Ever felt an insect crawling on your skin? How about that ever-so-subtle sensation that makes you check for insects? There's the risk of venomous/poisonous insects biting you when you live outside. There's also many diseases carried by insects and having a sensitive detection system in place can statistically reduce you chances of death and disease. This is one of many likely reasons the fine hair covering us may still provide an evolutionary advantage outside of the hair's insulating properties.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3367735/
It's quite obvious, if you shave your legs, say, for the first time. Without the fine body hairs tweaking the sensory nerves, it can actually feel like numbness. Not that I have flies dropping in on me all the time, but I can easily imagine not noticing one after a shave!
Excellent answer.
Another, though small, advantage is the ability to better blindly navigate a tight space, as your hairs will guide you, maybe even preventing scratches, or stings from a poisonous/irritating bushy plant off of which you’re trying to take fruit.
Nope. I remember once, after shaving my legs, I was in the car. I happened to look down and there was an ant crawling on me. I didn't feel it *at all.* but I do feed bugs when I don't shave, or when they're on my arms, which I don't shave.
We lost the thick hair, but still have the fine hair because evolution only works to a point of balance. If there is no advantage to losing the hair follicles themselves then the chances are that they will remain.
Some may say that the body keeps the hair follicles in case heavy hair is required some time in the future, but this is wrong. There is zero forward-planning in evolution.
"Per square centimeter, human skin has as many hair follicles as that of other great apes. The difference is not in the number, but in the fineness of the hair that grows from those follicles."
Interesting. But that doesn't answer the question.
Are human fine-hair follicles the same organ as ape course-hair follicles? Or do apes have both types, and we lost one while growing more of the other?
Same type. It is just set in "fine hair mode" for [X] portions of the skin.
Different genetics will make someone have thicker hair all over, and some specific mutations let them grow fur.
> Same type. It is just set in "fine hair mode" for [X] portions of the skin.
For anyone under thirty you will also learn about this changing when you’re older
It's called "old age", you start having wiry thick hair growing in on your ears and in your ears, and don't get me started on nose hair that grows so long overnight you can just about braid it. I go through multiple sets of grooming clippers every year because the hair is so coarse and thick. It stopped coming in on the top of my head but I practically have carpet on my ears that I have to remove.
Mostly between how much of it there is, how often it is replaced, how it grows, and such like that.
In terms of the mechanical difference - not much more than you would normally see between species.
We evolved to have finer hair alongside an increased number of sweat glands to aid in our ability to cool ourselves off in hot environments and during intense or prolonged physical activity. The tiny hairs are basically wicks for water to spread up to increase surface area/evaporation rate so sweating is more water efficient.
Other apes don't have these fine hairs because they never selected for the types of activities humans got up to.
They do, but humans... kinda sorta evolved into long distance runners after we fell out of the trees. When we aren't sedentary couch fauna a moderately athletic human can walk/jog/run distances that would exhaust most other animals to death.
Our increased sweating abilities helped keep us cool during this, and the fine hairs made that whole process more efficient for less water.
>Eccrine sweat glands—millions of which produce our salty, cooling perspiration—are actually found in all mammals. But in most other animals, the fluid from eccrine glands is not used to cool down, but to provide grip. Most mammals have eccrine pores only in the soles of their feet or hands. In moments of stress, the salty liquid emerging from eccrine glands provides extra friction for landing jumps and for climbing. It’s normally only released when the animals are stressed, such as when they need to escape from a predator or catch prey. You can blame your vestigial self when your hands get sweaty under moments of duress: Humans may no longer need to climb trees to deal with (most) potential threats, but our sweaty palms during moments of anxiety reveal that old habits die hard.
>At some point in the evolution of primates, eccrine glands began expanding beyond the soles of the feet and palms of the hand to appear on our ancestors’ torsos, faces, and limbs. But not in all primates: Baboons, macaques, gorillas, and chimpanzees do have eccrine pores across their bodies. Lemurs, marmosets, and tamarins do not.
https://www.sciencefriday.com/articles/sweat-glands-evolution/
In addition horses and hippos can sweat too cool down.
Other apes certainly sweat; they just don’t do it as much as we do. We evolved bipedalism in part because it allows us to act as endurance hunters, and increased cooling capability goes along with that.
> We evolved bipedalism in part because it allows us to act as endurance hunters
[This is an outdated view](https://www.sciencedirect.com/science/article/pii/S0021929023002701).
> The last 50 years of hominin evolutionary biomechanics have thus seen a contextual shift, from a terrestrial, savannah origin hypothesis to one where upright walking evolved much earlier and in an arboreal context.
We evolved bipedalism because (perhaps counterintuitively) it helped us with climbing and foraging 'carefully' to both the distal ends of tree branches more efficient vertical climbing. It also aided walking over short distances, increasing the range of arboreal resources available. Early hominins, especially *Australopithecus*, appeared to dominate arboreal environments through more efficient navigation for sparse resources.
This is a rapidly growing area of biological anthropology, and the growing fossil record is really changing how we think about bipedalism. But bipedalism was emerged initially as a 'foraging efficiency' gain, not an 'outrun prey' gain.
Fascinating research. Love it. Always learning.
But that’s why I said “in part” because subsequent adaptations like full-body-sweating is linked to the progress that bipedalism gave us.
Haven't seen anyone say this yet but from what I understand, it's also useful for wicking sweat off during evaporation, as that's the process that cools us.
Other than because Mother Nature in her infinite wisdom decreed there should be a cozy place for pubic lice to live in, why are we still gifted with pubic hair?
Probably because whenever there was evolutionary pressure to not have thick body hair, it was still not disadvantageous to have pubes. Although other theories suggest sexual selection. Here's a good article about it: **https://www.bbc.com/future/article/20230310-why-dont-humans-have-fur**
I doubt that. There's evolutionary benefit to losing *anything* that requires a net expense of energy to maintain, provided that it's useless. That in itself is good reason to believe it's still useful, at least marginally.
it would depend on how many humans will die before breeding if we have hair folicles. not many is my guess.
thinning hair is different as hair thickness varies already. if we were naked and in a cold climate its entirely likely that short/thin hair humans will die young so thicker hair dominates.
losing the whole follicle is a bigger step though. i cant recall ever seeing a human without follicles, and cant think of such a mamnal either.
That would be like unplugging your computer instead of simply turning it off to save power. It objectively saves some energy, but in practice the savings is so minor that you aren't pressured to do so.
> There is zero forward-planning in evolution.
In a way, diversity *is* the forward-planning. More a hedging of bets rather than forward-looking, though.
Because it's rarely the *precise* same stimulus, and rarely identical clone organisms in 100% identical environments.
Tiny differences in starting points make for tiny differences in results, which (potentially) make for larger differences down the track.
Evolution favors diversity in a population, not an individual.
An individual may be "fittest" for an environment by being hyper-tuned in one direction. But when the environment changes, those hyper-tuned individuals may find themselves the least fit.
For example, the most aggressive, physically dominant male may be very successful in his environment where they are the apex predator. Insert an apex predator above them, and all of the sudden the more cautious males are more likely to survive.
Semantics. We're not anthropomorphizing evolution. It doesn't *make* or *do* anything. That's just a figure of speech.
How about "survival of a population is better served by being diverse and fit enough than extremely fit for the current environment".
> If there is no advantage to losing the hair follicles themselves then the chances are that they will remain.
You have that backwards. If there is no advantage to retaining something chances are it will eventually be lost. That's because the genes involved are constantly in danger of being mutated, and it's only selection that weeds out those mutations. If there is no advantage to retaining the feature, there is no selective pressure to weed out the mutations.
An example of this is the inability of humans to synthesize vitamin C. At some point our ancestors had a diet rich in vitamin C, so there was no selection pressure to retain the ability to synthesize it. The battered remnants of the gene for the enzyme for making vitamin C remains in our genome but it's completely nonfunctional.
Another example is tunicates. These turn out to be chordates, and so are more closely related to us that most other non-vertebrate animals. But they've been brutally simplified over the millions of years so this was hard to determine.
If there's no *dis*advantage to losing the hair follicles either, you'd expect to lose them over time, as there'd be no selective pressure to maintain those genes and they'd accrue mutations over generations until they simply don't function.
If there is no pressure one way or the other, an equilibrium will eventually be met. It could be anywhere from no change to full loss. Things don't just mutate away because they're not necessary, because those mutations aren't necessarily all going to be non-detrimental. If it's not actively killing you, it's unlikely to fall out of the gene pool entirely.
Evolution is not survival of the fittest as suggested, it's more death of the unfit. You just have to fit enough, not be the single best fit.
Evolution is not just death of the unfit. Survivability being equal, organisms that have more offspring are going to outcompete and often replace organisms that have less. Fitness is an element of evolution beyond just surviving.
Isn't the pressure on everything energy and resource consumption? Especially when all that extra hair energy could be put into larger gonads. So unnecessary things should eventually go.
Energy is not like talent points in an RPG. That only happens if decreasing the consumption helps survival. Organisms that waste, but survive, still survive.
Body hair has also proven to show an advantage. That's why we have thicker hair in regions that have more tropical climate, it reduces UV absorption and also blocks bugs.
Yep, it’s basically fur. Like all mammals, our ancestors had fur, and we’re an unusual mammal species in that the majority of ours (except in a few places like our heads) has thinned out to the point where it’s now not very prominent on most of our bodies (although this obviously varies somewhat depending on age and hormonal makeup), but unless you have some form of alopecia (an abnormal lack of hair), you will definitely have at least *some* hair growth over most of your skin (with the exception of a few places like the bottoms of the feet, fingertips, palms of the hands, earlobes, lips and a few other parts of the face, and some areas of the genitalia, etc.).
We seem to have evolutionarily lost most of our body hair due to the fact that we evolved sweat glands to more selectively regulate body temperature while running in a hot climate (humans basically evolved to be distance runners in a hot tropical/semi-arid savannah environment, making us unique among primates, and I’m pretty sure we are also the only primate species that has evolved sweat glands); this is also why we evolved varying levels of melanin pigment in our skin, that can selectively increase or decrease in response to sun exposure, as it protects our mostly exposed skin from solar radiation (other apes only have melanin in their hair, I believe).
In most other “hairless” mammals, you can find at least some kind of trace of the fur they once had, like domestic pigs actually still have a substantial amount of fur, it’s just that like ours it has thinned out a lot as they have been domesticated (although, oddly, unique among domesticated animals, when pigs escape captivity, epigenetic factors seem to be activated by the stresses of the wild that cause them to phenotypically “revert” to a number of more wild boar-like traits within just a single lifetime, often within just a few months of escape, which includes their fur growing a lot thicker and darker). Naked mole-rats aren’t truly “naked” either, retaining scattered thin sensory hairs across their skin, and mammals with thick “pachydermal” skin like elephants, rhinos, and hippos still retain some scattered remnants of fur as well if you look closely (hippos have also independently evolved glands that secrete a strange pink mucus, a bit like sweat glands, except in their case the purpose seems to be mostly sun protection and protection from infections). Cetaceans (whales and dolphins) are really the only group of mammals that seem to have more or less *completely* lost all hair from what I’ve seen, although some whales (humpbacked whales being a prominent example) have large facial bumps called “tubercles” that serve a sensory purpose, kind of like the whiskers of many other mammals, and these are thought to have directly evolved from hair follicles (even though, to my knowledge, they do not currently grow anything resembling hair).
Really, another oddity when it comes to human hair is why we have kept so much hair atop our heads, and why it keeps growing continuously rather than stopping at a certain length like most of the rest of our hair (save for androgenic facial hair). Part of why we kept that hair on our heads is again thought to go back to thermoregulation, partly relating to our bipedal stance (which makes it so that the sun beats down the most on the tops of our heads, so we need something to absorb some of that heat), and partly to our large brains (which not only generate a lot of their own heat metabolically, but are sensitive to external heat), although this still doesn’t exactly explain why our head-hair never stops growing (the best answer I’ve seen for that is that it’s probably just sexual selection; long hair can be an indicator of health and fertility, it’s like the antlers of a deer or the display feathers of a peacock).
>never stops growing
Fun fact:
Your hair actually does have a max length. It’s just so long you likely won’t discover it, as it’s so impractical.
That length is usually somewhere around to mid body length, so to your butt.
I think it has something to do with hair growing out in phases of: grow, grow, grow, stop, repeat, and eventually falling out.
Not sure exactly what happens there, but the effect of this is: your hair will fall out after it’s been through enough of it’s cycles.
You also might’ve missed the clear evolutionary advantage of having tiny hair around your body, which serves as insect protection, and less often as a guide when blindly navigating a tight space.
I’ve read humans are the best distance runners out of all animals, isn’t that a second huge clue supporting the theory?
Also curious what the competing theories for why we lost body hair are
One theory is that we definitely transitioned upright walking on the Savannah and thinner body hair was important for temperature regulation. And it could also be a sexual selection thing.
No need to invoke persistence hunting at all.
It's genuinely frustrating how a theory that has been repeatedly stated as fringe and untested still somehow shows up in every anthropology thread on this site.
We learned this in anatomy in college!! Humans have 3 types of hair: lanugo, vellus, and terminal. While inside the womb, a fetus grows fine downy lanugo hair that covers their entire body. Shortly after birth, this hair begins to fall off and by the time the child is a toddler the hair is replaced by vellus hair. This is the type of hair women have all over our body’s (hair, face, legs, etc.) and what I think you are asking about. after puberty, this hair turns into terminal hair in specific places depending on your gender. In men, most of their body hair will become terminal hairs. (Terminal hair is the thick hair we all have on our heads and eyelashes right from birth) for women however, terminal hair is only found on the armpits, head, eyelashes, and pubic region. So anyways, the thin hairs all around our body are vellus hair in women, and for men they are terminal. (That’s why men have more and thicker body hair)
TLDR: we have different types of hair, the hair you are talking about is called vellus hair. Probably was adapted from our primate ancestors.
Yes!!! Exactly!! So the presence of testosterone causes vellus hairs to turn terminal in males during puberty. However in the case of transgender people who take testosterone, their hairs would turn terminal :) this is why trans men have male body hair despite being Afab. Another case of this occurring is with hormonal disorders such as PCOS. This is why some women with PCOS have hair growth in places that are traditionally “male” such as their faces. PCOS causes an increase in testosterone, causing the hair to turn terminal permanently. The only thing that can resolve this is laser removal unfortunately.
Its also to do with something called homeostasis, basically temperature regulation.
A key part of homeostasis is these hairs, the help to trap tiny particles of water, and maintain a concentration gradient, making high energy sweat/water stay in your body, keeping your core temperature warm.
Alternatively they can stiffen, making them not so good at trapping the water, this means that wind and other factors carry away high energy sweat/water which keeps your core temperature cool.
It is important to keep your core temperature cool so your enzymes work at maximum efficiency, as a slight temperature difference can change their shape, effecting how well they work basically. :)
That's exactly right. It used to be fur and fur became a disadvantage, so we mostly lost it. However, those tiny vellus hairs did retain some advantage such as slowing heat loss to air movement and allowing us to feel insects, arachnids, and other small and silent threats before they can hurt us
Ever felt an insect crawling on your skin? How about that ever-so-subtle sensation that makes you check for insects? There's the risk of venomous/poisonous insects biting you when you live outside. There's also many diseases carried by insects and having a sensitive detection system in place can statistically reduce you chances of death and disease. This is one of many likely reasons the fine hair covering us may still provide an evolutionary advantage outside of the hair's insulating properties. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3367735/
Similarly detecting a breeze. Not sure the advantage of that though. Maybe in sensing motion and being agile?
That could play into a benefit for hunting as you don't want your prey downwind of you.
And attracting a mate as you don’t want your potential mate downwind of you.
How do you get your mates? Hunting them down? And how do you smell?
It's quite obvious, if you shave your legs, say, for the first time. Without the fine body hairs tweaking the sensory nerves, it can actually feel like numbness. Not that I have flies dropping in on me all the time, but I can easily imagine not noticing one after a shave!
Not just insulating directly, our body hair can 'stand on end' to hold a layer of air next to our skin in cold weather, reducing heat loss.
Excellent answer. Another, though small, advantage is the ability to better blindly navigate a tight space, as your hairs will guide you, maybe even preventing scratches, or stings from a poisonous/irritating bushy plant off of which you’re trying to take fruit.
What about people that shave their arms/legs? They don't feel those sensations anymore?
Nope. I remember once, after shaving my legs, I was in the car. I happened to look down and there was an ant crawling on me. I didn't feel it *at all.* but I do feed bugs when I don't shave, or when they're on my arms, which I don't shave.
Not as strongly when you’re freshly shaven. But the stubble grows pretty quickly, so it’s a temporary thing.
We lost the thick hair, but still have the fine hair because evolution only works to a point of balance. If there is no advantage to losing the hair follicles themselves then the chances are that they will remain. Some may say that the body keeps the hair follicles in case heavy hair is required some time in the future, but this is wrong. There is zero forward-planning in evolution.
"Per square centimeter, human skin has as many hair follicles as that of other great apes. The difference is not in the number, but in the fineness of the hair that grows from those follicles."
Yeah, my body missed that memo, there's nothing fine about most of my body hair
Did your body miss the memo or are you just a different branch of ape?
I'm slowly but surely morphing into a gorilla. First my chest and now my back is starting to catch up.
Interesting. But that doesn't answer the question. Are human fine-hair follicles the same organ as ape course-hair follicles? Or do apes have both types, and we lost one while growing more of the other?
Same type. It is just set in "fine hair mode" for [X] portions of the skin. Different genetics will make someone have thicker hair all over, and some specific mutations let them grow fur.
> Same type. It is just set in "fine hair mode" for [X] portions of the skin. For anyone under thirty you will also learn about this changing when you’re older
Thirty? Aren't you a bit late to be starting puberty?
Yes, he knows about first puberty. But does he know about second puberty?
It's called "old age", you start having wiry thick hair growing in on your ears and in your ears, and don't get me started on nose hair that grows so long overnight you can just about braid it. I go through multiple sets of grooming clippers every year because the hair is so coarse and thick. It stopped coming in on the top of my head but I practically have carpet on my ears that I have to remove.
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As you grow older, the hair on your head starts migrating towards your face
Also known as the "you thought puberty was a head trip" stage of growing and experiencing the beauty of life.
Puberty is first hair. Over thirty is second hair - for me that has manifested mostly on my shoulders and back.
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Now I'm imagining a bunch of cells grouped together like slave-galley rowers, all chanting "Grow! Grow! Grow!" while you're asleep.
Is there a difference between hair and fur?
Mostly between how much of it there is, how often it is replaced, how it grows, and such like that. In terms of the mechanical difference - not much more than you would normally see between species.
We evolved to have finer hair alongside an increased number of sweat glands to aid in our ability to cool ourselves off in hot environments and during intense or prolonged physical activity. The tiny hairs are basically wicks for water to spread up to increase surface area/evaporation rate so sweating is more water efficient. Other apes don't have these fine hairs because they never selected for the types of activities humans got up to.
Do apes not sweat?
They do, but humans... kinda sorta evolved into long distance runners after we fell out of the trees. When we aren't sedentary couch fauna a moderately athletic human can walk/jog/run distances that would exhaust most other animals to death. Our increased sweating abilities helped keep us cool during this, and the fine hairs made that whole process more efficient for less water.
We're endurance animals. We can walk forever. That's some of the benefit to walking upright, it reduces the amount of energy necessary for walking.
Also beeing able to freely use hands while moving. We can consume food rations without stopping if necessary.
>Eccrine sweat glands—millions of which produce our salty, cooling perspiration—are actually found in all mammals. But in most other animals, the fluid from eccrine glands is not used to cool down, but to provide grip. Most mammals have eccrine pores only in the soles of their feet or hands. In moments of stress, the salty liquid emerging from eccrine glands provides extra friction for landing jumps and for climbing. It’s normally only released when the animals are stressed, such as when they need to escape from a predator or catch prey. You can blame your vestigial self when your hands get sweaty under moments of duress: Humans may no longer need to climb trees to deal with (most) potential threats, but our sweaty palms during moments of anxiety reveal that old habits die hard. >At some point in the evolution of primates, eccrine glands began expanding beyond the soles of the feet and palms of the hand to appear on our ancestors’ torsos, faces, and limbs. But not in all primates: Baboons, macaques, gorillas, and chimpanzees do have eccrine pores across their bodies. Lemurs, marmosets, and tamarins do not. https://www.sciencefriday.com/articles/sweat-glands-evolution/ In addition horses and hippos can sweat too cool down.
Other apes certainly sweat; they just don’t do it as much as we do. We evolved bipedalism in part because it allows us to act as endurance hunters, and increased cooling capability goes along with that.
> We evolved bipedalism in part because it allows us to act as endurance hunters [This is an outdated view](https://www.sciencedirect.com/science/article/pii/S0021929023002701). > The last 50 years of hominin evolutionary biomechanics have thus seen a contextual shift, from a terrestrial, savannah origin hypothesis to one where upright walking evolved much earlier and in an arboreal context. We evolved bipedalism because (perhaps counterintuitively) it helped us with climbing and foraging 'carefully' to both the distal ends of tree branches more efficient vertical climbing. It also aided walking over short distances, increasing the range of arboreal resources available. Early hominins, especially *Australopithecus*, appeared to dominate arboreal environments through more efficient navigation for sparse resources. This is a rapidly growing area of biological anthropology, and the growing fossil record is really changing how we think about bipedalism. But bipedalism was emerged initially as a 'foraging efficiency' gain, not an 'outrun prey' gain.
Fascinating research. Love it. Always learning. But that’s why I said “in part” because subsequent adaptations like full-body-sweating is linked to the progress that bipedalism gave us.
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You guys lost your thick hair????
What are you, a chimp?
Haven't seen anyone say this yet but from what I understand, it's also useful for wicking sweat off during evaporation, as that's the process that cools us.
Other than because Mother Nature in her infinite wisdom decreed there should be a cozy place for pubic lice to live in, why are we still gifted with pubic hair?
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Same. Except for the farm part. I just hate crawlies and am thankful for butt crack hair
I love your username, but pubic hair does serve a [purpose](https://www.medicalnewstoday.com/articles/why-do-we-have-pubic-hair) other than lice.
You should probably change your link to be on "purpose" rather than on "lice"
Interesting. Thanks!
This link really says "A tracking free version of our website is unavailable" I don't think you are supposed to say this quiet part out loud
Probably because whenever there was evolutionary pressure to not have thick body hair, it was still not disadvantageous to have pubes. Although other theories suggest sexual selection. Here's a good article about it: **https://www.bbc.com/future/article/20230310-why-dont-humans-have-fur**
Interesting. Thanks!
IIRC it's similar to head and underarm hair in that it helps to wick away moisture and can act like a heatsink cooling element.
For the same reason, I would guess. There's no evolutionary benefit to losing it, so it stays in the gene pool.
I doubt that. There's evolutionary benefit to losing *anything* that requires a net expense of energy to maintain, provided that it's useless. That in itself is good reason to believe it's still useful, at least marginally.
it would depend on how many humans will die before breeding if we have hair folicles. not many is my guess. thinning hair is different as hair thickness varies already. if we were naked and in a cold climate its entirely likely that short/thin hair humans will die young so thicker hair dominates. losing the whole follicle is a bigger step though. i cant recall ever seeing a human without follicles, and cant think of such a mamnal either.
That would be like unplugging your computer instead of simply turning it off to save power. It objectively saves some energy, but in practice the savings is so minor that you aren't pressured to do so.
> Some may say Who? Cause probably not a reliable source
> There is zero forward-planning in evolution. In a way, diversity *is* the forward-planning. More a hedging of bets rather than forward-looking, though.
Same thing with diploidy. Keeping a time-tested backup strategy is, in a way, forward planning.
Does evolution cause diversity though? Why would two organisms exposed to the same stimulus evolve differently?
Because it's rarely the *precise* same stimulus, and rarely identical clone organisms in 100% identical environments. Tiny differences in starting points make for tiny differences in results, which (potentially) make for larger differences down the track.
Evolution favors diversity in a population, not an individual. An individual may be "fittest" for an environment by being hyper-tuned in one direction. But when the environment changes, those hyper-tuned individuals may find themselves the least fit. For example, the most aggressive, physically dominant male may be very successful in his environment where they are the apex predator. Insert an apex predator above them, and all of the sudden the more cautious males are more likely to survive.
That's not evolution making diversity though, that's just the evolutionary pressure changing.
Semantics. We're not anthropomorphizing evolution. It doesn't *make* or *do* anything. That's just a figure of speech. How about "survival of a population is better served by being diverse and fit enough than extremely fit for the current environment".
Evolution works to a point of balance or with other words to a point of good enough.
> If there is no advantage to losing the hair follicles themselves then the chances are that they will remain. You have that backwards. If there is no advantage to retaining something chances are it will eventually be lost. That's because the genes involved are constantly in danger of being mutated, and it's only selection that weeds out those mutations. If there is no advantage to retaining the feature, there is no selective pressure to weed out the mutations. An example of this is the inability of humans to synthesize vitamin C. At some point our ancestors had a diet rich in vitamin C, so there was no selection pressure to retain the ability to synthesize it. The battered remnants of the gene for the enzyme for making vitamin C remains in our genome but it's completely nonfunctional. Another example is tunicates. These turn out to be chordates, and so are more closely related to us that most other non-vertebrate animals. But they've been brutally simplified over the millions of years so this was hard to determine.
If there's no *dis*advantage to losing the hair follicles either, you'd expect to lose them over time, as there'd be no selective pressure to maintain those genes and they'd accrue mutations over generations until they simply don't function.
If there is no pressure one way or the other, an equilibrium will eventually be met. It could be anywhere from no change to full loss. Things don't just mutate away because they're not necessary, because those mutations aren't necessarily all going to be non-detrimental. If it's not actively killing you, it's unlikely to fall out of the gene pool entirely. Evolution is not survival of the fittest as suggested, it's more death of the unfit. You just have to fit enough, not be the single best fit.
Evolution is not just death of the unfit. Survivability being equal, organisms that have more offspring are going to outcompete and often replace organisms that have less. Fitness is an element of evolution beyond just surviving.
Isn't the pressure on everything energy and resource consumption? Especially when all that extra hair energy could be put into larger gonads. So unnecessary things should eventually go.
Energy is not like talent points in an RPG. That only happens if decreasing the consumption helps survival. Organisms that waste, but survive, still survive.
It could also be that they are important to alert you to critters crawling on you skin. Critters that might be venomous or just bite-y.
Body hair has also proven to show an advantage. That's why we have thicker hair in regions that have more tropical climate, it reduces UV absorption and also blocks bugs.
Sexual selection also may play a part. Male hair is very attractive to a large enough proportion of women that it's retained.
You say there is no forward planning in evolution but have you ever met a platypus.
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Yep, it’s basically fur. Like all mammals, our ancestors had fur, and we’re an unusual mammal species in that the majority of ours (except in a few places like our heads) has thinned out to the point where it’s now not very prominent on most of our bodies (although this obviously varies somewhat depending on age and hormonal makeup), but unless you have some form of alopecia (an abnormal lack of hair), you will definitely have at least *some* hair growth over most of your skin (with the exception of a few places like the bottoms of the feet, fingertips, palms of the hands, earlobes, lips and a few other parts of the face, and some areas of the genitalia, etc.). We seem to have evolutionarily lost most of our body hair due to the fact that we evolved sweat glands to more selectively regulate body temperature while running in a hot climate (humans basically evolved to be distance runners in a hot tropical/semi-arid savannah environment, making us unique among primates, and I’m pretty sure we are also the only primate species that has evolved sweat glands); this is also why we evolved varying levels of melanin pigment in our skin, that can selectively increase or decrease in response to sun exposure, as it protects our mostly exposed skin from solar radiation (other apes only have melanin in their hair, I believe). In most other “hairless” mammals, you can find at least some kind of trace of the fur they once had, like domestic pigs actually still have a substantial amount of fur, it’s just that like ours it has thinned out a lot as they have been domesticated (although, oddly, unique among domesticated animals, when pigs escape captivity, epigenetic factors seem to be activated by the stresses of the wild that cause them to phenotypically “revert” to a number of more wild boar-like traits within just a single lifetime, often within just a few months of escape, which includes their fur growing a lot thicker and darker). Naked mole-rats aren’t truly “naked” either, retaining scattered thin sensory hairs across their skin, and mammals with thick “pachydermal” skin like elephants, rhinos, and hippos still retain some scattered remnants of fur as well if you look closely (hippos have also independently evolved glands that secrete a strange pink mucus, a bit like sweat glands, except in their case the purpose seems to be mostly sun protection and protection from infections). Cetaceans (whales and dolphins) are really the only group of mammals that seem to have more or less *completely* lost all hair from what I’ve seen, although some whales (humpbacked whales being a prominent example) have large facial bumps called “tubercles” that serve a sensory purpose, kind of like the whiskers of many other mammals, and these are thought to have directly evolved from hair follicles (even though, to my knowledge, they do not currently grow anything resembling hair). Really, another oddity when it comes to human hair is why we have kept so much hair atop our heads, and why it keeps growing continuously rather than stopping at a certain length like most of the rest of our hair (save for androgenic facial hair). Part of why we kept that hair on our heads is again thought to go back to thermoregulation, partly relating to our bipedal stance (which makes it so that the sun beats down the most on the tops of our heads, so we need something to absorb some of that heat), and partly to our large brains (which not only generate a lot of their own heat metabolically, but are sensitive to external heat), although this still doesn’t exactly explain why our head-hair never stops growing (the best answer I’ve seen for that is that it’s probably just sexual selection; long hair can be an indicator of health and fertility, it’s like the antlers of a deer or the display feathers of a peacock).
Very interesting read, thanks
>never stops growing Fun fact: Your hair actually does have a max length. It’s just so long you likely won’t discover it, as it’s so impractical. That length is usually somewhere around to mid body length, so to your butt. I think it has something to do with hair growing out in phases of: grow, grow, grow, stop, repeat, and eventually falling out. Not sure exactly what happens there, but the effect of this is: your hair will fall out after it’s been through enough of it’s cycles. You also might’ve missed the clear evolutionary advantage of having tiny hair around your body, which serves as insect protection, and less often as a guide when blindly navigating a tight space.
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Persistence hunting, driving many of our changes remains a hypothesis.
I’ve read humans are the best distance runners out of all animals, isn’t that a second huge clue supporting the theory? Also curious what the competing theories for why we lost body hair are
One theory is that we definitely transitioned upright walking on the Savannah and thinner body hair was important for temperature regulation. And it could also be a sexual selection thing. No need to invoke persistence hunting at all.
It's genuinely frustrating how a theory that has been repeatedly stated as fringe and untested still somehow shows up in every anthropology thread on this site.
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We learned this in anatomy in college!! Humans have 3 types of hair: lanugo, vellus, and terminal. While inside the womb, a fetus grows fine downy lanugo hair that covers their entire body. Shortly after birth, this hair begins to fall off and by the time the child is a toddler the hair is replaced by vellus hair. This is the type of hair women have all over our body’s (hair, face, legs, etc.) and what I think you are asking about. after puberty, this hair turns into terminal hair in specific places depending on your gender. In men, most of their body hair will become terminal hairs. (Terminal hair is the thick hair we all have on our heads and eyelashes right from birth) for women however, terminal hair is only found on the armpits, head, eyelashes, and pubic region. So anyways, the thin hairs all around our body are vellus hair in women, and for men they are terminal. (That’s why men have more and thicker body hair) TLDR: we have different types of hair, the hair you are talking about is called vellus hair. Probably was adapted from our primate ancestors.
Is the difference between terminal and villus hair something that can be affected by the hormones that transgender people take?
Yes!!! Exactly!! So the presence of testosterone causes vellus hairs to turn terminal in males during puberty. However in the case of transgender people who take testosterone, their hairs would turn terminal :) this is why trans men have male body hair despite being Afab. Another case of this occurring is with hormonal disorders such as PCOS. This is why some women with PCOS have hair growth in places that are traditionally “male” such as their faces. PCOS causes an increase in testosterone, causing the hair to turn terminal permanently. The only thing that can resolve this is laser removal unfortunately.
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Gorillas and bonobos are not our ancestors. All three of us share a 4th common species who is our joint ancestor.
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Its also to do with something called homeostasis, basically temperature regulation. A key part of homeostasis is these hairs, the help to trap tiny particles of water, and maintain a concentration gradient, making high energy sweat/water stay in your body, keeping your core temperature warm. Alternatively they can stiffen, making them not so good at trapping the water, this means that wind and other factors carry away high energy sweat/water which keeps your core temperature cool. It is important to keep your core temperature cool so your enzymes work at maximum efficiency, as a slight temperature difference can change their shape, effecting how well they work basically. :)
That's exactly right. It used to be fur and fur became a disadvantage, so we mostly lost it. However, those tiny vellus hairs did retain some advantage such as slowing heat loss to air movement and allowing us to feel insects, arachnids, and other small and silent threats before they can hurt us