[Article updated on 25 April 2020.]
In the state of nature, people were generally polygamous, as are most animals. With many animals, the male leaves the female soon after mating and long before any offspring are born.
According to genetic studies, it is only relatively recently, about 10,000 years ago, that monogamy began to prevail over polygamy in human populations. Monogamous unions may have developed in tandem with sedentary agriculture, helping to maintain land and property within the same narrow kin group.
Polygamy may enable a male to sire more offspring, but monogamy can, in certain circumstances, represent a more successful overall reproductive strategy. By sticking with the same female, a male is able to ensure that the female’s offspring are also his, and prevent this offspring from being killed by male rivals intent on returning the female to fertility (breastfeeding being a natural contraceptive).
Historically, most cultures that permitted polygamy permitted polygyny (a man taking two or more wives) rather than polyandry (a woman taking two or more husbands).
In the Gallic War , Julius Cæsar claimed that, among ancient Britons, ‘ten and even twelve men have wives in common’, particularly brothers, or fathers and sons—which to me sounds more like group marriage than polyandry proper.
Let’s talk about the rarer polyandry first. Polyandry is typically tied to scarcity of land and resources, as, for example, in certain parts of the Himalayas, and serves to limit population growth. If it involves several brothers married to the one wife (fraternal polyandry), it also protects the family’s land from division.
In Europe, this was generally achieved through the feudal rule of primogeniture (‘first born’), still practised among the British aristocracy, by which the eldest legitimate son inherits the entire estate (or almost) of both his parents. Primogeniture has antecedents in the Bible, with, most notably, Esau selling his ‘birthright’ to his younger brother Jacob.
Today, most countries that permit polygamy—invariably in the form of polygyny—are countries with a Muslim majority or sizeable Muslim minority. In some countries, such as India, polygamy is legal only for Muslims. In others, such as Russia and South Africa, it is illegal but not criminalized.
Under Islamic marital jurisprudence, a man can take up to four wives, so long as he treats them all equally. While it is true that Islam permits polygyny, it does not require or impose it: marriage can only occur by mutual consent, and a bride is able to stipulate that her husband-to-be is not to take a second wife. Monogamy is by far the norm in Muslim societies, as most men cannot afford to maintain more than one family, and many of those who could would rather not. That said, polygyny remains very common across much of West Africa.
Polygamy is illegal and criminalized across Europe and the Americas, as well as in China, Australia, and other countries. Even so, there are many instances of polygamy in the West, especially within immigrant communities and certain religious groups such as the Fundamentalist Church of Jesus Christ of Latter-Day Saints (FLDS Church) and other Mormon fundamentalists.
So what are the pros and cons of polygamy (or polygyny)? A man who takes more than one wife satisfies more of his sexual appetites, signals high social status, and generally feels better about himself. His many children supply him with a ready source of labour, and the means, through arranged marriages, to create multiple, reliable, and durable social, economic, and political alliances. Polygyny may be costly, but in the long term it can make a rich man richer still.
Even in monogamous societies, powerful men often establish long-term sexual relationships with women other than their wives (concubinage), although in this case the junior partners and their children born to them do not enjoy the same legal protections as the ‘legitimate’ wife and children.
Louis XIV of France, the Sun King, had a great number of mistresses, both official and unofficial. His chief mistress at any one time carried the title of maîtresse-en-titre , and the most celebrated one, Françoise-Athénaïs, Marquise de Montespan, bore him no fewer than seven children.
In some cases, a man might get divorced to marry a much younger woman (serial monogamy), thereby monopolizing the reproductive lifespan of more than one woman without suffering the social stigma of polygamy.
As I argue in my book, For Better For Worse , if divorce has become so common, it is in part because people are living for much longer, whereas in the past death would have done the job of divorce. ‘Till death do us part’ means a great deal more today than it ever did.
Polygyny might even benefit the women involved, who may come to enjoy one another’s company, and share out the burdens of housekeeping and childrearing. Younger wives may add to the status and standing of the first wife, while at the same time subtracting from her responsibilities. In times of war, with high male absenteeism and mortality, polygyny supports population growth and replenishment by ensuring that every female can find a mate.
But of course polygyny also has drawbacks, especially when viewed through a modern, Western lens.
First and foremost, polygyny sanctions and perpetuates gender inequality, with co-wives officially and patently subordinated to their husband.
Women in polygynous unions tend to marry at a younger age, into a setup that, by its very nature, fosters jealousy, competition, and conflict, with instances of co-wives poisoning one another’s offspring in a bid to further their own.
Although the husband ought in principle to treat his co-wives equally, in practice he will almost inevitably favour one over the others—most likely the youngest, most recent one.
Tensions may be reduced by establishing a clear hierarchy among the co-wives, or if the co-wives are sisters (sororal polygyny), or if they each keep a separate household (hut polygyny).
While polygyny may benefit the men involved, it denies wives to other men, especially young, low-status men, who, like all men, tend to measure their success by their manhood, that is, by the twin parameters of social status and fertility.
With little to lose or look forward to, these frustrated men are much more likely to turn to crime and violence, including sexual violence and warmongering. It is perhaps telling that polygamy is practiced in almost all of the 20 most unstable countries on the Fragile States Index.
All this is only aggravated by the brideprice, a payment from the groom to the bride’s family. Brideprice is a frequent feature of polygynous unions and is intended to compensate the bride’s family for the loss of a pair of hands.
Divorce typically requires that the brideprice be returned, leaving many women with no choice but to remain in miserable or abusive marriages.
If polygynous unions are common, the resulting shortage of brides inflates the brideprice, raising the age at which young men can afford to marry while incentivizing families to hive off their daughters at the soonest opportunity, even at the cost of interrupting their education.
Brideprice is often paid in cows, leading some young men to resort to cattle raids and other forms of crime. Gang leaders and warlords attract new recruits with the promise of a bride or an offer to cover their brideprice.
Polygyny also tends to disadvantage the offspring. On the one hand, children in polygamous families share in the genes of an alpha male and stand to benefit from his protection, resources, influence, outlook, and expertise.
But on the other hand, their mothers are younger and less educated, and they receive a divided share of their father’s attention, which may be directed at his latest wife, or at amassing resources for his next one.
They are also at greater risk of violence from their kin group, particularly the extended family. Overall, the infant mortality in polygynous families is considerably higher than in monogamous families.
So draw your own conclusions.
See my related article, Polyamory: A New Way of Loving
Dupanloup I et al. (2003): A recent shift from polygyny to monogamy in humans is suggested by the analysis of worldwide Y-chromosome diversity. J Mol Evol. 57(1):85–97.
Fragile-States Index 2017. The Fund for Peace; DHS; MICS.