Sociologists and anthropologists generally define marriage as the socially recognized and accepted sexual union between two adult individuals. In particular, anthropologists have ascribed to marriage some functions they deem fundamental for maintaining relations between human groups. Specifically, some men belonging to a certain social group could establish relationships and create alliances with other social groups through the exchange of women. The customary prohibition of incest and rules supporting exogamy, which forbid marriage between members of the same family, seem to support this possibility.