There’s a Strange Correlation Between Brain Size and Yawning, Study Reveals: ScienceAlert

A large-scale animal study from 2021 revealed something interesting about yawning: Vertebrates with larger brains and more neurons tend to have longer yawns.

Researchers collected data on 1,291 separate yawns from zoo tours and online videos, covering a total of 55 mammal species and 46 bird species. They found “robust positive correlations” between how long an animal yawns and the size of its brain.

“We went to several zoos with a camera and waited at the animals’ enclosures for the animals to yawn,” ethologist Jorg Massen of Utrecht University in the Netherlands said in a 2021 statement. “It was quite a long haul.”

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 bother yawning at all.

“Although the pattern of yawning is fixed, its duration has co-evolved with brain size and neuron number,” the researchers wrote in their paper.

“Furthermore, this feature appears to be conserved across a wide range of animals, so its evolutionary origins can be traced back to at least the common ancestor of birds and mammals and potentially even further.”

The analysis was set up to test a hypothesis put forward in 2007 by one of the researchers who worked on this study: that yawning is an important way to cool down the brain. It therefore follows that larger brains need longer yaws to properly cool them.

That seems to be supported by this data, which also shows that mammals yawn longer than birds. Birds have a higher core temperature than mammals, which means a greater temperature difference with the surrounding air, which means that a shorter gape is enough to draw in somewhat cooler air.

Similar conclusions were reached in a 2016 study involving humans, although in that case only 205 yawns and 24 species were measured. It found that the shortest yawns (0.8 seconds) came from mice, while the longest yawns (6.5 seconds) came from humans.

“Through the simultaneous inhalation of cool air and the stretching of the muscles around the oral cavities, yawning increases the flow of cooler blood to the brain and thus has a thermoregulatory function,” explained ethologist Andrew Gallup of the State University of New York. SUNY).

The researchers make no connection to intelligence, only the size of the brain and the number of neurons it packs; nor is there any reference to the frequency of the yawn. For example, we humans tend to yawn between 5-10 times a day.

It is also contagious as you may have noticed. One hypothesis for this is that it serves a social function, getting a group in the same frame of mind and perhaps helping to synchronize sleep patterns. (However, more research will be needed to find out.)

“Getting video footage of so many animals yawning requires a lot of patience, and the subsequent coding of all those yawns has made me immune to the contagiousness of yawning,” noted biologist Margarita Hartlieb of the University of Vienna, Austria.

While more research needs to be done to tease out the reasons why we yawn at all, the study’s authors conclude that “these findings provide further support for distinct predictions derived from the brain cooling hypothesis.”

The research was published in Communication biology.

A version of this article was first published in May 2021.

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