Credit: Flickr user theogeo
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.
Gallup’s work is disputed; even the commenters on Grrlscientist’s post point out that there are other, simpler explanations for the trends shown in the research. For example, budgerigars may be “yawning” to cool their whole bodies, not their brains. Humans have sweat glands for this purpose, while birds do not, so this research wouldn’t explain human yawning. In addition, Gallup’s research doesn’t explain why yawning seems to be contagious. If the function of yawning is to cool my brain, why do I do it more often when I see others yawning?
Spanish-language blogger Anibal Monasterio Astobiza points to an article by Jennifer Yoon and Claudio Tennie speculating on the possible causes of contagious yawning. Yoon and Tennie say yawning could be an expression of empathy, simple mimicry, or a learned behavior that is reinforced (i.e., dogs that imitate humans tend to be treated better than dogs that don’t imitate humans). Humans who are likely to be more empathetic also exhibit more contagious yawning, so maybe yawning is contagious between humans and dogs for similar reasons. Yoon and Tennie say more research is needed to know for sure.
Jason Goldman agrees, and suggests several possible new experiments. Researchers could see whether yawning was contagious between adult dogs and puppies. If puppies don’t copy yawns the way human babies do, it suggests that dogs learn to mimic human yawns later in life. They could also compare dog-dog contagion to dog-human contagion. Maybe dogs actually copy humans yawning more often as a result of domestication.
So why don’t we know more about yawning? Why aren’t these additional studies being done? I suspect it’s because yawning generally isn’t a very big problem. While excessive yawning can be problematic, normal, day-to-day yawning doesn’t generally bother anyone other than those of us who wonder why we do it so frequently.
Dave Munger is editor of ResearchBlogging.org, where you can find thousands of blog posts on this and myriad other topics. Each week, he writes about recent posts on peer-reviewed research from across the blogosphere. See previous Research Blogging columns »
Originally published July 28, 2010