The Modern Synthesis as a Limited Consensus 531
the Princeton conference on genetics, paleontology and evolution—Simpson
(1949, p. 224) had emphasized the dominance of selection in quantum evolution,
while not denying other factors. But by 1953, he had completed his personal
transition. Quantum evolution now merits only four pages in an enlarged final
chapter on modes of evolution. More importantly, this concept has now mutated to
a meaning that Simpson had explicitly denied before: merely a name for phyletic
evolution when the process operates at a maximal rate—an evolutionary tempo
differing only in degree from the leisurely, gradual transformation of populations
in ordinary geological time. Quantum evolution, he now writes, "is not a different
sort of evolution from phyletic evolution, or even a distinctly different element of
the total phylogenetic pattern. It is a special, more or less extreme and limiting case
of phyletic evolution" (p. 389). He lists quantum evolution as one category among
the four styles of phyletic evolution (p. 385)—with all four characterized by "the
continuous maintenance of adaptation." The bold hypothesis (1944) of an
absolutely inadaptive phase has been replaced by the semantic notion of a
relatively inadaptive phase (an intermediary stage inferior in design to either the
ancestral or the descendant Bauplan). But relative inadaptation poses no threat to
the adaptationist paradigm. Even the strictest Darwinian will feel no Angst if the fit
of phenotype to environment decreases for an intermediate form in a new habitat,
relative to the ancestor in a different original place; (the two forms, after all, cannot
directly compete). Even less Angst will then accompany an acknowledgment that
this intermediate form may be less well designed than its own future descendant
(for selection should engender increasing adaptation through time, especially as a
population adjusts to a strikingly new environment). In short, such relatively
inadaptive populations can only be regarded as adequately adapted to their own
environments at their own time (unsubjected, as they must be, to competition with
better adapted ancestors in a different habitat, or with improved future descendants
in this new world). Quantum evolution, by linguistic redefinition, therefore moves
comfortably under the umbrella of the adaptationist program. Simpson now even
suggests that quantum evolution may be more rigidly controlled by selection than
any other mode of evolution (though he still invokes inadaptation for the initial
trigger): "Indeed the relatively rapid change in such a shift is more rigidly adaptive
than are slower phases of phyletic change, for the direction and the rate of change
result from strong selection pressure once the threshold is crossed" (p. 391).
MAYR AT THE INCEPTION (1942) AND CODIFICATION (1963):
SHIFTING FROM THE "GENETIC CONSISTENCY" TO THE
"ADAPTATIONIST" PARADIGMIf we consider the synthesis as a fusion of three equally robust disciplines—
experimental genetics, population genetics, and studies of natural history expressed
primarily by systematics (and not as an imposition of the first two, as modernisms,
upon a hidebound, or even moribund, third mode of study)—