tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I
had always been much struck by such adaptations, and until these could
be explained it seemed to me almost useless to endeavour to prove by
indirect evidence that species have been modified.

After my return to England 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. My
first note-book was opened in July 1837. 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
enquiries, 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. But how selection could be applied to organisms
living in a state of nature remained for some time a mystery to me.

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; but I
was so anxious to avoid prejudice, that I determined not for some time
to write even the briefest sketch of it. In June 1842 I first allowed
myself the satisfaction of writing a very brief abstract of my theory in
pencil in 35 pages; and this was enlarged during the summer of 1844 into
one of 230 pages, which I had fairly copied out and still possess.

But at that time I overlooked one problem of great importance; and it is
astonishing to me, except on the principle of Columbus and his egg,
how I could have overlooked it and its solution. This problem is the
tendency in organic beings descended from the same stock to diverge in
character as they become modified. That th