Curly and Cool: How curly hair keeps the brain from overheating

Curly hair can do much more than just make you look pretty. According to a recent study, early humans’ curly hair may have been an adaptation that allowed them to conserve water while keeping cool. The study, which was released on Thursday in the journal PNAS, provides new information about how the evolutionarily adapted hair texture may have allowed our brains to develop into their current sizes. Researchers, including those from Penn State, looked at how human hair textures affect how the body temperature is regulated. Let’s take a closer look. Also read: Going Grey: Why does your hair change colour as you age? Curls keep us cool Humans are unique among mammals in that their bodies are almost completely hairless, but their scalps are covered in hair, which fascinated researchers at Pennsylvania State University. Contrary to common opinion, tightly curled hair doesn’t “trap” heat; rather, it shields the hair from heat exposure. This is true even though tightly curled hair has long been perceived as thick or likened to “wool.”

The study’s authors say it is an evolutionary mechanism that is meant to protect the human brain from overheating. “We find evidence for a significant reduction in solar radiation influx to the scalp in the presence of hair. Particularly, we find that hair that is more tightly curled offers increased protection against heat gain from solar radiation,” the study states. “Humans evolved in equatorial Africa, where the sun is overhead for much of the day, year in and year out,” study co-author Nina Jablonski from Penn State said in a statement. “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,” Dr Jablonski explained. According to studies, the brain is heat-sensitive and produces more heat as it expands, with too much of it potentially leading to heat stroke. Sweating results in the loss of water and electrolytes, despite the fact that humans designed sweat glands to effectively stay cool. Also read: How is onion beneficial for our hair? Our hair has evolved Researchers employed a thermal manikin (mannequins), an electric, temperature-controlled human model usually used in medical or art studies, to examine how heat is transported from the human skin to the environment in order to determine how hair textures affect heat gain from solar radiation. According to the study, all of the wigs used in the trial were made of Chinese-sourced black human hair. They placed the manikin in a climate-controlled wind tunnel and configured it to maintain a consistent surface temperature of 95F (35C), which is comparable to the normal surface temperature of the skin. By observing the quantity of electricity needed by the manikin to maintain a constant temperature, they were able to take baseline measurements of body heat loss. The manikin’s head was then exposed to lamps that mimicked solar radiation under four different hair conditions: none, straight, moderately curly, and tightly curly. To assess the amount of solar radiation reaching the head, they calculated the difference in total heat loss between the lamp measurements and the base measurements. Calculations of heat loss at various wind speeds and after wetting the scalp to mimic sweating were also made. All of this assisted scientists in simulating how various hair textures might impact heat gain in 86 degrees Fahrenheit (or 30 degrees Celsius) heat and 60 per cent relative humidity - conditions similar to those in tropical Africa. The study said, “Sweating works in tandem with a seemingly hairless body to create a highly-effective cooling system. But sweating also increases the need for fluid replacement and thus can lead to dehydration. Therefore, scalp hair may have offered significant additional benefits to a person." While it was discovered that all hair reduced solar radiation to the scalp, tightly curled hair offered the strongest defence against the sun’s radiative heat while reducing the need to perspire to stay cool. Researchers have found that the crowns of early people’s heads in equatorial Africa increasingly took the brunt of sunlight. “Tightly curled human hair form does not lay flat on the scalp and therefore increases the distance between the surface of the hair and the surface of the scalp,” the authors noted, suggesting that the evolution of hair “might be explained by thermoregulation pressures experienced in hot and arid environments." Another study author Tina Lasisi said, “Around two million years ago we see Homo erectus, which had the same physical build as us but a smaller brain size. And by one 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. We think scalp hair provided a passive mechanism to reduce the amount of heat gained from solar radiation that our sweat glands couldn’t,” Dr Lasisi explained. We can better grasp how human hair evolved thanks to preliminary study findings. Similarly, the latest findings can help clarify if a particular hair type might perform better in a given situation. “When you think about the military or different athletes exercising 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?” Dr Lasisi explained. With inputs from agencies Read all the  Latest News ,  Trending News ,  Cricket News ,  Bollywood News , India News  and  Entertainment News  here. Follow us on  Facebook,  Twitter and  Instagram.