The study found modern humans have two genetically distinct types of head lice. One type is found worldwide and evolved on the ancestors of our species, Homo sapiens. The second type is found only in the Americas, evolved on another early human species (possibly Homo erectus) and jumped to Homo sapiens during fights, sex, sharing of clothes or perhaps cannibalism.

"We've discovered the 'smoking louse' that reveals direct contact between two early species of humans," probably in Asia about 25,000 to 30,000 years ago, says study leader Dale Clayton, a professor of biology at the University of Utah. "Kids today have head lice that evolved on two species of cavemen. One species led to us. The other species went extinct."

Alan Rogers, a co-author of the study and professor of anthropology at the University of Utah, says: "The record of our past is written in our parasites."

The analysis of lice genes also confirmed two other key developments in human evolution. First, it verified studies showing how and when various species branched off the family tree of primates and humans. Second, it confirmed the "out of Africa" theory that the population of Homo sapiens mushroomed after a small band of the early humans left Africa sometime between 150,000 and 50,000 years ago.

The study will be published online Oct. 5 in the Public Library of Science journal PLoS Biology. The study's first author is former University of Utah postdoctoral fellow David L. Reed, now assistant curator of mammals at the University of Florida's Florida Museum of Natural History. Other authors are Vincent Smith of Scotland's University of Glasgow, and Shaless Hammond, who worked in Clayton
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4-Oct-2004