Experts May Have Figured Out Why We Yawn

Summary

Researchers propose that yawning serves to reset and rebalance the throat muscles to maintain an open airway.

Abstract

Yawning has long puzzled scientists, but a new hypothesis suggests it may be a mechanism to maintain muscle balance in the throat. This hypothesis, put forward by Christiaan Doelman and colleagues, posits that yawning helps to widen the throat and keep the airway open, aiding in various functions such as breathing, chewing, swallowing, and vocalization. The study reviews existing research and concludes that yawning is not primarily a social behavior, as previously thought, but rather a physiological necessity observed across most living things, including humans and other vertebrates. The muscle-reset function of yawning could explain why it occurs during periods of drowsiness, stress, and after eating, as these are times when the throat muscles may need to be recalibrated to function properly.

Opinions

Christiaan Doelman believes that the social aspect of yawning is not its main function, as it only accounts for about 10% of yawning episodes.
The brain-cooling hypothesis, which links yawning to regulating brain temperature, has not been supported by follow-up research.
Yawning's association with empathy and its contagious nature suggest it may play a minor social role in bonding and empathy.
The new hypothesis emphasizes the importance of yawning in maintaining a dynamic and functional airway passage, which is essential for various activities such as breathing and eating.
The study suggests that yawning may be particularly important for vertebrates, whose throat muscles can either collapse from low muscle tone or tighten due to stress, necessitating a reset mechanism.

One of human physiology’s great mysteries may be solved, finally.

Yawning is a mystery that has long defied explanation.

Along with humans — who begin yawning in the womb just 12 weeks after conception — most other living things also yawn. That includes dogs, cats, and other mammals, but also birds, reptiles, and amphibians.

Any behavior that exists so broadly within the animal kingdom must serve a purpose, but experts have struggled to determine what that purpose could be. There have been many hypotheses, but so far none has stood up to rigorous scrutiny.

‘Social yawning makes up just 10 percent of yawning episodes, so I don’t think the social part is the main function of yawning.’

Human beings yawn when they’re sleepy, but also when they’re first waking up. The association between yawning and drowsiness led some researchers to guess that yawning helps regulate the brain’s temperature. While there may be something to this, the so-called “brain-cooling hypothesis” hasn’t panned out in follow-up work.

Other researchers have shown that yawning is more likely to take place during periods of high stress — such as during intense athletic competitions — and also after eating. Why does this happen? No one quite knows. Among some primates, yawning is more common among males. In those situations, it may be a way of displaying fearsome canine teeth — a kind of passive aggressive “don’t mess with me” signal — but work on humans has shown yawning is equally common among men and women.

Meanwhile, researchers have also found that yawning is contagious. Seeing someone else yawn — or even thinking or reading about yawning — can bring on a bout of yawns. Studies have also found that yawning appears to be more common among people who are especially empathic. This has led to speculation that yawning may serve some social function — that it’s a form of social “mirroring” that allows human beings to establish closer bonds. But this appears to be just a minor (and maybe late-developing) function of yawning.

“Social yawning makes up just 10 percent of yawning episodes, so I don’t think the social part is the main function of yawning,” says Christiaan Doelman, MD, a researcher in the Department of Head and Neck Surgical Oncology at University Medical Center Utrecht in the Netherlands.

Doelman is the author of a 2022 study that reviewed the existing research on yawning. In that study paper, he and his co-authors proposed a new explanation for why we yawn — one that helps makes sense of the disparate situations that can provoke a bout of yawning.

“Our hypothesis states that yawning recovers a complex muscle balance that widens the throat and helps keep the airway open,” he says.

Doelman explains that the mouth and throat form a “dynamic” airway passage that has to adapt to facilitate healthy breathing, but also chewing, swallowing, and vocalization. Sometimes this passage needs to be open wide to allow air to flow freely into the lungs, while other times it needs to constrict in order to guide food down the right tube or produce certain sounds.

“Good muscle balance is essential,” he says. “If the muscles are too loose, the airway will collapse, but if the muscles are too tight, the airway can’t open as wide.” He and his study coauthors say that yawning performs a necessary sort of muscle-reset function. “Yawning helps restore muscle tone and balance,” he says.

In support of his hypothesis, he points to several older research papers that have shown the pharyngeal lumen (basically, the part of the throat behind the mouth and nasal cavities but above the chest and esophagus) grows wider, or dilates, following a yawn.

“Yawning as a key player in dilation may explain frequent yawning around drowsiness [and] around sleep,” he and his study coauthors wrote. They also point out that muscle dilation and repositioning following a yawn might be helpful after periods of heavy use or overstimulation, which could explain why yawning picks up after periods of eating or during times of anxiety (which causes muscle tension and sometimes teeth gritting).

“Yawning is happening in many vertebrates, and what they all have in common is that the throat could collapse due to low muscle tone or muscle tightness due to stress,” he says. “No other movement has been described to restore that muscle tone.”

Put simply, yawning is a way to help reset and rebalance the muscles of the throat to ensure proper functioning.

Doelman says that follow-up work is needed to confirm his group’s hypothesis. But if they’re right, one of the great and quirky mysteries of human physiology — why we yawn — may finally be answered.