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Old 02-27-2017, 08:25 AM
lazybratsche lazybratsche is offline
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Join Date: Feb 2006
Posts: 3,662
Proto-eyes are very useful, and found throughout the tree of life. Plenty of single celled critters have eye spots, that simply measure the amount of light. Those can be coupled to locomotion mechanisms to move the critter to an environment with the right amount of light. Need to photosynthesize but you're in the dark? Start moving in a straight line, if the light gets stronger keep going, else turn around and try again.

Between simple eye spots and our image-forming eyes, there are plenty of useful intermediates. If you block light on one side of an eye spot, you now have a directional way to measure light. Put several eye spots in a pit, and you can measure the light in several directions at once. Cover that pit with a small opening and now you have a pinhole lens that can form an image. Cover the opening with a clear substance and light sensing cells are protected. Change the shape of the clear covering and now the image is clearer. Etc...