Now how does this correlate with natural selection...
Suppose you have a swamp with a bunch of frogs and three different kinds of beetles for food...
What might affect the survival of each variety of bug?
What if one kind blends in with the ferns along the water's edge?
Then if those ferns died because the swamp changed?
If all were brightly three beetles were brightly colored, could one make itself camoflaged?
What if one of the beetles happened to be green and lots of green lilypads started growing on the surface of the pond?
Would the other beetles make themselves turn green?
So, when you have lots of different bacteria that have never been exposed to arythromycin and you start taking the antibiotic for the first time what is likely to happen? Can a bacteria suddenly develop a resistance to the drug?
What if some of the bacteria are naturally mildly resistant to the antibiotic?
And if you stop taking your medicine early? What will happen the next time you take arythromycin?