Today, let us forge our own happiness. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Hamlet talks to his father's ghost and curses his mother:

O most pernicious woman!
O villain, villain, smiling, damned villain! ...
That one may smile and smile, and be a villain; ...

Smiles can be pretty frightening. "The skull of life suddenly showed through its smile," Wrote Dorothy Canfield Fisher.

So what do smiles really mean? Nineteenth-century scientists were obsessed with the human head and face. They measured skulls and tried to correlate brain size with ability. Phrenologists tried to learn human characteristics from the shapes of skulls. Criminologists tried to define the criminal face.

The French neurologist Guillaume Duchenne mapped 100 facial muscles in 1862. In the course of that work, he had something to say about smiling. He pointed out that false, or even half-hearted, smiles involved only muscles of the mouth. But "the sweet emotions of the soul," he said, activate the pars lateralis muscle around the eyes.

Since then, physiologists have talked about the Duchenne marker in a smile. It's a slight crinkling of crows-feet and a droop in the eyelid toward the temples -- along with a lift of the cheeks and the corners of the mouth. You know the sign. You recognize true delight in a friend's face.

Now psychologist Paul Ekman has gone back to the smile and found out something very important about it. The Duchenne smile, it seems, is accompanied by increased activity in the left prefrontal cortex -- known to be the seat of positive emotions.

The most fascinating thing Ekman found is: You can work it in reverse. If you put on a Duchenne smile, you can activate your pleasure centers. You can literally make yourself happy by smiling. But not completely so. A spontaneous smile activates even more reactions than you can access with a voluntary smile.

So it's no surprise that we're put off by a false smile. Once we know the real thing, the fake becomes offensive. I've always had particular trouble with the classic fixed smile of a ballerina -- for just that reason. There's no Duchenne marker, and it chills me.

Ekman has shown us something we've suspected for a long time. It is that we create our own realities. You cannot fake happiness, but you can create it within yourself. And when you do, you deeply touch those around you. Another Frenchman, the 17th-century moralist La Rochefoucauld, had the idea. He wrote,

To win that wonder of the world,
A smile from her bright eyes,
I fought my King, and would have hurled
The gods out of their skies.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Goleman, D., When Is a Smile Really a Smile?. New York Times, SCIENCE, Tuesday, Oct. 26, 1993, pp. B-5 and B-10.

The Brain Behind That Happy Face. Science, Vol. 262, 15 Oct., 1993, pg. 336.