Trivia.
Most human beings have an overbite, but we didn't always. Once upon a time we had neither an overbite or an underbite, but something in the middle. Our jaw was aligned so the bottom edge of our top teeth rested on the top edge of our bottom teeth.
According to a documentary i watched a couple of years ago, things changed because our eating habits did.
It's all because of the fact we started using forks when we ate. We started cutting meat into more bite sized chunks. Whereas before the fork was really common we'd hold a large piece of meat in our hands and rip chunks off using our teeth.