Months before you were born, one of your genes, called Pax-6, turned on and helped your developing body build eyes. However, we are not the only species equipped with a copy of this gene. Other mammals, birds, fish, and even insects also carry a version of Pax-6. In fact, Pax-6seems to do about the same job in all of these species. The human version of the gene can be inserted in a fly and still trigger the building of an insect eye! This suggests that Pax-6 is an ancient gene that was present in the common ancestor of most animals on Earth today and that was inherited by descendents as distantly related as flies, humans, and hummingbirds!