Yawning is one of the most cliched actions in our society. Trying to send a signal that it’s past your bedtime? Give an exaggerated yawn. Bored by a topic of conversation? Here comes that yawn.
But when you think about it, yawning is a pretty strange phenomenon, and if you’ve ever seen someone yawn and felt an irresistible urge to yawn alongside them, you might’ve wondered if yawning is contagious, and what, exactly, is going on.
There are many different and unconfirmed theories about why we yawn. But one thing neurologists and evolutionary biologists agree on is this: Contagious yawning is real in highly social species, including humans. Meaning one yawn can start a chain event.
Why do we yawn?
Yawning is an involuntary reflex where the mouth is opened wide, and the lungs take in a lot of air, which is then slowly exhaled. During that time the eardrums stretch and the eyes may close tight, maybe even water. The average adult yawns approximately 20 times per day, and when you feel a yawn coming on, it can be nearly impossible to suppress.
No thought or action is needed to produce a yawn, though it’s still a rather complex, if primitive, reflex that originates in the brain stem, according to Thomas Scammell, a neurologist at Harvard Medical School who studies sleep.
According to the National Library of Medicine, the reflex of yawning can also help equalize air pressure in your ears, making it a great tool during air travel or a fast elevator ride.
Andrew Gallup, an evolutionary biologist at State University of New York Polytechnic Institute who has spent years and years trying to figure out why we yawn, explains that “while yawns primarily occur [during] transitions between sleeping and waking, they are also triggered under a variety of contexts and changes in state.”
A growing body of research suggests that yawning may be prompted by rises in brain temperature. Supporting this theory, previous studies have proposed that the purpose of yawning is to cool the brain, or to stretch internal organs like lungs as well as tissues, helping the body to liven up, which can stabilize our internal physiological functions and bring our bodies into homeostasis.
These types of internally, physiologically driven yawns are called spontaneous yawns. But there’s also the phenomenon of infectious yawning, which happens when we see or hear someone like us doing it.
Many animals experience contagious yawning
Scientists believe that yawning may have evolved to help animals, including humans, bond with one another and make group decisions. Functional brain scans of individuals seeing other people yawn have shown increased activation in the ventromedial prefrontal cortex of the brain, which is involved in several functions, most notably decision making, according to neuroscientists.
Researchers have studied contagious yawning in chimpanzees, dogs, elephants, and, recently, lions. In a 2021 study published in Animal Behaviour, researchers observed that after seeing other lions’ yawns, the big cats also tended to coordinate their movements. After yawning together, “two lions would engage in highly synchronous behavior,” says the study’s senior author, Elisabetta Palagi, an animal behavioralist at the University of Pisa in Pisa, Italy. For instance, if the two lions were lying down, and one yawned, the other yawned. Then, if the first yawner stood up, so did the other animal. In a 2021 study published in Animal Behaviour, researchers observed that after seeing other lions’ yawns, the big cats also tended to coordinate their movements. After yawning together, “two lions would engage in highly synchronous behavior,” says the study’s senior author, Elisabetta Palagi, an animal behavioralist at the University of Pisa. For instance, if the two lions were lying down, and one yawned, the other yawned. Then, if the first yawner stood up, so did the other animal.
Researchers believe that this contagious yawning is a form of communication between higher-order animals, and is especially important in social species such as lions, who work together to hunt, raise cubs, and ward off interlopers, says Palagi.
Why are yawns contagious for humans?
Likewise in humans, contagious yawning may have evolved for the same reason: to synchronize group behavior.
“Yawns tend to become more frequent during times of day that coincide with transitions in activity,” Gallup says. So, this behavior could have evolved “to increase alertness and vigilance within a group.” Contagious yawning could therefore “promote collective awareness and threat detection.”
Gallup further explains that back in our ancestral cave-dweller days, if one member of a group was feeling a little woozy and started yawning, seeing that behavior might, in turn, “increase the observer’s vigilance to compensate for the low arousal and vigilance of the yawner. The spreading of yawn contagion might then increase the vigilance of the entire group,” Gallup explains.
Gallup conducted a study last year testing this hypothesis, showing participants an array of images that included snakes (threatening) and frogs (non-threatening). He timed how fast participants “could pick out those images after seeing videos of people yawning or moving their mouths in other ways,” Gallup says. What he found is that after seeing other people yawn, participants’ ability to identify and detect snakes quickly improved while the identification of frogs remained the same.
In humans, studies indicate that our contagious yawning may also be a form of empathizing with other people experiencing a feeling, which — in the case of yawning — usually means stress, anxiety, boredom, or fatigue. Yawning may be related to a phenomenon called social mirroring (originating from mirror neurons in the brain), where we imitate the actions of others if we think it will benefit us or strengthen social bonds. Other behaviors that fall into this category include leg crossing and laughing.
But don’t worry: Just because you’re not that susceptible to contagious yawning doesn’t necessarily mean that you’re not an empathetic person. Gallup points out that there’s a lot of variability among people in terms of who is susceptible to catching yawns and who is not. Though a few studies suggest that differences in empathy may account for this response, Gallup says that “other studies have failed to replicate these results. Further work is needed to examine the connection.”
Or maybe you’re just well rested from a good night’s sleep!
How is a sleep researcher impacted by studying yawns?
As someone who focuses the majority of his time and energy on sleep and yawning, Gallup is uniquely close to yawning, which begs the question: Does he think he yawns more than the average person?
“When I first started studying this subject, I was yawning excessively,” Gallups says. “I was reading the literature and writing notes and writing papers, and I found that I was just yawning all the time. But [after a while], I became kind of habituated to the effects.”
He still yawns contagiously during social interactions, he admits. Research shows you’re more likely to catch a yawn from someone you care about, like a friend or family member, or someone with whom you have some type of bond or relationship. So the next time you struggle to stifle that yawn, rest assured: It’s perfectly normal, even if it does set off a cascade of yawns with your companions.