Species as Individuals in the Hierarchical Theory of Selection 687
Darwinism, but should rather be integrated with natural selection into a more
complete and more generous account of evolution. Most neutral changes, after all,
occur "below" the level of visibility to conventional Darwinian processes acting at
the organismic level. Moreover, although most nucleotide changes may be neutral
at their origin, the variability thus provided may then become indispensable for
adaptive evolution of phenotypes if environmental change promotes formerly
neutral substitutions to organismic visibility—an important style of cross-level
exaptation (Vrba and Gould, 1986; Gould and Lloyd, 1999) that may serve as a
chief prerequisite to the evolution of substantial phenotypic novelty. Kimura
writes, for example (1985, p. 43): "Of course, Darwinian change is necessary to
explain change at the phenotypic level—fish becoming man—but in terms of
molecules, the vast majority of them are not like that. My view is that in every
species, there is an enormous amount of molecular change. Eventually, some
changes become phenotypically important; if the environment changes, some of
the neutral molecules may be selected and this of course follows the Darwinian
scheme." Thus, Kimura's statement exemplifies the central principle that the
various levels of evolution's hierarchy work in characteristically different ways—
and that levels can interact fruitfully in these disparate modes.
The chronological reaction of Darwinian hardliners to the neutral theory can
be epitomized in a famous, if sardonic, observation about the fate of controversial
theories. Tradition attributes this rueful observation to T. H. Huxley, but some
form of the statement may well date to antiquity, the usual situation for such
"universal" maxims. In any case, the earliest reference I know comes from the
great embryologist von Baer, who attributed the line to Agassiz (von Baer, 1866, p.
63, my translation): "Agassiz says that when a new doctrine is presented, it must
go through three stages. First, people say that it isn't true, then that it is against
religion, and, in the third stage, that it has long been known."
The first two stages unfolded in their conventional manner, with quizzical
denial followed by principled refutation in theory (see p. 521 on Mayr's argument
that neutralism cannot be true because we now know the ubiquity of selection).
However, the third stage—still stubbornly occupied by some strict Darwinians—
arose with an interesting twist, providing a cardinal illustration for this section's
major theme: the dangers of parochialism, particularly the tendency to interpret all
evolution from an organismal vantage point. Instead of simply stating that
neutralism has long been known (so what's the big deal?), detractors now tend to
say: "well, yes, it's true, and let's be generous and give Kimura and company due
credit. But, after all, neutral substitutions only occur at sites without consequence
for organismic phenotypes. So why focus upon such changes? Without any
organismal effect, they can't be important in evolution. And no one can blame
Darwin or Darwinian tradition for ignoring an invisible phenomenon."
This exculpation of Darwin cannot be faulted in logic, but the rest of the
argument reflects a narrow and discouraging attitude. Isn't the claim of
unimportance absurd prima facie? How can anyone advance an argument for