There's a fair amount of variation in between the two generally recognized sexes, as well. Intersex/ambiguously gendered people are born all the time... even chromosomally speaking there are people who do not fit within XX and XY. Doctors and parents in the past have tried to force these children into one sex (and often gender role) or the other and it can have disastrous consequences.
Objection, Your Honor. He's reciting the opening to Quantum Leap.