Adaptationist lesson II: Allometry and Antlers

Bryant (
29 Aug 1996 21:26:16 -0600

[Part two of a modest critique of anti-adaptationist notions. I'm
cross-posting to sci.ethology in case folks there are interested.
The rest of the thread is at sci.anthropology.]--Bryant


II. Allometric antlers?

Likewise, Gould's emphasis on the force of allometric developmental rules
has been re-examined in adaptationist light. Gould has argued that
allometry (the scaling of cervid antlers to body size, for instance, or
primate brains to bodies) is an evolutionary "constraint," limiting the
opportunities for natural selection to shape species. He has attributed
this allometric constraint to some obscure, unspecified embryonic detail of
ontogeny--which no doubt exists. What is questionable is whether it
constitutes a constraint to adaptation.

Cronin (1992, pp. 95-97) outlines adaptationists' re-analyses of Gould's
arguments. If one stops ignoring differences in mating behavior between
the species Gould cites, one sees that antler size "relates to body size
only because both are independently related to intensity of competition
between males."

Far from being side-effects as some of Gould's predecessors argued about
deer antlers, it appears that they are actually (jeepers!) weapons!

The more intense the competition of combat, the stouter the weapons.
Like the presence of pleoitropically maintained side-effect traits, the
presence of apparent allometric laws of nature is seen, when subjected to
some scrutiny, not to be an argument against the pervasiveness of natural
selection in evolution, but yet another example of it!



Reference: Cronin, 1991. The Ant and the Peacock, Cambridge Univ. Press.