Yawns are a loaded bodily function. Too many and you’re rude, not enough and you have the empathy of a psychopath.
But a new study has made an interesting discovery: the length of your yawn correlates to how heavy your brain is, and how many neurons it has.
The longer the yawn, the bigger the brain, according to the study, published in the journal Biology Letters.
Research found that the length of a yawn accurately predict the size of an animal’s brain, and their findings can be applied to people, too.
The researchers watched YouTube videos of cats, dogs, gorillas, foxes, camels, hedgehog, horses, rats, chimpanzees and more, and measured their yawns.
They found that the longest yawners were humans, whose brains weigh an average of three pounds.
Among the runners-up were chimpanzees, horses and camels. And the shorter yawners were mice, rabbits and rats.
Andrew Gallup, evolutionary psychologist and one of the study’s researchers, says that we yawn to cool our brains. He writes for Academic Minute:
When you yawn, your gaping jaw increases circulation to your skull, pumping warm blood out of your brain.
At the same time, inhaling deeply brings a wave of air into your nasal and oral cavities, cooling cranial arteries through convection.
These two processes dissipate heat in much the same way that a radiator cools a car engine.