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curly hair kept us cool and may have made our brains bigger

We may have found something new, something truly amazing about the evolution of curly hair.

Curly hair may have helped humans stay cool while conserving water, according to researchers who studied human hair textures’ role in regulating body temperature. ALSO, the findings hypothesize how this evolutionary adaptation may have enabled our brains 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. 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.
Nina Jablonski, Evan Pugh University Professor of Anthropology at Penn State.

For the study, the scientists used a manikin – a human model that uses electric power to simulate body heat – to test the effects of solar radiation on different human hair wigs.

The experiments involved shining lamps’ heads to mimic solar radiation with windspeeds. They also wetted the scalp to simulate sweating on the manikin’s head to measure heat loss in its’ body.

The team then ran their results through a model to study how the diverse hair textures would affect heat gain in 30 degrees Celsius heat and 60% relative humidity, like environments in equatorial Africa.

The researchers found that while all types and textures of hair reduced solar radiation to the scalp, tightly curled hair provided the best protection from the sun’s heat.

As early humans evolved to walk upright in equatorial Africa, the tops of their heads increasingly experienced a lot of direct solar radiation impact. The brain is sensitive to heat, generating heat, significantly the larger it grows.

As humans lost much of their body hair, they developed efficient sweat glands to keep cool. But sweating comes at a cost — lost water and electrolytes.

So, scalp hair likely evolved as a way to reduce the amount of heat gained from solar radiation, thereby keeping humans cool without the body having to expend extra resources.

Around 2 million years ago we see Homo erectus, which had the same physical build as us but a smaller brain size.

And by 1 million years ago, we’re basically at modern-day brain sizes, give or take.

Something released a physical constraint that allowed our brains to grow.

Researchers think scalp hair provided a passive mechanism to reduce the amount of heat gained from solar radiation that our sweat glands couldn’t.

The study on these amazing curly hair findings was published on June 6 in the Proceedings of the National Academy of Sciences.

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