Scientists studying the origins of the coronavirus have found similar strains in bats and pangolins, leading to speculation that it jumped from one or perhaps both of those animals to humans earlier this year. But a new study floats a different idea: that the virus was spreading in humans for years, undetected and growing ever more dangerous, reports Science Alert. Under this scenario, the virus would have passed from animals to humans a while back, but it would have been harmless to us at the time. "Then, as a result of gradual evolutionary changes over years or perhaps decades, the virus eventually gained the ability to spread from human to human and cause serious, often life-threatening disease," writes National Institutes of Health chief Francis Collins at his blog. Collins was not involved with the study by US, UK, and Australian researchers in Nature Medicine.
The scientists found that while strains found in bats and pangolins were indeed similar to SARS-CoV-2, the strain causing the current pandemic, the gap between the animal and humans versions remains too large, per the South China Morning Post. (The human strain has a genetic mutation that makes it particularly lethal for us, and the SCMP goes into detail on that.) It's possible that a closer version in animals exists and just hasn't been found yet, but the researchers suggest it's more likely that the strain mutated within humans as it slowly spread. Among other things, that raises the possibility the disease did not originate in Wuhan, China, where the first cases were detected. Another key component of the study: The researchers say it's all but impossible that the coronavirus originated in a lab—it has all the hallmarks of a natural origin. (Read more coronavirus stories.)