Text 1201, 76 rader
Skriven 2004-12-27 12:58:00 av Tim Tyler (1:278/230)
Ärende: Re: "Genes are followers
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CNCabej <cncabej@aol.com> wrote or quoted:
> N.C.

> >> However, with a little research anyone could find such "crackpots" even
> >> here in sbe. But my source is from a scientific work: "The direct
> >> specification of an arbitrary wiring pattern of 10^4 connections 
> >> between 10^10 neurons in the human cerebral cortex would, for 
> >> instance, take more than 10^15 bits of information. This is to be 
> >> compared to the little more than 10^9 bits in human
> >> genome." (von der Malsburg, in The Handbook of Brain Theory and Neural
> >> Networks, 2002). Now imagine: this immense information is only needed for
> >> establishing neuronal connections in the cerebral cortex alone.
> 
> JM:
> >Yes, but these 10^15 bits of post-development "information" might be encoded
> >(i.e. compressed) in the 10^9 bits of the genome. 
> 
> N.C.:
> First, you see that the 10^15 bits is not my "crackpot". Second, from a
> qualitative point of view, no one has been able to even speculate on how the
> genetic information could provide that information.   
> 
> JM:
> > Or perhaps they are not really information at all - they are random 
> > connections.  I suspect that both of these hypotheses play a big part 
> > in the explanation. 
> 
> N.C:
> They can be anything but random connections. On the contrary, in general they
> are highly and amazingly specific.
>
> JM:
> A third hypothesis (yours?) -
> >that a significant fraction of those 10^15 bits are carried by cytoplasmic
> >factors in the egg - is obviously inadequate.  The cytoplasmic factors don't
> >carry anything close to the required amount of information.
> 
> N.C.:
> To me this seems to be a misunderstanding: no one has ever hypothesized that
> and certainly I didn't. 

The source of the information under discussion is relatively well 
understood - as the following quote should indicate:

``The ontogenetic program is limited in the amount of 
  information that can be stored, thereby rendering the 
  complete specification of the organism impossible. A well-
  known example is that of the human brain with some 1010 
  neurons and 1014 connections, far too large a number to be 
  completely specified in the four-character genome of length 
  approximately 3 x 109. Therefore, upon reaching a certain 
  level of complexity, there must emerge a different process 
  that permits the individual to integrate the vast quantity 
  of interactions with the outside world. This process is 
  known as epigenesis, and primarily includes the nervous 
  system, the immune system, and the endocrine system. These 
  systems are characterized by the possession of a basic 
  structure that is entirely defined by the genome (the innate 
  part), which is then subjected to modification through 
  lifetime interactions of the individual with the environment 
  (the acquired part). The epigenetic processes can be loosely 
  grouped under the heading of learning systems.''

 - http://www.cs.bgu.ac.il/~sipper/poe.html
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