1232 THE STRUCTURE OF EVOLUTIONARY THEORY
- Preadaptation can only describe a potential future utility of a feature operating
in a different manner in an ancestor. The thermoregulating feather may be called a
preadaptation for flight. But when birds then coopt feathers as essential components
of an airborne wing, we surely cannot continue to call them preadaptations for their
current utility! I simply refuse to be called a "wannabe scientist" (or even a
"promising scientist") because I once had a dream, and even (in retrospect) some
inherent capacity for its realization, as a kid on the streets of New York. - What term in all our lexicon has ever come to us so inherently "prepackaged"
for inevitable trouble and misunderstanding? The motivation behind the name may be
clear and fair enough—the desire to recognize a different potential in a current
actuality. But in our real world, where we so often allow our hopes for intrinsic
meaning to obscure the realities of a natural order— random and senseless in human
terms, and replete with "bad things happening to good people"—we guarantee
ourselves nothing but trouble when we invent a word with a "plain meaning" of
foreordination as a description and definition of our best examples to illustrate the
precisely opposite concepts of fortuity and contingency. The resulting, entirely
predictable, confusions became legion in biology classrooms, and professors
developed a tradition for explicating and apologizing in advance whenever they
mentioned "preadaptation." Terms that automatically evoke such embarrassment
must be fatally flawed and fit only for the favored anathematization of my childhood
years: "good riddance to bad garbage."
I could present a catalog of such textbook apologies, but will cite only
Frazzetta's lament (1975, p. 212) to prove that my fulminations at least cannot be
called idiosyncratic: "The association between the word 'preadaptation' and dubious
teleology still lingers, and I can often produce a wave of nausea in some evolutionary
biologists when I use the word unless I am quick to say what I mean by it."
To rectify this odd situation of a missing term at the center of a key subject in
evolutionary biology, Vrba and I proposed that features coopted for a current utility
following an origin for a different function (or for no function at all) be called
exaptations—that is, useful (or aptus) as a consequence of (ex) their form—in
contrast with adaptations, or features directly crafted for their current utility.
Adaptations have functions, and exaptations, following Williams's recommendation,
have effects. We summarize our recommendations in Table 11-1 (from Gould and
Vrba, 1982).
This coinage completes a logical structure that has been recognized ever since
Darwin (and made explicit ever since Nietzsche) but that never included a term for
one of the central rooms in the edifice. (My reasoning may be both simplistic and
self-serving, but I can imagine only one explanation for such a curious situation:
following Darwinian traditions, and especially under the orthodoxy of the "hardened"
version of the Modern Synthesis, biologists became so accustomed to regarding all
evolutionary change as adaptation directed by natural selection that they lost sight of
the importance, or even the existence, of an undeniable corollary—that many (indeed
most) features, as a