In the mid-1950s, Alfred Kinsey devised the Kinsey scale in an attempt to measure sexual orientation. The 7 point scale has a rating of 0 ("exclusively heterosexual") to 6 ("exclusively homosexual"). Bisexuals cover most of the scales' values (1-5) which ranges between "predominantly heterosexual, only incidentally homosexual" (1) to "predominantly homosexual, only incidentally heterosexual" (5). In the middle of the scale (3) is "equally heterosexual and homosexual".
Although observed in a variety of forms in human societies and in the animal kingdom throughout recorded history, the term "bisexuality" (like the terms "hetero-" and "homosexuality") was only coined in the 19th century.
Some view that bisexuality is a distinct sexual orientation on a par with heterosexuality or homosexuality. This views bisexuality as something clearly distinct from these other two sexualities, with a clear attraction to both men and women required.
Others view bisexuality as more ambiguous. Some people who might be classified by others as bisexual on the basis of their sexual behavior self-identify primarily as homosexual. Equally, otherwise heterosexual people who engage in occasional homosexual behaviour could be considered bisexual, but may not identify as such. For some who believe that sexuality is a distinctly defined aspect of the character, this ambiguity is problematic. It is sometimes argued that the behaviour of bisexuals may be explained by a subconscious homophobia or peer pressure. On the other hand, some believe that the majority of people contain aspects of homosexuality and heterosexuality, but that the intensities of these can vary from person to person. Some people who engage in bisexual behavior may be supportive of lesbian and gay people, but still self-identify as straight; others may consider any labels irrelevant to their positions and situations.
Some bisexuals make a distinction between gender and sex. Gender is defined in these situations as social or psychological category, characterised by the normal practices of men and women. For example, the fact that women wear dresses in Western Society whilst men traditionally do not is a gender issue. Sex is defined as the biological difference between males and females, prior to any social conditioning. Bisexuals in this sense may be attracted to more than one gender but only to one sex. For example, a male bisexual may be attracted to aspects of men and masculinity, but not to the male body. Such a person's attractions may manifest themselves through sexual activities other than anal sex with other males.
Bisexuality is often misunderstood as a form of adultery or polyamory, and a popular misconception is that bisexuals must always be in relationships with men and women simultaneously. Rather, individuals attracted to both males and females, like people of any other orientation, may live a variety of sexual lifestyles. These include: lifelong monogamy, serial monogamy, polyamory, polyfidelity, casual sexual activity with individual partners, casual group sex, and celibacy. For those with more than one sexual partner, these may or may not all be of the same gender.