The Essence of Darwinism and the Basis of Modern Orthodoxy 155
not vice versa—and the various forms of gradualism converged to a single,
coordinated view of life that extended its compass far beyond natural selection and
even evolution itself. This situation inspired Huxley's frustration as he
remonstrated with Darwin (see the famous quote on p. 151): you will have enough
trouble convincing people about natural selection; why do you insist upon uniting
this theory with an unnecessary and, by the way, false claim for gradualism?
We can best sense this overarching Darwinian conviction in a lovely passage
that conflates all three senses of gradualism—the rationalist argument against
creationism, the validation of natural selection by insensible intermediacy, and the
slow pace of change at geological scales—all in the context of Darwin's homage to
his guru Lyell, and his aesthetic and ethical convictions about the superiority of
these "noble views" about natural causation and the nature of change:
I am well aware that this doctrine of natural selection ... is open to the same
objections which were at first urged against Sir Charles Lyell's noble views
on "the modern changes of the earth, as illustrative of geology;" but we
now very seldom hear the action, for instance, of the coast-waves, called a
trifling and insignificant cause, when applied to the excavation of gigantic
valleys or to the formation of the longest lines of inland cliffs. Natural
selection can act only by the preservation and accumulation of
infinitesimally small inherited modifications, each profitable to the
preserved being; and as modern geology has almost banished such views as
the excavation of a great valley by a single diluvial wave, so will natural
selection, if it be a true principle, banish the belief in the continued creation
of new organic beings, or of any great and sudden modification in their
structure (pp. 95-96).The adaptationist program
Darwin's three constraints on the nature of variation form a single conceptual
thrust: variation only serves as a prerequisite, a source of raw material incapable of
imparting direction or generating evolutionary change by itself. Gradualism, in the
second meaning of insensible intermediacy, then guarantees that the positive force
of modification proceeds step by tiny step. Therefore, the explanation of evolution
must reside in specifying the causes of change under two conditions that logically
entail a primary focus on adaptation as a canonical result: we know the general
nature of change (gradualism), and we have eliminated an internal source from
variation itself (the argument for isotropy). Change must therefore arise by
interaction between external conditions (both biotic and abiotic) and the
equipotential raw material of variation. Such gradual adjustment of one to the other
must yield adaptation as a primary outcome.
Adaptational results flow logically from the mechanisms defining all other
subbranches on the limb of Darwinism designated here as the "creativity of natural
selection." But Darwin constructed this limb in reverse order in the