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Carl Zimmer is one of the world's most respected science journalists, a regular columnist at The New York Times, and author of a dozen widely read books—most, but not all, about some aspect of evolutionary theory. So when Mr. Zimmer writes about human sexual evolution, one expects him to get it right. But he keeps getting it wrong in ways that offer a fascinating insight into just how difficult it can be—even for the most intellectually-gifted among us—to move beyond mainstream thinking when it comes to human sexuality.
Zimmer's recent column about the "problem" of monogamy in mammals offers several striking examples of the kinds of intellectual omissions and cognitive contortions required to stick with the dominant narrative when alternatives may be too emotionally threatening to consider.
The first problem is apparent before the article even begins, in the caption under a photo of Titi monkeys explains that they are "monogamous—a way of life found in just nine percent of mammal species." This triples the widely accepted prevalence of monogamy in mammals, which is about 3 percent. (ed: For a thorough academic review of this question, see this paper.) Zimmer doesn't specify his source for this figure but possibly sheds some light on the confusion in his second paragraph, writing, "In nine percent of all mammal species, males and females will share a common territory for more than one breeding season, and in some cases, bond for life."
So maybe this elastic definition of "monogamy" accounts for the monogamy inflation? Maybe. Still, any man who has lived with a female house-mate will tell you that "sharing territory" and "monogamy" can be two very different things.
Zimmer continues, "This 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." So, it's clear Zimmer is talking about sexual monogamy, and not just splitting the rent (social monogamy).
In his summary of the state of research into monogamy, Dr. Ulrich Reichard of the Max Planck Institute for Evolutionary Anthropology uses a more precise definition of monogamy, "Living together as a monogamous pair, that close social relationship between a male and a female, is relatively rare in mammals, only occurring in around three percent of species." Further, he stipulates that "Behavioral observations show that living together in social monogamy does not equate to monogamous mating or reproduction."
Precisely.
See the problems? First, Zimmer has tripled the widely-accepted estimate of how common monogamy is among mammals, using a strangely imprecise definition of what the term means, a definition that obscures the crucial fact that social monogamy and sexual monogamy are not at all the same thing.
Don't get me wrong. I respect Zimmer's scholarship immensely, which is why these mistakes are so striking. And the mistakes aren't just elementary; they're persistent.
A little further on, Zimmer cites another study about primates, "which are especially monogamous — males and females bond in over a quarter of primate species." Again, "bonding" is not monogamy, so to conflate one with the other is both misleading and utterly unnecessary—unless you're striving to make monogamy seem more prevalent among primates than it actually is. There are many examples of social bonding among mammals that have nothing to do with sexuality, much less any implied lifelong sexual exclusivity. Furthermore, most primatologists claim that only about 15 percent of primates are thought to be sexually monogamous, not "over a quarter." (For an amusing round-up of the state of primatological research, take a look at this article.) The anthropological literature is also replete with examples of human societies that feature prominent, often lasting male/female bonding but that are not necessarily sexually monogamous. (See, for example, Cultures of Multiple Fathers, Sarah Hrdy's Mothers and Others, or Sex at Dawn.
Perhaps you think I'm just being nitpicky about statistical details. Fair enough (though you've got to admit that these are some pretty significant differences: an unexplained jump from three percent to nine percent ain't nothing). But I get a special kind of irritated when popular science writers refer to chimps in illustrating "the primate origins" of this or that, but misrepresent the import of bonobos, or leave them out of the discussion entirely. It's crucial to include both because they are equally related to humans, and yet exhibit very different behaviors—especially regarding sexuality and violence.
It's as if you've got two twin brothers. One of them is LGBT-friendly, feminist pacifist, traveling the world selflessly building schools in poor communities, loved by all (but also unashamedly non-monogamous). The other is an occasional psychopath in prison for serial rape and murder (also non-monogamous, but in a nasty sort of way). Imagine how you'd feel if, when people talked about your "nature," they only referred to your brother in prison—dropping your kind, peaceful brother from the conversation.
Well, that's what journalists are doing when they drop the bonobo from any discussion of the primate origins of human sexuality or violence—and it's what Zimmer does in this piece:
"One source of clues to the origin of human mating lies in our closest relatives, chimpanzees, and bonobos. They live in large groups where the females mate with lots of males when they're ovulating. Male chimpanzees will fight with each other for the chance to mate, and they've evolved to produce extra sperm to increase their chances that they get to father a female's young. Our own ancestors split off from the ancestors of chimpanzees about seven million years ago."
Hey, what happened to the bonobos? Readers unfamiliar with the differences between the species are left to assume males from both species fight over females, which is totally false. In fact, the roles of sex and violence in bonobo troops are the reverse of what's found among chimps. As primatologist Frans de Waal famously put it, "Chimps use violence to get sex, while bonobos use sex to avoid violence."
This is not to say there's no conflict or occasional tension in bonobo troops, but in over fifty years of observation—in captivity and in the wild—no bonobo has ever been seen to kill or rape another bonobo. So the impression Zimmer leaves, that our male primate ancestors fought over access to females is, at best, only half right. In journalism, as in science, "half right" is pretty much the same as totally wrong.
Zimmer ends the piece with the tired, old line about monogamy originating because "Fathers ... had evolved the ability to hunt and scavenge meat, and they were supplying some of that food to their children." This line of reasoning has been a perennial favorite since the "Man the Hunter" symposium, in 1966. It ignores several fundamental facts, including:
- Without strictly enforced female fidelity, there would be no way for our male ancestors to know who "their children" were—even assuming they knew that one sex act could cause pregnancy, which is not widely understood even today.
- There is no evidence of strictly enforced female fidelity in hunter-gatherer societies that have been studied. To the contrary, such studies are full of examples of a decidedly relaxed approach to sexuality, as mentioned above.
- Immediate-return hunter-gatherers who live in social and ecological conditions similar to those of our ancestors are nearly universally "fiercely egalitarian," and share virtually everything within the band—especially meat. Even if a man knew which children were genetical "his," if he tried to favor them by directing the meat from his hunting success exclusively to them, he would find himself quickly banished from the society—a virtual death sentence.
- Men in foraging societies generally hunt in groups, making individual ownership of the kills as difficult to establish as it would be socially disastrous.
- When the man off hunting, who is protecting his wife and child?
- And so on.
The point is that our ancestors did not live in independent nuclear family units, spread across some kind of prehistoric suburban landscape. They lived in highly interdependent immediate-return band level groups that were fiercely egalitarian and violently opposed to the selfishness most of us—including Zimmer, apparently—assume to be an eternal, intrinsic feature of human nature. In such social groups, the nuclear-family based hoarding of resources central to this vision of human evolution can't and doesn't occur. In Sex at Dawn, we call this tendency to project contemporary conditions into our vision of prehistory "Flintstonization." It's been almost fifty years since Macho Man the Hunter came on the scene. Isn't it time we updated our understanding of human sexual evolution, Mr. Zimmer?
