clan, social group based on actual or alleged unilineal descent from a common ancestor. Such groups have been known in all parts of the world and include some that claim the parentage or special protection of an animal, plant, or other object (see totem). They also include such familiar groups as the Highland clans of Scotland (the English word clan comes from Gaelic). Most clans stress mutual obligations and duties. Clan descent is traced in one line only, male or female. The word clan has by some been restricted to those descended through the mother (matrilineal) in contrast to the gens, descended through the father (patrilineal). The word sib has been much used to cover both types. A clan includes several family groups. Most clans are exogamous and regard marriages among their members as incest. A clan is distinguished from a lineage in that a clan merely claims common ancestry; a lineage can be traced to a common progenitor. A clan may have several lineages. Several clans may be combined into a larger social group called a phratry. If a tribe includes two clans or phratries, each clan or phratry is called a moiety.
See Sir Iain Moncreiffe, The Highland Clans (1967); R. Fox, Kinship and Marriage (1984); E. Gellner, The Concept of Kinship (1987).