A large study has shown that vertebrates with larger brains and more neurons yawn longer. According to the theory, this is because yawning cools the brain. The bigger the brain, the longer the yawn should last.
Researchers collected 1,291 different yawns on trips to the zoo or through online videos. The yawns were from 101 different animal species: 55 mammals and 46 birds. They discovered the link between the length of the yawn and the size of the brain.
“We went to various zoos with a camera and waited at the animal enclosures for the animals to yawn,” says behavioral biologist Jorg Massen of Utrecht University.
Mammals vs. birds
Scientists have also found that mammals yawn longer than birds. This supports the theory about cooling the brain. Birds have a higher body temperature. Because there is a greater temperature difference with the air outside, they don’t have to yawn as long.
“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,” explains behavioral biologist Andrew Gallup of New York State University.
However, no link is made with intelligence in the research, only with the size of the brain and the number of neurons present.