Why Do We Yawn?

 

   We all do it, and even some animalsa s well, when we’re ready to go to sleep and sometimes when we awake.We do it when we’re bored, and we might do it under stress. We can even catch it from another person, but as common as yawning is, scientists have struggled to explain why we yawn. Recent research suggests some possible explanations.

 

    One theory among chasmologists—scientists who study yawning—is that the act is a form of social behavior. Contagious yawns are quite common—about half the people who see or hear a yawn will yawn too. Christian Hess of the University of Bern in Switzerland thinks the easy spread

of yawns helped early humans learn to

synchronize their desire to go to sleep and

awake at the same time, allowing them to

coordinate their daily activities.

Maryland psychologist Robert Provine

is one chasmologist who thinks a yawn

stirs up our brains. So when we’re sleepy, a

yawn wakes us up, and if we need mental

sharpness to deal with stress, the yawn

provides it. As part of this theory, the yawn

could be stimulating the flow of

cerebrospinal fluid, which clears out

chemicals in the brain that make us sleepy.

The brain-stimulating yawn also has a

social component: Provine says a

contagious yawn spawned by stress could

signal members of a group to prepare for

danger.

Instead of synchronizing bedtimes or

sweeping out unwanted chemicals, a yawn

could regulate temperature. That’s the

theory of Andrew Gallup, a psychologist at

the State University of New York at

Oneonta. Basically, he says, “We yawn to

cool our brains.” Yawning increases the

flow of blood to the brain, forcing out

warm blood that has gathered there.

Simultaneously, the yawn brings cooling

air into the body through the mouth and

nose. A typical yawn, Gallup said, can

lower the temperature in the brain by 0.2

degrees Fahrenheit. A string of yawns can

lower it by half a degree more.

Working off this theory, Gallup and

some scientists in Vienna tested the

incidence of contagious yawning at

different temperatures. Their results

suggested that contagious yawning most

often takes place when the outside

temperature is in a “thermal window” of

around 68 degrees Fahrenheit (20 degrees

Celsius). Yawning decreases when the

outside temperature and body temperature are close, or when it’s cold outside.