Re: Evolution, "adaptation", and what's currently adaptive
Bryant (mycol1@unm.edu)
29 Aug 1996 12:19:06 -0600
In article <lpiotrow.388.3224993B@magnus.acs.ohio-state.edu>,
Len Piotrowski <lpiotrow@magnus.acs.ohio-state.edu> wrote:
>In article <501i8n$3bcg@argo.unm.edu> mycol1@unm.edu (Bryant) writes:
>
>>>You haven't identified an adaptation, so I guess you've lost the bet. Their
>>>"fitness effects" are only asserted.
>>>They are just-so-stories.
You're probably correct. We may never know the precise selective
pressures which led to the evolution of sugar receptors on the tongue.
But more generally, here's what dismays me about your apparent stance:
You offer no alternative to natural selection for the creation of the
functionally complex taste buds and brain modules for detecting sugar.
Why did they arise? Complex traits without selective advantage can, as you
suggest, be maintained even in the face of mutation accumulation, if
they're pleiotropically tied to some trait that is favored selectively.
But this does not speak to the *origin* of the trait.
Ultimately, you either concede the power of selection and look for
testable ways to get at the trait's function, or you throw it on the
dustbin of drift and hope you're right.
Bryant
>>Adaptations are traits shaped and retained by selection for their
>>fitness-enhancing benefits. Hence, eyes are adaptations for seeing. Fair
>>enough?
>
>Quite a eyeful that one. To rephrase the proposition: eyes are
>adaptations because they see.
Eyes are adaptations because they have design features unlikely to have
accumulated by chance. They serve fitness-enhancing functions.
The only alternative to random accumulation in evolution is selection.
>Offhand I would respond along several different
>tracks. But chief among them, and most important to this discussion, is the
>functional trope implied by this remark. Eyes are needed to see. Where did
>the need to see come from?
Selective pressures in the environment. Seeing shadows obviously
provided early sighted critters (with their crude eyes) with some,
perhaps slight, survival or reproductive advantage over the blind.
>Another difficulty I have with tropes such as these is the idea that
>structures like "eyes" somehow develop in isolation. If "eyes" have such
>fitness value for "seeing" why do we not see eye organisms devoted to seeing?
>A mammal without eyes is just as incongruous as a mammal without legs, or
>hearts, or brains, or tongues with taste receptors. To parse the whole system
>into separate pieces and talk about their individual affects on overall
>fitness, and thereby use that exercise to account for why they appear their
>in the first place, obscures processes and structures of relation and
>interaction that represent the system as a whole.
Because, Lenny, individuals aren't passed on. Genotypes are not, either;
they're broken up during meiosis. Ultimately, although selection acts on
the individual for whatever net fitness his or her components offer in a
given environment, only genes are selected for or against. Some are
linked, but Mendelian inheritence takes us further than you suggest above.
>It doesn't change the fact the adaptationists employ functionalist
>interpretations to explain the evolution of "traits." And besides, I haven't
>seen any testing of the logical implications of your hypotheses!
I haven't offered any. If you would like to go over some examples of
adaptationism that actually do, I'd be happy to go over them. I've
recently written a preliminary paper on the probable adaptations of baby
cries and of postpartum depression in women. Would either of those be
suitable?
>>>The problem is with your definition of human behavior as "outputs of physical
>>>phenotype."
>
>>Sigh. OK. So this boils down to a duelistic/spiritualist interpretation
>>of the generation of behavior, then, Lenny?
>
>I have no idea what your talking about here. Care to elaborate on this theory
>of human behavior? I can probably assure you without even hearing your
>explanation that you will be far from the mark.
I was asking if your comment about behaviors not being part of a
phenotype meant that you think they arise from some non-physical entity,
as seems the only logical alternative to my posit, which you critique,
that behaviors are the output of physical phenotype.
Gotta run.
Bryant
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