[wideminded]

How about we just check your chromosomes? If you are XX, you're female. if you are XY, you are male.

It's pretty rare but there are some medical conditions where an XY individual is to all outward appearances a normal or even a very attractive woman, to the extent that even a doctor would not know anything was wrong until they ran some tests.

[DiogenesLamp]

It's pretty rare but there are some medical conditions where an XY individual is to all outward appearances a normal or even a very attractive woman, to the extent that even a doctor would not know anything was wrong until they ran some tests.

For exceptional conditions, an exceptional standard can be used. For the other 99.9% of the population, the X-Y chromosome thing works.