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