Christopher Ryan Ph.D.

Sex at Dawn


But Honey, I Thought You Meant "Socially" Monogamous!

Social monogamy and sexual monogamy aren't the same. Someone tell the NY Times!

Posted Sep 19, 2013

There's been an interesting reaction to my previous post, in which I express some frustration over Carl Zimmer's recent piece in the New York Times. A reader, Katherine Haines, has kindly forwarded me an email she wrote to the Times, calling their attention to my critique—and their response. Ms. Haines asked them to clarify the source and reasoning behind Zimmer's contention that nine percent of mammals are monogamous, whereas most biologists put the number at around three percent (and over 25 percent of primates vs. the more common estimate of about 15 percent). Here's the response from the science desk at the paper:

We have reviewed the article and do not think it needs rewriting or correcting.

For the 9 percent figure, the source is a paper in the Aug. 2 edition of Science, "The Evolution of Social Monogamy in Mammals":

From the full text of the paper:
'Of the 2545 mammalian species whose social systems could be classified, breeding females were classified as solitary in 1741 species (68%), socially monogamous in 229 species (9%), and living in social groups in 575 species (23%)."

And then:
"The proportion of socially monogamous species in our sample is slightly higher than frequently reported earlier estimates [3% (1)]"

Mr. Zimmer interviewed multiple scientists for his article, many of whom are quoted, and read papers in peer-reviewed journals. He concedes that, not surprisingly, there is some some debate in the scientific community on what the right definition of monogamy should be. (In fact, the headline on a recent article highlighted that the debate is ongoing.) But the fact that Dr. Ryan doesn't necessarily agree with the definition that other scientists use does not mean Mr. Zimmer doesn't understand science. (Emphasis mine)

Of course, neither I nor Ms. Haines accused Mr. Zimmer of not understanding science. Still, as I pointed out in my piece, there's a world of difference between social monogamy and sexual monogamy. Social monogamy is about who you hang out with most of the time, while sexual monogamy is about sex, DNA, and "mating" — the gears that make evolutionary wheels spin. What are we talking about here: house-mates or parents? 

Confusion is never far when one word can mean different things. ("But honey, I thought we were only socially monogamous!)  So let's clarify. This is from a recent, mainstream scientific survey of research into monogamy:

"Social monogamy refers to a male and female's social living arrangement (e.g., shared use of a territory, behaviour indicative of a social pair, and/or proximity between a male and female) without inferring any sexual interactions or reproductive patterns. In humans, social monogamy equals monogamous marriage. Sexual monogamy is defined as an exclusive sexual relationship between a female and a male based on observations of sexual interactions. Finally, the term genetic monogamy is used when DNA analyses can confirm that a female-male pair reproduce exclusively with each other. A combination of terms indicates examples where levels of relationships coincide, e.g., sociosexual and sociogenetic monogamy describe corresponding social and sexual, and social and genetic monogamous relationships, respectively."1 (My emphasis.)

Note that social monogamy doesn't infer any "sexual interactions or reproductive patterns." It's just about spending time together. Sexual monogamy, on the other hand, is about "an exclusive sexual relationship." Big difference, right? As far apart as China and Chinatown. 

When Zimmer writes that, "[Monogamy] is a problem — a scientific one — because male mammals could theoretically have more offspring by giving up on monogamy and mating with lots of females," he's clearly not talking about living arrangements. He's talking about sex: the kind of mating that results in offspring. And yet, the paper he's writing about—the one the science desk of The New York Times says is the source of his inflated numbers on how prevalent "monogamy" is among mammals (and primates)—is not about sexual monogamy at all. It's about social monogamy. It's right there in the title: "The Evolution of Social Monogamy in Mammals."

Look, this isn't just about giving Carl Zimmer a hard time. He's an excellent journalist with a profound understanding of many different areas of scientific inquiry. He's got a difficult, important job and does it very well most of the time—which is all anyone can ask. Plus, as one commenter on my previous post helpfully pointed out, "Mr. Zimmer is admired by thousands of genuine scientists. You, on the other hand, are admired by Dan Savage." Much as I treasure Dan's admiration, I take the point.

But this matters, because if we're talking about two different things—sexual monogamy and social monogamy—we need to be clear about that. In the midst of discussing sex, Zimmer says that monogamy occurs in nine percent of mammals and over a quarter of primates. That's simply not true. It's like telling your friends that crab meat only costs $4 a pound at Costco, without specifying that what you're talking about is the dyed fish paste some people call "crab meat" but which has as much in common with crabs as hot dogs do with dogs—and sells for a fraction the cost of actual, you know, crab meat.

Monogamy is a very charged issue. People want to know how common it is. How "natural" it is. They want to know if their attraction for people other than their spouse is a flaw in their wiring, a deficiency in their marriage, or an utterly predictable response of a non-monogamous primate. They look to people like Zimmer and respected media outlets like the Times to help them answer those questions. As it stands, they're being misinformed, and the science desk at the Times doesn't seem to care.

1. Reichard, U.H. (2003). "Monogamy: Past and present". In Reichard, U.H., Boesch, C. Monogamy: Mating strategies and partnerships in birds, humans, and other mammals. Cambridge: Cambridge University Press. pp. 3–25. ISBN 0-521-52577-2.