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The face we present to the world is constantly changing as different combinations of its 42 muscles contract and contort it. Humans can produce thousands of distinct facial expressions 鈥 including 19 different types of smile, according to research by the American psychologist Paul Ekman. However, only one of these is a 鈥済enuine鈥 or Duchenne smile.
Discovered by French anatomist Duchenne de Boulogne in 1862, the key difference between this 鈥渞eal鈥 happy smile and a 鈥渇ake鈥 happy smile lies in the orbicularis oculi 鈥 muscles that wrap around the eyes. All smiling involves contraction of the zygomatic major muscles, which lifts the corners of the mouth. But a Duchenne smile is characterised by the additional contraction of the orbicularis oculi, crumpling the skin around the eyes into crows鈥 feet.
Duchenne鈥檚 finding was largely overlooked at the time, but Ekman showed that he was right, and named the smile of pure pleasure in his honour. Since then, the Duchenne smile鈥檚 reputation has grown. One study, for example, looked at photos of professional baseball players from the 1950s and found that Duchenne smilers had a 70 per cent chance of living until age 80 compared with 50 per cent for non-smilers. 聽The researchers put it down to the health benefits associated with happiness. Ekman, meanwhile, found that a Duchenne smile 鈥 but not other smiles 鈥 is accompanied by activity in the left frontal cortex of the brain, a region involved in experiencing enjoyment.
However, more recent findings paint the Duchenne smile in a different light. First, there鈥檚 the discovery that, contrary to popular belief, . Not everyone is able to do this, but a substantial minority of people can. What鈥檚 more, a huge meta-analysis of research into facial expressions reveals that most of the time people who are genuinely happy do not smile at all. Another study found that when they scored a strike, only when they turned to look at fellow bowlers.
This all fits with a new idea that challenges the whole idea of what facial expressions are for. Some psychologists believe they are not reliable guides to our emotions at all, but tools that we use to manipulate others. In this view, a smile is not genuine or fake, at all. Instead, it is a signal to indicate that we wish to collaborate or bond with someone.
