After several years without being invited to a wedding, my wife and I attended two in the last few weeks. We have passed through a period when most friends of our own age are already married and are now entering one where their children are tying the knot. As if to redress the balance, though, another pair of friends is now considering divorce. Overall, our acquaintances seem to be fairly typical: According to the Pew Research Center, roughly 2.1 million Americans will get married in 2019, and 850,000 — almost half as many — will divorce.
Our acquaintances are also typical in that many of them are single. Fifty years ago, 72 percent of Americans over the age of 18 were married; today, only half are. But this is not because Americans divorce more than they used to do. In fact, they divorce less often. While 56 percent of American marriages ended in divorce in the early 1980s, only 41 percent now do so. Marriage rates are falling partly because more people never marry (23 percent of men and 17 percent of women, as against 10 percent and 8 percent in 1960) and partly because those who do marry do so later (median ages of 29.5 for men and 27.4 for women, compared with 22.8 and 20.3 in 1960).
Journalists and politicians regularly treat marriage and divorce rates as metrics for morality, but they are not. Marriages are strategic alliances, and like everything involving strategy, they combine an unchanging logic with cultural specifics. Humans are rational, strategic actors. Marriage is losing ground not because Americans are more feckless than they used to be but because the conditions that for so long made it a profitable form of alliance are changing — particularly for women.
Squaring the Circle
Through most of history, most marriages have been alliances in which one man and one woman pool their labor, property and genes, creating a joint household. Many societies have also allowed multipartner marriages (usually, one man marrying several women), and some allow same-sex marriage. These alliances can look very different from the monogamous, heterosexual kind, but they nevertheless follow most or all of the same strategic principles.
What marks marriage off from other alliances into which we might enter, such as friendships, is the way it is enforced. Two or more people commit before their gods, ancestors and communities to follow agreed-on rules. Despite all the cultural variations between societies, these rules always come down more or less to loving, honoring and perhaps obeying one another. If the partners follow through, this pact solves many of the collective action and credible commitment problems that bedevil other kinds of coalitions, providing the family with material and psychological benefits that cannot be gained any other way.
In particular, the different chromosomes that heterosexual spouses bring with them fit their bodies for complementary tasks, most obviously in the breeding and rearing of children. Love, honor and a certain amount of obedience can even solve what evolutionists sometimes call the "sperm-and-egg" problem. For a male, passing genetic material onto a new generation is easy. It's also cheap, since the typical young man creates about a thousand sperm per second. Consequently, males who have sex with multiple females leave a bigger imprint on the human genome than males who do not, and natural selection has therefore given us men who want to have sex with lots of women. For women, though, passing on genetic material is expensive and difficult. Women produce only one egg per month, and, once the egg is fertilized, must carry the baby for another nine months. A woman who chooses her partners carefully, accepting sperm only from a male whom she expects (a) to give her the kind of children she wants and (b) to stick around to help raise them will typically leave a bigger imprint on the genome than one who chooses less wisely. Women have therefore evolved to be picky.
What marks marriage off from other alliances into which we might enter, such as friendships, is the way it is enforced.
Marriage offers a way to square this circle. Having sworn before their gods, ancestors and communities to follow the rules, husbands and wives who behave badly are subject to much more serious sanctions than mere friends with benefits who have taken no such oaths.
Tolstoy famously said that every unhappy family is unhappy in its own way, but in fact, the almost infinite number of ways to punish sinning spouses seem to come down to four basic weapons. All are also available to mere friends with benefits, but the oaths taken at a wedding before vengeful, powerful third parties raise the stakes. The first weapon is guilt. It is always difficult and painful to disappoint someone you love, which means that in a marriage that is working well, the partners effectively police themselves.
Next comes shame, or, to put it more coldly, reputational costs. Look, the betrayed spouse says to anyone who will listen, at what the bastard/bitch did after everything I've done for him/her! None of us is wholly immune to the fear of being revealed to all as a wicked person.
The third weapon is economics. If one partner controls vital resources, he/she is in a strong position to bargain over sex or any other bone of contention.
Finally, there is violence. Husbands are typically better placed to deploy this than wives, although many a woman scorned has called on her male kin to thrash her scoundrel of a husband to within an inch of his life, and plenty of cuckolded husbands have taken matters into their own hands.
Every documented human society has evolved some institution recognizable as marriage, enforced by these four kinds of sanctions. This is not a coincidence: without marital alliances, people would have a much harder time trusting each other enough to raise the next generation, let alone cooperating in all the other complicated tasks that our lives demand.
Costs and Benefits
These aspects of marriage are universals, relevant to every spouse in every time and place, parts of the unvarying strategic logic governing alliances. That is why the stories of Anna Karenina, Abelard and Heloise, and Helen of Troy immediately make sense to everyone, despite cultural differences. We understand intuitively that marriage involves trade-offs between costs and benefits, and that cheating can and should have consequences, even when these are tragic.
Yet as every strategist knows, simply following logic is never enough: We always need to understand how logical abstractions interact with the surrounding environment. Human beings have not changed much genetically in the last 30,000 or 40,000 years, yet in the course of just 50 years, the proportion of Americans in marriages has fallen by one-third. The explanation seems to be that conditions have changed so much across this half-century that rational actors, pursuing sensible goals, are increasingly concluding that the costs of marriage alliances now outweigh the benefits.
We should neither be surprised by this nor conclude that it proves that the modern world is morally bankrupt. The forms and functions of marriage have in fact changed dramatically many times in the past, even as the strategic logic behind marriage remains unchanged. If we can treat the foraging societies documented by 20th-century anthropologists as rough proxies for what life was like in the first 95 percent of human history, when everyone lived by hunting and gathering, it seems that early marriages tended to be rather loose alliances. Foragers certainly celebrate weddings before their ancestors and neighbors, enforce expectations, feel possessive about their spouses, and distinguish between children born in and out of wedlock, but they rarely do any of these things very strongly. Divorce and remarriage are usually easy, and extramarital sex and bastardy carry little stigma.
The main reason for this seems to be that property is relatively unimportant in most foraging societies. It is almost impossible for members of highly mobile bands to own land or flocks of animals, and therefore impossible to bequeath them to children. As a result, while sex outside wedlock still produces anger, having an illegitimate baby is not an economic crime, the way it is when inheriting property really matters.
The forms and functions of marriage have changed dramatically many times in the past, even as the strategic logic behind marriage remains unchanged.
The obstacles to accumulating wealth also make it difficult to enforce marriage rules through economic sanctions. The division of labor is strongly gendered in most foraging societies, with men hunting and women gathering. Some people are of course better at these activities than others, but hunting and gathering are both usually done in groups, making it difficult for one spouse to punish another by withholding vital resources. When an entire hunter-gatherer band decides that someone's behavior merits punishment, they can certainly deliver it, on a sliding scale from mockery to murder, but the targets of such sanctions tend to be overassertive men who try to set themselves up as chiefs over everyone else, rather than spouses who have failed in their duties.
Foragers regularly tell anthropologists that husbands or wives who fail in their duties should feel guilty, suffer shame and perhaps be beaten too — but not too much. Spouses who tried to kill each other over extramarital affairs would just look ridiculous. This forms a striking contrast with the evidence surviving from farming societies (which began to appear about 11,500 years ago in the Middle East and subsequently spread over most of the planet). As soon as people stop moving around in pursuit of wild animals and plants and begin intensively farming specific pieces of land, property becomes all-important. Having access to good, well-watered land, animals to work it and a house to live in are literally life-and-death issues.
For farmers, nothing matters more than inheriting from the right parents, which makes a wife's chastity all-important. The more a farming society develops toward large, dense populations and highly productive agriculture, the more it also evolves toward patriarchy, with men doing most of the work in the fields and controlling most economic assets and women doing the increasingly complex jobs of storing and processing food within the household and rearing children. The balance of power within marriages shifts dramatically toward men, which is why Tolstoy's Anna Karenina opens with Prince Oblonsky's wife banishing him to the couch for three nights after he has slept with the maid but ends with Anna throwing herself under a train after committing adultery.
The logic of marriage alliances is much the same in farming as in foraging societies, but the circumstances surrounding families are so different that matrimony functions in entirely different ways. Almost everyone who can do so marries because it is difficult for single men (and almost impossible for single women) to survive unless they are rich enough to afford large domestic staffs. Divorce is rarely easy to obtain — for wives because they are so weak relative to their husbands, and for husbands, because their wives' families have strong incentives to prevent husbands from sending their wives back home (while keeping their children) if someone better comes along. Gendered inequality has been so extreme in many farming societies that rich men have been able to take multiple wives, leaving poor men with no marriage partners. In extreme cases, rulers even maintain harems of hundreds of subordinate wives.
By the 18th century, patriarchal marriage was the norm everywhere except for those jungles, deserts and tundras that farmers did not want, where foraging survived. Since then, however, industrialized societies based on fossil fuels have once again transformed the circumstances governing how the logic of marriage alliances plays out. Industrialization created millions of new jobs in which brawn mattered less than brains, especially in offices organizing the output from the new factories. The more a society relaxed its rules about the need to keep women in the home, the larger its labor force grew; and the more that women moved into paid labor, the more money could be made from machines doing the household drudgery that had previously kept mothers, wives, sisters and daughters so busy. Economic historians in fact often call vacuum cleaners, washing machines and electric irons "engines of liberation."
Rising wealth in 19th- and especially 20th-century industrialized societies produced bigger, healthier, better-fed women, who in turn gave birth to bigger, healthier, better-fed babies. As infant mortality tumbled, parents needed fewer babies, which created a market for better contraception. Smaller families gave women even more time to work outside the home, and increased incentives to educate girls as well as boys.
The result of all these interacting forces has been a dramatic decline in the economic imbalance between men and women. When farming began widening gender imbalances 11,500 years ago, the guilt, shame and violence brought on by breaching the rules of marriage increased in tandem. In the 20th century, that process has gone into reverse, and guilt, shame and violence correspondingly lost potency as tools for enforcing marital norms. In rich, democratic societies, celebrities now earn big bucks airing their infidelities in public, while anyone caught beating an unfaithful spouse faces jail time. After centuries when powerful men had to keep their mistresses hidden, in the 1990s, President Bill Clinton was able to continue in office despite having multiple marital indiscretions described on television. Even more remarkably, Hillary Clinton was able to run for the same office in 2016 — and win more votes than her rival, who had fidelity issues of his own — despite being a betrayed wife.
A Changing Game
Marriage remains an important strategic alliance, allowing those who enter into it to pool resources, labor and genes. It continues to be distinguished from other kinds of alliances by the religious and social sanctions enforcing its rules, and roughly half of American adults still think that the material and/or psychological benefits of such an alliance outweigh the costs. How long that will remain the case is hard to say. Perhaps weddings of the kind I attended this summer will turn into exercises in nostalgia — which, in some ways, they already are — with most people opting for other kinds of alliances that offer better versions of the same benefits at lower costs. Or perhaps marriage will hang on by being redefined more broadly. After all, just a generation ago, few Americans imagined that the Supreme Court would legalize same-sex marriage in 2015. Only one thing seems certain: As American society continues to change, so, too, will the ways rational actors play the marriage game.