Of 19 different types of smile, only six occur when we’re having a good time. The rest happen when we’re in pain, embarrassed, uncomfortable, horrified or even miserable. A smile may mean contempt, anger or incredulity, that we’re lying or that we’ve lost.

While genuine, happy smiles exist as a reward for when we’ve done something helpful to our survival, the ‘non-enjoyment’ smiles are less about what you’re feeling inside and more about what you want to signal to others. “Some evolved to signal that we’re cooperative and non-threatening; others have evolved to let people know, without aggression, that we are superior to them in this present interaction,” says Paula Niedenthal, a psychologist at the University of Wisconsin-Madison.

Many are polite gestures which demonstrate that we’re following the rules. But they can also be an effective way of manipulating others or distracting them from our true feelings. More often than not, the universal symbol of happiness is used as a mask.

Duchenne smile

The first steps to decoding this multi-purpose expression came from the 19th Century neurologist Duchenne de Boulogne. He was the son of a French pirate and had a penchant for electrocuting his patients – among other things, he was a founding father of electrotherapy. Duchenne was interested in the mechanics of facial expressions, including how the muscles of the face contract to produce a smile. The best way to study this, he decided, was to attach electrodes to a person’s face and jolt their muscles into action.

Fear smile

One clue comes from our closest cousins. In fact, though the felt smile may seem like the most natural today, some scientists think it may have evolved from an expression with a very different meaning. “When bonobo chimpanzees are afraid they’ll expose their teeth and draw their lips back so that their gums are exposed,” says Zanna Clay, a primatologist at the University of Birmingham.

Miserable smile

We now know that smiling is indeed instinctive, but not just when we’re happy. The ‘miserable smile’ is a stoical grin-and-bear-it expression – a slight, asymmetric smile with an expression of deep sadness pasted over the top.

The dampened smile

But it’s a little bit more complicated than that. As it turns out, genuine, happy smiling hasn’t always been as celebrated as it is today. Back in 17th Century Europe, wearing your emotions openly was considered highly improper; it was an established fact that only the poor smiled with their teeth showing. The ‘smile revolution’ finally kicked off over a century later in Paris, kick-started by French nobles who were having such a good time in the newly opened coffee houses that they brought the smile back into fashion.

– Zaria Gorvett

Read More: There are 19 types of smile but only six are for happiness

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