This is not tricky. We have evolved two body plans. That is all. Sometimes things go wrong with a person and they are infertile. They still have one or other of those body plans. That is how a doctor knows whether to look at (say) sperm quality, or ovulation problems.
You have yet again failed to account for people who do not develop any gonads or people who develop both.
Well no, we've evolved a great many body 'plans', and we broadly group observed forms into two categories. This is why I described your notion as intelligent design. There are no plans, only commonly observed forms.