The clan groupings of the Somali people are important social units, and clan membership plays a central part in Somali culture and politics. Clans are patrilineal and are often divided into sub-clans, sometimes with many sub-divisions. The tombs of the founders of the Darod, Dir and Isaaq major clans as well as the Abgaal sub-clan of the Hawiye are all located in northern Somalia. Tradition holds this general area as an ancestral homeland of the Somali people.