3 ideas
After famine, overpopulation and war, a world council adopts 'Solution Three': it reproduces humanity largely from clones of one Black man and one white woman, chosen for intelligence and lack of aggression. Ordinary women gestate and raise the clone embryos, and heterosexual reproduction is pushed to the margins. The novel follows how the clones begin to differ from one another and how the planned order starts to fray.
In this society homosexuality is the approved norm and heterosexual attraction is treated as a stigmatized deviance, because the state wants to hold down the birth rate. Reversing which sexuality counts as 'normal' shows that sexual morality can be a tool of state demographic goals rather than a natural fact. It also shows that the mechanics of stigma, secrecy and shame work the same way whichever group is the target.
The regime relies on uniform, engineered crops and a genetically narrow human population. This removes the variation a system needs to survive shocks, so a single blight or unforeseen stress can threaten everything at once. Diversity, including the 'deviant' heterosexual reproduction the state suppresses, turns out to be the hidden reserve the system needs to recover.