Cheerful Chimps: Are Animals Really Happy When They Smile?

A smiling face might not signal what we think, if there’s anything to be learned from other primates.

I can’t stand TV sitcoms and Hollywood movies featuring monkeys and apes. Every time I see a dressed-up simian actor produce one of their silly grins, I cringe. People may think they’re hilarious, but I know their mood is the opposite of happy. It’s hard to get these animals to bare their teeth without scaring them — only punishment and domination can call forth these expressions. Behind the scenes, a trainer is waving his electric cattle prod or leather whip to make clear what will happen if the animals fail to obey. They are terrified.

The bared-teeth grin is not to be confused with a wide-open mouth and intense staring eyes. That fierce face, which looks like an intention to bite, acts as a threat. In a grin, the mouth is closed, but the lips are retracted to expose the teeth and gums. The row of bright white teeth makes it a conspicuous signal, visible from far away, yet its meaning is the exact opposite of a threat.

Many questions surround the grin, such as how this toothy expression became a friendly one in our species and where it came from. The latter question may seem odd, but everything in nature is a modification of something older. Our hands came from the forelimbs of land vertebrates, which derived from the pectoral fins of fish. Our lungs evolved out of fish bladders.
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