Curly-Haired People: You Are Cooler Than Others

A new Penn State study reported by Smithsonian Magazine has determined that humans in general evolved with more hair on our heads for a reason: to cool off our growing brains. And according to the researchers who authored the paper published in Proceedings of the National Academy of Sciences, curly-haired people stay the coolest. "Previous studies on mammalian coats have shown that hair can limit the amount of sunlight reaching the skin," lead author Tina Lasisi tells Newsweek, "but we were particularly surprised by the significant reduction in solar heat radiation impact provided by tightly coiled hair." The tight curls, it seems, create more distance (and air) between a person's scalp and the top of their hair, per a PSU news release.

"The brain is a large and very heat-sensitive organ that also generates a lot of heat," Lasisi tells National Geographic. Keeping it cool in Equatorial Africa was likely an important factor in human evolution, "especially in a period of time when we see the brain size of our species growing," she adds. Her team determined the cooling properties of hair using a "thermal manikin" dubbed "Newton." First, they brought up its body temperature to humanlike levels, then exposed the manikin to the equivalent of 86-degree sunlight. Then came the wigs. After testing straight-haired, loosely curled, and tightly coiled wigs, they found straight hair was better than a bare head—reducing the head's heat factor roughly in half—but the tight curls were best of all.

Lasisi tells Newsweek that after early humans evolved larger brains, we were able to "employ other behavioral and social strategies to cope with heat," which likely reduced any evolutionary advantage in curly hair. In this study, the Penn State group was looking at "the biophysical aspects of heat transfer" as that relates to different hair textures, Lasisi says. She notes that in the future it might be valuable "to understand the implications of our findings in the context of human physiology." (More scientific study stories.)