The Modern Synthesis as a Limited Consensus 541
processes: 1) the maintenance and improvement of adaptedness, and 2) the
origin and development of diversity.
Since (2) was so almost totally ignored by the pre-Synthesis
geneticists, I focussed in 1942 on (2). By the 1950s the study of diversity
had been fully admitted to evolutionary biology, owing to the efforts of
Dobzhansky, myself, Rensch and Stebbins, and in my 1963 book I could
devote a good deal of attention to (1). This was rather easy because, as you
know, I used to be a Lamarckian. And Lamarckians are adaptationists.
Hence, it is not that from 1942 to 1963 I had become an adaptationist,
rather I reconciled in 1963 my adaptationist inclination with the Darwinian
mechanism (Letter of December 20, 1991).(Mayr then added a handwritten footnote, demoting to insignificance the one
subject for which he did acknowledge a reversal of opinion between the two books:
"Neutral polymorphism is an infinitesimal percentage of all evolutionary
phenomena. Don't make a mountain out of this little mole-hill.")
I do not deny Mayr's stable adaptationist preferences (through his ontogenetic
change in explanatory preferences from Lamarck to Darwin). This personal
stability provides an even better reason for regarding as important, and therefore
generally indicative, the textual evidence of transition from pluralism in 1942 to
adaptationist hardening in 1963 (for Mayr's 1942 text may therefore, by
implications of his own testimony, be reporting the conventional pluralistic
wisdom of the time despite Mayr's own personal preference for adaptationism). On
the subject of adaptation—not the major concern of either book (for both treat
speciation and the production of diversity as their primary topics)—Mayr recorded
a professional consensus both times, largely passively I suspect (hence his personal
inattention to the alteration). Scientists must struggle to identify and understand
these influences of "shared culture," for such a "background" consensus fuels the
sources of unconscious bias for each of us at every moment of our careers.
WHY HARDENING?
I have documented the adaptationist hardening of the Modern Synthesis in some
detail, but I have not addressed an obvious and pressing question: why did this
conceptual trend occur? Several aspects of an answer seem clear, but I can offer no
full or satisfying resolution.
The culture of science trains us to believe that such major shifts of emphasis
record improvements in knowledge won by empirical research and discovery. I do
not deny that observation did play a significant role, at least in illustrating, with
some elegant examples, the power of adaptation. Consider, for example, the
"ecological genetics" of E. B. Ford and his panselectionist school in England. Their
commitment to adaptationist explanations of effectively all variation among
populations, and their documentation of strong selection coefficients in nature,
buoyed the strict Darwinian faith. Dobzhansky's