Scientists have four theories about why we yawn. One is that it helps wake us up and keep us alert by increasing heart rate and oxygen intake. Another is that it expels excess carbon dioxide. A third is that it evolved as a form of communication. The fourth is that it stretches the jaw and neck muscles before and after sleep. However, no one knows for sure why people yawn.
Scientists aren’t really sure why we yawn, however, there are four popular theories. Some believe that we yawn when we’re tired because it helps wake us up or keeps us from falling asleep. The reasoning behind this is that every time you yawn, your heart rate increases by up to 30%. A yawn causes the lungs to expand to their maximum capacity, which allows them to take in more oxygen. The increased heart rate causes your blood to take in the extra oxygen at a faster rate, helping you stay alert. The same physiological response produced by a yawn helps energize you and keep you going when you awaken from sleep, even though you may not necessarily be tired.
Another theory as to why we yawn when tired has to do with excess carbon dioxide in the body. It is believed that exhaling during a yawn expels the carbon dioxide responsible for fatigue. In this way the carbon dioxide theory is very similar to the one set out above. However, experiments designed to test this theory had participants breathe in high concentrations of carbon dioxide. Studies have shown that increased exposure to carbon dioxide didn’t cause people to yawn more than usual.
A third theory concerns evolution. Some researchers speculate that our ancestors yawned as a form of communication. A yawn would mean that members of a group change their activity. One of these activities could very well be going to sleep. This would not only explain why people yawn when they’re tired, but also why yawning is contagious. In fact, yawning is so suggestive that you can easily start a chain of yawns just by faking one. Even reading or thinking about the word yawn could make you yawn right now.
Finally, it is believed that yawning is simply a way to stretch the jaw and neck muscles before and after sleep, just like you would stretch any other part of the body. Stretching is important both before and after sleep to help your body relax, release tension, and maintain proper alignment. This means that yawning when you’re tired helps prepare your body for sleep.
These theories all sound reasonable, but they’re still just theories. No one knows for sure why people yawn. There hasn’t been much research on the subject probably because people have yawned all their lives, even before birth, and most of the time it’s not annoying other than when someone expects you to pay attention to them!
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