Try to get through this post without yawning! Researchers comparing the “yawn contagion” effect between humans and our closest evolutionary cousins found that both species are just as quick to catch a yawn from strangers or mere acquaintances. A chummy relationship between individuals, on the other hand, is more important to feeling empathy than the fact that the individuals might be from the same species. 

The ability to experience someone else’s emotions is hard to quantify. To measure the most basic form of empathy -- called emotional contagion -- scientists look for the transmission of a feeling from one individual to another. You can see that in the mirroring of facial expressions between an “emitting face” and a “receiving face.” Previous studies have shown that in humans and bonobos, yawn contagion follows an emphatic trend -- occurring more frequently between relatives, mates, and friends. 

To directly compare the empathic abilities of ourselves with bonobos (Pan paniscus), a team led by Elisabetta Palagi from the University of Pisa observed the two species during everyday activities over the course of five years. They gathered data from 33 adult humans (1,375 total yawn events) in social situations at work and during meals, for example, and 16 adult bonobos (2,123 total yawn events) in zoos in the Netherlands and Germany. The team compared two features of the yawn contagion in particular: how many times the individuals responded to someone else’s yawns, and how quickly. 

When the yawner and the responder weren’t friends or kin, bonobos responded just as frequently and promptly as humans did. However, humans responded more frequently and more promptly than bonobos when it was a buddy or a relative doing the yawning. 

“It seems that the basal level of empathetic capacity is the same in the two species,” Palagi tells the Scientist. “But when an emotional bonding comes into play, people overcome bonobos.” 

In a press release, the researchers say the positive feedback linking emotional affinity and the mirroring process seems to spin faster in humans than in bonobos. In humans, such over-activation may explain various other kinds of unconscious, imitative responses, like happy, pained, and angry facial expressions.

The work was published in PeerJ this week.