Hey, uh, where did you hear that the number of genders has been scientifically proven? Do you mean sex? Which, btw, while in humans there are only two normally occurring genders, weird quirks of genetics and developmental problems can create people who are "intersex" and thus aren't either sex. Meaning scientifically, there are more than two sexes, albeit all but two being very rare.

Getting back to gender, it's a social construct, it's the roles in society we've assigned to members of different biological sexes. The idea being that even if someone is biologically male, they identify more socially with female, or vice versa. So this person has male sex but female gender. There are also people that don't identify as either. Usually these people prefer to be called "nonbinary." I have a few friends like this, and they don't identify as "a cucumber, mayonnaise, apache helicopter" or whatever. (Nobody identifies as that. It's a strawman made to make transgender people seem ridiculous, kind of like how people were saying if we let gays marry then people will marry dogs next.) These people usually prefer having nonbinary pronouns, such as them/their or xi/xir rather than he/him or she/her. By making these shitty transgender jokes you're delegitimizing a very real issue of body dismorphia that has been proven by science. Look it up, people that are transgender have brain chemistry and activity that matches their preferred gender, not their biological sex.