Everybody knows that yawns are contagious.

But why?

There seems to be no easy explanation for this. Atleast one scientist, Dr. Robert Provine, professor of psychology at University of Maryland, spent time researching this topic. He devoted several years to the yawn phenomenon
There is very little research on yawning because for most people yawning is not a problem.

Everyone yawns - babies, kids, teenagers, adults. Some birds, reptiles and most mammals also yawn. However, the reason why we yawn is a bit of a mystery.

Here are a few things that are known about yawns:

  • The average duration of a yawn is about 6 seconds.
  • In humans, the earliest occurrence of a yawn happens at about 11 weeks after conception - that's BEFORE the baby is born!
  • Yawns become contagious to people between the first and second years of life.

A part of the brain that plays an important role in yawning is the hypothalamus. Research has shown that some neurotransmitters (for example, dopamine, excitatory amino acids, nitric oxide) and neuropeptides increase yawning if injected in the hypothalamus of animals.

Dr. Robert Provine says:
The contagiousness of yawns suggests that we've inherited a mechanism for the perception of and triggering of yawns.

He theorizes the infectious yawn, catching only in humans, evolved for a purpose.

It is possible that yawns are contagious because at one time in evolutionary history, the yawn served to coordinate the social behavior of a group of animals. When one member of the group yawned to signal an event, all the other members of the group also yawned. Yawns may still be contagious these days because of a leftover response (a vestigial response) that is not used anymore. None of this has been proven true and yawns are still one of the mysteries of the mind.

1. Provine, R.R. Contagious yawning and infant imitation. Bulletin Psychonomic Soc., 27:125-126, 1989.
2. Provine, R.R. Yawning: effects of stimulus interest. Bulletin Psychonomic Soc., 24:437-438, 1986.
3. Provine, R.R. Faces as releasers of contagious yawning: an approach to face detection using normal human subjects. Bulletin Psychonomic Soc., 27:211-214, 1989.
4. Provine, R.R. Yawning as a sterotyped action pattern and releasing stimulus. Ethology, 72:109-122, 1986.
5. Provine, R.R., Hamernik, H.B. and Curchack, B.B. Yawning: relation to sleeping and stretching in humans. Ethology, 76:152-160, 1987.
6. Edmonton Public Library

This is by Jack Valko
Special to http://ABCNEWS.com

  • The physiological theory states that a yawn is a reflex that occurs when your brain recognizes a need for more oxygen. Yawning is contagious because everyone in a room is likely to be shy on fresh air at the same time. A yawn may also be stimulated by external cues, much like watching someone eat can make you hungry.
  • The boredom theory is based on the assumption that if everyone finds something boring, they will yawn. This doesn’t explain why we yawn when bored, however, unless it’s an instinctive way we use body language to say something is uninspiring.
  • The evolutionary theory says that we yawn to display our teeth, a behavior left over from our more primitive beginnings. Yawning could act as a warning to others. These days it would seem an obsolete display, since we’ve supposedly become more civilized.

    Since no one has figured out exactly why yawning seems to be contagious, the real cause will remain a mystery for now. I bet you’re about ready to yawn right now. If so, I hope the boredom theory is wrong — otherwise I might be out of a job.

  • There is an easy physical explanation for the contagiousness of yawns: When you yawn, you equalise the pressure between your inner ear and the outside world. This is why yawning helps when your ears are popping, on an aeroplane or in a train tunnel for instance.

    But of course, when you equalise the pressure in this way you cause a change in the pressure of the surrounding air. This means that the pressure in the ears of people nearby no longer matches the pressure in the air around, so they have to yawn to compensate. If there are more people around, you can set off a whole chain reaction.

    So there you have it.

    ...and if you have a better explanation of that I'd like to hear it.

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