Ancestral facial hair.

Our closest ancestors, the chimpanzee and bonobo, both grow facial hair around the mouth area. What is noteworthy is that this is the case in both males and females of the species.

Female chimpanzee with facial hair:

enter image description here

Dichotomy of facial hair in humans.

Our own species has a notable dichotomy in facial hair between males and females. I'm interested in what broadly speaking are the theories on facial hair. Could it be as simple as sexual selection over tens, or hundreds of millennia?

A previous answer eludes to a sexual selection direction, but my question is primarily why do human females not grow nearly as much facial hair as their male counterparts? Is this just a typical sexual dichotomy? I suppose here I am interested at a molecular level - is beard growth absent, or suppressed in women?

Speaking physiologically androgen is a hormone that drives hair growth and this hormone is more prevalent in males. Although females do have vellus hair coverage on their face, the thicker androgenic hair isn't typically present. A cursory search didn't reveal to me if this is due to less follicles in the first place so androgen would have little effect, or less hormone release.

To answer the question "Why do men grow facial hair" I think three smaller questions are raised:

  • What is the point of facial hair? (If there is any beyond sexual selection...)
  • What selected thick androgenic facial hair out of human females?
  • At a molecular level, have females lost the "facial hair gene", or gained a "facial hair suppressor gene"?
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    $\begingroup$ Why exclude "they look dashing"? That's sexual selection at work. $\endgroup$ – canadianer Aug 26 '15 at 18:32
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    $\begingroup$ @canadianer I'm guessing that we didn't have vogue telling us that beards and tweed is a winning combo over evolutionary time scales. Without being facetious you have a point and that all the literature comes up with that I have found. It is absolutely reasonable that it's sexual selection. $\endgroup$ – James Aug 26 '15 at 18:41
  • $\begingroup$ @what In this question I am making the case that ancestrally, the closest species to us have no dichotomy of beards between sexes. Humans evolved this dichotomy. I'm pretty sure black populations have bearded males, and less bearded females as well as white populations. Also the cold doesn't explain why or how females lost the facial hair. If anything, that would be a selective pressure to keep facial hair for women. $\endgroup$ – James Sep 8 '15 at 7:46
  • $\begingroup$ @what The idea of chimp vellus facial hair is somewhat interesting. If anything this would complicate things - how has androgenic hair evolved in males, and not in females. $\endgroup$ – James Sep 8 '15 at 7:51

I don't think this is a complete answer, but I know that historically hair, like horse tail has been used as a part of armor, because it is flexible and difficult to cut through (see dragoon helmet picture).

Protection could be one of the primary purposes of facial hair in human males, who are more likely to experience aggression or be hunters.

enter image description here

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