Creationists and evolutionists don’t agree on much, but they both believe that monogamy is the most “natural” form of reproduction for the human species. This seems counterintuitive. Yes, the Bible recounts the story of creation, but it also describes the rampant polygamy of Abraham, Jacob, David, and Solomon and other titans of the faith. Yes, nesting birds, voles, and a few other animals are monogamous, but most mammals reproduce with one dominant male controlling a large harem of females. Polygamy seems “natural,” monogamy “supernatural.”
Yet, for the past millennium, Christians and post-Christian liberals alike – Aquinas, Calvin, Locke, Hume, and Jefferson -- all agreed that God created humans to reproduce by becoming “two in one flesh,” not three or four. And modern evolutionary scientists, from Claude Lèvi-Strauss to Bernard Chapais, have concluded the same: that pair-bonding is part of the “deep structure” of human reproduction that humans have evolved as their best strategy for survival and success.
Both traditional theorists and modern scientists point to four facts of human nature that commend monogamy. First, unlike most other animals, humans crave sex all the time, especially when they are young and most fertile. They don’t have a short rutting or mating season, followed by a long period of sexual quietude.
Second, unlike most other animals, human babies are born weak, fragile, and utterly dependent for many years. They are not ready to run, swim, or fly away upon birth or shortly thereafter. They need food, shelter, clothing, and education. Most human mothers have a hard time caring fully for their children on their own, especially if they already have several others. They need help, especially from the fathers.
Third, however, most fathers will bond and help with a child only if they are certain of their paternity. Put a baby cradle on a sidewalk, medieval and modern Western experimenters have shown, and most women will stop out of natural empathy. Most men will walk by, unless they are unusually charitable. Once assured of their paternity, however, most men will bond deeply with their children, help with their care and support, and defend them at great sacrifice. For they will see their children as a continuation and extension of themselves, of their name, property, and teachings, of their own bodies and beings, of their genes, we now say.
Fourth, unlike virtually all other animals, humans have the freedom and the capacity to engage in species-destructive behavior in pursuit of their own sexual gratification. Given the lower risks and costs to them, men have historically been more prone to extramarital sex than women, exploiting prostitutes, concubines, and servant girls in so doing and yielding a perennial underclass of “bastards” who have rarely fared well in any culture.
Given these four factors, nature has strongly inclined rational human persons to develop enduring and exclusive sexual relationships, called marriages, as the best form and forum of sexual bonding and reproductive success. Faithful and healthy monogamous marriages are designed to provide for the sexual needs and desires of a husband and wife. They ensure that both fathers and mothers are certain that a baby born to them is theirs. They ensure that husband and wife will together care for, nurture, and educate their children until they mature. And they deter both spouses from destructive sexual behavior outside the home.
Polygamy might ensure paternal certainty, but only at ample cost. Social science studies of polygamous families in Africa and Asia, and in isolated Fundamentalist Mormon communities in North America have documented these costs. While a polygamous man usually has his sexual needs met, his multiple wives often do not, producing rivalry and discord in the home. While a polygamous father may know who his children are, his children have to work hard to get his attention, affection, and resources which are dissipated over multiple wives and children. While polygamy might seem to contain extramarital sex better than monogamy, the opposite is often true. A polygamous man, not schooled by monogamous habits, will always be tempted to add another attractive woman to his harem. A co-wife, once pushed aside by another, will be sorely tempted to test her neighbor’s or servant’s bed, unless threatened with grave retribution. And single men, with fewer chances to marry, will resort more readily to prostitution, seduction, and other destructive sexual behavior.
The Western tradition reminds us that the biblical polygamists did not fare well. Think of the endless family discord of Abraham with Sarah and Hagar, or Jacob with Rachel and Leah. Think of King David who murdered Uriah the Hittite to add the shapely Bathsheba to his already ample harem. Or King Solomon with his thousand wives, whose children ended up raping, abducting, and killing each other. Anthropologists point to similar problems in modern polygamous households. They show further that young girls are often tricked or coerced into marrying older wealthy men and that women and children of modern polygamy are often poorly educated, impoverished, and chronically dependent on welfare.
Even so, our human natural inclinations toward monogamy have always been wobbly. The reality today is that a good number of folks, buoyed in part by the sexual revolution, have sex and children without marriage, let alone monogamous marriage, whether straight or gay. In the modern West, some 40 percent of all children, and some 60 percent of all poor children are born outside of marriage and without the ongoing support of fathers or marriage-based kinship structures. The modern social welfare state has helped to buffer and spread out the costs of this “species-destructive” sexual and reproductive behavior. With Western governments on the fiscal ropes, however, it’s not clear how long that support will continue. Of course, we should cherish sexual liberty and autonomy. But we should also develop laws, policies, and curricula to teach the basics about the nature of human sex and marriage, and to encourage and facilitate citizens to live their sexual lives in accordance with the natural norms and limits that govern us all.
John Witte Jr., is director of the Center for the Study of Law and Religion at Emory University, and author of a forthcoming title, “Why Two in One Flesh: The Western Case for Monogamy over Polygamy.”