The Modern Synthesis as a Limited Consensus 521
modern revisions—from neutralism,* to punctuated equilibrium, to a common
feeling that the theme of developmental constraints not only gives substance to an
old truth, but also confutes the hardened version's commitment to Darwin's (I
should really say Fisher's) billiard ball against Galton's polyhedron.
My example shall trace the transformation of adaptation from an option to be
ascertained (albeit favored and granted a dominant relative frequency) to an a
priori assumption of near ubiquity (save in trivial or derivative situations without
evolutionary importance)—in other words the burnishing of Galton's polyhedron to
the billiard ball of pure functionalism (allowing no significant pushing back from
internal structure upon the direction of evolutionary change). This hardening
buttressed (or rather, in my view, overly rigidified and sclerotised) one leg on the
essential Darwinian tripod of support—the second theme of functionalism against
internalist and structuralist forces (see Chapters 2, 4, and 5).
But hardening pervaded all major themes of Darwinian central logic, and the
other two legs of the tripod also experienced their own form of petrifaction (treated
in less detail in Section 4 of this chapter). Pluralistic (and, admittedly, often loose)
thinking about levels of selection yielded to an explicit promulgation of organismic
selection as the only acceptable mode—as a virtual campaign to root out group
selection accompanied the battle of Williams (1966) against Wynne-Edwards
(1962). Thirdly, a willingness to grant some independence, or at least some
puzzlement, to patterns in macroevolution (see Haldane and Huxley's respectful
view of orthogenesis, as discussed in the last section), ceded to the hard view that
all phenomena measured in millions of years must be explained by smooth
extrapolation from palpable causes on generational scales in modern populations—
and that the paleontological record can therefore only present a pageant of products
generated by known causes, and not provide an independent theory or even a set of
additional causal principles.
I have used a particular method to demonstrate the hardening of the
Synthesis—textual comparison of early and later works by key authors. Ontogeny
can be an unconscious trickster. In trying to forge sense and continuity in
*If the Synthesis had retained the pluralism of its early years, Kimura's neutral
theory would have been welcomed from the first, under the criterion that any result
legitimated by the mechanics and mathematics of known genetic processes thereby
secured a rightful place (Wrightful in this particular case)—though Kimura's claim would
have been viewed as surprising in the light of adaptationist preferences. But when the
Synthesis hardened, and adaptationism itself became the primary criterion for
acceptability, Kimura's theory seemed beyond the pale to many evolutionists. I shall
never forget a decisive moment in my own early career, when I began to understand the
difference between theoretical power and potentially dangerous overconfidence: Ernst
Mayr rising (at the annual meeting of the Evolution Society in New York) to confute the
claim for neutralism in synonymous third position substitutions. Such changes could not,
a priori and in principle he stated, be neutral. Alterations in the third position must impart
some difference, perhaps energetic, that selection can "see" even if the coded amino acid
does not alter. This must be so, he stated, because we now know that all substantial
change is adaptive.