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From: doug@escher.UUCP (Douglas J Freyburger)
Newsgroups: net.sci
Subject: Re: darwinism
Message-ID: <34@escher.UUCP>
Date: Sun, 23-Jun-85 18:08:29 EDT
Article-I.D.: escher.34
Posted: Sun Jun 23 18:08:29 1985
Date-Received: Tue, 25-Jun-85 02:37:17 EDT
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Organization: NASA/JPL, Pasadena, CA
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> For some days the following question is bothering me. If the evolution
> theory is right, then why the human brain evolved to about six times
> as that of an orung-otung and yet human uses only about 5 percent of the
> brain cells? If the other cells were not needed then why produce them? Does

	I have followed parts of the discussion about
percentage of brains cells used, but I have three other
suggestions as to why humans have such large brains.

1)	Humans have very long lifespans compared to other
creatures (mammals) of similar mass.  This is also in terms
of "heartbeats per life" since the heart rate typical of a
species is related to its typical mass.  Most mammals live
to a maximun of about 10^9 beats, but that's between 25 and
30 years for a human.  Anyways, since
humans live very long, and since brain cells stop
replicating very early on in most (all?) mammal species, we
need the extras so our elders don't get feeble quickly.
Then, having experienced elders as knowledge stores, tribes
with the trait tended to survive better.  I remember
reading something like this in a physical anthropology
text, but it was written in terms of language and
intelligence.  It sounds reasonable phrased either way.

2)	There could be some sort of "critical mass"
required for a typically human task, like complete
language, or tool making, or something.  I know there are
arguments of what a "typically human task" is, but you
still get the idea.  I've used Z80 and Vaxen before, and
there are programs that simply can't be run on the smaller
machine's address space.  It could be a similar situation
with humans versus orangutangs.  I don't think the number
of neurons is linear with brain mass or volume, or that its
linear with processing power either.  Still there might be
some sort of threshhold involved.

3)	The specialization of the human brain involves most
of its mass being in the cerebrum (the part on the top if I
got the name wrong).  That part is a new invention in
evolution.  Since it is so new, it is probably done
brute-force.  Other creatures have had plenty of time for
their systems to be incrementally optimized by evolution,
but humans have had less than a million years (or less than five
million, depending on where you start using the word
"human").  Ants and bees have been around for N times that
long, and they get along with VERY few neurons.  If this is
the case, I hope our incremental optimization involves more
functionality instead of less mass for the same
functionality.  I don't really want to end up in the sort
of efficiency trap that the ants did.

		Doug Freyburger
		JPL 171-235, Pasadena< CA 91106
DOUG@JPL-VLSI, doug@aerospace, ...trwrba!escher!doug, etc.