From MSNBC:
Head lice live in the hair on the head. But body lice, a larger variety, are misnamed: they live in clothing. Head lice, as a species, go back millions of years, while body lice are a more recent arrival. Stoneking, an evolutionary anthropologist, had a hunch that he could calculate when body lice evolved from head lice by comparing the two varieties’ DNA, which accumulates changes at a regular rate. (It’s like calculating how long it took a typist to produce a document if you know he makes six typos per minute.) That fork in the louse’s family tree, he and colleagues at Germany’s Max Planck Institute for Evolutionary Anthropology concluded, occurred no more than 114,000 years ago. Since new kinds of creatures tend to appear when a new habitat does, that’s when human ancestors must have lost their body hair for good—and made up for it with clothing that, besides keeping them warm, provided a home for the newly evolved louse.
If you had asked paleoanthropologists a generation ago what lice DNA might reveal about how we became human, they would have laughed you out of the room. But research into our origins and evolution has come a long way.
More here.