The lowest international incidence of incest is one per million per year. In the United States, Weinberg has reported incidences ranging from 1.2 cases per million in 1910 to 1.1 per million in 1930. It has been shown that incest frequency diminishes during war and increases during postwar periods. The crime is infrequent in all types of societies - some communities (e.g. the Mormons) and some primitive races have permitted incestuous unions. It has also prevailed historically in the social elites of many countries.