the ones who failed, biology, history, logic and sociology seems to be you losers. prove anything i've said to be false with some documents. you both are just looking foolish with irrational ad hominem fallacy remarks like that.
Burden of proof is on the one making the extraordinary claims, but since you already rejected that, fine, let's deal with the worst of your "facts".
the only thing binary about human sexuality is what kind of gamete is produced by one's gonads. beyond that, there is too much variation, both physically and psychologically, to label everybody male or female. historically, cultures have recognized at least three sexes, male, female and intersex, and transgender people. The consensus among medical authorities today describe agender and bigender people as well.
I'm not even going to touch the linguistic slight of hand you clumsily tried to do with your "cultures" reference, because I don't need to. Let us cut right to the core of it: when you say, paraphrasing, that "there is too much variation (in genetic expression and mental condition) to label everyone as one of two sexes", you might as well be saying "there is too much variation in digit configuration to say that humans have five fingers on each hand." Or insert any number of other traits - two arms, two legs, no tail, no fur, etc. Yes, there are rare genetic defects that can cause aberrations in all of those statements, but they are exactly that...
aberrations, cause by
a defect. The same is true of the smattering of genetic conditions that get collectively lumped into "intersex". They are
defects in the normal expression, they are not an alternate state of the human condition. Almost all of them come with other defects - mental retardation, physical handicaps, sterility, or some combination of those, normally. Or else they are
so subtle that they don't even express, and people live their entire life without knowing they have them, unless they happen to get a genetic workup done.
Intersex people aren't a different gender - they're the human equivalent of a screwed up fast food order.