Yawning doesn’t need be a sign of boredom. Rather, it appears to be a measure of brain size. Vertebrates with larger brains yawn longer, according to a study of more than one hundred species of mammals and birds. The findings of the study, which was conducted by an international team of scientists centered around biologist Jorg Massen of Utrecht University and Andrew Gallup of the State University of New York Polytechnic Institute, have been published on 6 May 2021 in the scientific journal Communications Biology.
We yawn about 5 to 10 times per day. But not only humans exhibit this peculiar behaviour. Yawning has been reported across vertebrates, and biologists are wondering why this behavior has evolved. Research by behavioral biologists Jorg Massen, Andrew Gallup, and colleagues now provides a strong indication that the duration of yawning is linked to brain size and the number of neurons in the brain.
Yawning cools the brain
Despite popular belief, yawning does not function to oxygenate our blood. Instead, recent discoveries by the lab of Gallup show that yawning cools the brain. “Through the simultaneous inhalation of cool air and the stretching of the muscles surrounding the oral cavities, yawning increases the flow of cooler blood to the brain, and thus has a thermoregulatory function,” according to Gallup.
Several studies have supported that idea. For example, they showed that the temperature of the brain drops rapidly after yawning, and that the ambient temperature determines how often yawning occurs. In addition, they found that people rarely yawn when they hold a cool pack to their head or neck, or do other things that cool the brain.