A preliminary report posted online claimed that a mutation had made the virus more transmissible. Geneticists say the evidence isn’t there. All viruses mutate, and the coronavirus is no exception. But there is no compelling evidence yet that it is evolving in a way that has made it more contagious or more deadly. A preprint study — posted online, but not published in a scientific journal and not yet peer-reviewed — has set the internet afire by suggesting otherwise. The mutation, they wrote, “is of urgent concern,” because it made the coronavirus more transmissible. Following media coverage, the prospect of a turbocharged strain hopscotching around the world has unnerved many people who already had enough on their minds. But experts in viral evolution are far from convinced. For one thing, there is no new strain: Unlike the flu, the coronavirus so far has not split into clearly distinct forms. It does mutate, but that’s what viruses do. Just because a mutation becomes more common isn’t proof that it is altering how the virus functions.