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Article 2130 of comp.ai.philosophy:
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>From: robison@chloro.harvard.edu (Keith Robison)
Newsgroups: comp.ai.philosophy
Subject: Re: Scaled up slug brains
Message-ID: <robison.692764882@chloro>
Date: 15 Dec 91 02:41:22 GMT
References: <12677@pitt.UUCP> <60044@netnews.upenn.edu> <12689@pitt.UUCP> <40650@dime.cs.umass.edu>
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yodaiken@chelm.cs.umass.edu (victor yodaiken) writes:

>In article <12689@pitt.UUCP> geb@dsl.pitt.edu (gordon e. banks) writes:
>>In article <60044@netnews.upenn.edu> weemba@libra.wistar.upenn.edu (Matthew P Wiener) writes:
>>>Well, OK.  What is the evidence that human brains are merely a scaled
>>>up version of slug brains?  (Besides certain USENET posters and US vice
>>>presidents?)
>>>
>>The words "scaled up" are my detractors', not mine...
>>...I think the analogy holds.  The worm has the same basic elements
>>as the human, although the human may have additional elements that
>>do not exist in the worm, it appears that it is mainly a matter of
>>complexity of connections and not new and different structures that
>>characterize the differences, at least on an anatomic and neurochemical
>>level.

>Appears to whom? I must say that you have an interesting approach
>to science. We understand a tiny bit of how system X works, system
>Y is vastly more complicated than system X but contains similar looking
>structures --- so assume that some unproven model of X is also a model of
>Y. Steel gear boxes can be constructed from the same ingredients as
>steel I-beams. Thus, using your approach, we conclude that a model of 
>the behavior of a steel I-beam can be extended to describe the behavior of
>a gear box.


	No, by this approach we conclude that studying the properties of steel
will tell us something about the properties of I-beams and gears, and that I 
pick whichever system is the best for the techniques I have on hand.
Don't forget, we're talking biology here, and worms (C.elegans), "slugs"
(Aplysia), flies (Drosophila), and us probably had a common ancestor AFTER 
the emergence of simple behavorial learning, as it is so widespread amongst
multicellular animals.  Besides, simple conditioning can be found amongst
unicellular organisms, so the ground work for complex neural systems was
probably already present before the emergence of neurons.
	This does not mean that ALL of the properties of invertebrate neural 
systems will be found in vertebrate systems (or vice versa), but that MANY of
them will be the same.  The existing molecular evidence suggests that this
is true.  If you think this is preposterous, ponder for a moment that the same
sorts of genes which set up the gross physical structure of your brain set up 
the body plan of insects, and that the vertebrate forms were found using the 
fruit fly genes.  Clearly there are differences, but the fact remains that 
invertebrates are often amenable to analyses which are impossible or 
impractical with vertebrates (compare screening 10,000 mice for a learning 
mutant versus screening 10,000 flies).  This certainly is an interesting
approach to science, IT WORKS!



Keith Robison
Harvard University
Program in Biochemistry, Molecular, Cellular, and Developmental Biology

robison@nucleus.harvard.edu


