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From: cam@edai.ed.ac.uk (Chris Malcolm    cam@uk.ac.ed.edai   031 667 1011 x2550)
Newsgroups: comp.ai
Subject: Re: evolution of intelligence
Message-ID: <491@edai.ed.ac.uk>
Date: 3 Aug 89 23:23:18 GMT
References: <2153@hub.UUCP> <2355@bingvaxu.cc.binghamton.edu>
Reply-To: cam@edai (Chris Malcolm)
Organization: University of Edinburgh, Edinburgh
Lines: 66

In article <2355@bingvaxu.cc.binghamton.edu> cjoslyn@bingvaxu.cc.binghamton.edu.cc.binghamton.edu (Cliff Joslyn) writes:
>In article <2153@hub.UUCP> silber@voodoo.ucsb.edu writes:

[I wrote >>>>]

>>>>Note that the largest and most rapid recent evolutionary change which   
>>>>the human race has suffered is a very considerable change in brian size;
>>>>this is usually presumed to be correlated with becoming cleverer. If we
>>
>>What do you mean by 'rapid', what do you mean by 'human species'? even the
>>proto-humans of three-million years ago didn't have pea-brains.  
>
>Further, there are many other gross morphological differences between
>humans and non-humans: erect posture, loss of estrus, loss of most body
>hair, growth of speech mechanisms.  No doubt the selective pressures on
>all of the above interacted with brain development in our ancestors in a
>complex, circular way.  Unless someone can provide a decent objective
>measure of "size of evolutionary change" it would seem like simple
>prejudice to say that brain increase is the most "significant" of all of
>these. 

The discussion started with assertions that the special human
characteristic was our mentality - abstract thought etc. - and that
human mental capacity had evolved so slowly and so long ago that it must
therefore be virtually identical - in genetic endowment - among races,
sexes, and individuals. 

Three million year old proto-humans didn't have pea brains, but they did
have brains noticeably smaller than ours - a vague memory suggests about
half-way between us and chimps. I think that Cro-Magnon and Neanderthal
man were the first to reach the range of modern brain size, and that
that corresponded in time with a steep acceleration in the rate of
improvement of artefacts and art.  Upright posture was developed in
proto-humans before modern brain size.  As far as I know it is not known
when we lost hair or estrus, but my hunch - call it prejudice if you
will - is that these are less connected with mental powers than brain
size :-) Speech, semantics, and brain-power, are, I agree, a chicken and
egg problem.

Cliff's point about an objective measure of amount of evolutionary
change is good, but I don't see how we can get it short of decoding the
chromosomes. The much-quoted 1% difference between humans and
chimpanzees is meaningless without knowing how the code works. For
example, I could take a sponge cake recipe and make a 1% change - in the
recipe - by saying "use a hundred times as much butter and sheep's
brains instead of eggs".

Note that even if our brains had fully evolved 100 million years ago,
that doesn't mean the genetic endowment of brainpower would have evened
out between individuals; it could be advantageous to have a mix of
mental talents, just as it is advantageous to have a mix of blood types,
or mixes of castes in termite colonies.

In summary, by "rapid", "recent", and "significant" what I meant was
that in the fossil record from proto-ape to human the last major change
of dimension was cranium size, and that this happened sufficiently much
faster than the previous development of cranium size in mammals and
primates in general, that words like "sudden", "startling", "explosive"
are sometimes used to describe it. For some special reason, at that
time, having a small brain was frequently fatal, or at least
unattractive to the opposite sex (the peacock-tail theory of
brain-power).
-- 
Chris Malcolm    cam@uk.ac.ed.edai   031 667 1011 x2550
Department of Artificial Intelligence, Edinburgh University
5 Forrest Hill, Edinburgh, EH1 2QL, UK