Why did our close evolutionary cousins, the Neanderthals, go extinct? It’s one of the big questions in anthropology that may never be fully answered. Some of the proposed factors include climate change and increased competition from Homo sapiens. But what is often missing from this discussion is a factor notorious for decimating human populations: disease.

Researchers from the Federal University of São Paulo have uncovered the oldest known human viruses in 50,000-year-old Neanderthal bones. This discovery raises new questions about the role viruses might have played in the extinction of Neanderthals.

To find these ancient viruses, the team analyzed DNA from Neanderthal remains found in Chagyrskaya Cave, Russia. They were searching for remnants of three types of DNA viruses: adenovirus, herpesvirus, and papillomavirus. Remarkably, they found traces of all three, making these the oldest human viruses ever discovered.

Previously, a 2018 study that sampled DNA from 300 Bronze Age skeletons across Europe and Asia discovered 12 ancient hepatitis B virus (HBV) genomes, including an extinct variant. Then in 2022, researchers at the University of Copenhagen discovered a 31,600-year-old virus in two human milk teeth uncovered in Siberia — this was the previous record holder until this new find.

Ancient Viruses Unearthed

The presence of these viruses in Neanderthal remains suggests that Neanderthals suffered from the same viruses that affect humans today. Adenoviruses, for instance, can cause illnesses like the common cold and acute gastroenteritis. Herpesviruses, including the Epstein-Barr virus, can trigger mononucleosis and multiple sclerosis. Papillomaviruses are known for their link to cervical cancer.

This discovery leads to the possibility that Neanderthals might have been particularly susceptible to these viruses. However, it’s important to note that contamination is a significant concern in paleogenetics. In this case, the researchers are confident contamination was not a factor as they compared ancient virus sequences with modern ones. None of these ancient samples matched relatively recent viral strains.

“The reconstructed ancient viral genomes of adenovirus, herpesvirus and papillomavirus revealed conserved segments, with nucleotide similarity to extant viral genomes, and variable regions in coding regions with substantial divergence to extant close relatives,” the scientists in Brazil wrote.

The fact that viruses infected Neanderthals was never up for debate. All primates are routinely infected with viruses, bacteria, fungi, and a host of other pathogens. In fact, diseases routinely jump between primates. For instance, a recent study involving two chimpanzee sanctuaries in Uganda and Zambia found that 58 percent of the chimpanzees carried drug-resistant strains of the Staphylococcus aureus bacteria probably acquired from ten of the human veterinarians working at the sanctuaries who also carried the bacteria.

Another study investigated five devastating respiratory disease outbreaks in the Chimpanzee population of Côte d’Ivoire in West Africa between 1999 and 2006. Nearly all the endangered chimps in the region became sick and many died. Researchers from Emory University found that tissue samples gathered from chimp victims tested positive for one of two germs — human respiratory syncytial virus (HRSV) or human metapneumovirus (HMPV).

Possible Impact on Neanderthal Extinction

If humans can infect chimps very easily, one might presume that Homo sapiens and Neanderthal encounters resulted in a germ exchange. The two species of humans were close enough to interbreed, since 2% of the DNA of people of European or Asian descent is Neanderthal in origin. This means they were definitely close enough to swap all kinds of diseases, including viruses, as this recent research shows.

While the new findings do not claim that viruses were the sole cause of the Neanderthal extinction, they support the idea that viruses could have played a role.

If validated, these findings could significantly alter our perspective on the health challenges faced by Neanderthals and their eventual decline. By examining ancient DNA, scientists continue to piece together the complex puzzle of our ancestors’ lives and deaths.

The findings appeared in the preprint server bioRxiv.