When society replaced nature as the creator of our reality, humanism replaced theism. Postmodernism is a late form of modernism, as it holds that as humanity creates different realities, there is no one reality at all. Modernism (from modus: way, as if ours is the only) is the anthropocentric antithesis to the theocentric thesis of fundamentalism, and postmodernism is the biocentric synthesis of the two, but they all put themselves at the center of the universe. To move beyond our egocentrism, we need to move beyond humanism, to posthumanism, which sees nothing at the center of our reality but rather sees all there is as just another level in evolution.
1 Nietzsche, Genealogy of Morals III:14
2 Ken Gemes, University of London: Nihilism and the Death of God