by Leigh Hunt. This is not a new book. I read it years ago. Strangely compelling. About a planet that had 3 sexes. They seemed to die out and humans settled there. Guess what happens? Very well done.

I just re-read it and the sequel Speaking Stones. I notice that Amazon has a comment from a reader about the first book that the subject matter (unconventional gender/sexuality) might be disturbing to some readers. I think the people on this board might like it. I did.