August 20, 2003
Naked ape: Humans lost body hair long before finding clothes
Naked ape: Humans lost body hair long before finding clothes, scientists say
By NICHOLAS WADE New York TimesTuesday, August 19, 2003
One of the most distinctive evolutionary changes as humans parted company from their fellow apes was their loss of body hair. But why and when human body hair disappeared, together with the matter of when people first started to wear clothes, are questions that have long lain beyond the reach of archaeology and paleontology.
Ingenious solutions to both issues have now been proposed, independently, by two research groups analyzing changes in DNA. The result, if the dates are accurate, is something of an embarrassment. It implies that we were naked for more than a million years before we started wearing clothes.
Alan R. Rogers, an evolutionary geneticist at the University of Utah, has figured out when humans lost their hair by an indirect method depending on the gene that determines skin color. Mark Stoneking of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, believes he has established when humans first wore clothes. His method, too, is indirect: It involves dating the evolution of the human body louse, which infests only clothes.
Meanwhile a third group of researchers, resurrecting a suggestion of Charles Darwin's, has come up with a novel explanation of why humans lost their body hair in the first place.
Mammals need body hair to keep warm, and lose it only for special evolutionary reasons. Whales and walruses shed their hair to improve speed in their new medium, the sea. Elephants and rhinoceroses have specially thick skins and are too bulky to lose much heat on cold nights. But why did humans, the only hairless primates, lose their body hair?
Mark Pagel of the University of Reading in England and Walter Bodmer of the John Radcliffe Hospital in Oxford have proposed a solution to the mystery and their idea, if true, goes far toward explaining contemporary attitudes about hirsuteness.
Humans lost their body hair, they say, to free themselves of external parasites that infest fur -- blood-sucking lice, fleas and ticks and the diseases they spread.
Once hairlessness had evolved through natural selection, Pagel and Bodmer suggest, it then became subject to sexual selection, the development of features in one sex that appeal to the other.
Among the newly furless humans, bare skin would have served, like the peacock's tail, as a signal of fitness. The pains women take to keep their bodies free of hair -- joined now by some men -- may be no mere fashion statement but the latest echo of an ancient instinct.
Pagel's and Bodmer's article appeared in a recent issue of The Proceedings of the Royal Society.
Some experts could take some convincing. "There are all kinds of notions as to the advantage of hair loss, but they are all just-so stories," said Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York.
Answer may lie in pigment
Causes aside, when did humans first lose their body hair?
Rogers saw a way to get a fix on the date after reading an article about a gene that helps determine skin color. The gene, called MC1R, specifies a protein that serves as a switch between the two kinds of pigment made by human cells. Eumelanin, which protects against the ultraviolet rays of the sun, is brown-black; pheomelanin, which is not protective, is a red-yellow color.
As soon as the ancestral human population in Africa started losing its fur, Rogers surmised, people would have needed dark skin as a protection against sunlight. Anyone who had a version of the MC1R gene that produced darker skin would have had a survival advantage, and in a few generations, this version of the gene would have made a clean sweep through the population.
There may have been several clean sweeps, each one producing a more effective version of the MC1R gene.
From the number of silent mutations in African versions of the MC1R gene, Rogers and two colleagues, David Iltis and Stephen Wooding, calculate that the last sweep probably occurred 1.2 million years ago, when the human population consisted of a mere 14,000 breeding individuals.
In other words, humans have been hairless at least since this time, and maybe for much longer. Their article is to appear in a future issue of Current Anthropology.
Lice provide a clue
Remarkable as it may seem that genetic analysis can reach back and date an event deep in human history, there is a second approach to determining when people lost their body hair or at least started to wear clothes. It has to do with lice.
Humans have the distinction of being host to three different kinds: the head louse, the body louse and the pubic louse. The body louse, unlike all other kinds that infect mammals, clings to clothing, not hair. It presumably evolved from the head louse after humans lost their body hair and started wearing clothes.
Stoneking, together with Ralf Kittler and Manfred Kayser, report in today's issue of Current Biology that they compared the DNA of human head and body lice from around the world, as well as chimpanzee lice as a point of evolutionary comparison.
From study of the DNA differences, they find that the human body louse indeed evolved from the louse, as expected, but that this event took place surprisingly recently, sometime between 42,000 and 72,000 years ago. Humans must have been wearing clothes at least since this time.
The head louse would probably have colonized clothing quite soon after the niche became available -- within thousands and tens of thousands of years, Stoneking said. So body lice were probably not in existence when humans and Neanderthals diverged some 250,000 or more years ago. This implies that the common ancestor of humans and Neanderthals did not wear clothes and, therefore, Neanderthals probably didn't either.