Have You Ever Wondered Why Yawns are Contagious?

Every human yawns. So do many other vertebrates, including snakes, dogs, cats, sharks, and chimpanzees. Yawning is contagious, but not everyone catches a yawn. About 60-70% of people yawn when they see another person yawn in real life, in a photo, or even read about yawning. Contagious yawning also exists in animals, but it does not necessarily work the same way it does in humans. Scientists have come up with many theories about why we catch yawn. Here are some of the main ideas:

Yawning signals empathy

Probably the most popular theory on contagious yawning is that yawning serves as a form of nonverbal communication. Those who yawn show that they are attuned to a person’s emotions. Scientific evidence comes from a 2010 College of Connecticut study, which concluded that yawning does not become contagious until age four, when empathy skills develop. 

In the study, children with autism, who may have impaired empathy development, were less likely to start yawning than their peers. A 2015 study looked at contagious yawning in adults. College students were given personality tests and asked to watch video clips of faces that included yawning. The results showed that students with lower empathy were less likely to yawn. Other studies have found a link between decreased contagious yawning and schizophrenia, another disorder associated with decreased empathy.

Relationship between contagious yawning and age

However, the link between yawning and empathy is not conclusive. A study by the Duke Center for Human Genome Variation published in the journal PLOS ONE sought to determine the factors contributing to contagious yawning. 

In the study, 328 healthy volunteers were presented with a questionnaire that measured sleepiness, energy levels, and empathy. Survey participants watched a video of people yawning and counted how many times they yawned. While most people yawned, not all did. Of the 328 participants, 222 yawned at least once. Repeating the video test several times revealed whether a person yawning contagiously was a stable trait.

In the Duke study, no relationship was found between empathy, time of day, or intelligence and contagious yawning, but there was a statistical relationship between age and yawning. Older participants were less likely to yawn. However, because age-related yawning accounted for only 8% of responses, the researchers intend to search for a genetic basis for contagious yawning.

Contagious yawning in animals

Studying contagious yawning in other animals could show how humans catch it.

A study conducted at Kyoto College’s Primate Research Institute in Japan examined how chimpanzees respond to yawning. The results, published in The Royal Society Biology Letters, showed that two of the six chimpanzees in the study yawned contagiously when they saw videos of other chimpanzees yawning. Three chimpanzee infants in the study did not catch a yawn, suggesting that young chimpanzees, like human infants, may lack the intellectual development to catch a yawn. Another interesting finding of the study was that chimpanzees yawned only in response to videos of actual yawning but not in response to videos of chimpanzees opening their mouths.

A College of London study found that dogs can pick up yawns from humans. In the study, 21 of 29 dogs yawned when a human yawned in front of them but did not respond when the human opened their mouth. The results support a link between age and contagious yawning, as only dogs older than seven months were susceptible to contagious yawning. Dogs are not the only pets known to catch yawns from humans. Even cats, which yawn less frequently, have been known to yawn when they see people yawning.

Contagious yawning in animals can serve as a means of communication. Siamese fighting fish yawn when they see their reflection or another fighting fish, usually just before an attack. This could be a threatening behavior or serve to oxygenate the fish’s tissues before exertion. Adelie and the emperor penguins yawn at each other as part of their courtship ritual.

Contagious yawning is associated with temperature in both animals and humans. Most scientists suspect it is a thermoregulatory behavior, while some researchers believe it is used to signal a potential threat or stressful situation. A 2010 study of budgerigars found that yawning increased when the temperature was brought close to body temperature.

Humans often yawn when they are tired or bored. Similar behavior is seen in animals. One study found that the brain temperature of sleep-deprived rats was higher than their core temperature. Yawning lowers brain temperature and possibly improves brain function. Contagious yawning could be a social behavior communicating to a group that it is time to rest.

The bottom line is that scientists aren’t entirely sure why contagious yawning occurs. It has been linked to empathy, age, and temperature, but the reason isn’t fully understood. Not everyone catches yawn. Those who don’t yawn may simply be too young, too old, or have a genetic predisposition to not yawn, but not necessarily a lack of empathy.