The Structure of Evolutionary Theory

516 THE STRUCTURE OF EVOLUTIONARY THEORY

also acknowledged this factual substrate as a primary source of legitimate doubts,
then common among taxonomists, about Darwinism: "But when we have pushed
our analysis as far as possible, there is no doubt that innumerable characters show
no sign of possessing selective value, and, moreover, these are exactly the
characters which enable a taxonomist to distinguish one species from another. This
had led many able zoologists and botanists to give up Darwinism" (1932, pp. 11 3 -
114).
Haldane even presents the interesting argument that we have been fooled into
accepting a dominant frequency for adaptation by a pronounced bias in the fossil
record—the differential preservation of species with persistently large populations
subject to control by small Fisherian differentials in natural selection. Perhaps most
species exist as much smaller populations, and therefore become subject to
Wrightian dynamics of genetic drift—even if such species rarely enter the fossil
record and therefore fail to leave evidence for their dominant relative frequency.
Haldane even cites the highest of all authorities to buttress this idea:

But Wright's theory certainly supports the view taken in this book that the

evolution in large random-mating populations, which is recorded by

paleontology, is not representative of evolution in general, and perhaps

gives a false impression of the events occurring in less numerous species. It

is a striking fact that none of the extinct species, which, from the abundance

of their fossil remains, are well known to us, appear to have been in our

own ancestral line. Our ancestors were mostly rather rare creatures.

"Blessed are the meek: for they shall inherit the earth" (1932, pp. 213-214).

J. S. HUXLEY: PLURALISM OF THE TYPE

As with Haldane, Huxley also credited a well-received lecture that he had
presented on Darwinism as the stimulus for writing his much longer book—a 1936
presidential address to the British Association on "Natural selection and
evolutionary progress." Huxley maintained the focus of this lecture in presenting a
thoughtful, but partisan, defense of Darwinism throughout Evolution, The Modern
Synthesis, beginning with a wry comment on the extensive pessimism so common
before the movement he christened: "The death of Darwinism has been proclaimed
not only from the pulpit, but from the biological laboratory; but, as in the case of
Mark Twain, the reports seem to have been greatly exaggerated, since today
Darwinism is very much alive" (1942, p. 22).
Huxley encapsulates the central logic of Darwinism in much the same way,
and with the same intent, that I advocate in this book. He recognizes the three main
characteristics of variation as central (pp. 22-24)—copiousness (though not
pervasive enough for mutation pressure to overwhelm selection), small-ness of
phenotypic effect, and nondirectionality—and he credits Mendelism