Species as Individuals in the Hierarchical Theory of Selection 685
century theories of probability also eschewed ontological randomness in favor of
causal production by interaction of so many fundamentally orthogonal mechanisms
that stochastic formulations would best fit the observed results—the philosophical
solution traditionally adopted by the scientific determinists who invented
probability theory, most notably by Laplace himself.)
For these primarily societal reasons, theories of random change enjoyed little
currency before our own century, when for both external reasons of a new cultural
context (spawned by such events as the breakup of colonial empires, the
devastation of World Wars, and the consequent questioning of predictable progress
as time's direction), and internal prods from the mathematical apparatus of
population genetics, random models of change became a major and controversial
subject in evolutionary theory. I shall not review this well-known story, centering
on the life and work of Sewall Wright (see Wright's own magnificent four-volume
summing up, and Provine's fine biography). I only need to remind readers that
genetic drift (often called "the Sewall Wright effect" in early literature), while
unimpeachable in theory, and therefore surely operative in nature, received very
short shrift, especially as the Modern Synthesis hardened around its adaptationist
core (see Chapter 7). The Synthesis did not and could not deny genetic drift;
instead, supporters resorted to the classical argument for dismissal in natural
history—relegation to insignificant relative frequency. I learned the argument as a
near mantra in all my graduate classes during the mid 1960's: fixation by genetic
drift can only occur in populations so tiny that most will already be on the brink of
extinction.
Genetic drift at the traditional organismic level enjoys far more respect and
currency today, but the basic argument of the Synthesis does have merit at this
hierarchical level. Sexually-reproducing, multicellular organisms generally share
two properties that greatly limit the efficacy of genetic drift: they live in
populations far too large for random fixation in the face of nearly any measurable
selection pressure; moreover, the style of individuality manifested by organisms,
based on well-balanced functional integration among sub-parts, renders the traits of
these interactors particularly subject to scrutiny by natural selection.
Do these good reasons for demoting random change at the organismic level
doom this alternative style of evolution to weakness or impotency throughout the
hierarchy? Clearly not, as the recent history of our profession proves; moreover,
we may even invert the standard hope for extrapolation from the level we know
best, and assert instead that the organismic level discourages random change as a
peculiarity of individuality in this realm—and that analogs of genetic drift at other
levels should expect healthy, if not dominant, relative frequencies.
All evolutionists also know that ideas of random change have enjoyed
greatest success, based on inherent plausibility, at the genie level, where the so-
called "neutral theory of molecular evolution," most strongly associated with the
great Japanese geneticist Motoo Kimura (1968, 1983, 1985, 1991a and b), but
initiated and developed by others as well (Jukes, 1991), has of-