Bisexuality has been defined as the proclivity to act or to undertake actions that are sexual in nature with both male and female partners. Various theories for the origins and extent of bisexuality exist, especially in relation to the prevalence of pure heterosexuality and homosexuality. However, the concept of bisexuality has also been applied generally to the concept of a scale, referred to as the sexual orientation continuum, which measures the extent to which one is inclined toward heterosexual activity or homosexual activity.

Throughout history, bisexuality has been relegated to extreme views. It has either been widely accepted as the standard or template form of sexuality for humans, or it has been rejected as a social theory or assumption that can explain one's sexual identification. Contemporary debates about the origins of sexual orientation or sexual identity are reflected similarly in the subject of bisexuality. There are a number of theorists who think that genetic factors might be at work, others who believe the environment has the strongest influence and others who emphasize the role of hormones in sexual behavior.

Many communities, particularly conservative, religious ones, support heterosexuality as the norm. This can manifest either socially or based on scientific theory. Socially, it has been linked with political and social movements that discriminate against those who do not considering themselves to be homosexual. Others go as far as to believe it is an extension of cultural or political influences that aim to spread the practice of non-heterosexual behavior. Another view is that bisexuality exists as a transitional mentality for homosexual individuals who wish to hide their homosexuality or do not yet realize they are exclusively attracted to the same sex, or who refuse to drop their heterosexual "identity" because of social prejudice. Both streams of thought rebuff many scientific studies that have led concluded that sexuality is not uniform or exclusive.

According to the American Psychiatric Association, "to date there are no replicated scientific studies supporting any specific biological etiology for homosexuality. Similarly, no specific psychosocial or family dynamic cause for homosexuality has been identified, including histories of childhood sexual abuse." This statement would indicate that much of the debate about the origins of bisexuality lies in social, cultural and political sensitivity, whereas in fact, there is no conclusive evidence that bisexuality is developed out of a primarily or solely biological source, or a primarily or solely environmental source. While socially, it has become common to consider homosexuality or bisexuality a genetic or biological phenomenon, many activists in the lesbian/gay/bisexual/transsexual community have shied away from this point, fearing that should future research identify biological influence, it could lead to genetic screening or prenatal testing and mass abortions.

Sigmund Freud and Alfred Kinsey are the most famous advocates for either a base form of bisexuality or a continuum of sexual preference. Freud assumed that bisexuality was the default and that attraction to, or sexual activity with one or the other, gender would be latent later in life while the other manifested itself. Kinsey included the continuum in the analysis of those whom he interviewed during his surveys on sex. Studies have shown bisexuals to be more sexually active and to engage in more sexual fantasy than heterosexuals or homosexuals. Their activity tends to be more intense; for example, female bisexuals have been found to have more intense orgasms on average than women with other sexual orientations.

Research in bisexuality is considered by many to be inadequate or inefficient. Many charge that the research is commonly done in tandem with research on homosexuality, which would discount the theories and their derivatives common among the likes of Freud and Kinsey. Additionally, research focusing exclusively on bisexuality is scant and sporadic.

Jay Paul in 1985 and A.P. MacDonald in 1983 charged that the lack of research was a result of a social bias by scientists, who have accepted a cultural norm of Western countries where sexuality is categorical and worse, limited to only two forms. Some go as far as to say this perception, blatant or latent, compromises much of the research on sexuality and even homosexuality itself. This concept has been labeled the "heterosexual/homosexual binary," which may also be reinforced by a number of political factors, particularly pressure exerted by activists in the gay rights community on self-proclaimed bisexuals to identify one way or the other.

It is possible this is an attitude born out of the fear that the prevalence of bisexuals could compromise arguments for the acceptance of homosexuals and give credence to the environmental impact on sexual development. This, in turn, might motivate conservative activists to exert undue pressure on homosexuals to conform with heterosexual practices. There have long existed for efforts in conservative, particularly religious communities, to reverse homosexuality through therapy. These therapeutic efforts have been criticized by scientists, who consider them fool-hardy and dangerous to patients.

Selected full-text books and articles on this topic

Dual Attraction: Understanding Bisexuality
Martin S. Weinberg; Colin J. Williams; Douglas W. Pryor.
Oxford University Press, 1995
Sexual Pathways: Adapting to Dual Sexual Attraction
Mark J. K. Williams.
Praeger Publishers, 1999
Psychological Perspectives on Lesbian, Gay, and Bisexual Experiences
Linda D. Garnets; Douglas C. Kimmel.
Columbia University Press, 2003 (2nd edition)
Lesbian and Bisexual Identities: Constructing Communities, Constructing Selves
Kristin G. Esterberg.
Temple University Press, 1997
Lesbian, Gay, and Bisexual Identities in Families: Psychological Perspectives
Charlotte J. Patterson; Anthony R. D'Augelli.
Oxford University Press, 1998
Bisexualities and AIDS: International Perspectives
Peter Aggleton.
Taylor & Francis, 1996
Working with Lesbian, Gay, Bisexual, and Transgender College Students: A Handbook for Faculty and Administrators
Ronni L. Sanlo.
Greenwood Press, 1998
Mapping Desire: Geographies of Sexualities
David Bell; Gill Valentine.
Routledge, 1995
Librarian’s tip: Chap. 3 "Locating Bisexual Identites"
Toward an Understanding of Behaviourally Bisexual Men: The Influence of Context and Culture
Stokes, Joseph P.; Miller, Robin L.; Mundhenk, Rhonda.
The Canadian Journal of Human Sexuality, Vol. 7, No. 2, Summer 1998
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
Risk Factors for Internalizing and Externalizing Problems among Gay, Lesbian, and Bisexual Adolescents
Elze, Diane E.
Social Work Research, Vol. 26, No. 2, June 2002
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
Queerly Phrased: Language, Gender, and Sexuality
Anna Livia; Kira Hall.
Oxford University Press, 1997
Librarian’s tip: Chap. 2 "The Elusive Bisexual: Social Categorization and Lexico-Semantic Change"
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