Kin Groups and Descent. Every Marubo is member of a section. Each section has a name. A person never marries a member of his or her own section or his or her mother's section and always belongs to the same section as his or her mother's mother. Thus, it is possible to suppose the existence of matrilineal units, each formed by two sections. As of late 1990, there are twelve such units (there were more in the past), but two of them will become extinct because they do not have women.
Kinship Terminology. Generally, each kinship term or one of its variants is applied to people of alternate generations; there are some distinctions between the term a person applies to members of his or her own matrilineal unit and the others. The crossing of these two sets leads to four clusters of kinship terms. The Marubo are reticent in declaring their personal names; these are transmitted, like section membership and the distribution of kinship terms, through alternate generations.