In the standard history about human sexuality, monogamy and pair-bonding evolved as a way to ensure the paternity of children and their survival to reproductive age. If that's true, you would think that after thousands of years of genetically and culturally mandated monogamy, we would be a little bit better at it. Some studies estimate that between 30 and 60 percent of all married Americans will cheat at some point in their marriage and a little less than half of all marriages in the US end in divorce. And those numbers don't take into account the couples that never make it to the altar.
The new book Sex at Dawn: The Prehistoric Origins of Modern Sexuality by psychologist Christopher Ryan and psychiatrist Cacilda Jethá takes a look at the sex lives of our prehistoric ancestors in the hopes of answering this perplexing question: Why are humans so bad at monogamy?
Ryan and Jethá propose that our true fall from grace was the move from tight-knit, cooperative bands of hunter-gatherers to competitive agriculturists. Life in prehistoric communities was far from the solitary and short existence that Hobbes envisioned. Rather, if one survived past infancy, the life expectancy was 70 years of peaceful cooperation with one's community, sharing all resources and ensuring that no one went without. And, according to this book, one of those shared resources was probably each other's body. Not only could promiscuous, non-reproductive sex be a strong part of group cohesion, but also the rearing of offspring would be more successful if everyone felt a responsibility for each child. As the authors put it:
Institutionalized sharing of resources and sexuality spreads and minimizes risk, assures food won't be wasted in a world without refrigeration, eliminates the effects of male infertility, promotes the genetic health of individuals, and assures a more secure social environment for children and adults alike. Far from utopian romanticism, foragers insist on egalitarianism because it works on the most practical levels.
If this is indeed an accurate portrayal of our ancestors’ social life, then we should be able to find some evidence in modern times to support it, and herein lies the real strength of Ryan and Jethá's book: they present just such evidence from a variety of different academic fields in a way that laypeople can understand.
From anthropology, they present case studies of modern-day societies where the norms for sexual relations are far from monogamous, even where social institutions similar to marriage exist. Among the Warao people of Brazil, for example, during special ritual festivities, ordinary relations are suspended and adults are free to have sex with anyone. The conception of children during one of these trysts is considered especially auspicious. For the Mosuo in China, an individual's autonomy is sacred and each woman is given a room of her own with a door leading into the house and a door leading onto the street. Who comes and goes through the street door is her business, neatly separating the realms of familial love and sexual affection.
From the fields of genetics and biology, we learn that we are just as closely related to the free-loving bonobo as we are to the more possessive chimp. Why should our mating rituals be more similar to the chimps when our physiology is more closely related to the bonobo? Unlike chimps, for example, but like bonobos, human females have a capacity and willingness for sex at any time, not just during ovulation. And like bonobos, the small size differential between women and men suggests that there is not a long genetic history of male competition over mating.
And from psychology, we are given studies showing humans are sexually excited by the sight and sound of other members of their species having sex, something that doesn't make much evolutionary sense unless you add the idea of sperm competition rather than individual competition as the main evolutionary arena.
Beyond these few examples, Ryan and Jethá put together an extremely convincing case for reexamining the standard ideas of human sexuality, and they do so with impressive grace and wit. Even the chapter titles were enough to get me giggling (“How Darwin Insults Your Mother” and “The Pervert's Lament” come to mind). Yet what the book doesn't offer us is any guidance on what we should do with this new information. Even if you accept their argument, you must still deal with the fact that monogamy is demanded and assumed by most partners and by society at large and that we have been socialized to feel romantic and sexual jealousy. It is not quite as easy as just saying monogamy is unnatural and problematic.