CW: images from fur farms
Put simply, if SARS-CoV-2 came about by frequent recombination through contact with common virus-carrying animals in the wild, we would expect it to display a mix of genome segments shared between it and several of their close cousins. However, if SARS-CoV-2 came about through manipulation in a lab, such as through gain-of-function research, we would expect a close match to one and only one “initial” strain, with the remainder of the genome failing to match any other wild strains. The discovery that SARS-CoV-2 does indeed have what biologists call a mosaic genome makes it abundantly clear that it could not have arisen through laboratory manipulation of an initial, single strain, through gain-of-function research or otherwise.