Where Late the Sweet Birds Sang (1976) by Kate Wilhelm is an apocalyptic future where mankind's only hopes rests in cloning technology. A collection of three arcs, a triptych, the stories tell the history of this venture, where it goes right, where it goes wrong, and the implications that it makes real. The book itself is just short of hard SF, with minimal fancifulness. The book won the Hugo award and was short listed for many other awards.
The first story concerns one of the clone creators, how the world fell into ruin, the origin of the project, and how the new clone generation thinks differently from the older generation. The second story follows clones who leave the community to go exploring, and the psychological effects of being removed from all their identical brothers and sisters. The final story is that of a non-clone who grows up among the clones, and the challenges that he faces fitting in.
There's no one single explanation for the future. Weather goes wacky. Men go to war. A-bombs get dropped. Viruses get out. All of these together manage to mostly wipe out mankind. In unison, they make a grim future for the species. Its because of this that cloning becomes necessary.
With necessary comes uncomfortable moral decisions. When the species itself is hovering on the brink of extinction, what becomes justifiable? Over and over, we see those decision made, for better and worse, and the results of those decisions. In context, they make sense, yet they remain disturbing, as they ought to be. From those decisions come a new culture, and it both feels uncomfortable and makes uncomfortable decisions as well. Once you have clones, the very definition of human becomes questionable, and it's that question which comes up again and again, continuously challenging the easy answer.