Comment by Lawrence O. Gostin

Of the three possibilities — natural, accidental, or deliberate — the most scientific evidence yet identified supports natural emergence. More than half of the earliest Covid-19 cases were connected to the Huanan market, and epidemiologic mapping revealed that the concentration of cases was centered there. In January 2020, Chinese officials cleared the market without testing live animals, but positive environmental samples, including those from an animal cage and a hair-and-feather–removal machine, indicated the presence of both SARS-CoV-2 and Covid-susceptible animals. Recently released findings included raccoon dog DNA, pointing to a possible SARS-CoV-2 progenitor. Samples from early cases in humans also contained two different SARS-CoV-2 lineages. Although only one lineage spread globally, the existence of multiple lineages suggests that a SARS-CoV-2 epidemic in animals may have led to multiple spillover events.