October 17, 2013
Human Yawns Are Contagious To Chimps, But Only Older Ones
[ Watch The Video: Is A Human Yawn Contagious To Chimpanzees? ]
Brett Smith for redOrbit.com - Your Universe OnlineAs fellow primates separated by only a few branches on the evolutionary tree, humans share many behaviors with chimpanzees. Now, research has shown that the older a chimp is, the more likely it is to respond to a familiar face yawning with a yawn of its own, according to a new study in the journal PLOS ONE.
Referred to as 'contagious yawning,' humans – as well as dogs and other primates – are more likely to yawn after watching someone else yawn.
In the study, researchers at a primate rehabilitation facility in Sierra Leone tried to spread contagious actions to chimpanzees by yawing, gaping open their mouths and wiping their nose in front of 33 orphaned chimpanzees, including twelve infants 1 to 4 years old, and 21 juveniles 5 to 8 years old. A trial sequence included a baseline social session, three experimental sessions with the contagious behaviors, and three post-experimental sessions where social interactions continued without the behaviors. Each primate separately saw an unfamiliar human and a familiar human performing the entire sequence.
The team watched as the very young chimps failed to respond to their gestures. However, older juvenile chimps "caught" the contagion and yawned in response.
Study author Elainie Alenkaer Madsen, an evolutionary psychologist at Sweden's Lund University, said the primate's behavior isn’t caused by the same cognitive empathy exhibited by humans, who can place themselves in someone else's state of mind.
“I think we’re talking more about affective empathy,” Madsen explained to the Los Angeles Times. “It’s the kind of empathy where, instead of thinking your way into how someone else might be experiencing the world or feeling, you just feel it. Like when someone cuts their finger you feel sick in your stomach.”
Previous research has shown that cognitive empathy doesn’t appear in humans until about 4 years of age. Prior to the study, scientists had yet to show that other primates can develop this type of empathy.
The latest findings build on a 2011 study that found that adult chimpanzees are more likely to yawn in reaction to members of their own social circle.
“We’re more likely to empathize with those we’re familiar with, so we really expected the adoptive mother of the chimps would be able to provoke more contagious yawning, with the younger chimps in particular,” Madsen said. “But there was no such thing, which is puzzling. Maybe chimps just respond differently to humans than they would to other chimps," she suggested.
A study published in PLOS ONE in August showed that dogs also yawn contagiously – particularly if the initial yawn comes from its owner.
The study, which included 25 volunteers and their dogs, found that the pets were not only more responsive to their owners’ yawns – many of them could tell the difference between a fake and actual yawn. The study authors also noted that dogs do not contagiously yawn across the various breeds. They said that the breeding of dogs over the years has specifically attuned the animals’ attention to taking cues from humans.
“During domestication, dogs have become selected to maintain attention towards humans, which seems to be critical for dog-human communication and social learning,” the study authors wrote. “Thus, it is possible that dogs are predisposed to respond more intensively, or only, to human social cues rather than (cues from other breeds).”