I'm no CS expert (I got a 2-2, and only just scraped that ;-) but we use GA's in the evolution of the scores for SpamAssassin. My recommendation for speed is to look into the GAlib at http://lancet.mit.edu/ga/. It's a C++ library, but that's what you have to use for speed - and GA's tend to be quite slow.

Alternatively, also check out MyBeasties - a Perl library for doing GA's. I'm sure going through the source code to that module will tell you everything you need to know.

Sorry this doesn't answer your question more directly - I'm still waiting for the caffeine to sink in - I might be able to make more sense of it later ;-)