Saturday, November 21, 2015

Evolution of long head hair

Swan princess, John Bauer (1882-1918). Human head hair is of relatively recent origin, reaching incredible lengths in some groups but not in others.


I've published an article on the evolution of long head hair in humans. The following is the abstract:

In many humans, head hair can grow to a much greater length than hair elsewhere on the body. This is a "derived" form that evolved outside Africa and probably in northern Eurasia. The ancestral form, which is frizzier and much shorter, survives in sub-Saharan Africans and in other groups whose ancestors never left the tropics. This original hair form is nonetheless relatively straight and silky during infancy. Head hair thus seems to have lengthened in two stages: 1) retention of the infant hair form at older ages; and 2) further lengthening to mid-back and even waist lengths. These changes seem to have gone farther in women, whose head hair is thicker and somewhat longer. The most popular evolutionary explanations are: 1) relaxation of selection for short hair; and 2) sexual selection for women with long hair. Neither hypothesis is satisfactory. The first one cannot explain why head hair lengthened so dramatically over so little time. The second hypothesis suffers from the assumption that some populations have remained naturally short-haired because they consider long-haired women undesirable. Almost the opposite is true in traditional African cultures, which have a long history of lengthening and straightening women's hair. It is argued here that sexual selection produced different outcomes in different populations not because standards of beauty differed but because the intensity of sexual selection differed. In the tropical zone, sexual selection acted more on men than on women and was thus too weak to enhance desirable female characteristics. This situation reversed as ancestral humans spread northward into environments that tended to limit polygyny while increasing male mortality. Because fewer men were available for mating, women faced a more competitive mate market and were selected more severely.


Frost, P. (2015). Evolution of long head hair in humans, Advances in Anthropology, 5, 274-281.



Reader said...

Desmond Morris, "The Naked Woman": "The bizarre human hair pattern acts as a species flag -- a display that sets us apart from all our close relatives... If we try to picture a little group of our remote ancestors, long before they developed clothing or any kind of cutting implement, it is clear they would look very different from everything else on the planet. With their naked bodies surmounted by long swishing capes or gigantic woolly bushes, they would immediately be identifiable as members of this newfangled species that walks about on its hind legs. This may seem an odd way to label a species, but a quick look at the other apes and monkeys soon shows how often strange hair patterns have arisen as species identification markers. There is a rich variety of crests, manes, capes, beards, moustaches and brightly colored hair patches. Primates are predominantly visual animals and it follows that displaying conspicuous visual signals will be the quickest and most efficient way of distinguishing one species from another."

"In their primeval condition, our remote human ancestors, with their naked bodies and long head hair, could be spotted far off the distance, and easily differentiated from their furry-bodied cousins. Coming slightly closer, it would then be possible to distinguish between the sexes. The males, with their hairy faces, could not be confused with the naked-faced females."

So there you go. The long human head hair is a species marker.

Malcolm Smith said...

If the ancestral head hair was short and frizzy, why has it disappeared in the Australian Aborigines, who are a remnant of a very ancient out-of-Africa offshoot? The Melanesians, who are closely related to the Australians, still have frizzy hair. What about the Dravidians? And why has it never been lost in Africa - except in the Sahel and Horn, where the inhabitants have been interbreeding with Caucasians for generations?

Santoculto said...

Sometimes i think ''blacks'' and other people with curly hair are more eletric, ;), than those with straight hair. Interesting that straight hair are predominant among human populations with the least dominant personality profile. ;)

Ad delirium

Joyce said...

@Santoculto, human evolution was apparently not driven by "personality"(a subjective qualifier) and straight haired people have been more successful for reasons other than being straight haired.

Joyce said...

No evidence for fewer men than women outside Africa. If anything, patriarchy or very stratified societies left lower class men no choice at all because men in power or even better off commoners had more than one wives. I did not know that African hair was naturally shorter until I came upon your blog, interesting. I doubt that it was sexual selection, because the climate had a lot of wild swings during glacial and the ancestors of Eurasians probably had hard time to simply survive. Maybe low light caused mutation in curly genes or straighter hair caught less snow, but I have to agree that a lot of men like long hair.