What Is A Yawn And Why Do People Yawn?
The Evolutionary And Physiological Reasons Behind Yawning
Jul 4, 2009
Everybody yawns, adults, children, infants and even some birds, reptiles and mammals. Yawning is often associated with being bored or tired, but there are actually other reasons behind the need to yawn.
Are Yawns Really Contagious?
Studies have shown that the contagiousness of yawning is a sign of empathy, and that evolutionarily speaking it was a way of maintaining group vigilance or alertness. It is also believed that in the past, yawning was used as a way of people signaling each other and that it remains contagious now as a leftover response from human ancestors.
Studies of children without autism, compared with children with autism, showed that the autistic children were less likely to yawn after witnessing a yawn then non-autistic children. Autistic children are known to have difficulty showing empathy. And although many species yawn, it appears to only be contagious in humans and other primates such as apes and chimpanzees.
The Purpose Of Yawning
Yawning cools the brain when it is overheated. The brain works best when cool and humans as well as other animals have evolved adaptations to accommodate this. There is a thermal window for when it is best to yawn. A study by Andrew Gallup (reported on by Jennifer Viegas, "Yawning cools the brain", ABC Science) from Binghamton University showed that parakeets yawn most when they are in increasing ambient temperatures.
Yawning when temperatures are higher than body temperature would mean breathing in warm air, considered counterproductive, and yawning when temperatures are cold would mean taking in and sending cold air to the brain, which could cause a thermal shock.
Sleep deprivation and exhaustion increase deep brain temperatures and also prompt yawning in an attempt to cool the brain. Yawning can also be used as a seizure signal and excess yawning could indicate brain-cooling problems.
A bout of excessive yawning is often a sign an epileptic seizure is about to occur in an epileptic patient. Multiple sclerosis (MS) involves thermoregulatory dysfunction and sufferers of MS also have bouts of excessive yawning.
Yawning is also a way to stretch the facial muscles. Muscles in the face are relaxed after an open-mouthed yawn, and yawning with mouth closed is not as effective.
Interesting Yawning Facts
- Yawning increases blood pressure, heart rate and flexes muscles and joints of the face.
- Yawns usually last for approximately 6 seconds.
- The earliest occurrence of yawning is 11 weeks after conception (i.e., 11 week old fetus).
- 55% of people yawn after witnessing someone else yawn. Sometimes the original yawn doesn’t even need to be a real yawn for it to trigger another person’s desire to yawn.
- Yawning becomes contagious after the first year or two of life.
- Yawning in certain primates (e.g., macaques) is an aggressive or dominant behaviour, a way to show off teeth and to threaten.
- Yawning in front of dogs may relax them.
- Yawning is a behaviour that can help maintain attention and alertness.
Resource and further reading:
"Yawning cools the brain", by Jennifer Viegas, ABC Science, July 2009
"Why We Yawn", ThinkQuest, July 2009
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