The Synthesis and Species 211can be postulated.” A species subject to different conditions at the extremes of its
range will adapt at those extremes, and hybrid forms will be disadvantageous if the
migration rate is less than the rate of increase of the favorable forms in the envi-
ronment to which they are adapted. Fisher champions as a mode of speciation the
selectionist account of Darwin and Wallace, and yet still allows for the Wagner-style
mode of allopatric isolation.
At this point we have reached the beginnings of the Modern Synthesis, and
hence the modern debate. We are now equipped to put the modern debate into con-
text, especially claims of conceptual novelty. To that we now turn, beginning with
Theodosius Dobzhansky’s discussion shortly after Fisher’s book, which defined the
modern species debate.Theodosius Dobzhansky’s Definition
We may arbitrarily mark the beginnings of the modern debate with Dobzhansky’s
classic 1935 essay, “A critique of the species concept in biology,”^7 although Poulton’s
essay is also crucial. It’s not really so arbitrary—from Dobzhansky’s essay and the
book that followed it^8 flowed both the present debate over what species are, and the
birth of the Modern Synthesis. Dobzhansky’s work was an attempt to take Darwin
seriously about species by a working systematist not imbued with the British defla-
tionary tradition. And he introduced two of the major innovations in the debate—
the idea of species as evolutionary players, and the idea that genetic exchange
marked out these players. It seems that when typostrophic views of evolution were
abandoned, the issue from the Great Chain of what divisions nature forced upon us
and what divisions were of our own convenience came back to the fore. Later, Mayr
described the Synthesis as being a “shared species problem.”^9 It remains a shared
problem.
Theodosius Dobzhansky was perhaps the most significant of all the synthesists^10
through the middle of the twentieth century. He introduced Sewall Wright’s ideas on
drift into the synthetic orthodoxy (often to considerable opposition), and his work on
the laboratory and field genetics of Drosophila spp. revolutionized the field.^11
Dobzhansky published his paper, later substantially included in the chapter on
species in his Genetics and the Origin of Species, which discussed Lotsy’s revi-
sion of Poulton’s notion of syngamy as the foundation for a genetic population: “an
habitually interbreeding community of individuals.”^12 Dobzhansky says of the syn-
gameon approach to species that it applies only to panmictic populations of organ-
isms, and which, although attractive in its simplicity, is therefore inapplicable in
the case of many species that are divided into reproductively separated populations.
(^7) Dobzhansky 1935.
(^8) Dobzhansky 1937.
(^9) Mayr and Provine 1980, 1.
(^10) In order to identify those active in the so-called “Modern Synthesis,” which is not looking so modern
any more, we need a term. I trust I can be excused this one.
(^11) Depew and Weber 1995, 291–297, 300–302.
(^12) Dobzhansky 1941, 311.