The ancestors of the coronavirus have been hiding in bats for decades, ready to infect humans.

The ancestors of the new coronavirus may have been circulating in undetected bats for decades. And those coronaviruses probably also had the ability to infect humans, according to a new study.

To understand where the new coronavirus, known as SARS-CoV-2, comes from, and how it spread to humans, scientists need to trace its evolutionary history through the virus’s genes, which are encoded in ribonucleic acid or RNA. But the evolutionary history of SARS-CoV-2 is complicated, because coronavirus are known to exchange frequently genetic material with other coronaviruses.