Therefore virus must arisen natural selection , manipulation.If argument seems hard grasp , ’ ’ strained.The authors ’ basic assumption , spelt , anyone trying make bat virus bind human cells could one way.First would calculate strongest possible fit human ACE2 receptor spike protein virus latches onto it.They would design spike protein accordingly ( selecting right string amino acid units compose ) .Since SARS2 spike protein calculated best design , Andersen paper says , therefore ’ manipulated.But ignores way virologists fact get spike proteins bind chosen targets , calculation splicing spike protein genes viruses serial passage.With serial passage , time virus ’ progeny transferred new cell cultures animals , successful selected one emerges makes really tight bind human cells .