Article image

Curly hair kept early humans cool before air conditioning

Human hair, with its varied textures, does more than just crown our heads and serve aesthetic purposes. It might just be the secret that enabled early humans to beat the heat, stay hydrated, and as a surprising consequence, foster the growth of our modern-day brain sizes. According to recent research, the key might lie in our curly locks.

The investigation, led by researchers at Penn State University and Loughborough University, delved into the role of different hair textures in regulating body temperature. The findings suggest that our ancestors’ tightly curled hair served a crucial function in the torrid heat of equatorial Africa, where human evolution took its course.

Connection between human heads and sunlight

Professor Nina Jablonski elaborated on the connection between our scalps and the intense sunlight of our ancestral home. “Humans evolved in equatorial Africa, where the sun is overhead for much of the day, year in and year out,” she explained. “We found that tightly curled hair allowed humans to stay cool and actually conserve water.”

To understand this unique evolutionary adaptation, the research team used a thermal manikin – a human-shaped model that simulates body heat – to study how different hair textures affect heat gain from solar radiation. The manikin was programmed to maintain an average skin surface temperature of 95 degrees Fahrenheit (35 degrees Celsius) and was set in a climate-controlled wind tunnel.

How the study was conducted

George Havenith, director of the Environmental Ergonomics Research Centre at Loughborough University, described how the experiments were conducted. After establishing base measurements of body heat loss, the researchers simulated solar radiation with lamps and studied how heat loss varied under four different scalp hair conditions – bald, straight-haired, moderately curled, and tightly curled.

By comparing heat loss with and without the lamp exposure, the researchers determined how much solar radiation the scalp absorbed. They also factored in varying wind speeds and simulated sweating to model realistic conditions. The researchers then studied how these hair textures would handle heat and humidity typical of equatorial Africa.

What the research team discovered

The team discovered that all hair types reduced solar radiation to the scalp. However, tightly curled hair stood out as the champion, offering superior sun protection and minimizing the need to sweat for cooling. This research was reported on June 6 in the Proceedings of the National Academy of Sciences.

Tina Lasisi, who conducted this research as part of her doctoral dissertation at Penn State, explains the significance of these findings: “Walking upright is the setup and brain growth is the payoff of scalp hair,” she says. As early humans started walking upright, their scalps bore the brunt of the sun’s rays. The brain, a heat-sensitive organ that generates heat, especially when growing larger, needed protection from overheating.

Excessive heat can lead to conditions like heat stroke. Although humans have developed efficient sweat glands to cool down, sweating comes with a cost – water and electrolytes. Lasisi believes that scalp hair evolved as a way to keep humans cool without the body having to expend additional resources.

Insights gained into human evolution

She points out that about 2 million years ago, Homo erectus, similar to modern humans in physical build but with a smaller brain size, walked the earth. 

“By one million years ago, we’re basically at modern-day brain sizes, give or take. We think scalp hair provided a passive mechanism to reduce the amount of heat gained from solar radiation that our sweat glands couldn’t,” says Lasisi.

This interesting research brings us a step closer to understanding the intricate process of human evolution and the multifaceted roles of our physical traits. The use of the thermal manikin, a tool usually used for testing protective clothing, opens new avenues for anthropological research. It helps quantify human data without putting humans in potentially risky situations, as noted by Jablonski.

Implications for life in the 21st century

In addition to unlocking the mysteries of human evolution, the research could have real-world implications for today. Lasisi, who is set to start as an assistant professor of anthropology at the University of Michigan in the fall, compares the protective nature of hair to the role of melanin in our skin.

“The work that’s been done on skin color and how melanin protects us from solar radiation can shape some of the decisions that a person makes in terms of the amount of sunscreen needed in certain environments,” said Lasisi. “I imagine that similar decision making can occur with hair.”

She goes on to reflect on the potential implications for different professions or activities that involve exposure to varied climates. This could include military personnel or athletes who exercise in diverse environments. 

“Our findings give you a moment to reflect and think: is this hairstyle going to make me overheat more easily? Is this the way that I should optimally wear my hair?” Lasisi proposed.

Main takeaways from this interesting study

In conclusion, the humble curl of our hair is more than just a stylistic feature – it might be a testament to a crucial evolutionary adaptation that helped us grow, thrive, and even develop our present-day brain sizes. 

As science continues to uncover these intriguing connections, it becomes increasingly evident that our evolutionary past continues to influence our present and potentially shape our future.

This study represents an interdisciplinary effort involving experts from multiple universities. Key contributors include James Smallcombe from Loughborough University and the University of Australia, Larry Kenney, professor of physiology, kinesiology, and Marie Underhill Noll Chair in Human Performance from Penn State, along with Mark Shriver, professor of anthropology, and Benjamin Zydney, a Penn State alum and former undergraduate research assistant.

The National Science Foundation and the Wenner-Gren Foundation financially supported this research, emphasizing its importance in deepening our understanding of human evolution and potentially influencing our choices and decisions in daily life.

More about human hair 

Human hair has a fascinating evolutionary history. It’s unique to each person and serves a variety of crucial roles that go beyond aesthetics.

Physical protection for your head

One of the major evolutionary benefits of hair is protection. Hair on our heads shields the scalp from the harmful ultraviolet radiation of the sun. As we saw from the recent research, tightly curled hair does an exceptional job at this, reducing the absorption of solar radiation and helping to keep us cool.

Hair also provides a physical barrier against foreign particles. Eyelashes and eyebrows protect our eyes from dust and other tiny particles, while hair within our nostrils filters out unwanted particles from the air we breathe.

Sensory perception

Interestingly, body hair also plays a role in sensory perception. Hair follicles are surrounded by a network of nerve endings, making them sensitive to touch. This could have been beneficial in our evolutionary past, allowing us to sense the presence of insects or other potential threats on our skin.

Communication and perceived attractiveness

Moreover, hair plays a significant role in communication and sexual selection. For example, long, lustrous hair is often considered a sign of health and fertility, potentially making it an attractive trait for potential mates. Similarly, certain hairstyles can communicate social or cultural identity.

Controls perspiration

Sweat also plays a part in this story. Humans, unlike most mammals, have relatively hairless bodies but are one of the sweatiest creatures on the planet. The evolution of sweating helped our ancestors stay cool while hunting and gathering during the hottest parts of the day. Hair on our heads likely evolved to help wick sweat away from the body, increasing the cooling effect.

Furthermore, hair color and texture can be linked to our geographic and ancestral roots. For example, tightly coiled hair, which is common among people of African descent, is believed to have evolved in response to the intense sun and heat of the equatorial region. In contrast, straight hair, often associated with people of East Asian descent, might have evolved to provide warmth and protection from the cold in northern climates.

All in all, human hair is a complex trait that has been shaped by a myriad of evolutionary pressures. It serves multiple functions, from thermoregulation and protection to communication and even attraction. These diverse roles underscore the fact that human hair is much more than a mere accessory; it’s a testament to our evolutionary journey and survival story.


Check us out on EarthSnap, a free app brought to you by Eric Ralls and

News coming your way
The biggest news about our planet delivered to you each day