Marriage Laws » United States » Polygyny » Monogamy

Marriage, Fidelity, and Polygamy

Monogamy is the most common form of pair-bonding in contemporary societies, especially in Western industrialized countries. Monogamy is intended to be a life-long comittment, with complete sexual fidelity of the spouses to each other. However, when viewed from an evolutionary psychology perspective, the pressures on men and women to break that committment are not the same. As men age, they retain their capacity for reproduction and are subject to selective forces that may involve increasing their inclusive fittness if they can successfully attract another woman. This may account for the restlessness that husbands often experience in a marriage, in which "opportunitstic polygyny" is the result. Women are much more limited in their reproductive opportunities as they age, and have a greater interest in insuring the survival and success of their existing children. The confluence of these forces creates pressures on marriage, the result of which is high divorce rate (over 50% according to some recent estimates). The leading factor in the dissolution of marriages in the United States is dissatisfaction of the man.

These arguments suggest that early human populations may have been polygynous (definition: one man, one or more wives) and that monogamy may be a product of subsequent human development. In fact, a survey of 1,154 past and present human societies indicates that most (980) permit a man to have more than one wife. Additional data come from a survey of primates and their patterns of pair-bonding. Among the apes, differences in body size between males and females reflect the extent of polygyny. Gorillas are very dimorphic (very large males, small females) and they have a social system that is highly polygynous, with one male defending his association with several females. On the other end of the scale, gibbons are completely monogamous, and the males and females are identical in size. The size dimorphism in humans suggests that ancestral populations were "mildly" polygynous, somewhere between chimps and gibbons.

Even though polygyny is allowed in most human cultures, it is actually not common. Most marriages, even in polygynous societies, are in fact monogamous. This is because of economic considerations. Most men in most societies cannot afford the cost of a second wife, even if it is permitted. Among the monogamous societies, over half can be described as "nonstratified." Economic equality among men in a society tends to short-circuit polygyny. If the wealth and influence of men is about the same, why would a woman chose to share a husband when she can have one of her own? A woman in such a society who choses "half a husband" (polygyny) over a whole ones is settling for much less in the way of material well-being. Marriages in such societies can be described as "economically imposed" monogamy.

What is more difficult to explain is the small number of societies (including ours!) in which economic stratification occurs along with monogamy. Marriages in these affluent societies can be described as "ecologically imposed" monogamy. When viewed purely from an evolutionary perspective, most women in such societies are probably better off with polygyny, and most men are probably better off with monogamy. Moreover, polygyny would have the effect of creating a subclass of young, unmarried males with no prospects for either marriage or children (due to the fact that the highest ranking males would have several wives). Young, unmarried men in lower economic brackets are far more likely to commit violent crimes, abuse drugs and alcohol, and adopt a high-risk criminal life than married men with families. As stated in your book "A polygynous nation, in which large numbers of low-income men remain mateless, is not the kind of country many of us would want to live in."

Polygyny in economically stratified societies appears to have emerged in response to political power-sharing among males in ancestral societies. Most modern industrialized nations are nominally monogamous, but in fact the soaring divorce rate makes our society one of "serial monogamy", which is equivalent in some ways to polygyny. One man often has more than one woman as his mate during his lifetime, but not at the same time. In many ways, our system is the worst of both worlds for women and children--men are allowed to divorce, often to remarry a younger wife, and when they do, the standard of living for their former spouses and children usually goes down, while their standard of living goes up.

"Whenever marital institutions--in either kind of society--are allowed to dissolve, so that divorce and unwed motherhood are rampant, and many children no longer live with natural parents, there will ensue a massive waste of the most precious evolutionary resource--love. Whatever the relative merits of monogamy and polygyny, what we have now--serial monogamy, de facto polygyny--is, in an important sense, the worst of all worlds."