According to Mohamed Eno and Abdi Kusow, the Somali caste communities are ethnically indistinguishable from each other, but upper castes have stigmatized the lower ones with mythical narratives such as they being of unholy origins or being engaged in dirty occupations. The four strata social system – high lineage, low lineage, caste groups and slaves – found among the Somalis has been common in the Horn of Africa region, states Donald Levine, and is also found among ethnic groups such as Afar, Amhara, Borana, Leqa, Sidamo, Kefa, Janjero and other peoples.