1:

Ask any drug company, which keeps having to produce better and better drugs to fight the bugs which keep evolving resistance to the present drugs.

2:

Evolving or “survival of the fittest”? I have always wondered that?

Do the non immune bugs die out and the immune ones breed and make up seemingly a new virus, or just an old one now the majority?

3:

It’s related to the speed with which bacteria and viruses reproduce.

They reproduce in a matter of minutes, and their rate of mutation is correspondingly more rapid.

There may be only an occasional mutation which protects bugs against antibiotis, but with billions of them around, it only needs one to survive the antibiotic and start reproducing.

Most of the non-mutants get killed off, leaving the field clear for the new variety to reproduce.

This is one of the reasons that scientists have expressed alarm over the past couple of decades about livestock being fed antibiotics, partly to keep them healthy but also partly to fatten them for market without the need to keep checking for sick ones and remove them. Bugs, in general, don’t mind which kind of mammal they inhabit, and mutants from animals can move into the human population with devestating results.

Two examples.

HIV moving from monkeys/apes in Africa to humans. Bird flu moving from birds to humans, initially in Asia but now in other parts of the world.

Ken Smith