This essay uses the case of PKU as a portal through which to view shifting and contested views about genetics and reproductive behavior. In the early 1960s, the development of an effective therapy for PKU converged with the development of a test that could reliably detect the condition in newborns. As a result, infants born with the condition were enabled to reach adulthood and reproduce. However, by the early 1980s, a "second-generation" effect of screening was manifest, whereby many infants born to women who had been salvaged by screening were themselves severely damaged. In the 1940s, Lionel Penrose employed the case of PKU to demonstrate what was wrong with eugenics. Twenty years later, it would be used to illustrate why controls on reproduction were needed.
