“They were cruel,” says Kevin, who witnessed his sister’s humiliation at school. “Teased every day. It wasn’t a weekly thing. Or a monthly thing. This was a daily thing. They’d call her names, ignore her, not involve her in the groups.”

“It started the first day of kindergarten,” Linda says. “Even the teacher didn’t accept her. The teachers knew there was something different.”

By then, Joan also knew that there was “something different” about her. But she didn’t know what. “You know generally what a girl is like,” John says, “and you know generally what a guy is like. And everyone is telling you that you’re a girl. But you say to yourself, ‘I don’t feel like a girl.’ You think girls are supposed to be delicate and like girl things – tea parties, things like that. But I like to do guy stuff. It doesn’t match. So you figure, ‘Well, there’s something wrong here. If I’m supposed to be like this girl over here but I’m acting like this guy, I guess I gotta be an it.’ ”

Joan’s personal difficulties were obvious in her functioning in the classroom. Though tests had revealed her to be in the normal intelligence range, she seemed unable, or unwilling, to master the skills required in kindergarten. When the school threatened to hold Joan back, Linda complained to Dr. Money. He wrote a letter to the school, urging that Joan, despite her emotional difficulties, be promoted to first grade. But her problems only got worse. On Oct. 29, 1971, a few weeks after she started first grade, her behavior prompted a teacher to file a report with the district’s Child Guidance Clinic. The teacher noted that Joan “has been doing just the opposite of anything the other children do” and described the girl as “very negativistic.”

It was at a December 1972 meeting of the American Association for the Advancement of Science in Washington, D.C. that John Money unveiled, for the first time, his “twins case.” Time magazine ran a full-page story on the debut, which happened to coincide, that same week, with the release of Money’s book Man Woman, Boy Girl. Co-authored with his colleague Dr. Anke Ehrhardt, the book contained his first written account of the extraordinary twins case.

Man Woman, Boy Girl made mention of Joan’s “tomboyish traits” in passing but focused on the ways in which she conformed to the stereotypes of female behavior – examples of which were culled from Linda’s hopeful cataloging, over the years, of Joan’s fitful attempts to act more like a girl. “One thing that really amazes me is that she is so feminine,” Linda is quoted as saying. “I’ve never seen a little girl so neat and tidy as she can be when she wants to be.” No mention was made of the problems Joan had been having in school.

Indeed, the account portrayed the experiment as an unqualified success - a conclusion bolstered by what Money pointed out was an “extreme unusualness” to the case. He was referring, of course, to the existence of the identical male twin, whose interest in “cars and gas pumps and tools” was contrasted to his sister’s interest in “dolls, a doll house and a doll carriage” – a sharp division of tastes along gender lines that seemed to provide compelling evidence that boys and girls are made, not born. The significance of the case to the then-burgeoning women’s movement was obvious, since feminists had been arguing against a biological basis for sex differences for years. Indeed, Money’s own papers from the 1950’s on the total psychosexual flexibility of newborns were cited by Kate Millett in her best-selling, seminal 1970 feminist text, Sexual Politics. Money’s new twins case buttressed the feminist claim that the observable differences in the tastes, attitudes and behaviors of men and women are attributable solely to cultural expectations.

“This dramatic case,” Time duly reported in its Jan. 8, 1973, edition, “provides strong support for a major contention of women’s liberationists: that conventional patterns of masculine and feminine behavior can be altered. It also casts doubt on the theory that major sexual differences, psychological as well as anatomical, are immutably set by the genes at conception.” The New York Times Book Review hailed Man Woman Boy Girl as “the most important volume in the social sciences to appear since the Kinsey reports” and praised Money for producing “real answers to that ancient question: Is it heredity or environment?” But it was on the pediatric wards of hospitals around the world that the twins case would have its most lasting impact.

“It was the hallmark case,” says Dr. William Reiner a child psychologist at Johns Hopkins. “It was the hallmark because it was followed and written up a number of times by Money and then essentially was the source of his statements – and subsequent statements in any of the pediatric textbooks in endocrinology, urology, surgery and psychology – that you can reassign the sex of a child because it’s the social situation that is the most important.” The undisputed success of the twins case legitimized the practice of infant sex reassignment globally, says Reiner. Once confined principally to Johns Hopkins, the procedure soon spread and today is performed in virtually every major country, with the possible exception of China and India. While no annual tally of infant sex reassignments has ever been made, Reiner makes a rough, “conservative” estimate that three to five cases crop up in every major American city each year – giving the U.S. alone a total of 100 to 200 sex reassignments a year. Globally, he puts the figure at perhaps 1,000 per year. In the 25 years since Money’s twins case was first published, as many as 15,000 similar sex reassignments may have been performed.