Bisexuality

Bisexuality is defined in many sources as romantic attraction, sexual attraction, or sexual behavior toward both males and females. It is also defined as the attraction to more than one gender, to people of both the same and different genders, or to people regardless of their sex or gender identity.
The term bisexuality is mainly used for people who experience both heterosexual and homosexual attraction. Bisexuality is one of the three main classifications of sexual orientation along with heterosexuality and homosexuality, all of which exist on the heterosexual–homosexual continuum. A bisexual identity does not necessarily equate to equal sexual attraction to both sexes; commonly, people who have a distinct but not exclusive sexual preference for one sex over the other also identify themselves as bisexual.
Scientists do not know the exact determinants of sexual orientation, but they theorize that it is caused by a complex interplay of genetic, hormonal, and environmental influences, and do not view it as a choice. Although no single theory on the cause of sexual orientation has yet gained widespread support, scientists favor biologically based theories. There is considerably more evidence supporting nonsocial, biological causes of sexual orientation than social ones, especially for males.
Bisexuality has been observed in various human societies, as well as elsewhere in the animal kingdom, throughout recorded history. The term bisexuality, like the terms hetero- and homosexuality, was coined in the 19th century by Charles Gilbert Chaddock.

Definitions

Sexual orientation, identity, and behavior

Bisexuality is variously defined as romantic or sexual attraction to both males and females, to more than one gender, or attraction to both people of the same gender and different genders. The American Psychological Association states that "sexual orientation falls along a continuum. In other words, someone does not have to be exclusively homosexual or heterosexual, but can feel varying degrees of both. Sexual orientation develops across a person's lifetime–different people realize at different points in their lives that they are heterosexual, bisexual or homosexual." Attraction can take numerous forms for bisexuals, such as sexual, romantic, emotional, or physical.Sexual attraction, behavior, and identity may also be incongruent, as sexual attraction or behavior may not necessarily be consistent with identity. Some individuals identify themselves as heterosexual, homosexual, or bisexual without having had any sexual experience. Others have had homosexual experiences but do not consider themselves to be gay, lesbian, or bisexual. Likewise, self-identified gay or lesbian individuals may occasionally sexually interact with members of the opposite sex but do not identify as bisexual. The terms queer, polysexual, heteroflexible, homoflexible, ''men who have sex with men and women who have sex with women may also be used to describe sexual identity or identify sexual behavior.
Some sources state that bisexuality encompasses romantic or sexual attraction to all gender identities or that it is romantic or sexual attraction to a person irrespective of that person's biological sex or gender, equating it to or rendering it interchangeable with pansexuality. The concept of pansexuality deliberately rejects the gender binary, the "notion of two genders and indeed of specific sexual orientations", as pansexual people are open to relationships with people who do not identify as strictly men or women. Sometimes the phrase bisexual umbrella, or bisexual community'', is used to describe any non-monosexual behaviors, attractions, and identities, usually for purposes of collective action and challenging monosexist cultural assumptions. The term "bisexual community" includes those who identify as bisexual, pansexual/omnisexual, biromantic, polysexual, or sexually fluid.
The bisexual activist Robyn Ochs defines bisexuality as "the potential to be attracted—romantically and/or sexually—to people of more than one sex and/or gender, not necessarily at the same time, not necessarily in the same way, and not necessarily to the same degree."
According to Rosario, Schrimshaw, Hunter, Braun :
Bisexuality as a transitional identity has also been examined. In a longitudinal study about sexual identity development among lesbian, gay, and bisexual youths, Rosario et al. "found evidence of both considerable consistency and change in LGB sexual identity over time". Youths who had identified as both gay/lesbian and bisexual prior to baseline were approximately three times more likely to identify as gay/lesbian than as bisexual at subsequent assessments. Of youths who had identified only as bisexual at earlier assessments, 60 to 70 percent continued to thus identify, while approximately 30 to 40 percent assumed a gay/lesbian identity over time. Rosario et al. suggested that "although there were youths who consistently self-identified as bisexual throughout the study, for other youths, a bisexual identity served as a transitional identity to a subsequent gay/lesbian identity."
By contrast, a longitudinal study by Lisa M. Diamond, which followed women identifying as lesbian, bisexual, or unlabeled, found that "more women adopted bisexual/unlabeled identities than relinquished these identities", over a ten-year period. The study also found that "bisexual/unlabeled women had stable overall distributions of same-sex/other-sex attractions". Diamond has also studied male bisexuality, noting that survey research found "almost as many men transitioned at some point from a gay identity to a bisexual, queer or unlabeled one, as did from a bisexual identity to a gay identity."
There may also be a difference between sexual and romantic attractions in bisexuals over time. One study found that in the short term bisexual men and women were much more likely to change their sexual behavior than heterosexual or homosexual individuals. Bisexual men were less likely to have a change in romantic attraction but those that did were more likely to have a greater change than in sexual feelings while bisexual women were more likely than bisexual men to have a change in romantic attraction. This suggests that sexual and romantic attraction is not fixed for bisexual individuals and changes over time.

Kinsey scale

In the 1940s, the zoologist Alfred Kinsey created a scale to measure the continuum of sexual orientation from heterosexuality to homosexuality. Kinsey studied human sexuality and argued that people have the capability of being hetero- or homosexual even if this trait does not present itself in the current circumstances. The Kinsey scale is used to describe a person's sexual experience or response at a given time. It ranges from 0, meaning exclusively heterosexual, to 6, meaning exclusively homosexual. People who rank anywhere from 2 to 4 are often considered bisexual; they are often not fully one extreme or the other. The sociologists Martin S. Weinberg and Colin J. Williams write that, in principle, people who rank anywhere from one to five could be considered bisexual.
Psychologist Jim McKnight writes that while the idea that bisexuality is a form of sexual orientation intermediate between homosexuality and heterosexuality is implicit in the Kinsey scale, that conception has been "severely challenged" since the publication of Homosexualities, by Weinberg and the psychologist Alan P. Bell.

Criticism

The Kinsey scale is criticized for various reasons. One of the main reasons is the inverse relation in attraction to males and females that the Kinsey scale represents. The Kinsey scale implies that having a higher level attraction to one gender results in less attraction to the other, which some studies do not support. This aspect of the Kinsey scale can impact the results of studies that utilize the scale, as there is a biological difference between bisexuals and gay people.

Other scales

Klein Sexual Orientation Grid
* A more descriptive orientation grid that takes into account: Sexual attraction, sexual behavior, sexual fantasies, emotional preference, social preference, lifestyle preference, and self-identification. It also has different measures for certain variables and is not binary by design.
Shively Scale
* Measures physical and affectional attraction on two separate scales.
Sell Assessment of Sexual Orientation
* Measures sexual attraction, sexual orientation identity, and sexual behavior and reports the extent of all of those factors.
Multidimensional Scale of Sexuality
* Uses nine categories to categorize bisexuality. These categories are evaluated on sexual behavior, sexual attraction, arousal to erotic material, emotional factors, and sexual dreams and fantasies. The combined answers to all of these questions make up the score.
Demographics and prevalence

Scientific estimates as to the prevalence of bisexuality have varied from 0.7 to 8 percent. The Janus Report on Sexual Behavior, published in 1993, concluded that 5 percent of men and 3 percent of women considered themselves bisexual, while 4 percent of men and 2 percent of women considered themselves homosexual.
A 2002 survey in the United States by the National Center for Health Statistics found that 1.8 percent of men ages 18–44 considered themselves bisexual, 2.3 percent homosexual, and 3.9 percent as "something else". The same study found that 2.8 percent of women ages 18–44 considered themselves bisexual, 1.3 percent homosexual, and 3.8 percent as "something else". In 2007, an article in the Health section of The New York Times stated that "1.5 percent of American women and 1.7 percent of American men identify themselves bisexual." Also in 2007, it was reported that 14.4 percent of young US women identified themselves as "not strictly heterosexual", with 5.6 percent of the men identifying as gay or bisexual. A study in the journal Biological Psychology in 2011 reported that there were men who identify themselves as bisexuals and who were aroused by both men and women. In the first large-scale government survey measuring Americans' sexual orientation, the NHIS reported in July 2014 that only 0.7 percent of Americans identify as bisexual.
A collection of recent Western surveys finds that about 10% of women and 4% of men identify as mostly heterosexual, 1% of women and 0.5% of men as bisexual, and 0.4% of women and 0.5% of men as mostly homosexual.
Across cultures, there is some variance in the prevalence of bisexual behavior, but there is no persuasive evidence that there is much variance in the rate of same-sex attraction. The World Health Organization estimates a worldwide prevalence of men who have sex with men between 3 and 16%, many of whom have sex with women as well.
A YouGov survey found that the proportion of young adults living in the United Kingdom identifying as bisexual surged 14 percentage points from 2015 to 2019.