What do chimps express when smiling

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. The grin, it seems, derives from a defensive reflex. For example, when we peel a citrus fruit — an action that risks spraying drops of acidic juice into our face — we automatically pull our lips back from our teeth. Fear and unease also pull at the corners of our mouths.

Films of people riding roller coasters often show not delighted smiles but terrified grimaces. The same happens in other primates. In a rhesus monkey group at the Vilas Park Zoo in Madison, Wisconsin — where I studied as a primatologist — the mighty alpha female, Orange, needed only to walk around to evoke the expression from others in her troop.

All the females she passed would flash her grins — especially if she walked in their direction, and even more so if she honored their huddle by joining them.

Among rhesus monkeys like Orange and her troop, this expression is percent unidirectional: It is given by the subordinate to the dominant, never the other way around. As such, it is an unambiguous marker of the hierarchy. Every species has signals for this purpose, though. Chimpanzees lower themselves in the presence of high-ranking individuals and issue a special kind of grunt to greet them. But the original primate signal to make clear that you rank below someone else is a grin with the mouth corners pulled back.

However, far more underlies this expression than fear. When a monkey is simply scared, such as when it spots a snake or predator, it freezes to avoid detection or else it runs away as fast as possible. Kids who are born blind never see anybody smile, but they show the same kinds of smiles under the same situations as sighted people.

McAndrew suggests several books that will be of interest to readers seeking more information on this topic:. Edited by Paul Ekman. Cambridge University Press, Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.

ScienceDaily, 10 June University of Portsmouth. Chimps can vary their smiles like humans. Retrieved November 10, from www. But a new study Scientists are studying how moths have evolved passive defenses over millions of years to resist their primary Current theories hold that apes are worse ScienceDaily shares links with sites in the TrendMD network and earns revenue from third-party advertisers, where indicated.

Kyoto University. Smiling baby monkeys and the roots of laughter: Macaque findings point to older smile origins. Retrieved November 10, from www. It is the first time such Researchers investigated one such signal, the 'leaf clip' This new tree ScienceDaily shares links with sites in the TrendMD network and earns revenue from third-party advertisers, where indicated.

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