 However, the linguistic differences between the caste and slave systems between Soninke and northern ethnic groups of Africa such as the Tuareg people and Moors suggests that these evolved separately.Louis Dumont, the 20th-century author famous for his classic "Homo Hierarchicus", recognized the social stratification among the ethnic groups in West Africa, but suggested that sociologists should invent a new term for West African social stratification system.Other scholars consider this a bias and isolationist because the West African system shares all elements in Dumont's system, including economic, ritual, spiritual, endogamous, elements of pollution, segregative and spread over a large region.