From newshub.ccs.yorku.ca!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!rpi!usc!wupost!darwin.sura.net!europa.asd.contel.com!uunet!tdatirv!sarima Thu Dec 26 23:57:39 EST 1991
Article 2322 of comp.ai.philosophy:
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>From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: comp.ai.philosophy
Subject: Re: Scaled up slug brains
Message-ID: <346@tdatirv.UUCP>
Date: 19 Dec 91 19:43:47 GMT
References: <349@idtg.UUCP> <45031@mimsy.umd.edu> <330@tdatirv.UUCP> <45102@mimsy.umd.edu>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 60

In article <45102@mimsy.umd.edu> harwood@umiacs.umd.edu (David Harwood) writes:
|In article <330@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes:
|>In article <45031@mimsy.umd.edu> harwood@umiacs.umd.edu (David Harwood) writes:
|>|(How many genes do slugs have anyway? They don't look like they have many.)
|>
|>They have aproximately the same number as we do.  All multicellular animals
|>have DNA contents that are of the same order of magnitude. ...

|>Brain structure, at least in forms with complex brains, tends to be *very*
|>conservative.  The brains of the apes even have the same sulci as ours do,
|>and *that* is just a topological feature to allow better packing!
|>
|\\\\\\\\\\\\\\\
|	Our President has a "brain structure" which "tends to be very
|conservative" too.

The point is that ther is little anatomical variation in brain structure
when compared to anatomical variation in other body parts.

This suggest a deep-seated, fundamental continuity of function.
In evolution, stability of form usually means stability of function.
The least changed of all proteins in the world are the cytochromes that
have almost the same function in every living thing on Earth.

|	Same order of magnitude? Are we talking about the complexity
|of a combinatorial system, eg involving the number of viable genetic
|"programs"?

No.  I do not think such a thing is even estimable at this time.
We know too little about embryology to know what constitutes a 'viable'
genetic program.

|	This is entirely misleading. I've already pointed out 
|(in another posting) that even small genetic variation makes for large
|anatomical and physiological variation. Chimps may be 99+% like us,
|but their brains do not have specialized language-processing areas,
|and do not show related, major lateralization of function. A variation of
|3/1 (?) in number of genes (what I asked) is immense in any case.

Hmm, well I may have misunderstood.  You said something about slugs not
having many genes.  This is not true, they have many thousands, just like
we do.  Most of them are even rather similar, being involved in basic cellular
metabolism and generalized embryonic development (for instance the master
embryonic regulator, the homeobox, is present in all 'higher' animals).

Much of the differences between slugs and humans may well reside in detail
embryonic development regulators.  A small fraction of the total.

Which is indeed what you pointed out for the chimp and humans.  The question
is how much of the differences in the brain are fundamental, versus merely
quantitative.

Also, I believe some recent results have demonstrated lateralization in
chimpanzees.  (I think I saw an announcement to that effect in Science
News).  I find most of the differences to be scale issues.  Even lateralization
is essentially a mechanism for increasing capacity in a fixed compartment.
-- 
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uunet!tdatirv!sarima				(Stanley Friesen)



