Religion protects families. Families are about kinship. Social anthropology studies the different kinship structures that different people have, i.e. "uncle" or "aunt" may mean something different within different societies and may be quite different from culture to culture in comparison. I once attended a CUNY grad lecture on the preference for "cross-cousin marriage" in nomadic peoples of the deserts. There your preferred though not necessarily ones mate, would be "a child of one's mother's brother or father's sister" which the speaker thought was a way of keeping widely separated people together when marriages were proposed. Recent data has shown that "cousin" marriages are also very fertile producing many children. Perhaps religion attempts to provide a "survival of the fittest" society in its proscription and divorce, i.e., three witnesses required for infidelity grounds in Islamic law in the Philippines. These ideas and culture have to be understood further as not a threat to our ways and means to ends.