1230 THE STRUCTURE OF EVOLUTIONARY THEORY
of crafting (usually construed as God's creating) a feature for a particular utility has
been called "adaptation"—following the etymology of fashioning for (ad) a use
(aptus). No problem so far; only an apt choice of terminology. But if "adaptation"
denotes the process of crafting or creating for a use, what shall we call the resulting
structure so used. We usually call the structure an "adaptation" as well—again no
intrinsic problem, for we often use the same noun for a process and its results
("construction," "building," etc. to cite some analogs in the same architectural
domain).
But problems may arise in historical systems if the current utility of an
adaptation (the noun used for the result) did not arise by the process (also called
adaptation) that built the result at its initial appearance—for, under the Nietzsche-
Darwin principle of quirky functional shift, the form of the current adaptation
(feature) may have arisen by adaptation (process) for a very different role. (Similarly,
the building on my corner now serves as a shelter and soup kitchen for homeless
people—a utility not directly related to the purpose of its initial building as a church.
We may not become confused in this case because we know the short history of this
site, and the current use does not stray far from the stated ideals of the broader
institution that originally raised the structure. But we could make some serious errors
if we maintained a strong interest in long histories with spotty records featuring
multiple episodes of functional shifting, and then assumed that the use of a current
building automatically revealed the intention of its original building. When we
recognized and generalized the error in such reasoning, we might even want to make
a terminological distinction between our name for the current object and our name for
the process of its original construction.)
In fact, I am not inventing an abstract or overfine distinction here. This very
problem has been directly, even urgently, addressed in some of the most widely read
and respected writings in evolutionary biology. When Williams (1966) composed his
classic defense and explication of adaptation, he wisely identified adaptation as an
"onerous" concept, to be invoked only when truly necessary, and restricted to a clear
domain of unambiguous definition and use. He recommended, in particular, that the
term be applied to a current feature only when we can "attribute the origin and
perfection of this design to a long period of selection for effectiveness in this
particular role" (1966, p. 6). He even advocated a terminological distinction between
the use of such a genuine adaptation (its "function") and the use, potentially just as
crucial to an organism's survival, of a feature not crafted by selection for its current
role (and therefore not an adaptation in Williams's restricted terminology). Williams
suggested that we call this second form of fortuitous utility an "effect"—giving as an
incisive, if somewhat facetious, example the propensity of flying fishes to fall back
into the water as an effect (not the function) of the organism's mass. In other words,
Williams invoked the term "effect" to designate the operation of a useful character
not built by selection for its current role.
Although Darwin never formalized the issue, he clearly intended to restrict
"adaptation" to Williams's sense of structures built by selection for their current