The organizers of the letter, Jesse Bloom, who studies the evolution of viruses at the Fred Hutchinson Cancer Research Center in Seattle, and David Relman, a microbiologist at Stanford University, said they strove to articulate a wait-and-see viewpoint that they believe is shared by many scientists. Many of the signers have not spoken out before. “Most of the discussion you hear about SARS-CoV-2 origins at this point is coming from, I think, the relatively small number of people who feel very certain about their views,” Dr. Bloom said. He added: “Anybody who’s making statements with a high level of certainty about this is just outstripping what’s possible to do with the available evidence.” The new letter stated: “Theories of accidental release from a lab and zoonotic spillover both remain viable.”