Plural marriage is the norm across the ethnographic record, and monogamy is the historical outlier. George Murdock's Ethnographic Atlas, surveying around 1,200 societies, classifies roughly 85 percent as permitting polygyny, around 16 percent as practicing it widely, and a tiny handful as practicing polyandry. Strict monogamy as a legal and moral mandate is a relatively recent and geographically narrow phenomenon, propagated through the spread of Greco-Roman institutions, Christianity, and modern Western law. The fact that polygyny was the dominant human mating pattern for most of recorded history is uncomfortable for both the romantic story of monogamous love and the progressive story of marriage equality, but it is a fact, and any serious thinking about marriage as an institution has to begin from it rather than around it.
Polygyny — one man, multiple wives — is overwhelmingly the more common form. It correlates with stratified societies where wealthy or powerful men accumulate wives, while poorer men marry late or not at all. Walter Scheidel's historical work shows that elite polygyny was standard from Mesopotamia through the Ottoman Empire, with the harem as the most extreme form. The institution generates a predictable structural problem: if some men have many wives, other men have none. The unmarriageable male population becomes a source of raiding, conquest, and social instability. Some historians argue that the imposition of socially enforced monogamy on European elites was one of the institutional innovations that enabled large-scale cooperation, by binding elite men into the same marital constraint as everyone else and freeing up potential wives for the lower ranks.
Polyandry — one woman, multiple husbands — is rare but real. It clusters in environments of extreme resource scarcity, particularly the Himalayan highlands of Tibet, Nepal, and Ladakh, where fraternal polyandry (brothers sharing a wife) preserved household labor and prevented land fragmentation. The Mosuo of southwestern China practice a form of walking marriage where women have multiple sequential partners, and some Amazonian societies recognize multiple "partible paternity" fathers for a single child. The rarity of polyandry compared to polygyny reflects, in part, the biological asymmetry of reproductive investment — a woman can have only so many children regardless of partner count — but also the social asymmetry of property and power. Where the environment forces resource pooling, polyandry emerges. Where it does not, it almost never does.
Contemporary law has converged toward monogamy with significant exceptions. Most Western countries criminalize bigamy; Islamic-majority countries generally permit polygyny under various restrictions; some sub-Saharan African states permit both Islamic and customary polygyny. Within Western countries, religious subcultures — Mormon fundamentalists, certain Hasidic groups, some Muslim immigrant communities — practice unofficial polygyny under the cover of cohabitation. The legal regime increasingly accommodates these arrangements indirectly through child welfare, partner benefits, and tolerance of cohabitation, while formally maintaining monogamy. The result is a patchwork of de jure monogamy and de facto pluralism that satisfies no one.
Janet Bennion's ethnographic work in Mormon fundamentalist communities provides one of the most detailed pictures of contemporary Western polygyny. Her findings complicate both the conservative defense and the liberal critique. The women in these marriages, in her interviews, report a complex mix: solidarity with sister-wives, occasional rivalry, religious meaning, and economic precarity. Some report genuine satisfaction; others report coercion and harm. The pattern depends heavily on the community's economic structure, the husband's character, and the women's own networks. The institution is neither a paradise of female solidarity nor a uniform horror. It is a structure that produces wildly different outcomes depending on its frame.
The collective question for contemporary law is whether de jure monogamy is the right policy when de facto pluralism is widespread and when the historical record is overwhelmingly polygynous. The progressive case for legal recognition of plural marriage, often framed as the next step after same-sex marriage, runs into a problem that gay marriage did not: polygyny produces predictable population-level effects, including unmarriageable men, accelerated marital coercion of young women, and inequality of marital opportunity. The case for retaining legal monogamy rests not on its naturalness — it is not natural — but on its leveling effect. The case against rests on the failure of monogamy to prevent the realities it claims to constrain, and on the autonomy claim that consenting adults should be able to form any household they choose.
A unity-aware reading sees the question as a genuine trade-off, not a moral certainty in either direction. Strict legal monogamy distributes marital opportunity more evenly but criminalizes consenting plural arrangements. Permissive plural marriage law respects autonomy but tends, statistically, to concentrate marriage opportunities among wealthier or higher-status men, leaving a tail of unmarriageable men whose effects on society are well documented. There is no clean answer. What is clear is that the question cannot be resolved by appealing to either "tradition" or "equality" as decisive; both lead in multiple directions. The collective task is to think clearly about which set of trade-offs a particular society can sustain, and to design law that mitigates the worst failure modes of whichever choice it makes. Strict monogamy enforced honestly. Plural marriage with consent verification, age protections, and exit rights for women. Both can work; neither works automatically.