From: ian@inf.ethz.ch (Ian)
Newsgroups: sci.nanotech
Subject: Re: Evolution and nanotech
Date: 29 Aug 92 06:15:30 GMT
Organization: Dept. Biochemistry, University of Bristol, UK

In article <Aug.27.21.32.01.1992.6666@planchet.rutgers.edu> dsiebert@icaen.uiowa.edu (Doug Siebert) writes:
"In article <Aug.26.21.59.27.1992.1069@planchet.rutgers.edu" JoSH writes:
""
 (deleted)
""
"" I'm speaking of is from CS, genetic algorithms in particular.
"" Early researchers found, not surprizingly, that making small 
"" random changes in computer programs almost always caused them 
"" simply not to work.  The probability of getting from one 
"" working program to another working program is no better than 
"" arriving at the second program in one fell swoop from alphabet
"" soup.  Evolution doesn't work that way.  It works when small
"" changes in structure produce small changes in system performance,
"" as in the "classifier systems" that G.A. research actually uses.
"" These have many higher-level cognates in biological systems, 
"" including diffusive transport, pattern (shape) directed control
"" of primitive operations, and so forth.
"" --JoSH]
"
"I don't think the comparison you make is valid.  I don't think that a genetic
"mutation corresponds to changing a computer program, but rather a change in
"the memory of a computer somewhere.

Genetic change does equate to changing a computer program, or more exactly
to changing the copies of the program that get passed to the replicators
offspring.  A change in computer memory is more akin to somatic mutation, ie
mutation in tissue other than the genitals, which affects the individual but 
not its descendants (assuming it can still produce any :-).

"Many genetic changes are essentially
""random" and don't increase an organism's chances for survival.

This is still undecided but a popular theory holds that most mutations are
neutral-ish.

"
" (Nice discussion of mutating machine code deleted)
"

" And JoSH comments:
"[Minor damage to mechanisms happens all the time, and does indeed change
" their appearance and degrade their functionality.  However you will never
" find a car that has accumulated enough dings and scratches to convert
" it into a piano.

This isn't valid because cars don't reproduce.  In any case the valid
comparison with genetics is not towards denting a car but rather to scribbling
on the blue-prints.

" Evolution requires a *long* sequence of cumulative
" changes, and and needs a fairly complex structure in the evolving
" organism to support it (including sex).

What makes you thing that evolution requires sex ?  Viruses and
bacteria evolve far, far faster than any sexually reproducing organism. 

" On the other hand, the equivalent of genetic damage, causing perhaps
" the sort of problem Ian originally mentioned (i.e. suppressing the
" useful function of a self-replicating device) could certainly happen.
" However, it would not lead to evolution.  It would be more like cancer
" in the (self-reproducing) cells of an individual organism.  
" It is a useful avenue of discussion to explore methods of preventing
" this; but don't confuse it with evolution.  It isn't.

As I mentioned above if it was somatic change it doesn't lead to evolution
but if the replicators offspring inherit the change then it is evolution.
Only a very tiny piece of evolution, I'll admit, but it is evolution.
That's only terminology, however, The real question is how much of a problem 
would it be and how do we solve it ?

[Bacteria exchange genetic material more readily than sexual reproducers,
 across species even, and virii can undergo variation by including
 snippets of the host genome.  One main thrust of Holland's work
 (see "Adaptation in Natural and Artificial Systems", particularly
 the revised version, MIT Press, 1992) is that evolution is a search
 procedure over the design space.  If there is no sex (or other 
 mechanism to distribute selected variations) the long sequence 
 of cumulative changes must be traceable back along the ultimate
 organism's *single path* lineage.  With sex, the traceback is a
 family tree.  In CS terms, without sex, the search is sequential,
 but with sex, it is parallel, with the parallelism increasing 
 exponentially with the number of generations.
 --JoSH]