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184 5 Biological Species and Speciation—Mayr’s First Synthesis
Based on his background as a naturalist-systematist in Russia during the 1920s,
Dobzhansky (1937) produced a first synthesis between the views of the naturalistssystematists
and the geneticists. The other “architects” of the evolutionary synthesis
widened the path which Dobzhansky had blazed–Ernst Mayr (1942e, species
and speciation), Julian Huxley (1942, general evolution), George Gaylord Simpson
(1944, paleontology), Bernhard Rensch (1947, macroevolution), and Ledyard
Stebbins (1950, botany). 1 Because most mutations are very small, Th. Dobzhansky
(1937) and E. Mayr (1942e) were able to demonstrate that there was no conflict
between the results of the population geneticists and those of the systematists who
had discussed gradual differentiation of populations and geographical speciation
for a long time (although, until the early 1930s, based largely on the assumption
of the Lamarckian inheritance of acquired characters). The original Darwinian
paradigm of variation and selection was confirmed during the evolutionary synthesis.
Between 1937 and 1950, the “architects” combined in synthetic publications
the results of their own research with those of population genetics. The process
of this unification of evolutionary biology is referred to as the evolutionary synthesis
and the product as the synthetic evolutionary theory (Synthetic Darwinism,
Junker 2004). Mayr’s specific contributions to the evolutionary synthesis were his
analyses of the nature of biological species and of the origin of organic diversity
(speciation) making “the species problem” a central concern of evolutionary
biology. Speciation and other processes in evolution are not simply a matter of
genes but of populations and of species. His 1942 volume explained a large part of
evolutionary theory well-known to naturalists-systematists but not to geneticists,
particularly species and speciation and the role of geography in the evolution of
populations and species. He discussed populations at various intermediate stages
between variously differentiated subspecies and variously differentiated biological
species in line with gradual Darwinian change. Mayr’s work demonstrated the
importance of taxonomic research for evolutionary theory.
At an international conference in Princeton, New Jersey, in January 1947 there
was general agreement among the participating geneticists and naturalists-systemists
on the nature of species, the gradualness of evolution, the importance of natural
selection, and the populational aspect of the gradual origin of species. A synthesis
indeed had taken place, but it goes without saying that, by present standards, this
synthesis was still incomplete. It did not include molecular evolution, comparative
genomics, evolutionary developmental biology or phylogenetics, i.e., the actual,
detailed history of life on Earth (Wilkins 2007). Some differences that remained
at that time included the problem of the target of selective demands which, for
the population geneticists, continued to be the gene, whereas the naturalistssystematists
insisted, as had Darwin, that it was the individual organism as a whole.
The individual either survives or it does not; it either reproduces successfully or it
1 It should be noted that the “Evolutionary Synthesis” was an international research program
to which also several other European biologists contributed, especially E. Baur,
N. Timoféeff-Ressovsky, and W. Zimmermann in Germany, S. Chetverikov and N. Dubinin
in the Soviet Union, G. Teissier in France, and A. Buzzati-Traverso in Italy (Mayr
1999a; Reif et al. 2000; Junker 2004); see p. 357.