What is Bigfoot? Is there life on other planets? Let’s tackle another age-old mystery: Why do we yawn, and why is it so darn contagious? The average yawn lasts for about six seconds. Our mouth opens and our jaw drops, allowing as much air as possible to fill our lungs. Our abdominal muscles flex and our diaphragm pushes down. It’s involuntary - even babies in the womb have been observed yawning as early as 11 weeks along.

What causes a yawn? Science has only theories. We know that we are more likely to yawn when we are fatigued, bored or drowsy. We know that our heart rate actually increases by as much as 30% during a yawn. We know that it can occur during sexual arousal. It has even been observed in Olympic athletes just before an event.

What we don’t know is why it might be useful. Hippocrates believed that yawning is a mechanism to rid the body of fever. Current theories abound:

•The physiological theory: Our bodies induce a yawn to draw in more oxygen or remove a build-up of carbon dioxide. Note, however, that we don’t yawn during exercise, when our body craves more oxygen. Also, giving extra oxygen does not appear to decrease or prevent yawning.

•The evolution theory: Yawning began with our ancestors, who used it to show their teeth and intimidate others.

•The boredom theory: We yawn when we are bored or tired. This, however, doesn’t explain why athletes may yawn right before a competition.

•The brain-cooling theory: We yawn in situations where our brains are warmer and need to be cooled off. Cool brains work better, so yawning keeps us more alert.

We are likewise baffled by the fact that yawning is truly contagious. It starts to become transmissible during the first year or two of life. Repeated studies show that when one person in a group begins to yawn, more than half of the group will follow within five minutes. Studies also show that those close to us, through family or friendship, are more likely to “catch” our yawn. Contagious yawning also occurs in chimpanzees and other animals, when it is seen or even heard.

Studies show that we grow more susceptible to contagious yawning as we age. Those with autism and schizophrenia, conditions that involve impaired social skills, exhibit less contagious yawning. This led to a theory, since disproven, that those with higher levels of empathy are more likely to exhibit contagious yawning. Detailed studies have also looked for links with intelligence, or time of day, but the only consistent link found was age.

Since so little is understood about a physiological cause of yawning, social scientists are examining behavioral theories. Some have argued that because yawns are contagious, they serve as a form of communication. It’s unclear as to what that yawn is communicating, but I hope that if I happen to see you reading this column, you are not doing it!

Dr. Alan Frischer is former chief of staff and former chief of medicine at Downey Regional Medical Center. Write to him in care of this newspaper at 8301 E. Florence Ave., Suite 100, Downey, CA 90240.

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Published: June 12, 2014 - Volume 13 - Issue 09