Viral evolution
adenine, cytosine, uracil, guanine
Darwinian evolution
Species undergo random mutation
Making most less fit
But making a few more fit
Fit means compete, survive, reproduce
Natural selection will ‘select’ the more fit
Viruses usually become less virulent over time
Increased virulence / transmissibility
Mutations that increase transmissibility
Mutations that can avoid antibodies
Mutations that can avoid vaccination defences
Source