Christopher Ryan and Cacilda Jethá, Sex At Dawn. The Prehistoric Origins of Modern Sexuality, New York, Harper Collins, 2010

This is a book about a subject almost everyone in American and European universities has a personal stake in: monogamy. And it is quite critical of it. With books like this, reviewers should perhaps start disclosing their conflicts of interest, so readers could discount the biases in their assessment. Maybe I will be critical just because my partner cheated on me and I cannot help feeling personally offended by the authors’ case. Or maybe I will praise it in order to justify my own non-monogamous desires. The book is dedicated by the authors to “all our relations” so you may guess right from the start whose side are they on -they do not say much about themselves. So let me dedicate in turn this review to my own relations and we will be even.

Sex at Dawn is indeed an argument against those who consider monogamy our most natural family arrangement. Or, to be more precise, against the most rational among them, the scientifically inspired monogamists. Ryan and Jethá (a psychologist and physician) target the “standard” account of monogamy among evolutionary psychologist, which they probably consider the strongest case for it. They try to debunk it, under the assumption (I guess) that if the reader is convinced by their argument s/he will become more open-minded about non-monogamous family arrangements. As they put it themselves, the most important practical consequence of reading this book should be for couples to openly speak about the meaning of being faithful to each other.

For evolutionary psychologists (the authors apologize for the simplification and I concur), monogamy would be the best way for males to make sure that they are really fathering their female partner’s kids; these latter would obtain in exchange their help in raising them. Both partners will try to cheat on each other to increase their reproductive success through sexual competition: men will try to mate with as many other women as possible hoping that someone else will help in raising their own progeny; women with less desirable partners will try to get pregnant with more successful males, making the former raise the kids. On the grounds of this biological equilibrium, our species would have arranged different cultural variations of the same theme (monogamy).

The authors do not question sexual competition, but claim it operates at a different scale. Drawing on evidence from anthropology (hunter-gatherer societies) and ethology (primates), the authors argue that our species evolved forming promiscuous groups whose members had non-exclusive sex with each other as a bonding mechanism and cooperated in raising their progeny. Sexual competition would occur inside the vagina where sperm from different men would “fight” each other chemically for fecundating the ovule with the non-neutral intervention of the host’s organs. In other words, we would be capable of living in non-monogamous cooperative arrangements, enjoying less sexual frustration, letting our cells do the sexual competition for us behind our back.

Sperm competition in humans is controversial: I admit it as a possibility but a popular science book is probably not the best source to make a conclusive case. The evidence provided in Sex at Down is nonetheless entertaining to read (if you are unfamiliar with this literature) and discuss with your friends. I often found myself disagreeing with the way in which the authors present it, time and again bringing grist to their mill, sometimes at the expenses of fairness and accuracy –e.g., we have data about the quality of our semen and throughout the last fifty years it seems to decrease, but can we really extrapolate this recent trend to the very origins of monogamy, thousands of years ago? (Was semen really so good then?). On a more theoretical note, since this is a book about “the prehistoric origins of modern sexuality”, I miss an account of how monogamy came to prevail. We know it starts with agriculture, but how come it has lasted this long despite all its drawbacks? Monogamy may make us unhappy, but perhaps there is a trade-off and we are getting something in exchange. Almost every piece of evidence presented in this book seems to perform evolutionary functions and monogamy should be no exception. But this is just a guess.

My main contention is though that monogamy is no less natural than non-monogamy: since this is a debate among rationalists, we will easily agree that our species does not do supernatural things, especially when it comes to reproduction. Maybe non-monogamous regimes did wonders for us thousands of years ago, but this is not a particularly good argument for bringing them back today. Not that I am against them, mind you, but I do not need to be “historically justified” to try any alternative to monogamy. As a matter of fact, I cannot imagine anybody struggling to stay in a monogamous relationship, just because evolutionary psychologists claim that this is the natural thing to do.

However, I concur with the authors that monogamy is a topic that every couple should discuss rather than take for granted and, all in all, this book is a good place to start the conversation. Given the number of pro-monogamy prejudices we carry with us, it may be fair to load the dice in the other direction.

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