[deepnotderp]

There is a spectrum of gender, it's just that 99.99%+ of the population fits into male or female, that doesn't mean that the other combinations don't exist however. And of course there are more combinations than XY and XX, that's been known since like the 1950s! They're rare, but not absent. Transgender is more complicated, but there are initial signs (difference in diffusibility of brain matter in mri scans and effect of fetal testosterone levels) that there are biological reasons involved there as well. In the animal world, there are freemartins that are similar.

[lawless123]

My mind was changed on this. I used to believe it was simple, you're XX or you're XY. Even two people with the same genes could be quite different if those genes are expressed differently.

[deepnotderp]

Exactly, i used to be of the same mindset, turns out biology isn't that simple.