But recently, three distinct versions of the virus seem to have independently converged on some of the same mutations, despite being thousands of miles apart in the United Kingdom, South Africa, and Brazil. (A mutation is a genetic change; a variant is a virus with a specific set of mutations.) The fact that these mutations have popped up not one, not two, but now three times—that we know of—in variants with unusual behavior suggests that they confer an evolutionary advantage to the virus. All three variants seem to be becoming more common. And all three are potentially more transmissible.

“Anytime when you have mutations that come up independently of each other in multiple places, it’s really a sign,” says Vineet Menachery, a coronavirus researcher at the University of Texas Medical Branch. Now scientists are scrambling to figure out if and how these mutations might give the viruses an edge.

It’s still early, and data on the variant in Brazil are particularly sparse. In addition to sharing certain mutations, though, these variants simply have a large number of mutations, some unique to each variant. Gaining a whole suite of mutations quickly should be a very uncommon event. But with the virus so widespread right now, very uncommon events will happen—and will happen more than once. The usual two-per-month mutation rate may undersell how the coronavirus can mutate in unusual situations. “It’s a little bit of a wake-up call,” Kristian Andersen, a microbiologist at Scripps Research, told me.