Jeremy W Bowman

Humans are remarkable in many respects, but perhaps the most obvious way in which we differ from other animals is in our hairlessness. We have hair on our heads that is capable of growing indefinitely long — unlike the fur of other animals — and yet almost everywhere else on our bodies the hair is so thin and downy that we appear to be the "naked ape". Why?

We are descended from creatures that had more hair than we have, so sometime during the course of our evolution we lost our hair. Why?

Because many of us still have head hair, I'll refer to what we lost (but which animals retain) as "fur".

There are three "traditional" theories of why we lost our fur. The first is that we are an "aquatic ape" — that is, we lived in much closer proximity to water than other apes, with all that that entails. In many ways this is an attractive theory, and it is explored in rich and entertaining detail by Elaine Morgan in her book The Aquatic Ape.

The second theory is that we needed to lose fur primarily for purposes of temperature regulation. The third theory is that we lost our fur because it's easier to control parasites such as lice that way (although for obvious reasons we seem not to have lost the ease with which we pick up head lice and pubic lice).

I   think all of these theories of fur loss are mistaken. My own theory of fur loss is simply that we started to wear clothes. It would have been too hot to have fur underneath clothes, so we lost the fur. The "traditional" explanations of fur loss get things in exactly the wrong order, I think, by supposing that our forbears started to wear clothes after losing their fur, and that they lost their fur first because of some sort of environmental selective pressure.

But I submit that it happened the other way around. We started to wear clothes for various reasons — not least as an (extended) ornament for sexual selection — and afterwards began to lose our fur.

Clothes are just "made" for sexual selection. A man who wears a tiger-skin cloak is a man who can kill tigers. Wow. A woman who wears a patterned woven fabric is someone who can weave patterns. Or she can pay someone else to weave them for her. Wow again. These are convincing signals of strength, intelligence, wealth, and general fitness. Furthermore, clothes can carry identifying marks of a person's group membership.

Human head hair is much better suited than animal hair to work as sexual ornament: a woman with flowing, cascading hair is healthy and fertile, a man with a beard is mature, and even a bald man can look sort of "venerable" in his own way, rather like a silverback gorilla. My theory of fur loss says that clothes have a function similar to that of head hair. Proto-clothes might have begun as group-identifying armbands, or coverings for the head, or protection for the more vulnerable parts of the body such as the genitals. All of these might have developed in their own way — into fuller "uniform", into protection from thorns, weather and armed combat, into various sexually "teasing" garments...

Only then, after clothes have become a quite well-developed part of early human culture, would it have become necessary for the fur to thin out. (And with some people it hasn't thinned all that much.)

But why — you might ask — would overheating be such a problem if people can simply take their clothes off? — It's a matter of adding up the numerous extra conveniences/inconveniences that go with clothing versus the lack of clothing, fur versus lack of fur, and trying to guess how they all add up over the long run.

I can't hope to list them all. But here are few thoughts: people who remove clothing during the heat of the day and carry it with them certainly do have an extra burden, but that is offset by not having to light fires during the cold of the night, by having extra protection from mosquitoes, by being able to venture into inhospitable places (high altitudes and latitudes, through thick vegetation; into water, onto burning sand, under relentless sunshine, snow, rain, etc., etc.). Above all, perhaps, they have greater protection if involved in violence. Unfortunately, humans everywhere have a propensity to get involved in violence. People who have a lot of fur have the disadvantage of not being able to use clothes as efficiently as those who have less fur. Furry people cannot exploit clothing "technology" as well as furless people.

I would speculate that just as language would have been an advantage to just about any creature that had the intelligence to use it, so clothing too would have been an advantage to any creature that was able to wear it. But of course, only humans have the intelligence or technology to exploit either.

Quite apart from the practicalities of clothing, as soon as it becomes an ornament of sexual selection, not having it becomes a significant disadvantage. Look at how much money men and women are prepared to spend on clothes today. Clothes are more than a practical alternative to fur.

But what about Africans and South Americans who wear hardly any clothing?

Some groups of humans wear very little clothing, sure, but why suppose that they are somehow more authentically human than the rest of us? The vast majority of humans wear clothing, and the few that wear little clothing wear at least some clothing — so clothing "technology" is not completely alien to them as it is to other animals. I submit that they wear little clothing simply because they live in a hot climate, and most important of all they have to deal with very limited quantities of water (which clothes need to be washed in). It is not because clothing is somehow not "naturally" human.

Even if we accept that the inhabitants of central Africa live in the same geographical location as proto-humans, they are descended from humans from a much wider "catchment area", most of whom probably wore more clothing than they do.

The late Larry Trask (the linguist) used to remind everyone that all groups of humans, without exception, speak sophisticated language, and the same applies to technology. Every human society has the know-how to light fires, to make houses, weapons, fishing nets, etc.. We are by nature a linguistically and technologically sophisticated animal.

Our technological abilities evolved at the same time as our brains, and our brains evolved at the same time as the rest of our bodies — and it shows. Our hands are shaped for extremely sophisticated feats of manual dexterity (from tying a knot or making a weapon to playing a musical instrument). The dexterity is as much a feat of the brain as the hand. Our livers are capable of metabolizing alcohol, because our brains can deal with the technology of fermenting drinks.

If our hands and our livers reflect our specifically human technological abilities, i.e. brain evolution, why not our skin too?

The idea that clothes are a "cultural" development that has nothing to do with the physical evolution of our bodies is a "blank slate" assumption. Like language, technology isn't solely the result of culture, because it also requires the evolution of the brain. The specific details of each technology are learned, like the specific details of each language. But the ability to utilize technology is innate, like the ability to learn language. The three "traditional" theories of hair loss all assume that clothing is somehow "unnatural". It's much like the idea that humans are naturally "grunters" (as in the movie "One Million Years BC") rather than speakers of language.

(Read about the other theories of fur loss in a recent Scientific American here: Why did we lose our fur?)