3 The New York Years (1931–1953)

362 11 History and Philosophy of Biology—Mayr’s Third Synthesis
to the importance of “population thinking” (the uniqueness of individuals) in his
letters, e.g.:
“It is interesting to see in which way the methods of research have changed
during our lifetime! Local populations are now studied increasingly. It is no longer
stated the Yellowhammer does this or that, but 25% of the males in the Song
Sparrow population of central Ohio have been nonmigratory and 75% migratory,
etc. Such variations within populations in particular have been underestimated or
entirely neglected by earlier biologists. […] I consider the replacement of the ‘type’
as the object of study by the population as the most basic revolution in biology”
(9 August 1948). “As soon as you think of species or subspecies or any other type
of biological phenomenon as populations it is easy to see how selection can affect
it. It is also easy to see how the bridge can be made from one of these populations
to the next one. […] In Germany the question was always asked as to what does
the thrush do or the chaffinch or the nightingale. In other words, the type was
investigated rather than the population of which it is composed” (14 March 1949).
“In connection with my book on the principles and methods of taxonomy, which
I am now working on, I had to do a little thinking about the history of the field.
[…] it became abundantly clear to me that the world of biology owes to taxonomy
one of its greatest concepts, namely, the population concept [emphasis added].
The anatomists (and many paleontologists) are still confirmed typologists and so
were the geneticists until they were awakened by three students who had been
trained by taxonomists: Goldschmidt, Sumner, and Dobzhansky. The taxonomists
had started to think in these terms easily fifty to 75 years earlier by collecting
‘series’ and by collecting in adjacent localities” (28 April 1950). “Actually, no two
populations of a species are ever quite the same, they differ in their winter quarters,
in the beginning of the breeding season, in the average number of eggs they lay,
young they raise, and preferred nesting sites, etc. In some cases these differences
are gliding [clinal], in others they are quite abrupt. To attach names to these
differences is usually not helpful” (4 June 1968).
Typologists and populationists may be distinguished in this way: For a typologist
(essentialist) the underlying essence of a phenomenon (well-defined, fixed,
unchangeable, and separated from others by decided gaps) has reality and variation
is irrelevant and no more than deviation from the type (“noise”). In population
thinking variation is considered the reality (all individuals are unique), while the
statistics and in particular the mean values of samples and populations are the
abstractions. Natural selection and gradual evolution are meaningless for the typologist
to whom the concept of race is also an all-or-none phenomenon. As early as
1924 Mayr had opposed the typological dogma of the creationist origin of animal
species in a letter to Erwin Stresemann (p. 28).
Although the principles of “new systematics” as applied by Stresemann, Rensch,
and Mayr since the 1920s are based on the study of populations rather than types
and Mayr’s species definition of 1942 refers to populations, none of them conceptualized
“population thinking” based on the uniqueness of individuals until Mayr did
so during the late 1940s. He established the fact that Darwin was the first to apply
population thinking when he proposed the concept of natural selection (p. 350).