The different strata of the Zarma-Songhai people have included the kings and warriors, the scribes, the artisans, the weavers, the hunters, the fishermen, the leather workers and hairdressers (Wanzam), and the domestic slaves (Horso, Bannye). Each caste reveres its own guardian spirit. Some scholars such as John Shoup list these strata in three categories: free (chiefs, farmers and herders), servile (artists, musicians and griots), and the slave class. The servile group were socially required to be endogamous, while the slaves could be emancipated over four generations. The highest social level, states Shoup, claim to have descended from king "Sonni 'Ali Ber" and their modern era hereditary occupation has been "Sohance" (sorcerer). The traditionally free strata of the Zerma people have owned property and herds, and these have dominated the political system and governments during and after the French colonial rule. Within the stratified social system, the Islamic system of polygynous marriages is a part of the Zarma people tradition, with preferred partners being cross cousins, and a system of ritualistic acceptance between co-wives. This endogamy is similar to other ethnic groups in West Africa.