Of course, we know there are brain differences between men and women but they have more to do with things like multi-tasking and spatial recognition and some men will fall more into the female spectrum and vice versa.
So, the question remains: why is 1% of the population consistently not fitting adequately into their birth sex and the gender role set out for them?
As tempting as it might be for some to dismiss this as mental illness the truth is that transgender people are as high functioning as anyone else and only suffer stigma through persecution so there is something going on that we do not comprehend yet.
It makes sense that socialization does play a role but I will point to the case of David Reimer as one which greatly negates its importance. If David (who was raised as a girl from birth) was so sure he was a boy, what was it that made him think that? No other historical case that we know of has ever given us such a clear picture that gender identity cannot be strictly about social rearing and it proved John Money wrong in his ideas. Hence to dismiss outright the idea that the brain has no gender is being a little disingenuous.
The aforementioned film leans in the direction of dismissing the idea of a gendered brain but I wouldn’t be so sure about that.
How convenient then for the producers that this pivotal case was left out of the documentary.