All human groups regulate marriage and kinship with other groups. Kinship has been defined as the recognition of relationships based on descent and marriage. Relations based on brotherhood or sisterhood is found among the primates. The well known anthropologist R. Fox maintains that the combination of “alliance” with “descent” in one system was a unique human innovation. Simply stated no other species has in-laws. This innovation allowed humans to link up and ally with other groups. By maintaining ties with a son or daughter who moved to another group after marriage, humans created relationship with the group to which the offering had moved.
The most important aspect of kinship is that it is not simply about biological relationship, it is about social relationship. Biological connections are very narrow. Kinship on the other hand, can be extended as far as the local conventions require. In many human communities every known person is treated as a kinsman so that marriages are simply renewals of links that have already existed. With kinship humans could depend on each other in times of food shortage or incursion by a hostile group. This also ensured sharing the knowledge of a large number of groups. Since, it ensures a healthy flow of genes over a large area, communities having kinship would have a greater chance of biological survival and expansion.