Last Friday, my girlfriend and I went to a show at a local bar. We didn’t know when the thing was starting so we ended up arriving way early. When we got there, among the very few people there was a group of one guy and two girls. The girls, I learned, were his fiancé and girlfriend. Later, a woman showed up who I knew was living with her husband, kids, and boyfriend.

These sorts of encounters make it hard for me to take seriously a talking point that you hear an awful lot in discussions of relationships, politicized (should gay unions be legally recognized?) or otherwise (what makes the perfect relationship?) The talking point is this: Polygamy is this weird institution that only backwards people from primitive cultures will ever engage in. The truth, I think, is this: polygamy is one of several strange but significant trends that is inevitably going to result from the sexual revolution.

Here’s the weak version of that thesis. Human beings may not exhibit infinite variety, but we exhibit quite a bit. For every norm there’s at least a few oddballs that deviate from it. So even if the vast majority of people want monogamy deep down, there’s going to be a few who want polygamy. Add to that assumption our modern ideas about sexual freedom: even if the government only actively supports some kinds of relationships, it has no business coercively interfering with ones it doesn’t like. Furthermore, people really shouldn’t frown too heavily alternative relationships, even if they dislike them–an idea explicitly advocated by liberal great John Stewart Mill, and adopted in a vaguer way by many modern liberals. Under such circumstances, the few polygamy enthusiasts are likely to arrange quasi-polygamous unions, simply because they want to and government non-support isn’t that big of a deterrent.

Now the stronger version of the thesis. Actually, it’s not just oddballs who will want polygamy. Almost everyone will. Historically, men have had multiple wives wherever they could get away with it, a fact often missed because sometimes they’re not called “wives” or even “concubines.” For example, Roman law officially mandated monogamy, but implicitly acknowledged that female slaves are, in effect, concubines. Similarly, the feudal lords of Christendom had a tendency to hire more maids for their castles than they could possibly put to work. And what do the women think of this? Some times, no doubt, they’ve been forced into these arrangements, but, as anthropologist Laura Betzig once put it, many women would rather be the third wife of JFK than the first wife of Bozo the Clown. In evolutionary terms, men will always want polygamy because the relationship between number of wives and offspring is pretty direct, while women will often want it because a rich man may have more than enough resources to spread among his many children, while an attractive man may have better genes.

Given these facts about human psychology, the man-man-woman relationship mentioned in the introduction should remain an oddity, but multi-woman arrangements may become popular, and should increase in popularity as the social stigma lessens. Probably the great harems of early civilization will never be possible as long as men in power can’t get their way by killing off whoever they happen to dislike. Maybe, though, we’ll see something akin to what occurs in a lot of hunter-gather bands: the most successful 10-15% of men wind up with an extra wife or two.

This makes the social policy issues around polygamy more than talking points for gay-rights. What to think of them? A simple argument for supporting gay marriage but not polygamy is that gender isn’t an important part of current marriage laws, so it’s easy to cut-and-paste those laws onto gay relationships, but monogamy is so important to the current regime that changes are infeasible. But what if some clever experts in family law had a reasonable proposal? Would it be a good idea? The idea that polygamy hurts women is hard to make sense of if we guarantee personal autonomy, with the right to sign away the possibility of polygamy in pre-nups: “Opposed to polygamous marriage? Then don’t get one!”

The people who have a real interest in enforced monogamy is men–both the men who would lose out in a competition for mates, and the men who would succeed only with difficulty and don’t want to play that game. This seems to be a pretty strong reason for making life difficult for would-be polyamists–as difficult as we can make it without infringing personal autonomy. We can’t eliminate all sexual competition and male alienation, but we can at least reduce it by not giving official sanction to polygamy. Even under such a policy, though, I expect informal polygamy to become an increasingly noticeable part of society in the rich and liberal world.

That’s all I have to say about that–though in the next two weeks I plan to write about related issues in our social future.