Curly hair evolved as protection from the heat of the Sun

Curly hair better protects the head from the heat of the Sun, keeping body temperature cooler and reducing water lost through sweating: their appearance in human evolution would have allowed our ancestors to develop a larger brain. This is the conclusion of the Pennsylvania State University study published in the journal of the American Academy of Sciences (PNAS).

The researchers compared different hair types by making a thermal mannequin, powered by electricity, wear different wigs to simulate the production of body heat. After setting a surface temperature of 35 degrees (similar to that of the epidermis), they placed the dummy in a wind tunnel with a controlled ambient temperature of 30 degrees and a relative humidity of 60%, so as to simulate the conditions of equatorial Africa, where our ancestors lived. Under the rays of a lamp, used to simulate the sun's rays, it has been shown that all types of hair (straight, wavy and curly) protect the head from sunlight, but curly hair is more effective in reducing absorbed heat and therefore sweating.

"Humans evolved in equatorial Africa, where the Sun is overhead for most of the day, year after year," said Nina Jablonski, a professor of anthropology at Pennsylvania State University. "Here the scalp and top of the head receive much more constant levels of intense solar radiation in the form of heat. We wanted to understand how this affects the evolution of our hair. We found that curly hair allowed humans to stay cool and conserve water."

To benefit above all would have been the brain: this organ, in fact, is very sensitive to heat and the more it increases in size, the more it produces. Having an efficient thermoregulation system may have been key to its development.