The coronavirus spike protein , adapted attack bat cells , needs repeated jumps another species , fail , gains lucky mutation.Mutation — change one RNA units — causes different amino acid unit incorporated spike protein makes spike protein better able attack cells species.Through several mutation-driven adjustments , virus adapts new host , say animal bats frequent contact.The whole process resumes virus moves intermediate host people.In case SARS1 , researchers documented successive changes spike protein virus evolved step step dangerous pathogen.After gotten bats civets , six changes spike protein became mild pathogen people.After 14 changes , virus much better adapted humans , four , epidemic took .