The alternatives to Nature

The question that has long troubled philosophers and students of the Human condition concerns the prime causal mechanism in the shaping of intellect. Is this an in-built genetic disposition? Or do societal factors have the greatest impact? Or is the most important factor the post-modern, post-religion, post-Judeo-Christian ethical society in which we now live - the “God is Dead” era.
More simply, Nature, Nurture or Nietzsche?