The Evolutionary Benefits of Hair: From Cooling to Growth Stimulation.
Curly hair in early humans was an adaptive trait that protected them from the sun's heat and minimized the need for sweating, allowing for brain growth by conserving water and reducing heat. Researchers used a thermal manikin and human hair wigs to examine how diverse hair textures affect heat gain from solar radiation. They found that tightly curled hair provided the best protection from the sun's radiative heat while minimizing the need to sweat to stay cool. The study sheds light on an evolutionary adaptation that enabled the human brain to grow to modern-day sizes.