Wavy hair may have evolved in early humans as an adaptation to high ultraviolet light in Africa. Straight hair allows UV light to penetrate deeper into the scalp, whereas wavy hair provides more protection. As humans lost body hair and skin darkened, wavy or curly hair would have helped block UV penetration compared to straight hair near the equator. Later, as people migrated to less sunny areas, straight hair may have evolved to help increase UV absorption when skin became paler.