[nl]

And of course it gets even more complex when you consider how things like hormonal changes (either natural or unnatural) effect gender.

Also there seem to be other factors which aren't understood yet:

The researchers identified a region of the hypothalamus, known as the bed nucleus of the stria terminalis (BSTc), as being responsible for sexual behaviour. This area is always larger in men than women. However, in their study of six MTF GID sufferers, a female‐sized BSTc was present in all subjects. Additionally, the size of the BSTc was not influenced by taking sex hormones in adulthood. This implies that these individuals had a powerful biological force compelling them to be female, rather than just a psychological conviction.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600127/

But.. I guess yelling "SJW" is much easier, or something.