Scientists find strange connection between brain size and yawning

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(ORDO NEWS) — A large-scale animal study in 2021 revealed something interesting about yawning: Vertebrates with larger brains and more neurons tend to yawn longer.

The researchers collected data on 1,291 individual yawns during trips to the zoo and online videos covering a total of 55 mammal and 46 bird species.

They found “robust positive correlations” between how long an animal yawns and its brain size.

“We went to several zoos with a camera and waited outside the enclosures for the animals to yawn,” said ethologist Jörg Massen from the University of Utrecht in the Netherlands. “It’s been quite a long journey.”

The study could fill in some of the gaps in our knowledge about yawning, including why it happens in the first place and why animals like giraffes don’t need to worry about it at all.

“While the pattern of yawning is fixed, its duration depends on brain size and the number of neurons,” the researchers write.

“Moreover, this function appears to be conserved across a wide variety of animals, such that its evolutionary origin can be traced back at least to a common ancestor of birds and mammals, and perhaps even further.”

The study was carried out to test a hypothesis put forward in 2007 by one of the scientists studying how yawning helps to cool the brain. It turned out that big brains need longer yawns to properly cool them down.

This seems to be supported by these data, which also show that mammals yawn longer than birds.

Birds have a higher body temperature than mammals, which means a larger temperature difference with the surrounding air, meaning that a shorter yawn is enough to draw in slightly cooler air.

Similar conclusions were reached in a 2016 human study, although only 205 yawns and 24 species were measured in this case.

It was found that the shortest yawns (0.8 seconds) were in mice and the longest yawns (6.5 seconds) were in humans.

“By simultaneously inhaling cool air and stretching the muscles surrounding the mouth, yawning increases cool blood flow to the brain and thus has a thermoregulatory function,” explained ethologist Andrew Gallup of the State University of New York.

The researchers make no reference to intelligence, only to the size of the brain and the number of neurons it resides in. Nor is there any reference to frequency of yawning. For example, people tend to yawn 5-10 times a day.


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