SF & Fantasy novels dealing with gender/sexual identity

In a parallel world in which Neanderthals, rather than homo sapiens, became the dominant intelligent species, a dangerous scientific experiment traps a Neanderthal physicist on Earth. ...

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The capstone and crowning achievement of the Future History series, from the New York Times bestselling Grand Master of Science Fiction... Time Enough for Love follows Lazarus Long through a vast and magnificent timescape of centuries and worlds. Heinlein's longest and most ambitious work, it is the story of a man so in love with Life that he refused to stop living it; and so in love with Time that he became his own ancestor. ...

The moon colony, Luna, is a virtual paradise where every need is provided for: food, prolonged lifespans, digital memories, and instant sex-changes. But the pointlessness of this easy life is making the inhabitants suicidal--including the central computer that monitors their existence. As humanity teeters on the edge of self-destruction, newspaper reporter Hildy Johnson sets out to find a new frontier. ...

When a mysterious genetic crisis threatens the existence of Athos, a planet forbidden to women, obstetrician Ethan Urquhart is forced into an alliance with Elli Quinn, a gorgeous female secret agent, to save his world. ...