"Modern" eyes first appeared about 550 million years ago, having evolved through random mutations and natural selection from simple light-sensitive patches on the skin. Researchers at Lund University have calculated that the development of the camera-like eye from a light-sensitive patch might require roughly 1,829 steps (each involving no more than one percent change) and only 364,000 years. This is so fast that eyes could have evolved 1,500 times.
Different eye types have emerged, but, generally, the process probably involved changes in the patch that created a depression, which deepened into a pit capable of sharpening sight that eventually narrowed, allowing light to enter through a pin-hole like aperture. With time, a layer of cells and pigment lined the back (retina), transparent tissue lined the front (lens), and liquids provided a curvature.
Rollover the image to name the eyes portrayed.
* A Pessimistic Estimate of the Time Required for an Eye to Evolve
Nilsson, Dan-E.; Pelger, Susanne. Proceedings: Biological Sciences, Volume 256, Issue 1345, pp. 53-58
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