Probing the origins of humanity is actually a lot like being a dentist. The bones of our hominid ancestors tend to fall apart, leaving behind a smattering of shards. But teeth, made of enamel, can do a better job of withstanding the ravages of time. And teeth–particularly those of mammals–are not just tough but interesting. Mammals–us included–have several kinds of teeth, each of which is covered with distinctive bumps, cusps, and roots. All those details vary from one species to another. So even if you find a fragment of a tooth, you may be able to figure out what species it belongs to. And if you have enough teeth to compare to each other, you can probe some pretty profound