Nearly all people born in the developed world are assigned a sex at birth and it almost never has anything to do with their individual genetic profile (as that is almost never tested at birth). The only criterion used to determine the sex to be placed on someone’s birth certificate for 99% of individuals is whether they have a vagina or a penis.
The point
@SkyBlueFlux was making is that sex (and, by extension, the entirely social construct of “gender”) is far more complex than that, with people who possess vaginas and/or penises exhibiting collections of characteristics (genetic in origin or otherwise) that do not neatly fit in to either societies normally narrow “male” or “female” constructs, or the very limited and simplistic nature of sex and gender that most have been taught in school (which itself causes many of the problems already discussed in the thread).
FWIW, there are 6 “common” sex karyotypes, with many more less common ones based on permutational possession of X and Y chromosomes, with scientists still debating whether it is accurate to define humans as only have two sexes based on possession of XY or XX combinations.
I think this is an interesting primer on the debate for anyone interested.
Biologists now think there is a larger spectrum than just binary female and male
www.scientificamerican.com