You've probably experienced this phenomenon before. Your friend yawns and you suddenly find yourself doing the same. It's called "contagious yawning" and you're not alone. According to the authors of one yawning study published by the Royal Society, 42 to 55 percent of adults yawn during or shortly after viewing another person's yawn.
The Potential Cause
While the biological reasons for spontaneous yawning are still vague, current research by Atsushi Senju and others suggests that "contagious yawning"---yawning stimulated by viewing another person yawn---may be a phenomenon reliant on the brain's capacity to exhibit empathy.
Empathy in the Brain
A study at Drexel University in 2005 using fMRI scans found that the self-processing area of a participants' brain lit up when viewing someone yawn. Activity in this area, according to the researchers, suggests an empathetic reason for the response.
Children Under 4
The empathy theory is also supported by studies involving children under 4 who appear to be much less susceptible to contagious yawning than adults. This suggests that social development, specifically the brain's capacity to exhibit empathy, could play a key role in contagious yawning.
In Older Children With Autism
The same conclusion is supported in studies in older children with autism spectrum disorder who rarely exhibit the contagious yawning phenomenon. Autism spectrum disorder affects the children's ability to properly socialize, partly due to an inability to put themselves in "someone else's shoes." Given their findings in this study, published in Biology Letters, researchers believe the lack of contagious yawning by those with an inhibited ability to empathize pinpoints empathy as a key component into understanding why we yawn when others do.
In Chimpanzees
Finally, not all animals display signs of contagious yawning, but the neighboring species of humans, chimpanzees, appear to exhibit this behavior as well. Researchers in Japan took a group of chimpanzees and showed them videos of other chimps yawning. Two out of the six females yawned more when exposed to this video and none yawned less. And displaying no susceptibility to contagious yawning much like their human counterparts, the infant chimps did not yawn at all.
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