Dr. Mel Grumbach, a pediatric endocrinologist at the University of California, San Francisco, and a world authority on the subject, confirms that the findings detailed in Money’s twins case were the decisive factor in the widespread acceptance of the practice. “”Doctors] were very influenced by the twin experience.” he says. “John Money stood up at a conference and said, ‘I’ve got these two twins, and one of them is now a girl, and the other is a boy.’ They were saying they took this normal boy and changed him over to a girl. That’s powerful. That’s really powerful. I mean, what is your response to that? This case was used to reinforce the fact that you can really do anything. You can take a normal XY male and convert it into a female in the neonatal period and it won’t make any difference.” Grumbach adds, “John Money is a major figure, and what he says gets handed down and accepted as gospel by some.”

But not all. In the seven years since he had first published his challenge to Money, Mickey Diamond, who had been hired as a biology professor at the University of Hawaii, continued his laboratory research into how the sexual nervous system is organized before birth. His studies had further convinced him that neither intersexes nor normal children are born psychosexually undifferentiated – a conviction that made him view with alarm the expanding practice of infant sex reassignment. And he was more convinced than ever that converting a non-intersexual infant from one sex to the other would be impossible. “But I didn’t have any proof at the time,” Diamond says. “I didn’t have anything except a theoretical argument to challenge the case.”

Diamond vowed to follow the case of the sex-changed twin closely – a decision, he says, that was affected by purely scientific motives. But if, by now, Diamond also felt a degree of personal involvement in his dispute with Money, that was perhaps understandable: In the chapter directly following his account of the twins case in Man Woman, Boy Girl, Money lashed out at Diamond and his colleagues, characterizing their work as “instrumental in wrecking the lives of unknown numbers of hermaphroditic youngsters.”

In 1967, at the time of John’s castration, Money stipulated that he see the child once a year for counseling. The trips, which were sometimes separated by as many as 18 months, were, as Money put it in his letter to the Thiessens’ lawyer, meant to “guard against the psychological hazards” associated with growing up as a sex-reassigned child. But according to the Thiessens and to contemporaneous clinical notes, the trips to the Psychohormonal Research Unit at Johns Hopkins only exacerbated the confusion, fear and dread that Joan was already suffering.

“You get the idea something happened to you,” John says of those mysterious annual visits to the unit, “but you don’t know what – and you don’t want to know.” Kevin, who was also required on each visit to submit to sessions with Dr. Money, found the trips equally bewildering and unsettling: “For the life of me, I couldn’t understand why, out of all the kids in my class, why am I the only one going with my [sister] to Baltimore to talk to this doctor? It made us feel like we were aliens.” The twins developed a conviction that everyone, from their parents to Dr. Money and his colleagues, was keeping something from them. “There was something not adding up,” Kevin says. “We knew that at a very early age. But we didn’t make the connection. We didn’t know.”

All they did know was that from the time they were 6 years old, Dr. Money wanted to talk to them, both singly and together, about subjects that, as Joan would later complain to an outside therapist, “I can’t even talk to my mom about.”

“Dr. Money would ask me, ‘Do you ever dream of having sex with women?’ ” Kevin recalls. “He’d say, ‘Do you ever get an erection?’ And the same with Joan. ‘Do you think about this? About that?’ ”

While attempting to probe the twins’ sexual psyches, Money also tried his hand at programming Kevin’s and Joan’s respective sense of themselves as boy and girl. One of his theories of how children form their different “gender schemes” – Money’s term – was that they must understand, at an early age, the differences between male and female sex organs. Pornography, he believed, was ideal for this purpose. “Explicit sexual pictures,” he wrote in his book Sexual Signatures, “can and should be used as part of a child’s sex education”; such pictures, he said, “reinforce his or her own gender identity and gender role.”

“He would show us pictures of kids, boys and girls, with no clothes on,” Kevin says. John recalls that Dr. Money also showed them pictures of adults engaged in sexual intercourse: “He’d say to us, ‘I want to show you pictures of things that moms and dads do.’ ”

During these visits, the twins discovered that Money had two sides to his personality. “One when mom and dad weren’t around,” Kevin says, “and another when they were.” When their parents were present, they say, Money was avuncular, mild-spoken. But alone with the children, he could be irritable or worse. Especially when they defied him. The children were particularly resistant to Money’s request that they remove their clothes and inspect each other’s genitals. Though they could not know this, such inspections were central to Money’s theory of how children develop a sense of themselves as boy or girl – and thus, in Money’s mind, were crucial to the successful outcome of Joan’s sex reassignment. As Money stressed in his writings of the period: “The firmest possible foundations for gender schemes are the differences between male and female genitals and reproductive behavior, a foundation our culture strives mightily to withhold from children. All young primates explore their own and each others’ genitals . . . and that includes human children everywhere.... The only thing wrong about these activities is not to enjoy them.”