"When a virus attacks a species, it typically becomes immune to that virus through genetic evolution," study co-author Zach Wood, a postdoctoral researcher in the School of Biology and Ecology at the University of Maine, told Live Science. Such evolution works slowly, as those who are more susceptible die off and only those who survive pass on their genes. But nowadays, humans mostly don't need to adapt to such threats genetically. Instead, we adapt by developing vaccines and other medical interventions, which are not the results of one person's work but rather of many people building on the accumulated "mutations" of cultural knowledge. By developing vaccines, human culture improves its collective "immune system," said study co-author Tim Waring, an associate professor of social-ecological systems modeling at the University of Maine. And sometimes, cultural evolution can lead to genetic evolution. "The classic example is lactose tolerance," Waring told Live Science. "Drinking cow's milk began as a cultural trait that then drove the [genetic] evolution of a group of humans." In that case, cultural change preceded genetic change, not the other way around.