Marriage could be polygynous, cross cousins being preferred partners.
Marriage between cross cousins, that is, between children of siblings of different sex, is considered ideal in many tribes; that of parallel cousins, children of siblings of the same sex, is frequently prohibited.
Matrilineal descent is observed and cross-cousin marriage preferred.
Cross-cousin, the child of one's mother's brother or father's sister.
Cross-cousin marriage often acts as a device to strengthen alliances between clans.
Many societies that emphasize avunculate relationships also prefer cross-cousin marriages.
These marriages were not made at random, however, for (as among the Nambikwara) cross-cousin marriage was preferred; in a matrilineal society a man married his mother's brother's daughter; in a patrilineal society he married his father's sister's daughter.
Even when a cross-cousin is the preferential mate, actual instances of such marriages in a given society may be small, for such decisions are also influenced by local customs governing succession, inheritance, and residence.
In those that differentiate between cross-cousins and parallel cousins, cross-cousin marriage is usually preferred or sometimes even obligatory, while marriage between parallel cousins often falls under incest taboos.
