X-Message-Number: 4033
Date: Fri, 17 Mar 1995 21:52:52 -0800
From: John K Clark <>
Subject: SCI.CRYONICS Symbols

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 (Thomas Donaldson) Wrote:

	    >My problem is not with the Turing thesis. My problem comes
	    >from the practical fact that the speed of a computation often    
	    >matters a great deal. [...]  there are plenty of
	    >machines out there which are much more powerful than a Turing
	    >machine.
	    
Like what? As Perry Metzger pointed out in #4010 speed is not an
issue, A Turing machine can be made to work at any arbitrary speed. 
	     
	    >if you reread your original definition there was no
	    >mention of any conventions. 
	    
You said you intended to misrepresent me and I see your right on
schedule. For the record:

On Sunday March 12 in message #3999 I said:
"A symbol stands for or represents something else because of a
convention, in this case the mechanism of the brain, not because
of a similarity. Symbols substitute abstract representations for
concrete objects and are realized by changing the structure of a
material object. A symbol must symbolize something, so a
computer bit or a letter are just a tokens, but words are symbols." 
		

	      >As for DNA, to speak of it as a "code" omits 
	      >the fact that it is not just a code: it is a physical chemical
	      >which has effects on other chemicals. Codes and conventions 
	      >(and symbols too) have an arbitrary character; DNA does not. 
	      >It is only when we try to understand it that we think of it as 

	      >a "code"... but without its special chemical characteristics it
	      	      >would do nothing at all.
		   
No, your wrong on two counts:
1) The genetic code effects the way messenger RNA manufactures
protein NOT the way DNA duplicates itself or the way the
information in DNA is transcribed into RNA , it has nothing to
do with DNA. 
    
2) The nucleotide triplet CAU in messenger RNA symbolizes the
amino acid histidine for example but their are no "special
chemical characteristics " that relate one to the other. One
type of transfer RNA has an anticodon that connects to the CAU
triplet of messenger RNA like a key fitting into a lock. At
another part of the transfer RNA molecule an amino acid can be
attached, in this case histidine. However transfer RNA can't
tell one amino acid from another, the amino acid attachment part
is identical in all tRNA molecules but in practice those that
have the anticodon for CAU are only attached to histidine. The
reason for this is an enzyme ( aminocyl-tRNA synthetase) , this
enzyme can tell one amino acid from another, and tell one tRNA
molecule from another and a attach a animo acid to it. This
enzyme does NOT look at the anticodon at all but at another part
of the transfer RNA, the DHU loop. In the lab the DHU loop from
one type of tRNA has been grafted onto another type of tRNA and
that changes the genetic code. It's also interesting that this 
enzyme is a protein encoded by, what else, the genetic code.
   
The bottom line is that the CAU triplet has no chemical affinity
for histidine, the only reason it symbolizes histidine is
because of a convention, and as far as anybody can determine
this convention, the genetic code, is as arbitrary as the metric
system. As I mentioned before Francis Crick devised his own
genetic code that was much better and produced far fewer errors
than natures.   
   
	    >So why is it that a tree which grows in the sunlight is not
	    >using  symbols when its leaves make energy? 
	    
Because even if the leaves have information of some sort encoded
in them the tree doesn't have a convention to extract it so the
leaves don't symbolize anything. 
	   
	   >And if the earthworm under the tree is using primitive
	   >symbols, just what  are they?
	   
There must be neurons, or more likely groups of neurons, that
symbolize up, down, wet, dry, light, dark and perhaps a few more.
	   
Now I'd like to repeat a question of my own that I've not
received an answer to. Since you don't think in symbols but
employ the actual object, how do you fit something as hot and
big as the sun in your head when you think about it?
				
				John K Clark            

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