“You can think of these genetic adaptations like footprints from long-extinct dinosaurs preserved in fossilized mud. Even without having access to the viruses themselves, scientists who study prehistoric epidemics will be able to learn about the pathogens that drove them,” says David Enard, an evolutionary biologist at the University of Arizona who argues in new research that when humans first met Neanderthals, they got infected from unfamiliar Neanderthal viruses, against which they had no immunity.
