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Why Do We Yawn?



Yawning is something that all people do. In fact, yawning begins when a baby is still in utero.

It’s not a strictly human act, and most mammals, and even some birds and reptiles also yawn. But why do we yawn? What is the function of a yawn, and why are yawns contagious?

Why do we yawn(Photo: rustyparts)

No Clear Answers

The short answer to those questions is that scientists aren’t entirely sure. While several studies have been done, and the reason for yawning has been discussed since ancient Greece, there are still no definitive answers.

Still, it’s fun to look at some of the theories. Let’s start out with some debunked theories of why we yawn, and then move on to some hypotheses with more scientific support.

400BC – To Stave Off Fever?

Hippocrates
Hippocrates offered the first theory about why we yawn. He hypothesized that yawning occurred just about the time that a person was about to break out in a fever. He thought that yawning would remove unhealthy air from the lungs.

Later studies showed that yawning likely has nothing to do with respiratory functions, so Hippocrates theory proved to be incorrect. Thanks for playing!

Does Yawning Help Increase Heart Rate?


As history progressed, scientists continued to be interested in finding the reason that we yawn. In the 17th century, scientists guessed that yawning had an impact on circulatory functions such as creating an increased heart rate.

Modern studies show that yawning does not increase heart rate, but the act could have other impacts on the circulatory system. The jury is still out on this one.

Is Yawning a Cooling Mechanism?

One of the current theories about why we yawn is that the act serves as a cooling mechanism.

National Geographic News cited a theory by Gary Hack and Andrew Gallup. In the article, Christine Dell’Amore wrote, “Yawning causes the walls of the maxillary sinus to expand and contract like bellows…which lowers its temperature.”

Further evidence to back up this theory is that people tend to yawn more when a warm or hot towel is placed on their forehead than when a cool or cold towel is placed on their forehead.

However, this can’t be the whole answer as it doesn’t explain why we yawn more when we’re tired, bored, etc…

Is Yawning a Purely Emotional Action?

Another popular theory is that yawning is not a physiological action but an emotional one. There is some evidence to support this:

  • Studies have shown that boredom causes yawning.
  • People who tend to show more empathy are more likely to experience contagious yawning.
  • Many people will yawn when reading about or discussing yawning.

yawning when tired
How many times have you yawned since you started reading this article?

You haven’t undergone any dramatic physiological changes, so what is causing you to yawn?

Yet, for all the evidence that points to yawning being purely emotional, there is other evidence that points to yawning having roots in physiology.

For example, if dopamine, nitric oxide or other neurotransmitters are injected into a lab animal’s hypothalamus’ the amount of yawning increases. For all of the studies that have tried to pinpoint why we yawn, no one has yet provided a definitive answer.

There is one thing that we can all agree on. When a baby sloth yawns… its adorable.

Bonus: Some Interesting Facts about Yawning

  • A study at Yerkes National Primate Research Center showed that chimps yawn when they see
    other chimps that they know yawning.
  • Experts at the University of Porto, located in Portugal, found that human yawns are contagious
    to their dogs.
  • The average length of a yawn is six seconds.
  • In general, men’s yawns last longer than women’s yawns.
  • When yawning and stretching occur at the same time it is called pandiculation.

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