The Binary Delusion
How Biology Defies the Myth of Two Sexes
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Publisher Description
A human physiology expert lays out the basic facts to explain why the idea of biological sex as a binary is simply wrong
Biological sex is as nuanced as gender. Many of us are biologically more typically masculine in some ways and more typically feminine in others. The constellation of traits that make up our sex identity are wide-ranging and often overlap. Height, strength, body hair, genitalia, hormonal balances—these are all part of the picture. How should we think about this kind of variation?
The Binary Delusion explores the actual diversity of our biological sex characteristics, from g******s to brains. Some people may have typically female g******s and a Y chromosome and testes, rather than ovaries. This anatomy is intermediate, not completely male and not completely female, and it occurs in nature all the time. Depending on how you choose to count, up to 6% of the population—about 20 million people in the US or 500 million worldwide—likely have sex traits that aren’t exactly male or exactly female.
As a biologist, Dr. Berkowitz worries that more people aren’t aware of this fundamental fact of human life. Nearly all of us manipulate our bodies in one way or another to make them appear more typically masculine or feminine. The only way to make sense of these apparent contradictions is that our society insists—regardless of our biology—that each body look a specific way from infancy until death. It’s a disturbingly limited view of self-expression, and Dr. Berkowitz argues that it’s worse than that: it’s unscientific.
PUBLISHERS WEEKLY
Berkowitz (Governing Behavior), a biology professor at the University of Oklahoma, delivers an accessible rebuttal to claims that biological sex is an immutable binary. Responding to recent political efforts—including a 2025 presidential executive order defining sex as either male or female—he argues that biology tells a far more complicated story. Drawing on genetics, endocrinology, and developmental biology, Berkowitz demonstrates that variation is common at nearly every level of sex differentiation. While XX (typically female) and XY (typically male) chromosome patterns predominate, atypical configurations occur regularly. Conditions such as congenital adrenal hyperplasia, for example, can produce individuals with XX chromosomes and male-appearing genitalia. Intersex people constitute as much as 6% of the population, Berkowitz explains, noting that even the most conservative estimate, 1.7%, makes them as common as redheads. He also forcefully critiques the medical double standard that permits surgeries on intersex infants while banning gender-affirming care for transgender people, arguing that such policies primarily serve to reinforce the belief in binary sex categorization. Elsewhere, he illustrates how sex classification in sports has forced athletes to get medical treatment for situations that do not constitute medical problems, which is incompatible with international human rights norms. Lucid, provocative, and grounded in science, this is a valuable overview of a contentious subject.
