|Defining the Sexes|
|In the 18th and 19th centuries, the view prevailing in the medical profession and among anthropologists was that men and women differed fundamentally-both physically and mentally. There is an extensive body of literature on sex and gender differences as well as on the body structure and psyche of "woman" - "naturally" written by men.
Some Institute staff members concerned themselves with the anthropology of woman, e.g. Hans Friedenthal who worked on gender-specific hair growth and Baron von Reitzenstein who researched breast shapes in women.
With 19th century descriptions of the sexes as point of departure, Hirschfeld developed a pluralist sexual theory for the 20th century: the theory of sexual transitions. It assumed that all physical and mental human characteristics expressed themselves in male and female forms: genitals, body size, bone structure, skull, pelvis, joints, muscular system, strength of hands, larynx, hair growth, breathing and perspiration, gait and form of greeting, mimicry, handwriting, etc. The "absolute man", an individual with exclusively male characteristics, and the "absolute woman", with exclusively female characterstics, constituted opposing, extreme ideal types 1 . According to this theory, all people were mixed forms of the most diverse combinations of male and female features. Hirschfeld calculated the number of possible sexual types: at least 43 046 721.