Unlike most primates, humans have a unique pattern of hair growth, with dense scalp hair contrasting sharply with relatively sparse body hair. One widely accepted theory suggests that early humans lost body hair to enhance sweating, allowing for better temperature regulation and supporting the expansion of our heat-sensitive brains. Meanwhile, the retention of scalp hair may have provided a natural barrier against the sun as hominins became bipedal and traveled long distances. Both scalp and body hair grow in cycles: anagen (active growth), telogen (resting), and exogen (shedding). While body hair has shorter growth cycles, head hair can grow continuously for two to six years. The evolutionary reason behind this remains uncertain, but scientists speculate that sexual selection may have played a role. However, why human head hair evolved so differently from our closest relatives remains an unanswered question.
