You should study some embryology! Symmetry is easy, once a basic symmetrical body plan is established (e.g., a worm). Mutations of many genes produce symmetrical results based on fundamentals of embryological development; evolution does NOT generally have to wait for two mutations, one for each side of the body!
These are well-studied issues, not some novel idea at all.
So there's nothing "perplexing" about this at all, from what I know.
Think your examples through a little...for example:
" if eyes evolved from light-sensitive cells, why didn't these cells pop up all over the place? What we have is two perfectly aligned eyes pointing forwards."
Well, they mave have popped up all over the place. But if all you have is basic light sensitivity, what use is having light detectors everywhere?
Better to organize these in a ways that gives directional sensitivity, like the "eye cups" of simple organisms. When the "cup" specializes further, you can get a focused image, etc.
Now, at this point, one might argue that an extra "eye" would be helpful in humans, but embryological and genetically you now have an extremely difficult problem - how do you make such a huge change to a complex, specialized system?
Evolutionary biology shows through fossil records, and embryology shows through its basic principles, that simple body plans are easily altered, but major changes in complex, specialized body structures are slow and rare.
So, why don't we have eyes everywhere? Because specialized eye cups have an advantage over randomly placed light detectors. The rest is history. Why are the eyes symetrically placed? Embryology.
[This message has been edited by Zhimbo, 10-23-2003]
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