Laughter is the blunderbuss of positive social signals--loud, arresting, a little bit crude. The smile, by contrast, is a marvel of subtlety, conveying nuances of meaning so fine that we're not even aware of them much of the time. Says Dacher Keltner, a psychologist at the University of California, Berkeley: "The word smile doesn't characterize all the rich ways we signal positive emotions."
He should know: the smile is Keltner's research specialty, and he has analyzed thousands of smiling faces to untangle their complex physiology. Some of the muscles involved in smiling are under our voluntary control--the zygmaticus major, for example, which pulls the lip corners up. Tighten those, and you have what Keltner refers to as the "Pan American smile," after the forced grins of flight attendants. It's not necessarily phony. It's a smile of politeness rather than happiness. Even infants will show it when a stranger enters a room. We use these muscles, says Keltner, "to be entertaining, to dramatize. Some neat examples: the feigned smile of polite enjoyment when your boss is telling a joke you've heard a thousand times, or the smile when people greet each other, when they press their lips together."
But another batch of smile muscles is generally beyond our control. One is the orbicularis oculi, which surrounds the eye; only about 5% of people can willfully control it. "When that muscle contracts," says Keltner, "it gives you crow's-feet, a little gleam in your eye, raises your cheek up and impouches the lower eyelid." Those are key features of the "Duchenne smile," named for the 18th century French physiologist who first described it. It's considered the most heartfelt smile, because it is linked to feelings of happiness and activation of the left hemisphere of the brain, which is associated with positive emotions. "Young infants show it when their mom approaches," notes Keltner. He has found that when people see a picture of a Duchenne smiler, even when it's presented subliminally, "it makes you smile in return, and feel calmer, more relaxed."
As part of his research, Keltner analyzed the smiles of women pictured in yearbooks dating back to 1960, then followed up with the women themselves. Amazingly, he found that, decades later, those with Duchenne smiles turned out to be happier people than the Pan Am smilers. "They got married earlier, and they are happier in their marriage, feel less stress, feel broader well-being," Keltner says.
It isn't the eyes, in short, that are windows onto the soul; it's the smiles that surround them. --By Michael D. Lemonick. Reported by Daniel Cray/ Los Angeles