The title of this essay was taken from James Watson’s quip to a Time magazine reporter that we used to believe that our destiny was in the stars, but we now know it is in our genes (Nash & Thompson 1989). Notice the contrast not just between metaphysical and biological explanations, but also the contrast between believing and knowing. His remark captures nicely the way in which the Human Genome Project (HGP) has enlivened and legitimated material explanations of the human condition, and leads readily to deterministic idioms. Determinism has become our default framework for understanding genetics.