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Why We Yawn

Yawning Cools Brain, Study Suggests, but Is Yawning Really a Social Cue?
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What We Say When We Yawn

Gallup says his brain cooling theory of yawning is the only theory that explains all these experimental results. But he has not yet convinced those who prefer another theory.

University of Geneva physician Adrian G. Guggisberg, MD, agrees with Gallup that changes in room temperature can trigger yawning. But he's wary of the brain cooling theory. And he offers an alternative interpretation of Gallup's Tucson study.

"The fact that yawning is suppressed during high temperatures suggest that it fails precisely when we need it," Guggisberg tells WebMD. "There are other [ways to regulate body temperature], such as sweating, and it is unclear why we would need another regulator which fails when it matters."

Yawn theorists split into two camps. Like Gallup, one side says yawning must have a physiological cause, and a physical benefit. The other side says yawning is a form of communication that offers various social benefits.

Guggisberg prefers the social theory of yawning. He sees the physiological effects of yawning as too small to account for their persistence through evolution. But he sees the contagious effect of yawning as a key clue.

"The more people are susceptible to contagious yawning, the better their social competence and empathy," Guggisberg says. "In humans it is clear that yawning has a social effect. It is probably an unconscious behavior. It is not clear what yawning communicates or what it achieves. But clearly it transmits some information that has some effect on brain networks or behavior."

Across cultures, Guggisberg says, the yawn is understood as a sign of sleepiness and boredom. The yawn thus communicates to others that one is experiencing a moderately unpleasant experience but not an immediate threat.

"We might have to get used to the idea that yawns have a primarily social rather than primarily physiological effect," Guggisberg and colleagues wrote in a recent article.

Gallup argues that whatever message yawning communicates, it is far too ambiguous and subtle to be so well-conserved throughout evolutionary history.

"It is not that I don't think there is any social function to yawning, because clearly it is contagious," Gallup says. "But we have to think of it as a process driven by physiological triggers we are unable to control. If it happens in a meeting, it should not be a sign of disrespect or insult."

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