Sometime in the waning days of 2019, a novel coronavirus began spreading in the Chinese city of Wuhan.
It would take several weeks for local doctors and health officials to realize the new virus was responsible for a spate of mysterious cases of a pneumonia-like illness that did not respond to standard treatments.
As physicians at various hospitals treated a handful of increasingly sick patients, they realized that many of them had ties to the Huanan Market, where live animals were available for sale.
Viruses have been known to jump from animals to humans in markets like this. That makes, the one in Wuhan a prime suspect in the search for the origins of the COVID-19 pandemic.
Michael Worobey, an evolutionary biologist at the University of Arizona, has pieced together clues from earliest days of the outbreak. Writing in the journal Science, he strengthens the case that the Huanan Market was the most likely source of the SARS-CoV-2 virus.
Here’s a closer look at some of the key events.