Why Are Yawns Contagious?

(essay received today via email)

Did you yawn just reading this title? We yawn not only when we're sleepy, but also when we see someone else yawn, read about yawns, or even think about yawning. Sneezing, coughing, and burping aren't contagious. What is it about yawns that can set off a chain reaction? Scientists are still trying to figure that one out. But they have some ideas.

What is a yawn?

Scientific American defines yawning as a "stereotypical reflex characterized by a single deep inhalation with the mouth open and stretching of muscles of the jaw and trunk." It's involuntary. We aren't the only ones who yawn. Cats, dogs, and even fish yawn. The average yawn lasts about six seconds, and your heart rate can rise as much as 30 percent during a yawn.

Why do we yawn?

Yawning could be a signal of changing conditions within your body, Mark A. W. Andrews, associate professor of physiology at the Lake Erie College of Osteopathic Medicine, told Scientific American. That is, we yawn when our state of alertness is changing. That is why we yawn when we're tired and when we wake up.

It was once thought that we yawned in order to suck in more air when oxygen levels were low in our lungs. But scientists now know that the lungs can't sense oxygen levels--so that theory goes out the window. Besides, fetuses yawn even though their lungs are not ventilated. And there is absolutely no credence to the idea that we yawn when we're bored.

So why are yawns contagious?

Professor Andrews told Scientific American yawns may be contagious because we human animals are trying to communicate changing environmental conditions to others, possibly as a way to synchronize behavior. Obviously, this would be one of those caveman-type mechanisms that is no longer needed that our bodies remember and still do.

When we yawn, we draw in more oxygen and remove a build-up of carbon dioxide. Larger groups produce more carbon dioxide. So one theory holds that we yawn when we're in large groups of people to purge the carbon dioxide--and in so doing, we set off a chain reaction. But Robert Provine, a psychologist at the University of Maryland, Baltimore County, tested the theory and says it's bunk. Giving people additional oxygen didn't decrease yawning and decreasing the amount of carbon dioxide in a subject's environment also didn't prevent yawning, notes the How Stuff Works Web site.

Whatever the reason for yawns being contagious, How Stuff Works reports that 55 percent of people will yawn within five minutes of seeing someone else yawn. In addition, blind people will yawn after hearing others yawning. (Dude, that is crazy!!) And we're sure that reading and writing about yawns is enough to induce one!

--Cathryn Conroy