"Does polygamy between consenting adults harm anyone else?" Yes, answers the Guardian's Andrew Brown, looking at some fascinating new anthropological research. Polygamy, he explains, winds up encouraging dangerous competition and poor childrearing.
The men who fail to get wives will be driven by competition that it increasingly dangerous to society and to themselves ... the winners, who get wives of their own, find their own behaviour distorted by polygamy. Because the competition for women is so fierce, making them valuable objects rather than loveable people, men ... must control them more carefully. The same dynamic places pressure on the recruitment of younger and younger brides into the marriage market, because in a polygynous society you can never have enough of them. Finally, the men will reduce their investment in any particular wives and children, partly because their resources will be much more widely spread; partly because they will increasingly spend their efforts on getting more wives rather than looking after the ones they have.
Meanwhile, though society may be forever bemoaning monogamy's flaws, it turns out that monogamy, in fact, "gives huge advantages to the societies which practice it." While "highly polygynous countries" wind up with "low saving rates, high fertility, and low GDP per capita," the anthropologist Brown quotes says that, apart from economic advantages conferred by monogamy, its "anthropologically peculiar institutions ... may be one of the foundations of Western civilization, and may explain why democratic ideals and notions of human rights first emerged as a Western phenomenon." This leads Brown to wonder: is monogamy the "root of all equality" in the West?