Head lice have been bugging humans for so long, their DNA actually holds information about the history of our species.
Lice are one of the oldest known parasites to live on humans. Since the two species have coevolved for millennia, studying lice can offer clues to how humans evolved as well.
A new analysis of lice genetic diversity suggests that lice came to the Americas twice on human hosts – once during the first wave of human migration across the Bering Strait, and again during European colonization.
In the new study, published in journal PLOS ONE, researchers analyzed the genetic variation in 274 human lice from 25 geographic sites around the world.
A genetic analysis based on louse DNA revealed the existence of two distinct clusters of lice, according to the study. Cluster I had a worldwide distribution, while cluster II was found in Europe and the Americas. The only lice with ancestry from both clusters are found in the Americas.
"This distinct group appears to be the result of a mixture between lice descended from populations that arrived with the First People and those descended from European lice, which were brought over during the colonization of the Americas," the authors noted in a press release.
The researchers also identified a genetic relationship between lice in Asia and Central America, supporting the idea that people from East Asia migrated to North America and became the first Native Americans. These people then spread south into Central America, where modern louse populations today still retain a genetic signature from their distant Asian ancestors, according to the study.
The study says its findings support existing ideas about human migration and provide additional knowledge about how lice have evolved.
"Human lice are more than annoying human parasites, they are 'satellites' of our evolution," the study authors said in a statement. "Because human lice feed on human blood, they need us to survive, and over millions of years this resulted in a long co-evolutionary history together."