A Gift from the Culture
"A Gift from the Culture", published in 1987, is a short work of space opera, by the Scottish science fiction author Iain M. Banks. The story is an early venture into the "complex and unusual and very distant" setting of the Culture, which Banks would further develop through various of full length novels, stories, and his essay "A Few Notes on the Culture".
Single-gender world
In the Culture series of novels and stories by Iain M. Banks, humans can and do relatively easily (and reversibly) change sex.