Genetic Analysis 289Mendelian reductionist approach, emphasizing largely the effects of selection on
single alleles of specific genes (the evolution of industrial melanism in moths, the
evolution of mimicry in African moth species, the evolution of seasonal polymor-
phisms in snails, etc.). The American geneticists, especially Dobzhansky and his
school, concentrated more on problems of whole genotypes, such as speciation
(Sturtevant) and chromosomal polymorphisms (Dobzhansky) in Drosophila.
The triumph of reductionist Mendelism was at the 1940s with the emergence of
the “New Synthesis” that defined natural populations and the forces that affect
their evolution in terms of gene alleles’ frequencies [Huxley, 1943]. This notion
dominated population genetics for the next decades. Attempts to emphasize the
role of non-genetic constraints, such as the anatomical-physiological factors (e.g.
by Goldschmidt [1940]), or the environmental (and evolutionary-historical) con-
straints (for example by Waddington [1957]) were largely overlooked.
The introduction of the analysis of electrophoretic polymorphisms [Hubby and
Lewontin, 1966; Lewontin and Hubby, 1966] allowed a molecular analysis of allele
variation that was also largely independent of the classical morphological and
functional genetic markers (see also Lewontin [1991]). Although genes were still
treated as algebraic point entities, inter-genic interacting system, such as “linkage
disequilibrium” were considered [Lewontin and Kojima, 1960]. The New Synthesis
was, however, seriously challenged when it was realized that a great deal of the
variation at the molecular level was determined by stochastic processes, rather
than because of differences in fitness [Kimura, 1968; King and Jukes, 1969].
This assault on the notion of the New Synthesis was intensified when, in 1972
Gould and Eldridge, two paleontologists, suggested a model of evolution by “punc-
tuated equilibrium”, or long periods of little evolutionary change interspersed with
(geologically) relatively short period of fast evolutionary change. Moreover, in the
periods of (relatively) fast evolution large one-step “macromutational” changes
were established [Eldredge and Gould, 1972]. Although it could be shown that
analytically the claims of punctuated equilibrium could be reduced to those of
classical population genetics [Charlesworthet al., 1982], these ideas demanded re-
examination of the developmental conceptions that, as a rule, could not accept
one-step major developmental changes since these called for disturbance in many
systems and hence would have caused severe disturbances in developmental and
reproductive coordination.
The need to reexamine the reductionist assumptions of genetic population anal-
ysis and to pay more consideration to constraints on the genetic determinations
of intra- and extra-organismal factors coincided with the resurrection of devel-
opmental genetics. However, the major change in the analysis of evolution and
development came from the molecular perspective. These allowed first of all de-
tailed upward analysis, from the specific DNA sequences to the early products,
rather than the analyses based on end-of-developmental pathway markers. Yet,
arguably, the most significant development was the possibility ofin-vitroDNA
hybridization. This molecular extension of genetic analysissensu strictofinally
overcame the empirical impossibility to study (most)in vivointerspecific hybrids.