Biological Species and Speciation—Mayr’s First Synthesis

Abstract

Ernst Mayr’s early interests in evolution and genetics (pp. 26–29, 45) led to his decisive contributions to the modern synthesis of the late 1930s and 1940s, when a largely unified evolutionary theory emerged. Biological evolution comprises two components–adaptive development of populations during long geological periods (anagenesis, evolution as such) and multiplication of species during relatively short periods (speciation, cladogenesis). Evolution as such and the theory of common descent were accepted by biologists within a few years of the publication of the Origin in 1859 during the first Darwinian revolution. A synthesis of modern genetics and evolution as such was accomplished when, by 1932, the mathematical geneticists R.A. Fisher, J.B.S. Haldane and S. Wright had convincingly shown that small mutations and natural selection play themain roles in the gradual process of adaptive evolution of populations through time, thereby solving one of the two major problems of evolutionary biology, the problem of anagenesis, a historical accomplishment which Mayr (1999k, 2004a) called the “Fisherian synthesis.” During the so-called Evolutionary Synthesis of the period 1937–1950 (the second Darwinian revolution) the other main problems of evolutionary biology were solved or generally accepted (gradualism, speciation, and natural selection) and the processes of speciation were combined with those of adaptive evolution (Mayr 1993a). None of the mathematical geneticists had discussed the phenomenon of speciation or did so only superficially.