Darwin convinced most of the world that a modern eye evolved gradually from a simple structure, but he didnt even try to explain where the starting point - The light sensitive spot - came from.
Well, Darwin knew nothing of what we know about genetics, so couldn't have discussed mutations. Once we do know about these, it's not as if light sensitive materials are particularly unusual or hard to synthesise in nature. Light sensitive cells aren't found only in eyes - they can be found in many plants including, for example,
the guard cells of onions; and in the animal kingdom we come across them in
butterfly genitalia.
Light-sensitive cells can perform important functions in the absence of a central nervous system - some jellyfish and worms have simple eyes which send impulses directly to its muscles, causing the animal to instinctively move away from predators or, in the case of
at least one type of rag worm, to prompt migrations in response to the rising and setting of the sun.
If your complaint is that we should not be allowed to come to any conclusion about the origin of a structure, however tentative, unless we can identify the exact mutation responsible for every step in its development, this seems unnessecarily restrictive to me. Should we just give up on all scientific endeavour because it's all pointless before we reach some grand, unifying Theory of Everything?
Edited by caffeine, : To correct bad links - why must every forum on the internet have slightly different conventions for tags? Thanks for pointing this out Jack
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