Your Yawn Reveals the Size of Your Brain

The length of your yawn offers a clue to the weight of your brain and the number of neurons inside.

The duration of your yawns can reveal your brain's weight and how many neurons you have in the outer layer of that all-essential organ, a new study reports.

The findings, reported in the journal Biology Letters, suggest scientists could estimate the brain weight of any animal just by timing their yawns. The findings apply to people, too.

"The human brain weighs between 1,250–1,450 grams, or roughly 3 pounds," said Andrew Gallup, a Princeton University researcher and one of the world's leading experts on yawning. He co-authored the new paper with Omar Eldakar of the University of Arizona.

"Importantly, neither the size of the body nor the anatomical structures specific to yawning (cranium and mandible) are driving these effects, because gorillas, camels, horses, lions, walruses and African elephants all have shorter average yawns than humans," the authors wrote.

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Here are some of the top yawners identified in the study, listed by average duration: mouse, rat, possum, cat, dog, hedgehog, white-faced capuchin, horse, gorilla, chimpanzee, African elephant -- and human.

The scientists also found that primates tend to have longer and more varied yawn lengths compared with other mammals, likely because they have more varied behaviors and more complex brain structures.

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Gallup said yawning helps circulation in the brain and cools it down, boosting mental processing.

Yawns can also be contagious, which may "promote the collective attention and group vigilance, and may help coordinate behavior," Gallup said. The latest findings, he said, could also "improve our understanding of the relationship between yawning and various neurological diseases and medical conditions."

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