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Someone starts and it spreads…why is yawning contagious?
Whether at work, school or a dinner, once someone yawns, it is over…more yawning, then someone gets up and the fun bubble has popped. But what happens? Why is yawning contagious? In 400 B.C., Hippocrates thought yawning removed bad air from the lungs before a fever. In the 17th and 18th century, doctors believed yawning increased oxygen in the blood, blood pressure, heart rate and blood flow itself. So it made sense you would want to follow the example…but what makes the body do it involuntary?
In the past, people have had many hypotheses. In the last century, consensus moved toward the idea that yawning cools down the brain, so when ambient conditions and temperature of the brain itself increase, yawning episodes increase.
Typically a yawn lasts four to seven seconds and happens in fits of two or three. It involves the following steps:
- A long inhale (breathing in) using your nose and then mouth.
- A brief episode of powerful muscle stretching around your mouth and throat.
- A rapid exhale (breathing out) using your mouth with muscle tension release.
Yawning is mostly involuntary, meaning you don’t have control over it. And most scientists consider it a reflex.
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And yawning occurs in just about every species. It happens when an animal is tired. It can be used as a threat display in some species. Yawning can occur during times of social conflict and stress, something researchers call a displacement behavior. So it isn’t just a human reaction, it is the animal kingdom also….so why does it happen and why is so darn contagious?
Yawning is a common but perplexing human function. Scientists have several theories but nothing concrete. Common triggers of yawning include tiredness, boredom, waking up and stress. A current theory about yawning is the arousal hypothesis states yawning activates your brain. This theory is tied to the fact tiredness and boredom tend to trigger yawning the most.
Seeing or hearing other people yawn can also cause you to yawn. The wide-open mouth can be contagious, especially in social species such as humans, chimpanzees, bonobos, macaques and wolves. In addition, research on humans tell us people who are more empathetic tend to be more susceptible to contagious yawning. When you see someone else yawn, the networks in your brain responsible for empathy and social skills are activated.
Is yawning contagious for dogs also. In U.K. biologists tested for contagious yawning between people and man’s best friend. Although 5 of the 19 dogs studied did yawn in response to an unfamiliar person’s yawn, the researchers couldn’t prove the yawns were contagious. But, cognitive and behavioral scientists at the University of Tokyo once again tested contagious yawning in canines while controlling for stress. This time researchers found dogs were more likely to yawn in response to a familiar person. They concluded dogs can “catch” a yawn from humans and yawning is a social rather than an stress-based behavior.
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University of Nebraska psychologists looked at contagious yawning in shelter dogs. They found some dogs yawned when exposed to human yawning and had elevated cortisol levels, a proxy for stress. Levels of the cortisol stress hormone did not rise in dogs who didn’t yawn in response to a human yawn. This finding suggests some dogs find human yawning stressful and others do not. More research is needed to evaluate this aspect of the human-dog relationship.
The jury’s still out on the true why of yawning. But when it comes to inter-species yawning, collect your own anecdotal data. Try an experiment at home, yawn and see if your pet yawns back.
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Anthony Washington
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