Humans are social animals, and as such, our well-being often depends on our ability to gauge the emotions of those around us. Smiling is one major social cue. Despite this, until recently, science had only gotten to grips with the anatomy of the smile in terms of facial muscles and contractions.
A smile is not this floating thing, like a Cheshire Cat, Paula Niedenthal, a psychologist at the University of Clermont-Ferrand in France, told the New York Times. She and her colleagues have dug beyond surface-level anatomy and down to the smile's neurological roots. Their work was published in a recent issue of the journal Behavioral and Brain Sciences.
Smiles, they found, come in several distinct varieties. We sometimes smile from pure pleasure, and other times to strengthen bonds with other people. The smiles we display in those situations differ both neurologically and anatomically from the ones we can't help showing when we're embarrassed, and the bared-teethed ones we use to exert dominance; those differ from the raised-eyebrow smiles we use in greeting, and the fake ones we sometimes exhibit, say, when a boss cracks a lame joke.
Another significant finding by Niedenthal and her colleagues is that we smile in response to other smilers. And a smile-in-response is not just a simple show of camaraderie: In fact, it spurs all the brain activity experienced by the original smiler. For example, if a woman smiles from joy, certain regions of her brain light up on a brain scan. When her companion sees her smile, he won't be able to help but smile as well, and when he does, the same regions of his brain light up with signs of joy.
If, on the other hand, a person observes a fake smile, his impulse will still be to smile in response, but subconsciously, he can tell the difference: His brain will not flare up with the emotions faked by the original smiler. Niedenthal believes this subtle awareness of the authenticity of facial expressions helps us navigate social interactions.
But we're not as good at spotting false smiles as we could be. Despite the fact that smiles play a crucial role in our lives, research by Paul Ekman at the University of California, San Francisco, has shown that the average person is surprisingly bad at distinguishing between genuine and fake ones. Evolutionary psychologists aren't at all sure how to interpret this finding.
In this online test on the BBC website, viewers are asked to judge the authenticity of 20 short clips of people smiling. See for yourself how attuned you are.
Got a question? Send us an email and we'll look for an expert who can crack it.
Follow Natalie Wolchover on Twitter @nattyover
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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.