I'm currently half-way through Ann Leckie's novel Provenance, and am finding myself really confused by the pronouns and sexes. Can anyone explain what's going on? I'm getting the impression that maybe there are three sexes, a male, a female, and a neuter, which I guess would require some major biological changes in Homo sapiens...? It seems like a different setup than Ancillary Justice. Are there two different divisions of humanity, the Radchaai with one sex and the rest of humanity with three? It seems like there are distinctions that are important enough to be marked with the pronouns and other vocabulary, but I can't figure out what those distinctions would be. Are the pronouns like "e" and "eir" for a neuter gender? What is a "neman" or a "nuncle?" Do people choose their sexual identity when they become adults? If so, is this a physical (surgical?) choice, or just some kind of choice of what clothes to wear? Is the linguistic stuff just something about the culture of the protagonist, or is it language being used to describe some set of biological or social facts that are present in other cultures as well?
Related: Is everyone really female in Ancillary Justice or is the ancillary just unable to tell?