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Old 02-27-2017, 08:36 AM
WhyNot WhyNot is offline
Join Date: Jul 2004
Location: Sweet Home Chicago
Posts: 33,496
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?
It didn't happen just once. It's happened, as best as we can tell, some 50 or more different times.

The general pattern seems to be that a Thing mutates some area of a cell or cells so that they can sense light. This is usually a good thing, and that Thing has better opportunities to feed and to avoid predators, and so it makes more babies than other Things. (These Things are often unicellular, so the beginning of the evolution of the eye goes waaaaay back.)

Eventually, one of the Thing's descendants, now multicellular, has a mutation that forms a depression in a group of cells that can sense light. This is way cool, because now the Thing can tell which direction light is coming from. Even better for finding food, avoiding prey, and finding mating partners. More babies with light sensors with depressions are made and survive than babies without the depression in their light sensors.

The next mutation is a constriction of this depression, which aims light waves better, and allows the Thing to see light, direction, and some rudimentary shapes of items in the environment.

Another mutation may provide a layer of transparent cells over this eye, protecting it from injury and infection. Fluid forms between the transparent layer and the light/direction/shape sensing area, and this allows the Thing to leave the water and see on land. It also, in some Things, allowed for the first differentiation of color.

Sometimes a mutation happens that causes a group of cells to line up in a vertical fold. Those are eyes with lenses, that allow for greater focus. Sometimes these lines mutate and split, forming a cornea.

And so on.

Far from the Creationist argument that an eye isn't useful unless all the components are in place at once (and how unlikely would it be for a Thing to mutate all these mutations at once? Very.) the eye is a whole bunch of different mutations that each gave Things better evolutionary fitness in their environment.