<P> In 1802, philosopher William Paley called it a miracle of "design". Charles Darwin himself wrote in his Origin of Species, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". However, he went on that despite the difficulty in imagining it, its evolution was perfectly feasible: </P> <P>... if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory . </P> <P> He suggested a stepwise evolution from "an optic nerve merely coated with pigment, and without any other mechanism" to "a moderately high stage of perfection", and gave examples of existing intermediate steps . Darwin's suggestions were soon shown to be correct, and current research is investigating the genetic mechanisms underlying eye development and evolution . </P> <P> Biologist D.E. Nilsson has independently theorized about four general stages in the evolution of a vertebrate eye from a patch of photoreceptors . Nilsson and S. Pelger estimated in a classic paper how many generations are needed to evolve a complex eye in vertebrates . Another researcher, G.C. Young, has used the fossil record to infer evolutionary conclusions, based on the structure of eye orbits and openings in fossilized skulls for blood vessels and nerves to go through . All this adds to the growing amount of evidence that supports Darwin's theory . </P>

According to lecture the evolution of complex adaptations such as the eye