Almost all nomadic people are organized in tribal associations, the exceptions being the saluba, the tinkers and traders of the desert, and black beduin, descendants of former slaves. Not all tribal people, however, are beduin because urban and agricultural peoples may maintain tribal identities.

Structurally, tribal groups are defined by common patrilineal descent that unites individuals in increasingly larger segments. The lineage is the unit that shares joint responsibility for avenging the wrongs its members may suffer and, conversely, paying compensation to anyone whom its members have aggrieved. Although tribes may differ in their status, all lineages of a given tribe are considered equal. Water wells, aside from the newer deep wells drilled by the government, are held in common by lineages. Among nomads, lineage membership is the basis of summer camps all animals, although owned by individual households, bear the lineage's brand. The lineage is the nexus between the individual and the tribe. To be ostracized by one's lineage leaves the individual little choice but to sever all tribal links it is to lose the central element in one's social identity.

Above the level of lineage, there are three to five larger segments that together make up the tribe. Donald Cole, an anthropologist who studied the Al (see Glossary) Murrah, a tribe of camel-herding nomads in eastern and southern Arabia, notes that four to six patrilineally related lineages are grouped together in a clan (seven clans comprise the Al Murrah tribe). However the subdivisions of a tribe are defined, they are formed by adding larger and larger groups of patrilineally related kin. The system permits lineages to locate themselves relative to all other groups on a "family tree."

In practice, effective lineage and tribal membership reflect ecological and economic constraints. Among nomads, those who summer together are considered to be a lineage's effective membership. On the individual level, adoption is, and long has been, a regular occurrence. A man from an impoverished lineage will sometimes join his wife's group. His children will be considered members of their mother's lineage, although this contravenes the rules of patrilineal descent.

The process of adjusting one's view of genealogical relationships to conform to the existing situation applies upward to larger and larger sections of a tribe. Marriages and divorces increase the number of possible kin to whom an individual can trace a link and, concomitantly, of the ways in which one can view potential alliances and genealogical relationships. The vicissitudes of time, the history of tribal migrations, the tendency of groups to segment into smaller units, the adoption of client tribes by those stronger, a smaller tribe's use of the name of one more illustrious--all tend to make tenuous the tie between actual descent and the publicly accepted view of genealogy. At every level of tribal organization, genealogical "fudging" brings existing sociopolitical relationships into1e2 to conformity with the rules of patrilineal descent. The genealogical map, therefore, is as much a description of extant social relations as a statement of actual lines of descent.

Data as of December 1992