The genetic study of the lice strongly suggests they -- and clothing -- arose soon after modern Homo sapiens began moving out of Africa and into the cooler regions of Europe.

Lice provide a unique insight into the development of clothing, according to the researchers, working in Germany. Only humans carry this particular species of louse, which lays its eggs in clothing and spreads typhus, among other diseases.

"It seems fairly obvious that the body louse arose when humans made frequent use of clothing," molecular anthropologist Mark Stoneking said in a telephone interview.

Stoneking and colleagues Ralf Kittler and Manfred Kayser, all of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, report their findings in this week's issue of the journal Current Biology.

Experts are eager to know when people first started to wear clothes. But while stones, tools and other evidence of human behavior survive for millennia, clothing does not.

WARNINGS ABOUT COOTIES

Stoneking, an American, thought of a way to figure it out when his son came home from school with a teacher's note.

"It was one of those notices where they let parents know some kid in the classroom has come down with head lice," Stoneking said.

"One of the points it made was that you only get head lice from other humans ... you can't get them from your dog, your cat, etc. And lice cannot survive more than 24 hours away from the human body," he added.

"It occurred to me then that if that is really true, that the spread of human lice around the world would have been driven by humans."

Three species of louse infect humans -- head lice, known to generations as "cooties," body lice and pubic lice or "crabs." Experts agree body lice are a subspecies of head lice and that body lice probably evolved when people started to wear clothing.

Stoneking's team used a molecular clock to find out when body lice evolved.

They looked at the DNA found in the mitochondria of cells. This DNA is inherited virtually intact from the mother, with any changes happening through mutation alone.

The rate of mutation can be calculated, with a certain number of changes expected with each generation. By comparing the mitochondrial DNA of body lice to that of a cousin -- chimpanzee lice -- the researchers were able to date it back to around 70,000 years ago.

This, Stoneking said, fits in with growing evidence that modern humans evolved in Africa and migrated out around 100,000 years ago. A comparison of body lice from around the world shows their genetic diversity mirrors that of humans, as well, also supporting the idea that they evolved in Africa first.

As with people, lice found in different parts of Africa are more different from one another genetically than an African louse versus a European louse, for example.

Stoneking is now starting to look at pubic lice, or crabs. He at first believed they might shed light on when humans lost their heavy body hair.

"But I found out that entomologists and taxonomists pretty much are united in agreeing that human pubic lice are more related to gorilla lice than to head lice. I don't want to speculate on what our ancestors were up to to get gorilla lice in the pubic area," Stoneking said.

August 18, 2003

BACK (Humans' fur)

© Yahoo! News