A young chimpanzee will yawn when a human does, regardless of whether the face is familiar, according to a study that suggests contagious yawning grows stronger in our primate cousins as they grow up.
Researchers yawned, gaped or wiped their nose in front of 33 chimpanzees orphaned by Central Africa’s illegal bush meat trade and housed at a Sierra Leone primate rehabilitation center. They expected the chimps would more readily copy their “mother,” a villager who feeds, cuddles and grooms the captive chimps, some of which arrived when they were a few months old.
Instead, infant chimps didn’t respond to the human gestures. The older juveniles, however, “caught” the contagion, yawning readily at their adoptive mother and researchers alike, according to a study published online this week in the journal PLOS One.
The study, published Wednesday, was the first to demonstrate the contagion across primate species, according to its lead investigator and face-maker, Elainie Alenkaer Madsen, an evolutionary psychologist at Sweden’s Lund University.
While you’re stifling that contagious yawn, stifle your instinct to assume the chimps are just like us. Madsen, who also has made faces at puppies, says the primates aren’t showing the cognitive empathy exhibited by humans, who can readily put themselves in someone else’s shoes.
“I think we’re talking more about affective empathy,” Madsen said. “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.”
Even among humans, the theory of mind required to infer someone else’s mental state doesn’t appear until about 4 years of age. And research has yet to demonstrate that other primates ever develop a theory of mind.