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From: malc@tahoe.unr.edu (Malcolm L. Carlock)
Newsgroups: sci.bio,talk.origins
Subject: Re: sexual selection and investment
Message-ID: <1153@tahoe.unr.edu>
Date: 5 Apr 88 07:16:46 GMT
References: <1988Mar13.160941.22096@utzoo.uucp> <25527@cca.CCA.COM> <2403@saturn.ucsc.edu> <25669@cca.CCA.COM> <1125@3comvax.3Com.Com> <4736@aw.sei.cmu.edu> <1137@3comvax.3Com.Com> <368@nancy.UUCP>
Reply-To: malc@tahoe.unr.edu.UUCP (Malcolm L. Carlock)
Organization: Univ. of Nev., Reno-Mathematics
Lines: 48
Keywords: neoteny, humans as physically "underdeveloped" apes
Summary: Looks like humans have LOST sexual dimorphism


Concerning the debate over whether humans have become less sexually
dimorphic, or the other pongidae (gorillas, chimps, orangs) more dimorphic:

An important characteristic that distinguishes adult humans from adult
members of the other pongidae is the fact that the opening at the base of
the skull through which the spinal cord passes (sorry, I can't remember
what it's called) remains nearly centered at the bottom of the skull
throughout the life of the individual, helping to allow an upright posture.

In the case of the other pongidae, infants are born with this opening
in the central position (as in humans), but as an infant matures, the opening
migrates toward the rear of the skull, resulting in a more horizontal attachment
of the head to the body, in harmony with a more hunched ("apelike") adult
posture.

The result of all this is that adult humans tend to resemble INFANT chimps/
gorillas/orangs MUCH more than they resemble the adults of those groups
(large head relative to body, small face, spinal cord opening at bottom of
skull, etc.)

What is all this leading to?  Well . . .

A common characteristic of mammals, including apes, is that sexual dimorphism
prior to puberty is almost nonexistent (other than obvious differences in the
construction of sexual organs).

Since adult humans tend to resemble infant apes, and infant apes display far
less sexual dimorphism than adult apes, then it would seem that humans have
indeed "lost" some of their sexual dimorphism relative to the other pongidae.

. . .

The phenomenon of one species actually being an underdeveloped form of another
species (in this case, humans being (physically) "underdeveloped" apes) is
known as neoteny, and much evidence has been accumulated which supports the
neotenic view of human development.  For an interesting discussion of neoteny,
see Stephen Jay Gould's book, "The Mismeasure of Man" (well worth reading in
any case).


Cordially,

Malcolm L. Carlock
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malc@tahoe.unr.edu.UUCP			       University of Nevada, Reno