The Green Millennium by Fritz Leiber

Phil's first impulse was to jump out of the jeep and hunt around. But the chill in his heart told him Lucky was farther away than that. Besides, the place was a regular jungle and one man could hunt through it forever for anything cat-size.

He did not recognize the square at all, but he guessed from the schoolgirls that he was in an intellectual residential neighborhood. At first he thought the school was one for girls, but then he noticed a few lone boys among the homeward-bound students and decided that most of the families in this area must be deliberately having as many girls as possible. When sex-determination had become possible through centrifuging human sperm to separate the male-producing and female-producing types, most parents decided to have sons, especially for their firstborn. They often told themselves they would have daughters later, but unfortunately small families were the rule. The resulting over-production of males had led to some ineffectual state laws forbidding sex-determination, an unsuccessful attempt at self-regulation by the medical profession, a lot of talk in Congress, and an almost fanatically determined movement among a class of thoughtful people to produce only daughters.