Yawn Contagion Grows as Chimps Age: It's Not Just Humans

Do you feel like yawning? When someone else yawns nearby, you may feel like yawning yourself. This particular phenomenon is known as yawn contagion and is widely seen in humans. Yet we're not the only ones that have "contagious" yawns. It turns out that chimps also suffer from yawn contagion and that their susceptibility to it only increases as they grow older.

In order to examine yawn contagion, the scientists looked at two factors in chimps: their age and their emotional closeness to the person yawning. In all, they examined 33 orphaned chimpanzees, including 12 infants that were between one and four years and 21 juveniles that were between 5 and 8 years. During trials, a human repeatedly either yawned, gaped or nose-wiped during one session and then followed it by three sessions where these key behaviors weren't used.  Each set of trials was performed by an unfamiliar human and a familiar human.

So what were the results? It turns out that yawning, but not nose-wiping was contagious. More interestingly, though, was the fact that it was contagious for juvenile chimpanzees but not infant chimpanzees. The researchers managed to elicit 24 yawns from the juvenile chimps and absolutely none from the infants.

"The results of the study reflect a general developmental pattern, shared by humans and other animals," said Elainie Madsen, one of the researchers, in a news release. "Given that contagious yawning may be an empathetic response, the results can also be taken to mean that empathy develops slowly over the first years of a chimpanzee's life."

In fact, it's likely that chimps become increasingly susceptible to yawn contagion as they age because they develop an increased capacity to empathize. Emotional closeness to the person yawning did not affect contagion, which points to the fact that it's more about a general developmental pattern. In addition, the study reveals that cross-species yawn contagion is possible in chimps, which had previously only been demonstrated in dogs.

The findings are published in the journal PLOS One.