Readers reply As you get older everything gets hairier and closer to the ground. If we lived long enough we’d end up as a shagpile carpet. Lafferty I think the question misunderstands evolution a little bit. Not every human trait confers evolutionary advantage. Some traits are just the byproduct of something, such as excess testosterone in the case of hair. IngridCZ Probably sexual selection, hairy men being preferred as sexual partners by women and/or less hairy women being preferred by men. One theory is that’s it’s easier to judge the health of a potential partner when the skin is visible. Blemishes, skin disease, rashes, etc, are signs of bad health and therefore a less desirable partner for reproduction. So a visibly smooth, even skin is an attractive quality in a partner, and people got less hairy. For men, this would be counterbalanced by testosterone promoting body hair growth and other qualities that increase chances of reproduction, such as body strength, so men ended up hairier than women. Llorona What I was taught when I was younger was that body hair, especially pubic hair, is meant to function as a kind of launch pad for pheromones. Maybe pheromones are more important for men than they are for women. Simother My thought is that it is easier to bond with a new born child who can touch the mother’s skin without an insulating “fur” in between. Also, hairless people seem younger, and younger women are on average more fertile. Henna Kahra, Uppsala As is often a sexist given, the question is asked from the perspective of the male as being the norm. It should actually read: “What evolutionary advantage is there to a male having more body hair than a female?” Elaine Sporko The body hair genes are probably a hangover from Homo sapiens sapiens interbreeding with H sapiens neanderthalis. Modern human genes involved in making keratin, a protein constituent of skin, hair, and nails, contain high levels of genetic introgression (when genes are reinforced by frequent back crossing). For example, the genes of approximately 66% of east Asians contain a POUF23L variant introgressed from neanderthals, while 70% of Europeans possess an introgressed allele of BNC2. Neanderthal variants affect the risk of developing several diseases, including lupus, biliary cirrhosis, Crohn’s disease, type 2 diabetes, and Sars-CoV-2. Palaeontologists have long pointed to the Middle East, southern Europe and the Indian subcontinent as the areas most likely to have been co-inhabited by both kinds of human. Coincidentally, these are the regions where male body hair as a secondary sexual characteristic is more commonly expressed. Hippaferalkus A trait that consumes resources, like growing a beard or, in other animals, manes or horns, would be a disadvantage if there were not some compensating evolutionary advantage. The evolutionary pressure would be to change the visible response to the presence of a hormone if there was a net balance of disadvantage in expression. There is nothing unusual about sexual dimorphism in many species. There’s a general idea that the most spectacular differences are about proving fitness to survive and potentially breed despite an obvious disadvantage of being more visible to predators, or devoting energy to features or behaviours that have no obvious useful function, such as plumes, tail streamers or displays in many birds. Selection for the most extreme examples of dimorphism is about being preferred as mates and those genes being passed on. leadballoon Certainly – at least in certain parts of east London, anyway – possession of an particularly extravagant and fulsome beard is a strong indicator that the owner professionally makes a really good cup of coffee or has direct access to craft beers – both surely strong mating advantages to a modern urban homo sapien? HaveYouFedTheFish I’m far from an expert, but I once read something about sexual preferences in relation to birds once, talking about the tail length preferred by females, but I see no reason it shouldn’t apply to human hairiness. The gist was that some birds of that species preferred longer tails and some shorter tails. If a female bird chooses a mate with a longer tail, that means that the children have an increased chance of both having a longer tail and also of inheriting the preference itself for longer tails. The result of this is that all it takes is, say, 55% of birds preferring longer tails and, over time, their offspring will outnumber those who prefer shorter tails. This doesn’t work if the longer tail provides an evolutionary disadvantage, because of course then they would be less likely to survive to reproduce. But where no evolutionary advantage or disadvantage exists, it really is as simple as preferences being to an extent hereditary. In fact, these birds now exist at an evolutionary point where their tails are the longest they can possibly be before the bird loses the ability to fly. Logically, therefore, all it would take is a few more women to prefer less hairy men than hairy men, and over time that would translate to a preference of the majority. The point being that sexual selection doesn’t always have to relate to evolution – where a characteristic has no impact on survival or reproduction. It really can be as simple as a personal preference being inherited from one’s parents and passed on to one’s offspring. Barattin Less body hair aids balance when naked in a wind tunnel due to less wind resistance. Literally everyone knows that. zblargx Women with beards for babies to pull at might well be inclined to cut their breastfeeding shorter. rosiecyp What I really want to understand is what evolutionary advantage comes from the acceleration in hair growth from my nose and ears in my 50s, 15 years after going bald! DewinDwl Less hair means fewer parasites/fleas/ticks, lower risk of vector-related bacterial, viral or parasitic disease, which is probably an advantage for a nursing mother and her child in a cave. More hair, better insulation, higher tolerance to cold, which is probably an advantage for a hunter-gatherer. I think that at the time, men spent more time out of the cave looking for food. Also, male animal species are generally more flamboyant, so a magnificent hair display may make a more attractive mate for a female, as it could be a sign of higher testosterone levels, strength and dominance. One of the things I can not understand is if there is indeed any evolutionary advantage of being shortsighted (not being able to see clearly for distance without glasses). An entertaining explanation would be that shortsighted males were not able to out to hunt and therefore had to stay in the cave helping out with domestic issues, as well as having more opportunities to procreate and therefore having an advantage on passing on their genes over the alpha male of the group, who was out hunting! Petros Aristodemou Women have a thicker layer of adipose tissue as it provides extra energy storage that they need for reproductive function. Men’s thinner adipose layer means they lose more heat. The extra body hair compensates somewhat for this. Alan Martin Most traits do not offer an advantage per se, but don’t confer a disadvantage. Humans relative hairlessness may have been the byproduct of, say walking upright. Or a larger brain. However we got like this, it has not affected our ability to reproduce or to adapt to all climate on earth. Hence, it persists. Pseudaletia Turn the question around – why do men have more hair than women? Hair by itself likely confers no evolutionary advantage, it’s not an adaptation. Nor does it have an evolutionary cost. But it probably correlates with something that is adaptive – testosterone levels perhaps? Female choice for whatever it correlates with has exerted selection pressure over millennia, resulting in greater male hair. Or it correlates with something that gives men a competitive advantage – again, perhaps testosterone. Blackcappedchickadee Elaine Morgan hypothesised a period in evolutionary history in which people did a lot of their hunting and gathering in and near the water. She offered the possibility that there was a gender divide in the types of hunting and gathering that people did then, with women doing more of the water-based stuff. Hence a thicker layer of all-over body fat and less hair (for streamlining). I’m in no position to judge on the details but her theory overall seems to have some decent grounding, although it’s not currently fashionable. BrianO_Blivion Some more Elaine Morgan points: other mammals who have similarly less body hair and more fat layer are elephants, walrus, seals, who are accepted as having had periods of evolution in or at the edge of the sea. In these aqua mammals the pattern of body hair grows following the flow of water when swimming. Human breasts are extra fatty (rounded), nothing to do with sexual attraction, which is a western oddity, but to be more easily grabbed by infants when slippery and wet. The aqua mammals all have midwife attendance at births. Elaine Morgan is indeed brilliant. ShanMorgain Evolutionary biologists have identified many problems with many of Morgan’s hypotheses and arguments. Her work is superficially appealing, but does not stand up to scrutiny and has been largely dismissed by experts. littlepump Body hair helps us manage the skin biome, the population of good bacteria, viruses and fungi that inhabits our surfaces. Thus it is not just a visual sexual signal, as most of the comments here address, rather it has function. A survey of male hospital doctors found that those who created an open wound on their faces by daily shaving carried significantly more infection on their faces than their bearded colleagues. Dirkum Reading these comments I think there is a common misconception that evolution is linear and agenda-driven, as if we are heading toward a perfect solution. But evolution is merely imperfect genetic reproduction – mutation. Whether those mutations offer an advantage is decided by environment. There may well be earlier iterations of a species that died out that would now be dominant. In regard to female hair being driven by anything more than a by-product of hormones – I’d be surprised. There are men with less hair than women. Races with less hair than others. The environment decides and we make our micro selections from what’s on offer. That becomes our culture. And providing our cultural preferences don’t endanger our wellbeing we survive another round to pass it on. theoliverwall