When I was your age, whooping cough wasn’t what it is today. I’m sure we all know the stereotypical grandfather telling stories like that, but — at least in this case — if he started his story off like that then he is actually right. Over the last few years, this once-common childhood illness, has evolved in response to its own vaccine, in other words this isn’t your parents’ pertussis.
In DNA mutation is often a bad thing. It’s sort of like building a car, there are far more wrong ways to one together than there are right ways. Still, mutation happens often which brings with it good (and more often bad) things. Usually mutation is spontaneous, it has no real rhyme or reason (in a broad sense) and while it brings things like cancers, it also can bring amazingly beneficial traits too. Maybe this is why a pond-dwelling, single-celled organism called Oxytricha trifallax is so keen on mixing things up. By that I mean it has the remarkable ability to break its own DNA into nearly a quarter-million pieces and rapidly reassemble those pieces when it’s time to mate.