How lice evolved alongside humans to become the perfect pests — and trackers of human migration

• Head lice have plagued communities for centuries across the world.
• They have evolved — and traveled — with humans to continually survive and find new hosts.
• Now, a new study suggests lice DNA can help track human migration from continent to continent.

Since humans have had hair, we've probably also had lice.

The small parasites, which live on human heads, have plagued school classrooms and sleepovers alike for centuries, but a new study shows a previously undiscovered good side to them — their DNA could hold answers to human migratory patterns.

Marina Ascunce, who works as an evolutionary geneticist at the US Department of Agriculture, told NPR the lice were like "heirlooms of our past."

Ascunce and her colleagues recently published a study in PLOS One revealing their results.

To complete the study, the researchers looked at 175 head lice from 18 sampling locations and nine geographic regions.

The researchers found that two different genetic clusters were present in the lice's DNA, which indicated that head lice came to the Americas two separate times, per the study.

For Ascunce, the findings suggest that the lice were first brought to the Americas tens of thousands of years ago, when humans crossed the Bering Strait from Asia into North America, per NPR.

More recently, around the 16th century, European colonizers brought their own head lice to the Americas when they arrived, according to NPR.

"These lice are mirroring the colonization of the Americas," Ascunce told NPR. "The two migration waves."

The study also suggested, per its conclusion, that the distinction between the clusters could be a result of some kind of internal mechanism preventing the lice from genetically intermixing.

One specialist, invertebrate biologist Alejandra Perotti, told NPR the study had a good approach, but shouldn't be considered conclusive due to its small sampling size.

"If you look at the data they gather, some of the populations have only one louse, including Africa, for example," Perotti said to NPR. "So there is an issue with the sampling size."

But not to worry — Ascunce and her fellow researchers are already planning further studies, per NPR, where they plan to look for potential louse interactions between early humans and Neanderthals, who would have also had lice.