This is an entertaining, educating, and fairly persuasive book. Roughgarden is very deliberately writing this book primarily to make an argument, and secondarily to educate. This is sometimes a slightly infelicitous mix; she uses general, rather than scientific vocabulary, most of the time, sometimes to the detriment of the argument she is making.

Roughgarden is an evolutionary biologist, and some of the arguments she is making are are far more relevant to the field than to the layperson, so I may be misunderstanding her somewhat, but I believe she is arguing, basically: 1) Diversity is the engine of evolution, and when we classify diversity as deviance, we are, in the best case scenario, missing the point, and in the worst case scenario, doing actual harm to ecologies, species, and people. Specifically, we are misunderstanding sexual and gender diversity, because of our ideas of how gender works in humans.

Her second disagreement with the field is, as I understand it, that 2) sexual selection is not even a thing. This point was much more fuzzily caught by me, because my understanding of this part of the theory is pretty surface. She seems to be arguing that, firstly, we should understand reproduction of sexed species to be a cooperative, rather than competitive endeavour, or at least, not discount cooperative theories of animal behaviour, just because we expect to see a competitive one. And secondly, sexual selection theory produces a lot of evo. psych. douchebaggery, so really, why keep it? (I'm going to be as up front as possible: I'm pretty sure her argument is better than I am representing it here! But I missed out on a lot of it.)

I think Roughgarden is on her strongest ground when she argues that gender diversity in nature is far broader than even science usually represents it as. Anyone familiar with Humon's comics knows that nature has a lot of ways of doing gender, but Roughgarden goes further. In cases such as the side-blotched lizard, which in Humon's comics is described as having two male 'types', Roughgarden argues that as these male types demonstrate distinct reproductive behaviours, and distinct phenotypes, does it not make sense to speak of them as being different genders? If clownfish are born male, and may later become female, then really, does it not make more sense to say there is only one gender of clownfish?

A note on vocabulary: Roughgarden is usually speaking of gender, but she sometimes refers to "biological sex" by which she means something highly specific: the property an organism has of producing large or small gametes. She doesn't care about your gonads, your hormones, your gender presentation, or your plumbing when she speaks of biological sex; she only cares about your gamete size. That is, she is a trans woman, and she would consider herself "biologically male." I would not generalize from this to make any assumptions about how any other trans folk might consider themselves, and in the common parlance, "biological sex" is usually used to make essentializing assumptions about gender. That is not how Roughgarden is using it. She means gametes. This obviously has nothing to do with how we deal with gender socially, since most people who have not given birth are simply assuming we have the gametes associated with the gender we were assigned at birth.

Roughgarden argues that because we assume that animals are bi-gendered, bi-sexed, and 'naturally' heterosexual, we (by which she means both the population at large, and the scientific community) miss or misrepresent what is actually going on. She provides quite a few charming examples. One, that of the bighorn sheep, illustrates a problem I have with her vocabulary: she occasionally sacrifices accuracy for accessibility in ways that I think confuse the point. She delightfully describes the typical male bighorn sheep: he spends most of his life in an all male society, engaging in plenty of sexual activity with the other males. He only engages in sex with females during the rutting season, and only during the three or so days when a given female is receptive/permits it.

Some males, however, are not interested in hot ram-on-ram action. These males live with the females year round, and adopt some female behaviours, like squatting to pee. Roughgarden points out that, rather hilariously, these males are considered aberrant, and somewhat 'effeminate.' And here is where it gets confusing. She says: "The 'aberrant' ram is the one who is straight—the lack of interest in homosexuality is considered pathological. [...] According to the researchers, what's aberrant is that a macho-looking bighorn ram acts feminine! He pees like a female—even worse than being gay!"

And while she makes her point about the incredibly confused state of affairs that occurs when we try to impose our gender roles on animals, I find that the use of 'gay' and 'straight' and even homosexual and heterosexual, to a lesser degree, really confuse the issue. For one thing, it's not clear to me that the rams who don't have an interest in other rams are actually interested in ewes, and for another, 'male-oriented except for reproductive purposes' is not how we usually understand the term 'gay,' either. (I have no doubt that a non-zero, and perhaps substantial? number of gay men would be perfectly happy to have intercourse with a woman for a brief period, if the outcome was a child, and there was a socially supported mechanism for doing so, but that's not how the identity is constructed.)

Which leads me to simultaneous frustration that Roughgarden does not go into more detail in her cases (Do the ewes engage in ewe-on-ewe? Does ram-on-ram decrease during mating season? SO MANY QUESTIONS) and also perfectly illustrates the problem with trying to impose human sexual orientations onto animals.

(Pages 139-40 includes a hilarious account of agricultural science attempting to determine the genetic origin of gayness in sheep. Recommended universally.)

Roughgarden also argues that a lot of same-gender animal sexual activity which is understood as either deceptive or occurring because the animal is too dumb to realize they are mounting another of their gender, is either because, a) the animal knows perfectly well what gender they are mounting, and prefers it that way, or because b) sexual activity can have survival benefits beyond propelling one's gamete's into the crucible of genetic recombination; it can be fun, promote social bonding, or be an exchange of favours. (I think this has something to do with her sexual selection argument, again, but I am SUPER NOT CLEAR ON THAT PART.)

Roughgarden is skeptical-to-hostile to most forms of genetic engineering, cloning, etc., both because she distrusts capitalism's motives in interfering with the genome, and because, once again, it is a counter-diversity force. Fair enough on both points, lady.

I found Roughgarden fairly persuasive, although she lost me when she got into the extreme biological nerdery. She goes into a level of chromosomal detail that was frankly quite wasted on me. She was most convincing (and in fairness, entertaining, so in all likelihood, my own level of interest played a part) when she discusses different animal models of gender and sexuality. She's least convincing when she leaves her area of expertise. In the opening of her chapter, "Psychological Perspectives" she says, "some reviewers felt a purely biological account of gender and sexuality was incomplete and needed to be rounded out with psychological perspectives. Reviewers felt that transexualism in particular needed more discussion. Well, okay."

I think the aforesaid reviewers should consider the resulting chapter to be their punishment.

(I also think she makes an error discussing the naked mole rat. She seems to imply the queen actually gains vertebrae during pregnancy, but my googling and wandering around in various databases suggests that the vertebrae themselves elongate. THIS IN NO WAY AFFECTS HER ARGUMENT BUT I CAN'T LET IT GO.)

Those caveats aside, this is a well written and well argued book.

The book closes by arguing that human gender and sexual diversity should, by and large, be understood as part of 'evolution's rainbow', rather than pathologised, and she advocates spreading this idea as widely as possible. I think this would be beautiful.