 Head hair was an exception, which was a survival trait because it provides thermal insulation of the scalp from the sun, protects against ultraviolet radiation exposure(UV), and also provides cooling (when sweat evaporates from soaked hair).The ability to grow straight hair has been observed among Homo sapiens sub-groups in less sunny regions further away from the equator.Relative to kinked Afro-textured hair, straight hair allows more UV light to pass to the scalp (which is essential for the production of vitamin D, that is important for bone development).