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Speaker 1: Welcome to Brainsteff front House, stuff works dot com where
Speaker 1: smart happens Him Marshall Brain with today's question, what makes
Speaker 1: us yawn? The next time you're in a meeting, try
Speaker 1: this little experiment. Take a big yawn, cover your mouth
Speaker 1: out of courtesy, and watch and see how many other
Speaker 1: people in the room yawn with you. There's a good
Speaker 1: chance that you'll set off a chain reaction of yawns.
Speaker 1: In fact, before you finish here, it's likely that you
Speaker 1: will yawn at least once. Just hearing about yawning will
Speaker 1: sometimes make people yawn, just as seeing or hearing someone
Speaker 1: else yawn makes us yawned. What's behind this mysterious epidemic
Speaker 1: of yawning? First, let's look at what a yawn is.
Speaker 1: Yawning is an involuntary action that causes us to open
Speaker 1: our mouths wide and breathe in deeply. We know it's involuntary,
Speaker 1: because we do it even before we're born. Research shows
Speaker 1: that eleven week old fetuses yawn. There are many parts
Speaker 1: of the body that are in action when you yawn. First,
Speaker 1: your mouth opens and your jaw drops, allowing as much
Speaker 1: air to be taken in as possible. When you inhale,
Speaker 1: the air taken in is filling your lungs to capacity.
Speaker 1: Your abdominal muscles flex, and your diaphragm is pushed down.
Speaker 1: The air you breathe in expands the lungs, and then
Speaker 1: some of the air is blown back out. While the
Speaker 1: dictionary tells us that yawning is caused by being fatigued
Speaker 1: at drowsy or board, scientists are discovering that there is
Speaker 1: more to yawning than most people think. Not much known
Speaker 1: about why we yawn or if it serves any useful function,
Speaker 1: and very little research has been done on the subject. However,
Speaker 1: there are several theories about why we yawned. Here are
Speaker 1: the three most common. The first is the physiological theory
Speaker 1: our bodies induced yawning to draw in more oxygen or
Speaker 1: remove a build up of carbon dioxide. This theory helps
Speaker 1: explain why we yawning. Groups, larger groups produce more carbon dioxide,
Speaker 1: which means our bodies would act to draw in more
Speaker 1: oxygen and get rid of excess carbon dioxide. However, if
Speaker 1: our bodies make us yawned to draw and needed oxygen,
Speaker 1: wouldn't we yawn during exercise? A leading expert on yawning
Speaker 1: has tested this theory. Giving people additional oxygen didn't decrease yawning,
Speaker 1: and changing the amount of carbon dioxide in the subject's
Speaker 1: environment also didn't prevent yawning, so this doesn't necessarily seem
Speaker 1: to be a very valid theory. Then there's the evolution theory.
Speaker 1: Some think that yawning is something that began with our ancestors,
Speaker 1: the idea that yawning developed from early man as a
Speaker 1: signal for us to change activities or to do something differently.
Speaker 1: Then there's the boredom theory. In the Dictionary, yawning is
Speaker 1: said to be caused by boredom, fatigue, or drowsiness. Although
Speaker 1: we do tend to yawn when bored are tired, this
Speaker 1: theory doesn't explain why Olympic athletes yawned right before they
Speaker 1: compete in their event. It's doubtful that they're bored with
Speaker 1: the world watching them. The simple truth is that even
Speaker 1: though humans have been yawning for possibly as long as
Speaker 1: they have existed, we have no clue as to why
Speaker 1: we do it. Maybe it serves some healthful purpose. It
Speaker 1: does cause us to draw in more air, but so
Speaker 1: does exercise. There's still much we don't understand about our brains,
Speaker 1: so maybe yawning is triggered by some area of the
Speaker 1: brain we have yet to discover. We do know that
Speaker 1: yawning is not limited demand. Cats, dogs, even fish yawned,
Speaker 1: which leads us back to the idea that yawning might
Speaker 1: be some form of communication. For more on this and
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