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A computer simulation of gradual eye evolution by Dan Nilsson and Susanne Pelger, which claims, βit would take less than 364,000 years for a camera eye to evolve from a light-sensitive patch.β They start from a light-sensitive layer, with a transparent coating in front and a light-absorbing layer behind.
First, this layer bends gradually into a cup, so it can tell the direction of light rays increasingly well. This continues until it is curved into a hemisphere filled with the transparent substance. Secondly, bringing the ends together, closing the aperture, would gradually increase the sharpness of the image, as a pinhole camera does, because a smaller hole cuts out light, and as there are diffraction effects if the hole is too small, there is a limit to this process. So thirdly, the shape and refractive index gradient of the transparent cover change gradually to a finely focusing lens.