We all know that we yawn when we feel “tired” and it is said that yawning is contagious. But why do we yawn at all? This was a question that imperiled Andrew Gallup and colleagues who studied 109 creatures across 19 species and concluded that the bigger the brain, the bigger your yawn. Yawn duration is related to both brain size and the number of cortical neurons. In my book, The Genetics of Health, I wrote about the inverse relationship between brain size and gut size i.e. the more visceral abdominal fat we have, the smaller our brains become. My book was about genes and wellness and noted how dancing the tango reduced Parkinson’s disease symptoms. Others have noted from gene studies that conditions like Parkinson’s disease also reduce yawning suggesting that dopamine-producing neurons of the brain’s hypothalamus are necessary for yawning.
What happens when we yawn? We suck in air and stretch our jaws – this compresses the veins in our cheeks and brings cooler blood to our brains (by increasing heart rate) thereby cooling the brain. It has now been confirmed by several researchers that yawning is a cooling mechanism for the brain that tends to re-boot the brain when our body’s computer appears to be over-heating.
Here are some yawn durations – naturally we humans are on top as we are the brainiest of creatures with an average yawn-time of 6.5 seconds. Guess who came in second? Rather unexpectedly camels are brainier than we expect. Here is a list of yawn-times:
Humans 6.5 seconds
Camels 4.8 seconds
Dogs 2.4 seconds
Cats 1.97 seconds
Mice 0.8 seconds
As a dog-lover I’m pleased dogs scored higher than cats, although I am not casting any aspersions on cats (and don’t want to upset cat-people). Some scientists have said that while yawning may cool the brain, it does not do so to a great extent. Gallup was quoted in this article from Scientific American as saying, “Whether yawning functions specifically to cool the brain can still be debated, but there is no debate on whether yawning has thermoregulatory consequences.”
More recently people decided to test this heat-control theory by using simple logic. If yawning is meant to cool the brain, then shouldn’t we yawn more in summer rather than winter? A recent study by Massen found that as predicted, the proportion of pedestrians reporting yawning was significantly lower during winter than in summer (18.3% vs. 41.7%), with temperature being the only significant predictor of these differences across seasons. We do yawn more in summer! And if we cool our foreheads using a cold towel, it cools our brains and can prevent too much yawning.
But what’s yawning got to do with love? In a news report based on a 2011 study, Italian researchers observed more than 100 men and women of different backgrounds from as they went about their daily lives – eating, walking, waiting etc. They noted if others nearby picked up their yawns i.e. how contagious their yawns were. Men and women did not yawn differently; nor did different ethnic groups. Here was the clincher: A reciprocal yawn was most likely among family members, then friends, then acquaintances – in other words, the closer you are to someone the more they pick up your yawns. Yawning together can therefore indicate how close a couple’s relationship is.
I thought I’d test this theory on my dog Zack. His yawn-duration was
way above-average for a dog (says this biased “dad”) and he confirms that a contagious yawn is indeed an expression of love.