THINK of a yawn. Your jaw tightens, your nostrils flare and you suck in a
great lungful of air as your mouth stretches open wide. If it鈥檚 a good yawn,
you鈥檒l hold that pose until your neck muscles clench, your eardrums ring and
your eyes start to water. You might even finish it off with a yelp of pleasure
or a satisfied sigh.
Are you yawning yet? You will be. And when you do, so will the guy across the
room. And the woman next to him. Because yawning is contagious, and once you
start, there鈥檚 almost nothing you can do to stop. Of course, the big question
is: why do we yawn at all? What can we possibly get out of a six-second stint
with our mouths agape鈥攂esides an opportunity to offend our conversational
partners? Is it a craving for oxygen? Too much carbon dioxide in the blood? Time
for bed?
It鈥檚 none of the above, says Robert Provine, a psychologist at the University
of Maryland, Baltimore County, who first became curious about yawning when he
realised that nobody had really studied this common鈥攊f not always
appropriate鈥攂ehaviour. 鈥淢ost scientists are looking for the deep and
obscure,鈥� Provine says. 鈥淚 look for the significance of the everyday behaviours
that people have neglected. Perhaps it鈥檚 my perverse nature.鈥� So he, and some
similarly perverse psychologists, set out to determine when, why and how we
yawn. Along the way, they found something unexpected: yawning appears to prime
our brains for change.
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Conventional wisdom has long held that we yawn to invigorate our weary brains
with a refreshing burst of oxygen. If this were true, Provine reasoned, then
people who are running low on oxygen鈥攐r high on carbon
dioxide鈥攕hould yawn more often than normal. To test this theory, Provine
first had to figure out how to make people yawn.
Actually, it wasn鈥檛 all that difficult. People yawn all the time. But to bump
the frequency even higher, Provine took advantage of yawning鈥檚 legendary
contagiousness and asked a bunch of undergraduates to think or read about
yawning. (Why the mere mention of yawning might trigger your jaw to drop isn鈥檛
clear鈥攂ut have you noticed that you鈥檙e yawning more than usual as you read
this feature?)
Huffing and puffing
Back in the lab, Provine told the students to think about yawning while they
inhaled mixtures of air that were either high in oxygen, high in carbon dioxide
or normal with respect to both gases. Although the doctored mixes made the
undergrads breathe faster, neither altered their baseline rate of yawning, which
held steady at about 24 yawns per hour. Exercise, which also speeds up
breathing, didn鈥檛 change the yawning rate either.
The results just didn鈥檛 make sense to Provine. So convinced was he that
yawning and breathing were linked, he tested another round of undergraduates
using even higher concentrations of O2 and CO2. But the
results were the same. 鈥淚 had them huffing and puffing and still saw no effect,鈥�
says Provine.
Why then do we yawn? To ready our brains for switching gears, says Ronald
Baenninger, a psychologist at Temple University in Philadelphia. Baenninger
asked people to wear motion-sensing wristbands as they went about their normal
routines and to hit a button on the device whenever they yawned. After
collecting data for two weeks, Baenninger found that yawning tended to precede
periods of activity. Within 15 minutes of yawning, his subjects were generally
engaged in some form of hustle or bustle.
There is also plenty of anecdotal evidence that yawning helps the brain to
gear up for something big, says Provine. Olympic athletes yawn before a
competition, paratroopers yawn before their first jump, undergraduates yawn
before final exams, and violinists yawn before a concert. 鈥淚鈥檝e never seen so
much yawning as before a marathon,鈥� notes Baenninger. And it鈥檚 not that the
runners, jumpers and virtuosos are tired or bored, he says. They鈥檙e simply
working to maintain a certain level of physiological arousal, so they鈥檒l be
prepared for the main event.
鈥淲e yawn in situations where there is nothing to stimulate us, but it would
be bad to lose the level of arousal,鈥� Baenninger explains. Why we yawn before
bed, though, is still a mystery, he says. Perhaps we struggle to stay awake and
alert, but sleep simply wins out in the end.
What makes a yawn so refreshing? It鈥檚 not the oxygen, agrees Baenninger. But
the secret may still lie in the blood: yawning routes an extra helping of blood
to the brain. What the blood does once it鈥檚 there is anyone鈥檚 guess, but
Baenninger believes that it helps to perk us up. In support of this theory,
researchers have found that people also yawn when they are suffering from a
haemorrhage or motion sickness, both of which tend to decrease the amount of
blood available to the brain.
So yawning marks a change in the activity of the brain鈥攐r 鈥渂rain
state鈥�, in psychologists鈥� parlance. Addicts going through opiate withdrawal yawn
compulsively, says Provine. So do people with brain lesions. But schizophrenics
almost never yawn, he notes.
Cascade yawning
Yawning in preparation for a change of pace鈥攐r brain state鈥攊s not
exclusive to humans, says Baenninger. Male Siamese fighting fish yawn before
attacking a rival. Lions, wolves and primates in zoos are prone to fits of
yawning about an hour before feeding time鈥攑erhaps so that they鈥檒l be fully
primed for the biggest activity of the day. Damsel fish yawn between exertions,
such as eating and courting, says Arthur Myrberg, a marine biologist at the
University of Miami.
Still, if yawning is simply a tool that animals and humans use to keep their
minds focused and ready for action, why is it so contagious? Perhaps yawning
plays a role in synchronising the activity of a group, says Provine. A
domino-like cascade of yawning could help to signal group members that it鈥檚 time
to get it together and do something. Such organisation may be especially
important for creatures like primates that live in family groups, says
Baenninger. One young male may wake, stretch and let out a noisy yawn. Pretty
soon, the entire troupe will have yawned itself awake and be ready to go hunting
for food鈥攁n activity that would be risky for a lone individual.
Such a scenario begs the question of whether yawning is catching in animals
as well as humans. Unfortunately, primates in the wild can go hours without
yawning, so it鈥檚 hard to know if their yawns are contagious, says Baenninger.
Fish appear to be immune to catching yawns.
Happily for Provine, that鈥檚 not so for undergraduates. He showed his students
videos of people yawning to find out just what part of the yawn makes it so
infectious. Apparently it鈥檚 not the gaping mouth. Students who saw a video of a
yawning face with the mouth blocked out yawned just as often as students who saw
the full thing鈥攅yes, mouth and all. So while covering your mouth might be
considered polite, it probably won鈥檛 protect your office mates or your dinner
date from catching your eye-watering, nose-scrunching, jaw-dropping yawn.