266 THE STRUCTURE OF EVOLUTIONARY THEORY
worthy of overturning as the essential thrust of a revolutionary theory (see pp. 116-
125). Paley's totality presents a subtle, coherently reasoned brief for an
adaptationist natural theology.
First of all, Paley cannot be caricatured as a Panglossian perfectionist. He
states explicitly that we cannot use perfection as a criterion for identifying good
design, or even as the necessary mark of divinity in craftsmanship: "It is not
necessary that a machine be perfect, in order to show with what design it was
made: still less necessary, where the only question is, whether it were made with
any design at all" (p. 5).
Paley also provides, if only occasionally, positive arguments for imperfection,
as in feathers of an ostrich's wing. "The filaments hang loose and separate from
one another, forming only a kind of down; which constitution of the feathers,
however it may fit them for the flowing honors of a lady's headdress, may be
reckoned an imperfection in the bird, inasmuch as wings, composed of these
feathers, although they may greatly assist in running, do not serve for flight" (p.
236). And he acknowledges that the creator's preference for utility lies revealed in
the overwhelming relative frequency, not the ubiquity, of adaptation (but adding
the conventional rider, still commonly advanced today, that, if we look hard
enough, we will discover uses for traits now judged "nonadaptive"). "Instances...
where the part appears to be totally useless, I believe to be extremely rare:
compared with the number of those, of which the use is evident, they are beneath
any assignable proportions; and perhaps, have never been submitted to a trial and
examination sufficiently accurate, long enough continued, or often enough
repeated" (Paley, 1803, p. 64).
In fact, Paley uses adaptationism primarily as a theoretical argument about
depth of causality, not as an excuse to rhapsodize about happy nature. Opponents
who wish to see "physical law" as the source of form might cite sexual generation
and embryology as leading examples. But these processes only provide the
immediate physical continuity of efficient causation: "The truth is, generation is
not a principle but a process" (p. 453). We need a deeper reason, a true principle,
for the evident adaptation of form to function—in short, a final cause. Even if
watches gave birth to new watches, Paley argues, we would not identify ontogeny
as the ultimate source of timekeeping. Neither can embryology be the cause of
optical excellence in the human eye, if only because "things generated possess a
clear relation to things not generated" (p. 455)—the eye to external light and to the
objects we need to see in this case. (We now recognize this otherwise persuasive
argument as wrong only because life, unbeknownst to Paley, possesses history and
mutability.)
But the main case for taking Paley seriously lies in his formulation and
refutation of opposing visions. Anyone can spin out a rationale for an idée fixe, but
a well-crafted system requires both full analysis and principled denial of
alternatives. Natural Theology merits our respect, and becomes a key document for
this chapter on the history of functionalism vs. formalism, because Paley
recognized the structuralist alternative and provided a coherent defense.