Why humans have no fur: Bare skin --> Bigger brains (Scientific American)

[brandon]

It might seem rather obvious why we are not covered with thick fur. Even so, you might find an article in the February 2010 issue of Scientific American very interesting.

I summarize the article below, but you can listen to an audio version of the article at
http://www.airsla.org/broadcasts/Science100123.mp3
(It may take a minute or more to download.)

The Naked Truth: Recent findings lay bare the origins of human hairlessness -- and hint that naked skin was a key factor in the emergence of other human traits

By NINA G. JABLONSKI
Head, Deptartment of Anthropology, Pennsylvania State University

Among primates, humans are unique in having nearly naked skin. Every other member of our extended family has a dense covering of fur -- from the short, black pelage of the howler monkey to the flowing copper coat of the orangutan --  as do most other mammals.

The article goes through why most mammals have fur, and why very large mammals living in warm climates, such as elephants, rhinoceroses and hippopotamuses have very little. As you might guess, such large animals have a low surface area to body mass ratio, so cooling is a bigger problem than keeping warm.

Humans keep cool by sweating, and we have an extraordinarily large number of eccrine (sweat) glands. This combination of sweat glands and minimal fur allows humans to dissipate heat very effectively.

According to a 2007 paper in Sports Medicine by Daniel E. Lieberman of Harvard University and Dennis M. Bramble of the University of Utah, our cooling system is so superior that in a marathon on a hot day, a human could outcompete a horse.

I think that might be the case in general, even on a not-particularly-hot day. That's why the Pony Express needed to use a relay system with their horses:

A total of about 184 Pony Express stations were placed at intervals of about 10 miles (16 km) along the approximately 2,000 miles (3,200 km) route.[7] This was roughly the maximum distance a horse could travel at full gallop. The rider changed to a fresh horse at each station,

http://en.wikipedia.org/wiki/Pony_Express#Operation

But why did we suddenly need to dissipate so much heat when our evolutionary ancestors were comfortable with fur coats?

According to Dr. Jablonski,
 

Perhaps not surprisingly, the transformation seems to have begun with climate change.

Starting around three million years ago, the earth entered into a phase of global cooling that had a drying effect in East and Central Africa, where the ancestors of humans lived.

There was less rainfall, and the forests were replaced by open savanna grasslands. The foods that our mostly-vegetarian ancestors lived on (fruits, leaves, tubers and seeds) became scarcer. No longer could our ancestors lounge around in the forests, foraging for food.

Our ancestors had to travel further, and add other foods to the menu, notably meat.

Stone tools and butchered animal bones show up in fossils from 2.6 million years ago, according to the article.

Dr. Jablonski notes that animal foods are rarer on the landscape than plant food, so carnivorous animals "need to range farther and wider than their herbivorous counterparts to procure a sufficient amount of food."

Dr. Jablonski points out another important difference between plant and animal food sources: Most animal food sources are mobile, and you often have to chase them. (A very important point she neglects to mention, perhaps because it is obvious, is that our ancestors didn't have sharp claws and fangs like cats, so their best bet for taking down something like a gazelle would have been to tire it out, and then perhaps spear it, assuming they had invented the spear by then.)

Dr. Jablonski also notes that being a good runner would help our ancestors avoid becoming some other animal's dinner, while exposed on the open savanna.

Human ancestors became better-adapted to the open savanna with longer legs and shorter arms, better suited to running. Sustained running would result in severe overheating, so the most successful of our ancestors would be those with the least fur.

So losing body fur was, like most evolutionary changes, a matter of survival of the fittest for a particular environment. Even though the earth was undergoing global cooling, human ancestors were forced into the open savanna, where the ability to run significant distances without overheating was the key to survival.

By 1.6 million years ago, a human ancestor, Homo ergaster, had essentially modern human proportions. Dr. Jablonski further notes that fossils show knee, hip and ankle joint wear, indicating that these ancestor did in fact walk and run a lot.

Dr. Jablonski cites genetic studies indicating that the gene for darkly pigmented skin is about 1.2 million years old. Presumably our fur-covered ancestors had pinkish skin under their fur, as chimpanzees still do. When our ancestors lost their protective fur covering, dark-colored skin would have become essential to minimize sun damage in the African savanna.

Dr. Jablonski also references studies of lice that suggest that humans went furless and naked for approximately one million years before wearing clothing.

Even though furlessness might have evolved primarily to enable sustained running, the ability to effectively dissipate heat enabled the development of larger brains. Brains produce a large amount of heat, and it is essential to prevent the brain from overheating. So we wouldn't have been able to develop our higher language, reasoning and spatial abilities in a hot environment if we were covered in fur. It's very hard to talk while panting, so that wouldn't have worked too well. I suppose we could have evolved big elephant ears, or maybe some ridges on our heads to radiate heat, but neither of those options would be very aerodynamic. So the furless, naked, body worked best.

[Karla]

Fascinating stuff!

(A very important point she neglects to mention, perhaps because it is obvious, is that our ancestors didn't have sharp claws and fangs like cats, so their best bet for taking down something like a gazelle would have been to tire it out, and then perhaps spear it, assuming they had invented the spear by then.)

This bit caught my eye. I remember seeing a documentary about a traditional style of hunting in some Savannah type place. The hunter would walk for days tracking some prey (a big cat I think)  until it reached the point of exhaustion and could no longer evade the human. The hunter  would only carry a single spear and would also be completely naked.

[rc]

wow that is werid

[Pisco]

I found another interesting article: Can people unlearn their naked shame?

Once we were all happy to walk around naked, now we're not. But can an experiment in nudity help us understand why we are so embarrassed by being seen in the buff and help shed our inhibitions?

It's a classic anxiety nightmare - you're standing in front of a room full of work colleagues, your boss is there, maybe even that new colleague you've been trying to impress. And you're stark naked. Ouch.

Why are we so ashamed of being seen naked? Is there something deep in human nature that finds naked skin abhorrent? Some prudishness inherited from our Victorian ancestors?

And how can you explain the rebels who shun convention to spend their weekends hanging out with similar-minded nudists, insisting nothing could be more normal?

Eight ordinary people - none of them nudists - were recently brought together for an experiment filmed by the BBC's Horizon programme, to test some of the scientific theories that explain why naked bodies make us so uncomfortable.

Among them were Phil, 39, from Birmingham and Kath, 40, from Dorset. Kath's greatest worry was that people would laugh at her. Some of the men in the group were more concerned about inappropriate excitement.

Man's nakedness

Phil was first to feel the cameras burning into his skin. A matter of hours after meeting the other volunteers, he found himself before a full-length mirror, instructed to remove all of his clothes. When he discovered the mirror was two-way and he was being watched, his red face, beating heart and soaring blood pressure told a story.

Performing the same task, Kath admitted she wanted "the floor to open up." When we are naked in public, most of us feel exposed.

And of course, a naked human is just that bit more naked than other primates. We have only minimal body hair, they have fur. Why?

It's one of the greatest mysteries in evolution, and even bothered Charles Darwin. One of the theories is that we lost our fur as a way of dealing with the heat of the sun. It's controversial, as most mammals use fur to protect them from the sun. But some anthropologists believe our ancestors' unique ability to sweat, along with their upright stance, meant we could cool quicker without fur - prompting the onset of human nudity.

They reckon that evolutionary step towards nudity had huge implications for the human race. With a souped-up cooling system, our ancestors could afford to develop ever-bigger brains - leading to culture, tools, fire, and language.

Red for 'no-go'

"Really, without losing hair, without our sweatiness, we wouldn't have been able to evolve the big brains that characterise us today," says anthropologist Professor Nina Jablonski of Penn State University. "Essentially, being hairless was the key to much of human evolution."

So there's reason to believe our nudity arose out of practical need, but that doesn't answer why we're so ashamed by it.

Attitudes towards nakedness may be the result of the need for long-term pair bonding
But it seems this shame can be unlearned - witness, for example, the work of artist Spencer Tunick, who frequently corrals hundreds of volunteers to strip off en masse in public places for his photographs.

After a series of experiments, Phil and Kath, who had been so self-conscious at the start, each came face-to-face with a newly stripped fellow volunteer. They were invited to paint the body in front of them, colour coding every patch of skin to show how uncomfortable they felt touching that part of the body - red for no-go; yellow for squirming and green for fine.

Phil drew the line at colouring his subject's genitals, but Kath had lost all her inhibitions. Within moments she'd painted her subject completely green.. Every inch.

Learned shame

It was an example of how flexible our attitudes to nudity are. And it explains how nudists can carry on as normal when they're surrounded by naked people. Over a couple of days, the volunteers had unlearned many of the social conventions that normally govern their life, and reached a new consensus that permitted them to be naked in each other's company.

It chimes with the psychologists' theory that we are not born with a shame of nudity. Instead we learn it, as an important behavioural code that allows us to operate in human society.

With the long immature period of a young human, mum and dad need to form a stable pair bond to do the looking after. But humans are more social than any other primate, living and moving in large social groups.

Psychologist Professor Dan Fessler, of the University of California, Los Angeles, says our gregariousness "poses a challenge... because those groups of course provide a source of temptation. Potentially both sexes can benefit by cheating on their partners."

That's where our shame of nudity comes in. Over thousands of generations, we've learned that showing off a naked body sends out sexual signals that threaten the security of mating pairs. And we've chosen to agree that that is a bad thing.

Shame is the ideal emotion to enforce that code of conduct. Because it feels unpleasant, we avoid it at all costs. And because it's such a visible emotion, everyone around gets a clear message that you know you've messed up.

Social contract

"All around the world individuals feel great shame when they know that others know that they have failed to be adequately modest," Prof Fessler says. "Essentially, they're signalling to those around them 'I understand what the social norm is and I understand that you know that I have failed in this regard, so please don't hurt me.'

"Nudity is a threat to the basic social contract. They have exposed their body and their sexual selves in a way that presents an opportunity for sexual behaviour outside of the principal union."

But as this code of conduct is something we learn, rather than are born with, we can re-learn it, if common consensus allows. As Phil reflected: "One thing I think I'll take away is how easy it was to bond with complete strangers in what should really be an artificial environment and one that by all society's standards we should feel uncomfortable with."

Would all this knowledge prepare Phil and Kath to push the boundaries of acceptable behaviour back in the real world? As the weekend drew to a close, they were presented their final, surprise challenge.

They are invited to walk naked in the street to waiting taxis, which they do. They have overcome a significant bit of socialisation.

[didiosa1980]

Wonderful articles! Love all of the information you guys have.    I remember seeing a movie on Netflix about the development of humans and that trading hair for sweat glands was an interesting thought. It's really fascinating when you think about how humans evolved and what led from one thing to another. When you really think about it, the climate changes and HAIR helped us develop the ability to think more and develop language. It's quite awesome in its own way really.

[Daft]

didiosa1980, I think you might like this tv show: http://www.i-naked.info/documentaries/vid1/

It's about nudity, and it has a whole section about the human evolution, and how we lost most of our body hair. It brings some interesting conclusions.

[Baseballfan]

Some men do.    Human Warewolves .

[genxnaturist]

Great Artical

As far as hunting.  One of the oldest types which is still used in Africa by some tribes is basically long job.  Hunters would find say a Gaziel or some animal and start to chase it.  This is done for many hours.  They run the animal to state of exhaustion.  Towards the end the animal is breathing hard, panting, and all that.  Human hunters are still fine.  Then animal collapses from exhaustion and they go for the kill.

Michael

[Steggsaurus]

great articles.

i think the key to making nudity more socially acceptable is understanding exactly why it became taboo in the first place.

[didiosa1980]

As far as hunting.  One of the oldest types which is still used in Africa by some tribes is basically long job.  Hunters would find say a Gaziel or some animal and start to chase it.  This is done for many hours.  They run the animal to state of exhaustion.  Towards the end the animal is breathing hard, panting, and all that.  Human hunters are still fine.  Then animal collapses from exhaustion and they go for the kill.

That's pretty cool. Goes to show the tenacity of the human being.

[joeyn]

As far as hunting.  One of the oldest types which is still used in Africa by some tribes is basically long job.  Hunters would find say a Gaziel or some animal and start to chase it.  This is done for many hours.  They run the animal to state of exhaustion.  Towards the end the animal is breathing hard, panting, and all that.  Human hunters are still fine.  Then animal collapses from exhaustion and they go for the kill.

That's pretty cool. Goes to show the tenacity of the human being.

Yes. I read an article in Sports Illustrated about how humans were built for running.

:)
Joey

[brandon]

Humans are indeed excellent runners, but I've tried running nude, and... I'm not convinced the male anatomy is especially well evolved for that. There's a lot of flapping and slapping that goes on, not unlike 

I think a moderately heavy loincloth would keep most of the flapping and slapping under control. Maybe our human ancestors invented the loincloth way back at the time running became important to survival when they left the forest (or the forest left them, due to climate change.)

I'll admit that I was wearing shoes on pavement. Maybe running barefoot on the savanna produces less penis motion. Or maybe African runners were more efficient, putting more energy into forward motion, with less vertical motion.

Still, I'm surprised the scrotum and penis don't retract when running the way they do in cold water.  That would also minimize the risk of testicular torsion, which can occur during running, and can be fatal. (I realize that overheating the testes is also not favorable to reproduction, so there would be a tradeoff.)

Anyone else with insights on nude running?

[Karla]

It's the same for women and breasts. They're best strapped down for running and jumping.

[MrDude]

I think fur is helpful to prevent heat loss, the alternative is a thick layer of fat (like pigs).
Since humans have developed ways to prevent heat loss (i.e. clothes) they lost their original fur (of monkeys)

[brandon]

It's the same for women and breasts. They're best strapped down for running and jumping.

Women might have needed to run to avoid being eaten by a lion, but in general, it is thought that women stayed with the kids and engaged in local gathering of fruits, roots and grubs. Supposedly they didn't participate in hunting.

If running had been essential to women's survival, breasts wouldn't have become so big. Lots of other species get by with fairly flat breasts. I don't know if large breasts have a biological advantage or if they are mainly the result of sexual selection. Perhaps they are a counterbalance to having a baby on one's back.

Adoloscent females and women with modern bras actually can be competitive runners, whether in sprints or marathons. That makes me think that women used to run, and large breasts are a more recent attribute. Unfortunately soft tissue is not preserved, so it may be difficult to determine that.

I think fur is helpful to prevent heat loss, the alternative is a thick layer of fat (like pigs).
Since humans have developed ways to prevent heat loss (i.e. clothes) they lost their original fur (of monkeys)

According to studies of clothing lice, which are distinct from fur lice or coarse hair lice, the order of events is that humans lost their fur long before they acquired clothing. As noted in the opening post, skin color changed to dark skin 1.2 million years ago. That would have occurred in conjunction with the loss of body fur and the move from the forest to the open savanna. The lice theory suggests clothing is only 50,000 to 100,000 years old, as I recall. However I think the loin cloth might have been invented over a million years ago. It might have been small enough and loose enough to remain lice free, or might have had a different type of lice.

As noted in the opening post, skeletal structures were suited to running 1.6 million years ago. I don't know when the human penis grew to its modern length. Most ape penises are shorter. Since our ancestors probably didn't have pot bellies, and a pregnant woman can't be re-impregnated, there is no need for humans to have long penises. I think they are the result of sexual selection. (The females were more attracted to them, or other males were intimidated by them, so males with long penises got more mating opportunities.)