When the Greeks were gathering forces for their expedition against Troy, Achilles, their greatest warrior, failed to answer the call, so Odysseus was sent off to Thessaly to fetch him. When he arrived, Achilles was nowhere to be found: his mother, afraid for her son’s life, had disguised him as a girl and hid him away among the royal women. She was a goddess, so this trick was no sweat, but Odysseus knew a few tricks of his own. He would leave them in peace, he said, but first he wished to offer some gifts to the ladies. He went into their chamber with a chest full of jewelry, fragrances, and fine clothing, and as soon as he opened the top the women gathered around, elbowing each other as they picked out their treasures. Amid this squabbling one of them noticed a glint deep in the chest, reached in, pulled out a silver-studded sword, and slashed through the air with a confident hand. Odysseus had found his man.

The theory sounds nice, but is it true? To test it properly you’d have to raise a child uncontaminated by the usual cultural pressures, which would be next to impossible. Suppose, however, you were able to surgically alter a child and then raise it as a member of the opposite sex. Now you have the pervasiveness of the culture working for you instead. A boy raised as a girl would receive all the same messages society sends to biological girls, and according to the theory these signals ought to affect him in the same way.

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As Nature Made Him: The Boy Who Was Raised as a Girl, by John Colapinto, tells the story of David Reimer, a Canadian who came to the attention of medical science as the result of a bungled circumcision and who was subjected to exactly this sort of gender swapping. Comparisons with Josef Mengele would be unfair, however, in that these doctors, including the most prestigious and respected names in the fields of psychology and sexual identity, believed they were treating Reimer, not experimenting on him. They were already convinced that male and female are social categories, not biological essences. And Colapinto shows how they used this single case, one of the most famous in sex research, to offer definitive proof to mainstream medicine that gender identity really is an open matter at birth.

Money was not a medical doctor, but a psychologist specializing in psychohormonal research. In the 1950s his studies of intersexual babies–those born with ambiguous genitals–convinced him that sexual identity was malleable until the second or third year, a view perfectly suited to the behaviorism that then ruled the social sciences. People were ready to hear that gender identity (a term coined by Money) was an open matter, just as sexual orientation would be seen in the following decades. Money was celebrated as the pioneer in this field, and he enjoyed a reputation that was practically unassailable. So when he generalized his findings from hermaphrodites to all human beings, claiming that “sexual behavior and orientation as male or female does not have an innate, instinctive basis,” few seriously questioned him.

A key part of the program was the family’s annual visit to Baltimore, when Money would interview the twins and direct the treatment. Brenda, with the sure instinct of childhood, soon came to see this man as her mortal enemy, and for years she fought him in a titanic struggle over the vaginal surgery he told her she needed to become completely female. The more he pushed, the more sullen and combative she became. From his first mention of the surgery when she was just seven (her response: “I wouldn’t do that”) to his final attempt to persuade her five years later, she budged not an inch. On this last occasion he brought in a female transsexual–one of his success stories–to explain the benefits of the surgery, but all Brenda could see was a man wearing makeup and a dress. Believing that the two of them were about to drag her off to the operating room she ran screaming out of the building. She later told her parents that if they ever took her back to Money she would kill herself.

But success of any kind, at least in this country, depends on the market. If Money had put his considerable talents behind a theory that repelled his funders and colleagues he would have had his head shot off the instant he stuck it above the grass. His audience–academics, feminists, progressives–wanted to hear that sexual identity and behavior are not defined only by biology, as indeed they still do. In 1999, Colapinto reports, Money was being funded by the NIH to the tune of $135,956. Meanwhile defenders have emerged from his large academic fief to say that the Reimers themselves ruined Brenda’s treatment by failing to follow through adequately. Children born with defective genitals and those who have been injured accidentally are still being treated according to Money’s protocols today.