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Re: Evolution, "adaptation", and what's currently adaptive
Bryant (mycol1@unm.edu)
28 Aug 1996 15:37:53 -0600
In article <lpiotrow.384.322446AE@magnus.acs.ohio-state.edu>,
Len Piotrowski <lpiotrow@magnus.acs.ohio-state.edu> wrote:
>I appreciate the concern and hope I can clarify my position on "adaptationist"
>speculations. Let me be clear, I am not "hostile" towards such things. My main
>problem with Bryant's original post was the incongruity of his critique of
>Gould & Lewontin's claim juxtaposed against his clearly functional
>adaptationist examples. I was curious to discover how he rationalized such a
>situation in his own mind. I'm still not at all certain how he's convinced
>himself there is no problem.
Perhaps I should backtrack and clarify. Maybe I've been unusually sloppy
in explaining myself.
Gould et al say that the adaptationist program (theoretical biology,
basically) suffers from a Panglossian outlook: every single trait is
optimally designed to enhance fitness. Most adaptationists I know would
agree to the contrary, that most traits you can imagine measuring on an
organism do not constitute traits retained for their fitness benefits.
That is, most traits are not adaptations.
I have said that this is not so, and have cited, for instance, the male
nipple as a nice example of a trait which is not a direct product of
natural selection. The male nipple has no apparent likely fitness effects.
It is probably a developmental side-effect of some kind. Baggage.
Where I did suggest functional design with likely fitness benefits were
the appetite for sugar (not shared by all species, interestingly) and
sexual jealousy (which is sexually dimorphic in humans and seems to serve
male fitness via motivating mate guarding and thus paternity assurance).
I am still not sure exactly what the problem is, from your perspective.
I gather that suggesting any adaptationist explanations is sinfully
Panglossian, since you equated my two speculations with Gould's
charactiture of seeing adaptation in every single trait.
Here's the rub: if a trait ain't selectively favored, it's either baggage
(pleiotropically maintained or with such low fitness effects that it
simply isn't selected against, which seems unlikely to me given the
accumulation of mutations which would degrade the more complex traits in
this group), or it's a recent mutation, or it's a result of genetic
drift (accident). The early part of this century saw evolutionary theory
prematurely dismiss trait after trait as "pleiotropic" or the result of
drift, both very difficult notions to test. Only when adaptationist
alternatives were tested were the presumed functionlessness natures of
these traits abandoned.
Whereas mutation and drift are random events, natural selection is
non-random, as are its evolutionary effects. You seem to posit random
forces of evolution as viable explanations for highly non-random
phenomenon, such as taste buds which detect sugar. This is possible, if
sugar detection involves only one or two loci, I guess. Sure seems
likely, though, that detecting sugar might effect eating behaviors, and
that this would have had fitness effects. Maybe I'm mistaken.
Finally, although I may have been pretty clumsy with my examples, I
believe it is fair to describe the brain (and thus the emotions and
cravings generated within it!) as vulnerable to natural selection.
Behaviors themselves have fitness effects, and the physical origin of
those behaviors, the nervous system, is therefore subject to natural
selection.
Bryant
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