Eugenicists claimed that criminal behavior was a result of defective genes. Most eugenicists adhered to the prevailing social theory of the early decades of the twentieth century that "culture does not make the man, but man makes the culture," meaning that poor people gravitate toward and contribute to a poverty-stricken environment, and thus create their own degenerate conditions. Thus, while not denying that poor social and cultural background might contribute to criminality, eugenicists argued that criminality, like many other social traits, was ultimately biological in origin.
Eugenicists were concerned with the noticeable rise in crime rates, especially in the fast-developing urban areas of the United States. They conducted both family pedigree studies and surveys by ethnic and national origin to show that criminality ran high in certain families and groups. Cyril Burt's pedigree analyses in England (on delinquency) supported eugenicists' views that if a trait ran in families it must be genetic. Similarly, Harry H. Laughlin gathered data on incarceration rates by country of origin to show that immigrants to the U.S. from eastern and southern Europe and the Mediterranean countries were disproportionately represented in prisons than "old stock" Americans or recent immigrants from Germany and other Nordic or Anglo-Saxon countries. Laughlin's data had such serious statistical problems that, according to a critique at the time, totally invalidated the conclusions. However, these data formed a cornerstone of the argument Laughlin made to the House Committee on Immigration and Naturalization to curb immigration from Southern and eastern Europe and the Mediterranan. They were also highly influential in eugenicists' lobbying efforts for sterilization laws that would prevent incarcerated criminals from giving birth to "criminal" offspring. If the number of criminals could be reduced through these biological measures eugenicists argued, it would save the state millions of dollars a year.
Eugenicists were not so naive as to claim that social and economic conditions had no effect in bringing about criminal behavior. In 1928 Charles B. Davenport of the Eugenics Record Office at Cold Spring Harbor, wrote an article titled "Crime, Heredity and Environment," in which he recognized that laws change from time to time, and vary from country to country. What would be technically a criminal act at one place and point in time would not necessarily be a criminal act at another place or point in time. Davenport solved this problem by arguing that criminality was the result of a more general genetic defect known as "feeble-inhibition," that is, criminals were people who could not control (inhibit) their impulses. They could not plan for the future and consequently did whatever came to mind at the moment, regardless of the consequences.
Biological arguments for criminality continued from Laughlin and Davenport's day to the present. In 1939, rather late in the eugenics era, Harvard anthropologist Earnest A. Hooten compiled a massive statistical publication, The American Criminal: An Anthropological Study, in which he argued even more strongly than Laughlin that criminality was a biological trait found more in certain ethnic and national groups than others. In 1965, a group of researchers in Scotland found that a significant percentage of men in prison had an extra Y-chromosome (they were XYY while most males are XY), suggesting a chromosomal cause for criminality. In 1985 Harvard psychologist Richard Herrnstein and political scientist James Q. Wilson published a highly-publicized book, Crime and Human Nature that surveyed vast amounts of literature from the twentieth century, arguing for a biological basis for criminality. In the 1990s, with large grants from the National Institutes of Mental Health, prominent researchers, largely in departments of psychiatry and psychology around the United States, have revived the argument that there is a genetic basis for criminality, pointing especially to the possibility that low levels of a neurotransmitter, dopamine oxidase, may be at the root of uncontrolled ("feebly-inhibited") behavior. At the moment, however, the status of such studies remains unconfirmed by independent research teams.