Curly hair kept early humans cool

[Judi Lynn]

8 June 2023

Tightly curled scalp hair protected early humans from the sun’s radiative heat, allowing their brains to grow to sizes comparable to those of modern humans

Loughborough researchers worked with Penn State University, in the USA, to study heat transfer through human hair wigs and the environment to examine how diverse hair textures affect heat gain from solar radiation

Curly hair does more than simply look good – it may explain how early humans stayed cool while conserving water, according to researchers who studied the role human hair textures play in regulating body temperature. The findings can shed light on an evolutionary adaptation that enabled the human brain to grow to modern-day sizes.

“Humans evolved in equatorial Africa, where the sun is overhead for much of the day, year in and year out,” said Nina Jablonski, Evan Pugh University Professor of Anthropology at Penn State. “Here the scalp and top of the head receive far more constant levels of intense solar radiation as heat. We wanted to understand how that affected the evolution of our hair. We found that tightly curled hair allowed humans to stay cool and actually conserve water.”

The Loughborough research team, led by Professor George Havenith, used a thermal manikin – a human-shaped model that uses electric power to simulate body heat and allows scientists to study heat transfer between human skin and the environment – and human hair wigs to examine how diverse hair textures affect heat gain from solar radiation. The scientists programmed the manikin to maintain a constant surface temperature of 35 degrees Celsius, similar to the average surface temperature of skin, and set it in a climate-controlled wind tunnel.

The team took base measurements of body heat loss by monitoring the amount of electricity required by the manikin to maintain a constant temperature. Then they shone lamps on the manikin’s head to mimic solar radiation under four scalp hair conditions – none, straight, moderately curled and tightly curled.

More:
https://www.lboro.ac.uk/news-events/news/2023/june/curly-hair-kept-early-humans-cool/