[David Freedman (OP)]

How come during evolution men evolved keeping facial hair and women lost theirs. Fully realising these are generalisations.

[Kryptid]

How come during evolution men evolved keeping facial hair and women lost theirs. Fully realising these are generalisations.

I can only speculate here, but perhaps the beard was a secondary sexual characteristic that was meant to show a man's health and testosterone levels as a sign of fitness to women. If such was the case, it seems to be waning nowadays, as some races have trouble growing thick beards and then there are women who prefer clean-shaven men.

An alternative hypothesis might be that the beard offered some degree of protection in fights between men. I honestly have no idea how plausible that would be, though.

[Halc]

An alternative hypothesis might be that the beard offered some degree of protection in fights between men. I honestly have no idea how plausible that would be, though.

You might have some agreement out there:

Within the context of the AAT, losing facial hair is advantageous for swimming. One of the little talked about huge holes in traditional PAs non-AAT theories is the belief that males played a major role in procuring food. I don't know of any other species where males obtain food to share with females and young. However, there are many species where females obtain food to share and many others where females choose where to graze or otherwise get food. Clearly, males contributing to food gathering appeared late in our evolution and is related to attracting mates and pair bonding. My point is, females spent more time in the water gathering food and their success was critical to the survival of their young, so the loss of facial hair among females is more valuable to the species. On the other hand, males are much more violent than females. Consider that today the number one cause of death among US African-American males age 15 to 30 is other African American males aged 15 to 30. However, homicide is not a significant cause of death for US African-American females. When males fight the target is usually the face. Having a beard protects the face in two ways. It provides a small amount of direct cushioning and (because hair is somewhat slippery) tends to turn many blows into glancing blows. Many of the cuts that occur when shaven man fight are due to the shear forces created when the adversaries hand briefly sticks to the facial skin while the hand is still advancing. The best example of this today is among rugby players. Rugby is a very violent sport in which the participants do not wear helmets or padding. However, beards are very common among rugby players to cut down on their facial injuries. Again, with females doing most of the food gathering and males even having the option of stealing a portion from the females, the advantage of facial armor outweighs the disadvantage of slightly more drag when swimming.

http://aquatic-human-ancestor.org/anatomy/hair.html where AAT=Aquatic Ape Theory

Still, this might argue for fixed length hair (fur) which has the same advantages. Hair that grows to unchecked lengths (as it does on both human male and female heads) must have more advantage than simple deflection of blows.

[evan_au]

men evolved keeping facial hair and women lost theirs

This glosses over the bigger question: Assuming humanity had an ancestor who had hair all over (except the palms of the hands and soles of the feet), why did they lose most of it?
One hypothesis is Halc's mention of AAT=Aquatic Ape Theory

Hair that grows to unchecked lengths

Hair follicles on the head go through the same growth and resting phases as hair on other parts of the body - just on a longer timescale. When the hair follicle goes through this cycle, the hair ends and falls out naturally. This provides a finite length on an individual hair.
https://en.wikipedia.org/wiki/Human_hair_growth#Telogen_phase

I understand that many of those cases where someone has hair extending 3m or more are a result of binding up their hair, so that even the hair which has fallen out is bound up and anchored by the still-growing hair.
https://en.wikipedia.org/wiki/Xie_Qiuping

[Bored chemist]

One hypothesis is Halc's mention of AAT=Aquatic Ape Theory

Other explanations are also available.

[David Freedman (OP)]

I can come as beards being a hangover from an indication of testerone etc levels in attracting a mate. As food gathering, and rearing young there are numerous spieces where gender cooperate in this. Pack animals hunt together etc. Numerous spieces of birds rear there young together. As for beards stopping damage from violence to the face,why stop there. The aquatic ape theory I heard 40 years ago and seems no closer to verification. Interested all the post and tha post that other explanations. Thanks Dave

[Halc]

I can come as beards being a hangover from an indication of testerone etc levels in attracting a mate.

Agree, so long as you remember that the testosterone level is not there to attract a mate, but rather it is the female that is bred to be attracted to the testosterone level.

As food gathering, and rearing young there are numerous spieces where gender cooperate in this.

Yes there are, but you wouldn't know it to read the paragraph I quoted Morgan who says "I don't know of any other species where males obtain food to share with females and young". You name several of the examples that also came immediately to mind to me.

The aquatic ape theory I heard 40 years ago and seems no closer to verification.

Well, the aquatic part is certainly obvious. One has to be blind not to see that. But all the details about hair distribution, social roles, the loss of estrus, etc. remain speculation.