Along with the whereabouts of Bigfoot and the answer to whether we are alone in the universe, the mechanism behind contagious yawning remains one of life's great mysteries. Though previous studies have suggested a link to empathy, new research suggests this is not the case, rendering it still largely unexplained.
The study, published in the journal PLOS ONE, was conducted by researchers from the Duke Center for Human Genome Variation in North Carolina. They say their findings show that contagious yawning may decrease with age, and that it is also not linked with tiredness or energy levels.
Contagious yawning occurs not only in humans, but also in chimpanzees and other animals, in response to hearing about, seeing or thinking about yawning.
But Elizabeth Cirulli, author of the latest study and assistant professor at Duke University School of Medicine, says:
"The lack of association in our study between contagious yawning and empathy suggests that contagious yawning is not simply a product of one's capacity for empathy."
Cirulli and colleagues say their study is the most comprehensive research to date looking at factors that influence contagious yawning.
They explain that this phenomenon differs from spontaneous yawning, in that it does not occur merely when someone is tired or bored. While spontaneous yawning is observed in the womb, contagious yawning begins in early childhood.
Older individuals less likely to yawn contagiously
Individuals with autism or schizophrenia - which involve social skills that are impaired - exhibit less contagious yawning even though they still yawn spontaneously, explain the investigators.
Does this photo make you yawn? If so, you are susceptible to contagious yawning.
But why certain people are more or less susceptible to contagious yawning is not well understood. The team says previous studies have shown a relationship between contagious yawning and empathy, as well as intelligence or time of day.
To investigate further, Cirulli and her colleagues focused on better defining how certain factors affect sensitivity to contagious yawning.
They used 328 healthy volunteers who completed cognitive testing, a demographic survey and a questionnaire that included empathy, energy level and sleepiness measures.
While the participants watched a 3-minute video of people yawning, the team recorded how many yawns were made and found that certain participants were less susceptible to contagious yawns than others.
In total, 222 of the 328 participants yawned contagiously at least once, and the number of yawns was consistent, which the team says demonstrates that contagious yawning is a stable trait.
Contrary to previous studies, the investigators say they did not find a strong connection between contagious yawning and empathy, intelligence or time of day. In fact, the only link was age; as age increased, the researchers say participants were less likely to yawn.
Cirulli explains further:
"Age was the most important predictor of contagious yawning, and even age was not that important. The vast majority of variation in the contagious yawning response was just not explained."
The team says age only explained 8% of the variability in contagious yawn response.
Further research investigates potential genetic links
It seems the mystery around contagious yawning remains. But the researchers say because variability in contagious yawning is still unexplained, they are now investigating whether there are genetic influences that affect it.
If so, they believe identifying these influences could help them to better understand schizophrenia and autism, in addition to general human functioning.
"It is possible that if we find a genetic variant that makes people less likely to have contagious yawns, we might see that variant or variants of the same gene also associated with schizophrenia or autism," Cirulli says.
But she adds that if they do not find an association, investigating further can still provide "a better understanding of the biology behind contagious yawning," which can inform them "about the pathways involved in these conditions."