From archeology Mensa group - Interesting

I recall lecturing on the evolution of the eye, in which we have living examples of every stage of that evolution. There are phototropic and photophobic single celled organisms wherein the entire surface of the organism is sensitive to light. There are others, more evolved, which have one small area of the cell wall sensitive to light. These swim in spiral pattern, scanning their environment for light sources. In the next step forward, that spot is recessed, enabling a sharper focus. Finally, a protective membrane covers the light sensitive and, becomes a lens, etc., etc. All it takes is sufficient time, the environmental advantage of seeing and individual variation in the ability to detect light and its direction. Given a few billion years and voila, the complex eyes of higher organisms.

Henry Miller