One of the best arguments for monogamy is an argument against polygamy. That is, if you ask Joseph Henrich, whose expertise was called upon last year during a Canadian Supreme Court's reconsideration of a ban on plural marriage.
In a 64-page affidavit, the University of British Columbia professor used his areas of expertise -- psychology, anthropology and economics -- to demonstrate the social harm associated with men taking multiple wives. Implicit in his argument was an endorsement of monogamy, which, he wrote, "seems to redirect male motivations in ways that generate lower crime rates, greater GDP per capita, and better outcomes for children." His interest isn't in the individual, emotional experience of sexual and romantic exclusivity so much as the evolution of cultural norms and how they impact society.
Last week, I spoke with an expert who explained why monogamy makes biological sense. This time around, I spoke with Henrich about the evolutionary basis for monogamy.
You've argued that there's a connection between monogamy and democracy. What's the link there?
That's not a link I'd want to make too strongly, but it has been argued by historians that monogamy precedes, and then seems to go along with, the emergence of democratic ideals. In the Western tradition, the earliest we can trace laws about monogamy is actually to Athens when the first notions of democracy began to be instituted. The argument is that it's meant to create equality among citizens so that, essentially, there'll be wives available to all Athenian men, rather than having all the rich men take many wives. Although, men were still allowed to have slave concubines just so as long as they were non-Athenian women.
You can think of it as a first kind of effort to level the playing field. By saying that both the king and the peasant can only have one wife each, it's the first step toward saying that all men were created equal.
Open marriage has been on the cultural radar recently, but it isn't actually a new idea, right?
In many small-scale societies, there's an institution that looks like marriage, where people "pair bond," but there's philandering on the side by both men and women. They'll often just cycle to another pair bond. It's not uncommon for hunter gatherers to have three, four or five pair bonds in the course of their life, while getting children from each one.
There are these groups in South America where people believe that the fetus is formed by ejaculations from multiple males, so the kids can have multiple fathers. You improve the survival of your child by getting him or her a second father. So when women first get pregnant, they'll seek out sexual liaisons with other men because then those men believe they have a fatherly responsibility to the child. Social norms in this case say that the husband, the primary father, cannot get upset about it, that it's perfectly OK for the woman to go out and seek these other mates -- but the ethnography suggests that these guys are really grumpy about it. You have an innate jealous reaction that's stamped down by local social norms.
What's the argument in favor of outlawing polygamy?
The core of the argument is that polygyny -- when men marry multiple wives -- takes up all the women and creates an underclass of men that have no access to partners, and those guys cause trouble. They commit crimes and engage in substance abuse.
There is also less equality for women and more strife in the home. Women are in short supply, which increases male competition, and so men use violence against women to control the household. Also, if you have one male with lots of wives, there are all sorts of stepmothers and unrelated adults in the same household as children, and that increases the likelihood of violence. The biggest risk factor for spouses killing each other is a large age difference, and in polygamous households you inevitably end up with a large age difference between at least some of the spouses.
We also have other natural experiments. The one-child policy in China creates the same kind of surplus of men because of the preference for sons [and the use of sex-selective abortion and infanticide.] You can see 18 years after you implement the one-child policy, you get extra men and that predicts extra crime. You can see the same thing in India as well. There's a Stanford economist who argues that when men can't invest in getting another wife, they then invest more in their own production. Rather than basically saving up in order to get a second wife or a third wife, they invest more in the children of the one wife they have, and in other types of economic production.
So marriage functions as a social control.
Right, and we even have some idea of the hormonal mechanisms. There's research that looks at men before and after they get married and before and after they have children. The early evidence suggests that males have two testosterone drops during those periods, and it's high testosterone levels that lead to a high level of mate-seeking and risk-taking.
Interestingly, one study was done in a polygynous society that found males don't suffer the same testosterone drop. That makes good sense because if you get married in a polygynous society, you're still on the mating market. Think of testosterone as a mating hormone: It doesn't go down because you're still looking around -- or you're looking less than you would be otherwise, if for no other reason than people are watching and expecting you to not be looking.
Which goes back to the element of social control.
One of the keys to understanding marriage is third parties. Marriage is not only a contract between two people, because there are all these outside parties with expectations about how two married people are supposed to behave. Failure to live up to that has reputational consequences.
It seems there are comparisons that can be made between, on the one hand, human marriage and infidelity and, on the other hand, socially monogamous, pair-bonding animals that sexually stray.
Here's the crucial difference: There's no evidence, at least not that I know of, of animals policing each other. In voles, the uninvolved third parties don't get upset at the vole who strays.
What do we know about mistresses and the impact affairs have in terms of diverting resources?
There seems to be at least anecdotal evidence that wealthy, high-status males not only marry serially but also have mistresses that they divert large funds to. That would be an interesting question to investigate -- I don't actually know of empirical data on that.
Clearly our system of monogamous marriage is supported by particular romantic ideals. How do concepts of romantic love differ in polygamous societies?
The best anthropology can tell us is that there's romantic love everywhere. It's not some strange Western cultural notion; the idea that it should be linked to marriage is the more unusual part. Marriage is about building households and this involves linking up kinship groups, so lots of societies by cultural evolution have decided to take away the responsibility from the young couple in deciding who should mate because there are bigger things at play.
In the smaller scale human societies, it still seems that pair bonds are created by romantic love, but these pair bonds aren't that durable. It seems that social norms are actually what make the pair bond more durable.