[supercat]

Have they changed into a new species?

What exactly does the term "species" mean, given that from what I understand the conventional definition doesn't form an equivalence relation (which would mean that if A and B are the same species, and B and C are the same species, A and C would have to likewise be the same species)?

For that matter, why is there any need to argue that nothing resembling evolution happened at all? The story of the Flood doesn't work unless some new species or subspecies appeared in Post-diluvian times. While evolution would not have to be the mechanism for such appearances, I see no reason to favor any other theory.

[Theo]

I agree with your questioning the term "species." The biblical term would be "kind" (or "baramin"). Let me encourage you to either skim or read this webpage. Check out, especially, the three models, specifically the "orchard" one. Fascinating stuff! Variation and natural selection seem to be real phenomena. "Evolution" (the beneficial increase of genetic information over generations) doesn't.