This is an amusing and light read, salted with sarcastic quips and, of course, covering a salacious topic. It endeavors to refute the "common wisdom" of just about every field (history, biology, anthropology, etc.) on the subject of human mating systems, and while it appears to succeed here and there, it is largely done by attacking an exaggerated straw man, or by refuting overstatements made in popular science books or in newspaper articles. The lion's share of sources includes the likes of Matt Ridley, Desmond Morris, E. O. Wilson, and Richard Dawkins -- authors who (1) are rarely actively pursuing primary scientific research in what they write about, and (2) are writing for the general public, with, naturally, a tendency to exaggerate and generalize -- so these popular texts are easy targets. At times, Ryan and Jethá demonstrate an imperfect understanding of evolution (e.g. no evolutionary biologist needs to ask the rhetorical question at the end of the middle paragraph on p. 53); at other times they allow inconsistencies to slip by unaddressed. For example, if the true state of hunter-gatherer humans is to share everything, show no jealousy, and for women not to barter with sex, how is it that the bride and groom at a Canela marriage must be instructed not to be jealous (p. 138), or that a Canela bride-to-be participates in orgies in exchange for meat (p. 120)? Overall, it's an entertaining, quick read, but not without flaws in some of its claims and conclusions.
The biggest shortcoming of this book is its epistemological framework: it seeks to uncover our true "human nature," but "human nature" itself is a flawed concept, and early sociobiologists were long-ago admonished for using this term. Biologists know that phenotype (i.e. what gets expressed) is a function of genotype (the genes), the environment (the sum of all external influences, food, temperature, etc), and ontogeny (our development). In its simplest form, any given genotype has a phenotype that responds in complex and varied ways relative to the environment -- this is known as a "norm of reaction" ([...]). When barley is grown a low altitude it behaves very differently form when it's grown a high altitude -- so it makes little sense to ask "what is the true nature of barley" because there is no such thing. Seeking the "true nature" of a species is a holdover from ancient notions of Greek essentialism, which we now know is fundamentally wrong. It is just as "natural" for an all-sharing-commune to also share sex freely, or for a married couple (where the husband invests considerable paternal care) to desire sexual exclusivity (even if this is not always achieved), or for new brides to willingly join in the polygynous family of a wealthy and powerful man -- i.e., depending on the environment, we should expect humans to behave quite differently, and each case is just as "natural" as any other. There is no single "human nature" to be discovered -- at best, we can say that there is a norm-of-reaction to be discovered.
Humans have clearly evolved complex and distinct behaviors capable of responding differently in each distinct environment. That by itself is remarkable, and although Ryan and Jethá are convincing when then claim that bonobo-like behaviors were common in human pre-history, they fail to show that human pre-history did not also include quasi-monogamy (as is now dominant), serial-monogamy, and various degrees of polygyny. Given the wide range of habitats that humans lived in (tundra, boreal forest, rain forest, savannah, estuaries, island archipelagoes, etc) it certainly should not surprise us that humans have adapted to a multitude of different circumstances. Ryan and Jethá argue that a history of intense sperm competition is written on our bodies -- and that may well be true, but it's not incompatible with quasi-monogamy, serial-monogamy, or polygyny. Who can say how many children, born to the king's concubines, were actually fathered by the game-keeper? And if, as some studies claim, some 10% to 20% of kids are not actually the children of the fathers who think they are his children, that by itself is more than enough selection pressure to evolve larger testicles. Finally, the two-fold size difference in European and Asian testicles would seem to imply that some radically different mating systems were present in the pre-agricultural years during the separation of these two populations.
Finally, Ryan and Jethá are guilty of the naturalistic fallacy -- believing that what is "natural" is also good. They may deplore the frustrated husbands who seek out porn to quiet their bonobo impulses, but how about the frustrated bullies who suffer in prison for merely exercising their evolution-given muscles to resolve a dispute? Surely many a dispute in pre-history was resolved by men using brute force to the reproductive advantage of the winner, which is why men are more muscular than women. Does that make it unfair for us to outlaw crime or domestic abuse? Why should promiscuity be any more "natural" than bulling?
Nonetheless, the general point that humans need to learn to relax about social morays is a good one. We are certainly capable of far greater latitude in our mating behaviors than what our priests, politicians, and grandmothers would have us believe. The advent of reliable contraception and an increasing number of self-sufficient women in the workplace ought to allow society to attenuate urges of sexual jealousy and liberalize our relationships -- but without having to give up our privacy, possessions, and suburban homes in favor of communes.
