Nothing in biology is really binary anyways. Male and female are just useful groupings because we’re a sexually dimorphic species, but as with anything in nature, that’s mostly a spectrum anyways, with strong representations at the anchoring ends.
Why say it's limited to biology? Even the binary logic in your computer can sometimes get stuck in a metastable state that's neither a 1 nor a 0. It's fundamentally impossible to completely prevent because of how physics works.
I mean having an X or Y are pretty damn binary. DNA strand has binary pairs (A-T, C-G). The resulting codons have anitcodon pairs. Then within biological functions you have the parasympathetic system vs the parasympathetic system which do opposite things across the whole body, pro vs anti inflmmatory agents, activators vs inhibitors nearly on every level of biology.
Its actually rather astounding how much binary pairs play a role from the very core of physics.
Gametes are binary - functional gametes in anisogamous species are either egg or sperm.
On the other hand, the XX vs XY karotype (chromosome set) is just very strongly correlated with sex.
The master switch for sex determination in humans (and most mammals) is the SRY gene, usually found on the Y chromosome. Its presence or absence determines whether a developing embryo takes the path towards producing sperm or producing eggs.
SRY can migrate to the X chromosome (resulting in males with an XX karotype) or can be broken by mutation (resulting in females with a XY karotype, usually infertile because other stages of development of the reproductive system depend on having two X chromosomes).
Having and X or Y (or even multiple of each, as some people do, XXY and XYY are real, even single X or Y too) is binary, what's not binary is how it doesn't perfectly correlate with the sex (not even getting into gender here) that the person in question belongs to.
Sure what I was responding to is "Nothing in biology is really binary anyways". Certainly not everything is binary, we don't have two simple models of all people despite nucleotides having binary pairs, but there is a lot of damn binary in biology.
XXY and XYY and whatnot are all variations within a sex. Sex is defined by gamete size, females produce the larger gametes and males produce the smaller gametes. In humans, this is binary and immutable.
