Rate of Evolution
The first fossils of eyes that have been found to date are from the lower Cambrian period (about 540 million years ago). This period saw a burst of apparently rapid evolution, dubbed the "Cambrian explosion". One of the many hypotheses for "causes" of this diversification, the "Light Switch" theory of Andrew Parker, holds that the evolution of eyes initiated an arms race that led to a rapid spate of evolution. Earlier than this, organisms may have had use for light sensitivity, but not for fast locomotion and navigation by vision.
Since the fossil record, particularly of the Early Cambrian, is so poor, it is difficult to estimate the rate of eye evolution. Simple modelling, invoking small mutations exposed to natural selection, demonstrates that a primitive optical sense organ based upon efficient photopigments could evolve into a complex human-like eye in approximately 400,000 years.
Read more about this topic: Evolution Of The Eye
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—Patrick Mullahy (b. 1912)