Kin Groups and Descent. Kinship in San Bartolomé is formally bilateral, but there is a slight bias toward patrilineality in practice. Family names are transmitted patrilineally; they take a binomial form in which the first surname is in Spanish, the second in Tzotzil. Each Tzotzil surname is linked to one and only one Spanish surname, but most Spanish surnames in local use are tied to more than one Tzotzil surname. There are no corporate social groups based on family names, but rules of exogamy prohibit marriage between two individuals with the same Tzotzil patronymic. Codescendants of the same grandparents may not marry.
Ritual kinship ( compadrazgo ) is established by the sponsorship of ceremonies, particularly child baptism. Primary relatives do not become compadres. After the ceremony, all the ancestors of a child being baptized and the current spouses of those ancestors still alive are regarded as compadres of the ritual sponsor and all of the sponsor's ancestors. Compadrazgo thus establishes an explicitly bounded corporate group, and the living members of the group have social functions as a group.
Kinship Terminology. The cross-generational principle of age relative to Ego affects all terms for consanguineal relatives. For example, father's brother, brother, and brother's son are all called by the same term if they are older than Ego. Another term is used for younger brother and other collateral relatives younger than Ego, even if those relatives are in an ascending generation. Kinship terms and accompanying behavior emphasize the inequality between elder and younger consanguineal relatives. Affinal terms, on the other hand, are reciprocal and reflect status equality for those of the same generation relative to the couple whose marriage established the affinal relationship. Kinship is recognized bilaterally. Lineal relatives older than Ego are distinguished from collateral relatives. The line blurs among relatives younger than Ego, particularly in the second descending generation.
Although most terms are shared, the terminological system used by men is not the same as that used by women; differences include both the delineation of classes of relatives and individual lexical items. For example, men's terms for collateral relatives distinguish males from females when these are younger than Ego, whereas women use a single term for younger collaterals of both sexes. The women's term is not phonetically similar to either of the terms used by men.
In the case of ritual kinship, only the terms for ritual kin are used, even though compadres might also be related by birth or by marriage. Where there is neither ritual, nor consanguineal, nor affinal kinship, kinship terms for collateral relatives are extended to all members of the community on the basis of relative age. Kinship terminology used in this extended sense marks senior/junior status inequality. Only compadres and same-generation affinals are seen as equals.