Evolutionary advantage to beards and mustaches

Factual Questions
41

But as I pointed out many mammals do, and a great many primates. That large bright pink gumline and the ability to withdraw the upper lip seen in the gelada is a decorative feature purely intended to accentuate the threat display. And have you never seen a dog or cat raise its hackles? What is that if not a blatant threat display feature?

Well of course they are. When else would an animal make use of features that have evolved to enhance a threat display if not when they are being menacing? It seems that you either want an example of a dog raising its hackles when it isn’t being menacing, or an example of a static display feature like a mane that doesn’t also indicate fitness. IOW your position can never be falsified no matter how many examples I throw at you. When the feature is static like a mane then you say it simply indicates health. When a feature is able to be activated as needed then you say that it is just a menacing activity and that the feature itself doesn’t exist.

Simple question: what eveidence could I provide that would convince you? If the hackles of a dog or the lip of a gelada or the mane of a lion aren’t; evidence then what possible evidence could I produce that mammals have features designed to enhance threats?

That makes no sense at all. If none of those things will deter a mammal seeking a meal then how did any of those things evolve?

I think the point here is that humans don’t just rely the face to display menace. We also shout, posture and so forth. The beard presumably enhances those displays without significantly affecting our passive communication ability.

The problem with this is that you now need to postulate why the other great apes have neither facial nor head hair. Human head and beard hair is very different to the hair on the rest of our bodies and the head and facial hair of the other great apes. By saying that we simply stopped growing hair everywhere else you need to provide some evidence that a hominid ever existed that had the equivalent of head or beard hair all over its body.

The problem is that male HGs didn’t do any more adventuring than women. Indeed because they concentrated on plants and small game women covered far more diverse territory than men, and were more likely to be scratched, stung, bitten by small game and so forth. IOW women had as much or more need for the protection of a beard then men did. Added to that is the age problem. Are you suggesting that young men needed less protection than old men?

42

Given that none of the other great apes have a mane we are forced to assume that our last common ancestor had a hairless face. That goes back several million years at least.

The why do none of the other hominoids have particularly hairy faces today? Here is an orang. Not a particularly hairy face. Here is a gorilla. Not a particualrly hairy face. Here is a chimpanzee. Not a particualrly hairy face. Here Isa bonobo. Not a particularly hairy face.

While some these apes have more hair than people their faces are not particularly hairy. Certainly none of them have hair on their faces that ever approaches the thickness or length of the human beard. In addition they universally have hairless lower lips and chins, the area of first and thickest hair growth in human males. So to answer your question, we are forced to assume that all humans had hairless faces equivalent to that of the other great apes as long as humans existed.

The problem with this is that it’s turtles all the way down. Modern human beards aren’t like ape body hair. They are distinctly longer and thicker than anything found in any other ape. You still haven’t explained why some ancestral population developed this luxurious facial hair in the first place. All you’ve done is said that beards evolve, and then were deselected in females. You still haven’t explained why humans evolved beards in the first place. All you’ve done is come up with an explanation of why they might have disappeared in women after they evolved.

This is like positing that human female shave breasts by starting with a baseless assumption that once all humans had breasts. You are needlessly multiplying entities. Now not only do you need to explain why humans grew beards, you also need to explain why they were lost in females. Ockham’s razor dictates that we reject your theory out of hand unless you can find some evidence of a hominoid population that was universally bearded.

43

You don’t know how many times I have come in from hunting wooly mammoths in the dead of winter and grunted to my wife that I am certainly glad I had my beard to keep my face warm.

My wife invaribly grunts that she is happy that I have it too so she can use it as a blanket at night when the cave gets really cold.

44

I always thought of it as similar to a lion’s mane. It is a sign of sexual maturity - in other words a good sperm donor. I would assume this trait evolved very early on and is something of a relic, which is why many ethnicities are relatively beardless.

Does it have to be anything more than that?

45

As Colibri alreads pointed out, the problem is that women don’t especially find beards attractive, hence the reason why men spend so much time and effort shaving. Sure some women find beards attractive, but as many or more find them unattractive. That contrasts markedly with traits like the mane of a lion, the tail of a peacock or human breast where all members of the opposite sex find the traits attractive.

IOW the trait is very unikely to be used to signal a good mate because if it did then all women would find it attractive, rather than a majority finding it mildly unattractive.

46

You are missing my point. There are plenty of ways that mammals menace competition and predators. Just about all of them are something activated in the time of need.

A beard, because it is a static feature, is essentially useless as a way to menace other humans. They see the beard when you’re angry or defensive or not. Just about every physical feature in nature that is intended to scare opponents has a inactive state. That is pretty much the whole point. I just can’t see any way where a static beard would be an effective tool for scaring other people. Thats all I’m pointing out.

You proposed that modern people being frightened by a jumping rat and a goose spreading it’s wings is evidence of prehistoric man also being frightened by them. I think it’s silly to presume that what scares your local soccer mom has much impact on what would have scared a wild human. I’m pretty certain that a hungry protohuman would have had no trouble ignoring those factors and getting himself a meal.

Rats and dragons and geese evolved those displays to scare off lesser natural predators for which it worked fine. People are probably smart enough to ignore these things and as such are largely immune to superficial displays of threat. If a hungry early man was able to look past that squawking goose to get a meal, it seems reasonable to suppose early man would ignore the hairy beard of that rival tribesman. Especially if he saw that hairy beard on all of his fellow tribesman across the campfire too.

Fair enough, but I’m still skeptical that a beard in any way helps to enhance such a display. Of course the late onset of facial hair works against this argument much like many others.

I think it’s wrong to look to the apes as a indicator. They don’t walk upright and a have score of other differences which are much greater than relative beardedness. They just aren’t close enough ancestors to make the case that we must use their relative facial hairlessness as evidence that we evolved to be bearded from unbeardedness.

It could very well be that modern apes and ourselves have both become relatively less hairy than our ancestors.

It could be that ancient apes evolved to be hairier in the face (while still hairy all over) as a result of learning to walk upright, presuming it puts the face higher into the winds and weather. And that their knuckle walking cousins didn’t.

There’s no reason to believe that there was necessarily a state where early people were totally hairless and grew beards out of the blue. We could have been bearded AND hairy (regardless of what modern apes look like) and evolved to lose all but facial hair.

47

I think that we disagree about what qualifies as a hairy face. I see what you mean in that they do not all look like ZZ Top, but neither are they smoothfaced like a modern human woman. The bonobo comes the closest, and interestingly they also have an estrus cycle that is closest to the human model afaik. Besides which, beard, beard, beard, and her too. All females, btw.

I did not mean to imply that males and females both had heavy beards, which the females then lost. My suggestion is that whatever sex-neutral terminal facial hair was present (and I would argue that it was more than in modern man, although probably not a full beard) on the face became sensitive to sex hormones - along with hair on the back, thighs, and other places (French site). In females, this would result in less facial hair than the baseline in the presence of adequate fertility hormones. In males and those females with some forms of decreased fertility, it would result in heavier facial hair or no change from the baseline. Thus the male beard and the female no-beard developed simultaneously from whatever the precursor semi-beard state was. But the reason that the trait persisted because of its expression in females, not males. As you said, men nearly universally prefer a hairless female face, whereas women don’t universally prefer a hairy male face.
The initial population didn’t need to be universally heavily bearded; just hairier than modern women.

48

Can we please have a reference for this claim? You seem to be employing circular argument. You started arguing that features such as the mane of lions and humans or the hump on Bos indicus bulls are not threat displays because they can never be deactivated, and therefore they must be simply condition indicators. You are now arguing that you know that these things can’t be threat displays because all mammalian threat displays are activated in times of need.

Your argument has become entirely circular. You need to present some evidence to present either your premise or your conclusion, ie either evidence that manes are not threat displays or evidence that all mammalian threat displays can be activated. You can’t use an unsupported premise as evidence for the conclusion, nor can you use an unsupported conclusion as evidence for a premise. That is circular reasoning.

Can you understand why carrying machine gun would scare other people? Do you understand that even if I walk around armed 24/7 I am still more threatening to potential rivals if I am armed with a machinegun? More sensibly do you understand that even if a person is 6’ 5” and weighs 110 kg he is threatening, despite the fact that his size can’t b turned off? If something is menacing it is not perceived as less menacing just because it always exists. There may be advantages in being able to deactivate such displays but I can’t understand the logic that it can’t be effective just because it always exists.

First off we’d better clear up what you mean by a “lesser predator”? You started by saying that mammals in general couldn’t be bluffed. Are you suggesting that foxes or bears can not be bluffed by these displays either?

What is that based on? By what logic would a hungry human be less likely to be bluffed than a hungry bear?

Once again though this is argument form assertion. You argue that mammals can’t be bluffed, which flies in the face of the evidence. Then when the evidence is presented you argue that it doesn’t apply to humans. From that unsupported position you extrapolate that beard can’t have worked either.

Once again, you need some evidence for one of your contentions, either the premises or the conclusion. We know that most other predatory mammals are easily buffed. We know that modern humans are easily bluffed. Can we please have some evidence that humans can’t be bluffed, or that they can’t be bluffed by beards specifically? An argument base don assertion tells us nothing.

So you are proposing that beardlessness in fact evolved three times? That the last common ancestor of hominids and the other hominoidae were bearded, and that our ancestors evolved to become beardless and so did the ancestors of the chimps and gorillas after they split, and that the ancestors of the oranges also became beardless as well after they split from the human line? Once again, Ockham’s razor dictates that we reject this. The simplest explanation that explains the known facts is that the common ancestor was beardless, and that beardedness evolved only in the hominid line.

It could be, but without any evidence you are needlessly multiplying entities. In an attempt to explain why human males have beards you produced a scenario where you now need to explain why the common ancestor had a beard, why humans devloped a thicker beard, why human females lost their beard and why the other great apes lost their beard. With no evidence at all you have solve done problem by producing 4 other equally perplexing problems.

Can I assume that you don’t; subscribe to the idea that Ockham’s razor is a useful tool?

That is possible, but once again you’re needlessly multiplying entities. You are creating entirely speculative scenarios to explain away flaws in an entirely speculative scenario.

If we want to play this game then maybe human males used their beard hair to weave baskets to give to potential mates. It is no more implausible and no more supported by the evidence, but at least it has the advantage that it doesn’t needlessly multiply entities. It explains why human males have beards without needing to explain the other 4 entities that your explanation creates. NB, of course I don’t; believe this, but it highlights the reason why baseless speculation built on baseless speculation is fruitless and should be avoided.

Yes, there is a reason. If all the taxa on earlier-dividing branches of a phylogenetic tree possess a trait, and it is only the taxa on a more recently dividing branch lack that trait, it is assumed the trait is pending evidence contrary. Standard assumption in evolutionary, and once again base don Ockham’s razor. In short you don’t force yourself to assume that a trait evolved two or three times when you could just readily explain the facts by assuming it evolved once.

We could have, but it would be a remarkable coincidence that the same trait evolved three times in three different lineages on two different continents and very different environments and social dynamics. That is far more puzzling and more demanding of an answer than why humans have beards.

49

I never said they had hairless faces, I said they had relatively hairless faces. Relative to the rest of their bodies they have no excess hair on the face. That is in stark contrast to the human beard and something that needs explaining if what you say is correct.

This has now become a Just So story. Not only did the most fertile females happen to develop a trait that made their beards fail to develop (a plausible enough theory although entirely lacking in evidence), but now the male sin the same group happen to develop a related mutation that causes the hair to grow thicker. Why would that happen? What are the odds of the two mutations co-occurring?

You seem to be implying that single mutation simply made facial hair sensitive to generic “sex hormones”. How could that be? What single mutation could possibly make something sensitive to both androgens and oestrogens but in opposing effects?

Once again you have multiplied entities and produced needless questions. You have explained that the male beard grew thicker because a mutation happened to occur that caused beard growth to respond to androgens. That is sufficient. The added entity that females were once bearded and also developed a secondary mutation that caused the beard to fail to develop requires at leats two other explanations for no reason.

But you haven’t even explained how the trait could arise. You have presented one possible entirely speculative reason why females might become less hairy, but in no way have you explained why males would become more hairy. Your entire hypotheses seems to rely on the idea that single mutation can make a trait sensitive to both androgens and oestrogens but in diametrically opposed effects. Is that possible? Has it ever occurred anywhere else? Can you present evidence of this? If not then you have once again multiplied entities. Now we need to explain how this freak mutation managed to occur, or how two opposed mutations co-occurred without actually coming any closer to solving the original problem than “a mutation made me grow thicker facial hair”.

50

Do we have reason to think that the same preferences prevailed among human females back when beards evolved, though? After all, there have been plenty of societies where it was standard for men to wear full beards and shaving was unknown.

I guess the question is: Can there be a human sexual preference innate enough to encourage the evolution of a physical trait specifically for sexual selection, but simultaneously weak enough to be overridden at a later evolutionary stage by changing cultural trends?

If so, then female attraction to beards might be one such preference. Maybe women were instinctively attracted to male hirsuteness, but not all that strongly: strongly enough to encourage the initial development of male facial hair, but weakly enough to permit the development of individual preferences for or against facial hair once male facial hair depilation became widespread for non-sexual reasons (i.e., to deprive foes of a convenient handhold in battle).

51

I think the challenge here would be showing that anything is being overridden at all. I think that most women just don’t like beards very much. It’s not that society tells them not to like beards, they innately don’t like beards. Indeed it seems that female dislike has been one of the main reasons why men have shaved in many societies.

Contrast that with other sexual features such as breasts or genitalia that, at various times and places, have been covered up and disguised for cultural reasons. In those cases teh sexual attarction never diminished, if any thing the basence of the stimulus nmade them more attractive. Cultural trends may have removed those things fom view but they nevertheless remained attractive to a large proportion of the population, indicating the attraction was innate.

IOW I’d have to see some evidence that women find facial hair unattractive or neutral for social reasons. All the evidence suggests that they find it unattractive or neutral simply because of personal choice/preference. After all in the modern USA men can wear beards or not as they choose with no social consequence, and that has been the case since at least the mid 19th century when big beards went out of fashion. Yet women today still don’t find beards anything like universally attractive as you might expect in the absence of social pressure, suggetsing that any evolutionary preference for beards is undetectable.

52

You’ve obviously never seen me naked.

53

Does it? Do you have a cite for that? AFAIK, shaving came into widespread use among the Greeks and Romans as part of military discipline, and then became culturally preferred as a badge of civilization and a distinguishing mark from the “barbarians”. Aspiring “barbarians” in the classical orbit then imitated the practice of shaving as a mark of social standing, and so the custom spread. I’m not sure we can conclude that female sexual preference for clean-shaven males is innate rather than primarily influenced by cultural mores. (The fact that beards go in and out of fashion in different eras and societies suggests that cultural trends at least strongly influence their appeal to women.)

Similarly with short head hair on males. Many women in modern societies do prefer men with short hair, but if long head hair evolved as a sexual selection trait, clearly there must have originally been some general tendency of female attraction to long hair on males.

Are we sure about this, though? Is there really zero social stigma against beards at present? Some schools and workplaces still have dress codes prohibiting facial hair, most notably in the military (except where beards are mandated by the serviceman’s religion). I’m not sure it’s accurate to claim that we’ve really got a level playing field nowadays when it comes to the cultural acceptance of beards.

54

Well of course I don’t have a cite that shaving started to appeal to women, nobody wrote that sort of thing down 6000 years ago. Note however that shaving was widespread among the Egyptians some thousands of years before the Romans even existed, so defintitely didn’t start in Rome.

Not necessarily. I know of no HG societies where men have long hair, they all cut or burn their hair to keep it trimmed. It may well be that men have short hair simply because women have long hair, and sexual attraction to long hair in women is near universal. IOW the trait evolved because it favours females with the trait, while men got it simply because there is no penatly against it. Its nuisance value or lack of attaction to females seems to have dicated that all but the wealthiest men have always worn short hair when given the choice.

We haven’t got a level playing field WRT to anything, and we never have. That applies to clothing, height wealth, artistic ability, intelligence or any other trait you can name that we assuem has sexual attraction value. If we carry this argument through we have to proclaim that nothing has sexual attraction value. After all strong men aren’t favoured in all positions, nor are smart men, or wealthy men or artistic men and so forth.

What we have to do is look at the preponderance of evidence. To put a figure on it we will say that 95% of the time having a beard makes absolutely no difference to a person’s social status in this society. In term sof welath, occupation etc. I doubt that you could find a statistical difefrence between bearded and unbearded men. That should mean that if beards are a sexual attractant then at least 98% of women should fine beards attractive, the rest being dissuaded by that 5% difference in other fields. They don’t.

Let me draw this comparison: being left handed has no significant impact on social status. Yes there are rare sitautions where being left handed may be a negative but they are trivial, on par with being bearded. Yet we don’t start presupposing that being left handed is attarctive absent any evdience just because of an insignificant social bias against left handers. What we say is that there is no reason to believe the trait is inherently attractive.

Basically if the penalty for having a trait is minimal, yet the incidence of people with an attraction to the trait is also minmal the logical conclusion is that the trait isn’t inherently attractive.

55

Yes, but it seems to have been part of a fashion for total depilation of body hair by both sexes, originating with upper classes and spreading as a social status symbol. Face-shaving and hair-cutting as a specifically masculine custom seems to have become widespread as part of military culture in classical antiquity.

:confused: How about various American Indian societies where long flowing hair, clubbed or braided, was standard for males?

But where does that 95% figure come from? I’m not convinced that social prejudice against beards is really that minimal.

I mean, your arguments would be convincing if the factual assertions you make are true, but so far you don’t seem to have much evidence to back them up.

I’m not saying that there necessarily is an innate (albeit weak) female attraction to facial hair, just that I don’t think we can conclude definitively that there isn’t one based on what we know about fashions in personal grooming in historical and modern societies.

56

:dubious: So you are asying that it wasn’t shaving, or that somehow it doesn’t count because both sexes eliminated excess hair? By this standard modern societies don’t shave either. The point is that men were removing their facial hair for the purposes of fashion.

Well, no. As I pointed out I know of no HG societies where the males have long hair and I can name several that shaved and plenty more that kept thier haoir trimmed. That certainly indicates that the trait was established long before any miltary culture ever existed.

Can you name an American Indian HG group that grew long hair? I would be genuinely interested to see evidence of this.

I made it up. I thought that was clear. But let’s hear how much you think having a beard would cost a person sociually. One way to presicely define this might be to give us your thoughts on lost income, which in a capitalist society would be the best test of social penalty.

Let’s assume that people with beards suffer even a 75% social penalty, which frankly I think is ridiculous. The idea that people with beards are frowned upon to the extent of not getting 1/4 of the jobs they apply for, not getting invited to 1/4 of parties and so forth. That still means we should expect a majority of women to find beards attarctive, which isn’t the case. A majority of women at best find beards to be neutral even after a century of minimal social penalty.

Which claims have I made that you ewant to see evdience for? You only need to ask.

But this is nothing but an argument from ignorance. You admit we have no evidence but suggest we should entertain the idea just because it can’t be disproved. That’s hardly logical. A better question is why we shouldn’t simply dismiss it out of hand given the total lack of any sort of evidence and the evidence against it in terms of any sort of universal attarction to beards?

Why is this argument any different to me arguing that there is a subverted sexual attraction of women towards short men, and that only social pressure prevents all women from finding short men attractive? It makes about as much sense and has about as much evidence to support it. And why stop their, why not posit attraction to black me, or poor men, or illiterate men or any of million other traits that we know most women don’t find attaractive but which carry social penalties?

57

What do you mean, ‘excess’ hair? Humans are >90% haircovered. Women and children have the same number of hair follices on their faces as men, and probably the same number as the rest of the great apes. That hair can be terminal hair (coarse) or villous hair (peach fuzz). The way that you change patterns of terminal hair growth is to alter the sensitivity of the follicles to various stimuli.

Of course it’s a Just So story. I believe that I’ve mentioned that already. All of these explanations are Just So stories. Again, this is a variety of Just So story that fits the facts but comes at things from a different angle- looking at female no-beardism as the evolved trait, rather than male beardism. What makes all of these Just So stories is that we don’t have time machines and can’t really get data on hair growth patterns from hominid fossils, nor can we ask Lucy whether she thought beards were sexy.

Facial hair is directly sensitive to androgens. It is only sensitive to estrogens insofar as elevated circulating estrogen levels induce the production of a protein that binds up androgens (and estrogens) and make them unavailable. Women produce enough innate androgens that they would grow terminal facial hair if not for that binding effect. When their estrogen levels fall, the binding protein levels fall and androgen effects are unmasked (see menopause). The sex hormone binding globulin (SHBG) has other effects in the body - I didn’t make it up as a ‘beard controlling’ protein for the purposes of argument.

Thus the only ‘mutation’ needed to get beards in men and non-beards in women is to make facial hair differentiation from villous to terminal hair sensitive to some arbitrarily selected level of androgens. The hair is already there; the underlying mechanism of villous vs terminal hair is already there; just the control switch is altered. There is no second mutation. I do not claim that ancestral human females were hairier than modern great apes. Females and males could have been hairy in the face in the same way that orangs, gorillas, bonobos, and chimps are. The testosterone-sensitivity mutation leads to moustaches and heavier beards in men and smoother faces in women simultaneously.

And it wasn’t that the ‘most fertile females’ developed the trait; it was that the trait served as a proxy indicator for fertility. If a female has the trait and is fertile, she has a smooth face. If she doesn’t have the trait, she has a hairy face. If she has the trait and an endocrine problem, she has a hairy face: perhaps hairier than baseline, perhaps not, but hairier than the fertile one. The males inherit the mutation(s) from their mothers. If the mutation was to just turn off all terminal hair development on the face, men and women would both be smoothfaced, and there might be some advantage to that (fewer fleas?) but it would be less likely for that trait to spread through the population to the same extent as hormone-controlled female smoothfacedness.

I anticipate that you will argue that no ape has meter-long facial hair, so you can’t get long beards from the relatively short terminal facial hairs of apes. But the length that a hair can grow to is a different issue. If pressed, I will argue that men can have long beards so that women can have long scalp hair - a tweak to the system that controls hair length by limiting the time a given follicle can actively produce hair before going dormant and starting over. After all, societies in which men can grow loooong beards also have women who can grow loooooong scalp hair. My wife, bless her Mediterranean ancestry, has some long villous hairs in her ‘sideburn’ area, but you wouldn’t call them ‘beard’ hairs.

No, as above.

Males became hairier as part of the same process that made females less hairy. The fact that males got beards out of the deal is incidental and not selected for, which is why not all men alive today can grow luxurious beards. But bearded women are rare enough that people will pay money to see them.

I agree with you on this. And men today find smooth-faced women well-nigh universally attractive, suggesting that there is an evolutionary preference.

58

Sure: the Salish, Crow, and Mojave, just to name three. As the link notes,

If the idea can’t be disproved, then we should definitely acknowledge it as a possibility. That’s certainly more logical than deciding that the idea can be definitively dismissed just because we can’t prove it.

59

Dude, I’m exhausted with this pedantic argument. But the answer to this question should be easily apparent. People are smart. Therefore, yes, a person is less likely to be bluffed than a bear or whatever. I’m of the opinion (and it’s just that, an opinion so pardon me if I don’t have a citation) that comparing geese and bulls and bears and rats reactions to those of people is inherently flawed because people can reason.

And because people can reason…

This hypothetical is pretty pointless as a comparison because being very large or carrying as weapon actually makes you more dangerous and a reasoning human is able to put two-and-two together.

A beard doesn’t make you more dangerous and therefore, in my opinion, an intelligent human wouldn’t be effectively threatened by it.

If you don’t like that idea, fine, but I’m sick of your parsing my comments for little holes in my logic since I’m merely speculating like everyone else. All the other points are completely off topic from the OP.

60

I already explained this. The hair in the beard is no more dense than the hair anywhere else on the body. In contrast the human bear is notably more dense than hair elsewhere on the body, and for that matter denser than the hair of other apes.

Well, no. If there is some sort of reasoning or logic or falsifiability behind an explanation then it becomes an actual hypothesis, rather than an attempt to explain something away by invoking multiple entities.

No, it isn’t. As you already noted we need two mutations: one that make s facial hair sensitive to androgens for no apparent reasons. That then has to be either followed or preceded by a second mutation that produces a protein that binds up androgens. Those are two distinct processes: one that makes the hairs sensitive to androgens, and one that stops them being sensitive to androgens. If an individual woman evolved hair that produced the androgen binding protein before she had evolved facial hair sensitive to androgen then it would be an unexpressed mutation, hence no selective pressure. But if a woman evolved the androgen binding protein for other causes first (as I suspect you are arguing), and then later evolved facial hair sensitive to androgens she would never have developed facial hair because she would never have had circulating androgens.

In short you are back at your starting point. Your hypothesis makes no sense because if women always had the androgen absorbing protein being expressed then no fertile woman would ever have expressed facial hair. The only women who would ever have displayed increased facial hair are those who were infertile. IOW the mutation would actually reduce mate selection and reduce reproductive fitness in any woman carrying the mutation. As such the mutation would rapidly be weeded out and never get passed on.

This is the flaw in the hypothesis you are running. It relies on the fact that the first women with this trait women are carrying a mutation that only ever gets expressed to advertise their lack of fitness. If we assume the ancestral woman has beard hair of density X. Then this woman evolves beard hair sensitive to androgens. She will still produce beard hair of density X because that is the default condition, i.e. it is the condition that exists in all men, women and children regardless of androgen levels. It is hair that is not a secondary sexual characteristic. Only if the woman is infertile will the androgen levels cause beard hair to increase to density X+1. IOW the trait only becomes expressed when the woman is advertising her own lack of fitness. Such a trait can’t get passed on.

As such the trait of having androgen sensitive facial hair gives no benefit at all and presents a massive evolutionary liability.

No, it doesn’t. Think about it for a second. Imagine if we genetically engineered a chimpanzee troupe to produce a patch of testosterone sensitive hair on the backs of their hands.

The fertile female chimps won’t produce any less hair on their hands just because the hair is now testosterone sensitive. They will produce exactly the same amount they always did because they have a protein that absorbs most testosterone in circulation. So fertile female chimp hands will look exactly like they always did: ie indistinguishable from the hands of pre-pubescent chimps.

However the infertile female chimps will produce more hair on their hands. Only in these infertile chimps will the gene ever be expressed. As such any female carrying the gene only gets two possible outcomes: non-expression if she is fertile, or expression as an advertisement of infertility. Since a non-expressed gene can’t be selected for the only possible selective pressure is negative.

This seems patently untrue. American Indians for example are famous for being beardless, yet the women almost universally cultivated long scalp hair.