  GM of the germ line for either therapeutic or enhancement purposes and GM of somatic cells for enhancement purposes have not yet been carried out in  humans.[59] Of the four classes of interventions delineated by somatic-cell/germ-line and therapy/enhancement distinctions, only germ-line GM for enhancement purposes remains particularly contentious among bioethicists (Allhoff 2005). Of course, GM of the germ line of plants and nonhuman animals has become  commonplace,[60] and some commentators argue that the use of GM for enhancement purposes in humans is inevitable (Baylis and Robert 2004; Stock 2003). After all, look at parents who seek every advantage for their child on route to an Ivy League education, athletes who use illegal performance-enhancing drugs, increased use of plastic surgery, recreational use of Viagra, etc. Genetic modification of the germ line might be even more likely to be embraced for positive/enhancement than negative/therapeutic purposes, since if IVF is being used, concerns about a particular disease can be allayed with PGD and selective implantation. However, as more and more conditions—whether diseases or not—can be screened for in embryos, distinctions between therapy and enhancement and enhancement for health vs. social purposes—already problematic conceptually, a situation compounded by the newfound plasticity of the species adaptive norm—may break down even further in practice.