A better analogy for the author’s clarification would be “Red and blue, each with a continuum of variation in hue”. There’s still no purple, just different shades of red and different shades of blue. I don’t really have more to add beyond pointing out that this is the author of the paper directly clarifying that point.

You’re free to invent whatever categories you find useful of course. But biologists will continue to recognize human sex as binary, because that is a useful description of the reality they encounter.

People’s bodies are still organized around the production of either sperm or ova, even if they’re unable to reproduce due to a developmental issue. You can call that a third category if it’s useful to you, but that doesn’t form a third sex as understood by biologists.

Intersex is a confusing term, and doesn’t dispute the binary. People are still male or female, with https://en.wikipedia.org/wiki/Disorders_of_sex_development

From the author of that paper:

https://xcancel.com/ClaireAinsworth/status/888365994577735680

In your piece ‘Sex Redefined’ are you making the claim there are more than 2 sexes?

No, not at all. Two sexes, with a continuum of variation in anatomy/physiology.

Do you have a particular edge case in mind? One that’s commonly brought up is https://en.wikipedia.org/wiki/Ovotesticular_syndrome, but that doesn’t fall outside the sex binary. Having a bit of nonfunctional tissue doesn’t affect one’s sex.

Colors aren’t a great analogy either, because in anisogamous species, gametes are strictly binary. There’s sperm and ova, with 0 overlap and 0 other options. “Purple gametes” just don’t exist.

This also isn’t my opinion, this is the accepted definition in the field of biology.

This is often a point of confusion, but human sex is binary. There’s edge cases that require clarification as to how they fit into the binary, but don’t disprove it.

Human sexuality overall is complex and that’s why we differentiate gender from sex. The sex binary and gender spectrum complement each other though, and don’t clash.

If you’re interested in learning more, here’s some background reading:

https://en.wikipedia.org/wiki/Gonochorism

We fall into that category, where we have two body plans, each organized around producing either sperm or ova. Other species have more body plans, such as recognizably distinct males, females, and hermaphrodites:

https://en.wikipedia.org/wiki/Trioecy

Those species are a good contrast. Humans don’t have that variation, and so sex is binary in humans.

There’s literature that explains this specifically in detail, though most of it doesn’t really explicitly talk about it, much like math papers don’t generally explain that integers can be added together.

Male seahorse get pregnant, but that doesn’t make them trans, they’re unambiguously male. This is a great example of why sex is defined by gamete size. If it weren’t, we couldn’t talk about males and females in any useful way across the animal kingdom.

Clownfish would be a better example as they’re sequential hermaphrodites, but that doesn’t have any bearing on the human sex binary.

Why should chess and darts be treated differently? There’s evidence that males have an advantage in darts:

https://www.mdx.ac.uk/news/2023/2/linda-duffy-darts-psychology/

Given how many sports that males have an advantage in, it certainly seems reasonable to have sex-based competitions as the default.

AI art isn’t theft, so the rest of your question falls apart.

In regards to sharing art, it’s trying to fight technological progress and it’s bound to lose. Copyright is dead and that’s a good thing. We shouldn’t simp for legal systems pushed by and that benefit large corporations over creators.