Sorry what I really meant was that "I think we're probably still figuring out the actual cause of why the rats behave the way they do"

In general I don't think it's as simple as being one way or the other, some people certainly seem to innately feel they were born into the wrong gender, and just want that set right, while there seem to be other people for whom it seems to be fluid, that want to be able to choose and change. I don't see it's much of any of the rest of our business other than we should make them welcome in society just like anyone else.

As far as it being a 'social construct' I think the whole thing that "people with XX chromosomes must be women and people with XY must be men, or alternatively people born with penises ...." is obviously a social thing - likely tied to rigorous western sex roles and trying to force people into them - other cultures have provided places for people with differing genders - Fa'afafine, Hijra etc and traditionally treated them differently than in the west ... so yes definitely a 'social construct'