50,000-Year-Old Neanderthal Bones Have Remains of Human Viruses, Scientists Find

The preliminary analysis is a first step in testing the theory that infectious diseases played a role in Neanderthals’ extinction

Green and yellow color-enhanced close-ups of adenovirus
Color-enhanced transmission electron microscope images of adenovirus, which is a common cause of respiratory illnesses. Researchers identified adenovirus remnants, as well as herpesvirus and HPV, in Neanderthal remains in a new study. BSIP / UIG via Getty Images

Scientists have detected remnants of three types of viruses in 50,000-year-old Neanderthal bones. The findings, researchers say, are a first step in testing the theory that viral infections could have played a role in the extinction of Neanderthals.

In a paper posted to the preprint site bioRxiv, the researchers detected fragments of adenovirus (which causes cold-like illnesses), herpesvirus (linked to cold sores) and papillomavirus (HPV) in Neanderthal genome data. The findings have not yet been peer reviewed.

If confirmed, the new findings would be the oldest human viruses ever recovered, setting a record previously held by a 31,000-year-old adenovirus, reports New Scientist’s James Woodford.

“This DNA contains… a mixture of various DNAs, from the Neanderthal individual themselves, plus bacteria, fungus and viruses that might have infected this individual,” Marcelo Briones, a co-author of the new study and a genome researcher at the Federal University of São Paulo in Brazil, writes in an email to Gizmodo’s Isaac Schultz. “We show that the degree of such changes in the viral genome reads recovered are consistent with the age of the Neanderthal bones, thus showing that they are not present-day contaminants.”

“Taken together, our data indicate that these viruses might represent viruses that really infected Neanderthals,” he tells New Scientist.

Neanderthals, the closest extinct relative to modern humans, lived from about 400,000 to 40,000 years ago, when they mysteriously vanished. Today, between 1 and 4 percent of the DNA in modern humans of non-African descent comes from Neanderthals; African people have about 0.5 percent Neanderthal DNA.

Scientists don’t know what led to Neanderthals’ extinction, but they have some hypotheses. Modern humans could have outcompeted them for resources, for one. As they interbred with humans, genetically distinct Neanderthals could have gradually disappeared. Or, maybe Neanderthals were less adaptable to environmental or climatic changes than modern humans were, and the start of the last ice age spurred their decline.

Another idea is that infectious diseases, possibly introduced by the ancestors of modern humans, could have contributed to Neanderthals’ extinction. Evidence suggests that Neanderthals and human ancestors interbred and traded genes tied to disease, as well as spread infections between their populations as modern humans’ ancestors carried diseases out of Africa.

For the new paper, researchers wanted to test the theory that infections drove Neanderthals to extinction by trying to identify remnants of viral DNA in Neanderthal genes. They examined genome data from Neanderthal bones uncovered in the Chagyrskaya cave in Russia, finding evidence of bacteria, fungi and viruses.

The researchers detected the three viruses in a single individual, which they say is not surprising, since the pathogens are highly contagious and tied to social behavior. Present-day individuals are exposed to about ten viral species during their lifetimes, the authors write.

While the viruses are types that infect humans, these specific samples are inert, so they can’t cause illness now.

The findings suggest researchers have a lot more to learn about past diseases that could have affected modern humans’ ancestors and extinct relatives, Sally Wasef, a paleogeneticist at Queensland University of Technology in Australia who did not contribute to the work, tells New Scientist. But this field of discovery is still new, she adds, and needs more exploration.

“The current tools used to authenticate ancient DNA results from humans might not apply to viruses, which have shorter DNA strands by default,” she tells the publication.

The new findings do not confirm viruses played a role in Neanderthals’ disappearance, but they provide proof of concept results that show the species could be infected by human diseases.

In 2018, researchers proposed a related scenario—that human ancestors were also infected by Neanderthal diseases, but they eventually developed resistance through interbreeding.

However, as Briones tells Gizmodo, Neanderthals had a smaller overall population and lower genetic diversity, traits that made them less equipped to deal with new pathogens. The ancestors of modern humans may have had “a higher genetic resistance against infectious diseases… compared to Neanderthals,” he adds. “It is more likely that archaic anatomically modern humans infected Neanderthals than the reverse.”

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