Blogs > HNN > Head-scratching puzzle: What lice have to say about human evolution

Mar 12, 2007 7:55 pm

Head-scratching puzzle: What lice have to say about human evolution

One of the more embarrassing mysteries of human evolution is that people are host to no fewer than three kinds of louse while most species have just one.

Even bleaker for the human reputation, the pubic louse, which gets its dates and residence-swapping opportunities when its hosts are locked in intimate embrace, does not seem to be a true native of the human body. Its closest relative is the gorilla louse. (Don't even think about it.)

Louse specialists now seem at last to have solved the question of how people came by their superabundance of fellow travelers. And in doing so they have shed light on the two major turning points in the history of fashion — when people lost their body hair, and when they first made clothing.

Three kinds of louse call Homo sapiens their home, but each occupies a different niche on the human body. The head louse, Pediculus humanus, lives in the forest of fine hairs on the human scalp. Its cousin, the body louse, lives not on the skin but in clothes. And the exclusive territory of the pubic louse, Phthirus pubis, is the coarser hairs of the crotch.

Lice are intimately adapted to their hosts and cannot long survive away from the body's blood and warmth. If their host evolves into two species, the lice will do likewise. So biologists have long been scratching their heads over the fact that the human head louse is a sister species to the chimpanzee louse, but the pubic louse is closely related to the gorilla louse.

By comparing louse DNA, a team lead by Dr. David Reed of the University of Florida has now reconstructed how this strange situation probably came about. Reed's team collected pubic lice from a public health clinic in Salt Lake City. Persuading a gorilla to donate its lice for scientific research is a less routine matter, but samples were obtained by members of the Mountain Gorilla Veterinary Project, which provides free health care to gorillas in the wild.

The number of DNA differences between the gorilla louse and the pubic louse indicates that they diverged some 3.3 million years ago, Reed and colleagues report in Thursday's issue of the journal Biomed Central Biology. Among people, the pubic louse is usually spread by sexual contact but the gorilla louse could have been contracted in some other way....

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