Unilineal descent is the rule by which a person's descent is reckoned through one sex only. Where the line runs through fathers it is patrilineal, and a man's children belong to his group; where it runs through mothers it is matrilineal, and a woman's children belong to hers. Because each individual is assigned to exactly one line, the rule creates groups with unambiguous membership — lineages, clans, and in India gotras and kuls — that can hold property, act at law, worship a common ancestor and regulate marriage.
How it works
Meyer Fortes showed why anthropology found these groups so useful: they are corporate. A unilineal group persists as its members are born and die, owns land and shrines as a single jural person, and can be segmented — lineage splitting into sub-lineage, and that into household — so that a society without a state can still order feud, alliance and inheritance. Radcliffe-Brown treated the descent group as the skeleton of primitive social structure. The rule normally carries exogamy with it: one may not marry within the descent group, which forces alliances outward.
Contrasts
Bilateral or cognatic descent traces relatives through both parents equally and so yields no closed group, only an ego-centred kindred that dies with the individual — the pattern of modern urban families and of the Kandyan Sinhalese. Double descent, recorded among the Yako of Nigeria, applies both rules at once for different purposes, patrilineal for land and residence, matrilineal for movable goods and ritual. Parallel descent, rarer still, assigns sons to the father's line and daughters to the mother's.
Points of debate
Descent theory was challenged by alliance theory, which held that marriage exchange, not descent, is the organising principle. Critics also noted that a strict lineage model fits African cases better than South Asian ones, where locality, caste and the joint household often matter more than genealogical depth. T. N. Madan's study of Kashmiri Pandits shows patriliny operating through household and property rather than large corporate lineages.
For the UPSC answer
Define unilineal descent as reckoning through a single sex, name the two forms, and stress corporateness following Fortes. Contrast bilateral and double descent explicitly, since questions usually turn on the comparison, and close with the descent-versus-alliance debate.
References & further reading
- Radcliffe-Brown, A. R. and Forde, D. (eds.) (1950). African Systems of Kinship and Marriage. Oxford University Press.
- Fortes, M. (1953). The Structure of Unilineal Descent Groups. American Anthropologist, 55(1).
- Madan, T. N. (1965). Family and Kinship: A Study of the Pandits of Rural Kashmir. Asia Publishing House.