A study of large animals from 2021 revealed something interesting about yawning: Vertebrates with larger brains and more neurons tend to yawn longer.
Researchers collected data on 1,291 different yawns from zoo visits and online videos, including 55 species of mammals and 46 species of birds. They found “strong correlations” between the length of an animal’s yawn and its brain size.
“We went to several zoos with a camera and waited near the enclosure for the animals to yawn,” anthropologist Jorg Massen of the University of Utrecht in the Netherlands said in a statement in 2021. “That was very long.”
The research could fill some gaps in our knowledge about yawning – including why it happens in the first place, and why animals such as mammals don’t need to worry about yawning at all.
“Although the pattern of yawning is stable, its timing evolved with brain growth and neuron numbers,” the researchers wrote in their paper.
Moreover, this function appears to be conserved across animal species, so that it evolved from the common ancestor of birds and mammals and possibly beyond.”
The study was designed to test a hypothesis proposed in 2007 by one of the researchers who conducted the study: that yawning is an important way to cool down the brain. Therefore, it follows that larger brains need to yawn longer to properly cool down.
This would seem 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 short yawn is enough to draw in some cooler air.
Similar results were reached in a 2016 human study, although in this case, only 205 yawns and 24 species were tested. It found that the shortest yawns (0.8 seconds) came from mice, and the longest yawns (6.5 seconds) from humans.
“By inhaling cold air at the same time as stretching the muscles around the oral cavity, yawning increases the flow of cold blood to the brain, and thus has a thermoregulatory function,” said Andrew Gallup of the University of the State of New York ( SUNY).
The researchers do not make any link to intelligence, brain size and the number of neurons it carries; and there is no mention of the repetition of yawning. For example, we humans tend to yawn between 5-10 times a day.
It’s contagious, too, as you’ve noticed. One theory of this is that it serves a social purpose, bringing the group into a similar mindset and perhaps helping to coordinate sleeping patterns. (More research will be needed to figure that one out, though.)
A biologist named Margarita Hartlieb, from the University of Vienna, Austria, said: “Finding videos of many animals yawning requires a lot of patience, and this yawning keeps me from getting sick.”
Although there is a lot of research to test the reasons why we yawn at all, the authors of the study found that “these findings provide additional support for the different predictions that come from the brain freeze theory.”
This study was published in Communications Biology.
A version of this article was originally published in May 2021.