Page:Prolegomena to history- the relation of history to literature, philosophy, and science (IA prolegomentohist00teggiala).pdf/105

 questions of the origin of life, and addressed himself to the investigation of the changes that are to be observed between successive generations of plants and animals at the present time. "After my return to England," he wrote in his Autobiography, "it appeared to me that by following the example of Lyell in Geology, and by collecting all facts which bore in any way on the variation of animals and plants under domestication and nature, some light might perhaps be thrown on the whole subject." He assumed, as Hutton had done, that Nature was uniform in her ways of working, and that if the factors in the process of change now going on could be discovered they might with confidence be taken as applicable throughout the past. He assumed, in short, that things have come to be as they are through the continuous operation of processes that are now to be observed in nature.

Darwin found it impracticable to observe changes among animals living under natural conditions, and hence his investigations were largely concerned with "domesticated productions." He soon perceived that the keystone of man's success in making useful races of animals and plants was the selection exercised in breeding, that without the intelligent interference of the breeder there would be no new race. The problem then presented itself, and remained for some time a mystery to him, how selection could be applied to organisms living in a state of nature—in Weismann's words, "how what was purposive could conceivably be brought about without the intervention of a directing power." The next step he thus describes: "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