A recent study from Penn State, as reported by Smithsonian Magazine, suggests that humans evolved with more hair on our heads to help cool down our growing brains. The researchers, publishing their findings in Proceedings of the National Academy of Sciences, discovered that people with curly hair tend to stay the coolest. Lead author Tina Lasisi explains that previous studies have shown that hair can limit sunlight reaching the skin, but they were surprised by the significant reduction in solar heat radiation impact provided by tightly coiled hair. The tight curls create more distance and air between a person’s scalp and the top of their hair, acting as a natural air conditioner.
According to Lasisi, the brain is a large and heat-sensitive organ that generates a lot of heat. Keeping it cool in Equatorial Africa was likely crucial for human evolution, especially as the brain size of our species grew. The researchers used a “thermal manikin” called “Newton” to determine the cooling properties of hair. They exposed the manikin to 86-degree sunlight after bringing its body temperature to human-like levels. They tested straight-haired, loosely curled, and tightly coiled wigs and found that straight hair was better than a bare head in reducing heat, but tightly coiled hair performed the best.
Lasisi notes that after early humans evolved larger brains, they were able to employ other strategies, such as behavioral and social adaptations, to cope with heat. This likely reduced the evolutionary advantage of having curly hair. The Penn State group focused on the biophysical aspects of heat transfer in relation to different hair textures. In the future, further research could explore the implications of these findings in the context of human physiology.
Overall, this study sheds light on the role of hair in regulating temperature and suggests that curly hair may have provided an advantage in cooling the brain during the evolution of humans.
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