Internalism and Laws of Form 269
dirt, it is, of all animals, the neatest" (p. 294). Paley defends adaptation with an
explicit rejection of the strongest argument for constraint (what Darwin would later
call "correlation of growth"). Recalling his opening metaphor, Paley writes:
"Observe then, in this structure, that which we call relation. There is no natural
connection between a small sunk eye and a shovel palmated foot. Palmated feet
might have been joined with goggle eyes; or small eyes might have been joined
with feet of any other form. What was it therefore which brought them together in
the mole? That which brought together the barrel, the chain, and the fusee, in a
watch: design; and design, in both cases, inferred, from the relation which the parts
bear to one another in the prosecution of a common purpose" (p. 296).
- But what can an adaptationist say about the overarching homologies of
broad taxonomic structure? Are these widespread properties not formal constraints,
logically prior to any subsequent utility forged by specific tinkering with such
common elements? (We certainly acknowledge such priority today, but we also
recognize Darwin's incisive argument that these "phyletic" constraints may have
arisen as ancestral adaptations—see last section. Paley enjoyed no conceptual
access to this legitimate adaptationist exit from the dilemma.)
In a clever twist of argument, Paley turns homology to the cause of adaptation
in two steps:
(1) God devised general plans with foreknowledge of their requisite
modification for specific purposes in individual species. For if these grand
homologies had been generated automatically by abstract laws of nature, with no
reference to final causality, how could such widespread structures be so subtly
subject to such varied adaptation in the service of so many particular modes of
life? "Whenever we find a general plan pursued, yet with such variations in it, as
are, in each case, required by the particular exigency of the subject to which it is
applied, we possess, in such a plan and such adaptation, the strongest evidence,
that can be afforded, of intelligence and design ... If the general plan proceeded
from any fixed necessity in the nature of things, how could it accommodate itself
to the various wants and uses which it had to serve, under different circumstances,
and on different occasions?" (Paley, 1803, p. 227).
(2) Yet Paley recognized the potential circularity in this claim, if taken by
itself. To be sure, once such homologies have been established, they may be
examined for susceptibility to adaptive modification. But why did God proceed in
this manner at all? Why didn't he just make each species from scratch, optimally
suited for its own peculiar mode of life? Why bother with common plans at all,
when creatures sharing the plans work so differently? Here, at the crux of his
difficulty, Paley invokes a venerable solution that has always (both then and now)
struck critics as at least slightly sophistic (in the sense that any potential refutation
could be so "accommodated," thus making the theory irrefutable, untestable, and
therefore useless): God shows his greatness by limiting his own power with
ordered principles (secondary causes based on natural laws) and structural designs
(grand homologies):