In 1965 in the Canadian town of Winnipeg, Janet Reimer gave birth to twin boys - Bruce and Brian. Six months later a bungled circumcision left Bruce without a penis. Based on a radical new theory of gender development the decision was taken to raise Bruce as a girl. In 1967 Bruce became Brenda and for the next three decades this case would be at the heart of one of the most controversial theories in the history of science. The man behind this work was world-renowned psychologist Dr John Money. In the 1950s Dr Money developed a theory that revolutionised our understanding of gender. Money believed that what he called our 'gender identity' - what makes us think, feel and behave as boys or girls - is not fully formed by the time of birth. While we may have some innate sense of being a boy or a girl, for up to two years after birth, our brains are, in effect, malleable and we can be taught to grow up as either a boy or girl by how we are raised - by the toys we are given, the guidance w