What is this science fiction short story about sex determined at puberty, and three genders?

Question

I think I read this in a Gardner Dozois Anthology of Best Short Science Fiction Year X. The year would have been 2005 or earlier. The story was about a boy and a girl, about 13 years old initially. They lived in a world that was essentially the same as here, as our Earth. Reproduction was quite different though, and that is the beginning of what I don't understand.

Men and women can't reproduce without the assistance of an "uncle" as this third sex is called. Adult men and adult women look like adult men and women in our world. The third sex is an overweight, sexually ambiguous person who the boy, the protagonist, describes as smelling yeasty. He occasionally sees his family's 'uncle' or de facto sex facilitator, visit the family. One time he catches a glimpse of his parents during a visit. The father is standing behind the uncle and the mother is in front. It isn't just his family who is like this. Everyone's is.

At puberty, it is determined whether one becomes male, female, or an uncle. I don't know if this happens naturally, or if it is facilitated in some unspecified way that I didn't pick up on. The boy and the girl are good friends and talk a lot. As they transition through what seems like human puberty, they kiss, and are sexually intimate. They are worried about anyone finding out that they're having sex, but not because they are too young, or fearful of getting pregnant. Rather, sex is not supposed to be like that, and should only be with uncles.

The normal age when children go through the process of puberty that determines which of the three genders they will be is at about 14. The boy still hasn't had this happen yet by the time he is 16. The girl is a year younger, at 15. They are puzzled why the boy hasn't gone through whatever this mysterious gender transition is yet. One day after they have sex as usual in their hideaway, something happens, and the boy wakes up in the hospital. The girl visits him, and tells him that he nearly died. Surgical intervention was necessary for him to go through puberty. He can no longer have sex like he did before, and by the end of the story, the girl has become an 'uncle'.

The story has a 1950s era feel to it, of family life and suburbia, and is tinged with melancholy.

What is the name of this short story?

Answer 1

This story is almost certainly "Grownups" by Ian R. Macleod. It was first published in Asimov's in 1992, and later appeared in Gardner Dozois' "The Year's Best Science Fiction: Tenth Annual Collection" in 1993. It can be read at the Baen website.

A summary gives these details:

All children are born as girls or boys, and go through normal female or male puberty; but around age 15 most of them will suddenly “grow up” through a process in which “the male’s testicles and scrotal sac contracted back inside the body, hauled up on some fleshy block and tackle […] the female’s ovaries made their peristaltic voyage along the fallopian tubes to nestle down in the useless womb, close to the equally useless cervix”. A minority of children (female and male) will instead undergo gradual metamorphosis into the third gender, “uncles”. Uncles apparently look more or less like adult men but have large bellies and breasts. They carry the babies conceived through three-way intercourse with a woman and a man, and give birth through openings that form in their bellies.

The growing up process, passing from child to adult, is a rapid change, and appears somewhat dangerous to the children. The story deals with two children, Bobby and May, and May's older brother died during the process. Usually a doctor is in attendance and considerable bleeding is involved.

From about the age of 10 children are given a special milk drink that they call "bitter milk". Its function is gradually revealed during the course of the story, and it seems to act to bring on the growing-up process. May and Bobby rebel against taking it, and secretly pour it down the drain and replace it with a mixture of milk, vinegar, flour, and lemon juice which has a similar consistency and taste. As a result they are the last in their cohort to undergo the change, and it has medical complications for them. As the OP recalled, Bobby had to be taken to hospital and almost died during the process, and May also experienced complications and became an uncle.