Curly hair might have evolved as defense against sun: Study
Curly hair evolved as a protective adaptation to shield our ancestors' heads from the sun's heat after they began walking upright. This key finding was published in the Proceedings of the National Academy of Sciences by Dr. Tina Lasisi and her colleagues at Pennsylvania State University. They investigated how different hair types affect the amount of heat gained when sunlight shines on the scalp.
Researchers used a thermal mannequin for their experiments
During their experiments, the researchers placed different human hair wigs on a thermal mannequin. This mannequin uses electricity to simulate body heat and is typically used to test protective clothing. By doing this, the team could study how different hair textures - bald, straight, moderately curled, and tightly curled - impact the transfer of heat between the environment and human skin.
Mannequin was placed in a climate-controlled wind tunnel
The thermal mannequin was set to have a surface temperature similar to human skin, around 95F (35°C). It was then placed in a climate-controlled wind tunnel. The researchers monitored the amount of electricity needed to keep the mannequin's temperature constant. This helped them establish a baseline to measure how much heat the model was losing from its body.
Difference in total heat loss for each hair type calculated
The researchers measured the change in heat loss for each hair type by comparing it to the baseline measurement. This helped them determine how much solar radiation reached the mannequin's head. The researchers also measured how varying wind speeds in the tunnel impacted heat loss from the mannequin. They also simulated sweating by wetting the scalp to observe its effects.
Research concluded that tightly curled hair provided most effective protection
Finally, the researchers ran their findings through the model to understand how different hair types would influence heat gain in a climate similar to parts of equatorial Africa. They discovered that all types of hair reduced the amount of sunlight reaching the scalp. However, tightly curled hair provided the most effective protection, reducing the need to sweat for cooling.
Curly hair prevented loss of water and electrolytes through sweating
Dr. Tina Lasisi, co-author, explained, as early humans began to walk upright, their heads faced more exposure to the sun's rays. Although humans developed sweat glands to cool down, sweating leads to water and electrolyte loss. According to her, scalp hair likely evolved to minimize heat gain from the sun, helping our ancestors stay cool while reducing the loss of water and electrolyte.
Cool heads helped ancestors grow bigger brains
Dr. Tina Lasisi added that around two million years ago, our ancestors called Homo erectus had a smaller brain size. However, after one million years, our ancestors reached brain sizes similar to ours today. Since the brain is sensitive to heat and produces more heat as it grows, Dr. Lasisi believes, having a cool head was important for our ancestors to grow bigger brains.
