Tribes and clans
From Dragon Eye Atlas
Tribes and clans are a concept of social organisation based upon extended family relationships.
Generally, within a tribe or clan, most members are somehow related to each other. The closeness is one of the differences between these two otherwise similar concepts. While a clan is essentially an extended family and the only way to become a member of a clan is by birth or marriage, tribes combine relationship with community and can accept new members without a blood relationship having to be formed.