Eric Michael Johnson reviews “Sex at Dawn” by Christopher Ryan and Cacilda Jethá over at SEED:

But why should a species often described as monogamous be so hypersexual? Monogamous animals by definition don’t have to compete for reproduction and, as a result, are generally characterized by a low level of sexual activity. But according to Ryan and Jethá humans top a very short list of species that engage in sex for pleasure. “No animal spends more of its allotted time on Earth fussing over sex than Homo sapiens,” they write. In fact, the animal world is filled with species who confine their sexual behavior to just a few periods each year, the only times when conception is possible. Among apes the only monogamous species are the gibbons whose infrequent, reproduction-only copulations make them much better adherents of the Vatican’s guidelines than we are. In this way, Ryan and Jethá argue, repressing our sexuality should not be confused with reining in an “animal” nature; rather, it is denying one of the most unique aspects of what it means to be human.

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However, by looking at modern indigenous societies and comparing the findings of anthropologists with the latest results in behavioral psychology and biology, Ryan and Jethá piece together a remarkably coherent pattern from an otherwise fractured understanding of human sexuality. From societies that believe that multiple men are necessary for a successful pregnancy (what researchers refer to as “partible paternity”) to those where not having an extra-marital tryst will cause a man to be labeled “stingy of one’s genitals” by his female suitors, the authors conclude that marriage may be an established social arrangement among many hunter-gatherers but it’s one in which sexuality is decidedly fluid. A range of physiological evidence from Western populations is further offered to support this position, from the year-round libido in both sexes, to the unusually large size of men’s genitalia compared to other apes, to the shifting sexual strategy during various stages in women’s reproductive cycle (and lest we forget multiple female orgasms?). All suggest that our species is adapted for several concurrent sexual partners.