3 The New York Years (1931–1953)

186 5 Biological Species and Speciation—Mayr’s First Synthesis
however, one advantage. They show clearly that Goldschmidt’s contention that
subspecies are not the building material of new species is wrong. In fact, about
60% of these subspecies are considered good species by the majority of living
ornithologists.
There is one genetical phenomenon which seems to be of particular interest to
the taxonomist. This is what one of the Russians, I believe Severtsov, has called
‘homologous series of mutations.’ It is the fact that the common and most
conspicuous mutations in the genus Drosophila (or any other genus) occur
in every species of the genus, while the characters that separate the various
taxonomic units are much more stable and much harder to define than “white”
or “sooty.” If you have a D. melanogaster which has defect mutations in regard
to its eye, to its wing and to its abdomen, a qualifying biologist will still tell
you without hesitation that this is D. melanogaster.
The same is true for birds. The real differential characters between species
seem to be of a different kind than typical gene mutations. I am well aware
that most of these statements are mere “hunches” and are hard to substantiate,
but whatever experiments have been made with geographical races or species
seem to indicate that many characters of geographical races do not inherit
in Mendelian fashion. I would like to refer to the latest Peromyscus studies
of the Michigan school. We get the same thing with our wild populations in
continental birds. There is a perfect blending from one population to the next.
Birds have one great advantage, i.e., that their taxonomy is better known than
that of any other group of animals. They also have one great disadvantage,
which is that they are hard to keep in captivity and that their reproduction is
very slow as compared with insects. I believe that the task of the bird student
will be to make suggestions to the geneticist interested in evolution, but it will
be up to the experimental entomologist to prove or disprove these suggestions.
I am very willing to help you in getting taxonomic papers that might be of
interest to you. The majority of taxonomic papers, however, is purely descriptive
and would mean nothing to you. Rensch has compiled up to 1929 most
of the literature which has a bearing on this subject. Since then a good many
scattered contributions were made, but it is hard to say what would be significant
and what not. Why do you not send me specific questions? They are more
easily answered.
Yours sincerely, (Ernst Mayr, 1935)
This letter again documents Mayr’s and many other zoologists’ belief that two
different types of characters are involved in the differentiation of populations:
(1) conspicuous but unimportant Mendelian characters and (2) blending characters
important for geographical divergence. After reading Dobzhansky’s (1933)
paper on “Geographic variation in lady-beetles” Mayr had exclaimed “Here is finally
a geneticist who understands us taxonomists!” (Mayr 1980n: 419) and had
written him a “fan letter” on 7 November 1935 emphasizing the need for an integration
of genetic and taxonomic research, as he had tried in his early paper
on the snowfinches (Mayr 1927f; see here p. 45). Dobzhansky answered him on
12 November 1935: