David Reimer Gender Reassignment Case (1966)

After a botched circumcision destroyed infant David Reimer's penis, psychologist John Money convinced his parents to raise him as a girl ("Brenda") and used the case to promote the theory that gender identity is entirely learned. Money reported the experiment as a success for decades. In reality, Reimer rejected his female identity from childhood, transitioned back to male at age 15, and ultimately died by suicide at 38. The case is now cited as evidence that gender identity has a strong biological component.