This paper analyzes the development of evolutionary theory in the period from 1918 to 1932. It argues that: (i) Fisher's work in 1918 constituted a not fully satisfactory reduction of biometry to Mendelism; (ii) there was a synthesis in the 1920s but that this synthesis was mainly one of classical genetics with population genetics, with Haldane's The Causes of Evolution being its founding document; (iii) the most important achievement of the models of theoretical population genetics was to show that natural (...) selection sufficed as a mechanism for evolution; and (iv) Haldane formulated a prospective evolutionary theory in the 1920s whereas Fisher and Wright formulated retrospective theories of evolutionary history. (shrink)