The history of human genetics and eugenics in Denmark in the second half of the 20th century has hardly been examined so far. Nevertheless Danish research and eugenic practices were well known and admired throughout the academic world from its foundation in the late 1930s till the 1960s, especially for its nation-wide, comprehensive registry of genetic diseases. The proposed paper compares the development of human genetics and eugenics in the USA and Denmark in the 1940s and 1950s. The focus lies on spatial concepts in the discourse on human genetics. The paper draws mainly on archival sources from Denmark: personal papers of leading scholars and research institutes in the field of human genetics. In 1938 the institute of human genetics and eugenics was founded at the University of Copenhagen with a generous grant from the Rockefeller Foundation. One of its most important goals was to establish a nation-wide registry of all patients with hereditary diseases and their family members. It ought to support the application of eugenic sterilization and abortion according to the Danish law. At the same time such a registry was the primary means of research in human genetics up to the late 1950s and strongly desired in other countries as the United States, too. It seemed especially valuable when installed in a “Western”, “civilized” country such as Denmark: the Danish population was considered relatively homogenous and well filed in health and welfare systems at the same time. The main promise was to “follow and control” the “rate of mutations” in modern human populations exposed to technological and societal progress ‒ including the pressing question of the genetic effects of nuclear irradiation. The paper argues that populations were constructed as relatively hermetic “genetic containers” by these research practices.