https://xcancel.com/zaelefty/status/1706048337764327460
We do not all start out as females in the womb.
We all begin as males or females depending on our genetic profile, which determines the sex development path we will take. While we do all begin phenotypically indifferent (undifferentiated), this does not mean we’re all female from the beginning.
In the embryo, the gonads begin bipotential (they differentiate into testes or ovaries based on genetic triggers), and the fetus has the primordial genital ducts of both sexes before one is regressed and the other differentiates more and stabilizes.
People often assume that “undifferentiated” = female, but developing as a female is an active, gene-directed process that requires a specific path of differentiation.
Before any of this differentiation occurs, the sex of embryos cannot be identified by observation, even though their sex can be ascertained by using a marker, their sex chromosomes (and if we need more precise info, their genetic profile).
References:
[1] Rey et al. Sexual Differentiation. In: EndoText.
[2] Leon, N., Reyes, A., Harley, V. (2019). Differences of sex development: the road to diagnosis. Lancet Diabetes Endocrinology.
But what if I wanted to start out female because they are fundamentally cooler than me?
Having experienced the scalding hot water my wife showers comfortably in, they might just be objectively “cooler”, lol.