The paradox of polygamy II: Why most women benefit from polygamy and most men benefit from monogamy
Would you be the third wife of Matt Damon?
Contrary to popular belief, most women benefit from polygynous society, and most men benefit from monogamous society. This is because polygynous society allows some women to share a resourceful man of high status. George Bernard Shaw (who was one of the founders of the London School of Economics and Political Science where I teach) put it best, when he observed, “The maternal instinct leads a woman to prefer a tenth share in a first rate man to the exclusive possession of a third rate one.”
Or, as the comedian Bill Maher asked his panel on his TV show Politically Incorrect on January 7, 1998, “Would you rather be the second or third wife of Mel Gibson or the only wife of Willard Scott?”, to which one of the panelists, the conservative commentator and activist Susan Carpenter McMillan, responded, “If it comes to Mel Gibson, I wouldn’t care if I was one, two, or three.” Of course, this was back when Mel Gibson was highly desirable. Substitute Matt Damon for Mel Gibson. The cast of characters changes in a decade, but the principle remains the same.
In contrast, most men benefit from monogamous society. Given a 50-50 sex ratio, monogamous society virtually guarantees a wife for every man, even a third-rate one. Under polygyny, some third-rate men may not find a wife at all, or, even if they are lucky enough to find one, their wife will not be as desirable as the one they can secure for themselves under monogamy, because under polygyny more desirable women would have become the second, third, or tenth wife of more desirable men.
The exceptions to this rule are highly desirable women, who benefit from monogamous society, and highly desirable men, who benefit from polygynous society. A highly desirable woman can marry a highly desirable man under any circumstances, but under polygyny she’d have to share her desirable husband with other women, whereas under monogamy she can monopolize him. A highly desirable man can acquire multiple wives under polygyny, but must confine himself to only one wife (albeit a highly desirable one) under monogamy.
It’s the nature of the statistical (“bell curve”) distribution, however, that most people are not extreme on either side; for example, most people are not extremely tall or extremely short, but of more or less average height. Similarly, most men and women are neither extremely desirable nor extremely undesirable. So most men benefit under monogamy, and most women benefit under polygyny.
When men imagine what living in a polygynous society might be like, they imagine themselves married to several wives. What they don’t realize, however, is that, more than likely, they would be left without any wife in a polygynous society. Polygynous marriage in a polygynous society is always limited to a minority of men. If 50% of men have two wives each, then the other 50% cannot have any wives. If 25% of men have four wives each, then the other 75% cannot have any wives. When women imagine what living in a polygynous society might be like, they imagine themselves having to share their current, no-good loser of a husband with other women. What they don’t realize is that they could be sharing Matt Damon or Bill Gates with other women.
Once we begin to look at things through the lens of evolutionary psychology and biology, they start to look quite different. Something that we previously thought was quite bizarre and morally wrong, like polygyny, begins to look quite natural and common. The perspective also gives us a new insight, like how women, not men, mostly benefit in polygynous societies.
Satoshi Kanazawa
The Scientific Fundamentalist
Monogamous Societies Superior to Polygamous Societies
The title is rather loud and non-objective. But that seems to me to be the upshot of Henrich et al.’s The puzzle of monogamous marriage (open access). In the abstract they declare that “normative monogamy reduces crime rates, including rape, murder, assault, robbery and fraud, as well as decreasing personal abuses.” Seems superior to me. As a friend of mine once observed, “If polygamy is awesome, how come polygamous societies suck so much?” Case in point is Saudi Arabia. Everyone assumes that if it didn’t sit on a pile of hydrocarbons Saudi Arabia would be dirt poor and suck. As it is, it sucks, but with an oil subsidy. The founder of modern Saudi Arabia was a polygamist, as are many of his male descendants (out of ~2,000). The total number of children he fathered is unknown! (the major sons are accounted for, but if you look at the genealogies of these Arab noble families the number of daughters is always vague and flexible, because no one seems to have cared much)
So how did monogamy come to be so common? If you follow Henrich’s work you will not be surprised that he posits “cultural group selection.” That is, the advantage of monogamy can not be reduced just to the success of monogamous individuals within a society. On the contrary, males who enter into polygamous relationships likely have a higher fitness than monogamous males within a given culture.
To get a sense of what they mean by group selection I recommend you read this review of the concept by David B. A major twist here though is that they are proposing that the selective process operates upon cultural, not genetic, variation (memes, not genes). Why does this matter? Because inter-cultural differences between two groups in competition can be very strong, and arise rather quickly, while inter-group genetic differences are usually weak due to the power of gene flow. To give an example of this, Christian societies in Northern Europe adopted normative monogamy, while pagans over the frontier did not (most marriages may have been monogamous, but elite males still entered into polygamous relationships). The cultural norm was partitioned (in theory) totally across the two groups, but there was almost no genetic difference. This means that very modest selection pressures can still work on the level of groups for culture, where they would not be effective for biological differences between groups (because those differences are so small) in relation to individual selection (within group variation would remain large).
From what I gather much of the magic of gains of economic productivity and social cohesion, and therefore military prowess, of a given set of societies (e.g., Christian Europe) in this model can be attributed to the fact of the proportion of single males. By reducing the fraction constantly scrambling for status and power so that they could become polygamists in their own right the general level of conflict was reduced in these societies. Sill, the norm of monogamy worked against the interests of elite males in a relative individual sense. Yet still, one immediately recalls that elite males in normatively monogamy societies took mistresses and engaged in serial monogamy. Additionally, there is still a scramble for mates among males in monogamous societies, though for quality and not quantity. These qualifications weaken the thesis to me, though they do not eliminate its force in totality.
In the end I am not convinced of this argument about group selection, though the survey of the empirical data on the deficiencies of societies which a higher frequency of polygamy was totally unsurprising. I recall years ago reading of a Muslim male who wondered how women would get married if men did not marry more than once. He outlined how wars mean that there will always be a deficit of males! One is curious about the arrow of causality is here; is polygamy a response to a shortage of males, or do elite polygamist make sure that there is a shortage of males? (as is the case among Mormon polygamists in the SA)
Finally, I do not think one can discount the fact that despite the long term ultimate evolutionary logic, over shorter time periods other dynamics can take advantage of proximate mechanisms. For example, humans purportedly wish to maximize fitness via our preference for sexual intercourse. But in the modern world humans have decoupled sex and reproduction, and our fitness maximizing instincts are now countervailed by our conscious preference for smaller families. Greater economic production is not swallowed up by population growth, but rather greater individual affluence. This may not persist over the long term for evolutionary reasons, but it persists long enough that it is a phenomenon worth examining. Similarly, the tendencies which make males polygamous may exist in modern monogamous males, but be channeled in other directions. One could posit that perhaps males have a preference to accumulate status. In a pre-modern society even the wealthy usually did not have many material objects. Land, livestock, and women, were clear and hard-to-fake signalers to show what a big cock you had. Therefore, polygamy was a common cultural universal evoked out of the conditions at hand. Today there are many more options on the table. My point is that one could make a group selective argument for the demographic transition, but to my knowledge that is not particularly popular. Rather, we appeal to common sense understandings of human psychology and motivation, and how they have changed over the generations.
Addendum: When I say polygamy, I mean polygyny. I would say polygyny, but then readers get confused. Also, do not confuse social preference for polygyny with lack of female power. There are two modern models of polygynous societies, the African, and the Islamic. The Islamic attitude toward women shares much with the Hindu monogamist view, while in African societies women are much more independent economic actors, albeit within a patriarchal context. The authors note that this distinction is important, because it seems monogamy (e.g., Japan) is a better predictor of social capital than gender equality as such, despite the correlation.
Citation: Joseph Henrich, Robert Boyd, and Peter J. Richerson, The puzzle of monogamous marriage, Phil. Trans. R. Soc. B March 5, 2012 367 (1589) 657-669;
By Razib Khan | January 30, 2012 9:14 pm http://blogs.discovermagazine.com/gnxp/2012/01/monogamous-societies-superior-to-polygamous-societies/#.XEJKEBqIbxw
#22: Polygamy Is Feminist
Polygamy is alive and well in parts of America. According to researchers at Brigham Young University, there are 30,000 to 50,000 people currently living a polygamist lifestyle in the United States, many of them in sects that splintered from the mainstream Mormon church when it renounced polygamy in 1890. A separate study reported on NPR estimates that 50,000 to 100,000 Muslims in America may be quietly living polygamist lives. And around the world polygamy is a far more common phenomenon, especially in Africa and Asia. For the most part though, it is condemned in the West as being sexist towards women.
But Marina Adshade, an economics professor at Dalhousie University and the author of Big Think's "Dollars and Sex" blog, tells us that polygyny (the practice of a man having multiple wives) can actually be economically beneficial to women—and should not be outlawed by the government. Adshade bases her argument on the economic criterion for optimality called “Pareto efficiency.”
“A situation is Pareto efficient, or optimal if, and only if, no one can be made better off without making someone else worse off,” she explains. To demonstrate her point, Adshade asks us to consider a society with the following characteristics:
- There are equal numbers of men and women.
- Resources (land for example) are unequally distributed among men only.
- Men make women offers of marriage and women have the right to refuse.
In forcing such a community to switch from polygyny to monogamy, the women would actually be the ones who lose out and the men would benefit, says Adshade.
Consider the following scenario: “A man makes a woman an offer of marriage and part of that offer is in terms of the standard of living of her and the children they will have together in the future. Say she receives two offers of marriage, one from a man who has plenty of resources and already has one wife (so that she will be wife number two) and a second from a man who has little resources and has no wives (so she will be the one and only wife). If she accepts the offer of the rich man over the poor man, and since she is acting in her own best interest, then she must prefer polygyny over monogamy. A change in marriage systems that forces her to be the only wife of the poor man necessarily makes her worse off. We know this because she could have accepted his offer in the first place and chose not to.
“The person in this story who benefits from the change from polygyny to monogamy though is the poor man who with the current system has no wife. He made a marriage offer to the woman and, since he is acting in his own best interest, if she had accepted the offer he would have been better off than he is without her. He had that offer refused though because she had a more appealing alternative. If there was a system of monogamy she might have accepted his offer because that alternative was no longer available.
“In polygynous societies with individual choice the truly disadvantaged are the poorer men who end up with no wives or families of their own. You can argue that the change to a monogamous society makes them better off but while it does so it makes the wives of the wealthy men worse off, so that change cannot meet the criterion for Pareto efficiency.” In other words, the shift from polygyny to monogamy would make women worse off, so the most economically sound policy would be to allow it to continue.
Stepping back from the economics of this debate, Adshade also argues that polygyny doesn’t inherently endanger the welfare of women and children. Firstly, she says it’s not true that women in polygamous societies have no say in marriage choices. “In fact, statistically, in societies without monogamy, there is actually slightly more opportunity for the bride and groom to either choose or have the right to refuse matches. Also there is evidence that in polygynous societies women have more control, not less, over the number of children they have.”
As for child welfare, she says, the results are mixed. But "there is plenty of evidence, despite the efforts of researchers to prove otherwise, that children in polygynous households are better off.” James Fenske, a professor at Oxford, is one such researcher who has found that polygyny in western Africa has historically lowered child mortality rates. “If their mothers choose their husbands based on their children’s best interests as well as their own we would expect this to be the case,” Adshade says.
Takeaway
Though reviled in the West, polygyny is actually quite common throughout the world. According to the Ethnographic Atlas, studying over a thousand societies from 1962-1980, there were over 1,000 polygamous societies, compared to just 186 monogamous ones. Adshade says that as long as women have a say in the matter, allowing polygyny to persist in those countries and communities where it already exists is actually better for women than forcing them to adopt a monogamous life. Plus polygynous relationships may actually be more stable than monogamous ones.
Why We Should Reject This
The case of the Fundamentalist Church of Jesus Christ of Latter Day Saints is evidence that women in polygynist societies often do not have the right to refuse marriage and are thus subjected to misogyny and often child abuse. Even putting this fact aside, Joseph Henrich, an anthropologist at the University of British Columbia, says there are good socioeconomic reasons why polygyny is illegal, even under the ideal situations that Adshade proposes.
If more people were allowed to pursue such a lifestyle—and Heinrich thinks they would “given what we know about both male and female mating preferences”—there would arise a large pool of unmarried males who were unable to attract a mate. Henrich believes this would lead to an increase in crime and antisocial behavior because, other things being equal, unmarried men tend to be more violent and more generally criminal than married men. Plus, this system would unfairly handicap poor and uneducated men, who could not compete with richer and thus more attractive mates who would be free to collect as many wives as they could handle.
Even for the men who successfully attract mates, their behavior is necessarily distorted by the practice of polygyny, Henrich says. Fiercer competition for wives promotes the idea of women as valuable objects rather than humans worthy of love, and as a result men feel the need to guard them more carefully. The same competition pushes the age at which girls are recruited for marriage lower. And men will also spend less time and fewer resources on individual wives and children: “Polygynous men invest less time in their offspring both because they have more offspring and because they continue to invest in seeking additional wives,” says Henrich.
More Resources
— "The Link Between Polygyny and Child Mortality" [PDF] a 2009 presentation by James Fenke
— Joseph Henrich's affidavit to the Canadian Supreme Court providing his argument against polygyny [PDF]
— The Ethnographic Atlas Codebook published by World Cultures in 1986.
19 August, 2010
https://bigthink.com/dangerous-ideas/22-polygamy-is-feminist
Why Not Polygamy?
People are pretty creeped out by polygamy. The mere mention of this marital arrangement invariably conjures mental images of gaggles of young, conservatively-frocked girls being corralled by the authorities out of the sprawling complexes that were once lorded by their lecherous husbands. Indeed, many of the most publicized practitioners of polygyny, the wedding of one man to more than one wife, have not done much to promote positive public relations for their preferred family arrangement. Does this mean that polygyny is inherently bad for women and society? The answer might surprise you.
The most popular critiques of polygamy come from strange (but frequent) bedfellows — feminist scholars and family values conservatives. Feminists contend that when a man takes more than one wife, he devalues both his original spouse and each additional spouse that he collects. In their view, the institution of polygyny simply multiplies the already problematic power dynamics that already exist between husband and wife. What’s more, in a society where women are believed to be at an inherent disadvantage to the position of men, feminists question whether polygyny can really be considered a voluntary choice to begin with.
Conservative critics, ever the watchdogs of sexual decency and permissible behaviors, attest that polygamy is nothing more than a ruse to indulge in animalistic amounts of sex with multiple partners. Forgetting or forgiving the fact that the early patriarchs of the world’s largest religions famously indulged in this now-taboo act, conservative critics of polygamy see the practice as an affront to the cherished institution of traditional marriage. They argue that children are best raised in a household with one mother and one father and that any alternative arrangement would have damaging effects on children’s psyches. In fact, polygamy is routinely trotted out as the next horrid stop on the slippery slope of allowing (gasp!) gay marriage.
Let us first address the feminist critique. Is polygyny a bad deal for women? At first glance, it seems hard to disagree: the image of a solitary man surrounded by a growing harem of successively more-youthful brides rouses feelings of pity for the plights of the auxiliary wives and disgust at the hubris of the husband for whom one spouse is simply not enough. But let us momentarily place our visceral reactions aside and consider the economics of the affair; why might a woman voluntarily agree to this kind of arrangement instead of a traditional marriage?
Imagine that you are a young woman surveying the prospects for potential partners within your community. You would, of course, like to find yourself hitched to the most eligible bachelor; the handsome and healthy go-getter with big plans for the future and an even bigger heart to care for one lucky lady. Unfortunately for you, so does every other girl in town. As the singles in this town dine, dance, ditch, and ultimately discover their approximate sexual counterpart, you may look across at the knight in faded armor with which you’ve ended up — a man with but a fraction of the ambition, skills, charm, and resources of your heart’s (and wallet’s) true desire — and find that you would rather play second-fiddle as the second wife of the alpha male than remain the sole wife of the lesser lout that you could land on your own. Of course, you will have to share your spouse with another woman, but the benefits of having access to a portion of a near-perfect husband might outweigh those of having a disappointing husband all to yourself. In this scenario where women freely agree to participate in a plural marriage, polygyny can be a powerful engine to improving women’s welfare; by allowing alpha males to stay longer on the mating market, it gives more women a crack at landing a great man who can provide for her…and his other wives.
The conservative critique, on its face, is grounded in a specific moral foundation that many people may not share. Simply put, fewer people are concerned about the “sanctity of marriage” than they were in the halcyon days of the 1950’s. True monogamy, wherein a person has one spouse for their entire life time, is rapidly disappearing. Even people who purport to believe in the institution of monogamy don’t exactly practice what they preach: serial monogamy has become the new normal. People already marry more than one person over the course of their lives, they just space it out and create a lot of social strife in the process. Bitter divorce proceedings pit children against parents, cause lasting emotional wounds, and split up familial wealth.
If a marriage is heading south because of waning romantic tidings between spouses but the parents are thoughtful enough to try to stay together for their children, it’s hard to see how agreeing to invite more spouses into the relationship is objectively more damaging to their children than the alternative of inevitable ruthless court squabbles over dividing assets and haggling over visitation rights. In fact, the children would probably benefit from having more parental figures to care for them in addition to avoiding the awkward tension between their parents that inevitably results from divorce. Viewed in this light, polygamy should actually be embraced by family values conservatives as a way to strengthen family bonds and increase support systems for children.
Given the rise of serial monogamy, the conservative critique is likely not directed at protecting true monogamy per se, but rather at maintaining the social status quo. This is where the conservative critique brings up a valuable point. Monogamy is, essentially, a tacit collusive agreement among men to restrict competition in the mating market. Men benefit from monogamy because the “lesser louts” are given a higher probability of landing a mate even though they may not have much to offer their spouse. By managing to wrangle a wife through monogamous collusion, these louts, then, are given a purpose and sense of happiness that generally keeps them off the streets and out of trouble. What might happen if this collusion were to end?
More sophisticated arguments against polygyny consider the social ramifications of a world where huge numbers of men are unable to find mates and become restless and unruly. They point out that in early human history, when gender ratios became skewed to the point where a large portion of men could not find wives within their community, warfare erupted as the surplus men attempted to poach the resources and women of a neighboring tribe. These critics propose an excellent challenge, but they neglect to consider the pacifying nature of the moral Flynn effect that has since tempered and tamed our society. In fact, the advent of polygyny and unleashing of sexual competition could provide the couch potatoes and basement dwellers of the world with just the kick in the ass that they need to get their acts together. The growing pains of having to fully compete on the mating market would certainly be a unwelcome shock to the sedentary betas who are used to exerting a bare minimum of effort and still managing to snag a significant other, but over time their lives would likely be fuller and more satisfying as they improved themselves and eventually found a mate by virtue of their character instead of through collusive social norms. And, of course, women would then have a larger pool of attractive suitors from which to choose.
Large economic changes tend to have dramatic effects on the social makeup of society. Our hunter-gathering ancestors preferred polygamistic relationships. The dawn of the agricultural revolution resulted in the institution of monogamy. The fruits of the industrial revolution allowed women to enter the job force and eventually strike it out on their own. As we approach the cusp of the next post-industrial economic era, the makeup of our familial institutions is likely to change in tandem. Polygamy is again a candidate to be a dominant social institution. To me, it doesn’t sound half bad.
Feb 19, 2013
https://theumlaut.com/why-not-polygamy-3665280a2a67
Marriage is about power, property and control
– it’s time to rethink it
It’s been a busy few weeks for ticking things off the Gay Agenda. First, Starbucks launched an ad campaign with lesbians in it and then, in almost as momentous news, Australia said yes to same-sex marriage. Almost 80% of Australians voted in the historic national postal survey, with 61.6% of people in favour of treating gay people like everyone else, and 38.4% against. Unlike a result of, say, 52% versus 48%, that’s a pretty unambiguous indicator of what Australia wants and what it values. As prime minister Malcolm Turnbull said, the country “voted yes for fairness, yes for commitment, yes for love”.
Now, don’t get me wrong, I think it’s great that Australia voted for marriage equality. Being of a homosexual persuasion, I’m all for gay people having equal rights. They tend to come in very handy. And I’m certainly all for fairness, commitment and love. But I’m just not sure that marriage, as an institution, has anything to do with fairness, commitment or love. Quite the opposite, in fact; marriage has long been about power, property and control. It has traditionally been a way of commoditising women and regulating female sexuality and, in many ways, it still is.
We’ve moved on, of course, from the days of coverture when, as William Blackstone describes in Commentaries on the Laws of England (1765), marriage meant that “the very being or legal existence of the woman is suspended during the marriage, or at least is incorporated and consolidated into that of the husband: under whose wing, protection, and cover, she performs every thing”. We’ve moved on from the days when raping your spouse was totally fine under the law – although it’s worth remembering that it wasn’t until 1991 that marital rape became a crime in England and Wales. Nevertheless, marriage still hasn’t been properly modernised. In both countries, marriage certificates still have only the names of the couple’s fathers, not their mothers, for example, although there have been numerous efforts to change this recently.
The traditions we’ve established around marriage also reinforce outdated gender norms. The diamond engagement rings; the white dresses; the father walking the bride down the aisle; the fact that it’s still considered unusual for a woman to propose. I’m surprised by how many strong, smart, feminist women I know seem to have one foot in the 1950s when it comes to marriage. Not to mention that heterosexual marriage still largely benefits men. Studies show that while tying the knot seems to reduce the chances of men kicking the bucket early, unmarried women don’t experience the same negative health effects as single men.
As for marriage encouraging commitment … Well, I’m sorry to say it, but straight people have diluted the institution of marriage. The great and the good of the heterosexual world all seem to treat marriage like an impulse purchase. The president of the United States, for example, has had three wives. Kim Kardashian, the unofficial president, has had three husbands – her second marriage to Kris Humphries famously lasted only 72 days. Which, to be fair, is longer than Britney Spears’ 55-hour marriage. This, perhaps, is down to the burgeoning wedding-industrial complex and the fact that, in many ways, marriage has become more a celebration of consumption than of commitment.
You don’t have to participate in all that, you might say. It’s perfectly possible to get married without spending a fortune on a diamond ring or having a traditional wedding. It’s perfectly possible to have an equal relationship and stay married for longer than 55 hours. Of course. And, to reiterate, I’m glad that Australia voted yes for marriage equality. It’s a heartening sign of progress. But what I think would be even more heartening is if more of us voted no to marriage and if society normalised a more inherently equal form of partnership; one that isn’t permeated by old-fashioned ideals. I don’t often say this, but the French are an inspiration in that regard. France created a system of civil unions in 1999 – the pacte civil de solidarité or Pacs – as a stepping stone to gay marriage. As it turns out, it was enthusiastically embraced by heterosexual couples who weren’t enamoured with traditional marriages and wanted an alternative way to formalise their relationship.
In the UK, gay couples can have a civil partnership but heterosexuals can’t, despite the fact that many straight couples are eager for a more modern alternative to marriage and have been fighting for a change in the law. Earlier this year, Charles Keidan and Rebecca Steinfeld, a couple from London, lost their court of appeal battle to be able to choose a civil partnership over a marriage. I don’t normally feel sorry for straight people claiming “heterosexual discrimination”, but in this case, they’re absolutely right to be angry. Extending civil partnerships to everyone in the UK is vital if we want to call ourselves an equal, progressive society.
So, now that Australia has put gay marriage equality to the vote, perhaps it’s time for the UK to put straight partnership equality to the vote. After all, who doesn’t love a referendum?
• This article was amended on 21 November 2017. An earlier version said marriage certificates in the UK only have the name of the couple’s fathers, not their mothers. This has been corrected to say in England and Wales.
Arwa Mahdawi It’s great that Australia voted yes for marriage equality, but a more heartening sign of progress would be an equal form of partnership for everyone
Polygamy Good for Men, Bad for Women
Mormon shift from polygamy to monogamy in the 1800s reduced sexual pressures on men by more than half, according to a new study.
The change closed the reproductive gap between men with many wives and men with none. It also brought men's competition for wives in line with wives' competition for husbands.
The research also revealed that while polygamous men had dozens of children, the practice of having multiple wives (and thus sexual partners) had the opposite effect on women: For every wife added to the fold, the average number of children per wife dropped by one.
"The more wives a woman's husband has, the fewer children she is going to have personally," study author Michael Wade, a biologist at Indiana University Bloomington, told LiveScience. "That's interesting, and evolutionary biologists would say then that polygamy is good for males and maybe not so good for females."
Wade and his colleagues reported their findings in the March issue of the journal Evolution and Human Behavior.
Polygamy to monogamy
Mormons make an excellent test case for evolutionary biologists for two reasons, Wade said. First, they keep precise genealogical records. Second, Mormons are a rare example of a group of people who changed their mating practices. In 1862, Congress made polygamy illegal in U.S. territories, including the Mormon stronghold of Utah. In 1890, the Mormon church issued a declaration ending the practice. Of married Utah men born in 1833, almost 18 percent had multiple wives, Wade and his colleagues estimate. By a few decades later, less than 1 percent of married men were in polygamous relationships.
"Here with this single population there's a change, an externally driven change, in the system of mating from polygamous to monogamous," Wade said. "And even better, nothing else changes. They don't change their lifestyle, they don't change what they eat, or where they live."
The researchers decided to find out how the change affected the evolutionary pressures on Mormon men and women, particularly sexual selection, in which there is competition between males (or females) to win a mate. It's this pressure that explains a male peacock's glitzy tail. Polygamy exacerbates such sexual selection. After all, for every man with five wives, there are four men with no wives at all. Thus, the multiple-wife system separates men into those with huge amounts of offspring and those with no children at all.
"The bigger that difference, the stronger selection is," Wade said.
To measure selection, the researchers pulled genealogical data on almost 150,000 men and women born between 1830 and 1894 and almost 635,000 of their offspring from the Utah Population Database — a sample size 18 times larger than those of all previous studies on the topic combined. The researchers used U.S. Census Bureau data to round out their estimates of the number of people who never had children. They also corrected for "serial monogamists," or people who had been widowed and remarried, but weren't involved in polygamous relationships.
Many questions
Unsurprisingly, the men who acquired lots of wives also produced more children. For each additional spouse, a man could expect about six more kids. Each wife in the relationship could expect to produce an average of one fewer child for every additional wife.
When polygamy was outlawed, the reproductive gap between successful polygamous men and wife-less singletons plummeted by 58 percent, the researchers found.
"If you only have one partner, the maximum [number of offspring] for the male is going to be the same as the maximum for the females," Wade said. So the end of polygamy brought the genders into line, he said. "The variation from one male to the next with monogamy becomes almost equal to the variation from one woman to the next with monogamy."
That's no surprise, said Henry Harpending, a professor of anthropology at the University of Utah, who was not involved in the research. Historical Mormons are particularly interesting to study, Harpending told LiveScience, because there is little question as to the paternity of offspring. In other polygamous cultures, Harpending said, marriage doesn't always mean sexual exclusivity, making similar studies difficult.
"This is the best that this has ever been done, and it's very impressive," Harpending said of the study. However, he cautioned, the variation in reproductive success seen in the Mormon population doesn't necessarily mean that evolutionary selection is taking place.
"The guys that have three wives may have three wives because it's simply random or because they're better at something," Harpending said. "If it's because they're better at something, then that's changing the gene pool and that's selection. If it's just random — my Uncle Charlie helped me buy a farm and I got three wives — then that doesn't change the gene pool."
There are also alternative explanations beside selection to explain findings like the cost of extra wives for women, Harpending said. Perhaps those women's husbands are older and less fertile, or perhaps they'd previously been widowed and had thus missed a potentially fertile year, he said.
"What I'd like to see done is life histories of women, so we could ask, 'What's the effect of being widowed?' 'What is the per-year birth rate for a woman, age-corrected and correct for husband's age?'" Harpending said. "There are so many questions."
Stephanie Pappas
https://www.livescience.com/13010-polygamy-good-men-bad-women.html
