Everyone knows yawning is contagious. If you yawn, someone else will probably yawn shortly thereafter. As I did the research for this column, I noticed that nearly every article about yawning pointed out that just reading the article itself could make you yawn. Even your dog will yawn if it sees you yawning. That last observation has been confirmed scientifically, in an elegant experiment discussed last week by psychology graduate student Jason Goldman. Ramiro Joly-Mascheroni, Atsushi Senju, and Alex Shepherd had an experimenter visit dogs in their homes and yawn as the dogs looked on. In 21 of the 29 dogs tested, the dog yawned after seeing the human yawn. In a control condition, the experimenter made a yawning motion with his mouth but didn’t make other yawning gestures and sounds. Under these circumstances none of the dogs yawned. The research was published in Biology Letters. Goldman points out that yawning has been observed in many species of vertebrates, including dogs, cats, chimpanzees, and birds. But why do we yawn? Does it serve any real purpose (besides, perhaps, subtly hinting to a conference presenter that his or her allotted speaking time has elapsed)?
The biologist who blogs as “Grrlscientist” points to a pair of studies that seem to support one explanation: Yawns help cool the brain. Andrew Gallup, who led both studies, says the brain is more efficient when cooler, so if yawns allow us to cool our brains, then they may allow us to think more clearly. In one study, researchers had humans hold either cold towels or warm towels to their foreheads: people yawned more frequently when exposed to the warm towels. In the second study, budgerigars (parakeets) were observed in environments of varying temperatures. When the temperature was warmer, the budgerigars yawned more frequently, suggesting they might be using yawns to cool off. At extremely high temperatures, yawning again decreased, perhaps because yawns don’t help when the temperature is too warm.