RECORD: Darwin, C. R. 1876.10.12. After reading Moritz Wagner in Ausland. CUL-DAR45.30. Edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed by Christine Chua and edited by John van Wyhe 10.2022. RN1
NOTE: See record in the Darwin Online manuscript catalogue, enter its Identifier here. Reproduced with permission of the Syndics of Cambridge University Library William Huxley Darwin. The volume CUL-DAR45 contains notes for Natural selection chap. 4 'Variation under nature'.
See Life and letters, vol. 3, pp. 158-9: "The following letter bears on the same subject. It refers to Professor M. Wagner's Essay, published in Das Ausland, May 31, 1875:
C. Darwin to Moritz Wagner.
Down, October 13, 1876.
DEAR SIR,—I have now finished reading your essays, which have interested me in a very high degree, notwithstanding that I differ much from you on various points. For instance, several considerations make me doubt whether species are much more variable at one period than at another, except through the agency of changed conditions. I wish, however, that I could believe in this doctrine, as it removes many difficulties. But my strongest objection to your theory is that it does not explain the manifold adaptations in structure in every organic being—for instance in a Picus for climbing trees and catching insects—or in a Strix for catching animals at night, and so on ad infinitum. No theory is in the least satisfactory to me unless it clearly explains such adaptations. I think that you misunderstand my views on isolation. I believe that all the individuals of a species can be slowly modified within the same district, in nearly the same manner as man effects by what I have called the process of unconscious selection. . . . I do not believe that one species will give birth to two or more new species, as long as they are mingled together within the same district. Nevertheless I cannot doubt that many new species have been simultaneously developed within the same large continental area; and in my 'Origin of Species' I endeavoured to explain how two new species might be developed, although they met and intermingled on the borders of their range. It would have been a strange fact if I had overlooked the importance of isolation, seeing that it was such cases as that of the Galapagos Archipelago, which chiefly led me to study the origin of species. In my opinion the greatest error which I have committed, has been not allowing sufficient weight to the direct action of the environment, i.e. food, climate, &c., independently of natural selection. Modifications thus caused, which are neither of advantage nor disadvantage to the modified organism, would be especially favoured, as I can now see chiefly through your observations, by isolation in a small area, where only a few individuals lived under nearly uniform conditions.
When I wrote the 'Origin,' and for some years afterwards, I could find little good evidence of the direct action of the environment; now there is a large body of evidence, and your case of the Saturnia is one of the most remarkable of which I have heard. Although we differ so greatly, I hope that you will permit me to express my respect for your long-continued and successful labours in the good cause of natural science.
I remain, dear Sir, yours very faithfully,
CHARLES DARWIN."
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Keep.
Oct 12 1876 After reading Moritz Wagner in Ausland. (extract from my letter)
I can now see, thanks chiefly to your discussion, that modification due, as I believe, to the direct action of changed conditions, (& not influenced by N. selection would be far more easily effected in a small completely isolated area, having consequently nearly uniform conditions, than in an open area, where probably intercrossing might would tend to prevent any such modification; for in these cases as the modifications are not advantageous to the unmodified form, there wd be no suppression through natural s. of such forms.— Hence frequency of vicarious or representative species on isolated isld. —
[in margin:] But then comes the insoluble difficulty on conditions sufficiently different —as in Sandwich Isld shells — seeing how widely many species range — Peach buds & sports
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Modification thus caused when are neither of no [illeg] or [illeg] to the [illeg] the [illeg] would be especially favoured, as I can now see, chiefly owing to your observation, by isolation in a small area, when only a few intermediates lived under under nearly uniform uniform conditions.
Citation: John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
File last updated 17 October, 2022