12.3 Sexual preference is not binary

You may have heard things like “most people are bisexual,” and “sexual preferences exist on a continuum,” but are such claims scientific? That is, do we have evidence to justify such statements?

Figure 12.2 The Kinsey Scale

Some key work on sexuality was conducted in the 1940’s and 1950’s by the biologist Alfred Kinsey. Alfred Kinsey pioneered research in human sexuality through thousands of interviews and the development of “The Kinsey Scale” of human sexual preferences. The Kinsey Scale is a 7-point metric that categorizes individuals from 0 (exclusively heterosexual) to 6 (exclusively homosexual), and includes the midpoint 3 (equally homosexual and heterosexual).

Figure 12.3 Alfred Charles Kinsey

Kinsey’s main contributions were to (1) reveal that many people have preferences that aren’t “0” or “6”—in other words, sexual preferences do exist on a continuum; and (2) revolutionize how we view female sexuality—that is, women are not just recipients of sex, women have sexual desires, and women cheat, fantasize, and masturbate. For many people, these ideas may be obvious, but at the time they were shocking and revolutionary.

Figure 12.4 Above: distribution of Kinsey scores for 147 men and 238 women (who were not exclusively heterosexual) in an Australian sample from 2000.


More recent work has investigated the “continuum” concept of sexuality, with a focus on the prevalence of bisexuality. For example, an analysis of several reports revealed the presence of bisexuality in from ~2% to ~6% of individuals who identified as heterosexual, and from ~18% to ~88% in self-identified homosexuals. In the latter example, far more women, on average, expressed bisexual tendencies than did male homosexuals. In sum, bisexuality is fairly common, and sexual preference is not binary.

Diamond, L. M. Sexual Fluidity in Male and Females. Curr. Sex. Heal. Reports 8, 249–256 (2016).

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  1. From Bailey, J. M. & Martin, N. A. Genetics and Environmental Influences on Sexual Orientation and Its Correlates in an Australian Twin Sample. (2000). doi:10.1037/0022-3514.78.3.524


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The Evolution and Biology of Sex Copyright © 2020 by Sehoya Cotner and Deena Wassenberg is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.