Obviously it can't be just a case of who smiles the most. I've been thinking about this a lot lately and I really don't have many answers.
I have some theories of my own, however I'd really appreciate if someone could shed light on this. To explain how this is relevant to surgery, well it's moreso I know people with retrognathic mandibles develop deep, premature nasolabial folds. However I see the issues of nasolabial folds involving more than just the mandible. Perhaps also the forward projection of the malars and amount of fat around that part of the face.