CLAN, a social group of fundamental importance in the social structure of many primitive societies.
The most important character of the clan is its exogamy i.e., marriage within the clan is forbidden, and regarded as incest (see EXOGAMY) . This tabu applies even to persons between whom no genealogical relationship can be traced. Although for scien tific purposes the clan is defined as an exogamous group, the term is frequently used in popular literature for groups that are not exogamous, such as the tribe ; and that rather vague entity, the Scottish clan, though sharing some of the characters of the clan, is not an exogamous group, whatever it may once have been. Partly for these reasons, American writers use the term "sib" instead of "clan." The clan is a unilateral group; that is to say, membership of the clan is determined, either by descent through the mother ("matrilineal clan," "mother-sib," or "clan," as it has been va riously named) or by descent through the father ("patrilineal clan," "father-sib," or "gens"). This does not mean, however, that descent from some original ancestor can be traced, though belief in such descent is usually present. The clan, therefore, has only a slight resemblance to the family (q.v.) which necessarily con tains members of more than one clan, though it is possible that the clan has evolved from the family by emphasis of one line of descent.
Although the clan is not a kinship-group—for kinship implies not only relationship by direct descent, but the ability to trace it genealogically—nevertheless, it is common for members of a clan to address one another by means of relationship-terms used be tween close kin, and this carries with it the same sort of social relations as we find between close kin, though in less degree. This is a natural result of the classificatory system of relationships which is frequently associated with it, but even in the absence of this system it is common for distant members of a clan to claim brotherhood with one another, and to feel that kind of solidarity found in the case of the family. This solidarity is a most striking character of the clan. The individual identifies himself with his clan in a peculiarly intimate way, so that clan-responsibility for the action of individual members is common. This unity of the clan frequently extends into the political and economic sphere.
The unity of the clan is frequently emphasized by the posses sion of a totem (see ToTEMISM) . Where clans are much inter spersed and widely diffused, clan-identity may thus be estab lished and maintained, which even the classificatory system of relationships need not reveal. It is doubtful whether habitation of a common territory is ever the common tie uniting members of a clan, but localized clans do sometimes occur, though it is prob able that in such cases the localization is secondary, and the com mon tie is belief in common descent.
Not uncommon is a grouping of clans into wider units, the simplest form of this being a dual organization (q.v.) in which the clans are grouped into two exogamous divisions. It is also not uncommon for there to be a division of function between the clans of a tribe, occasionally economic, e.g., in India, but more usually political or religious, e.g., in some African kingdoms.