Blonde Girl With Long Hair Posing On The Tree

Texture
Curly hair
Jablonski agrees that it was evolutionarily advantageous for pre-humans to retain the hair on their heads in order to protect the scalp as they walked upright in the intense African (equatorial) UV light. While some might argue that, by this logic, humans should also express hairy shoulders given that these body parts would putatively be exposed to similar conditions, the protection of the head, the seat of the brain that enabled humanity to become one of the most successful species on the planet (and which also is very vulnerable at birth), was arguably a more urgent issue (axillary hair in the underarms and groin were also retained as signs of sexual maturity). During the gradual process by which Homo erectus made a transition from furry to naked skin, their hair texture putatively changed gradually from straight (the condition of most mammals, including humanity's closest cousins—chimpanzees), to Afro-like or 'kinky' (i.e. tightly coiled). In this sense, during the period in which humans were gradually losing their straight body hair and thereby exposing initially the pale skin underneath their fur to the sun, straight hair would have been an adaptive liability. Hence, tightly coiled or 'kinky' Afro-hair may have evolved to prevent the entry of UV light into the body during the transition toward dark, UV-protected skin.
Alternatively, some intuit that tightly coiled hair that grows into a typical Afro-like formation would have greatly reduced the ability of the head and brain to cool. They reason that although hair density in African peoples is much less than their European counterparts, in the intense sun the effective 'woolly hat' produced would have been a disadvantage. However, anthropologists such as Nina Jablonski make the opposite argument with regards to this hair texture. Specifically, Jablonski's assertions suggest that the adjective "woolly" in reference to Afro-hair is a misnomer to the extent that it connotes the high heat insulation derivable from the true wool of sheep. Instead, the relatively sparse density of Afro-hair, combined with its springy coils actually results in an airy, almost sponge-like effect. This, in turn, Jablonski argues, more likely facilitates an increase in the circulation of cool air onto the scalp. Further, Afro-hair does not respond so easily to moisture and sweat as straight hair. Thus it does not stick to the neck and scalp when wet. Rather, unless totally drenched, it tends to retain its basic springy puffiness. In this sense, the trait may enhance comfort levels in intense equatorial climates compared to straight hair (which, on the other hand, tends to naturally fall over the ears and neck to a degree that provides slightly enhanced comfort levels in cold climates relative to tightly coiled hair).