What the Size of Your Smile Says About You

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So much more than than a pair of upturned lips, the smile is the most scientifically studied human facial expression. In her new book, Lip Service, Yale psychology professor Marianne LaFrance, PhD, draws on the latest research-in fields from biology to anthropology to computer science-in an effort to shed some light on the happy face.

Here, six facts that may make you, well, you know.

People with big grins live longer. In a study published last year, researchers pored over an old issue of the Baseball Register, analyzing photos of 230 players. They found that on average, the guys with bright, bigmouthed beams lived 4.9 years longer than the players with partial smiles, and 7 years longer than the players who showed no grin at all. We can't credit wide smiles for long life spans, of course, but smiles reveal positive feelings, and positive feelings are linked to well-being.

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Smiles exert subliminal powers. When study subjects are shown an image of a smiling face for just four milliseconds-a flash so quick, the viewers don't consciously register the image-they experience a mini emotional high. Compared with control groups, the smile-viewers perceive the world in a better light: To them, boring material is more interesting, neutral images look more positive, even bland drinks seem tastier.

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There are three degrees of happiness... An article in the British Medical Journal reported that it is indeed possible to spread the love: Within social networks, when one person is happy, the feeling migrates to two people beyond her. So if you smile, a friend of a friend is more likely to smile, too.

...and two types of smiles. Genuine smiles and fake smiles are governed by two separate neural pathways. We know this is true because people with damage to a certain part of the brain can still break into a spontaneous grin even though they're unable to smile at will. Scientists speculate that our ancestors evolved the neural circuitry to force smiles because it was evolutionarily advantageous to mask their fear and fury.

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To spot a faker, check the eyes. When someone smiles out of genuine delight, a facial muscle called the orbicularis oculi involuntarily contracts, crinkling the skin around the eyes. Most of us are incapable of deliberately moving this muscle, which means that when a person fakes a smile, her orbicularis oculi likely won't budge.

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Smiles have accents. When reading facial expressions, different cultures home in on different parts of the face. In the United States, we focus on mouths; the Japanese, by contrast, search for feeling in the eyes.