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diff --git a/22728-8.txt b/22728-8.txt new file mode 100644 index 0000000..277dae4 --- /dev/null +++ b/22728-8.txt @@ -0,0 +1,10549 @@ +The Project Gutenberg EBook of The Foundations of the Origin of Species, by +Charles Darwin + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Foundations of the Origin of Species + Two Essays written in 1842 and 1844 + +Author: Charles Darwin + +Editor: Francis Darwin + +Release Date: September 22, 2007 [EBook #22728] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK FOUNDATIONS ORIGIN OF SPECIES *** + + + + +Produced by Geetu Melwani, David Clarke, LN Yaddanapudi +and the Online Distributed Proofreading Team at +http://www.pgdp.net (This file was produced from images +generously made available by The Internet Archive/Canadian +Libraries) + + + + + + + + + +THE FOUNDATIONS OF THE ORIGIN OF SPECIES + +CAMBRIDGE UNIVERSITY PRESS + +London: FETTER LANE, E.C. + +C. F. CLAY, MANAGER + +{Illustration} + +Edinburgh: 100, PRINCES STREET + +ALSO + +London: H. K. LEWIS, 136, GOWER STREET, W.C. + +Berlin: A. ASHER AND CO. + +Leipzig: F. A. BROCKHAUS + +New York: G. P. PUTNAM'S SONS + +Bombay and Calcutta: MACMILLAN AND Co., LTD. + +_All rights reserved_ + +{Illustration: Charles Darwin from a photograph by Maull & Fox in 1854} + + + + +THE FOUNDATIONS OF THE ORIGIN OF SPECIES + +TWO ESSAYS WRITTEN IN 1842 AND 1844 + +by + +CHARLES DARWIN + + +Edited by his son + +FRANCIS DARWIN + +Honorary Fellow of Christ's College + + +Cambridge: + +at the University Press + +1909 + + + Astronomers might formerly have said that God ordered each planet + to move in its particular destiny. In same manner God orders each + animal created with certain form in certain country. But how much + more simple and sublime power,--let attraction act according to + certain law, such are inevitable consequences,--let animal(s) be + created, then by the fixed laws of generation, such will be their + successors. + + From DARWIN'S _Note Book_, 1837, p. 101. + + + TO THE MASTER AND FELLOWS + OF CHRIST'S COLLEGE, THIS + BOOK IS DEDICATED BY THE + EDITOR IN TOKEN OF RESPECT + AND GRATITUDE + + + + +CONTENTS + + +ESSAY OF 1842 + PAGES + +INTRODUCTION xi + + +PART I + + § i. On variation under domestication, and on the principles + of selection 1 + + § ii. On variation in a state of nature and on the natural + means of selection 4 + + § iii. On variation in instincts and other mental attributes 17 + + +PART II + + §§ iv. and v. On the evidence from Geology. (The reasons for + combining the two sections are given in the Introduction) 22 + + § vi. Geographical distribution 29 + + § vii. Affinities and classification 35 + + § viii. Unity of type in the great classes 38 + + § ix. Abortive organs 45 + + § x. Recapitulation and conclusion 48 + + +ESSAY OF 1844 + + +PART I + + +CHAPTER I 57-80 + +ON THE VARIATION OF ORGANIC BEINGS UNDER DOMESTICATION; +AND ON THE PRINCIPLES OF SELECTION. + + Variation + On the hereditary tendency + Causes of Variation + On Selection + Crossing Breeds + Whether our domestic races have descended from one or more wild stocks + Limits to Variation in degree and kind + In what consists Domestication--Summary + + +CHAPTER II 81-111 + +ON THE VARIATION OF ORGANIC BEINGS IN A WILD STATE; +ON THE NATURAL MEANS OF SELECTION; AND ON THE +COMPARISON OF DOMESTIC RACES AND TRUE SPECIES. + + Variation + Natural means of Selection + Differences between "Races" and "Species":-first, in their trueness + or variability + Difference between "Races" and "Species" in fertility when crossed + Causes of Sterility in Hybrids + Infertility from causes distinct from hybridisation + Points of Resemblance between "Races" and "Species" + External characters of Hybrids and Mongrels + Summary + Limits of Variation + + +CHAPTER III 112-132 + +ON THE VARIATION OF INSTINCTS AND OTHER MENTAL +ATTRIBUTES UNDER DOMESTICATION AND IN A STATE OF +NATURE; ON THE DIFFICULTIES IN THIS SUBJECT; AND +ON ANALOGOUS DIFFICULTIES WITH RESPECT TO CORPOREAL +STRUCTURES. + + Variation of mental attributes under domestication + Hereditary habits compared with instincts + Variation in the mental attributes of wild animals + Principles of Selection applicable to instincts + Difficulties in the acquirement of complex instincts by Selection + Difficulties in the acquirement by Selection of complex corporeal + structures + + +PART II + +ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW +THAT SPECIES ARE NATURALLY FORMED RACES, DESCENDED +FROM COMMON STOCKS. + + +CHAPTER IV 133-143 + +ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE +THEORY OF COMMON DESCENT; AND ON THEIR ABSENCE +IN A FOSSIL STATE + + +CHAPTER V 144-150 + +GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES. + + Gradual appearance of species + Extinction of species + + +CHAPTER VI + +ON THE GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS +IN PAST AND PRESENT TIMES. + + +SECTION FIRST 151-174 + + Distribution of the inhabitants in the different continents + Relation of range in genera and species + Distribution of the inhabitants in the same continent + Insular Faunas + Alpine Floras + Cause of the similarity in the floras of some distant mountains + Whether the same species has been created more than once + On the number of species, and of the classes to which they belong + in different regions + + +SECOND SECTION 174-182 + + Geographical distribution of extinct organisms + Changes in geographical distribution + Summary on the distribution of living and extinct organic beings + + +SECTION THIRD 183-197 + + An attempt to explain the foregoing laws of geographical + distribution, on the theory of allied species having a + common descent + Improbability of finding fossil forms intermediate between + existing species + + +CHAPTER VII 198-213 + +ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION +OF ORGANIC BEINGS. + + Gradual appearance and disappearance of groups + What is the Natural System? + On the kind of relation between distinct groups + Classification of Races or Varieties + Classification of Races and Species similar + Origin of genera and families + + +CHAPTER VIII 214-230 + +UNITY OF TYPE IN THE GREAT CLASSES; AND +MORPHOLOGICAL STRUCTURES. + + Unity of Type + Morphology + Embryology + Attempt to explain the facts of embryology + On the graduated complexity in each great class + Modification by selection of the forms of immature animals + Importance of embryology in classification + Order in time in which the great classes have first appeared + + +CHAPTER IX 231-238 + +ABORTIVE OR RUDIMENTARY ORGANS. + + The abortive organs of Naturalists + The abortive organs of Physiologists + Abortion from gradual disuse + + +CHAPTER X 239-255 + +RECAPITULATION AND CONCLUSION. + + Recapitulation + Why do we wish to reject the Theory of Common Descent? + Conclusion + + +INDEX 257 + + Portrait _frontispiece_ + Facsimile _to face_ p. 50 + + + + +INTRODUCTION + + +We know from the contents of Charles Darwin's Note Book of 1837 that he +was at that time a convinced Evolutionist{1}. Nor can there be any doubt +that, when he started on board the _Beagle_, such opinions as he had +were on the side of immutability. When therefore did the current of his +thoughts begin to set in the direction of Evolution? + + {1} See the extracts in _Life and Letters of Charles Darwin_, ii. + p. 5. + +We have first to consider the factors that made for such a change. On +his departure in 1831, Henslow gave him vol. I. of Lyell's _Principles_, +then just published, with the warning that he was not to believe what he +read{2}. But believe he did, and it is certain (as Huxley has forcibly +pointed out{3}) that the doctrine of uniformitarianism when applied to +Biology leads of necessity to Evolution. If the extermination of a +species is no more catastrophic than the natural death of an individual, +why should the birth of a species be any more miraculous than the birth +of an individual? It is quite clear that this thought was vividly +present to Darwin when he was writing out his early thoughts in the 1837 +Note Book{4}:-- + +"Propagation explains why modern animals same type as extinct, which is +law almost proved. They die, without they change, like golden pippins; +it is a _generation of species_ like generation _of individuals_." + +"If _species_ generate other _species_ their race is not utterly cut +off." + + {2} The second volume,--especially important in regard to + Evolution,--reached him in the autumn of 1832, as Prof. Judd has + pointed out in his most interesting paper in _Darwin and Modern + Science_. Cambridge, 1909. + + {3} Obituary Notice of C. Darwin, _Proc. R. Soc._ vol. 44. + Reprinted in Huxley's _Collected Essays_. See also _Life and + Letters of C. Darwin_, ii. p. 179. + + {4} See the extracts in the _Life and Letters_, ii. p. 5. + +These quotations show that he was struggling to see in the origin of +species a process just as scientifically comprehensible as the birth of +individuals. They show, I think, that he recognised the two things not +merely as similar but as identical. + +It is impossible to know how soon the ferment of uniformitarianism began +to work, but it is fair to suspect that in 1832 he had already begun to +see that mutability was the logical conclusion of Lyell's doctrine, +though this was not acknowledged by Lyell himself. + +There were however other factors of change. In his Autobiography{5} he +wrote:--"During the voyage of the _Beagle_ I had been deeply impressed +by discovering in the Pampean formation great fossil animals covered +with armour like that on the existing armadillos; secondly, by the +manner in which closely allied animals replace one another in proceeding +southward over the Continent; and thirdly, by the South American +character of most of the productions of the Galapagos archipelago, and +more especially by the manner in which they differ slightly on each +island of the group; none of the islands appearing to be very ancient in +a geological sense. It was evident that such facts as these, as well as +many others, could only be explained on the supposition that species +gradually become modified; and the subject haunted me." + + {5} _Life and Letters_, i. p. 82. + +Again we have to ask: how soon did any of these influences produce an +effect on Darwin's mind? Different answers have been attempted. +Huxley{6} held that these facts could not have produced their essential +effect until the voyage had come to an end, and the "relations of the +existing with the extinct species and of the species of the different +geographical areas with one another were determined with some +exactness." He does not therefore allow that any appreciable advance +towards evolution was made during the actual voyage of the _Beagle_. + + {6} _Obituary Notice_, _loc. cit._ + +Professor Judd{7} takes a very different view. He holds that November +1832 may be given with some confidence as the "date at which Darwin +commenced that long series of observations and reasonings which +eventually culminated in the preparation of the _Origin of Species_." + + {7} _Darwin and Modern Science._ + +Though I think these words suggest a more direct and continuous march +than really existed between fossil-collecting in 1832 and writing the +_Origin of Species_ in 1859, yet I hold that it was during the voyage +that Darwin's mind began to be turned in the direction of Evolution, and +I am therefore in essential agreement with Prof. Judd, although I lay +more stress than he does on the latter part of the voyage. + +Let us for a moment confine our attention to the passage, above quoted, +from the Autobiography and to what is said in the Introduction to the +_Origin_, Ed. i., viz. "When on board H.M.S. 'Beagle,' as naturalist, I +was much struck with certain facts in the distribution of the +inhabitants of South America, and in the geological relations of the +present to the past inhabitants of that continent." These words, +occurring where they do, can only mean one thing,--namely that the facts +suggested an evolutionary interpretation. And this being so it must be +true that his thoughts _began to flow in the direction of Descent_ at +this early date. + +I am inclined to think that the "new light which was rising in his +mind{8}" had not yet attained any effective degree of steadiness or +brightness. I think so because in his Pocket Book under the date 1837 he +wrote, "In July opened first note-book on 'transmutation of species.' +Had been greatly struck _from about month of previous March_{9} on +character of South American fossils, and species on Galapagos +Archipelago. These facts origin (_especially latter_), of all my views." +But he did not visit the Galapagos till 1835 and I therefore find it +hard to believe that his evolutionary views attained any strength or +permanence until at any rate quite late in the voyage. The Galapagos +facts are strongly against Huxley's view, for Darwin's attention was +"thoroughly aroused{10}" by comparing the birds shot by himself and by +others on board. The case must have struck him at once,--without waiting +for accurate determinations,--as a microcosm of evolution. + + {8} Huxley, _Obituary_, p. xi. + + {9} In this citation the italics are mine. + + {10} _Journal of Researches_, Ed. 1860, p. 394. + +It is also to be noted, in regard to the remains of extinct animals, +that, in the above quotation from his Pocket Book, he speaks of March +1837 as the time at which he began to be "greatly struck on character of +South American fossils," which suggests at least that the impression +made in 1832 required reinforcement before a really powerful effect was +produced. + +We may therefore conclude, I think, that the evolutionary current in my +father's thoughts had continued to increase in force from 1832 onwards, +being especially reinforced at the Galapagos in 1835 and again in 1837 +when he was overhauling the results, mental and material, of his +travels. And that when the above record in the Pocket Book was made he +unconsciously minimised the earlier beginnings of his theorisings, and +laid more stress on the recent thoughts which were naturally more vivid +to him. In his letter{11} to Otto Zacharias (1877) he wrote, "On my +return home in the autumn of 1836, I immediately began to prepare my +Journal for publication, and then saw how many facts indicated the +common descent of species." This again is evidence in favour of the view +that the later growths of his theory were the essentially important +parts of its development. + + {11} F. Darwin's _Life of Charles Darwin_ (in one volume), 1892, p. + 166. + +In the same letter to Zacharias he says, "When I was on board the +_Beagle_ I believed in the permanence of species, but as far as I can +remember vague doubts occasionally flitted across my mind." Unless Prof. +Judd and I are altogether wrong in believing that late or early in the +voyage (it matters little which) a definite approach was made to the +evolutionary standpoint, we must suppose that in 40 years such advance +had shrunk in his recollection to the dimensions of "vague doubts." The +letter to Zacharias shows I think some forgetting of the past where the +author says, "But I did not become convinced that species were mutable +until, I think, two or three years had elapsed." It is impossible to +reconcile this with the contents of the evolutionary Note Book of 1837. +I have no doubt that in his retrospect he felt that he had not been +"convinced that species were mutable" until he had gained a clear +conception of the mechanism of natural selection, _i.e._ in 1838-9. + +But even on this last date there is some room, not for doubt, but for +surprise. The passage in the Autobiography{12} is quite clear, namely +that in October 1838 he read Malthus's _Essay on the principle of +Population_ and "being well prepared to appreciate the struggle for +existence ..., it at once struck me that under these circumstances +favourable variations would tend to be preserved, and unfavourable ones +to be destroyed. The result of this would be the formation of new +species. Here then I had at last got a theory by which to work." + + {12} _Life and Letters_, i. p. 83. + +It is surprising that Malthus should have been needed to give him the +clue, when in the Note Book of 1837 there should occur--however +obscurely expressed--the following forecast{13} of the importance of the +survival of the fittest. "With respect to extinction, we can easily see +that a variety of the ostrich (Petise{14}), may not be well adapted, and +thus perish out; or on the other hand, like Orpheus{15}, being +favourable, many might be produced. This requires the principle that the +permanent variations produced by confined breeding and changing +circumstances are continued and produce<d> according to the adaptation of +such circumstances, and therefore that death of species is a consequence +(contrary to what would appear in America) of non-adaptation of +circumstances." + + {13} _Life and Letters_, ii. p. 8. + + {14} Avestruz Petise, _i.e. Rhea Darwini_. + + {15} A bird. + +I can hardly doubt, that with his knowledge of the interdependence of +organisms and the tyranny of conditions, his experience would have +crystallized out into "a theory by which to work" even without the aid +of Malthus. + +In my father's Autobiography{16} he writes, "In June 1842 I first +allowed myself the satisfaction of writing a very brief abstract of my +theory in pencil in 35 pages; and this was enlarged during the summer of +1844 into one of 230 pages{17}, which I had fairly copied out and still +possess." These two Essays, of 1842 and 1844, are now printed under the +title _The Foundations of the Origin of Species_. + + {16} _Life and Letters_, i. p. 84. + + {17} It contains as a fact 231 pp. It is a strongly bound folio, + interleaved with blank pages, as though for notes and additions. + His own MS. from which it was copied contains 189 pp. + +It will be noted that in the above passage he does not mention the MS. +of 1842 as being in existence, and when I was at work on _Life and +Letters_ I had not seen it. It only came to light after my mother's +death in 1896 when the house at Down was vacated. The MS. was hidden in +a cupboard under the stairs which was not used for papers of any value, +but rather as an overflow for matter which he did not wish to destroy. + +The statement in the Autobiography that the MS. was written in 1842 +agrees with an entry in my fathers Diary:-- + +"1842. May 18th went to Maer. June 15th to Shrewsbury, and on 18th to +Capel Curig.... During my stay at Maer and Shrewsbury (five years after +commencement) wrote pencil sketch of my species theory." Again in a +letter to Lyell (June 18, 1858) he speaks of his "MS. sketch written out +in 1842{18}." In the _Origin of Species_, Ed. i. p. 1, he speaks of +beginning his speculations in 1837 and of allowing himself to draw up +some "short notes" after "five years' work," _i.e._ in 1842. So far +there seems no doubt as to 1842 being the date of the first sketch; but +there is evidence in favour of an earlier date{19}. Thus across the +Table of Contents of the bound copy of the 1844 MS. is written in my +father's hand "This was sketched in 1839." Again in a letter to Mr +Wallace{20} (Jan. 25, 1859) he speaks of his own contributions to the +Linnean paper{21} of July 1, 1858, as "written in 1839, now just twenty +years ago." This statement as it stands is undoubtedly incorrect, since +the extracts are from the MS. of 1844, about the date of which no doubt +exists; but even if it could be supposed to refer to the 1842 Essay, it +must, I think, be rejected. I can only account for his mistake by the +supposition that my father had in mind the date (1839) at which the +framework of his theory was laid down. It is worth noting that in his +Autobiography (p. 88) he speaks of the time "about 1839, when the theory +was clearly conceived." However this may be there can be no doubt that +1842 is the correct date. Since the publication of _Life and Letters_ I +have gained fresh evidence on this head. A small packet containing 13 +pp. of MS. came to light in 1896. On the outside is written "First +Pencil Sketch of Species Theory. Written at Maer and Shrewsbury during +May and June 1842." It is not however written in pencil, and it consists +of a single chapter on _The Principles of Variation in Domestic +Organisms_. A single unnumbered page is written in pencil, and is headed +"Maer, May 1842, useless"; it also bears the words "This page was +thought of as introduction." It consists of the briefest sketch of the +geological evidence for evolution, together with words intended as +headings for discussion,--such as "Affinity,--unity of type,--foetal +state,--abortive organs." + + {18} _Life and Letters_, ii. p. 116. + + {19} _Life and Letters_, ii. p. 10. + + {20} _Life and Letters_, ii. p. 146. + + {21} _J. Linn. Soc. Zool._ iii. p. 45. + +The back of this "useless" page is of some interest, although it does +not bear on the question of date,--the matter immediately before us. + +It seems to be an outline of the Essay or sketch of 1842, consisting of +the titles of the three chapters of which it was to have consisted. + +"I. The Principles of Var. in domestic organisms. + +"II. The possible and probable application of these same principles to +wild animals and consequently the possible and probable production of +wild races, analogous to the domestic ones of plants and animals. + +"III. The reasons for and against believing that such races have really +been produced, forming what are called species." + +It will be seen that Chapter III as originally designed corresponds to +Part II (p. 22) of the Essay of 1842, which is (p. 7) defined by the +author as discussing "whether the characters and relations of animated +things are such as favour the idea of wild species being races descended +from a common stock." Again at p. 23 the author asks "What then is the +evidence in favour of it (the theory of descent) and what the evidence +against it." The generalised section of his Essay having been originally +Chapter III{22} accounts for the curious error which occurs in pp. 18 +and 22 where the second Part of the Essay is called Part III. + + {22} It is evident that _Parts_ and _Chapters_ were to some extent + interchangeable in the author's mind, for p. 1 (of the MS. we have + been discussing) is headed in ink Chapter I, and afterwards altered + in pencil to Part I. + +The division of the Essay into two parts is maintained in the enlarged +Essay of 1844, in which he writes: "The Second Part of this work is +devoted to the general consideration of how far the general economy of +nature justifies or opposes the belief that related species and genera +are descended from common stocks." The _Origin of Species_ however is +not so divided. + +We may now return to the question of the date of the Essay. I have found +additional evidence in favour of 1842 in a sentence written on the back +of the Table of Contents of the 1844 MS.--not the copied version but the +original in my father's writing: "This was written and enlarged from a +sketch in 37 pages{23} in Pencil (the latter written in summer of 1842 +at Maer and Shrewsbury) in beginning of 1844, and finished it <_sic_> in +July; and finally corrected the copy by Mr Fletcher in the last week in +September." On the whole it is impossible to doubt that 1842 is the date +of the earlier of the two Essays. + + {23} On p. 23 of the MS. of the _Foundations_ is a reference to the + "back of p. 21 bis": this suggests that additional pages had been + interpolated in the MS. and that it may once have had 37 in place + of 35 pp. + +The sketch of 1842 is written on bad paper with a soft pencil, and is in +many parts extremely difficult to read, many of the words ending in mere +scrawls and being illegible without context. It is evidently written +rapidly, and is in his most elliptical style, the articles being +frequently omitted, and the sentences being loosely composed and often +illogical in structure. There is much erasure and correction, apparently +made at the moment of writing, and the MS. does not give the impression +of having been re-read with any care. The whole is more like hasty +memoranda of what was clear to himself, than material for the convincing +of others. + +Many of the pages are covered with writing on the back, an instance of +his parsimony in the matter of paper{24}. This matter consists partly of +passages marked for insertion in the text, and these can generally +(though by no means always) be placed where he intended. But he also +used the back of one page for a preliminary sketch to be rewritten on a +clean sheet. These parts of the work have been printed as footnotes, so +as to allow what was written on the front of the pages to form a +continuous text. A certain amount of repetition is unavoidable, but much +of what is written on the backs of the pages is of too much interest to +be omitted. Some of the matter here given in footnotes may, moreover, +have been intended as the final text and not as the preliminary sketch. + + {24} _Life and Letters_, i. p. 153. + +When a word cannot be deciphered, it is replaced by:--<illegible>, the +angular brackets being, as already explained, a symbol for an insertion +by the editor. More commonly, however, the context makes the +interpretation of a word reasonably sure although the word is not +strictly legible. Such words are followed by an inserted mark of +interrogation <?>. Lastly, words inserted by the editor, of which the +appropriateness is doubtful, are printed thus <variation?>. + +Two kinds of erasure occur in the MS. of 1842. One by vertical lines +which seem to have been made when the 35 pp. MS. was being expanded into +that of 1844, and merely imply that such a page is done with: and +secondly the ordinary erasures by horizontal lines. I have not been +quite consistent in regard to these: I began with the intention of +printing (in square brackets) all such erasures. But I ultimately found +that the confusion introduced into the already obscure sentences was +greater than any possible gain; and many such erasures are altogether +omitted. In the same way I have occasionally omitted hopelessly obscure +and incomprehensible fragments, which if printed would only have +burthened the text with a string of <illegible>s and queried words. Nor have I +printed the whole of what is written on the backs of the pages, where it +seemed to me that nothing but unnecessary repetition would have been the +result. + +In the matter of punctuation I have given myself a free hand. I may no +doubt have misinterpreted the author's meaning in so doing, but without +such punctuation, the number of repellantly crabbed sentences would have +been even greater than at present. In dealing with the Essay of 1844, I +have corrected some obvious slips without indicating such alterations, +because the MS. being legible, there is no danger of changing the +author's meaning. + +The sections into which the Essay of 1842 is divided are in the original +merely indicated by a gap in the MS. or by a line drawn across the page. +No titles are given except in the case of § VIII.; and § II. is the only +section which has a number in the original. I might equally well have +made sections of what are now subsections, _e.g. Natural Selection_ p. +7, or _Extermination_ p. 28. But since the present sketch is the germ of +the Essay of 1844, it seemed best to preserve the identity between the +two works, by using such of the author's divisions as correspond to the +chapters of the enlarged version of 1844. The geological discussion with +which Part II begins corresponds to two chapters (IV and V) of the 1844 +Essay. I have therefore described it as §§ IV. and V., although I cannot +make sure of its having originally consisted of two sections. With this +exception the ten sections of the Essay of 1842 correspond to the ten +chapters of that of 1844. + +The _Origin of Species_ differs from the sketch of 1842 in not being +divided into two parts. But the two volumes resemble each other in +general structure. Both begin with a statement of what may be called the +mechanism of evolution,--variation and selection: in both the argument +proceeds from the study of domestic organisms to that of animals and +plants in a state of nature. This is followed in both by a discussion of +the _Difficulties on Theory_ and this by a section _Instinct_ which in +both cases is treated as a special case of difficulty. + +If I had to divide the _Origin_ (first edition) into two parts without +any knowledge of earlier MS., I should, I think, make Part II begin with +Ch. VI, _Difficulties on Theory_. A possible reason why this part of the +argument is given in Part I of the Essay of 1842 may be found in the +Essay of 1844, where it is clear that the chapter on instinct is placed +in Part I because the author thought it of importance to show that +heredity and variation occur in mental attributes. The whole question is +perhaps an instance of the sort of difficulty which made the author give +up the division of his argument into two Parts when he wrote the +_Origin_. As matters stand §§ IV. and V. of the 1842 Essay correspond to +the geological chapters, IX and X, in the _Origin_. From this point +onwards the material is grouped in the same order in both works: +geographical distribution; affinities and classification; unity of type +and morphology; abortive or rudimentary organs; recapitulation and +conclusion. + +In enlarging the Essay of 1842 into that of 1844, the author retained +the sections of the sketch as chapters in the completer presentment. It +follows that what has been said of the relation of the earlier Essay to +the _Origin_ is generally true of the 1844 Essay. In the latter, +however, the geological discussion is, clearly instead of obscurely, +divided into two chapters, which correspond roughly with Chapters IX and +X of the _Origin_. But part of the contents of Chapter X (_Origin_) +occurs in Chapter VI (1844) on Geographical Distribution. The treatment +of distribution is particularly full and interesting in the 1844 Essay, +but the arrangement of the material, especially the introduction of § +III. p. 183, leads to some repetition which is avoided in the _Origin_. +It should be noted that Hybridism, which has a separate chapter (VIII) +in the _Origin_, is treated in Chapter II of the Essay. Finally that +Chapter XIII (_Origin_) corresponds to Chapters VII, VIII and IX of the +work of 1844. + +The fact that in 1842, seventeen years before the publication of the +_Origin_, my father should have been able to write out so full an +outline of his future work, is very remarkable. In his Autobiography{25} +he writes of the 1844 Essay, "But at that time I overlooked one problem +of great importance.... This problem is the tendency in organic beings +descended from the same stock to diverge in character as they become +modified." The absence of the principle of divergence is of course also +a characteristic of the sketch of 1842. But at p. 37, the author is not +far from this point of view. The passage referred to is: "If any +species, _A_, in changing gets an advantage and that advantage ... is +inherited, _A_ will be the progenitor of several genera or even families +in the hard struggle of nature. _A_ will go on beating out other forms, +it might come that _A_ would people <the> earth,--we may now not have one +descendant on our globe of the one or several original creations{26}." +But if the descendants of _A_ have peopled the earth by beating out +other forms, they must have diverged in occupying the innumerable +diverse modes of life from which they expelled their predecessors. What +I wrote{27} on this subject in 1887 is I think true: "Descent with +modification implies divergence, and we become so habituated to a belief +in descent, and therefore in divergence, that we do not notice the +absence of proof that divergence is in itself an advantage." + + {25} _Life and Letters_, i. p. 84. + + {26} In the footnotes to the Essay of 1844 attention is called to + similar passages. + + {27} _Life and Letters_, ii. p. 15. + +The fact that there is no set discussion on the principle of divergence +in the 1844 Essay, makes it clear why the joint paper read before the +Linnean Society on July 1, 1858, included a letter{28} to Asa Gray, as +well as an extract{29} from the Essay of 1844. It is clearly because the +letter to Gray includes a discussion on divergence, and was thus, +probably, the only document, including this subject, which could be +appropriately made use of. It shows once more how great was the +importance attached by its author to the principle of divergence. + + {28} The passage is given in the _Life and Letters_, ii. p. 124. + + {29} The extract consists of the section on _Natural Means of + Selection_, p. 87. + +I have spoken of the hurried and condensed manner in which the sketch of +1842 is written; the style of the later Essay (1844) is more finished. +It has, however, the air of an uncorrected MS. rather than of a book +which has gone through the ordeal of proof sheets. It has not all the +force and conciseness of the _Origin_, but it has a certain freshness +which gives it a character of its own. It must be remembered that the +_Origin_ was an abstract or condensation of a much bigger book, whereas +the Essay of 1844 was an expansion of the sketch of 1842. It is not +therefore surprising that in the _Origin_ there is occasionally evident +a chafing against the author's self-imposed limitation. Whereas in the +1844 Essay there is an air of freedom, as if the author were letting +himself go, rather than applying the curb. This quality of freshness and +the fact that some questions were more fully discussed in 1844 than in +1859, makes the earlier work good reading even to those who are familiar +with the _Origin_. + +The writing of this Essay "during the summer of 1844," as stated in the +Autobiography{30}, and "from memory," as Darwin says elsewhere{31}, was +a remarkable achievement, and possibly renders more conceivable the +still greater feat of the writing of the _Origin_ between July 1858 and +September 1859. + + {30} _Life and Letters_, i. p. 84. + + {31} _Life and Letters_, ii. p. 18. + +It is an interesting subject for speculation: what influence on the +world the Essay of 1844 would have exercised, had it been published in +place of the Origin. The author evidently thought of its publication in +its present state as an undesirable expedient, as appears clearly from +the following extracts from the _Life and Letters_, vol. ii. pp. +16--18: + +_C. Darwin to Mrs Darwin._ + +DOWN, _July 5, 1844_. + +"... I have just finished my sketch of my species theory. If, as I +believe, my theory in time be accepted even by one competent judge, it +will be a considerable step in science. + +"I therefore write this in case of my sudden death, as my most solemn +and last request, which I am sure you will consider the same as if +legally entered in my will, that you will devote £400 to its +publication, and further will yourself, or through Hensleigh{32}, take +trouble in promoting it. I wish that my sketch be given to some +competent person, with this sum to induce him to take trouble in its +improvement and enlargement. I give to him all my books on Natural +History, which are either scored or have references at the end to the +pages, begging him carefully to look over and consider such passages as +actually bearing, or by possibility bearing, on this subject. I wish you +to make a list of all such books as some temptation to an editor. I also +request that you will hand over <to> him all those scraps roughly divided +into eight or ten brown paper portfolios. The scraps, with copied +quotations from various works, are those which may aid my editor. I also +request that you, or some amanuensis, will aid in deciphering any of the +scraps which the editor may think possibly of use. I leave to the +editor's judgment whether to interpolate these facts in the text, or as +notes, or under appendices. As the looking over the references and +scraps will be a long labour, and as the _correcting_ and enlarging and +altering my sketch will also take considerable time, I leave this sum of +£400 as some remuneration, and any profits from the work. I consider +that for this the editor is bound to get the sketch published either at +a publisher's or his own risk. Many of the scraps in the portfolios +contain mere rude suggestions and early views, now useless, and many of +the facts will probably turn out as having no bearing on my theory. + + {32} Mrs Darwin's brother. + +"With respect to editors, Mr Lyell would be the best if he would +undertake it; I believe he would find the work pleasant, and he would +learn some facts new to him. As the editor must be a geologist as well +as a naturalist, the next best editor would be Professor Forbes of +London. The next best (and quite best in many respects) would be +Professor Henslow. Dr Hooker would be _very_ good. The next, Mr +Strickland{33}. If none of these would undertake it, I would request you +to consult with Mr Lyell, or some other capable man, for some editor, a +geologist and naturalist. Should one other hundred pounds make the +difference of procuring a good editor, I request earnestly that you will +raise £500. + + {33} After Mr Strickland's name comes the following sentence, which + has been erased, but remains legible. "Professor Owen would be very + good; but I presume he would not undertake such a work." + +"My remaining collections in Natural History may be given to any one or +any museum where <they> would be accepted...." + +<The following note seems to have formed part of the original letter, +but may have been of later date:> + +"Lyell, especially with the aid of Hooker (and of any good zoological +aid), would be best of all. Without an editor will pledge himself to +give up time to it, it would be of no use paying such a sum. + +"If there should be any difficulty in getting an editor who would go +thoroughly into the subject, and think of the bearing of the passages +marked in the books and copied out of scraps of paper, then let my +sketch be published as it is, stating that it was done several years +ago{34}, and from memory without consulting any works, and with no +intention of publication in its present form." + + {34} The words "several years ago, and" seem to have been added at + a later date. + +The idea that the sketch of 1844 might remain, in the event of his +death, as the only record of his work, seems to have been long in his +mind, for in August, 1854, when he had finished with the Cirripedes, and +was thinking of beginning his "species work," he added on the back of +the above letter, "Hooker by far best man to edit my species volume. +August 1854." + +I have called attention in footnotes to many points in which the +_Origin_ agrees with the _Foundations_. One of the most interesting is +the final sentence, practically the same in the Essays of 1842 and 1844, +and almost identical with the concluding words of the _Origin_. I have +elsewhere pointed out{35} that the ancestry of this eloquent passage may +be traced one stage further back,--to the Note Book of 1837. I have +given this sentence as an appropriate motto for the _Foundations_ in its +character of a study of general laws. It will be remembered that a +corresponding motto from Whewell's _Bridgewater Treatise_ is printed +opposite the title-page of the _Origin of Species_. + + {35} _Life and Letters_, ii. p. 9. + +Mr Huxley who, about the year 1887, read the Essay of 1844, remarked +that "much more weight is attached to the influence of external +conditions in producing variation and to the inheritance of acquired +habits than in the _Origin_." In the _Foundations_ the effect of +conditions is frequently mentioned, and Darwin seems to have had +constantly in mind the need of referring each variation to a cause. But +I gain the impression that the slighter prominence given to this view in +the _Origin_ was not due to change of opinion, but rather because he had +gradually come to take this view for granted; so that in the scheme of +that book, it was overshadowed by considerations which then seemed to +him more pressing. With regard to the inheritance of acquired characters +I am not inclined to agree with Huxley. It is certain that the +_Foundations_ contains strong recognition of the importance of germinal +variation, that is of external conditions acting indirectly through the +"reproductive functions." He evidently considered this as more important +than the inheritance of habit or other acquired peculiarities. + +Another point of interest is the weight he attached in 1842-4 to +"sports" or what are now called "mutations." This is I think more +prominent in the _Foundations_ than in the first edition of the +_Origin_, and certainly than in the fifth and sixth editions. + +Among other interesting points may be mentioned the "good effects of +crossing" being "possibly analogous to good effects of change in +condition,"--a principle which he upheld on experimental grounds in his +_Cross and Self-Fertilisation_ in 1876. + +In conclusion, I desire to express my thanks to Mr Wallace for a +footnote he was good enough to supply: and to Professor Bateson, Sir W. +Thiselton-Dyer, Dr Gadow, Professor Judd, Dr Marr, Col. Prain and Dr +Stapf for information on various points. I am also indebted to Mr +Rutherford, of the University Library, for his careful copy of the +manuscript of 1842. + +CAMBRIDGE, + +_June 9, 1909._ + + + + +EXPLANATION OF SIGNS, &c. + + +[] Means that the words so enclosed are erased in the original MS. + +<> Indicates an insertion by the Editor. + +_Origin_, Ed. vi. refers to the Popular Edition. + + + + +PART I. + + +§ I. <ON VARIATION UNDER DOMESTICATION, AND ON THE PRINCIPLES OF +SELECTION.> + +An individual organism placed under new conditions [often] sometimes +varies in a small degree and in very trifling respects such as stature, +fatness, sometimes colour, health, habits in animals and probably +disposition. Also habits of life develope certain parts. Disuse +atrophies. [Most of these slight variations tend to become hereditary.] + +When the individual is multiplied for long periods by buds the variation +is yet small, though greater and occasionally a single bud or individual +departs widely from its type (example){36} and continues steadily to +propagate, by buds, such new kind. + + {36} Evidently a memorandum that an example should be given. + +When the organism is bred for several generations under new or varying +conditions, the variation is greater in amount and endless in kind +[especially{37} holds good when individuals have long been exposed to +new conditions]. The nature of the external conditions tends to effect +some definite change in all or greater part of offspring,--little food, +small size--certain foods harmless &c. &c. organs affected and +diseases--extent unknown. A certain degree of variation (Müller's +twins){38} seems inevitable effect of process of reproduction. But more +important is that simple <?> generation, especially under new conditions +[when no crossing] <causes> infinite variation and not direct effect of +external conditions, but only in as much as it affects the reproductive +functions{39}. There seems to be no part (_beau ideal_ of liver){40} of +body, internal or external, or mind or habits, or instincts which does +not vary in some small degree and [often] some <?> to a great amount. + + {37} The importance of exposure to new conditions for several + generations is insisted on in the _Origin_, Ed. i. p. 7, also p. + 131. In the latter passage the author guards himself against the + assumption that variations are "due to chance," and speaks of "our + ignorance of the cause of each particular variation." These + statements are not always remembered by his critics. + + {38} Cf. _Origin_, Ed. i. p. 10, vi. p. 9, "Young of the same + litter, sometimes differ considerably from each other, though both + the young and the parents, as Müller has remarked, have apparently + been exposed to exactly the same conditions of life." + + {39} This is paralleled by the conclusion in the _Origin_, Ed. i. + p. 8, that "the most frequent cause of variability may be + attributed to the male and female reproductive elements having been + affected prior to the act of conception." + + {40} The meaning seems to be that there must be some variability in + the liver otherwise anatomists would not speak of the 'beau ideal' + of that organ. + +[All such] variations [being congenital] or those very slowly acquired +of all kinds [decidedly evince a tendency to become hereditary], when +not so become simple variety, when it does a race. Each{41} parent +transmits its peculiarities, therefore if varieties allowed freely to +cross, except by the _chance_ of two characterized by same peculiarity +happening to marry, such varieties will be constantly demolished{42}. +All bisexual animals must cross, hermaphrodite plants do cross, it seems +very possible that hermaphrodite animals do cross,--conclusion +strengthened: ill effects of breeding in and in, good effects of +crossing possibly analogous to good effects of change in condition <?>{43}. + + {41} The position of the following passage is uncertain. "If + individuals of two widely different varieties be allowed to cross, + a third race will be formed--a most fertile source of the variation + in domesticated animals. <In the _Origin_, Ed. i. p. 20 the author + says that "the possibility of making distinct races by crossing has + been greatly exaggerated."> If freely allowed, the characters of + pure parents will be lost, number of races thus <illegible> but + differences <?> besides the <illegible>. But if varieties differing + in very slight respects be allowed to cross, such small variation + will be destroyed, at least to our senses,--a variation [clearly] + just to be distinguished by long legs will have offspring not to be + so distinguished. Free crossing great agent in producing uniformity + in any breed. Introduce tendency to revert to parent form." + + {42} The swamping effect of intercrossing is referred to in the + _Origin_, Ed. i. p. 103, vi. p. 126. + + {43} A discussion on the intercrossing of hermaphrodites in + relation to Knight's views occurs in the _Origin_, Ed. i. p. 96, + vi. p. 119. The parallelism between crossing and changed conditions + is briefly given in the _Origin_, Ed. i. p. 267, vi. p. 391, and + was finally investigated in _The Effects of Cross and + Self-Fertilisation in the Vegetable Kingdom_, 1876. + +Therefore if in any country or district all animals of one species be +allowed freely to cross, any small tendency in them to vary will be +constantly counteracted. Secondly reversion to parent form--analogue of +_vis medicatrix_{44}. But if man selects, then new races rapidly +formed,--of late years systematically followed,--in most ancient times +often practically followed{45}. By such selection make race-horse, +dray-horse--one cow good for tallow, another for eating &c.--one plant's +good lay <illegible> in leaves another in fruit &c. &c.: the same plant +to supply his wants at different times of year. By former means animals +become adapted, as a direct effect to a cause, to external conditions, +as size of body to amount of food. By this latter means they may also be +so adapted, but further they may be adapted to ends and pursuits, which +by no possibility can affect growth, as existence of tallow-chandler +cannot tend to make fat. In such selected races, if not removed to new +conditions, and <if> preserved from all cross, after several generations +become very true, like each other and not varying. But man{46} selects +only <?> what is useful and curious--has bad judgment, is +capricious,--grudges to destroy those that do not come up to his +pattern,--has no [knowledge] power of selecting according to internal +variations,--can hardly keep his conditions uniform,--[cannot] does not +select those best adapted to the conditions under which <the> form <?> lives, +but those most useful to him. This might all be otherwise. + + {44} There is an article on the _vis medicatrix_ in Brougham's + _Dissertations_, 1839, a copy of which is in the author's library. + + {45} This is the classification of selection into methodical and + unconscious given in the _Origin_, Ed. i. p. 33, vi. p. 38. + + {46} This passage, and a similar discussion on the power of the + Creator (p. 6), correspond to the comparison between the selective + capacities of man and nature, in the _Origin_, Ed. i. p. 83, vi. p. + 102. + + +§ II. <ON VARIATION IN A STATE OF NATURE AND ON THE NATURAL MEANS OF +SELECTION.> + +Let us see how far above principles of variation apply to wild animals. +Wild animals vary exceedingly little--yet they are known as +individuals{47}. British Plants, in many genera number quite uncertain +of varieties and species: in shells chiefly external conditions{48}. +Primrose and cowslip. Wild animals from different [countries can be +recognized]. Specific character gives some organs as varying. Variations +analogous in kind, but less in degree with domesticated animals--chiefly +external and less important parts. + + {47} i.e. they are individually distinguishable. + + {48} See _Origin_, Ed. i. p. 133, vi. p. 165. + +Our experience would lead us to expect that any and every one of these +organisms would vary if <the organism were> taken away <?> and placed +under new conditions. Geology proclaims a constant round of change, +bringing into play, by every possible <?> change of climate and the death +of pre-existing inhabitants, endless variations of new conditions. These +<?> generally very slow, doubtful though <illegible> how far the +slowness <?> would produce tendency to vary. But Geolog<ists> show +change in configuration which, together with the accidents of air and +water and the means of transportal which every being possesses, must +occasionally bring, rather suddenly, organism to new conditions and <?> +expose it for several generations. Hence <?> we should expect every now +and then a wild form to vary{49}; possibly this may be cause of some +species varying more than others. + + {49} When the author wrote this sketch he seems not to have been so + fully convinced of the general occurrence of variation in nature as + he afterwards became. The above passage in the text possibly + suggests that at this time he laid more stress on _sports_ or + _mutations_ than was afterwards the case. + +According to nature of new conditions, so we might expect all or +majority of organisms born under them to vary in some definite way. +Further we might expect that the mould in which they are cast would +likewise vary in some small degree. But is there any means of selecting +those offspring which vary in the same manner, crossing them and keeping +their offspring separate and thus producing selected races: otherwise as +the wild animals freely cross, so must such small heterogeneous +varieties be constantly counter-balanced and lost, and a uniformity of +character [kept up] preserved. The former variation as the direct and +necessary effects of causes, which we can see can act on them, as size +of body from amount of food, effect of certain kinds of food on certain +parts of bodies &c. &c.; such new varieties may then become adapted to +those external [natural] agencies which act on them. But can varieties +be produced adapted to end, which cannot possibly influence their +structure and which it is absurd to look <at> as effects of chance. Can +varieties like some vars of domesticated animals, like almost all wild +species be produced adapted by exquisite means to prey on one animal or +to escape from another,--or rather, as it puts out of question effects +of intelligence and habits, can a plant become adapted to animals, as a +plant which cannot be impregnated without agency of insect; or hooked +seeds depending on animal's existence: woolly animals cannot have any +direct effect on seeds of plant. This point which all theories about +climate adapting woodpecker{50} to crawl <?> up trees, <illegible> +miseltoe, <sentence incomplete>. But if every part of a plant or animal +was to vary <illegible>, and if a being infinitely more sagacious than +man (not an omniscient creator) during thousands and thousands of years +were to select all the variations which tended towards certain ends ([or +were to produce causes <?> which tended to the same end]), for instance, +if he foresaw a canine animal would be better off, owing to the country +producing more hares, if he were longer legged and keener +sight,--greyhound produced{51}. If he saw that aquatic <animal would +need> skinned toes. If for some unknown cause he found it would +advantage a plant, which <?> like most plants is occasionally visited by +bees &c.: if that plant's seed were occasionally eaten by birds and were +then carried on to rotten trees, he might select trees with fruit more +agreeable to such birds as perched, to ensure their being carried to +trees; if he perceived those birds more often dropped the seeds, he +might well have selected a bird who would <illegible> rotten trees or +[gradually select plants which <he> had proved to live on less and less +rotten trees]. Who, seeing how plants vary in garden, what blind foolish +man has done{52} in a few years, will deny an all-seeing being in +thousands of years could effect (if the Creator chose to do so), either +by his own direct foresight or by intermediate means,--which will +represent <?> the creator of this universe. Seems usual means. Be it +remembered I have nothing to say about life and mind and _all_ forms +descending from one common type{53}. I speak of the variation of the +existing great divisions of the organised kingdom, how far I would go, +hereafter to be seen. + + {50} The author may possibly have taken the case of the woodpecker + from Buffon, _Histoire Nat. des Oiseaux_, T. vii. p. 3, 1780, where + however it is treated from a different point of view. He uses it + more than once, see for instance _Origin_, Ed. i. pp. 3, 60, 184, + vi. pp. 3, 76, 220. The passage in the text corresponds with a + discussion on the woodpecker and the mistletoe in _Origin_, Ed. i. + p. 3, vi. p. 3. + + {51} This illustration occurs in the _Origin_, Ed. i. pp. 90, 91, + vi. pp. 110, 111. + + {52} See _Origin_, Ed. i. p. 83, vi. p. 102, where the word + _Creator_ is replaced by _Nature_. + + {53} Note in the original. "Good place to introduce, saying reasons + hereafter to be given, how far I extend theory, say to all + mammalia--reasons growing weaker and weaker." + +Before considering whether <there> be any natural means of selection, and +secondly (which forms the 2nd Part of this sketch) the far more +important point whether the characters and relations of animated +<things> are such as favour the idea of wild species being races <?> +descended from a common stock, as the varieties of potato or dahlia or +cattle having so descended, let us consider probable character of +[selected races] wild varieties. + +_Natural Selection._ De Candolle's war of nature,--seeing contented face +of nature,--may be well at first doubted; we see it on borders of +perpetual cold{54}. But considering the enormous geometrical power of +increase in every organism and as <?> every country, in ordinary cases +<countries> must be stocked to full extent, reflection will show that +this is the case. Malthus on man,--in animals no moral [check] restraint +<?>--they breed in time of year when provision most abundant, or season +most favourable, every country has its seasons,--calculate +robins,--oscillating from years of destruction{55}. If proof were wanted +let any singular change of climate <occur> here <?>, how astoundingly +some tribes <?> increase, also introduced animals{56}, the pressure is +always ready,--capacity of alpine plants to endure other +climates,--think of endless seeds scattered abroad,--forests regaining +their percentage{57},--a thousand wedges{58} are being forced into the +oeconomy of nature. This requires much reflection; study Malthus and +calculate rates of increase and remember the resistance,--only +periodical. + + {54} See _Origin_, Ed. i. pp. 62, 63, vi. p. 77, where similar + reference is made to De Candolle; for Malthus see _Origin_, p. 5. + + {55} This may possibly refer to the amount of destruction going on. + See _Origin_, Ed. i. p. 68, vi. p. 84, where there is an estimate + of a later date as to death-rate of birds in winter. "Calculate + robins" probably refers to a calculation of the rate of increase of + birds under favourable conditions. + + {56} In the _Origin_, Ed. i. pp. 64, 65, vi. p. 80, he instances + cattle and horses and certain plants in S. America and American + species of plants in India, and further on, as unexpected effects + of changed conditions, the enclosure of a heath, and the relation + between the fertilisation of clover and the presence of cats + (_Origin_, Ed. i. p. 74, vi. p. 91). + + {57} _Origin_, Ed. i. p. 74, vi. p. 91. "It has been observed that + the trees now growing on ... ancient Indian mounds ... display the + same beautiful diversity and proportion of kinds as in the + surrounding virgin forests." + + {58} The simile of the wedge occurs in the _Origin_, Ed. i. p. 67; + it is deleted in Darwin's copy of the first edition: it does not + occur in Ed. vi. + +The unavoidable effect of this <is> that many of every species are +destroyed either in egg or [young or mature (the former state the more +common)]. In the course of a thousand generations infinitesimally small +differences must inevitably tell{59}; when unusually cold winter, or hot +or dry summer comes, then out of the whole body of individuals of any +species, if there be the smallest differences in their structure, +habits, instincts [senses], health &c, <it> will on an average tell; as +conditions change a rather larger proportion will be preserved: so if +the chief check to increase falls on seeds or eggs, so will, in the +course of 1000 generations or ten thousand, those seeds (like one with +down to fly{60}) which fly furthest and get scattered most ultimately +rear most plants, and such small differences tend to be hereditary like +shades of expression in human countenance. So if one parent <?> fish +deposits its egg in infinitesimally different circumstances, as in +rather shallower or deeper water &c., it will then <?> tell. + + {59} In a rough summary at the close of the Essay, occur the + words:--"Every creature lives by a struggle, smallest grain in + balance must tell." + + {60} Cf. _Origin_, Ed. i. p. 77, vi. p. 94. + +Let hares{61} increase very slowly from change of climate affecting +peculiar plants, and some other <illegible> rabbit decrease in same +proportion [let this unsettle organisation of], a canine animal, who +formerly derived its chief sustenance by springing on rabbits or +running them by scent, must decrease too and might thus readily become +exterminated. But if its form varied very slightly, the long legged +fleet ones, during a thousand years being selected, and the less fleet +rigidly destroyed must, if no law of nature be opposed to it, alter +forms. + + {61} This is a repetition of what is given at p. 6. + +Remember how soon Bakewell on the same principle altered cattle and +Western, sheep,--carefully avoiding a cross (pigeons) with any breed. +We cannot suppose that one plant tends to vary in fruit and another +in flower, and another in flower and foliage,--some have been selected +for both fruit and flower: that one animal varies in its covering and +another not,--another in its milk. Take any organism and ask what is +it useful for and on that point it will be found to vary,--cabbages +in their leaf,--corn in size <and> quality of grain, both in times +of year,--kidney beans for young pod and cotton for envelope of seeds +&c. &c.: dogs in intellect, courage, fleetness and smell <?>: pigeons +in peculiarities approaching to monsters. This requires +consideration,--should be introduced in first chapter if it holds, I +believe it does. It is hypothetical at best{62}. + + {62} Compare _Origin_, Ed. i. p. 41, vi. p. 47. "I have seen it + gravely remarked, that it was most fortunate that the strawberry + began to vary just when gardeners began to attend closely to this + plant. No doubt the strawberry had always varied since it was + cultivated, but the slight varieties had been neglected." + +Nature's variation far less, but such selection far more rigid and +scrutinising. Man's races not [even so well] only not better adapted to +conditions than other races, but often not <?> one race adapted to its +conditions, as man keeps and propagates some alpine plants in garden. +Nature lets <an> animal live, till on actual proof it is found less able +to do the required work to serve the desired end, man judges solely by +his eye, and knows not whether nerves, muscles, arteries, are developed +in proportion to the change of external form. + +Besides selection by death, in bisexual animals <illegible> the +selection in time of fullest vigour, namely struggle of males; even in +animals which pair there seems a surplus <?> and a battle, possibly as in +man more males produced than females, struggle of war or charms{63}. +Hence that male which at that time is in fullest vigour, or best armed +with arms or ornaments of its species, will gain in hundreds of +generations some small advantage and transmit such characters to its +offspring. So in female rearing its young, the most vigorous and skilful +and industrious, <whose> instincts <are> best developed, will rear more +young, probably possessing her good qualities, and a greater number will +thus <be> prepared for the struggle of nature. Compared to man using a +male alone of good breed. This latter section only of limited +application, applies to variation of [specific] sexual characters. +Introduce here contrast with Lamarck,--absurdity of habit, or chance?? +or external conditions, making a woodpecker adapted to tree{64}. + + {63} Here we have the two types of sexual selection discussed in + the _Origin_, Ed. i. pp. 88 et seq., vi. pp. 108 et seq. + + {64} It is not obvious why the author objects to "chance" or + "external conditions making a woodpecker." He allows that variation + is ultimately referable to conditions and that the nature of the + connexion is unknown, i.e. that the result is fortuitous. It is not + clear in the original to how much of the passage the two ? refer. + +Before considering difficulties of theory of selection let us consider +character of the races produced, as now explained, by nature. Conditions +have varied slowly and the organisms best adapted in their whole course +of life to the changed conditions have always been selected,--man +selects small dog and afterwards gives it profusion of food,--selects a +long-backed and short-legged breed and gives it no particular exercise +to suit this function &c. &c. In ordinary cases nature has not allowed +her race to be contaminated with a cross of another race, and +agriculturists know how difficult they find always to prevent +this,--effect would be trueness. This character and sterility when +crossed, and generally a greater amount of difference, are two main +features, which distinguish domestic races from species. + +[Sterility not universal admitted by all{65}. _Gladiolus_, _Crinum_, +_Calceolaria_{66} must be species if there be such a thing. Races of +dogs and oxen: but certainly very general; indeed a gradation of +sterility most perfect{67} very general. Some nearest species will not +cross (crocus, some heath <?>), some genera cross readily (fowls{68} and +grouse, peacock &c.). Hybrids no ways monstrous quite perfect except +secretions{69} hence even the mule has bred,--character of sterility, +especially a few years ago <?> thought very much more universal than it now +is, has been thought the distinguishing character; indeed it is obvious +if all forms freely crossed, nature would be a chaos. But the very +gradation of the character, even if it always existed in some degree +which it does not, renders it impossible as marks <?> those <?> suppose +distinct as species{70}]. Will analogy throw any light on the fact of +the supposed races of nature being sterile, though none of the domestic +ones are? Mr Herbert <and> Koelreuter have shown external differences will +not guide one in knowing whether hybrids will be fertile or not, but the +chief circumstance is constitutional differences{71}, such as being +adapted to different climate or soil, differences which [must] probably +affect the whole body of the organism and not any one part. Now wild +animals, taken out of their natural conditions, seldom breed. I do not +refer to shows or to Zoological Societies where many animals unite, but +<do not?> breed, and others will never unite, but to wild animals caught +and kept _quite tame_ left loose and well fed about houses and living +many years. Hybrids produced almost as readily as pure breds. St Hilaire +great distinction of tame and domestic,--elephants,--ferrets{72}. +Reproductive organs not subject to disease in Zoological Garden. +Dissection and microscope show that hybrid is in exactly same condition +as another animal in the intervals of breeding season, or those animals +which taken wild and _not bred_ in domesticity, remain without breeding +their whole lives. It should be observed that so far from domesticity +being unfavourable in itself <it> makes more fertile: [when animal is +domesticated and breeds, productive power increased from more food and +selection of fertile races]. As far as animals go might be thought <an> +effect on their mind and a special case. + + {65} The meaning is "That sterility is not universal is admitted by + all." + + {66} See _Var. under Dom._, Ed. 2, i. p. 388, where the garden + forms of _Gladiolus_ and _Calceolaria_ are said to be derived from + crosses between distinct species. Herbert's hybrid _Crinums_ are + discussed in the _Origin_, Ed. i. p. 250, vi. p. 370. It is well + known that the author believed in a multiple origin of domestic + dogs. + + {67} The argument from gradation in sterility is given in the + _Origin_, Ed. i. pp. 248, 255, vi. pp. 368, 375. In the _Origin_, I + have not come across the cases mentioned, viz. crocus, heath, or + grouse and fowl or peacock. For sterility between closely allied + species, see _Origin_, Ed. i. p. 257, vi. p. 377. In the present + essay the author does not distinguish between fertility between + species and the fertility of the hybrid offspring, a point on which + he insists in the _Origin_, Ed. i. p. 245, vi. p. 365. + + {68} Ackermann (_Ber. d. Vereins f. Naturkunde zu Kassel_, 1898, p. + 23) quotes from Gloger that a cross has been effected between a + domestic hen and a _Tetrao tetrix_; the offspring died when three + days old. + + {69} No doubt the sexual cells are meant. I do not know on what + evidence it is stated that the mule has bred. + + {70} The sentence is all but illegible. I think that the author + refers to forms usually ranked as varieties having been marked as + species when it was found that they were sterile together. See the + case of the red and blue _Anagallis_ given from Gärtner in the + _Origin_, Ed. i. p. 247, vi. p. 368. + + {71} In the _Origin_, Ed. i. p. 258, where the author speaks of + constitutional differences in this connexion, he specifies that + they are confined to the reproductive system. + + {72} The sensitiveness of the reproductive system to changed + conditions is insisted on in the _Origin_, Ed. i. p. 8, vi. p. 10. + + The ferret is mentioned, as being prolific in captivity, in _Var. + under Dom._, Ed. 2, ii. p. 90. + +But turning to plants we find same class of facts. I do not refer to +seeds not ripening, perhaps the commonest cause, but to plants not +setting, which either is owing to some imperfection of ovule or pollen. +Lindley says sterility is the [curse] bane of all propagators,--Linnæus +about alpine plants. American bog plants,--pollen in exactly same state +as in hybrids,--same in geraniums. Persian and Chinese{73} lilac will +not seed in Italy and England. Probably double plants and all fruits owe +their developed parts primarily <?> to sterility and extra food thus <?> +applied{74}. There is here gradation <in> sterility and then parts, like +diseases, are transmitted hereditarily. We cannot assign any cause why +the Pontic Azalea produces plenty of pollen and not American{75}, why +common lilac seeds and not Persian, we see no difference in healthiness. +We know not on what circumstances these facts depend, why ferret breeds, +and cheetah{76}, elephant and pig in India will not. + + {73} Lindley's remark is quoted in the _Origin_, Ed. i. p. 9. + Linnæus' remark is to the effect that Alpine plants tend to be + sterile under cultivation (see _Var. under Dom._, Ed. 2, ii. p. + 147). In the same place the author speaks of peat-loving plants + being sterile in our gardens,--no doubt the American bog-plants + referred to above. On the following page (p. 148) the sterility of + the lilac (_Syringa persica_ and _chinensis_) is referred to. + + {74} The author probably means that the increase in the petals is + due to a greater food supply being available for them owing to + sterility. See the discussion in _Var. under Dom._, Ed. 2, ii. p. + 151. It must be noted that doubleness of the flower may exist + without noticeable sterility. + + {75} I have not come across this case in the author's works. + + {76} For the somewhat doubtful case of the cheetah (_Felis jubata_) + see _Var. under Dom._, Ed. 2, ii. p. 133. I do not know to what + fact "pig in India" refers. + +Now in crossing it is certain every peculiarity in form and constitution +is transmitted: an alpine plant transmits its alpine tendency to its +offspring, an American plant its American-bog constitution, and <with> +animals, those peculiarities, on which{77} when placed out of their +natural conditions they are incapable of breeding; and moreover they +transmit every part of their constitution, their respiration, their +pulse, their instinct, which are all suddenly modified, can it be +wondered at that they are incapable of breeding? I think it may be truly +said it would be more wonderful if they did. But it may be asked why +have not the recognised varieties, supposed to have been produced +through the means of man, [not refused to breed] have all bred{78}. +Variation depends on change of condition and selection{79}, as far as +man's systematic or unsystematic selection <has> gone; he takes external +form, has little power from ignorance over internal invisible +constitutional differences. Races which have long been domesticated, and +have much varied, are precisely those which were capable of bearing +great changes, whose constitutions were adapted to a diversity of +climates. Nature changes slowly and by degrees. According to many +authors probably breeds of dogs are another case of modified species +freely crossing. There is no variety which <illegible> has been <illegible> +adapted to peculiar soil or situation for a thousand years and another +rigorously adapted to another, till such can be produced, the question +is not tried{80}. Man in past ages, could transport into different +climates, animals and plants which would freely propagate in such new +climates. Nature could effect, with selection, such changes slowly, so +that precisely those animals which are adapted to submit to great +changes have given rise to diverse races,--and indeed great doubt on +this head{81}. + + {77} This sentence should run "on which depends their incapacity to + breed in unnatural conditions." + + {78} This sentence ends in confusion: it should clearly close with + the words "refused to breed" in place of the bracket and the + present concluding phrase. + + {79} The author doubtless refers to the change produced by the + _summation_ of variation by means of selection. + + {80} The meaning of this sentence is made clear by a passage in the + MS. of 1844:--"Until man selects two varieties from the same stock, + adapted to two climates or to other different external conditions, + and confines each rigidly for one or several thousand years to such + conditions, always selecting the individuals best adapted to them, + he cannot be said to have even commenced the experiment." That is, + the attempt to produce mutually sterile domestic breeds. + + {81} This passage is to some extent a repetition of a previous one + and may have been intended to replace an earlier sentence. I have + thought it best to give both. In the _Origin_, Ed. i. p. 141, vi. + p. 176, the author gives his opinion that the power of resisting + diverse conditions, seen in man and his domestic animals, is an + example "of a very common flexibility of constitution." + +Before leaving this subject well to observe that it was shown that a +certain amount of variation is consequent on mere act of reproduction, +both by buds and sexually,--is vastly increased when parents exposed for +some generations to new conditions{82}, and we now find that many +animals when exposed for first time to very new conditions, are <as> +incapable of breeding as hybrids. It [probably] bears also on supposed +fact of crossed animals when not infertile, as in mongrels, tending to +vary much, as likewise seems to be the case, when true hybrids possess +just sufficient fertility to propagate with the parent breeds and _inter +se_ for some generations. This is Koelreuter's belief. These facts throw +light on each other and support the truth of each other, we see +throughout a connection between the reproductive faculties and exposure +to changed conditions of life whether by crossing or exposure of the +individuals{83}. + + {82} In the _Origin_, Ed. i. Chs. I. and V., the author does not + admit reproduction, apart from environment, as being a cause of + variation. With regard to the cumulative effect of new conditions + there are many passages in the _Origin_, Ed. i. e.g. pp. 7, 12, vi. + pp. 8, 14. + + {83} As already pointed out, this is the important principle + investigated in the author's _Cross and Self-Fertilisation_. + Professor Bateson has suggested to me that the experiments should + be repeated with gametically pure individuals. + +_Difficulties on theory of selection_{84}. It may be objected such +perfect organs as eye and ear, could never be formed, in latter less +difficulty as gradations more perfect; at first appears monstrous and to +<the> end appears difficulty. But think of gradation, even now manifest, +(Tibia and Fibula). Everyone will allow if every fossil preserved, +gradation infinitely more perfect; for possibility of selection a +perfect <?> gradation is required. Different groups of structure, slight +gradation in each group,--every analogy renders it probable that +intermediate forms have existed. Be it remembered what strange +metamorphoses; part of eye, not directly connected with vision, might +come to be [thus used] gradually worked in for this end,--swimming +bladder by gradation of structure is admitted to belong to the ear +system,--rattlesnake. [Woodpecker best adapted to climb.] In some cases +gradation not possible,--as vertebræ,--actually vary in domestic +animals,--less difficult if growth followed. Looking to whole animals, a +bat formed not for flight{85}. Suppose we had flying fish{86} and not +one of our now called flying fish preserved, who would have guessed +intermediate habits. Woodpeckers and tree-frogs both live in countries +where no trees{87}. + + {84} In the _Origin_ a chapter is given up to "difficulties on + theory": the discussion in the present essay seems slight even when + it is remembered how small a space is here available. For _Tibia_ + &c. see p. 48. + + {85} This may be interpreted "The general structure of a bat is the + same as that of non-flying mammals." + + {86} That is truly winged fish. + + {87} The terrestrial woodpecker of S. America formed the subject of + a paper by Darwin, _Proc. Zool. Soc._, 1870. See _Life and + Letters_, vol. iii. p. 153. + +The gradations by which each individual organ has arrived at its present +state, and each individual animal with its aggregate of organs has +arrived, probably never could be known, and all present great +difficulties. I merely wish to show that the proposition is not so +monstrous as it at first appears, and that if good reason can be +advanced for believing the species have descended from common parents, +the difficulty of imagining intermediate forms of structure not +sufficient to make one at once reject the theory. + + +§ III. <ON VARIATION IN INSTINCTS AND OTHER MENTAL ATTRIBUTES.> + +The mental powers of different animals in wild and tame state [present +still greater difficulties] require a separate section. Be it remembered +I have nothing to do with origin of memory, attention, and the different +faculties of the mind{88}, but merely with their differences in each of +the great divisions of nature. Disposition, courage, pertinacity <?>, +suspicion, restlessness, ill-temper, sagacity and <the> reverse +unquestionably vary in animals and are inherited (Cuba wildness dogs, +rabbits, fear against particular object as man Galapagos{89}). Habits +purely corporeal, breeding season &c., time of going to rest &c., vary +and are hereditary, like the analogous habits of plants which vary and +are inherited. Habits of body, as manner of movement d^o. and d^o. +Habits, as pointing and setting on certain occasions d^o. Taste for +hunting certain objects and manner of doing so,--sheep-dog. These are +shown clearly by crossing and their analogy with true instinct thus +shown,--retriever. Do not know objects for which they do it. Lord +Brougham's definition{90}. Origin partly habit, but the amount +necessarily unknown, partly selection. Young pointers pointing stones +and sheep--tumbling pigeons--sheep{91} going back to place where born. +Instinct aided by reason, as in the taylor-bird{92}. Taught by parents, +cows choosing food, birds singing. Instincts vary in wild state (birds +get wilder) often lost{93}; more perfect,--nest without roof. These +facts [only clear way] show how incomprehensibly brain has power of +transmitting intellectual operations. + + {88} The same proviso occurs in the _Origin_, Ed. i. p. 207, vi. p. + 319. + + {89} The tameness of the birds in the Galapagos is described in the + _Journal of Researches_ (1860), p. 398. Dogs and rabbits are + probably mentioned as cases in which the hereditary fear of man has + been lost. In the 1844 MS. the author states that the Cuban feral + dog shows great natural wildness, even when caught quite young. + + {90} In the _Origin_, Ed. i. p. 207, vi. p. 319, he refuses to + define instinct. For Lord Brougham's definition see his + _Dissertations on Subjects of Science etc._, 1839, p. 27. + + {91} See James Hogg (the Ettrick Shepherd), Works, 1865, _Tales and + Sketches_, p. 403. + + {92} This refers to the tailor-bird making use of manufactured + thread supplied to it, instead of thread twisted by itself. + + {93} _Often lost_ applies to _instinct_: _birds get wilder_ is + printed in a parenthesis because it was apparently added as an + after-thought. _Nest without roof_ refers to the water-ousel + omitting to vault its nest when building in a protected situation. + +Faculties{94} distinct from true instincts,--finding [way]. It must I +think be admitted that habits whether congenital or acquired by practice +[sometimes] often become inherited{95}; instincts, influence, equally +with structure, the preservation of animals; therefore selection must, +with changing conditions tend to modify the inherited habits of animals. +If this be admitted it will be found _possible_ that many of the +strangest instincts may be thus acquired. I may observe, without +attempting definition, that an inherited habit or trick (trick because +may be born) fulfils closely what we mean by instinct. A habit is often +performed unconsciously, the strangest habits become associated, d^o. +tricks, going in certain spots &c. &c., even against will, is excited by +external agencies, and looks not to the end,--a person playing a +pianoforte. If such a habit were transmitted it would make a marvellous +instinct. Let us consider some of the most difficult cases of instincts, +whether they could be _possibly_ acquired. I do not say _probably_, for +that belongs to our 3rd Part{96}, I beg this may be remembered, nor do I +mean to attempt to show exact method. I want only to show that whole +theory ought not at once to be rejected on this score. + + {94} In the MS. of 1844 is an interesting discussion on _faculty_ + as distinct from _instinct_. + + {95} At this date and for long afterwards the inheritance of + acquired characters was assumed to occur. + + {96} Part II. is here intended: see the Introduction. + +Every instinct must, by my theory, have been acquired gradually by +slight changes <illegible> of former instinct, each change being useful +to its then species. Shamming death struck me at first as remarkable +objection. I found none really sham death{97}, and that there is +gradation; now no one doubts that those insects which do it either more +or less, do it for some good, if then any species was led to do it more, +and then <?> escaped &c. &c. + + {97} The meaning is that the attitude assumed in _shamming_ is not + accurately like that of death. + +Take migratory instincts, faculty distinct from instinct, animals have +notion of time,--like savages. Ordinary finding way by memory, but how +does savage find way across country,--as incomprehensible to us, as +animal to them,--geological changes,--fishes in river,--case of sheep in +Spain{98}. Architectural instincts,--a manufacturer's employee in making +single articles extraordinary skill,--often said seem to make it almost +<illegible>, child born with such a notion of playing{99},--we can +fancy tailoring acquired in same perfection,--mixture of +reason,--water-ouzel,--taylor-bird,--gradation of simple nest to most +complicated. + + {98} This refers to the _transandantes_ sheep mentioned in the MS. + of 1844, as having acquired a migratory instinct. + + {99} In the _Origin_, Ed. i. p. 209, vi. p. 321, Mozart's + pseudo-instinctive skill in piano-playing is mentioned. See _Phil. + Trans._, 1770, p. 54. + +Bees again, distinction of faculty,--how they make a +hexagon,--Waterhouse's theory{100},--the impulse to use whatever faculty +they possess,--the taylor-bird has the faculty of sewing with beak, +instinct impels him to do it. + + {100} In the discussion on bees' cells, _Origin_, Ed. i. p. 225, + vi. p. 343, the author acknowledges that his theory originated in + Waterhouse's observations. + +Last case of parent feeding young with different food (take case of +Galapagos birds, gradation from Hawfinch to Sylvia) selection and habit +might lead old birds to vary taste <?> and form, leaving their instinct of +feeding their young with same food{101},--or I see no difficulty in +parents being forced or induced to vary the food brought, and selection +adapting the young ones to it, and thus by degree any amount of +diversity might be arrived at. Although we can never hope to see the +course revealed by which different instincts have been acquired, for we +have only present animals (not well known) to judge of the course of +gradation, yet once grant the principle of habits, whether congenital or +acquired by experience, being inherited and I can see no limit to the +[amount of variation] extraordinariness <?> of the habits thus acquired. + + {101} The hawfinch-and _Sylvia-_types are figured in the _Journal + of Researches_, p. 379. The discussion of change of form in + relation to change of instinct is not clear, and I find it + impossible to suggest a paraphrase. + +_Summing up this Division._ If variation be admitted to occur +occasionally in some wild animals, and how can we doubt it, when we see +[all] thousands <of> organisms, for whatever use taken by man, do vary. +If we admit such variations tend to be hereditary, and how can we doubt +it when we <remember> resemblances of features and character,--disease +and monstrosities inherited and endless races produced (1200 cabbages). +If we admit selection is steadily at work, and who will doubt it, when +he considers amount of food on an average fixed and reproductive powers +act in geometrical ratio. If we admit that external conditions vary, as +all geology proclaims, they have done and are now doing,--then, if no +law of nature be opposed, there must occasionally be formed races, +[slightly] differing from the parent races. So then any such law{102}, +none is known, but in all works it is assumed, in <?> flat contradiction +to all known facts, that the amount of possible variation is soon +acquired. Are not all the most varied species, the oldest domesticated: +who <would> think that horses or corn could be produced? Take dahlia and +potato, who will pretend in 5000 years{103} <that great changes might +not be effected>: perfectly adapted to conditions and then again brought +into varying conditions. Think what has been done in few last years, +look at pigeons, and cattle. With the amount of food man can produce he +may have arrived at limit of fatness or size, or thickness of wool <?>, +but these are the most trivial points, but even in these I conclude it +is impossible to say we know the limit of variation. And therefore with +the [adapting] selecting power of nature, infinitely wise compared to +those of man, <I conclude> that it is impossible to say we know the limit +of races, which would be true <to their> kind; if of different +constitutions would probably be infertile one with another, and which +might be adapted in the most singular and admirable manner, according to +their wants, to external nature and to other surrounding +organisms,--such races would be species. But is there any evidence <that> +species <have> been thus produced, this is a question wholly independent +of all previous points, and which on examination of the kingdom of +nature <we> ought to answer one way or another. + + {102} I should interpret this obscure sentence as follows, "No such + opposing law is known, but in all works on the subject a law is (in + flat contradiction to all known facts) assumed to limit the + possible amount of variation." In the _Origin_, the author never + limits the power of variation, as far as I know. + + {103} In _Var. under Dom._ Ed. 2, ii. p. 263, the _Dahlia_ is + described as showing sensitiveness to conditions in 1841. All the + varieties of the _Dahlia_ are said to have arisen since 1804 + (_ibid._ i. p. 393). + + + + +PART II{104}. + + {104} In the original MS. the heading is: Part III.; but Part II. + is clearly intended; for details see the Introduction. I have not + been able to discover where § IV. ends and § V. begins. + + +§§ IV. & V. <ON THE EVIDENCE FROM GEOLOGY.> + +I may premise, that according to the view ordinarily received, the +myriads of organisms peopling this world have been created by so many +distinct acts of creation. As we know nothing of the <illegible> will of a +Creator,--we can see no reason why there should exist any relation +between the organisms thus created; or again, they might be created +according to any scheme. But it would be marvellous if this scheme +should be the same as would result from the descent of groups of +organisms from [certain] the same parents, according to the +circumstances, just attempted to be developed. + +With equal probability did old cosmogonists say fossils were created, as +we now see them, with a false resemblance to living beings{105}; what +would the Astronomer say to the doctrine that the planets moved <not> +according to the law of gravitation, but from the Creator having willed +each separate planet to move in its particular orbit? I believe such a +proposition (if we remove all prejudices) would be as legitimate as to +admit that certain groups of living and extinct organisms, in their +distribution, in their structure and in their relations one to another +and to external conditions, agreed with the theory and showed signs of +common descent, and yet were created distinct. As long as it was thought +impossible that organisms should vary, or should anyhow become adapted +to other organisms in a complicated manner, and yet be separated from +them by an impassable barrier of sterility{106}, it was justifiable, +even with some appearance in favour of a common descent, to admit +distinct creation according to the will of an Omniscient Creator; or, +for it is the same thing, to say with Whewell that the beginnings of all +things surpass the comprehension of man. In the former sections I have +endeavoured to show that such variation or specification is not +impossible, nay, in many points of view is absolutely probable. What +then is the evidence in favour of it and what the evidence against it. +With our imperfect knowledge of past ages [surely there will be some] it +would be strange if the imperfection did not create some unfavourable +evidence. + + {105} This passage corresponds roughly to the conclusion of the + _Origin_, see Ed. i. p. 482, vi. p. 661. + + {106} A similar passage occurs in the conclusion of the _Origin_, + Ed. i. p. 481, vi. p. 659. + +Give sketch of the Past,--beginning with facts appearing hostile under +present knowledge,--then proceed to geograph. distribution,--order of +appearance,--affinities,--morphology &c., &c. + +Our theory requires a very gradual introduction of new forms{107}, and +extermination of the old (to which we shall revert). The extermination +of old may sometimes be rapid, but never the introduction. In the groups +descended from common parent, our theory requires a perfect gradation +not differing more than breed<s> of cattle, or potatoes, or cabbages in +forms. I do not mean that a graduated series of animals must have +existed, intermediate between horse, mouse, tapir{108}, elephant [or +fowl and peacock], but that these must have had a common parent, and +between horse and this <?> parent &c., &c., but the common parent may +possibly have differed more from either than the two do now from each +other. Now what evidence of this is there? So perfect gradation in some +departments, that some naturalists have thought that in some large +divisions, if all existing forms were collected, a near approach to +perfect gradation would be made. But such a notion is preposterous with +respect to all, but evidently so with mammals. Other naturalists have +thought this would be so if all the specimens entombed in the strata +were collected{109}. I conceive there is no probability whatever of +this; nevertheless it is certain all the numerous fossil forms fall +in<to>, as Buckland remarks, _not_ present classes, families and genera, +they fall between them: so is it with new discoveries of existing forms. +Most ancient fossils, that is most separated <by> space of time, are most +apt to fall between the classes--(but organisms from those countries +most separated by space also fall between the classes <_e.g._> +Ornithorhyncus?). As far as geological discoveries <go> they tend towards +such gradation{110}. Illustrate it with net. Toxodon,--tibia and +fibula,--dog and otter,--but so utterly improbable is <it>, in _ex. gr._ +Pachydermata, to compose series as perfect as cattle, that if, as many +geologists seem to infer, each separate formation presents even an +approach to a consecutive history, my theory must be given up. Even if +it were consecutive, it would only collect series of one district in our +present state of knowledge; but what probability is there that any one +formation during the _immense_ period which has elapsed during each +period will _generally_ present a consecutive history. [Compare number +living at one period to fossils preserved--look at enormous periods of +time.] + + {107} See _Origin_, Ed. i. p. 312, vi. p. 453. + + {108} See _Origin_, Ed. i. pp. 280, 281, vi. p. 414. The author + uses his experience of pigeons for examples for what he means by + _intermediate_; the instance of the horse and tapir also occurs. + + {109} The absence of intermediate forms between living organisms + (and also as regards fossils) is discussed in the _Origin_, Ed. i. + pp. 279, 280, vi. p. 413. In the above discussion there is no + evidence that the author felt this difficulty so strongly as it is + expressed in the _Origin_, Ed. i. p. 299,--as perhaps "the most + obvious and gravest objection that can be urged against my theory." + But in a rough summary written on the back of the penultimate page + of the MS. he refers to the geological evidence:--"Evidence, as far + as it does go, is favourable, exceedingly incomplete,--greatest + difficulty on this theory. I am convinced not insuperable." + Buckland's remarks are given in the _Origin_, Ed. i. p. 329, vi. p. + 471. + + {110} That the evidence of geology, as far as it goes, is + favourable to the theory of descent is claimed in the _Origin_, Ed. + i. pp. 343-345, vi. pp. 490-492. For the reference to _net_ in the + following sentence, see Note 1, p. 48, {Note 161} of this Essay. + +Referring only to marine animals, which are obviously most likely to be +preserved, they must live where <?> sediment (of a kind favourable for +preservation, not sand and pebble){111} is depositing quickly and over +large area and must be thickly capped, <illegible> littoral deposits: +for otherwise denudation <will destroy them>,--they must live in a +shallow space which sediment will tend to fill up,--as movement is <in?> +progress if soon brought <?> up <?> subject to denudation,--[if] as +during subsidence favourable, accords with facts of European +deposits{112}, but subsidence apt to destroy agents which produce +sediment{113}. + + {111} See _Origin_, Ed. i. p. 288, vi. p. 422. "The remains that do + become embedded, if in sand and gravel, will, when the beds are + upraised, generally be dissolved by the percolation of rain-water." + + {112} The position of the following is not clear:--"Think of + immense differences in nature of European deposits,--without + interposing new causes,--think of time required by present slow + changes, to cause, on very same area, such diverse deposits, + iron-sand, chalk, sand, coral, clay!" + + {113} The paragraph which ends here is difficult to interpret. In + spite of obscurity it is easy to recognize the general resemblance + to the discussion on the importance of subsidence given in the + _Origin_, Ed. i. pp. 290 et seq., vi. pp. 422 et seq. + +I believe safely inferred <that> groups of marine <?> fossils only +preserved for future ages where sediment goes on long <and> +continuous<ly> and with rapid but not too rapid deposition in <an> area +of subsidence. In how few places in any one region like Europe will <?> +these contingencies be going on? Hence <?> in past ages mere [gaps] +pages preserved{114}. Lyell's doctrine carried to extreme,--we shall +understand difficulty if it be asked:--what chance of series of +gradation between cattle by <illegible> at age <illegible> as far back +as Miocene{115}? We know then cattle existed. Compare number of +living,--immense duration of each period,--fewness of fossils. + + {114} See Note 3, p. 27. + + {115} Compare _Origin_, Ed. i. p. 298, vi. p. 437. "We shall, + perhaps, best perceive the improbability of our being enabled to + connect species by numerous, fine, intermediate, fossil links, by + asking ourselves whether, for instance, geologists at some future + period will be able to prove that our different breeds of cattle, + sheep, horses, and dogs have descended from a single stock or from + several aboriginal stocks." + +This only refers to consecutiveness of history of organisms of each +formation. + +The foregoing argument will show firstly, that formations are distinct +merely from want of fossils <of intermediate beds>, and secondly, that +each formation is full of gaps, has been advanced to account for +_fewness_ of _preserved_ organisms compared to what have lived on the +world. The very same argument explains why in older formations the +organisms appear to come on and disappear suddenly,--but in [later] +tertiary not quite suddenly{116}, in later tertiary gradually,--becoming +rare and disappearing,--some have disappeared within man's time. It is +obvious that our theory requires gradual and nearly uniform +introduction, possibly more sudden extermination,--subsidence of +continent of Australia &c., &c. + + {116} The sudden appearance of groups of allied species in the + lowest known fossiliferous strata is discussed in the _Origin_, Ed. + i. p. 306, vi. p. 446. The gradual appearance in the later strata + occurs in the _Origin_, Ed. i. p. 312, vi. p. 453. + +Our theory requires that the first form which existed of each of the +great divisions would present points intermediate between existing ones, +but immensely different. Most geologists believe Silurian{117} fossils +are those which first existed in the whole world, not those which have +chanced to be the oldest not destroyed,--or the first which existed in +profoundly deep seas in progress of conversion from sea to land: if they +are first they <? we> give up. Not so Hutton or Lyell: if first +reptile{118} of Red Sandstone <?> really was first which existed: if +Pachyderm{119} of Paris was first which existed: fish of Devonian: +dragon fly of Lias: for we cannot suppose them the progenitors: they +agree too closely with existing divisions. But geologists consider +Europe as <?> a passage from sea to island <?> to continent (except +Wealden, see Lyell). These animals therefore, I consider then mere +introduction <?> from continents long since submerged. + + {117} Compare _Origin_, Ed. i. p. 307, vi. p. 448. + + {118} I have interpreted as _Sandstone_ a scrawl which I first read + as _Sea_; I have done so at the suggestion of Professor Judd, who + points out that "footprints in the red sandstone were known at that + time, and geologists were not then particular to distinguish + between Amphibians and Reptiles." + + {119} This refers to Cuvier's discovery of _Palæotherium_ &c. at + Montmartre. + +Finally, if views of some geologists be correct, my theory must be given +up. [Lyell's views, as far as they go, are in _favour_, but they go so +little in favour, and so much more is required, that it may <be> viewed as +objection.] If geology present us with mere pages in chapters, towards +end of <a> history, formed by tearing out bundles of leaves, and each page +illustrating merely a small portion of the organisms of that time, the +facts accord perfectly with my theory{120}. + + {120} This simile is more fully given in the _Origin_, Ed. i. p. + 310, vi. p. 452. "For my part, following out Lyell's metaphor, I + look at the natural geological record, as a history of the world + imperfectly kept, and written in a changing dialect; of this + history we possess the last volume alone, relating only to two or + three countries. Of this volume, only here and there a short + chapter has been preserved; and of each page, only here and there a + few lines. Each word of the slowly-changing language, in which the + history is supposed to be written, being more or less different in + the interrupted succession of chapters, may represent the + apparently abruptly changed forms of life, entombed in our + consecutive, but widely separated formations." Professor Judd has + been good enough to point out to me, that Darwin's metaphor is + founded on the comparison of geology to history in Ch. i. of the + _Principles of Geology_, Ed. i. 1830, vol. i. pp. 1-4. Professor + Judd has also called my attention to another + passage,--_Principles_, Ed. i. 1833, vol. iii. p. 33, when Lyell + imagines an historian examining "two buried cities at the foot of + Vesuvius, immediately superimposed upon each other." The historian + would discover that the inhabitants of the lower town were Greeks + while those of the upper one were Italians. But he would be wrong + in supposing that there had been a sudden change from the Greek to + the Italian language in Campania. I think it is clear that Darwin's + metaphor is partly taken from this passage. See for instance (in + the above passage from the _Origin_) such phrases as "history ... + written in a changing dialect"--"apparently abruptly changed forms + of life." The passage within [] in the above paragraph:--"Lyell's + views as far as they go &c.," no doubt refers, as Professor Judd + points out, to Lyell not going so far as Darwin on the question of + the imperfection of the geological record. + +_Extermination._ We have seen that in later periods the organisms have +disappeared by degrees and [perhaps] probably by degrees in earlier, and +I have said our theory requires it. As many naturalists seem to think +extermination a most mysterious circumstance{121} and call in +astonishing agencies, it is well to recall what we have shown concerning +the struggle of nature. An exterminating agency is at work with every +organism: we scarcely see it: if robins would increase to thousands in +ten years how severe must the process be. How imperceptible a small +increase: fossils become rare: possibly sudden extermination as +Australia, but as present means very slow and many means of escape, I +shall doubt very sudden exterminations. Who can explain why some species +abound more,--why does marsh titmouse, or ring-ouzel, now little +change,--why is one sea-slug rare and another common on our coasts,--why +one species of Rhinoceros more than another,--why is <illegible> tiger of +India so rare? Curious and general sources of error, the place of an +organism is instantly filled up. + + {121} On rarity and extinction see _Origin_, Ed. i. pp. 109, 319, + vi. pp. 133, 461. + +We know state of earth has changed, and as earthquakes and tides go on, +the state must change,--many geologists believe a slow gradual cooling. +Now let us see in accordance with principles of [variation] +specification explained in Sect. II. how species would probably be +introduced and how such results accord with what is known. + +The first fact geology proclaims is immense number of extinct forms, and +new appearances. Tertiary strata leads to belief, that forms gradually +become rare and disappear and are gradually supplied by others. We see +some forms now becoming rare and disappearing, we know of no sudden +creation: in older periods the forms _appear_ to come in suddenly, scene +shifts: but even here Devonian, Permian &c. [keep on supplying new links +in chain]--Genera and higher forms come on and disappear, in same way +leaving a species on one or more stages below that in which the form +abounded. + + +<GEOGRAPHICAL DISTRIBUTION.> + +§ VI. Let us consider the absolute state of distribution of organisms of +earth's face. + +Referring chiefly, but not exclusively (from difficulty of transport, +fewness, and the distinct characteristics of groups) to Mammalia; and +first considering the three or four main [regions] divisions; North +America, Europe, Asia, including greater part of E. Indian Archipelago +and Africa are intimately allied. Africa most distinct, especially most +southern parts. And the Arctic regions, which unite N. America, Asia and +Europe, only separated (if we travel one way by Behring's St.) by a +narrow strait, is most intimately allied, indeed forms but one +restricted group. Next comes S. America,--then Australia, Madagascar +(and some small islands which stand very remote from the land). Looking +at these main divisions separately, the organisms vary according to +changes in condition{122} of different parts. But besides this, barriers +of every kind seem to separate regions in a greater degree than +proportionally to the difference of climates on each side. Thus great +chains of mountains, spaces of sea between islands and continents, even +great rivers and deserts. In fact the amount <of> difference in the +organisms bears a certain, but not invariable relation to the amount of +physical difficulties to transit{123}. + + {122} In the _Origin_, Ed. i. p. 346, vi. p. 493, the author begins + his discussion on geographical distribution by minimising the + effect of physical conditions. He lays great stress on the effect + of _barriers_, as in the present Essay. + + {123} Note in the original, "Would it be more striking if we took + animals, take Rhinoceros, and study their habitats?" + +There are some curious exceptions, namely, similarity of fauna of +mountains of Europe and N. America and Lapland. Other cases just <the> +reverse, mountains of eastern S. America, Altai <?>, S. India <?>{124}: +mountain summits of islands often eminently peculiar. Fauna generally of +some islands, even when close, very dissimilar, in others very similar. +[I am here led to observe one or more centres of creation{125}.] + + {124} Note by Mr A. R. Wallace. "The want of similarity referred + to, is, between the mountains of Brazil and Guiana and those of the + Andes. Also those of the Indian peninsula as compared with the + Himalayas. In both cases there is continuous intervening land. + + "The islands referred to were, no doubt, the Galapagos for + dissimilarity from S. America; our own Islands as compared with + Europe, and perhaps Java, for similarity with continental Asia." + + {125} The arguments against multiple centres of creation are given + in the _Origin_, Ed. i. p. 352, vi. p. 499. + +The simple geologist can explain many of the foregoing cases of +distribution. Subsidence of a continent in which free means of +dispersal, would drive the lowland plants up to the mountains, now +converted into islands, and the semi-alpine plants would take place of +alpine, and alpine be destroyed, if mountains originally were not of +great height. So we may see, during gradual changes{126} of climate on a +continent, the propagation of species would vary and adapt themselves to +small changes causing much extermination{127}. The mountains of Europe +were quite lately covered with ice, and the lowlands probably partaking +of the Arctic climate and Fauna. Then as climate changed, arctic fauna +would take place of ice, and an inundation of plants from different +temperate countries <would> seize the lowlands, leaving islands of arctic +forms. But if this had happened on an island, whence could the new forms +have come,--here the geologist calls in creationists. If island formed, +the geologist will suggest <that> many of the forms might have been +borne from nearest land, but if peculiar, he calls in creationist,--as +such island rises in height &c., he still more calls in creation. The +creationist tells one, on a <illegible> spot the American spirit of +creation makes _Orpheus_ and _Tyrannus_ and American doves, and in +accordance with past and extinct forms, but no persistent relation +between areas and distribution, Geologico-Geograph.-Distribution. + + {126} In the _Origin_, Ed. i. p. 366, vi. p. 516, the author does + not give his views on the distribution of alpine plants as original + but refers to Edward Forbes' work (_Geolog. Survey Memoirs_, 1846). + In his autobiography, Darwin refers to this. "I was forestalled" he + says, "in only one important point, which my vanity has always made + me regret." (_Life and Letters_, i. p. 88.) + + {127} <The following is written on the back of a page of the MS.> + Discuss one or more centres of creation: allude strongly to + facilities of dispersal and amount of geological change: allude to + mountain-summits afterwards to be referred to. The distribution + varies, as everyone knows, according to adaptation, explain going + from N. to S. how we come to fresh groups of species in the same + general region, but besides this we find difference, according to + greatness of barriers, in greater proportion than can be well + accounted for by adaptation. <On representive species see _Origin_, + Ed. i. p. 349, vi. p. 496.> This very striking when we think of + cattle of Pampas, plants <?> &c. &c. Then go into discussion; this + holds with 3 or 4 main divisions as well as the endless minor ones + in each of these 4 great ones: in these I chiefly refer to mammalia + &c. &c. The similarity of type, but not in species, in same + continent has been much less insisted on than the dissimilarity of + different great regions generically: it is more striking. + + <I have here omitted an incomprehensible sentence.> Galapagos + Islands, Tristan d'Acunha, _volcanic_ islands covered with craters + we know lately did not support any organisms. How unlike these + islands in nature to neighbouring lands. These facts perhaps more + striking than almost any others. [Geology apt to affect geography + therefore we ought to expect to find the above.] + Geological-geographical distribution. In looking to past times we + find Australia equally distinct. S. America was distinct, though + with more forms in common. N. America its nearest neighbour more in + common,--in some respects more, in some less allied to Europe. + Europe we find <?> equally European. For Europe is now part of Asia + though not <illegible>. Africa unknown,--examples, Elephant, + Rhinoceros, Hippopotamus, Hyaena. As geology destroys geography we + cannot be surprised in going far back we find Marsupials and + Edentata in Europe: but geology destroys geography. + +Now according to analogy of domesticated animals let us see what would +result. Let us take case of farmer on Pampas, where everything +approaches nearer to state of nature. He works on organisms having +strong tendency to vary: and he knows <that the> only way to make a +distinct breed is to select and separate. It would be useless to +separate the best bulls and pair with best cows if their offspring run +loose and bred with the other herds, and tendency to reversion not +counteracted; he would endeavour therefore to get his cows on islands +and then commence his work of selection. If several farmers in different +_rincons_{128} were to set to work, especially if with different +objects, several breeds would soon be produced. So would it be with +horticulturist and so history of every plant shows; the number of +varieties{129} increase in proportion to care bestowed on their +selection and, with crossing plants, separation. Now, according to this +analogy, change of external conditions, and isolation either by chance +landing <of> a form on an island, or subsidence dividing a continent, or +great chain of mountains, and the number of individuals not being +numerous will best favour variation and selection{130}. No doubt change +could be effected in same country without any barrier by long continued +selection on one species: even in case of a plant not capable of +crossing would easier get possession and solely occupy an island{131}. +Now we can at once see that <if> two parts of a continent isolated, new +species thus generated in them, would have closest affinities, like +cattle in counties of England: if barrier afterwards destroyed one +species might destroy the other or both keep their ground. So if island +formed near continent, let it be ever so different, that continent would +supply inhabitants, and new species (like the old) would be allied with +that continent. An island generally very different soil and climate, and +number and order of inhabitants supplied by chance, no point so +favourable for generation of new species{132},--especially the +mountains, hence, so it is. As isolated mountains formed in a plain +country (if such happens) is an island. As other islands formed, the old +species would spread and thus extend and the fauna of distant island +might ultimately meet and a continent formed between them. No one doubts +continents formed by repeated elevations and depressions{133}. In +looking backwards, but not so far that all geographical boundaries are +destroyed, we can thus at once see why existing forms are related to the +extinct in the same manner as existing ones are in some part of existing +continent. By chance we might even have one or two absolute parent +fossils. + + {128} _Rincon_ in Spanish means a _nook_ or _corner_, it is here + probably used to mean a small farm. + + {129} The following is written across the page: "No one would + expect a set of similar varieties to be produced in the different + countries, so species different." + + {130} <The following passage seems to have been meant to follow + here.> The parent of an organism, we may generally suppose to be in + less favourable condition than the selected offspring and therefore + generally in fewer numbers. (This is not borne out by horticulture, + mere hypothesis; as an organism in favourable conditions might by + selection be adapted to still more favourable conditions.) + + Barrier would further act in preventing species formed in one part + migrating to another part. + + {131} <The following notes occur on the back of the page.> Number + of species not related to capabilities of the country: furthermore + not always those best adapted, perhaps explained by creationists by + changes and progress. <See p. 34, note 1.{Note 134}> + + Although creationists can, by help of geology, explain much, how + can he explain the marked relation of past and present in same + area, the varying relation in other cases, between past and + present, the relation of different parts of same great area. If + island, to adjoining continent, if quite different, on mountain + summits,--the number of individuals not being related to + capabilities, or how &c.--our theory, I believe, can throw much + light and all facts accord. + + {132} See _Origin_, Ed. i. p. 390, vi. p. 543. + + {133} On oscillation see _Origin_, Ed. i. p. 291, vi. p. 426. + +The detection of transitional forms would be rendered more difficult on +rising point of land. + +The distribution therefore in the above enumerated points, even the +trivial ones, which on any other <theory?> can be viewed as so many +ultimate facts, all follow <in> a simple manner on the theory of the +occurrence of species by <illegible> and being adapted by selection to +<illegible>, conjoined with their power of dispersal, and the steady +geographico-geological changes which are now in progress and which +undoubtedly have taken place. Ought to state the opinion of the +immutability of species and the creation by so many separate acts of +will of the Creator{134}. + + {134} <From the back of MS.> Effect of climate on stationary island + and on continent, but continent once island. Moreover repeated + oscillations fresh diffusion when non-united, then isolation, when + rising again immigration prevented, new habitats formed, new + species, when united free immigration, hence uniform characters. + Hence more forms <on?> the island. Mountain summits. Why not true + species. First let us recall in Part I, conditions of variation: + change of conditions during several generations, and if frequently + altered so much better [perhaps excess of food]. Secondly, continued + selection [while in wild state]. Thirdly, isolation in all or nearly + all,--as well to recall advantages of. + + [In continent, if we look to terrestrial animal, long continued + change might go on, which would only cause change in numerical + number <? proportions>: if continued long enough might ultimately + affect all, though to most continents <there is> chance of + immigration. Some few of whole body of species must be long affected + and entire selection working same way. But here isolation absent, + without barrier, cut off such <illegible>. We can see advantage of + isolation. But let us take case of island thrown up by volcanic + agency at some distances, here we should have occasional visitants, + only in few numbers and exposed to new conditions and <illegible> + more important,--a quite new grouping of organic beings, which would + open out new sources of subsistence, or <would> control <?> old + ones. The number would be few, can old have the very best opportunity. + <The conquest of the indigenes by introduced organisms shows that + the indigenes were not perfectly adapted, see _Origin_, Ed. i. p. + 390.> Moreover as the island continued changing,--continued slow + changes, river, marshes, lakes, mountains &c. &c., new races as + successively formed and a fresh occasional visitant. + + If island formed continent, some species would emerge and + immigrate. Everyone admits continents. We can see why Galapagos and + C. Verde differ <see _Origin_, Ed. i. p. 398>], depressed and raised. + We can see from this repeated action and the time required for a + continent, why many more forms than in New Zealand <see _Origin_, + Ed. i. p. 389 for a comparison between New Zealand and the Cape> no + mammals or other classes <see however, _Origin_, Ed. i. p. 393 for + the case of the frog>. We can at once see how it comes when there + has been an old channel of migration,--Cordilleras; we can see why + Indian Asiatic Flora,--[why species] having a wide range gives + better chance of some arriving at new points and being selected, and + adapted to new ends. I need hardly remark no necessity for change. + + Finally, as continent (most extinction <?> during formation of + continent) is formed after repeated elevation and depression, and + interchange of species we might foretell much extinction, and that + the survivor would belong to same type, as the extinct, in same + manner as different part of same continent, which were once + separated by space as they are by time <see _Origin_, Ed. i. pp. + 339 and 349>. + + As all mammals have descended from one stock, we ought to expect + that every continent has been at some time connected, hence + obliteration of present ranges. I do not mean that the fossil + mammifers found in S. America are the lineal successors <ancestors> + of the present forms of S. America: for it is highly improbable + that more than one or two cases (who will say how many races after + Plata bones) should be found. I believe this from numbers, who have + lived,--mere <?> chance of fewness. Moreover in every case from + very existence of genera and species only few at one time will + leave progeny, under form of new species, to distant ages; and the + more distant the ages the fewer the progenitors. An observation may + be here appended, bad chance of preservation on rising island, the + nurseries of new species, appeal to experience <see _Origin_, Ed. + i. p. 292>. This observation may be extended, that in all cases, + subsiding land must be, in early stages, less favourable to + formation of new species; but it will isolate them, and then if + land recommences rising how favourable. As preoccupation is bar to + diffusion to species, so would it be to a selected variety. But it + would not be if that variety was better fitted to some not fully + occupied station; so during elevation or the formation of new + stations, is scene for new species. But during elevation not + favourable to preservation of fossil (except in caverns <?>); when + subsidence highly favourable in early stages to preservation of + fossils; when subsidence, less sediment. So that our strata, as + general rule will be the tomb of old species (not undergoing any + change) when rising land the nursery. But if there be vestige will + generally be preserved to future ages, the new ones will not be + entombed till fresh subsidence supervenes. In this long gap we + shall have no record: so that wonderful if we should get + transitional forms. I do not mean every stage, for we cannot expect + that, as before shown, until geologists will be prepared to say + that although under unnaturally favourable condition we can trace + in future ages short-horn and Herefordshire <see note 2, p. 26>. + {Note 115} + + +§ VII. <AFFINITIES AND CLASSIFICATION.> + +Looking now to the affinities of organisms, without relation to their +distribution, and taking all fossil and recent, we see the degrees of +relationship are of different degrees and +arbitrary,--sub-genera,--genera,--sub-families, families, orders and +classes and kingdoms. The kind of classification which everyone feels is +most correct is called the natural system, but no can define this. If we +say with Whewell <that we have an> undefined instinct of the importance +of organs{135}, we have no means in lower animals of saying which is +most important, and yet everyone feels that some one system alone +deserves to be called natural. The true relationship of organisms is +brought before one by considering relations of analogy, an otter-like +animal amongst mammalia and an otter amongst marsupials. In such cases +external resemblance and habit of life and _the final end of whole +organization_ very strong, yet no relation{136}. Naturalists cannot +avoid these terms of relation and affinity though they use them +metaphorically. If used in simple earnestness the natural system ought +to be a genealogical <one>; and our knowledge of the points which are +most easily affected in transmission are those which we least value in +considering the natural system, and practically when we find they do +vary we regard them of less value{137}. In classifying varieties the +same language is used and the same kind of division: here also (in +pine-apple){138} we talk of the natural classification, overlooking +similarity of the fruits, because whole plant differs. The origin of +sub-genera, genera, &c., &c., is not difficult on notion of genealogical +succession, and accords with what we know of similar gradations of +affinity in domesticated organisms. In the same region the organic +beings are <illegible> related to each other and the external conditions +in many physical respects are allied{139} and their differences of same +kind, and therefore when a new species has been selected and has +obtained a place in the economy of nature, we may suppose that +generally it will tend to extend its range during geographical changes, +and thus, becoming isolated and exposed to new conditions, will slightly +alter and its structure by selection become slightly remodified, thus we +should get species of a sub-genus and genus,--as varieties of +merino-sheep,--varieties of British and Indian cattle. Fresh species +might go on forming and others become extinct and all might become +extinct, and then we should have <an> extinct genus; a case formerly +mentioned, of which numerous cases occur in Palæontology. But more often +the same advantages which caused the new species to spread and become +modified into several species would favour some of the species being +preserved: and if two of the species, considerably different, each gave +rise to group of new species, you would have two genera; the same thing +will go on. We may look at case in other way, looking to future. +According to mere chance every existing species may generate another, +but if any species, A, in changing gets an advantage and that advantage +(whatever it may be, intellect, &c., &c., or some particular structure +or constitution) is inherited{140}, A will be the progenitor of several +genera or even families in the hard struggle of nature. A will go on +beating out other forms, it might come that A would people earth,--we +may now not have one descendant on our globe of the one or several +original creations{141}. External conditions air, earth, water being +same{142} on globe, and the communication not being perfect, organisms +of widely different descent might become adapted to the same end and +then we should have cases of analogy{143}, [they might even tend to +become numerically representative]. From this often happening each of +the great divisions of nature would have their representative eminently +adapted to earth, to <air>{144}, to water, and to these in <illegible> +and then these great divisions would show numerical relations in their +classification. + + {135} After "organs" is inserted, apparently as an + afterthought:--"no, and instance metamorphosis, afterwards + explicable." + + {136} For analogical resemblances see _Origin_, Ed. i. p. 427, vi. + p. 582. + + {137} "Practically when naturalists are at work, they do not + trouble themselves about the physiological value of the + characters.... If they find a character nearly uniform, ... they + use it as one of high value," _Origin_, Ed. i. p. 417, vi. p. 573. + + {138} "We are cautioned ... not to class two varieties of the + pine-apple together, merely because their fruit, though the most + important part, happens to be nearly identical," _Origin_, Ed. i. + p. 423, vi. p. 579. + + {139} The whole of this passage is obscure, but the text is quite + clear, except for one illegible word. + + {140} <The exact position of the following passage is uncertain:> + "just as it is not likely every present breed of fancy birds + and cattle will propagate, only some of the best." + + {141} This suggests that the author was not far from the principle + of divergence on which he afterwards laid so much stress. See + _Origin_, Ed. i. p. 111, vi. p. 134, also _Life and Letters_, i. p. + 84. + + {142} That is to say the same conditions occurring in different + parts of the globe. + + {143} The position of the following is uncertain, "greyhound and + racehorse have an analogy to each other." The same comparison + occurs in the _Origin_, Ed. i. p. 427, vi. p. 583. + + {144} _Air_ is evidently intended; in the MS. _water_ is written + twice. + + +§ VIII. UNITY [OR SIMILARITY] OF TYPE IN THE GREAT CLASSES. + +Nothing more wonderful in Nat. Hist. than looking at the vast number of +organisms, recent and fossil, exposed to the most diverse conditions, +living in the most distant climes, and at immensely remote periods, +fitted to wholely different ends, yet to find large groups united by a +similar type of structure. When we for instance see bat, horse, +porpoise-fin, hand, all built on same structure{145}, having bones{146} +with same name, we see there is some deep bond of union between +them{147}, to illustrate this is the foundation and objects <?> <of> +what is called the Natural System; and which is foundation of +distinction <?> of true and adaptive characters{148}. Now this wonderful +fact of hand, hoof, wing, paddle and claw being the same, is at once +explicable on the principle of some parent-forms, which might either be +<illegible> or walking animals, becoming through infinite number of small +selections adapted to various conditions. We know that proportion, +size, shape of bones and their accompanying soft parts vary, and hence +constant selection would alter, to almost any purpose <?> the framework +of an organism, but yet would leave a general, even closest similarity in +it. + + {145} Written between the lines occurs:--"extend to birds and other + classes." + + {146} Written between the lines occurs:--"many bones merely + represented." + + {147} In the _Origin_, Ed. i. p. 434, vi. p. 595, the term + _morphology_ is taken as including _unity of type_. The paddle of + the porpoise and the wing of the bat are there used as instances of + morphological resemblance. + + {148} The sentence is difficult to decipher. + +[We know the number of similar parts, as vertebræ and ribs can vary, +hence this also we might expect.] Also <if> the changes carried on to a +certain point, doubtless type will be lost, and this is case with +Plesiosaurus{149}. The unity of type in past and present ages of certain +great divisions thus undoubtedly receives the simplest explanation. + + {149} In the _Origin_, Ed. i. p. 436, vi. p. 598, the author speaks + of the "general pattern" being obscured in the paddles of "extinct + gigantic sea-lizards." + +There is another class of allied and almost identical facts, admitted by +the soberest physiologists, [from the study of a certain set of organs +in a group of organisms] and refers <? referring> to a unity of type of +different organs in the same individual, denominated the science of +"Morphology." The <? this> discovered by beautiful and regular series, +and in the case of plants from monstrous changes, that certain organs in +an individual are other organs metamorphosed. Thus every botanist +considers petals, nectaries, stamens, pistils, germen as metamorphosed +leaf. They thus explain, in the most lucid manner, the position and +number of all parts of the flower, and the curious conversion under +cultivation of one part into another. The complicated double set of jaws +and palpi of crustaceans{150}, and all insects are considered as +metamorphosed <limbs> and to see the series is to admit this phraseology. +The skulls of the vertebrates are undoubtedly composed of three +metamorphosed vertebræ; thus we can understand the strange form of the +separate bones which compose the casket holding man's brain. These{151} +facts differ but slightly from those of last section, if with wing, +paddle, hand and hoof, some common structure was yet visible, or could +be made out by a series of occasional monstrous conversions, and if +traces could be discovered of <the> whole having once existed as walking or +swimming instruments, these organs would be said to be metamorphosed, as +it is they are only said to exhibit a common type. + + {150} See _Origin_, Ed. i. p. 437, vi. p. 599. + + {151} The following passage seems to have been meant to precede the + sentence beginning "These facts":--"It is evident, that when in + each individual species, organs are metamorph. a unity of type + extends." + +This distinction is not drawn by physiologists, and is only implied by +some by their general manner of writing. These facts, though affecting +every organic being on the face of the globe, which has existed, or does +exist, can only be viewed by the Creationist as ultimate and +inexplicable facts. But this unity of type through the individuals of a +group, and this metamorphosis of the same organ into other organs, +adapted to diverse use, necessarily follows on the theory of +descent{152}. For let us take case of Vertebrata, which if{153} they +descended from one parent and by this theory all the Vertebrata have +been altered by slow degrees, such as we see in domestic animals. We +know that proportions alter, and even that occasionally numbers of +vertebræ alter, that parts become soldered, that parts are lost, as tail +and toes, but we know <that?> here we can see that possibly a walking organ +might <?> be converted into swimming or into a gliding organ and so on to a +flying organ. But such gradual changes would not alter the unity of type +in their descendants, as parts lost and soldered and vertebræ. But we +can see that if this carried to extreme, unity lost,--Plesiosaurus. Here +we have seen the same organ is formed <?> <for> different purposes +<ten words illegible>: and if, in several orders of vertebrata, we could +trace origin <of> spinous processes and monstrosities &c. we should say, +instead of there existing a unity of type, morphology{154}, as we do +when we trace the head as being the vertebræ metamorphosed. Be it +observed that Naturalists, as they use terms of affinity without +attaching real meaning, here also they are obliged to use metamorphosis, +without meaning that any parent of crustacean was really an animal with +as many legs as crustacean has jaws. The theory of descent at once +explains these wonderful facts. + + {152} This is, I believe, the first place in which the author uses + the words "theory of descent." + + {153} The sentence should probably run, "Let us take the case of + the vertebrata: if we assume them to be descended from one parent, + then by this theory they have been altered &c." + + {154} That is "we should call it a morphological fact." + +Now few of the physiologists who use this language really suppose that +the parent of insect with the metamorphosed jaw, was an insect with +[more] so many legs, or that the parent of flowering plants, originally +had no stamens, or pistils or petals, but some other means of +propagation,--and so in other cases. Now according to our theory during +the infinite number of changes, we might expect that an organ used for a +purpose might be used for a different one by his descendant, as must +have been the case by our theory with the bat, porpoise, horse, &c., +which are descended from one parent. And if it so chanced that traces of +the former use and structure of the part should be retained, which is +manifestly possible if not probable, then we should have the organs, on +which morphology is founded and which instead of being metaphorical +becomes plain and <and instead of being> utterly unintelligible becomes +simple matter of fact{155}. + + {155} In the _Origin_, Ed. i. p. 438, vi. p. 602, the author, + referring to the expressions used by naturalists in regard to + morphology and metamorphosis, says "On my view these terms may be + used literally." + +<_Embryology._> This general unity of type in great groups of organisms +(including of course these morphological cases) displays itself in a +most striking manner in the stages through which the foetus passes{156}. +In early stage, the wing of bat, hoof, hand, paddle are not to be +distinguished. At a still earlier <stage> there is no difference between +fish, bird, &c. &c. and mammal. It is not that they cannot be +distinguished, but the arteries{157} <illegible>. It is not true that +one passes through the form of a lower group, though no doubt fish more +nearly related to foetal state{158}. + + {156} See _Origin_, Ed. i. p. 439, vi. p. 605. + + {157} In the _Origin_, Ed. i. p. 440, vi. p. 606, the author argues + that the "loop-like course of the arteries" in the vertebrate + embryo has no direct relation to the conditions of existence. + + {158} The following passages are written across the page:--"They + pass through the same phases, but some, generally called the higher + groups, are further metamorphosed. + + ? Degradation and complication? no tendency to perfection. + + ? Justly argued against Lamarck?" + +This similarity at the earliest stage is remarkably shown in the course +of the arteries which become greatly altered, as foetus advances in life +and assumes the widely different course and number which characterize +full-grown fish and mammals. How wonderful that in egg, in water or air, +or in womb of mother, artery{159} should run in same course. + + {159} An almost identical passage occurs in the _Origin_, Ed. i. p. + 440, vi. p. 606. + +Light can be thrown on this by our theory. The structure of each +organism is chiefly adapted to the sustension of its life, when +full-grown, when it has to feed itself and propagate{160}. The structure +of a kitten is quite in secondary degree adapted to its habits, whilst +fed by its mother's milk and prey. Hence variation in the structure of +the full-grown species will _chiefly_ determine the preservation of a +species now become ill-suited to its habitat, or rather with a better +place opened to it in the economy of Nature. It would not matter to the +full-grown cat whether in its young state it was more or less eminently +feline, so that it become so when full-grown. No doubt most variation, +(not depending on habits of life of individual) depends on early +change{161} and we must suspect that at whatever time of life the +alteration of foetus is effected, it tends to appear at same period. +When we <see> a tendency to particular disease in old age transmitted by +the male, we know some effect is produced during conception, on the +simple cell of ovule, which will not produce its effect till half a +century afterwards and that effect is not visible{162}. So we see in +grey-hound, bull-dog, in race-horse and cart-horse, which have been +selected for their form in full-life, there is much less (?) difference +in the few first days after birth{163}, than when full-grown: so in +cattle, we see it clearly in cases of cattle, which differ obviously in +shape and length of horns. If man were during 10,000 years to be able to +select, far more diverse animals from horse or cow, I should expect +there would be far less differences in the very young and foetal state: +and this, I think, throws light on above marvellous fact. In larvæ, +which have long life selection, perhaps, does much,--in the pupa not so +much{164} There is no object gained in varying form &c. of foetus +(beyond certain adaptations to mother's womb) and therefore selection +will not further act on it, than in giving to its changing tissues a +tendency to certain parts afterwards to assume certain forms. + + {160} The following: "Deaths of brothers <when> old by same peculiar + disease" which is written between the lines seems to have been a + memorandum which is expanded a few lines lower. I believe the case + of the brothers came from Dr R. W. Darwin. + + {161} See the discussion to this effect in the _Origin_, Ed. i. pp. + 443-4, vi. p. 610. The author there makes the distinction between a + cause affecting the germ-cell and the reaction occurring at a late + period of life. + + {162} Possibly the sentence was meant to end "is not visible till + then." + + {163} See _Origin_, Ed. i. pp. 444-5, vi. p. 611. The query + appended to _much less_ is justified, since measurement was + necessary to prove that the greyhound and bulldog puppies had not + nearly acquired "their full amount of proportional difference." + + {164} <The following discussion, from the back of the page, is in + large measure the same as the text.> I think light can be thrown on + these facts. From the following peculiarities being hereditary, [we + know that some change in the germinal vesicle is effected, which + will only betray itself years after] diseases--man, goitre, gout, + baldness, fatness, size, [longevity <illegible> time of reproduction, + shape of horns, case of old brothers dying of same disease]. And we + know that the germinal vesicle must have been affected, though no + effect is apparent or can be apparent till years afterwards,--no + more apparent than when these peculiarities appear by the exposure + of the full-grown individual. <That is, "the young individual is as + apparently free from the hereditary changes which will appear + later, as the young is actually free from the changes produced by + exposure to certain conditions in adult life."> So that when we see + a variety in cattle, even if the variety be due to act of + reproduction, we cannot feel sure at what period this change became + apparent. It may have been effected during early age of free life + <or> foetal existence, as monsters show. From arguments before used, + and crossing, we may generally suspect in germ; but I repeat it + does not follow, that the change should be apparent till life fully + developed; any more than fatness depending on heredity should be + apparent during early childhood, still less during foetal + existence. In case of horns of cattle, which when inherited must + depend on germinal vesicle, obviously no effect till cattle + full-grown. Practically it would appear that the [hereditary] + peculiarities characterising our domestic races, therefore + resulting from vesicle, do not appear with their full characters + in very early states; thus though two breeds of cows have calves + different, they are not so different,--grey-hound and bull-dog. + And this is what is <to> be expected, for man is indifferent to + characters of young animals and hence would select those full-grown + animals which possessed the desirable characteristics. So that from + mere chance we might expect that some of the characters would be + such only as became fully apparent in mature life. Furthermore we + may suspect it to be a law, that at whatever time a new character + appears, whether from vesicle, or effects of external conditions, + it would appear at corresponding time <see _Origin_, Ed. i. p. 444>. + Thus diseases appearing in old age produce children with d^o.,--early + maturity,--longevity,--old men, brothers, of same disease--young + children of d^o. I said men do not select for quality of + young,--calf with big bullocks. Silk-worms, peculiarities which, + appear in caterpillar state or cocoon state, are transmitted to + corresponding states. The effect of this would be that if some + peculiarity was born in a young animal, but never exercised, it + might be inherited in young animal; but if exercised that part of + structure would be increased and would be inherited in + corresponding time of life after such training. + + I have said that man selects in full-life, so would it be in + Nature. In struggle of existence, it matters nothing to a feline + animal, whether kitten eminently feline, as long as it sucks. + Therefore natural selection would act equally well on character + which was fully <developed> only in full age. Selection could tend + to alter no character in foetus, (except relation to mother) it would + alter less in young state (putting on one side larva condition) but + alter every part in full-grown condition. Look to a foetus and its + parent, and again after ages foetus and its <i. e. the above + mentioned parents> descendant; the parent more variable <?> than + foetus, which explains all.] + +Thus there is no power to change the course of the arteries, as long as +they nourish the foetus; it is the selection of slight changes which +supervene at any time during <illegible> of life. + +The less differences of foetus,--this has obvious meaning on this view: +otherwise how strange that a [monkey] horse, a man, a bat should at one +time of life have arteries, running in a manner, which is only +intelligibly useful in a fish! The natural system being on theory +genealogical, we can at once see, why foetus, retaining traces of the +ancestral form, is of the highest value in classification. + + +§ IX. <ABORTIVE ORGANS.> + +There is another grand class of facts relating to what are called +abortive organs. These consist of organs which the same reasoning power +that shows us how beautifully these organs in some cases are adapted to +certain end, declares in other cases are absolutely useless. Thus teeth +in Rhinoceros{165}, whale, narwhal,--bone on tibia, muscles which do not +move,--little bone of wing of Apteryx,--bone representing extremities in +some snake,--little wings within <?> soldered cover of beetles,--men and +bulls, mammæ: filaments without anthers in plants, mere scales +representing petals in others, in feather-hyacinth whole flower. Almost +infinitely numerous. No one can reflect on these without astonishment, +can anything be clearer than that wings are to fly and teeth <to bite>, +and yet we find these organs perfect in every detail in situations where +they cannot possibly be of their normal use{166}. + + {165} Some of these examples occur in _Origin_, Ed. i. pp. 450-51, + vi. pp. 619-20. + + {166} The two following sentences are written, one down the margin, + the other across the page. "Abortive organs eminently useful in + classification. Embryonic state of organs. Rudiments of organs." + +The term abortive organ has been thus applied to above structure (as +_invariable_ as all other parts{167}) from their absolute similarity to +monstrous cases, where from _accident_, certain organs are not +developed; as infant without arms or fingers with mere stump +representing them: teeth represented by mere points of ossification: +headless children with mere button,--viscera represented by small +amorphous masses, &c.,--the tail by mere stump,--a solid horn by minute +hanging one{168}. There is a tendency in all these cases, when life is +preserved, for such structures to become hereditary. We see it in +tailless dogs and cats. In plants we see this strikingly,--in Thyme, in +_Linum flavum_,--stamen in _Geranium pyrenaicum_{169}. Nectaries abort +into petals in Columbine <_Aquilegia_>, produced from some accident and +then become hereditary, in some cases only when propagated by buds, in +other cases by seed. These cases have been produced suddenly by accident +in early growth, but it is part of law of growth that when any organ is +not used it tends to diminish (duck's wing{170}?) muscles of dog's ears, +<and of> rabbits, muscles wither, arteries grow up. When eye born +defective, optic nerve (Tuco Tuco) is atrophied. As every part whether +useful or not (diseases, double flowers) tends to be transmitted to +offspring, the origin of abortive organs whether produced at the birth +or slowly acquired is easily understood in domestic races of organisms: +[a struggle between the atrophy and hereditariness. Abortive organs in +domestic races.] There will always be a struggle between atrophy of an +organ rendered useless, and hereditariness{171}. Because we can +understand the origin of abortive organs in certain cases, it would be +wrong to conclude absolutely that all must have had same origin, but the +strongest analogy is in favour of it. And we can by our theory, for +during infinite changes some organ, we might have anticipated, would +have become useless. <We can> readily explain the fact, so astounding +on any other view, namely that organs possibly useless have been formed +often with the same exquisite care as when of vital importance. + + {167} I imagine the meaning to be that abortive organs are specific + characters in contrast to monstrosities. + + {168} Minute hanging horns are mentioned in the _Origin_, Ed. i. p. + 454, vi. p. 625, as occurring in hornless breeds of cattle. + + {169} _Linum flavum_ is dimorphic: thyme gynodiæcious. It is not + clear what point is referred to under _Geranium pyrenaicum_. + + {170} The author's work on duck's wings &c. is in _Var. under + Dom._, Ed. 2, i. p. 299. + + {171} The words _vis medicatrix_ are inserted after "useless," + apparently as a memorandum. + +Our theory, I may remark would permit an organ <to> become abortive with +respect to its primary use, to be turned to any other purpose, (as the +buds in a cauliflower) thus we can see no difficulty in bones of male +marsupials being used as fulcrum of muscles, or style of +marygold{172},--indeed in one point of view, the heads of [vertebrated] +animal may be said to be abortive vertebræ turned into other use: legs +of some crustacea abortive jaws, &c., &c. De Candolle's analogy of table +covered with dishes{173}. + + {172} In the male florets of certain Compositæ the style functions + merely as a piston for forcing out the pollen. + + {173} <On the back of the page is the following.> If abortive organs + are a trace preserved by hereditary tendency, of organ in ancestor + of use, we can at once see why important in natural classification, + also why more plain in young animal because, as in last section, the + selection has altered the old animal most. I repeat, these wondrous + facts, of parts created for no use in past and present time, all + can by my theory receive simple explanation; or they receive none + and we must be content with some such empty metaphor, as that of De + Candolle, who compares creation to a well covered table, and says + abortive organs may be compared to the dishes (some should be empty) + placed symmetrically! + +<The following passage was possibly intended to be inserted here.> +Degradation and complication see Lamarck: no tendency to perfection: if +room, [even] high organism would have greater power in beating lower +one, thought <?> to be selected for a degraded end. + + +§ X. RECAPITULATION AND CONCLUSION. + +Let us recapitulate the whole <?> <of> these latter sections by taking +case of the three species of Rhinoceros, which inhabit Java, Sumatra, +and mainland of Malacca or India. We find these three close neighbours, +occupants of distinct but neighbouring districts, as a group having a +different aspect from the Rhinoceros of Africa, though some of these +latter inhabit very similar countries, but others most diverse stations. +We find them intimately related [scarcely <?> differences more than some +breeds of cattle] in structure to the Rhinoceros, which for immense +periods have inhabited this one, out of three main zoological divisions +of the world. Yet some of these ancient animals were fitted to very +different stations: we find all three <illegible> of the generic character +of the Rhinoceros, which form a [piece of net]{174} set of links in the +broken chain representing the Pachydermata, as the chain likewise forms +a portion in other and longer chains. We see this wonderfully in +dissecting the coarse leg of all three and finding nearly the same bones +as in bat's wings or man's hand, but we see the clear mark in solid +tibia of the fusion into it of the fibula. In all three we find their +heads composed of three altered vertebræ, short neck, same bones as +giraffe. In the upper jaws of all three we find small teeth like +rabbit's. In dissecting them in foetal state we find at a not very early +stage their form exactly alike the most different animals, and even with +arteries running as in a fish: and this similarity holds when the young +one is produced in womb, pond, egg or spawn. Now these three undoubted +species scarcely differ more than breeds of cattle, are probably +subject to many the same contagious diseases; if domesticated these +forms would vary, and they might possibly breed together, and fuse into +something{175} different <from> their aboriginal forms; might be selected +to serve different ends. + + {174} The author doubtless meant that the complex relationships + between organisms can be roughly represented by a net in which the + knots stand for species. + + {175} Between the lines occurs:--"one <?> form be lost." + +Now the Creationist believes these three Rhinoceroses were created{176} +with their deceptive appearance of true, not <illegible> relationship; +as well can I believe the planets revolve in their present courses not +from one law of gravity but from distinct volition of Creator. + + {176} The original sentence is here broken up by the insertion + of:--"out of the dust of Java, Sumatra, these <?> allied to past + and present age and <illegible>, with the stamp of inutility in + some of their organs and conversion in others." + +If real species, sterile one with another, differently adapted, now +inhabiting different countries, with different structures and instincts, +are admitted to have common descent, we can only legitimately stop where +our facts stop. Look how far in some case a chain of species will lead +us. <This probably refers to the Crustacea, where the two ends of the +series have "hardly a character in common." _Origin_, Ed. i. p. 419.> +May we not jump (considering how much extermination, and how imperfect +geological records) from one sub-genus to another sub-genus. Can genera +restrain us; many of the same arguments, which made us give up species, +inexorably demand genera and families and orders to fall, and classes +tottering. We ought to stop only when clear unity of type, independent +of use and adaptation, ceases. + +Be it remembered no naturalist pretends to give test from external +characters of species; in many genera the distinction is quite +arbitrary{177}. But there remains one other way of comparing species +with races; it is to compare the effects of crossing them. Would it not +be wonderful, if the union of two organisms, produced by two separate +acts of Creation, blended their characters together when crossed +according to the same rules, as two races which have undoubtedly +descended from same parent stock; yet this can be shown to be the case. +For sterility, though a usual <?>, is not an invariable concomitant, it +varies much in degree and has been shown to be probably dependent on +causes closely analogous with those which make domesticated organisms +sterile. Independent of sterility there is no difference between +mongrels and hybrids, as can be shown in a long series of facts. It is +strikingly seen in cases of instincts, when the minds of the two species +or races become blended together{178}. In both cases if the half-breed +be crossed with either parent for a few generations, all traces of the +one parent form is lost (as Kölreuter in two tobacco species almost +sterile together), so that the Creationist in the case of a species, +must believe that one act of creation is absorbed into another! + + {177} Between the lines occur the words:--"Species vary according + to same general laws as varieties; they cross according to same + laws." + + {178} "A cross with a bull-dog has affected for many generations + the courage and obstinacy of greyhounds," _Origin_, Ed. i. p. 214, + vi. p. 327. + +{Illustration: Facsimile of the original manuscript of the paragraph on +p. 50.} + + +CONCLUSION. + +Such are my reasons for believing that specific forms are not immutable. +The affinity of different groups, the unity of types of structure, the +representative forms through which foetus passes, the metamorphosis of +organs, the abortion of others cease to be metaphorical expressions and +become intelligible facts. We no longer look <an> on animal as a savage does +at a ship{179}, or other great work of art, as a thing wholly beyond +comprehension, but we feel far more interest in examining it. How +interesting is every instinct, when we speculate on their origin as an +hereditary or congenital habit or produced by the selection of +individuals differing slightly from their parents. We must look at every +complicated mechanism and instinct, as the summary of a long history, +<as the summing up> of{180} useful contrivances, much like a work of art. +How interesting does the distribution of all animals become, as throwing +light on ancient geography. [We see some seas bridged over.] Geology +loses in its glory from the imperfection of its archives{181}, but how +does it gain in the immensity of the periods of its formations and of +the gaps separating these formations. There is much grandeur in looking +at the existing animals either as the lineal descendants of the forms +buried under thousand feet of matter, or as the coheirs of some still +more ancient ancestor. It accords with what we know of the law impressed +on matter by the Creator, that the creation and extinction of forms, +like the birth and death of individuals should be the effect of +secondary [laws] means{182}. It is derogatory that the Creator of +countless systems of worlds should have created each of the myriads of +creeping parasites and [slimy] worms which have swarmed each day of life +on land and water <on> [this] one globe. We cease being astonished, however +much we may deplore, that a group of animals should have been directly +created to lay their eggs in bowels and flesh of other,--that some +organisms should delight in cruelty,--that animals should be led away by +false instincts,--that annually there should be an incalculable waste +of eggs and pollen. From death, famine, rapine, and the concealed war of +nature we can see that the highest good, which we can conceive, the +creation of the higher animals has directly come. Doubtless it at first +transcends our humble powers, to conceive laws capable of creating +individual organisms, each characterised by the most exquisite +workmanship and widely-extended adaptations. It accords better with [our +modesty] the lowness of our faculties to suppose each must require the +fiat of a creator, but in the same proportion the existence of such laws +should exalt our notion of the power of the omniscient Creator{183}. +There is a simple grandeur in the view of life with its powers of +growth, assimilation and reproduction, being originally breathed into +matter under one or a few forms, and that whilst this our planet has +gone circling on according to fixed laws, and land and water, in a cycle +of change, have gone on replacing each other, that from so simple an +origin, through the process of gradual selection of infinitesimal +changes, endless forms most beautiful and most wonderful have been +evolved{184}. + + {179} The simile of the savage and the ship occurs in the _Origin_, + Ed. i. p. 485, vi. p. 665. + + {180} In the _Origin_, Ed. i. p. 486, vi. p. 665, the author speaks + of the "summing up of many contrivances": I have therefore + introduced the above words which make the passage clearer. In the + _Origin_ the comparison is with "a great mechanical + invention,"--not with a work of art. + + {181} See a similar passage in the _Origin_, Ed. i. p. 487, vi. p. + 667. + + {182} See the _Origin_, Ed. i. p. 488, vi. p. 668. + + {183} The following discussion, together with some memoranda are on + the last page of the MS. "The supposed creative spirit does not + create either number or kind which <are> from analogy adapted to site + (viz. New Zealand): it does not keep them all permanently adapted + to any country,--it works on spots or areas of creation,--it is not + persistent for great periods,--it creates forms of same groups in + same regions, with no physical similarity,--it creates, on islands + or mountain summits, species allied to the neighbouring ones, and + not allied to alpine nature as shown in other mountain + summits--even different on different island of similarly + constituted archipelago, not created on two points: never mammifers + created on small isolated island; nor number of organisms adapted + to locality: its power seems influenced or related to the range of + other species wholly distinct of the same genus,--it does not + equally effect, in amount of difference, all the groups of the same + class." + + {184} This passage is the ancestor of the concluding words in the + first edition of the _Origin of Species_ which have remained + substantially unchanged throughout subsequent editions, "There is + grandeur in this view of life, with its several powers, having been + originally breathed into a few forms or into one; and that whilst + this planet has gone cycling on according to the fixed law of + gravity, from so simple a beginning endless forms most beautiful + and most wonderful have been, and are being, evolved." In the 2nd + edition "by the Creator" is introduced after "originally breathed." + +N.B.--There ought somewhere to be a discussion from Lyell to show that +external conditions do vary, or a note to Lyell's works <work?>. + +Besides other difficulties in ii. Part, non-acclimatisation of plants. +Difficulty when asked _how_ did white and negro become altered from +common intermediate stock: no facts. We do NOT know that species are +immutable, on the contrary. What arguments against this theory, except +our not perceiving every step, like the erosion of valleys{185}. + + {185} Compare the _Origin_, Ed. i. p. 481, vi. p. 659, "The + difficulty is the same as that felt by so many geologists, when + Lyell first insisted that long lines of inland cliffs had been + formed, and great valleys excavated, by the slow action of the + coast-waves." + + + + +THE ESSAY OF 1844 PART I + + + + +CHAPTER I + +ON THE VARIATION OF ORGANIC BEINGS UNDER DOMESTICATION; AND ON THE +PRINCIPLES OF SELECTION + + +The most favourable conditions for variation seem to be when organic +beings are bred for many generations under domestication{186}: one may +infer this from the simple fact of the vast number of races and breeds +of almost every plant and animal, which has long been domesticated. +Under certain conditions organic beings even during their individual +lives become slightly altered from their usual form, size, or other +characters: and many of the peculiarities thus acquired are transmitted +to their offspring. Thus in animals, the size and vigour of body, +fatness, period of maturity, habits of body or consensual movements, +habits of mind and temper, are modified or acquired during the life of +the individual{187}, and become inherited. There is reason to believe +that when long exercise has given to certain muscles great development, +or disuse has lessened them, that such development is also inherited. +Food and climate will occasionally produce changes in the colour and +texture of the external coverings of animals; and certain unknown +conditions affect the horns of cattle in parts of Abyssinia; but whether +these peculiarities, thus acquired during individual lives, have been +inherited, I do not know. It appears certain that malconformation and +lameness in horses, produced by too much work on hard roads,--that +affections of the eyes in this animal probably caused by bad +ventilation,--that tendencies towards many diseases in man, such as +gout, caused by the course of life and ultimately producing changes of +structure, and that many other diseases produced by unknown agencies, +such as goitre, and the idiotcy resulting from it, all become +hereditary. + + {186} The cumulative effect of domestication is insisted on in the + _Origin_, see _e.g. Origin_, Ed. i. p. 7, vi. p. 8. + + {187} This type of variation passes into what he describes as the + direct effect of conditions. Since they are due to causes acting + during the adult life of the organism they might be called + individual variations, but he uses this term for congenital + variations, _e.g._ the differences discoverable in plants raised + from seeds of the same pod _(Origin_, Ed. i. p. 45, vi. p. 53). + +It is very doubtful whether the flowers and leaf-buds, annually produced +from the same bulb, root, or tree, can properly be considered as parts +of the same individual, though in some respects they certainly seem to +be so. If they are parts of an individual, plants also are subject to +considerable changes during their _individual_ lives. Most +florist-flowers if neglected degenerate, that is, they lose some of +their characters; so common is this, that trueness is often stated, as +greatly enhancing the value of a variety{188}: tulips break their +colours only after some years' culture; some plants become double and +others single, by neglect or care: these characters can be transmitted +by cuttings or grafts, and in some cases by true or seminal propagation. +Occasionally a single bud on a plant assumes at once a new and widely +different character: thus it is certain that nectarines have been +produced on peach trees and moss roses on provence roses; white +currants on red currant bushes; flowers of a different colour from that +of the stock, in Chrysanthemums, Dahlias, sweet-williams, Azaleas, &c., +&c.; variegated leaf-buds on many trees, and other similar cases. These +new characters appearing in single buds, can, like those lesser changes +affecting the whole plant, be multiplied not only by cuttings and such +means, but often likewise by true seminal generation. + + {188} <It is not clear where the following note is meant to come>: + Case of Orchis,--most remarkable as not long cultivated by + seminal propagation. Case of varieties which soon acquire, like + _Ægilops_ and Carrot (and Maize) _a certain general character_ and + then go on varying. + +The changes thus appearing during the lives of individual animals and +plants are extremely rare compared with those which are congenital or +which appear soon after birth. Slight differences thus arising are +infinitely numerous: the proportions and form of every part of the +frame, inside and outside, appear to vary in very slight degrees: +anatomists dispute what is the "beau ideal" of the bones, the liver and +kidneys, like painters do of the proportions of the face: the proverbial +expression that no two animals or plants are born absolutely alike, is +much truer when applied to those under domestication, than to those in a +state of nature{189}. Besides these slight differences, single +individuals are occasionally born considerably unlike in certain parts +or in their whole structure to their parents: these are called by +horticulturists and breeders "sports"; and are not uncommon except when +very strongly marked. Such sports are known in some cases to have been +parents of some of our domestic races; and such probably have been the +parents of many other races, especially of those which in some senses +may be called hereditary monsters; for instance where there is an +additional limb, or where all the limbs are stunted (as in the Ancon +sheep), or where a part is wanting, as in rumpless fowls and tailless +dogs or cats{190}. The effects of external conditions on the size, +colour and form, which can rarely and obscurely be detected during one +individual life, become apparent after several generations: the slight +differences, often hardly describable, which characterize the stock of +different countries, and even of districts in the same country, seem to +be due to such continued action. + + {189} Here, as in the MS. of 1842, the author is inclined to + minimise the variation occurring in nature. + + {190} This is more strongly stated than in the _Origin_, Ed. i. p. + 30. + + +_On the hereditary tendency._ + +A volume might be filled with facts showing what a strong tendency there +is to inheritance, in almost every case of the most trifling, as well as +of the most remarkable congenital peculiarities{191}. The term +congenital peculiarity, I may remark, is a loose expression and can only +mean a peculiarity apparent when the part affected is nearly or fully +developed: in the Second Part, I shall have to discuss at what period of +the embryonic life connatal peculiarities probably first appear; and I +shall then be able to show from some evidence, that at whatever period +of life a new peculiarity first appears, it tends hereditarily to appear +at a corresponding period{192}. Numerous though slight changes, slowly +supervening in animals during mature life (often, though by no means +always, taking the form of disease), are, as stated in the first +paragraphs, very often hereditary. In plants, again, the buds which +assume a different character from their stock likewise tend to transmit +their new peculiarities. There is not sufficient reason to believe that +either mutilations{193} or changes of form produced by mechanical +pressure, even if continued for hundreds of generations, or that any +changes of structure quickly produced by disease, are inherited; it +would appear as if the tissue of the part affected must slowly and +freely grow into the new form, in order to be inheritable. There is a +very great difference in the hereditary tendency of different +peculiarities, and of the same peculiarity, in different individuals and +species; thus twenty thousand seeds of the weeping ash have been sown +and not one come up true;--out of seventeen seeds of the weeping yew, +nearly all came up true. The ill-formed and almost monstrous "Niata" +cattle of S. America and Ancon sheep, both when bred together and when +crossed with other breeds, seem to transmit their peculiarities to their +offspring as truly as the ordinary breeds. I can throw no light on these +differences in the power of hereditary transmission. Breeders believe, +and apparently with good cause, that a peculiarity generally becomes +more firmly implanted after having passed through several generations; +that is if one offspring out of twenty inherits a peculiarity from its +parents, then its descendants will tend to transmit this peculiarity to +a larger proportion than one in twenty; and so on in succeeding +generations. I have said nothing about mental peculiarities being +inheritable for I reserve this subject for a separate chapter. + + {191} See _Origin_, Ed. i. p. 13. + + {192} _Origin_, Ed. i. p. 86, vi. p. 105. + + {193} It is interesting to find that though the author, like his + contemporaries, believed in the inheritance of acquired characters, + he excluded the case of mutilation. + + +_Causes of Variation._ + +Attention must here be drawn to an important distinction in the first +origin or appearance of varieties: when we see an animal highly kept +producing offspring with an hereditary tendency to early maturity and +fatness; when we see the wild-duck and Australian dog always becoming, +when bred for one or a few generations in confinement, mottled in their +colours; when we see people living in certain districts or circumstances +becoming subject to an hereditary taint to certain organic diseases, as +consumption or plica polonica,--we naturally attribute such changes to +the direct effect of known or unknown agencies acting for one or more +generations on the parents. It is probable that a multitude of +peculiarities may be thus directly caused by unknown external agencies. +But in breeds, characterized by an extra limb or claw, as in certain +fowls and dogs; by an extra joint in the vertebræ; by the loss of a +part, as the tail; by the substitution of a tuft of feathers for a comb +in certain poultry; and in a multitude of other cases, we can hardly +attribute these peculiarities directly to external influences, but +indirectly to the laws of embryonic growth and of reproduction. When we +see a multitude of varieties (as has often been the case, where a cross +has been carefully guarded against) produced from seeds matured in the +very same capsule{194}, with the male and female principle nourished +from the same roots and necessarily exposed to the same external +influences; we cannot believe that the endless slight differences +between seedling varieties thus produced, can be the effect of any +corresponding difference in their exposure. We are led (as Müller has +remarked) to the same conclusion, when we see in the same litter, +produced by the same act of conception, animals considerably different. + + {194} This corresponds to _Origin_, Ed. i. p. 10, vi. p. 9. + +As variation to the degree here alluded to has been observed only in +organic beings under domestication, and in plants amongst those most +highly and long cultivated, we must attribute, in such cases, the +varieties (although the difference between each variety cannot possibly +be attributed to any corresponding difference of exposure in the +parents) to the indirect effects of domestication on the action of the +reproductive system{195}. It would appear as if the reproductive powers +failed in their ordinary function of producing new organic beings +closely like their parents; and as if the entire organization of the +embryo, under domestication, became in a slight degree plastic{196}. We +shall hereafter have occasion to show, that in organic beings, a +considerable change from the natural conditions of life, affects, +independently of their general state of health, in another and +remarkable manner the reproductive system. I may add, judging from the +vast number of new varieties of plants which have been produced in the +same districts and under nearly the same routine of culture, that +probably the indirect effects of domestication in making the +organization plastic, is a much more efficient source of variation than +any direct effect which external causes may have on the colour, texture, +or form of each part. In the few instances in which, as in the +Dahlia{197}, the course of variation has been recorded, it appears that +domestication produces little effect for several generations in +rendering the organization plastic; but afterwards, as if by an +accumulated effect, the original character of the species suddenly gives +way or breaks. + + {195} _Origin_, Ed. i. p. 8, vi. p. 10. + + {196} For _plasticity_ see _Origin_, Ed. i. pp. 12, 132. + + {197} _Var. under Dom._, Ed. ii. I. p. 393. + + +_On Selection._ + +We have hitherto only referred to the first appearance in individuals of +new peculiarities; but to make a race or breed, something more is +generally{198} requisite than such peculiarities (except in the case of +the peculiarities being the direct effect of constantly surrounding +conditions) should be inheritable,--namely the principle of selection, +implying separation. Even in the rare instances of sports, with the +hereditary tendency very strongly implanted, crossing must be prevented +with other breeds, or if not prevented the best characterized of the +half-bred offspring must be carefully selected. Where the external +conditions are constantly tending to give some character, a race +possessing this character will be formed with far greater ease by +selecting and breeding together the individuals most affected. In the +case of the endless slight variations produced by the indirect effects +of domestication on the action of the reproductive system, selection is +indispensable to form races; and when carefully applied, wonderfully +numerous and diverse races can be formed. Selection, though so simple in +theory, is and has been important to a degree which can hardly be +overrated. It requires extreme skill, the results of long practice, in +detecting the slightest difference in the forms of animals, and it +implies some distinct object in view; with these requisites and +patience, the breeder has simply to watch for every the smallest +approach to the desired end, to select such individuals and pair them +with the most suitable forms, and so continue with succeeding +generations. In most cases careful selection and the prevention of +accidental crosses will be necessary for several generations, for in new +breeds there is a strong tendency to vary and especially to revert to +ancestral forms: but in every succeeding generation less care will be +requisite for the breed will become truer; until ultimately only an +occasional individual will require to be separated or destroyed. +Horticulturalists in raising seeds regularly practise this, and call it +"roguing," or destroying the "rogues" or false varieties. There is +another and less efficient means of selection amongst animals: namely +repeatedly procuring males with some desirable qualities, and allowing +them and their offspring to breed freely together; and this in the +course of time will affect the whole lot. These principles of selection +have been _methodically_ followed for scarcely a century; but their +high importance is shown by the practical results, and is admitted +in the writings of the most celebrated agriculturalists and +horticulturalists;--I need only name Anderson, Marshall, Bakewell, Coke, +Western, Sebright and Knight. + + {198} Selection is here used in the sense of isolation, rather than + as implying the summation of small differences. Professor Henslow + in his _Heredity of Acquired Characters in Plants_, 1908, p. 2, + quotes from Darwin's _Var. under Dom._, Ed. i. II. p. 271, a + passage in which the author, speaking of the direct action of + conditions, says:--"A new sub-variety would thus be produced + without the aid of selection." Darwin certainly did not mean to + imply that such varieties are freed from the action of natural + selection, but merely that a new form may appear without + _summation_ of new characters. Professor Henslow is apparently + unaware that the above passage is omitted in the second edition of + _Var. under Dom._, II. p. 260. + +Even in well-established breeds the individuals of which to an +unpractised eye would appear absolutely similar, which would give, it +might have been thought, no scope to selection, the whole appearance of +the animal has been changed in a few years (as in the case of Lord +Western's sheep), so that practised agriculturalists could scarcely +credit that a change had not been effected by a cross with other breeds. +Breeders both of plants and animals frequently give their means of +selection greater scope, by crossing different breeds and selecting the +offspring; but we shall have to recur to this subject again. + +The external conditions will doubtless influence and modify the results +of the most careful selection; it has been found impossible to prevent +certain breeds of cattle from degenerating on mountain pastures; it +would probably be impossible to keep the plumage of the wild-duck in the +domesticated race; in certain soils, no care has been sufficient to +raise cauliflower seed true to its character; and so in many other +cases. But with patience it is wonderful what man has effected. He has +selected and therefore in one sense made one breed of horses to race and +another to pull; he has made sheep with fleeces good for carpets and +other sheep good for broadcloth; he has, in the same sense, made one dog +to find game and give him notice when found, and another dog to fetch +him the game when killed; he has made by selection the fat to lie mixed +with the meat in one breed and in another to accumulate in the bowels +for the tallow-chandler{199}; he has made the legs of one breed of +pigeons long, and the beak of another so short, that it can hardly feed +itself; he has previously determined how the feathers on a bird's body +shall be coloured, and how the petals of many flowers shall be streaked +or fringed, and has given prizes for complete success;--by selection, he +has made the leaves of one variety and the flower-buds of another +variety of the cabbage good to eat, at different seasons of the year; +and thus has he acted on endless varieties. I do not wish to affirm that +the long-and short-wooled sheep, or that the pointer and retriever, or +that the cabbage and cauliflower have certainly descended from one and +the same aboriginal wild stock; if they have not so descended, though it +lessens what man has effected, a large result must be left unquestioned. + + {199} See the Essay of 1842, p. 3. + +In saying as I have done that man makes a breed, let it not be +confounded with saying that man makes the individuals, which are given +by nature with certain desirable qualities; man only adds together and +makes a permanent gift of nature's bounties. In several cases, indeed, +for instance in the "Ancon" sheep, valuable from not getting over +fences, and in the turnspit dog, man has probably only prevented +crossing; but in many cases we positively know that he has gone on +selecting, and taking advantage of successive small variations. + +Selection{200} has been _methodically_ followed, as I have said, for +barely a century; but it cannot be doubted that occasionally it has been +practised from the remotest ages, in those animals completely under the +dominion of man. In the earliest chapters of the Bible there are rules +given for influencing the colours of breeds, and black and white sheep +are spoken of as separated. In the time of Pliny the barbarians of +Europe and Asia endeavoured by cross-breeding with a wild stock to +improve the races of their dogs and horses. The savages of Guyana now do +so with their dogs: such care shows at least that the characters of +individual animals were attended to. In the rudest times of English +history, there were laws to prevent the exportation of fine animals of +established breeds, and in the case of horses, in Henry VIII's time, +laws for the destruction of all horses under a certain size. In one of +the oldest numbers of the _Phil. Transactions_, there are rules for +selecting and improving the breeds of sheep. Sir H. Bunbury, in 1660, +has given rules for selecting the finest seedling plants, with as much +precision as the best recent horticulturalist could. Even in the most +savage and rude nations, in the wars and famines which so frequently +occur, the most useful of their animals would be preserved: the value +set upon animals by savages is shown by the inhabitants of Tierra del +Fuego devouring their old women before their dogs, which as they +asserted are useful in otter-hunting{201}: who can doubt but that in +every case of famine and war, the best otter-hunters would be preserved, +and therefore in fact selected for breeding. As the offspring so +obviously take after their parents, and as we have seen that savages +take pains in crossing their dogs and horses with wild stocks, we may +even conclude as probable that they would sometimes pair the most useful +of their animals and keep their offspring separate. As different races +of men require and admire different qualities in their domesticated +animals, each would thus slowly, though unconsciously, be selecting a +different breed. As Pallas has remarked, who can doubt but that the +ancient Russian would esteem and endeavour to preserve those sheep in +his flocks which had the thickest coats. This kind of insensible +selection by which new breeds are not selected and kept separate, but a +peculiar character is slowly given to the whole mass of the breed, by +often saving the life of animals with certain characteristics, we may +feel nearly sure, from what we see has been done by the more direct +method of separate selection within the last 50 years in England, would +in the course of some thousand years produce a marked effect. + + {200} See _Origin_, Ed. i. p. 33, vi. p. 38. The evidence is given + in the present Essay rather more fully than in the _Origin_. + + {201} _Journal of Researches_, Ed. 1860, p. 214. "Doggies catch + otters, old women no." + + +_Crossing Breeds._ + +When once two or more races are formed, or if more than one race, or +species fertile _inter se_, originally existed in a wild state, their +crossing becomes a most copious source of new races{202}. When two +well-marked races are crossed the offspring in the first generation take +more or less after either parent or are quite intermediate between them, +or rarely assume characters in some degree new. In the second and +several succeeding generations, the offspring are generally found to +vary exceedingly, one compared with another, and many revert nearly to +their ancestral forms. This greater variability in succeeding +generations seems analogous to the breaking or variability of organic +beings after having been bred for some generations under +domestication{203}. So marked is this variability in cross-bred +descendants, that Pallas and some other naturalists have supposed that +all variation is due to an original cross; but I conceive that the +history of the potato, Dahlia, Scotch Rose, the guinea-pig, and of many +trees in this country, where only one species of the genus exists, +clearly shows that a species may vary where there can have been no +crossing. Owing to this variability and tendency to reversion in +cross-bred beings, much careful selection is requisite to make +intermediate or new permanent races: nevertheless crossing has been a +most powerful engine, especially with plants, where means of propagation +exist by which the cross-bred varieties can be secured without incurring +the risk of fresh variation from seminal propagation: with animals the +most skilful agriculturalists now greatly prefer careful selection from +a well-established breed, rather than from uncertain cross-bred stocks. + + {202} The effects of crossing is much more strongly stated here + than in the _Origin_. See Ed. i. p. 20, vi. p. 23, where indeed the + opposite point of view is given. His change of opinion may be due + to his work on pigeons. The whole of the discussion on crossing + corresponds to Chapter VIII of the _Origin_, Ed. i. rather than to + anything in the earlier part of the book. + + {203} The parallelism between the effects of a cross and the + effects of conditions is given from a different point of view in + the _Origin_, Ed. i. p. 266, vi. p. 391. See the experimental + evidence for this important principle in the author's work on + _Cross and Self-Fertilisation_. Professor Bateson has suggested + that the experiments should be repeated with gametically pure + plants. + +Although intermediate and new races may be formed by the mingling of +others, yet if the two races are allowed to mingle quite freely, so that +none of either parent race remain pure, then, especially if the parent +races are not widely different, they will slowly blend together, and the +two races will be destroyed, and one mongrel race left in its place. +This will of course happen in a shorter time, if one of the parent +races exists in greater number than the other. We see the effect of this +mingling, in the manner in which the aboriginal breeds of dogs and pigs +in the Oceanic Islands and the many breeds of our domestic animals +introduced into S. America, have all been lost and absorbed in a mongrel +race. It is probably owing to the freedom of crossing, that, in +uncivilised countries, where inclosures do not exist, we seldom meet +with more than one race of a species: it is only in enclosed countries, +where the inhabitants do not migrate, and have conveniences for +separating the several kinds of domestic animals, that we meet with a +multitude of races. Even in civilised countries, want of care for a few +years has been found to destroy the good results of far longer periods +of selection and separation. + +This power of crossing will affect the races of all _terrestrial_ +animals; for all terrestrial animals require for their reproduction the +union of two individuals. Amongst plants, races will not cross and blend +together with so much freedom as in terrestrial animals; but this +crossing takes place through various curious contrivances to a +surprising extent. In fact such contrivances exist in so very many +hermaphrodite flowers by which an occasional cross may take place, that +I cannot avoid suspecting (with Mr Knight) that the reproductive action +requires, at _intervals_, the concurrence of distinct individuals{204}. +Most breeders of plants and animals are firmly convinced that benefit is +derived from an occasional cross, not with another race, but with +another family of the same race; and that, on the other hand, injurious +consequences follow from long-continued close interbreeding in the same +family. Of marine animals, many more, than was till lately believed, +have their sexes on separate individuals; and where they are +hermaphrodite, there seems very generally to be means through the water +of one individual occasionally impregnating another: if individual +animals can singly propagate themselves for perpetuity, it is +unaccountable that no terrestrial animal, where the means of observation +are more obvious, should be in this predicament of singly perpetuating +its kind. I conclude, then, that races of most animals and plants, when +unconfined in the same country, would tend to blend together. + + {204} The so-called Knight-Darwin Law is often misunderstood. See + Goebel in _Darwin and Modern Science_, 1909, p. 419; also F. + Darwin, _Nature_, Oct. 27, 1898. + + +_Whether our domestic races have descended from one or more wild +stocks._ + +Several naturalists, of whom Pallas{205} regarding animals, and Humboldt +regarding certain plants, were the first, believe that the breeds of +many of our domestic animals such as of the horse, pig, dog, sheep, +pigeon, and poultry, and of our plants have descended from more than one +aboriginal form. They leave it doubtful, whether such forms are to be +considered wild races, or true species, whose offspring are fertile when +crossed _inter se_. The main arguments for this view consist, firstly, +of the great difference between such breeds, as the Race-and Cart-Horse, +or the Greyhound and Bull-dog, and of our ignorance of the steps or +stages through which these could have passed from a common parent; and +secondly that in the most ancient historical periods, breeds resembling +some of those at present most different, existed in different countries. +The wolves of N. America and of Siberia are thought to be different +species; and it has been remarked that the dogs belonging to the +savages in these two countries resemble the wolves of the same country; +and therefore that they have probably descended from two different wild +stocks. In the same manner, these naturalists believe that the horse of +Arabia and of Europe have probably descended from two wild stocks both +apparently now extinct. I do not think the assumed fertility of these +wild stocks any very great difficulty on this view; for although in +animals the offspring of most cross-bred species are infertile, it is +not always remembered that the experiment is very seldom fairly tried, +except when two near species _both_ breed freely (which does not readily +happen, as we shall hereafter see) when under the dominion of man. +Moreover in the case of the China{206} and common goose, the canary and +siskin, the hybrids breed freely; in other cases the offspring from +hybrids crossed with either pure parent are fertile, as is practically +taken advantage of with the yak and cow; as far as the analogy of plants +serves, it is impossible to deny that some species are quite fertile +_inter se_; but to this subject we shall recur. + + {205} Pallas' theory is discussed in the _Origin_, Ed. i. pp. 253, + 254, vi. p. 374. + + {206} See Darwin's paper on the fertility of hybrids from the + common and Chinese goose in _Nature_, Jan. 1, 1880. + +On the other hand, the upholders of the view that the several breeds of +dogs, horses, &c., &c., have descended each from one stock, may aver +that their view removes all _difficulty about fertility_, and that the +main argument from the high antiquity of different breeds, somewhat +similar to the present breeds, is worth little without knowing the date +of the domestication of such animals, which is far from being the case. +They may also with more weight aver that, knowing that organic beings +under domestication do vary in some degree, the argument from the great +difference between certain breeds is worth nothing, without we know the +limits of variation during a long course of time, which is far from the +case. They may argue that almost every county in England, and in many +districts of other countries, for instance in India, there are slightly +different breeds of the domestic animals; and that it is opposed to all +that we know of the distribution of wild animals to suppose that these +have descended from so many different wild races or species: if so, they +may argue, is it not probable that countries quite separate and exposed +to different climates would have breeds not slightly, but considerably, +different? Taking the most favourable case, on both sides, namely that +of the dog; they might urge that such breeds as the bull-dog and +turnspit have been reared by man, from the ascertained fact that +strictly analogous breeds (namely the Niata ox and Ancon sheep) in other +quadrupeds have thus originated. Again they may say, seeing what +training and careful selection has effected for the greyhound, and +seeing how absolutely unfit the Italian greyhound is to maintain itself +in a state of nature, is it not probable that at least all +greyhounds,--from the rough deerhound, the smooth Persian, the common +English, to the Italian,--have descended from one stock{207}? If so, is +it so improbable that the deerhound and long-legged shepherd dog have so +descended? If we admit this, and give up the bull-dog, we can hardly +dispute the probable common descent of the other breeds. + + {207} _Origin_, Ed. i. p. 19, vi. p. 22. + +The evidence is so conjectural and balanced on both sides that at +present I conceive that no one can decide: for my own part, I lean to +the probability of most of our domestic animals having descended from +more than one wild stock; though from the arguments last advanced and +from reflecting on the slow though inevitable effect of different races +of mankind, under different circumstances, saving the lives of and +therefore selecting the individuals most useful to them, I cannot doubt +but that one class of naturalists have much overrated the probable +number of the aboriginal wild stocks. As far as we admit the difference +of our races <to be> due to the differences of their original stocks, so +much must we give up of the amount of variation produced under +domestication. But this appears to me unimportant, for we certainly know +in some few cases, for instance in the Dahlia, and potato, and rabbit, +that a great number of varieties have proceeded from one stock; and, in +many of our domestic races, we know that man, by slowly selecting and by +taking advantage of sudden sports, has considerably modified old races +and produced new ones. Whether we consider our races as the descendants +of one or several wild stocks, we are in far the greater number of cases +equally ignorant what these stocks were. + + +_Limits to Variation in degree and kind._ + +Man's power in making races deends, in the first instance, on the stock +on which he works being variable; but his labours are modified and +limited, as we have seen, by the direct effects of the external +conditions,--by the deficient or imperfect hereditariness of new +peculiarities,--and by the tendency to continual variation and +especially to reversion to ancestral forms. If the stock is not variable +under domestication, of course he can do nothing; and it appears that +species differ considerably in this tendency to variation, in the same +way as even sub-varieties from the same variety differ greatly in this +respect, and transmit to their offspring this difference in tendency. +Whether the absence of a tendency to vary is an unalterable quality in +certain species, or depends on some deficient condition of the +particular state of domestication to which they are exposed, there is no +evidence. When the organization is rendered variable, or plastic, as I +have expressed it, under domestication, different parts of the frame +vary more or less in different species: thus in the breeds of cattle it +has been remarked that the horns are the most constant or least variable +character, for these often remain constant, whilst the colour, size, +proportions of the body, tendency to fatten &c., vary; in sheep, I +believe, the horns are much more variable. As a general rule the less +important parts of the organization seem to vary most, but I think there +is sufficient evidence that every part occasionally varies in a slight +degree. Even when man has the primary requisite variability he is +necessarily checked by the health and life of the stock he is working +on: thus he has already made pigeons with such small beaks that they can +hardly eat and will not rear their own young; he has made families of +sheep with so strong a tendency to early maturity and to fatten, that in +certain pastures they cannot live from their extreme liability to +inflammation; he has made (_i.e._ selected) sub-varieties of plants with +a tendency to such early growth that they are frequently killed by the +spring frosts; he has made a breed of cows having calves with such large +hinder quarters that they are born with great difficulty, often to the +death of their mothers{208}; the breeders were compelled to remedy this +by the selection of a breeding stock with smaller hinder quarters; in +such a case, however, it is possible by long patience and great loss, a +remedy might have been found in selecting cows capable of giving birth +to calves with large hinder quarters, for in human kind there <are> no +doubt hereditary bad and good confinements. Besides the limits already +specified, there can be little doubt that the variation of different +parts of the frame are connected together by many laws{209}: thus the +two sides of the body, in health and disease, seem almost always to vary +together: it has been asserted by breeders that if the head is much +elongated, the bones of the extremities will likewise be so; in +seedling-apples large leaves and fruit generally go together, and serve +the horticulturalist as some guide in his selection; we can here see the +reason, as the fruit is only a metamorphosed leaf. In animals the teeth +and hair seem connected, for the hairless Chinese dog is almost +toothless. Breeders believe that one part of the frame or function being +increased causes other parts to decrease: they dislike great horns and +great bones as so much flesh lost; in hornless breeds of cattle certain +bones of the head become more developed: it is said that fat +accumulating in one part checks its accumulation in another, and +likewise checks the action of the udder. The whole organization is so +connected that it is probable there are many conditions determining the +variation of each part, and causing other parts to vary with it; and man +in making new races must be limited and ruled by all such laws. + + {208} _Var. under Dom._, Ed. ii. vol. II. p. 211. + + {209} This discussion corresponds to the _Origin_, Ed. i. pp. 11 + and 143, vi. pp. 13 and 177. + + +_In what consists Domestication._ + +In this chapter we have treated of variation under domestication, and it +now remains to consider in what does this power of domestication +consist{210}, a subject of considerable difficulty. Observing that +organic beings of almost every class, in all climates, countries, and +times, have varied when long bred under domestication, we must conclude +that the influence is of some very general nature{211}. Mr Knight alone, +as far as I know, has tried to define it; he believes it consists of an +excess of food, together with transport to a more genial climate, or +protection from its severities. I think we cannot admit this latter +proposition, for we know how many vegetable products, aborigines of this +country, here vary, when cultivated without any protection from the +weather; and some of our variable trees, as apricots, peaches, have +undoubtedly been derived from a more genial climate. There appears to be +much more truth in the doctrine of excess of food being the cause, +though I much doubt whether this is the sole cause, although it may well +be requisite for the kind of variation desired by man, namely increase +of size and vigour. No doubt horticulturalists, when they wish to raise +new seedlings, often pluck off all the flower-buds, except a few, or +remove the whole during one season, so that a great stock of nutriment +may be thrown into the flowers which are to seed. When plants are +transported from high-lands, forests, marshes, heaths, into our gardens +and greenhouses, there must be a considerable change of food, but it +would be hard to prove that there was in every case an excess of the +kind proper to the plant. If it be an excess of food, compared with that +which the being obtained in its natural state{212}, the effects continue +for an improbably long time; during how many ages has wheat been +cultivated, and cattle and sheep reclaimed, and we cannot suppose their +_amount_ of food has gone on increasing, nevertheless these are amongst +the most variable of our domestic productions. It has been remarked +(Marshall) that some of the most highly kept breeds of sheep and cattle +are truer or less variable than the straggling animals of the poor, +which subsist on commons, and pick up a bare subsistence{213}. In the +case of forest-trees raised in nurseries, which vary more than the same +trees do in their aboriginal forests, the cause would seem simply to lie +in their not having to struggle against other trees and weeds, which in +their natural state doubtless would limit the conditions of their +existence. It appears to me that the power of domestication resolves +itself into the accumulated effects of a change of all or some of the +natural conditions of the life of the species, often associated with +excess of food. These conditions moreover, I may add, can seldom remain, +owing to the mutability of the affairs, habits, migrations, and +knowledge of man, for very long periods the same. I am the more inclined +to come to this conclusion from finding, as we shall hereafter show, +that changes of the natural conditions of existence seem peculiarly to +affect the action of the reproductive system{214}. As we see that +hybrids and mongrels, after the first generation, are apt to vary much, +we may at least conclude that variability does not altogether depend on +excess of food. + + {210} See _Origin_, Ed. i. p. 7, vi. p. 7. + + {211} <Note in the original.> "Isidore G. St Hilaire insists that + breeding in captivity essential element. Schleiden on alkalies. + <See _Var. under Dom._, Ed. ii. vol. II. p. 244, note 10.> What is + it in domestication which causes variation?" + + {212} <Note in the original.> "It appears that slight changes of + condition <are> good for health; that more change affects the + generative system, so that variation results in the offspring; + that still more change checks or destroys fertility not of the + offspring." Compare the _Origin_, Ed. i. p. 9, vi. p. 11. What the + meaning of "not of the offspring" may be is not clear. + + {213} In the _Origin_, Ed. i. p. 41, vi. p. 46 the question is + differently treated; it is pointed out that a large stock of + individuals gives a better chance of available variations + occurring. Darwin quotes from Marshall that sheep in small lots can + never be improved. This comes from Marshall's _Review of the + Reports to the Board of Agriculture_, 1808, p. 406. In this Essay + the name Marshall occurs in the margin. Probably this refers to + _loc. cit._ p. 200, where unshepherded sheep in many parts of + England are said to be similar owing to mixed breeding not being + avoided. + + {214} See _Origin_, Ed. i. p. 8, vi. p. 8. + +After these views, it may be asked how it comes that certain animals +and plants, which have been domesticated for a considerable length of +time, and transported from very different conditions of existence, have +not varied much, or scarcely at all; for instance, the ass, peacock, +guinea-fowl, asparagus, Jerusalem artichoke{215}. I have already said +that probably different species, like different sub-varieties, possess +different degrees of tendency to vary; but I am inclined to attribute in +these cases the want of numerous races less to want of variability than +to selection not having been practised on them. No one will take the +pains to select without some corresponding object, either of use or +amusement; the individuals raised must be tolerably numerous, and not so +precious, but that he may freely destroy those not answering to his +wishes. If guinea-fowls or peacocks{216} became "fancy" birds, I cannot +doubt that after some generations several breeds would be raised. Asses +have not been worked on from mere neglect; but they differ in _some_ +degree in different countries. The insensible selection, due to +different races of mankind preserving those individuals most useful to +them in their different circumstances, will apply only to the oldest and +most widely domesticated animals. In the case of plants, we must put +entirely out of the case those exclusively (or almost so) propagated by +cuttings, layers or tubers, such as the Jerusalem artichoke and laurel; +and if we put on one side plants of little ornament or use, and those +which are used at so early a period of their growth that no especial +characters signify, as asparagus{217} and seakale, I can think of none +long cultivated which have not varied. In no case ought we to expect to +find as much variation in a race when it alone has been formed, as when +several have been formed, for their crossing and recrossing will +greatly increase their variability. + + {215} See _Origin_, Ed. i. p. 42, vi. p. 48. + + {216} <Note in the original.> There are white peacocks. + + {217} <Note in the original.> There are varieties of asparagus. + + +_Summary of first Chapter._ + +To sum up this chapter. Races are made under domestication: 1st, by the +direct effects of the external conditions to which the species is +exposed: 2nd, by the indirect effects of the exposure to new conditions, +often aided by excess of food, rendering the organization plastic, and +by man's selecting and separately breeding certain individuals, or +introducing to his stock selected males, or often preserving with care +the life of the individuals best adapted to his purposes: 3rd, by +crossing and recrossing races already made, and selecting their +offspring. After some generations man may relax his care in selection: +for the tendency to vary and to revert to ancestral forms will decrease, +so that he will have only occasionally to remove or destroy one of the +yearly offspring which departs from its type. Ultimately, with a large +stock, the effects of free crossing would keep, even without this care, +his breed true. By these means man can produce infinitely numerous +races, curiously adapted to ends, both most important and most +frivolous; at the same time that the effects of the surrounding +conditions, the laws of inheritance, of growth, and of variation, will +modify and limit his labours. + + + + +CHAPTER II + +ON THE VARIATION OF ORGANIC BEINGS IN A WILD STATE; ON THE NATURAL MEANS +OF SELECTION; AND ON THE COMPARISON OF DOMESTIC RACES AND TRUE SPECIES + + +Having treated of variation under domestication, we now come to it in a +_state of nature_. + +Most organic beings in a state of nature vary exceedingly little{218}: I +put out of the case variations (as stunted plants &c., and sea-shells in +brackish water{219}) which are directly the effect of external agencies +and which we do not _know are in the breed_{220}, or are _hereditary_. +The amount of hereditary variation is very difficult to ascertain, +because naturalists (partly from the want of knowledge, and partly from +the inherent difficulty of the subject) do not all agree whether certain +forms are species or races{221}. Some strongly marked races of plants, +comparable with the decided sports of horticulturalists, undoubtedly +exist in a state of nature, as is actually known by experiment, for +instance in the primrose and cowslip{222}, in two so-called species of +dandelion, in two of foxglove{223}, and I believe in some pines. Lamarck +has observed that, as long as we confine our attention to one limited +country, there is seldom much difficulty in deciding what forms to call +species and what varieties; and that it is when collections flow in from +all parts of the world that naturalists often feel at a loss to decide +the limit of variation. Undoubtedly so it is, yet amongst British plants +(and I may add land shells), which are probably better known than any in +the world, the best naturalists differ very greatly in the relative +proportions of what they call species and what varieties. In many genera +of insects, and shells, and plants, it seems almost hopeless to +establish which are which. In the higher classes there are less doubts; +though we find considerable difficulty in ascertaining what deserve to +be called species amongst foxes and wolves, and in some birds, for +instance in the case of the white barn-owl. When specimens are brought +from different parts of the world, how often do naturalists dispute this +same question, as I found with respect to the birds brought from the +Galapagos islands. Yarrell has remarked that the individuals of the same +undoubted species of birds, from Europe and N. America, usually present +slight, indefinable though perceptible differences. The recognition +indeed of one animal by another of its kind seems to imply some +difference. The disposition of wild animals undoubtedly differs. The +variation, such as it is, chiefly affects the same parts in wild +organisms as in domestic breeds; for instance, the size, colour, and the +external and less important parts. In many species the variability of +certain organs or qualities is even stated as one of the specific +characters: thus, in plants, colour, size, hairiness, the number of the +stamens and pistils, and even their presence, the form of the leaves; +the size and form of the mandibles of the males of some insects; the +length and curvature of the beak in some birds (as in Opetiorynchus) are +variable characters in some species and quite fixed in others. I do not +perceive that any just distinction can be drawn between this recognised +variability of certain parts in many species and the more general +variability of the whole frame in domestic races. + + {218} In Chapter II of the first edition of the _Origin_ Darwin + insists rather on the presence of variability in a state of nature; + see, for instance, p. 45, Ed. vi. p. 53, "I am convinced that the + most experienced naturalist would be surprised at the number of the + cases of variability ... which he could collect on good authority, + as I have collected, during a course of years." + + {219} See _Origin_, Ed. i. p. 44, vi. p. 52. + + {220} <Note in the original.> Here discuss _what is a species_, + sterility can most rarely be told when crossed.--Descent from common + stock. + + {221} <Note in the original.> Give only rule: chain of intermediate + forms, and _analogy_; this important. Every Naturalist at first when + he gets hold of new variable type is _quite puzzled_ to know what to + think species and what variations. + + {222} The author had not at this time the knowledge of the meaning + of dimorphism. + + {223} <Note in original.> Compare feathered heads in very different + birds with spines in Echidna and Hedgehog. <In _Variation under + Domestication_, Ed. ii. vol. II. p. 317, Darwin calls attention to + laced and frizzled breeds occurring in both fowls and pigeons. In + the same way a peculiar form of covering occurs in Echidna and the + hedgehog.> + + Plants under very different climate not varying. Digitalis shows + jumps <?> in variation, like Laburnum and Orchis case--in fact hostile + cases. Variability of sexual characters alike in domestic and wild. + +Although the amount of variation be exceedingly small in most organic +beings in a state of nature, and probably quite wanting (as far as our +senses serve) in the majority of cases; yet considering how many animals +and plants, taken by mankind from different quarters of the world for +the most diverse purposes, have varied under domestication in every +country and in every age, I think we may safely conclude that all +organic beings with few exceptions, if capable of being domesticated and +bred for long periods, would vary. Domestication seems to resolve itself +into a change from the natural conditions of the species [generally +perhaps including an increase of food]; if this be so, organisms in a +state of nature must _occasionally_, in the course of ages, be exposed +to analogous influences; for geology clearly shows that many places +must, in the course of time, become exposed to the widest range of +climatic and other influences; and if such places be isolated, so that +new and better adapted organic beings cannot freely emigrate, the old +inhabitants will be exposed to new influences, probably far more varied, +than man applies under the form of domestication. Although every species +no doubt will soon breed up to the full number which the country will +support, yet it is easy to conceive that, on an average, some species +may receive an increase of food; for the times of dearth may be short, +yet enough to kill, and recurrent only at long intervals. All such +changes of conditions from geological causes would be exceedingly slow; +what effect the slowness might have we are ignorant; under domestication +it appears that the effects of change of conditions accumulate, and then +break out. Whatever might be the result of these slow geological +changes, we may feel sure, from the means of dissemination common in a +lesser or greater degree to every organism taken conjointly with the +changes of geology, which are steadily (and sometimes suddenly, as when +an isthmus at last separates) in progress, that occasionally organisms +must suddenly be introduced into new regions, where, if the conditions +of existence are not so foreign as to cause its extermination, it will +often be propagated under circumstances still more closely analogous to +those of domestication; and therefore we expect will evince a tendency +to vary. It appears to me quite _inexplicable_ if this has never +happened; but it can happen very rarely. Let us then suppose that an +organism by some chance (which might be hardly repeated in 1000 years) +arrives at a modern volcanic island in process of formation and not +fully stocked with the most appropriate organisms; the new organism +might readily gain a footing, although the external conditions were +considerably different from its native ones. The effect of this we might +expect would influence in some small degree the size, colour, nature of +covering &c., and from inexplicable influences even special parts and +organs of the body. But we might further (and <this> is far more important) +expect that the reproductive system would be affected, as under +domesticity, and the structure of the offspring rendered in some degree +plastic. Hence almost every part of the body would tend to vary from the +typical form in slight degrees, and in no determinate way, and therefore +_without selection_ the free crossing of these small variations +(together with the tendency to reversion to the original form) would +constantly be counteracting this unsettling effect of the extraneous +conditions on the reproductive system. Such, I conceive, would be the +unimportant result without selection. And here I must observe that the +foregoing remarks are equally applicable to that small and admitted +amount of variation which has been observed in some organisms in a state +of nature; as well as to the above hypothetical variation consequent on +changes of condition. + +Let us now suppose a Being{224} with penetration sufficient to perceive +differences in the outer and innermost organization quite imperceptible +to man, and with forethought extending over future centuries to watch +with unerring care and select for any object the offspring of an +organism produced under the foregoing circumstances; I can see no +conceivable reason why he could not form a new race (or several were he +to separate the stock of the original organism and work on several +islands) adapted to new ends. As we assume his discrimination, and his +forethought, and his steadiness of object, to be incomparably greater +that those qualities in man, so we may suppose the beauty and +complications of the adaptations of the new races and their differences +from the original stock to be greater than in the domestic races +produced by man's agency: the ground-work of his labours we may aid by +supposing that the external conditions of the volcanic island, from its +continued emergence and the occasional introduction of new immigrants, +vary; and thus to act on the reproductive system of the organism, on +which he is at work, and so keep its organization somewhat plastic. With +time enough, such a Being might rationally (without some unknown law +opposed him) aim at almost any result. + + {224} A corresponding passage occurs in _Origin_, Ed. i. p. 83, vi. + p. 101, where however Nature takes the place of the selecting + Being. + +For instance, let this imaginary Being wish, from seeing a plant growing +on the decaying matter in a forest and choked by other plants, to give +it power of growing on the rotten stems of trees, he would commence +selecting every seedling whose berries were in the smallest degree more +attractive to tree-frequenting birds, so as to cause a proper +dissemination of the seeds, and at the same time he would select those +plants which had in the slightest degree more and more power of drawing +nutriment from rotten wood; and he would destroy all other seedlings +with less of this power. He might thus, in the course of century after +century, hope to make the plant by degrees grow on rotten wood, even +high up on trees, wherever birds dropped the non-digested seeds. He +might then, if the organization of the plant was plastic, attempt by +continued selection of chance seedlings to make it grow on less and less +rotten wood, till it would grow on sound wood{225}. Supposing again, +during these changes the plant failed to seed quite freely from +non-impregnation, he might begin selecting seedlings with a little +sweeter <or> differently tasted honey or pollen, to tempt insects to visit +the flowers regularly: having effected this, he might wish, if it +profited the plant, to render abortive the stamens and pistils in +different flowers, which he could do by continued selection. By such +steps he might aim at making a plant as wonderfully related to other +organic beings as is the mistletoe, whose existence absolutely depends +on certain insects for impregnation, certain birds for transportal, and +certain trees for growth. Furthermore, if the insect which had been +induced regularly to visit this hypothetical plant profited much by it, +our same Being might wish by selection to modify by gradual selection +the insect's structure, so as to facilitate its obtaining the honey or +pollen: in this manner he might adapt the insect (always presupposing +its organization to be in some degree plastic) to the flower, and the +impregnation of the flower to the insect; as is the case with many bees +and many plants. + + {225} The mistletoe is used as an illustration in _Origin_, Ed. i. + p. 3, vi. p. 3, but with less detail. + +Seeing what blind capricious man has actually effected by selection +during the few last years, and what in a ruder state he has probably +effected without any systematic plan during the last few thousand years, +he will be a bold person who will positively put limits to what the +supposed Being could effect during whole geological periods. In +accordance with the plan by which this universe seems governed by the +Creator, let us consider whether there exists any _secondary_ means in +the economy of nature by which the process of selection could go on +adapting, nicely and wonderfully, organisms, if in ever so small a +degree plastic, to diverse ends. I believe such secondary means do +exist{226}. + + {226} <Note in original.> The selection, in cases where adult lives + only few hours as Ephemera, must fall on larva--curious speculation + of the effect <which> changes in it would bring in parent. + + +_Natural means of Selection{227}._ + + {227} This section forms part of the joint paper by Darwin and + Wallace read before the Linnean Society on July 1, 1858. + +De Candolle, in an eloquent passage, has declared that all nature is at +war, one organism with another, or with external nature. Seeing the +contented face of nature, this may at first be well doubted; but +reflection will inevitably prove it is too true. The war, however, is +not constant, but only recurrent in a slight degree at short periods and +more severely at occasional more distant periods; and hence its effects +are easily overlooked. It is the doctrine of Malthus applied in most +cases with ten-fold force. As in every climate there are seasons for +each of its inhabitants of greater and less abundance, so all annually +breed; and the moral restraint, which in some small degree checks the +increase of mankind, is entirely lost. Even slow-breeding mankind has +doubled in 25 years{228}, and if he could increase his food with greater +ease, he would double in less time. But for animals, without artificial +means, _on an average_ the amount of food for each species must be +constant; whereas the increase of all organisms tends to be geometrical, +and in a vast majority of cases at an enormous ratio. Suppose in a +certain spot there are eight pairs of [robins] birds, and that _only_ +four pairs of them annually (including double hatches) rear only four +young; and that these go on rearing their young at the same rate: then +at the end of seven years (a short life, excluding violent deaths, for +any birds) there will be 2048 robins, instead of the original sixteen; +as this increase is quite impossible, so we must conclude either that +robins do not rear nearly half their young or that the average life of a +robin when reared is from accident not nearly seven years. Both checks +probably concur. The same kind of calculation applied to all vegetables +and animals produces results either more or less striking, but in +scarcely a single instance less striking than in man{229}. + + {228} Occurs in _Origin_, Ed. i. p. 64, vi. p. 79. + + {229} Corresponds approximately with _Origin_, Ed. i. pp. 64-65, + vi. p. 80. + +Many practical illustrations of this rapid tendency to increase are on +record, namely during peculiar seasons, in the extraordinary increase of +certain animals, for instance during the years 1826 to 1828, in La +Plata, when from drought, some millions of cattle perished, the whole +country _swarmed_ with innumerable mice: now I think it cannot be +doubted that during the breeding season all the mice (with the exception +of a few males or females in excess) ordinarily pair; and therefore that +this astounding increase during three years must be attributed to a +greater than usual number surviving the first year, and then breeding, +and so on, till the third year, when their numbers were brought down to +their usual limits on the return of wet weather. Where man has +introduced plants and animals into a new country favourable to them, +there are many accounts in how surprisingly few years the whole country +has become stocked with them. This increase would necessarily stop as +soon as the country was fully stocked; and yet we have every reason to +believe from what is known of wild animals that _all_ would pair in the +spring. In the majority of cases it is most difficult to imagine where +the check falls, generally no doubt on the seeds, eggs, and young; but +when we remember how impossible even in mankind (so much better known +than any other animal) it is to infer from repeated casual observations +what the average of life is, or to discover how different the percentage +of deaths to the births in different countries, we ought to feel no +legitimate surprise at not seeing where the check falls in animals and +plants. It should always be remembered that in most cases the checks are +yearly recurrent in a small regular degree, and in an extreme degree +during occasionally unusually cold, hot, dry, or wet years, according to +the constitution of the being in question. Lighten any check in the +smallest degree, and the geometrical power of increase in every +organism will instantly increase the average numbers of the favoured +species. Nature may be compared to a surface, on which rest ten thousand +sharp wedges touching each other and driven inwards by incessant +blows{230}. Fully to realise these views much reflection is requisite; +Malthus on man should be studied; and all such cases as those of the +mice in La Plata, of the cattle and horses when first turned out in S. +America, of the robins by our calculation, &c., should be well +considered: reflect on the enormous multiplying power _inherent and +annually in action_ in all animals; reflect on the countless seeds +scattered by a hundred ingenious contrivances, year after year, over the +whole face of the land; and yet we have every reason to suppose that the +average percentage of every one of the inhabitants of a country will +_ordinarily_ remain constant. Finally, let it be borne in mind that this +average number of individuals (the external conditions remaining the +same) in each country is kept up by recurrent struggles against other +species or against external nature (as on the borders of the arctic +regions{231}, where the cold checks life); and that ordinarily each +individual of each species holds its place, either by its own struggle +and capacity of acquiring nourishment in some period (from the egg +upwards) of its life, or by the struggle of its parents (in short lived +organisms, when the main check occurs at long intervals) against and +compared with other individuals of the _same_ or _different_ species. + + {230} This simile occurs in _Origin_, Ed. i. p. 67, not in the + later editions. + + {231} <Note in the original.> In case like mistletoe, it may be + asked why not more species, no other species interferes; answer + almost sufficient, same causes which check the multiplication of + individuals. + +But let the external conditions of a country change; if in a small +degree, the relative proportions of the inhabitants will in most cases +simply be slightly changed; but let the number of inhabitants be small, +as in an island{232}, and free access to it from other countries be +circumscribed; and let the change of condition continue progressing +(forming new stations); in such case the original inhabitants must cease +to be so perfectly adapted to the changed conditions as they originally +were. It has been shown that probably such changes of external +conditions would, from acting on the reproductive system, cause the +organization of the beings most affected to become, as under +domestication, plastic. Now can it be doubted from the struggle each +individual (or its parents) has to obtain subsistence that any minute +variation in structure, habits, or instincts, adapting that individual +better to the new conditions, would tell upon its vigour and health? In +the struggle it would have a better _chance_ of surviving, and those of +its offspring which inherited the variation, let it be ever so slight, +would have a better _chance_ to survive. Yearly more are bred than can +survive; the smallest grain in the balance, in the long run, must tell +on which death shall fall, and which shall survive{233}. Let this work +of selection, on the one hand, and death on the other, go on for a +thousand generations; who would pretend to affirm that it would produce +no effect, when we remember what in a few years Bakewell effected in +cattle and Western in sheep, by this identical principle of selection. + + {232} See _Origin_, Ed. i. pp. 104, 292, vi. pp. 127, 429. + + {233} Recognition of the importance of minute differences in the + struggle occurs in the Essay of 1842, p. 8 note 3.{Note 59} + +To give an imaginary example, from changes in progress on an island, let +the organization{234} of a canine animal become slightly plastic, which +animal preyed chiefly on rabbits, but sometimes on hares; let these same +changes cause the number of rabbits very slowly to decrease and the +number of hares to increase; the effect of this would be that the fox or +dog would be driven to try to catch more hares, and his numbers would +tend to decrease; his organization, however, being slightly plastic, +those individuals with the lightest forms, longest limbs, and best +eye-sight (though perhaps with less cunning or scent) would be slightly +favoured, let the difference be ever so small, and would tend to live +longer and to survive during that time of the year when food was +shortest; they would also rear more young, which young would tend to +inherit these slight peculiarities. The less fleet ones would be rigidly +destroyed. I can see no more reason to doubt but that these causes in a +thousand generations would produce a marked effect, and adapt the form +of the fox to catching hares instead of rabbits, than that greyhounds +can be improved by selection and careful breeding. So would it be with +plants under similar circumstances; if the number of individuals of a +species with plumed seeds could be increased by greater powers of +dissemination within its own area (that is if the check to increase fell +chiefly on the seeds), those seeds which were provided with ever so +little more down, or with a plume placed so as to be slightly more acted +on by the winds, would in the long run tend to be most disseminated; and +hence a greater number of seeds thus formed would germinate, and would +tend to produce plants inheriting this slightly better adapted down. + + {234} See _Origin_, Ed. i. p. 90, vi. p. 110. + +Besides this natural means of selection, by which those individuals are +preserved, whether in their egg or seed or in their mature state, which +are best adapted to the place they fill in nature, there is a second +agency at work in most bisexual animals tending to produce the same +effect, namely the struggle of the males for the females. These +struggles are generally decided by the law of battle; but in the case +of birds, apparently, by the charms of their song{235}, by their beauty +or their power of courtship, as in the dancing rock-thrush of Guiana. +Even in the animals which pair there seems to be an excess of males +which would aid in causing a struggle: in the polygamous animals{236}, +however, as in deer, oxen, poultry, we might expect there would be +severest struggle: is it not in the polygamous animals that the males +are best formed for mutual war? The most vigorous males, implying +perfect adaptation, must generally gain the victory in their several +contests. This kind of selection, however, is less rigorous than the +other; it does not require the death of the less successful, but gives +to them fewer descendants. This struggle falls, moreover, at a time of +year when food is generally abundant, and perhaps the effect chiefly +produced would be the alteration of sexual characters, and the selection +of individual forms, no way related to their power of obtaining food, or +of defending themselves from their natural enemies, but of fighting one +with another. This natural struggle amongst the males may be compared in +effect, but in a less degree, to that produced by those agriculturalists +who pay less attention to the careful selection of all the young animals +which they breed and more to the occasional use of a choice male{237}. + + {235} These two forms of sexual selection are given in _Origin_, + Ed. i. p. 87, vi. p. 107. The Guiana rock-thrush is given as an + example of bloodless competition. + + {236} <Note in original.> Seals? Pennant about battles of seals. + + {237} In the Linnean paper of July 1, 1858 the final word is + _mate_: but the context shows that it should be _male_; it is + moreover clearly so written in the MS. + + +_Differences between "Races" and "Species":--first, in their trueness or +variability._ + +Races{238} produced by these natural means of selection{239} we may +expect would differ in some respects from those produced by man. Man +selects chiefly by the eye, and is not able to perceive the course of +every vessel and nerve, or the form of the bones, or whether the +internal structure corresponds to the outside shape. He{240} is unable +to select shades of constitutional differences, and by the protection he +affords and his endeavours to keep his property alive, in whatever +country he lives, he checks, as much as lies in his power, the selecting +action of nature, which will, however, go on to a lesser degree with all +living things, even if their length of life is not determined by their +own powers of endurance. He has bad judgment, is capricious, he does +not, or his successors do not, wish to select for the same exact end for +hundreds of generations. He cannot always suit the selected form to the +properest conditions; nor does he keep those conditions uniform: he +selects that which is useful to him, not that best adapted to those +conditions in which each variety is placed by him: he selects a small +dog, but feeds it highly; he selects a long-backed dog, but does not +exercise it in any peculiar manner, at least not during every +generation. He seldom allows the most vigorous males to struggle for +themselves and propagate, but picks out such as he possesses, or such as +he prefers, and not necessarily those best adapted to the existing +conditions. Every agriculturalist and breeder knows how difficult it is +to prevent an occasional cross with another breed. He often grudges to +destroy an individual which departs considerably from the required type. +He often begins his selection by a form or sport considerably departing +from the parent form. Very differently does the natural law of selection +act; the varieties selected differ only slightly from the parent +forms{241}; the conditions are constant for long periods and change +slowly; rarely can there be a cross; the selection is rigid and +unfailing, and continued through many generations; a selection can +_never be made_ without the form be _better_ adapted to the conditions +than the parent form; the selecting power goes on without caprice, and +steadily for thousands of years adapting the form to these conditions. +The selecting power is not deceived by external appearances, it tries +the being during its whole life; and if less well <?> adapted than its +_congeners_, without fail it is destroyed; every part of its structure +is thus scrutinised and proved good towards the place in nature which it +occupies. + + {238} In the _Origin_ the author would here have used the word + _variety_. + + {239} The whole of p. 94 and 15 lines of p. 95 are, in the MS., + marked through in pencil with vertical lines, beginning at "Races + produced, &c." and ending with "to these conditions." + + {240} See _Origin_, Ed. i. p. 83, vi. p. 102. + + {241} In the present Essay there is some evidence that the author + attributed more to _sports_ than was afterwards the case: but the + above passage points the other way. It must always be remembered + that many of the minute differences, now considered small + mutations, are the small variations on which Darwin conceived + selection to act. + +We have every reason to believe that in proportion to the number of +generations that a domestic race is kept free from crosses, and to the +care employed in continued steady selection with one end in view, and to +the care in not placing the variety in conditions unsuited to it; in +such proportion does the new race become "true" or subject to little +variation{242}. How incomparably "truer" then would a race produced by +the above rigid, steady, natural means of selection, excellently trained +and perfectly adapted to its conditions, free from stains of blood or +crosses, and continued during thousands of years, be compared with one +produced by the feeble, capricious, misdirected and ill-adapted +selection of man. Those races of domestic animals produced by savages, +partly by the inevitable conditions of their life, and partly +unintentionally by their greater care of the individuals most valuable +to them, would probably approach closest to the character of a species; +and I believe this is the case. Now the characteristic mark of a +species, next, if not equal in importance to its sterility when crossed +with another species, and indeed almost the only other character +(without we beg the question and affirm the essence of a species, is its +not having descended from a parent common to any other form), is the +similarity of the individuals composing the species, or in the language +of agriculturalists their "trueness." + + {242} See _Var. under Dom._, Ed. ii. vol. II. p. 230. + + +_Difference between "Races" and "Species" in fertility when crossed._ + +The sterility of species, or of their offspring, when crossed has, +however, received more attention than the uniformity in character of the +individuals composing the species. It is exceedingly natural that such +sterility{243} should have been long thought the certain characteristic +of species. For it is obvious that if the allied different forms which +we meet with in the same country could cross together, instead of +finding a number of distinct species, we should have a confused and +blending series. The fact however of a perfect gradation in the degree +of sterility between species, and the circumstance of some species most +closely allied (for instance many species of crocus and European heaths) +refusing to breed together, whereas other species, widely different, +and even belonging to distinct genera, as the fowl and the peacock, +pheasant and grouse{244}, Azalea and Rhododendron, Thuja and Juniperus, +breeding together ought to have caused a doubt whether the sterility did +not depend on other causes, distinct from a law, coincident with their +creation. I may here remark that the fact whether one species will or +will not breed with another is far less important than the sterility of +the offspring when produced; for even some domestic races differ so +greatly in size (as the great stag-greyhound and lap-dog, or cart-horse +and Burmese ponies) that union is nearly impossible; and what is less +generally known is, that in plants Kölreuter has shown by hundreds of +experiments that the pollen of one species will fecundate the germen of +another species, whereas the pollen of this latter will never act on the +germen of the former; so that the simple fact of mutual impregnation +certainly has no relation whatever to the distinctness in creation of +the two forms. When two species are attempted to be crossed which are so +distantly allied that offspring are never produced, it has been observed +in some cases that the pollen commences its proper action by exserting +its tube, and the germen commences swelling, though soon afterwards it +decays. In the next stage in the series, hybrid offspring are produced +though only rarely and few in number, and these are absolutely sterile: +then we have hybrid offspring more numerous, and occasionally, though +very rarely, breeding with either parent, as is the case with the common +mule. Again, other hybrids, though infertile _inter se_, will breed +_quite_ freely with either parent, or with a third species, and will +yield offspring generally infertile, but sometimes fertile; and these +latter again will breed with either parent, or with a third or fourth +species: thus Kölreuter blended together many forms. Lastly it is now +admitted by those botanists who have longest contended against the +admission, that in certain families the hybrid offspring of many of the +species are sometimes perfectly fertile in the first generation when +bred together: indeed in some few cases Mr Herbert{245} found that the +hybrids were decidedly more fertile than either of their pure parents. +There is no way to escape from the admission that the hybrids from some +species of plants are fertile, except by declaring that no form shall be +considered as a species, if it produces with another species fertile +offspring: but this is begging the question{246}. It has often been +stated that different species of animals have a sexual repugnance +towards each other; I can find no evidence of this; it appears as if +they merely did not excite each others passions. I do not believe that +in this respect there is any essential distinction between animals and +plants; and in the latter there cannot be a feeling of repugnance. + + {243} <Note in the original.> If domestic animals are descended from + several species and _become_ fertile _inter se_, then one can see + they gain fertility by becoming adapted to new conditions and + certainly domestic animals can withstand changes of climate without + loss of fertility in an astonishing manner. + + {244} See Suchetet, _L'Hybridité dans la Nature_, Bruxelles, 1888, + p. 67. In _Var. under Dom._, Ed. ii. vol. II. hybrids between the + fowl and the pheasant are mentioned. I can give no information on + the other cases. + + {245} _Origin_, Ed. i. p. 250, vi. p. 370. + + {246} This was the position of Gärtner and of Kölreuter: see + _Origin_, Ed. i. pp. 246-7, vi. pp. 367-8. + + +_Causes of Sterility in Hybrids._ + +The difference in nature between species which causes the greater or +lesser degree of sterility in their offspring appears, according to +Herbert and Kölreuter, to be connected much less with external form, +size, or structure, than with constitutional peculiarities; by which is +meant their adaptation to different climates, food and situation, &c.: +these peculiarities of constitution probably affect the entire frame, +and no one part in particular{247}. + + {247} <Note in the original.> Yet this seems introductory to the + case of the heaths and crocuses above mentioned. <Herbert observed + that crocus does not set seed if transplanted before pollination, + but that such treatment after pollination has no sterilising effect. + (_Var. under Dom._, Ed. ii. vol. II. p. 148.) On the same page is + a mention of the Ericaceæ being subject to contabescence of the + anthers. For _Crinum_ see _Origin_, Ed. i. p. 250: for _Rhododenron_ + and _Calceolaria_ see p. 251.> + +From the foregoing facts I think we must admit that there exists a +perfect gradation in fertility between species which when crossed are +quite fertile (as in Rhododendron, Calceolaria, &c.), and indeed in an +extraordinary degree fertile (as in Crinum), and those species which +never produce offspring, but which by certain effects (as the exsertion +of the pollen-tube) evince their alliance. Hence, I conceive, we must +give up sterility, although undoubtedly in a lesser or greater degree of +very frequent occurrence, as an unfailing mark by which _species_ can be +distinguished from _races_, _i.e._ from those forms which have descended +from a common stock. + + +_Infertility from causes distinct from hybridisation._ + +Let us see whether there are any analogous facts which will throw any +light on this subject, and will tend to explain why the offspring of +certain species, when crossed, should be sterile, and not others, +without requiring a distinct law connected with their creation to that +effect. Great numbers, probably a large majority of animals when caught +by man and removed from their natural conditions, although taken very +young, rendered quite tame, living to a good old age, and apparently +quite healthy, seem incapable under these circumstances of +breeding{248}. I do not refer to animals kept in menageries, such as at +the Zoological Gardens, many of which, however, appear healthy and live +long and unite but do not produce; but to animals caught and left partly +at liberty in their native country. Rengger{249} enumerates several +caught young and rendered tame, which he kept in Paraguay, and which +would not breed: the hunting leopard or cheetah and elephant offer other +instances; as do bears in Europe, and the 25 species of hawks, belonging +to different genera, thousands of which have been kept for hawking and +have lived for long periods in perfect vigour. When the expense and +trouble of procuring a succession of young animals in a wild state be +borne in mind, one may feel sure that no trouble has been spared in +endeavours to make them breed. So clearly marked is this difference in +different kinds of animals, when captured by man, that St Hilaire makes +two great classes of animals useful to man:--the _tame_, which will not +breed, and the _domestic_ which will breed in domestication. From +certain singular facts we might have supposed that the non-breeding of +animals was owing to some perversion of instinct. But we meet with +exactly the same class of facts in plants: I do not refer to the large +number of cases where the climate does not permit the seed or fruit to +ripen, but where the flowers do not "set," owing to some imperfection of +the ovule or pollen. The latter, which alone can be distinctly examined, +is often manifestly imperfect, as any one with a microscope can observe +by comparing the pollen of the Persian and Chinese lilacs{250} with the +common lilac; the two former species (I may add) are equally sterile in +Italy as in this country. Many of the American bog plants here produce +little or no pollen, whilst the Indian species of the same genera freely +produce it. Lindley observes that sterility is the bane of the +horticulturist{251}: Linnæus has remarked on the sterility of nearly all +alpine flowers when cultivated in a lowland district{252}. Perhaps the +immense class of double flowers chiefly owe their structure to an excess +of food acting on parts rendered slightly sterile and less capable of +performing their true function, and therefore liable to be rendered +monstrous, which monstrosity, like any other disease, is inherited and +rendered common. So far from domestication being in itself unfavourable +to fertility, it is well known that when an organism is once capable of +submission to such conditions <its> fertility is increased{253} beyond the +natural limit. According to agriculturists, slight changes of +conditions, that is of food or habitation, and likewise crosses with +races slightly different, increase the vigour and probably the fertility +of their offspring. It would appear also that even a great change of +condition, for instance, transportal from temperate countries to India, +in many cases does not in the least affect fertility, although it does +health and length of life and the period of maturity. When sterility is +induced by domestication it is of the same kind, and varies in degree, +exactly as with hybrids: for be it remembered that the most sterile +hybrid is no way monstrous; its organs are perfect, but they do not act, +and minute microscopical investigations show that they are in the same +state as those of pure species in the intervals of the breeding season. +The defective pollen in the cases above alluded to precisely resembles +that of hybrids. The occasional breeding of hybrids, as of the common +mule, may be aptly compared to the most rare but occasional reproduction +of elephants in captivity. The cause of many exotic Geraniums producing +(although in vigorous health) imperfect pollen seems to be connected +with the period when water is given them{254}; but in the far greater +majority of cases we cannot form any conjecture on what exact cause the +sterility of organisms taken from their natural conditions depends. Why, +for instance, the cheetah will not breed whilst the common cat and +ferret (the latter generally kept shut up in a small box) do,--why the +elephant will not whilst the pig will abundantly--why the partridge and +grouse in their own country will not, whilst several species of +pheasants, the guinea-fowl from the deserts of Africa and the peacock +from the jungles of India, will. We must, however, feel convinced that +it depends on some constitutional peculiarities in these beings not +suited to their new condition; though not necessarily causing an ill +state of health. Ought we then to wonder much that those hybrids which +have been produced by the crossing of species with different +constitutional tendencies (which tendencies we know to be eminently +inheritable) should be sterile: it does not seem improbable that the +cross from an alpine and lowland plant should have its constitutional +powers deranged, in nearly the same manner as when the parent alpine +plant is brought into a lowland district. Analogy, however, is a +deceitful guide, and it would be rash to affirm, although it may appear +probable, that the sterility of hybrids is due to the constitutional +peculiarities of one parent being disturbed by being blended with those +of the other parent in exactly the same manner as it is caused in some +organic beings when placed by man out of their natural conditions{255}. +Although this would be rash, it would, I think, be still rasher, seeing +that sterility is no more incidental to _all_ cross-bred productions +than it is to all organic beings when captured by man, to assert that +the sterility of certain hybrids proved a distinct creation of their +parents. + + {248} <Note in original.> Animals seem more often made sterile by + being taken out of their native condition than plants, and so are + more sterile when crossed. + + We have one broad fact that sterility in hybrids is not closely + related to external difference, and these are what man alone gets + by selection. + + {249} See _Var. under Dom._, Ed. ii. vol. II. p. 132; for the case + of the cheetah see _loc cit._ p. 133. + + {250} _Var. under Dom._, Ed. ii. vol. II. p. 148. + + {251} Quoted in the _Origin_, Ed. i. p. 9. + + {252} See _Var. under Dom._, Ed. ii. vol. II. p. 147. + + {253} _Var. under Dom._, Ed. ii. vol. II. p. 89. + + {254} See _Var. under Dom._, Ed. ii. vol. II. p. 147. + + {255} _Origin_, Ed. i. p. 267, vi. p. 392. This is the principle + experimentally investigated in the author's _Cross-and + Self-Fertilisation_. + +But it may be objected{256} (however little the sterility of certain +hybrids is connected with the distinct creations of species), how comes +it, if species are only races produced by natural selection, that when +crossed they so frequently produce sterile offspring, whereas in the +offspring of those races confessedly produced by the arts of man there +is no one instance of sterility. There is not much difficulty in this, +for the races produced by the natural means above explained will be +slowly but steadily selected; will be adapted to various and diverse +conditions, and to these conditions they will be rigidly confined for +immense periods of time; hence we may suppose that they would acquire +different constitutional peculiarities adapted to the stations they +occupy; and on the constitutional differences between species their +sterility, according to the best authorities, depends. On the other hand +man selects by external appearance{257}; from his ignorance, and from +not having any test at least comparable in delicacy to the natural +struggle for food, continued at intervals through the life of each +individual, he cannot eliminate fine shades of constitution, dependent +on invisible differences in the fluids or solids of the body; again, +from the value which he attaches to each individual, he asserts his +utmost power in contravening the natural tendency of the most vigorous +to survive. Man, moreover, especially in the earlier ages, cannot have +kept his conditions of life constant, and in later ages his stock pure. +Until man selects two varieties from the same stock, adapted to two +climates or to other different external conditions, and confines each +rigidly for one or several thousand years to such conditions, always +selecting the individuals best adapted to them, he cannot be said to +have even commenced the experiment. Moreover, the organic beings which +man has longest had under domestication have been those which were of +the greatest use to him, and one chief element of their usefulness, +especially in the earlier ages, must have been their capacity to undergo +sudden transportals into various climates, and at the same time to +retain their fertility, which in itself implies that in such respects +their constitutional peculiarities were not closely limited. If the +opinion already mentioned be correct, that most of the domestic animals +in their present state have descended from the fertile commixture of +wild races or species, we have indeed little reason now to expect +infertility between any cross of stock thus descended. + + {256} _Origin_, Ed. i. p. 268, vi. p. 398. + + {257} <Notes in original.> Mere difference of structure no guide to + what will or will not cross. First step gained by races keeping + apart. <It is not clear where these notes were meant to go.> + +It is worthy of remark, that as many organic beings, when taken by man +out of their natural conditions, have their reproductive system <so> +affected as to be incapable of propagation, so, we saw in the first +chapter, that although organic beings when taken by man do propagate +freely, their offspring after some generations vary or sport to a degree +which can only be explained by their reproductive system being <in> some way +affected. Again, when species cross, their offspring are generally +sterile; but it was found by Kölreuter that when hybrids are capable of +breeding with either parent, or with other species, that their +offspring are subject after some generations to excessive +variation{258}. Agriculturists, also, affirm that the offspring from +mongrels, after the first generation, vary much. Hence we see that both +sterility and variation in the succeeding generations are consequent +both on the removal of individual species from their natural states and +on species crossing. The connection between these facts may be +accidental, but they certainly appear to elucidate and support each +other,--on the principle of the reproductive system of all organic +beings being eminently sensitive to any disturbance, whether from +removal or commixture, in their constitutional relations to the +conditions to which they are exposed. + + {258} _Origin_, Ed. i. p. 272, vi. p. 404. + + +_Points of Resemblance between "Races" and "Species{259}."_ + + {259} This section seems not to correspond closely with any in the + _Origin_, Ed. i.; in some points it resembles pp. 15, 16, also the + section on analogous variation in distinct species, _Origin_, Ed. + i. p. 159, vi. p. 194. + +Races and reputed species agree in some respects, although differing +from causes which, we have seen, we can in some degree understand, in +the fertility and "trueness" of their offspring. In the first place, +there is no clear sign by which to distinguish races from species, as is +evident from the great difficulty experienced by naturalists in +attempting to discriminate them. As far as external characters are +concerned, many of the races which are descended from the same stock +differ far more than true species of the same genus; look at the +willow-wrens, some of which skilful ornithologists can hardly +distinguish from each other except by their nests; look at the wild +swans, and compare the distinct species of these genera with the races +of domestic ducks, poultry, and pigeons; and so again with plants, +compare the cabbages, almonds, peaches and nectarines, &c. with the +species of many genera. St Hilaire has even remarked that there is a +greater difference in size between races, as in dogs (for he believes +all have descended from one stock), than between the species of any one +genus; nor is this surprising, considering that amount of food and +consequently of growth is the element of change over which man has most +power. I may refer to a former statement, that breeders believe the +growth of one part or strong action of one function causes a decrease in +other parts; for this seems in some degree analogous to the law of +"organic compensation{260}," which many naturalists believe holds good. +To give an instance of this law of compensation,--those species of +Carnivora which have the canine teeth greatly developed have certain +molar teeth deficient; or again, in that division of the Crustaceans in +which the tail is much developed, the thorax is little so, and the +converse. The points of difference between different races is often +strikingly analogous to that between species of the same genus: trifling +spots or marks of colour{261} (as the bars on pigeons' wings) are often +preserved in races of plants and animals, precisely in the same manner +as similar trifling characters often pervade all the species of a genus, +and even of a family. Flowers in varying their colours often become +veined and spotted and the leaves become divided like true species: it +is known that the varieties of the same plant never have red, blue and +yellow flowers, though the hyacinth makes a very near approach to an +exception{262}; and different species of the same genus seldom, though +sometimes they have flowers of these three colours. Dun-coloured horses +having a dark stripe down their backs, and certain domestic asses having +transverse bars on their legs, afford striking examples of a variation +analogous in character to the distinctive marks of other species of the +same genus. + + {260} The law of compensation is discussed in the _Origin_, Ed. i. + p. 147, vi. p. 182. + + {261} <Note in original.> Boitard and Corbié on outer edging red in + tail of bird,--so bars on wing, white or black or brown, or white + edged with black or <illegible>: analogous to marks running through + genera but with different colours. Tail coloured in pigeons. + + {262} <Note in original.> Oxalis and Gentian. <In Gentians blue, + yellow and reddish colours occur. In Oxalis yellow, purple, violet + and pink.> + + +_External characters of Hybrids and Mongrels._ + +There is, however, as it appears to me, a more important method of +comparison between species and races, namely the character of the +offspring{263} when species are crossed and when races are crossed: I +believe, in no one respect, except in sterility, is there any +difference. It would, I think, be a marvellous fact, if species have +been formed by distinct acts of creation, that they should act upon each +other in uniting, like races descended from a common stock. In the first +place, by repeated crossing one species can absorb and wholly obliterate +the characters of another, or of several other species, in the same +manner as one race will absorb by crossing another race. Marvellous, +that one act of creation should absorb another or even several acts of +creation! The offspring of species, that is hybrids, and the offspring +of races, that is mongrels, resemble each other in being either +intermediate in character (as is most frequent in hybrids) or in +resembling sometimes closely one and sometimes the other parent; in both +the offspring produced by the same act of conception sometimes differ in +their degree of resemblance; both hybrids and mongrels sometimes retain +a certain part or organ very like that of either parent, both, as we +have seen, become in succeeding generations variable; and this tendency +to vary can be transmitted by both; in both for many generations there +is a strong tendency to reversion to their ancestral form. In the case +of a hybrid laburnum and of a supposed mongrel vine different parts of +the same plants took after each of their two parents. In the hybrids +from some species, and in the mongrel of some races, the offspring +differ according as which of the two species, or of the two races, is +the father (as in the common mule and hinny) and which the mother. Some +races will breed together, which differ so greatly in size, that the dam +often perishes in labour; so it is with some species when crossed; when +the dam of one species has borne offspring to the male of another +species, her succeeding offspring are sometimes stained (as in Lord +Morton's mare by the quagga, wonderful as the fact{264} is) by this +first cross; so agriculturists positively affirm is the case when a pig +or sheep of one breed has produced offspring by the sire of another +breed. + + {263} This section corresponds roughly to that on _Hybrids and + Mongrels compared independently of their fertility_, _Origin_, Ed. + i. p. 272, vi. p. 403. The discussion on Gärtner's views, given in + the _Origin_, is here wanting. The brief mention of prepotency is + common to them both. + + {264} See _Animals and Plants_, Ed. ii. vol. I. p. 435. The + phenomenon of _Telegony_, supposed to be established by this and + similar cases, is now generally discredited in consequence of + Ewart's experiments. + + +_Summary of second chapter_{265}. + + {265} The section on p. 109 is an appendix to the summary. + +Let us sum up this second chapter. If slight variations do occur in +organic beings in a state of nature; if changes of condition from +geological causes do produce in the course of ages effects analogous to +those of domestication on any, however few, organisms; and how can we +doubt it,--from what is actually known, and from what may be presumed, +since thousands of organisms taken by man for sundry uses, and placed +in new conditions, have varied. If such variations tend to be +hereditary; and how can we doubt it,--when we see shades of expression, +peculiar manners, monstrosities of the strangest kinds, diseases, and a +multitude of other peculiarities, which characterise and form, being +inherited, the endless races (there are 1200 kinds of cabbages{266}) of +our domestic plants and animals. If we admit that every organism +maintains its place by an almost periodically recurrent struggle; and +how can we doubt it,--when we know that all beings tend to increase in a +geometrical ratio (as is instantly seen when the conditions become for a +time more favourable); whereas on an average the amount of food must +remain constant, if so, there will be a natural means of selection, +tending to preserve those individuals with any slight deviations of +structure more favourable to the then existing conditions, and tending +to destroy any with deviations of an opposite nature. If the above +propositions be correct, and there be no law of nature limiting the +possible amount of variation, new races of beings will,--perhaps only +rarely, and only in some few districts,--be formed. + + {266} I do not know the authority for this statement. + + +_Limits of Variation._ + +That a limit to variation does exist in nature is assumed by most +authors, though I am unable to discover a single fact on which this +belief is grounded{267}. One of the commonest statements is that plants +do not become acclimatised; and I have even observed that kinds not +raised by seed, but propagated by cuttings, &c., are instanced. A good +instance has, however, been advanced in the case of kidney beans, which +it is believed are now as tender as when first introduced. Even if we +overlook the frequent introduction of seed from warmer countries, let me +observe that as long as the seeds are gathered promiscuously from the +bed, without continual observation and _careful_ selection of those +plants which have stood the climate best during their whole growth, the +experiment of acclimatisation has hardly been begun. Are not all those +plants and animals, of which we have the greatest number of races, the +oldest domesticated? Considering the quite recent progress{268} of +systematic agriculture and horticulture, is it not opposed to every +fact, that we have exhausted the capacity of variation in our cattle and +in our corn,--even if we have done so in some trivial points, as their +fatness or kind of wool? Will any one say, that if horticulture +continues to flourish during the next few centuries, that we shall not +have numerous new kinds of the potato and Dahlia? But take two varieties +of each of these plants, and adapt them to certain fixed conditions and +prevent any cross for 5000 years, and then again vary their conditions; +try many climates and situations; and who{269} will predict the number +and degrees of difference which might arise from these stocks? I repeat +that we know nothing of any limit to the possible amount of variation, +and therefore to the number and differences of the races, which might be +produced by the natural means of selection, so infinitely more efficient +than the agency of man. Races thus produced would probably be very +"true"; and if from having been adapted to different conditions of +existence, they possessed different constitutions, if suddenly removed +to some new station, they would perhaps be sterile and their offspring +would perhaps be infertile. Such races would be undistinguishable from +species. But is there any evidence that the species, which surround us +on all sides, have been thus produced? This is a question which an +examination of the economy of nature we might expect would answer either +in the affirmative or negative{270}. + + {267} In the _Origin_ no limit is placed to variation as far as I + know. + + {268} <Note in original.> History of pigeons shows increase of + peculiarities during last years. + + {269} Compare an obscure passage in the Essay of 1842, p. 14. + + {270} <Note in original.> Certainly <two pages in the MS.> ought to + be here introduced, viz., difficulty in forming such organ, as eye, + by selection. <In the _Origin_, Ed. i., a chapter on _Difficulties + on Theory_ follows that on _Laws of Variation_, and precedes that + on _Instinct_: this was also the arrangement in the Essay of 1842; + whereas in the present Essay _Instinct_ follows _Variation_ and + precedes _Difficulties_.> + + + + +CHAPTER III + +ON THE VARIATION OF INSTINCTS AND OTHER MENTAL ATTRIBUTES UNDER +DOMESTICATION AND IN STATE OF NATURE; ON THE DIFFICULTIES IN THIS +SUBJECT; AND ON ANALOGOUS DIFFICULTIES WITH RESPECT TO CORPOREAL +STRUCTURES + + +_Variation of mental attributes under domestication._ + +I have as yet only alluded to the mental qualities which differ greatly +in different species. Let me here premise that, as will be seen in the +Second Part, there is no evidence and consequently no attempt to show +that _all_ existing organisms have descended from any one common +parent-stock, but that only those have so descended which, in the +language of naturalists, are clearly related to each other. Hence the +facts and reasoning advanced in this chapter do not apply to the first +origin of the senses{271}, or of the chief mental attributes, such as of +memory, attention, reasoning, &c., &c., by which most or all of the +great related groups are characterised, any more than they apply to the +first origin of life, or growth, or the power of reproduction. The +application of such facts as I have collected is merely to the +differences of the primary mental qualities and of the instincts in the +species{272} of the several great groups. In domestic animals every +observer has remarked in how great a degree, in the individuals of the +same species, the dispositions, namely courage, pertinacity, suspicion, +restlessness, confidence, temper, pugnaciousness, affection, care of +their young, sagacity, &c., &c., vary. It would require a most able +metaphysician to explain how many primary qualities of the mind must be +changed to cause these diversities of complex dispositions. From these +dispositions being inherited, of which the testimony is unanimous, +families and breeds arise, varying in these respects. I may instance the +good and ill temper of different stocks of bees and of horses,--the +pugnacity and courage of game fowls,--the pertinacity of certain dogs, +as bull-dogs, and the sagacity of others,--for restlessness and +suspicion compare a wild rabbit reared with the greatest care from its +earliest age with the extreme tameness of the domestic breed of the same +animal. The offspring of the domestic dogs which have run wild in +Cuba{273}, though caught quite young, are most difficult to tame, +probably nearly as much so as the original parent-stock from which the +domestic dog descended. The habitual "_periods_" of different families +of the same species differ, for instance, in the time of year of +reproduction, and the period of life when the capacity is acquired, and +the hour of roosting (in Malay fowls), &c., &c. These periodical habits +are perhaps essentially corporeal, and may be compared to nearly similar +habits in plants, which are known to vary extremely. Consensual +movements (as called by Müller) vary and are inherited,--such as the +cantering and ambling paces in horses, the tumbling of pigeons, and +perhaps the handwriting, which is sometimes so similar between father +and sons, may be ranked in this class. _Manners_, and even tricks which +perhaps are only _peculiar_ manners, according to W. Hunter and my +father, are distinctly inherited in cases where children have lost their +parent in early infancy. The inheritance of expression, which often +reveals the finest shades of character, is familiar to everyone. + + {271} A similar proviso occurs in the chapter on instinct in + _Origin_, Ed. i. p. 207, vi. p. 319. + + {272} The discussion occurs later in Chapter VII of the _Origin_, + Ed. i. than in the present Essay, where moreover it is fuller in + some respects. + + {273} In the margin occurs the name of Poeppig. In _Var. under + Dom._, Ed. ii. vol. I. p. 28, the reference to Poeppig on the Cuban + dogs contains no mention of the wildness of their offspring. + +Again the tastes and pleasures of different breeds vary, thus the +shepherd-dog delights in chasing the sheep, but has no wish to kill +them,--the terrier (see Knight) delights in killing vermin, and the +spaniel in finding game. But it is impossible to separate their mental +peculiarities in the way I have done: the tumbling of pigeons, which I +have instanced as a consensual movement, might be called a trick and is +associated with a taste for flying in a close flock at a great height. +Certain breeds of fowls have a taste for roosting in trees. The +different actions of pointers and setters might have been adduced in the +same class, as might the peculiar _manner_ of hunting of the spaniel. +Even in the same breed of dogs, namely in fox-hounds, it is the fixed +opinion of those best able to judge that the different pups are born +with different tendencies; some are best to find their fox in the cover; +some are apt to run straggling, some are best to make casts and to +recover the lost scent, &c.; and that these peculiarities undoubtedly +are transmitted to their progeny. Or again the tendency to point might +be adduced as a distinct habit which has become inherited,--as might the +tendency of a true sheep dog (as I have been assured is the case) to run +round the flock instead of directly at them, as is the case with other +young dogs when attempted to be taught. The "transandantes" sheep{274} +in Spain, which for some centuries have been yearly taken a journey of +several hundred miles from one province to another, know when the time +comes, and show the greatest restlessness (like migratory birds in +confinement), and are prevented with difficulty from starting by +themselves, which they sometimes do, and find their own way. There is a +case on good evidence{275} of a sheep which, when she lambed, would +return across a mountainous country to her own birth-place, although at +other times of year not of a rambling disposition. Her lambs inherited +this same disposition, and would go to produce their young on the farm +whence their parent came; and so troublesome was this habit that the +whole family was destroyed. + + {274} <Note in original.> Several authors. + + {275} In the margin "Hogg" occurs as authority for this fact. For + the reference, see p. 17, note 4. + +These facts must lead to the conviction, justly wonderful as it is, that +almost infinitely numerous shades of disposition, of tastes, of peculiar +movements, and even of individual actions, can be modified or acquired +by one individual and transmitted to its offspring. One is forced to +admit that mental phenomena (no doubt through their intimate connection +with the brain) can be inherited, like infinitely numerous and fine +differences of corporeal structure. In the same manner as peculiarities +of corporeal structure slowly acquired or lost during mature life +(especially cognisant <?> in disease), as well as congenital peculiarities, +are transmitted; so it appears to be with the mind. The inherited paces +in the horse have no doubt been acquired by compulsion during the lives +of the parents: and temper and tameness may be modified in a breed by +the treatment which the individuals receive. Knowing that a pig has been +taught to point, one would suppose that this quality in pointer-dogs was +the simple result of habit, but some facts, with respect to the +occasional appearance of a similar quality in other dogs, would make one +suspect that it originally appeared in a less perfect degree, "_by +chance_," that is from a congenital tendency{276} in the parent of the +breed of pointers. One cannot believe that the tumbling, and high flight +in a compact body, of one breed of pigeons has been taught; and in the +case of the slight differences in the manner of hunting in young +fox-hounds, they are doubtless congenital. The inheritance of the +foregoing and similar mental phenomena ought perhaps to create less +surprise, from the reflection that in no case do individual acts of +reasoning, or movements, or other phenomena connected with +consciousness, appear to be transmitted. An action, even a very +complicated one, when from long practice it is performed unconsciously +without any effort (and indeed in the case of many peculiarities of +manners opposed to the will) is said, according to a common expression, +to be performed "instinctively." Those cases of languages, and of songs, +learnt in early childhood and _quite_ forgotten, being _perfectly_ +repeated during the unconsciousness of illness, appear to me only a few +degrees less wonderful than if they had been transmitted to a second +generation{277}. + + {276} In the _Origin_, Ed. i., he speaks more decidedly against the + belief that instincts are hereditary habits, see for instance pp. + 209, 214, Ed. vi. pp. 321, 327. He allows, however, something to + habit (p. 216). + + {277} A suggestion of Hering's and S. Butler's views on memory and + inheritance. It is not, however, implied that Darwin was inclined + to accept these opinions. + + +_Hereditary habits compared with instincts._ + +The chief characteristics of true instincts appear to be their +invariability and non-improvement during the mature age of the +individual animal: the absence of knowledge of the end, for which the +action is performed, being associated, however, sometimes with a degree +of reason; being subject to mistakes and being associated with certain +states of the body or times of the year or day. In most of these +respects there is a resemblance in the above detailed cases of the +mental qualities acquired or modified during domestication. No doubt the +instincts of wild animals are more uniform than those habits or +qualities modified or recently acquired under domestication, in the same +manner and from the same causes that the corporeal structure in this +state is less uniform than in beings in their natural conditions. I have +seen a young pointer point as fixedly, the first day it was taken out, +as any old dog; Magendie says this was the case with a retriever which +he himself reared: the tumbling of pigeons is not probably improved by +age: we have seen that in the case above given that the young sheep +inherited the migratory tendency to their particular birth-place the +first time they lambed. This last fact offers an instance of a domestic +instinct being associated with a state of body; as do the +"transandantes" sheep with a time of year. Ordinarily the acquired +instincts of domestic animals seem to require a certain degree of +education (as generally in pointers and retrievers) to be perfectly +developed: perhaps this holds good amongst wild animals in rather a +greater degree than is generally supposed; for instance, in the singing +of birds, and in the knowledge of proper herbs in Ruminants. It seems +pretty clear that bees transmit knowledge from generation to generation. +Lord Brougham{278} insists strongly on ignorance of the end proposed +being eminently characteristic of true instincts; and this appears to me +to apply to many acquired hereditary habits; for instance, in the case +of the young pointer alluded to before, which pointed so steadfastly the +first day that we were obliged several times to carry him away{279}. +This puppy not only pointed at sheep, at large white stones, and at +every little bird, but likewise "backed" the other pointers: this young +dog must have been as unconscious for what end he was pointing, namely +to facilitate his master's killing game to eat, as is a butterfly which +lays her eggs on a cabbage, that her caterpillars would eat the leaves. +So a horse that ambles instinctively, manifestly is ignorant that he +performs that peculiar pace for the ease of man; and if man had never +existed, he would never have ambled. The young pointer pointing at white +stones appears to be as much a mistake of its acquired instinct, as in +the case of flesh-flies laying their eggs on certain flowers instead of +putrifying meat. However true the ignorance of the end may generally be, +one sees that instincts are associated with some degree of reason; for +instance, in the case of the tailor-bird, who spins threads with which +to make her nest <yet> will use artificial threads when she can procure +them{280}; so it has been known that an old pointer has broken his point +and gone round a hedge to drive out a bird towards his master{281}. + + {278} Lord Brougham's _Dissertations on Subjects of Science_, etc., + 1839, p. 27. + + {279} This case is more briefly given in the _Origin_, Ed. i. p. + 213, vi. p. 326. The simile of the butterfly occurs there also. + + {280} "A little dose, as Pierre Huber expresses it, of judgment or + reason, often comes into play." _Origin_, Ed. i. p. 208, vi. p. + 320. + + {281} In the margin is written "Retriever killing one bird." This + refers to the cases given in the _Descent of Man_, 2nd Ed. (in 1 + vol.) p. 78, of a retriever being puzzled how to deal with a + wounded and a dead bird, killed the former and carried both at + once. This was the only known instance of her wilfully injuring + game. + +There is one other quite distinct method by which the instincts or +habits acquired under domestication may be compared with those given by +nature, by a test of a fundamental kind; I mean the comparison of the +mental powers of mongrels and hybrids. Now the instincts, or habits, +tastes, and dispositions of one _breed_ of animals, when crossed with +another breed, for instance a shepherd-dog with a harrier, are blended +and appear in the same curiously mixed degree, both in the first and +succeeding generations, exactly as happens when one _species_ is crossed +with another{282}. This would hardly be the case if there was any +fundamental difference between the domestic and natural instinct{283}; +if the former were, to use a metaphorical expression, merely +superficial. + + {282} See _Origin_, Ed. i. p. 214, vi. p. 327. + + {283} <Note in original.> Give some definition of instinct, or at + least give chief attributes. <In _Origin_, Ed. i. p. 207, vi. p. + 319, Darwin refuses to define instinct.> The term instinct is often + used in <a> sense which implies no more than that the animal does + the action in question. Faculties and instincts may I think be + imperfectly separated. The mole has the faculty of scratching + burrows, and the instinct to apply it. The bird of passage has the + faculty of finding its way and the instinct to put it in action at + certain periods. It can hardly be said to have the faculty of + knowing the time, for it can possess no means, without indeed it be + some consciousness of passing sensations. Think over all habitual + actions and see whether faculties and instincts can be separated. + We have faculty of waking in the night, if an instinct prompted us + to do something at certain hour of night or day. Savages finding + their way. Wrangel's account--probably a faculty inexplicable by + the possessor. There are besides faculties "_means_," as conversion + of larvæ into neuters and queens. I think all this generally + implied, anyhow useful. <This discussion, which does not occur in + the _Origin_, is a first draft of that which follows in the text, + p. 123.> + + +_Variation in the mental attributes of wild animals._ + +With respect to the variation{284} of the mental powers of animals in a +wild state, we know that there is a considerable difference in the +disposition of different individuals of the same species, as is +recognised by all those who have had the charge of animals in a +menagerie. With respect to the wildness of animals, that is fear +directed particularly against man, which appears to be as true an +instinct as the dread of a young mouse of a cat, we have excellent +evidence that it is slowly acquired and becomes hereditary. It is also +certain that, in a natural state, individuals of the same species lose +or do not practice their migratory instincts--as woodcocks in Madeira. +With respect to any variation in the more complicated instincts, it is +obviously most difficult to detect, even more so than in the case of +corporeal structure, of which it has been admitted the variation is +exceedingly small, and perhaps scarcely any in the majority of species +at any one period. Yet, to take one excellent case of instinct, namely +the nests of birds, those who have paid most attention to the subject +maintain that not only certain individuals <? species> seem to be able +to build very imperfectly, but that a difference in skill may not +unfrequently be detected between individuals{285}. Certain birds, +moreover, adapt their nests to circumstances; the water-ouzel makes no +vault when she builds under cover of a rock--the sparrow builds very +differently when its nest is in a tree or in a hole, and the +golden-crested wren sometimes suspends its nest below and sometimes +places it _on_ the branches of trees. + + {284} A short discussion of a similar kind occurs in the _Origin_, + Ed. i. p. 211, vi. p. 324. + + {285} This sentence agrees with the MS., but is clearly in need of + correction. + + +_Principles of Selection applicable to instincts._ + +As the instincts of a species are fully as important to its preservation +and multiplication as its corporeal structure, it is evident that if +there be the slightest congenital differences in the instincts and +habits, or if certain individuals during their lives are induced or +compelled to vary their habits, and if such differences are in the +smallest degree more favourable, under slightly modified external +conditions, to their preservation, such individuals must in the long run +have a better _chance_ of being preserved and of multiplying{286}. If +this be admitted, a series of small changes may, as in the case of +corporeal structure, work great changes in the mental powers, habits and +instincts of any species. + + {286} This corresponds to _Origin_, Ed. i. p. 212, vi. p. 325. + + +_Difficulties in the acquirement of complex instincts by Selection._ + +Every one will at first be inclined to explain (as I did for a long +time) that many of the more complicated and wonderful instincts could +not be acquired in the manner here supposed{287}. The Second Part of +this work is devoted to the general consideration of how far the general +economy of nature justifies or opposes the belief that related species +and genera are descended from common stocks; but we may here consider +whether the instincts of animals offer such a _primâ facie_ case of +impossibility of gradual acquirement, as to justify the rejection of any +such theory, however strongly it may be supported by other facts. I beg +to repeat that I wish here to consider not the _probability_ but the +_possibility_ of complicated instincts having been acquired by the slow +and long-continued selection of very slight (either congenital or +produced by habit) modifications of foregoing simpler instincts; each +modification being as useful and necessary, to the species practising +it, as the most complicated kind. + + {287} This discussion is interesting in differing from the + corresponding section of the _Origin_, Ed. i. p. 216, vi. p. 330, + to the end of the chapter. In the present Essay the subjects dealt + with are nest-making instincts, including the egg-hatching habit of + the Australian bush-turkey. The power of "shamming death." + "Faculty" in relation to instinct. The instinct of lapse of time, + and of direction. Bees' cells very briefly given. Birds feeding + their young on food differing from their own natural food. In the + _Origin_, Ed. i., the cases discussed are the instinct of laying + eggs in other birds' nests; the slave-making instinct in ants; the + construction of the bee's comb, very fully discussed. + +First, to take the case of birds'-nests; of existing species (almost +infinitely few in comparison with the multitude which must have existed, +since the period of the new Red Sandstone of N. America, of whose habits +we must always remain ignorant) a tolerably perfect series could be made +from eggs laid on the bare ground, to others with a few sticks just +laid round them, to a simple nest like the wood-pigeons, to others more +and more complicated: now if, as is asserted, there occasionally exist +slight differences in the building powers of an individual, and if, +which is at least probable, that such differences would tend to be +inherited, then we can see that it is at least _possible_ that the +nidificatory instincts may have been acquired by the gradual selection, +during thousands and thousands of generations, of the eggs and young of +those individuals, whose nests were in some degree better adapted to the +preservation of their young, under the then existing conditions. One of +the most surprising instincts on record is that of the Australian +bush-turkey, whose eggs are hatched by the heat generated from a huge +pile of fermenting materials, which it heaps together; but here the +habits of an allied species show how this instinct _might possibly_ have +been acquired. This second species inhabits a tropical district, where +the heat of the sun is sufficient to hatch its eggs; this bird, burying +its eggs, apparently for concealment, under a lesser heap of rubbish, +but of a dry nature, so as not to ferment. Now suppose this bird to +range slowly into a climate which was cooler, and where leaves were more +abundant, in that case, those individuals, which chanced to have their +collecting instinct strongest developed, would make a somewhat larger +pile, and the eggs, aided during some colder season, under the slightly +cooler climate by the heat of incipient fermentation, would in the long +run be more freely hatched and would probably produce young ones with +the same more highly developed collecting tendencies; of these again, +those with the best developed powers would again tend to rear most +young. Thus this strange instinct might _possibly_ be acquired, every +individual bird being as ignorant of the laws of fermentation, and the +consequent development of heat, as we know they must be. + +Secondly, to take the case of animals feigning death (as it is commonly +expressed) to escape danger. In the case of insects, a perfect series +can be shown, from some insects, which momentarily stand still, to +others which for a second slightly contract their legs, to others which +will remain immovably drawn together for a quarter of an hour, and may +be torn asunder or roasted at a slow fire, without evincing the smallest +sign of sensation. No one will doubt that the length of time, during +which each remains immovable, is well adapted to <favour the insect's> +escape <from> the dangers to which it is most exposed, and few will deny +the _possibility_ of the change from one degree to another, by the means +and at the rate already explained. Thinking it, however, wonderful +(though not impossible) that the attitude of death should have been +acquired by methods which imply no imitation, I compared several +species, when feigning, as is said, death, with others of the same +species really dead, and their attitudes were in no one case the same. + +Thirdly, in considering many instincts it is useful to _endeavour_ to +separate the faculty{288} by which they perform it, and the mental power +which urges to the performance, which is more properly called an +instinct. We have an instinct to eat, we have jaws &c. to give us the +faculty to do so. These faculties are often unknown to us: bats, with +their eyes destroyed, can avoid strings suspended across a room, we know +not at present by what faculty they do this. Thus also, with migratory +birds, it is a wonderful instinct which urges them at certain times of +the year to direct their course in certain directions, but it is a +faculty by which they know the time and find their way. With respect to +time{289}, man without seeing the sun can judge to a certain extent of +the hour, as must those cattle which come down from the inland mountains +to feed on sea-weed left bare at the changing hour of low-water{290}. A +hawk (D'Orbigny) seems certainly to have acquired a knowledge of a +period of every 21 days. In the cases already given of the sheep which +travelled to their birth-place to cast their lambs, and the sheep in +Spain which know their time of march{291}, we may conjecture that the +tendency to move is associated, we may then call it instinctively, with +some corporeal sensations. With respect to direction we can easily +conceive how a tendency to travel in a certain course may possibly have +been acquired, although we must remain ignorant how birds are able to +preserve any direction whatever in a dark night over the wide ocean. I +may observe that the power of some savage races of mankind to find their +way, although perhaps wholly different from the faculty of birds, is +nearly as unintelligible to us. Bellinghausen, a skilful navigator, +describes with the utmost wonder the manner in which some Esquimaux +guided him to a certain point, by a course never straight, through newly +formed hummocks of ice, on a thick foggy day, when he with a compass +found it impossible, from having no landmarks, and from their course +being so extremely crooked, to preserve any sort of uniform direction: +so it is with Australian savages in thick forests. In North and South +America many birds slowly travel northward and southward, urged on by +the food they find, as the seasons change; let them continue to do this, +till, as in the case of the sheep in Spain, it has become an urgent +instinctive desire, and they will gradually accelerate their journey. +They would cross narrow rivers, and if these were converted by +subsidence into narrow estuaries, and gradually during centuries to arms +of the sea, still we may suppose their restless desire of travelling +onwards would impel them to cross such an arm, even if it had become of +great width beyond their span of vision. How they are able to preserve a +course in any direction, I have said, is a faculty unknown to us. To +give another illustration of the means by which I conceive it _possible_ +that the direction of migrations have been determined. Elk and reindeer +in N. America annually cross, as if they could marvellously smell or see +at the distance of a hundred miles, a wide tract of absolute desert, to +arrive at certain islands where there is a scanty supply of food; the +changes of temperature, which geology proclaims, render it probable that +this desert tract formerly supported some vegetation, and thus these +quadrupeds might have been annually led on, till they reached the more +fertile spots, and so acquired, like the sheep of Spain, their migratory +powers. + + {288} The distinction between _faculty_ and _instinct_ corresponds + in some degree to that between perception of a stimulus and a + specific reaction. I imagine that the author would have said that + the sensitiveness to light possessed by a plant is _faculty_, while + _instinct_ decides whether the plant curves to or from the source + of illumination. + + {289} <Note in the original in an unknown handwriting.> At the time + when corn was pitched in the market instead of sold by sample, the + geese in the town fields of Newcastle <Staffordshire?> used to + know market day and come in to pick up the corn spilt. + + {290} <Note in original.> Macculloch and others. + + {291} I can find no reference to the _transandantes_ sheep in + Darwin's published work. He was possibly led to doubt the accuracy + of the statement on which he relied. For the case of the sheep + returning to their birth-place see p. 17, note 4.{Note 91} + +Fourthly, with respect to the combs of the hive-bee{292}; here again we +must look to some faculty or means by which they make their hexagonal +cells, without indeed we view these instincts as mere machines. At +present such a faculty is quite unknown: Mr Waterhouse supposes that +several bees are led by their instinct to excavate a mass of wax to a +certain thinness, and that the result of this is that hexagons +necessarily remain. Whether this or some other theory be true, some such +means they must possess. They abound, however, with true instincts, +which are the most wonderful that are known. If we examine the little +that is known concerning the habits of other species of bees, we find +much simpler instincts: the humble bee merely fills rude balls of wax +with honey and aggregates them together with little order in a rough +nest of grass. If we knew the instinct of all the bees, which ever had +existed, it is not improbable that we should have instincts of every +degree of complexity, from actions as simple as a bird making a nest, +and rearing her young, to the wonderful architecture and government of +the hive-bee; at least such is _possible_, which is all that I am here +considering. + + {292} _Origin_, Ed. i. p. 224, vi. p. 342. + +Finally, I will briefly consider under the same point of view one other +class of instincts, which have often been advanced as truly wonderful, +namely parents bringing food to their young which they themselves +neither like nor partake of{293};--for instance, the common sparrow, a +granivorous bird, feeding its young with caterpillars. We might of +course look into the case still earlier, and seek how an instinct in the +parent, of feeding its young at all, was first derived; but it is +useless to waste time in conjectures on a series of gradations from the +young feeding themselves and being slightly and occasionally assisted in +their search, to their entire food being brought to them. With respect +to the parent bringing a different kind of food from its own kind, we +may suppose either that the remote stock, whence the sparrow and other +congenerous birds have descended, was insectivorous, and that its own +habits and structure have been changed, whilst its ancient instincts +with respect to its young have remained unchanged; or we may suppose +that the parents have been induced to vary slightly the food of their +young, by a slight scarcity of the proper kind (or by the instincts of +some individuals not being so truly developed), and in this case those +young which were most capable of surviving were necessarily most often +preserved, and would themselves in time become parents, and would be +similarly compelled to alter their food for their young. In the case of +those animals, the young of which feed themselves, changes in their +instincts for food, and in their structure, might be selected from +slight variations, just as in mature animals. Again, where the food of +the young depends on where the mother places her eggs, as in the case of +the caterpillars of the cabbage-butterfly, we may suppose that the +parent stock of the species deposited her eggs sometimes on one kind and +sometimes on another of congenerous plants (as some species now do), and +if the cabbage suited the caterpillars better than any other plant, the +caterpillars of those butterflies, which had chosen the cabbage, would +be most plentifully reared, and would produce butterflies more apt to +lay their eggs on the cabbage than on the other congenerous plants. + + {293} This is an expansion of an obscure passage in the Essay of + 1842, p. 19. + +However vague and unphilosophical these conjectures may appear, they +serve, I think, to show that one's first impulse utterly to reject any +theory whatever, implying a gradual acquirement of these instincts, +which for ages have excited man's admiration, may at least be delayed. +Once grant that dispositions, tastes, actions or habits can be slightly +modified, either by slight congenital differences (we must suppose in +the brain) or by the force of external circumstances, and that such +slight modifications can be rendered inheritable,--a proposition which +no one can reject,--and it will be difficult to put any limit to the +complexity and wonder of the tastes and habits which may _possibly_ be +thus acquired. + + +_Difficulties in the acquirement by Selection of complex corporeal +structures._ + +After the past discussion it will perhaps be convenient here to consider +whether any particular corporeal organs, or the entire structure of any +animals, are so wonderful as to justify the rejection _primâ facie_ of +our theory{294}. In the case of the eye, as with the more complicated +instincts, no doubt one's first impulse is to utterly reject every such +theory. But if the eye from its most complicated form can be shown to +graduate into an exceedingly simple state,--if selection can produce the +smallest change, and if such a series exists, then it is clear (for in +this work we have nothing to do with the first origin of organs in their +simplest forms{295}) that it may _possibly_ have been acquired by +gradual selection of slight, but in each case, useful deviations{296}. +Every naturalist, when he meets with any new and singular organ, always +expects to find, and looks for, other and simpler modifications of it in +other beings. In the case of the eye, we have a multitude of different +forms, more or less simple, not graduating into each other, but +separated by sudden gaps or intervals; but we must recollect how +incomparably greater would the multitude of visual structures be if we +had the eyes of every fossil which ever existed. We shall discuss the +probable vast proportion of the extinct to the recent in the succeeding +Part. Notwithstanding the large series of existing forms, it is most +difficult even to conjecture by what intermediate stages very many +simple organs could possibly have graduated into complex ones: but it +should be here borne in mind, that a part having originally a wholly +different function, may on the theory of gradual selection be slowly +worked into quite another use; the gradations of forms, from which +naturalists believe in the hypothetical metamorphosis of part of the ear +into the swimming bladder in fishes{297}, and in insects of legs into +jaws, show the manner in which this is possible. As under domestication, +modifications of structure take place, without any continued selection, +which man finds very useful, or valuable for curiosity (as the hooked +calyx of the teazle, or the ruff round some pigeons' necks), so in a +state of nature some small modifications, apparently beautifully adapted +to certain ends, may perhaps be produced from the accidents of the +reproductive system, and be at once propagated without long-continued +selection of small deviations towards that structure{298}. In +conjecturing by what stages any complicated organ in a species may have +arrived at its present state, although we may look to the analogous +organs in other existing species, we should do this merely to aid and +guide our imaginations; for to know the real stages we must look only +through one line of species, to one ancient stock, from which the +species in question has descended. In considering the eye of a +quadruped, for instance, though we may look at the eye of a molluscous +animal or of an insect, as a proof how simple an organ will serve some +of the ends of vision; and at the eye of a fish as a nearer guide of the +manner of simplification; we must remember that it is a mere chance +(assuming for a moment the truth of our theory) if any existing organic +being has preserved any one organ, in exactly the same condition, as it +existed in the ancient species at remote geological periods. + + {294} The difficulties discussed in the _Origin_, Ed. i. p. 171, + vi. p. 207, are the rarity of transitional varieties, the origin of + the tail of the giraffe; the otter-like polecat (_Mustela vison_); + the flying habit of the bat; the penguin and the logger-headed + duck; flying fish; the whale-like habit of the bear; the + woodpecker; diving petrels; the eye; the swimming bladder; + Cirripedes; neuter insects; electric organs. + + Of these, the polecat, the bat, the woodpecker, the eye, the + swimming bladder are discussed in the present Essay, and in + addition some botanical problems. + + {295} In the _Origin_, Ed. vi. p. 275, the author replies to + Mivart's criticisms (_Genesis of Species_, 1871), referring + especially to that writer's objection "that natural selection is + incompetent to account for the incipient stages of useful + structures." + + {296} <The following sentence seems to have been intended for + insertion here> "and that each eye throughout the animal kingdom is + not only most useful, but _perfect_ for its possessor." + + {297} _Origin_, Ed. i. p. 190, vi. p. 230. + + {298} This is one of the most definite statements in the present + Essay of the possible importance of _sports_ or what would now be + called _mutations_. As is well known the author afterwards doubted + whether species could arise in this way. See _Origin_, Ed. v. p. + 103, vi. p. 110, also _Life and Letters_, vol. iii. p. 107. + +The nature or condition of certain structures has been thought by some +naturalists to be of no use to the possessor{299}, but to have been +formed wholly for the good of other species; thus certain fruit and +seeds have been thought to have been made nutritious for certain +animals--numbers of insects, especially in their larval state, to exist +for the same end--certain fish to be bright coloured to aid certain +birds of prey in catching them, &c. Now could this be proved (which I am +far from admitting) the theory of natural selection would be quite +overthrown; for it is evident that selection depending on the advantage +over others of one individual with some slight deviation would never +produce a structure or quality profitable only to another species. No +doubt one being takes advantage of qualities in another, and may even +cause its extermination; but this is far from proving that this quality +was produced for such an end. It may be advantageous to a plant to have +its seeds attractive to animals, if one out of a hundred or a thousand +escapes being digested, and thus aids dissemination: the bright colours +of a fish may be of some advantage to it, or more probably may result +from exposure to certain conditions in favourable haunts for food, +_notwithstanding_ it becomes subject to be caught more easily by certain +birds. + + {299} See _Origin_, Ed. i. p. 210, vi. p. 322, where the question + is discussed for the case of instincts with a proviso that the same + argument applies to structure. It is briefly stated in its general + bearing in _Origin_, Ed. i. p. 87, vi. p. 106. + +If instead of looking, as above, at certain individual organs, in order +to speculate on the stages by which their parts have been matured and +selected, we consider an individual animal, we meet with the same or +greater difficulty, but which, I believe, as in the case of single +organs, rests entirely on our ignorance. It may be asked by what +intermediate forms could, for instance, a bat possibly have passed; but +the same question might have been asked with respect to the seal, if we +had not been familiar with the otter and other semi-aquatic carnivorous +quadrupeds. But in the case of the bat, who can say what might have been +the habits of some parent form with less developed wings, when we now +have insectivorous opossums and herbivorous squirrels fitted for merely +gliding through the air{300}. One species of bat is at present partly +aquatic in its habits{301}. Woodpeckers and tree-frogs are especially +adapted, as their names express, for climbing trees; yet we have species +of both inhabiting the open plains of La Plata, where a tree does not +exist{302}. I might argue from this circumstance that a structure +eminently fitted for climbing trees might descend from forms inhabiting +a country where a tree did not exist. Notwithstanding these and a +multitude of other well-known facts, it has been maintained by several +authors that one species, for instance of the carnivorous order, could +not pass into another, for instance into an otter, because in its +transitional state its habits would not be adapted to any proper +conditions of life; but the jaguar{303} is a thoroughly terrestrial +quadruped in its structure, yet it takes freely to the water and catches +many fish; will it be said that it is _impossible_ that the conditions +of its country might become such that the jaguar should be driven to +feed more on fish than they now do; and in that case is it impossible, +is it not probable, that any the slightest deviation in its instincts, +its form of body, in the width of its feet, and in the extension of the +skin (which already unites the base of its toes) would give such +individuals a better _chance_ of surviving and propagating young with +similar, barely perceptible (though thoroughly exercised), +deviations{304}? Who will say what could thus be effected in the course +of ten thousand generations? Who can answer the same question with +respect to instincts? If no one can, the _possibility_ (for we are not +in this chapter considering the _probability_) of simple organs or +organic beings being modified by natural selection and the effects of +external agencies into complicated ones ought not to be absolutely +rejected. + + {300} <Note in original.> No one will dispute that the gliding is + most useful, probably necessary for the species in question. + + {301} <Note in original.> Is this the Galeopithecus? I forget. + <_Galeopithecus_ "or the flying Lemur" is mentioned in the + corresponding discussion in the _Origin_, Ed. i. p. 181, vi. p. 217, + as formerly placed among the bats. I do not know why it is described + as partly aquatic in its habits.> + + {302} In the _Origin_, Ed. vi. p. 221, the author modified the + statement that it _never_ climbs trees; he also inserted a sentence + quoting Mr Hudson to the effect that in other districts this + woodpecker climbs trees and bores holes. See Mr Darwin's paper, + _Zoolog. Soc. Proc._, 1870, and _Life and Letters_, iii. p. 153. + + {303} Note by the late Alfred Newton. Richardson in _Fauna + Boreali-Americana_, i. p. 49. + + {304} <Note in original.> See Richardson a far better case of a + polecat animal <_Mustela vison_>, which half-year is aquatic. + <Mentioned in _Origin_, Ed. i. p. 179, vi. p. 216.> + + + + +PART II{305} + +ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW THAT SPECIES ARE +NATURALLY FORMED RACES, DESCENDED FROM COMMON STOCKS + + {305} In the _Origin_ the division of the work into Parts I and II + is omitted. In the MS. the chapters of Part II are numbered afresh, + the present being Ch. I of Pt. II. I have thought it best to call + it Ch. IV and there is evidence that Darwin had some thought of + doing the same. It corresponds to Ch. IX of _Origin_, Ed. i., Ch. X + in Ed. vi. + + + + +CHAPTER IV + +ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE THEORY OF COMMON +DESCENT; AND ON THEIR ABSENCE IN A FOSSIL STATE + + +I must here premise that, according to the view ordinarily received, the +myriads of organisms, which have during past and present times peopled +this world, have been created by so many distinct acts of creation. It +is impossible to reason concerning the will of the Creator, and +therefore, according to this view, we can see no cause why or why not +the individual organism should have been created on any fixed scheme. +That all the organisms of this world have been produced on a scheme is +certain from their general affinities; and if this scheme can be shown +to be the same with that which would result from allied organic beings +descending from common stocks, it becomes highly improbable that they +have been separately created by individual acts of the will of a +Creator. For as well might it be said that, although the planets move in +courses conformably to the law of gravity, yet we ought to attribute +the course of each planet to the individual act of the will of the +Creator{306}. It is in every case more conformable with what we know of +the government of this earth, that the Creator should have imposed only +general laws. As long as no method was known by which races could become +exquisitely adapted to various ends, whilst the existence of species was +thought to be proved by the sterility{307} of their offspring, it was +allowable to attribute each organism to an individual act of creation. +But in the two former chapters it has (I think) been shown that the +production, under existing conditions, of exquisitely adapted species, +is at least _possible_. Is there then any direct evidence in favour <of> or +against this view? I believe that the geographical distribution of +organic beings in past and present times, the kind of affinity linking +them together, their so-called "metamorphic" and "abortive" organs, +appear in favour of this view. On the other hand, the imperfect evidence +of the continuousness of the organic series, which, we shall immediately +see, is required on our theory, is against it; and is the most weighty +objection{308}. The evidence, however, even on this point, as far as it +goes, is favourable; and considering the imperfection of our knowledge, +especially with respect to past ages, it would be surprising if evidence +drawn from such sources were not also imperfect. + + {306} In the Essay of 1842 the author uses astronomy in the same + manner as an illustration. In the _Origin_ this does not occur; the + reference to the action of secondary causes is more general, _e.g._ + Ed. i. p. 488, vi. p. 668. + + {307} It is interesting to find the argument from sterility given + so prominent a place. In a corresponding passage in the _Origin_, + Ed. i. p. 480, vi. p. 659, it is more summarily treated. The author + gives, as the chief bar to the acceptance of evolution, the fact + that "we are always slow in admitting any great change of which we + do not see the intermediate steps"; and goes on to quote Lyell on + geological action. It will be remembered that the question of + sterility remained a difficulty for Huxley. + + {308} Similar statements occur in the Essay of 1842, p. 24, note 1, + and in the _Origin_, Ed. i. p. 299. + +As I suppose that species have been formed in an analogous manner with +the varieties of the domesticated animals and plants, so must there have +existed intermediate forms between all the species of the same group, +not differing more than recognised varieties differ. It must not be +supposed necessary that there should have existed forms exactly +intermediate in character between any two species of a genus, or even +between any two varieties of a species; but it is necessary that there +should have existed every intermediate form between the one species or +variety of the common parent, and likewise between the second species or +variety, and this same common parent. Thus it does not necessarily +follow that there ever has existed <a> series of intermediate sub-varieties +(differing no more than the occasional seedlings from the same +seed-capsule,) between broccoli and common red cabbage; but it is +certain that there has existed, between broccoli and the wild parent +cabbage, a series of such intermediate seedlings, and again between red +cabbage and the wild parent cabbage: so that the broccoli and red +cabbage are linked together, but not _necessarily_ by directly +intermediate forms{309}. It is of course possible that there _may_ have +been directly intermediate forms, for the broccoli may have long since +descended from a common red cabbage, and this from the wild cabbage. So +on my theory, it must have been with species of the same genus. Still +more must the supposition be avoided that there has necessarily ever +existed (though one _may_ have descended from <the> other) directly +intermediate forms between any two genera or families--for instance +between the genus _Sus_ and the Tapir{310}; although it is necessary +that intermediate forms (not differing more than the varieties of our +domestic animals) should have existed between Sus and some unknown +parent form, and Tapir with this same parent form. The latter may have +differed more from Sus and Tapir than these two genera now differ from +each other. In this sense, according to our theory, there has been a +gradual passage (the steps not being wider apart than our domestic +varieties) between the species of the same genus, between genera of the +same family, and between families of the same order, and so on, as far +as facts, hereafter to be given, lead us; and the number of forms which +must have at former periods existed, thus to make good this passage +between different species, genera, and families, must have been almost +infinitely great. + + {309} In the _Origin_, Ed. i. p. 280, vi. p. 414 he uses his + newly-acquired knowledge of pigeons to illustrate this point. + + {310} Compare the _Origin_, Ed. i. p. 281, vi. p. 414. + +What evidence{311} is there of a number of intermediate forms having +existed, making a passage in the above sense, between the species of the +same groups? Some naturalists have supposed that if every fossil which +now lies entombed, together with all existing species, were collected +together, a perfect series in every great class would be formed. +Considering the enormous number of species requisite to effect this, +especially in the above sense of the forms not being _directly_ +intermediate between the existing species and genera, but only +intermediate by being linked through a common but often widely different +ancestor, I think this supposition highly improbable. I am however far +from underrating the probable number of fossilised species: no one who +has attended to the wonderful progress of palæontology during the last +few years will doubt that we as yet have found only an exceedingly small +fraction of the species buried in the crust of the earth. Although the +almost infinitely numerous intermediate forms in no one class may have +been preserved, it does not follow that they have not existed. The +fossils which have been discovered, it is important to remark, do tend, +the little way they go, to make good the series; for as observed by +Buckland they all fall into or between existing groups{312}. Moreover, +those that fall between our existing groups, fall in, according to the +manner required by our theory, for they do not directly connect two +existing species of different groups, but they connect the groups +themselves: thus the Pachydermata and Ruminantia are now separated by +several characters, <for instance> the Pachydermata{313} have both a +tibia and fibula, whilst Ruminantia have only a tibia; now the fossil +Macrauchenia has a leg bone exactly intermediate in this respect, and +likewise has some other intermediate characters. But the Macrauchenia +does not connect any one species of Pachydermata with some one other of +Ruminantia but it shows that these two groups have at one time been less +widely divided. So have fish and reptiles been at one time more closely +connected in some points than they now are. Generally in those groups in +which there has been most change, the more ancient the fossil, if not +identical with recent, the more often it falls between existing groups, +or into small existing groups which now lie between other large existing +groups. Cases like the foregoing, of which there are many, form steps, +though few and far between, in a series of the kind required by my +theory. + + {311} _Origin_, Ed. i. p. 301, vi. p. 440. + + {312} _Origin_, Ed. i. p. 329, vi. p. 471. + + {313} The structure of the Pachyderm leg was a favourite with the + author. It is discussed in the Essay of 1842, p. 48. In the present + Essay the following sentence in the margin appears to refer to + Pachyderms and Ruminants: "There can be no doubt, if we banish all + fossils, existing groups stand more separate." The following occurs + between the lines "The earliest forms would be such as others could + radiate from." + +As I have admitted the high improbability, that if every fossil were +disinterred, they would compose in each of the Divisions of Nature a +perfect series of the kind required; consequently I freely admit, that +if those geologists are in the right who consider the lowest known +formation as contemporaneous with the first appearances of life{314}; or +the several formations as at all closely consecutive; or any one +formation as containing a nearly perfect record of the organisms which +existed during the whole period of its deposition in that quarter of the +globe;--if such propositions are to be accepted, my theory must be +abandoned. + + {314} _Origin_, Ed. i. p. 307, vi. p. 448. + +If the Palæozoic system is really contemporaneous with the first +appearance of life, my theory must be abandoned, both inasmuch as it +limits _from shortness of time_ the total number of forms which can have +existed on this world, and because the organisms, as fish, mollusca{315} +and star-fish found in its lower beds, cannot be considered as the +parent forms of all the successive species in these classes. But no one +has yet overturned the arguments of Hutton and Lyell, that the lowest +formations known to us are only those which have escaped being +metamorphosed <illegible>; if we argued from some considerable districts, +we might have supposed that even the Cretaceous system was that in which +life first appeared. From the number of distant points, however, in +which the Silurian system has been found to be the lowest, and not +always metamorphosed, there are some objections to Hutton's and Lyell's +view; but we must not forget that the now existing land forms only 1/5 +part of the superficies of the globe, and that this fraction is only +imperfectly known. With respect to the fewness of the organisms found in +the Silurian and other Palæozoic formations, there is less difficulty, +inasmuch as (besides their gradual obliteration) we can expect +formations of this vast antiquity to escape entire denudation, only when +they have been accumulated over a wide area, and have been subsequently +protected by vast superimposed deposits: now this could generally only +hold good with deposits accumulating in a wide and deep ocean, and +therefore unfavourable to the presence of many living things. A mere +narrow and not very thick strip of matter, deposited along a coast where +organisms most abound, would have no chance of escaping denudation and +being preserved to the present time from such immensely distant +ages{316}. + + {315} <Pencil insertion by the author.> The parent-forms of Mollusca + would probably differ greatly from all recent,--it is not directly + that any one division of Mollusca would descend from first time + unaltered, whilst others had become metamorphosed from it. + + {316} _Origin_, Ed. i. p. 291, vi. p. 426. + +If the several known formations are at all nearly consecutive in time, +and preserve a fair record of the organisms which have existed, my +theory must be abandoned. But when we consider the great changes in +mineralogical nature and texture between successive formations, what +vast and entire changes in the geography of the surrounding countries +must generally have been effected, thus wholly to have changed the +nature of the deposits on the same area. What time such changes must +have required! Moreover how often has it not been found, that between +two conformable and apparently immediately successive deposits a vast +pile of water-worn matter is interpolated in an adjoining district. We +have no means of conjecturing in many cases how long a period{317} has +elapsed between successive formations, for the species are often wholly +different: as remarked by Lyell, in some cases probably as long a period +has elapsed between two formations as the whole Tertiary system, itself +broken by wide gaps. + + {317} <Note in original.> Reflect on coming in of the Chalk, + extending from Iceland to the Crimea. + +Consult the writings of any one who has particularly attended to any one +stage in the Tertiary system (and indeed of every system) and see how +deeply impressed he is with the time required for its accumulation{318}. +Reflect on the years elapsed in many cases, since the latest beds +containing only living species have been formed;--see what Jordan Smith +says of the 20,000 years since the last bed, which is above the boulder +formation in Scotland, has been upraised; or of the far longer period +since the recent beds of Sweden have been upraised 400 feet, what an +enormous period the boulder formation must have required, and yet how +insignificant are the records (although there has been plenty of +elevation to bring up submarine deposits) of the shells, which we know +existed at that time. Think, then, over the entire length of the +Tertiary epoch, and think over the probable length of the intervals, +separating the Secondary deposits. Of these deposits, moreover, those +consisting of sand and pebbles have seldom been favourable, either to +the embedment or to the preservation of fossils{319}. + + {318} _Origin_, Ed. i. p. 282, vi. p. 416. + + {319} _Origin_, Ed. i. pp. 288, 300, vi. pp. 422, 438. + +Nor can it be admitted as probable that any one Secondary formation +contains a fair record even of those organisms which are most easily +preserved, namely hard marine bodies. In how many cases have we not +certain evidence that between the deposition of apparently closely +consecutive beds, the lower one existed for an unknown time as land, +covered with trees. Some of the Secondary formations which contain most +marine remains appear to have been formed in a wide and not deep sea, +and therefore only those marine animals which live in such situations +would be preserved{320}. In all cases, on indented rocky coasts, or any +other coast, where sediment is not accumulating, although often highly +favourable to marine animals, none can be embedded: where pure sand and +pebbles are accumulating few or none will be preserved. I may here +instance the great western line of the S. American coast{321}, tenanted +by many peculiar animals, of which none probably will be preserved to a +distant epoch. From these causes, and especially from such deposits as +are formed along a line of coast, steep above and below water, being +necessarily of little width, and therefore more likely to be +subsequently denuded and worn away, we can see why it is improbable that +our Secondary deposits contain a fair record of the Marine Fauna of any +one period. The East Indian Archipelago offers an area, as large as most +of our Secondary deposits, in which there are wide and shallow seas, +teeming with marine animals, and in which sediment is accumulating; now +supposing that all the hard marine animals, or rather those having hard +parts to preserve, were preserved to a future age, excepting those which +lived on rocky shores where no sediment or only sand and gravel were +accumulating, and excepting those embedded along the steeper coasts, +where only a narrow fringe of sediment was accumulating, supposing all +this, how poor a notion would a person at a future age have of the +Marine Fauna of the present day. Lyell{322} has compared the geological +series to a work of which only the few latter but not consecutive +chapters have been preserved; and out of which, it may be added, very +many leaves have been torn, the remaining ones only illustrating a +scanty portion of the Fauna of each period. On this view, the records +of anteceding ages confirm my theory; on any other they destroy it. + + {320} <Note in original.> Neither highest or lowest fish (_i.e._ + Myxina <?> or Lepidosiren) could be preserved in intelligible + condition in fossils. + + {321} _Origin_, Ed. i. p. 290, vi. p. 425. + + {322} See _Origin_, Ed. i. p. 310, vi. p. 452 for Lyell's metaphor. + I am indebted to Prof. Judd for pointing out that Darwin's version + of the metaphor is founded on the first edition of Lyell's + _Principles_, vol. I. and vol. III.; see the Essay of 1842, p. 27. + +Finally, if we narrow the question into, why do we not find in some +instances every intermediate form between any two species? the answer +may well be that the average duration of each specific form (as we have +good reason to believe) is immense in years, and that the transition +could, according to my theory, be effected only by numberless small +gradations; and therefore that we should require for this end a most +perfect record, which the foregoing reasoning teaches us not to expect. +It might be thought that in a vertical section of great thickness in the +same formation some of the species ought to be found to vary in the +upper and lower parts{323}, but it may be doubted whether any formation +has gone on accumulating without any break for a period as long as the +duration of a species; and if it had done so, we should require a series +of specimens from every part. How rare must be the chance of sediment +accumulating for some 20 or 30 thousand years on the same spot{324}, +with the bottom subsiding, so that a proper depth might be preserved for +any one species to continue living: what an amount of subsidence would +be thus required, and this subsidence must not destroy the source whence +the sediment continued to be derived. In the case of terrestrial +animals, what chance is there when the present time is become a +pleistocene formation (at an earlier period than this, sufficient +elevation to expose marine beds could not be expected), what chance is +there that future geologists will make out the innumerable transitional +sub-varieties, through which the short-horned and long-horned cattle +(so different in shape of body) have been derived from the same parent +stock{325}? Yet this transition has been effected in _the same country_, +and in a far _shorter time_, than would be probable in a wild state, +both contingencies highly favourable for the future hypothetical +geologists being enabled to trace the variation. + + {323} See _More Letters_, vol. I. pp. 344-7, for Darwin's interest + in the celebrated observations of Hilgendorf and Hyatt. + + {324} This corresponds partly to _Origin_, Ed. i. p. 294, vi. p. + 431. + + {325} _Origin_, Ed. i. p. 299, vi. p. 437. + + + + +CHAPTER V + +GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES{326} + + {326} This chapter corresponds to ch. X of _Origin_, Ed. i., vi. + ch. XI, "On the geological succession of organic beings." + + +In the Tertiary system, in the last uplifted beds, we find all the +species recent and living in the immediate vicinity; in rather older +beds we find only recent species, but some not living in the immediate +vicinity{327}; we then find beds with two or three or a few more extinct +or very rare species; then considerably more extinct species, but with +gaps in the regular increase; and finally we have beds with only two or +three or not one living species. Most geologists believe that the gaps +in the percentage, that is the sudden increments, in the number of the +extinct species in the stages of the Tertiary system are due to the +imperfection of the geological record. Hence we are led to believe that +the species in the Tertiary system have been gradually introduced; and +from analogy to carry on the same view to the Secondary formations. In +these latter, however, entire groups of species generally come in +abruptly; but this would naturally result, if, as argued in the +foregoing chapter, these Secondary deposits are separated by wide +epochs. Moreover it is important to observe that, with our increase of +knowledge, the gaps between the older formations become fewer and +smaller; geologists of a few years standing remember how beautifully +has the Devonian system{328} come in between the Carboniferous and +Silurian formations. I need hardly observe that the slow and gradual +appearance of new forms follows from our theory, for to form a new +species, an old one must not only be plastic in its organization, +becoming so probably from changes in the conditions of its existence, +but a place in the natural economy of the district must [be made,] come +to exist, for the selection of some new modification of its structure, +better fitted to the surrounding conditions than are the other +individuals of the same or other species{329}. + + {327} _Origin_, Ed. i. p. 312, vi. p. 453. + + {328} In the margin the author has written "Lonsdale." This refers + to W. Lonsdale's paper "Notes on the age of the Limestone of South + Devonshire," _Geolog. Soc. Trans._, Series 2, vol. V. 1840, p. 721. + According to Mr H. B. Woodward (_History of the Geological Society + of London_, 1907, p. 107) "Lonsdale's 'important and original + suggestion of the existence of an intermediary type of Palæozoic + fossils, since called Devonian,' led to a change which was then + 'the greatest ever made at one time in the classification of our + English formations'." Mr Woodward's quotations are from Murchison + and Buckland. + + {329} <Note in original.> Better begin with this. If species really, + after catastrophes, created in showers over world, my theory false. + <In the above passage the author is obviously close to his theory of + divergence.> + +In the Tertiary system the same facts, which make us admit as probable +that new species have slowly appeared, lead to the admission that old +ones have slowly disappeared, not several together, but one after +another; and by analogy one is induced to extend this belief to the +Secondary and Palæozoic epochs. In some cases, as the subsidence of a +flat country, or the breaking or the joining of an isthmus, and the +sudden inroad of many new and destructive species, extinction might be +locally sudden. The view entertained by many geologists, that each fauna +of each Secondary epoch has been suddenly destroyed over the whole +world, so that no succession could be left for the production of new +forms, is subversive of my theory, but I see no grounds whatever to +admit such a view. On the contrary, the law, which has been made out, +with reference to distinct epochs, by independent observers, namely, +that the wider the geographical range of a species the longer is its +duration in time, seems entirely opposed to any universal +extermination{330}. The fact of species of mammiferous animals and fish +being renewed at a quicker rate than mollusca, though both aquatic; and +of these the terrestrial genera being renewed quicker than the marine; +and the marine mollusca being again renewed quicker than the Infusorial +animalcula, all seem to show that the extinction and renewal of species +does not depend on general catastrophes, but on the particular relations +of the several classes to the conditions to which they are exposed{331}. + + {330} Opposite to this passage the author has written "d'Archiac, + Forbes, Lyell." + + {331} This passage, for which the author gives as authorities the + names of Lyell, Forbes and Ehrenberg, corresponds in part to the + discussion beginning on p. 313 of _Origin_, Ed. i., vi. p. 454. + +Some authors seem to consider the fact of a few species having +survived{332} amidst a number of extinct forms (as is the case with a +tortoise and a crocodile out of the vast number of extinct sub-Himalayan +fossils) as strongly opposed to the view of species being mutable. No +doubt this would be the case, if it were presupposed with Lamarck that +there was some inherent tendency to change and development in all +species, for which supposition I see no evidence. As we see some species +at present adapted to a wide range of conditions, so we may suppose that +such species would survive unchanged and unexterminated for a long time; +time generally being from geological causes a correlative of changing +conditions. How at present one species becomes adapted to a wide range, +and another species to a restricted range of conditions, is of difficult +explanation. + + {332} The author gives Falconer as his authority: see _Origin_, Ed. + i. p. 313, vi. p. 454. + + +_Extinction of species._ + +The extinction of the larger quadrupeds, of which we imagine we better +know the conditions of existence, has been thought little less wonderful +than the appearance of new species; and has, I think, chiefly led to the +belief of universal catastrophes. When considering the wonderful +disappearance within a late period, whilst recent shells were living, of +the numerous great and small mammifers of S. America, one is strongly +induced to join with the catastrophists. I believe, however, that very +erroneous views are held on this subject. As far as is historically +known, the disappearance of species from any one country has been +slow--the species becoming rarer and rarer, locally extinct, and finally +lost{333}. It may be objected that this has been effected by man's +direct agency, or by his indirect agency in altering the state of the +country; in this latter case, however, it would be difficult to draw any +just distinction between his agency and natural agencies. But we now +know in the later Tertiary deposits, that shells become rarer and rarer +in the successive beds, and finally disappear: it has happened, also, +that shells common in a fossil state, and thought to have been extinct, +have been found to be still living species, but very _rare_ ones{334}. +If the rule is that organisms become extinct by becoming rarer and +rarer, we ought not to view their extinction, even in the case of the +larger quadrupeds, as anything wonderful and out of the common course of +events. For no naturalist thinks it wonderful that one species of a +genus should be rare and another abundant, notwithstanding he be quite +incapable of explaining the causes of the comparative rareness{335}. Why +is one species of willow-wren or hawk or woodpecker common in England, +and another extremely rare: why at the Cape of Good Hope is one species +of rhinoceros or antelope far more abundant than other species? Why +again is the same species much more abundant in one district of a +country than in another district? No doubt there are in each case good +causes: but they are unknown and unperceived by us. May we not then +safely infer that as certain causes are acting _unperceived_ around us, +and are making one species to be common and another exceedingly rare, +that they might equally well cause the final extinction of some species +without being perceived by us? We should always bear in mind that there +is a recurrent struggle for life in every organism, and that in every +country a destroying agency is always counteracting the geometrical +tendency to increase in every species; and yet without our being able to +tell with certainty at what period of life, or at what period of the +year, the destruction falls the heaviest. Ought we then to expect to +trace the steps by which this destroying power, always at work and +scarcely perceived by us, becomes increased, and yet if it continues to +increase ever so slowly (without the fertility of the species in +question be likewise increased) the average number of the individuals of +that species must decrease, and become finally lost. I may give a single +instance of a check causing local extermination which might long have +escaped discovery{336}; the horse, though swarming in a wild state in La +Plata, and likewise under apparently the most unfavourable conditions in +the scorched and alternately flooded plains of Caraccas, will not in a +wild state extend beyond a certain degree of latitude into the +intermediate country of Paraguay; this is owing to a certain fly +depositing its eggs on the navels of the foals: as, however, man with a +_little_ care can rear horses in a tame state _abundantly_ in Paraguay, +the problem of its extinction is probably complicated by the greater +exposure of the wild horse to occasional famine from the droughts, to +the attacks of the jaguar and other such evils. In the Falkland Islands +the check to the _increase_ of the wild horse is said to be loss of the +sucking foals{337}, from the stallions compelling the mares to travel +across bogs and rocks in search of food: if the pasture on these islands +decreased a little, the horse, perhaps, would cease to exist in a wild +state, not from the absolute want of food, but from the impatience of +the stallions urging the mares to travel whilst the foals were too +young. + + {333} This corresponds approximately to _Origin_, Ed. i. p. 317, + vi. p. 458. + + {334} The case of _Trigonia_, a great Secondary genus of shells + surviving in a single species in the Australian seas, is given as + an example in the _Origin_, Ed. i. p. 321, vi. p. 463. + + {335} This point, on which the author laid much stress, is + discussed in the _Origin_, Ed. i. p. 319, vi. p. 461. + + {336} _Origin_, Ed. i. p. 72, vi. p. 89. + + {337} This case does not occur in the _Origin_, Ed. + +From our more intimate acquaintance with domestic animals, we cannot +conceive their extinction without some glaring agency; we forget that +they would undoubtedly in a state of nature (where other animals are +ready to fill up their place) be acted on in some part of their lives by +a destroying agency, keeping their numbers on an average constant. If +the common ox was known only as a wild S. African species, we should +feel no surprise at hearing that it was a very rare species; and this +rarity would be a stage towards its extinction. Even in man, so +infinitely better known than any other inhabitant of this world, how +impossible it has been found, without statistical calculations, to judge +of the proportions of births and deaths, of the duration of life, and of +the increase and decrease of population; and still less of the causes of +such changes: and yet, as has so often been repeated, decrease in +numbers or rarity seems to be the high-road to extinction. To marvel at +the extermination of a species appears to me to be the same thing as to +know that illness is the road to death,--to look at illness as an +ordinary event, nevertheless to conclude, when the sick man dies, that +his death has been caused by some unknown and violent agency{338}. + + {338} An almost identical sentence occurs in the _Origin_, Ed. i. + p. 320, vi. p. 462. + +In a future part of this work we shall show that, as a general rule, +groups of allied species{339} gradually appear and disappear, one after +the other, on the face of the earth, like the individuals of the same +species: and we shall then endeavour to show the probable cause of this +remarkable fact. + + {339} _Origin_, Ed. i. p. 316, vi. p. 457. + + + + +CHAPTER VI + +ON THE GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS IN PAST AND PRESENT +TIMES + + +For convenience sake I shall divide this chapter into three +sections{340}. In the first place I shall endeavour to state the laws of +the distribution of existing beings, as far as our present object is +concerned; in the second, that of extinct; and in the third section I +shall consider how far these laws accord with the theory of allied +species having a common descent. + + {340} Chapters XI and XII in the _Origin_, Ed. i., vi. chs. XII and + XIII ("On geographical distribution") show signs of having been + originally one, in the fact that one summary serves for both. The + geological element is not separately treated there, nor is there a + separate section on "how far these laws accord with the theory, + &c." + + In the MS. the author has here written in the margin "If same + species appear at two spot at once, fatal to my theory." See + _Origin_, Ed. i. p. 352, vi. p. 499 + + +SECTION FIRST. + + +_Distribution of the inhabitants in the different continents._ + +In the following discussion I shall chiefly refer to terrestrial +mammifers, inasmuch as they are better known; their differences in +different countries, strongly marked; and especially as the necessary +means of their transport are more evident, and confusion, from the +accidental conveyance by man of a species from one district to another +district, is less likely to arise. It is known that all mammifers (as +well as all other organisms) are united in one great system; but that +the different species, genera, or families of the same order inhabit +different quarters of the globe. If we divide the land{341} into two +divisions, according to the amount of difference, and disregarding the +numbers of the terrestrial mammifers inhabiting them, we shall have +first Australia including New Guinea; and secondly the rest of the +world: if we make a three-fold division, we shall have Australia, S. +America, and the rest of the world; I must observe that North America is +in some respects neutral land, from possessing some S. American forms, +but I believe it is more closely allied (as it certainly is in its +birds, plants and shells) with Europe. If our division had been +four-fold, we should have had Australia, S. America, Madagascar (though +inhabited by few mammifers) and the remaining land: if five-fold, +Africa, especially the southern eastern parts, would have to be +separated from the remainder of the world. These differences in the +mammiferous inhabitants of the several main divisions of the globe +cannot, it is well known, be explained by corresponding differences in +their conditions{342}; how similar are parts of tropical America and +Africa; and accordingly we find some _analogous_ resemblances,--thus +both have monkeys, both large feline animals, both large Lepidoptera, +and large dung-feeding beetles; both have palms and epiphytes; and yet +the essential difference between their productions is as great as +between those of the arid plains of the Cape of Good Hope and the +grass-covered savannahs of La Plata{343}. Consider the distribution of +the Marsupialia, which are eminently characteristic of Australia, and in +a lesser degree of S. America; when we reflect that animals of this +division, feeding both on animal and vegetable matter, frequent the dry +open or wooded plains and mountains of Australia, the humid impenetrable +forests of New Guinea and Brazil; the dry rocky mountains of Chile, and +the grassy plains of Banda Oriental, we must look to some other cause, +than the nature of the country, for their absence in Africa and other +quarters of the world. + + {341} This division of the land into regions does not occur in the + _Origin_, Ed. i. + + {342} _Origin_, Ed. i. p. 346, vi. p. 493. + + {343} Opposite this passage is written "_not botanically_," in Sir + J. D. Hooker's hand. The word _palms_ is underlined three times and + followed by three exclamation marks. An explanatory note is added + in the margin "singular paucity of palms and epiphytes in Trop. + Africa compared with Trop. America and Ind. Or." <=East Indies>. + +Furthermore it may be observed that _all_ the organisms inhabiting any +country are not perfectly adapted to it{344}; I mean by not being +perfectly adapted, only that some few other organisms can generally be +found better adapted to the country than some of the aborigines. We must +admit this when we consider the enormous number of horses and cattle +which have run wild during the three last centuries in the uninhabited +parts of St Domingo, Cuba, and S. America; for these animals must have +supplanted some aboriginal ones. I might also adduce the same fact in +Australia, but perhaps it will be objected that 30 or 40 years has not +been a sufficient period to test this power of struggling <with> and +overcoming the aborigines. We know the European mouse is driving before +it that of New Zealand, like the Norway rat has driven before it the old +English species in England. Scarcely an island can be named, where +casually introduced plants have not supplanted some of the native +species: in La Plata the Cardoon covers square leagues of country on +which some S. American plants must once have grown: the commonest weed +over the whole of India is an introduced Mexican poppy. The geologist +who knows that slow changes are in progress, replacing land and water, +will easily perceive that even if all the organisms of any country had +originally been the best adapted to it, this could hardly continue so +during succeeding ages without either extermination, or changes, first +in the relative proportional numbers of the inhabitants of the country, +and finally in their constitutions and structure. + + {344} This partly corresponds to _Origin_, Ed. i. p. 337, vi. p. + 483. + +Inspection of a map of the world at once shows that the five divisions, +separated according to the greatest amount of difference in the +mammifers inhabiting them, are likewise those most widely separated from +each other by barriers{345} which mammifers cannot pass: thus Australia +is separated from New Guinea and some small adjoining islets only by a +narrow and shallow strait; whereas New Guinea and its adjoining islets +are cut off from the other East Indian islands by deep water. These +latter islands, I may remark, which fall into the great Asiatic group, +are separated from each other and the continent only by shallow water; +and where this is the case we may suppose, from geological oscillations +of level, that generally there has been recent union. South America, +including the southern part of Mexico, is cut off from North America by +the West Indies, and the great table-land of Mexico, except by a mere +fringe of tropical forests along the coast: it is owing, perhaps, to +this fringe that N. America possesses some S. American forms. Madagascar +is entirely isolated. Africa is also to a great extent isolated, +although it approaches, by many promontories and by lines of shallower +sea, to Europe and Asia: southern Africa, which is the most distinct in +its mammiferous inhabitants, is separated from the northern portion by +the Great Sahara Desert and the table-land of Abyssinia. That the +distribution of organisms is related to barriers, stopping their +progress, we clearly see by comparing the distribution of marine and +terrestrial productions. The marine animals being different on the two +sides of land tenanted by the same terrestrial animals, thus the shells +are wholly different on the opposite sides of the temperate parts of +South America{346}, as they are (?) in the Red Sea and the +Mediterranean. We can at once perceive that the destruction of a barrier +would permit two geographical groups of organisms to fuse and blend into +one. But the original cause of groups being different on opposite sides +of a barrier can only be understood on the hypothesis of each organism +having been created or produced on one spot or area, and afterwards +migrating as widely as its means of transport and subsistence permitted +it. + + {345} On the general importance of barriers, see _Origin_, Ed. i. + p. 347, vi. p. 494. + + {346} _Origin_, Ed. i. p. 348, vi. p. 495. + + +_Relation of range in genera and species._ + +It is generally{347} found, that where a genus or group ranges over +nearly the entire world, many of the species composing the group have +wide ranges: on the other hand, where a group is restricted to any one +country, the species composing it generally have restricted ranges in +that country{348}. Thus among mammifers the feline and canine genera are +widely distributed, and many of the individual species have enormous +ranges [the genus Mus I believe, however, is a strong exception to the +rule]. Mr Gould informs me that the rule holds with birds, as in the +owl genus, which is mundane, and many of the species range widely. The +rule holds also with land and fresh-water mollusca, with butterflies and +very generally with plants. As instances of the converse rule, I may +give that division of the monkeys which is confined to S. America, and +amongst plants, the Cacti, confined to the same continent, the species +of both of which have generally narrow ranges. On the ordinary theory of +the separate creation of each species, the cause of these relations is +not obvious; we can see no reason, because many allied species have been +created in the several main divisions of the world, that several of +these species should have wide ranges; and on the other hand, that +species of the same group should have narrow ranges if all have been +created in one main division of the world. As the result of such and +probably many other unknown relations, it is found that, even in the +same great classes of beings, the different divisions of the world are +characterised by either merely different species, or genera, or even +families: thus in cats, mice, foxes, S. America differs from Asia and +Africa only in species; in her pigs, camels and monkeys the difference +is generic or greater. Again, whilst southern Africa and Australia +differ more widely in their mammalia than do Africa and S. America, they +are more closely (though indeed very distantly) allied in their plants. + + {347} <Note in original.> The same laws seem to govern distribution + of species and genera, and individuals in time and space. <See + _Origin_, Ed. i. p. 350, vi. p. 497, also a passage in the last + chapter, p. 146.> + + {348} _Origin_, Ed. i. p. 404, vi. p. 559. + + +_Distribution of the inhabitants in the same continent._ + +If we now look at the distribution of the organisms in any one of the +above main divisions of the world, we shall find it split up into many +regions, with all or nearly all their species distinct, but yet +partaking of one common character. This similarity of type in the +subdivisions of a great region is equally well-known with the +dissimilarity of the inhabitants of the several great regions; but it +has been less often insisted on, though more worthy of remark. Thus for +instance, if in Africa or S. America, we go from south to north{349}, or +from lowland to upland, or from a humid to a dryer part, we find wholly +different species of those genera or groups which characterise the +continent over which we are passing. In these subdivisions we may +clearly observe, as in the main divisions of the world, that +sub-barriers divide different groups of species, although the opposite +sides of such sub-barriers may possess nearly the same climate, and may +be in other respects nearly similar: thus it is on the opposite sides of +the Cordillera of Chile, and in a lesser degree on the opposite sides of +the Rocky mountains. Deserts, arms of the sea, and even rivers form the +barriers; mere preoccupied space seems sufficient in several cases: thus +Eastern and Western Australia, in the same latitude, with very similar +climate and soils, have scarcely a plant, and few animals or birds, in +common, although all belong to the peculiar genera characterising +Australia. It is in short impossible to explain the differences in the +inhabitants, either of the main divisions of the world, or of these +sub-divisions, by the differences in their physical conditions, and by +the adaptation of their inhabitants. Some other cause must intervene. + + {349} _Origin_, Ed. i. p. 349, vi. p. 496. + +We can see that the destruction of sub-barriers would cause (as before +remarked in the case of the main divisions) two sub-divisions to blend +into one; and we can only suppose that the original difference in the +species, on the opposite sides of sub-barriers, is due to the creation +or production of species in distinct areas, from which they have +wandered till arrested by such sub-barriers. Although thus far is pretty +clear, it may be asked, why, when species in the same main division of +the world were produced on opposite sides of a sub-barrier, both when +exposed to similar conditions and when exposed to widely different +influences (as on alpine and lowland tracts, as on arid and humid soils, +as in cold and hot climates), have they invariably been formed on a +similar type, and that type confined to this one division of the world? +Why when an ostrich{350} was produced in the southern parts of America, +was it formed on the American type, instead of on the African or on +Australian types? Why when hare-like and rabbit-like animals were formed +to live on the Savannahs of La Plata, were they produced on the peculiar +Rodent type of S. America, instead of on the true{351} hare-type of +North America, Asia and Africa? Why when borrowing Rodents, and +camel-like animals were formed to tenant the Cordillera, were they +formed on the same type{352} with their representatives on the plains? +Why were the mice, and many birds of different species on the opposite +sides of the Cordillera, but exposed to a very similar climate and soil, +created on the same peculiar S. American type? Why were the plants in +Eastern and Western Australia, though wholly different as species, +formed on the same peculiar Australian types? The generality of the +rule, in so many places and under such different circumstances, makes it +highly remarkable and seems to demand some explanation. + + {350} The case of the ostrich (_Rhea_) occurs in the _Origin_, Ed. + i. p. 349, vi. p. 496. + + {351} <Note in original.> There is a hare in S. America,--so bad + example. + + {352} See _Origin_, Ed. i. p. 349, vi. p. 497. + + +_Insular Faunas._ + +If we now look to the character of the inhabitants of small +islands{353}, we shall find that those situated close to other land have +a similar fauna with that land{354}, whilst those at a considerable +distance from other land often possess an almost entirely peculiar +fauna. The Galapagos Archipelago{355} is a remarkable instance of this +latter fact; here almost every bird, its one mammifer, its reptiles, +land and sea shells, and even fish, are almost all peculiar and distinct +species, not found in any other quarter of the world: so are the +majority of its plants. But although situated at the distance of between +500 and 600 miles from the S. American coast, it is impossible to even +glance at a large part of its fauna, especially at the birds, without at +once seeing that they belong to the American type{356}. Hence, in fact, +groups of islands thus circumstanced form merely small but well-defined +sub-divisions of the larger geographical divisions. But the fact is in +such cases far more striking: for taking the Galapagos Archipelago as an +instance; in the first place we must feel convinced, seeing that every +island is wholly volcanic and bristles with craters, that in a +geological sense the whole is of recent origin comparatively with a +continent; and as the species are nearly all peculiar, we must conclude +that they have in the same sense recently been produced on this very +spot; and although in the nature of the soil, and in a lesser degree in +the climate, there is a wide difference with the nearer part of the S. +American coast, we see that the inhabitants have been formed on the same +closely allied type. On the other hand, these islands, as far as their +physical conditions are concerned, resemble closely the Cape de Verde +volcanic group, and yet how wholly unlike are the productions of these +two archipelagoes. The Cape de Verde{357} group, to which may be added +the Canary Islands, are allied in their inhabitants (of which many are +peculiar species) to the coast of Africa and southern Europe, in +precisely the same manner as the Galapagos Archipelago is allied to +America. We here clearly see that mere geographical proximity affects, +more than any relation of adaptation, the character of species. How many +islands in the Pacific exist far more like in their physical conditions +to Juan Fernandez than this island is to the coast of Chile, distant 300 +miles; why then, except from mere proximity, should this island alone be +tenanted by two very peculiar species of humming-birds--that form of +birds which is so exclusively American? Innumerable other similar cases +might be adduced. + + {353} For the general problem of Oceanic Islands, see _Origin_, Ed. + i. p. 388, vi. p. 541. + + {354} This is an illustration of the general theory of barriers + (_Origin_, Ed. i. p. 347, vi. p. 494). At i. p. 391, vi. p. 544 the + question is discussed from the point of view of means of transport. + Between the lines, above the words "with that land," the author + wrote "Cause, formerly joined, no one doubts after Lyell." + + {355} _Origin_, Ed. i. p. 390, vi. p. 543. + + {356} See _Origin_, Ed. i. p. 397, vi. p. 552. + + {357} The Cape de Verde and Galapagos Archipelagoes are compared in + the _Origin_, Ed. i. p. 398, vi. p. 553. See also _Journal of + Researches_, 1860, p. 393. + +The Galapagos Archipelago offers another, even more remarkable, example +of the class of facts we are here considering. Most of its genera are, +as we have said, American, many of them are mundane, or found +everywhere, and some are quite or nearly confined to this archipelago. +The islands are of absolutely similar composition, and exposed to the +same climate; most of them are in sight of each other; and yet several +of the islands are inhabited, each by peculiar species (or in some cases +perhaps only varieties) of some of the genera characterising the +archipelago. So that the small group of the Galapagos Islands typifies, +and follows exactly the same laws in the distribution of its +inhabitants, as a great continent. How wonderful it is that two or three +closely similar but distinct species of a mocking-thrush{358} should +have been produced on three neighbouring and absolutely similar islands; +and that these three species of mocking-thrush should be closely related +to the other species inhabiting wholly different climates and different +districts of America, and only in America. No similar case so striking +as this of the Galapagos Archipelago has hitherto been observed; and +this difference of the productions in the different islands may perhaps +be partly explained by the depth of the sea between them (showing that +they could not have been united within recent geological periods), and +by the currents of the sea sweeping _straight_ between them,--and by +storms of wind being rare, through which means seeds and birds could be +blown, or drifted, from one island to another. There are however some +similar facts: it is said that the different, though neighbouring +islands of the East Indian Archipelago are inhabited by some different +species of the same genera; and at the Sandwich group some of the +islands have each their peculiar species of the same genera of plants. + + {358} In the _Origin_, Ed. i. p. 390, a strong point is made of + birds which immigrated "with facility and in a body" not having + been modified. Thus the author accounts for the small percentage of + peculiar "marine birds." + +Islands standing quite isolated within the intra-tropical oceans have +generally very peculiar floras, related, though feebly (as in the case +of St Helena{359} where almost every species is distinct), with the +nearest continent: Tristan d'Acunha is feebly related, I believe, in its +plants, both to Africa and S. America, not by having species in common, +but by the genera to which they belong{360}. The floras of the numerous +scattered islands of the Pacific are related to each other and to all +the surrounding continents; but it has been said, that they have more of +an Indo-Asiatic than American character{361}. This is somewhat +remarkable, as America is nearer to all the Eastern islands, and lies in +the direction of the trade-wind and prevailing currents; on the other +hand, all the heaviest gales come from the Asiatic side. But even with +the aid of these gales, it is not obvious on the ordinary theory of +creation how the possibility of migration (without we suppose, with +extreme improbability, that each species with an Indo-Asiatic character +has actually travelled from the Asiatic shores, where such species do +not now exist) explains this Asiatic character in the plants of the +Pacific. This is no more obvious than that (as before remarked) there +should exist a relation between the creation of closely allied species +in several regions of the world, and the fact of many such species +having wide ranges; and on the other hand, of allied species confined to +one region of the world having in that region narrow ranges. + + {359} "The affinities of the St Helena flora are strongly South + African." Hooker's _Lecture on Insular Floras_ in the _Gardeners' + Chronicle_, Jan. 1867. + + {360} It is impossible to make out the precise form which the + author intended to give to this sentence, but the meaning is clear. + + {361} This is no doubt true, the flora of the Sandwich group + however has marked American affinities. + + +_Alpine Floras._ + +We will now turn to the floras of mountain-summits which are well known +to differ from the floras of the neighbouring lowlands. In certain +characters, such as dwarfness of stature, hairiness, &c., the species +from the most distant mountains frequently resemble each other,--a kind +of analogy like that for instance of the succulency of most desert +plants. Besides this analogy, Alpine plants present some eminently +curious facts in their distribution. In some cases the summits of +mountains, although immensely distant from each other, are clothed by +the same identical species{362} which are likewise the same with those +growing on the likewise very distant Arctic shores. In other cases, +although few or none of the species may be actually identical, they are +closely related; whilst the plants of the lowland districts surrounding +the two mountains in question will be wholly dissimilar. As +mountain-summits, as far as their plants are concerned, are islands +rising out of an ocean of land in which the Alpine species cannot live, +nor across which is there any known means of transport, this fact +appears directly opposed to the conclusion which we have come to from +considering the general distribution of organisms both on continents and +on islands--namely, that the degree of relationship between the +inhabitants of two points depends on the completeness and nature of the +barriers between those points{363}. I believe, however, this anomalous +case admits, as we shall presently see, of some explanation. We might +have expected that the flora of a mountain summit would have presented +the same relation to the flora of the surrounding lowland country, which +any isolated part of a continent does to the whole, or an island does to +the mainland, from which it is separated by a rather wide space of sea. +This in fact is the case with the plants clothing the summits of _some_ +mountains, which mountains it may be observed are particularly isolated; +for instance, all the species are peculiar, but they belong to the forms +characteristic of the surrounding continent, on the mountains of +Caraccas, of Van Dieman's Land and of the Cape of Good Hope{364}. On +some other mountains, for instance <in> Tierra del Fuego and in Brazil, +some of the plants though distinct species are S. American forms; whilst +others are allied to or are identical with the Alpine species of Europe. +In islands of which the lowland flora is distinct <from> but allied to +that of the nearest continent, the Alpine plants are sometimes (or +perhaps mostly) eminently peculiar and distinct{365}; this is the case +on Teneriffe, and in a lesser degree even on some of the Mediterranean +islands. + + {362} See _Origin_, Ed. i. p. 365, vi. p. 515. The present + discussion was written before the publication of Forbes' celebrated + paper on the same subject; see _Life and Letters_, vol. I. p. 88. + + {363} The apparent breakdown of the doctrine of barriers is + slightly touched on in the _Origin_, Ed. i. p. 365, vi. p. 515. + + {364} In the _Origin_, Ed. i. p. 375, vi. p. 526, the author points + out that on the mountains at the Cape of Good Hope "some few + representative European forms are found, which have not been + discovered in the inter-tropical parts of Africa." + + {365} See Hooker's _Lecture on Insular Floras_ in the _Gardeners' + Chronicle_, Jan. 1867. + +If all Alpine floras had been characterised like that of the mountain of +Caraccas, or of Van Dieman's Land, &c., whatever explanation is possible +of the general laws of geographical distribution would have applied to +them. But the apparently anomalous case just given, namely of the +mountains of Europe, of some mountains in the United States (Dr Boott) +and of the summits of the Himalaya (Royle), having many identical +species in common conjointly with the Arctic regions, and many species, +though not identical, closely allied, require a separate explanation. +The fact likewise of several of the species on the mountains of Tierra +del Fuego (and in a lesser degree on the mountains of Brazil) not +belonging to American forms, but to those of Europe, though so immensely +remote, requires also a separate explanation. + + +_Cause of the similarity in the floras of some distant mountains._ + +Now we may with confidence affirm, from the number of the then floating +icebergs and low descent of the glaciers, that within a period so near +that species of shells have remained the same, the whole of Central +Europe and of North America (and perhaps of Eastern Asia) possessed a +very cold climate; and therefore it is probable that the floras of these +districts were the same as the present Arctic one,--as is known to have +been to some degree the case with then existing sea-shells, and those +now living on the Arctic shores. At this period the mountains must have +been covered with ice of which we have evidence in the surfaces polished +and scored by glaciers. What then would be the natural and almost +inevitable effects of the gradual change into the present more temperate +climate{366}? The ice and snow would disappear from the mountains, and +as new plants from the more temperate regions of the south migrated +northward, replacing the Arctic plants, these latter would crawl{367} up +the now uncovered mountains, and likewise be driven northward to the +present Arctic shores. If the Arctic flora of that period was a nearly +uniform one, as the present one is, then we should have the same plants +on these mountain-summits and on the present Arctic shores. On this view +the Arctic flora of that period must have been a widely extended one, +more so than even the present one; but considering how similar the +physical conditions must always be of land bordering on perpetual frost, +this does not appear a great difficulty; and may we not venture to +suppose that the almost infinitely numerous icebergs, charged with +great masses of rocks, soil and _brushwood_{368} and often driven high +up on distant beaches, might have been the means of widely distributing +the seeds of the same species? + + {366} In the margin the author has written "(Forbes)." This may + have been inserted at a date later than 1844, or it may refer to a + work by Forbes earlier than his Alpine paper. + + {367} See _Origin_, Ed. i. p. 367, vi. p. 517. + + {368} <Note in original.> Perhaps vitality checked by cold and so + prevented germinating. <On the carriage of seeds by icebergs, see + _Origin_, Ed. i. p. 363, vi. p. 513.> + +I will only hazard one other observation, namely that during the change +from an extremely cold climate to a more temperate one the conditions, +both on lowland and mountain, would be singularly favourable for the +diffusion of any existing plants, which could live on land, just freed +from the rigour of eternal winter; for it would possess no inhabitants; +and we cannot doubt that _preoccupation_{369} is the chief bar to the +diffusion of plants. For amongst many other facts, how otherwise can we +explain the circumstance that the plants on the opposite, though +similarly constituted sides of a wide river in Eastern Europe (as I was +informed by Humboldt) should be widely different; across which river +birds, swimming quadrupeds and the wind must often transport seeds; we +can only suppose that plants already occupying the soil and freely +seeding check the germination of occasionally transported seeds. + + {369} A note by the author gives "many authors" apparently as + authority for this statement. + +At about the same period when icebergs were transporting boulders in N. +America as far as 36° south, where the cotton tree now grows in South +America, in latitude 42° (where the land is now clothed with forests +having an almost tropical aspect with the trees bearing epiphytes and +intertwined with canes), the same ice action was going on; is it not +then in some degree probable that at this period the whole tropical +parts of the two Americas possessed{370} (as Falconer asserts that +India did) a more temperate climate? In this case the Alpine plants of +the long chain of the Cordillera would have descended much lower and +there would have been a broad high-road{371} connecting those parts of +North and South America which were then frigid. As the present climate +supervened, the plants occupying the districts which now are become in +both hemispheres temperate and even semi-tropical must have been driven +to the Arctic and Antarctic{372} regions; and only a few of the loftiest +points of the Cordillera can have retained their former connecting +flora. The transverse chain of Chiquitos might perhaps in a similar +manner during the ice-action period have served as a connecting road +(though a broken one) for Alpine plants to become dispersed from the +Cordillera to the highlands of Brazil. It may be observed that some +(though not strong) reasons can be assigned for believing that at about +this same period the two Americas were not so thoroughly divided as they +now are by the West Indies and tableland of Mexico. I will only further +remark that the present most singularly close similarity in the +vegetation of the lowlands of Kerguelen's Land{373} and of Tierra del +Fuego (Hooker), though so far apart, may perhaps be explained by the +dissemination of seeds during this same cold period, by means of +icebergs, as before alluded to{374}. + + {370} Opposite to this passage, in the margin, the author has + written:--"too hypothetical." + + {371} The Cordillera is described as supplying a great line of + invasion in the _Origin_, Ed. i. p. 378. + + {372} This is an approximation to the author's views on + trans-tropical migration (_Origin_, Ed. i. pp. 376-8). See + Thiselton-Dyer's interesting discussion in _Darwin and Modern + Science_, p. 304. + + {373} See Hooker's _Lecture on Insular Floras_ in the _Gardeners' + Chronicle_, Jan. 1867. + + {374} <Note by the author.> Similarity of flora of coral islands + easily explained. + +Finally, I think we may safely grant from the foregoing facts and +reasoning that the anomalous similarity in the vegetation of certain +very distant mountain-summits is not in truth opposed to the conclusion +of the intimate relation subsisting between proximity in space (in +accordance with the means of transport in each class) and the degree of +affinity of the inhabitants of any two countries. In the case of several +quite isolated mountains, we have seen that the general law holds good. + + +_Whether the same species has been created more than once._ + +As the fact of the same species of plants having been found on +mountain-summits immensely remote has been one chief cause of the belief +of some species having been contemporaneously produced or created at two +different points{375}, I will here briefly discuss this subject. On the +ordinary theory of creation, we can see no reason why on two similar +mountain-summits two similar species may not have been created; but the +opposite view, independently of its simplicity, has been generally +received from the analogy of the general distribution of all organisms, +in which (as shown in this chapter) we almost always find that great and +continuous barriers separate distinct series; and we are naturally led +to suppose that the two series have been separately created. When taking +a more limited view we see a river, with a quite similar country on both +sides, with one side well stocked with a certain animal and on the other +side not one (as is the case with the Bizcacha{376} on the opposite +sides of the Plata), we are at once led to conclude that the Bizcacha +was produced on some one point or area on the western side of the +river. Considering our ignorance of the many strange chances of +diffusion by birds (which occasionally wander to immense distances) and +quadrupeds swallowing seeds and ova (as in the case of the flying +water-beetle which disgorged the eggs of a fish), and of whirlwinds +carrying seeds and animals into strong upper currents (as in the case of +volcanic ashes and showers of hay, grain and fish{377}), and of the +possibility of species having survived for short periods at intermediate +spots and afterwards becoming extinct there{378}; and considering our +knowledge of the great changes which _have_ taken place from subsidence +and elevation in the surface of the earth, and of our ignorance of the +greater changes which _may have_ taken place, we ought to be very slow +in admitting the probability of double creations. In the case of plants +on mountain-summits, I think I have shown how almost necessarily they +would, under the past conditions of the northern hemisphere, be as +similar as are the plants on the present Arctic shores; and this ought +to teach us a lesson of caution. + + {375} On centres of creation see _Origin_, Ed. i. p. 352, vi. p. + 499. + + {376} In the _Journal of Researches_, Ed. 1860, p. 124, the + distribution of the Bizcacha is described as limited by the river + Uruguay. The case is not I think given in the _Origin_. + + {377} In the _Origin_, Ed. i. a special section (p. 356, vi. p. + 504) is devoted to _Means of Dispersal_. The much greater + prominence given to this subject in the _Origin_ is partly + accounted for by the author's experiments being of later date, + _i.e._ 1855 (_Life and Letters_, vol. II. p. 53). The carriage of + fish by whirlwinds is given in the _Origin_, Ed. i. p. 384, vi. p. + 536. + + {378} The case of islands serving as halting places is given in the + _Origin_, Ed. i. p. 357, vi. p. 505. But here the evidence of this + having occurred is supposed to be lost by the subsidence of the + islands, not merely by the extinction of the species. + +But the strongest argument against double creations may be drawn from +considering the case of mammifers{379} in which, from their nature and +from the size of their offspring, the means of distribution are more in +view. There are no cases where the same species is found in _very +remote_ localities, except where there is a continuous belt of land: +the Arctic region perhaps offers the strongest exception, and here we +know that animals are transported on icebergs{380}. The cases of lesser +difficulty may all receive a more or less simple explanation; I will +give only one instance; the nutria{381}, I believe, on the eastern coast +of S. America live exclusively in fresh-water rivers, and I was much +surprised how they could have got into rivulets, widely apart, on the +coast of Patagonia; but on the opposite coast I found these quadrupeds +living exclusively in the sea, and hence their migration along the +Patagonian coast is not surprising. There is no case of the same +mammifer being found on an island far from the coast, and on the +mainland, as happens with plants{382}. On the idea of double creations +it would be strange if the same species of several plants should have +been created in Australia and Europe; and no one instance of the same +species of mammifer having been created, or aboriginally existing, in +two as nearly remote and equally isolated points. It is more +philosophical, in such cases, as that of some plants being found in +Australia and Europe, to admit that we are ignorant of the means of +transport. I will allude only to one other case, namely, that of the +Mydas{383}, an Alpine animal, found only on the distant peaks of the +mountains of Java: who will pretend to deny that during the ice period +of the northern and southern hemispheres, and when India is believed to +have been colder, the climate might not have permitted this animal to +haunt a lower country, and thus to have passed along the ridges from +summit to summit? Mr Lyell has further observed that, _as in space, so +in time_, there is no reason to believe that after the extinction of a +species, the self-same form has ever reappeared{384}. I think, then, we +may, notwithstanding the many cases of difficulty, conclude with some +confidence that every species has been created or produced on a single +point or area. + + {379} "We find no inexplicable cases of the same mammal inhabiting + distant points of the world." _Origin_, Ed. i. p. 352, vi. p. 500. + See also _Origin_, Ed. i. p. 393, vi. p. 547. + + {380} <Note by the author.> Many authors. <See _Origin_, Ed. i. p. + 394, vi. p. 547.> + + {381} _Nutria_ is the Spanish for otter, and is now a synonym for + _Lutra_. The otter on the Atlantic coast is distinguished by minute + differences from the Pacific species. Both forms are said to take + to the sea. In fact the case presents no especial difficulties. + + {382} In _Origin_, Ed. i. p. 394, vi. p. 548, bats are mentioned as + an explicable exception to this statement. + + {383} This reference is doubtless to _Mydaus_, a badger-like animal + from the mountains of Java and Sumatra (Wallace, _Geographical + Distribution_, ii. p. 199). The instance does not occur in the + _Origin_ but the author remarks (_Origin_, Ed. i. p. 376, vi. p. + 527) that cases, strictly analogous to the distribution of plants, + occur among terrestrial mammals. + + {384} See _Origin_, Ed. i. p. 313, vi. p. 454. + + +_On the number of species, and of the classes to which they belong in +different regions._ + +The last fact in geographical distribution, which, as far as I can see, +in any way concerns the origin of species, relates to the absolute +number and nature of the organic beings inhabiting different tracts of +land. Although every species is admirably adapted (but not necessarily +better adapted than every other species, as we have seen in the great +increase of introduced species) to the country and station it frequents; +yet it has been shown that the entire difference between the species in +distant countries cannot possibly be explained by the difference of the +physical conditions of these countries. In the same manner, I believe, +neither the number of the species, nor the nature of the great classes +to which they belong, can possibly in all cases be explained by the +conditions of their country. New Zealand{385}, a linear island +stretching over about 700 miles of latitude, with forests, marshes, +plains and mountains reaching to the limits of eternal snow, has far +more diversified habitats than an equal area at the Cape of Good Hope; +and yet, I believe, at the Cape of Good Hope there are, of phanerogamic +plants, from five to ten times the number of species as in all New +Zealand. Why on the theory of absolute creations should this large and +diversified island only have from 400 to 500 (? Dieffenbach) +phanerogamic plants? and why should the Cape of Good Hope, characterised +by the uniformity of its scenery, swarm with more species of plants than +probably any other quarter of the world? Why on the ordinary theory +should the Galapagos Islands abound with terrestrial reptiles? and why +should many equal-sized islands in the Pacific be without a single +one{386} or with only one or two species? Why should the great island of +New Zealand be without one mammiferous quadruped except the mouse, and +that was probably introduced with the aborigines? Why should not one +island (it can be shown, I think, that the mammifers of Mauritius and St +Iago have all been introduced) in the open ocean possess a mammiferous +quadruped? Let it not be said that quadrupeds cannot live in islands, +for we know that cattle, horses and pigs during a long period have run +wild in the West Indian and Falkland Islands; pigs at St Helena; goats +at Tahiti; asses in the Canary Islands; dogs in Cuba; cats at Ascension; +rabbits at Madeira and the Falklands; monkeys at St Iago and the +Mauritius; even elephants during a long time in one of the very small +Sooloo Islands; and European mice on very many of the smallest islands +far from the habitations of man{387}. Nor let it be assumed that +quadrupeds are more slowly created and hence that the oceanic islands, +which generally are of volcanic formation, are of too recent origin to +possess them; for we know (Lyell) that new forms of quadrupeds succeed +each other quicker than Mollusca or Reptilia. Nor let it be assumed +(though such an assumption would be no explanation) that quadrupeds +cannot be created on small islands; for islands not lying in mid-ocean +do possess their peculiar quadrupeds; thus many of the smaller islands +of the East Indian Archipelago possess quadrupeds; as does Fernando Po +on the West Coast of Africa; as the Falkland Islands possess a peculiar +wolf-like fox{388}; so do the Galapagos Islands a peculiar mouse of the +S. American type. These two last are the most remarkable cases with +which I am acquainted; inasmuch as the islands lie further from other +land. It is possible that the Galapagos mouse may have been introduced +in some ship from the S. American coast (though the species is at +present unknown there), for the aboriginal species soon haunts the goods +of man, as I noticed in the roof of a newly erected shed in a desert +country south of the Plata. The Falkland Islands, though between 200 and +300 miles from the S. American coast, may in one sense be considered as +intimately connected with it; for it is certain that formerly many +icebergs loaded with boulders were stranded on its southern coast, and +the old canoes which are occasionally now stranded, show that the +currents still set from Tierra del Fuego. This fact, however, does not +explain the presence of the _Canis antarcticus_ on the Falkland Islands, +unless we suppose that it formerly lived on the mainland and became +extinct there, whilst it survived on these islands, to which it was +borne (as happens with its northern congener, the common wolf) on an +iceberg, but this fact removes the anomaly of an island, in appearance +effectually separated from other land, having its own species of +quadruped, and makes the case like that of Java and Sumatra, each having +their own rhinoceros. + + {385} The comparison between New Zealand and the Cape is given in + the _Origin_, Ed. i. p. 389, vi. p. 542. + + {386} In a corresponding discussion in the _Origin_, Ed. i. p. 393, + vi. p. 546, stress is laid on the distribution of Batrachians not + of reptiles. + + {387} The whole argument is given--more briefly than here--in the + _Origin_, Ed. i. p. 394, vi. p. 547. + + {388} See _Origin_, Ed i. p. 393, vi. p. 547. The discussion is + much fuller in the present Essay. + +Before summing up all the facts given in this section on the present +condition of organic beings, and endeavouring to see how far they admit +of explanation, it will be convenient to state all such facts in the +past geographical distribution of extinct beings as seem anyway to +concern the theory of descent. + + +SECTION SECOND. + + +_Geographical distribution of extinct organisms._ + +I have stated that if the land of the entire world be divided into (we +will say) three sections, according to the amount of difference of the +terrestrial mammifers inhabiting them, we shall have three unequal +divisions of (1st) Australia and its dependent islands, (2nd) South +America, (3rd) Europe, Asia and Africa. If we now look to the mammifers +which inhabited these three divisions during the later Tertiary periods, +we shall find them almost as distinct as at the present day, and +intimately related in each division to the existing forms in that +division{389}. This is wonderfully the case with the several fossil +Marsupial genera in the caverns of New South Wales and even more +wonderfully so in South America, where we have the same peculiar group +of monkeys, of a guanaco-like animal, of many rodents, of the Marsupial +Didelphys, of Armadilloes and other Edentata. This last family is at +present very characteristic of S. America, and in a late Tertiary epoch +it was even more so, as is shown by the numerous enormous animals of the +Megatheroid family, some of which were protected by an osseous armour +like that, but on a gigantic scale, of the recent Armadillo. Lastly, +over Europe the remains of the several deer, oxen, bears, foxes, +beavers, field-mice, show a relation to the present inhabitants of this +region; and the contemporaneous remains of the elephant, rhinoceros, +hippopotamus, hyæna, show a relation with the grand Africo-Asiatic +division of the world. In Asia the fossil mammifers of the Himalaya +(though mingled with forms long extinct in Europe) are equally related +to the existing forms of the Africo-Asiatic division; but especially to +those of India itself. As the gigantic and now extinct quadrupeds of +Europe have naturally excited more attention than the other and smaller +remains, the relation between the past and the present mammiferous +inhabitants of Europe has not been sufficiently attended to. But in fact +the mammifers of Europe are at present nearly as much Africo-Asiatic as +they were formerly when Europe had its elephants and rhinoceroses, etc.; +Europe neither now nor then possessed peculiar groups as does Australia +and S. America. The extinction of certain peculiar forms in one quarter +does not make the remaining mammifers of that quarter less related to +its own great division of the world: though Tierra del Fuego possesses +only a fox, three rodents, and the guanaco, no one (as these all belong +to S. American types, but not to the most characteristic forms) would +doubt for one minute <as to> classifying this district with S. America; +and if fossil Edentata, Marsupials and monkeys were to be found in +Tierra del Fuego, it would not make this district more truly S. American +than it now is. So it is with Europe{390}, and so far as is known with +Asia, for the lately past and present mammifers all belong to the +Africo-Asiatic division of the world. In every case, I may add, the +forms which a country has is of more importance in geographical +arrangement than what it has not. + + {389} See _Origin_, Ed. i. p. 339, vi. p. 485. + + {390} In the _Origin_, Ed. i. p. 339, vi. p. 485, which corresponds + to this part of the present Essay, the author does not make a + separate section for such cases as the occurrence of fossil + Marsupials in Europe (_Origin_, Ed. i. p. 340, vi. p. 486) as he + does in the present Essay; see the section on _Changes in + geographical distribution_, p. 177. + +We find some evidence of the same general fact in a relation between the +recent and the Tertiary sea-shells, in the different main divisions of +the marine world. + +This general and most remarkable relation between the lately past and +present mammiferous inhabitants of the three main divisions of the world +is precisely the same kind of fact as the relation between the different +species of the several sub-regions of any one of the main divisions. As +we usually associate great physical changes with the total extinction of +one series of beings, and its succession by another series, this +identity of relation between the past and the present races of beings in +the same quarters of the globe is more striking than the same relation +between existing beings in different sub-regions: but in truth we have +no reason for supposing that a change in the conditions has in any of +these cases supervened, greater than that now existing between the +temperate and tropical, or between the highlands and lowlands of the +same main divisions, now tenanted by related beings. Finally, then, we +clearly see that in each main division of the world the same relation +holds good between its inhabitants in time as over space{391}. + + {391} "We can understand how it is that all the forms of life, + ancient and recent, make together one grand system; for all are + connected by generation." _Origin_, Ed. i. p. 344, vi. p. 491. + + +_Changes in geographical distribution._ + +If, however, we look closer, we shall find that even Australia, in +possessing a terrestrial Pachyderm, was so far less distinct from the +rest of the world than it now is; so was S. America in possessing the +Mastodon, horse, [hyæna,]{392} and antelope. N. America, as I have +remarked, is now, in its mammifers, in some respects neutral ground +between S. America and the great Africo-Asiatic division; formerly, in +possessing the horse, Mastodon and three Megatheroid animals, it was +more nearly related to S. America; but in the horse and Mastodon, and +likewise in having the elephant, oxen, sheep, and pigs, it was as much, +if not more, related to the Africo-Asiatic division. Again, northern +India was much more closely related (in having the giraffe, +hippopotamus, and certain musk-deer) to southern Africa than it now is; +for southern and eastern Africa deserve, if we divide the world into +five parts, to make one division by itself. Turning to the dawn of the +Tertiary period, we must, from our ignorance of other portions of the +world, confine ourselves to Europe; and at that period, in the presence +of Marsupials{393} and Edentata, we behold an _entire_ blending of those +mammiferous forms which now eminently characterise Australia and S. +America{394}. + + {392} The word _hyæna_ is erased. There appear to be no fossil + Hyænidæ in S. America. + + {393} See note 1{390}, p. 175, also _Origin_, Ed. i. p. 340, vi. p. 486. + + {394} <Note by the author.> And see Eocene European mammals in + N. America. + +If we now look at the distribution of sea-shells, we find the same +changes in distribution. The Red Sea and the Mediterranean were more +nearly related in these shells than they now are. In different parts of +Europe, on the other hand, during the Miocene period, the sea-shells +seem to have been more different than at present. In{395} the Tertiary +period, according to Lyell, the shells of N. America and Europe were +less related than at present, and during the Cretaceous still less like; +whereas, during this same Cretaceous period, the shells of India and +Europe were more like than at present. But going further back to the +Carbonaceous period, in N. America and Europe, the productions were much +more like than they now are{396}. These facts harmonise with the +conclusions drawn from the present distribution of organic beings, for +we have seen, that from species being created in different points or +areas, the formation of a barrier would cause or make two distinct +geographical areas; and the destruction of a barrier would permit their +diffusion{397}. And as long-continued geological changes must both +destroy and make barriers, we might expect, the further we looked +backwards, the more changed should we find the present distribution. +This conclusion is worthy of attention; because, finding in widely +different parts of the same main division of the world, and in volcanic +islands near them, groups of distinct, but related, species;--and +finding that a singularly analogous relation holds good with respect to +the beings of past times, when none of the present species were living, +a person might be tempted to believe in some mystical relation between +certain areas of the world, and the production of certain organic forms; +but we now see that such an assumption would have to be complicated by +the admission that such a relation, though holding good for long +revolutions of years, is not truly persistent. + + {395} <Note by the author.> All this requires much verification. + + {396} This point seems to be less insisted on in the _Origin_. + + {397} _Origin_, Ed. i. p. 356, vi. p. 504. + +I will only add one more observation to this section. Geologists +finding in the most remote period with which we are acquainted, namely +in the Silurian period, that the shells and other marine +productions{398} in North and South America, in Europe, Southern Africa, +and Western Asia, are much more similar than they now are at these +distant points, appear to have imagined that in these ancient times the +laws of geographical distribution were quite different than what they +now are: but we have only to suppose that great continents were extended +east and west, and thus did not divide the inhabitants of the temperate +and tropical seas, as the continents now do; and it would then become +probable that the inhabitants of the seas would be much more similar +than they now are. In the immense space of ocean extending from the east +coast of Africa to the eastern islands of the Pacific, which space is +connected either by lines of tropical coast or by islands not very +distant from each other, we know (Cuming) that many shells, perhaps even +as many as 200, are common to the Zanzibar coast, the Philippines, and +the eastern islands of the Low or Dangerous Archipelago in the Pacific. +This space equals that from the Arctic to the Antarctic pole! Pass over +the space of quite open ocean, from the Dangerous Archipelago to the +west coast of S. America, and every shell is different: pass over the +narrow space of S. America, to its eastern shores, and again every shell +is different! Many fish, I may add, are also common to the Pacific and +Indian Oceans. + + {398} <Note by the author.> D'Orbigny shows that this is not so. + + +_Summary on the distribution of living and extinct organic beings._ + +Let us sum up the several facts now given with respect to the past and +present geographical distribution of organic beings. In a previous +chapter it was shown that species are not exterminated by universal +catastrophes, and that they are slowly produced: we have also seen that +each species is probably only once produced, on one point or area once +in time; and that each diffuses itself, as far as barriers and its +conditions of life permit. If we look at any one main division of the +land, we find in the different parts, whether exposed to different +conditions or to the same conditions, many groups of species wholly or +nearly distinct as species, nevertheless intimately related. We find the +inhabitants of islands, though distinct as species, similarly related to +the inhabitants of the nearest continent; we find in some cases, that +even the different islands of one such group are inhabited by species +distinct, though intimately related to one another and to those of the +nearest continent:--thus typifying the distribution of organic beings +over the whole world. We find the floras of distant mountain-summits +either very similar (which seems to admit, as shown, of a simple +explanation) or very distinct but related to the floras of the +surrounding region; and hence, in this latter case, the floras of two +mountain-summits, although exposed to closely similar conditions, will +be very different. On the mountain-summits of islands, characterised by +peculiar faunas and floras, the plants are often eminently peculiar. The +dissimilarity of the organic beings inhabiting nearly similar countries +is best seen by comparing the main divisions of the world; in each of +which some districts may be found very similarly exposed, yet the +inhabitants are wholly unlike;--far more unlike than those in very +dissimilar districts in the same main division. We see this strikingly +in comparing two volcanic archipelagoes, with nearly the same climate, +but situated not very far from two different continents; in which case +their inhabitants are totally unlike. In the different main divisions of +the world, the amount of difference between the organisms, even in the +same class, is widely different, each main division having only the +species distinct in some families, in other families having the genera +distinct. The distribution of aquatic organisms is very different from +that of the terrestrial organisms; and necessarily so, from the barriers +to their progress being quite unlike. The nature of the conditions in an +isolated district will not explain the number of species inhabiting it; +nor the absence of one class or the presence of another class. We find +that terrestrial mammifers are not present on islands far removed from +other land. We see in two regions, that the species though distinct are +more or less related, according to the greater or less _possibility_ of +the transportal in past and present times of species from one to the +other region; although we can hardly admit that all the species in such +cases have been transported from the first to the second region, and +since have become extinct in the first: we see this law in the presence +of the fox on the Falkland Islands; in the European character of some of +the plants of Tierra del Fuego; in the Indo-Asiatic character of the +plants of the Pacific; and in the circumstance of those genera which +range widest having many species with wide ranges; and those genera with +restricted ranges having species with restricted ranges. Finally, we +find in each of the main divisions of the land, and probably of the sea, +that the existing organisms are related to those lately extinct. + +Looking further backwards we see that the past geographical distribution +of organic beings was different from the present; and indeed, +considering that geology shows that all our land was once under water, +and that where water now extends land is forming, the reverse could +hardly have been possible. + +Now these several facts, though evidently all more or less connected +together, must by the creationist (though the geologist may explain some +of the anomalies) be considered as so many ultimate facts. He can only +say, that it so pleased the Creator that the organic beings of the +plains, deserts, mountains, tropical and temperature forests, of S. +America, should all have some affinity together; that the inhabitants of +the Galapagos Archipelago should be related to those of Chile; and that +some of the species on the similarly constituted islands of this +archipelago, though most closely related, should be distinct; that all +its inhabitants should be totally unlike those of the similarly volcanic +and arid Cape de Verde and Canary Islands; that the plants on the summit +of Teneriffe should be eminently peculiar; that the diversified island +of New Zealand should have not many plants, and not one, or only one, +mammifer; that the mammifers of S. America, Australia and Europe should +be clearly related to their ancient and exterminated prototypes; and so +on with other facts. But it is absolutely opposed to every analogy, +drawn from the laws imposed by the Creator on inorganic matter, that +facts, when connected, should be considered as ultimate and not the +direct consequences of more general laws. + + +SECTION THIRD. + + +_An attempt to explain the foregoing laws of geographical distribution, +on the theory of allied species having a common descent._ + +First let us recall the circumstances most favourable for variation +under domestication, as given in the first chapter--viz. 1st, a change, +or repeated changes, in the conditions to which the organism has been +exposed, continued through several seminal (_i.e._ not by buds or +divisions) generations: 2nd, steady selection of the slight varieties +thus generated with a fixed end in view: 3rd, isolation as perfect as +possible of such selected varieties; that is, the preventing their +crossing with other forms; this latter condition applies to all +terrestrial animals, to most if not all plants and perhaps even to most +(or all) aquatic organisms. It will be convenient here to show the +advantage of isolation in the formation of a new breed, by comparing the +progress of two persons (to neither of whom let time be of any +consequence) endeavouring to select and form some very peculiar new +breed. Let one of these persons work on the vast herds of cattle in the +plains of La Plata{399}, and the other on a small stock of 20 or 30 +animals in an island. The latter might have to wait centuries (by the +hypothesis of no importance){400} before he obtained a "sport" +approaching to what he wanted; but when he did and saved the greater +number of its offspring and their offspring again, he might hope that +his whole little stock would be in some degree affected, so that by +continued selection he might gain his end. But on the Pampas, though +the man might get his first approach to his desired form sooner, how +hopeless would it be to attempt, by saving its offspring amongst so many +of the common kind, to affect the whole herd: the effect of this one +peculiar "sport{401}" would be quite lost before he could obtain a +second original sport of the same kind. If, however, he could separate a +small number of cattle, including the offspring of the desirable +"sport," he might hope, like the man on the island, to effect his end. +If there be organic beings of which two individuals _never_ unite, then +simple selection whether on a continent or island would be equally +serviceable to make a new and desirable breed; and this new breed might +be made in surprisingly few years from the great and geometrical powers +of propagation to beat out the old breed; as has happened +(notwithstanding crossing) where good breeds of dogs and pigs have been +introduced into a limited country,--for instance, into the islands of +the Pacific. + + {399} This instance occurs in the Essay of 1842, p. 32, but not in + the _Origin_; though the importance of isolation is discussed + (_Origin_, Ed. i. p. 104, vi. p. 127). + + {400} The meaning of the words within parenthesis is obscure. + + {401} It is unusual to find the author speaking of the selection of + _sports_ rather than small variations. + +Let us now take the simplest natural case of an islet upheaved by the +volcanic or subterranean forces in a deep sea, at such a distance from +other land that only a few organic beings at rare intervals were +transported to it, whether borne by the sea{402} (like the seeds of +plants to coral-reefs), or by hurricanes, or by floods, or on rafts, or +in roots of large trees, or the germs of one plant or animal attached to +or in the stomach of some other animal, or by the intervention (in most +cases the most probable means) of other islands since sunk or destroyed. +It may be remarked that when one part of the earth's crust is raised it +is probably the general rule that another part sinks. Let this island +go on slowly, century after century, rising foot by foot; and in the +course of time we shall have instead <of> a small mass of rock{403}, +lowland and highland, moist woods and dry sandy spots, various soils, +marshes, streams and pools: under water on the sea shore, instead of a +rocky steeply shelving coast, we shall have in some parts bays with mud, +sandy beaches and rocky shoals. The formation of the island by itself +must often slightly affect the surrounding climate. It is impossible +that the first few transported organisms could be perfectly adapted to +all these stations; and it will be a chance if those successively +transported will be so adapted. The greater number would probably come +from the lowlands of the nearest country; and not even all these would +be perfectly adapted to the new islet whilst it continued low and +exposed to coast influences. Moreover, as it is certain that all +organisms are nearly as much adapted in their structure to the other +inhabitants of their country as they are to its physical conditions, so +the mere fact that a _few_ beings (and these taken in great degree by +chance) were in the first case transported to the islet, would in itself +greatly modify their conditions{404}. As the island continued rising we +might also expect an occasional new visitant; and I repeat that even one +new being must often affect beyond our calculation by occupying the room +and taking part of the subsistence of another (and this again from +another and so on), several or many other organisms. Now as the first +transported and any occasional successive visitants spread or tended to +spread over the growing island, they would undoubtedly be exposed +through several generations to new and varying conditions: it might also +easily happen that some of the species _on an average_ might obtain an +increase of food, or food of a more nourishing quality{405}. According +then to every analogy with what we have seen takes place in every +country, with nearly every organic being under domestication, we might +expect that some of the inhabitants of the island would "sport," or have +their organization rendered in some degree plastic. As the number of the +inhabitants are supposed to be few and as all these cannot be so well +adapted to their new and varying conditions as they were in their native +country and habitat, we cannot believe that every place or office in the +economy of the island would be as well filled as on a continent where +the number of aboriginal species is far greater and where they +consequently hold a more strictly limited place. We might therefore +expect on our island that although very many slight variations were of +no use to the plastic individuals, yet that occasionally in the course +of a century an individual might be born{406} of which the structure or +constitution in some slight degree would allow it better to fill up some +office in the insular economy and to struggle against other species. If +such were the case the individual and its offspring would have a better +_chance_ of surviving and of beating out its parent form; and if (as is +probable) it and its offspring crossed with the unvaried parent form, +yet the number of the individuals being not very great, there would be a +chance of the new and more serviceable form being nevertheless in some +slight degree preserved. The struggle for existence would go on annually +selecting such individuals until a new race or species was formed. +Either few or all the first visitants to the island might become +modified, according as the physical conditions of the island and those +resulting from the kind and number of other transported species were +different from those of the parent country--according to the +difficulties offered to fresh immigration--and according to the length +of time since the first inhabitants were introduced. It is obvious that +whatever was the country, generally the nearest from which the first +tenants were transported, they would show an affinity, even if all had +become modified, to the natives of that country and even if the +inhabitants of the same source (?) had been modified. On this view we +can at once understand the cause and meaning of the affinity of the +fauna and flora of the Galapagos Islands with that of the coast of S. +America; and consequently why the inhabitants of these islands show not +the smallest affinity with those inhabiting other volcanic islands, with +a very similar climate and soil, near the coast of Africa{407}. + + {402} This brief discussion is represented in the _Origin_, Ed. i. + by a much fuller one (pp. 356, 383, vi. pp. 504, 535). See, + however, the section in the present Essay, p. 168. + + {403} On the formation of new stations, see _Origin_, Ed. i. p. + 292, vi. p. 429. + + {404} _Origin_, Ed. i. pp. 390, 400, vi. pp. 543, 554. + + {405} In the MS. _some of the species ... nourishing quality_ is + doubtfully erased. It seems clear that he doubted whether such a + problematical supply of food would be likely to cause variation. + + {406} At this time the author clearly put more faith in the + importance of sport-like variation than in later years. + + {407} _Origin_, Ed. i. p. 398, vi. p. 553. + +To return once again to our island, if by the continued action of the +subterranean forces other neighbouring islands were formed, these would +generally be stocked by the inhabitants of the first island, or by a few +immigrants from the neighbouring mainland; but if considerable obstacles +were interposed to any communication between the terrestrial productions +of these islands, and their conditions were different (perhaps only by +the number of different species on each island), a form transported from +one island to another might become altered in the same manner as one +from the continent; and we should have several of the islands tenanted +by representative races or species, as is so wonderfully the case with +the different islands of the Galapagos Archipelago. As the islands +become mountainous, if mountain-species were not introduced, as could +rarely happen, a greater amount of variation and selection would be +requisite to adapt the species, which originally came from the lowlands +of the nearest continent, to the mountain-summits than to the lower +districts of our islands. For the lowland species from the continent +would have first to struggle against other species and other conditions +on the coast-land of the island, and so probably become modified by the +selection of its best fitted varieties, then to undergo the same process +when the land had attained a moderate elevation; and then lastly when it +had become Alpine. Hence we can understand why the faunas of insular +mountain-summits are, as in the case of Teneriffe, eminently peculiar. +Putting on one side the case of a widely extended flora being driven up +the mountain-summits, during a change of climate from cold to temperate, +we can see why in other cases the floras of mountain-summits (or as I +have called them islands in a sea of land) should be tenanted by +peculiar species, but related to those of the surrounding lowlands, as +are the inhabitants of a real island in the sea to those of the nearest +continent{408}. + + {408} See _Origin_, Ed. i. p. 403, vi. p. 558, where the author + speaks of Alpine humming birds, rodents, plants, &c. in S. America, + all of strictly American forms. In the MS. the author has added + between the lines "As world has been getting hotter, there has been + radiation from high-lands,--old view?--curious; I presume Diluvian + in origin." + +Let us now consider the effect of a change of climate or of other +conditions on the inhabitants of a continent and of an isolated island +without any great change of level. On a continent the chief effects +would be changes in the numerical proportion of the individuals of the +different species; for whether the climate became warmer or colder, +drier or damper, more uniform or extreme, some species are at present +adapted to its diversified districts; if for instance it became cooler, +species would migrate from its more temperate parts and from its higher +land; if damper, from its damper regions, &c. On a small and isolated +island, however, with few species, and these not adapted to much +diversified conditions, such changes instead of merely increasing the +number of certain species already adapted to such conditions, and +decreasing the number of other species, would be apt to affect the +constitutions of some of the insular species: thus if the island became +damper it might well happen that there were no species living in any +part of it adapted to the consequences resulting from more moisture. In +this case therefore, and still more (as we have seen) during the +production of new stations from the elevation of the land, an island +would be a far more fertile source, as far as we can judge, of new +specific forms than a continent. The new forms thus generated on an +island, we might expect, would occasionally be transported by accident, +or through long-continued geographical changes be enabled to emigrate +and thus become slowly diffused. + +But if we look to the origin of a continent; almost every geologist will +admit that in most cases it will have first existed as separate islands +which gradually increased in size{409}; and therefore all that which has +been said concerning the probable changes of the forms tenanting a small +archipelago is applicable to a continent in its early state. +Furthermore, a geologist who reflects on the geological history of +Europe (the only region well known) will admit that it has been many +times depressed, raised and left stationary. During the sinking of a +continent and the probable generally accompanying changes of climate the +effect would be little, _except_ on the numerical proportions and in the +extinction (from the lessening of rivers, the drying of marshes and the +conversion of high-lands into low &c.) of some or of many of the +species. As soon however as the continent became divided into many +isolated portions or islands, preventing free immigration from one part +to another, the effect of climatic and other changes on the species +would be greater. But let the now broken continent, forming isolated +islands, begin to rise and new stations thus to be formed, exactly as in +the first case of the upheaved volcanic islet, and we shall have equally +favourable conditions for the modification of old forms, that is the +formation of new races or species. Let the islands become reunited into +a continent; and then the new and old forms would all spread, as far as +barriers, the means of transportal, and the preoccupation of the land by +other species, would permit. Some of the new species or races would +probably become extinct, and some perhaps would cross and blend +together. We should thus have a multitude of forms, adapted to all kinds +of slightly different stations, and to diverse groups of either +antagonist or food-serving species. The oftener these oscillations of +level had taken place (and therefore generally the older the land) the +greater the number of species <which> would tend to be formed. The +inhabitants of a continent being thus derived in the first stage from +the same original parents, and subsequently from the inhabitants of one +wide area, since often broken up and reunited, all would be obviously +related together and the inhabitants of the most _dissimilar_ stations +on the same continent would be more closely allied than the inhabitants +of two very _similar_ stations on two of the main divisions of the +world{410}. + + {409} See the comparison between the Malay Archipelago and the + probable former state of Europe, _Origin_, Ed. i. p. 299, vi. p. + 438, also _Origin_, Ed. i. p. 292, vi. p. 429. + + {410} _Origin_, Ed. i. p. 349, vi. p. 496. The arrangement of the + argument in the present Essay leads to repetition of statements + made in the earlier part of the book: in the _Origin_ this is + avoided. + +I need hardly point out that we now can obviously see why the number of +species in two districts, independently of the number of stations in +such districts, should be in some cases as widely different as in New +Zealand and the Cape of Good Hope{411}. We can see, knowing the +difficulty in the transport of terrestrial mammals, why islands far from +mainlands do not possess them{412}; we see the general reason, namely +accidental transport (though not the precise reason), why certain +islands should, and others should not, possess members of the class of +reptiles. We can see why an ancient channel of communication between two +distant points, as the Cordillera probably was between southern Chile +and the United States during the former cold periods; and icebergs +between the Falkland Islands and Tierra del Fuego; and gales, at a +former or present time, between the Asiatic shores of the Pacific and +eastern islands in this ocean; is connected with (or we may now say +causes) an affinity between the species, though distinct, in two such +districts. We can see how the better chance of diffusion, from several +of the species of any genus having wide ranges in their own countries, +explains the presence of other species of the same genus in other +countries{413}; and on the other hand, of species of restricted powers +of ranging, forming genera with restricted ranges. + + {411} _Origin_, Ed. i. p. 389, vi. p. 542. + + {412} _Origin_, Ed. i. p. 393, vi. p. 547. + + {413} _Origin_, Ed. i. pp. 350, 404, vi. pp. 498, 559. + +As every one would be surprised if two exactly similar but peculiar +varieties{414} of any species were raised by man by long continued +selection, in two different countries, or at two very different periods, +so we ought not to expect that an exactly similar form would be produced +from the modification of an old one in two distinct countries or at two +distinct periods. For in such places and times they would probably be +exposed to somewhat different climates and almost certainly to different +associates. Hence we can see why each species appears to have been +produced singly, in space and in time. I need hardly remark that, +according to this theory of descent, there is no necessity of +modification in a species, when it reaches a new and isolated country. +If it be able to survive and if slight variations better adapted to the +new conditions are not selected, it might retain (as far as we can see) +its old form for an indefinite time. As we see that some sub-varieties +produced under domestication are more variable than others, so in +nature, perhaps, some species and genera are more variable than others. +The same precise form, however, would probably be seldom preserved +through successive geological periods, or in widely and differently +conditioned countries{415}. + + {414} _Origin_, Ed. i. p. 352, vi. p. 500. + + {415} _Origin_, Ed. i. p. 313, vi. p. 454. + +Finally, during the long periods of time and probably of oscillations of +level, necessary for the formation of a continent, we may conclude (as +above explained) that many forms would become extinct. These extinct +forms, and those surviving (whether or not modified and changed in +structure), will all be related in each continent in the same manner and +degree, as are the inhabitants of any two different sub-regions in that +same continent. I do not mean to say that, for instance, the present +Marsupials of Australia or Edentata and rodents of S. America have +descended from any one of the few fossils of the same orders which have +been discovered in these countries. It is possible that, in a very few +instances, this may be the case; but generally they must be considered +as merely codescendants of common stocks{416}. I believe in this, from +the improbability, considering the vast number of species, which (as +explained in the last chapter) must by our theory have existed, that +the _comparatively_ few fossils which have been found should chance to +be the immediate and linear progenitors of those now existing. Recent as +the yet discovered fossil mammifers of S. America are, who will pretend +to say that very many intermediate forms may not have existed? Moreover, +we shall see in the ensuing chapter that the very existence of genera +and species can be explained only by a few species of each epoch leaving +modified successors or new species to a future period; and the more +distant that future period, the fewer will be the _linear_ heirs of the +former epoch. As by our theory, all mammifers must have descended from +the same parent stock, so is it necessary that each land now possessing +terrestrial mammifers shall at some time have been so far united to +other land as to permit the passage of mammifers{417}; and it accords +with this necessity, that in looking far back into the earth's history +we find, first changes in the geographical distribution, and secondly a +period when the mammiferous forms most distinctive of two of the present +main divisions of the world were living together{418}. + + {416} _Origin_, Ed. i. p. 341, vi. p. 487. + + {417} _Origin_, Ed. i. p. 396, vi. p. 549. + + {418} _Origin_, Ed. i. p. 340, vi. p. 486. + +I think then I am justified in asserting that most of the above +enumerated and often trivial points in the geographical distribution of +past and present organisms (which points must be viewed by the +creationists as so many ultimate facts) follow as a simple consequence +of specific forms being mutable and of their being adapted by natural +selection to diverse ends, conjoined with their powers of dispersal, and +the geologico-geographical changes now in slow progress and which +undoubtedly have taken place. This large class of facts being thus +explained, far more than counterbalances many separate difficulties and +apparent objections in convincing my mind of the truth of this theory of +common descent. + + +_Improbability of finding fossil forms intermediate between existing +species._ + +There is one observation of considerable importance that may be here +introduced, with regard to the improbability of the chief transitional +forms between any two species being found fossil. With respect to the +finer shades of transition, I have before remarked that no one has any +cause to expect to trace them in a fossil state, without he be bold +enough to imagine that geologists at a future epoch will be able to +trace from fossil bones the gradations between the Short-Horns, +Herefordshire, and Alderney breeds of cattle{419}. I have attempted to +show that rising islands, in process of formation, must be the best +nurseries of new specific forms, and these points are the least +favourable for the embedment of fossils{420}: I appeal, as evidence, to +the state of the _numerous_ scattered islands in the several great +oceans: how rarely do any sedimentary deposits occur on them; and when +present they are mere narrow fringes of no great antiquity, which the +sea is generally wearing away and destroying. The cause of this lies in +isolated islands being generally volcanic and rising points; and the +effects of subterranean elevation is to bring up the surrounding +newly-deposited strata within the destroying action of the coast-waves: +the strata, deposited at greater distances, and therefore in the depths +of the ocean, will be almost barren of organic remains. These remarks +may be generalised:--periods of subsidence will always be most +favourable to an accumulation of great thicknesses of strata, and +consequently to their long preservation; for without one formation be +protected by successive strata, it will seldom be preserved to a distant +age, owing to the enormous amount of denudation, which seems to be a +general contingent of time{421}. I may refer, as evidence of this +remark, to the vast amount of subsidence evident in the great pile of +the European formations, from the Silurian epoch to the end of the +Secondary, and perhaps to even a later period. Periods of elevation on +the other hand cannot be favourable to the accumulation of strata and +their preservation to distant ages, from the circumstance just alluded +to, viz. of elevation tending to bring to the surface the +circum-littoral strata (always abounding most in fossils) and destroying +them. The bottom of tracts of deep water (little favourable, however, to +life) must be excepted from this unfavourable influence of elevation. In +the quite open ocean, probably no sediment{422} is accumulating, or at a +rate so slow as not to preserve fossil remains, which will always be +subject to disintegration. Caverns, no doubt, will be equally likely to +preserve terrestrial fossils in periods of elevation and of subsidence; +but whether it be owing to the enormous amount of denudation, which all +land seems to have undergone, no cavern with fossil bones has been found +belonging to the Secondary period{423}. + + {419} _Origin_, Ed. i. p. 299, vi. p. 437. + + {420} "Nature may almost be said to have guarded against the + frequent discovery of her transitional or linking forms," _Origin_, + Ed. i. p. 292. A similar but not identical passage occurs in + _Origin_, Ed. vi. p. 428. + + {421} _Origin_, Ed. i. p. 291, vi. p. 426. + + {422} _Origin_, Ed. i. p. 288, vi. p. 422. + + {423} _Origin_, Ed. i. p. 289, vi. p. 423. + +Hence many more remains will be preserved to a distant age, in any +region of the world, during periods of its subsidence{424}, than of its +elevation. + + {424} _Origin_, Ed. i. p. 300, vi. p. 439. + +But during the subsidence of a tract of land, its inhabitants (as before +shown) will from the decrease of space and of the diversity of its +stations, and from the land being fully preoccupied by species fitted to +diversified means of subsistence, be little liable to modification from +selection, although many may, or rather must, become extinct. With +respect to its circum-marine inhabitants, although during a change from +a continent to a _great_ archipelago, the number of stations fitted for +marine beings will be increased, their means of diffusion (an important +check to change of form) will be greatly improved; for a continent +stretching north and south, or a quite open space of ocean, seems to be +to them the only barrier. On the other hand, during the elevation of a +small archipelago and its conversion into a continent, we have, whilst +the number of stations are increasing, both for aquatic and terrestrial +productions, and whilst these stations are not fully preoccupied by +perfectly adapted species, the most favourable conditions for the +selection of new specific forms; but few of them in their early +transitional states will be preserved to a distant epoch. We must wait +during an enormous lapse of time, until long-continued subsidence shall +have taken the place in this quarter of the world of the elevatory +process, for the best conditions of the embedment and the preservation +of its inhabitants. Generally the great mass of the strata in every +country, from having been chiefly accumulated during subsidence, will be +the tomb, not of transitional forms, but of those either becoming +extinct or remaining unmodified. + +The state of our knowledge, and the slowness of the changes of level, do +not permit us to test the truth of these remarks, by observing whether +there are more transitional or "fine" (as naturalists would term them) +species, on a rising and enlarging tract of land, than on an area of +subsidence. Nor do I know whether there are more "fine" species on +isolated volcanic islands in process of formation, than on a continent; +but I may remark, that at the Galapagos Archipelago the number of forms, +which according to some naturalists are true species, and according to +others are mere races, is considerable: this particularly applies to the +different species or races of the same genera inhabiting the different +islands of this archipelago. Furthermore it may be added (as bearing on +the great facts discussed in this chapter) that when naturalists confine +their attention to any one country, they have comparatively little +difficulty in determining what forms to call species and what to call +varieties; that is, those which can or cannot be traced or shown to be +probably descendants of some other form: but the difficulty increases, +as species are brought from many stations, countries and islands. It was +this increasing (but I believe in few cases insuperable) difficulty +which seems chiefly to have urged Lamarck to the conclusion that species +are mutable. + + + + +CHAPTER VII + +ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION OF ORGANIC +BEINGS{425} + + {425} Ch. XIII of the _Origin_, Ed. i., Ch. XIV Ed. vi. begins with + a similar statement. In the present Essay the author adds a + note:--"The obviousness of the fact (_i.e._ the natural grouping of + organisms) alone prevents it being remarkable. It is scarcely + explicable by creationist: groups of aquatic, of vegetable feeders + and carnivorous, &c., might resemble each other; but why as it is. + So with plants,--analogical resemblance thus accounted for. Must + not here enter into details." This argument is incorporated with + the text in the _Origin_, Ed. i. + + +_Gradual appearance and disappearance of groups._ + +It has been observed from the earliest times that organic beings fall +into groups{426}, and these groups into others of several values, such +as species into genera, and then into sub-families, into families, +orders, &c. The same fact holds with those beings which no longer exist. +Groups of species seem to follow the same laws in their appearance and +extinction{427}, as do the individuals of any one species: we have +reason to believe that, first, a few species appear, that their numbers +increase; and that, when tending to extinction, the numbers of the +species decrease, till finally the group becomes extinct, in the same +way as a species becomes extinct, by the individuals becoming rarer and +rarer. Moreover, groups, like the individuals of a species, appear to +become extinct at different times in different countries. The +Palæotherium was extinct much sooner in Europe than in India: the +Trigonia{428} was extinct in early ages in Europe, but now lives in the +seas of Australia. As it happens that one species of a family will +endure for a much longer period than another species, so we find that +some whole groups, such as Mollusca, tend to retain their forms, or to +remain persistent, for longer periods than other groups, for instance +than the Mammalia. Groups therefore, in their appearance, extinction, +and rate of change or succession, seem to follow nearly the same laws +with the individuals of a species{429}. + + {426} _Origin_, Ed. i. p. 411, vi. p. 566. + + {427} _Origin_, Ed. i. p. 316, vi. p. 457. + + {428} _Origin_, Ed. i. p. 321, vi. p. 463. + + {429} In the _Origin_, Ed. i. this preliminary matter is replaced + (pp. 411, 412, vi. pp. 566, 567) by a discussion in which + extinction is also treated, but chiefly from the point of view of + the theory of divergence. + + +_What is the Natural System?_ + +The proper arrangement of species into groups, according to the natural +system, is the object of all naturalists; but scarcely two naturalists +will give the same answer to the question, What is the natural system +and how are we to recognise it? The most important characters{430} it +might be thought (as it was by the earliest classifiers) ought to be +drawn from those parts of the structure which determine its habits and +place in the economy of nature, which we may call the final end of its +existence. But nothing is further from the truth than this; how much +external resemblance there is between the little otter (Chironectes) of +Guiana and the common otter; or again between the common swallow and the +swift; and who can doubt that the means and ends of their existence are +closely similar, yet how grossly wrong would be the classification, +which put close to each other a Marsupial and Placental animal, and two +birds with widely different skeletons. Relations, such as in the two +latter cases, or as that between the whale and fishes, are denominated +"analogical{431}," or are sometimes described as "relations of +adaption." They are infinitely numerous and often very singular; but are +of no use in the classification of the higher groups. How it comes, that +certain parts of the structure, by which the habits and functions of the +species are settled, are of no use in classification, whilst other +parts, formed at the same time, are of the greatest, it would be +difficult to say, on the theory of separate creations. + + {430} _Origin_, Ed. i. p. 414, vi. p. 570. + + {431} _Origin_, Ed. i. p. 414, vi. p. 570. + +Some authors as Lamarck, Whewell &c., believe that the degree of +affinity on the natural system depends on the degrees of resemblance in +organs more or less physiologically important for the preservation of +life. This scale of importance in the organs is admitted to be of +difficult discovery. But quite independent of this, the proposition, as +a general rule, must be rejected as false; though it may be partially +true. For it is universally admitted that the same part or organ, which +is of the highest service in classification in one group, is of very +little use in another group, though in both groups, as far as we can +see, the part or organ is of equal physiological importance: moreover, +characters quite unimportant physiologically, such as whether the +covering of the body consists of hair or feathers, whether the nostrils +communicated with the mouth{432} &c., &c., are of the highest generality +in classification; even colour, which is so inconstant in many species, +will sometimes well characterise even a whole group of species. Lastly, +the fact, that no one character is of so much importance in determining +to what great group an organism belongs, as the forms through which the +embryo{433} passes from the germ upwards to maturity, cannot be +reconciled with the idea that natural classification follows according +to the degrees of resemblance in the parts of most physiological +importance. The affinity of the common rock-barnacle with the +Crustaceans can hardly be perceived in more than a single character in +its mature state, but whilst young, locomotive, and furnished with eyes, +its affinity cannot be mistaken{434}. The cause of the greater value of +characters, drawn from the early stages of life, can, as we shall in a +succeeding chapter see, be in a considerable degree explained, on the +theory of descent, although inexplicable on the views of the +creationist. + + {432} These instances occur with others in the _Origin_, Ed. i. p. + 416, vi. p. 572. + + {433} _Origin_, Ed. i. p. 418, vi. p. 574. + + {434} _Origin_, Ed. i. pp. 419, 440, vi. pp. 575, 606. + +Practically, naturalists seem to classify according to the resemblance +of those parts or organs which in related groups are most uniform, or +vary least{435}: thus the æstivation, or manner in which the petals etc. +are folded over each other, is found to afford an unvarying character in +most families of plants, and accordingly any difference in this respect +would be sufficient to cause the rejection of a species from many +families; but in the Rubiaceæ the æstivation is a varying character, and +a botanist would not lay much stress on it, in deciding whether or not +to class a new species in this family. But this rule is obviously so +arbitrary a formula, that most naturalists seem to be convinced that +something ulterior is represented by the natural system; they appear to +think that we only discover by such similarities what the arrangement of +the system is, not that such similarities make the system. We can only +thus understand Linnæus'{436} well-known saying, that the characters do +not make the genus; but that the genus gives the characters: for a +classification, independent of characters, is here presupposed. Hence +many naturalists have said that the natural system reveals the plan of +the Creator: but without it be specified whether order in time or place, +or what else is meant by the plan of the Creator, such expressions +appear to me to leave the question exactly where it was. + + {435} _Origin_, Ed. i. pp. 418, 425, vi. pp. 574, 581. + + {436} _Origin_, Ed. i. p. 413, vi. p. 569. + +Some naturalists consider that the geographical position{437} of a +species may enter into the consideration of the group into which it +should be placed; and most naturalists (either tacitly or openly) give +value to the different groups, not solely by their relative differences +in structure, but by the number of forms included in them. Thus a genus +containing a few species might be, and has often been, raised into a +family on the discovery of several other species. Many natural families +are retained, although most closely related to other families, from +including a great number of closely similar species. The more logical +naturalist would perhaps, if he could, reject these two contingents in +classification. From these circumstances, and especially from the +undefined objects and criterions of the natural system, the number of +divisions, such as genera, sub-families, families, &c., &c., has been +quite arbitrary{438}; without the clearest definition, how can it be +possible to decide whether two groups of species are of equal value, and +of what value? whether they should both be called genera or families; or +whether one should be a genus, and the other a family{439}? + + {437} _Origin_, Ed. i. pp. 419, 427, vi. pp. 575, 582. + + {438} This is discussed from the point of view of divergence in the + _Origin_, Ed. i. pp. 420, 421, vi. pp. 576, 577. + + {439} <Footnote by the author.> I discuss this because if Quinarism + true, I false. <The Quinary System is set forth in W. S. Macleay's + _Horæ Entomologicæ_, 1821.> + + +_On the kind of relation between distinct groups._ + +I have only one other remark on the affinities of organic beings; that +is, when two quite distinct groups approach each other, the approach is +_generally_ generic{440} and not special; I can explain this most easily +by an example: of all Rodents the Bizcacha, by certain peculiarities in +its reproductive system, approaches nearest to the Marsupials; of all +Marsupials the Phascolomys, on the other hand, appears to approach in +the form of its teeth and intestines nearest to the Rodents; but there +is no special relation between these two genera{441}; the Bizcacha is no +nearer related to the Phascolomys than to any other Marsupial in the +points in which it approaches this division; nor again is the +Phascolomys, in the points of structure in which it approaches the +Rodents, any nearer related to the Bizcacha than to any other Rodent. +Other examples might have been chosen, but I have given (from +Waterhouse) this example as it illustrates another point, namely, the +difficulty of determining what are analogical or adaptive and what real +affinities; it seems that the teeth of the Phascolomys though _appearing +closely_ to resemble those of a Rodent are found to be built on the +Marsupial type; and it is thought that these teeth and consequently the +intestines may have been adapted to the peculiar life of this animal and +therefore may not show any real relation. The structure in the Bizcacha +that connects it with the Marsupials does not seem a peculiarity related +to its manner of life, and I imagine that no one would doubt that this +shows a real affinity, though not more with any one Marsupial species +than with another. The difficulty of determining what relations are real +and what analogical is far from surprising when no one pretends to +define the meaning of the term relation or the ulterior object of all +classification. We shall immediately see on the theory of descent how it +comes that there should be "real" and "analogical" affinities; and why +the former alone should be of value in classification--difficulties +which it would be I believe impossible to explain on the ordinary theory +of separate creations. + + {440} In the corresponding passage in the _Origin_, Ed. i. p. 430, + vi. p. 591, the term _general_ is used in place of _generic_, and + seems a better expression. In the margin the author gives + Waterhouse as his authority. + + {441} _Origin_, Ed. i. p. 430, vi. p. 591. + + +_Classification of Races or Varieties._ + +Let us now for a few moments turn to the classification of the generally +acknowledged varieties and subdivisions of our domestic beings{442}; we +shall find them systematically arranged in groups of higher and higher +value. De Candolle has treated the varieties of the cabbage exactly as +he would have done a natural family with various divisions and +subdivisions. In dogs again we have one main division which may be +called the _family_ of hounds; of these, there are several (we will call +them) _genera_, such as blood-hounds, fox-hounds, and harriers; and of +each of these we have different _species_, as the blood-hound of Cuba +and that of England; and of the latter again we have breeds truly +producing their own kind, which may be called races or varieties. Here +we see a classification practically used which typifies on a lesser +scale that which holds good in nature. But amongst true species in the +natural system and amongst domestic races the number of divisions or +groups, instituted between those most alike and those most unlike, seems +to be quite arbitrary. The number of the forms in both cases seems +practically, whether or not it ought theoretically, to influence the +denomination of groups including them. In both, geographical +distribution has sometimes been used as an aid to classification{443}; +amongst varieties, I may instance, the cattle of India or the sheep of +Siberia, which from possessing some characters in common permit a +classification of Indian and European cattle, or Siberian and European +sheep. Amongst domestic varieties we have even something very like the +relations of "analogy" or "adaptation{444}"; thus the common and Swedish +turnip are both artificial varieties which strikingly resemble each +other, and they fill nearly the same end in the economy of the +farm-yard; but although the swede so much more resembles a turnip than +its presumed parent the field cabbage, no one thinks of putting it out +of the cabbages into the turnips. Thus the greyhound and racehorse, +having been selected and trained for extreme fleetness for short +distances, present an analogical resemblance of the same kind, but less +striking as that between the little otter (Marsupial) of Guiana and the +common otter; though these two otters are really less related than <are> +the horse and dog. We are even cautioned by authors treating on +varieties, to follow the _natural_ in contradistinction of an artificial +system and not, for instance, to class two varieties of the +pine-apple{445} near each other, because their fruits accidentally +resemble each other closely (though the fruit may be called _the final +end_ of this plant in the economy of its world, the hothouse), but to +judge from the general resemblance of the entire plants. Lastly, +varieties often become extinct; sometimes from unexplained causes, +sometimes from accident, but more often from the production of more +useful varieties, and the less useful ones being destroyed or bred out. + + {442} In a corresponding passage in the _Origin_, Ed. i. p. 423, + vi. p. 579, the author makes use of his knowledge of pigeons. The + pseudo-genera among dogs are discussed in _Var. under Dom._, Ed. + ii. vol. I. p. 38. + + {443} _Origin_, Ed. i. pp. 419, 427, vi. pp. 575, 582. + + {444} _Origin_, Ed. i. pp. 423, 427, vi. pp. 579, 583. + + {445} _Origin_, Ed. i. p. 423, vi. p. 579. + +I think it cannot be doubted that the main cause of all the varieties +which have descended from the aboriginal dog or dogs, or from the +aboriginal wild cabbage, not being equally like or unlike--but on the +contrary, obviously falling into groups and sub-groups--must in chief +part be attributed to different degrees of true relationship; for +instance, that the different kinds of blood-hound have descended from +one stock, whilst the harriers have descended from another stock, and +that both these have descended from a different stock from that which +has been the parent of the several kinds of greyhound. We often hear of +a florist having some choice variety and breeding from it a whole group +of sub-varieties more or less characterised by the peculiarities of the +parent. The case of the peach and nectarine, each with their many +varieties, might have been introduced. No doubt the relationship of our +different domestic breeds has been obscured in an extreme degree by +their crossing; and likewise from the slight difference between many +breeds it has probably often happened that a "sport" from one breed has +less closely resembled its parent breed than some other breed, and has +therefore been classed with the latter. Moreover the effects of a +similar climate{446} may in some cases have more than counterbalanced +the similarity, consequent on a common descent, though I should think +the similarity of the breeds of cattle of India or sheep of Siberia was +far more probably due to the community of their descent than to the +effects of climate on animals descended from different stocks. + + {446} A general statement of the influence of conditions on + variation occurs in the _Origin_, Ed. i. pp. 131-3, vi. pp. 164-5. + +Notwithstanding these great sources of difficulty, I apprehend every +one would admit, that if it were possible, a genealogical classification +of our domestic varieties would be the most satisfactory one; and as far +as varieties were concerned would be the natural system: in some cases +it has been followed. In attempting to follow out this object a person +would have to class a variety, whose parentage he did not know, by its +external characters; but he would have a distinct ulterior object in +view, namely, its descent in the same manner as a regular systematist +seems also to have an ulterior but undefined end in all his +classifications. Like the regular systematist he would not care whether +his characters were drawn from more or less important organs as long as +he found in the tribe which he was examining that the characters from +such parts were persistent; thus amongst cattle he does value a +character drawn from the form of the horns more than from the +proportions of the limbs and whole body, for he finds that the shape of +the horns is to a considerable degree persistent amongst cattle{447}, +whilst the bones of the limbs and body vary. No doubt as a frequent rule +the more important the organ, as being less related to external +influences, the less liable it is to variation; but he would expect that +according to the object for which the races had been selected, parts +more or less important might differ; so that characters drawn from parts +generally most liable to vary, as colour, might in some instances be +highly serviceable--as is the case. He would admit that general +resemblances scarcely definable by language might sometimes serve to +allocate a species by its nearest relation. He would be able to assign a +clear reason why the close similarity of the fruit in two varieties of +pine-apple, and of the so-called root in the common and Swedish turnips, +and why the similar gracefulness of form in the greyhound and +racehorse, are characters of little value in classification; namely, +because they are the result, not of community of descent, but either of +selection for a common end, or of the effects of similar external +conditions. + + {447} _Origin_, Ed. i. p. 423, vi. p. 579. In the margin Marshall + is given as the authority. + + +_Classification of "races" and species similar._ + +Thus seeing that both the classifiers of species and of varieties{448} +work by the same means, make similar distinctions in the value of the +characters, and meet with similar difficulties, and that both seem to +have in their classification an ulterior object in view; I cannot avoid +strongly suspecting that the same cause, which has made amongst our +domestic varieties groups and sub-groups, has made similar groups (but +of higher values) amongst species; and that this cause is the greater or +less propinquity of actual descent. The simple fact of species, both +those long since extinct and those now living, being divisible into +genera, families, orders &c.--divisions analogous to those into which +varieties are divisible--is otherwise an inexplicable fact, and only not +remarkable from its familiarity. + + {448} _Origin_, Ed. i. p. 423, vi. p. 579. + + +_Origin of genera and families._ + +Let us suppose{449} for example that a species spreads and arrives at +six or more different regions, or being already diffused over one wide +area, let this area be divided into six distinct regions, exposed to +different conditions, and with stations slightly different, not fully +occupied with other species, so that six different races or species +were formed by selection, each best fitted to its new habits and +station. I must remark that in every case, if a species becomes modified +in any one sub-region, it is probable that it will become modified in +some other of the sub-regions over which it is diffused, for its +organization is shown to be capable of being rendered plastic; its +diffusion proves that it is able to struggle with the other inhabitants +of the several sub-regions; and as the organic beings of every great +region are in some degree allied, and as even the physical conditions +are often in some respects alike, we might expect that a modification in +structure, which gave our species some advantage over antagonist species +in one sub-region, would be followed by other modifications in other of +the sub-regions. The races or new species supposed to be formed would be +closely related to each other; and would either form a new genus or +sub-genus, or would rank (probably forming a slightly different section) +in the genus to which the parent species belonged. In the course of +ages, and during the contingent physical changes, it is probable that +some of the six new species would be destroyed; but the same advantage, +whatever it may have been (whether mere tendency to vary, or some +peculiarity of organization, power of mind, or means of distribution), +which in the parent-species and in its six selected and changed +species-offspring, caused them to prevail over other antagonist species, +would generally tend to preserve some or many of them for a long period. +If then, two or three of the six species were preserved, they in their +turn would, during continued changes, give rise to as many small groups +of species: if the parents of these small groups were closely similar, +the new species would form one great genus, barely perhaps divisible +into two or three sections: but if the parents were considerably +unlike, their species-offspring would, from inheriting most of the +peculiarities of their parent-stocks, form either two or more sub-genera +or (if the course of selection tended in different ways) genera. And +lastly species descending from different species of the newly formed +genera would form new genera, and such genera collectively would form a +family. + + {449} The discussion here following corresponds more or less to the + _Origin_, Ed. i. pp. 411, 412, vi. pp. 566, 567; although the + doctrine of divergence is not mentioned in this Essay (as it is in + the _Origin_) yet the present section seems to me a distinct + approximation to it. + +The extermination of species follows from changes in the external +conditions, and from the increase or immigration of more favoured +species: and as those species which are undergoing modification in any +one great region (or indeed over the world) will very often be allied +ones from (as just explained) partaking of many characters, and +therefore advantages in common, so the species, whose place the new or +more favoured ones are seizing, from partaking of a common inferiority +(whether in any particular point of structure, or of general powers of +mind, of means of distribution, of capacity for variation, &c., &c.), +will be apt to be allied. Consequently species of the same genus will +slowly, one after the other, _tend_ to become rarer and rarer in +numbers, and finally extinct; and as each last species of several allied +genera fails, even the family will become extinct. There may of course +be occasional exceptions to the entire destruction of any genus or +family. From what has gone before, we have seen that the slow and +successive formation of several new species from the same stock will +make a new genus, and the slow and successive formation of several other +new species from another stock will make another genus; and if these two +stocks were allied, such genera will make a new family. Now, as far as +our knowledge serves, it is in this slow and gradual manner that groups +of species appear on, and disappear from, the face of the earth. + +The manner in which, according to our theory, the arrangement of species +in groups is due to partial extinction, will perhaps be rendered clearer +in the following way. Let us suppose in any one great class, for +instance in the Mammalia, that every species and every variety, during +each successive age, had sent down one unaltered descendant (either +fossil or living) to the present time; we should then have had one +enormous series, including by small gradations every known mammiferous +form; and consequently the existence of groups{450}, or chasms in the +series, which in some parts are in greater width, and in some of less, +is solely due to former species, and whole groups of species, not having +thus sent down descendants to the present time. + + {450} The author probably intended to write "groups separated by + chasms." + +With respect to the "analogical" or "adaptive" resemblances between +organic beings which are not really related{451}, I will only add, that +probably the isolation of different groups of species is an important +element in the production of such characters: thus we can easily see, in +a large increasing island, or even a continent like Australia, stocked +with only certain orders of the main classes, that the conditions would +be highly favourable for species from these orders to become adapted to +play parts in the economy of nature, which in other countries were +performed by tribes especially adapted to such parts. We can understand +how it might happen that an otter-like animal might have been formed in +Australia by slow selection from the more carnivorous Marsupial types; +thus we can understand that curious case in the southern hemisphere, +where there are no auks (but many petrels), of a petrel{452} having been +modified into the external general form so as to play the same office +in nature with the auks of the northern hemisphere; although the habits +and form of the petrels and auks are normally so wholly different. It +follows, from our theory, that two orders must have descended from one +common stock at an immensely remote epoch; and we can perceive when a +species in either order, or in both, shows some affinity to the other +order, why the affinity is usually generic and not particular--that is +why the Bizcacha amongst Rodents, in the points in which it is related +to the Marsupial, is related to the whole group{453}, and not +particularly to the Phascolomys, which of all Marsupialia is related +most to the Rodents. For the Bizcacha is related to the present +Marsupialia, only from being related to their common parent-stock; and +not to any one species in particular. And generally, it may be observed +in the writings of most naturalists, that when an organism is described +as intermediate between two _great_ groups, its relations are not to +particular species of either group, but to both groups, as wholes. A +little reflection will show how exceptions (as that of the Lepidosiren, +a fish closely related to _particular_ reptiles) might occur, namely +from a few descendants of those species, which at a very early period +branched out from a common parent-stock and so formed the two orders or +groups, having survived, in nearly their original state, to the present +time. + + {451} A similar discussion occurs in the _Origin_, Ed. i. p. 427, + vi. p. 582. + + {452} _Puffinuria berardi_, see _Origin_, Ed. i. p. 184, vi. p. + 221. + + {453} _Origin_, Ed. i. p. 430, vi. p. 591. + +Finally, then, we see that all the leading facts in the affinities and +classification of organic beings can be explained on the theory of the +natural system being simply a genealogical one. The similarity of the +principles in classifying domestic varieties and true species, both +those living and extinct, is at once explained; the rules followed and +difficulties met with being the same. The existence of genera, families, +orders, &c., and their mutual relations, naturally ensues from +extinction going on at all periods amongst the diverging descendants of +a common stock. These terms of affinity, relations, families, adaptive +characters, &c., which naturalists cannot avoid using, though +metaphorically, cease being so, and are full of plain signification. + + + + +CHAPTER VIII + +UNITY OF TYPE IN THE GREAT CLASSES; AND MORPHOLOGICAL STRUCTURES + + +_Unity of Type_{454}. + + {454} _Origin_, Ed. i. p. 434, vi. p. 595. Ch. VIII corresponds to + a section of Ch. XIII in the _Origin_, Ed. i. + +Scarcely anything is more wonderful or has been oftener insisted on than +that the organic beings in each great class, though living in the most +distant climes and at periods immensely remote, though fitted to widely +different ends in the economy of nature, yet all in their internal +structure evince an obvious uniformity. What, for instance, is more +wonderful than that the hand to clasp, the foot or hoof to walk, the +bat's wing to fly, the porpoise's fin{455} to swim, should all be built +on the same plan? and that the bones in their position and number should +be so similar that they can all be classed and called by the same names. +Occasionally some of the bones are merely represented by an apparently +useless, smooth style, or are soldered closely to other bones, but the +unity of type is not by this destroyed, and hardly rendered less clear. +We see in this fact some deep bond of union between the organic beings +of the same great classes--to illustrate which is the object and +foundation of the natural system. The perception of this bond, I may +add, is the evident cause that naturalists make an ill-defined +distinction between true and adaptive affinities. + + {455} _Origin_, Ed. i. p. 434, vi. p. 596. In the _Origin_, Ed. i. + these examples occur under the heading _Morphology_; the author + does not there draw much distinction between this heading and that + of _Unity of Type_. + + +_Morphology._ + +There is another allied or rather almost identical class of facts +admitted by the least visionary naturalists and included under the name +of Morphology. These facts show that in an individual organic being, +several of its organs consist of some other organ metamorphosed{456}: +thus the sepals, petals, stamens, pistils, &c. of every plant can be +shown to be metamorphosed leaves; and thus not only can the number, +position and transitional states of these several organs, but likewise +their monstrous changes, be most lucidly explained. It is believed that +the same laws hold good with the gemmiferous vesicles of Zoophytes. In +the same manner the number and position of the extraordinarily +complicated jaws and palpi of Crustacea and of insects, and likewise +their differences in the different groups, all become simple, on the +view of these parts, or rather legs and all metamorphosed appendages, +being metamorphosed legs. The skulls, again, of the Vertebrata are +composed of three metamorphosed vertebræ, and thus we can see a meaning +in the number and strange complication of the bony case of the brain. In +this latter instance, and in that of the jaws of the Crustacea, it is +only necessary to see a series taken from the different groups of each +class to admit the truth of these views. It is evident that when in each +species of a group its organs consist of some other part metamorphosed, +that there must also be a "unity of type" in such a group. And in the +cases as that above given in which the foot, hand, wing and paddle are +said to be constructed on a uniform type, if we could perceive in such +parts or organs traces of an apparent change from some other use or +function, we should strictly include such parts or organs in the +department of morphology: thus if we could trace in the limbs of the +Vertebrata, as we can in their ribs, traces of an apparent change from +being processes of the vertebræ, it would be said that in each species +of the Vertebrata the limbs were "metamorphosed spinal processes," and +that in all the species throughout the class the limbs displayed a +"unity of type{457}." + + {456} See _Origin_, Ed. i. p. 436, vi. p. 599, where the parts of + the flower, the jaws and palpi of Crustaceans and the vertebrate + skull are given as examples. + + {457} The author here brings _Unity of Type_ and _Morphology_ + together. + +These wonderful parts of the hoof, foot, hand, wing, paddle, both in +living and extinct animals, being all constructed on the same framework, +and again of the petals, stamina, germens, &c. being metamorphosed +leaves, can by the creationist be viewed only as ultimate facts and +incapable of explanation; whilst on our theory of descent these facts +all necessary follow: for by this theory all the beings of any one +class, say of the mammalia, are supposed to be descended from one +parent-stock, and to have been altered by such slight steps as man +effects by the selection of chance domestic variations. Now we can see +according to this view that a foot might be selected with longer and +longer bones, and wider connecting membranes, till it became a swimming +organ, and so on till it became an organ by which to flap along the +surface or to glide over it, and lastly to fly through the air: but in +such changes there would be no tendency to alter the framework of the +internal inherited structure. Parts might become lost (as the tail in +dogs, or horns in cattle, or the pistils in plants), others might become +united together (as in the feet of the Lincolnshire breed of pigs{458}, +and in the stamens of many garden flowers); parts of a similar nature +might become increased in number (as the vertebræ in the tails of pigs, +&c., &c. and the fingers and toes in six-fingered races of men and in +the Dorking fowls), but analogous differences are observed in nature and +are not considered by naturalists to destroy the uniformity of the +types. We can, however, conceive such changes to be carried to such +length that the unity of type might be obscured and finally be +undistinguishable, and the paddle of the Plesiosaurus has been advanced +as an instance in which the uniformity of type can hardly be +recognised{459}. If after long and gradual changes in the structure of +the co-descendants from any parent stock, evidence (either from +monstrosities or from a graduated series) could be still detected of the +function, which certain parts or organs played in the parent stock, +these parts or organs might be strictly determined by their former +function with the term "metamorphosed" appended. Naturalists have used +this term in the same metaphorical manner as they have been obliged to +use the terms of affinity and relation; and when they affirm, for +instance, that the jaws of a crab are metamorphosed legs, so that one +crab has more legs and fewer jaws than another, they are far from +meaning that the jaws, either during the life of the individual crab or +of its progenitors, were really legs. By our theory this term assumes +its literal meaning{460}; and this wonderful fact of the complex jaws of +an animal retaining numerous characters, which they would probably have +retained if they had really been metamorphosed during many successive +generations from true legs, is simply explained. + + {458} The solid-hoofed pigs mentioned in _Var. under Dom._, Ed. ii. + vol. II. p. 424 are not _Lincolnshire pigs_. For other cases see + Bateson, _Materials for the Study of Variation_, 1894, pp. 387-90. + + {459} In the margin C. Bell is given as authority, apparently for + the statement about Plesiosaurus. See _Origin_, Ed. i. p. 436, vi. + p. 598, where the author speaks of the "general pattern" being + obscured in "extinct gigantic sea lizards." In the same place the + suctorial Entomostraca are added as examples of the difficulty of + recognising the type. + + {460} _Origin_, Ed. i. p. 438, vi. p. 602. + + +_Embryology_. + +The unity of type in the great classes is shown in another and very +striking manner, namely, in the stages through which the embryo passes +in coming to maturity{461}. Thus, for instance, at one period of the +embryo, the wings of the bat, the hand, hoof or foot of the quadruped, +and the fin of the porpoise do not differ, but consist of a simple +undivided bone. At a still earlier period the embryo of the fish, bird, +reptile and mammal all strikingly resemble each other. Let it not be +supposed this resemblance is only external; for on dissection, the +arteries are found to branch out and run in a peculiar course, wholly +unlike that in the full-grown mammal and bird, but much less unlike that +in the full-grown fish, for they run as if to ærate blood by +branchiæ{462} on the neck, of which even the slit-like orifices can be +discerned. How wonderful it is that this structure should be present in +the embryos of animals about to be developed into such different forms, +and of which two great classes respire only in the air. Moreover, as the +embryo of the mammal is matured in the parent's body, and that of the +bird in an egg in the air, and that of the fish in an egg in the water, +we cannot believe that this course of the arteries is related to any +external conditions. In all shell-fish (Gasteropods) the embryo passes +through a state analogous to that of the Pteropodous Mollusca: amongst +insects again, even the most different ones, as the moth, fly and +beetle, the crawling larvæ are all closely analogous: amongst the +Radiata, the jelly-fish in its embryonic state resembles a polype, and +in a still earlier state an infusorial animalcule--as does likewise the +embryo of the polype. From the part of the embryo of a mammal, at one +period, resembling a fish more than its parent form; from the larvæ of +all orders of insects more resembling the simpler articulate animals +than their parent insects{463}; and from such other cases as the embryo +of the jelly-fish resembling a polype much nearer than the perfect +jelly-fish; it has often been asserted that the higher animal in each +class passes through the state of a lower animal; for instance, that the +mammal amongst the vertebrata passes through the state of a fish{464}: +but Müller denies this, and affirms that the young mammal is at no time +a fish, as does Owen assert that the embryonic jelly-fish is at no time +a polype, but that mammal and fish, jelly-fish and polype pass through +the same state; the mammal and jelly-fish being only further developed +or changed. + + {461} _Origin_, Ed. i. p. 439, vi. p. 604. + + {462} The uselessness of the branchial arches in mammalia is + insisted on in the _Origin_, Ed. i. p. 440, vi. p. 606. Also the + uselessness of the spots on the young blackbird and the stripes of + the lion-whelp, cases which do not occur in the present Essay. + + {463} In the _Origin_, Ed. i. pp. 442, 448, vi. pp. 608, 614 it is + pointed out that in some cases the young form resembles the adult, + _e.g._ in spiders; again, that in the Aphis there is no "worm-like + stage" of development. + + {464} In the _Origin_, Ed. i. p. 449, vi. p. 618, the author speaks + doubtfully about the recapitulation theory. + +As the embryo, in most cases, possesses a less complicated structure +than that into which it is to be developed, it might have been thought +that the resemblance of the embryo to less complicated forms in the same +great class, was in some manner a necessary preparation for its higher +development; but in fact the embryo, during its growth, may become less, +as well as more, complicated{465}. Thus certain female Epizoic +Crustaceans in their mature state have neither eyes nor any organs of +locomotion; they consist of a mere sack, with a simple apparatus for +digestion and procreation; and when once attached to the body of the +fish, on which they prey, they never move again during their whole +lives: in their embryonic condition, on the other hand, they are +furnished with eyes, and with well articulated limbs, actively swim +about and seek their proper object to become attached to. The larvæ, +also, of some moths are as complicated and are more active than the +wingless and limbless females, which never leave their pupa-case, never +feed and never see the daylight. + + {465} This corresponds to the _Origin_, Ed. i. p. 441, vi. p. 607, + where, however, the example is taken from the Cirripedes. + + +_Attempt to explain the facts of embryology._ + +I think considerable light can be thrown by the theory of descent on +these wonderful embryological facts which are common in a greater or +less degree to the whole animal kingdom, and in some manner to the +vegetable kingdom: on the fact, for instance, of the arteries in the +embryonic mammal, bird, reptile and fish, running and branching in the +same courses and nearly in the same manner with the arteries in the +full-grown fish; on the fact I may add of the high importance to +systematic naturalists{466} of the characters and resemblances in the +embryonic state, in ascertaining the true position in the natural system +of mature organic beings. The following are the considerations which +throw light on these curious points. + + {466} _Origin_, Ed. i. p. 449, vi. p. 617. + +In the economy, we will say of a feline animal{467}, the feline +structure of the embryo or of the sucking kitten is of quite secondary +importance to it; hence, if a feline animal varied (assuming for the +time the possibility of this) and if some place in the economy of +nature favoured the selection of a longer-limbed variety, it would be +quite unimportant to the production by natural selection of a +long-limbed breed, whether the limbs of the embryo and kitten were +elongated if they _became_ so _as soon_ as the animal had to provide +food for itself. And if it were found after continued selection and the +production of several new breeds from one parent-stock, that the +successive variations had supervened, not very early in the youth or +embryonic life of each breed (and we have just seen that it is quite +unimportant whether it does so or not), then it obviously follows that +the young or embryos of the several breeds will continue resembling each +other more closely than their adult parents{468}. And again, if two of +these breeds became each the parent-stock of several other breeds, +forming two genera, the young and embryos of these would still retain a +greater resemblance to the one original stock than when in an adult +state. Therefore if it could be shown that the period of the slight +successive variations does not always supervene at a very early period +of life, the greater resemblance or closer unity in type of animals in +the young than in the full-grown state would be explained. Before +practically{469} endeavouring to discover in our domestic races whether +the structure or form of the young has or has not changed in an exactly +corresponding degree with the changes of full-grown animals, it will be +well to show that it is at least quite _possible_ for the primary +germinal vesicle to be impressed with a tendency to produce some change +on the growing tissues which will not be fully effected till the animal +is advanced in life. + + {467} This corresponds to the _Origin_, Ed. i. pp. 443-4, vi. p. + 610: the "feline animal" is not used to illustrate the + generalisation, but is so used in the Essay of 1842, p. 42. + + {468} _Origin_, Ed. i. p. 447, vi. p. 613. + + {469} In the margin is written "Get young pigeons"; this was + afterwards done, and the results are given in the _Origin_, Ed. i. + p. 445, vi. p. 612. + +From the following peculiarities of structure being inheritable and +appearing only when the animal is full-grown--namely, general size, +tallness (not consequent on the tallness of the infant), fatness either +over the whole body, or local; change of colour in hair and its loss; +deposition of bony matter on the legs of horses; blindness and deafness, +that is changes of structure in the eye and ear; gout and consequent +deposition of chalk-stones; and many other diseases{470}, as of the +heart and brain, &c., &c.; from all such tendencies being I repeat +inheritable, we clearly see that the germinal vesicle is impressed with +some power which is wonderfully preserved during the production of +infinitely numerous cells in the ever changing tissues, till the part +ultimately to be affected is formed and the time of life arrived at. We +see this clearly when we select cattle with any peculiarity of their +horns, or poultry with any peculiarity of their second plumage, for such +peculiarities cannot of course reappear till the animal is mature. +Hence, it is certainly _possible_ that the germinal vesicle may be +impressed with a tendency to produce a long-limbed animal, the full +proportional length of whose limbs shall appear only when the animal is +mature{471}. + + {470} In the _Origin_, Ed. i. the corresponding passages are at pp. + 8, 13, 443, vi. pp. 8, 15, 610. In the _Origin_, Ed. i. I have not + found a passage so striking as that which occurs a few lines lower + "that the germinal vesicle is impressed with some power which is + wonderfully preserved, &c." In the _Origin_ this _preservation_ is + rather taken for granted. + + {471} <In the margin is written> Aborted organs show, perhaps, + something about period <at> which changes supervene in embryo. + +In several of the cases just enumerated we know that the first cause of +the peculiarity, when _not_ inherited, lies in the conditions to which +the animal is exposed during mature life, thus to a certain extent +general size and fatness, lameness in horses and in a lesser degree +blindness, gout and some other diseases are certainly in some degree +caused and accelerated by the habits of life, and these peculiarities +when transmitted to the offspring of the affected person reappear at a +nearly corresponding time of life. In medical works it is asserted +generally that at whatever period an hereditary disease appears in the +parent, it tends to reappear in the offspring at the same period. Again, +we find that early maturity, the season of reproduction and longevity +are transmitted to corresponding periods of life. Dr Holland has +insisted much on children of the same family exhibiting certain diseases +in similar and peculiar manners; my father has known three brothers{472} +die in very old age in a _singular_ comatose state; now to make these +latter cases strictly bear, the children of such families ought +similarly to suffer at corresponding times of life; this is probably not +the case, but such facts show that a tendency in a disease to appear at +particular stages of life can be transmitted through the germinal +vesicle to different individuals of the same family. It is then +certainly possible that diseases affecting widely different periods of +life can be transmitted. So little attention is paid to very young +domestic animals that I do not know whether any case is on record of +selected peculiarities in young animals, for instance, in the first +plumage of birds, being transmitted to their young. If, however, we turn +to silk-worms{473}, we find that the caterpillars and coccoons (which +must correspond to a _very early_ period of the embryonic life of +mammalia) vary, and that these varieties reappear in the offspring +caterpillars and coccoons. + + {472} See p. 42, note 5.{Note 160} + + {473} The evidence is given in _Var. under Dom._, I. p. 316. + +I think these facts are sufficient to render it probable that at +whatever period of life any peculiarity (capable of being inherited) +appears, whether caused by the action of external influences during +mature life, or from an affection of the primary germinal vesicle, it +_tends_ to reappear in the offspring at the corresponding period of +life{474}. Hence (I may add) whatever effect training, that is the full +employment or action of every newly selected slight variation, has in +fully developing and increasing such variation, would only show itself +in mature age, corresponding to the period of training; in the second +chapter I showed that there was in this respect a marked difference in +natural and artificial selection, man not regularly exercising or +adapting his varieties to new ends, whereas selection by nature +presupposes such exercise and adaptation in each selected and changed +part. The foregoing facts show and presuppose that slight variations +occur at various periods of life _after birth_; the facts of +monstrosity, on the other hand, show that many changes take place before +birth, for instance, all such cases as extra fingers, hare-lip and all +sudden and great alterations in structure; and these when inherited +reappear during the embryonic period in the offspring. I will only add +that at a period even anterior to embryonic life, namely, during the +_egg_ state, varieties appear in size and colour (as with the +Hertfordshire duck with blackish eggs{475}) which reappear in the egg; +in plants also the capsule and membranes of the seed are very variable +and inheritable. + + {474} _Origin_, Ed. i. p. 444, vi. p. 610. + + {475} In _Var. under Dom._, Ed. ii. vol. I. p. 295, such eggs are + said to be laid early in each season by the black Labrador duck. In + the next sentence in the text the author does not distinguish the + characters of the vegetable capsule from those of the ovum. + +If then the two following propositions are admitted (and I think the +first can hardly be doubted), viz. that variation of structure takes +place at all times of life, though no doubt far less in amount and +seldomer in quite mature life{476} (and then generally taking the form +of disease); and secondly, that these variations tend to reappear at a +corresponding period of life, which seems at least probable, then we +might _a priori_ have expected that in any selected breed the _young_ +animal would not partake in a corresponding degree the peculiarities +characterising the _full-grown_ parent; though it would in a lesser +degree. For during the thousand or ten thousand selections of slight +increments in the length of the limbs of individuals necessary to +produce a long-limbed breed, we might expect that such increments would +take place in different individuals (as we do not certainly know at what +period they do take place), some earlier and some later in the embryonic +state, and some during early youth; and these increments would reappear +in their offspring only at corresponding periods. Hence, the entire +length of limb in the new long-limbed breed would only be acquired at +the latest period of life, when that one which was latest of the +thousand primary increments of length supervened. Consequently, the +foetus of the new breed during the earlier part of its existence would +remain much less changed in the proportions of its limbs; and the +earlier the period the less would the change be. + + {476} This seems to me to be more strongly stated here than in the + _Origin_, Ed. i. + +Whatever may be thought of the facts on which this reasoning is +grounded, it shows how the embryos and young of different species might +come to remain less changed than their mature parents; and practically +we find that the young of our domestic animals, though differing, differ +less than their full-grown parents. Thus if we look at the young +puppies{477} of the greyhound and bulldog--(the two most obviously +modified of the breeds of dog)--we find their puppies at the age of six +days with legs and noses (the latter measured from the eyes to the tip) +of the same length; though in the proportional thicknesses and general +appearance of these parts there is a great difference. So it is with +cattle, though the young calves of different breeds are easily +recognisable, yet they do not differ so much in their proportions as the +full-grown animals. We see this clearly in the fact that it shows the +highest skill to select the best forms early in life, either in horses, +cattle or poultry; no one would attempt it only a few hours after birth; +and it requires great discrimination to judge with accuracy even during +their full youth, and the best judges are sometimes deceived. This shows +that the ultimate proportions of the body are not acquired till near +mature age. If I had collected sufficient facts to firmly establish the +proposition that in artificially selected breeds the embryonic and young +animals are not changed in a corresponding degree with their mature +parents, I might have omitted all the foregoing reasoning and the +attempts to explain how this happens; for we might safely have +transferred the proposition to the breeds or species naturally selected; +and the ultimate effect would necessarily have been that in a number of +races or species descended from a common stock and forming several +genera and families the embryos would have resembled each other more +closely than full-grown animals. Whatever may have been the form or +habits of the parent-stock of the Vertebrata, in whatever course the +arteries ran and branched, the selection of variations, supervening +after the first formation of the arteries in the embryo, would not tend +from variations supervening at corresponding periods to alter their +course at that period: hence, the similar course of the arteries in the +mammal, bird, reptile and fish, must be looked at as a most ancient +record of the embryonic structure of the common parent-stock of these +four great classes. + + {477} _Origin_, Ed. i. p. 444, vi. p. 611. + +A long course of selection might cause a form to become more simple, as +well as more complicated; thus the adaptation of a crustaceous{478} +animal to live attached during its whole life to the body of a fish, +might permit with advantage great simplification of structure, and on +this view the singular fact of an embryo being more complex than its +parent is at once explained. + + {478} _Origin_, Ed. i. p. 441, vi. p. 607. + + +_On the graduated complexity in each great class._ + +I may take this opportunity of remarking that naturalists have observed +that in most of the great classes a series exists from very complicated +to very simple beings; thus in Fish, what a range there is between the +sand-eel and shark,--in the Articulata, between the common crab and the +Daphnia{479},--between the Aphis and butterfly, and between a mite and a +spider{480}. Now the observation just made, namely, that selection might +tend to simplify, as well as to complicate, explains this; for we can +see that during the endless geologico-geographical changes, and +consequent isolation of species, a station occupied in other districts +by less complicated animals might be left unfilled, and be occupied by a +degraded form of a higher or more complicated class; and it would by no +means follow that, when the two regions became united, the degraded +organism would give way to the aboriginally lower organism. According to +our theory, there is obviously no power tending constantly to exalt +species, except the mutual struggle between the different individuals +and classes; but from the strong and general hereditary tendency we +might expect to find some tendency to progressive complication in the +successive production of new organic forms. + + {479} Compare _Origin_, Ed. i. p. 419, vi. p. 575. + + {480} <Note in original.> Scarcely possible to distinguish between + non-development and retrograde development. + + +_Modification by selection of the forms of immature animals._ + +I have above remarked that the feline{481} form is quite of secondary +importance to the embryo and to the kitten. Of course, during any great +and prolonged change of structure in the mature animal, it might, and +often would be, indispensable that the form of the embryo should be +changed; and this could be effected, owing to the hereditary tendency at +corresponding ages, by selection, equally well as in mature age: thus if +the embryo tended to become, or to remain, either over its whole body or +in certain parts, too bulky, the female parent would die or suffer more +during parturition; and as in the case of the calves with large hinder +quarters{482}, the peculiarity must be either eliminated or the species +become extinct. Where an embryonic form has to seek its own food, its +structure and adaptation is just as important to the species as that of +the full-grown animal; and as we have seen that a peculiarity appearing +in a caterpillar (or in a child, as shown by the hereditariness of +peculiarities in the milk-teeth) reappears in its offspring, so we can +at once see that our common principle of the selection of slight +accidental variations would modify and adapt a caterpillar to a new or +changing condition, precisely as in the full-grown butterfly. Hence +probably it is that caterpillars of different species of the Lepidoptera +differ more than those embryos, at a corresponding early period of life, +do which remain inactive in the womb of their parents. The parent during +successive ages continuing to be adapted by selection for some one +object, and the larva for quite another one, we need not wonder at the +difference becoming wonderfully great between them; even as great as +that between the fixed rock-barnacle and its free, crab-like offspring, +which is furnished with eyes and well-articulated, locomotive +limbs{483}. + + {481} See p. 42, where the same illustration is used. + + {482} _Var. under Dom._, Ed. ii. vol. I. p. 452. + + {483} _Origin_, Ed. i. p. 441, vi. p. 607. + + +_Importance of embryology in classification._ + +We are now prepared to perceive why the study of embryonic forms is of +such acknowledged importance in classification{484}. For we have seen +that a variation, supervening at any time, may aid in the modification +and adaptation of the full-grown being; but for the modification of the +embryo, only the variations which supervene at a very early period can +be seized on and perpetuated by selection: hence there will be less +power and less tendency (for the structure of the embryo is mostly +unimportant) to modify the young: and hence we might expect to find at +this period similarities preserved between different groups of species +which had been obscured and quite lost in the full-grown animals. I +conceive on the view of separate creations it would be impossible to +offer any explanation of the affinities of organic beings thus being +plainest and of the greatest importance at that period of life when +their structure is not adapted to the final part they have to play in +the economy of nature. + + {484} _Origin_, Ed. i. p. 449, vi. p. 617. + + +_Order in time in which the great classes have first appeared._ + +It follows strictly from the above reasoning only that the embryos of +(for instance) existing vertebrata resemble more closely the embryo of +the parent-stock of this great class than do full-grown existing +vertebrata resemble their full-grown parent-stock. But it may be argued +with much probability that in the earliest and simplest condition of +things the parent and embryo must have resembled each other, and that +the passage of any animal through embryonic states in its growth is +entirely due to subsequent variations affecting _only_ the more mature +periods of life. If so, the embryos of the existing vertebrata will +shadow forth the full-grown structure of some of those forms of this +great class which existed at the earlier periods of the earth's +history{485}: and accordingly, animals with a fish-like structure ought +to have preceded birds and mammals; and of fish, that higher organized +division with the vertebræ extending into one division of the tail ought +to have preceded the equal-tailed, because the embryos of the latter +have an unequal tail; and of Crustacea, entomostraca ought to have +preceded the ordinary crabs and barnacles--polypes ought to have +preceded jelly-fish, and infusorial animalcules to have existed before +both. This order of precedence in time in some of these cases is +believed to hold good; but I think our evidence is so exceedingly +incomplete regarding the number and kinds of organisms which have +existed during all, especially the earlier, periods of the earth's +history, that I should put no stress on this accordance, even if it held +truer than it probably does in our present state of knowledge. + + {485} _Origin_, Ed. i. p. 449, vi. p. 618. + + + + +CHAPTER IX + +ABORTIVE OR RUDIMENTARY ORGANS + + +_The abortive organs of naturalists._ + +Parts of structure are said to be "abortive," or when in a still lower +state of development "rudimentary{486}," when the same reasoning power, +which convinces us that in some cases similar parts are beautifully +adapted to certain ends, declares that in others they are absolutely +useless. Thus the rhinoceros, the whale{487}, etc., have, when young, +small but properly formed teeth, which never protrude from the jaws; +certain bones, and even the entire extremities are represented by mere +little cylinders or points of bone, often soldered to other bones: many +beetles have exceedingly minute but regularly formed wings lying under +their wing-cases{488}, which latter are united never to be opened: many +plants have, instead of stamens, mere filaments or little knobs; petals +are reduced to scales, and whole flowers to buds, which (as in the +feather hyacinth) never expand. Similar instances are almost +innumerable, and are justly considered wonderful: probably not one +organic being exists in which some part does not bear the stamp of +inutility; for what can be clearer{489}, as far as our reasoning powers +can reach, than that teeth are for eating, extremities for locomotion, +wings for flight, stamens and the entire flower for reproduction; yet +for these clear ends the parts in question are manifestly unfit. +Abortive organs are often said to be mere representatives (a +metaphorical expression) of similar parts in other organic beings; but +in some cases they are more than representatives, for they seem to be +the actual organ not fully grown or developed; thus the existence of +mammæ in the male vertebrata is one of the oftenest adduced cases of +abortion; but we know that these organs in man (and in the bull) have +performed their proper function and secreted milk: the cow has normally +four mammæ and two abortive ones, but these latter in some instances are +largely developed and even (??) give milk{490}. Again in flowers, the +representatives of stamens and pistils can be traced to be really these +parts not developed; Kölreuter has shown by crossing a diæcious plant (a +Cucubalus) having a rudimentary pistil{491} with another species having +this organ perfect, that in the hybrid offspring the rudimentary part is +more developed, though still remaining abortive; now this shows how +intimately related in nature the mere rudiment and the fully developed +pistil must be. + + {486} In the _Origin_, Ed. i. p. 450, vi. p. 619, the author does + not lay stress on any distinction in meaning between the terms + _abortive_ and _rudimentary_ organs. + + {487} _Origin_, Ed. i. p. 450, vi. p. 619. + + {488} _Ibid._ + + {489} This argument occurs in _Origin_, Ed. i. p. 451, vi. p. 619. + + {490} _Origin_, Ed. i. p. 451, vi. p. 619, on male mammæ. In the + _Origin_ he speaks certainly of the abortive mammæ of the cow + giving milk,--a point which is here queried. + + {491} _Origin_, Ed. i. p. 451, vi. p. 620. + +Abortive organs, which must be considered as useless as far as their +ordinary and normal purpose is concerned, are sometimes adapted to other +ends{492}: thus the marsupial bones, which properly serve to support the +young in the mother's pouch, are present in the male and serve as the +fulcrum for muscles connected only with male functions: in the male of +the marigold flower the pistil is abortive for its proper end of being +impregnated, but serves to sweep the pollen out of the anthers{493} +ready to be borne by insects to the perfect pistils in the other +florets. It is likely in many cases, yet unknown to us, that abortive +organs perform some useful function; but in other cases, for instance in +that of teeth embedded in the solid jaw-bone, or of mere knobs, the +rudiments of stamens and pistils, the boldest imagination will hardly +venture to ascribe to them any function. Abortive parts, even when +wholly useless to the individual species, are of great signification in +the system of nature; for they are often found to be of very high +importance in a natural classification{494}; thus the presence and +position of entire abortive flowers, in the grasses, cannot be +overlooked in attempting to arrange them according to their true +affinities. This corroborates a statement in a previous chapter, viz. +that the physiological importance of a part is no index of its +importance in classification. Finally, abortive organs often are only +developed, proportionally with other parts, in the embryonic or young +state of each species{495}; this again, especially considering the +classificatory importance of abortive organs, is evidently part of the +law (stated in the last chapter) that the higher affinities of organisms +are often best seen in the stages towards maturity, through which the +embryo passes. On the ordinary view of individual creations, I think +that scarcely any class of facts in natural history are more wonderful +or less capable of receiving explanation. + + {492} The case of rudimentary organs adapted to new purposes is + discussed in the _Origin_, Ed. i. p. 451, vi. p. 620. + + {493} This is here stated on the authority of Sprengel; see also + _Origin_, Ed. i. p. 452, vi. p. 621. + + {494} _Origin_, Ed. i. p. 455, vi. p. 627. In the margin R. Brown's + name is given apparently as the authority for the fact. + + {495} _Origin_, Ed. i. p. 455, vi. p. 626. + + +_The abortive organs of physiologists._ + +Physiologists and medical men apply the term "abortive" in a somewhat +different sense from naturalists; and their application is probably the +primary one; namely, to parts, which from accident or disease before +birth are not developed or do not grow{496}: thus, when a young animal +is born with a little stump in the place of a finger or of the whole +extremity, or with a little button instead of a head, or with a mere +bead of bony matter instead of a tooth, or with a stump instead of a +tail, these parts are said to be aborted. Naturalists on the other hand, +as we have seen, apply this term to parts not stunted during the growth +of the embryo, but which are as regularly produced in successive +generations as any other most essential parts of the structure of the +individual: naturalists, therefore, use this term in a metaphorical +sense. These two classes of facts, however, blend into each other{497}; +by parts accidentally aborted, during the embryonic life of one +individual, becoming hereditary in the succeeding generations: thus a +cat or dog, born with a stump instead of a tail, tends to transmit +stumps to their offspring; and so it is with stumps representing the +extremities; and so again with flowers, with defective and rudimentary +parts, which are annually produced in new flower-buds and even in +successive seedlings. The strong hereditary tendency to reproduce every +either congenital or slowly acquired structure, whether useful or +injurious to the individual, has been shown in the first part; so that +we need feel no surprise at these truly abortive parts becoming +hereditary. A curious instance of the force of hereditariness is +sometimes seen in two little loose hanging horns, quite useless as far +as the function of a horn is concerned, which are produced in hornless +races of our domestic cattle{498}. Now I believe no real distinction can +be drawn between a stump representing a tail or a horn or the +extremities; or a short shrivelled stamen without any pollen; or a +dimple in a petal representing a nectary, when such rudiments are +regularly reproduced in a race or family, and the true abortive organs +of naturalists. And if we had reason to believe (which I think we have +not) that all abortive organs had been at some period _suddenly_ +produced during the embryonic life of an individual, and afterwards +become inherited, we should at once have a simple explanation of the +origin of abortive and rudimentary organs{499}. In the same manner as +during changes of pronunciation certain letters in a word may become +useless{500} in pronouncing it, but yet may aid us in searching for its +derivation, so we can see that rudimentary organs, no longer useful to +the individual, may be of high importance in ascertaining its descent, +that is, its true classification in the natural system. + + {496} _Origin_, Ed. i. p. 454, vi. p. 625. + + {497} In the _Origin_, Ed. i. p. 454, vi. p. 625, the author in + referring to semi-monstrous variations adds "But I doubt whether + any of these cases throw light on the origin of rudimentary organs + in a state of nature." In 1844 he was clearly more inclined to an + opposite opinion. + + {498} _Origin_, Ed. i. p. 454, vi. p. 625. + + {499} See _Origin_, Ed. i. p. 454, vi. p. 625. The author there + discusses monstrosities in relation to rudimentary organs, and + comes to the conclusion that disuse is of more importance, giving + as a reason his doubt "whether species under nature ever undergo + abrupt changes." It seems to me that in the _Origin_ he gives more + weight to the "Lamarckian factor" than he did in 1844. Huxley took + the opposite view, see the Introduction. + + {500} _Origin_, Ed. i. p. 455, vi. p. 627. + + +_Abortion from gradual disuse._ + +There seems to be some probability that continued disuse of any part or +organ, and the selection of individuals with such parts slightly less +developed, would in the course of ages produce in organic beings under +domesticity races with such parts abortive. We have every reason to +believe that every part and organ in an individual becomes fully +developed only with exercise of its functions; that it becomes developed +in a somewhat lesser degree with less exercise; and if forcibly +precluded from all action, such part will often become atrophied. Every +peculiarity, let it be remembered, tends, especially where both parents +have it, to be inherited. The less power of flight in the common duck +compared with the wild, must be partly attributed to disuse{501} during +successive generations, and as the wing is properly adapted to flight, +we must consider our domestic duck in the first stage towards the state +of the Apteryx, in which the wings are so curiously abortive. Some +naturalists have attributed (and possibly with truth) the falling ears +so characteristic of most domestic dogs, some rabbits, oxen, cats, +goats, horses, &c., &c., as the effects of the lesser use of the muscles +of these flexible parts during successive generations of inactive life; +and muscles, which cannot perform their functions, must be considered +verging towards abortion. In flowers, again, we see the gradual abortion +during successive seedlings (though this is more properly a conversion) +of stamens into imperfect petals, and finally into perfect petals. When +the eye is blinded in early life the optic nerve sometimes becomes +atrophied; may we not believe that where this organ, as is the case with +the subterranean mole-like Tuco-tuco <_Ctenomys_>{502}, is frequently +impaired and lost, that in the course of generations the whole organ +might become abortive, as it normally is in some burrowing quadrupeds +having nearly similar habits with the Tuco-tuco? + + {501} _Origin_, Ed. i. p. 11, vi. p. 13, where drooping-ears of + domestic animals are also given. + + {502} _Origin_, Ed. i. p. 137, vi. p. 170. + +In as far then as it is admitted as probable that the effects of disuse +(together with occasional true and sudden abortions during the embryonic +period) would cause a part to be less developed, and finally to become +abortive and useless; then during the infinitely numerous changes of +habits in the many descendants from a common stock, we might fairly have +expected that cases of organs becom<ing> abortive would have been numerous. +The preservation of the stump of the tail, as usually happens when an +animal is born tailless, we can only explain by the strength of the +hereditary principle and by the period in embryo when affected{503}: but +on the theory of disuse gradually obliterating a part, we can see, +according to the principles explained in the last chapter (viz. of +hereditariness at corresponding periods of life{504}, together with the +use and disuse of the part in question not being brought into play in +early or embryonic life), that organs or parts would tend not to be +utterly obliterated, but to be reduced to that state in which they +existed in early embryonic life. Owen often speaks of a part in a +full-grown animal being in an "embryonic condition." Moreover we can +thus see why abortive organs are most developed at an early period of +life. Again, by gradual selection, we can see how an organ rendered +abortive in its primary use might be converted to other purposes; a +duck's wing might come to serve for a fin, as does that of the penguin; +an abortive bone might come to serve, by the slow increment and change +of place in the muscular fibres, as a fulcrum for a new series of +muscles; the pistil{505} of the marigold might become abortive as a +reproductive part, but be continued in its function of sweeping the +pollen out of the anthers; for if in this latter respect the abortion +had not been checked by selection, the species must have become extinct +from the pollen remaining enclosed in the capsules of the anthers. + + {503} These words seem to have been inserted as an afterthought. + + {504} _Origin_, Ed. i. p. 444, vi. p. 611. + + {505} This and similar cases occur in the _Origin_, Ed. i. p. 452, + vi. p. 621. + +Finally then I must repeat that these wonderful facts of organs formed +with traces of exquisite care, but now either absolutely useless or +adapted to ends wholly different from their ordinary end, being present +and forming part of the structure of almost every inhabitant of this +world, both in long-past and present times--being best developed and +often only discoverable at a very early embryonic period, and being full +of signification in arranging the long series of organic beings in a +natural system--these wonderful facts not only receive a simple +explanation on the theory of long-continued selection of many species +from a few common parent-stocks, but necessarily follow from this +theory. If this theory be rejected, these facts remain quite +inexplicable; without indeed we rank as an explanation such loose +metaphors as that of De Candolle's{506}, in which the kingdom of nature +is compared to a well-covered table, and the abortive organs are +considered as put in for the sake of symmetry! + + {506} The metaphor of the dishes is given in the Essay of 1842, p. + 47, note 3.{Note 173} + + + + +CHAPTER X + +RECAPITULATION AND CONCLUSION + + +_Recapitulation._ + +I will now recapitulate the course of this work, more fully with respect +to the former parts, and briefly <as to> the latter. In the first +chapter we have seen that most, if not all, organic beings, when taken +by man out of their natural condition, and bred during several +generations, vary; that is variation is partly due to the direct effect +of the new external influences, and partly to the indirect effect on the +reproductive system rendering the organization of the offspring in some +degree plastic. Of the variations thus produced, man when uncivilised +naturally preserves the life, and therefore unintentionally breeds from +those individuals most useful to him in his different states: when even +semi-civilised, he intentionally separates and breeds from such +individuals. Every part of the structure seems occasionally to vary in a +very slight degree, and the extent to which all kinds of peculiarities +in mind and body, when congenital and when slowly acquired either from +external influences, from exercise, or from disuse <are inherited>, is +truly wonderful. When several breeds are once formed, then crossing is +the most fertile source of new breeds{507}. Variation must be ruled, of +course, by the health of the new race, by the tendency to return to the +ancestral forms, and by unknown laws determining the proportional +increase and symmetry of the body. The amount of variation, which has +been effected under domestication, is quite unknown in the majority of +domestic beings. + + {507} Compare however Darwin's later view:--"The possibility of + making distinct races by crossing has been greatly exaggerated," + _Origin_, Ed. i. p. 20, vi. p. 23. The author's change of opinion + was no doubt partly due to his experience in breeding pigeons. + +In the second chapter it was shown that wild organisms undoubtedly vary +in some slight degree: and that the kind of variation, though much less +in degree, is similar to that of domestic organisms. It is highly +probable that every organic being, if subjected during several +generations to new and varying conditions, would vary. It is certain +that organisms, living in an _isolated_ country which is undergoing +geological changes, must in the course of time be so subjected to new +conditions; moreover an organism, when by chance transported into a new +station, for instance into an island, will often be exposed to new +conditions, and be surrounded by a new series of organic beings. If +there were no power at work selecting every slight variation, which +opened new sources of subsistence to a being thus situated, the effects +of crossing, the chance of death and the constant tendency to reversion +to the old parent-form, would prevent the production of new races. If +there were any selective agency at work, it seems impossible to assign +any limit{508} to the complexity and beauty of the adaptive structures, +which _might_ thus be produced: for certainly the limit of possible +variation of organic beings, either in a wild or domestic state, is not +known. + + {508} In the _Origin_, Ed. i. p. 469, vi. p. 644, Darwin makes a + strong statement to this effect. + +It was then shown, from the geometrically increasing tendency of each +species to multiply (as evidenced from what we know of mankind and of +other animals when favoured by circumstances), and from the means of +subsistence of each species on an _average_ remaining constant, that +during some part of the life of each, or during every few generations, +there must be a severe struggle for existence; and that less than a +grain{509} in the balance will determine which individuals shall live +and which perish. In a country, therefore, undergoing changes, and cut +off from the free immigration of species better adapted to the new +station and conditions, it cannot be doubted that there is a most +powerful means of selection, _tending_ to preserve even the slightest +variation, which aided the subsistence or defence of those organic +beings, during any part of their whole existence, whose organization had +been rendered plastic. Moreover, in animals in which the sexes are +distinct, there is a sexual struggle, by which the most vigorous, and +consequently the best adapted, will oftener procreate their kind. + + {509} "A grain in the balance will determine which individual shall + live and which shall die," _Origin_, Ed. i. p. 467, vi. p. 642. A + similar statement occurs in the 1842 Essay, p. 8, note 3.{Note 59} + +A new race thus formed by natural selection would be undistinguishable +from a species. For comparing, on the one hand, the several species of a +genus, and on the other hand several domestic races from a common stock, +we cannot discriminate them by the amount of external difference, but +only, first, by domestic races not remaining so constant or being so +"true" as species are; and secondly by races always producing fertile +offspring when crossed. And it was then shown that a race naturally +selected--from the variation being slower--from the selection steadily +leading towards the same ends{510}, and from every new slight change in +structure being adapted (as is implied by its selection) to the new +conditions and being fully exercised, and lastly from the freedom from +occasional crosses with other species, would almost necessarily be +"truer" than a race selected by ignorant or capricious and short-lived +man. With respect to the sterility of species when crossed, it was shown +not to be a universal character, and when present to vary in degree: +sterility also was shown probably to depend less on external than on +constitutional differences. And it was shown that when individual +animals and plants are placed under new conditions, they become, without +losing their healths, as sterile, in the same manner and to the same +degree, as hybrids; and it is therefore conceivable that the cross-bred +offspring between two species, having different constitutions, might +have its constitution affected in the same peculiar manner as when an +individual animal or plant is placed under new conditions. Man in +selecting domestic races has little wish and still less power to adapt +the whole frame to new conditions; in nature, however, where each +species survives by a struggle against other species and external +nature, the result must be very different. + + {510} Thus according to the author what is now known as + _orthogenesis_ is due to selection. + +Races descending from the same stock were then compared with species of +the same genus, and they were found to present some striking analogies. +The offspring also of races when crossed, that is mongrels, were +compared with the cross-bred offspring of species, that is hybrids, and +they were found to resemble each other in all their characters, with the +one exception of sterility, and even this, when present, often becomes +after some generations variable in degree. The chapter was summed up, +and it was shown that no ascertained limit to the amount of variation is +known; or could be predicted with due time and changes of condition +granted. It was then admitted that although the production of new races, +undistinguishable from true species, is probable, we must look to the +relations in the past and present geographical distribution of the +infinitely numerous beings, by which we are surrounded--to their +affinities and to their structure--for any direct evidence. + +In the third chapter the inheritable variations in the mental phenomena +of domestic and of wild organic beings were considered. It was shown +that we are not concerned in this work with the first origin of the +leading mental qualities; but that tastes, passions, dispositions, +consensual movements, and habits all became, either congenitally or +during mature life, modified and were inherited. Several of these +modified habits were found to correspond in every essential character +with true instincts, and they were found to follow the same laws. +Instincts and dispositions &c. are fully as important to the +preservation and increase of a species as its corporeal structure; and +therefore the natural means of selection would act on and modify them +equally with corporeal structures. This being granted, as well as the +proposition that mental phenomena are variable, and that the +modifications are inheritable, the possibility of the several most +complicated instincts being slowly acquired was considered, and it was +shown from the very imperfect series in the instincts of the animals now +existing, that we are not justified in _prima facie_ rejecting a theory +of the common descent of allied organisms from the difficulty of +imagining the transitional stages in the various now most complicated +and wonderful instincts. We were thus led on to consider the same +question with respect both to highly complicated organs, and to the +aggregate of several such organs, that is individual organic beings; and +it was shown, by the same method of taking the existing most imperfect +series, that we ought not at once to reject the theory, because we +cannot trace the transitional stages in such organs, or conjecture the +transitional habits of such individual species. + +In the Second Part{511} the direct evidence of allied forms having +descended from the same stock was discussed. It was shown that this +theory requires a long series of intermediate forms between the species +and groups in the same classes--forms not directly intermediate between +existing species, but intermediate with a common parent. It was admitted +that if even all the preserved fossils and existing species were +collected, such a series would be far from being formed; but it was +shown that we have not _good_ evidence that the oldest known deposits +are contemporaneous with the first appearance of living beings; or that +the several subsequent formations are nearly consecutive; or that any +one formation preserves a nearly perfect fauna of even the hard marine +organisms, which lived in that quarter of the world. Consequently, we +have no reason to suppose that more than a small fraction of the +organisms which have lived at any one period have ever been preserved; +and hence that we ought not to expect to discover the fossilised +sub-varieties between any two species. On the other hand, the evidence, +though extremely imperfect, drawn from fossil remains, as far as it does +go, is in favour of such a series of organisms having existed as that +required. This want of evidence of the past existence of almost +infinitely numerous intermediate forms, is, I conceive, much the +weightiest difficulty{512} on the theory of common descent; but I must +think that this is due to ignorance necessarily resulting from the +imperfection of all geological records. + + {511} Part II begins with Ch. IV. See the Introduction, where the + absence of division into two parts (in the _Origin_) is discussed. + + {512} In the recapitulation in the last chapter of the _Origin_, + Ed. i. p. 475, vi. p. 651, the author does not insist on this point + as the weightiest difficulty, though he does so in Ed. i. p. 299. + It is possible that he had come to think less of the difficulty in + question: this was certainly the case when he wrote the 6th + edition, see p. 438. + +In the fifth chapter it was shown that new species gradually{513} +appear, and that the old ones gradually disappear, from the earth; and +this strictly accords with our theory. The extinction of species seems +to be preceded by their rarity; and if this be so, no one ought to feel +more surprise at a species being exterminated than at its being rare. +Every species which is not increasing in number must have its +geometrical tendency to increase checked by some agency seldom +accurately perceived by us. Each slight increase in the power of this +unseen checking agency would cause a corresponding decrease in the +average numbers of that species, and the species would become rarer: we +feel not the least surprise at one species of a genus being rare and +another abundant; why then should we be surprised at its extinction, +when we have good reason to believe that this very rarity is its regular +precursor and cause. + + {513} <The following words:> The fauna changes singly <were inserted + by the author, apparently to replace a doubtful erasure>. + +In the sixth chapter the leading facts in the geographical distribution +of organic beings were considered--namely, the dissimilarity in areas +widely and effectually separated, of the organic beings being exposed to +very similar conditions (as for instance, within the tropical forests of +Africa and America, or on the volcanic islands adjoining them). Also the +striking similarity and general relations of the inhabitants of the same +great continents, conjoined with a lesser degree of dissimilarity in the +inhabitants living on opposite sides of the barriers intersecting +it--whether or not these opposite sides are exposed to similar +conditions. Also the dissimilarity, though in a still lesser degree, in +the inhabitants of different islands in the same archipelago, together +with their similarity taken as a whole with the inhabitants of the +nearest continent, whatever its character may be. Again, the peculiar +relations of Alpine floras; the absence of mammifers on the smaller +isolated islands; and the comparative fewness of the plants and other +organisms on islands with diversified stations; the connection between +the possibility of occasional transportal from one country to another, +with an affinity, though not identity, of the organic beings inhabiting +them. And lastly, the clear and striking relations between the living +and the extinct in the same great divisions of the world; which +relation, if we look very far backward, seems to die away. These facts, +if we bear in mind the geological changes in progress, all simply follow +from the proposition of allied organic beings having lineally descended +from common parent-stocks. On the theory of independent creations they +must remain, though evidently connected together, inexplicable and +disconnected. + +In the seventh chapter, the relationship or grouping of extinct and +recent species; the appearance and disappearance of groups; the +ill-defined objects of the natural classification, not depending on the +similarity of organs physiologically important, not being influenced by +adaptive or analogical characters, though these often govern the whole +economy of the individual, but depending on any character which varies +least, and especially on the forms through which the embryo passes, and, +as was afterwards shown, on the presence of rudimentary and useless +organs. The alliance between the nearest species in _distinct_ groups +being general and not especial; the close similarity in the rules and +objects in classifying domestic races and true species. All these facts +were shown to follow on the natural system being a genealogical system. + +In the eighth chapter, the unity of structure throughout large groups, +in species adapted to the most different lives, and the wonderful +metamorphosis (used metaphorically by naturalists) of one part or organ +into another, were shown to follow simply on new species being produced +by the selection and inheritance of successive _small_ changes of +structure. The unity of type is wonderfully manifested by the similarity +of structure, during the embryonic period, in the species of entire +classes. To explain this it was shown that the different races of our +domestic animals differ less, during their young state, than when full +grown; and consequently, if species are produced like races, the same +fact, on a greater scale, might have been expected to hold good with +them. This remarkable law of nature was attempted to be explained +through establishing, by sundry facts, that slight variations originally +appear during all periods of life, and that when inherited they tend to +appear at the corresponding period of life; according to these +principles, in several species descended from the same parent-stock, +their embryos would almost necessarily much more closely resemble each +other than they would in their adult state. The importance of these +embryonic resemblances, in making out a natural or genealogical +classification, thus becomes at once obvious. The occasional greater +simplicity of structure in the mature animal than in the embryo; the +gradation in complexity of the species in the great classes; the +adaptation of the larvæ of animals to independent powers of existence; +the immense difference in certain animals in their larval and mature +states, were all shown on the above principles to present no difficulty. + +In the <ninth> chapter, the frequent and almost general presence of +organs and parts, called by naturalists abortive or rudimentary, which, +though formed with exquisite care, are generally absolutely useless +<was considered>. <These structures,> though sometimes applied to uses +not normal,--which cannot be considered as mere representative parts, +for they are sometimes capable of performing their proper +function,--which are always best developed, and sometimes only +developed, during a very early period of life,--and which are of +admitted high importance in classification,--were shown to be simply +explicable on our theory of common descent. + + +_Why do we wish to reject the theory of common descent?_ + +Thus have many general facts, or laws, been included under one +explanation; and the difficulties encountered are those which would +naturally result from our acknowledged ignorance. And why should we not +admit this theory of descent{514}? Can it be shown that organic beings +in a natural state are _all absolutely invariable_? Can it be said that +the _limit of variation_ or the number of varieties capable of being +formed under domestication are known? Can any distinct line be drawn +_between a race and a species_? To these three questions we may +certainly answer in the negative. As long as species were thought to be +divided and defined by an impassable barrier of _sterility_, whilst we +were ignorant of geology, and imagined that the _world was of short +duration_, and the number of its past inhabitants few, we were justified +in assuming individual creations, or in saying with Whewell that the +beginnings of all things are hidden from man. Why then do we feel so +strong an inclination to reject this theory--especially when the actual +case of any two species, or even of any two races, is adduced--and one +is asked, have these two originally descended from the same parent womb? +I believe it is because we are always slow in admitting any great +change of which we do not see the intermediate steps. The mind cannot +grasp the full meaning of the term of a million or hundred million +years, and cannot consequently add up and perceive the full effects of +small successive variations accumulated during almost infinitely many +generations. The difficulty is the same with that which, with most +geologists, it has taken long years to remove, as when Lyell propounded +that great valleys{515} were hollowed out [and long lines of inland +cliffs had been formed] by the slow action of the waves of the sea. A +man may long view a grand precipice without actually believing, though +he may not deny it, that thousands of feet in thickness of solid rock +once extended over many square miles where the open sea now rolls; +without fully believing that the same sea which he sees beating the rock +at his feet has been the sole removing power. + + {514} This question forms the subject of what is practically a + section of the final chapter of the _Origin_ (Ed. i. p. 480, vi. p. + 657). + + {515} _Origin_, Ed. i. p. 481, vi. p. 659. + +Shall we then allow that the three distinct species of rhinoceros{516} +which separately inhabit Java and Sumatra and the neighbouring mainland +of Malacca were created, male and female, out of the inorganic materials +of these countries? Without any adequate cause, as far as our reason +serves, shall we say that they were merely, from living near each other, +created very like each other, so as to form a section of the genus +dissimilar from the African section, some of the species of which +section inhabit very similar and some very dissimilar stations? Shall we +say that without any apparent cause they were created on the same +generic type with the ancient woolly rhinoceros of Siberia and of the +other species which formerly inhabited the same main division of the +world: that they were created, less and less closely related, but still +with interbranching affinities, with all the other living and extinct +mammalia? That without any apparent adequate cause their short necks +should contain the same number of vertebræ with the giraffe; that their +thick legs should be built on the same plan with those of the antelope, +of the mouse, of the hand of the monkey, of the wing of the bat, and of +the fin of the porpoise. That in each of these species the second bone +of their leg should show clear traces of two bones having been soldered +and united into one; that the complicated bones of their head should +become intelligible on the supposition of their having been formed of +three expanded vertebræ; that in the jaws of each when dissected young +there should exist small teeth which never come to the surface. That in +possessing these useless abortive teeth, and in other characters, these +three rhinoceroses in their embryonic state should much more closely +resemble other mammalia than they do when mature. And lastly, that in a +still earlier period of life, their arteries should run and branch as in +a fish, to carry the blood to gills which do not exist. Now these three +species of rhinoceros closely resemble each other; more closely than +many generally acknowledged races of our domestic animals; these three +species if domesticated would almost certainly vary, and races adapted +to different ends might be selected out of such variations. In this +state they would probably breed together, and their offspring would +possibly be quite, and probably in some degree, fertile; and in either +case, by continued crossing, one of these specific forms might be +absorbed and lost in another. I repeat, shall we then say that a pair, +or a gravid female, of each of these three species of rhinoceros, were +separately created with deceptive appearances of true relationship, with +the stamp of inutility on some parts, and of conversion in other parts, +out of the inorganic elements of Java, Sumatra and Malacca? or have they +descended, like our domestic races, from the same parent-stock? For my +own part I could no more admit the former proposition than I could admit +that the planets move in their courses, and that a stone falls to the +ground, not through the intervention of the secondary and appointed law +of gravity, but from the direct volition of the Creator. + + {516} The discussion on the three species of _Rhinoceros_ which + also occurs in the Essay of 1842, p. 48, was omitted in Ch. XIV of + the _Origin_, Ed. i. + +Before concluding it will be well to show, although this has +incidentally appeared, how far the theory of common descent can +legitimately be extended{517}. If we once admit that two true species of +the same genus can have descended from the same parent, it will not be +possible to deny that two species of two genera may also have descended +from a common stock. For in some families the genera approach almost as +closely as species of the same genus; and in some orders, for instance +in the monocotyledonous plants, the families run closely into each +other. We do not hesitate to assign a common origin to dogs or cabbages, +because they are divided into groups analogous to the groups in nature. +Many naturalists indeed admit that all groups are artificial; and that +they depend entirely on the extinction of intermediate species. Some +naturalists, however, affirm that though driven from considering +sterility as the characteristic of species, that an entire incapacity to +propagate together is the best evidence of the existence of natural +genera. Even if we put on one side the undoubted fact that some species +of the same genus will not breed together, we cannot possibly admit the +above rule, seeing that the grouse and pheasant (considered by some good +ornithologists as forming two families), the bull-finch and canary-bird +have bred together. + + {517} This corresponds to a paragraph in the _Origin_, Ed. i. p. + 483, vi. p. 662, where it is assumed that animals have descended + "from at most only four or five progenitors, and plants from an + equal or lesser number." In the _Origin_, however, the author goes + on, Ed. i. p. 484, vi. p. 663: "Analogy would lead me one step + further, namely, to the belief that all animals and plants have + descended from some one prototype." + +No doubt the more remote two species are from each other, the weaker the +arguments become in favour of their common descent. In species of two +distinct families the analogy, from the variation of domestic organisms +and from the manner of their intermarrying, fails; and the arguments +from their geographical distribution quite or almost quite fails. But if +we once admit the general principles of this work, as far as a clear +unity of type can be made out in groups of species, adapted to play +diversified parts in the economy of nature, whether shown in the +structure of the embryonic or mature being, and especially if shown by a +community of abortive parts, we are legitimately led to admit their +community of descent. Naturalists dispute how widely this unity of type +extends: most, however, admit that the vertebrata are built on one type; +the articulata on another; the mollusca on a third; and the radiata on +probably more than one. Plants also appear to fall under three or four +great types. On this theory, therefore, all the organisms _yet +discovered_ are descendants of probably less than ten parent-forms. + + +_Conclusion._ + +My reasons have now been assigned for believing that specific forms are +not immutable creations{518}. The terms used by naturalists of affinity, +unity of type, adaptive characters, the metamorphosis and abortion of +organs, cease to be metaphorical expressions and become intelligible +facts. We no longer look at an organic being as a savage does at a +ship{519} or other great work of art, as at a thing wholly beyond his +comprehension, but as a production that has a history which we may +search into. How interesting do all instincts become when we speculate +on their origin as hereditary habits, or as slight congenital +modifications of former instincts perpetuated by the individuals so +characterised having been preserved. When we look at every complex +instinct and mechanism as the summing up of a long history of +contrivances, each most useful to its possessor, nearly in the same way +as when we look at a great mechanical invention as the summing up of the +labour, the experience, the reason, and even the blunders of numerous +workmen. How interesting does the geographical distribution of all +organic beings, past and present, become as throwing light on the +ancient geography of the world. Geology loses glory{520} from the +imperfection of its archives, but it gains in the immensity of its +subject. There is much grandeur in looking at every existing organic +being either as the lineal successor of some form now buried under +thousands of feet of solid rock, or as being the co-descendant of that +buried form of some more ancient and utterly lost inhabitant of this +world. It accords with what we know of the laws impressed by the +Creator{521} on matter that the production and extinction of forms +should, like the birth and death of individuals, be the result of +secondary means. It is derogatory that the Creator of countless +Universes should have made by individual acts of His will the myriads of +creeping parasites and worms, which since the earliest dawn of life have +swarmed over the land and in the depths of the ocean. We cease to be +astonished{522} that a group of animals should have been formed to lay +their eggs in the bowels and flesh of other sensitive beings; that some +animals should live by and even delight in cruelty; that animals should +be led away by false instincts; that annually there should be an +incalculable waste of the pollen, eggs and immature beings; for we see +in all this the inevitable consequences of one great law, of the +multiplication of organic beings not created immutable. From death, +famine, and the struggle for existence, we see that the most exalted end +which we are capable of conceiving, namely, the creation of the higher +animals{523}, has directly proceeded. Doubtless, our first impression is +to disbelieve that any secondary law could produce infinitely numerous +organic beings, each characterised by the most exquisite workmanship and +widely extended adaptations: it at first accords better with our +faculties to suppose that each required the fiat of a Creator. +There{524} is a [simple] grandeur in this view of life with its several +powers of growth, reproduction and of sensation, having been originally +breathed into matter under a few forms, perhaps into only one{525}, and +that whilst this planet has gone cycling onwards according to the fixed +laws of gravity and whilst land and water have gone on replacing each +other--that from so simple an origin, through the selection of +infinitesimal varieties, endless forms most beautiful and most wonderful +have been evolved. + + {518} This sentence corresponds, not to the final section of the + _Origin_, Ed. i. p. 484, vi. p. 664, but rather to the opening + words of the section already referred to (_Origin_, Ed. i. p. 480, + vi. p. 657). + + {519} This simile occurs in the Essay of 1842, p. 50, and in the + _Origin_, Ed. i. p. 485, vi. p. 665, _i.e._ in the final section of + Ch. XIV (vi. Ch. XV). In the MS. there is some erasure in pencil of + which I have taken no notice. + + {520} An almost identical sentence occurs in the _Origin_, Ed. i. + p. 487, vi. p. 667. The fine prophecy (in the _Origin_, Ed. i. p. + 486, vi. p. 666) on "the almost untrodden field of inquiry" is + wanting in the present Essay. + + {521} See the last paragraph on p. 488 of the _Origin_, Ed. i., vi. + p. 668. + + {522} A passage corresponding to this occurs in the sketch of 1842, + p. 51, but not in the last chapter of the _Origin_. + + {523} This sentence occurs in an almost identical form in the + _Origin_, Ed. i. p. 490, vi. p. 669. It will be noted that man is + not named though clearly referred to. Elsewhere (_Origin_, Ed. i. + p. 488) the author is bolder and writes "Light will be thrown on + the origin of man and his history." In Ed. vi. p. 668, he writes + "Much light &c." + + {524} For the history of this sentence (with which the _Origin of + Species_ closes) see the Essay of 1842, p. 52, note 2{Note 184}: + also the concluding pages of the Introduction. + + {525} These four words are added in pencil between the lines. + + + + +INDEX + + +For the names of Authors, Birds, Mammals (including names of classes) +and Plants, see sub-indexes under _Authors_, _Birds_, _Mammals_ and +_Plants_. + + + Acquired characters, _see_ Characters + + Affinities and classification, 35 + + America, fossils, 177 + + Analogy, resemblance by, 36, 82, 199, 205, 211 + + Animals, marine, preservation of as fossils, 25, 139, 141; + --marine distribution, 155, 196 + + Australia, fossils, 177 + + AUTHORS, NAMES OF:--Ackerman on hybrids, 11; + Bakewell, 9, 91; + Bateson, W., xxix, 69 _n._, 217; + Bellinghausen, 124; + Boitard and Corbié, 106 _n._; + Brougham, Lord, 17, 117; + Brown, R., 233; + Buckland on fossils, 24, 137, 145 _n._; + Buffon on woodpecker, 6; + Bunbury (_Sir_ H.), rules for selection, 67; + Butler, S., 116 _n._; + d'Archiac, 146 _n._; + Darwin, C., origin of his evolutionary views, xi-xv; + --on Forbes' theory, 30; + --his _Journal of Researches_ quoted, 67 _n._, 168 _n._; + --his _Cross-and Self-Fertilisation_, 69 _n._, 103 _n._; + --on crossing Chinese and common goose, 72 _n._; + Darwin, Mrs, letter to, xxvi; + Darwin, F., on Knight's Law, 70 _n._; + Darwin, R. W., fact supplied by, 42 _n._, 223; + Darwin and Wallace, joint paper by, xxiv, 87 _n._; + De Candolle, 7, 47, 87, 204, 238; + D'Orbigny, 124, 179 _n._; + Ehrenberg, 146 _n._; + Ewart on telegony, 108 _n._; + Falconer, 167; + Forbes, E., xxvii, 30, 146 _n._, 163 _n._, 165 _n._; + Gadow, Dr, xxix; + Gärtner, 98, 107; + Goebel on Knight's Law, 70 _n._; + Gould on distribution, 156; + Gray, Asa, letter to, publication of in Linnean paper explained, xxiv; + Henslow, G., on evolution without selection, 63 _n._; + Henslow, J. S., xxvii; + Herbert on hybrids, 12, 98; + --sterility of crocus, 99 _n._; + Hering, 116 _n._; + Hogg, 115 _n._; + Holland, Dr, 223; + Hooker, J. D., xxvii, xxviii, 153 _n._; + --on Insular Floras, 161, 164, 167; + Huber, P., 118; + Hudson on woodpecker, 131 _n._; + Humboldt, 71, 166; + Hunter, W., 114; + Hutton, 27, 138; + Huxley, 134 _n._; + --on Darwin, xi, xii, xiv; + --on Darwin's Essay of 1844, xxviii, 235; + Judd, xi, xiii, xxix, 28, 141 _n._; + Knight, A., 3 _n._, 65, 114; + --on Domestication, 77; + Knight-Darwin Law, 70 _n._; + Kölreuter, 12, 97, 98, 104, 232; + Lamarck, 42 _n._, 47, 82, 146, 200; + --reasons for his belief in mutability, 197; + Lindley, 101; + Linnean Society, joint paper, _see_ Darwin and Wallace; + Linnæus on sterility of Alpine plants, 101; + --on generic characters, 201; + Lonsdale, 145 _n._; + Lyell, xxvii, 134 _n._, 138, 141 and _n._, 146 _n._, 159, 171, 173, + 178; + --his doctrine carried to an extreme, 26; + --his geological metaphor, 27 _n._, 141; + --his uniformitarianism, 53 _n._; + --his views on imperfection of geological record, 27; + Macculloch, 124 _n._; + Macleay, W. S., 202; + Magendie, 117; + Malthus, xv, 7, 88, 90; + Marr, Dr, xxix; + Marshall, 65; + --on sheep and cattle, 78 and _n._; + --on horns of cattle, 207; + Mivart, criticisms, 128 _n._; + Mozart as a child, his skill on the piano compared to instinct, + 19 _n._; + Müller on consensual movements, 113; + --on variation under uniform conditions, (2), 62; + --on recapitulation theory, 219; + Murchison, 145 _n._; + Newton, Alfred, 132 _n._; + Owen, R., xxvii, 219; + Pallas, 68, 69; + Pennant, 93 _n._; + Pliny on selection, 67; + Poeppig, 113 _n._; + Prain, Col., xxix; + Rengger, sterility, 100; + Richardson, 132 _n._; + Rutherford, H. W., xxix; + St Hilaire on races of dogs, 106; + --on sterility of tame and domestic animals, 12, 100; + Smith, Jordan, 140; + Sprengel, 233; + Stapf, Dr, xxix; + Strickland, xxvii; + Suchetet, 97 _n._; + Thiselton-Dyer, Sir W., xxix, 167; + Wallace, xxiv, xxix, 30, 170 _n._; + Waterhouse, 125, 126; + Western, Lord, 9, 65, 91; + Whewell, xxviii, 200; + Woodward, H. B., 145 _n._; + Wrangel, 119 _n._; + Zacharias, Darwin's letter to, xv + + + Barriers and distribution, 30, 154, 157, 178 + + Bees, 113, 117; + combs of Hive-bee, 19, 121, 125, 126 + + Beetles, abortive wings of, 45 + + BIRDS, transporting seeds, 169; + feeding young with food different to their own, 19, 126; + migration, 123, 124; + nests, 120, 121, 122, 126; + of Galapagos, 19, 159; + rapid increase, 88; + song, 117 + + BIRDS, NAMES OF:--Apteryx, 45, 236; + Duck, 46, 61, 65, 128, 224 _n._; + Fowl, domestic, 59, 82 _n._, 97, 113, 114, 217; + Goose, 72; + --periodic habit, 124 _n._; + Grouse, hybridised, 97, 102; + Guinea-fowl, 79; + Hawk, sterility, 100; + --periodic habit, 124; + Opetiorynchus, 83; + Orpheus, 31; + Ostrich, distribution of, 158; + Owl, white barn, 82; + Partridge, infertility of, 102; + Peacock, 79, 97, 102; + Penguin, 128 _n._, 237; + Petrel, 128 _n._; + Pheasant, 97, 102; + Pigeon, 66, 82, 110 _n._, 113, 114, 116, 117, 129, 135; + _see_ Wood-pigeon; + Rhea, 158; + Robins, increase in numbers, 88, 90; + Rock-thrush of Guiana, 93; + Swan, species of, 105; + Tailor-bird, 18, 118; + Turkey, Australian bush-turkey, 121 _n._, 122; + Tyrannus, 31; + Water-ouzel, 18 _n._, 120; + Woodcock, loss of migratory instinct, 120; + Woodpecker, 6, 16, 128 _n._, 148; + --in treeless lands, 16, 131; + Wood-pigeon, 122; + Wren, gold-crested, 120; + --willow, 105, 148 + + Breeds, domestic, parentage of, 71 + + Brothers, death of by same peculiar disease in old age, 42 _n._, + 44 _n._, 223 + + Bud variation, 58; + _see_ Sports + + Butterfly, cabbage, 127 + + + Catastrophes, geological, 145, 147 + + Caterpillars, food, 126, 127 + + Characters, acquired, inheritance of, 1, 57, 60, 225; + --congenital, 60; + --fixed by breeding, 61; + --mental, variation in, 17, 112, 119; + --running through whole groups, 106; + --useless for classification, 199 + + Cirripedes, 201, 229 + + Classification, natural system of, 35, 199, 206, 208; + --by any constant character, 201; + --relation of, to geography, 202; + --a law that members of two distinct groups resemble each other not + specifically but generally, 203, 212; + --of domestic races, 204; + --rarity and extinction in relation to, 210 + + Compensation, law of, 106 + + Conditions, direct, action of, 1, 57 _n._, 62, 65; + --change of, analogous to crossing, 15, 77 _n._, 105; + --accumulated effects of, 60, 78; + --affecting reproduction, 1, 4, 78, 99; + --and geographical distribution, 152 + + Continent originating as archipelago, bearing of on distribution, 189 + + Cordillera, as channel of migration, 34 _n._, 191 + + Correlation, 76 + + Creation, centres of, 168, 192 + + Crocodile, 146 + + _Cross-and Self-Fertilisation_, early statement of principles of, 15, + 69 _n._, 103 _n._ + + Crossing, swamping effect of, 2, 69, 96; + --of bisexual animals and hermaphrodite plants, 2; + --analogous to change in conditions, 3, 15, 69; + --in relation to breeds, 68; + --in plants, adaptations for, 70 + + + Death, feigned by insects, 123 + + Difficulties, on theory of evolution, 15, 121, 128, 134 + + Disease, hereditary, 43 _n._, 58, 222 + + Distribution, geographical, 29, 31, 151, 174, 177; + --in space and time, subject to same laws, 155; + --occasional means of (seeds, eggs, &c.), 169 + + Disuse, inherited effects of, 46, 57 + + Divergence, principle of, xxv, 37 _n._, 145 _n._, 208 _n._ + + Domestication, variation under, 57, 62; + --accumulated effects of, 75, 78; + --analysis of effects of, 76, 83 + + + Ears, drooping, 236 + + Elevation, geological, favouring birth of new species, 32, 34 _n._, + 35 _n._, 185-189; + --alternating with subsidence, importance of for evolution, 33, 190; + --bad for preservation of fossils, 194 + + Embryo, branchial arches of, 42, 220; + --absence of special adaptation in, 42, 44 _n._, 220, 228; + --less variable than parent, hence importance of embryology for + classification, 44 _n._, 229; + --alike in all vertebrates, 42, 218; + --occasionally more complicated than adult, 219, 227 + + Embryology, 42, 218; + its value in classification, 45, 200; + law of inheritance at corresponding ages, 44 _n._, 224; + young of very distinct breeds closely similar, 44 _n._, 225 + + Ephemera, selection falls on larva, 87 _n._ + + Epizoa, 219 + + Essay of 1842, question as to date of, xvi; + description of MS., XX; + compared with the _Origin_, xxii + + Essay of 1844, writing of, xvi; + compared with that of 1842 and with the _Origin_, xxii + + Evolution, theory of, why do we tend to reject it, 248 + + Expression, inheritance of, 114 + + Extinction, 23, 147, 192; + locally sudden, 145; + continuous with rarity, 147, 198 + + Extinction and rarity, 198 + + Eye, 111 _n._, 128, 129, 130 + + + Faculty, in relation to instinct, 123 + + Faunas, alpine, 30, 170, 188; + of Galapagos, 31 _n._, 82, 159; + insular-alpine very peculiar, 188; + insular, 159, 160 + + Fauna and flora, of islands related to nearest land, 187 + + Fear of man, inherited, 17, 113 + + Fertility, interracial, 103, 104 + + Fish, colours of, 130, 131; + eggs of carried by water-beetle, 169; + flying, 128 _n._; + --transported by whirlwind, 169 + + Floras, alpine, 162; + of oceanic islands, 162; + alpine, related to surrounding lowlands, 163; + alpine, identity of on distant mountains, 163; + alpine resembling arctic, 164; + arctic relation to alpine, 164 + + Flower, morphology of, 39, 216; + degenerate under domestication if neglected, 58; + changed by selection, 66 + + Fly, causing extinction, 149 + + Flying, evolution of, 16, 131 + + Food, causing variations, 1, 58, 77, 78 + + Formation (geological) evidence from Tertiary system, 144; + (geological), groups of species appear suddenly in Secondary, 26, 144; + Palæozoic, if contemporary with beginning of life, author's theory + false, 138 + + Formations, most ancient escape denudation in conditions unfavourable to + life, 25, 139 + + Forms, transitional, 24, 35 _n._, 136, 142, 194; + on rising land, 196; + indirectly intermediate, 24, 135 + + Fossils, Silurian, not those which first existed in the world, 26, 138; + falling into or between existing groups and indirectly intermediate, + 24, 137; + conditions favourable to preservation, not favourable to existence + of much life, 25, 139, 141 + + Fruit, attractive to animals, 130 + + + Galapagos Islands and Darwin's views, xiv; + physical character of in relation to fauna, 31 _n._, 159 + + Galapagos Islands, fauna, 31 _n._, 82 + + Gasteropods, embryology, 218 + + Genera, crosses between, 11, 97; + wide ranging, has wide ranging species, 155; + origin of, 209 + + Geography, in relation to geology, 31 _n._, 174, 177 + + Geographical distribution, _see_ Distribution + + Geology, as producing changed conditions, 4; + evidence from, 22, 133; + "destroys geography," 31 _n._ + + Glacial period, effect of on distribution of alpine and arctic plants, + 165 + + + Habit in relation to instinct, 17, 113, 115, 116 + + Habits in animals taught by parent, 18 + + Heredity, _see_ Inheritance + + Homology of limbs, 38, 214 + + Homology, serial, 39, 215 + + Hybrid, fowls and grouse, 11; + fowl and peacock, 97; + pheasant and grouse, 97; + Azalea and Rhododendron, 97 + + Hybrids, gradation in sterility of, 11, 72, 97; + sterility of not reciprocal, 97; + variability of, 78; + compared and contrasted with mongrel, 107 + + + Individual, meaning of term, 58 + + Inheritance of acquired characters, _see_ Character + + Inheritance, delayed or latent, 43, 44 _n._, 223; + of character at a time of life corresponding to that at which it + first appeared, 43, 44 _n._, 223; + germinal, 44, 222, 223 + + Insect, adapted to fertilise flowers, 87; + feigning death, 123; + metamorphosis, 129; + variation in larvæ, 223 + + Instinct, variation in, 17, 112; + and faculty, 18, 123; + guided by reason, 18, 19, 118; + migratory, 19; + migratory, loss of by woodcocks, 120; + migratory, origin of, 125; + due to germinal variation rather than habit, 116; + requiring education for perfection, 117; + characterised by ignorance of end: _e.g._ butterflies laying eggs, + 17, 118; + butterflies laying eggs on proper plant, 118, 127; + instinct, natural selection applicable to, 19, 120 + + Instinct, for finding the way, 124; + periodic, _i.e._ for lapse of time, 124; + comb-making of bee, 125; + birds feeding young, 19, 126; + nest-building, gradation in, 18, 120, 121, 122; + instincts, complex, difficulty in believing in their evolution, 20, 121 + + Intermediate forms, _see_ Forms + + Island, _see_ Elevation, Fauna, Flora + + Island, upheaved and gradually colonised, 184 + + Islands, nurseries of new species, 33, 35 _n._, 185, 189 + + Isolation, 32, 34 _n._, 64, 95, 183, 184 + + + Lepidosiren, 140 _n._, 212 + + Limbs, vertebrate, of one type, 38, 216 + + + MAMMALS, arctic, transported by icebergs, 170; + distribution, 151, 152, 193; + distribution of, ruled by barriers, 154; + introduced by man on islands, 172; + not found on oceanic islands, 172; + relations in time and space, similarity of, 176; + of Tertiary period, relation of to existing forms in same region, 174 + + MAMMALS, NAMES OF:-- + Antelope, 148; + Armadillo, 174; + Ass, 79, 107, 172; + Bat, 38, 123, 128 _n._, 131, 132, 214; + Bear, sterile in captivity, 100; + --whale-like habit, 128 _n._; + Bizcacha, 168, 203, 212; + Bull, mammæ of, 232; + Carnivora, law of compensation in, 106; + Cats, run wild at Ascension, 172; + --tailless, 60; + Cattle, horns of, 75, 207; + --increase in S. America, 90; + --Indian, 205; + --Niata, 61, 73; + --suffering in parturition from too large calves, 75; + Cheetah, sterility of, 100 and _n._; + Chironectes, 199; + Cow, abortive mammæ, 232; + Ctenomys, _see_ Tuco-tuco; + Dog, 106, 114; + --in Cuba, 113 and _n._; + --mongrel breed in oceanic islands, 70; + --difference in size a bar to crossing, 97; + --domestic, parentage of, 71, 72, 73; + --drooping ears, 236; + --effects of selection, 66; + --inter-fertile, 14; + --long-legged breed produced to catch hares, 9, 10, 91, 92; + --of savages, 67; + --races of resembling genera, 106, 204; + --Australian, change of colour in, 61; + --bloodhound, Cuban, 204; + --bull-dog, 113; + --foxhound, 114, 116; + --greyhound and bull-dog, young of resembling each other, 43, + 44 _n._, 225; + --pointer, 114, 115, 116, 117, 118; + --retriever, 118 _n._; + --setter, 114; + --shepherd-dog and harrier crossed, instinct of, 118, 119; + --tailless, 60; + --turnspit, 66; + Echidna, 82 _n._; + Edentata, fossil and living in S. America, 174; + Elephant, sterility of, 12, 100; + Elk, 125; + Ferret, fertility of, 12, 102; + Fox, 82, 173, 181; + Galeopithecus, 131 _n._; + Giraffe, fossil, 177; + --tail, 128 _n._; + Goat, run wild at Tahiti, 172; + Guanaco, 175; + Guinea-pig, 69; + Hare, S. American, 158 _n._; + Hedgehog, 82 _n._; + Horse, 67, 113, 115, 148, 149; + --checks to increase, 148, 149; + --increase in S. America, 90; + --malconformations and lameness inherited, 58; + --parentage, 71, 72; + --stripes on, 107; + --young of cart-horse and racehorse resembling each other, 43; + Hyena, fossil, 177; + Jaguar, catching fish, 132; + Lemur, flying, 131 _n._; + Macrauchenia, 137; + Marsupials, fossil in Europe, 175 _n._, 177; + --pouch bones, 232, 237; + Mastodon, 177; + Mouse, 153, 155; + --enormous rate of increase, 89, 90; + Mule, occasionally breeding, 97, 102; + Musk-deer, fossil, 177; + _Mustela vison_, 128 _n._, 132 _n._; + Mydas, 170; + Mydaus, 170; + Nutria, _see_ Otter; + Otter, 131, 132, 170; + --marsupial, 199, 205, 211; + Pachydermata, 137; + Phascolomys, 203, 212; + Pig, 115, 217; + --in oceanic islands, 70; + --run wild at St Helena, 172; + Pole-cat, aquatic, 128 _n._, 132 _n._; + Porpoise, paddle of, 38, 214; + Rabbit, 74, 113, 236; + Rat, Norway, 153; + Reindeer, 125; + Rhinoceros, 148; + --abortive teeth of, 45, 231; + --three oriental species of, 48, 249; + Ruminantia, 137 and _n._; + Seal, 93 _n._, 131; + Sheep, 68, 78, 117, 205; + --Ancon variety, 59, 66, 73; + --inherited habit of returning home to lamb, 115; + --transandantes of Spain, their migratory instinct, 114, 117, + 124 _n._; + Squirrel, flying, 131; + Tapir, 135, 136; + Tuco-tuco, blindness of, 46, 236; + Whale, rudimentary teeth, 45, 229; + Wolf, 71, 72, 82; + Yak, 72 + + Metamorphosis, literal not metaphorical, 41, 217 + + Metamorphosis, _e.g._ leaves into petals, 215 + + Migrants to new land, struggle among, 33, 185 + + Migration, taking the place of variation, 188 + + Monstrosities, as starting-points of breeds, 49, 59; + their relation to rudimentary organs, 46, 234 + + Morphology, 38, 215; + terminology of, no longer metaphorically used, 41, 217 + + Mutation, _see_ Sports + + + Natural selection, _see_ Selection + + Nest, bird's, _see_ Instinct + + + Ocean, depth of, and fossils, 25, 195 + + Organisms, gradual introduction of new, 23, 144; + extinct related to, existing in the same manner as representative + existing ones to each other, 33, 192; + introduced, beating indigenes, 153; + dependent on other organisms rather than on physical surroundings, 185; + graduated complexity in the great classes, 227; + immature, how subject to natural selection, 42, 220, 228; + all descended from a few parent-forms, 52, 252 + + Organs, perfect, objection to their evolution, 15, 128; + distinct in adult life, indistinguishable in embryo, 42, 218; + rudimentary, 45, 231, 232, 233; + rudimentary, compared to monstrosities, 46, 234; + rudimentary, caused by disuse, 46, 235; + rudimentary, adapted to new ends, 47, 237 + + Orthogenesis, 241 _n._ + + Oscillation of level in relation to continents, 33, 34 _n._, 189 + + + Pallas, on parentage of domestic animals, 71 + + Pampas, imaginary case of farmer on, 32, 184 + + Perfection, no inherent tendency towards, 227 + + Plants, _see also_ Flora; + fertilisation, 70; + migration of, to arctic and antarctic regions, 167; + alpine and arctic, migration of, 31, 166; + alpine, characters common to, 162; + alpine, sterility of, 13, 101 + + PLANTS, NAMES OF:--Ægilops, 58 _n._; + Artichoke (Jerusalem), 79; + Ash, weeping, seeds of, 61; + Asparagus, 79; + Azalea, 13, 59, 97; + Cabbage, 109, 135, 204; + Calceolaria, 11, 99; + Cardoon, 153; + Carrot, variation of, 58 _n._; + Chrysanthemum, 59; + Crinum, 11, 99; + Crocus, 96, 99 _n._; + Cucubalus, crossing, 232; + Dahlia, 21, 59, 63, 69, 74, 110; + Foxglove, 82; + Gentian, colour of flower, 107 _n._; + Geranium, 102; + Gladiolus, crossed, ancestry of, 11; + Grass, abortive flowers, 233; + Heath, sterility, 96; + Hyacinth, colours of, 106; + --feather-hyacinth, 229; + Juniperus, hybridised, 97; + Laburnum, peculiar hybrid, 108; + Lilac, sterility of, 13, 100; + Marigold, style of, 47, 233, 237; + Mistletoe, 6, 86, 87, 90 _n._; + Nectarines on peach trees, 59; + Oxalis, colour of flowers of, 107 _n._; + Phaseolus, cultivated form suffers from frost, 109; + Pine-apple, 207; + Poppy, Mexican, 154; + Potato, 69, 74, 110; + Rhododendron, 97, 99; + Rose, moss, 59; + --Scotch, 69; + Seakale, 79; + Sweet-william, 59; + Syringa, persica and chinensis, _see_ Lilac; + Teazle, 129; + Thuja, hybridised, 97; + Tulips, "breaking" of, 58; + Turnip, Swedish and common, 205; + Vine, peculiar hybrid, 108; + Yew, weeping, seeds of, 61 + + Plasticity, produced by domestication, 1, 63 + + Plesiosaurus, loss of unity of type in, 41, 217 + + Pteropods, embryology, 218 + + + Quadrupeds, extinction of large, 147 + + Quinary System, 202 + + + Race, the word used as equivalent to variety, 94 + + Races, domestic, classification of, 204 + + Rarity, 28, 148; + and extinction, 28, 149, 210 + + Recapitulation theory, 42, 219, 230, 239 + + Record, geological, imperfection of, 26, 140 + + Regions, geographical, of the world, 29, 152, 174; + formerly less distinct as judged by fossils, 177 + + Resemblance, analogical, 36, 199 + + Reversion, 3, 64, 69, 74 + + "Roguing," 65 + + Rudimentary organs, _see_ Organs + + + Savages, domestic animals of, 67, 68, 96 + + Selection, human, 3, 63; + references to the practice of, in past times, 67; + great effect produced by, 3, 91; + necessary for the formation of breeds, 64; + methodical, effects of, 3, 65; + unconscious, 3, 67 + + Selection, natural, xvi, 7, 87; + natural compared to human, 85, 94, 224; + of instincts, 19, 120; + difficulty of believing, 15, 121, 128 + + Selection, sexual, two types of, 10, 92 + + Silk-worms, variation in larval state, 44 _n._, 223 + + Skull, morphology of, 39, 215 + + Species, representative, seen in going from N. to S. in a continent, + 31 _n._, 156; + representative in archipelagoes, 187; + wide-ranging, 34 _n._, 146; + and varieties, difficulty of distinguishing, 4, 81, 197; + sterility of crosses between, supposed to be criterion, 11, 134; + gradual appearance and disappearance of, 23, 144; + survival of a few among many extinct, 146 + + Species, not created more than once, 168, 171, 191; + evolution of, compared to birth of individuals, 150, 198, 253; + small number in New Zealand as compared to the Cape, 171, 191; + persistence of, unchanged, 192, 199 + + Sports, 1, 58, 59, 64, 74, 95, 129, 186, 206, 224 + + Sterility, due to captivity, 12, 77 _n._, 100; + of various plants, 13, 101; + of species when crossed, 11, 23, 96, 99, 103; + produced by conditions, compared to sterility due to crossing, 101, 102 + + Struggle for life, 7, 91, 92, 148, 241 + + Subsidence, importance of, in relation to fossils, 25, 35 _n._, 195; + of continent leading to isolation of organisms, 190; + not favourable to birth of new species, 196 + + Swimming bladder, 16, 129 + + System, natural, is genealogical, 36, 208 + + + Telegony, 108 + + Tibia and fibula, 48, 137 + + Time, enormous lapse of, in geological epochs, 25, 140 + + Tortoise, 146 + + Transitional forms, _see_ Forms + + Trigonia, 147 _n._, 199 + + Tree-frogs in treeless regions, 131 + + Type, unity of, 38, 214; + uniformity of, lost in Plesiosaurus, 217; + persistence of, in continents, 158, 178 + + + Uniformitarian views of Lyell, bearing on evolution, 249 + + Use, inherited effects of, _see_ Characters, acquired + + + Variability, as specific character, 83; + produced by change and also by crossing, 105 + + Variation, by Sports, _see_ Sports; + under domestication, 1, 57, 63, 78; + due to causes acting on reproductive system, _see_ Variation, germinal; + --germinal, 2, 43, 62, 222; + individual, 57 _n._; + causes of, 1, 4, 57, 61; + due to crossing, 68, 69; + limits of, 74, 75, 82, 109; + small in state of nature, 4, 59 _n._, 81, 83; + results of _without_ selection, 84; + --minute, value of, 91; + analogous in species of same genus, 107; + of mental attributes, 17, 112; + in mature life, 59, 224, 225 + + Varieties, minute, in birds, 82; + resemblance of to species, 81 _n._, 82, 105 + + Vertebrate skull, morphology of, 215 + + + Wildness, hereditary, 113, 119 + + +CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS + + + + + +--------------------------------------------------------------+ + | Transcriber's Notes & Errata | + | | + | Inline transcriber's notes are enclosed in curly brackets. | + | | + | Footnote anchors and labels are enclosed in curly brackets. | + | | + | The footnotes have been renumbered consecutively. | + | | + | Because of this, the changed footnote numbers are appended | + | in curly brackets to the internal cross-references. | + | | + | Superscript letters are denoted by a preceding caret e.g., | + | d^o | + | | + | 'oe' ligatures have been rendered as separate letters. | + | | + | The following typographical errors have been corrected. | + | | + | |simplication |simplification | | + | |care |case | | + | |apparant |apparent | | + | | + | The following words were found in both hyphenated and | + | unhyphenated forms. The figures in parentheses are the | + | number of instances of each. | + | | + | |after-thought (1) |afterthought (2) | | + | |blood-hound (2) |bloodhound (1) | | + | |bull-dog (7) |bulldog (2) | | + | |co-descendants (1) |codescendants (1) | | + | |feather-hyacinth (2) |feather hyacinth (1) | | + | |grey-hound (2) |greyhound (10) | | + | |high-lands (3) |highlands (2) | | + | |long-legged (2) |long legged (1) | | + | |race-horse (2) |racehorse (4) | | + | |shepherd-dog (3) |shepherd dog (1) | | + | |sub-divisions (3) |subdivisions (4) | | + | |table-land (2) |tableland (1) | | + | | + +--------------------------------------------------------------+ + + + + + + +End of the Project Gutenberg EBook of The Foundations of the Origin of +Species, by Charles Darwin + +*** END OF THIS PROJECT GUTENBERG EBOOK FOUNDATIONS ORIGIN OF SPECIES *** + +***** This file should be named 22728-8.txt or 22728-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/2/7/2/22728/ + +Produced by Geetu Melwani, David Clarke, LN Yaddanapudi +and the Online Distributed Proofreading Team at +http://www.pgdp.net (This file was produced from images +generously made available by The Internet Archive/Canadian +Libraries) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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