In 1968, Stoller wrote Sex and Gender, where he hypothesized "The sense of core gender identity...is derived from three sources: the anatomy and physiology of the genitalia; the attitudes of parents, siblings and peers toward the child's gender role; and a biological force that may more or less modify the attitudinal (environmental) forces." In it, he argued that sex-changes should be utilized as a research technique but only offered to those termed "true transexuals", those who "had never been very feminine in childhood, had never lived acceptably in a masculine role, and who had not derived pleasure from their penis (p 251)." However, these criteria became widely influential and most patients would use the "winning psychosexual history", as therapy shifted from analysis of transgender people to a stepping stone to transition.
