Brain size (was Re: AAT QUESTIONS...)

pete (VINCENT@REG.TRIUMF.CA)
16 Aug 1995 09:23:07 GMT

HARRY R. ERWIN (herwin@osf1.gmu.edu) sez:

`The large brain probably reflects entry into the treeless savannah.
`Adaption to living in that environment also probably led to reduced sexual
`dimorphism, loss of tree-climbing features, the initial appearence of the
`pair bond, secondaru sexual characteristics rudimentary speech (originally
`developed as representational behavior similar to bee dancing) and
`increased complexity of social behavior.

Ooo. Now this is an interesting comment. (hi, y'all, I'm back from
a short vacation) The increase in brain size is something we haven't
kicked around much here that I recall. I'm curious as to why you
think there's a correlation between brain increase and savanna living.
I have lots of loose speculation about mechanisms for increased brain
size, (though I'm not sure how close the relationship is between actual
cortex volume and computational ability), relating to complex
social behaviour, as you mentioned, as well as a need for lots of
fine motor skills in manipulation of the newly freed forelimbs,
which I believe would have been used to launch stone projectiles
maybe millions of years before we got in the habit of modifying them.

..Excuse me while I indulge in some of that loose speculation...
I guess that what I see as prerequisites for development of our
sort of intelligence are a complex social environment, to encourage
some abstract conceptualization and communication, plus a
need for lots of motor cortex to drive complex movement, thus
increasing the amount of spare neocortex lying around loose
to provide a home for the abstractions to ferment into a
coherent world model. But none of this requires a savanna to
work. Of course, it doesn't explain why lots of other social
mammals didn't develop large brains, and substantial intelligence,
either. Let's see... social carnivores, like lions and wolves,
are so physically well suited to their niche that they wouldn't
require the excess baggage. Most of the other mammals large
enough to pack a big brain are either solitary, or ruminants
with pretty simple social systems, and no need for fine motor control.
The only exceptions that immediately occur to me are other
primates, and elephants. As big brains seem to be so useful,
it's odd that they wouldn't show up more often, least in these
candidates.

--

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    vincent@triumf.ca   <== faster       %    Pete Vincent

    vincent@freenet.vancouver.bc.ca      % Disclaimer: all I know I

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