Re: Evolution, "adaptation", and what's currently adaptive
Len Piotrowski (lpiotrow@magnus.acs.ohio-state.edu)
Wed, 28 Aug 1996 19:08:43 GMT
In article <501i8n$3bcg@argo.unm.edu> mycol1@unm.edu (Bryant) writes:
>[snip]
>>You haven't identified an adaptation, so I guess you've lost the bet. Their
>>"fitness effects" are only asserted.
>Nope, they're probable for the reasons I described.
They are just-so-stories.
> It also seems
>unlikely that sugar receptors on the tongue would have evolved by drift
>(accident), which is the only viable alternative to a selective
>(adaptationist) explanation.
Even if there were no negative impact on having sugar receptors on the tongue,
why wouldn't they be retained if they once appeared? Is sugar's contribution
to muscular metabolism only a side-effect of it's adaptation to brain
development? Did the brain's development have to wait on the evolution of
sugar receptors on the tongue? How did sugar receptors increase fitness
before it affected brain development? Must sugar receptors and brain
development have happened all-at-once?
In a related manner, are the sensations that psychoactive drugs have on the
mind thus a functionally equivalent adaptation like "sugar craving?" Should we
expect an evolutionary surge in brain development with the increased use of
psychoactive drugs just because of the supposed "need" to have it?
>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. 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?
Besides this obvious conundrum, the proposition appears to me to be
inadequate as proof of a fitness model. Without, "eyes" we all would agree
there would be problems in "seeing," since by definition "seeing" is done by
"eyes." But I submit there are ways of seeing as there are kinds of eyes.
There are plenty of examples of sightless organisms that are perfectly fit for
their circumstance. There are ways of "seeing" that don't include "eyes"
as we know it. The degrees of "seeingness" and kinds of "eyes" are
problematic with regard to fitness. Is one eye any less fit than two. Is a
mildly impaired eye any less fit than one with 20/20 vision? Is a shark's eye
any less fit than a human eye? Are the blind less fit and incapable of
"seeing" than an eyeful person?
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.
>And sugar receptors on the human/primate tongue are reasonably described
>as adaptations for detecting sources of sugar.
They may reasonably be described as sugar detectors. The adaptive value of
sugar detection on the human/primate tongue is problematic.
>And the sugar
>appetite/reward system in the brain is probably an adaptation for
>encouraging the consumption of sugar, a limiting resource.
I have no knowledge of such a "sugar appetite/reward system" in the human
brain. Nor am I aware that sugar is a limiting resource, by which I suppose
you to mean that access and consumption of "sugar" differentially affects the
survival of individuals. Neither do I perceive in this model the means by
which a "sugar appetite/reward system" could have acted to affect the
development of the brain before it's parts were in full existence! What came
first, the limiting resource, the sugar receptors on the tongue, the "sugar
appetite/reward system," or the development of the brain? Functional
adaptationist and behaviorist explanations intrinsically have a problem
with this cause-and-effect relationship.
>>>claimed that Gould et al.'s characterization of the adaptationist program
>>>is exaggerative and inaccurate.
>>
>>... and yet, as you apparently admitted above, this accurately describes your
>>own point of view!
>Um, you're reading a different thread than I am. I just said that his
>characterizations are exaggerated. I do not "admit" that adaptationism
>sees current utility in all traits. Or even optimality in the design of
>most traits.
Uh, you're reading belies your practice. The problem is with your
critique versus your actual examples.
>>However, when skepticism about your functional adaptationist
>>explanation for "sugar craving" and "jealousy" is voiced, you apparently are
>>quick to discredit non-adaptationist alternatives. A somewhat contradictory
>>stance.
>Not at all, Lenny. As I've said: I'm an adaptationist. I do not object
>to the belief that natural selection is a more powerful evolutionary
>force than genetic drift.
I don't think this was the point. It involved your functionalist explanations
for "sugar craving" and "jealousy" not whether or not "natural selection is a
more powerful evolutionary force than genetic drift."
> I do object to this stance being characterized
>as Panglosian. Adaptationists are not *just* speculating about the
>evolved functions of traits--they're testing their hypotheses!
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!
>>Whatever. Either you are what you claimed above ("I never claimed that I don't
>>subscribe to the adaptationist program") or you shift your point of view as it
>>suits you. You can't critique Gould & Lewontin's claim on the one hand as
>>overstated, and yet deny the possibility of non-adaptionist explanations for
>>your own examples on the other, except by assertion (parsimonious or not).
>I don't "deny the possibility." Give me some reasonable alternatives for
>the evolution of sugar-detecting taste buds on your tongue, Lenny.
They didn't evolve at all in the strict sense that they must have had an
effect on my fitness, or the fitness of my species' ancestors. Much less does
sugar have an effect on brain development! If anything, sugar has more of an
effect on immediate muscle activity, not the evolutionary or developmental
structure of the brain. Your question is more neutrally asked - how come
sugar-detecting taste buds appeared on our tongues? This eliminates the
immediate need to account for them in our human condition as an adaptive
necessity. After all, our mouths aren't dominated by sugar-detecting taste
buds, despite that luxurious "sugar appetite/reward system" your so found of.
I am satisfied to wonder about these processes as something quite ancient. If
you admit to "sugar detection on the human/primate tongue" then you will
have to reach back to a common ancestor. The same "sugar appetite/reward
system" appears to have a quite different effect on non-human primates, neh?
At any rate, to point out the functional nature of your argument doesn't
impose upon me the necessity to account for your subjects in some other
manner. I'm merely elucidating an apparent incongruity between your critique
of Gould & Lewontin's claim and your own practice.
>My
>thinking that they are probably adaptations is not the same as asserting
>that every trait has current and optimal utility.
OKay.
>In other words, for the zillionth time: I'm an adaptationist. YET
>(jeepers!) I object to Gould's mischaracterization of adaptationism.
And, by jimminy, your adaptationist practice is what Gould was complaining
about!
>>>this
>>>is silly. Your assertion would render nearly *all* thinking about ultimate
>>>causation (be it about hearts or brains or tongues) utterly moot.
>>
>>I would disagree.
>*HOW*?! You dismissed evolutionary speculation about traits for which we
>don't have a genetic loci identified!
Holding a genetic loci in your hand isn't the only way to identify the
existence of one, or do you disagree? Reducing complicated questions "about
hearts or brains or tongues" to an ultimate causation is somewhat troubling as
well.
>>>>The brain and heart are at least physical objects. "Sugar craving" and
>>>>"jealousy" are somewhat problematical in this regard.
>>
>>>They, like behaviors, are outputs of physical phenotype (in the brain,
>>>the tongue, etc.). Where's the problem?
>>
>>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 assert that the nervous system generates behavioral responses to
>environmental cues. You seem to think that the nervous system is not
>"physical."
Hardly! Then again, you wouldn't want to take a post-modern spin on the nature
of the signifier and signified, would you? <g> At any rate, I assert that
human behavior is generated from the interaction of meaningful environmental
cues and the meaningful interaction with other human beings. I take it this is
a somewhat different world from the one you propose above.
Cheers,
--Lenny__
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