These findings shed light on the role of hair texture in body temperature regulation and provide insights into how humans adapted to their environment.

Curly hair played a vital role in the early survival of the human species, according to new research, which suggests the previously overlooked feature provided protection against intense solar radiation and facilitated the growth of the human brain to its modern-day size.

“Humans evolved in equatorial Africa, where the sun is overhead for much of the day, year in and year out,” Professor Nina Jablonski, the Evan Pugh University Professor of Anthropology at Penn State, said in a university release.

“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 research team employed a thermal manikin and human-hair wigs within a controlled environment to investigate how these attributes impacted the evolution of hair.

The study revealed that tightly curled hair provides optimal protection against solar radiation, minimising the necessity to sweat excessively to remain cool. This is crucial since the brain is susceptible to heat and generates its own, and excessive radiation could induce perilous conditions.

As humans progressively lost body hair, they evolved efficient sweat glands to manage body temperature.

However, sweating requires water and electrolytes, potentially creating a deficiency. It appears that curly hair evolved as a passive means to reduce heat gain from solar radiation, permitting humans to stay cool without consuming additional resources.

Furthermore, the research indicates that scalp hair relaxed a physical constraint, enabling the brain to grow to contemporary sizes. Around two million years ago, Homo erectus resembled us in physical stature but had a smaller brain.

Approximately one million years ago, the human brain reached its present dimensions. The existence of scalp hair lessened the heat absorbed from solar radiation, supplementing the sweat glands’ role in body cooling.

This discovery offers an in-depth view of how humans adapted to their surroundings. The innovative use of tools like thermal manikins enables the collection of human data that would typically be difficult to obtain.