Re: naked bipeds
David Froehlich (eohippus@curly.cc.utexas.edu)
Sat, 21 Oct 1995 16:30:54 -0500
On 20 Oct 1995, H. M. Hubey wrote:
> >You betray some misunderstandings about evolution when you say the route
> >for the change must be "positively adaptive at every step".
>
> The only thing missing is if there's no input or if the actual
> variable has no direction. If there's no change at all (i.e.
> in the genes/chromosomes, IOW no mutations) then it wouldn't matter
> what the input was. There's always input because that's the
> environment. If there's always mutation then zero is practically
> nonexistent. That leaves either positive or negative. If it's not
> positive it must be negative. For a good approximation we could
> consider every change as positive or negative (even if we cannot
> tell which it is).
YAAFI. There are plenty of cases where we can see various kinds of
selection. Directional, stabilizing, and disruptive selection can take
place. It has been demonstrated (e.g. Darwin's finches) that changes can
and will occur that are not adaptive but merely not maladaptive
(neutral). It has also been demonstrated that random effects are in some
cases more common than adaptive changes (what is the use of eye color in
humans?) You want to take a completely mathematical determinist view of
this and there is a large stochastic component.
> A more
> >realisitic statement would be that the route for the change must not be
> >maladaptive at any step (or at least not too maladaptive). There is
> >every reason to think that a great deal of what happens in evolution is
> >random, and happens when newly evolved features are not selected for or
> >against.
>
> This third category is produced because we cannot tell simply
> by looking (or any other way, at least these days) if the
> change was adaptive (positive) or maladaptive(negative). But
> regardless of whether we know which it is, it is one of them
> almost all the time.
Why does a change have to be adaptive or maladaptive? You are making a
big assumption here. You have a point that some of the neutral
characters could have an undiscovered benefit or cost, however as you
point out so often, there is a continuoum of these characters and if the
+ or - is so small that it doesn't effect reproductive rates then it is
effectively neutral. It has been theorized that most mutations are going
to be maladaptive because the genome is so finely tweaked, however many
third codon changes to do not effect the protein because they code for
the same amino acid. Other, non fatal mutations are likely to be
invisible to the organism.
> >As far as naked bipedalism goes: you seem fixated on the idea that
> >functional hairlessness and bipedalism must have evolved at the same
> >time. This is not a fixation shared by paleoanthropologists.
>
> Is there any evidence one way or the other, aside from the usual
> analogy? IOW do they say there was hair because the skull
> looked a lot like a chimp? Hasn't this kind of thinking bitten
> the dust at least once before i.e. brain growth lead to bipedalism
> or something like that because it required tool use etc etc....
Ancient history, that bit the dust in the 50's. You assume that
bipedalism and hairlessness are correlated and we have no evidence of
that one way or the other. All we can do is argue by analogy to
organisms today that are also hairless (and as has been demonstrated by
everybody under the sun, this is a bad analogy because the other hairless
animals are doing different things).
If you assume something at the start of the analysis you can never test
it. The opposite view is that these aren't correlated because we cannot
demonstrate it (isn't this a better position?)
David J. Froehlich Phone: 512-471-6088
Vertebrate Paleontology Laboratory Fax: 512-471-5973
J.J. Pickle Research Campus
The University of Texas, Austin, Texas 78712
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