Older Chimps Yawn in Response to Humans

As chimpanzees age, they become more susceptible to catching yawns from humans, a new study shows. The researchers, from Lund University, argue in the open-access journal PLOS One that a possible reason for this phenomenon could be attributed to an increasing ability to empathize as they grow.

The scientists examined 33 orphaned chimpanzees -- 12 between 1-4 years old and 21 between 5-8 years old -- through a trial sequence of seven sessions five minutes in length. These consisted of a baseline session, three experimental sessions in which the human yawned, gaped or wiped his or her nose, and three post-experimental sessions characterized by social interactions absent of the key behaviors.

This sequence was carried out twice: once in which the chimpanzee was familiar with the human and another in which it was not.

Yawning, but not nose wiping, was contagious for the 5-8 year-old chimpanzees, the researchers observed. Meanwhile, the younger group showed no susceptibility to either.

Based on this, the scientists surmised that yawning is contagious for chimpanzees only as they grow, possibly due to an increased ability to empathize. However, there was no difference observed when the sequence was carried out with familiar versus unfamiliar humans.

"The results of the study reflect a general developmental pattern, shared by humans and other animals," researcher Elainie Madsen said in a statement. "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."

A study published earlier this year found that dogs yawn in response to their owners, though the Japanese researchers said it was not clear whether this was to reduce stress or the result of a sense of empathy between the dog and the human.