The concept of "lesbian" to differentiate
women with a shared sexual orientation evolved in the 20th century. Throughout history,
women have not had the same freedom or independence as
men to pursue homosexual relationships, but neither have they
met the same harsh punishment as homosexual
men in some societies. Instead, lesbian relationships have often been regarded as harmless, unless a participant attempts to assert privileges traditionally enjoyed by
men. As a result, little in history was documented to give an accurate description of how female homosexuality was expressed. When early sexologists in the late 19th century began to categorize and describe homosexual behavior, hampered by a lack of knowledge about homosexuality or
women's sexuality, they distinguished lesbians as
women who did not adhere to female gender roles. They classified them as mentally ill—a designation which has been reversed since the late 20th century in the global scientific community.