What would you need to find (what sort of evidence) in order to disprove the theory of evolution (or at least detract from it)?
The theory of evolution by natural selection is sometimes claimed to be an unfalsifiable theory, since it appears that no matter what fossil evidence we uncover, a 'just so' evolutionary story could be told to fit it. However, this simple-minded position seems to wrong. There does appear to be plenty of that evidence could tell against the theory if that evidence were discovered. For example, if the age of the earth were discovered to be much shorter than is required for evolution by natural selection to operate (say, a few thousand years), then that would be good reason to reject the theory. Fortunately, we have every reason to think that the earth is old enough for evolution by natural selection to have operated, and so no reason to reject the theory.