A study led by Andrew Gallup, a postdoctoral research associate in Princeton University’s Department of Ecology and Evolutionary Biology, is the first involving humans to show that yawning frequency varies with the season and that people are less likely to yawn when the heat outdoors exceeds body temperature. Gallup and his co-author Omar Eldakar, a postdoctoral fellow in the University of Arizona’s Center for Insect Science, report this month in the journal Frontiers in Evolutionary Neuroscience that this seasonal disparity indicates that yawning could serve as a method for regulating brain temperature.
Gallup and Eldakar documented the yawning frequency of 160 people in the winter and summer in Tucson, Ariz., with 80 people for each season. They found that participants were more likely to yawn in the winter, as opposed to the summer when ambient temperatures were equal to or exceeding body temperature. The researchers concluded that warmer temperatures provide no relief for overheated brains, which, according to the thermoregulatory theory of yawning, stay cool via a heat exchange with the air drawn in during a yawn.
Gallup describes the findings as follows:
This provides additional support for the view that the mechanisms controlling the expression of yawning are involved in thermoregulatory physiology. Despite numerous theories posited in the past few decades, very little experimental research has been done to uncover the biological function of yawning, and there is still no consensus about its purpose among the dozen or so researchers studying the topic today
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