Study: Yes, yawning is contagious, but reasons unclear

Warning: This story may make you yawn. That's because yawning is so highly contagious that even reading about it, much less seeing or hearing someone yawn, is enough to get many people going.

Why? Contrary to popular theory and a number of studies, it may not be all about empathy – the capacity to share the emotions and experiences of others, a new study suggests.

"Empathy does play a role, but it's just not the huge role people were thinking," says study author Elizabeth Cirulli, an assistant professor of medicine at Duke University School of Medicine. The study, among the biggest ever to examine this little quirk, was published online Friday by PLOS ONE.

The research included 328 healthy adults, ages 18 to 83. Participants took tests that measure empathetic traits, such as feeling distress over another person's misfortune and easily identifying with fictional characters. They also took cognitive performance tests, because one previous study suggested contagious yawning might be linked with higher intelligence, Cirulli says.

Participants then watched a three-minute video showing lots of people — from babies to old folks, of various races and both genders — yawning their heads off. They clicked on a button each time they yawned, too.

Result: 68% yawned at least once. The average was four times, and one person yawned 15 times. The rate was a bit higher than in some studies, and Cirulli says it's possible that the fact people knew their yawns were being counted led some to yawn more.

Another finding: When 129 subjects watched the video a second time, those who yawned the first time were likely to yawn again, suggesting that whatever causes contagious yawning is a stable trait.

Easy-yawners did score a bit higher on the tests of empathy and cognitive performance. Those differences faded away when researchers factored in age. In the final statistical analysis, only age was clearly associated with contagious yawning: Younger adults showed the most susceptibility. Even age did not explain most of the variation among people, Cirulli says.

What does? Cirulli, a genetics researcher, leans toward some yet-to-be-determined genetic difference. She hopes to find it through blood tests. She also hopes her findings shed some light on schizophrenia and autism, since people with those disorders don't do much contagious yawning.

The new study is well-done and raises questions about the empathy theory established by previous research, says one scientist who did some of that research, Steven Platek, an associate professor of psychology at Georgia Gwinnett College in Lawrenceville, Ga.

But, he says, the previous findings remain compelling. Platek has found that contagious yawning is most common among family members, followed by friends, acquaintances, then strangers. Similar patterns have been found in chimpanzees. In an unpublished study, Platek says he found that whites and blacks tend to yawn together along racial lines.

"I really like the idea of looking for some genetic component" to help explain all the findings, he says. He says he's betting any genetic difference still involves social interaction.

He notes that scientists aren't sure why people yawn on their own, when tired or bored, though the leading theory is that it has something to do with cooling the brain.

"Nobody really knows much about yawning," he says.