288 AFRICAN POLITICAL SYSTEMS
Those clans which are associated with tribes have generally greater lineage extension and depth than those which are not so associated, and the larger the tribe the more significance this association has for the Nuer. It is in the largest tribes, territorially and numerically, and those which have expanded most and assimilated most foreigners, like the Lou and Eastern Gaajak and Gaajok tribes, that we find the greatest attention paid to the distinct and dominant position of the aristocratic clans. Indeed, not only do political relations affect the clan structural form, splitting it into segments along the lines of political fission, but also the clan system may be said to have a corresponding action on the political structure. In a confusion of lineages of different clan origin and in an amorphous network of cognatic links, the political structure is given consistent form, in the language of kinship, by one clan—a single system of lineages—being made to correspond to the tribe and to its structure of opposed segments. Just as a man is a member of a tribal segment opposed to other segments of the same order and yet also a member of the tribe which embraces all these segments, so also he is a member of a lineage opposed to other lineages of the same order and yet also a member of the clan which embraces all these lineages, and there is a strict correspondence between these two sets of affiliations, since the lineage is embodied in the segment and the clan in the tribe. Moreover, the distance in clan structure between two lineages of a dominant clan tends to correspond to the distance in tribal structure between the two sections with which they are associated. Thus the system of lineages of the dominant clan enables the Nuer to think of their tribe in the highly consistent form of clan structure. In each segment the network of kinship ties are given unity and coherence by their common relationship to the lineage of the dominant clan that resides there, and as these separate lineages are composite in relation to other clans so the whole tribe is built around an exclusive agnatic framework. Though the sections may tend to draw apart and to split, a common agnatic value, shared by the dominant lineages contained in them, endures.
IV. Age-set System
Another tribal institution is the age-set system, which is socially more significant among the Nuer than among other Nilotic peoples of the Sudan. Nuer boys pass into the grade of manhood through