This is an exhilarating and yet strange book, written by a passionate and highly talented scientist. The book is exhilarating because it weaves personal experience and academic research into a highly politicized plea for tolerance of, indeed affection for, diversity of sexual expression. The book is strange because the object of attack, Darwinian sexual selection theory, is not a real political enemy at all. I dare say that a huge majority of evolutionary biologists both accept Darwin's theory in some form, yet also accept homosexuality, same-sex marriage, and sex change (Roughgarden reports elsewhere that when she went to Condoleezza Rice, Provost at her home institution, Stanford University, to ask if she could keep her job as tenured professor after she had a sex change operation, Rice was totally supportive). Conversely, those who are intolerant of sexual diversity are most likely to be Creationists for whom Darwinism is as close to the Devil as homosexuality. Roughgarden, it is clear, chooses her battles emotionally, not strategically.
Roughgarden rejects Darwin's theory of sexual selection because (a) it is incorrect, and (b) it perpetrates intolerance of human sexual diversity. It is wrong because it portrays sex in animals as highly uniform, with females investing heavily in each gamete (eggs are very large) and being coy and conservative concerning mating, and males being promiscuous and investing very little in gametes (sperm being exceedingly tiny). It is perpetrates intolerance because it promotes the myth that divergence from the sexual stereotype is abnormal and pathological.
Roughgarden has been accused of committing the "naturalistic fallacy," which says that "was is, is good." In this case, it is easy to think that Roughgarden claims that because there is sexual diversity in nature, and because there is homosexuality and gender change in nature, therefore it is natural that humans are sexually diverse, and those that oppose diversity are enemies of the nature expression of sexuality. This argument is of course fatally flawed. It is easy to find species in which adultery is common, species in which a new male mate kills the young of the previous male, species in which individuals abandon their young with high probability, species in which females generally mate with all the males in the group, and species in which individuals eat each other's feces. This does not make adultery, killing and abandoning offspring, or sharing feces at dinnertime, acceptable practice for humans. In fact, Roughgarden does not commit the naturalistic fallacy. Her argument is that since Victorian times we have lived in a culture that is hostile to sexual diversity, that this is a morally bad cultural bias, and it both oppresses gays, lesbians, and transsexuals today, and accounts for the poor interpretation of sexual dynamics in Darwinian theory. Moreover, she argues that it is illegitimate to use the argument that these diverse sexual practices are "against nature" as a valid critique, just as criticisms of adultery cannot be based on the absence or rarity of "adultery" in other species.
About 80% of this book is a pure pleasure to read, as well as being extremely informative concerning the variety of sexual behaviors in the animal world and a wide variety of human cultures through time and space. Evolution's Rainbow is also a good source of instruction in evolutionary biology as long as "Darwin's theory of sexual selection" is not in question.
The basic argument of the book is that sex is basically cooperative, not competitive and conflictive, as is presented in standard evolutionary theory. I am not sympathetic to this argument. I learned standard evolutionary biology, and accepted both the widespread validity of the coy female/promiscuous male theory without (a) believing that it is universally valid for the animal world, or (b) at all valid for humans. Moreover, I learned from modern biological theory that cooperation is just as important as competition and conflict. Indeed, the modern biological interpretation of the increase in biological complexity since the first bacteria is due to the synergy of cooperation among units of one level of complexity leading to the emergence of a new level of complexity. This process is inherently cooperative, but the emergence of a new level depends on suppressing conflict among individuals on the older level. All of biological life, I learned and I still believe, is an interaction of cooperation and conflict. This include relations between (among?) the sexes in reproduction and nurturing of offspring.
It is not impossible to treat Roughgarden's "counterexamples" as merely oddities or simple exceptions to the rule. Certainly this is what I thought before I read this book. She has convinced me that this is a poor way to think of sexual diversity in the animal world. She has also convinced me that there may be subtle but important forms of sociality in animals to which one is blind if one interprets everything through the lens of Darwin's version of sexual selection. She has not proved the case even in a single species, but she certainly raises plausible alternatives to traditional explanations.
A major issue is treated confusedly in the book, and I have found it to be perpetrated in even the most erudite reviews of the book. Darwin's theory of male decoration was what has been called the "sexy male" theory, as developed analytically by Ronald Fisher and others. This theory says that through random drift, females come to prefer some fitness-neutral aspects of the male, and the female will both mate preferentially with males having this attribute and pass the gene preferring this attribute on to her offspring. There is thus "runaway sexual selection" which is fitness-reducing for the species since it is costly to produce the trait for the male, and costly to be choosy over the trait for the female. As far as I can tell, and I have studied this theory closely, it has absolutely no support either theoretically or empirically. It is just a dead theory, despite its being a favorite of evolutionary psychology--a field dominated by researchers who cannot understand the math and do not study non-humans, but who are great popularizers and appear to have convinced a gullible public of its importance.
The correct version of the Darwinian sexual selection theory is the "costly signaling" approach, which says that decorated males are likely to have "good genes," and hence to increase the fitness of the female's offspring. Roughgarden implicitly accepts the "good genes" approach without argument, merely complaining that females care about the total contribution of the male, not just the quality of the genes passed on to the offspring. However, her general critique of the standard account of sexual dynamics in Darwinian evolutionary theory is misguided. Roughgarden gives no proof that the "good genes" theory is incorrect, or that her "social selection" theory is universally, or even frequently, superior. Her alternatives are creative and interesting, such her suggestion that male decoration is a signal of general prosociality. But it is certainly not proved. Moreover, her claim that the standard signaling theory behind the good genes model is based on generalized "deceit" perpetrated by the male is just wrong. The first principle of signaling theory is that signals that persist over time must be on balance veridical, or else the receiver would increase fitness by ignoring the signal, so some mutant that ignores the signal will eventually emerge and will eventually displace the gullible signal receivers.
Roughgarden rejects the "good genes" theory on grounds that females care about their mates' total contribution to the social resources of the group, not just the genetic quality of the male. But, what determines such total contribution if not the genetic quality of the male? One can hypothesize that males have certain personal characteristics that are not incorporated in its genome, but for most species, this is not at all plausible.
I suspect that Roughgarden's research will broaden and enrich existing models of strategic sexual interaction rather than replace them. Despite Roughgarden's insistence that her ideas are an alternative to Darwin's, I find the two quite compatible, and I suspect Darwin, were he still around, would agree.
Another peculiarity of the book is that Roughgarden treats all deviations of sexuality from the standard coy female/promiscuous male model as adaptations that improve the fitness of the individuals involved. I believe generally that costly species' characteristics that required many cooperative mutations to occur are almost certain to be adaptations. But the huge variety of sexual practices and their close association with speciation makes it likely that much of this variety is random drift rather than an adaptation. In particular, it does not follow from "evolution's rainbow" that extensive sexual diversity is adaptive either for the individual or the group. Moreover, who cares? We can accept sexual diversity for its own sake, not because it arose as an adaption or is serves some adaptive purpose in modern society.
Many researchers, even those with strong moral incentives to do scientific research, are put off by how intimately Roughgarden links her moral principles to her scientific theories. This certainly makes me uncomfortable. I can work with other research intimately for years without finding out, or being interested in the least in, their political or moral positions. No one knows from my published work on human cooperation and conflict what my political and ethical view are, and I am happy to keep it that way. On the other hand, Roughgarden's personal commitment is refreshing and is an attractive aspect of this book