Chapter 8

LICE AGE

A long time ago human beings were hairy all over, like monkeys. Nowadays, however, we wear clothes to keep us warm.

How did this switch happen? Did we lose the fur and then decide to invent clothes? Or did we invent clothing and then lose the body hair that we no longer needed?

The answer isn't in any history books, because writing hadn't been invented yet when it happened. But fortunately, our little friends the parasites remember. They carry the answer in their genes.

Lice are bloodsuckers that live on people's heads. So small that you can barely see them, they hide in your hair. Once they've infested one person, they spread like a rumor, carrying trench fever, typhus, and relapsing fever. Like most bloodsuckers, lice are unpopular. That's why the word lousy is generally not a compliment.

You can't fault lousy loyalty, though. Human lice have been with us for five million years, since our ancestors split off from chimpanzees. That's a long run together. (The tapeworm, for comparison, has only been inside us for about eight thousand years, a total parasite-come-lately.) At the same time we were evolving away from monkeys, our parasites were evolving from monkey parasites - coming along for the ride.

But I bet that our lice wish they hadn't bothered. You see, while the chimps stayed hairy, we humans lost most of our body hair. So now human lice have only our hairy heads to hide in. On top of that, they're always getting poisoned by shampoo and conditioner, which is why lice have become rare in wealthy countries.

But lice aren't utterly doomed. When people started wearing clothing, some lice evolved to take advantage of the new situation. They developed claws that are adapted for clinging to fabric instead of hair. So these days, there are two species of human lice: hair-loving head lice and clothes-loving body lice.

Evolution marches on. Maybe one day we'll have space suit lice.

So what does this have to do with the invention of clothing?

Not long ago, scientists compared the DNA of three kinds of lice: head lice, body lice, and the old original chimp lice. As time passes, DNA changes at a fixed rate, so scientists can tell roughly how long ago any two species split up from each other. Comparing lice DNA soon settled the question of what came first - the clothes or the nakedness.

Here's how it happened:

Human lice and monkey lice split off from each other about 1.8 million years ago. That's when ancient humans lost their body hair and the lice we inherited from the chimps had to adapt, evolving to stick to our heads.

But head lice and body lice didn't split until seventy-two thousand years ago, an eternity later (especially in lice years). That's when human beings invented clothes, and body lice evolved to reclaim some of their lost real estate. They got brand-new claws and spread down into our brand-new clothing.

So that's the answer: Clothes got invented after we lost our body hair. And not right away; our primate ancestors ran around naked and hairless for well over a million years.

That part of human evolution is written in lousy history, in the genes of the things that suck our blood.