SEX IS A SPECTRUM
The Biological Limits of the Binary
by Agustín Fuentes
Princeton University Press. 216 pages, $24.95
THIS IS THE BOOK on biology that you wish you could have read in high school. In the introduction to Sex Is a Spectrum, author Agustín Fuentes invites the reader to imagine being a fish called the bluehead wrasse, living off the coast of Florida. Presumably “you” produce eggs. But then the only male in your group gets eaten, your body changes, and you produce sperm because your group needs a sperm-producer. The author’s choice of organism to represent the diverse and surprising world of biological sex seems intended to undercut almost any reader’s culturally imposed beliefs about gender. As a bluehead wrasse, would you be more aggressive as an egg-producer or a sperm-producer? Unless you’re a marine biologist, it seems impossible to know.
Fuentes, a professor of anthropology at Princeton, carefully places humans in the kaleidoscopic field of living organisms. By the time he introduces “Animal Sex Biology” in chapter two, he has settled on the terms “large-gamete-producing individuals” for those who produce eggs, the genetic material that eventually becomes a new organism after being fertilized, and “small-gamete-producing individuals” for those who produce sperm, or the material that does the fertilizing. Aside from this general distinction, we’re warned that “the assumption of fixed ‘sex’ differences and ‘sex’ uniformity either between or within species is a major stumbling block to understanding biology and behavior in organisms.”
To provide just a sampling of the possible ways in which reproduction shapes bodies and behavior, Fuentes describes the Hymenoptera (bees, ants, and wasps) in which two types of genetic systems produce three types of bodies, including “workers,” those that can produce “large gametes” (eggs) but rarely reproduce. Then there are the Hemiptera (scale insects such as aphids, bed bugs, and cicadas), in which reproductive physiology can be dependent on the temperature of the environment, and large gametes can develop into zygotes without any need for small gametes in a process that could be called “virgin birth.” Then there are earthworms, all of which develop functioning testes and ovaries such that fertilization can occur with the mutual exchange of sperm between two individuals.
In “Humans Then,” the author delves into human evolution and our resemblance to other primates. He points out that, like our distant primate cousins, we have large, complicated brains and lives centered around social relationships, in which infants are often a center of focus because they need so much care. And because of our focus on social interaction, what we think of as “sexual” interaction is not simply based on a biological drive to reproduce.
In the chapter “Humans Now,” Fuentes refers to “3G males” and “3G females” as categories in which the genes, gonads, and genitals of individuals seem to be consistent. He explains that the gender of a baby that is assigned at birth is usually based on the appearance of genitals, which may be inconsistent with the other G’s. The physical transformation of puberty is described in detail, especially in terms of the production of estrogen (the “female” hormone) and testosterone (the “male” hormone), though all humans produce both in different quantities. Intriguingly, he notes that testosterone levels, widely thought of as the essence of maleness, often respond to external stimuli rather than being consistent from birth.
In “No Biological Battle of the Sexes,” Fuentes clinches his central thesis, that any assumption of a gender binary is an oversimplification of reality. He regards such thinking as harmful to the accumulation of scientific knowledge and to the kind of human interaction that seems to be a defining feature of our species. The information in this book can be used in a fight against gender essentialism or any of its misbegotten offshoots: machismo, misogyny, homophobia, transphobia, et al. Even if you are not arming yourself for an ideological war, you could read Sex Is a Spectrum for its entertainment value. This reviewer is especially charmed by an image of lactating “male” fruit bats, but your preference may vary.
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Jean Roberta is a widely published writer based in Regina, Canada.
