Most scientists say SARS-CoV-2 probably has a natural origin, and was transmitted from an animal to humans. Scientists don’t have enough evidence about the origins of SARS-CoV-2 to rule out the lab-leak hypothesis, or to prove the alternative—that the virus has a natural origin. People have made a number of arguments for a lab origin for SARS-CoV-2 that are currently conjecture. Some lab-leak proponents contend that the virus contains unusual features and genetic sequences signalling that it was engineered by humans. As for finding an intermediate host animal, researchers in China have tested more than 80,000 wild and domesticated animals; none have been positive for SARS-CoV-2.