Book Review: Sex at Dawn

Summary: An interesting but sloppy argument that would have been much improved by more careful use of evolutionary reasoning.

Sex at Dawn, by Christopher Ryan and Cacilda Jetha, is a bestselling science book that sets out to present a radically new model of human prehistory. The authors’ thesis is that, prior to the invention of agriculture, the human species lived in small, roaming hunter-gatherer bands that had no notion of personal property or privacy. In these tribal societies, they say, promiscuous sex was the norm, and this acted as a social glue: since no man knew which children were his, every man cooperated in raising all the tribe’s children, to the benefit of all, and there was virtually no warfare or violence. The book’s strongly-implied conclusion is that monogamy is unnatural and harmful to human beings, and that we’d all be happier if we recognized this.

Reading this book, I found myself in the odd situation of endorsing where the authors end up, just not the road they took to get there. There’s no reason to expect every person to slot neatly into a cultural mold of abstinence until marriage and then till-death-do-us-part fidelity, and the moral guardians who’ve treated this pattern as one-size-fits-all have caused enormous and senseless suffering. I think our culture would be much healthier if we recognized that human sexuality is fluid and multidimensional, that people’s preferences and desires can change over a lifetime, and that negotiation and consent are more important values than monogamy. But we can defend this conclusion for its own sake, without recourse to dubious speculation about what’s “natural” for human beings, and I think Sex at Dawn often strays into very dubious and speculative territory indeed.

Ryan and Jetha’s argument is based in part on anthropological evidence, drawn from observations of present-day hunter-gatherer and pastoralist societies, which I’ll address in a followup post. But I want to begin with a few questions about the basic logic behind their argument:

Evolutionary Logic and the Standard Narrative

The first thought I had while reading SaD was: How did a society like the one it posits ever evolve? The book’s depiction of a utopian free-loving past, where everyone cooperated peacefully without jealousy or fidelity, apparently defies some fundamental principles of evolutionary logic. Most important of them is this: genes which give their bearers an advantage their own replication will dominate at the expense of those that don’t. That reasoning should apply with a vengeance here. In any group of human beings, if some men cared about paternity while others didn’t, the ones who did care would invest resources largely in their own offspring, while the ones who didn’t would spread their resources thin, investing in their own children and the other men’s children indiscriminately. (Even if you somehow started out with no men who cared about paternity, a mutant who did care would be bound to arise eventually.)

What would happen as a result? Obviously, the children of men who care about paternity would get more overall resources, would therefore be more likely to survive, to thrive and to have children of their own, and would make a greater contribution to the gene pool of the next generation, passing on their genes for jealousy and paternal care. Meanwhile, the children of the indiscriminate men would get fewer resources, would be less likely to reproduce, and would be less likely to pass on their genes for not caring about paternity. When this scenario is extended over many generations of evolutionary time, the gene for concern for paternity should drive its competitors to extinction. Ryan and Jetha don’t seem to have an argument for why this inexorable evolutionary logic doesn’t apply in this case.

Now, it’s true that there are other apes where paternity is unknown, especially the bonobo, which Ryan and Jetha rely on heavily as an example. But just as this reasoning would predict, bonobos are matrilineal, and paternal investment in offspring is little or nonexistent, because male bonobos don’t put in much effort for children they can’t be sure are theirs. But this isn’t the case in humans, which again points to the conclusion that concern for paternity played at least some role in our evolutionary past.

What irked me more was Ryan and Jetha’s cavalier treatment of the nature-versus-nurture question. They’d have us believe that concern for paternity is strictly a cultural trait, arising with the invention of agriculture and sedentary societies – they call paternity a “nonissue” [p.104] to men who lived before agriculture, and monogamy a “culturally imposed aberration” [p.109], despite the fact that some form of pair-bonding is ubiquitous in cultures throughout the world. But when it serves their purposes, they switch to arguing that other human behaviors are genetically hardwired and are evidence for our orgiastic past, like women being noisier than men during sex [p.255], or men who prefer porn that features group sex [p.231]. No evidence for these traits being genetically determined is presented other than anecdote.

But what annoyed me most of all is that the authors don’t even seem to understand the reigning paradigm they’re attacking. As part of their argument for the unnaturalness of monogamy, Ryan and Jetha point out that genetic testing shows infidelity is common among species once thought to be monogamous, like swans and prairie voles [p.136]. They also illustrate the violent lengths that human society goes to in order to enforce monogamy, citing horrific laws like Iran’s which mandate stoning for adulterers. They conclude, “No creature needs to be threatened with death to act in accord with its own nature” [p.98].

But this is completely off-base. The standard narrative doesn’t say that human beings evolved to be monogamous, but that we evolved to want our partners to be monogamous, a drastically different claim. Men want women to be faithful because they don’t want to spend their resources raising another man’s child; women want men to be faithful because they don’t want him to divide his efforts between them and another partner. But at the same time, each partner also has an evolutionary incentive to cheat: men to mate with as many women as possible, to broadcast their genes more widely; women to mate with higher-status partners who might have superior genes. The tug-of-war between these conflicting impulses is what produces the uneasy equilibrium we see. What’s even more puzzling is that, earlier in the book, Ryan and Jetha present a perfectly adequate summary of this model [p.7]; but when it comes time to argue against it, they only thrash at straw men.

Now, I’m not saying the standard narrative is a universal key to human behavior, nor am I saying it’s instinctive programming that can’t be altered by culture or personal choice. To the extent that mating strategies are genetically influenced, human beings undoubtedly have multiple reproductive strategies that we can switch between depending on what works best, just as we find in any other complex, successful and diverse species. But if you’re going to discuss this idea, the least you can do is get it right. Ryan and Jetha’s stumble over this basic point makes me more skeptical when it comes to arguments I’m not as familiar with.

Coming up: A discussion of Ryan and Jetha’s anthropological evidence, including the prevalence of warfare and the existence or non-existence of sexual jealousy in primitive societies.

Image credit: Shutterstock

About Adam Lee

Adam Lee is an atheist writer and speaker living in New York City. His new novel, Broken Ring, is available in paperback and e-book. Read his full bio, or follow him on Twitter.

  • http://deusdiapente.wordpress.com J. Quinton

    The first thought I had while reading SaD was: How did a society like the one it posits ever evolve? The book’s depiction of a utopian free-loving past, where everyone cooperated peacefully without jealousy or fidelity, apparently defies some fundamental principles of evolutionary logic. Most important of them is this: genes which give their bearers an advantage their own replication will dominate at the expense of those that don’t. That reasoning should apply with a vengeance here. In any group of human beings, if some men cared about paternity while others didn’t, the ones who did care would invest resources largely in their own offspring, while the ones who didn’t would spread their resources thin, investing in their own children and the other men’s children indiscriminately. (Even if you somehow started out with no men who cared about paternity, a mutant who did care would be bound to arise eventually.)

    What would happen as a result? Obviously, the children of men who care about paternity would get more overall resources, would therefore be more likely to survive, to thrive and to have children of their own, and would make a greater contribution to the gene pool of the next generation, passing on their genes for jealousy and paternal care. Meanwhile, the children of the indiscriminate men would get fewer resources, would be less likely to reproduce, and would be less likely to pass on their genes for not caring about paternity. When this scenario is extended over many generations of evolutionary time, the gene for concern for paternity should drive its competitors to extinction. Ryan and Jetha don’t seem to have an argument for why this inexorable evolutionary logic doesn’t apply in this case.

    Now, it’s true that there are other apes where paternity is unknown, especially the bonobo, which Ryan and Jetha rely on heavily as an example. But just as this reasoning would predict, bonobos are matrilineal, and paternal investment in offspring is little or nonexistent, because male bonobos don’t put in much effort for children they can’t be sure are theirs. But this isn’t the case in humans, which again points to the conclusion that concern for paternity played at least some role in our evolutionary past.

    The only way I can see these paragraphs not contradicting each other is if you posit that humans have always been patrilineal. I haven’t read Sex at Dawn, so I don’t know if they make that argument. But it doesn’t follow necessarily that evolutionary “logic” has to be patrilineal or the species would die out, due to the the very existence of bonobos.

    Do we have any evidence either way, that human societies were matrilineal or patrilineal before the agricultural revolution?

  • http://www.politicalflavors.com Elizabeth

    In Natalie Angier’s book, “Woman, An Intimate Geography” she makes the case that in hunter gatherer tribes, the mothers and grandmothers provided most of their children’s calories through foraging, gathering, etc. Of meat that the men hunted, she says very little ever got back to the women and children. Some was eaten immediately as one works up an appetite hunting, sacrificed to gods, or traded. If this is true, it would make sense that paternal investment or lack thereof might not have a significant effect on the children’s survival.

  • morteng

    If promiscuous sex was the norm in a band, it wouldn’t matter if they cared about paternity, since they couldn’t know which children were theirs. If they were truly promiscuous and not serial monogamists, at least.

  • tprc62

    I thought there was a good argument in the book that early humans thought that babies are made from the contributions of multiple male partners. Multiple male partners were believed to ALL be the fathers in a very real sense. This was advantageous since a child would then have multiple fathers for support, and would seem to make sense in the kind of group living arrangements that existed then. My understanding is that some modern hunter/gatherer tribes still have this belief.

  • Jack

    Ryan and Jetha point out that genetic testing shows infidelity is common among species once thought to be monogamous, like swans and prairie voles [p.136].

    I haven’t read Ryan and Jetha, but I have seen the paper they are probably citing concerning prairie voles (Ophir et al 2008), and it is a gross misrepresentation of that paper to suggest that it shows that prairie voles are not monogamous. The extra-pair matings occur at a relatively low frequency. Most matings are intra-pair; the authors describe the species as “socially monogamous”, although not strictly “genetically monogamous”.

  • Adam Lee

    The only way I can see these paragraphs not contradicting each other is if you posit that humans have always been patrilineal. I haven’t read Sex at Dawn, so I don’t know if they make that argument. But it doesn’t follow necessarily that evolutionary “logic” has to be patrilineal or the species would die out, due to the the very existence of bonobos.

    No, that isn’t a contradiction. The argument is this: From an evolutionary perspective, for there to be paternal care and involvement in raising offspring, there has to be some way that fathers can know, even if imperfectly, which children are genetically theirs. If a species has a social structure such that fathers can’t have any confidence about about which children are theirs, then there’s no selective pressure for them to contribute to the care of offspring. Conversely, if a species has a social structure where paternal care and involvement are important, then there will be selective pressure for males to care about their mates’ fidelity, so that they don’t spend resources on someone else’s children. (This argument doesn’t apply to mothers, obviously, because they always know which children are theirs.)

    You could look at it this way: on the fitness landscape, there are two peaks, two attractors. One is the state where paternal investment is high and males care about females’ fidelity; the other is the state where paternal investment is low and males don’t know or don’t care about fidelity. Bonobos occupy the latter peak. Most evolutionary psychologists would say that humans are on the former. But Ryan and Jetha would have us sitting awkwardly in the middle, in between the two peaks, yet feeling no selective pull one way or the other. I’m not convinced that this is plausible.

    Jack: I looked up the references, and that’s not the paper they cite. One of their references is to a February 2005 Scientific American article (!). The other is a quote from Thomas Insel of the National Institute of Mental Health, but Ryan and Jetha don’t give a clear reference to where he said it. The Ophel paper is a good one to know about, though.

  • Barael

    Looks like you’re mixing evolution with psychology. This is strictly verboten!

  • Azkyroth

    Looks like you’re mixing evolution with psychology. This is strictly verboten!

    *yawn*

  • Frafor4912

    The argument that men must have been since day one worried all the time about making sure their efforts only went in favor of those carrying their genes is a very biased one. It is a typical attitude in which they want to make us believe that because in a society where we measure with money whatever each individual is supposed to have a right to, our species “must have been” like that forever.

    A society where every individual cares for every other man, woman or child—which seems to be the way of the Bonobos—is most likely to generate individuals with genes compatible and efficient for such societies.

    However, something terrible must have happened to the planet; a catastrophe that ruined the habitat of our species and pushed our brains into elaborating new MEMES or immediate solutions for survival. That’s when we started hunting—the need to eat cadavers of animals—and eventually, 10,000 years ago, we started doing agriculture, a method of food production that generated a different social organization.

    Our ancestors didn’t need to worry about whose the children were, since they were all participating simultaneously in the process. Everybody was happy with no special meme arrangement. The meme elaboration is a response of a material condition forcing—for survival—the humans to adapt to.

    When the brain needs to interfere, it does so with success, but with no guarantee that such success will be 100% compatible with the genes. It doesn’t have to be. That’s part of the randomness in its existence


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