We’re an innately sexist and aggressive species. That’s the thesis of David Barash’s new book Out of Eden: The Surprising Consequences of Polygamy. Barash argues that the preponderance of evidence from evolutionary biology suggests that ancient human males competed with each other for women, with winning males forming harems.
Patriarchy: It’s our genetic heritage.
But that doesn’t mean it has to be our future. Though he lays out his evidence forthrightly, Barash does not advocate for a return to retrograde gender roles. On the contrary he says that human biology is more complicated than it appears. There’s lots of evidence, for example, that women always have taken multiple partners as well, though usually in a quieter, ad hoc way, rather than via institutionalized harems. For the romantics, it turns out we have many adaptations that make monogamy possible and appealing—not least our propensity to love.
Out of Eden is, as the title suggests, a book about choice. Barash hopes that learning about our polygamous history will make more people free to choose how to live in the present. I spoke to Barash about polygamy, monogamy and how humans are, and aren’t, tied to our biology.
What evidence is there that polygyny, or male harem-keeping, is natural?
There are a number of things. One is the reality of sexual dimorphism or difference in body size between men and women, with males being consistently larger and more aggressive than females. And that in itself is strong evidence for polygyny in any species. There’s a direct correlation between the degree of polygyny, that is to say how many females constitute a harem, and the degree of sexual dimorphism.
When you have a highly polygynous species, like elephant seals, where one male may be mated to up to 40 females, the males are hugely larger than the females. They’re up to four times larger and immensely more aggressive.
When you look at species that are mildly polygynous, the degree of sexual dimorphism is still there, but milder, as with human beings. And then if you look at the relatively few species that are monogamous, like robins and gibbons, there’s basically no sexual dimorphism. Male and female body size is comparable, and male and female aggressiveness is comparable.
Another major indicator of polygyny, or harem-keeping, is bimaturism, which is the difference between the sexes as to when they undergo sexual maturation.
You’d expect that females should become sexually mature later because it’s more demanding for them to be pregnant. But what we find is that in harem-forming species the females become sexually mature earlier than the males. The reason for that is that if you’re a male, you’re competing with other males. It’s not in your interest to become sexually mature when you’re insufficiently strong or experienced. That’s why in humans girls become sexually mature several years before boys.
So the argument is that human males have evolved to compete for harems, which results in men being bigger and in boys maturing later so they don’t get killed off before they’re ready to compete.
That’s right. There’s also the fact that before the rise of colonialism most human societies were harem-forming. Over 80 percent.
You say that humans are polygamous but not promiscuous.
Well, if you’re polygamous it means you form mating systems in which you mate with more than one member of the other sex. But “promiscuous” implies a lack of concern about who you’re mating with. Whereas if you’re a harem member as a woman, it’s expected that you’ll mate with just the one guy. And if you’re a harem-keeper you’re expected to mate with your wives.
And women are evolutionarily polygamous, too.
Yes. There’s a difference between polygyny, which is traditional harem formation, and polygamy, which is one of one sex with more than one of the other. And it’s important to note that humans are polygynous, naturally, one male and many females. But they’re also polyandrous, which is one female inclined to mate with more than one male. And that’s been more hidden, and that’s why we don’t show as many obvious biological indications of our polyandry. But we are both polygynous and polyandrous, so we’re polygamous.
If we’re naturally polygamous, why are there so many cultures that set up monogamy as an ideal? And how do we even manage to be monogamous?
There are a number of answers. One is that we manage it only with difficulty. And that should be intuitively obvious to anyone who attempts to be monogamous. That’s not to say it’s impossible. But it takes a committed decision to achieve it.
It’s important to emphasize that human beings are not at the mercy of our biology in this regard. We can make all sorts of decisions. And one of those decisions is whether we want to be monogamous. Maybe the hallmark of human beings as opposed to other animals is that we’re not at the mercy of our biology. We can choose to behave how we wish. And those people who may choose to be polyandrous or polygynous, as long as they’re not hurting someone else as far as I’m concerned, they have every right to do so.
It’s really important that people be aware of their polygamous inclinations. Because what often happens is that people can be blindsided by those inclinations. They may think they’ve found the perfect love of their life and intend to be monogamous. And then they may find themselves looking at someone else with a degree of lust. Or they may find their partner looking at someone with a degree of lust. If you are not aware of our underlying polygamous tendencies, there’s a danger of being blindsided by our biology. And they may think ‘I’m just a horrible person,’ or ‘I’m not cut out for monogamy.’
The truth is no one is cut out for monogamy. That doesn’t mean we can’t do it. Just like no one is cut out to play the violin or learn a second language. But we can do it. It’s important to not be blindsided and not take an interest in someone else as somehow indicating that your partner is inadequate or that you’re inadequate. What it means is that you’re a healthy human being. Congratulations!
You say in your book that there are some ways in which we’re geared towards monogamy.
There are some biological characteristics in humans that make monogamy possible. For example, there’s oxytocin, a hormone associated not only with satisfying sex but with increased trust. And there’s the fact that our neurons themselves are plastic. They change and grow. Though there’s no direct evidence for this, it’s possible that one thing that happens in an ongoing relationship is that those neurons involved will grow and mature.
There are also social issues. One argument is that monogamy provides opportunities for men that they wouldn’t otherwise have. When I give talks about our natural inclination towards polygyny, the men in the audience are often kind of licking their chops, saying I wish I lived in those days, when I could have had a harem.
The reality is that if there’s one guy with a harem of four women that means that there are three other guys who are left out altogether. So men’s assumption that they would be the harem-keepers is just mathematically unlikely. So monogamy is a particularly good deal for men. Because otherwise you get a lot of excluded men.
It could be that one thing that happened historically was that there was a deal whereby wealthy and powerful men who would otherwise be harem-keepers gave that up at least officially, and in return they got a degree of social cohesion they wouldn’t otherwise have.
And there’s the big thing about parenting. Given how helpless our infants are, it really helps to have more than one committed adult. So there are certainly factors that make monogamy possible, and in many cases make it a really good idea.
The general move towards equality in all sorts of ways would suggest equality in regard to mating, too. If you’re one of several wives, in some sense you’re not as important as the one guy on the other side. And that obviously goes counter to our egalitarian impulses. At least for those of us who have egalitarian impulses, as opposed to the Donald Trumps of the world.
Noah Berlatsky edits the comics and culture site the Hooded Utilitarian and is the author of Wonder Woman: Bondage and Feminism in the Marston/Peter Comics 1941-1948.