Internalism and Laws of Form 333
(and his borrowed example from Owen surely indicates respect and attention).
Darwin linked the efficacy of natural selection to a set of assumptions about the
nature of variation (see pp. 141-146). But he could not be satisfied with such an
abstraction, and he recognized that any complete theory required an understanding
of mechanisms of variation. Darwin presented his major discussion of constraint in
Chapter 5 on "Laws of Variation"—for any exception to his trio of necessary
properties for variation (copious, small in extent, and undirected) would
compromise the exclusive power of natural selection by granting a role to
"internal" principles of variation in the direction of evolutionary change. Any
exception, in short, would represent a "law of variation" acting not only as a source
of raw material, but also as a subsidiary to natural selection among causes of
change. (In both the Origin (1859) and in his extended treatise on The Variation of
Animals and Plants Under Domestication (1868), Darwin employed the phrase
"laws of variation" to specify properties that could produce evolutionary change
independent of natural selection. He proposed a threefold taxonomy of "use and
disuse," "direct action of the external environment"—the bases of evolutionary
theories often attributed to Lamarck and Geoffroy respectively—and "correlation
of growth," or structural constraint as discussed in this chapter. Properties of
variation that merely supplied raw material for natural selection—the indispensable
trio of copious, small, and undirected—apparently did not count among the "laws,"
for Darwin viewed these properties as auxiliaries or handmaidens of selection.)
Darwin begins his discussion by admitting contemporary ignorance about
causes of variation: "I have hitherto sometimes spoken as if the variations— so
common and multiform in organic beings under domestication, and in a lesser
degree in those in the state of nature—had been due to chance. This, of course, is a
wholly incorrect expression, but it serves to acknowledge plainly our ignorance of
the cause of each particular variation" (1859, p. 131).
When we do not know the underlying causal bases of important and related
phenomena, taxonomies based upon overt expressions become our best practical
procedure for specification and understanding. Darwin therefore tries to gather the
phenomena of variation into categories. Most categories either enhance adaptation
by routes other than natural selection (use and disuse, and direct effects of the
environment—Lamarckism and Geoffroyism in later parlance), or, at most, serve
to enhance or slow down selection by affecting the amount of available raw
material in variation. Only one category truly challenges the functionalist credo by
embracing the primary structuralist theme of internal constraint upon adaptation,
with consequential no functionality for certain features. Darwin names this
category "correlations of growth," and offers a definition: "I mean by this
expression that the whole organization is so tied together during its growth and
development, that when slight variations in any one part occur, and are
accumulated through natural selection, other parts become modified. This is a very
important subject, most imperfectly understood" (1859, p. 143). Note, even here,
how Darwin defends the primacy of selection (by the "sequelae" argument