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Why are humans relatively hairless as a species?

I've heard a couple of theories explaining this.

One is that not having hair allows us to sweat more, meaning we can keep cool so our stamina is greater - allowing us to chase prey down over longer distances.

However, I can't remember exactly where I read this, so it could be nonsense.

The other explanation I've heard is that's hairlessness is sexually selected. But I think that's a bit of a cop-out answer. Plus I don't know why humans would chose hairlessness over hairiness without some kind of context?

Anyone here have any ideas...?

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Reply 1

Scienceisgood

I think it could possibly be due to some kind of hygiene factor.
Generally, dirt and stuff can stick to hair better than to hairless and smooth skin meaning bacteria can grow at a much larger rate. =l

PERSONAL theory, just mine, don't know if this is proven in some way though. Also, I know sweat contains some kind of anti-bacterial properties and sweat is less likely to touch long hair (the tips) than the skin.

Haven't done any research into this but is just something I think about when pondering this possibility/reasoning as to why humans are hairless.

EDIT
Other than the typical homeostasis reason because evolution doesn't assign one purpose to one region of the body. Example in humans - teeth are used in the digestive system and can be used to attack others.

(edited 9 years ago)

Reply 2

Puddles the Monkey

Original post by Scienceisgood

Hmm. Interesting.

But how much impact would this have on preventing disease...?

Reply 3

Scienceisgood

Original post by Puddles the Monkey

Hmm. Interesting.

But how much impact would this have on preventing disease...?

Think about babies, they are generally born entirely bald (typically no head hair but some people like myself born with full head of hair...).
Anyway, babies typically have a very weak immune system, hence why there are indirect immune boosting properties such as antigens in breast milk. As a result, this aids in the prolonged life of the child because it helps them gain short term immunity to life threatening diseases.

Especially where babies are prone to sticking all kinds of things in their mouth. =l

Reply 4

Puddles the Monkey

Original post by Scienceisgood

But surely hair would only have an impact on bacteria entering via the skin...? How would being hairless affect their internal immune system? Once bacteria is in their mouth it's in their mouth, right? Hair/no hair makes no difference?

Reply 5

Scienceisgood

Also, it aids in finding sexual partners because being entirely bald and growing body hair, i.e. pubic, underarm etc.. is a visually obvious sign from a distance that you have hit puberty and is a drop dead giveaway you are able to fertalise females or get pregnant.

Reply 6

Scienceisgood

Original post by Puddles the Monkey

Think how many times you run your hands through your hair daily (including underarm, pubic etc...) and how many times you touch your mouth?

Reply 7

Puddles the Monkey

Original post by Scienceisgood

Think how many times you run your hands through your hair daily (including underarm, pubic etc...) and how many times you touch your mouth?

Ahh I see. I can see how that makes sense!

(Although babies don't really have the motor skills to do those things :wink:

)

Why aren't chimps and gorillas hairless then? They sit around all day running their hands through each others fur.

Reply 8

Scienceisgood

Original post by Puddles the Monkey

Ahh I see. I can see how that makes sense!

(Although babies don't really have the motor skills to do those things :wink:

)

Why aren't chimps and gorillas hairless then? They sit around all day running their hands through each others fur.

That you'd have to do your research on, I'm just providing you with some natural/sexual selection methods of humans, other apes are a mystery to me. =l
I do however know chimps all have HIV but it doesn't affect/harm them and is just there.

So, sorry about not being able to help there. :redface:

EDIT:
Actually, just learned they have something similar to HIV but it is not HIV, it is SIV (Simion Immunodeficiency virus)

(edited 9 years ago)

Reply 9

Puddles the Monkey

Original post by Scienceisgood

That makes a lot of sense. :smile:

Reply 10

nexttime

Same as with other species that hunt on the plains - heat regulation, as said. We are even more hairless than other species as our ability to carry and utilise novel water sources means we can afford to sweat more and be even better at keeping cool. Its becoming increasingly apparent that humans hunted by endurance - harassing prey over many many hours until they collapsed from heat exhaustion. Our amazing thermoregulation (compared to other mammals) is central to that theory.

The infection thing is not it. Do you think our armpits are hygienic? Or for that matter, how about the few kilos of faeces you carry around with you in your gut all day? We evolve alongside the bacteria that's everywhere around us. There is no getting away from it. The only reason it doesn't just kill us all is that that would be counter-productive - they'd be killing their own incubators and their own transport! Its not evolutionarily beneficial to kill your host.

Reply 11

Puddles the Monkey

Original post by nexttime

I spoke to someone yesterday who said that hairless skin is actually less hygienic than having hair?

Reply 12

nexttime

Original post by Puddles the Monkey

I spoke to someone yesterday who said that hairless skin is actually less hygienic than having hair?

Well, define 'hygienic'. If its purely number of bacteria per square inch then our skin is worse than any toilet surface, urine, blood, any bin, almost all mud or dirt...

Reply 13

Puddles the Monkey

Original post by nexttime

Well, define 'hygienic'. If its purely number of bacteria per square inch then our skin is worse than any toilet surface, urine, blood, any bin, almost all mud or dirt...

I meant compared to having fur. :smile:

Reply 14

Amphiprion

Turns out the hairless nature of humans is largely attributed to a single mutation of a single gene around 6 million years ago. WHY it became so widespread is a subject of debate.

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2443.2012.01592.x/full

This paper [above] suggests bipedalism (walking upright on 2 legs) and hairlessness are actually detrimental features in an evolutionary context and that these features became widespread for a social reason. They suggest that the accidental evolution of hairlessness lead to bipedalism and that this led to the family unit as we recognise it today driving reproductive success, thereby further driving the hairless nature of humans and the global prevalence.

In other primates the young cling onto the hair of the mother somewhere on the body, in hairless humanoids this wasnt possible. Hairlessness = mother must stand upright to carry her young in order to stay mobile. Mobility was important to reduce chance of conflict with various threats and in order to forrage etc. By the mother having to walk bipedally and carry her young, it became necessary for males to gather/supply food etc by himself to support the mother/infant. This may have made the female more generous in offering sexual intercourse as a reward for continued support by the male. This made sexual reproduction between a male and a hairless (or less hairy) female more common, thereby leading to greater reproductive success, thereby increasing the number of individuals carrying the hairless gene etc etc.

https://ejournals.library.ualberta.ca/index.php/eureka/article/viewFile/16985/13555

This second paper suggests it is an aesthetic sexually selected feature with roots in a desire to distance ourselves from an animalistic history. Essentially that we've always just been way arrogant and were like, yo screw being an animal, I aint no dumb mammoth I want me a smooth, hairless ass male to inject me with DNA.

Reply 15

ApeMob

*scoff* I've seen some hairy bastards :closedeyes:

but really the hair naturally grows the most where the body needs the most protections.

Reply 16

Amphiprion

Original post by ApeMob

*scoff* I've seen some hairy bastards :closedeyes:

but really the hair naturally grows the most where the body needs the most protections.

Yea buuuutt our ancestors would have been hair covered like modern apes. Which means we didn't grow hair as we needed it, we grew a full body coat of hair and then we lost most of it. Apes didn't.

Reply 17

ApeMob

Original post by Amphiprion

Yea buuuutt our ancestors would have been hair covered like modern apes. Which means we didn't grow hair as we needed it, we grew a full body coat of hair and then we lost most of it. Apes didn't.

There is science behind it, if you know then feel free to enlighten me otherwise I know what I know and hair covers parts for protection that the rest of the body doesn't need, as it does need sun and oxygen and moisture that other parts easily infected don't need. :closedeyes:

Those parts are naturally covered in the most hair. &As humans evolve I'm sure so will our needs and we will probably look diff as time goes by anyhow.

(edited 9 years ago)

Reply 18

Kåte

It could be because, unlike other animals, we dress ourselves for warmth and so hair isn't needed so much now to keep our body temperature within the optimum range. Without clothes, the hairy folk would be more likely to survive and pass on their genes.

(edited 9 years ago)

Reply 19

Juichiro

Original post by Puddles the Monkey

If that was true, I would expect to see some other top predators also hairless but thing is none of them have our low level of hairlessness. So I don't think the boldened bit is true.