Our bodies are pretty complicated mechanisms, and they’re complex in ways we don’t fully understand. For example, why do some people have naturally curly hair? According to new research, there may have been a good evolutionary reason.

A recently published research article by Tina Lasisi and her colleagues at Pennsylvania State University examined how hair regulates scalp temperature in direct sunlight by using different wigs on a “thermal mannequin.”

The mannequin was placed in a climate-controlled chamber within a wind tunnel and heated to the average body temperature of 95 degrees Fahrenheit. Scientists then studied the amount of heat transferred between its skin and the surrounding environment. Three different black-human-hair wigs were used—one straight, one moderately curly, and one tightly curled. Heat loss was calculated for each texture at different windspeeds. “The brain is a large and very heat-sensitive organ that also generates a lot of heat,” explains Lasisi. “So we figured, evolutionarily, this could be important—especially in a period of time when we see the brain size of our species growing.”

Their findings suggest that, although all types of hair provide sun protection, tightly curled hair better protects the scalp from solar radiation and it doesn’t lie flat against the skin while wet—a real advantage in hot conditions that can make humans sweat, like those our ancestors would have endured in Africa millions of years ago.

But if curly hair provides an evolutionary advantage, why do so many people today, like me, have straight hair?

Good question. Lasisi thinks any genetic predispositions for early hominins’ hairstyles were probably variable. At a later point, curly hair may have lost its evolutionary advantage, and straight hair may have been favored by other types of genetic selection. “Maybe once we had those larger brains, we also had all these cultural adaptations to avoid overheating, like better sources of water,” she says. “And at that point, maybe there wasn’t such a selective pressure for curly hair.” And other factors, such as hair structure, density, and color must also be considered.

In any event, it’s another interesting way to analyze our bodies.

For more detail, see “Why Curly Hair was an Evolutionary Advantage” by Tom Metcalfe (https://www.nationalgeographic.com/premium/article/curly-hair-evolutionary-advantage-brain-protect?).