Homosexuality has been a subject of scientific study for many years. Much of the research has focused on whether homosexuality is a product of biology or psychological conditioning. That nature-nurture question often has entered into ethical and political debates about homosexuality. For example, in the early 1990s two studies were released that indicated that homosexuality may be biological. One study identified distinctive neural structures in homosexual men (LeVay 1993). The other correlated a genetic marker with male homosexuality (Hamer and Copeland 1994).

Those studies received significant media attention because they seemed to strike at the heart of the political debate about gay rights. Opponents of gay rights had argued that homosexuality is a choice and that homosexuals seek "special rights" for a deviant and destructive lifestyle. Consequently, gay rights advocates began to argue that the studies mentioned above showed that homosexuality is not a choice but an innate...