The Zarma people have traditionally been a socially stratified society, like the Songhai people, featuring castes, state Jean-Pierre Olivier de Sardan, Tal Tamari and other scholars. According to the medieval and colonial era descriptions, their vocation has been hereditary, and each stratified group has been endogamous. The social stratification embedded slavery, wherein the lowest strata of the population inherited slavery, and second the "Zima" or priests and Islamic clerics had to be initiated but did not automatically inherit that profession, making the cleric strata a pseudo-caste. According to Ralph Austen – a professor emeritus of African history, the caste system among the Zarma people was not as well developed as the caste system historically found in the African ethnic groups further west to them.