Can you explain further? I’m a biochemist / medical lab scientist, and between my studies in genetics, human sexuality, and endocrinology, it seems pretty well figured out. Between “normal” X/Y chromosomes, various chromosomal abnormalities (X, XXX, XXY, XYY, etc), and mutations like androgen insensitivity syndrome it seems there is significant causal data. Not sure if they’ve studied these with knockout mice but it’s well beyond inference at this point.

I’m not sealioning here, it has been like a decade since I was actively learning this stuff and I’m sure there have been more discoveries. In general though it seems like we know the genetics, we know the hormones and receptors involved, the developmental process and various maladies are known, etc.