I am currently reading a book called "The Gene - An Intimate History" by Siddhartha Mukherjee. In the book, he has a short section on the genetics of sex and gender identity, and I wanted to share what he says to hear your thoughts.
First, he presents the cases of Swyer Syndrome, where people have XY chromosomes, but present and almost always report a female gender identity. He also presents the famous case of David Reimer, who was brought up as a girl after a botched surgery, realised he was male, changed gender, and eventually killed himself.
He brings these cases to make the point that gender identity in both cases does seem to be some fixed characteristic, that it is not necessarily aligned with our genetics or with how we are externally treated. I certainly know in the Reimer case that there were a great many other compounding factors that affected the poor man, and contributed to his suicide.
He then goes on to make the point that despite the binary nature of sex (XY/XX), or more accurately, the gene(s) in a particular region of the X chromosome (SRY gene region), that there is a mechanism for trans people. What he argues is that while there may be a master gene that turns male sex and female sex on and off, there can be a cascade of genes that create what we are debating as gender identity. I'm explaining it poorly, but as a gender critical person, it does give some pause.
Quoting from an article
"Mukherjee compares the master regulator to an army commander. At top of the hierarchy is gender anatomy; countless variations exist downstream in the composition of the army, each with slightly different components. You might have male identity with differing sexual attractions, or you might have differing aspects of male identity. He continues, The way that these genes—this genetic information percolates down into the individual, the way this hierarchy percolates down into an individual might be very different from one person to another and therefore create the kind of infinite ripples or variations in human identity that we experience in human life."
bigthink.com/21st-century-spirituality/can-transgenderism-be-explained-with-genetics
I just wondered if you'd come across this, and what you thought of it.