Unilineal descent groups (clans, moieties, etc), appear to perform which important social functions?

They seem to perform which vital social capacity is to control who is and who is not a reasonable marriage accomplice. 
A genealogy is a unilineal descent group that can exhibit their basic plunge from a known apical progenitor. Unilineal ancestries can be matrilineal or patrilineal, contingent upon whether they are followed by moms or fathers, separately.