Issues pertaining to human sexuality and gender roles have long been of interest to psychologists, and have been of general interest to nearly every generation of human beings. The nature of romantic and erotic attraction dominates the world of literature, music, and other art forms, while the efforts to understand what drives or determines the way that individuals manifest romantic and erotic attraction and inhabit gender roles has been the subject of extensive research in recent decades. The earliest research into these areas largely presumed that issues such as gender identity and sexual orientation were generally innate, and that environmental factors during childhood, adolescence, and other developmental stages were responsible for the manifestation of gender identity issues, homosexuality, bisexuality, and other deviations from what was considered to be normal expressions of gender identity and sexual orientation. In recent years a number of researchers have uncovered evidence of biological and physiological factors that influence gender identity and sexual orientation, serving to underpin the so-called “nature vs. nurture” debate with regards to these issues. In the article “Biased-Interaction Theory of Psychosexual Development: ‘How Does One Know if One is Male or Female?’ ” (Diamond, 2007) a strong case is made for the theory that the development of gender identity and sexual orientation requires the interplay of both inherent biological factors and environmental factors.