Monogamy

Christianity did not have to argue its way to monogamy from scratch, because Roman law already recognised one wife at a time, and the earliest churches grew inside that legal culture. What Christianity added was a reason. The gospels have Jesus citing the passage in Genesis about a man leaving his parents and the two becoming one flesh, and the letters develop a comparison between marriage and the union of Christ with the church. A union of that shape cannot be divided between several partners without losing the thing it is being compared to.

The pastoral letters require an overseer to be the husband of one wife, a phrase that has been read for two thousand years as excluding polygamy, or remarriage after widowhood, or serial divorce, depending on who is reading. The medieval West then made marriage a sacrament and indissoluble, and the Council of Trent fixed that position against the Reformation, which had reopened the question of divorce but not of plurality.

The rule travelled with the missions and met societies where plural marriage was ordinary. That produced a practical problem the churches have never resolved cleanly: a man with four wives who wishes to be baptised is asked to dismiss three, and the women dismissed lose their standing and their support. African churches, including African Initiated Churches, have taken a range of positions on this, and it remains a live pastoral question rather than a settled one.

Judaism arrived at the same practice by an entirely different road, and the difference is instructive. Scripture does not forbid a man more than one wife and reports it of the patriarchs and the kings without censure, so the change could not be made by exegesis. It was made by enactment. A ban attributed to Rabbenu Gershom of Mainz, around the year 1000, prohibited polygamy for the communities under his authority, and it was accepted across Ashkenaz. Sephardi and Mizrahi communities living in the Islamic world, where plural marriage was lawful, did not adopt it, and the permission stood among them into the modern period.

The state of Israel closed the gap by legislation rather than by ruling, criminalising bigamy and requiring rabbinic courts to work within that, with transitional arrangements for immigrants from countries where the practice was legal. The chief rabbinate has generally treated the Ashkenazi ban as effectively universal in practice.

Set against the rest of the map, monogamy is a rule in some traditions and an assumption in others. Islamic law permits up to four wives on conditions and many Muslim-majority states now restrict or regulate it. Hindu law in India prohibits it by statute for most citizens. Many African, South Asian and Indigenous traditions carried it as custom rather than as doctrine. The atlas records monogamy as a settled Christian teaching and a modern legal norm across much of the world rather than as a universal religious rule.