When someone yawns near us, we naturally feel an irresistible urge to yawn in response. Even dogs seem to yawn when humans do it. This contagious behavior has fascinated psychologists and behaviorists for many years, and while there are many reasons scientists have proposed for why people yawn (it’s a bit complicated, what we know for sure is that’s important and actually has a purpose), social cohesion might play an important role. The more emphatic you are, the likelier it is you’ll yawn in response. On the contrary, psychopaths barely register yawns and seem impenetrable.

Psycopaths aren’t impressed by yawning. Image: Dexter

Previously, scientists found a link between empathy and yawning. This got researchers at  Baylor University thinking: “does this mean that psychopaths, who inherently show low empathy, yawn less frequently?” To answer this question, the team of psychologists asked 135 participants to take the  Psychopathic Personality Inventory-Revised (PPI-R) test. Those who ranked high on the coldheartedness scale were less likely to yawn when another person did so.

Another characteristic owing to psychopaths is fearlessness. Again, the researchers tested their participants by seeing how easily they got startled. Those persons who ranked high on the PPI-R test – which, in their defense, doesn’t necessarily make them psychopathic – were less likely to become startled, as reported in the journal Personality and Individual Differences. The same people also yawn less frequently. Previously, another study found autistic children also yawn very rarely in a social setting.

Though debatable, the main purpose of yawning seems to be cooling the brain. The researchers’ hypothesis is as follows: when you start to yawn, powerful stretching of the jaw increases blood flow in the neck, face, and head. The deep intake of breath during a yawn forces downward flow of spinal fluid and blood from the brain. In the last phase, the cool air breathed into the mouth cools these fluids. The fact that animals, including humans, contagiously yawn may be attributed as an evolutionary adaptation to keep a group vigilant.

“What this tells us is it’s a very complicated system, and there are probably many different roles for yawning,” says Gregory Collins, a researcher at the University of Texas Health Science Center in San Antonio who has identified some of the chemical processes at work in the brain.

In any event, evidence points to the fact that yawning is both triggered socially and elicits social response at the same time. Don’t get too worried yet, though. Chronically yawning around your friends to spot the psycho might not work well for you.

“The take-home lesson is not that if you yawn and someone else doesn’t, the other person is a psychopath,” Rundle cautions. “A lot of people didn’t yawn, and we know that we’re not very likely to yawn in response to a stranger we don’t have empathetic connections with.

“But what we found tells us there is a neurological connection — some overlap — between psychopathy and contagious yawning. This is a good starting point to ask more questions.”