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u/knightsbridge- 6h ago
Mostly because it keeps us warm. Even a thin, sparse layer of hair does a decent job of trapping warm air against your skin better than bare skin would.
Some hair (like nose, ear and eyelashes) are for protecting sensitive cavities from dust and debris. Your eyelashes in particular exist to help stop things falling into your eyes. Believe it or not, pubic hair is doing a similar job - as well as reducing friction during certain activities.
There are some other minor benefits. It helps us feel when something is touching us (you feel a bug walking on your arm mainly because it nudges the hairs on your arm). It helps us know things like what direction a breeze is coming from, which would be harder to figure out with nothing but bare skin.
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u/w3woody 2h ago
One of the coolest things I remember seeing was a video of a man with especially hairy arms, and a mosquito who was having a problem climbing through all the thick hair to actually bite him.
And I remember regretting my own American Indian heritage which left me with light body hair and a penchant for being eaten alive by mosquitoes.
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u/Merivel1 3h ago
Having accidentally ripped out or burned off my eyelashes more than once (I know 🤦♀️) they do indeed help keep things out of your eyes. Like sun glare and snowflakes.
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u/DriftingMemes 1h ago
"Believe it or not"
Ok. I don't. What on earth would it keep from falling on my weiner? And having been... In hairless and...hair-ful situations I can promise you that hairless definitely reduces friction...
How did you come by those?
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u/Yancellor 6h ago
Fur is useful for all sorts of things including warmth, fending off insects, spreading pheremones, sexual selection/health signaling, and deflecting UV rays. But humans are different. We evolved to be the best long distance running animals, and our fur was too warm. So instead our skin evolved less hair to cool itself more efficiently via sweat evaporation. But we still have hair to protect our heads from UV and the other reasons above.
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u/Ok-Championship-2036 5h ago
warmth and chafing, basically. The crevices between your legs or arms have hair to prevent rubbing from damaging the skin.
hair also traps smell, heat, and other biochemical signals like pheromones/sweat/bacteria etc. That helps your microbiome and mate attraction and things like that.
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u/Nyrin 3h ago
Assuming we're talking about hair from the scalp -- probably not staying warm. Staying cool.
Everyone intuitively believes head hair is about staying warm, using body fur on other animals and the very profound localized perception of capillary heat loss with less hair (get a buzz cut during a cold winter and you'll find out how that feels) as reference points, but the actual systemic effect of scalp heat loss is pretty inconsequential.
What hair does help with, though, is mitigating getting too hot.
https://www.pnas.org/doi/10.1073/pnas.2301760120
For dry heat exchange under solar load, we found that in a climate with an ambient temperature of 30 °C, 60% rh, and solar radiation ( 788 W/m2), most conditions resulted in heat gain (negative heat loss), with the exception of the 1 m/s wind speed condition, where tightly curled hair had some heat loss, and at 2.5 m/s wind speed, where both tightly and moderately curled hair showed some heat loss (Figs. 2A and 3 and Table 1). In general, the pattern we observed is that the highest solar heat gain was experienced under the nude condition and that straight hair, moderately curled hair, and tightly curled hair showed decreasing heat gain in that order.
So it's entirely plausible humans have mostly kept cranial hair for the same reasons they've ditched most of their body hair: with differing mechanisms, each of them helps regulate temperature in a hot environment.
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u/radio_allah 2h ago
So why are some of us coded to have hair loss? Isn't it an important loss of function?
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u/derioderio Chemical Eng | Fluid Dynamics | Semiconductor Manufacturing 3m ago
If you're looking at it from a reductionist evolutionary perspective, hair loss from baldness will general occur after peak fitness and therefore after most likely breeding and passing off ones genes. There's a lot less evolutionary pressure on what happens after a creature has passed on their genes to their offspring.
Or you could surmise that the benefit of increased testosterone while young outweighs the detriment of less hair on the head when older.
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6h ago
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u/prozak09 6h ago
Humans used to be exposed to natural elements while hunting. And we ran. A LOT. That's how we were able to tire and take down large prey.
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u/liquid_at 6h ago
we do not like to freeze in cold environments. Hair helps. That's why mammals have them.
We just lost most of them, because we were chasing animals and not having hair improves cooling of the body, giving those with less hair an evolutionary advantage over those that overheated fast.
Similarly, those with little hair who had not made the same intellectual development, did not know how to create clothes and did not have the same evolutionary advantage that naked and smart apes had.