This paper assesses ideas about moral andreproductive duty in American eugenics duringthe early twentieth century. While extremeeugenicists, including Charles Davenport andPaul Popenoe, argued that social leaders andbiologists must work to prevent individuals whowere ``unfit'' from reproducing, moderates,especially Edwin G. Conklin, presented adifferent view. Although he was sympathetic toeugenic goals and participated in eugenicorganizations throughout his life, Conklinrealized that eugenic ideas rarely could meetstrict scientific standards of proof. Withthis in mind, he did not restrict his eugenicvision to hereditary measures. Relying onhis experience as an embryologist, Conklininstead attempted to balance more extremeeugenic claims – that emphasized the absolutelimits posed by heredity – with his own view of``the possibilities of development.'' Throughhis critique he argued that most human beingsnever even begin to approach their hereditarypotential; he moderated his own eugenicrhetoric so that it preserved individualopportunity and responsibility, or what hasoften been labeled the American Dream.