a few small lineages, each consisting of a few hundred to a few thousand members. They trace their foundation to between four and eight generations. Members are socially contracted to support each other in jural and political duties, including paying or receiving dia or blood compensation (mag in Somali). Compensation is obligatory in regards to actions committed by or against a dia-paying group, including blood-compensation in the event of damage, injury or death. Social stratification Within traditional Somali society (as in other ethnic groups of the Horn of Africa and the wider region), there has been social stratification. According to the historian Donald Levine, these comprised high-ranking clans, low-ranking clans, caste groups, and slaves. This rigid hierarchy and concepts of lineal purity contrast with the relative egalitarianism in clan leadership and political control. Nobles constituted the upper tier and were known as bilis. They consist of individuals of ethnic Somali ancestral origin, and have been endogamous. The lower tier was designated as Sab, and was distinguished by its heterogeneous constitution and agropastoral lifestyle as well as some linguistic and cultural differences. A third Somali caste strata was made up of artisanal groups, which were endogamous and hereditary. Among the caste groups, the Midgan were traditionally hunters and circumcision performers.Е. de Larajasse (1972), Somali-English and Somali-English Dictionary, Trubner, pages 108, 119, 134, 145, 178 The Tumal (also spelled Tomal) were smiths and leatherworkers, and the Yibir (also spelled Yebir) were the tanners and magicians., Quote: "Many of these items were not made by nomads but by a caste of artisans called the Saab, considered subservient (...) The Yibir, also members of the Saab caste, were responsible for crafting amulets (hardas), prayer mats, and saddles, and for performing rituals designed to protect nomads from snakes and scorpions, illnesses and harm during marriage and childbirth". According to the anthropologist Virginia Luling, the artisanal caste groups of the north closely resembled their higher caste kinsmen, being generally Caucasoid like other ethnic Somalis. Although ethnically indistinguishable from each other, state Mohamed Eno and Abdi Kusow, upper castes have stigmatized the lower ones. Outside of the Somali caste system were slaves of Bantu origin and physiognomy. Their distinct physical features and occupations differentiated them from Somalis and positioned them as inferior within the social hierarchy.Mohamed A. Eno and Abdi M. Kusow (2014), Racial and Caste Prejudice in Somalia, Journal of Somali Studies, Iowa State University Press,