Gender identity, which applies of course to transpeople as well as others all over the sexuality spectrum.
This is an interesting article which raises several interesting points, not the least of which is that most of our primate social structures evolved or developed over 100,000 yrs or so of hunter gatherer existence. If, say, western male domination or western religion developed as a "reaction" to earlier matricentral organizing principles (and, certainly, there's a good body of evidence to support the idea that the earliest religions were faily uniformly goddess-centric) then it's worth considering that, as well, many of these structures were outgrowths of early civilization, primitive agriculture, modes of existence that are themselves outdated in today's interconnected, post industrial information age.
My point is that, in my opinion, changes to the human animal's circumstances have always led to dislocations, big and small, to our way of relating and existing with each other. The changes, now, are coming at a breakneck pace. Our social structures have not caught up.