Blue Orange
Gone to Texas
Well, one of the strengths of leaving it ambiguous in a game setting is you can always decide it's one or the other if it serves plot purposes. For me, D&D is based on fantasy novels which are ultimately based on myth, I know of no real-world myth that uses evolution; some god is always involved. So I guess I'd go with divine creation.
That said you could definitely have evolution occurring after the fact, particularly if some god decides to wipe out some species; you have divine selection as well as natural selection, and divine fiat as well as mutation. (The divine 'protection racket' in most mythologies thus becomes painfully explicit.) Plus wizards are usually portrayed as the analogues of scientists, so you could always have some weird wizard inventing the owlbear or something. You have all kinds of interesting dramatic plotlines if you want them--can the creations of an evil god turn against evil? (This was done with the draconians in later editions of Dragonlance, for instance.)
That said you could definitely have evolution occurring after the fact, particularly if some god decides to wipe out some species; you have divine selection as well as natural selection, and divine fiat as well as mutation. (The divine 'protection racket' in most mythologies thus becomes painfully explicit.) Plus wizards are usually portrayed as the analogues of scientists, so you could always have some weird wizard inventing the owlbear or something. You have all kinds of interesting dramatic plotlines if you want them--can the creations of an evil god turn against evil? (This was done with the draconians in later editions of Dragonlance, for instance.)