Mammals have fur over most of their bodies, but at some point during evolution, we humans lost that fur covering. Researchers at Washington University School of Medicine in St. Louis argue that hair on the head is somehow different from fur because fur stops growing when it reaches a certain length, but our head hair continues to grow. To drive home their argument, they ask in a recent article in the journal Evolutionary Anthropology, "Have you ever seen a chimpanzee getting a haircut?"