118 THE STRUCTURE OF EVOLUTIONARY THEORY
rooted by the theory of natural selection. Darwin's essential argument begins with a
definition of the dominant philosophy for natural history in his day— natural
theology in the Paleyan mode.
At the outset of Chapter 4,1 will say more about Paley and the alternative
vision of continental natural theology (adaptationism vs. laws of form). For now, a
simple statement of the two chief precepts of Paleyan biology will suffice:
NATURAL THEOLOGY IN GENERAL. The rational and harmonious construction
of nature displays the character and benevolence of a creating God. In the last four
chapters of his book, Paley tells us what we may infer about God from the works
of creation. God's existence, of course, shines forth in his works, but this we know
from many other sources. More specifically (and with a Paleyan chapter for each),
nature instructs us about God's personality, his natural attributes, his unity, and
(above all) his goodness.
PALEY'S PARTICULAR VERSION OF NATURAL THEOLOGY. Natural theology has
been expressed in two basic modes (see Chapter 4), one primarily continental (laws
of form), the other mainly British (adaptationism). Paley held that God manifests
his creating power in the exquisite design of organisms for their immediate
function. We all know Paley's famous opening metaphor: if I find a watch lying
abandoned on an open field, I can conclude from the complex set of parts, all
shaped to a common purpose and all well designed for a specific end, that some
higher intelligence constructed the watch both directly and for a particular use.
Since organisms show even more complexity and even more exquisite design, they
must have been fashioned by an even greater intelligence. But fewer biologists
know Paley's more specific argument against the alternative version of natural
theology (laws of form), as presented in his chapter 15 on "relations." The parts of
organisms exist in concert not because laws of form or symmetry demand one
feature to balance another, but "from the relation which the parts bear to one
another in the prosecution of a common purpose" (1803 edition, p. 296)—that is, to
secure an optimal adaptation of the whole.
At the very outset of the Origin, Darwin tells us that his explanation of
evolution will stress the Paleyan problem of exquisite adaptation. He writes, in the
Introduction, that we could obtain sufficient confidence about evolution by
"reflecting on the mutual affinities of organic beings, on their embryological
relations, their geographical distribution, geological succession, and other such
facts" (1859, p. 3). "Nevertheless," he continues, "such a conclusion, even if well
founded, would be unsatisfactory, until it could be shown how the innumerable
species inhabiting this world have been modified, so as to acquire that perfection
of structure and coadaptation which most justly excites our admiration" (1859, p.
3). The explanation of adaptation therefore stands forth as the primary problem of
evolution. Many lines of evidence prove that evolution occurred. But if we wish to
learn how evolution works, we must study adaptation.
This basic Darwinian argument operates as a close copy of Paley's defense,
recast in evolutionary language, for the English alternative in natural theology.