Second only to rodents, bats make up around a fifth of all mammals, with over 1,500 species of winged nightflyers. According to biologists, 50 million years of evolutionary adaptation make bats uniquely suited to not only contracting and spreading pathogens, but also resisting them. “The genes that are selected for are mostly immune-related.”Among bats, these pathogens spread even more because many species live in highly social colonies. Taken together, this means bats pass diseases between one another in tandem with the genes necessary for developing immunity better than most other animals. This avoidable close contact between humans and bats is what ultimately can cause diseases to leap between species.