Structural Constraints, Spandrels, and Exaptation 1239
been that of a boundary marker, while its secondary function was loanword spelling.
Runic-p has every appearance of having been coopted. Non-essential in the runic
system, it must have been essential in some system, presumably the parent of Older
Futhark."
In a fascinating exegesis of Emil Durkheim's seminal, late 19th century
sociological studies of the division of labor, Catton (1998) invoked our concept of
exaptation to explain a central error that Durkheim might not have committed if he
had recognized the principle of functional shift, either from Darwin (whom he studied
intensely), or from the more nearly contemporary Nietzsche. Durkheim recognized
(correctly) that division of labor, and the attendant specialization of tasks in society,
can greatly reduce competition and lead to "organic solidarity" (Catton, 1998, p. 89).
But he then erred in assuming that this current utility also permits the inference that
division of labor arose, in explicit analogy with speciation, as a direct adaptation for
its current function of reducing competition and stabilizing both social and economic
systems. "To Durkheim," Catton explains (p. 117), "it seemed abatement of
competition by means of differentiation was the necessary removal of an otherwise
insurmountable barrier to mutualistic interdependence. That was why division of
labor was supposed to result in organic solidarity."
But Catton then exposes the dilemma and logical error entailed by Durkheim's
commitment to an evolutionary analogy with speciation. For biologists argue, and
have demonstrated in many cases, that mutualistic interactions often evolve from
initial antagonisms and exploitations: "Evolutionary ecologists now know that
mutualism can evolve from antagonism ... by some modification of structure or
behavior that changes the outcome of an interaction from which the parties cannot
withdraw."
The secondarily evolved cooperation may remain "good" for both parties, while
so altering the initial state of the system that origins cannot be inferred from this
current utility. Catton (1998, p. 118) found our discussion of exaptation useful in
explaining this important concept to his colleagues. (He also shows his appreciation
of the corollary that secondary adaptation for a new role does not impeach the
exaptive origin of the coopted utility): "An adaptation has a function. An exaptation
has an effect. Once that effect becomes important in the life of an organic type (in its
new environment), natural selection may 'improve' the exapted trait, eventually
making it an adaptation, and converting the effect into a true function."
- Passage of the term from explicitly cited novelty to general and unreferenced
usage in evolutionary literature. The sequence may be bittersweet for originators, but
only the most narcissistic or insecure scientist could fail to take pleasure when a
concept of his invention, or an experiment of his doing, loses explicit connection to
his authorship by "evolution" into an ordinary term of art within the profession. This
form of acquired anonymity crowns the diffusion to general success of a suggestion
or innovation with a "point source" of origin, now happily forgotten and relegated to
the domain of antiquarian or historical studies.