RECORD: Darwin, C. R. [1857]. Draft fragment of Natural selection, chapter IX Hybridism. CUL-DAR77.112r. Edited by John van Wyhe (Darwin Online,

REVISION HISTORY: Transcribed by Christine Chua and edited by John van Wyhe 2.2023. RN1

NOTE: See record in the Darwin Online manuscript catalogue, enter its Identifier here. Reproduced with permission of the Syndics of Cambridge University Library and William Huxley Darwin. The volumes CUL-DAR 76-79 contain material for Darwin's book Cross and self fertilisation (1876).

Introduction by John van Wyhe

This manuscript fragment was originally catalogued as possibly part of the draft of Descent of man. However, the content indicates otherwise. For example, the only 'books' in which Darwin used the phrase "perfect fertility" are his unfinished Natural selection and then in Origin of species. The fragment is now in a folder of materials for Darwin's 1876 book Cross and self fertilisation because Darwin wrote a draft table for that book on the verso.

Darwin is here discussing "perfect fertility" vs. "sterility", i.e. if two crossed forms that were not the same species or variety will always have fertile or sterile offspring. This was considered by many naturalists of the time to delineate species. Darwin argued instead that the facts of crossed animals and plants showed a great deal of complexity and that there was no law of nature that meant species are never able to cross and produce fertile hybrids. The phrase "human beings" is very curious, Darwin used this only a handful of times in his publications, as can be discovered only in Darwin Online.

This fragment is most similar to Natural selection, chapter IX Hybridism, p. 444:

"Secondly, those many naturalists who believe that most of our domestic animals are descended each from several aboriginal species, & who, therefore, must believe either that perfect fertility between species when crossed is very far from uncommon in nature, or is a quality readily acquired under domestication, will feel little surprise at the fertility of varieties when crossed. On the view, indeed, of sterility being commonly lost between species when under domestication, it would be most strange if sterility were, also, to supervene between varieties under raised domesticcation."


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nor ought he to lay too much stress on their perfect on their perfect fertility, as if established, if this were established as a criterion of specific distinction agreement, even if fully established; for human beings are exposed to nearly the same fluctuating conditions of life as are his with his own domesticated animals, & we have seen in previous chapters that there is every reason to believe that the tendency to in two (wild) natural forms to be sterile when crossed, is eliminated by under domestication. If one naturalist should now

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Citation: John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online. (

File last updated 30 May, 2023