WEBVTT - How Does Yawning Work?

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<v Speaker 1>Welcome to Brainsteff front House, stuff works dot com where

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<v Speaker 1>smart happens Him Marshall Brain with today's question, what makes

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<v Speaker 1>us yawn? The next time you're in a meeting, try

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<v Speaker 1>this little experiment. Take a big yawn, cover your mouth

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<v Speaker 1>out of courtesy, and watch and see how many other

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<v Speaker 1>people in the room yawn with you. There's a good

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<v Speaker 1>chance that you'll set off a chain reaction of yawns.

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<v Speaker 1>In fact, before you finish here, it's likely that you

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<v Speaker 1>will yawn at least once. Just hearing about yawning will

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<v Speaker 1>sometimes make people yawn, just as seeing or hearing someone

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<v Speaker 1>else yawn makes us yawned. What's behind this mysterious epidemic

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<v Speaker 1>of yawning? First, let's look at what a yawn is.

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<v Speaker 1>Yawning is an involuntary action that causes us to open

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<v Speaker 1>our mouths wide and breathe in deeply. We know it's involuntary,

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<v Speaker 1>because we do it even before we're born. Research shows

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<v Speaker 1>that eleven week old fetuses yawn. There are many parts

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<v Speaker 1>of the body that are in action when you yawn. First,

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<v Speaker 1>your mouth opens and your jaw drops, allowing as much

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<v Speaker 1>air to be taken in as possible. When you inhale,

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<v Speaker 1>the air taken in is filling your lungs to capacity.

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<v Speaker 1>Your abdominal muscles flex, and your diaphragm is pushed down.

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<v Speaker 1>The air you breathe in expands the lungs, and then

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<v Speaker 1>some of the air is blown back out. While the

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<v Speaker 1>dictionary tells us that yawning is caused by being fatigued

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<v Speaker 1>at drowsy or board, scientists are discovering that there is

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<v Speaker 1>more to yawning than most people think. Not much known

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<v Speaker 1>about why we yawn or if it serves any useful function,

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<v Speaker 1>and very little research has been done on the subject. However,

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<v Speaker 1>there are several theories about why we yawned. Here are

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<v Speaker 1>the three most common. The first is the physiological theory

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<v Speaker 1>our bodies induced yawning to draw in more oxygen or

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<v Speaker 1>remove a build up of carbon dioxide. This theory helps

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<v Speaker 1>explain why we yawning. Groups, larger groups produce more carbon dioxide,

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<v Speaker 1>which means our bodies would act to draw in more

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<v Speaker 1>oxygen and get rid of excess carbon dioxide. However, if

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<v Speaker 1>our bodies make us yawned to draw and needed oxygen,

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<v Speaker 1>wouldn't we yawn during exercise? A leading expert on yawning

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<v Speaker 1>has tested this theory. Giving people additional oxygen didn't decrease yawning,

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<v Speaker 1>and changing the amount of carbon dioxide in the subject's

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<v Speaker 1>environment also didn't prevent yawning, so this doesn't necessarily seem

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<v Speaker 1>to be a very valid theory. Then there's the evolution theory.

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<v Speaker 1>Some think that yawning is something that began with our ancestors,

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<v Speaker 1>the idea that yawning developed from early man as a

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<v Speaker 1>signal for us to change activities or to do something differently.

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<v Speaker 1>Then there's the boredom theory. In the Dictionary, yawning is

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<v Speaker 1>said to be caused by boredom, fatigue, or drowsiness. Although

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<v Speaker 1>we do tend to yawn when bored are tired, this

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<v Speaker 1>theory doesn't explain why Olympic athletes yawned right before they

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<v Speaker 1>compete in their event. It's doubtful that they're bored with

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<v Speaker 1>the world watching them. The simple truth is that even

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<v Speaker 1>though humans have been yawning for possibly as long as

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<v Speaker 1>they have existed, we have no clue as to why

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<v Speaker 1>we do it. Maybe it serves some healthful purpose. It

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<v Speaker 1>does cause us to draw in more air, but so

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<v Speaker 1>does exercise. There's still much we don't understand about our brains,

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<v Speaker 1>so maybe yawning is triggered by some area of the

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<v Speaker 1>brain we have yet to discover. We do know that

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<v Speaker 1>yawning is not limited demand. Cats, dogs, even fish yawned,

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<v Speaker 1>which leads us back to the idea that yawning might

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<v Speaker 1>be some form of communication. For more on this and

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