I believe the problem is never showing evidence, but that the evidence is overwhelming. I could explain the general idea and, maybe, one or two specifics. People that use the XX/XY binary argument wouldn’t be able to explain either, but it’s usually only used because it conforms to a bias. And we are only talking about humans here. Language would implode if we tried to maintain convenient binaries and still back it up with science.
I don’t know. Sports conventions are not science. When I see the history of things being banned or allowed, it doesn’t always make sense. Then we have stuff like weight categories. Anyway, that’s beside the scope of this particular discussion.