Just like humans, chimpanzees yawn when they're bored or sleepy, and they also yawn contagiously when they see another chimp do it. That discovery could help unlock the secrets of human empathy.
Empathy is one of the more subtle mental processes to understand, because it involves someone perceiving the emotional response of another and then mimicking it. Researchers at Emory University's Yerkes National Primate Research Center have hit upon an ingenious proxy for this complex human interaction in the contagious yawning of chimpanzees, which itself reveals some remarkably nuanced social structures.
For a start, chimpanzees don't just yawn when they see any other chimpanzee yawn. The researchers considered 23 chimps, all of which came from one of two separate groups. The chimps watched short clips of their fellow primates yawning, some of which were chimps from their own group and some of which were from the other. The chimps yawned 50% more often when they watched a member of their own group do it as opposed to a stranger.
Researchers Matthew Campbell and Frans de Waal explain what this means in their paper:
"The idea is that yawns are contagious for the same reason that smiles, frowns and other facial expressions are contagious. Our results support the idea that contagious yawning can be used as a measure of empathy, because the biases we observed were similar to empathy biases previously seen in humans."
One of the best examples of this in humans is our response to the pain of others. We know that different parts of the brain are activated when we ourselves experience pain and when we watch others in pain. Studies have revealed the brain responds far more strongly when the other person in pain is from the same social group, suggesting empathy has a social component.
The question then is whether contagious yawning has similar biases. At least in chimps, this certainly appears to be the case. Of course, chimps enjoy a far more absolute distinction between "we" and "not we" than humans do - whereas chimps can very clearly categorize who is and isn't part of their social group, humans may struggle with the finer distinctions. This likely means that, if human yawning shows similar patterns, they will also be much more subtle than what we've seen in chimps.
Still, the researchers argue that chimp yawning can actually provide a shockingly useful window into the social and emotional connections that humans share, and they're optimistic that further research into the mechanics of chimp empathy - even if it's just yawning - can help clarify some of the finer points of our own interpersonal relationships. Campbell explains:
"Empathy is difficult to measure directly because it is a largely internal response: mimicking the emotional response of another. Contagious yawning allows for a measurement of empathic response that is purely behavioral, and thus can be applied more widely," Campbell writes. "Anyone who wants to increase human empathy towards outsiders should consider that techniques to this effect could be tested out on chimpanzees and other animals."
Via PLoS ONE.