Some viruses are old enemies of our species. Rhinoviruses gave ancient Egyptians colds, and endogenous retroviruses invaded the genomes of our primate ancestors tens of millions of years ago. Other viruses are younger. HIV, for example, became a human virus about a century ago. And other viruses are only just starting to patter down on our species, triggering outbreaks and raising fears of new global plagues. Of all these newly discovered viruses, none inspires more fear for the future than Ebola.
