Head lice crawling through human history

Head lice have been plaguing humans for thousands of years, and new research shows these blood-sucking parasites hitched a ride with humans during two separate waves of migration to the Americas.

Researchers from the US, Argentina and Mexico analysed genetic variation in 274 specimens of human lice (Pediculus humanus) from 25 geographic locations across Africa, Asia, Europe and the Americas. 

Their findings, published in PLOS One, reveal the evolution of the itchy troublemakers mirrors historical patterns of human migration and colonisation.

The analysis – using mitochondrial DNA and nuclear genetic diversity – identifies two distinct genetic clusters of head lice.

The first cluster has worldwide distribution. Whereas the second is restricted to Europe and the Americas, and is thought to be descended from a mix between the two groups that arrived with migration.

The findings suggest lice were brought to the Americas by the first peoples, and then again in a second wave aligned to European colonisation.

Head lice are one of the oldest parasites known to live on humans. The tiny insects have been cohabiting with people for at least 10,000 years – based on nits found in archaeological sites from Brazil and Israel.

As any parent of primary school or kindergarten children knows, lice can be rapidly transferred from one human to another via body contact, such as during a fight, living with others, and sharing headwear or combs.

And it’s their close relationship and co-evolution with humans, that makes studying lice useful in providing insights into human history, such as when humans started wearing clothes and patterns of migration.

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