*You mention karyotype, genes, hormone production, and hormone response, and then suggest that all of these somehow blur the boundaries of biological sex. In reality, sex is a binary developmental pathway, rooted in genetics and organised by tightly regulated embryonic processes. Humans start with bipotential gonads and both Müllerian and Wolffian duct systems. At around week 7 of gestation, the presence or absence of the SRY gene on the Y chromosome initiates either male or female development.
If SRY is present, it activates genes like SOX9, triggering testis development. The testes then produce Anti-Müllerian Hormone (AMH) to regress the Müllerian ducts and testosterone to stabilize the Wolffian ducts, forming male internal structures. If SRY is absent (in an XX embryo), the gonads develop into ovaries by default, the Müllerian ducts persist, and the Wolffian system regressesed.*
Sort of, but actually not quite - especially the second parag.
You also falsely imply that hormone balances and the body’s response to them drive gonadal development. That’s completely backwards! Gonadal development is driven by genetic signals, and the hormones come afterward. Testes or ovaries produce the hormones, not the other way around. Mutations that alter hormone receptors (like in CAIS or 5-alpha reductase deficiency) do affect the external phenotype, but they are disorders of sexual development within a binary system, not evidence of a third (or fourth/fifth/sixth) sex.
By gonadal development I was referring to the reproductive system at large. This development is driven by hormones. Specifically, the development of the testes and ovaries, along with the development of internal and external genitalia, is largely controlled by hormones produced by the developing gonads themselves, as well as hormones secreted by the pituitary gland.
Your reference to the brain and psychosexual development is a red herring. Yes, sex hormones affect some sexually dimorphic brain regions, particularly in utero. But these effects are statistical— not categorical — and are modulated heavily by neuroplasticity and environment.
Yes.
Brain imaging studies don’t support the idea of a “trans brain”
I'm not saying that there is anything as simple as the 'trans brain', don't be silly. But there are studies that have show differences in various measures in brains of trans people compared to cisgender controls. Obviously as with any area of science relating to understanding the complex, adaptive systems of the brain and cognition, our understanding is in its infancy.
and certainly don’t overturn the definition of biological sex.
Ideological and meaningless statement.
Got to run but can respond to the rest later.