Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!tdatirv!sarima
From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: sci.bio
Subject: Re: Paranormal phenomena and evolution
Message-ID: <138@tdatirv.UUCP>
Date: 14 Feb 91 21:14:20 GMT
References: <1435@gtx.com> <6735@harrier.ukc.ac.uk> <104@tdatirv.UUCP> <6747@harrier.ukc.ac.uk> <106@tdatirv.UUCP> <545@zds-ux.UUCP>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 41

In article <545@zds-ux.UUCP> gerry@zds-ux.UUCP (Gerry Gleason) writes:
>This discussion prompted me to speculate about just how the evolutionary
>pressures sort out on this issue.  I would think that the average height
>previous to the recent change would have been in some sense optimal, and
>probably hadn't changed much for a while.  Doesn't this mean that there
>is the possibility that there is now an evolutionary pressure toward being
>shorter?  I know it would depend on the nature of the pressure and whether
>it is still operating.  Say that being 4 inches taller increases your risk
>for heart attack or other conditions.  Wouldn't the actually taller population
>be selected back toward the "optimum"?  Then if the behavioral conditions
>are removed the population would immediately become shorter than it originally
>was.

Yow!!  Good question!  It is certainly possible.  Though I do not know how
we could test it, given the (entirely appropriate) reluctance to experiment
on humans.

There is also another possibility.  It turns out that something superficially
similar to 'inheritance of acquired characteristics' does occur.  Essentially,
when the environment forces a particular growth form on an organism, then any
genetic predisposition to that growth form is selected for.  This reulsts,
eventually in a race that takes the 'enforced' growth form even when it is
no longer enforced.

The classical example of this is plants growing on exposed headlands next
to the ocean.  In these environments the salt spray caused erect, exposed
branches to be killed, resulting in a low-growing, matted growth form.
This growth form shows up even in plants grwon from inland seed sources,
that are clearly genetically able to grow taller.  However, when a seeds
from the coastal plants are grown inland, away from the salt spray, they
continue to grow low and flat.  [Note, I am talking about plants from the
same species, for instance mule-fat here in California].

Applied to the human size situation this could mean that prior to modern
diets human size was limited by the environment, and our genetics had
evolved to minimize the impact of this 'forced' (dietary) size limit.
In this case, we have now been released from the selection for limited
size and the genetic component of our size may also be increasing (slowly).
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uunet!tdatirv!sarima				(Stanley Friesen)