The Evolutionary Psychiatry blog, recently discovered, has a great summary of the modern Nature/Environment debate, as applied to Schizophrenia. Short:
Optimal nature + optimal environment avoids disease/disorder in most folks. If the environment is notably sub-optimal, optimal genetics are required to maintain optimum functioning. If genetics are sub-optimal, then optimal environment is necessary to maintain optimum functioning. Don't try sub-optimal environments with sub-optimal genetics or else you're screwed.