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

Clara N. Fitzgerald (cfitzger@s.psych.uiuc.edu)
7 Sep 1995 17:38:33 GMT

Troy Kelley <tkelley@hel4.brl.mil> writes:

>From: H. M. Hubey, hubey@pegasus.montclair.edu
>Date: 2 Sep 1995 21:10:48 -0400

>There are differences in the human brain, in terms of certain structures
>being bigger or different than other animals.

>Also, because early humans spent so much of their time shaping objects,
>particularly stone tools, and because this skill had such a direct impact
Let's not forget baskets, pottery, etc...
>on the survivle of the species ... these areas of
>the human brain are particularly well developed. This might also help
>explain why males tend to be more spatially oriented than females, who
>tend to be more verbally oriented. It might also help to explain why so
I'd put the difference more to throwing skill than manual dexterity.
>many people are right-handed (this is just a personnel theory of mine).
>Since spatial relations are controled by the right side of the brain, and
>the human right hand is controled by the left side of the brain, this
>leaves the two areas independent of each other and can allow each side to
>utilize all of its resources to work together to shape tools. The
Left-handed people have the pattern for language/spatial tasks
reversed (well, most of them), so there would be no preference for
rightness. The theory I've seen is that social factors would favor
whichever hand the majority favored (lots of left-hand taboos about
eating, etc, which have persisted to at least a generation ago [all
students forced to write with their right hands]), and this majority
would grow until balanced by the need for recovery from injury (don't
hard-wire everything, because you'll lose flexibility in case of
accident. Research shows that most women, whose brains tend to be
less divided, recover better from strokes). This may also explain
why a larger proportion of left-handers have mental problems - if the
normal development of the brain is randomly damaged in 10% of
people (just to keep the numbers easy) in a population where 10%
should be left handed, such that what would have been the non-dominant
side of the brain must perform the dominant tasks, 9 of the would-be
rights will become left, 1 of the would-be lefts would become right,
resulting in 81 normal rights, 1 changed right, 9 normal lefts,
and 9 changed lefts. A larger than proportional number of left-handers
are also geniuses in some field, which probably interacts with the
difficulty of growing up in a right-handed world.
I'll have to look up some more books on the topic...

>problem with this theory is that most apes and chimps are right handed
>as well, and they have not been shaping stone tools, at least that I know
>of. But it still could be that similar operations are being performed, in
>that when chimps are using their right hand (digging for termites with a
>tig) they are still using the right side of their brain's to process
>spatial information.
They have been making tools (such as termite fishing twigs), and
Kanzi has learned to make chipped blades by throwing rocks together,
and used them to cut a rope on a box holding food. There's a new book
_Kanzi:the ape at the brink of the human mind_ by Sue Savage-Rumbaugh
and Roger Lewin, ISBN 0471585912 (1994:Wiley), which I have found but
haven't read yet. Kanzi also seems to understand spoken English,
but I've only seen part of one test, on videotape. I don't know if
they've done any brain scans on him...

>It is interesting to note that increases in intelligence came about the
>same time our increases in tool development was taking place.
How are you measuring intelligence, as brain size was increasing
before evidence of stone tools are found?

--

-Clara A. N. Fitzgerald     cfitzger@s.psych.uiuc.edu

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