Kin Groups and Descent. The Yakö were the first group with double unilineal descent to be well described. The lowest-level patrilineal group was the eponama (pl. yeponama ), which traced descent to a common ancestry, three to five generations back. The men of this group normally lived with their wives in a cluster of several adjacent compounds and recognized a senior man as their head, although the position was not formally recognized. These patrilineages were aggregated into patricians ( yepun ; sing. kepun ) that were also territorially compact. Each had a name that referred both to the group and to its dwelling area. In some contexts, the men would imply that they shared common descent from a patrilineal ancestor, but, when they were quarreling, they would assert distinct origins. Nevertheless, they all recognized the relevance of a common shrine ( e-pund-det ; lit. "shrine of the patrician"), at which the dead of the patrician were supplicated by the obot kepun, a formal, primarily secular, official. This man was, ex officio, one of the leaders of the ward, although the majority of ward leaders were not heads of patricians. All those born within the patrician were bound by rules of exogamy. Matriclans ( yajima ; sing. lejima ) were complementary to the patrilineal kin groups. Because residence was patrilocal for men whereas women moved out, the members of any matrilineal group were necessarily dispersed within a town and, to a limited extent (limited because most marriages were endogamous within a town), between towns. Formally, the rights and duties of the two sets of kin groups did not conflict. Patrikin were concerned with land, residence, and work. Matrikin groups were concerned with the transmission of property that could be physically moved and with claims over individuals. At death, an individual's wealth went to the matrikin, and responsibility for debts was borne by them. If an individual injured or killed another, recompense was paid between matrikin. A sorcerer was thought to be able to attack only a junior matrilineal relative, just as, in the past, only a senior matrikinsman could sell a junior into slavery. The ties of matrikinship were deeply ambivalent.
Kinship Terminology. Kinship terminology is complicated by the necessity, in formal contexts, of expressing relationships to Ego's own matrilineage and own patrilineage, as well as relationships to Ego's father's matrilineage and mother's patrilineage. In practice, most kin are addressed by name most of the time, and kinship terms are used primarily as terms of reference, except where particular deference—usually because of a marked difference in age—needs to be expressed, or where groups of kin gather for rites and ceremonies and have specific rights and duties—particularly at funerals. The mother's brother and all senior male matrikin are referred to by the same term as the one used for sons of Ego's own mother and her sisters: it is most simply translated as "brother"; however, the mother's brother may be addressed by a respectful term that is also used when speaking of one's own father. The father's brother is referred to and addressed by the term used for one's own father, and his children are, literally, "children of the father." A single reciprocal term ( okpan ; pl. yakpay ) is used between Ego and the mother's patrikin and between Ego and children of the father's matrikin (and, thus, between Ego and the children of the mother's brother).