In the past 20 years, new coronaviruses have emerged from animals with remarkable regularity. In 2002, SARS-CoV jumped from civets into people. Ten years later, MERS emerged from camels. Then in 2019, SARS-CoV-2 began to spread around the world. For many scientists, this pattern points to a disturbing trend: Coronavirus outbreaks aren't rare events and will likely occur every decade or so.