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Why Do We Yawn

Updated: Mar 5

Author: Edgar Zhu

Editors: Kira Tian and Cynthia Zhang

Artist: Tiffany Gao

HUHHHHH?! One of your classmates just yawned, but many others started yawning too. Was everyone exhausted? Why is yawning contagious? Scientists have made several speculations to answer this question.

One theory is that yawning happens in order to “cool our brains down”. Some scientists believe that the cold air you breathe in when you yawn cools the blood in your face, which in turn cools your brain, allowing it to work faster. Another idea argues that oxygen deprivation causes us to yawn. When tissues around the lungs detect a decrease in oxygen levels in the lungs, we yawn to take in more air in response. Evolutionary theory suggests that humans yawn to show their teeth as a warning to others. Snakes that coil up in the grass yawn before moving; hippopotamus in the water yawn first before emerging from water. However, as humans have moved into a more civilized society, yawning as a warning to others has become obsolete. Thus, human yawns are most likely an evolutionary relic that has outlived their usefulness.

But why are yawns contagious? In 2013, scientists in Zurich, Switzerland, had 11 healthy subjects watch a set of videos. Several of the faces in the video were yawning, laughing, or expressionless. Unsurprisingly, the subjects yawned more than half the time when they saw the video.

Empathy ability is the ability to imagine yourself as others. A Czech psychologist named Pradzech asked volunteers to see a video of yawning. Results showed that nearly half of the subjects yawned in response. Empathy tests found that these people were very likely affected by yawning empathy. Pradzech concluded that 60 to 70 percent of humans will automatically reciprocate a yawn if they see anyone yawning. These people also scored high on empathy tests. Using functional magnetic resonance imaging scans, he found that during contagious yawning, the posterior cingulate and precuneus in our brain help process our emotions. "Having this ability to put ourselves in another person's shoes and feel their emotions means we are susceptible to contagious yawning," he said. The next time your classmate yawns, try to hold back.



Mary Bridget Reilly, A Real Yawner: Causes, Concerns and Communications of the ​Yawn,

University of Cincinnati, 23 October 2003

Provine, Robert R. Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond ​

(Harvard University Press; 2012) 246 pages; examines the evolutionary context ​for


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