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Thursday
Jul052012

Sex at Dawn: The Prehistoric Origins of Modern Sexuality (Book Review)

All group-living nonhuman primates, such as chimpanzees and the lesser known bonobos, are polygamous. Perhaps not coincidentally, researchers have documented infidelity in every human culture. Yet, most evolutionary biologists agree that monogamy is natural to humans and that it has evolved to assure the survival of our species through guaranteed paternal child support. In other words, without monogamy there is no guarantee a guy would stick around to invest in his offspring. Christopher Ryan and Cacilda Jethá, authors of Sex at Dawn,1 argue that a driving force behind this assured “male parental investment” is the certainty that it’s the particular male’s genes that are passed on to any offspring in which he invests. A monogamous bond insures a man will not accidentally support another man’s child, while it simultaneously assures the female that her male partner will not share resources with another woman’s offspring.

If monogamy is so natural, however, then why is it that cultures need to sanction monogamy? And why is it that even in cultures with the most rigorous attempts to control and punish extra-marital sexual relations is adultery a regular occurrence? For something that supposedly runs against human nature, humans sure risk a lot in pursuit of mere sex. In Sex at Dawn, Ryan and Jethá continuously make the point throughout the book that no living thing should need to be forced into acting in accord with its own nature. Thus, there must be some reason non-monogamy is natural, and this is Ryan and Jethá’s basic argument: non-monogamy may have been vitally beneficial for the survival of our species in prehistoric times.

Specifically, one of the more controversial suggestions of the book is that concealed ovulation coupled with overlapping sexual relationships (that is, non-monogamy or having more than one partner at the same time) evolved to create paternity uncertainty. That is, the prehistoric male had no idea which sex act would result in conception and which child may have been his. This uncertainty was beneficial to a child’s chances of survival as all potential fathers took an interest in them and subsequently helped raise them. Additionally, the authors claim that an abundance of sexual opportunity diffused potential conflicts between men (who no longer had cause to fight over a particular female), and thereby helped build and maintain a more peaceful network of mutually beneficial relationships and communities.

Ryan and Jethá support their thesis with many (anecdotal) examples of societies still alive today that share the responsibility of parenting among all members of a community, and where overlapping sexual relationships are not only tolerated but encouraged, such as the Chinese Musuo. The Aché in Paraguay even account for multiple fatherhood in their language by distinguishing four types of fathers: “the one who puts it in, the one who mixed it, the one who spilled it out, and the one who provided the child’s essence”.

You think this example is too far removed from your everyday reality? Think again. Mardi Gras, the Brazilian carnival, and spring break are striking examples of practiced promiscuity in our culture today. Adoptions, as well as artificial insemination with donated sperm/egg are evidence that people are more than willing to raise children that are carrying someone else’s genes. To further support their theory, the authors of Sex at Dawn draw on a wide range of fascinating topics, such as the specific characteristics of human genitals, reduced sperm competition, and increased infertility rates.

So are we meant to be monogamous? Ryan and Jethá do not disregard monogamy or excuse infidelity per se. Instead, they suggest that monogamy did not evolve as our natural way to mate millions of years ago, but that it developed rather recently as an answer to the shift from nomadic, foraging communities to populated settlements based on agriculture and private property. This recent shift explains why we seem to have such a hard time being monogamous. The authors argue that the traditional notion of a long-term monogamous commitment as natural and crucial to the success of a relationship sets us up for unrealistic expectations and subsequent disappointment. And they suggest that healthy, natural and successful relationships do not have to include lifelong fidelity.

Popular sex-advice columnist Dan Savage is one of the more famous advocates of the book and has for years promoted the idea of responsible non-monogamy. A nice feature of Sex at Dawn is that it includes an interview between Savage and Ryan that discusses the ideas of the book in a casual, easy-to-read kind of way.

Whether you find Sex at Dawn compelling, merely plausible, or unconvincing, it certainly provides an interesting read that stimulates discourse and research on the topic.

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1Ryan, C., & Jethá, C. (2010). Sex at Dawn: The Prehistoric Origins of Modern Sexuality. New York: Harper Collins Publishers.  

Dr. Jana Richert - Science of Relationships articles | Website/CV
Jana's research examines what makes people engage in health risk behaviors and what makes them change these behaviors. She is interested how to communicate information in a way that is personally relevant. Her research draws on stage theories of health behavior change, and Jana is currently working on a web-based intervention promoting the HPV vaccination. 

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