It doesn’t happen a lot. About 1% of people are born with traits that signal that they may have been born hermaphrodite but that’s only traits the number of people born truely hermaphrodite with both male and female genitals is far less than that around 0.1% of people. Plus you’re saying there’s 4 genders based of only 2 genders genitals so you can either be a male female or a mixture of both still admitting there’s only 2 and any other genders are some mixture of the 2?! Anyway that’s not a very good argument. I could say 1-2% of people are born with missing arms/legs/fingers/toes but isn’t it still a fact that people born healthy have 2 arms 2 legs 5 fingers and 5 toes.