Abstract
It is generally accepted that in mammalian evolution from rodents to primates, including man, aggressiveness, and more particularly intra-species aggression related to the assertion of dominance in the social hierarchy of the group, is a characteristic of the male (Gray, 1971). There is also an increasing body of evidence which shows that mammalian behaviour patterns are basically female and that male patterns are determined by the action of the sex hormone testosterone on neural structures during critical phases of intra-uterine development (Seymour Levine, 1966). Ounsted and Taylor (1972) have proposed that the X chromosome is sexually neutral, essentially equivalent to an autosome, and that its role in sexual differentiation lies in that it maintains ovarian function in the female. The Y chromosome is sex-determining by causing potential autosomal and X-coded information to become manifest in the phenotype. This is achieved in part by determining the development of foetal testosterone during a critical phase of foetal life. In the absence of testosterone the fundamental female morphology would be established in either sex.