What exactly is it that makes someone a parent? Many people hold that parenthood is grounded, in the first instance, in the natural derivation of one person's genetic constitution from the genetic constitutions of others. We refer to this view as "Geneticism". In Part I we distinguish three forms of geneticism on the basis of whether they hold that direct genetic derivation is sufficient, necessary, or both sufficient and necessary, for parenthood. Parts two through four examine three arguments for geneticism: (...) the property argument, the causal argument, and the parity argument. We conclude that none of these arguments succeeds. (shrink)