The "third sex" theory of Karl Heinrich Ulrichs.
In the 1860s, with an innovative theory of the origin of homosexuality that saw it as neither a sin nor a sickness, the German lawyer Karl Heinrich Ulrichs became an outspoken defender of its practice. This paper describes the theory, placing it historically in the context of Ulrichs' life, and shows why, although progressive for its time, the theory eventually was abandoned.
D005783:Gender Identity; D005858:Germany; D006666:History of Medicine; D006716:Homosexuality; D006801:Humans; D007603:Jurisprudence / Q000266:history; D012727:Sex Characteristics