Which species is more diverse, humans or chimps? Most of us would be tempted to answer 'humans'. Unless you're a primatologist or you work at a zoo, you would likely have trouble telling one chimp apart from another, not to mention distinguishing between West African and Central African chimpanzees. By contrast, we can easily spot differences among humans - if asked to guess whether someone was from China, Pakistan, or Kenya, few of us would have any trouble getting the answer correct.

By the measure of genes though, humans are amazingly uniform. Humans are genetically less diverse than chimps, and both chimps and humans are much less diverse than a common species of fruit fly. Given our species' long history of racial conflict, our genetic uniformity may come as a surprise. Not too long ago people in polite company would debate whether different human races really all belonged to one species. Our DNA tells us that our genetic differences don't even come close to matching the variety found within a single, apparently monotonous fruit fly species.