The Foundations of the Origin of Species

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

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.

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