Is monogamy the root of all equality?

Does polygamy between consenting adults harm anyone else? The question has been raised in Canada, where polygamy has been illegal since the nineteenth century, but the supreme court in British Columbia is going to have to decide whether this law is unconstitutional. Doesn't it infringe the right of adults to arrange their lives by mutual consent? The original law was directed against Mormons, and the present test is also directed against a polygamous fundamentalist Mormon commune. Islam does not seem to have played a major part in the debate there, as it undoubtedly would here. But the interesting thing is that libertarians here line up with the most authoritarian religious groups: most of the motions filed to the court in favour of polygamy come from modern polyamorous groups.

However, there has been one brief filed against decriminalising polygamy, and it comes from a most remarkable source: the anthropologist Joe Henrich at the University of British Columbia in Vancouver. This has been the source of much of the most interesting and solid scientific research on religion in the last ten years. Henrich himself has an upcoming paper on Why people believe in God but not in Santa Claus, or Zeus.

The particular merit of this school is that it refines the ideas of evolutionary psychology to take cultural norms just as seriously, and to look at group level competition, which is mediated by culture, quite as seriously as individual competition within groups. Polygamy is a fascinating test case for this approach because the benefits all accrue to the alpha males who end up with most women, whereas the costs are paid by everyone else, and by society as a whole.

In a long affidavit to the court, Henrich considers the social and psychological benefits of monogamous marriage. These aren't widely accepted: using the larget available database of anthropological surveys Henrich concluded that 85% of human societies allow high-status men to have more than one wife. It;s important to notice that this is different from the observation that men (and women) will cheat on each other. That's mating behaviour, which Henrich distinguished from marriage, which is a set of socially accepted and enforced norms and arrangements. In fact he writes that "given our evolved mating psychology, the puzzle is not why societies are polygynous; it's why any society is monogamous, especially one in which males are highly unequal, (like ours)."

The answer he gives is that monogamy gives huge advantages to societies which practice it. It arose, like philosophy, among the Greeks, passed through the Romans, and then the Christian church took it over as an ideal and managed over the course of around a thousand years to establish it as the norm in Europe, even for the aristocracy.

With reasoning that is reminiscent of Darwin's on the spread of altruism, he writes

Societies possessing norms that more effectively shape, harness, reinforce, and suppress aspects of our evolved psychology in ways that benefit the group as a whole in competition with other societies spread at the expense of societies possessing fewer group-beneficial norms.

Monogamy may have spread, and continue to spread, because monogamous societies are more competitive: monogamy seems to redirect male motivations in ways that generate lower crime rates, greater GDP per capita, and better outcomes for children

The nub of his argument is that societies in which women have more than one husband simultaneously are vanishingly rare. And polygamy of this sort (strictly, polygyny) has very bad effects on society.

The men who fail to get wives will be driven by competition that it increasingly dangerous to society and to themselves. There is good data to show that unmarried men are more violent and more generally criminal than married ones, other things being equal. The worst affected are the poor and uneducated who are also the least likely to prosper in a free market in women where the winners can collect as many women as they can handle.

But 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, whether fathers, husbands, or brother, 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.

Henrich argues that these factors help to explain the measurable economic failures of highly polygynous countries, including low saving rates, high fertility, and low GDP per capita. And if polygyny is so bad, it turns out that monogamous marriage has unobvious advantages. In fact he considers that it was the seedbed of European ideas of democracy and, later, human rights and women's equality.

"The anthropologically peculiar institutions of imposed monogamous marriage may be one of the foundations of Western civilisation, and may explain why democratic ideals and notions of human rights first emerged as a Western phenomenon."

This is already quite long for a blog post and barely summarises his arguments. I certainly haven't given his supporting data. But it is all set out in here.