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It may be a mistake to assume evolution 'designed' anything at all. Its a drunkard's walk over the solution space. As soon as a relative optimum point is reached, evolution tends to stick there and not search for further, more-optimum solutions.

Witness the 'thumb' of a panda, which is uses to strip leaves from the eucalyptus branch. It has a thumb (toe on its paw) but no, evolution chose to extend a wrist bone in a kind of protuberance; the panda pulls the branch between that and its arm to strip leaves. Not ideal; kinda weird really. But evolution doesn't give a flip.




Evolution doesn't design, clearly. But its solutions are not determined by chance alone, either. The shapes of the solutions are partly determined by the contours of the available solution space. It's sort of like pressing soft material into a mold, I think. The trajectories of the individual bits of material are governed by chance; but after applying and releasing pressure, the macroscopic object invariably forms itself in the image of the mold.


Sure but the 'mold' is a complex surface with many local maximums. Once evolution reaches a local maximum, then drunkards walk is stalled - it moves incrementally in any directin - things get worse. It cannot leap across the gap to another local maximum; ok its unlikely it will make the leap.

So we get different populations with wildly different solutions to the same problem.


How optimum the solution is is related to how important and conserved the system is. The visual system is very old, and it has unquestionably been subject to intense selective pressure.


Then explain the half-dozen entirely different vision systems extant right now? They are very different; they have all been under selective pressure.


It would be interesting to see if they all succumb to the same kinds of illusions. I guess the important question is whether these illusions are arbitrary and reflect arbitrary choices by evolution, or if they are fundamentally hard and would be hard for any hypothetical vision system. My hunch is that they are fundamentally hard.




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