Article,
Darwinian Evolution by Mutations.
Eugenics Review, (1922)
Abstract
(from the text)
If we suppose then that a utation has occurred, and an entirely new gene is present in a single individual of population consisting of some thousands of millions, the hitsory of its survival may be broadly divided into two periods. In the first preiod its survival or extinction is due mainly to chance; in the second perios mainly to the general advantage or disadvantage in the struggle for existence which the new allelomorph confers, on the average and in combination with the existing currency of genetic types, as compared with the alternative allelomorph which it displaces.
(goes on to describe branching process calculation)
