The mouth-agape gesture is so quotidian and universal that it seems like it should already have one of those prosaic sidebars in a high school biology textbook. However, scientists have still not fully cracked the relative mystery behind the yawn (notably, some have argued it's a tool for regulating brain temperature) or figured out why a single occurrence of the phenomenon can ricochet across a crowded room so easily.
"Our results reveal that variables like empathy, tiredness, and Circadian preference have little effect on contagious yawning susceptibility."
Previous research has suggested that contagious yawning is positively correlated with empathy, but a new study from Elizabeth T. Cirulli and Alex J. Bartholomew at Duke's Center for Human Genome Variation that examined multiple variables finds no such connection. In fact, the new analysis, published last Friday in PLOS ONE, concludes that age is the only variable with even modest explanatory power. Younger people are more likely to yawn than older ones, but the amount of variance this statistical relationship explains is decidedly underwhelming.
After completing demographic questionnaires, cognitive tests, and a battery of sleep, empathy, and emotional contagion surveys, 328 subjects all watched a 183-second supercut of people yawning, while self-recording how many times they yawned themselves by "clicking an automated counter button." Nearly 68 percent (or 222) of the subjects experienced at least one contagious yawn during the experiment.
The regressive analyses of all the variables, however, didn't distill much.
Our results reveal that variables like empathy, tiredness, and Circadian preference have little effect on contagious yawning susceptibility...
The results demonstrate that the age of the participant was the only variable with a significant influence on whether or not they yawned. This association was not simply the result of the wide range of ages assessed here; even when restricting to participants aged below 40, age was still the only significant predictor of susceptibility to contagious yawning. Despite this strong association, age was only able to explain 8% of the variation in the yawning response, leaving the majority of variation unexplained by any known factors.
Because such a huge chunk was left unexplained by the variables tested (which also included time of day and intelligence), the authors suggest there's some "underlying genetic influence" causing the difference. Cirulli, the lead author, seemed skeptical of making conclusions about empathy from brain research that has shown that neural activity during contagious yawns occurs in the same areas used for interpreting others' emotion. "I would believe that the same area of the brain could process other people’s emotions and process other people’s yawns," she wrote in an email. "I would guess the same brain area could be involved and still have the two processes be under different genetic control and thus not be well correlated when related phenotypes are measured."
A rigorous genetic analysis of contagious yawners and their non-yawning counterparts is the next step toward understanding the phenomenon.