Say cheese! The science of smiling

Quick. Name something you do at least a hundred times a day. You might be playing with a friend, reading a book, or daydreaming. Then, all of a sudden, something makes you ... SMILE!

Have you ever thought about your smile? It seems simple: a slight upturn of the corners of your mouth, a twinkle in your eye, perhaps a flash of pearly whites, and voila, a winning smile. But hold on. Scientists speculate that humans display dozens of different kinds of smiles for dozens of different purposes. There are grins, jeers, smirks, and grimaces; social smiles, miserable smiles, broad smiles, and false smiles. Each is made by using slightly different muscles in the face, and many have nothing to do with being happy.

Smilology

We know a lot about smiling because, believe it or not, there are scientists studying every aspect of how and why we do it. And the more we know about smiling, the more we realize how much we don't know. Scientists still disagree as to whether smiling developed as an expression of emotion ("I'm happy") or as a way of signaling or communicating ("I want to be friendly"). Sometimes we smile when we are happy, but just as often we smile when we really, really, really want to have that chocolate bar and we know that Mom might give in if we smile sweetly. Who knew that such a simple look could be so difficult to figure out?

Why Are You Smiling?

People might say you have your dad's smile or your Aunt Brunhilda's grin, but what if they said you had the smile of a chimp? They might be right. One of the ways scientists study facial expressions, including smiling, is by observing the behavior of other animals, especially primates-that group of mammals that includes humans and our closest relatives, the apes and monkeys.

Some experts believe that the human smile evolved, not from feelings of happiness, but from the "silent bared-teeth display"-often called a "grimace"-that certain primates make when they are feeling threatened or startled. You know the look: lips pulled back to reveal all those monkey teeth. But this primate "smile" might actually mean "I'm afraid of you. Please don't attack me. I'm nice."

If you think about it, you can see how the primate's grimace of fear eventually came to be, among humans, a signal of friendship. Do you ever smile when you are nervous? Or perhaps you try to joke around when you are uncertain about something. The message you are sending is "I'm not sure about this, but I'm willing to work it out. Let's be friends."

Play-Faces

That's one theory about the origins of smiling, but there's a catch. The muscles that primates use to grimace are different from those we use to smile. And so some scientists believe that the smile could not have evolved from the grimace. So there's another theory-smiling has to do with the desire to play.

When they want to play, primates, and some other animals, display what scientists call the "relaxed open-mouth face," or the "play-face." This expression is very different from the silent bared-teeth display because the lips are relaxed and the mouth is open, but the teeth usually do not show. Tussling chimps show the play-face. Even kids chasing and wrestling each other put on the play-face. And the next time you play with a dog or cat, notice how its lips part as it eagerly anticipates your next move, as if to say "I want to play some more."

Could the play-face be a relative of the human smile? Maybe. The same muscles are used, and the play-face signals that it's time for fun, which can make you smile.

Baby Faces

But smiling isn't just for fun-it's a matter of survival. Scientists have discovered that newborn infants, even those who are born blind, know how to smile. There's nothing cuter than a smiling infant; adults just can't resist making a fuss over that darling baby smile. You've probably seen it happen: baby smiles, mom coos and smiles back, baby smiles some more. It's a regular smilefest. And that's precisely what nature intended. A baby's smile is designed to attract and hold mother's attention; it is an infant's way of bonding with the mother and encouraging her care.

Babies may be on to something. Research shows that smiling is healthy because it can trigger positive feelings. Perhaps that is also why smiling is contagious. When you smile at people, you'll notice that they generally smile back. But they will not respond to a frown by frowning or to a scowl by scowling. (Try it and see!)

The True Smile

The most recognizable of all smiles, however, the true smile, is brought on by genuine pleasure. It takes only two sets of facial muscles to create the true smile-one in the cheeks to pull up the corners of the mouth, and one around the eyes, causing them to narrow and crinkle. Because most people can't control those eye muscles, it is very hard to fake a true smile. People all over the world recognize the true smile: even among people who don't speak the same language, the true smile symbolizes peace and friendship.

Whatever science says, smiling is one of the nicest things you can do, for yourself and for others, so say cheese!

Scientists at the Massachusetts Institute of Technology have developed a robot that smiles back. They designed this robotic head, known as Kismet, to interact with people face-to-face. Four cameras, 21 motors, and 15 computers give Kismet its lifelike face and enable it to send and receive social cues. With ears that perk, eyebrows that furrow, eyes that blink, and lips that curl, Kismet can display realistic facial expressions, make sounds like a young child, and even learn.

See Kismet smile at www.ai.mit.edu/projects/humanoid-robotics-group/kismet/.

Copyright Carus Publishing Company Nov/Dec 2003
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