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Though considered a mark of boredom or fatigue, yawning might also be a trait of the hot-headed. Literally.

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.