Take, for instance, that presumption — apparently supported by science — that men are more enthusiastic risk-takers than women. The finding is based on male and female subjects’ responses to survey questions about their propensity to engage in risky behaviors. As Fine observes, however, “researchers have to make decisions about the kinds of risks they decide to investigate” — and the kinds of risk they have consistently decided upon have a culturally masculine cast, focused on activities like sports betting, financial investments, motorcycle riding and extreme sports like sky diving or bungee jumping. The author continues: “Although women routinely take risks, these often seem to slip under the research radar. For example, with divorce rates hovering close to 50 percent, being the one to quit or scale back your job when children arrive is a significant economic risk. Going on a date can end in sexual assault. Leaving a marriage is financially, socially and emotionally risky. In the United States, being pregnant is about 20 times more likely to result in death than is a sky dive.” Our habit of defining risk in traditionally male terms has rigged the game against the perception of women as risk-takers in their own right.

Well, then, what about the even more entrenched idea that evolution has primed men to desire many and varied sex partners? Here Fine quotes the Bradley University psychologist David Schmitt: “Consider that one man can produce as many as 100 offspring by indiscriminately mating with 100 women in a given year, whereas a man who is monogamous will tend to have only one child with his partner during that same time period.” Fine expertly fillets this familiar premise, noting, among other inconvenient facts, that “the probability of a woman becoming pregnant from a single randomly timed act of intercourse is about 3 percent,” and that in historical and traditional societies, as many as 80 to 90 percent of women of reproductive age at any one time might already be pregnant, or infertile while they were breast-feeding. “The theoretical possibility that a male could produce dozens of offspring if he mated with dozens of females is of little consequence if, in reality, there are few females available to fertilize,” Fine comments. Think about it: For every man on the prowl, there simply aren’t a hundred women available to bear his child. For all men not named Genghis Khan, monogamy must have started to look like a pretty smart bet.

Again and again, Fine questions the way we think of biological sex “as a fundamental force in development that creates not just two kinds of reproductive system, but two kinds of people.” (Or as she quotes yet another academic: “Psychologically, men and women are almost a different species.”) Fine offers a satisfying counterpoint to this claim: People, she writes, are so different from one another as to seem members of multiple species — a variety not constrained or contained by dichotomous categories of male and female. Indeed, the fantastic diversity of Earth’s life-forms is one of Fine’s recurring themes. To the many nonhuman species she writes about, the author brings her characteristically vivid descriptions and droll humor: We learn that male and female African forest weaver birds sing together, in unison; that male macaque monkeys sometimes carry and groom their babies; that female sandpipers are shamelessly promiscuous. (“While ‘promiscuous’ is a highly value-laden term, no moral judgment whatsoever is implied by its application here,” Fine writes. “Not even for those slutty sandpipers.”)

Fine is also quite funny when observing how gender roles play out in her own life, and how stereotypes attach to her vocation as a feminist science writer. When she told her young son — who, she notes, “has a strange, unchildlike interest in taxidermy” — that it was time to get the family dog neutered, he excitedly suggested turning the testicles into a key ring. Fine remarks: “Contrary to a prevailing view of the feminist as the kind of person who could think of no more inspiring and motivating a start to the workday than to unlock her office with a set of keys from which dangles a man-sized pair of testicles, I strongly vetoed my son’s suggestion.”

Colorful zoological anecdotes and amusing domestic interludes provide a welcome respite from the author’s hard-charging argument. If her book has a fault, it is that it is rather too thoroughly argued. The indomitable Fine amasses evidence, addresses objections and accumulates footnotes at such a brisk pace that the panting reader wishes at times for a water break.