Let’s start with definitions.  Polygamy = Marriage to more than one spouse.  Polygyny = Marriage of a husband and more than one wife.  Polyandry = Marriage of a wife and more than one husband.  Group marriage = Polygamous compositions other than polygyny and polyandry.  Hypergamy = Marriage into a superior class (‘marrying up’).


In 2007-2011, uncertainty about the constitutionality of Canada’s prohibition of polygamy prompted a reference case before the Supreme Court of British ColumbiaJoseph Henrich, an anthropologist, submitted an affidavit, warning that legalization of polygyny would cause major harms:

“A non-trivial increase in the incidence of polygyny, which is quite plausible if polygyny were legalized given what we know about both male and female mating preferences, would result in increased crime and antisocial behaviour by the pool of unmarried males it would create.

Greater degrees of polygyny drive down the age of first marriage for (all) females on average, and increase the age gap between husbands and wives.  This generally leads to females marrying before age 18, or being ‘promised’ in marriage prior to age 18.

Greater degrees of polygyny are associated with increased inequality between the sexes, and the relationship may be causal as men seek more control over women when women become scarce.

Polygynous men invest less in their offspring both because they have more offspring and because they continue to invest in seeking additional wives.  This implies that, on average, children in a more polygynous society will receive less parental investment.

Greater degrees of polygynous marriage may reduce national wealth (GDP) per capita both because of the manner in which male efforts are shifted to obtaining more wives and because of the increase in female fertility.”  (p. 3)


Henrich invokes all of the common rationales of prohibitions: Polygyny would cause harm to others (crime), self-harm (premature female marriage), inequality (spousal hierarchy), commodification (arranged marriages), and slippery slopes (less parental investment in each child, lower GDP per capita).  Henrich perforce draws evidence about polygyny from societies that aren’t ‘WEIRD’ (western, educated, industrialized, rich, democratic) because WEIRD societies prohibit polygyny.  He speculates that transition to monogamy was a necessary cause of the development of modern society.  (Compare similar arguments by Richard Posner against polygamy.)


The question arises: Would repeal of prohibition of polygamy in modern, WEIRD societies produce dynamics and outcomes like what Henrich discerns in the anthropology of non-WEIRD societies?


David Friedman paints a different picture because men and women ‘belong to themselves’ in modern societies.  Parents don’t ‘arrange’ their offspring’s marriages, and don’t have property rights in them.  By contrast, Henrich anachronistically assumes that females will be “‘promised’ in marriage prior to age 18.”


Friedman outlines the dynamics of polygamy in two simple models that include self-ownership.  First, a model of a marriage market with prices:

“[… .] how can women possibly be made better off by polygyny and men by polyandry?  That reaction reflects [ …] naive price theory.  Naive price theory is the theory that prices do not change.  If polygyny were introduced and nothing else changed, then it seems likely that women would be worse off—except for those who prefer to share the burden of putting up with a husband. But when polygyny is introduced, something else does change; the demand curve for wives shifts up, and so does the price for wives implicit in the marriage contract. Those wives who end up with one husband get him on more favorable terms—he must bid more for a wife because of the competition of his polygynous rivals. Those who accept polygynous marriages do so because the price they are offered is sufficient to at least balance, for them, the disadvantage of sharing a husband.”


Second, a simple model of matching without prices:

“The most desirable woman has her pick of mates, so she accepts the most desirable man; he, having his pick of mates, is only interested in her.  The second most desirable woman […] settles for the second most desirable man.  The process continues until all the members of whichever gender is less plentiful on the marriage market have been paired up, leaving the least desirable members of the other gender unmarried.  Suppose we now introduce polygyny. The most attractive woman can no longer be certain of marrying the most attractive man.  He may prefer two less attractive women—and they may each prefer half of him to all of a less attractive man.  If fewer men than women want to get married, some women may be choosing half of a husband over the alternative of no husband at all.  The result is no longer an unambiguous improvement from the standpoint of women, as it was in the first model.  Some women at the top of the hierarchy find themselves with less attractive men than before.  Neither is it an unambiguous worsening; some women who were previously unmarried may now have (half of) a husband, while others may get half of a man instead of all of a dolt.  It may or may not be an unambiguous improvement for the men. Some men benefit by getting two wives instead of one. In addition, every time a man near the top of the hierarchy settles for two (lower quality) women instead of one (high-quality) one, he opens up a rung on the ladder; the men below him move up a step and end up with more desirable wives than they could have before. [… .]  How can the change injure men? A man is worse off if someone above him marries two wives, both higher in the women’s hierarchy than the woman he was going to marry. That eliminates one step above him on the men’s ladder and two steps on the women’s, pushing his relative position down a step; he must be content with a woman one step below the one he could have gotten if monogamy were the rule.”


Alvin Roth echoes Friedman’s second model:

“legalizing certain kinds of voluntary transactions may change the terms of trade so as to disadvantage those who don’t wish to participate in them. [… .] for example, bans on polygamy might be understood as outlawing certain kinds of competition that would disadvantage some men and some women relative to the monogamous status quo, even while allowing others to engage in welfare-improving transactions.”  (p. 11)


It should come as no surprise that repeal of prohibition of polygamy might be ambiguous from a utilitarian perspective.  Major rule-changes that make nobody worse off—‘Pareto improvements’—are no mean feat.  Should utilitarian ambiguity override a presumption of liberty in marriage?


(On a separate note, Roth also classifies polygamy as a repugnant transaction (p. 20).)


Alex Tabarrok identifies two countervailing mechanisms, which cast doubt on Henrich’s claim that “children in a more polygynous society will receive less parental investment:”

“It is true that to the extent that polygyny increases the number of any particular man’s children that his attention will be divided.  But there are two counter effects.  First, there is a selection effect.  The men with more children will be the wealthier and healthier men–the better providers.  [… .] Polygyny […] decreases the fertility of the polygynous woman […], thus the attention of mothers will increase.”


Gary Becker draws an analogy between prohibition of polygamy and discrimination in the labor market:

“The claim that polygyny is unfair to women is strange since polygyny increases the demand for women as spouses in the same way that polyandry would increase the demand for men. If men were to take multiple wives, that increases the overall competition for women compared to a situation where each man can have at most one wife. This argument against polygyny is like arguing that a way to increase the economic prospects of minorities is to place an upper bound on how many members of these groups a company can employ.”


Unlike Henrich, Becker predicts that polygyny won’t spread:

“polygyny would be rare in modern societies even if fully allowed. […] the main motivation for polygyny has vanished with the arrival of the knowledge economy where fathers as well as mothers now want a small number of educated children rather than many ill-educated offspring.”


Bryan Caplan concurs: “Not much would change if you legalized gay marriage or polygamy; they’re just niche markets.”  Elsewhere, he elaborates:

“you’re most likely to see polygamy arise in places where the supply of women is high relative to demand. To take an extreme example, if half the male population dies in a war, the price of women is going to be low. This encourages polygamy, which partially mitigates the damage for women.”


Posner, however, disagrees about prevalence, too:

“I am not sure that it would be all that uncommon. Although few American couples want to have more than two or three children, a polygamous union is not a couple. If a couple has three children, the ratio of adults to children is 2:3. In a polygamous household consisting of a husband, two wives, and four children, the ratio of adults to children is higher: 3:4. So the per-parent burden is less, even though there are more children.”


Let’s take a closer look at whether a (hypothetical) substantial increase in prevalence of polygamy under legality would be bad.  As Thomas Sowell likes to reminds us, one always must ask: Compared to what?  Consider current prevalence of multiple partner fertility (MPF)—having children with more than one partner—in the United States.  In a groundbreaking study, Lindsay Monte finds:

“Multiple partner fertility is not a new phenomenon, but it is only in recent years that social science data have become inclusive enough to permit its study. (p. 1)  The most fundamental finding is that MPF is quite common.  […] more than a quarter of families with minor children have multiple partner fertility. (p. 10)  […] one or both parents has MPF in 44 percent of cohabiting families. (p. 5)  MPF mothers and fathers enter parenthood earlier than average. (p. 8)  The majority of MPF parents transition into MPF at the second child. (p. 8)  […] only 4.5 percent of MPF fathers live with all of their biological children. (p. 8)  […] fathers’ involvement with [their children of a first relationship] plummets when they have a child or children in a new union. […] (p. 2)  MPF mothers are a disproportionately large proportion of never married mothers (28.9 percent) compared to the proportion of MPF fathers among never married fathers (19.2 percent). (p. 8)  Even net of controls for sex, race, age, origin, educational attainment, and children ever born, MPF parents are still more likely to live in households below the poverty line than are either all parents or all adults. (p. 7)  MPF also means that custodial parents are likely relying on child support from absent parents, and child support is a less efficient means of economic support than a shared household budget. (p. 7)  […] 22.4 percent of MPF mothers live in households below the poverty line. (p. 9)  […] the exclusion of the incarcerated portion of the ‘institutionalized’ population may result in an undercount of the true level of MPF, particularly for men. (p. 9)”


One is reminded of Charles Murray’s portrait of Fishtown.  Monte’s findings indicate that most of the pathologies, which Henrich fears from legal polygamy, are present here and now, like caricatures, as correlates of adverse forms of multiple partner fertility on a major scale amidst a regime of prescribed monogamy.  Therefore, we should compare a hypothetical substantial prevalence of legal polygamy to massive, chaotic, ‘illegal,’ de facto polygyny and polyandry without contract and without commitment.  The pragmatic question, then, is: Would legal polygamy provide a cohesive, constructive substitute for adverse forms of multiple partner fertility?


And there is pathology in Murray’s Belmont, too.  For example, Friedman describes a wife’s vulnerability to opportunistic breach and serial polygamy by men in bourgeois monogamy:

“A couple marries. For the next twenty years, the wife is bearing and rearing children—a more than full-time job, as those who have tried it can attest. The husband supports the couple, but not very well, since he is still in the early stages of his career.  Finally the children are old enough to be only a part-time job and the wife can start living the life of leisure that she has earned. The husband gets promoted to vice-president. He divorces his wife and marries a younger woman.”


Would polygamy, by reconciling serial loves and established commitments, domesticate the husband, who otherwise would engage in opportunistic breach?


Becker postulates contractual protections for the first wife:

“What about a first wife who suddenly finds out that her husband is planning on taking additional wives? She could divorce him, share their property, and receive child support for any children they have in virtually all states without having to prove any ‘fault’ on his part. Moreover, she could write a contract before marriage stipulating that he cannot take additional wives. The contract could provide for damages In the event of a divorce due such a violation of the contract.”


Unlike Henrich, Elizabeth Brake notes that philosophers question whether polygyny would empower men to exert greater control over women:

“oppressiveness does not cleanly distinguish monogamous from polygamous relationships. […] if a polygamous ‘sister wife,’ for instance, has the legal right to marry outside the existing marriage, there is no structural inequality.”


Unlike Henrich, Arnold Kling fears not polygamy itself, but a combustible psychology of envy and jealousy around polygamy and inequality:

“My hypothesis is that the irrational resentment that many men feel over the high pay of CEO’s and others can be traced to a deep-seated fear that some other man will wind up with more than his share of mates, and the rest of us will be left with none.  The last thing we need is to turn that unconscious fear into something that is consciously justifiable.”


Robin Hanson contends that such envy about male sexual inequality doesn’t explain prohibition of polygamy:

“So yes, banning polygamy could be part of a larger coherent strategy to reduce male sexual inequality, to resist natural female hypergamy.  But banning polygamy and also polyandry and prostitution, while allowing lesbian relations and preventing natural punishment of wife affairs, well that looks nothing like a coherent strategy to reduce male sexual inequality.  We should look elsewhere to explain our pattern of what we ban and what we allow.”


Hanson’s answer is that prohibitions are exercises of prestige and dominance:

“It seems to me pretty obvious that we prohibit polygamy mainly because the folks who want to do it (rural religious communes) have low status in our society.  Also, since high status folks cheat and don’t want that discouraged via blackmail, we prohibit blackmail.  Yes there is an element of inertia, but gays have overcome such inertia in ways that polygamists can’t. Gays are common in high status communities and professions; for our elites, many of their best friends really are gay. Not at all true for polygamists.”


Let’s conclude with a contrast between philosophy and economics.  Philosopher Michael Huemer writes:

“What areas are most ripe for ethical revision? The area of sexual morality is probably the clearest case, since it is an area in which common moral attitudes exhibit multiple signs of unreliability.”


By contrast, Tabarrok elucidates the political economy of prohibition with an arresting twist:

“Polygyny will be bad for poor men who lose out in the competition for first wives to rich men who are on their second. […] On the whole, therefore, I see no strong arguments that banning polygamy (either polygyny or polyandry) is socially optimal but due to the power of the patriarchy I don’t expect polygyny to be approved of in the United States any time soon.”


The next post will be about drug prohibition.  If you would like background readings, I recommend essays by Jon Elster about addiction and by James Leitzel about potential regulations (exclusion and buyer licensing).


John Alcorn is Principal Lecturer in Formal Organizations, Shelby Cullom Davis Endowment, Trinity College, Connecticut.