How did the eye evolve? And of what use is a partially evolved eye?
Animals living today posess almost every kind of eye, from a simple light-sesitive cell to the full-blown human eye and everything in between. It is easy to see the evolutionary steps that were involved. There are many substances that are light-sensitive. An animal needs only a single light-sensitive cell somewhere in its body to be able to tell night from day, or shadow from light. Once the animal has one light-sensitive cell, it is a tivial matter of mutation for another animal to appear with multiple light-sensitive cells, which will enable it to see shapes and movement. Remember, the first animal to have even these primitive eyes would have a tremendous advantage over those without any eyes at all. The next step up is to have a lens, for the purposes of focusing on shapes near and far, in order to judge distance. The simplest type of lens is just a pinhole, and there are animals living today who have just such a lens. This could have developed if the light-sensitive cells evolved t
