How is a virus species defined ? As I understand it a species is a group of organisms that can reproduce viably with each other. But a virus doesn't reproduce like that, they clone themselves by hijacking a cell's machinery, so there is no notion of compatibility between viruses. The article says that Covid-19 is "similar" to SARS so it was put in the same species, but that seems a rather soft definition. Especially if there are trillions of different viruses like the article says, some objective criterion is needed. Not to mention viruses mutate all the time, at what point does it become a new species?