Scientists Agree: It's in His Kiss

Over 90 percent of human society engages in what, if you get right down to it, seems like a very strange thing to do: putting faces together and trading spit. But because it is so pervasive, scientists think there must be a good reason for it, some kind of evolutionary advantage. And humans aren't alone in this ritual. Chimpanzees kiss, foxes and dogs lick each other's faces, some birds tap their bills together, and elephants put their trunks in each other's mouths.

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