Curly hair evolved to keep early humans cool.
Curly hair kept our ancestors cool
Research suggests that tightly coiled hair could have evolved in people living in Africa thousands of years ago as it helped the body conserve water by minimising the need for sweating to stay cool.
The hair texture also provides a barrier against solar radiation to protect the scalp.
The experts are convinced that the findings - which have been published in the journal Proceedings of the National Academy of Science (Pnas) - could shed light on how the adaptation might have allowed human brains to increase in size.
Nina Jablonski, of Penn State University in the US, explained: "Humans evolved in equatorial Africa, where the sun is overhead for much of the day, year in and year out.
"Here the scalp and the 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."