The Yanomamo has a unique family organization. The reducing of nuclear family by age categories is one of these. Generally, the nuclear family is an important basic unit of human societies. However, when the Yanomamo becomes ten years old, one thirds of them live in a family with their parents, and one tenth of them are in such family when they comes to be twenty years old. This means that most marriageable aged Yanomamo men don't have a living father, who must die from attacks of raiders or accidents. In Yanomamo society, marriages are arranged by a father, but, in the case of absence of a father, they are arranged by elder men of their kinship or elder male friends. .
The Yanomamo usually marry more than one wife as a benefit and marker of social status. That is polygamy. It is sometimes explained as a result of male and female demographic imbalances; however, as for Yanomamo, there're more men than women in their populations because of female infanticide. So, polygamy is possible in such a situation only if some men do not marry or, more usually, if they marry at a much later age than women do. Because of this system, they are organized into lineage groups based on patrilineal descent that rarely extend because of the segmentation. This frequently happens due to disputes about women who are going to marry between cousins. The new group cannot gain ties with each other and be seen as enemies.
Lineage groups are used for territorial units, inhabiting a common settlement and normally foster mutual cooperation and support among their members, often focusing on organizing alliances and battles. They consider their sons and daughters within the web of marriage exchanges with allied lineage group. However, members of the same localized lineage are forbidden from marrying. So, exogamy and incest prohibitions among patrilineal relatives mark the patrilineages as significant units in the mutual exchange of marriage partners and in the consequent formation of alliances.