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Speaker 1: Hi Am Marshall Brain with today's question, what makes us yawn?

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Speaker 1: The next time you're in a meeting, try this little experiment.

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Speaker 1: Take a big yawn, cover your mouth out of courtesy,

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Speaker 1: and watch and see how many other people in the

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Speaker 1: room yawn with you. There's a good chance that you'll

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Speaker 1: set off a chain reaction of yawns. In fact, before

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Speaker 1: you finish here, it's likely that you will yawn at

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Speaker 1: least once. Just hearing about yawning will sometimes make people yawn.

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Speaker 1: Just to seeing or hearing someone else yawn makes us yawned.

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Speaker 1: What's behind this mysterious epidemic of yawning? First, let's look

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Speaker 1: at what a yawn is Yawning is an involuntary action

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Speaker 1: that causes us to open our mouths wide and breathe

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Speaker 1: in deeply. We know it's involuntary because we do it

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Speaker 1: even before we're born. Research shows that eleven week old

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Speaker 1: fetuses yawn. There are many parts of the body that

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Speaker 1: are in action when you yawn. First, your mouth opens

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Speaker 1: and your jaw drops, allowing as much air to be

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Speaker 1: taken in as possible. When you inhale, the air taken

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Speaker 1: in is filling your lungs to capacity. Your abdominal muscles flex,

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Speaker 1: and your diaphragm is pushed down. The air you breathe

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Speaker 1: in expands the lungs, and then some of the air

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Speaker 1: is blown back out. While the dictionary tells us that

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Speaker 1: yawning is caused by being fatigued at drowsy or board,

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Speaker 1: scientists are discovering that there is more to yawning. Most

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Speaker 1: people think not much is known about why we yawn

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Speaker 1: or if it serves any useful function, and very little

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Speaker 1: research has been done on the subject. However, there are

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Speaker 1: several theories about why we yawned. Here are the three

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Speaker 1: most common. The first is the physiological theory our bodies

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Speaker 1: induced yawning to draw in more oxygen or remove a

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Speaker 1: build up of carbon dioxide. This theory helps explain why

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Speaker 1: we yawning groups. Larger groups produce more carbon dioxide, which

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Speaker 1: means our bodies would act to draw in more oxygen

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Speaker 1: and get rid of excess carbon dioxide. However, if our

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Speaker 1: bodies make us yawn to draw and needed oxygen, wouldn't

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Speaker 1: we yawn during exercise? A leading expert on yawning has

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Speaker 1: tested this theory. Giving people additional oxygen didn't decrease yawning,

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Speaker 1: and changing the amount of carbon dioxide in the subject's

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Speaker 1: environment also didn't prevent yawning, so this doesn't necessarily seem

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Speaker 1: to be a very valid theory. Then there's the evolution theory.

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Speaker 1: Some think that yawning is something that began with our ancestors,

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Speaker 1: the idea that yawning developed from early man as a

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Speaker 1: signal for us to change activities or to do something differently.

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Speaker 1: Then there's the boredom theory. In the Dictionary, yawning is

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Speaker 1: said to be caused by boredom, fatigue, or drowsiness. Although

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Speaker 1: we do tend to yawn when bored are tired, this

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Speaker 1: theory doesn't explain why Olympic athletes yawned right before they

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

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Speaker 1: the world watching them. The simple truth is that even

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Speaker 1: though humans have been yawning for possibly as long as

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Speaker 1: they have existed, we have no clue as to why

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Speaker 1: we do it. Maybe it serves some healthful purpose. It

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Speaker 1: does cause us to draw in more air, but so

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

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Speaker 1: so maybe yawning is triggered by some area of the

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Speaker 1: brain we have yet to discover. We do know that

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Speaker 1: yawning is not limited demand. Cats, dogs, even ish yawned,

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Speaker 1: which leads aspect to the idea that yawning might be

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Speaker 1: some form of communication. For more illness and thousands of

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Speaker 1: other topics. Visit how stuff works dot com and don't

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Speaker 1: forget to check out the brain stuff blog on the

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Speaker 1: how stuff works dot com home page. You can also

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Speaker 1: hs W. Brain Stuff is sponsored by Harry's dot Com.

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Speaker 1: Get a great shaving experience for a fraction of the price.

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Speaker 1: The quality of the shave is so important that Harry's

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Speaker 1: purchased the factory that makes their blades. Fifteen dollars gets

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Speaker 1: you a set that includes a handle, three blades, and

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Speaker 1: shave cream. Go to Harry's dot com use the code

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