All organisms on Earth experience infection by viruses. This includes the estimated one trillion microbial species that inhabit every part of Earth’s surface, from deep-sea hydrothermal vents to the clouds (Locey and Lennon 2016). If we assume that each of these one trillion microorganisms hosts at least one virus, we begin to appreciate the vast…

There is perhaps no question that has plagued virologists and evolutionary biologists more than this: where do viruses come from? Frustratingly, the tools that we traditionally use to infer evolutionary history, struggle to place viruses in the Tree of Life1. Even more perplexing is that we have yet to identify a universal common ancestor for…