 While most discussions of the ethics of genetic enhancement have focused on whether the practice is ever permissible, some ethicists argue that it is not only permissible for parents to enhance their children, but a positive duty. Savulescu (2001) argues for what he calls the Principle of Procreative Beneficence: couples should use pre-genetic diagnosis and selective abortion to choose the child, of the children they could have, who will have the best life. This naturally extends to using genetic enhancement. Savulescu’s justification for the principle of Procreative Beneficence is that it seems irrational not to select the best child when no other reasons are relevant to one’s choice. But this seems like a very weak principle: it seems likely that at least some other reason will frequently apply. For example, prospective parents might just prefer to leave their child’s genetic makeup up to chance. If this is not an irrational preference, then it plausibly gives some reason for them not to select any particular embryo to implant. Savulescu’s view is extended in further papers which claim that the principle of Procreative Beneficence has greater moral weight than simply being a tiebreaker when no other reasons apply (Savulescu and Kahane 2009, 281; for criticism see Parker 2010, Carter and Gordon 2013, Bennett 2014). These and related issues are discussed at length in the entries on  enhancement and  eugenics.