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A Modern Unified Theory of Evolution 211
out every morning with their guns, and for every specimen that they brought back
I asked, ‘What do you call this one?’ I recorded the scientific name in one column
and the native name in another. Finally, when I had everything in the area, and
when I compared the list of scientific names and the list of native names, there
were 137 native names for 138 species. There were just two little greenish bush
warblers for which they had only a single name. At the time, I took this for granted
because as a naturalist I always believed in species, but whenever I read statements
by armchair biologists who deny the existence of species, I always marvel at the
remarkable coincidence that the scientist and the native in New Guinea should by
pure accident have an imagination that is so closely similar that they assign the
mountain birds of New Guinea to the same number of species” (Mayr 1956g: 5; see
also here p. 58, Mayr 1943e, 1949m, 1963b: 17, and Diamond 1966).
In later publications Mayr usually quoted the definition of the theoretical biological
species concept (the “nondimensional species”), sometimes without the
qualifying “actually or potentially” in front of “interbreeding,” because it is irrelevant
for species status whether the isolating mechanisms are challenged at a given
moment (e.g., Mayr 1949j, 1953b, 1969b, 1982d: 273).
Mayr (1949f: 290) considered an emended species definition: In case speciation
occurs without a complete separation of the populations an extended definition
may become advisable: “Species are groups of actually or potentially interbreeding
natural populations that are either completely reproductively isolated from other
such groups or whose genetic differentiation (owing to mutation, selection, etc.)
outweighs an actual or potential gene interchange with other such groups.” He
added “But there are also some serious objections to such an emendation.” After
ecological factors had been emphasized by various workers Mayr (1951l: 92) defined
the species as “an aggregate of interbreeding natural populations which are
not only reproductively isolated from other such aggregates but also ecologically
specialized sufficiently so as not to compete with other such species” or more
formally: “A species is a reproductive community of populations (reproductively
isolated from others) that occupies a specific niche in nature” (1982d: 273). The
reason why he added the qualifying clause “that occupies a specific niche in nature”wasthat“itseemedtomethatnopopulationhascompletedtheprocessof
speciation until it is able to coexist with its nearest relatives. […] Time will show
whether this additional qualification is useful or confusing” (1987e, p. 214).
If the ecological factor would be raised to a criterion for species status, such
a definition would reduce to subspecies status most closely related paraspecies
which are reproductively isolated but exclude each other because of ecological
competition. For this reason such a definition (with the above qualifying clause)
never caught on and Mayr (1992a: 222) himself returned to this simple wording:
“A species is an interbreeding community of populations that is reproductively
isolated from other such communities.” Local representative populations of species
have particular niches, but not a species as a whole.
In Mayr’s early publications of the 1940s and 1950s, there is no terminological
distinction between the species concept and the species taxon. In a lecture on “The
species as a systematic and as a biological problem” Mayr (1956g: 7) introduced