Marriage. Sio as a whole, including the outlying village of Nambariwa, tended to be an endogamous unit. People with common great-grandparents are not supposed to marry. Lineages are exogamous and people whose fathers or grandfathers were associated in the same men's house, whatever their genealogical connections, were likewise forbidden to marry. Postmarital residence tends to be patrilocal, but exceptions are frequent. Bride-wealth payments of pigs and valuables are assembled from a variety of kinsmen and in local theory are a mark of respect for the bride. The status of women is high and marriage resembles the egalitarian, companionate form of the West. The levirate and sororate are not practiced. Polygyny was approved but tended to be confined to big-men. Divorce under traditional conditions is said to have been rare.
Domestic Unit. The household comprised of a nuclear family is the basic domestic unit.
Inheritance. Inheritance is patrilineal, though inter vivos gifts of pigs, valuables, and economic trees from men to their sisters' sons are common. Pot-making skills, implements, and decorative designs pass from mother to daughter.
Socialization. Traditional male initiation ceremonies, in which the youths' maternal uncles had a prominent role in instructing them in "the laws," lapsed in the 1920s. Mission schools since then, but mainly a government school since 1959, have provided primary education.