The family is a universal group throughout Africa, with many different forms and functions. Everywhere the basic family unit is the elementary or nuclear family, a small domestic group made up of a husband, his wife, and their children; frequently, attached kin are included as well. This group is formed by a marriage and ends either with the death of one of the spouses or with divorce. Where polygyny is permitted, a husband and his wives form a compound family. Elementary and compound families in most parts of the continent traditionally have also been units of wider and longer-lasting families, known as joint or extended families. In these families, there are typically two or more generations, either a group of brothers and sons and their wives and children (a patrilineal joint family) or, in some places, a group of sisters and their husbands and children (a matrilineal joint family). This kind of family is long-lasting, and indeed self-perpetuating; a death makes no difference to its overall structure, and thus it can last over several generations, with a membership of up to a hundred people and more. As a general rule, joint and extended families are found in rural rather than in urban settlements, the latter more usually being occupied by many elementary families, each in isolation from the others. But here are many exceptions (e.g., the Yoruba of the traditional southern Nigerian cities, who maintain extended families even today).
The basis of kinship, in Africa as elsewhere, is descent from an ancestor. The most widespread descent group is known as the clan, which can be either patrilineal or matrilineal. The members of the former type of clan comprise all those who are born from a single founding ancestor through the male line only; those of the latter comprise all those born from a single founding ancestor or ancestress through the female line only. Patriliny is far more common in Africa than matriliny, which is limited mainly to parts of Zambia and Malawi, in central Africa, and to Ghana and Ivory Coast, in western Africa. Regardless of the means of descent, authority in the family and elsewhere is always formally held by men; therefore, men have domestic authority in both patrilineal and matrilineal families (formal matriarchy is unknown in Africa). Clans, which are rarely corporate units in Africa, are clusters of kin who claim a single common ancestry but can rarely, if ever, trace the actual links of descent. Usually clans are exogamous units and may recognize various ritual prohibitions, such as taboos on certain foods, that give them a sense of unity and of distinctiveness from others.
Clans are typically segmented into constituent groups, with each group recognizing a founding ancestor more recent than the clan founder; these are known in the literature as lineages, one of the criteria for a lineage being that its members—patrilineal or matrilineal—can trace actual kinship links between themselves. Lineages may themselves be segmented into smaller units, the smallest typically being the group around which a domestic family is established. Such a family (if patrilineal) includes the husband and his children, all members of the small lineage, and his wife, who by the rule of exogamy must come from another clan.
Other forms of descent are recognized, the most common of which is cognatic descent, whereby local kin groups are composed of members who recognize their common descent through both men and women. A few societies recognize both patrilineal and matrilineal descent simultaneously. Some societies in Africa do not formally recognize these forms of descent at all, but they are not typical and usually consist of long-settled urban dwellers.
Almost every African society has some form of descent group, however transitory, as the basis of its social organization. The recognition of these variations of ancestral descent is an effective way of constructing local groups that can last for several—often for many—generations and in which the close-knit ties of kinship provide powerful links through the notion of common "blood." By claiming exclusive ancestry, such a group can claim exclusive rights to clan and lineage property. Marriages between their members, by the rule of exogamy, cement them into larger communities and societies, each possessing its own sense of common ethnic and cultural "belonging." Although these traditional forms of family and kinship are lessening in importance, with the continuing need for urban and industrialized labor and the consequent increase in labor migration, the strength of kin groups remains great. They are well suited to traditional forms of production and exchange where these are found (which is still the case among the majority of African peoples), and they provide a sense of personal identity and security that is of high emotive value.