Herpes, tuberculosis, and tapeworms may have led to their demise
With the advent of agriculture around 12,000 years ago, humans were suddenly living in dense populations, becoming increasingly sedentary, and interacting with livestock. A far cry from hunter-gatherer life, these were ideal conditions for certain diseases to flourish and spread. The longstanding view is that many of the major human infectious diseases that exist today arose during this time.
But a study published in the American Journal of Physical Anthropology adds to a growing body of evidence indicating that some common diseases actually pre-date agriculture. In fact, the research indicates that modern humans carried these deadly diseases with them out of Africa. As they expanded into Europe and Asia, humans infected Neanderthals, who had inhabited the Eurasian landscape for some 200,000 years prior, with a slew of diseases such as tapeworm, tuberculosis, stomach ulcers, and types of herpes.
By studying pathogen genomes and DNA extracted from ancient bones, the researchers concluded that some infectious diseases have been “co-evolving with humans and our ancestors for tens of thousands to millions of years.”
While the study did not provide direct evidence of disease transfer between humans and Neanderthals, the newly established timeline indicates that such transfers were highly probable. Furthermore, it is already established that our ancestors interbred with Neanderthals, and this was a likely means of disease exchange.
"Humans migrating out of Africa would have been a significant reservoir of tropical diseases," said Dr. Charlotte Houldcroft, from Cambridge's Division of Biological Anthropology. "For the Neanderthal population of Eurasia, adapted to that geographical infectious disease environment, exposure to new pathogens carried out of Africa may have been catastrophic."
By the time they expanded into Europe, humans would have already been adapted to African diseases. But Neanderthals were defenseless against these hostile pathogens. Many of the infections likely to have transferred from humans to Neanderthals are chronic diseases that would have weakened their small hunter-gatherer bands, impacting their ability to forage, and ultimately spelling disaster for the species.
Climate change and competition with humans are also theorized to have contributed to their extinction. "It is probable that a combination of factors caused the demise of Neanderthals," said Houldcroft, "and the evidence is building that spread of disease was an important one."
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