Human scalp hair as a thermoregulatory adaptation

The evolution of human scalp hair might be explained by thermoregulation pressures experienced in hot and arid environments. Bipedal posture and a hairless body may have necessitated the development of scalp hair to minimize heat gain from solar radiation, particularly in hominins with large brains. We used a thermal manikin and human-hair wigs to examine this thermoregulatory hypothesis. We confirm that scalp hair reduces heat gain from solar radiation and find an effect of hair morphology. Our results show that tightly curled hair provides the most effective protection for the scalp against solar radiation, while minimizing the need for sweat to offset heat gain.