird, which lives in South America, has a
+very loud and peculiar call, that can be heard at a distance of two or
+three miles. The female is dusky-green; but the adult male is a
+beautiful white, excepting the extraordinary structure with which we are
+at present concerned. This is a tube about three inches long, which
+rises from the base of the beak. It is jet black, and dotted over with
+small downy feathers. The tube is closed at the top, but its cavity
+communicates with the palate, and thus the whole admits of being
+inflated from within, when, of course, it stands erect as represented in
+one of the two drawings. When not thus inflated, it hangs down, as
+shown in the second figure, which represents the plumage of a young
+male. (Fig. 124.)
+
+ [Illustration: FIG. 124.--The Bell-bird (_Chasmorhynchus niveus_,
+ 1/4 natural size). Drawn from nature (_R. Coll. Surg. Mus._). In the
+ drawing of the adult male the ornamental appendage is represented in
+ its inflated condition, during courtship; in the drawing of the
+ young male it is shown in its flaccid condition.]
+
+In another species of the genus there are three of these appendages--the
+two additional ones being mounted on the corners of the mouth. (Fig.
+125.) In all species of the genus (four in number) the tubes are
+inflated during courtship, and therefore perform the function of sexual
+embellishments. Now the point to which I wish to draw attention is, that
+so specialized and morphologically elaborate a structure cannot be
+regarded as merely adventitious. It must have been developed by some
+definite cause, acting through a long series of generations. And as no
+other function can be assigned to it than that of charming the female
+when it is erected in courtship, the peculiarity of form and mechanism
+which it presents--like the elaboration of patterns in cases where
+colour only is concerned--virtually compels us to recognise in sexual
+selection the only conceivable cause of its production.
+
+ [Illustration: FIG. 125.--_C. tricarunculatus_, 1/4 natural size.
+ Copied from the _Ibis_. The ornamental appendages of the male are
+ represented in a partly inflated condition.]
+
+For these reasons I think that Mr. Wallace's main objection falls to the
+ground. Passing on to his subsidiary objections, I do not see much
+weight in his merely negative difficulty as to there being an absence of
+evidence upon hen birds being charmed by the plumage, or the voice, of
+their consorts. For, on the one hand, it is not very safe to infer what
+sentiments may be in the mind of a hen; and, on the other hand, it is
+impossible to conceive what motive can be in the mind of a cock, other
+than that of making himself attractive, when he performs his various
+antics, displays his ornamental plumes, or sings his melodious songs.
+Considerations somewhat analogous apply to the difficulty of supposing
+so much similarity and constancy of taste on the part of female animals
+as Mr. Darwin's theory undoubtedly requires. Although we know very
+little about the psychology of the lower animals, we do observe in many
+cases that small details of mental organization are often wonderfully
+constant and uniform throughout all members of a species, even where it
+is impossible to suggest any utility as a cause.
+
+Again, as regards the objection that each bird finds a mate under any
+circumstances, we have here an obvious begging of the whole question.
+That every feathered Jack should find a feathered Jill is perhaps what
+we might have antecedently expected; but when we meet with innumerable
+instances of ornamental plumes, melodious songs, and the rest, as so
+many witnesses to a process of sexual selection having always been in
+operation, it becomes irrational to exclude such evidence on account of
+our antecedent prepossessions.
+
+There remains the objection that the principles of natural selection
+must necessarily swallow up those of sexual selection. And this
+consideration, I doubt not, lies at the root of all Mr. Wallace's
+opposition to the supplementary theory of sexual selection. He is
+self-consistent in refusing to entertain the evidence of sexual
+selection, on the ground of his antecedent persuasion that in the great
+drama of evolution there is no possible standing-ground for any other
+actor than that which appears in the person of natural selection. But
+here, again, we must refuse to allow any merely antecedent presumption
+to blind our eyes to the actual evidence of other agencies having
+co-operated with natural selection in producing the observed results.
+And, as regards the particular case now before us, I think I have shown,
+as far as space will permit, that in the phenomena of decorative
+colouring (as distinguished from merely brilliant colouring), of
+melodious song (as distinguished from merely tuneless cries), of
+enormous arborescent antlers (as distinguished from merely offensive
+weapons), and so forth--I say that in all these phenomena we have
+phenomena which cannot possibly be explained by the theory of natural
+selection; and, further, that if they are to be explained at all, this
+can only be done, so far as we can at present see, by Mr. Darwin's
+supplementary theory of sexual selection.
+
+I have now briefly answered all Mr. Wallace's objections to this
+supplementary theory, and, as previously remarked, I feel pretty
+confident that, at all events in the main, the answer is such as Mr.
+Darwin would himself have supplied, had there been a third edition of
+his work upon the subject. At all events, be this as it may, we are
+happily in possession of unquestionable evidence that he believed all
+Mr. Wallace's objections to admit of fully satisfactory answers. For his
+very last words to science--read only a few hours before his death at a
+meeting of the Zoological Society--were:
+
+ I may perhaps be here permitted to say that, after having carefully
+ weighed, to the best of my ability, the various arguments which
+ have been advanced against the principle of sexual selection, I
+ remain firmly convinced of its truth[49].
+
+ [49] Since the above exposition of the theory of sexual selection
+ was written, Mr. Poulton has published his work on the _Colours of
+ Animals_. He there reproduces some of the illustrations which occur
+ in Mr. and Mrs. Peckham's work on _Sexual Selection in Spiders_, and
+ furnishes appropriate descriptions. Therefore, while retaining the
+ illustrations, I have withdrawn my own descriptions.
+
+ Mr. Poulton has also in his book supplied a _résumé_ of the
+ arguments for and against the theory of sexual selection in general.
+ Of course in nearly all respects this corresponds with the _résumé_
+ which is given in the foregoing pages; but I have left the latter as
+ it was originally written, because all the critical part is
+ reproduced _verbatim_ from a review of Mr. Wallace's _Darwinism_, of
+ a date still earlier than that of Mr. Poulton's book--viz.
+ _Contemporary Review_, August, 1889.
+
+
+_Concluding Remarks._
+
+I will now conclude this chapter, and with it the present volume, by
+offering a few general remarks on what may be termed the philosophical
+relations of Darwinian doctrine to the facts of adaptation on the one
+hand, and to those of beauty on the other. Of course we are all aware
+that before the days of this doctrine the facts of adaptation in organic
+nature were taken to constitute the clearest possible evidence of
+special design, on account of the wonderful mechanisms which they
+everywhere displayed; while the facts of beauty were taken as
+constituting no less conclusive evidence of the quality of such special
+design as beneficent, not to say artistic. But now that the Darwinian
+doctrine appears to have explained scientifically the former class of
+facts by its theory of natural selection, and the latter class of facts
+by its theory of sexual selection, we may fitly conclude this brief
+exposition of the doctrine as a whole by considering what influence such
+naturalistic explanations may fairly be taken to exercise upon the
+older, or super-naturalistic, interpretations.
+
+To begin with the facts of adaptation, we must first of all observe that
+the Darwinian doctrine is immediately concerned with these facts only in
+so far as they occur in organic nature. With the adaptations--if they
+can properly be so called--which occur in all the rest of nature, and
+which go to constitute the Cosmos as a whole so wondrous a spectacle of
+universal law and perfect order, this doctrine is but indirectly
+concerned. Nevertheless, it is of course fundamentally concerned with
+them to the extent that it seeks to bring the phenomena of organic
+nature into line with those of inorganic; and therefore to show that
+whatever view we may severally take as to the kind of causation which is
+energizing in the latter we must now extend to the former. This is
+usually expressed by saying that the theory of evolution by natural
+selection is a mechanical theory. It endeavours to comprise all the
+facts of adaptation in organic nature under the same category of
+explanation as those which occur in inorganic nature--that is to say,
+under the category of physical, or ascertainable, causation. Indeed,
+unless the theory has succeeded in doing this, it has not succeeded in
+doing anything--beyond making a great noise in the world. If Mr. Darwin
+has not discovered a new mechanical cause in the selection principle,
+his labour has been worse than in vain.
+
+Now, without unduly repeating what has already been said in Chapter
+VIII, I may remark that, whatever we may each think of the measure of
+success which has thus far attended the theory of natural selection in
+explaining the facts of adaptation, we ought all to agree that,
+considered as a matter of general reasoning, the theory does certainly
+refer to a _vera causa_ of a strictly physical kind; and, therefore,
+that no exception can be taken to the theory in this respect on grounds
+of _logic_. If the theory in this respect is to be attacked at all, it
+can only be on grounds of _fact_--namely, by arguing that the cause does
+not occur in nature, or that, if it does, its importance has been
+exaggerated by the theory. Even, however, if the latter proposition
+should ever be proved, we may now be virtually certain that the only
+result would be the relegation of all the residual phenomena of
+adaptation to other causes of the physical order--whether known or
+unknown. Hence, as far as the matter of _principle_ is concerned, we may
+definitely conclude that the great naturalistic movement of our century
+has already brought all the phenomena of adaptation in organic nature
+under precisely the same category of mechanical causation, as similar
+movements in previous centuries have brought all the known phenomena of
+inorganic nature: the only question that remains for solution is the
+strictly _scientific_ question touching the particular causes of the
+mechanical order which have been at work.
+
+So much, then, for the phenomena of adaptation. Turning next to those of
+beauty, we have already seen that the theory of sexual selection stands
+to these in precisely the same relation as the theory of natural
+selection does to those of adaptation. In other words, it supplies a
+physical explanation of them; because, as far as our present purposes
+are concerned, it may be taken for granted, or for the sake of argument,
+that inasmuch as psychological elements enter into the question the
+cerebral basis which they demand involves a physical side.
+
+There is, moreover, this further point of resemblance between the two
+theories: neither of them has any reference to inorganic nature.
+Therefore, with the charm or the loveliness of landscapes, of earth and
+sea and sky, of pebbles, crystals, and so forth, we have at present
+nothing to do. How it is that so many inanimate objects are invested
+with beauty--why it is that beauty attaches to architecture, music,
+poetry, and many other things--these are questions which do not
+specially concern the biologist. If they are ever to receive any
+satisfactory explanation in terms of natural causation, this must be
+furnished at the hands of the psychologist. It may be possible for him
+to show, more satisfactorily than hitherto, that all beauty, whenever
+and wherever it occurs, is literally "in the eyes of the beholder"; or
+that objectively considered, there is no such thing as beauty. It may
+be--and in my opinion it probably is--purely an affair of the percipient
+mind itself, depending on the association of ideas with pleasure-giving
+objects. This association may well lead to a liking for such objects,
+and so to the formation of what is known as æsthetic feeling with regard
+to them. Moreover, beauty of inanimate nature must be an affair of the
+percipient mind itself, unless there be a creating intelligence with
+organs of sense and ideals of beauty similar to our own. And, apart from
+any deeper considerations, this latter possibility is scarcely entitled
+to be regarded as a probability, looking to the immense diversities in
+those ideals among different races of mankind. But, be this as it may,
+the scientific problem which is presented by the fact of æsthetic
+feeling, even if it is ever to be satisfactorily solved, is a problem
+which, as already remarked, must be dealt with by psychologists. As
+biologists we have simply to accept this feeling as a fact, and to
+consider how, out of such a feeling as a cause, the beauty of organic
+nature may have followed as an effect.
+
+Now we have already seen how the theory of sexual selection supposes
+this to have happened. But against this theory a formidable objection
+arises, and one which I have thought it best to reserve for treatment in
+this place, because it serves to show the principal difference between
+Mr. Darwin's two great generalizations, considered as generalizations in
+the way of mechanical theory. For while the theory of natural selection
+extends equally throughout the whole range of organic nature, the theory
+of sexual selection has but a comparatively restricted scope, which,
+moreover, is but vaguely defined. For it is obvious that the theory can
+only apply to living organisms which are sufficiently intelligent to
+admit of our reasonably accrediting them with æsthetic taste--namely, in
+effect, the higher animals. And just as this consideration greatly
+restricts the possible scope of the theory, as compared with that of
+natural selection, so does it render undefined the zoological limits
+within which it can be reasonably employed. Lastly, this necessarily
+undefined, and yet most important limitation exposes the theory to the
+objection just alluded to, and which I shall now mention.
+
+The theory, as we have just seen, is necessarily restricted in its
+application to the higher animals. Yet the facts which it is designed to
+explain are not thus restricted. For beauty is by no means restricted to
+the higher animals. The whole of the vegetable world, and the whole of
+the animal world at least as high up in the scale as the insects, must
+be taken as incapable of æsthetic feeling. Therefore, the extreme
+beauty of flowers, sea-anemones, corals, and so forth, cannot possibly
+be ascribed to sexual selection.
+
+Now, with regard to this difficulty, we must begin by excluding the case
+of the vegetable kingdom as irrelevant. For it has been rendered highly
+probable--if not actually proved--by Darwin and others, that the beauty
+of flowers and of fruits is in large part due to natural selection. It
+is to the advantage of flowering plants that their organs of
+fructification should be rendered conspicuous--and in many cases also
+odoriferous,--in order to attract the insects on which the process of
+fertilization depends. Similarly, it is to the advantage of all plants
+which have brightly coloured fruits that these should be conspicuous for
+the purpose of attracting birds, which eat the fruits and so disseminate
+the seed. Hence all the gay colours and varied forms, both of flowers
+and fruits, have been thus adequately explained as due to natural
+causes, working for the welfare, as distinguished from the beauty, of
+the plants. For even the distribution of colours on flowers, or the
+beautiful patterns which so many of them present, are found to be useful
+in guiding insects to the organs of fructification.
+
+Again, the green colouring of leaves, which lends so much beauty to the
+vegetable world, has likewise been shown to be of vital importance to
+the physiology of plant-life; and, therefore, may also be ascribed to
+natural selection. Thus, there remains only the forms of plants other
+than the flowers. But the forms of leaves have also in many cases been
+shown to be governed by principles of utility; and the same is to be
+said of the branching structure which is so characteristic of trees and
+shrubs, since this is the form most effectual for spreading out the
+leaves to the light and air. Here, then, we likewise find that the cause
+determining plant beauty is natural selection; and so we may conclude
+that the only reason why the forms of trees which are thus determined by
+utility appeal to us as beautiful, is because we are accustomed to these
+the most ordinary forms. Our ideas having been always, as it were,
+moulded upon these forms, æsthetic feeling becomes attached to them by
+the principle of association. At any rate, it is certain that when we
+contemplate almost any forms of plant-structure which, for special
+reasons of utility, differ widely from these (to us) more habitual
+forms, the result is not suggestive of beauty. Many of the tropical and
+un-tree-like plants--such as the cactus tribe--strike us as odd and
+quaint, not as beautiful. Be this however as it may, I trust I have said
+enough to prove that in the vegetable world, at all events, the
+attainment of beauty cannot be held to have been an object aimed at, so
+to speak, for its own sake. Even if, for the purposes of argument, we
+were to suppose that all the forms and colours in the vegetable world
+are due to special design, there could be no doubt that the purpose of
+this design has been in chief part a utilitarian purpose; it has not
+aimed at beauty exclusively for its own sake. For most of such beauty as
+we here perceive is plainly due to the means adopted for the attainment
+of life-preserving ends, which, of course, is a metaphorical way of
+saying that it is probably due to natural selection[50].
+
+ [50] The beauty of autumnal tints in fading leaves may possibly be
+ adduced _per contra_. But here we have to remember that it is only
+ some kinds of leaves which thus become beautiful when fading, while,
+ even as regards those that do, it is not remarkable that their
+ chlorophyll should, as it were, accidentally assume brilliant tints
+ while breaking down into lower grades of chemical constitution. The
+ case, in fact, is exactly parallel to those in the animal kingdom
+ which are considered in the ensuing paragraphs.
+
+Turning, then, to the animal kingdom below the level of insects, here we
+are bound to confess that the beauty which so often meets us cannot
+reasonably be ascribed either to natural or to sexual selection. Not to
+sexual selection for the reasons already given; the animals in question
+are neither sufficiently intelligent to possess any æsthetic taste, nor,
+as a matter of fact, do we observe that they exercise any choice in
+pairing. Not to natural selection, because we cannot here, as in the
+case of vegetables, point to any benefit as generally arising from
+bright colours and beautiful forms. On the principles of naturalism,
+therefore, we are driven to conclude that the beauty here is purely
+adventitious, or accidental. Nor need we be afraid to make this
+admission, if only we take a sufficiently wide view of the facts. For,
+when we do take such a view, we find that beauty here is by no means of
+invariable, or even of general, occurrence. There is no loveliness about
+an oyster or a lob-worm; parasites, as a rule, are positively ugly, and
+they constitute a good half of all animal species. The truth seems to
+be, when we look attentively at the matter, that in all cases where
+beauty does occur in these lower forms of animal life, its presence is
+owing to one of two things--either to the radiate form, or to the bright
+tints. Now, seeing that the radiate form is of such general occurrence
+among these lower animals--appearing over and over again, with the
+utmost insistence, even among groups widely separated from one another
+by the latest results of scientific classification--seeing this, it
+becomes impossible to doubt that the radiate form is due to some
+morphological reasons of wide generality. Whether these reasons be
+connected with the internal laws of growth, or to the external
+conditions of environment, I do not pretend to suggest. But I feel safe
+in saying that it cannot possibly be due to any design to secure beauty
+for its own sake. The very generality of the radiate form is in itself
+enough to suggest that it must have some physical, as distinguished from
+an æsthetic, explanation; for, if the attainment of beauty had here been
+the object, surely it might have been even more effectually accomplished
+by adopting a greater variety of typical forms--as, for instance, in the
+case of flowers.
+
+Coming then, lastly, to the case of brilliant tints in the lower
+animals, Mr. Darwin has soundly argued that there is nothing forced or
+improbable in the supposition that organic compounds, presenting as they
+do such highly complex and such varied chemical constitutions, should
+often present brilliant colouring _incidentally_. Considered merely as
+colouring, there is nothing in the world more magnificent than arterial
+blood; yet here the colouring is of purely utilitarian significance. It
+is of the first importance in the chemistry of respiration; but is
+surely without any meaning from an æsthetic point of view. For the
+colour of the cheeks, and of the flesh generally, in the _white_ races
+of mankind, could have been produced quite as effectually by the use of
+pigment--as in the case of certain monkeys. Now the fact that in the
+case of blood, as in that of many other highly coloured fluids and
+solids throughout the animal kingdom, the colour is _concealed_, is
+surely sufficient proof that the colour, if regarded from an æsthetic
+point of view, is accidental. Therefore, when, as in other cases, such
+colouring occurs upon the surface, and thus becomes apparent, are we not
+irresistibly led to conclude that its _exhibition_ in such cases is
+likewise accidental, so far as any question of æsthetic design is
+concerned?
+
+I have now briefly glanced at all the main facts of organic nature with
+reference to beauty; and, as a result, I think it is impossible to
+resist the general conclusion, that in organic nature beauty does not
+exist as an end _per se_. All cases where beauty can be pointed to in
+organic nature are seemingly due--either to natural selection, acting
+without reference to beauty, but to utility; to sexual selection, acting
+with reference to the taste of animals; or else to sheer accident. And
+if this general conclusion should be held to need any special
+verification, is it not to be found in the numberless cases where
+organic nature not only fails to be beautiful, but reveals itself as the
+reverse. Not again to refer to the case of parasites, what can be more
+unshapely than a hippopotamus, or more generally repulsive than a
+crocodile? If it be said that these are exceptions, and that the forms
+of animals as a rule are graceful, the answer--even apart from
+parasites--is obvious. In all cases where the habits of life are such as
+to render rapid locomotion a matter of utilitarian necessity, the
+outlines of an animal _must_ be graceful--else, whether the locomotion
+be terrestrial, aerial, or aquatic, it must fail to be swift. Hence it
+is only in such cases as that of the hippopotamus, rhinoceros,
+elephant, crocodile, and so forth, where natural selection has had no
+concern in developing speed, that the accompanying accident of
+gracefulness can be allowed to disappear. But if beauty in organic
+nature had been in itself what may be termed an artistic object on the
+part of a divine Creator, it is absurd to suggest that his design in
+this matter should only have been allowed to appear where we are able to
+detect other and very good reasons for its appearance.
+
+ * * * * *
+
+Thus, whether we look to the facts of adaptation or to those of beauty,
+everywhere throughout organic nature we meet with abundant evidence of
+natural causation, while nowhere do we meet with any independent
+evidence of supernatural design. But, having led up to this conclusion,
+and having thus stated it as honestly as I can, I should like to finish
+by further stating what, in my opinion is its logical bearing upon the
+more fundamental tenets of religious thought.
+
+As I have already observed at the commencement of this brief exposition,
+prior to the Darwinian theory of organic evolution, the theologian was
+prone to point to the realm of organic nature as furnishing a peculiarly
+rich and virtually endless store of facts, all combining in their
+testimony to the wisdom and the beneficence of the Deity. Innumerable
+adaptations of structures to functions appeared to yield convincing
+evidence in favour of design; the beauty so profusely shed by living
+forms appeared to yield evidence, no less convincing, of that design as
+beneficent. But both these sources of evidence have now, as it were,
+been tapped at their fountain-head: the adaptation and the beauty are
+alike receiving their explanation at the hands of a purely mechanical
+philosophy. Nay, even the personality of man himself is assailed; and
+this not only in the features which he shares with the lower animals,
+but also in his god-like attributes of reason, thought, and conscience.
+All nature has thus been transformed before the view of the present
+generation in a manner and to an extent that has never before been
+possible: and inasmuch as the change which has taken place has taken
+place in the direction of naturalism, and this to the extent of
+rendering the mechanical interpretation of nature universal, it is no
+wonder if the religious mind has suddenly awakened to a new and a
+terrible force in the words of its traditional enemy--Where is now thy
+God?
+
+This is not the place to discuss the bearings of science on
+religion[51]; but I think it is a place where one may properly point out
+the limits within which no such bearings obtain. Now, from what has just
+been said, it will be apparent that I am not going to minimise the
+change which has been wrought. On the contrary, I believe it is only
+stupidity or affectation which can deny that the change in question is
+more deep and broad than any single previous change in the whole history
+of human thought. It is a fundamental, a cosmical, a world-transforming
+change. Nevertheless, in my opinion, it is a change of a non-theistic,
+as distinguished from an a-theistic, kind. It has rendered impossible
+the appearance in literature of any future Paley, Bell, or Chalmers; but
+it has done nothing in the way of negativing that belief in a Supreme
+Being which it was the object of these authors to substantiate. If it
+has demonstrated the futility of their proof, it has furnished nothing
+in the way of disproof. It has shown, indeed, that their line of
+argument was misjudged when they thus sought to separate organic nature
+from inorganic as a theatre for the special or peculiar display of
+supernatural design; but further than this it has not shown anything.
+The change in question therefore, although greater in degree, is the
+same in kind as all its predecessors: like all previous advances in
+cosmological theory which have been wrought by the advance of science,
+this latest and greatest advance has been that of revealing the
+constitution of nature, or the method of causation, as everywhere the
+same. But it is evident that this change, vast and to all appearance
+final though it be, must end within the limits of natural causation
+itself. The whole world of life and mind may now have been annexed to
+that of matter and energy as together constituting one magnificent
+dominion, which is everywhere subject to the same rule, or method of
+government. But the ulterior and ultimate question touching the nature
+of this government as mental or non-mental, personal or impersonal,
+remains exactly where it was. Indeed, this is a question which cannot be
+affected by _any_ advance of science, further than science has proved
+herself able to dispose of erroneous arguments based upon ignorance of
+nature. For while the sphere of science is necessarily restricted to
+that of natural causation which it is her office to explore, the
+question touching the _nature of this natural causation_ is one which as
+necessarily lies without the whole sphere of such causation itself:
+therefore it lies beyond any possible intrusion by science. And not only
+so. But if the nature of natural causation be that of the highest order
+of known existence, then, although we must evidently be incapable of
+conceiving what such a Mind is, at least we seem capable of judging what
+in many respects it is not. It cannot be more than one; it cannot be
+limited either in space or time; it cannot be other than at least as
+self-consistent as its manifestations in nature are invariable. Now,
+from the latter deduction there arises a point of first-rate importance
+in the present connexion. For if the so-called First Cause be
+intelligent, and therefore all secondary causes but the expression of a
+supreme Will, in as far as such a Will is self-consistent, the operation
+of all natural causes must be uniform,--with the result that, as seen by
+us, this operation must needs appear to be what we call mechanical. The
+more unvarying the Will, the more unvarying must be this expression
+thereof; so that, if the former be absolutely self-consistent, the
+latter cannot fail to be as reasonably interpreted by the theory of
+mindless necessity, as by that of ubiquitous intention. Such being, as
+it appears to me, the pure logic of the matter, the proof of organic
+evolution amounts to nothing more than the proof of a natural process.
+What mode of being is ultimately concerned in this process--or in what
+it is that this process ultimately consists--is a question upon which
+science is as voiceless as speculation is vociferous.
+
+ [51] The best treatise on this subject is Prof. Le Conte's
+ _Evolution and its Relation to Religious Thought_ (Appleton & Co.
+ 1888).
+
+But, it may still be urged, surely the principle of natural selection
+(with its terrible basis in the struggle for existence) and the
+principle of sexual selection (with its consequence in denying beauty
+to be an end in itself) demonstrate that, _if_ there be design in
+nature, such design at all events cannot be beneficent. To this,
+however, I should again reply that, just as touching the major question
+of design itself, so as touching this minor question of the quality of
+such design as beneficent, I do not see how the matter has been much
+affected by a discovery of the principles before us. For we did not need
+a Darwin to tell us that the whole creation groaneth and travaileth
+together in pain. The most that in this connexion Darwin can fairly be
+said to have done is to have estimated in a more careful and precise
+manner than any of his predecessors, the range and the severity of this
+travail. And if it be true that the result of what may be called his
+scientific analysis of nature in respect of suffering is to have shown
+the law of suffering even more severe, more ubiquitous, and more
+necessary than it had ever been shown before, we must remember at the
+same time how he has proved, more rigidly than was ever proved before,
+that suffering is a condition to improvement--struggle for life being
+the _raison d'être_ of higher life, and this not only in the physical
+sphere, but also in the mental and moral.
+
+Lastly, if it be said that the _choice_ of such a method, whereby
+improvement is only secured at the cost of suffering, indicates a kind
+of callousness on the part of an intelligent Being supposed to be
+omnipotent, I confess that such does appear to me a legitimate
+conclusion--subject, however, to the reservation that higher knowledge
+might displace it. For, as far as matters are now actually presented to
+the unbiased contemplation of a human mind, this provisional inference
+appears to me unavoidable--namely, that if the world of sentient life be
+due to an Omnipotent Designer, the aim or motive of the design must have
+been that of securing a continuous advance of animal improvement,
+without any regard at all to animal suffering. For I own it does not
+seem to me compatible with a fair and honest exercise of our reason to
+set the sum of animal happiness over against the sum of animal misery,
+and then to allege that, in so far as the former tends to balance--or to
+over-balance--the latter, thus far is the moral character of the design
+as a whole vindicated. Even if it could be shown that the sum of
+happiness in the brute creation considerably preponderates over that of
+unhappiness--which is the customary argument of theistic apologists,--we
+should still remain without evidence as to this state of matters having
+formed any essential part of the design. On the other hand, we should
+still be in possession of seemingly good evidence to the contrary. For
+it is clearly a condition to progress by survival of the fittest, that
+as soon as organisms become sentient selection must be exercised with
+reference to sentiency; and this means that, if further progress is to
+take place, states of sentiency _must_ become so organized with
+reference to habitual experience of the race, that pleasures and pains
+shall answer respectively to states of agreement and disagreement with
+the sentient creature's environment. Those animals which found pleasure
+in what was deleterious to life would not survive, while those which
+found pleasure in what was beneficial to life would survive; and so
+eventually, in every species of animal, states of sentiency as agreeable
+or disagreeable must approximately correspond with what is good for the
+species or bad for the species. Indeed, we may legitimately surmise that
+the reason why sentiency (and, _a fortiori_, conscious volition) has
+ever appeared upon the scene at all, has been because it
+furnishes--through this continuously selected adjustment of states of
+sentiency to states of the sentient organism--so admirable a means of
+securing rapid, and often refined, adjustments by the organism to the
+habitual conditions of its life[52]. But, if so, not only is this state
+of matters a _condition_ to progress in the future; it is further, and
+equally, a _consequence_ of progress in the past.
+
+ [52] See _Mental Evolution in Animals_, pp. 110-111.
+
+However, be this as it may, from all that has gone before does it not
+become apparent that pleasure or happiness on the one hand, and pain or
+misery on the other, must be present in sentient nature? And so long as
+they are both seen to be equally necessary under the process of
+evolution by natural selection, we have clearly no more reason to regard
+the pleasure than the pain as an object of the supposed design. Rather
+must we see in both one and the same condition to progress under the
+method of natural causation which is before us; and therefore I cannot
+perceive that it makes much difference--so far as the argument for
+beneficence is concerned--whether the pleasures of animals outweigh
+their pains, or _vice versâ_.
+
+Upon the whole, then, it seems to me that such evidence as we have is
+against rather than in favour of the inference, that if design be
+operative in animate nature it has reference to animal enjoyment or
+well-being, as distinguished from animal improvement or evolution. And
+if this result should be found distasteful to the religious mind--if it
+be felt that there is no desire to save the evidences of design unless
+they serve at the same time to testify to the nature of that design as
+beneficent,--I must once more observe that the difficulty thus presented
+to theism is not a difficulty of modern creation. On the contrary, it
+has always constituted the fundamental difficulty with which natural
+theologians have had to contend. The external world appears, in this
+respect, to be at variance with our moral sense; and when the antagonism
+is brought home to the religious mind, it must ever be with a shock of
+terrified surprise. It has been newly brought home to us by the
+generalizations of Darwin; and therefore, as I said at the beginning,
+the religious thought of our generation has been more than ever
+staggered by the question--Where is now thy God? But I have endeavoured
+to show that the logical standing of the case has not been materially
+changed; and when this cry of Reason pierces the heart of Faith, it
+remains for Faith to answer now, as she has always answered before--and
+answered with that trust which is at once her beauty and her
+life--Verily thou art a God that hidest thyself.
+
+
+
+
+_APPENDIX AND NOTES_
+
+
+
+
+APPENDIX TO CHAPTER V.
+
+ON OBJECTIONS WHICH HAVE BEEN BROUGHT AGAINST THE THEORY OF ORGANIC
+EVOLUTION ON GROUNDS OF PALÆONTOLOGY.
+
+
+While stating in the text, and in a necessarily general way, the
+evidence which is yielded by palæontology to the theory of organic
+evolution, I have been desirous of not overstating it. Therefore, in the
+earlier paragraphs of the chapter, which deal with the most general
+heads of such evidence, I introduced certain qualifying phrases; and I
+will now give the reasons which led me to do so.
+
+Of all the five biological sciences which have been called into
+evidence--viz. those of Classification, Morphology, Embryology,
+Palæontology, and Geographical Distribution--it is in the case of
+palæontology alone that any important or professional opinions still
+continue to be unsatisfied. Therefore, in order that justice may be done
+to this line of dissent, I have thought it better to deal with the
+matter in a separate Appendix, rather than to hurry it over in the text.
+And, as all the difficulties or objections which have been advanced
+against the theory of evolution on grounds of palæontology must vary, as
+to their strength, with the estimate which is taken touching the degree
+of imperfection of the geological record, I will begin by adding a few
+paragraphs to what has already been said in the text upon this subject.
+
+First, then, as to the difficulties in the way of fossils being formed
+at all. We have already noticed in the text that it is only the more or
+less hard parts of organisms which under any circumstances can be
+fossilized; and even the hardest parts quickly disintegrate if not
+protected from the weather on land, or from the water on the sea-bottom.
+Moreover, as Darwin says, "we probably take a quite erroneous view when
+we assume 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 immense interval of
+time, by another and a 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." Next, as regards littoral animals, he shows the
+difficulty which they must have in becoming fossils, and gives a
+striking example in several of the existing species of a sub-family of
+cirripedes (_Chthamalinæ_), "which coat the rocks all over the world in
+infinite numbers," yet, with the exception of one species which inhabits
+deep water, no vestige of any of them has been found in any tertiary
+formation, although it is known that the genus _Chthamalus_ existed
+through the Chalk period. Lastly, "with respect to the terrestrial
+productions which lived through the secondary and palæozoic periods, it
+is superfluous to state our evidence is fragmentary in an extreme
+degree. For instance, until recently not a land shell was known
+belonging to either of these vast periods," with one exception; while,
+"in regard to mammiferous remains, a glance at the historical table in
+Lyell's Manual will bring home the truth, how accidental and rare has
+been 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 perhaps of even more importance than all these known causes which
+prevent the formation of fossils, is the existence of unknown causes
+which make for the same result. For example, the Flysch-formation is a
+formation of several thousand feet in thickness (as much as 6000 in some
+places), and it extends for at least 300 miles from Vienna to
+Switzerland; moreover, it consists of shale and sandstone. Therefore,
+alike in respect of time, space, and character, it is just such a
+formation as we should expect to find highly rich in fossils; yet,
+"although this great mass has been most carefully searched, no fossils,
+except a few vegetable remains, have been found."
+
+So much then for the difficulty, so to speak, which nature experiences
+in the manufacture of fossils. Probably not one per cent. of the species
+of animals which have inhabited the earth has left a single individual
+as a fossil, whereby to record its past existence.
+
+But of even more importance than this difficulty of making fossils in
+the first instance, is the difficulty of preserving them when they are
+made. The vast majority of fossils have been formed under water, and a
+large proportional number of these--whether the animals were marine,
+terrestrial, or inhabitants of fresh water--have been formed in
+sedimentary deposits either of sand, gravel, or other porous material.
+Now, where such deposits have been afterwards raised into the air for
+any considerable time--and this has been more or less the case with all
+deposits which are available for exploration--their fossiliferous
+contents will have been, as a general rule, dissolved by the percolation
+of rain-water charged with carbonic acid. Similarly, sea-water has
+recently been found to be a surprisingly strong solvent of calcareous
+material: hence, Saturn-like, the ocean devours her own progeny as far
+as shells and bones of all kinds are concerned--and this to an extent of
+which we have probably no adequate conception.
+
+Of still greater destructive influence, however, than these solvent
+agencies in earth and sea, are the erosive agencies of both. Any one who
+watches the pounding of the waves upon the shore; who then observes the
+effect of it upon the rocks broken into shingle, and on the shingle
+reduced to sand; who, looking behind him at the cliffs, sees there the
+evidence of the gradual advance of this all-pulverising power--an
+advance so gradual that no yard of it is accomplished until within that
+yard the "white teeth" have eaten well into the "bowels of the earth";
+who then reflects that this process is going on simultaneously over
+hundreds of thousands of miles of coast-lines throughout the world; and
+who finally extends his mental vision from space to time, by trying
+dimly to imagine what this ever-roaring monster must have consumed
+during the hundreds of millions of years that slowly rising and slowly
+sinking continents have exposed their whole areas to her jaws; whoever
+thus observes and thus reflects must be a dull man, if he does not begin
+to feel that in the presence of such a destroyer as this we have no
+reason to wonder at a frequent silence in the testimony of the rocks.
+
+But although the erosive agency of the sea is thus so inconceivably
+great, it is positively small if compared with erosive agencies on land.
+The constant action of rain, wind, and running water, in wearing down
+the surfaces of all lands into "the dust of continents to be"; the
+disintegrating effects on all but the very hardest rocks of winter
+frosts alternating with summer heats; the grinding power of ice in
+periods of glaciation; and last, but not least, the wholesale melting up
+of sedimentary formations whenever these have sunk for any considerable
+distance beneath the earth's surface:--all these agencies taken together
+constitute so prodigious a sum of energies combined through
+immeasureable ages in their common work of destruction, that when we
+try to realise what it must amount to, we can scarcely fail to wonder,
+not that the geological record is highly imperfect, but that so much of
+the record has survived as we find to have been the case. And, if we add
+to these erosive and solvent agencies on land the erosive and solvent
+agencies of the sea, we may almost begin to wonder that anything
+deserving the name of a geological record is in existence at all.
+
+That such estimates of the destructive powers of nature are not mere
+matters of speculative reasoning may be amply shown by stating one
+single fact, which, like so many others where the present subject is
+concerned, we owe to the generalizations of Darwin. Plutonic rocks,
+being those which have emerged from subterranean heat of melting
+intensity, must clearly at some time or another have lain beneath the
+whole thickness of sedimentary deposits, which at that time occupied any
+part of the earth's surface where we now find the Plutonic rocks exposed
+to view. Or, in other words, wherever we now find Plutonic rocks at the
+surface of the earth, we must conclude that all the sedimentary rocks by
+which they were covered when in a molten state have since been entirely
+destroyed; several vertical miles of the only kinds of rocks in which
+fossils can possibly occur must in all such cases have been abolished
+_in toto_. Now, in many parts of the world metamorphic rocks--which have
+thus gradually risen from Plutonic depths, while miles of various other
+rock-formations have been removed from their now exposed surfaces--cover
+immense areas, and therefore testify by their present horizontal range,
+no less than by their previously vertical depth, to the enormous scale
+on which a total destruction has taken place of everything that once lay
+above them. For instance, the granitic region of Parime is at least
+nineteen times the size of Switzerland; a similar region south of the
+Amazon is probably larger than France, Spain, Italy, and Great Britain
+all put together; and, more remarkable still, over the area of the
+United States and Canada, granitic rocks exceed in the proportion of 19
+to 12-1/2 the whole of the newer Palæozoic formations. Lastly, after
+giving these examples, Darwin adds the important consideration, that "in
+many regions the metamorphic and granitic rocks would be found much more
+widely extended than they appear to be, if all the sedimentary beds were
+removed which rest unconformably on them, and which could not have
+formed part of the original mantle under which they were crystallized."
+
+The above is a brief condensation of the already condensed statement
+which Darwin has given of the imperfection of the geological record; but
+I think it is enough to show, in a general way, how precarious must be
+the nature of any objections to the theory of evolution which are
+founded merely upon the silence of palæontology in cases where, if the
+record were anything like complete, we should be entitled to expect from
+it some positive information. But, as we have seen in the text,
+imperfect though the record be, in as far as it furnishes positive
+information at all, this is well-nigh uniformly in favour of the theory;
+and therefore, even on grounds of palæontology alone, it appears to me
+that Darwin is much too liberal where he concludes his discussion by
+saying,--"Those who believe that the geological record is in any degree
+perfect, will undoubtedly at once reject the theory." If in any measure
+reasonable, such persons ought rather to examine their title to such a
+belief; and even if they disregard the consensus of testimony which is
+yielded by all the biological sciences to the theory of evolution, they
+ought at least to hold their judgment in suspense until they shall have
+not only set against the apparently negative testimony which is yielded
+by geology its unquestionably positive testimony, but also well
+considered the causes which may--or rather must--have so gravely
+impaired the geological record.
+
+However, be this as it may, I will now pass on to consider the
+difficulties and objections which have been brought against the theory
+on grounds of palæontology.
+
+These may be classified under four heads. First, the absence of varietal
+links between allied species; second, the sudden appearance of whole
+groups of species--not only as genera and families, but even sometimes
+as orders and classes--without any forms leading up to them; third, the
+occurrence of highly organized types at much lower levels of geological
+strata than an evolutionist would antecedently expect; and, fourth, the
+absence of fossils of any kind lower down than the Cambrian strata.
+
+Now all these objections depend on estimates of the imperfection of the
+geological record much lower than that which is formed by Darwin.
+Therefore I have arranged the objections in their order of difficulty in
+this respect, or in the order that requires successively increasing
+estimates of the imperfection of the record, if they are to be
+successively answered.
+
+I think that the first of them has been already answered in the text, by
+showing that even a very moderate estimate of the imperfection of the
+record is enough to explain why intermediate _varieties_, connecting
+allied _species_, are but comparatively seldom met with. Moreover it was
+shown that in some cases, where shells are concerned, remarkably
+well-connected series of such varieties have been met with. And the same
+applies to species and genera in certain other cases, as in the equine
+family.
+
+But no doubt a greater difficulty arises where whole groups of species
+and genera, or even families and orders, appear to arise suddenly,
+without anything leading up to them. Even this the second difficulty,
+however, admits of being fully met, when we remember that in very many
+cases it has been proved, quite apart from the theory of descent, that
+superjacent formations have been separated from one another by wide
+intervals of time. And even although it often happens that intermediate
+deposits which are absent in one part of the world are present in
+another, we have no right to assume that such is always the case.
+Besides, even if it were, we should have no right further to assume that
+the faunas of widely separated geographical areas were identical during
+the time represented by the intermediate formation. Yet, unless they
+were identical, we should not expect the fossils of the intermediate
+formation, where extant, to yield evidence of what the fossils would
+have been in this same formation elsewhere, had it not been there
+destroyed. Now, as a matter of fact, "geological formations of each
+region are almost invariably intermittent"; and although in many cases a
+more or less continuous record of past forms of life can be obtained by
+comparing the fossils of one region and formation with those of another
+region and adjacent formations, it is evident (from what we know of the
+present geographical distribution of plants and animals) that not a few
+cases there must have been where the interruption of the record in one
+region cannot be made good by thus interpolating the fossils of another
+region. And we must remember it is by selecting the cases where this
+cannot be done that the objection before us is made to appear
+formidable. In other words, _unless_ whole groups of new species which
+are unknown in formation A appear suddenly in formation C of one region
+(X), where the intermediate formation B is absent; and _unless_ in some
+other region (Y), where B is present, the fossiliferous contents of B
+fail to supply the fossil ancestry of the new species in A (X); _unless_
+such a state of matters is found to obtain, the objection before us has
+nothing to say. But at best this is negative evidence; and, in order to
+consider it fairly, we ought to set against it the cases where an
+interposition of fossils found in B (Y) _does_ furnish the fossil
+ancestry of what would _otherwise_ have been an abrupt appearance of
+whole groups of new species in A (X). Now such cases are neither few
+nor unimportant, and therefore they deprive the objection of the force
+it would have had if the selected cases to the contrary were the general
+rule.
+
+In addition to these considerations, the following, some of which are of
+a more special kind, appear to me so important that I will quote them
+almost _in extenso_.
+
+ 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 the United States. We do not
+ make due allowance for the intervals of time which have elapsed
+ between our consecutive formations,--longer perhaps in many 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 parent form; and, in the succeeding
+ formation, such groups of 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;
+ and consequently that the transitional form would often long remain
+ confined to some one region; but that, when this adaptation had
+ once 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 spread
+ rapidly and widely throughout the world....
+
+ In geological treatises, published not many years ago, mammals were
+ 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 belongs to the middle of the secondary series;
+ and true mammals have 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
+ as far back as the miocene 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, no
+ less than at least thirty kinds of bird-like animals, some of
+ gigantic size, existed during that period? Not a fragment of bone
+ has been discovered in these beds. Not long ago palæontologists
+ maintained that the whole class of birds came suddenly into
+ existence during the eocene period; but now we know, on the
+ authority of Professor Owen, that a bird certainly lived during the
+ deposition of the upper green-sand. And still more recently that
+ strange bird, the Archeopteryx ... has been discovered in the
+ oolitic slates of Solenhofen. Hardly any recent discovery shows
+ more forcibly than this, how little we as yet know of the former
+ inhabitants of the world.
+
+ 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 stated that, from the 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 recognized; 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. Still more
+ recently, a Pyrgoma, a member of a distinct sub-family of sessile
+ cirripedes, has been discovered by Mr. Woodward in the upper chalk;
+ so that we now have abundant evidence of the existence of this
+ group of animals during the secondary period.
+
+ 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, according to Agassiz, in the
+ Chalk period. This group includes the large majority of existing
+ species. But certain Jurassic and Triassic forms are now commonly
+ admitted to be teleostean; and even some palæozoic forms have been
+ thus classed by one high authority. If the teleosteans had really
+ appeared suddenly in the northern hemisphere, the fact would have
+ been highly remarkable; but it would not have formed an insuperable
+ difficulty, unless it could likewise have been shown that at the
+ same period the species were suddenly and simultaneously developed
+ in other quarters of the world. 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 considerations, 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 knowledge
+ effected by the discoveries of the last dozen years, it seems to me
+ to be about as rash to dogmatize on the succession of organic
+ forms 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[53].
+
+ [53] _Origin of Species_, 282-5.
+
+In view of all the foregoing facts and considerations, it appears to me
+that the second difficulty on our list is completely answered. Indeed,
+even on a moderate estimate of the imperfection of the geological
+record, the wonder would have been if many cases had _not_ occurred
+where groups of species present the fictitious appearance of having been
+suddenly and simultaneously created in the particular formations where
+their remains now happen to be observable.
+
+Turning next to the third objection, there cannot be any question that
+every here and there in the geological series animals occur of a much
+higher grade zoologically than the theory of evolution would have
+expected to find in the strata where they are found. At any rate,
+speaking for myself, I should not have antecedently expected to meet
+with such highly differentiated insects as butterflies and dragonflies
+in the middle of the Secondaries: still less should I have expected to
+encounter beetles, cockroaches, spiders, and May-flies in the upper and
+middle Primaries--not to mention an insect and a scorpion even in the
+lower. And I think the same remark applies to a whole sub-kingdom in the
+case of Vertebrata. For although it is only the lowest class of the
+sub-kingdom which, so far as we positively know, was represented in the
+Devonian and Silurian formations, we must remember, on the one hand,
+that even a cartilaginous or ganoid fish belongs to the highest
+sub-kingdom of the animal series; and, on the other hand, that such
+animals are thus proved to have abounded in the very lowest strata where
+there is good evidence of there having been any forms of life at all.
+Lastly, the fact that Marsupials occur in the Trias, coupled with the
+fact that the still existing Monotremata are what may be termed animated
+fossils, referring us by their lowly type of organization to some period
+enormously more remote,--these facts render it practically certain that
+some members of this very highest class of the highest sub-kingdom must
+have existed far back in the Primaries.
+
+These things, I say, I should not have expected to find, and I think all
+other evolutionists ought to be prepared to make the same
+acknowledgment. But as these things have been found, the only possible
+way of accounting for them on evolutionary principles is by supposing
+that the geological record is even more imperfect than we needed to
+suppose in order to meet the previous objections. I cannot see, however,
+why evolutionists should be afraid to make this acknowledgment. For I do
+not know any reason which would lead us to suppose that there is any
+common measure between the distances marked on our tables of geological
+formations, and the times which those distances severally represent. Let
+the reader turn to the table on page 163, and then let him say why the
+30,000 feet of so-called Azoic rocks may not represent a greater
+duration of time than does the thickness of all the Primary rocks above
+them put together. For my own part I believe that this is probably the
+case, looking to the enormous ages during which these very early
+formations must have been exposed to destructive agencies of all kinds,
+now at one time and now at another, in different parts of the world.
+And, of course, we are without any means of surmising what ranges of
+time are represented by the so-called Primeval rocks, for the simple
+reason that they are non-sedimentary, and non-sedimentary rocks cannot
+be expected to contain fossils.
+
+But, it will be answered, the 30,000 feet of Azoic rocks, lying above
+the Primeval, _are_ sedimentary to some extent: they are not all
+completely metamorphic: yet they are all destitute of fossils. This is
+the fourth and last difficulty which has to be met, and it can only be
+met by the considerations which have been advanced by Lyell and Darwin.
+The former says:--
+
+ The total absence of any trace of fossils has inclined many
+ geologists to attribute the origin of the most ancient strata to an
+ azoic period, or one antecedent to the existence of organic beings.
+ Admitting, they say, the obliteration, in some cases, of fossils by
+ plutonic action, we might still expect that traces of them would
+ oftener be found in certain ancient systems of slate, which can
+ scarcely be said to have assumed a crystalline structure. But in
+ urging this argument it seems to be forgotten that there are
+ stratified formations of enormous thickness, and of various ages,
+ some of them even of tertiary date, and which we know were formed
+ after the earth had become the abode of living creatures, which
+ are, nevertheless, in some districts, entirely destitute of all
+ vestiges of organic bodies[54].
+
+ [54] _Elements of Geology_, p. 587.
+
+He then proceeds to mention sundry causes (in addition to plutonic
+action) which are adequate to destroy the fossiliferous contents of
+stratified rocks, and to show that these may well have produced enormous
+destruction of organic remains in these oldest of known formations.
+
+Darwin's view is that, during the vast ages of time now under
+consideration, it is probable that the distribution of sea and land over
+the earth's surface has not been uniformly the same, even as regards
+oceans and continents. Now, if this were the case, "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 naked 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 Cambrian epoch in a completely
+metamorphosed and denuded condition[55]." The probability of this view
+he sustains by certain general considerations, as well as particular
+facts touching the geology of oceanic islands, &c.
+
+ [55] _Origin of Species_, p. 289.
+
+On the whole, then, it seems to me but reasonable to conclude, with
+regard to all four objections in question, as Darwin concludes with
+regard to them:--
+
+ For my part, following out Lyell's metaphor, I look at the
+ geological record as a history of the world imperfectly kept,
+ 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, more or less different in the successive
+ chapters, may represent the forms of life, which are entombed in
+ our consecutive formations, and which falsely appear to us to have
+ been abruptly introduced. On this view, the difficulties above
+ discussed are greatly diminished, or even disappear[56].
+
+ [56] _Ibid._
+
+As far as I can see, the only reasonable exception that can be taken to
+this general view of the whole matter, is one which has been taken from
+the side of astronomical physics.
+
+Put briefly, it is alleged by one of the highest authorities in this
+branch of science, that there cannot have been any such enormous reaches
+of unrecorded time as would be implied by the supposition of there
+having been a lost history of organic evolution before the Cambrian
+period. The grounds of this allegation I am not qualified to examine;
+but in a general way I agree with Prof. Huxley in feeling that, from the
+very nature of the case, they are necessarily precarious,--and this in
+so high a degree that any conclusions raised on such premises are not
+entitled to be deemed formidable[57].
+
+ [57] See _Lay Sermons_, Lecture on Geological Reform.
+
+ * * * * *
+
+Turning now to plants, the principal and the ablest opponent of the
+theory of evolution is here unquestionably Mr. Carruthers[58]. The
+difficulties which he adduces may be classified under three heads, as
+follows:--
+
+ [58] See especially the following Presidential addresses:--Geol.
+ Assoc. Nov. 1876; Section D. Brit. Assoc., 1886; Lin. Soc., 1890.
+
+1. There is no evidence of change in specific forms of existing plants.
+Not only are the numerous species of plants which have been found in
+Egyptian mummies indistinguishable from their successors of to-day; but,
+what is of far more importance, a large number of our own indigenous
+plants grew in Great Britain during the glacial period (including under
+this term the warm periods between those of successive glaciations), and
+in no one case does it appear that any modification of specific type has
+occurred. This fact is particularly remarkable as regards leaves,
+because on the one hand they are the organs of plants which are most
+prone to vary, while on the other hand they are likewise the organs
+which lend themselves most perfectly to the process of fossilization, so
+that all details of their structure can be minutely observed in the
+fossil state. Yet the interval since the glacial period, although not a
+long one geologically speaking, is certainly what may be called an
+appreciable portion of time in the history of Dicotyledonous plants
+since their first appearance in the Cretaceous epoch. Again, if we
+extend this kind of enquiry so as to include the world as a whole, a
+number of other species of plants dating from the glacial epoch are
+found to tell the same story--notwithstanding that, in the opinion of
+Mr. Carruthers, they must all have undergone many changes of environment
+while advancing before, and retreating after, successive glaciations in
+different parts of the globe. Or, to quote his own words:--"The various
+physical conditions which of necessity affected these {41} species in
+their diffusion over such large areas of the earth's surface in the
+course of, say, 250,000 years, should have led to the production of many
+varieties; but the uniform testimony of the remains of this considerable
+pre-glacial flora, as far as the materials admit of a comparison, is
+that no appreciable change has taken place."
+
+2. There is no appearance of generalized forms among the earliest plants
+with which we are acquainted. For example, in the first dry land
+flora--the Devonian--we have representatives of the _Filices_,
+_Equisetaceæ_, and _Lycopodiaceæ_, all as highly specialized as their
+living representatives, and exhibiting the differential characters of
+these closely related groups. Moreover, these plants were even more
+highly organized than their existing descendants in regard to their
+vegetative structure, and in some cases also in regard to their
+reproductive organs. So likewise the Gymnosperms of that time show in
+their fossil state the same highly organized woody structure as their
+living representatives.
+
+3. Similarly, and more generally, the Dicotyledonous plants, which first
+appear in the Cretaceous rocks, appear there suddenly, without any forms
+leading up to them--notwithstanding that "we know very well the
+extensive flora of the underlying Wealden." Moreover, we have all the
+three great divisions of the Dicotyledons appearing together, and so
+highly differentiated that all the species are referred to existing
+genera, with the exception of a very few imperfectly preserved, and
+therefore uncertain fragments.
+
+Such being the facts, we may begin by noticing that, even at first
+sight, they present different degrees of difficulty. Thus, I cannot see
+that there is much difficulty with regard to those in class 2. Only if
+we were to take the popular (and very erroneous) view of organic
+evolution as a process which is always and everywhere bound to promote
+the specialization of organic types--only then ought we to see any real
+difficulty in the absence of generalized types preceding these existing
+types. Of course we may wonder why still lower down in the geological
+series we do not meet with more generalized (or ancestral) types; but
+this is the difficulty number 3, which we now proceed to examine.
+
+Concerning the other two difficulties, then, the only possible way of
+meeting that as to the absence of any parent forms lower down in the
+geological series is by falling back--as in the analogous case of
+animals--upon the imperfection of the geological record. Although it is
+certainly remarkable that we should not encounter any forms serving to
+connect the Dicotyledonous plants of the Chalk with the lower forms of
+the underlying Wealden, we must again remember that difficulties thus
+depending on the absence of any corroborative record, are by no means
+equivalent to what would have arisen in the presence of an adverse
+record--such, for instance, as would have been exhibited had the floras
+of the Wealden and the Chalk been inverted. But, as the case actually
+stands, the mere fact that Dicotyledonous plants, where they first
+occur, are found to have been already differentiated into their three
+main divisions, is in itself sufficient evidence, on the general theory
+of evolution, that there must be a break in the record as hitherto known
+between the Wealden and the Chalk. Nor is it easy to see how the
+opponents of this theory can prove their negative by furnishing evidence
+to the contrary. And although such might justly be deemed an unfair way
+of putting the matter, were this the only case where the geological
+record is in evidence, it is not so when we remember that there are
+numberless other cases where the geological record does testify to
+connecting links in a most satisfactory manner. For in view of this
+consideration the burden of proof is thrown upon those who point to
+particular cases where there is thus a conspicuous absence of
+transitional forms--the burden, namely, of proving that such cases are
+not due merely to a break in the record. Besides, the break in the
+record as regards this particular case may be apparent rather than real.
+For I suppose there is no greater authority on the pure geology of the
+subject than Sir Charles Lyell, and this is what he says of the
+particular case in question. "If the passage seem at present to be
+somewhat sudden from the flora of the Lower or Neocomian to that of the
+Upper Cretaceous period, the abruptness of the change will probably
+disappear when we are better acquainted with the fossil vegetation of
+the uppermost tracts of the Neocomian and that of the lowest strata of
+the Gault, or true Cretaceous series[59]."
+
+ [59] _Elements of Geology_, p. 280.
+
+Lastly, the fact of the flora of the glacial epoch not having exhibited
+any modifications during the long residence of some of its specific
+types in Great Britain and elsewhere, is a fact of some importance to
+the general theory of evolution, since it shows a higher degree of
+stability on the part of these specific types than might perhaps have
+been expected, supposing the theory to be true. But I do not see that
+this constitutes a difficulty against the theory, when we have so many
+other cases of proved transmutation to set against it. For instance, not
+to go further afield than this very glacial flora itself, it will be
+remembered that in an earlier chapter I selected it as furnishing
+specially cogent proof of the transmutation of species. What, then, is
+the explanation of so extraordinary a difference between Mr. Carruthers'
+views and my own upon this point? I believe the explanation to be that
+he does not take a sufficiently wide survey of the facts.
+
+To begin with, it seems to me that he exaggerates the vicissitudes to
+which the species of plants that he calls into evidence have been
+exposed while advancing before, and retreating after, the ice. Rather do
+I agree with Darwin that "they would not have been exposed during their
+long migrations to any great diversity of temperature; and as they all
+migrated in a body together, their mutual relations will not have been
+much disturbed; hence, in accordance with the principles indicated in
+this volume, these forms will not have been liable to much
+modification[60]." But, be this matter of opinion as it may, a much
+better test is afforded by those numerous cases all the world over,
+where arctic species have been left stranded on alpine areas by the
+retreat of glaciation; because here there is no room for differences of
+opinion as to a "change of environment" having taken place. Not to speak
+of climatic differences between arctic and alpine stations, consider
+merely the changes which must have taken place in the relations of the
+thus isolated species to each other, as well as to those of all the
+foreign plants, insects, &c., with which they have long been thrown into
+close association. If in _such_ cases no variation or transmutation had
+taken place since the glacial epoch, then indeed there would have been a
+difficulty of some magnitude. But, by parity of reasoning, whatever
+degree of difficulty would have been thus presented is not merely
+discharged, but converted into at least an equal degree of
+corroboration, when it is found that under such circumstances, in
+whatever part of the world they have occurred, some considerable amount
+of variation and transmutation has always taken place,--and this in the
+animals as well as in the plants. For instance, again to quote Darwin,
+"If we compare the present Alpine plants and animals of the several
+great European mountain-ranges one with another, though many of the
+species remain identically the same, some exist as varieties, some as
+doubtful forms or sub-species, and some as distinct yet closely allied
+species representing each other on the several ranges[61]." Lastly, if
+instead of considering the case of alpine floras, we take the much
+larger case of the Old and New World as a whole, we meet with much
+larger proofs of the same general facts. For, "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 will have been completely cut off from each other.
+This separation, as far as the more temperate productions are concerned,
+must have taken place long ages ago. As the plants and animals migrated
+southward, they will have become mingled in one great region with the
+native American productions, and would 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 Europe and N.
+America. Hence it has come, that when we compare the now living
+productions of the temperate regions of the New and Old Worlds, we find
+very few identical species; but we find in every 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[62]."
+
+ [60] _Origin of Species_, p. 332.
+
+ [61] _Origin of Species_, p. 332.
+
+ [62] _Ibid_. pp. 333-4.
+
+In view then of all the above considerations--and especially those
+quoted from Darwin--it appears to me that far from raising any
+difficulty against the theory of evolution, the facts adduced by Mr.
+Carruthers make in favour of it. For when once these facts are taken in
+connection with the others above mentioned, they serve to complete the
+correspondence between degrees of modification with degrees of time on
+the one hand, and with degrees of evolution, of change of environment,
+&c., on the other. Or, in the words of Le Conte, when dealing with this
+very subject, "It is impossible to conceive a more beautiful
+illustration of the principles we have been trying to enforce[63]."
+
+ [63] _Evolution and its Relation to Religious Thought_, p. 194.
+
+
+
+
+NOTE A TO PAGE 257.
+
+
+The passages in Dr. Whewell's writings, to which allusion is here made,
+are somewhat too long to be quoted in the text. But as I think they
+deserved to be given, I will here reprint a letter which I wrote to
+_Nature_ in March, 1888.
+
+ In his essay on the _Reception of the Origin of Species_, Prof.
+ Huxley writes:--
+
+ "It is interesting to observe that the possibility of a fifth
+ alternative, in addition to the four he has stated, has not dawned
+ upon Dr. Whewell's mind" (_Life and Lectures of Charles Darwin_,
+ vol. ii, p. 195).
+
+ And again, in the article _Science_, supplied to _The Reign of
+ Queen Victoria_, he says:--
+
+ "Whewell had not the slightest suspicion of Darwin's main theorem,
+ even as a logical possibility" (p 365).
+
+ Now, although it is true that no indication of such a logical
+ possibility is to be met with in the _History of the Inductive
+ Sciences_, there are several passages in the _Bridgewater Treatise_
+ which show a glimmering idea of such a possibility. Of these the
+ following are, perhaps, worth quoting. Speaking of the adaptation
+ of the period of flowering to the length of a year, he says:--
+
+ "Now such an adjustment must surely be accepted as a proof of
+ design, exercised in the formation of the world. Why should the
+ solar year be so long and no longer? or, this being such a length,
+ why should the vegetable cycle be exactly of the same length? Can
+ this be chance?... And, if not by chance, how otherwise could such
+ a coincidence occur than by an intentional adjustment of these two
+ things to one another; by a selection of such an organization in
+ plants as would fit them to the earth on which they were to grow;
+ by an adaptation of construction to conditions; of the scale of
+ construction to the scale of conditions? It cannot be accepted as
+ an explanation of this fact in the economy of plants, that it is
+ necessary to their existence; that no plants could possibly have
+ subsisted, and come down to us, except those which were thus
+ suited to their place on the earth. This is true; but it does not
+ at all remove the necessity of recurring to design as the origin of
+ the construction by which the existence and continuance of plants
+ is made possible. A watch could not go unless there were the most
+ exact adjustment in the forms and positions of its wheels; yet no
+ one would accept it as an explanation of the origin of such forms
+ and positions that the watch would not go if these were other than
+ they were. If the objector were to suppose that plants were
+ originally fitted to years of various lengths, and that such only
+ have survived to the present time as had a cycle of a length equal
+ to our present year, or one which could be accommodated to it, we
+ should reply that the assumption is too gratuitous and extravagant
+ to require much consideration."
+
+ Again, with regard to "the diurnal period," he adds:--
+
+ "Any supposition that the astronomical cycle has occasioned the
+ physiological one, that the structure of plants has been brought to
+ be what it is by the action of external causes, or that such plants
+ as could not accommodate themselves to the existing day have
+ perished, would be not only an arbitrary and baseless assumption,
+ but, moreover, useless for the purposes of explanation which it
+ professes, as we have noticed of a similar supposition with respect
+ to the annual cycle."
+
+ Of course these passages in no way make against Mr. Huxley's
+ allusions to Dr. Whewell's writings in proof that, until the
+ publication of the _Origin of Species_, the "main theorem" of this
+ work had not dawned on any other mind, save that of Mr. Wallace.
+ But these passages show, even more emphatically than total silence
+ with regard to the principle of survival could have done, the real
+ distance which at that time separated the minds of thinking men
+ from all that was wrapped up in this principle. For they show that
+ Dr. Whewell, even after he had obtained a glimpse of the principle
+ "as a logical possibility," only saw in it an "arbitrary and
+ baseless assumption." Moreover, the passages show a remarkable
+ juxtaposition of the very terms in which the theory of natural
+ selection was afterwards formulated. Indeed, if we strike out the
+ one word "intentional" (which conveys the preconceived idea of the
+ writer, and thus prevented him from doing justice to any
+ naturalistic view), all the following parts of the above quotations
+ might be supposed to have been written by a Darwinian. "If not by
+ chance, how otherwise could such a coincidence occur, than by an
+ _adjustment_ of these two things to one another; by a _selection_
+ of such an organization in plants as would _fit_ them to the earth
+ on which they were to grow; by an adaptation of _construction_ to
+ _conditions_; of the _scale_ of construction to the _scale_ of
+ conditions?" Yet he immediately goes on to say: "If the objector
+ were to suppose that plants were originally _fitted_ to years of
+ various lengths, and that such only have _survived_ to the present
+ time ... _as could be accommodated to it_ (i. e. the actual cycle),
+ we should reply that the assumption is too gratuitous and
+ extravagant to require much consideration." Was there ever a more
+ curious exhibition of failure to perceive the importance of a
+ "logical possibility"? And this at the very time when another mind
+ was bestowing twenty years of labour on its "consideration."
+
+
+
+
+NOTE B TO PAGE 295.
+
+
+Since these remarks were delivered in my lectures as here printed, Mr.
+Mivart has alluded to the subject in the following and precisely
+opposite sense:--
+
+ Many of the more noteworthy instincts lead us from manifestations
+ of purpose directed to the maintenance of the individual, to no
+ less plain manifestations of a purpose directed to the preservation
+ of the race. But a careful study of the interrelations and
+ interdependencies which exist between the various orders of
+ creatures inhabiting this planet shows us yet a more noteworthy
+ teleology--the existence of whole orders of such creatures being
+ directed to the service of other orders in various degrees of
+ subordination and augmentation respectively. This study reveals to
+ us, as a fact, the enchainment of all the various orders of
+ creatures in a hierarchy of activities, in harmony with what we
+ might expect to find in a world the outcome of a First Cause
+ possessed of intelligence and will[64].
+
+ [64] _On Truth_, p. 493.
+
+Having read this much, a Darwinian is naturally led to expect that Mr.
+Mivart is about to offer some examples of instincts or structures
+exemplifying what in the margin he calls the "Hierarchy of
+Ministrations." Yet the only facts he proceeds to adduce are the
+sufficiently obvious facts, that the inorganic world existed before the
+organic, plants before herbivorous animals, these before carnivorous,
+and so on: that is to say, everywhere the conditions to the occurrence
+of any given stage of evolution preceded such occurrence, as it is
+obvious that they must, if, as of course it is not denied, the
+possibility of such occurrence depended on the precedence of such
+conditions. Now, it is surely obvious that such a "hierarchy of
+ministrations" as this, far from telling against the theory of natural
+selection, is the very thing which tells most in its favour. The fact
+that animals, for instance, only appeared upon the earth after there
+were plants for them to feed upon, is clearly a necessity of the case,
+whether or not there was any design in the matter. Such "ministrations,"
+therefore, as plant-organisms yield to animal-organisms is just the kind
+of ministration that the theory of natural selection requires. Thus far,
+then, both the theories--natural selection and super-natural
+design--have an equal right to appropriate the facts. But now, if in no
+one instance can it be shown that the ministration of plant-life to
+animal-life is of such a kind as to subserve the interests of
+animal-life without at the same time subserving those of the plant-life
+itself, then the fact makes wholly in favour of the naturalistic
+explanation of such ministration as appears. If any plants had presented
+any characters pointing prospectively to needs of animals without
+primarily ministering to their own, then, indeed, there would have been
+no room for the theory of natural selection. But as this can nowhere be
+alleged, the theory of natural selection finds all the facts to be
+exactly as it requires them to be: such ministration as plants yield to
+animals becomes so much evidence of natural selection having slowly
+formed the animals to appropriate the nutrition which the plants had
+previously gathered--and gathered under the previous influence of
+natural selection acting on themselves entirely for their own sakes.
+Therefore I say it is painfully manifest that "the enchainment of all
+the various orders of creatures in a hierarchy of activities," is _not_
+"in harmony with what we might expect to find in a world the outcome of
+a First Cause possessed of intelligence and [beneficent] will." So far
+as any argument from such "enchainment" reaches, it makes entirely
+against the view which Mr. Mivart is advocating. In point of fact, there
+is a total absence of any such "ministration" by one "order of
+creatures" to the needs of any other order, as the beneficent design
+theory would necessarily expect; while such ministration as actually
+does obtain is exactly and universally the kind which the naturalistic
+theory requires.
+
+Again, quite independently, and still more recently, Mr. Mivart alluded
+in _Nature_ (vol. xli, p. 41) to the difficulty which the apparently
+exceptional case of gall-formation presents to the theory of natural
+selection. Therefore I supplied (vol. xli, p. 80) the suggestion given
+in the text, viz. that although it appears impossible that the sometimes
+remarkably elaborate and adaptive structures of galls can be due to
+natural selection acting directly on the plants themselves--seeing that
+the adaptation has reference to the needs of their parasites--it is
+quite possible that the phenomena may be due to natural selection acting
+indirectly on the plants, by always preserving those individual insects
+(and larvae) the character of whose secretions is such as will best
+induce the particular shapes of galls that are required. Several other
+correspondents took part in the discussion, and most of them accepted
+the above explanation. Mr. T. D. A. Cockerell, however, advanced another
+and very ingenious hypothesis, showing that there is certainly one
+conceivable way in which natural selection might have produced all the
+phenomena of gall-formation by acting directly on the plants
+themselves[65]. Subsequently Mr. Cockerell published another paper upon
+the subject, stating his views at greater length. The following is the
+substance of his theory as there presented:--
+
+ [65] _Nature_, vol. xli, p. 344.
+
+ Doubtless there were internal plant-feeding larvae before there
+ were galls: and, indeed, we have geological evidence that boring
+ insects date very far back indeed. The primitive internal feeders,
+ then, were miners in the roots, stems, twigs, or leaves, such as
+ occur very commonly at the present day. These miners are
+ excessively harmful to plant-life, and form a class of the most
+ destructive insect-pests known to the farmer: they frequently cause
+ the death of the whole or part of the plant attacked. Now, we may
+ suppose that the secretions of certain of these insects caused a
+ swelling to appear where the larvae lived, and on this excrescence
+ the larvae fed. It is easy to see that the greater the excrescence,
+ and the greater the tendency of the larvae to feed upon it, instead
+ of destroying the vital tissues, the smaller is the amount of harm
+ to the plant. Now the continued life and vitality of the plant is
+ beneficial to the larvae, and the larger or more perfect the gall,
+ the greater the amount of available food. Hence natural selection
+ will have preserved and accumulated the gall-forming tendencies, as
+ not only beneficial to the larvae, but as a means whereby the
+ larvae can feed with least harm to the plant. So far from being
+ developed for the exclusive benefit of the larvae, it is easy to
+ see that, allowing a tendency to gall-formation, natural selection
+ would have developed galls exclusively for the benefit of the
+ plants, so that they might suffer a minimum of harm from the
+ unavoidable attacks of insects.
+
+ But here it may be questioned--have we proof that internal feeders
+ tend to form galls? In answer to this I would point out that
+ gall-formation is a peculiar feature, and cannot be expected to
+ arise in every group of internal feeders. But I think we can afford
+ sufficient proof that wherever it has arisen it has been preserved;
+ and further, that even the highly complex forms of galls are
+ evolved from forms so simple that we hesitate to call them galls at
+ all[66].
+
+ [66] _Entomologist_, March, 1890.
+
+The paper then proceeds to give a number of individual cases. No doubt
+the principal objection to which Mr. Cockerell's hypothesis is open is
+one that was pointed out by Herr Wetterhan, viz. "the much greater
+facility afforded to the indirect action through insects, by the
+enormously more rapid succession of generations with the latter than
+with many of their vegetable hosts--oaks above all[67]." This
+difficulty, however, Mr. Cockerell believes maybe surmounted by the
+consideration that a growing plant need not be regarded as a single
+individual, but rather as an assemblage of such[68].
+
+ [67] _Nature_, vol. xli, p. 394.
+
+ [68] _Ibid._ vol. xli, pp. 559-560.
+
+
+
+
+NOTE C TO PAGE 394.
+
+
+The only remarks that Mr. Wallace has to offer on the _pattern of
+colours_, as distinguished from a mere _brilliancy of colour_, are added
+as an afterthought suggested to him by the late Mr. Alfred Tylor's book
+on _Colouration of Animals and Plants_ (1886). But, in the first place,
+it appears to me that Mr. Wallace has formed an altogether extravagant
+estimate of the value of this work. For the object of the work is to
+show, "that diversified colouration follows the chief lines of
+structure, and changes at points, such as the joints, where function
+changes." Now, in publishing this generalization, Mr. Tylor--who was not
+a naturalist--took only a very limited view of the facts. When applied
+to the animal kingdom as a whole, the theory is worthless; and even
+within the limits of mammals, birds, and insects--which are the classes
+to which Mr. Tylor mainly applies it--there are vastly more facts to
+negative than to support it. This may be at once made apparent by the
+following brief quotation from Prof. Lloyd Morgan:--
+
+ It can hardly be maintained that the theory affords us any adequate
+ explanation of the _specific_ colour-tints of the humming-birds, or
+ the pheasants, or the Papilionidae among butterflies. If, as Mr.
+ Wallace argues, the immense tufts of golden plumage in the bird of
+ paradise owe their origin to the fact that they are attached just
+ above the point where the arteries and nerves for the supply of the
+ pectoral muscles leave the interior of the body--and the
+ physiological rationale is not altogether obvious,--are there no
+ other birds in which similar arteries and nerves are found in a
+ similar position? Why have these no similar tufts? And why, in the
+ birds of paradise themselves, does it require four years ere these
+ nervous and arterial influences take effect upon the plumage?
+ Finally, one would inquire how the colour is determined and held
+ constant in each species. The difficulty of the Tylor-Wallace view,
+ even as a matter of origin, is especially great in those numerous
+ cases in which the colour is determined by delicate lines, thin
+ plates, or thin films of air or fluid. Mr. Poulton, who takes a
+ similar line of argument in his _Colours of Animals_ (p. 326), lays
+ special stress on the production of _white_ (pp. 201-202).
+
+As regards the latter point, it may be noticed that not in any part of
+his writings, so far as I can find, does Mr. Wallace allude to the
+highly important fact of colours in animals being so largely due to
+these purely physical causes. Everywhere he argues as if colours were
+universally due to pigments; and in my opinion this unaccountable
+oversight is the gravest defect in Mr. Wallace's treatment both of the
+facts and the philosophy of colouration in the animal kingdom. For
+instance, as regards the particular case of sexual colouration, the
+oversight has prevented him from perceiving that his theory of
+"brilliancy" as due to "a surplus of vital energy," is not so much as
+logically possible in what must constitute at least one good half of the
+facts to which he applies it--unless he shows that there is some
+connection between vital energy and the development of striations,
+imprisonment of air-bubbles, &c. But any such connection--so
+essentially important for his theory--he does not even attempt to show.
+Lastly, and quite apart from these remarkable oversights, even if Mr.
+Tylor's hypothesis were as reasonable and well-sustained as it is
+fanciful and inadequate, still it could not apply to _sexual_
+colouration: it could apply only to colouration as affected by
+physiological functions common to both sexes. Yet it is in order to
+furnish a "preferable substitute" for Mr. Darwin's theory of _sexual_
+colouration, that Mr. Wallace adduces the hypothesis in question as one
+of "great weight"! In this matter, therefore, I entirely agree with
+Poulton and Lloyd Morgan.
+
+
+
+
+INDEX
+
+
+A.
+
+Accident, Darwin's use of the word, 334-340;
+ beauty due to, 408, 409.
+
+Achromatin, 126-134.
+
+Acquired characters, _see_ Characters.
+
+_Acræa eurita_, 328.
+
+Adaptation, facts of, in relation to theory of natural selection,
+ 401-403, 411.
+
+Adaptive characters, _see_ Characters.
+
+Æsthetic sense in animals, 380-385;
+ _see_ Beautiful.
+
+Agassiz, Prof. A., on fauna of the Mammoth cave, 70.
+
+Alpine plants, 209, 210, 440-442.
+
+_Amauris niavius_, 328.
+
+_Amblyornis inornata_, 381-383.
+
+_Amphioxus_, 137, 138, 145, 146.
+
+Analogy, 38, 50-65, 176, 177, 347-350.
+
+Anthropoid, _see_ Apes.
+
+Antlers, 98-100, 167-169.
+
+Ants, co-operative instincts of, 268;
+ leaf-cutting, 332;
+ keeping aphides, 292.
+
+Ape, eye of, 75;
+ _appendix vermiformis_ of, 84-86.
+
+Apes, ears of, compared with those of man, 88;
+ muscles of, 77, 82, 83;
+ feet of, 77, 78;
+ tail of, compared with that of man, 82-84;
+ hair of, compared with that of man, 89-91;
+ teeth of, compared with those of man, 92-94;
+ flattening of tibiæ of, 95, 96.
+
+Aphides, 292.
+
+_Appendix vermiformis_ of man compared with that of orang, 84-86.
+
+_Apteryx_, 68, 69.
+
+_Archæopteryx_, 171-173.
+
+Arctic plants, 209, 210, 440-442.
+
+Argyll, Duke of, on natural selection, 334-362.
+
+Aristotle, his idea of scientific method, 1;
+ on classification, 23, 24.
+
+Arm, distribution of hair on, in man and apes, 89-92.
+
+_Arthropoda_, embryology of, 155.
+
+Artificial selection, analogy of, to natural selection, 295-314;
+ pictorial representations of products of, 298-312.
+
+Artiodactyls, 182-191.
+
+Association, principle of, in æsthetics, 404-407.
+
+Aster, 129-133.
+
+Attraction-spheres, 128, 132, 133.
+
+Australia, fauna of, 204, 205;
+ thriving of exotic species in, 286;
+ portrait of wild dog of, 304.
+
+Azores, 224, 225.
+
+
+B.
+
+Bacon, Lord, on scientific method, 2.
+
+_Balanoglossus_, 147, 148.
+
+_Baptanodon discus_, posterior limb of, 179-181.
+
+Barriers, in relation to geographical distribution, 216-224.
+
+Bats, 56, 224, 226, 240.
+
+Battle, law of, 385, 386.
+
+Baya-bird, 381.
+
+Bear, skeleton of, 174;
+ feet of, 178.
+
+Beautiful, the, sense of, in animals, 380-385;
+ standards of, 380-404;
+ Darwin's explanation of, in organic nature, 379-411;
+ facts of, in inorganic nature in relation to Darwin's theory of, in
+ organic, 404;
+ often determined by natural selection, 406, 407;
+ absent in many plants and animals, 408;
+ in nature often accidental, 409-411;
+ does not exist in organic nature as an end _per se_, 410, 411.
+
+Bees, co-operative instincts of, 268.
+
+Beetles, wingless, 68-70;
+ on oceanic islands, 224, 226, 229, 232.
+
+Bell, Dr., on natural theology, 412.
+
+Bell-bird, 396-398.
+
+_Bembidium_, 233.
+
+Bermudas, 225-227.
+
+Biology, ideas of method in, 1-9.
+
+Birds, ovum of, 124;
+ embryology of, 151-155;
+ paleontology of, 163-165, 172, 173;
+ brain of, 194-197;
+ as carriers of seed, eggs, and small organisms, 217, 218;
+ distribution of, 224-240;
+ æsthetic sense of, 380-385;
+ courtship of, 380-385.
+
+_Birgus latro_, 62-65.
+
+Blood, colour of arterial, 409.
+
+Boar, _see_ Pig.
+
+_Bombus lapidarius_, 331.
+
+Bower-birds, play-houses of, 381-383.
+
+Boyd-Dawkins, on flattening of early human tibiæ, 96.
+
+Brain, palæontology of, 194-197.
+
+British Isles, _see_ Islands.
+
+Broca, 363.
+
+Bronn, 363.
+
+Budding, _see_ Germination.
+
+Burdon-Sanderson, Prof., on electric organ of skate, 366.
+
+Butler, Bishop, on argument from ignorance, 41.
+
+Butterflies, defensive colouring of, 321-329.
+
+
+C.
+
+Cæsalpino, on classification, 24.
+
+Calf, embryology of, 153.
+
+Camel, foot of, 187-191.
+
+Canadian stag, 196, 198, 199.
+
+Canaries, portraits of, 303;
+ first mentioned by Gesner, 312, 313.
+
+Cape de Verde Archipelagoes, fauna of, 228.
+
+_Carcharias melanopterus_, 149.
+
+Carruthers, on evolution, 436-442.
+
+Caterpillars, colours and forms of, 319, 322-326.
+
+Cattle, portraits of, 311.
+
+Causation, natural, 402, 413, 414.
+
+Caves, faunas of dark, 70-72.
+
+Cell, physiological, and properties of the, 104-134.
+
+_Cerura vinula_, 325, 326.
+
+_Cervalces Americanus_, 196, 198, 199.
+
+_Cervus dicrocerus_, _issiodorensis_, _matheronis_, _pardinensis_,
+ _Sedgwickii_, _tetraceros_, 168.
+
+Chalmers, Dr., on natural theology, 412.
+
+Chameleons, 317.
+
+Characters, as adaptive, 273-276, 286-293, 349;
+ as specific, 274-276, 286-295;
+ as congenital and acquired, 274-276.
+
+_Chasmorhynchus niveus_, and _C. tricarunculatus_, 396-398.
+
+_Chelydra serpentina_, anterior limb of, 179-181.
+
+Chick, embryology of, 153.
+
+Chimpanzee, _see_ Apes.
+
+Chlorophyll, 408.
+
+_Chondracanthus cornutus_, 122.
+
+Cirripedes, 430.
+
+Classification, 23-49;
+ of organic nature by Genesis and Leviticus, 23;
+ artificial and natural, 24-26;
+ empirical rules of, 33-40;
+ Darwin on, 35, 36, 39,40;
+ form of, a nexus or tree, 29-32;
+ of organic forms like that of languages, 32;
+ single characters in relation to, 37;
+ aggregates of characters in relation to, 35-37;
+ adaptive and non-adaptive characters in relation to, 34, 35, 38, 39;
+ chains of affinities in relation to, 39-40;
+ biological differs from astronomical, 43.
+
+Cockerell, on vegetable galls, 447, 448.
+
+Colours, of plants and animals in relation to the theory of natural
+ selection, 317-332;
+ in relation to the theory of sexual selection, 391, 392, 394-396,
+ 408-410, 448-450.
+
+Colouring, _see_ Recognition marks, Protective, Seasonal, Warning, and
+ Mimicry.
+
+Congenital characters, _see_ Characters.
+
+Conjugation, of Protozoa, 115-117.
+
+Continuity, principle of, in nature, 15-21.
+
+Contrivance, Darwin's use of the word, 281.
+
+Co-operation, mutual, of species alleged, 445-448.
+
+Co-operative instincts, due to natural selection, 267, 269.
+
+Cope, Professor, his table of geological formations, 163, 164;
+ his table of palæontological development of feet, vertebral column, and
+ brain, 197.
+
+Correlation of growth, 357-362.
+
+_Cossonidæ_, 233.
+
+Courtship, _see_ Sexual Selection.
+
+Crabs, 62-65, 139.
+
+Cuttle-fish, 317.
+
+Cuvier, on method in natural history, 3-4;
+ on monkeys, 429.
+
+Cyst, _see_ Encystation.
+
+
+D.
+
+Darwin, Charles, his influence on ideas of method, 1-9;
+ on classification, 35, 36, 39, 40;
+ on vestigial characters in man, 77, 86, 87, 92;
+ on imperfection of geological record, 165, and Appendix;
+ on means of dispersal, 216, 218;
+ on geographical distribution, 218, 219;
+ on fauna of the Galapagos Archipelago, 227, 228;
+ on natural selection, 252, 253, 255, 256, 286, 375, 376;
+ his use of such words as 'accident,' 'fortuitous,' 'purpose,'
+ 'contrivance,' &c., 281, 334-340;
+ on sexual selection, 379-400.
+
+Darwin, Erasmus, his theory of evolution, 253.
+
+De Blainville, on the theory of descent, 258.
+
+De Candolle, on classification, 34.
+
+Deer, 98, 99, 167-169, 187, 191, 196, 198, 199.
+
+Degeneration, 269, 270, 342.
+
+Delamination, 139.
+
+_Diadema euryta_, 330.
+
+Diaster, 129-133.
+
+Dingo, _see_ Dog.
+
+_Dinornis_, 60, 61.
+
+_Diptera_ mimicking _Hymenoptera_, 329.
+
+Dog, dentition of, 39;
+ Dingo, 304;
+ domesticated varieties of, 305, 307;
+ hairless, 307;
+ skulls of, 307.
+
+Duck, logger-headed, 68.
+
+Dugong, eye of, 75.
+
+
+E.
+
+Eagle, eye of, 75.
+
+Ear, of whales, 65;
+ vestigial features of human, 76, 86-89;
+ of man and apes compared, 88.
+
+Eaton, Rev. A. E., on wingless insects, 70.
+
+_Echinodermata_, 125-127, 138, 155.
+
+Ectoderm, 137-142.
+
+Egg, _see_ Ovum.
+
+Eimer, 363.
+
+_Elaps fulvius_ imitated by non-venomous snakes, 330.
+
+Electric organs, 365-373.
+
+Elephant, foot of, 185, 186;
+ rate of propagation of, 261, 262.
+
+Elk, 196-198, 199.
+
+Embryo, human, _see_ Man.
+
+Embryogeny, _see_ Ontogeny.
+
+Embryology, 98-155.
+
+Embryos, comparative series of, 152, 153.
+
+_Encyclopædia Britannica_, eighth ed., on instinct, 289-291.
+
+Encystation of Protozoa, 115.
+
+Endoderm, 137-142.
+
+Equatorial plate, 129.
+
+_Equus_, _see_ Horse.
+
+_Erythrolamprus venustissimus_, 330.
+
+Evolution, organic, fact of, Section I;
+ Method of, Section II;
+ ideas upon, prior to Darwin, 253-258;
+ divergent, 266, 267.
+
+Ewart, Professor Cossar, on electric organ of skate, 364, 367.
+
+Existence, _see_ Struggle for.
+
+Eye, of octopus, 57, 58, 347-350;
+ absence of, in dark cave animals, 70-72;
+ nictitating membrane of, 74, 75;
+ development of, from cutaneous nerve-ending, 352-354.
+
+
+F.
+
+Feet, 51-59, 66, 77-80, 174-192, 197.
+
+Fertilization of ova, 127, 128;
+ of flowers by insects, 406.
+
+Fish, embryology of, 143-155;
+ palæontology of, 163, 165, 169-171;
+ brain of, 194-197;
+ distribution of, 224-246;
+ flying, 355.
+
+Fission, reproduction by, 106, 107.
+
+Flat fish, 317.
+
+Float, _see_ Swim-bladder.
+
+Flowers, fertilization of, by insects, 406.
+
+Fly, imitating a wasp, 329.
+
+Flying-fish, and squirrels, 355.
+
+_Foraminifera_, 346.
+
+Forbes, H. O., on scapulo-coracoid bones of _Dinornis_, 60.
+
+Fortuitous, Darwin's use of the word, 340.
+
+Fossils, _see_ Palæontology.
+
+Frogs, 317.
+
+
+G.
+
+Galapagos Islands, 227-231, 236, 237.
+
+_Galeus_, eye of, 75.
+
+Galls, vegetable, 293-295, 446-448.
+
+Gastræa, 137-140.
+
+_Gastrophysema_, 138.
+
+Gastrulation, 137, 140.
+
+Gegenbaur, 147, 181.
+
+Gemmation, reproduction by, 106, 107, 110, 111.
+
+Generalization, 5.
+
+Generalized types, 33.
+
+Genesis, classification of organic nature in, 23.
+
+Genial tubercle, 96.
+
+Geographical distribution, 204-248;
+ _see_ Glacial period, Barriers Transport of organisms, Oceanic
+ islands, &c.
+
+Geology, record of imperfect, 156-160, and Appendix;
+ _see_ Palæontology.
+
+Germs, prophetic, 272, 351-362.
+
+Gesner, on classification, 24;
+ on canaries, 313.
+
+Gill-arches, 146, 147, 150, 151.
+
+Gill-slits, 146, 147, 150-153.
+
+Gills, of young salamanders, 102;
+ origin of, in embryo, 144;
+ of fish, 150, 152.
+
+Giraffe, neck of, in relation to Lamarck's theory, 254.
+
+Glacial periods, effects of, on distribution of plants and animals,
+ 209, 210, and Appendix.
+
+Goose, Frizzled, portrait of, 304.
+
+Gorilla, _see_ Apes.
+
+Gray, Professor Asa, 337
+
+Great-toe, in man and apes, 79-81.
+
+Grouse, 317-319
+
+Growth, correlation of, 357, 362.
+
+_Gymnotus_, 365, 367.
+
+
+H.
+
+Häckel, on analogy between species and languages, 32;
+ on reproduction as discontinuous growth, 105, 106;
+ his ideal primitive vertebrate, 143, 144.
+
+Hair, vestigial characters of, in man, 89-92.
+
+Hales, 3.
+
+Haller, 3.
+
+Hamilton, Sir William, 272.
+
+Hands, 51-55, 66, 80-82, 174-192.
+
+Hare, 318, 319.
+
+Hartmann, on flattening of early human tibiæ, 96.
+
+Harvey, on Lord Bacon's writings, 2.
+
+Heart, development of, 154.
+
+Heilprin, on skulls of deer, 198, 199;
+ on fossil shells, 201, 202.
+
+Hen, ovum of, 122.
+
+Heredity, in relation to classification, 28-31;
+ in relation to embryology, 98-102;
+ chromatin-fibres in relation to, 134;
+ in relation to theories of organic evolution, 253-255, 260-264, 377.
+
+Hermit-crabs, 62-65, 288, 289.
+
+_Heteromera_, 233.
+
+Hilgendorf, on shells of _Planorbis_, 201.
+
+_Hipparion_, 191, 192.
+
+Hippopotamus, foot of, 187.
+
+Hog, _see_ Pig.
+
+Homology, 38, 50-65, 176, 177, 347-350, 357-359.
+
+Homopterous insect, imitating leaf-cutting ants, 331, 332.
+
+Hooker, Sir Joseph, on flora of St. Helena, 234.
+
+Horns, 98-100, 167-169.
+
+Horse, eye of, 75;
+ limb-bones of, 176, 177, 186, 188-192;
+ teeth of, 189-191;
+ portraits of domesticated breeds of, 309.
+
+Human, _see_ Man.
+
+_Humerus_, perforations of, in quadrumana and man, 94, 95.
+
+Humming-birds, restricted to the New World, 211.
+
+Hunter, 3;
+ on ear of whale, 65.
+
+Huxley, Prof., on mechanical selection, 283;
+ on age of the earth, 435, 436;
+ on Dr. Whewell, 243.
+
+Hyatt, on shells of _Planorbis_, 201.
+
+_Hydra_, 111, 122.
+
+_Hyrax_, foot of, 185, 186.
+
+
+I.
+
+Ignorance, argument from, 41, 42, 49.
+
+Illative Sense, 6.
+
+Imitative colours, 317-323, 326-332.
+
+Infant, feet of, 78, 79;
+ grasping power of, 81.
+
+Infertility, inter-specific, in relation to natural selection, 374-376.
+
+Insects, wingless, 68-70;
+ in primary formations, 163, Appendix;
+ on oceanic islands, 224-238;
+ in relation to galls, 293-295, 446-448;
+ defensive colouring of, 321-332;
+ fertilizing flowers, 406.
+
+Instincts, always of primary use to species presenting them, 286-293.
+
+Intercrossing, in relation to natural selection, 374-376.
+
+Inutility of specific characters, in relation to natural selection,
+ 374-376.
+
+Islands, oceanic, 224-237;
+ British, 238-241.
+
+
+J.
+
+Japan, hairless dog of, 101.
+
+Jelly-fish, 119, 120.
+
+
+K.
+
+_Kallima_, 323.
+
+Karyokinesis, 112-114, 128-134.
+
+Kepler, 272.
+
+Kerguelen Island, flightless insects of, 70.
+
+Kropotkin, Prince, on co-operative instincts, 269.
+
+
+L.
+
+_Lagopus mutus_, 317, 318.
+
+Lamarck, his method in natural history, 4;
+ his theory of evolution, 253-256.
+
+Lamprey, 148.
+
+Languages, classification of, resembles that of organic forms, 32.
+
+Lankester, E. Ray, on karyokinesis, 129, 130.
+
+Leaf insect, 322.
+
+Le Conte, on geological succession of animal classes, 164, 165;
+ on types of tails, 169-173;
+ on fossil shells of _Planorbis_, 201;
+ his work on the relation of the theory of evolution to religious
+ thought, 412.
+
+_Leptalis_, 328.
+
+_Leuculmis echinus_, 122.
+
+Leviticus, classification of organic nature in, 23.
+
+Life, origin of, 15.
+
+Linnæus, on method in natural history, 3;
+ on classification, 26, 35-40.
+
+Lion, skeleton of, 175;
+ feet of, 178.
+
+Lizard, heart and gill-arches of, 150.
+
+Lloyd Morgan, 273, 449, 450.
+
+Lungs, development of, 154, 354.
+
+Lyell, Sir Charles, on classification, 32;
+ on uniformitarianism, 258;
+ on rational species, 344;
+ on geological record, 420, 435, 439.
+
+
+M.
+
+Madeira, wingless beetles of, 68-70;
+ peculiar beetles of, 226, 227.
+
+Mammals, ovum of, 120-124;
+ embryology of, 151-155;
+ palæontology of, 163, 165, 167, 180-199;
+ limbs of, 174-178, 182-199;
+ brain of, 194-199;
+ of Australia and New Zealand, 204, 205;
+ distribution of, on islands, 224-240.
+
+Mammoth cave, fauna of, 70-72.
+
+Man, nictitating membrane of, 75;
+ vestigial muscles of, 76, 77, 82, 83;
+ tail of, compared with that of apes, 82-84;
+ hair of, compared with that of apes, 89-92;
+ teeth of, compared with those of apes, 92-94;
+ perforation of humerus of, 94, 95;
+ flattening of ancient tibiæ of, 95, 96;
+ embryology of, 119, 153;
+ hand of, 54;
+ arm of, 90, 91;
+ limb-bones of, 176, 177;
+ palæontology of, 163, 165;
+ brain of, 194, 195;
+ Mr. Syme on, 346, 347.
+
+Marsh, on palæontology of the horse, 188-190.
+
+Matthew, Patrick, on natural selection, 257.
+
+Mesoderm, 142.
+
+_Mesohippus_, 189, 192.
+
+Metaphyta, 104, 105.
+
+Metazoa, 104.
+
+Method, ideas of, in natural history, 1-9;
+ of organic evolution, 252-261.
+
+Meyer, Professor Ludwig, on helix of the human ear, 86.
+
+Mimicry, 320-322.
+
+Ministration, mutual, of species alleged, 445, 446.
+
+_Miohippus_, 189.
+
+Mivart, St. George, on eye of octopus, 57, 58, 348, 349;
+ on incipient organs, 362;
+ on mutual ministration of species, 445, 446.
+
+Mollusca, shells of, 19, 199-203;
+ eye of, 57, 58;
+ embryology of, 155;
+ palæontology of, 163, 165.
+
+Monkeys, why all, do not become men, 342-344.
+
+_Monotremata_, 205.
+
+Morgan, _see_ Lloyd Morgan.
+
+Morphology, 50-97.
+
+Mule, portrait of, 309.
+
+Multicellular organisms, 104.
+
+Multiplication, _see_ Reproduction.
+
+
+N.
+
+Nägeli, Prof., 337, 367.
+
+Natural History, ideas of method in, 1-9.
+
+Natural, interpretations as opposed to super-natural, 13-15;
+ causation, 13-15.
+
+Natural selection, 252-378, 401-410;
+ Wells, Matthew, and Whewell on, 257, 258, 443-445;
+ statement of theory of, 256-284;
+ of evidences of, 285-332;
+ of criticisms of, 333-378;
+ relation of theory of, to religious thought, 401-410;
+ preserves types, 264-267;
+ cessation and reversal of, 270, 342;
+ errors touching theory of, 270-284, 332-364;
+ definition of, 275-376;
+ antecedent standing of theory of, 277-284;
+ Prof. Owen on, 333, 334;
+ Duke of Argyll on, 334-362;
+ Mr. Syme on, 340, 341, 345;
+ need not always make for improvement, 341-347;
+ homology and analogy in relation to, 347-350;
+ often determines beauty, 406, 407;
+ in relation to the formation of galls, 293-295. 446-448.
+
+Nature, organic, 17;
+ inorganic, 1, 17, 18.
+
+_Nauplius_, 138.
+
+Neumayr, 19.
+
+New Zealand, fauna of, 68, 204, 205;
+ thriving of exotic species in, 286.
+
+Newman, on the Illative Sense, 6.
+
+Newton, his idea of scientific method, 6.
+
+Nictitating membrane, 74, 75.
+
+Notochord, 146.
+
+Novum Organon, the, on scientific method, 2.
+
+Nucleus, 105, 112-134.
+
+Nucleus-spindle, 129.
+
+Nut-hatch, Syrian, ornamented nests of, 381.
+
+
+O.
+
+Objective methods, 6.
+
+Oceanic islands, _see_ Islands.
+
+Octopus, eye of, 57, 58, 348-350.
+
+_[OE]dicnemus crepitans_, 320.
+
+Ontogeny, as recapitulation of phylogeny, 98-104.
+
+Orang Outang, _see_ Apes.
+
+_Oredon Culbertsoni_, 167.
+
+Origin of Species, the, influence exercised by, on ideas of method, 1-9
+
+_Orohippus_, 189.
+
+Otaria, eye of, 75.
+
+Ovum, 113-142;
+ human, 120-133;
+ amoeboid movements of young, 121-123;
+ segmentation of, 134, 135.
+
+Owen, on ear of whale, 65;
+ on natural selection, 333, 334.
+
+Owl, eye of, 75.
+
+
+P.
+
+Paddle, _see_ Whale, and _Baptanodon discus_.
+
+_Pagurus bernhardus_, 64.
+
+Pain, in relation to the theory of evolution, 417.
+
+Palæontology, 159-203;
+ general testimony of, 156-165;
+ testimony of, in particular cases, 165-203;
+ consideration of objections to theory of evolution founded on grounds
+ of, 156-165, and Appendix.
+
+_Palæotherium_, 190, 191.
+
+Paley, on natural theology, 98, 412.
+
+_Paludina_, successive forms of, 19.
+
+Panama, Isthmus of, 219.
+
+_Panniculus carnosis_, 77.
+
+_Papilio merope_, 330.
+
+Parasites, of animals, devoid of beauty, 408.
+
+Parsimony, law of, 272.
+
+Parthenogenesis, 119.
+
+Partridges, 319.
+
+Peacock, tail of, 378;
+ courtship of, 383.
+
+Peckham, Mr. and Mrs., on courtship of spiders, 388-390.
+
+Perissodactyls, 182-192.
+
+_Petromyzon marinus_, 148.
+
+_Phenacodus primævus_, 184, 185.
+
+Phylogeny, _see_ Ontogeny.
+
+Physiological selection, 376.
+
+Pig, embryology of, 153;
+ feet of, 176, 187;
+ portraits of wild and domesticated, 312.
+
+Pigeons, portraits of, 298, 299;
+ feather-footed, 359.
+
+Pilot fish, 289.
+
+_Planorbis_, transmutations of, 200, 201.
+
+Pleasure and pain, in relation to the theory of evolution, 417.
+
+_Plica semilunaris_, 75.
+
+_Pliohippus_, 189.
+
+Polar bear, skeleton of, 174;
+ feet of, 178.
+
+Polar bodies, 125, 126.
+
+Polar star, 129.
+
+Polyps, 114.
+
+Porpoises, 24, 25, 50.
+
+Poulton, E. B., on warning colours, 325, 326;
+ on mimicry, 331, 332;
+ sexual selection, 400, 401, 449, 450.
+
+Poultry, portraits of, 300-302.
+
+Pronucleus, 126-128.
+
+Prophetic types, 272, 351-362.
+
+_Prophysema primordiale_, 140.
+
+Protective colouring, 317-323.
+
+_Protohippus_, 189.
+
+Protozoa, 104.
+
+Ptarmigan, 317, 318.
+
+_Pterodactyl_, wing of, 56.
+
+Purpose, Darwin's use of the word, 281, 340.
+
+Puss moth, larva of, 325, 326.
+
+Python, 66, 67.
+
+
+Q.
+
+Quadrumana, muscles of, 76, 82, 83;
+ perforations of humeri of, 94, 95;
+ hair on phalanges of, 91.
+
+
+R.
+
+Rabbit, embryology of, 153;
+ multiplication of, in Australia, 286;
+ portraits of wild and domesticated breeds of, 308;
+ protective colouring of, 319, 320.
+
+Radiate form, beauty of, 408, 409.
+
+_Raia radiata_, and _batis_, 367-371.
+
+Rats, species of, restricted to Old and New Worlds, 212;
+ British and Norwegian, 285, 286.
+
+Rattle-snake, tail of, 289.
+
+Recognition marks, 271-273.
+
+Religion, in relation to Darwinism, 401-418.
+
+Reproduction, different methods of, 106-117;
+ essence of sexual, 110;
+ foreshadowing of sexual in unicellular organisms, 115-117.
+
+Reptiles, wing of flying, 56;
+ rudimentary limbs of, 67;
+ nictitating membrane of, 75;
+ branchial arches of, 150;
+ embryology of, 152;
+ palæontology of, 163, 165, 178-180;
+ brain of, 194-197;
+ distribution of, 224-240.
+
+_Rhinoceros_, foot of, 186.
+
+Robinson, Dr L., on grasping power of an infant's hands, 80-82.
+
+Rudimentary organs, 65-97.
+
+Ruminants, palæontology of, 167, 168.
+
+
+S.
+
+Sacrum of man, compared with that of apes, 82-84.
+
+_Sagitta_, 138.
+
+Salamander, young of terrestrial, living in water, 102;
+ embryology of, 152.
+
+Sandwich Islands, 234-237.
+
+Science, method of, 1-9.
+
+Sclater, W. L., on a case of mimicry, 331, 332.
+
+Scorpion in Silurian formation, 163.
+
+Sea, lamprey, 148;
+ destructive agency of the, 423, 424.
+
+Seal, 51, 52, 75.
+
+Seasonal changes of colour, 317-319.
+
+Selection, value, 275;
+ by physical processes, 282, 283, 335. _See also_ Natural selection,
+ Artificial selection, Sexual selection, Physiological selection.
+
+Sentiency, in relation to the theory of evolution, 417.
+
+Sex, difference of, restricted to Metazoa and Metaphyta, 105.
+
+Sexual reproduction, _see_ Reproduction.
+
+Sexual selection, theory of, 277, 378-410;
+ statement and evidences of, 379-391;
+ criticisms of, 391-400;
+ includes law of battle with that of charming, 385, 386;
+ in relation to religious thought, 411-418;
+ Tylor's theory substituted for, by Wallace, 449, 450.
+
+Shark, eye of, 75;
+ man-eating, 149;
+ and pilot-fish, 289.
+
+Sheep, limb-bones of, 176, 177;
+ portraits of, 310.
+
+Shells, of crabs, 62-64;
+ palæontology of mollusks, 199-203;
+ land on oceanic islands, 224-240.
+
+Silliman's Journal, on fauna of the Mammoth Cave, 70.
+
+Skate, electric organ of, 364-373.
+
+Skull, palæontology of, 194-199;
+ of bull-dog compared with that of deer-hound, 307.
+
+Slavonia, Tertiary deposits of, 18, 19.
+
+Species, not eternal, but either created or evolved, 13;
+ named as such through absence of intermediate forms, 18-20;
+ groups of, in classification, 20,
+ and appearing suddenly in geological formations, 427-432, 437-440;
+ origin of, coincide in space and time with pre-existing and allied
+ species, 22;
+ geographical distribution of, 204-248;
+ extinct and living allied on same areas, 213;
+ life of, preserved by natural selection, 264-270;
+ not room for more than one rational, 344;
+ characters of, 274-276, 286-295, 374-376;
+ inter-sterility of allied, 374-376;
+ mutual ministration of alleged, 445, 446.
+
+Specific characters, _see_ Characters.
+
+Speculation, method of, 3-9.
+
+Spencer, Herbert, on reproduction as discontinuous growth, 105, 106;
+ on use-inheritance, 253-256;
+ his failure to conceive the idea of natural selection, 257.
+
+Spermatozoa, 123, 126-128.
+
+Spiders, in primary formations, 163;
+ courtship of, 388, 389.
+
+Sponges, 122, 139, 140.
+
+Spontaneous, Darwin's use of the term, 340.
+
+Spores, 115.
+
+Squirrels, flying, 355.
+
+Sterility, _see_ Infertility.
+
+St. Helena, 231-234, 236-237.
+
+St. Hilaire, 4.
+
+Stick-insect, 322.
+
+Stoat, 318.
+
+_Strombus accipilrinus_, 201.
+
+_Strombus Leidy_, 201.
+
+Struggle for existence, 259-270.
+
+Subjective, methods, 6.
+
+Survival of the fittest, 335. _See also_ Natural selection.
+
+Swim-bladder of fish, 154, 354.
+
+Symbiosis, 269.
+
+Syme, David, on the theory of natural selection, 340, 341.
+
+
+T.
+
+Tail, types of, in fish and birds, 169-173.
+
+Tasmanian wolf, dentition of, 39.
+
+Teeth, of Tasmanian wolf, 39;
+ molar, of man, compared with those of apes, 92-94;
+ palæontology of horses', 189-191.
+
+Temperature, sense of, probable origin of that of sight, 353, 354.
+
+Tennyson, 266.
+
+Tibiæ, flattening of, 95, 96.
+
+Tissue-cells, _see_ Cell.
+
+Toes, 79, 80; _see also_ Feet.
+
+Tomes, C. S., on molar teeth of man and apes, 94.
+
+_Torpedo_, 365, 367.
+
+Tortoise, embryology of, 152, 154.
+
+_Toxopneustes variegatus_, and _T. lividus_, 122.
+
+Transport of organisms, means of, 207, 216-218.
+
+Tribal fitness, as distinguished from individual, 267-269.
+
+Trout, ovum of, 122.
+
+Turtle, eye of, 75.
+
+Tylor, Alfred, on colouration of animals, 448-450.
+
+Type, preserved by natural selection, 264-269;
+ improvement of, by natural selection, 269, 270;
+ prophetic, 272, 351-362.
+
+Types, as simple and generalized, 33.
+
+
+U.
+
+Unicellular organisms, 104.
+
+_Uraster_, 138.
+
+Utility, of specific characters, 274, 275;
+ of incipient characters, 351-363;
+ of electric organs, 365-373.
+
+
+V.
+
+Variation, in relation to natural selection, 263, 335-340, 377.
+
+Verification, 6-9.
+
+Vertebral column, embryology of 145, 146;
+ palæontology of, 192, 193.
+
+Vertebrated animal, ideal primitive, 143, 144;
+ embryology of, 143, 155.
+
+_Vespa vulgaris_, 331.
+
+Vestigial organs, 65-97.
+
+_Volucella inans_, and _V. bombylans_, 329.
+
+
+W.
+
+Wagner, Moritz, on geographical distribution, 216.
+
+Wallace, A. R., on origin of species as coincident in time and space
+ with pre-existing and allied species, 22;
+ on wingless insects, 70;
+ on absence of hair from human back, and function of on arms of
+ orang, 89;
+ on geographical distribution, 207, 231, 232, 233, 243;
+ on natural selection, 256;
+ on recognition marks, 271-273;
+ on alleged deductive consequences of the natural selection theory,
+ 273-276;
+ his theory of warning colours, 323, 324;
+ on sexual selection, 391-400, 450;
+ his principal defect in treating of animal colouration, 449, 450.
+
+Warning colours, 323-326.
+
+Wasp, imitated by a fly, 329.
+
+Water-cress, multiplication of, in New Zealand, 286.
+
+Weevils, on St. Helena, 232.
+
+Weismann, his theory of heredity, 130, 134.
+
+Wells, Dr., on natural selection, 257.
+
+Wetterhan, Prof., on vegetable galls, 448.
+
+Whales, 38, 50, 53, 54, 65, 180.
+
+Whewell, on natural selection, 257, 258, 443-445.
+
+Wings, 54-56, 60, 61, 68-70, 355.
+
+Wolf, Tasmanian, dentition of, 34.
+
+Wood, John, on vestigial muscles in man, 77.
+
+Woodward, on fossil cirripedes, 431.
+
+Woolner, on the human ear, 86.
+
+Worms, embryology of, 155.
+
+Wyman, Prof., on the great toe of human embryo, 79, 80.
+
+
+Z.
+
+_Zona pellucida_, 121.
+
+ +--------------------------------------------------------------+
+ | |
+ | Transcriber’s Notes and Errata |
+ | |
+ | The following words were found in both hyphenated and |
+ | unhyphenated forms in the text. The number of instances is |
+ | given in parentheses after each word. |
+ | |
+ | |deer-hound (2) |deerhound (1) | |
+ | |fresh-water (13) |freshwater (1) | |
+ | |inter-relations (1) |interrelations (1) | |
+ | |re-action (1) |reaction (1) | |
+ | |sea-weed (7) |seaweed (1) | |
+ | |super-natural (2) |supernatural (24) | |
+ | |wood-cut (3) |woodcut (3) | |
+ | |wood-cuts (4) |woodcuts (1) | |
+ | |
+ | There were 9 instances of 'larvae' and 3 instances of |
+ | 'larvæ'. |
+ | |
+ | The following typographical errors were corrected: |
+ | |
+ | |Error |Correction | |
+ | | | | |
+ | |arboresent |arborescent | |
+ | |the |The | |
+ | |dicussion |discussion | |
+ | |
+ | In the index, the page entry for "Lyell, Sir Charles ... on |
+ | geological record" was changed from '420' to '422'. |
+ | |
+ | Also, the page entry for "Natural selection ... definition |
+ | of" was changed from '275-376' to '275-276'. |
+ +--------------------------------------------------------------+
+
+
+
+
+
+End of the Project Gutenberg EBook of Darwin, and After Darwin (Vol. 1 and
+3, of 3), by George John Romanes
+
+*** END OF THIS PROJECT GUTENBERG EBOOK DARWIN ***
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