Both Christians and feminists staunchly oppose polygamy. Christians tend to emphasize the divine order established at creation, whereas feminists are more likely to emphasize that polygamy inherently subordinates women, but both are satisfied when a society with a long tradition of polygamy begins to favor monogamy as the norm.

There is a problem, however, with the view that the rise of monogamy automatically improves women’s status. The problem is not inherent in monogamy itself, but rather arises with the transition from a polygamous society to a monogamous one. When men still have the option of adding an additional wife, monogamously married women may acquiesce to their husband’s wishes in order to preserve the monogamy of their unions. Thus the decline of polygamy does not automatically mean that women are enjoying greater equality with men. The situation in Ghana suggests that they can become more subordinated.

Between 1988 and 2003, the percentage of women polygamously married in Ghana fell from 31% to 21%: In other words, the prevalence of polygamy dropped by a third in less than a generation. Given that monogamy is generally associated with greater gender equity, it would seem that that kind of drop would predict a rise in women’s empowerment.

Here’s what happened instead: Monogamously married women became more likely to conform to their husband’s desires for more children. It’s not surprising when considering that men generally add wives because they want more children, rather than have more children because they added wives. That means that as children started to cost more because they were in school during the day rather than helping family farms or in other enterprises, fewer men were motivated to take additional wives. A man in a traditional society might have wanted ten children and therefore married more than one wife, but his counterpart in a modernizing society who wants only six children might choose monogamy instead.

Does the monogamist’s wife benefit from his more modern orientation? There may be much about monogamy she enjoys, but bearing four or five children for the polygamist might have been sufficient, while the more “modern” husband wants six from her. It is easy to imagine that she might accept one or two more children far more easily than one more wife.

On average, the relative spousal power in polygamous couples did not shift in favor of men the way it did in monogamous couples. But the lack of change concealed the power imbalance between “senior” and  “junior” wives, with senior wives having more say in childbearing decisions. This also makes sense in the context of men wanting fewer children. A man might be much more content to let his first wife stop after three or four knowing that a junior wife could bear more for him. He might, however, strongly oppose the junior wife continuing after two or three. Lower fertility does not mean that all women have more influence in reproductive decisions, as is often assumed, and the rise of monogamy can work against women’s influence, at least in the short run.

When fertility is falling, most people assume that the change can be explained by modern contraception. The huge drop in fertility in Ghana did include uptake of pills and injectables, but couples also adjusted coital frequency to accord with their fertility preferences. That is not the kind of fertility control that happens without men’s active involvement.

While men’s active involvement in managing reproduction is a positive development, I am nonetheless disturbed by the evidence from Ghana showing an increase in men’s influence at the expense of  their wives’ empowerment. I don’t like thinking about what it might be like to be a junior wife having to stop at two children in a society where most women bear at least four. I also chafe at the idea that an outsider might label her as progressive because she’s stopped at the “modern” number of children while she might be continually saddened by not being empowered enough to have more.

The monogamously married woman not using contraception when she wants to stop after five children would also be mislabeled by outsiders as having “unmet need,” defined as wanting to space births or stop childbearing, but not using any method,whether traditional or modern. Common policy prescriptions include providing knowledge of alternative methods and including men in service delivery. Neither of those options acknowledges that a woman’s decision not to use contraception meets her need to stay monogamous.

Although few of us have personally known many polygamists, we are nonetheless familiar with how progress does not always lead to gender equality. Growth in women’s labor force participation in industrialized countries was heralded as tremendous progress, but then scholars drew attention to large shares of women who were working full-time in the paid labor force and then working a “second shift” at home because their husbands did little cleaning, cooking, or laundry. In this case, progress only added to women’s burden.

The rise of monogamy may be similar to the rise of women’s labor force participation in that the negative effects need not be long lasting. In Northern Europe, only 39% of women who work full-time also do the bulk of the domestic work. If fertility decline continues, it will lead to a further decline in polygamy because a single wife will be sufficient to give men all the children they want. Then polygamy will become an oddity rather than a live option that gives monogamously married men a bargaining chip that their wives lack.

So in the long-run, Ghana and other countries where polygamy has been widely practiced might become societies dominated by monogamy and greater gender equity in reproductive decisions. Gender equity is far better than women’s covert contraceptive use and far better than men deciding how many children their wives can have. Where there is a legacy of polygamy, however, progress is slow.