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Old 02-27-2017, 09:34 AM
Darren Garrison Darren Garrison is offline
Join Date: Oct 2016
Posts: 6,448
Originally Posted by adaher View Post
Now the eye, that brings me to another question. How DOES an eye evolve? An eye is very sophisticated, yet it has really only one purpose: to enable one to see. And until one can see, it's not doing anything to aid in survival. So how does that mutation happen? Did a fish just get born with a simple eye one day 4 billion years ago?
First stage is a patch of light-sensitive molecules on the surface of a cell.* All that they can show is that there is more light on one side of the cell than the other, but that is still useful--it can trigger the cell to ooze or rotate its cillia/flagella in a way that moves it towards or away from the light. Even bacteria have those.

Second stage is having versions of those light-sensitive molecules on the surface of patches of cells on a multi-cellular organism. Again, all they can show is that there is more light in one direction than another.

Third stage is having those patches of cells in a shallow pit, which allows the direction of the light to be more finely determined.

Fourth stage is having the pit become deeper, and partially closed over. This allows for a pinhole camera, and finally an eye that can form an image.

Fifth stage is forming a transparent membrane over that partially closed pit roof. This becomes a lens.

Every single step along this progression is useful, and earlier stages look "primitive" only when compared to later progressions.

*and at least one family of unicellular organisms has actually evolved an "eye" with a lens!