Chimpanzees are more likely to "catch" a yawn from a human if they are better-able to empathize with them.
The finding could mean the chimps develop more empathy for humans as they develop more empathy for them, a Public Library of Science news release reported.
Researchers looked at how two factors affected the monkey's susceptibility to catching human yawns: how old they were and their relationship to the yawner.
The scientists analyzed 33 orphaned chimpanzees, 12 were between the ages of two and four and 21 were between five and eight. The monkeys went through seven five-minute sessions.
"[They consisted of] a baseline session, followed by three experimental sessions, where the human repeatedly either yawned, gaped or nose-wiped, and three post-experimental sessions, where social interactions continued without the inclusion of the key behaviors. Each chimpanzee separately observed an unfamiliar human and a familiar human preforming the sequence," the news release reported.
The team found that yawning was contagious for the juveniles, but not other actions such as nose wiping. The human yawning session elicited a grand total of 24 yawns from the older group of monkeys, but zero from the infant group.
The team suggested the chimps could also be developing empathy for humans as they grew up. "Emotional closeness" was not found to have an effect on the chimpanzee's chance of yawning in the study.
"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," Elainie Madsen, a researcher from Lund University, said in the statement.
The only other animals that have been clinically shown to "catch" yawns from humans are dogs.
The study was published in the journal PLOS ONE.
