Eye question:
A discussion with my son made me wonder about the course of eye evolution. I’m pretty familiar with the easy and sensible step by step evolution of the eye from a patch of light sensitive cells, to a cupped patch, to a nautilus like eye, then with the addition of a cornea, and so on up to what we have today. What we have today includes the fact that the rod and cone cells are upside down, forcing the nerves to come off them into the eye, and so the nerves then bundle up and leave the eye through a hole in the back of the eye, resulting in our “blind spot”. A really stupid “design”.
Now, that suggests to me that the earlier stages also had this “nerves out the front” setup, so back to the cup stage, the nerves would have been inside the cup. Farther back, the nerves would have been sticking up in the air from the patch of light sensitive cells. I would have imagined that the light sensitive cells might have evolved from skin cells with the enervation from the bottom, but if that were the case, then wouldn’t the whole bad design have been avoided?
So - I know we have examples of the intermediate stages, both light sensitive cells as well as cups, and so on. Do some of them have the nerves sticking up? Or, are there other ideas about how this arrangement evolved, and from what precursors on the skin?
-Equinox
"Biological Evolution", I would think.
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