Scientists claim Neanderthals were doomed by everything from climate change to their big eyes. A new study offers a different theory: humans were at least partly responsible. UK researchers say humans who migrated out of Africa were "reservoirs of tropical disease" and may have infected Neanderthals across Europe with tapeworm, tuberculosis, a bacterium causing stomach ulcers, and the herpes virus. For Neanderthals who had adapted to the diseases of Europe, "exposure to new pathogens carried out of Africa may have been catastrophic," study author Charlotte Houldcroft says, per the University of Cambridge. "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."
Experts generally believe infectious disease exploded around 8,000 years ago when the adoption of agriculture allowed humans to settle in groups with livestock, per the International Business Times. However, an analysis of pathogen genomes and DNA from ancient bones suggests some diseases have been "co-evolving with humans and our ancestors for tens of thousands to millions of years," according to the study in the American Journal of Physical Anthropology. Tuberculosis, for example, has long been thought to have reached humans through livestock. But the evidence suggests "environmental bacteria were the likely ancestors of many pathogens that caused disease during the advent of agriculture, and that they initially passed from humans into their animals," Houldcroft says. Since Neanderthals were hominins, human diseases likely passed to them easily, especially during interbreeding. (Blame Neanderthals for your allergies.)