What we know about yawning, from why we do it to why it's contagious
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It's not obviously just mechanical, like a burp to release gas pressure, or just psychological, like a yelp to express fear or excitement. A yawn is more like a sneeze or a hiccup, an involuntary breath event that is sometimes more or less resistible.
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But what is really strange, almost unique among human behaviours, is that yawning is contagious.
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New research on chimpanzees by a British team of cognitive scientists shows contagious yawning is not only common in other species, and can happen between species, but that it can also be induced in chimps by an obviously artificial humanoid robot, an android 'agent' that is just a creepy looking disembodied head and shoulders, and which doesn't even breathe, but which can still give a believable facsimile of a yawn.
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The paper, published this month in Nature Scientific Reports, details an experiment in which the chimps were shown three behaviours by the android: a full wide-mouth yawn, a more moderate gaping mouth, and a closed mouth.
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'The results showed that adult chimpanzees exhibited across-agent yawn contagion, with a graded response: the highest contagion occurred when the android displayed a fully wide-open mouth (Yawn condition), a reduced response when the mouth was partially opened (Gape condition), and no contagion when the android's mouth was closed,' the paper says.
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And the chimps did not only yawn in response to the yawning robot. They also 'engaged in behaviours associated with drowsiness,' basically by preparing a comfortable place to lie down.
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'This suggests that yawning by an unfamiliar model may act as a contextual cue for rest, rather than merely triggering a motor resonance response,' the paper says.
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Diverse species exhibit contagious yawning, certainly mammals like dogs and cats, but even fish, whose respiratory system shares evolutionary origins with our own.
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Most vertebrates yawn, but those that are known to yawn contagiously are usually pack animals, somehow social. This suggests the evolutionary purpose of the yawn is at least partly at the level of the group, not just the individual. A sneeze just tries to blast stuff out of your nose, a burp just lets gas out of your belly, but a yawn means something to other people.
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Not always, of course, Yawning might, for example, help cool the brain for optimal performance, as one theory holds. But yawning also involves empathy, as its contagious aspect shows. It is a social phenomenon, and catching, like laughter.
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'What I find strange is that if we see someone walking, we don't an feel urge to walk. But with yawning, we do,' said Ramiro Joly-Mascheroni, a research fellow in social and cognitive neuroscience at City St. George's University of London in the U.K., in an interview.
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