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In a longitudinal study about sexual identity development among lesbian, gay, and bisexual (LGB) youths, Rosario et al.
"found evidence of both considerable consistency and change in LGB sexual identity over time".
From an anthropological perspective, there is large variation in the prevalence of bisexuality between different cultures.
Among some tribes, it appears to be non-existent while in others a universal, including the Sambia of New Guinea and similar Melanesian cultures.
and the concept is one of the three main classifications of sexual orientation along with heterosexuality and homosexuality, all of which exist on the heterosexual–homosexual continuum.
More modern studies estimating the demographics for bisexuality have varied.The American Psychiatric Association stated: "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." Research into how sexual orientation may be determined by genetic or other prenatal factors plays a role in political and social debates about homosexuality, and also raises fears about genetic profiling and prenatal testing.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 psychologist Jim Mc Knight 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 (1978), by Weinberg and the psychologist Alan P. Kinsey's 1948 work Sexual Behavior in the Human Male found that "46% of the male population had engaged in both heterosexual and homosexual activities, or 'reacted to' persons of both sexes, in the course of their adult lives".