From 'WEIRD' Monogamy to Informal Polygamy

In 2010, anthropologist Joseph Henrich and two co-authors published an enormously influential paper (“The weirdest people in the world?”) documenting the many ways in which “Western, Educated, Industrialized, Rich, & Democratic” (i.e., WEIRD) people differ psychologically from other populations around the world. They showed, for instance, that WEIRDos are more individualistic than “collectivist,” and more disposed to “impersonal” rather than “inter-personal pro-sociality,” to guilt rather than shame, and to “analytic” rather than “holistic” thinking. 

Henrich’s 2010 article was only descriptive, but he has recently published a monumental study, The WEIRDest People in the World, which attempts to explain the origins of this peculiar divergence of the West from the rest, with important and troubling implications for marriage and social policy in contemporary America. The heart of Henrich’s book is an account of how “the medieval Church shaped contemporary psychology through its demolition of Europe’s kin-based institutions.”¹

Henrich terms this loose collection of medieval social policies, the Church’s “Marriage and Family Plan” (MFP), which gradually restricted or even eliminated such traditional and widespread practices as cousin-marriage, remarriage after divorce, and, perhaps most importantly, polygamy. In time, these reforms transformed Europe from a collection of tribes ordered by extended kinship into a society of nuclear families interacting within impersonal markets and voluntary associations. And downstream from all of this—although it takes all of Henrich’s 600 or so pages to demonstrate it—are the profound technological, political, and social changes that we associate with the modern world. 

A crucial feature of the MFP, Henrich emphasizes, was its eradication of polygamy. Around 90% of human societies, he notes, have practiced a distinct form of polygamy called “polygynous marriage” [one husband with multiple wives],² and many others have practiced “serial monogamy,” with divorce and remarriage providing men easy access to multiple wives. Both are useful social forms if your top priority is producing heirs for elite families, but they have a number of unfortunate side-effects. In particular, polygyny encourages elite men to take multiple wives, which creates a surplus of low-status men who can’t marry, and so are often left frustrated and adrift. With little to lose, such men are far more likely, as Henrich documents, to commit crimes or take wild risks than are married men, whose social ties and (prospects for) children give them a stake in the future.³

Societies that are centrally concerned with the welfare of women and especially children couldn’t ask for a more potent social technology, which is perhaps why monogamy, despite its historically marginal status, has increasingly driven its competitors entirely out of the market in one society after another in recent centuries. 

By contrast, Henrich notes, monogamous marriage both encourages men to focus their time and energy on supporting one woman and their few children, and also “shifts men’s psychology,” and even their physiology (e.g., reducing their testosterone levels), “in ways that tend to reduce crime, violence, and zero-sum thinking while promoting broader trust, long-term investments, and steady economic accumulation.”⁴ In effect, monogamy represents a powerful means of domesticating male promiscuity and aggression. Societies that are centrally concerned with the welfare of women and especially children couldn’t ask for a more potent social technology, which is perhaps why monogamy, despite its historically marginal status, has increasingly driven its competitors entirely out of the market in one society after another in recent centuries. 

Unfortunately, monogamous marriage is on the decline in the United States,⁵ in part, because it has been eroded from within, particularly by the poor economic prospects of many lower-class men.⁶ Nonetheless, it is also threatened from without by the rise of what we might call “informal polygyny,” as the cultural norm for sexual partnering has shifted away from the constraints of marriage and family and toward “the pure relationship” or “liquid love,” in which sexual pairings are more and more fleeting products of passion. 

Unsurprisingly, this has yielded a situation in which high-status men enjoy multiple sexual partners (with only minimal social and legal requirements for providing for them and their children) and many low-status men finds themselves with few prospects for sex, much less marriage and children. There is no shortage today of ideological justifications for informal polygyny (“sex-positivity,” “polyamory”), and even a growing movement for legal recognition for polygamous marriage, but it’s hard to ignore the fact that this practice’s heavy costs are disproportionately borne by the poor, women, and children, for whom an intact nuclear family offers a crucial social safety net. Nonetheless, this recrudescence of polygyny is perhaps no surprise in our increasingly secular age. After all, as Henrich notes, “Nearly all modern legal prohibitions on polygynous marriage derive from WEIRD foundations, ultimately rooted in Christian doctrines” that restricted legitimate sex within monogamous marriage.⁷

Dr. Brendan Case (Th.D., Duke Divinity School) is the Associate Director for Research of The Human Flourishing Program at Harvard University, and author of The Accountable Animal (T&T Clark, 2021). 

1. Henrich, Joseph, The WEIRDest People in the World (New York, Farrar, Straus and Giroux, 2020): 249. 

2. Polyandry” (one wife with multiple husbands) is also attested in a few times and places, albeit much more rarely, for the obvious reason that while a single man can impregnate many women at a given time, a woman can only bear one man’s child at a time. Polyandry was once practiced on a society-wide basis in Tibet, where – in the judgment of the 18^th century Englishman Samuel Turner (1783) – “it helped prevent overpopulation, the greatest calamity that could befall an arid country” (quoted in Jurgen Österhammel, Unfabling the East: The Enlightenment’s Encounter with Asia, 645). 

3. Henrich, 285-86. 

4. Ibid., 287. 

5. There was, at the turn of the millennium, a 21-percentage point gap between married and never-married 25- to 34-year-olds in the United States…Less than 10 years later, that gap had not only vanished, but reversed: by 2014 there was an 11-percentage point gap between never-married and married young Americans, with the former now more numerous than the latter…In an unbelievably short time…the share of young adults in the United States who have never been married has eclipsed those who are married, with little evidence that the trend will dissipate anytime soon” (Mark Regnerus, Cheap Sex: The Transformation of Men, Marriage, and Monogamy, 180-81). 

6. Ibid., 184-188. 

7. Henrich, 268.