In a 2017 paper, they set out how, after nearly five years of collecting fecal samples from bats in the Yunnan cave, they had found coronaviruses in multiple individuals of four different species of bats, including one called the intermediate horseshoe bat, because of the half-oval flap of skin protruding like a saucer around its nostrils. The genome of that virus, Ms. Shi and her colleagues have now announced, is 96 percent identical to the Wuhan virus that has recently been found in humans. And those two constitute a pair distinct from all other known coronaviruses, including the one that causes SARS. In this sense, nCoV-2019 is novel — and possibly even more dangerous to humans than the other coronaviruses.

I say “possibly” because so far, not only do we not know how dangerous it is, we can’t know. Outbreaks of new viral diseases are like the steel balls in a pinball machine: You can slap your flippers at them, rock the machine on its legs and bonk the balls to the jittery rings, but where they end up dropping depends on 11 levels of chance as well as on anything you do. This is true with coronaviruses in particular: They mutate often while they replicate, and can evolve as quickly as a nightmare ghoul.

Peter Daszak, the president of EcoHealth Alliance, a private research organization based in New York that focuses on the connections between human and wildlife health, is one of Ms. Shi’s longtime partners. “We’ve been raising the flag on these viruses for 15 years,” he told me on Friday with calm frustration. “Ever since SARS.”