Just by reading the title of this post, or looking at the photos above you may have yawned. Why do we yawn and why is it contagious? Is yawning simply a sign of being tired? Prior explanations for the reasons why humans and some non-human species yawn have mostly been psychological and social. However, multiple recent studies (Gallup & Eldakar, 2011; Massen, Dusch, Eldakar, & Gallup, 2014) have investigated the answers to these questions and have come up with a pretty convincing physiological argument that yawning may be a thermoregulatory mechanism. Yawning can be classified into two categories: spontaneous and contagious. Spontaneous yawns follow a consistent circadian pattern, whereas contagious yawns are triggered by observing or thinking about other people yawning. There is some support for the social role of yawning, however evidence that yawning transmits some sort of specific information is lacking. Non-social yawning happens all the time across vertebrate species but until 2011 no hypothesis that involved underlying physiological reasons for yawning have been supported.
Recent studies have attempted to combine the social theories for why we yawn with possible physiological underlying mechanisms. In a 2011 study (Gallup & Eldakar) researchers counted the number of people who yawned in response to seeing pictures of people yawning both in the summer (~98.6 degrees) and in the winter months (~71.6 degrees) in Arizona. Yawning occurred more at lower temperatures when the temperature of the air was cooler than peoples’ internal body temperature. Keep in mind these findings were consistent “even after statistically controlling for other features such as humidity, time spent outside and the amount of sleep the night before” (Gallup). The thermoregulatory theory of yawning posits that when we breathe in cool air it cools down our brains. Gallup uses the comparison that “brains are like computers. They operate most efficiently when cool, and physical adaptations have evolved to allow maximum cooling of the brain” (Chan). In a study conducted three years later (Massen, Dusch, Eldakar, & Gallup) researchers similarly found that yawning is “constrained to an optimal thermal zone of ambient temperature.” They found a lower frequency of yawning at extreme temperatures, whereas mid-range ambient temperatures in the low 70s elicited the highest frequency of yawning. Researchers have suggested these results may provide a diagnostic tool for identifying diminished thermoregulation in cases where people excessively yawn. These results offer convincing evidence that yawning is more than just a mark of sleepiness or boredom.
Chan, Amanda L. “Yawning Cools Down The Brain, Study Finds.” The Huffington Post. TheHuffingtonPost.com, 22 Sept. 2011. Web. 17 Apr. 2015. <http://www.huffingtonpost.com/2011/09/22/yawn-cool-brain_n_975927.html>.
Gallup, A., & Eldakar, O. T., (2011). Contagious yawning and seasonal climate change. Evolutionary Neuroscience, 3, 1-4.
Massen, J. J., Dusch, K., Eldakar, O. T., Gallup, A. C., (2014). A thermal window for yawning in humans: Yawning as a brain cooling mechanism. Physiology and Behavior, 130, 145-148.
O’Connor, Anahad. “REALLY?; The Claim: Yawning Cools the Brain.” The New York Times. N.p., 04 Oct. 2011. Web. 17 Apr. 2015. <http://query.nytimes.com/gst/fullpage.html?res=9804E4DC1131F937A35753C1A9679D8B63>.