I’ve been reading the 335-page legal decision upholding Canada’s laws against polygamy, and boy is it juicy.
Before I dive into it, I want readers to understand why I am covering this topic: this evolutionary perspective doesn’t just inform how we eat, how we run, or how we sleep. It informs things as fundamental as how we date, how we marry, and how we organize society. Now back to the case at hand.
Here is the evolutionary portion of the decision, which is well worth reading in full. Two evolutionary psychologists testified in the proceedings, describing typical outcomes that can be expected from polygynous mating arrangements. Recall that polygyny means one male and multiple females (and is vastly, vastly more common in human history than polandry, which means one woman and multiple men).
Dr. Henrich explains the cold mathematics of polygyny:
This illustration reveals the underlying arithmetic that can result in a pool of low-status unmarried men. Imagine a society of 40 adults, 20 males and 20 females â¦ Suppose those 20 males vary from the unemployed high-school drop outs to CEOs, or billionaires â¦ Letâs assume that the twelve men with the highest status marry 12 of the 20 women in monogamous marriages. Then, the top five men (25% of the population) all take a second wife, and the top two (10%) take a third wife. Finally, the top guy takes a fourth wife. This means that of all marriages, 58% are monogamous. Only men in the to 10% of status or wealth married more than two women. The most wives anyone has is four.
The degree of polygynous marriage is not extreme in cross-cultural perspective â¦ but it creates a pool of unmarried men equal to 40% of the male population who are incentivized to take substantial risks so they can eventually participate in the mating and marriage market. This pattern is consistent with what we would expect from an evolutionary approach to humans, and with what is known empirically about male strategies. The evidence outlined below shows that the creation of this pool will likely have a number of outcomes.
(Readers may remember my post on increasing (sexual) inequality.)
Why does this matter? Here are the four sections of his testimony, focusing on polygyny’s effects on men, children, women, and society (admittedly speculative).
One more note before going into this testimony: I don’t know Dr. Henrich, I haven’t read his other work, and I don’t know his reputation. He is in the Department of Psychology at the University of British Columbia. Here’s his academic homepage. Judge for yourself.
Marriage civilizes men:
Dr. Henrich begins with an ample body of research that shows marriage makes men much less likely to commit crimes such as murder, robbery and rape. One such study showed that marriage reduced a manâs likelihood of committing a crime by 35%. This study was particularly compelling as it did not simply compare the criminality of married and unmarried men, but used longitudinal data to track boys from a reform school from age 17 to 70. In this study, crime rates not only decreased when those men were married, but increased when they divorced or were widowed. Other studies are consistent in showing the association between monogamous marriage and decreased male criminality.
He cites studies (not listed in the decision) that examine the relationship between crime and 1) the degree of polygyny across countries, 2) the percentage of unmarried males, and 3) sex ratio of males to females in countries like China, as a result of their one-child policy and a desire to have sons and abort / kill daughters.
Men in polygynous societies aren’t very good fathers:
Another major predicted consequence of widespread polygyny is decreased male parental investment. The underlying theory is that since married men would remain perennially in the marriage market, high-status men could choose to invest their resources in acquiring more wives rather than investing in their children. Similarly, the pool of unmarried men would be forced to invest their resources in attempting to improve their status so as to improve their chances of finding a bride.
As support for this proposition, Dr. Henrich relied on findings from 19th century census data from Mormon polygynous communities and from contemporary studies of African societies.
The study of historical Mormon polygynous communities showed that the children of poorer men (from the bottom 16% of wealth in that community) had higher survival rates than those of the richest men in the community (from the top 2%). The poor men had an average of 6.9 children survive until age 15. For the rich men, despite having more total offspring than the poor men and having over 10 times the wealth, only 5.5 children survived until age 15 on average. Dr. Henrich concludes that this data supports the idea âthat in polygynous systems poor, but married, men will have no choice but to invest in their offspring while rich, high-status men will invest in getting more wivesâ (at 47).
The patterns observed in recent studies of polygamous African societies are similar. The seven studies of this nature cited by Dr. Henrich reported that âchildren of polygynous families are at increased risk of diminished nutritional status, poor health outcomes, and mortalityâ (at 47). One study found that amongst the Dogon of Mali, even though per capita resources were equivalent between monogamous and polygamous households, children under age 10 in polygynous households were 7 to 11 times more likely to die.
Allegedly, when the competition for brides go up, men try to secure brides at younger ages. Male kin learn the value of their female relatives, start treating them like an economic resource, and exert control of women’s reproductive lives.
Competition drives men to use whatever connections, advantages, and alliances they have in order to obtain wives, including striking financial and reciprocal bargains with the fathers of daughters (this is the very common practice of brideprice). Once girls and young women become wives, older husbands (and brothers) will strive to âprotectâ their young wives from other males (to guarantee paternity of any offspring), and in the process dampen womenâs freedoms and exacerbate inequality.
Did monogamy lead to long term economic growth and greater democracy?
Dr. Henrich also predicted additional consequences of polygyny that he acknowledged were more speculative and could not be as thoroughly supported by empirical evidence.
One such prediction is that imposing monogamy may have the effect of increasing per capita GDP. Studies applying a theoretical economic model to the data from highly polygynous states showed that when monogamy is imposed âthe fertility rate goes down, the age gap goes down, saving rates go up, bride prices disappear, and GDP per capita goes way upâ (at 32). This model was based on the assumptions that men and women care about both having children and âconsumingâ, that men are capable of reproducing during much more of their life than women, and that men tend to prefer younger women. In this model, when a ban on polygyny prevents men from investing in obtaining further wives, they instead save and invest in production and consumption.
As noted earlier in the historical review of monogamy and polygamy, Dr. Henrich also speculates that the spread of monogamy may have helped create the conditions for the emergence of democracy and political equality. Anthropological research demonstrates a strong statistical linkage between democratic institutions and monogamy. The theory is that imposed monogamy may eventually lead to democracy by dissipating the pool of unmarried men that rulers harness in wars of aggression, and by imposing a basic principle of equality among men; the king and the peasant become alike in only being able to have one wife.
Fascinating stuff. There seem to be some good reasons why polgamy is a bad idea. I’m convinced.
Why is this important?
Well, in some circles, marriage is viewed as antiquated or quaint or tainted with religion or staid or defended irrationally. But we would be wise to examine long-standing traditions and see if there might not have been some reason for their continued existence. We are entering a brave new world of sexual dynamics, which will inevitably be a mixed bag of outcomes — some good, some bad. And the most important social dynamic will not be what happens to gay marriage, but what happens to monogamy under the onslaught of modernity.