Really, Homo sapiens is an unusual species. Other creatures of the same type pretty much all look alike. Sure, there are subtle differences, but it really is not a simple thing to tell one wolf from another. Or differentiate goldfish or ducks or chimpanzees. But humans? We can be six-foot-five beanpoles or five-foot-six, square-shouldered, barrel-chested fire hydrants. Some of us are as lithe and leggy as dancers, others as bulbous as hippos.