Of this book, Darwin himself says: "I worked on true Baconian principles, and without any theory--collected facts on a wholesale scale, more especially with respect to domesticated productions, by printed inquiries, by conversation with skilful breeders and gardeners, and by extensive reading. When I see the list of books of all kinds which I read and abstracted, including whole series of Journals and Transactions, I am surprised at my industry. I soon perceived that selection was the keystone of man's success in making useful races of animals and plants....
"In October, 1838, that is, fifteen months after I had begun my systematic inquiry, I happened to read '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 favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The result of this would be the formation of new species.... But at that time I overlooked one problem of great importance.... This problem is the tendency in organic beings descended from the same stock to diverge in character as they become modified. That they have diverged greatly is obvious from the manner in which species of all kinds can be classed under genera, genera under families, families under sub-orders, and so forth.... The solution, as I believe, is that the modified offspring of all dominant and increasing forms tend to become adapted to many and highly diversified places in the economy of nature."
The book was written slowly, each chapter requiring at least three months. When the "Origin of Species"--which had reached its thirty-third thousand in 1888--was published, it created the most profound sensation throughout the thinking world. Heretofore, most men of science had believed that each species had been separately created by the Almighty,--that species were immutable, unchanging.
Mr. Darwin, by twenty years of study, proved to his own mind, and now to most of the world, that there has been a gradual evolution, through unnumbered ages, of one form of animal life from another. He said, "Probably all the organic beings which have ever lived on the earth have descended from some one primordial form, into which life was first breathed."