Humans are generally furless, apart from the what grows on our craniums.
Adult males also grow fachial hair on our jaws, cheeks, and mouth.
What purpose dos that serve our species?
I suspect that the primary purpose is sexual differentiation. A species will do better if the members of the species can easily tell male from female. There may or may not be a reason that it’s facial hair, specifically, or that it’s males specifically who have it.
Must be the differentiation thing. If there were a functional advantage, men and women would all have their mouths in the middle of their scalps. You know, it’s not all that neat a design.
There are various speculations, but no definite answer. My own best guess is that they evolved as a behavioral signal used in competitive conflicts with other males, serving to making an individual look larger, fiercer, and more intimidating. They may thus be similar to the mane of male lions. The moustache may also to some extent serve to disguise the mouth and conceal emotional state, which could be of benefit in inter-male conflict.
While it is possible they also may be a sexual signal to females, one would suppose in this case that beards and moustaches would be innately appealing to most women. I think this is far from the case. Many women prefer a clean-shaven male. It’s unlikely that men would spend so much time and effort shaving if beards were generally attractive to women. (And yes, I acknowledge that cultural norms may have something to do with this. However, if beards really had evolved as an attraction to females I don’t think that being clean-shaven would be so widespread culturally.)
This is in contrast to another human secondary sexual feature, enlarged breasts in the female, which is probably a female-to-male sexual signal. Enlarged breasts (breasts larger than those of males) appear to be pretty much innately attractive to heterosexual human males. (Of course, there are some cultural influences here too, but I think this preference is far far more general than attraction of females to beards.) While breasts also have a utilitarian function in lactation, it is unnecessary for them to be enlarged all the time for this. In other apes, such as chimps, gorillas, and orangs, females do not maintain enlarged breasts when they are not lactating.
None. Every trait does not need to have an evolutionary advantage or disadvantage.
Is this a guess?
This is a non-answer. While every trait doesn’t necessarily have an advantage, such advantages can frequently be identified; and even if the trait is neutral or disadvantageous it may be linked to another trait that is advantageous.
Given how hairy some of our closest relatives in the animal kingdom are, I wonder if you aren’t looking at it backwards. Maybe the question is why we have so little hair elsewhere on our bodies, or why women have less facial/body hair than men?
In my opinion, the best hypothesis is that humans are adapted to be endurance runners. Hairlessness, together with profuse sweat glands, are adaptations connected to the need to shed heat while engaging in long-distance running under tropical conditions. Head hair could be a defense against overheating the most vulnerable part of the body, the brain, which is most exposed to sun. (On the other hand, it could be just ornamental.)
The relative hairiness of males and females would appear to counter this, since males would probably have done more endurance running. However, this may simply be a correlate of males having more testosterone, and testosterone’s role in promoting hair growth. The primary selection for hairlessness may have been on human males; females have less body hair because the have less testosterone, not because there was direct selection that they be less hairy than males.
You may be looking at the question backwards. Anywhere that men have testosterone-sensitive hair, women do to. Maybe humans have hormone-sensitive hair on their faces so that men can judge the potential fertility of women. Men have facial hair for the same reason we have nipples; not for our ‘needs’, but for the ‘needs’ of women (in this case, to signal fertility to men).
The ability to grow heavy facial hair is not uniform across all racial/ethnic groups. The women of one group may be more hirsute than the men of another group. Once you start trying to explain every feature of every group in terms of unique evolutionary advantage, you degenerate into ‘just-so’ stories.
What kind of correlation are you proposing between female testosterone levels and fertility?
How about something as simple as keeping the face warm during hunting expeditions?
Early humans evolved in equatorial Africa. That’s probably not it.
I can’t predict a woman’s fertility based only on an isolated testosterone level. Things are more complex than that, and I’m not an endocrinologist. However, hirsutism (the presence of coarse terminal hairs in androgen-dependent areas on the face and body in women) is frequently a sign of an underlying hormonal state that is not optimal for fertility.
Consider that peri- and postmenopausal women often report increased facial hair growth. As their estrogen and Sex Hormone Binding Globulin (SHBG) levels fall, effective androgen levels rise because less androgen is bound by SHBG.
Also consider polycystic ovary syndrome , the most common endocrinopathy in women, in which the abnormal ovary is the source of excess androgens. PCOS is a major cause of female infertility, and is implicated in up to 80% of cases of female hirsutism/hyperandrogenism.
And please think of my post above as having been edited to say “Anywhere that men have testosterone-sensitive hair, women do too.”
It only is nowadays, when barefaced boytoys are the screen idols of today; think Brad Pitt (go ahead, I don’t plan to). That trend is fairly recent, as is the trend for men to shave most evidence of puberty (including chest hair) off themselves. I don’t think you necessarily find that many clean-shaven faces in every nation, however. And some of us still like their men fuzzy. I’ve always been partial to moustaches on fellows, myself.
Did humans with facial hair have a better chance of reproducing more offspring than those without? Does facial hair indicate superior health?
It’s the same questions one might ask about the peacocks huge-ass tail. It’s actually a hinderence, but for some reason pea-hens like the aethetics of it.
Maybe facial hair just made us look scarier to predators? My GF thinks I look pretty scary when I don’t shave all weekend.
I’d just like to mention an important point that everyone seems to be neglecting: not all humans males have beards. It varies a lot from group to group, and amongst many east Asians, American Indians and some Indidgenous Australians beard growth is minimal or lacking. Beard growth also appears to have been very sparse amongst the Khoi type people of Africa, although interbreeding has obscured the trait.
Since this is the case it might well be that humans originally didn’t have beards, and that it is a trait that has evolved in only a single branch of humanity. The alternative is that the trait of beardlessness has evolved multiple times in populations after they left Africa. Either way any explanation of why people have beards is going to have to cope with the fact that the trait is far from universal.
Any explanation also has to deal with the fact that even in predominantly bearded populstions beard development varies, with many men not developing anything more than a goatee until they are on their late 20s or early 30s. That would seem to put the kibosh on ideas of beard as a dominance display or mating attractant since so many men don’t develop a beard until after what would presumably be the peak aggressive and reproductive ages.
The most convincing explanation I’ve heard is that a beard simply serves to disguise age. By covering facial lines a beard makes it much harder to effectively judge age. That makes it much harder for an opponent to guage a potential weakness in older men. This seems to explain why beard growth is confined primarily to the face where the signs of aging are clearest, and why beard growth typically increases with age. Of course the flaw with this theory woudl seem to be that the presence of a beard might be considered a sign of age in itself, however if it makes it difficult to distinguish a 30 year old from a 50 year old the advantage to the 50 year old would seem obvious.
Women of course would not have any incentive to grow beards if they only develop with age since any sign of aging tends to be a reproductive negative for women, even if their exact age can not be determined.
I’m not sure I’m getting what you are proposing. Humans in general have facial hair so that men can tell that women with an abnormal amount of testosterone are relatively infertile?
The clean-shaven look goes back to the Romans at least.
As I noted above, I don’t deny cultural influences affect whether beards are perceived as attractive by women. However, it seems to me that this attractiveness is not nearly so innate as, say, the attractiveness of female breasts to men. Therefore I don’t think its primary function is as male-to-female sexual signal.
Some good points. However, most sub-Saharan populations aside from the Khoi are bearded, so it’s not really clear what the ancestral condition might have been. But yeah, the wide variance in degree of beardedness globally does present a problem for any general explanation.
Another objection to this is that male pattern baldness is most prevalent in one of the most heavily bearded populations, that is, Europeans. The advantage of a beard to a 50-year old in disguising age would largely be nullified if he is also going bald.
*In this vale
Of toil and sin
Your head grows bald
But not your chin
Burma Shave
*