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/

[msongs]

1. so what about the curly hair people who develop bald spots nt

[wnylib]

2. And what about straight haired people who

live in hot, tropical climates, like the native people of Mesoamerica?

When, where, and how did straight hair develop? What advantages or disadvantages are there to straight hair?

[sybylla]

3. Indigenous Mesoamericans evolved in other parts of the world.

Also, Mesoamerica is predominantly rain forest. There would have been lots of cover and materials to make head coverings. No need to evolve curly hair.

None of this may have been true 50,000 to 100,000 years ago, but it has been true since the end of the last ice age.

[wnylib]

5. Yes, Native Americans evolved elsewhere, but

if curly hair is significant under a hot, tropical sun, which I don't doubt is true, wouldn't there be some disadvantage to straight haired people in hot, sunny climates? Not all of Mesoamerica is rainforest. Also, some Native Americans, like some Africans and Asians, have lived for millennia in hot, desert climates.

I don't doubt that tightly curled hair has advantages in a hot, humid climate. I just wonder if the advantages are being overstated in human evolution.

[sybylla]

6. Entirely possible.

On the other hand, evolution doesn't happen outside of environmental conditions.

Having studied mesoamerican cultures, I've not seen any studies showing that it is anything but tropical forest - rain forest or not - to the point that the forest quickly took over and covered all the beautiful classical Mayan pyramids. All that cover plus lush vegetation and fibers to produce clothing and headwear would negate curly hair evolution.

I don't know enough about the environment in which curly hair developed to comment further nor how many years such an evolution would take.

I do find the facts around the insulating properties of curly hair pretty logical in a way that makes me wonder why it took until the 21st century to even study it and prove it. I mean, we already knew this about the tight curls of sheep being both a cooling (in hot weather) and a warming (in cold weather) mechanism to moderate body temp.

[wnylib]

7. I've studied Mesoamerican cultures as part of

my Spanish major and anthropology minor. Mexico is part of Mesoamerica, with varied climate regions. Not all inhabited regions have a plush canopy. And there are rainforests in Africa to allow for a canopy, too.

https://www.google.com/search?q=yucatan+peninsula+imate&client=ms-android-americamovil-us-revc&ei=JJWGZKTdDc6ZptQPkLOniAU&oq=yucatan+peninsula+imate&gs_lcp=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&sclient=mobile-gws-wiz-serp#imgrc=ApkxgRdAZBJBSM

While large parts of Central America are tropical rainforest, other climates in those regions and in South America have been inhabited for several millennia.


https://www.google.com/search?q=central%20america%20climate%20zone%20map&tbm=isch&client=ms-android-americamovil-us-revc&prmd=imnv&hl=en&sa=X&ved=0CBgQtI8BKAJqFwoTCPCAp5L0vf8CFQAAAAAdAAAAABAc&biw=360&bih=560&dpr=2#imgrc=_8vG-14zziGoIM

[sybylla]

4. Bald spots tend to develop in middle age or later for most people (women, too).

What is middle age now may have been hard to achieve when curly hair evolved.