Next time you're in a meeting, try this little experiment: Take a big yawn, cover your mouth out of courtesy and watch to see how many people follow suit. There's a good chance you'll set off a chain reaction of deep breaths and wide-open mouths. And before you finish reading this article, it's likely you'll yawn at least once. Don't misunderstand, we aren't intending to bore you, but just reading about yawning will make you do it, just as seeing or hearing someone else yawn makes us do it, too.
So what's behind this mysterious epidemic of yawning?
First, let's look at what this bodily motion is: Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. We know it's involuntary because we do it even before we're born:
According to Robert Provine, a developmental neuroscientist at the University of Maryland, Baltimore County, research has shown that 11-week-old fetuses yawn. And while yawning is commonly associated with relaxation and drowsiness, your heart rate can rise as much as 30 percent during a yawn, and yawning is a sign of arousal, including sexual arousal [sources: Alexander, The Stress of Life].
Many parts of the body are in action when you yawn. First, your mouth opens, and your jaw drops, allowing as much air as possible to be taken in. When you inhale, the air taken in is filling your lungs. Your abdominal muscles flex, and your diaphragm is pushed down. The air you breathe in expands the lungs to capacity and then some of the air is blown back out.
Common Yawning Theories
While fatigue, drowsiness or boredom easily bring on yawns, scientists are discovering there's more to yawning than most people think. Not much is known about why we yawn or if it serves any useful function, and very little research has been done on the subject. However, there are several theories
about why we yawn. Here are the four most common:
The physiological theory:
Our bodies induce yawning to draw in more oxygen or remove a buildup of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. However, if our bodies make us yawn to draw in needed oxygen, wouldn't we yawn during exercise? Robert Provine, a developmental neuroscientist at the University of Maryland, Baltimore County and a leading expert on yawning, has tested this theory: 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 [source: University of Washington].
The evolution theory:
Some think that yawning began with our ancestors, who used yawning to show their teeth and intimidate others. An offshoot of this theory is the idea that yawning developed from early man as a signal for us to change activities [source: University of Washington].
The boredom theory:
Although we do tend to yawn when bored or tired, this theory doesn't explain why Olympic athletes yawn right before they compete in their event or why dogs tend to yawn just before they attack. It's doubtful either is bored [source: Patterson].
The brain-cooling theory:
A more recent theory proposed by researchers is that since people yawn more in situations where their brains are likely to be warmer -- tested by having some subjects breathe through their noses or press hot or cold packs to their foreheads -- it's a way to cool down their brains. What does it matter if our brains are cold or hot? Cool brains can think more clearly; hence, yawning might have developed to keep us alert [source: Nagourney].
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