Syzdekistan

When I have a conservation with someone who doesn’t believe in evolution, they often make the same old arguments that they repeat from the the anti-evolution groups. Given some knowledge of science and some critical thinking, these arguments can be shown to be patently false or to be a gross oversimplification of the science of evolution. One common argument is that the human eye is a perfect structure and since half an eye is useless, how could eyes have evolved? Given some thought, however, this argument is specious. First of all Darwin himself wrote in The Origin of Species several pages on how the evolution could have happened. Here are some possible steps:

* photosensitive cell
* aggregates of pigment cells without a nerve
* an optic nerve surrounded by pigment cells and covered by translucent skin
* pigment cells forming a small depression
* pigment cells forming a deeper depression
* the skin over the depression taking a lens shape
* muscles allowing the lens to adjust

Furthermore, the human eye isn’t perfect. Humans have pretty good vision, but many animals have much better vision. Eagles have incredible resolving power and squid eyes are designed much better than humans (we have a network of blood vessels over the retina while squids are better designed with their retinal blood vessels on the back of the retina). Furthermore, humans are limited to sensing basically three colors: red, green, and blue. Birds and reptiles can see four colors and some turtles can detect five colors (one of which is well into the ultraviolet). A few women can possibly see four colors. They probably are more able to distinguishing colors than the rest of us. On the other hand, it is not uncommon for men to be color blind and they actually have problems distinguishing colors. For a very fascinating discussion on the biology and genetics of color vision in humans, check out this article.