All viruses evolve over time, accumulating mutations as they replicate imperfectly inside a host’s cells in tremendous numbers and then spread through a population, with some of those mutations persisting through natural selection. The new coronavirus has proofreading machinery, however, and that reduces the “error rate” and the pace of mutation. It looks pretty much the same everywhere it has appeared, the scientists say, and there is no evidence that some strains are deadlier than others.
