Head lice migrated alongside humans to the Americas on multiple occasions

Lice are insects that have been infesting humans for as long as our species has existed, and their genes tell the story of their hosts' worldwide travels, as revealed in a study.

According to the extracted lice DNA, humans were unknowingly responsible for transporting these small pests to the New World on at least two occasions — a long time ago from Asia, and quite recently through European settlers, as observed in a PLOS ONE report published on November 8.

Regular head lice (Pediculus humanus capitis) are incapable of jumping or flying. Their only method of travel is crawling, which closely links their movements to that of their human hosts, explainings Marina Ascunce, an evolutionary geneticist at the U.S. Department of Agriculture’s Agricultural Research Service in Gainesville, Florida. 

Ascunce and her team investigated the DNA derived from 274 head lice discovered on people at 25 different locations worldwide, checking the differences in 15 tiny portions of the lice genetic code. They found that the lice were genetically divided into two main groups — one prevalent in Europe and North America, and the other in Asia and Central America.

The researchers speculate that the connection between Central America and Asian populations is attributable to ancient human migration across a land bridge into the Americas some thousands of years ago. Meanwhile, the other group of lice commonly found in the Americas showcases the more recent settlement of Europeans in the region.

Lice, acting as our evolutionary 'storytellers', are not entirely harmful, remarks Ascunce. "They can also allow us to perceive our history."

The remarkable genetic variation between European and Asian lice was unexpected, according to Ascunce and her team. For their future research, they plan on studying genes from more slowly evolving lice, which could offer clues as to how the genetic division occurred and could possibly reveal older events in human prehistory and the evolutionary changes they sparked.

Andrew Sweet, an evolutionary biologist not involved in the new research, claims the general study of 'lice evolution' can quicken our understanding of human and host evolution, since these parasitic insects have quicker generation times and mutation rates.

Sweet, a scholar at Arkansas State University in Jonesboro, adds, "From the parasites, one might be able to detect emergent evolutionary patterns before they become evident in the hosts."

Ascunce and her fellow researchers believe that using their methodology with other parasite species could deliver more knowledge about the evolutionary past of other host species that are not yet well-studied.

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