Geographic isolation in Darwin's thinking / Frank J. Sulloway.
Abstract:
"Here I shall consider three general questions concerning Darwin's changing views on isolation as an evolutionary factor. First, how, and in what ways, did the evidence of geographical distribution inspire his early (1837-44) evolutionary thinking following his return from the voyage of the Beagle? Second, why did Darwin, after writing the Essay of 1844, come to believe that species might arise sympatrically (i.e. locally ...)? And third, to what extent did Darwin succeed in reconciling his views after 1859 with the criticisms presented on this topic by the German naturalist and explorer Moritz Wagner (1868)?"
Studies in history of biology Vol. 3 (1979), p. 23-65