The social stratification historically evidenced among the Serer people has been, except for one difference, very similar to those found among Wolof, Fulbe, Toucouleur and Mandinka peoples found in Senegambia. They all have had strata of free nobles and peasants, artisan castes, and slaves. The difference is that the Serer people have retained a matrilineal inheritance system. According to historian Martin Klein the caste systems among the Serer emerged as a consequence of the Mandinka people's Sine-Saloum guelowar conquest, and when the Serer people sought to adapt and participate in the new Senegambian state system.