3 The New York Years (1931–1953)

Assistant Curator at the Museum of Natural History in Berlin 45
(St. Petersburg, 1868–1928) having studied skull and skeleton in these groups fully
confirmed in a personal letter to Mayr the latter’s results based on molt patterns
(see also Bock [2004b] who also supported Mayr’s earlier conclusion). Mayr ended
his article with an analysis of the history of dispersal of Leucosticte arctoa documenting
his early interest in zoogeographic questions. The detailed description
of geographic variation and speciation of the genus Leucosticte shows how familiar
Mayr was already at that time with the principles of geographic speciation.
This needs emphasis because it was later claimed that Mayr had learned about
geographic speciation from Sewall Wright’s 1932 paper (Ruse 1999: 118).
His efforts to elucidate the genetic basis of geographical variation and speciation
and to establish ties with genetics now found public expression for the first time. In
the general discussion of his paper on snow finches, Mayr (1927f: 611–612) laments
that the geneticists attempt “to analyze the factors of speciation without taking
into consideration the examples offered by nature.” He further deplored “how little
geneticists and systematists cooperate even today” and “that the geneticists still
today apply the Linnean species concept which is by now 170 years old (and in
many respects outdated),” the systematists had abandoned it long ago. His justified
criticism referred primarily to the mutationists among the classical geneticists,
for he (like most other naturalists) was unaware of the recent publications of
population geneticists emphasizing small mutations and they still adhered to
Lamarckian views explaining gradual evolution.
During the mid-1920s all of Mayr’s colleagues at the Museum of Natural History
in Berlin were deeply concerned with evolutionary questions and fighting against
the saltationist views of the “mutationists” like De Vries, Bateson and Johannsen
(as well as R. Goldschmidt and O. Schindewolf during the 1930s) who interpreted
evolution through macromutations (saltations). All of these latter scientists were
typologists who thought new species originated with major mutations and all of
them rejected natural selection. The Berlin zoologists at the Museum of Natural
History studied in detail the phenomenon of geographical variation in animals
leading to an emphasis on environmental factors. As long as mutations were believed
to cause large phenotypic changes, their only alternative was a Lamarckian
interpretation of the gradual (clinal) geographic variation they observed in numerous
continental species. They realized—like Darwin and Wallace previously—that
a thorough study of variation as well as adaptation in natural populations was an
indispensable precondition to understand the problems of evolution and speciation.
They all agreed that speciation was a slow process and that macromutations
à la de Vries and Morgan’s “freaky” Drosophila flies with yellow body color or
crumpled wings had nothing to do with the development of new species. These
naturalists divided characters into Mendelian (particulate) ones, which they considered
evolutionarily unimportant, and gradual or blending ones which, following
Darwin, should be the material of evolution. So the important thing that had to
happen, and which indeed happened during the 1920s (at first unnoticed by the
naturalists), was that the geneticists completely rejected the saltationist views of
the early Mendelians and showed that genetic changes could happen through very
small mutations which in the long run could be of great evolutionary importance.