How Neanderthals, prehistoric humans who lived until about 40,000 years ago, went extinct while modern humans, Homo sapiens, survived is one of the biggest unanswered questions in the story of our species. One theory, proposed in 2010, is that Neanderthals may have fallen victim to viral infections carried by modern humans. Now evidence that supports this idea has emerged with the discovery of DNA from three viruses found in 50,000-year-old Neanderthal bones.

​​​​​​​31st May 2024

After hundreds of thousands of years of successful adaptation to the changing climate (including several ice ages), it is not clear why Neanderthals failed to survive. The close timing of the arrival of modern humans and the disappearance of Neanderthals points the finger at us as the likely cause. It is possible that Homo sapiens with their superior tools and weapons could have out-competed Neanderthals for food and other resources. But like us, Neanderthals were skilled hunters and had complex social structures of their own, so it seems unlikely this was the main cause. Scientists have long wondered whether deadly diseases brought by the invaders could have been responsible—but how could this be proved?
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DNA discoveries

Researchers at the Federal University of São Paulo in Brazil sampled DNA from the 50,000-year-old skeletons of two male Neanderthals. The remains were first discovered in 2022 at Chagyrskaya cave in the Altai mountains of southern Siberia, Russia.

Amongst the Neanderthal genome, they found traces of DNA that resembled three modern viruses: adenovirus, which today causes common colds, herpesvirus, which causes cold sores and papillomavirus, which causes genital warts. The viral DNA obtained differed from that found in humans today, enabling the scientists to tell that they were not contracted from predators that fed on the remains, or from modern humans who might have handled the bones.

We know, however, that diseases brought by one group of humans to infect another group lacking in resistance to them, has occurred in more recent times. Smallpox and other diseases unwittingly carried by European explorers and settlers arriving in the Americas for the first time in the 16th century devastated Native American populations who had no previous contact with the virus that caused the diseases and to which they had no immunity.
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Neanderthals' immune systems had adapted gradually to the pathogens (disease-causing micro-organisms such as viruses and bacteria) in Europe and Asia. But modern humans travelling to the region carried pathogens from Africa that would have been mostly alien to Neanderthals. Pathogens that caused mild symptoms in one species could have been deadly in another. But why was it the Neanderthals who died out rather than the migrant Homo sapiens encountering alien Neanderthal pathogens also for the first time?

​​​​​​​Homo sapiens came from tropical and subtropical Africa, habitats with much more varied animal life. Microbes found there were highly capable of jumping from one species to another and infecting humans. So modern humans would have carried far more deadly pathogens—to which they themselves had already adapted and become immune—than Neanderthals. We modern humans survived while Neanderthals did not.