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By Jami Smith


Just hearing (or reading) the word can spur an involuntary response in human beings: big intake of breath, mouth opens, maybe some stretching, and then an exhale. Ahhhh.

This involuntary response is called the yawn contagion: dogs and chimps do it, humans tend to do it more around their friends, and it seems to be linked to our ability to empathize. Humans don’t develop the yawn contagion until about four years old, and autistic kids are less likely to be affected by a nearby yawn than other people. Now, a new study of chimpanzees demonstrates that the yawn contagion may be something that grows as we grow and unlike humans, chimpanzees don’t do it more around their friends.

Elainie Madsen and colleagues from Lund University studied sanctuary-kept chimpanzees. The team found that as the chimps grow from infants to juveniles, they develop increased susceptibility to the human yawn contagion.

The scientists examined the extent to which two factors affected chimpanzees’ susceptibility to yawn contagion: their age and their emotional closeness to the person yawning. The trial included orphaned chimpanzees—both infants and juveniles. A trial sequence consisted of seven five-minute sessions: a baseline session, followed by three experimental sessions in which the human repeatedly yawned, gaped, or nose-wiped, and three post-experimental sessions in which social interactions continued without the inclusion of the key behaviors. Each chimpanzee separately observed an unfamiliar human and a familiar human performing the sequence.

Researchers found that yawning, but not nose-wiping, was contagious for juvenile chimpanzees, while infants found neither yawning nor nose-wiping contagious. Chimpanzees appear to develop susceptibility to interspecies contagious yawning as they grow from infants to juveniles, possibly due to their developing ability to empathize with the person yawning. Emotional closeness with the yawning human did not affect contagion.

Yawning when others yawn, the study suggests, is a sign of empathy and a form of social bonding. Madsen expands, “The results of the study reflect a general developmental pattern, shared by humans and other animals. 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.”

The results are published this week in the open-access journal PLoS ONE.

Jami Smith is a science geek-wannabe and volunteers for Science Today.

Image: Bobjgalindo/Wikipedia

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