The Essence of Darwinism and the Basis of Modern Orthodoxy 143
literature and emerged as a key issue in the biometrician vs. Mendelian debates
early in our century (see Provine, 1971). Castle (1916,1919) pursued his famous
experiments on selection in hooded rats in order to test the hypothesis of limits
imposed by variability upon continued change. One of the most appealing features
of Mendelism—and a strong reason for acceptance following its "rediscovery" in
1900 —lay in the argument that mutation could restore variation "used up" by
selection. Nor has the issue abated today. In another form, copiousness underlay
the great debate between Dobzhansky and Muller (see Lewontin, 1974)—the
classical vs. the balance view in Dobzhansky's terminology. Kimura's (1963, 1983)
modern theory of neutralism may be invoked to acknowledge the fact of
copiousness while avoiding the pitfalls of genetic load—and therefore becomes
"neoclassical" in Lewontin's terminology.
SMALL IN EXTENT. If the variations that yielded evolutionary change were
large—producing new major features, or even new taxa in a single step—then
natural selection would not disappear as an evolutionary force. Selection would
still function in an auxiliary and negative role as headsman—to heap up the
hecatomb of the unfit, permit the new saltation to spread among organisms in
subsequent generations, and eventually to take over the population. But
Darwinism, as a theory of evolutionary change, would perish—for selection would
become both subsidiary and negative, and variation itself would emerge as the
primary, and truly creative, force of evolution, the source of occasionally lucky
saltation. For this reason, and quite properly, saltationist (or macromutational)
theories have always been viewed as anti-Darwinian—despite the protestations of
de Vries (see Chapter 5), who tried to retain the Darwinian label for his continued
support of selection as a negative force. The unthinking, knee-jerk response of
many orthodox Darwinians whenever they hear the word "rapid" or the name
"Goldschmidt," testifies to the conceptual power of saltation as a cardinal danger to
an entire theoretical edifice.
Darwin held firmly to the credo of small-scale variability as raw material
because both poles of his great accomplishment required this proviso. At the
methodological pole of using the present and palpable as a basis, by extrapolation,
for all evolution, Darwin longed to locate the source of all change in the most
ordinary and pervasive phenomenon of small-scale variation among members of a
population—Lyell's fundamental uniformitarian principle, recast for biology, that
all scales of history must be explained by currently observable causes acting within
their current ranges of magnitude and intensity. "I believe mere individual
differences suffice for the work," Darwin writes (p. 102). At the theoretical pole,
natural selection can only operate in a creative manner if its cumulating force
builds adaptation step by step from an isotropic pool of small-scale variability. If
the primary source of evolutionary innovation must be sought in the occasional
luck of fortuitous saltations, then internal forces of variation become the creative
agents of change, and natural selection can only help to eliminate the unfit after the
fit arise by some