This chapter argues that the Lamarckian ideas did play an important role in different ways in the eugenics movements in Japan and China, since Lamarckism offered a more humane alternative to the depressing aspect of Mendelism. It provides a foundation for the wishful belief that evolution is necessarily progressive. The chapter considers Lamarckism as a series of ideas emphasizing environmental factors and thereby could be applied as a social-control project under Jean-Baptiste Lamarck's tenet of inheritance of acquired characters. It examines the symptoms in the "national character" representation and the eugenicists' presentation of the need for eugenic measures. The chapter lays out the various diagnoses and remedies of public-health problems presented by the public hygienists, socialists, sociologists and eugenicists, and their subsequent social debates. It concludes with the disparate outcomes from the social debates: whereas a consensus on a comprehensive eugenic bill was achieved by both hygienists and eugenicists in the Japanese context.