From: w.p.coyne@newcastle.ac.uk
Newsgroups: sci.bio
Subject: Re: Evolution of the human brain's cognitive capacity
Date: 24 Dec 92 13:36:16 GMT
Reply-To: w.p.coyne@newcastle.ac.uk
Organization: Chemical & Process Engineering Dept, University of Newcastle, UK.

darice@yoyo.cc.monash.edu.au (Fred Rice) writes:

>I was wondering, is there an evolutionary explanation for the great
>capacities humans have to think?  I'm thinking about things like our
>ability to do advanced mathematics, for instance.  There is no
>evolutionary survival advantage in being able to solve differential
>equations, for instance.  If this is the case, then *why*, in
>evolutionary terms, can we do such things?

Maybe you should rephrase the question "What are the forces which have
pushed/pulled human intelligence up to the level where it has given
humans the ability to do such abstract things as differential 
equations?"

Various hypotheses have been put forward to try to explain how in 
just a few million years a species went from being "apes" to humans.
But from what I (definitely a non-expert) have seen there does not
seem to see widespread agreement.

     So baring in mind my non-expertise here is the explanation for
the main force which is the best I think I have heard:-

   Several million years ago continental drift moved the continents
   into positions where their climate became ultra sensitive to any 
   changes in the Earth's rotation (Milankovich cycles).  These changes
   resulted in a regular cycle of Ice Epochs which themselves were 
   divided into a series of ice age followed by warmer interglacial.
   The current Ice Epoch has lasted since (I forget, maybe 1 or 2 million
   years ago),  and it has consisted of ice ages of about 100,000 
   years followed by interglacials of up to 10 to 12 thousand years.

        The present interglacial has lasted about 12,000 years, which
   is longer than any other recent one.  [This is partly why in the 
   1970's there was all the fuss about "Is the next ice age about to 
   start"].

       The result of all of this on the climates of the different 
   regions of the Earth was that there were regular shifts from warmer
   to cooler, wetter to drier etc and back again.  Naturally as these
   shifts only lasted between 10,000 and 100,000 years animals and
   plants did not always have time to properly adapt to an environment
   before the climate changed again.

       It has been argued that during the long 100,000 periods humans
   branched into different subspecies or races and some were more 
   successful than others at specialising.  Once the climate changed 
    again many/most of the specialist were at a disadvantage to the 
   less specialist races and were more likely to die out.  
      
        A premium was put on adaptability and it was modern humans
    with their mental, not physical, specialisation which "won".
    Note though that without the repeated climate changes one of the
    less intelligent competitors would have driven them to extinction.


> Fred Rice
> darice@yoyo.cc.monash.edu.au   

further reading
  Imbrie and Imbrie, "the ice age", or some similar title.
  for a recent presentataion of the therory see
    "Children of the Ice" by John and Mary Gribbin.