Re: Adaptationism's Lessons (was Re: Evolution, "adaptation")
Paul Gallagher (m-pg0123@mrslate.cs.nyu.edu)
14 Sep 1996 18:05:22 -0400
wilkins@wehi.edu.au (John Wilkins) writes:
>Gould and Vrba's concept of "exaptation" strikes me as relevant here: why
>was it proposed? Adaptationists have always recognised that some
>adaptations are in fact holdovers from earlier rather than pirsent
>selection pressures. I suspect that it was to imply without actually
>saying so that selection is insufficient to account for all structures.
I don't see why you say this. Gould explains that exaptation is used in
place of preadaptation in part because of the connotations of preadaptation.
Preadaptation has strong connotations of non-selective origins. Exaptation
on the other hand tends to imply that previously existing adaptations are
reused for new purposes.
(Since Gould and Vrba are leading proponents of punctuated equilibria
theory, I suspect their need for the term arose from the fact that punc.
eq. and species sorting imply that adaptive change is concentrated in
brief episodes in extraordinary environments. If this is the case,
adaptation is highly opportunistic, much more so than would be case if
the organism were constantly being molded by intense directional
selection. Since adaptation arises in extraordinary environments, I
suspect it's likely that the present and original functions of a trait
will sometimes not coincide.)
In any case, exaptation is not meant to "imply that selection is
insufficient to account for all structures." If that were there secret
intention, the use of the term preadaptation would do the job much
better.
An interesting criticism of exaptation appears at:
http://info.itp.berkeley.edu/IB160/VDG/Fall94/Wells/Wells.html
Paul
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