• Researchers conducted a massive study on yawning
  • They found that animals with bigger brains and more neurons yawn longer
  • This supports the belief that yawning is a way to "cool" the brain

Yawning may be an indicator of brain size, a team of researchers said. In their study, published in the journal Communications Biology, they found that longer yawning corresponds to a bigger brain.

People and many animals yawn. Although it is often thought of as a sign of boredom, recent studies have shown that yawning may have evolved as a way to "cool" the brain.

The idea is that by inhaling cool air and stretching the muscles, the flow of cooler blood to the brain increases, study co-author, Andrew Gallup of the State University of New York Polytechnic Institute, explained in the Utrecht University (UU) news release.

Under this idea, it would then follow that creatures with bigger brains would require longer yawns to achieve the cooling effect compared to animals with smaller brains.

"Larger brains have greater thermolytic needs," the researchers wrote.

In previous small studies on mammals, researchers found evidence to support the hypothesis, UU said. In a 2016 study by Gallup and his colleagues, for instance, they found that yawn duration was a predictor of brain size and neuron number in mammals. In that study, the researchers studied 109 individuals from 19 mammal species.

For their new study, the researchers took it a step further and conducted the "largest study on yawning ever conducted." This time, they tested more animals and even added birds. They included mammals such as the chimpanzee, lion and capybara as well as birds such as the snowy owl, common raven and greylag goose.

"In this new study, we wanted to see how universal that theory is, and especially whether it holds true for birds," study co-author, Dr. Jorg Massen of UU, said in the university news release.

As the researchers explained, yawning in birds is still "very much understudied."

For the study, the researchers took videos of animals in zoos, waiting for them to yawn. They also looked at videos of yawning animals online. In total, they looked at 1,291 yawns, 622 of which were of mammals while 669 were of birds.

This comprised of 697 individual animals from 101 species. Among the animals, 55 were mammals while the rest were birds.

Longer yawns equals bigger brains

The researchers found that the duration of the animals' yawns increases along with their brain size and the number of neurons in their brains, UU said. What's more, they also found that mammals tend to yawn longer than birds, possibly because the heat exchange between the blood and the atmosphere is faster in birds.

"(T)hus birds would not be required to yawn as long to achieve the same cooling effect," the researchers wrote.

The researchers' findings suggest that the duration of yawning "co-evolved" with neuron numbers and brain size and may be traced back to mammals and birds' common ancestor. It also supports the hypothesis that yawning is a means of brain cooling.

Brains function well if they are at an "optimal" temperature, UU added, noting that increases in temperature can make us less alert. As Healthline noted, when we yawn, it's likely because that's what the body needs.

"(W)e should maybe stop considering yawning as rude, and instead appreciate that the individual is trying to stay attentive," Massen said, as per the UU news release.