That's What They All Do?

I saw a headline in a newspaper 'Covid-19: How and why is the virus mutating?'. I appreciate that this is a question to which many lay people will want an answer, especially at a time when one variant seems to rapidly follow another. The simple answer is that mutation is a fact of life. When DNA and RNA replicate, the mechanism is designed to produce exact copies. There are, however, ocassional flaws in the process (some spontaneous and others induced by chemicals, radiation etc). Organisms, like bacteria and viruses, that have a very short times between their generations will be much more prone to mutations than slower reproducing organisms like ourselves. The vast majority of mutations, result in organisms that are less effective than the original. These 'deleterious' mutations will be rapidly eliminated (they won't be able to thrive). Very ocassionally, a mutation will arise that confers some random benefit on the organism (easier access to the host's cells, resistance to an antibiotic or a vaccine etc). Simple Darwinian selection pressure will cause the new variant, to rapidly (each infected host cell can produce circa 10,000 viruses) replace their less effective originals. Viruses are constantly mutating and selecting. That's why we need a new vaccine each year for seasonal 'flu. The more infections you have, the greater the number of mutations. Simples!