Why do we yawn??
Fish do it, violinists do it, even salivating lions do it.
Think of a yawn. Your jaw-tightens. Your nostrils flare and you suck in
a great lung full of air as your mouth stretches open wide.
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 a contagious, andonce you start, there’s 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
– besides an opportunity to offend our conversational partners? Is
it craving for oxygen? Too much carbon dioxide in the blood? Time
for bed?
It’s none of the above.
According to Robert Provine as psychologist at the University of Maryland,
Baltimore County was the first who became curious about yawning when he
realized that nobody had really studied this common if not always appropriate
behaviour. And following Provine, many researchers found something
unexpected : yawning appears to prime our brains for change.
Conventional wisdom has long held that we yawn to invigorate our weary
brains with a refreshing burst of oxygen. But Provine reasoned, that
people who are running low on oxygen or high on carbon-dioxide should yawn
more often than normal.
Why we yawn before bed, though its still a mystery. Perhaps we
struggle to stay awake and alert, but sleep simply wins out in the end.
What makes a yawn so refreshing? It’s not the oxygen, but the
secret may still lie in the blood : yawning routes an extra helping of
blood to the brain. Yawning marks a change in the activity of the
brain or ‘brain state’.
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Some interesting facts on Yawning:
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The average duration of a yawn is about 6 seconds
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In humans, the earliest occurrence of a yawn happens at about 11 weeks
after conception - that's BEFORE the baby is born!
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Yawns become contagious to people between the first and second years of
life.
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A part of the brain that plays an important role in yawning is the hypothalamus.
Research has shown that some neurotransmitters (for example, dopamine,
excitatory amino acids, nitric oxide) and neuropeptides increase yawning
if injected in the hypothalamus of animals.
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| You know that when you are bored, you yawn. Scientists
have confirmed this observation by comparing the number of yawns in 17-19
year old students who watched music videos to the number of yawns in students
who watched an uninteresting color test bar pattern. As you might have
expected, people who watched the color test bar pattern yawned more (5.78
yawns in 30 minutes) than those who watched the "MTV-like" video (3.41
yawns in 30 minutes.) The average duration of yawns was also slightly longer
in the test bar viewing group. One unexpected finding was that yawns in
male students had a longer duration than those in female students. |
Many people assume that we yawn because our bodies are trying to get
rid of extra carbon dioxide (CO2) and to take in more oxygen (O2). This
may make some sense. According to this theory, when people are bored or
tired, they breathe more slowly. As breathing slows down, less oxygen makes
it to the lungs. As carbon dioxide builds up in the blood, a message to
the brain results in signals back to the lungs saying, "Take a deep breath,"
and a yawn is produced.
The only problem with this logical theory is that research shows that
it may not be true. In 1987, Dr. Robert Provine and his coworkers set up
an experiment to test the theory that high CO2/low O2 blood content causes
yawning. Air is normally made up of 20.95% O2, 79.02% N2 (nitrogen), 0.03%
CO2 (and a few other gases in low concentrations). The researchers gave
college students the following gases to breathe for 30 minutes: |
| Gas #1
100% O2 |
Gas #2
3% CO2, 21% O2 |
Gas #3
5% CO2, 21% O2 |
Gas #4
Normal Air |
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| Breathing 100% O2 (Gas #1) or either CO2 gas (Gas #2 and
#3) did cause the students to breathe at a faster rate. However, neither
CO2 gas nor 100% O2 caused the students to yawn more. These gases also
did not change the duration of yawns when they occurred.
The researchers also looked for a relationship between breathing and
yawning by having people exercise. Exercise, obviously, causes people to
breathe faster. However, the number of yawns during exercise was not different
from the number of yawns before or after exercise. Therefore, it appears
that yawning is not due to CO2/O2 levels in the blood and that yawning
and breathing are controlled by different mechanisms.
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So, the question remains - why do we yawn? Dr. Provine suggests that
perhaps yawning is like stretching. Yawning and stretching increase blood
pressure and heart rate and also flex muscles and joints. Evidence that
yawning and stretching may be related comes from the observation that if
you try to stifle or prevent a yawn by clenching your jaws shut, the yawn
is somewhat "unsatisfying." For some reason, the stretching of jaw and
face muscles is necessary for a good yawn. |
| It is possible that yawns are contagious because at one
time in evolutionary history, the yawn served to coordinate the social
behavior of a group of animals. When one member of the group yawned to
signal an event, all the other members of the group also yawned. Yawns
may still be contagious these days because of a leftover response (a "vestigial"
response) that is not used anymore. None of this has been proven true and
yawns are still one of the mysteries of the mind.
* Did you know? Here's a new vocabulary word for you: pandiculation.
Pandiculation is the act of stretching and yawning |
| Q U E S T I O N : Why is it that when one person
yawns, everyone else does? Is yawning somehow contagious? |
A N S W E R : There are three conflicting theories
as to why yawns are catching: a physiological theory, a boredom theory
and an evolutionary theory. Since I haven’t seen a study that proves one
theory over another, I’ll describe each one.
The physiological theory states that
a yawn is a reflex that occurs when your brain recognizes a need for more
oxygen. Yawning is contagious because everyone in a room is likely to be
shy on fresh air at the same time. A yawn may also be stimulated by external
cues, much like watching someone eat can make you hungry.
The boredom theory is based on the assumption
that if everyone finds something boring, they will yawn. This doesn’t explain
why we yawn when bored, however, unless it’s an instinctive way we use
body language to say something is uninspiring.
The evolutionary theory says that we
yawn to display our teeth, a behavior left over from our more primitive
beginnings. Yawning could act as a warning to others. These days it would
seem an obsolete display, since we’ve supposedly become more civilized.
Since no one has figured out exactly why yawning
seems to be contagious, the real cause will remain a mystery for now. |
According to Robert Provine, professor of psychology at
the University of Maryland Baltimore County, it’s no surprise if it does.
“Yawning is extraordinarily contagious,” says
Provine, who has published much of what is known about the subject, particularly
its behavioral aspects. “Seeing a person yawn triggers yawns. Reading about
yawning causes yawns. Sitting alone in a room thinking about yawning triggers
yawning.”
A brain mechanism, Provine explains, actually
detects a yawning face, which then triggers that behavior. “Once the neurological
machinery in our head gets underway,” he says, “it’s hard to stop a yawn.”
Not Just a Matter of Oxygen
The common theory about why we yawn is to get more oxygen to our brains.
But according to Provine, it is not so simple. In scientific experiments,
he discovered that even with 100 percent oxygen, his subjects yawned just
as much as when they had less.
Yawning, says Provine, which occurs as early
as the first trimester of prenatal development, is about transitions in
the body’s biology. Of course, one of those changes is from a state of
alertness to a state of sleepiness. But surprisingly, yawning can also
be a behavior that marks a transformation from sleepiness to alertness.
“At track and field events,” says Provine,
“sometimes you’ll find participants in the race of their life will be standing
around on the sidelines or in the starting block and they may be yawning.”
Or, for example, before a concert, a musician may yawn to prepare for an
increasingly energized state.
Yawning is also a way for people to synchronize
group behavior. “When you see someone yawn, you’re initiating a chain reaction
of biology,” Provine says. “So whatever changes in our body are brought
about by yawning, are synchronized in everyone that’s doing it.” |
| For more information on Yawning, you may want to read this
article a "The
neuropharmacology of Yawning": |
| Dr.Robert Provine's weblink. |
