What we know about yawning, from why we do it to why it's contagious
Yawning is strange.
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.
But what is really strange, almost unique among human behaviours, is that yawning is contagious.
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.
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.
“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.
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.
“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.
Diverse species exhibit contagious yawning, certainly mammals like dogs and cats, but even fish, whose respiratory system shares evolutionary origins with our own.
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.
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.
“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.
There are a few other behaviours like this. Itching and scratching can be contagious, and tickling seems to rely on an empathetic response to the tickler in order to elicit laughter as opposed to mere annoyance.
Joly-Mascheroni has been intrigued by this for years, and investigated it seriously for at least two decades, prompted in the first instance by once realizing he was able to make his dog yawn by yawning himself.
At the time, he was studying developmental disorders such as autism, which is often characterized by an inability to empathize or perceive what others are thinking. He was also interested in social interaction during sensory impairment, prompted by his late father’s worsening blindness.
A key early finding in this research program, of which the new paper is the latest contribution, was that children with autism do not yawn contagiously as much as other children. That seemed to suggest their impaired ability to imagine another person’s thoughts was interfering with the contagious aspect of yawning. Later work complicated this finding, by showing that if autistic children were instructed to keep looking at the yawner’s face, the difference would disappear.
Joly-Mascheroni hypothesized that it was not so much seeing the open mouth that caused the contagion, but rather the eye contact. So he did experiments with eye-tracking technology, but these were inconclusive. People tended to look at the yawning mouth more than the eyes.
The chimpanzees in the latest study with the android were from a rescue facility in Spain, and many had been traumatized in earlier life, used and abused in circuses or in advertising.
Some demonstrated behaviours comparable to human psychopathy or mental distress, such as rocking back and forth, which might also suggest an impaired empathetic reaction to other chimps or people. Human psychopaths, for example, don’t yawn contagiously, and they don’t feel tickling, in both cases Joly-Mascheroni said as a result of insensitivity to other people’s emotions, good or bad.
But the rescued chimps plainly love their current handlers, and Joly-Mascheroni said you would expect they would therefore be more susceptible to the effect of socially contagious yawning from these handlers.
But the opposite was true. The chimps would yawn contagiously with strangers more than with their familiar handlers. This is how he got thinking about androids, the ultimate strangers.
So while yawning remains mysterious, Joly-Mascheroni thinks he has a grasp on the basics. Yawning happens at the interface of rest and arousal, he said. It might signal to a group that it is time to sleep, or that some members are about to sleep so others should be awake. That is a plausible evolutionary origin with good explanatory power for the contagion. Yawning may have emerged as what the paper describes as “a pre-language form of communication.”
That may be why athletes often yawn before their events ( U.S. speed skater Apolo Ohno was famous for it ), and parachutists before their jumps. That may be why regular people often yawn as they are waking up. It’s not so much lingering tiredness as it is anticipating the looming arousal of the day.
“Yawning, despite its elusive primary functions, may still have an evolutionarily old, non-verbal communicative role, and its contagious aspect may help us find out more about how humans and animals developed adaptive functions, ways of communication, synchronisation and social interaction,” the paper says.