For a long time it was thought that the primary purpose of yawning was to increase oxygen to the circulatory system and the brain in order to improve alertness. In primitive times, the yawn might have silently signaled to others the need to be more alert as one of the group was tired and not quite ready for action. In modern times, people tend to feel offended in the presence of a yawner, thinking it a highly rude and irresponsible act of boredom that should be stifled in polite company.
Recent studies indicate, however, that, more important than supplying oxygen, yawning is a physical reaction to cool an “overheated” brain. A Princeton University/Arizona University study was the first to show that the frequency of yawning varies with the season and that people are less likely to yawn when the heat outdoors exceeds body temperature. Researchers, monitoring 160 people during winter and summer in Tucson, Arizona, discovered that subjects yawned twice as much in wintertime as in summer. Also, the longer a person was outside in winter, the more likely he was to yawn, while the exact opposite was found in summer. Taking into account other factors such as sleeping patterns and time spent outdoors, temperature was the only significant link to yawning frequency.
Since it is known that exposing the roof of the mouth to cooler air lowers brain temperature, researchers theorized that yawning in cooler temperatures works to cool the brain, while yawning in warmer conditions provides no similar relief. This discovery may lead to better understanding of diseases and conditions such as multiple sclerosis or epilepsy, which are accompanied by frequent yawning and thermoregulatory disfunction. Excessive yawning could be a useful diagnostic tool.
Study researcher Andrew Gallup of Princeton, who found the same phenomenon in parakeets which have relatively large brains, noted, “Brains are like computers. They operate most efficiently when cool, and physical adaptations have evolved to allow maximum cooling of the brain.”
So next time you yawn in someone’s face, you needn’t apologize. Just politely let them know that your body’s working according to design – keeping your brain cool!