Why do modern human beings have very little body hair compared to their ancestors?

I’m not sure I appreciate why we would lose this most useful feature, unless of course the Earth at one point in our history became very warm, or simply less hairy people were considered more attractive than hairy ones.

Or then again it could be a pointer that we all originate from temperate zones where the hair wasn’t needed.

Whats the dope on this one?

Is there reliable evidence that our ancestors were hairier?

Exactly how much haor our ancestors had is open to dispute, IIRC – there’s no accurate way to tell how much they did have. I once saw an interesting display that showed various ways of restoring a Neanderthal. If you didn’t make him hirsute, he looked surprisingly like a modern-day human.

Of course, considering that all of our closest relatives are much hairier that we are, it seems certain that our common ancestors were, as well. The likeliest explanation I’ve heard is that we became “plains apes”, living in the relatively treeless plains rather than brachiating in the jungles, and that we spent a lot of time running upright, so we developed our peculiar feet and also lost our hair and became sweatier to have a more efficient “air conditioner” system to control body heat.

Then there’s the “aquatic ape” theory that holdss that we lost our body hair to become more efficient swimmers. This issue seems to have developed into a quasi-religious one, so I’m going to be a coward and avoid it.

Ron Jeremy?

Just like otters, capybara and beavers had to lose their hair to become more efficient swimmers. Oh hang on, no they didn’t. Hair loss in aquatic mammals seems to be restricted to large mammals, which tend to have little hair whether aquatic or not, and those mammals that spend days at seas at a time. Semi-aquatic medium sized mammals, as humans ancestors are theorised to have been, invariably have more hair than their relatives, not less.

Although I personally think the heat loss theory is the most plausible there is another theory that is reasonable. Human males value youth in their sexual partners. Other chimpanzees tend to have less hair, particularly on the face, before puberty. Because of this there was a selection for hairless females which in turn was passed onto males simply because it posed no risk.

Doesn’t our clothing wear the hair thin?
How hairy would an average bloke be if he was constantly naked?

About as hairy as the (near) naked people on National Geographic. By which I mean not hairy.

My own theory (IANA anthropoligist) is that we lost our hair when we started wearing clothes. Clothes not only made body hair unnecessary, it was actually detrimental, as hair got pulled on by the clothing and was uncomfortable and possibly led to infections.

Hairlessness is not necessary for an efficient sweat system. See equines.

To add to what Blake noted, hominids don’t have a thick enough fat layer to survive in water without hair. If hairlessness evolved for speed in swimming, head-hair would be the first thing lost.

As for clothing, is their any indication that primitive hominids wore clothes? What are the benefits of wearing clothing in tropical Africa (where the surviving hominid species originated)?

One benefit of relative hairlessness: less area to cover when picking off bugs. Another benefit: easier to see the general healthiness of an individual when skin is uncovered. Thus unblemished skin is a sexual attractor.

Hairlessness as an indicator of youth is interesting. Do primates in general tend to be less hairy when young?

“About as hairy as the (near) naked people on National Geographic. By which I mean not hairy.”

Are the people in the National Geographic the “average bloke,” or are they just the average blokes for people that live in warm climates?

My ancestors are not from a warm climate, and I’m very hairy (except for my back, which I count as a blessing). Native Americans and Asians, in my experience, don’t usually have much body hair and they come from temperate or even cold climates.

I don’t think we’ve hit on the answer yet.

Again, see Ron Jeremy. . .

Again, see Ron Jeremy. . .

I’ve said it before, and I’ll say it again: the most likely explanation is that humans are neotenous apes.

I don’t see how anyone can substantiate the speculation that we are “less” hairy now-adays than generations before us. Without good science, this thread is left to speculation, and therefore anyone having an opinion on the topic has license to add their 2 cents.

My personal feeling is that we are no more or no less hairy than ever before. Granted, I’m not an evolutionist, so call me biased there.

No we haven’t, but you’ve offered the least plausible scenario. BTW, your ancestors did come from a warm climate. You only need to to go back about 75k years, and all our ancestors lived in (warm) Africa.

If you can show that, in geographic subpopulation of humans, hairiness and climate are correlated, you might have a theory to test. But you’ll find hairy folk living in (warm) India as well as northern Europe.

I’d recommend caution when using the word “Asian.” It’s a geographic term, not an ethnic one. My guess is that you’re talking about East Asians. South Asians and Middle-Easterners can be just as hairy as any Euro. (And let me lament the loss of the useful term “Oriental.”)

Thanks for that link to a previous thread, Darwin’s Finch. Definitely helpful. So neoteny/progenesis (retention of fetal characteristics) is how we’re hairless. But the real questions is why we’re hairless. What’s the advantage of neoteny for hominids?

I’ll take a guess: The primary benefit of neoteny is our big brains and large learning capacities. And hairlessness just comes along for the ride. So we’re hairless apes because we’re smart apes. Of course, that brings of the issue of what’s the advantage of being smart. Someone else can handle that.

Any other ideas?

That’s the gist of it. Hairlessness was not necessarily selected for in and of itself; it’s a side-effect of something that was selected for, and most likely for the reasons you mention. Neoteny allows for bigger brains, since development is drawn out over a longer time period. And because of those big brains, we have to be born before we’re “done”, which necessitates more intense bonding between parents and offspring, which allows for increased learning, and so on. Next thing you know, we’ve got societies which build skyscrapers and can travel to the moon and back. Granted that’s all quite an oversimplification, but, as I said, that’s the gist of it.

I wasn’t really offering any particular scenario, and I’m aware that our collective ancestors came from Africa. I suppose if we went back far enough we could all say that our ancestors had no body hair at all. It is a matter of degree. My point was that, in my experience, people with European ancestry tend to have more body hair (or at least more noticeable body hair) than do black people, Native Americans, or East Asians. I don’t have the slightest idea why that is (other than what I’ve picked up as possible answers thanks to this thread).

I might not remember this correctly, but I read somewhere that humans and chimps have the same number of body hairs, it’s just that heirs is courser, thicker and longer.
If that’s the case, then we don’t have less hair, just finer.