Until December 2020, the coronavirus variants didn’t seem at the time to be more infectious, or more dangerous in any intrinsic way. Emma Hodcroft, a molecular epidemiologist at the University of Bern and others who study the evolution of viruses provide a few overlapping answers to the question “Why now?” None of them perfectly explain what’s going on. Now with the vaccine roll out (in most developed countries), another set of questions spring to mind: How might the coronavirus continue to evolve? Will even more variants emerge that challenge our fight against the virus? And what does that mean for the pandemic? Here the experts outline four reasons we’re seeing these variants now. And it all boils down to one thing: evolution.