Overall good post, I have a few discussion elements.
This post is just a summary of a shitload of articles that I have read over the past few days. Sorry, I don't have links so if you are interested, I suggest that you do your own DD.
First of all, yes there is evidence for both transgender ( not that I ever denied that ) and non binary gender. In the case of trans, a trans female has the same brain patterns as a female, while having the body parts of a male, and vice versa for a trans male.
There is just as much evidence for gendered brains as there is for black people having lower IQs than white people. Which means: oh, sure, the reasearch is out there, but it's not very good research, and it tends to be refuted by neurologists.
Neurosexism: the myth that men and women have different brains
That said, our brains are
sexed. At a fundamental level, the cells in our brains are based on either male (XY) or female (XX) genetics. More nuanced, our brains are subjected to different hormone combinations. Our pituitary gland sends slightly different signals in females than in males. Male brains are exposed to considerably higher levels of testosterone, and female brains are exposed to considerably higher level of estradiol. Both of those hormones drive behavioral patterns. The hormones activate parts of the brain that are correlated with sex-differentiated behaviors, such as being maternal or being aggressive. If a male brain is exposed to estrogen, the parts of the brain associated with maternal behavior are activated, and the emotional responses tied to empathy are amplified. If a female brain is exposed to testosterone, the parts of the brain associated with aggression are activated, and the emotional responses tied to defensiveness are amplified.
There is no fundamental difference between the brain of a cisgender male and a transgender identified male
prior to the application of estrogen. The differences are solely a result of exogenous hormone exposure.
There are also differences as a result of plasticity. Our brains are conditioned throughout our lives, and that conditioning affects our behaviors to a degree. Little girls are taught and learn "how to be a girl" in a social sense. Little boys are indoctrinated into "how to be a boy" socially. That behavioral conditioning alters our thought patterns. As children (and even as adults), we're all subjected to classical, operant, and observational conditioning. As a result, in a society with strict behavioral and role division on the basis of sex, there will be observable differences in the cognitive patterns between males and females.
There are also, btw, functionally observable differences between homosexual and heterosexual people. There's an area of the brain that is responsible for sexual responses, and that area is activated on the basis of sex. We can actually observe the brain responding to sexual signals from males in homosexual men, and vice versa for homosexual women.
At the end of the day, there are no material differences between members of the same sex on the basis of their gender identity. All observed differences are either 1) so minute as to be completely meaningless or 2) the result of exogenous hormone exposure or 3) potentially the result of neural plasticity.
As far as non binary folks go, there are some people who are born with an XX XY chromosome combination instead of XX or XY. The assumption here is that such individuals may not adhere to one gender. However, the percent of people with this pattern is believed to be about .4%, which makes it very rare.
This chromosomal make-up is reflective of a disorder of sexual development, not with a nonbinary gender identity. The overwhelming majority of people with DSDs (also colloquially referred to as Intersex) are not transgender or nonbinary, they are in alignment with their physical sex. Similarly, the overwhelming majority of people who identify as trangender or nonbinary do not have a DSD condition at all.
Then I read at least one article that suggested that we are all somewhat non binary since there aren't really any strictly male or female qualities, and gender isn't about physical sex parts. Girls are not naturally drawn to pink and boys to blue. That's just cultural, just like more important myths like boys are better at math and science compared to girls. So, maybe we are all a little bit non binary, at least in the cultural sense.
That's the view held by most classical feminists, including me. For all intents, I completely qualify as nonbinary, and from her description, so does Toni. I'd guess that most humans would be considered nonbinary under that view of gender. Most also, however, hold that pronouns, intimate spaces, sports, prisons, etc. are divided on the basis of sex, not the basis of gender. Which is where a bit of the conflict comes into play.
Some people believe that sex doesn't matter and is completely irrelevant. As a woman who has been the victim of sexual assault and attempted rape... I rather strongly disagree.