It’s true that the instinct for monogamy is less strong in men than in women. This is illustrated by the fact that–though polygamous mariages are rare–when they do occur they overwhelmingly involve polygyny (having more than one wife) rather than polyandry (having more than one husband). Nevertheless, most men are monogamous. The fact that this happens across all cultures–even those that allow polygamy–indicates that there are reasons for male monogamy that are rooted in human nature.
What are those reasons?
Many point out that supporting more than one wife is hard, and so most men can only have one even where it is legal to have more than one. This is true, but it doesn’t change the fact that male monogamy is rooted in human nature. If human nature were such that males could support more than one wife easily, more would do so. Since that isn’t the case, human nature supports male monogamy. (Note that this argument also supports the traditional male role of provider/protector as having a basis in natural law. If men across cultures didn’t have to support their wives then their resources wouldn’t be consumed in doing so and they could take more wives.)
The difficulty of supporting more than one wife is only part of the problem, though. Here’s another and een more decisive factor: availability.
Among humans males and females exist in approximately equal numbers. Slightly more male babies are born, but men also have shorter life spans, so the numbers equal out. As you move up the age ladder, more and more women are present (because the males are dropping out) until women predominate at the high-end of the age ladder. Still, in society in general–and particularly during the childbearing years–the ratio of males to females never strays too far from 50-50.
This means that it is impossible for polygyny to ever become the predominant practice among human males. There aren’t enough women to allow that to happen. If there were five girls born to every one boy then that would suggest that polygyny should be the natural practice for males, but the fact that the sexes are approximately one-to-one strongly indicates that males should (and will) be overwhelmingly monogamous in marriage.
The only ways around this would be to change human nature in some way, such as removing the female impulse to monogamy, leading women to have multiple husbands. But that would probably destroy marriage altogether because if most women took multiple husbands, enabling most men to take multiple wives then the interconnectivity of who is married to whom would become intolerably complex and marriage as an institution would simply break down. That ain’t gonna happen because human offspring are far too dependent on their parents for far too long for societies to be successful if they don’t have marriage (which is why all existing societies do have it–again, a social institution flows directly from human nature).
Another, change in human nature could take place in male psychology so that humans operated like some species where all the breeding in a group is done by an alpha male with his harem. But this would only make polygyny the most common form of union when marriage occurs. For most men, marriage wouldn’t occur at all since the alpha males would be hoarding the women.
And that won’t happen in the real world because human psychology won’t permit it. There is no way ordinary, rank-and-file men would permit self-appointed alpha males to be the only ones who can get married. Ordinary men are too ornery, too organized, and too clever to let that happen. Any society which tried to impose such a situation on its male population would find itself quickly re-organized.
These considerations point out that human nature again drives us toward male as well as female monogamy. Human nature would have to change in fundamental ways for polygyny to become commonplace.
What we have said thus far deals with factors that don’t operate on the level of male desire. If males had no psychological impulse toward monogamy at all, the above factors would still ensure its dominance of marriag patterns. But I think there is more to the story than that. Though men may have “wandering eyes” more than women, this doesn’t mean that it is only factors external to the affections that lead them to be monogamous. If human nature has been set up so that monogyny is the norm among men, it is natural to expect that men’s affections too have been designed for it.
In other words, men also are monogamous because they want to be monogamous. They form unique emotional bonds with their wives and don’t want to have more than one. Though some–particularly in misanthropic feminist circles–might want to portray men as selfish pigs who will take as many wives as they can get–men themselves will tell one that this isn’t true. They really do form exclusive emotional attachments to their wives and regard something as wrong with men who don’t. Men are thus affectively monogamous by nature, just as women are.