ABSTRACT
This chapter provides the background to biological sex, which attempt to understand how conditions of intersexuality, homosexuality, and transsexuality may occur. C. N. Armstrong developed the concept of a sexual spectrum with man and woman at extreme ends of this spectrum, each being determined by wholly male or female determinants of biological sex. Conditions of intersex imply a discrepancy between chromosomal, gonadal, and phenotypic sex, in cases of transsexuality or gender identity disorder there is an incongruity between the biological sex and the psychological sex. The chapter considers research that has provided data to support possible biological contributions to, in particular, atypical sexual orientation and transsexuality. In cases of atypical sexual orientation and in gender identity disorder, the research suggests that structural, early humoral and genetic factors may predispose to an alteration in sexual orientation or in gender identity.
