let's say everyone had a penis and a vagina. if you get impregnated, tough luck spreading ur genes for 9 months. but what if your vagina didn't work? then you could spread genes ultra efficiency. so humans evolve to have dysfunctional vaginas, but wait! when 99% of people have dysfunctional vaginas, it's kinda better to have a working vagina. so it's split 50:50 between working vaginas and not working vaginas. now the not working vagina people evolve to be the most efficient possible, so they evolve to not have a vagina at all and have other features which help them in their role, this is a male. the people with working vaginas don't really change, they continue to have a penis and a vagina, what's the evolutionary reason for losing a penis? it doesn't disadvantage you. these are females. now, if you look at the real world, females don't have penises, they have just vaginas. therefore evolution isn't real
