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Why Do We Yawn?

In the past, whenever someone yawned, it was thought to relate to either sleepiness (because of low oxygen in the brain) or emotional boredom. However, there was no proof of actually why people yawn.

Yawning is defined as opening one’s mouth wide, with the jawbone extended to its lowest position, and inhaling deeply. Yawning is classified as a semi-voluntary action (to a degree, it is like a reflex), which is controlled by several neurotransmitters in the brain’s hypothalamus. All the vertebrates (amphibians, reptiles, birds, and mammals) yawn. Humans begin yawning around 12 weeks after birth.

The process of yawning dispenses surfactant, a biochemical which coats the alveoli (those tiny air sacs in the lungs), helping to keep the alveoli open. Some medical experts theorize that yawning in fetuses (pre-birth) may help them practice survival for life outside of the womb.
One of the new theories asserts that yawning is a contagious social reflex that is not generated by the mirror neuron network (which is involved in the classic monkey see, monkey do response of imitation). Rather, it speculates that yawning is an empathetic response to unifying members and establishing cooperation within a group. “Contagious yawning is associated with the same parts of the brain that deal with empathy. These regions, the precuneus and posterior temporal gyrus, are located in the back of the brain.” Meaning mammals, humans and primates, react in an empathetic manner to another’s actions as if they are saying, “I feel what you feel.”

Still another source combines the mirroring and empathy mechanisms to conclude, “An empathic person simply appreciates the feeling state of the other person. The origin of empathy seems to come from the physical "mirroring" that parents and other adults do with children.”

A different theory comes as a result of research at the State University of New York at Albany, (which was published in the journal Evolutionary Psychology), where scientists have come up with an unexpected theory – people yawn to raise blood flow and cool their brains!

Researchers set up experiments where 44 volunteers watched films of people behaving normally, laughing, or yawning. The volunteers were allowed to breathe in four ways: through their noses only, through their mouths only, with nose plugs, and normally (both nose and mouth).

The results showed that 50% of the volunteers (breathing normally or only through the mouth) yawned as they saw other people yawning. None of the volunteers breathing through their noses yawned at all. And, get this, those volunteers with cold packs on their forehead did not yawn either.

Furthermore, in “Yawning and Thermoregulation,” scientists came to the conclusion “The brain-cooling hypothesis further stipulates that, as ambient temperature increases and approaches (but does not exceed) body temperature, yawning should increase as a consequence.”

These research findings suggest that yawning contains an adaptive/functional factor that it is a derivative of other forms of behavior.
Interpreting the results further led scientists to conclude that breathing only through the nose causes the blood vessels in the nasal cavity to send cool blood to the brain, therefore eliminating any need to yawn.

In fact, the brain-cooling function also attempts to clarify why yawning can be contagious. Scientists speculate that contagious yawning is elicited by sympathetic mechanisms that act to sustain group vigilance. Meaning it’s a way to wake up everybody to be alert.

It turns out that paratroopers claim that they yawn right before they jump, which the scientists explain as an action, which moves them from sleepiness and boredom to wakeful alertness. 
Now here’s a new turn that seems to include a combination of behaviors, cooling of the brain, the waking up function, and a behavior that unites the cooperation of members of a group – all at the same time!

And as for the ‘aerobic yawn” when exercising, nobody really knows for certain. Perhaps, some theorize, it is to give the alveoli in your lungs a stimulation to remain open.

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Sources: Contagious Yawn 'Sign of Empathy' The University of Leeds Research British Association's Festival of Science in York 10 September 2007 Understanding Empathy St. Luke Institute Vol. VII, No. 3 May/June, 2003 The Empathic Brain: How, When and Why? Trends in Cognitive Sciences 10(10):435-41, 2006 Oct Yawning as a Brain Cooling Mechanism: Nasal Breathing and Forehead Cooling Diminish the Incidence of Contagious Yawning Evolutionary Psychology 2007 5(1): 92-101 (www.epjournal.net) Yawning and Thermoregulation in Budgerigars, Melopsittacus undulates Journal of Animal Behavior 2008.09.014   

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