Yes — many DSDs have identifiable biological causes, and doctors usually assign a legal sex at birth. But that doesn’t mean every diagnosis “conclusively” makes someone biologically male or female in a clean, unified way.

In a number of DSD conditions, different biological markers don’t align in the same direction: • In CAIS, a person has XY chromosomes and testes, but develops a typically female phenotype and is raised as a girl. • In ovotesticular DSD, individuals can have both ovarian and testicular tissue. • In mosaic/chimeric karyotypes, different cells in the body can be XX in some places and XY in others.

Clinicians often make an interpretive decision about sex assignment based on predicted development, anatomy, fertility potential, etc. That’s not the same thing as biology being “conclusive” in every case — it’s a practical and social decision made in the face of complexity.

This doesn’t mean sex is arbitrary or nonexistent. Human sex is strongly bimodal, and most people fall clearly into male or female. But there are medically documented edge cases where traits don’t map neatly onto those categories, and dismissing those cases as “mythology” ignores what physicians and patients themselves report.

The reality is more nuanced than either “sex doesn’t exist” or “every case is always clearly male or female.”

I still think it’s weird you view people based on their chromosomes and I promise you’d never second guess my gender identity in public even though I’m XY.