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From: ronald@uhunix1.uhcc.Hawaii.Edu (Ronald A. Amundson)
Newsgroups: sci.bio
Subject: Re: Paranormal phenomena and evolution
Message-ID: <11540@uhccux.uhcc.Hawaii.Edu>
Date: 20 Feb 91 07:20:09 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> <75075@bu.edu.bu.edu> <854@frc.frc.maf.govt.nz>
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In article <854@frc.frc.maf.govt.nz> jbj@frc.UUCP (Brian Jones) writes:
>
>During WWII my father, an engineer, was fighting in Burma with African troops.
>He noted that the African hill tribesmen (they all were - not sexist) used to
>easily outrun the much taller plains tribesmen in hill country, but on the flat 
>lost badly. Something to do with the lower centre of gravity in small people, he
>believed.
>
>If his observation is true, and it does make sense, then surely it is an
>example of evolutionary pressure? Now that there is no need to run to survive
>the advantage of short (or long) legs is removed.
>
>B. Jones
>            

Accepting this anecdote as evidence, it does not follow that this is
"surely" an example of evolutionary pressure.  One obvious and
uninteresting reason is that the hill people were accustomed to
running in hills, and the plains people on plains.  

A more interesting reason is that to show that a character difference
exerts selective force on a population it is necessary to show that
the difference between the two populations is _due to_ selection of
the character in question.  It is _not_ enough just to tell a story
about how a character is advantageous in a certain environment and
then conclude that since "it does make sense", the evolutionary force
has been demonstrated.  

For something to be an "evolutionary pressure" it must actually
_operate_ on the group in question -- it's not enough just to show
that it _might have_ operated.  As my grandmother-in-law once said,
"Maybe-chicken doesn't make soup".

Ron Amundson


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