A new study suggests that Neanderthals across Europe may well have been infected with diseases carried out of Africa by waves of anatomically modern humans, or Homo sapiens. As both were species of hominin, it would have been easier for pathogens to jump populations, say researchers. This might have contributed to the demise of Neanderthals.
     Researchers from the universities of Cambridge and Oxford Brookes have reviewed the latest evidence gleaned from pathogen genomes and DNA from ancient bones, and concluded that some infectious diseases are likely to be many thousands of years older than previously believed.
     Dr Charlotte Houldcroft, from Cambridge's Division of Biological Anthropology, says that many of the infections likely to have passed from humans to Neanderthals - such as tapeworm, tuberculosis, stomach ulcers and types of herpes - are chronic diseases that would have weakened the hunter-gathering Neanderthals, making them less fit and able to find food, which could have catalysed extinction of the species.
     "Humans migrating out of Africa would have been a significant reservoir of tropical diseases," says Houldcroft. "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."
     "However, it is unlikely to have been similar to Columbus bringing disease into America and decimating native populations. It's more likely that small bands of Neanderthals each had their own infection disasters, weakening the group and tipping the balance against survival," says Houldcroft.
     The longstanding view of infectious disease is that it exploded with the dawning of agriculture some 8,000 years ago, as increasingly dense and sedentary human populations coexisted with livestock, creating a perfect storm for disease to spread. The researchers say the latest evidence suggests disease had a much longer "burn in period" that pre-dates agriculture.
     There is as yet no hard evidence of infectious disease transmission between humans and Neanderthals; however, considering the overlap in time and geography, and not least the evidence of interbreeding, Houldcroft and co-author of the study and Dr Simon Underdown, a researcher in human evolution from Oxford Brookes University, say that it must have occurred.
     Neanderthals would have adapted to the diseases of their European environment. In turn, the humans, unlike Neanderthals, would have been adapted to African diseases, which they would have brought with them during waves of expansion into Europe and Asia.
The researchers describe Helicobacter pylori, a bacterium that causes stomach ulcers, as a prime candidate for a disease that humans may have passed to Neanderthals. Another candidate is herpes simplex 2, the virus which causes genital herpes.
Recent theories for the cause of Neanderthal extinction range from climate change to an early human alliance with wolves resulting in domination of the food chain. "It is probable that a combination of factors caused the demise of Neanderthals," says Houldcroft, "and the evidence is building that spread of disease was an important one."

Edited from Popular Archaeology (10 April 2016)