532 THE STRUCTURE OF EVOLUTIONARY THEORY
then the role played by Mayr and other field naturalists in building the synthesis
becomes fully constitutive and not only derivative. Mayr (1980), wearing his
historian's hat, has strongly defended such an account of the Synthesis against the
reductionist tradition that regards genetics as paramount, and the second phase of
the Synthesis largely as a whipping of older disciplines into line. I do not deny
Mayr's partisan motives in advancing this interpretation, but I also concur with his
judgment.
Dobzhansky, as argued above, became the beacon of the second phase
because he represented the only tradition, Russian genetics, that tried to fuse
experimental Mendelism with systematics and natural history, rather than imposing
the first upon the second (or ignoring the second entirely). At Mayr's 1974
conference, Dobzhansky vividly recalled the impediments to synthesis within
American traditions. He had originally left Russia to work with Thomas Hunt
Morgan, America's premier experimental geneticist. Dobzhansky recalled
Morgan's attitude to natural history:
"Naturalist" was a word almost of contempt with him, the antonym of
"scientist." Yet Morgan himself was an excellent naturalist, not only
knowing animals and plants but aesthetically enjoying them... Morgan
was profoundly skeptical about species as biological and evolutionary
realities. The species problem simply did not interest him... Biology had to
be strictly reductionistic. Biological phenomena had to be explained in
terms of chemistry and physics. Morgan himself knew little chemistry, but
the less he knew the more he was fascinated by the powers he believed
chemistry to possess. There was no surer way to impress him than to talk
about biological phenomena in ostensibly chemical terms (1980, p. 446).Morgan, Dobzhansky also remembered, "liked to say that genetics can be studied
without any reference to evolution." Could the Synthesis have taken root in such
soil?
Dobzhansky brilliantly set a different task for evolutionary theory—an
enterprise embodied in Darwin's title (but not treated as a major theme in his
book), and emerging from traditions of systematics and natural history (while
scarcely conceivable for someone with Morgan's, and to a large extent Darwin's,
views on the unreality of species): how can a theory originally constructed to
describe continuous change in natural populations also explain the discontinuous
structure of nature's taxonomic diversity? The central problem of evolution,
Dobzhansky asserted, is the origin of discontinuity among species.
This statement sounds commonplace today, but only because Dobzhansky and
the Synthesis moved the question to center stage. Morgan and virtually all
experimentalists had argued that the origin and nature of variation, and its manner
of spread through populations, defined the key issues in evolutionary theory.
Morgan disavowed the species problem as, at best, a hang-up of dull taxonomists
and, at worst, a bogus issue because species have no reality in