Is evolution by natural selection unidirectional or irreversible?

Question

Why or why not?

Use evidence from the rise of AZT resistance to justify your answer.

(this is a review question for an exam and I am completely stumped. thanks in advance for all the replies.)

Answer 1

There is absolutely no such thing as Evil-lution...(evolution????)

Answer 2

Evolution as a process lacks direction. It happens by change or a mutation but is a mindless thing. Evolution does not choose to progress, it happens and is either advantageous to the organism and that organism reproduces and passes that mutation on or it is a disadvantage to that organism and it does not live to pass on its genes.

But I must stress again that evolution does not pursue any goal, or direction. It is simply change, for worse or for better.