This is Scientific American — 60-Second Science. I'm Christopher Intagliata.
Not many scientific studies begin like this: "Many hours of watching YouTube clips. Trying to find as many yawns as possible." But for Andrew Gallup, an evolutionary psychologist who studies yawning at the State University of New York, it was all in a day's work.
Gallup says yawns have traditionally been known as a sign of sleepiness, or boredom. "But recent evidence suggests that yawning may function to promote brain cooling." The idea being, when you breathe in deeply, the incoming air slightly cools the brain. And stretching the jaw increases blood flow to the brain too — another cooling factor. Reason we do it at night? "At night time when we're about to go to sleep our brain and body temperatures are at their highest point throughout the day, and that's when we see the highest frequency of yawning."
And so Gallup and his colleagues found themselves hunting for cat videos on the internet (cat yawning sound) — along with clips of dogs, foxes, elephants, gorillas, hedgehogs, squirrels, rats, and walruses yawning. They timed all those yawns — and then compared them to each species' average brain weight, and the number of neurons in the cerebral cortex.
Their conclusion, published in Biology Letters, was that the length of a yawn was a remarkably good predictor of an animal's brain weight, and cortical neuron number — regardless of the size of its skull, or jawbone. "What that really represents is that yawning likely serves this very basic, and fundamental neurophysiological function." In other words — it helps the brain keep its cool.
Thanks for listening for Scientific American — 60-Second Science Science. I'm Christopher Intagliata.