Why do we yawn?

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Question: Why do people yawn?

Answer: Yawning might serve as a social action to communicate a lack of interest. It might also serve as a physiological way to regulate the body.

The study of yawning is anything but boring. It boasts a rich history of theories that go back to antiquity, but so far, the biological purpose for yawning remains a mystery.

Yawns Have Different Meanings

Not all yawns are the same. Most people yawn and stretch when they wake up or go to bed, yawn when they are bored, or yawn when they need to "pop" their ears after traveling in high altitudes. Sometimes people yawn just because they saw someone else yawn. Oscitation, the act of yawning, occurs in almost all vertebrates, or animals with backbones. Even birds and fish exhibit a form of mouth gaping similar to yawning. In humans, yawning can start when a baby is still in the womb.

A yawn is a coordinated movement of several parts of the body, including muscles in the chest and abdomen, along with the throat and mouth. Yawning distributes surfactant, a wetting agent, to coat the tiny air sacs in the lungs. Generally speaking, people cannot yawn on command. It is believed that yawning is a semi-voluntary action and partly a response controlled by neurotransmitters, chemicals that communicate information in the brain. Yawning is also associated with increased levels of neurotransmitters and certain hormones.

Hippocrates First Studied Why People Yawn

There are numerous theories about why people yawn, and scientists have yet to agree on one. One of the first theories for yawning can be traced back to Hippocrates, a Greek physician known as the "father of medicine." He hypothesized that yawning comes before a fever and is a way to remove bad air from the lungs. Based on modern evidence, however, it seems unlikely that yawning serves as a function of the respiratory system.

By the 17th and 18th centuries, scientists were challenging the Hippocratic theories of yawning. New theories focused on the circulatory system, suggesting that yawning causes an increase in blood pressure and heart rate. This would improve muscle activity and alertness. It might explain why many athletes yawn before playing sports. However, current tests have shown that neither the heart rate nor the brain's electrical activity increase after yawning.

Yawning May Be Psychological

Today, scientists continue to research the functions of yawning. Dr. Robert Provine, who studies contagious behavior, suggests that yawning is "associated with the change of a behavioral state - wakefulness to sleep, sleep to wakefulness, boredom to alertness.” And more recent studies have suggested that yawning might be connected to brain temperature. When the brain becomes warmer than it should be, people might yawn to cool it. It is theorized that cooler blood from the body floods into the brain while the warm blood flows out.

There are also explanations for yawning based on how humans evolved and how people interact with each other. Yawning may be linked to circadian rhythms - biological activity related to a 24-hour cycle - as a signal to go to bed or as a waking action. It might be a way for people to express disinterest or feelings of worry. Yawning can also be contagious.

Humans Cause Each Other To Yawn

Contagious yawning comes from witnessing someone or thinking about another person yawning. According to studies, 42 percent to 55 percent of adults will yawn during or after watching a videotape of another person yawning. It typically happens in older people. Traditionally, this behavior is not seen in humans under age 5 or people with autism.

Evolutionary psychologist Gordon Gallup says contagious yawning is related to empathy and understanding. Yawning activates the parts of the brain that deal with imitation and social behavior. When someone sees another person yawn, nerve cells called neurons in their brain fire, causing them to yawn as well. These "mirror neurons" can make one person feel what another person is feeling. They can also make someone perform an action they witness even if they do not actually feel the need.