One of Holland’s more remarkable students was John Koza. In 1987, while flying back to California from a conference in Italy, he had a lightbulb moment. Instead of evolving comparatively simple things like If… then… rules and gas pipeline controllers, why not evolve full-blown computer programs? And if that’s the goal, why stick with bit strings as the representation? A program is really a tree of subroutine calls, so better to directly cross over those subtrees than to shoehorn them into bit strings and run the risk of destroying perfectly good subroutines when you cross them over at a random
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