||Fernald RD. Casting a genetic light on the evolution of eyes. Science. 2006 Sep 29 313(5795):1914-8 DOI: 10.1126/science.1127889 p.1917 left column 2nd paragraphPubMed ID17008522
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||Primary source abstract: "Theoretical considerations of eye design allow us to find routes along which the optical structures of eyes may have evolved. If selection constantly favours an increase in the amount of detectable spatial information, a light-sensitive patch will gradually turn into a focused lens eye through continuous small improvements of design. An upper limit for the number of generations required for the complete transformation can be calculated with a minimum of assumptions."
||P.1917 left column 2nd paragraph: "Starting from a patch of light-sensitive epithelium, the simulation, under selection for improved visual acuity, produced a focused camera-type eye in less than 4×10^5 generations. For animals with generation times less than a year, this would be less than a half million years (primary source)." Primary source abstract: "Even with a consistently pessimistic approach the time required becomes amazingly short: only a few hundred thousand years."