Fact or Fiction: We only yawn when we’re tired?

By Casey Frye, CCNN Writer

yawning lady
Boy, all these coats have my body heating up! Time to… yawn? Yep! Apparently, our brains use yawns to cool down.

Have you ever sat down in a classroom and – no matter how hard you tried to resist – given in to a series of deep yawns? The air-gulping attack always seems to creep up during the warmest parts of the day, especially when people around you are yawning too. Common logic would say we’re just doing it because we feel sleepy, but according to recent research, it may be the behavioral response to an overheated brain!

One thing to note about yawns is that they are definitely not unique to humans. Cats, dogs, bears, lions, and a wide range of other critters in the animal kingdom love to rest on their haunches and treat themselves to a deep, satisfying yawn; as long as the creature has a brain and a backbone, you can practically guarantee they will yawn at some point. What’s strange, though, is that regardless of the creature in question, yawning always seems to come right after or immediately before a much needed period of sleep. How sure are researchers that the behavior is due to an overheated brain?

Over the past few years, there has been an overwhelming amount of evidence that supports this line of logic. One study implanted probes into rat brains and found that the rodents’ yawning response could predictably be triggered after increasing heat by less than 1 degree Fahrenheit. After the yawn, their brains cooled down significantly. A separate study found that participants were far more likely to yawn during the hot summer months compared to the frosty winter season. There is also reason to support the idea that stress – which is related to increasing body temperature – leads to more yawning!

Okay, okay, I get it; yawning cools down the brain. If that’s the case, why are they so darn contagious, and why do they happen to occur more when we’re exhausted? Well, researchers still need to conduct more experiments before they can provide a definite answer to both questions. One of the leading theories for why yawning is contagious is that it promotes a group to stay vigilant and alert for predators. This response isn’t as useful for humans who live in a civilized world, but in the dog-eat-dog world of the wild, it could be an invaluable group behavior. Basically, one member of the group yawns to cool down and refresh their brains, and the others can’t help but follow suit. As for why we tend to yawn when we are tired, the best answer is that our brains are more likely to be overheated after a long day’s work; who wouldn’t want a few seconds to cool down?

Featured image courtesy of Magnus Manske on Wikimedia. Image of frost-bitten yawner courtesy of Kevin Jaako on Flickr.