Conservative arguments tend to treat biological sex as a clean binary. Progressive arguments tend to treat it as almost infinitely fluid. Both are simplifications, and the actual developmental biology is more interesting, and more useful, than either one. Dr. Votaw-Freer, who is intersex, walks through it in Gender Centered using a framework drawn from developmental biology: six axes, not one switch.
There are two sexes, male and female, and the overwhelming majority of people develop cleanly into one or the other. But "male" and "female" aren't single facts decided at a single moment. They're the alignment of at least six distinct developmental processes, each running on its own timeline in the womb, each with its own opportunity to diverge from the rest:
In most people, all six axes line up. But because each one runs on its own schedule and responds to its own hormonal conditions, they don't always have to. When they don't, the result isn't a glitch. It's a different, well-documented way a human body can develop.
A rule with well-understood exceptions isn't a broken rule. It's a tendency, and human sex is a powerful, durable tendency with edges worth understanding rather than denying.
In an isolated region of the Dominican Republic, a genetic condition called 5-alpha reductase deficiency produces children who are chromosomally, gonadally, and hormonally male, but whose external genitalia initially develop along a female-appearing path because their bodies can't convert testosterone into the form needed to masculinize the genitals in the first trimester. At puberty, a second testosterone surge does what the first missed, and most of these children, raised as girls for a decade, go on to live as men. The condition was first described in a 1974 study in Science by endocrinologist Julianne Imperato-McGinley and colleagues.1 Five of six axes were male the entire time. Only the one axis most people use to assign sex at birth was, temporarily, out of step.
More broadly, intersex conditions, variations in chromosomes, hormones, or anatomy that don't follow the typical male or female pattern, are far more common than most people assume. A frequently cited 2000 review in the American Journal of Human Biology estimated that deviations from strictly "textbook" male or female development may occur in as much as 1–2% of births, though estimates vary widely depending on definition, and narrower definitions used by other researchers put the figure far lower.2 Most people with an intersex condition live their entire lives without ever having their chromosomes tested, which means the true rate is genuinely uncertain, and likely under-recorded either way.
It means the conservative claim that biological sex is a simple, exception-free binary doesn't survive contact with developmental biology. It also means the progressive claim that biology is so variable it can't ground meaningful categories overstates the case in the other direction. Two sexes remain the two poles nearly everyone develops toward. What isn't durable is the assumption that a glance at external anatomy in a delivery room reliably captures all six axes underneath it.
The book goes deeper into brain research, prenatal hormones, and what it means to live in a body that didn't read the script.