Internalism and Laws of Form 255
growth. We reject the first two today, and Darwin also grants them little space by
his qualifiers: "in some cases" and "being slightly affected." But Darwin put more
store by the third—laws of growth—as indicated by his only positive qualifier:
"being in all cases subjected to the several laws of growth." And we would offer
the same judgment today, since laws of growth, under the more fashionable
designation of "developmental constraints," have become a "hot topic" in
evolutionary biology once again (see Chapter 10). And now we come to the
Darwinian trope of argument, the ploy that makes this chapter (and, to a large
extent, this entire book) necessary.
Darwin wrote his crucial closing paragraph of Chapter 6 to argue that Unity
of Type should be subsumed under Conditions of Existence—for Unity of Type, he
asserted, only expresses past episodes of ordinary adaptation and natural selection,
subsequently inherited by numerous modern descendants. Unity of Type has
always defined the main arena for naturalists who view adaptation as secondary,
and some principle of morphological order (for many versions exist) as primary.
Darwin removed the rationale for a separate principle of Unity of Type by noting
that ancient adaptations would, if inherited throughout a subsequent lineage,
become sources of deep homology. Yet he could not deny—and had no desire to
subvert—the idea of morphological principles working separately from natural
selection, and building exceptions to adaptation. In this sense, Darwin supported
the concept of constraint, but only if this principle could be carefully circumscribed
within a category distinctly subsidiary to natural selection in relative frequency and
biological importance. Darwin fully understood the crucial role of relative
frequency in evolutionary arguments, and he rested his case for natural selection
squarely upon such a judgment of quantitative importance. In so doing, he pursued
the following strategy: take the old dichotomy, and show that both poles arise as
products of natural selection. Then, having removed constraint as the primary
cause of one pole (where a high relative frequency could not have been denied),
allow constraint to reenter as a subsidiary force to natural selection (with a
consequent guarantee of low relative frequency). Natural selection then becomes
the primary force of evolution. Recall the full title of Darwin's book: On the Origin
of Species by Means of Natural Selection, or the Preservation of Favored Races in
the Struggle for Life.
The classical form of a relative frequency argument upholds a favored
position and then degrades an alternative by two strategies, both used by Darwin in
making constraint subservient to natural selection.
NOOKS AND CRANNIES. Argue that your principle works nearly all the time,
while the alternative occupies just a few subordinate holes of absence. By
attributing both poles of the classic dichotomy (unity of type and conditions of
existence) to natural selection as a primary cause, thereby robbing constraint of its
potentially largest domain, Darwin granted dominance to adaptation.
SEQUELAE. Argue that your principle works as a prior and primary cause (in
both temporal order and effect), and that the alternative only produces