The most salient point against a lab leak theory:<p>> “RaTG13 couldn’t have naturally morphed into SARS-CoV-2,” he says. Neither could anybody have used RaTG13 as the backbone to engineer SARS-CoV-2, as some proponents of the lab leak theory have argued: the two viruses are different in 1,100 or so nucleotides spread across their whole genomes—a gap too large for any realistic effort. Making SARS-CoV-2 from RaTG13, says virologist Angela Rasmussen of the University of Saskatchewan in Canada, “would have required a feat of unprecedented genetic engineering.”