Why were marriages within the same Mongol clan forbidden?

In the context of Mongolian history and culture, the prohibition of marriage within the same clan is a practice known as exogamy. Mongols have historically placed great importance on protecting their ancestral heritage, and they consider it morally wrong to marry within one's own clan.1

This custom is rooted in the belief that members of the same clan share a common kinship lineage. By requiring individuals to seek partners outside of their own clan, the practice of exogamy serves to maintain social boundaries and prevent incest, which is typically defined by such unilineal descent groups. While these traditions were suppressed during the socialist era—when clan names and family trees were labeled as feudal—the practice remains a significant aspect of Mongolian social identity, and the use of clan names has been formally reinstated in modern Mongolia.21