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From: bjm@dcs.ed.ac.uk (Bruce McAdam)
Subject: mutation/sexual reproduction (was Re: Has anyone written a genui...)
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Date: Mon, 4 Dec 1995 11:49:13 GMT
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[Kinda messily trying to follow up to Peter Harrison's original message and
 Steve Dekorte's followup]

In article <49g7ev$4sq@news.onramp.net>, dekorte@suite.com (Steve Dekorte) writes:
> (Peter Harrison) writes:
> > There seems to be a misunderstanding that evolution works primarily by
> > mutation of DNA.  This principle has been ported to Evolution models,
> > hence the concept of 'mutation' of computer code.
> >
> > The problem is that direct mutations of DNA usually cause serious
> > problems with the resulting creature, not a viable creature.  The
> > answer to creating more complex adaptive creatures taken by nature was
> > sex.  Sexual Reproduction allows a diversity of viable creatures to
> > change, but without corrupting themselfs so they don't work in the
> > environment.
> 
> It seems to me that combining the gemones of individuals is just an 
> *additional* form of mutation with obvious benefits. 
> Understanding this and seeing that 2 genome 'sex' is popular in nature 
> for physical and not informational reasons leads us to ask why combining 
> >2 genomes is not a more popular form of mutation for GA/AL algorithms(?)

Evolution works neither by combining organisms' geneotypes or by mutating 
genotypes but by selecivly preserving the different variations in genotypes
that arise by ANY means.

Sexual reproduction has not arisen because it is successful at creating complex
organisms but because DNA which makes organisms reproduce survives better (a 
particularly interesting hypothesis is that this DNA is non-chromosomal and
does not affect the organism in any other way)

I would say it is likely that complex organisms (like ourselves) could not 
have arisen without sexual reproduction so it is probably a good idea to use
it primarily but mutation is also useful to keep the gene-pool topped up 
with different combinations of genes which have either not arisen before of
were not found useful before.  (I think research has shown that a GA can work
without any mutation).

If you are using some evolutionary approach to problem solving the best approach
may be to base your next generation on all aspects of your current generation.
i.e. have genomes surviving unchanged between generations, genomes created
by interpolating between a number of successful genomes (breeding) and genomes
created by trying somthing roughly like a successful genome (mutation).

-- 
   ___          ___     Bruce J. McAdam
__/__ \__    __/__ \___ Computer Science Undergraduate
_____|_| \__/_____| |__ The University of Edinburgh
  \____| |_____| |_/    bjm@dcs.ed.ac.uk
     \___/  \___/       http://www.tardis.ed.ac.uk/~bjm/
