The Left Hand of Darkness by Ursula K Le GuinRead about another entry on the list.
This book removes something so basic that we take it for granted: gender. The people on the planet of Gethen have no day-to-day gender. They go through phases during which they develop sexual organs and a sexual appetite, but they can impregnate a partner during one session, be impregnated the next, and not have any gender in between. Genly Ai is acting as an ambassador to Gethen from a federation of planets, and hopes that Gethen will join the fold.
Filming this means that not only do we need actors who have no visible gender, despite having many different body types, we need creators who can make a story in which the very concept of fixed gender is something that doesn’t even register as part of their experience. They will need to not only convince themselves of the absence of gender, but the audience as well, which probably means that high-profile actors probably shouldn’t be cast. A weird, high-concept fantasy world about interplanetary diplomacy with no stars to headline it? Impossible. But potentially amazing.
The Left Hand of Darkness is among Jeff Somers's top five sci-fi novels that explore gender in unexpected and challenging ways, Joel Cunningham's top twelve books with the most irresistible titles, Damien Walter's top five science fiction novels for people who hate sci-fi and Ian Marchant's top 10 books of the night. Charlie Jane Anders included it on her list of ten science fiction novels that will never be movies.