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Tim_Tyler comments on Surprised by Brains - Less Wrong

22 Post author: Eliezer_Yudkowsky 23 November 2008 07:26AM

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Comment author: Tim_Tyler 26 November 2008 09:03:03AM 1 point [-]

Oh, and I suppose evolution is trivial? [...] By comparison... yeah, actually.

Nature was compressing the search space long before large brains came along.

For example, bilateral symmetry is based partly on the observation that an even number of legs works best. Nature doesn't need to search the space of centipedes with an odd number of legs. It has thus compressed the search space by a factor of two. There are very many such economies - explored by those that study the evolution of evolvability.

Comment author: DilGreen 11 October 2010 02:42:05AM *  3 points [-]

Surely this is not an example of search-space compression, but an example of local islands of fitness within the space? Evolution does not 'make observations', or proceed on the basis of abstractions.

An even number of legs 'works best' precisely for the creatures who have evolved in the curtailed (as opposed to compressed) practical search space of a local maxima. This is not a proof that an even number of legs works best, period.

Once bilateral symmetry has evolved, the journey from bilateralism to any other viable body plan is simply too difficult to traverse. Nature DOES search the fringes of the space of centipedes with an odd number of legs- all the time.


That space just turns out to be inhospitable, time and time again. One day, under different conditions, it might not.

BTW, I am not claiming, either, that it is untrue that an even number of legs works best - simply that the evolution of creatures with even numbers of legs and any experimental study showing that even numbers of legs are optimal are two different things. Mutually reinforcing, but distinct.