My wife and I recently found ourselves comparing notes with friends who have children moving into the teenage years. We are anxious voyagers readying ourselves for stormy seas. Some of these discussions have pondered the best approach for “the talk”—on sex, dating, and marriage. And this has raised a fundamental issue for us: What is the basis for the Christian teaching on sex and marriage?

Of course, there is a strong biblical basis for the importance of marriage, from Genesis 1 to Revelation 19. But as an economist, I’m also interested in how to explain the biblical teaching on sex and the institution of marriage to millennials today. Economists like myself are infatuated with the study of institutions, but we mostly concern ourselves with rather stolid ones, like the ones that regulate capitalism. Yet in our creative displays, we engage more dynamic institutions such as dating and marriage.

When economists study institutions, we ask: What has caused such an arrangement to win out over others? Marriage is an institution that has arisen independently throughout the entire world in nearly every civilized era. But what natural basis is there, for example, to favor the institution of marriage over, say, cohabitation? What possible logic is there in criticizing something as appealing as extramarital sex? These are questions that teenagers want answers to. They will make sacrifices, but they need to know that the sacrifices make sense. Our rules and norms in local churches must be presented as rules and norms that will lead to our children’s flourishing.

I want to argue from the perspective of social science that the Christian teaching on sex and marriage is much more than a dated rule that ruins the fun of teenagers and adults. Rather, behind marriage lies a social justice issue related to biological asymmetries between men and women. Keeping sex within the context of a lifetime commitment creates the basis for a healthy relationship between the genders.

A Form of Stealing

From a biological perspective, both males and females are equally concerned with successful gene reproduction. But there are important asymmetries in how males and females meet this goal. Ignorance of these asymmetries is where much of today’s bad advice on sex and marriage originates.

Mainstream Western culture generally advocates a kind of psychological androgyny. The psychological differences between men and women, it is argued, are not innate but culturally created. Most Christians reject this view, partly because we recognize beauty in the differences in our psychologies that stem in part from our distinctive biologies. Biologically, females typically bear only one offspring at a time. As a result, a woman’s interest lies in the quality of that offspring and the health, protection, and resources required to help an infant flourish. It is possible for males, however, to reproduce their genes by producing many offspring at a time with many females. To put it bluntly, this gives males a different set of incentives in sex. The biological interest of women is in quality of sexual relationship; in men it is in quantity of sexual relationship.

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Thus, at its most base level, a sexual relationship between a man and a woman involves an exchange of sex for commitment, commitment on behalf of the man to the welfare of the woman and any resulting children. Seen in this light, the commitment of a man to a woman with whom he has a sexual relationship is not prudery; it is social justice. From a biological standpoint, sex devoid of genuine male-to-female commitment is a form of stealing. And a widespread social acceptance of sex without commitment represents an injustice against women and their deepest biological interests. The tragic irony is that the “sexual liberation” espoused by some secular feminists couldn’t play more perfectly into the short-term, selfish interests of men.

A society that encourages sex within the context of life commitment upholds its own collective long-term interest.

Limiting sex to the confines of a lifetime commitment between a man and a woman is God’s intention because, at least at the biological level, marriage as an institution promotes a fair exchange between the sometimes competing interests of men, women, and children. In this way, marriage solves what game theorists call a “prisoner’s dilemma”—defined as a situation in which everyone’s freedom to act in self-interest yields an outcome contrary to everyone’s collective interest. Solving a prisoner’s dilemma requires facilitating the common good over individual self-interest. A society that encourages sex within the context of life commitment upholds its own collective long-term interest. When a society encourages people to violate this norm, it undermines its own long-term interest. Marriage is a dominant institution all over the world because, despite all its challenges, it is hard to find another form of organizing the sexes that does as good a job at promoting human flourishing.

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Social norms, common expectations, and societal checks on the behavior of men have evolved in every culture to address the different biological drives of men and women. Nearly every negative outcome for children increases statistically without the presence of a committed man in the home. Children who grow up without their biological fathers do worse in school. They perform significantly worse on standardized tests, have poorer grades, and believe they have less potential than children who grow up with both biological parents. They also display higher levels of both shyness and aggression than do children who grow up with both biological parents.

Deviations from the sex-with-life-commitment paradigm lead (on average) to a set of consequences that have negative effects not only for a couple but for any children they have. In other words: Follow the advice the secular world has to offer on sex, and you are statistically more likely to have an unhappy life and lead others to have unhappy lives. Follow the advice of Scripture, and you are more likely to have a happier life, remembering that healthy relationships require considerable effort and commitment to the well-being of others over self. Unfortunately, Western culture’s staunch commitment to radical individualism and the right to do whatever we want (as long as it doesn’t “hurt anybody”) has kept us from seeing the wisdom behind traditional boundaries for sexual relationships.

Why Cohabitation Doesn’t Work

But hasn’t birth control changed the argument in favor of marriage? Birth control offers women, like men, the opportunity to engage in sexual relationships without the consequences of pregnancy. So at least in one respect, birth control has leveled the sexual playing field. But because our biology and emotions are tied closely to one another, birth control doesn’t always mitigate the need for the closeness and commitment that many women desire in a sexual relationship, a desire likely related to the need for commitment to children and to the vulnerability of pregnancy. Secular media have in recent years reported on the negative experiences women have within hookup culture on college campuses and beyond. Many women who are on board with the idea of female sexual empowerment in theory nonetheless attest to feeling used or emotionally hurt by casual sex. Although culture does its best to convince women that sex can be separated from closeness and commitment, this ultimately ends up promoting behavior strongly misaligned with their long-term interests.

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At its best, though, marriage does more than keep men’s sexuality in check. It also provides a commitment device that allows couples to work out difficult issues. There are issues, for example, that face a seriously dating or cohabiting couple—such as career choices, financial decisions, and where to live—that are difficult to work though outside the context of a marriage. Sadly, marriages do fail, but at a much lower rate than less committed relationships such as seriously dating and cohabitation, and at a lower rate among those who have foregone cohabitation before marriage.

Yet even in light of the failures of the modern sexual model, marriage rates seem to be falling, while cohabitation rates have been on the rise for decades. Data from top marriage researcher Philip Cohen at the University of Maryland show recent trends in singleness, cohabitation, and marriage from the US Current Population Survey, and marriage is not doing well. Why is this so?

Several years ago I investigated this question in a research paper published in an international social science journal. The rise in cohabitation rates began to occur in the early 1960s, when only a few hundred thousand couples were living together outside marriage. The increase has been dramatic; today there are about 7.5 million cohabiting couples. A number of factors could be responsible for this increase: the arrival of the Pill, legalization of abortion, and disaffection with marriage due to rising divorce rates. However, I found that the rise of cohabitation is most correlated with the increased number of women in the workforce: a 10 percent increase in women’s labor force participation results in a 6.4 to 14.6 percent increase in cohabitation. In tandem with men showing more interest in directly caring for children, this also creates a situation where women and men don’t “need each other” as they did when marriage fulfilled a more functional, economic role. Yet the desire for partnership and emotional intimacy remain—hence the rise of cohabitation.

Although some couples choose cohabitation to replace marriage, approximately three-fourths of cohabiting couples state that they are cohabiting as a precursor to marriage, as a kind of screening device. However, the data show this strategy doesn’t typically work. Many studies indicate that couples who live together before marriage are actually more likely to divorce later if they get married. This may be because cohabiting couples “slide into” marriage due to the high emotional costs of leaving a cohabiting relationship. Or it may be that couples establish poor relational patterns in the context of the more independent mindset in cohabitation that have a deleterious effect on later marriage. Whatever the case, the evidence seems to be that cohabitation-as-screening-device isn’t very effective.

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Not only is cohabitation ineffective as a screening device, at its core it also constitutes an injustice against women.

Not only is cohabitation ineffective as a screening device, at its core it also constitutes an injustice against women. Aside from offering men an increasingly socially acceptable arrangement in which sex without lifetime commitment is possible, cohabitation offers men the opportunity to exploit other asymmetries between the genders to the detriment of women. Although recent Gallup data indicate that more than 90 percent of young Americans desire children and a family, the timeframe for this is obviously unequal between the sexes. Because men can have children much later in life than women can, cohabitation provides what economists call an “option value” that advantages men relative to women. Here, a man can cohabit with a woman, perhaps into his 30s or 40s, retaining the option to either continue the relationship by (perhaps) marrying and having a family with his partner, or he can leave the relationship to pair subsequently with another woman (maybe a younger woman) as his former partner’s biological clock begins to expire.

Moreover, as the years of cohabitation between a man and a woman increase, male power within the relationship increases. Researchers who study attraction between men and women find that, in very broad brushstrokes, men tend to be attracted to women based on physical beauty; women tend to be attracted to men based on power, influence, or their “command of resources,” as termed by psychologist David Buss. As a cohabiting relationship lingers into a couple’s 30s and beyond, male attraction to the physical beauty of a woman may wane as the couple ages, but based on a typical age-earnings profile, the man’s ability to “command resources” will likely increase. Unlike the safer institution of marriage, which intends to build a mutual commitment even as the couple grows older together and faces economic ups and downs, the relative flimsiness of cohabitation creates a context where men are increasingly able to exert power over women.

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Till Death Do Us Part

The simple act of standing up in front of one’s friends and family and God and promising to be faithful partners “till death do us part” is not a trite relic of Christendom. It is wisdom, beauty, and love rolled into a single sacred institution that protects, stabilizes, and nurtures a lifelong relationship.

As a result, we can confidently communicate to our children is that the traditional model of sex and marriage is strongly supported not only by biblical faith but also by evidence and reason. If we want to communicate the wisdom of marriage to the next generation, we need to patiently articulate and demonstrate what gives life, joy, and sustained relational happiness. Let us create strong models of marriage for our kids. But let us also be able to articulate why it represents the best choice for their relationships as well.

Bruce Wydick is professor of economics at the University of San Francisco and distinguished research affiliate at the University of Notre Dame.

This article was made possible by a generous grant from the Templeton Foundation.

[ This article is also available in español. ]

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