Re: Evolution, "adaptation", and what's currently adaptive
Bryant (mycol1@unm.edu)
3 Sep 1996 17:46:29 -0600
In article <lpiotrow.397.322CA59C@magnus.acs.ohio-state.edu>,
Len Piotrowski <lpiotrow@magnus.acs.ohio-state.edu> wrote:
>>[bryant said:]
>>>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.
>>
>>Connecting a "taste bud" to your "brain modules" is not as easy as invoking
>>the power of "natural selection." You gracelessly slip away from your original
>>assertion of "sugar craving" genes under the smoke screen of tongue receptors
>>and brain comparators.
Actually, I presented no smoke screen. I did do two things, out in the
open. One, I pointed out that for sugar appetite/craving to be the
result of accidents rather than selection, so too must be the hardware
with which we detect sugar (the sugar-sensitive taste buds).
Secondly, I concluded that you're correct, that I shouldn't be advocating
a specific adaptationist hypothesis wrt these traits, since I originally
used them only as crude examples to illustrate how current adaptiveness
isn't always expected for adaptations.
>>Why don't you stop this squirming about and allow some
>>resolution to a problem before you transmogrify it into "What I really meant
>>to say was ..." !
I'm not squirming. I conceded to your point. I then clarified what I
thought were the worthy points remaining to be made before moving on.
You really do get worked up at the keyboard, don't you? :)
>>>Why did they arise?
>>
>>What do you perceive as needing to be "arisen?" "Functionally complex taste
>>buds" or "brain modules for detecting sugar?"
Sure, or since you seem to reject the presence of taste buds***, pick
another trait. Say, nipples. Or peni. Or vermaronasal organs.
***>>I have problems with your
>>presupposing descriptions for whatever these thingies are your trying
>>to validate as functional adaptations.
>>>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.
>>
>>Like survival of the organism as a whole ...
Yes, contributions to the survival of the organism will result in a
selective favoring of genes (as long as they lead to reproductive success
of some sort). But that's not the point I was making. Please do not be
embarassed to ask what "pleiotropy" means, etc., when you don't know.
No big deal. (This isn't a lame attempt at an insult. It's an offer to
help out.)
>>>Eyes are adaptations because they have design features unlikely to have
>>>accumulated by chance.
>>>They serve fitness-enhancing functions.
>>
>>You don't know why "they" first appeared, or why "they" happened to be
>>retained, or if and when "they" served as " fitness-enhancing functions"
>>or for whom or what. This kind of story is about useless to illustrate any
>>principle you may be striving for in describing meaningful human behavior as
>>the result of functional adaptation.
If you would stop using such vague and general descriptions, and come
down to describe an actual example--say, maternal reactions to baby
cries--it may help me understand your position.
>>>The only alternative to random accumulation in evolution is selection.
>>
>>"Random accumulation" of what? This is getting more and more remarkable.
Lenny, do you really not undestand the first thing about evolutionary
theory? You've been letting on that you do, but these details you find
so remarkable are basic intro biology. There are "forces of evolution".
They are selection, drift, flow, and mutation. Mutation, of course, is
the ultimate source of all allelic diversity. The frequencies of
different alleles are affected by selection, drift (accidents), and flow
(such as immigration from other populations).
Thus a trait can be explained, evolutionarily, as being a product of
drift, flow, or selection. Only selection can create functionally
complex traits like the scorpionfly "rape clamp"... So, when you reject
adaptationist explanations out of hand (rather than offering specific
critiques of a given hypothesis), you are in effect arguing that drift or
flow is what created the trait--the random, non-selected accumulation of
alleles.
That's pretty straight forward, yes?
>>>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.
>>
>>Just so ...
No, testable. There are living representatives of the various
fossil-evidenced steps of ancestral eye evolution. Blind some of a given
population's individuals and see if they reliably suffer fitness
impacts. That would be a reasonable indication that vision increased
fitness through past generations.
>>>Because, Lenny, individuals aren't passed on.
>>
>>I could quibble here about exactly who "passed on" if not Aunt Nell, but for
>>the sake of discussion, we're talking about the functional relevance of a
>>parsed part to a working system.
Exactly. Thanks for clarifying your position.
>>>Genotypes are not, either;
>>>they're broken up during meiosis.
>>You would concede they recombine to form functional wholes, now, wouldn't you?
>>Functional wholes that have prescribed fitness values!
Yep, collections of well-canalized alleles. Is this supposed to be an
argument against what I've been saying?!
>>>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.
>>
>>And so a problem source for the functional adaptationist point of view. The
>>system from which it was derived (the focal point of natural selection and
>>what is signified by "fitness") is nothing more than a hodge-podge of
>>individual traits, each viewed in isolation as a sequence of functional
>>necessities.
There are different intensities of selection on each trait, so that in a
given selective regime/environment, through deep time, traits are
selectively disfavored/favored to different degrees (indirectly, through
their contributions to individuals' fitness).
>>>[Bryant said:] Some are
>>>linked, but Mendelian inheritence takes us further than you suggest above.
>>
>>Why don't you enlighten me as to what you think I've suggested above?
You talked about your optinion that I shouldn't reducing whole
organisms to collections of "functional parts," if I recall.
>>Or must the baby have traveled the million year road to arrive
>>at this behavior? Could depression itself be a reflection of the failure of
>>the self-regulating mechanism to cope with abrupt changes in essential
>>physical properties, or intrinsic states of being?
Who exactly are you trying to impress with your assault on plain speaking?
There is good evidence that baby cries evolved, yes. Most primate
species have infant cries acoustically similar to that of humans.
Yes, I believe crying serves a (gasp!) function, and that the crying
behavior and the vocal architecture (including the relevant limbic
modules) reflect the selective advantage of crying to infants through
human evolution. Care to offer viable alternatives?
>>>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,
>>
>>I never made such claim. Your only recourse to a non-functionalist,
>>non-adaptationist explanation for human behavior can be described at the
>>very least as unimaginative, something you bewailed over in previous posts!
Lenny, that's inaccurate. You said that there was a problem with my
assertion that behaviors are tied to "physical phenotype."
If you want to backtrack to explain what you "really meant,"
be my guest.
>>--Lenny__
Bryant
|