In October 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, 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.
Below is the famous passage from Darwin’s notebook where these ideas were first recorded:
[Sept] 28th. Even the energetic language of «Decandoelle» does not convey the warring of the species as inference from Malthus.— «increase of brutes, must be prevented soley by positive checks, excepting that famine may stop desire.—» in Nature production does not increase, whilst no checks prevail, but the positive check of famine & consequently death..
…—The final cause of all this wedging, must be to sort out proper structure, and adapt it to change.—to do that for form, which Malthus shows is the final effect by means however of volition of this populousness on the energy of man. One may say there is a force like a hundred thousand wedges trying [to] force every kind of adapted structure into the gaps in the economy of nature, or rather forming gaps by thrusting out weaker ones.
- Charles Darwin, The Autobiography of Charles Darwin 1809-1882 (London: Collins, 1958).
- Charles Darwin, Notebook D [Transmutation of species (1838.07.15-1838.10.02)] 134e-135e.