The Modern Synthesis as a Limited Consensus 565
by the early Synthesis in its first phase of restriction—see pp. SOS-SOS.) Huxley
(1942, p. 41) spoke of "the illegitimacy of using data on the course of evolution to
make assertions as to its mechanism."* He continued:
As admitted by various paleontologists ... a study of the course of evolution
cannot be decisive in regard to the method of evolution. All that
paleontology can do in this latter field is to assert that, as regards the type
of organisms, which it studies, the evolutionary methods suggested by the
geneticists, and evolutionists shall not contradict its data. For instance, in
face of the gradualness of transformation revealed by paleontology in sea
urchins or horses it is no good suggesting that large mutations of the sort
envisaged by de Vries shall have played a major part in providing the
material for evolutionary change (1942, p. 38).
Even so iconoclastic a morphologist as D. Dwight Davis, who would later
tweak strict adaptationism so effectively in discussing formal and historical
constraints in his classic monograph on the giant panda (Davis, 1964), wrote for
the Princeton meeting on genetics, paleontology, and evolution (1949, p. 77):
"Paleontology supplies factual data on the actual rates of change in the skeleton
and the patterns of phyletic change in the skeleton. Because of the inherent
limitations of paleontological data, however, it cannot perceive the factors
producing such changes. Attempts to do so merely represent a superimposition of
neobiological concepts on paleontological data."
I admit, of course, that paleontologists have no access to mechanisms
requiring direct observation of ontogeny and ecological interaction. But to say, as
Davis does, that we cannot ever derive concepts of evolutionary mechanisms from
paleontological data—and must therefore gain all our causal understanding from
"neobiology"—seems excessively pessimistic, and consigns paleontology to
impotence. If paleontologists cannot gain insights about mechanisms, then
historical science of any kind becomes impossible, for all scientific study of the
past must make causal inferences from results of processes that cannot be directly
observed.
Moreover, if historical data hold such limited promise, then the consequences
become even more serious for science in general. For if we acknowledge that
extrapolationism can't suffice in principle because much of macro-evolution
proceeds by patterns of differential birth and death among species, and if we
cannot generate any theory about such higher-level sorting because we cannot
observe the constituent events directly, then much of evolution becomes
unknowable in principle. Fortunately, such pessimism may be firmly
*But Huxley's own later contentions belie this strong claim. For example, he argues
against uniform internal drives in parallelism, and for control by external selection, by noting
that characters do not always correlate in the same manner within parallel trends observed in
different lineages of fossils: "In all cases where fossils are abundantly preserved over a
considerable period, we find the same phenomena. The change of form is very gradual. It is
often along similar lines in related types. And in general it appears that different characters
vary independently" (1942, p. 32). But doesn't this statement qualify as an example of "using
data on the course of evolution to make assertions as to its mechanism"?