Britannica Sources used in this answer

How can exogamy require marriage outside a person’s own clan or lineage?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

consanguinity (Left) Absence of inbreeding: horizontal lines connect mates, vertical lines connect parents with their child; (right) an inbreeding loop: horizontal bar at top of loop connects brother and sister, all other lines and bars as above

Exogamy is a social custom that mandates marriage outside of a specific group, most commonly defined by kinship rather than geography or politics.12

In societies that utilize unilineal descent—where ancestry is traced exclusively through either the father (patrilineality) or the mother (matrilineality)—individuals are organized into distinct lineages, clans, or moieties. Because members of these groups are often viewed as sharing a common ancestor, they are frequently treated as close kin, similar to siblings.1

Consequently, marrying within one’s own clan or lineage is typically classified as a form of incest. By requiring marriage outside of these groups, exogamy functions as a regulatory mechanism that bars marriage between individuals who share a common lineage, thereby reinforcing social boundaries and defining permissible relationships within the community.13