From: collins@newton.apple.com (Scott Collins)
Date: Fri, 20 Aug 93 16:21:17 PDT
To: szabo@netcom.com (Nick Szabo)
Subject: Re: genetic algorithms for crypto analysis
Message-ID: <9308202305.AA26160@newton.apple.com>
MIME-Version: 1.0
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  >Sexual reproduction (aka string crossover)

Sexual reproduction is not string crossover.  Normal reproduction in a
typical GA picks two individuals from the population independently with
probability related to their fitness. In sexual reproduction, the pairs are
constrained such that selection is not independent e.g., 'males' mate with
'females'.

Sexual reproduction is one factor that dampens premature dominance of the
population by a few 'great' individuals, so that search can continue on
other hills, i.e. encourages diversity and thus IS good, as was previously
stated, in choppier solution spaces.

Also consider the dominance mechanism supported by the diploid chromosome. 
One reason why double-strand species like ourselves can more rapidly adapt
than haploid species.  Dominance protects solutions that were good once
(and might be again) from being sampled to death, by holding them in
abeyance (a 'recessive' trait) in a temporarily unfavorable environment. 
Again, this encourages diversity by dampening premature destruction of hard
won solutions.


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