The eyes may be said to be the windows of the soul, but a look at our eyes also sheds some interesting light upon diverse facets of human biology. In this list, our discoveries take us through a surprising story about the history of the blue eye mutation, lesser-known facts about eye color and disease correlations, hidden blind spots, and why we can shed three different types of tears.
Blue-eyed humans make up a significant percentage of the population in certain areas of Europe, Eurasia, and the lands inhabited by the diaspora of these populations. Despite a range in distribution, scientists have determined that blue-eyed individuals can be traced back to a single common ancestor who would have resided in the Baltic Sea region 6,000–10,000 years ago. Prior to a peculiar genetic change, all humans had brown eyes. A team led by Hans Eiberg from the University of Copenhagen discovered that blue-eyed humans were created by a genetic mutation on the OCA2 gene, which specifically cuts down melanin production in the iris. If the genetic effects went all the way, we would be seeing albinos rather than light-eyed individuals. Eiberg was the original identifier of OCA2 as the gene responsible for eye color, continuing research begun in 1996. The study compared people from across Eurasia and determined just how specific were the roots of the wide-ranging mutation. (continue reading)