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From: kuento@kuhub.cc.ukans.edu
Newsgroups: sci.bio
Subject: Re: Further Evolving Eyebrows
Message-ID: <26540.27343d31@kuhub.cc.ukans.edu>
Date: 4 Nov 90 21:09:21 GMT
References: <1371@cluster.cs.su.oz.au> <2431@anaxagoras.ils.nwu.edu> <4278@lib.tmc.edu>
Organization: University of Kansas Academic Computing Services
Lines: 39

In article <4278@lib.tmc.edu>, mitchell@thesis1.hsch.utexas.edu (Philip Mitchel) writes:
> In article <2431@anaxagoras.ils.nwu.edu> barger@ils.nwu.edu (Jorn Barger) writes:
>>Why did humans lose their fur?  This seems surely due to sexual selection, 
>>not natural selection.  But why this baldness became sexually attractive I 
>>have no clue. 
> 
> I'm curious... why is it that fur loss is surely due to sexual, not natural
> selection?  How much of a body's resources would it take to keep that
> much hair growing?  If that much can be saved by wearing the furs of
> other animals (or altering other behaviors to maintain the core
> temperature without the use of natural fur), mightn't that give the
> hairless an advantage over the hairy?  I'm not proposing this as The
> Answer to the question, it has just seemed a possible explanation.  It
> would (to my mind) also explain why we keep hair on our heads (the gain
> in heat conservation outweighing the metabolic loss, since the brain is
> such a greedy consumer of everything).  What say the learned among us?
> -- 
> Phil Mitchell                                 mitchell@thesis1.hsch.utexas.edu

The lack of hair on humans is one of those cases where one of the most
likely hypotheses for the trait have nothing at all to do with
selection. The idea is quite simple - via a change in the regulatory
genes, humans arose as neotenic variants of their hairy ancestors.
This gives us a higher forehead, larger relative cranial volume, a
change in limb proportions *and* a loss of a great deal of body hair
all in one mutational event - so selection is not a *causal* agent at
all. Once the neotenic mutants exist, selection can then modify the
traits, of course, but the bulk of the transition is one step. There
are numerous other examples of neoteny in nature, perhaps two of the
most obvious being the "gilled" salamanders (axolotls, mudpuppies),
and a vast array of "puppy-like" dog breeds. Neoteny is also typified
by very small genetic divergence between groups with large differences
in morphology - precisely as we see between ourselves and the great
apes. I seem to recall an article about all this by Stephen Jay Gould
not too long ago. It's always made sense to me...
----------------------------------------------------------------
Doug Yanega        (Snow Museum, Univ. of KS, Lawrence, KS 66045)
My card: 0 The Fool         "UT!"          Bitnet: Beeman@ukanvm
"This is my theory, such as it is....which is mine. AAH-HEM!"