Jumping parasites followed people and adapted along with them
As a rule, when studying the history of mankind, scientists turn to bones and artifacts. However, the latest research has shown that an important link in the puzzle of “what happened in ancient times?” became lice. Head parasites lived with humans throughout time. They adapted and survived the major upheavals of the world. Lice genetics may shed light on when and where human groups diverged and how they moved across continents.
Throughout the evolutionary journey from ape-like primates to upright humans, man's companion has been the louse. All routes are written in their genes, according to a new study published in the journal Plost One on November 9.
Scientists were able to find out that, for example, some lice in North and South America are hybrids of those parasites that were among the Native Americans, and others came to the New World via the Atlantic with European colonists.
«We humans do not live in a bubble. Louse – this is part of our life and history,” – says evolutionary geneticist Marina Askuns.
Lice may provide clues to ancient events not recorded by human DNA or archaeological evidence, according to Mikkel Winter Pedersen, a molecular paleoecologist at the University of Copenhagen. He believes that this discovery could provide a potentially new perspective on migration and human interaction.
Science magazine notes that one of the potential advantages of lice as markers of human migration is that the parasites can hybridize. Thus, the common genes of lice from different continents may indicate cases where groups of people came together, for example, to trade goods.
The New York Times recalls: In the early 2000s, David Reed of the University of Florida and his colleagues found that human lice are most closely related to similar parasites that live on chimpanzees. In other words, our lice have been following us along our evolutionary path for about 25 million years.
In another study, Dr. Reed compared human lice from different parts of the world. The researchers found that many of them belonged to one of two lineages. Remarkably, these lines came from a female louse that lived perhaps a million years ago. Scientists have suggested that this split occurred when people left Africa. Along with their own lice, they picked up lice from Neanderthals or some other extinct group of people. Since this discovery, scientists have conducted similar studies with other parasites, such as bedbugs, and pathogens, such as tuberculosis and the bacterium responsible for the Black Death.
In the new study, Dr. Askuns and her colleagues analyzed the DNA of 274 lice collected from humans in 25 locations around the world, including Honduras, France, Rwanda and Mongolia.
DNA revealed two geographic clusters of lice. One of them was present in Africa, Asia, and America. Among these lice, researchers have discovered a close genetic link between Honduras and Mongolia. They suspect the relationship is a sign that Asians, who first spread to the Americas about 23,000 years ago, brought lice with them.
The remaining members of the parasites formed a second cluster, which researchers found in Europe, and also in the United States, Mexico and Argentina. The researchers also found 33 hybrids of the two clusters, 25 of which lived in North and South America.
Dr. Marina Askuns and her colleagues see these results as a chronicle of modern history. “I see this as proof of concept that human lice are good markers for evolution and the study of human migration patterns. We can see the DNA of lice reflecting our own history,” — Askuns notes.
But if these parasites are indeed colonial hybrids, Dr. Askuns and her colleagues are puzzled that they haven't found more possibilities. The rarity of hybrids may be the result of some barrier to parasitic interbreeding. Dr. Askuns said lice research has only just begun. Next plans to study the entire genome, and scientists expect the new data to provide more information.
University of Reading invertebrate biologist Alejandra Perotti, who specializes in lice, said the work was intriguing, but she also pointed out imprecision and would like the researchers to expand and diversify the sample. Available data limit the authors' ability to draw conclusions about how lice from around the world are related to each other.