144 THE STRUCTURE OF EVOLUTIONARY THEORY
other process. Darwin, again using domestication as an analog, passionately
defends the central role of variation so small as to pass beneath nearly everyone's
notice (p. 32):
If selection consisted merely in separating some very distinct variety, and
breeding from it, the principle would be so obvious as hardly to be worth
notice; but its importance consists in the great effect produced by the ac-
cumulation in one direction, during successive generations, of differences
absolutely inappreciable by an uneducated eye—differences which I for
one have vainly attempted to appreciate. Not one man in a thousand has
accuracy of eye and judgment sufficient to become an eminent breeder. If
gifted with these qualities, and he studies his subject for years, and devotes
his lifetime to it with indomitable perseverance, he will succeed, and may
make great improvements; if he wants [that is, lacks] any of these qualities,
he will assuredly fail.Saltational variation has always served as a rallying point for non-Darwinian
evolutionary argument (see Chapters 4 and 5 for a full discussion). T. H. Huxley
centered his own doubts about natural selection firmly upon Darwin's preference
for change by insensible steps. Bateson (1894), in developing the concept of
homeosis, and D'Arcy Thompson (1917), in his ideas on non-continuity in certain
geometrical transformations, advanced saltation as an explicitly anti-Darwinian
argument. The early mutationists read Mendel as a warrant for discontinuous
change, and a disproof of strict Darwinism as espoused by the "biometricians."
Goldschmidt (1940; see Gould, 1982a) joined some interesting views on
developmental discontinuity to an untenable genetic theory, all the better to
espouse a saltationist view that made him the chief whipping boy of the Modern
Synthesis.
Reciprocally, Darwinians countered with strong and explicit support. R. A.
Fisher began his great book (1930) by rooting a defense of Darwin in a linkage of
copiousness with small-scale variation—specifically, by arguing for an inverse
correlation of frequency and effect, and then claiming that variations of large effect
therefore become too rare to serve as evolution's raw material.
UNDIRECTED. Textbooks of evolution still often refer to variation as "random. "
We all recognize this designation as a misnomer, but continue to use the phrase by
force of habit. Darwinians have never argued for "random" mutation in the
restricted and technical sense of "equally likely in all directions," as in tossing a
die. But our sloppy use of "random" (see Eble, 1999) does capture, at least in a
vernacular sense, the essence of the important claim that we do wish to convey—
namely, that variation must be unrelated to the direction of evolutionary change;
or, more strongly, that nothing about the process of creating raw material biases the
pathway of subsequent change in adaptive directions. This fundamental postulate
gives Darwinism its "two step" character, the "chance" and "necessity" of Monod's
famous formulation—the separation of a source of raw material (mutation,
recombination, etc.) from a force of change (natural selection).