It’s really fascinating stuff, and way more complex than they teach us in school. Hopefully, this is changing though. With how important survival is to evolution and how prevalent this stuff seems to be, I can’t imagine that there isn’t some reason that a species would have so many variations. I wonder how common it is for other species to have variations that aren’t simply the xx and xy equivalent in nature. I wonder if it is possible for there to be a 3rd chromosome type in any other species. It’s so cool that this is all something that is getting more and more awareness.