Social Organization. People regard their society as a body of kin who share a common language, culture, and territory and who are sharply set off from neighboring peoples. Dividing the body politic roughly in half are residential moieties, whose members maintain a friendly rivalry. The population is further subdivided into landowning patrilineages; the men of these groups formerly comprised men's clubhouses, whose activities included ancestral cult ritual and the not-so-friendly rivalries entailed in the competitive distribution of yams and pigs and exacting vengeance—or compensation—for death or injury inflicted by another group. Much of Sio social life, however, consists in participating in those relationships that serve to bind members of these groups together, namely, those between affines, maternal uncles and nephews, and age mates (formerly, men who had undergone initiation together as youths).
Political Organization. Traditional leaders combined a number of ascribed and achieved roles. First, they were firstborn sons, clubhouse leaders, and lineage heads. Second, they were expected to demonstrate superior performance in gardening, artisanship, trade, oratory, diplomacy, fighting skill, competitive feasting, and learning. Those who were preeminently successful in these varied activities, helped of course by their wives and supporters, were true big-men who wielded influence in the community at large.
Social Control. Antisocial and violent behaviors were dealt with by: the disposition to demand and accept compensation rather than to fight with weapons; the weight of public opinion, especially as articulated by influential leaders; and the fear of punishment by ancestral ghosts.
Conflict. The interior peoples were the traditional enemies in contrast to island and coastal neighbors with whom Sio had mainly peaceful dealings in trade. Their military posture was primarily defensive; the island village provided a natural defense and remote gardens were worked by associations that were large enough to cope with parties of raiders.