[DarkSavant]

So in Darwinian theory, if a species moved all the way to a single-cell blob from a complex finch, that would not be de-evolution, just evolution from one state to another.

Exactly, the only direction of evolution is survival. It has no care for the ideals of 'progress' or complexity. What survives over a long period is what was fittest for the environment.

[mlc9852]

Then why don't all species evolve for survival? Why are there extinctions at all? Shouldn't evolution prevent extinction?