Such claims are not new. They formed part of the core of the eugenics movement that swept through the Anglo-American world and many other countries during the first third of the 20th century. In the United States, however, the biological distinctions that mainly obsessed eugenicists were not those between whites and blacks, but those then believed to divide whites -- differences between the old-stock white, Anglo-Saxon, Protestant majority and the numerous Catholic and Jewish immigrants from Eastern and Southern Europe.

Eugenicists, who were themselves predominantly of the old majority, considered scholastic intelligence -- the kind indicated in IQ tests -- a paramount measure of human merit, ignoring other abilities such as business acumen and artistic creativity that such tests did not capture. To them, IQ tests appeared to determine that the newer immigrants were innately endowed with low intelligence, while their high birth rates seemed to indicate that they were spreading inferior genes into the population at a rapid rate. In the interest of reducing the proportion of the "less fit" in society, eugenicists in the United States helped restrict immigration from Eastern and Southern Europe. They promoted the passage of eugenic sterilization laws that disproportionately threatened lower-income groups. The laws and programs they fostered supplied a model for the Nazis, who sterilized several hundred thousand people and, brandishing their research into the genetics of individual and racial differences, claimed scientific justifications for the Holocaust.