Field of Science

Monogamy evolves

Polygamy is pretty popular. Most pre-industrial societies were polygamous in some way, and there are increasing pressures in the west for polygamy to be legalised. After all, it's surely just a matter of personal freedom of expression. If homosexuality and other forms of sexual expression are legal, then why not polygamy. Polygamy never hurt anyone, right?

Well flat wrong, actually, if the evidence presented by Joe Heinrich, at the University of British Columbia, is anything to go by. Heinrich does some pretty interesting research on human culture and cognition, some of which I've covered before on this blog.

But the background to his latest is rather unusual. You see, in Canada they're holding a court case to determine whether the criminalisation of polygamy is constitutional. And Heinrich has presented some pretty compelling evidence to suggest that if it isn't, then it darned well should be.

Bottom line is that, in highly stratified societies like most of those in the modern world (and unlike the forager societies that dominated our evolutionary past) polygamy results in surplus males with no prospects of marriage. That in turn causes all sorts of problems. What's more, polygamy tilts society towards viewing women as property for acquisition, and also decreases investment in children. In the long run, social justice and equality is undermined.

For more on all that, take a look at the write-up in the Vancouver Sun, or read the Heinrich's brief itself - it's fascinating stuff!

But what interests me, from the point of view of this blog at least, is what Heinrich infers from these facts. He suggests no less than that the invention of monogamy was the first step in building our modern, democratic society.

Like most sexual innovations, monogamy seems to have been invented by the Ancient Greeks. And, it seems, they devised it as a deliberate ploy to create stronger, more unified city states. Greek culture was highly successful, which lead to monogamy being adopted and then enforced by the Romans. The early Christians incorporated these ideas into their religion as it expanded (there's no particular stricture against polygamy even in the New Testament).

What we have here is an example of what Heinrich calls 'cultural group selection'. Those societies that adopt the most effective cultural practices are successful, and they dominate and eventually swallow up the less successful societies around them. And so, around the world nations are gradually adopting monogamy as a social norm (just as Canada is now considering abandoning it!).

According to Heinrich, exactly the same phenomenon gave rise to religion. Although we have all sorts of weird cognitive biases, there is nothing inherent within us that gives rise to religion. But, those societies that were able to most effectively make use of our cognitive biases were the most successful, and the edifice they created is what we call religion.

In other words, God evolved - but in a memetic, not genetic sense, with human society as the host.

But of course, just because a cultural invention was successful in the past, does not mean it will be so when the environment changes. Polygamy works for hunter-gatherer societies, but not for more settled ones - and especially not urban societies. Heinrich quotes Satoshi Kanazawa, who has shown that polygamy in the modern world is linked to increased crime rates.

Kanazawa has also shown that polygamy is linked to IQ. It seems that, even controlling for other factors, nations with higher average IQ are less acceptant of polygamy. He suggests that, the better people are at abstract reasoning, the more likely they are to reject polygamy as unworkable for modern societies.

And Kanazawa has, of course, shown exactly the same thing for religion.

Creative Commons License This article by Tom Rees was first published on Epiphenom. It is licensed under Creative Commons.


  1. I think this is clearly a huge giant muddle and leaping to the conclusion that multiple marriage in modern society would recreate the same problems as in pre-modern society is lazy thinking.

    I could just as easily say the trend is towards an increase in womens rights-- after all, if you are going to treat women as second class citizens who must get everything they need through male gateways, it *is* an improvement not to ALSO have to compete with other women for those scraps!

    And again, modern societies which still practice widespread polygamy have horrible human rights records for women-- which is going to bring down the average IQ of the country as women are going to have been given so many hurdles to overcome simply to exist that their IQ probably suffers.

    However, we've *never* had a society as close to true gender equality as now, and there is NO reason to suspect that multiple marriage within a legally gender-equal society would lead to the same sorts of trouble that it does in premodern societies.

    Some of those men will end up marrying themselves! Some of them would end up in a group married to a single woman!

    As long as the rights of women are maintained legally and culturally valued, I see NO reason to suspect that poly marriage would cause a problem.

  2. To reiterate what jemand said: if it's not simply polygamy, but also polyandry, there's no reason to think that this wouldn't work.

    There's a great series of posts at Slog about exactly this subject.

  3. You might actually read the report. Most consider China and India fairly modern, and he does employ control groups in the research.

    In India and China, where male-biased sex selection has resulted in more men than women, researchers found "bachelor bands that compete ferociously and engage in aggressive, violent and anti-social activities."
    China's one-child policy resulted in the number of "surplus" men nearly doubling ... along with the crime rates. In a recent study, researchers there concluded that for every 0.01 increase in sex ratio, property and violent crimes rise by three per cent.

    (Heinrich, from the SUN article)

  4. I'd like to reiterate what Le Fevre said: Jemand and Kevin, you clearly need to read the Vancouver Sun story.

    However, we've *never* had a society as close to true gender equality as now, and there is NO reason to suspect that multiple marriage within a legally gender-equal society would lead to the same sorts of trouble that it does in premodern societies.

    No reason?!? There are GOOD reasons to think that polygamy would have bad effects, because in present day societies polygamy leads to polygyny which leads to higher crime rates. Not hypothetically, but factually.

    Some of those men will end up marrying themselves! Some of them would end up in a group married to a single woman!

    Again, there's plenty of evidence showing that polygamy implies one husband and multiple wives.

    As long as the rights of women are maintained legally and culturally valued, I see NO reason to suspect that poly marriage would cause a problem.

    This is when you go read that article.

  5. I didn't go into the details of Heinrich's arguments, but they are well backed up by empirical data, as JA and Bjorn point out. It's not a slam dunk, but it's much more solid than evidence to the contrary.

    Heinrich also makes a good theoretical case. While you might expect that a polygamous society could include equal numbers of polygynous and polyandrous marriages, in practice polyandrous marriage are extremely rare - even in modern societies.

    The reason lies in reproductive strategies. Having multiple partners does not increase a females fertility, so it isn't favoured evolutionarily. For men it can do, in the right circumstances. Males can adopt two strategies - a single partner with high investment in offspring, or multiple partners with low investment in offspring.

    As to whether we were in our evolutionary past polyandrous, it seems unlikely and not just from a theoretical perspective. Humans are sexually dimorphic. It's relatively small, but it's there. Men are bigger than women. In other mammals, this is a good indicator of 'harem' type mating strategies, in which males fight each other to control a group of females.

    The idea mooted by the author of "Sex at Dawn" that there was common polyandry in prehistory seems to me to be wishful thinking. If we allow polygamy, it will mean polygyny, with all the negative effects that go with it.

  6. I should note that while Kanazawa's research is interesting, he's promoted some pretty wacky ideas in the past, which have made me skeptical about his approaches to others.

    And while the authors (there are two) of "Sex at Dawn" draw some dubious conclusions in their book, the central message there seems to be not that we need to reinstitute formal polygyny and polyandry, but that we should adjust our cultural and legal expectations in the light of evidence that our ancestors (and thus our own brains and bodies, male and female), were and are adapted to having multiple sexual partners.

    It may be that two-person marriage may still be the best strategy for modern societies, but that might not imply that all such marriages and partnerships need be monogamous, and it may help to try to remove the stigma from those that are not.

  7. Polyandry may be historically rare, but logic dictates it's something that should be encouraged in light of the arguments against polygamy. It would keep population growth down as well.

  8. Interestingly, all the polygamous relationships among my friends are polyandrous rather than polygynist. Yeah, I know it's anecdotal, but it's interesting.

  9. A point to emphasise is that there are certainly pre-Greek world cultural differences in the facultative practice of monogamy, and monogamy is, amongst humans, facultatively the norm and has been since before the Greeks, so we're really taking about "only monogamy" not "monogamy" being practiced at all.

    As a theory, I'd like to note, this has been generally around for a bit, though it's interesting to see it researched here. Kevin MacDonald's article "What is unique about Western culture?", for example, generally treads the same furrow (though with some other dubious things included).

    As to the talk of women's rights, the theory states that it's surplus males that causes the problem. I can't see that whether women have rights (let alone equal rights) or not has anything to do with this. The idea is that polygamy makes it bad for males and that then makes things worse for society (as those males become unproductive, not having anyone to support or care for and are prone to ever more extreme forms of destructive male competition).


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