‘The evidence for evolution by natural selection’ shows that domestication and hybrid fertility provided evidence for evolution and against the fixity of species by experimental intervention. But it was Darwin's interpretation of the directly observable facts of wild nature that carried the day for evolution. The same explanation of evolution was as obvious in Darwin's treatment of classification. The idea of a tree-like arrangement of organisms was common currency before Darwin. Darwin's development of this metaphor in genealogical terms illustrating the relationship between the variation and extinction of organisms united by the bond of inheritance through time will serve to summarize the main conclusions of the Origin of Species.