Why do we yawn?

Many people assume that we yawn because our bodies are trying to get rid of 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 breathing slows down, less oxygen makes it to the lungs. As carbon dioxide builds up in the blood, a message to the brain results in signals back to the lungs saying, "Take a deep breath," and a yawn is produced.

The only problem with the excess CO2 theory is that research shows that it may not be true. In 1987, Dr. Robert Provine and his coworkers set up an experiment to test the theory that high CO2/low O2 blood content causes yawning. Air is normally made up of 20.95% O2, 79.02% N2 (nitrogen), 0.03% CO2 (and a few other gases in low concentrations). The researchers gave college students the following gases 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 #2 and #3) did cause the students to breathe at a faster rate. However, neither CO2 gas nor 100% O2 caused the students to yawn more. These gases also did not change the duration of yawns when they occurred. The researchers also looked for a relationship between breathing and yawning by having people exercise. Exercise, obviously, causes people to breathe faster. However, the number of yawns during exercise was not different from the number of yawns before or after exercise. Therefore, it appears that yawning is not due to CO2/O2 levels in the blood and that yawning and breathing are controlled by different mechanisms.
 
All I remember is it’s from an extremely primitive part of the brain

And there’s some old visual/social link behind the reason why it’s passed on to others and to other creatures.


Google is your friend :p
 
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