Yawning
Why do we yawn and why are yawns contagious?

Before you read any more of this page,get a pencil (or pen) and paper.

I will wait....
I'm still waiting....
Did you get it?
Good!

With yourpencil and paper, keep track of the number of times you yawn while you arereading this page. I hope reading this page is not boring, but you mayfind that just thinking and reading about yawning makes you yawn. Theresults may surprise you. Did you yawn yet? If you did, make sure youcount it.

Everyone yawns - babies, kids, teenagers, adults. Some birds, reptilesand most mammals also yawn. However, the reason why we yawn is a bit of amystery. There is also very little research on yawning because for mostpeople yawning is not a problem. Here are a few things that are knownabout yawns:

  1. The average duration of a yawn is about 6 seconds.
  2. In humans, the earliest occurrence of a yawn happens at about 11 weeksafter conception - that's BEFORE the baby is born!
  3. Yawns become contagious to people between the first and second years of life.
  4. A part of the brain that plays an important role in yawning is thehypothalamus. Research has shown that some neurotransmitters (forexample, dopamine, excitatory amino acids, nitric oxide) and neuropeptidesincrease yawning if injected in the hypothalamus ofanimals.

You know that when you are bored, you yawn. Scientists have confirmedthis observation by comparing the number of yawns in 17-19 year oldstudents who watched music videos to the number of yawns in students whowatched an uninteresting color test bar pattern. As you might haveexpected, people who watched the color test bar pattern yawned more (5.78yawns in 30 minutes) than those who watched the "MTV-like" video (3.41yawnsin 30 minutes.) The average duration of yawns was also slightly longer inthe test bar viewing group. One unexpected finding was that yawns in malestudents had a longer duration than those in femalestudents.

Many people assume that we yawn because our bodies are trying to get ridof extra carbon dioxide (CO2) and to take in more oxygen(O2). This may make some sense. According to this theory,when people are bored or tired, they breathe more slowly. As breathingslows down, less oxygen makes it to the lungs. As carbon dioxide buildsup in the blood, a message to the brain results in signals back to thelungs saying, "Take a deep breath," and a yawn is produced.

The only problem with this logical theory is that research shows that itmay not be true. In 1987, Dr. Robert Provine and his coworkers set up anexperiment to test the theory that high CO2/low O2 blood content causesyawning. Air is normally made up of 20.95% O2, 79.02%N2 (nitrogen), 0.03% CO2 (and a few other gases inlow concentrations). The researchers gave college students the followinggases to breathe for 30 minutes:

Gas #1

100%O2

Gas #2

3% CO2, 21%O2

Gas #3

5% CO2, 21% O2

Gas #4

Normal Air

Breathing 100% O2 (Gas #1) or either CO2 gas (Gas #2and #3) did cause the students to breathe at a faster rate. However,neither CO2 gas nor 100% O2 caused the students toyawn more. These gases also did not change the duration of yawns whenthey occurred.

The researchers also looked for a relationship between breathing andyawning by having people exercise. Exercise, obviously, causes people tobreathe faster. However, the number of yawns during exercise was notdifferent from the number of yawns before or after exercise. Therefore,it appears that yawning is not due to CO2/O2 levelsin the blood and that yawning and breathing are controlled by differentmechanisms.

So, the question remains - why do we yawn? Dr. Provine suggests thatperhaps yawning is like stretching. Yawning and stretching increase bloodpressure and heart rate and also flex muscles and joints. Evidence thatyawning and stretching may be related comes from the observation that ifyou try to stifle or prevent a yawn by clenching your jaws shut, the yawnis somewhat "unsatisfying." For some reason, the stretching of jaw andface muscles is necessary for a good yawn.

It is possible that yawns are contagious because at one time inevolutionary history, the yawn served to coordinate the social behavior ofa group of animals. When one member of the group yawned to signal anevent, all the other members of the group also yawned. Yawns may stillbe contagious these days because of a leftover response (a "vestigial"response) that is not used anymore. None of this has been proven true andyawns arestill one of the mysteries of the mind.

So, how many times did you yawn?
Still interested in yawns? Try anexperiment to keep track of your ownyawning.

References:

  1. Provine, R.R. Contagious yawning and infant imitation. BulletinPsychonomic Soc., 27:125-126, 1989.
  2. Provine, R.R. Yawning: effects of stimulus interest. BulletinPsychonomic Soc., 24:437-438, 1986.
  3. Provine, R.R. Faces as releasers of contagious yawning: an approachto face detection using normal human subjects. BulletinPsychonomic Soc., 27:211-214, 1989.
  4. Provine, R.R. Yawning as a sterotyped action pattern and releasingstimulus. Ethology, 72:109-122, 1986.
  5. Provine, R.R., Hamernik, H.B. and Curchack, B.B. Yawning: relation tosleeping and stretching in humans. Ethology, 76:152-160, 1987.
  6. The neuropharmacology of yawning
  7. Yawning: no effect of 3-5% CO2, 100% O2, andexercise

GO TO: Explore the NervousSystem Experiments andActivities Table ofContents

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