The real reason we yawn

Yawning can be a problem at the office for Lindsay Eierman.

"I've explained, 'I'm sorry, I didn't get much sleep last night,' " says Ms. Eierman, a 26-year-old social worker from Durham, N.C.

But a lack of sleep may not be the problem.

Researchers are starting to unravel the mystery surrounding the yawn, one of the most common and often embarrassing behaviors. Yawning, they have discovered, is much more complicated than previously thought. Although all yawns look the same, they appear to have many different causes and to serve a variety of functions.

Yawning is believed to be a means to keep our brains alert in times of stress. Contagious yawning appears to have evolved in many animal species as a way to protect family and friends, by keeping everyone in the group vigilant. Changes in brain chemistry trigger yawns, which typically last about six seconds and often occur in clusters.

"What this tells us is it's a very complicated system, and there are probably many different roles for yawning," says Gregory Collins, a researcher at the University of Texas Health Science Center in San Antonio who has identified some of the chemical processes at work in the brain.

There are many misconceptions about yawning, which was long believed to be the body's way of correcting for a dearth of oxygen. Our tendency to yawn when other people yawn has long been incorrectly explained as primarily an expression of a person's empathy.

To unravel the mystery of yawning, scientists built upon early, observed clues. Yawning tends to occur more in summer. Most people yawn upon seeing someone else do it, but infants and people with autism or schizophrenia aren't so affected by this contagion effect. And certain people yawn at surprising times, like parachutists who are about to jump out of a plane or Olympic athletes getting ready to compete.

"There was probably some yawning soccer players in Brazil" before World Cup games, says Robert R. Provine, a neuroscientist at the University of Maryland, in Baltimore County.

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