GENDER DIFFERENCES IN BEHAVIOR - ACTIVATING EFFECTS OF CROSS-SEX HORMONES

The relative contribution of organizing and activating effects of sex hormones to the establishment of gender differences in behaviour is st ill unclear. In a group of 35 female-to-male transsexuals and a group of 15 male-to-female transsexuals a large battery of tests on aggressi on, sexual motivation and cognitive functioning was administered twice : shortly before and three months after the start of cross-sex hormone treatment. The administration of androgens to females was clearly ass ociated with an increase in aggression proneness, sexual arousability and spatial ability performance. In contrast, it had a deteriorating e ffect on verbal fluency tasks. The effects of cross-sex hormones were just as pronounced in the male-to-female group upon androgen deprivati on: anger and aggression proneness, sexual arousability and spatial ab ility decreased, whereas verbal fluency improved. This study offers ev idence that cross-sex hormones directly and quickly affect gender spec ific behaviours. If sex-specific organising effects of sex hormones do exist in the human, they do not prevent these effects of androgen adm inistration to females and androgen deprivation of males to become man ifest.