Over the summer, a friend of mine familiar with my strabismus, gave methe book, Survival of the Sickest, about why we have certain diseases, retroviruses and genetic disorders. The neurogeneticist author explains that blacks in the US have a tendency to sickle cell anemia because their blood chemistry is such that it prevented them from getting malaria in Africa but now makes them susceptible to sickle cell anemia. I think I told you about the example of why he thinks Type 1 diabetes is so prevalent in Scandinavia. He posits that those who could store more sugar during the Ice Age were more likely to survive and therefore passed on those sugar hoarding genes to the next generation. (Pardon my lay person’s dilution of medical terminology, but this is the way I understand it.)
So, this makes me think, why do 4-5% of the population have strabismus or amblyopia and no depth perception? What evolutionary benefit is there to have this segment of the population seeing flat? Back in the times of hunters and gatherers, having flat vision could keep people from being able to chase game and get food. Symmetry is supposed to be a marker of beauty and health. So, why have people with wandering eyes looking like freaks? The same question stands for why people have cleft palate and other deformities.