The uniform structure SARS2 genomes gives hint passage intermediate animal host , host identified nature.Proponents natural emergence suggest SARS2 incubated yet-to-be found human population gaining special properties.Or jumped host animal outside China.All conjectures possible , strained.Proponents lab leak simpler explanation.SARS2 adapted human cells start grown humanized mice lab cultures human cells , described Daszak ’ grant proposal.Its genome shows little diversity hallmark lab cultures uniformity.Proponents laboratory escape joke course SARS2 virus infected intermediary host species spreading people , identified — humanized mouse Wuhan Institute Virology.3 ) The furin cleavage site.The furin cleavage site minute part virus ’ anatomy one exerts great influence infectivity .