DUAL ORGANIZATION. A distinctive feature in the social structure of certain simple communities is their division into two complementary sections which have important functions in the social and ceremonial life of the people. This system of dual organization occurs most typically in many parts of Australia, Melanesia and N. America, and has been recorded from India and Assam ; its existence elsewhere has not been definitely established. The two sections, usually termed moieties or phratries, are uni lateral in character, membership being determined by descent through either the father or the mother. In Melanesia matrilineal descent predominates, elsewhere both matrilineal and patrilineal descent are common. An exceptional case is found among the Fox and Kickapoo of N. America, where the father usually, but not always, determines which moiety his child shall enter, so that often the first-born child will belong to one moiety and the next child to the other. The structure of the moieties also varies : in some communities they are simple undivided groups; in others they are each composed of a number of smaller sub-divisions or clans, e.g., among the Winnebago of N. America, where the one moiety consists of 28 clans and the other of 26.
The dual organization is very frequently con nected with the regulation of marriage. In most communities the moieties are exogamous, and consequently a man belonging to one moiety must always marry a woman belonging to the other. This feature is sometimes regarded as the distinctive characteristic of the dual organization, but although it is of most frequent occur rence there are several exceptions. Among certain N. American tribes, e.g. the Hidatsa, Yuchi, Western Mono and Iroquois, mar riage between members of the same moiety is not prohibited. When the moieties are exogamous a man is never permitted to marry any woman he chooses in the opposite moiety. The form of marriage is always dependent upon other factors, such as age, status and kinship, where certain relatives are prescribed as eli gible mates while marriage between others is not permitted. Thus the form of marriage most frequently found with the dual organi zation is that between cross-cousins; and, where the moieties are exogamous, it follows (whether descent be patrilineal or matri lineal) that cross-cousins belong to different moieties, while paral lel cousins between whom marriage is not permitted, become mem bers of the same moiety. The dual organization in such cases does not determine but merely systematizes the form of marriage. Only under exceptional circumstances can cross-cousin marriage result from the division of the community into moieties (see COUSIN
