The Binary Delusion: How Biology Defies the Myth of Two Sexes

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 genitals to brains. Some people may have typically female genitals 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.

Author: Ari Berkowitz
Publisher: Beacon Press
Published: 08/18/2026
Pages: 200
Binding Type: Hardcover
Weight: 0.95lbs
Size: 9.20h x 6.20w x 0.90d
ISBN: 9780807023402


Review Citation(s):
Publishers Weekly 06/01/2026

About the Author
Ari Berkowitz, Ph.D., is a Presidential Professor of Biology and Director of the Cellular & Behavioral Neurobiology Graduate Program at the University of Oklahoma. He is author of Governing Behavior: How Nerve Cell Dictatorships and Democracies Control Everything We Do.