The case study of John/Joan was conducted by Dr. John Money, a psychologist and sexologist who believed that gender identity was not innate, but learned through social and environmental factors. He wanted to test his theory on a boy who had lost his penis in a circumcision accident, and convinced his parents to raise him as a girl named Brenda. He also performed a sex reassignment surgery on him, which involved removing his testicles and creating an artificial vagina. He also prescribed him female hormones during puberty. He compared his development with that of his identical twin brother, Brian, who was raised as a boy.

Money claimed that the experiment was successful and that Brenda had accepted her female identity, but he concealed the fact that Brenda was unhappy and confused about her gender. She was ostracized and bullied by peers (who dubbed Brenda “cavewoman”). She rebelled against the feminine clothes and toys that her parents gave her, and was bullied at school for being different. She also had to undergo regular visits to Money, who made her and her brother engage in sexual play in front of him. When she was 14, she learned the truth about her past from her father, and decided to live as a male named David, undergoing surgeries to reconstruct his penis and received male hormone injections.

Brian and David were both traumatized. His brother died following an overdose at the age of 36. David took his own life at the age of 38.

The case study of John/Joan was exposed as a failure by Milton Diamond. Journalist John Colapinto, who interviewed David and wrote a book about his story. The case study sparked a lot of controversy and criticism about the ethics and validity of sex reassignment surgeries on children, especially those with intersex conditions or ambiguous genitalia. It also challenged the idea that gender identity is purely a social construct, and suggested that biological factors play a significant role in shaping one’s sense of self.