Related to the topic gender is sexual orientation, or a person's sexual, romantic, affectionate, and emotional attraction to members of the same sex, the opposite sex, or both. A person who is attracted to members of the opposite sex is heterosexual, or “straight.” A person who is attracted to members of the same sex is homosexual, or “gay” (male) or “lesbian” (female). A person who is attracted to members of both sexes is bisexual, or “bi.” Most sociologists today refer to sexual orientation rather than sexual preference. The latter implies that sexual attraction is a choice, which many researchers believe is not the case.
In the 1940s and 1950s, Alfred Kinsey and his associates discovered that sexual orientation exists along a continuum. Prior to Kinsey's research into the sexual habits of Americans, experts generally believed that most individuals were either heterosexual or homosexual. Kinsey speculated that the categories of sexual orientation were not so distinct. On his surveys, many Americans reported having had at least minimal attraction to members of the same gender, although most had never acted on this attraction. In short, Kinsey and colleagues brought to the attention of medical science the notion of heterosexuality, homosexuality, and bisexuality all being separate but related sexual orientations.
Homosexual transsexual is a term that has been used by some sexologists, psychologists and psychiatrists to describe transwomen who are attracted to men, and less often transmen who are attracted to women. The terms androphilic and gynephilic are replacing those terms in active use. The concept of categorizing transsexuals by sexual orientation originated with Magnus Hirschfeld in 1923. This specific term was defined by Kurt Freund in 1973, and used as part of a two type taxonomy by him in 1982. Even though homosexuality itself was removed from the Diagnostic and Statistical Manual of Mental Disorders, 2nd edition (DSM II) as a mental disorder diagnosis. In the DSM III the transsexualism was to be diagnosed and the sexual orientation of a transsexual specified using the terms homosexual, heterosexual, asexual, or unspecified. This concept arose because early investigators thought the main difference between a male transvestite and a male to female transsexual was same-sex attraction. The term or concept has since been used in articles by Harry Benjamin, Kurt Freund, Ray Blanchard, and others. More modern alternatives recognize that gender identity not sexuality define a transsexual, while still differentiating between androphilic and gynephilic research subjects.