GEOGRAPHY AND ITS IMPLICATIONS

In 1845, Darwin wrote to Joseph Dalton Hooker predicting that he (Hooker) would soon be recognized as the first authority in Europe on “that grand subject, that almost key-stone of the laws of creation: Geographical Distribution.” Darwin had already included a substantial section on the topic in his “Essay ” of 1844 and would interact extensively with Hooker on the topic over the next decade and more. The Origin of Species itself contains two chapters on distribution, occupying sixty-four pages, or just over 13 percent of the text of the first edition. These two chapters would be modified on minor points in the subsequent editions, but would remain essentially intact, serving as one of the main lines of support for his theory. Since they include his discussion of the distribution of species on the Galápagos Islands, they represent a key link in the process by which the theory was developed and then presented to the public.

It has always been recognized that the study of how species are located around the globe, on both a small and a large scale, was a key line of evidence leading Darwin toward the theory of common descent. The idea that divergence from a common ancestor was generated by a process that adapted populations to changes in their local environments (physical or organic) would eventually serve as one of his most convincing arguments in favour of natural selection.