> There is a known, massively complex, relationship between sex and gender but it's not 1:1
You could argue though that it's only complex because we (collectively) decided to complicate it in order to accommodate the preferences of small subsets of society. In some other country, society might collectively decide not to accommodate said wishes and instead treat sex and gender as immutable and indistinguishable. Such a course would result in a simpler classification system: XX = female, XY = male, anything else = unclassified (genetic defect handled on a case-by-case basis).
You could argue though that it's only complex because we (collectively) decided to complicate it in order to accommodate the preferences of small subsets of society. In some other country, society might collectively decide not to accommodate said wishes and instead treat sex and gender as immutable and indistinguishable. Such a course would result in a simpler classification system: XX = female, XY = male, anything else = unclassified (genetic defect handled on a case-by-case basis).