The more guys that have been inside her, the more likely she’s going to cheat. It’s really that simple. Every empirical study on this affirms this basic observation.

Factors found to facilitate infidelity

Number of sex partners: Greater number of sex partners before marriage predicts infidelity

As might be expected, attitudes toward infidelity specifically, permissive attitudes toward sex more generally and a greater willingness to have casual sex and to engage in sex without closeness, commitment or love (i.e., a more unrestricted sociosexual orientation) are also reliably related to infidelity (pg.71)

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Fincham, F. D., & May, R. W. (2017). Infidelity in romantic relationships. Current opinion in psychology, 13, 70–74. https://doi.org/10.1016/j.copsyc.2016.03.008

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A truism in psychology is that the best predictor of future behavior is past behavior. This is no less true in the realm of sexual behavior. Indeed, one of the strongest predictors of marital infidelity is one’s number of prior sex partners (pg.6)

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Haselton, M. G., Buss, D. M., Oubaid, V., & Angleitner, A. (2005). Sex, Lies, and Strategic Interference: The Psychology of Deception Between the Sexes. Personality and Social Psychology Bulletin, 31(1), 3–23. https://doi.org/10.1177/0146167204271303

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Men apparently assess and evaluate levels of sexual activity by a woman prior to long-term commitment—behavior that would have been observable or known through social reputation in the small-group lifestyles of our ancestors. Past behavior is a good predictor of future behavior, and having a large number of sex partners prior to marriage is a statistical predictor of infidelity after marriage (pg.92)

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Buss, D. M., & Schmitt, D. P. (2019). Mate preferences and their behavioral manifestations. Annual Review of Psychology, 70, 77–110. https://doi.org/10.1146/annurev-psych-010418-103408

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it would appear that the premaritally experienced females were more inclined to accept coitus with males other than their husbands after marriage. (pg.427)

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Kinsey, A. C., Pomeroy, W. B., Martin, C. E., & Gebhard, P. H. (1953). Sexual behavior in the human female. Saunders. https://psycnet.apa.org/record/1954-05526-000

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the odds ratio of 1.13 for lifetime sexual partners obtained with the face-to-face mode of interview indicates that the probability of infidelity increased by 13% for every additional lifetime sexual partner (pg.150)

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Whisman, M. A., & Snyder, D. K. (2007). Sexual infidelity in a national survey of American women: Differences in prevalence and correlates as a function of method of assessment. Journal of Family Psychology, 21(2), 147–154. https://doi.org/10.1037/0893-3200.21.2.147

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Generally speaking, respondents who report extensive premarital sexual experience report extensive extramarital activity. Measures of the locus of first intercourse and number of premarital partners show positive associations with (1) rating one's marriage as less happy than average, (2) the number of different extramarital partners, and (3) the intention to participate in mate-swapping activities (pg.221-222)

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Athanasiou, R., & Sarkin, R. (1974). Premarital sexual behavior and postmarital adjustment. Archives of Sexual Behavior, 3(3), 207–225. https://doi.org/10.1007/BF01541486

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promiscuity is in fact a good predictor of infidelity. Indeed, promiscuity among females accounted for almost twice as much variance in infidelity (r2 = .45) as it did for males (r2 = .25). (pg.177)

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Hughes, S. M., & Gallup, G. G., Jr. (2003). Sex differences in morphological predictors of sexual behavior: Shoulder to hip and waist to hip ratios. Evolution and Human Behavior, 24(3), 173–178. https://doi.org/10.1016/S1090-5138(02)00149-6

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Sexual promiscuity was significantly positively correlated with emotional promiscuity [r(356) = .261, p < .001], as well with sexual infidelity [r(323) = .595, p < .001] and emotional infidelity [r(323) = .676, p < .001] (pg.390)

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Pinto, R., & Arantes, J. (2017). The Relationship between Sexual and Emotional Promiscuity and Infidelity. Athens Journal of Social Sciences, 4(4), 385–398. https://doi.org/10.30958/ajss.4-4-3

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Each additional sex partner between age 18 and the first union increased the net odds of infidelity by 1% (pg.56)

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Treas, J., & Giesen, D. (2000). Sexual Infidelity Among Married and Cohabiting Americans. Journal of Marriage and Family, 62(1), 48–60. https://doi.org/10.1111/j.1741-3737.2000.00048.x

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A preliminary ANOVA analysis revealed that individuals reporting a past history of infidelity tended to have a greater number of past sexual partners than those without a history of infidelity (controlling for age; M = 3.78 versus 1.24), F(1,376) = 52.16, p < .001, d = .81. (pg.351)

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Barta, W. D., & Kiene, S. M. (2005). Motivations for infidelity in heterosexual dating couples: The roles of gender, personality differences, and sociosexual orientation. Journal of Social and Personal Relationships, 22(3), 339–360. https://doi.org/10.1177/0265407505052440

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Subjects reporting sex with men other than their husbands while they were married (who were 23% of the ever-married subjects) were significantly younger at first intercourse [17.7 versus 20.0 years, t(279) = 5.6, p < 0.011 and reported significantly more sexual partners [24.5 versus 3.9, t(280) = 6.5, p < 0.011 than did ever-married women who reported no extramarital affairs. (pg.150)

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Essock-Vitale, S. M., & McGuire, M. T. (1985). Women's lives viewed from an evolutionary perspective: I. Sexual histories, reproductive success, and demographic characteristics of a random sample of American women. Ethology & Sociobiology, 6(3), 137–154. https://doi.org/10.1016/0162-3095(85)90027-5

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A central purpose of this research was to identify correlates of betrayal. In addition to attitudes toward betrayal, a number of other factors were found to be associated with acts of betrayal. As predicted, such factors as sexual permissiveness, an avoidant romantic style, number of romantic relationships, and early onset of sexual intercourse were all correlated with a higher incidence of betrayal behaviors. These factors are likely to promote sexual activity with a larger number of partners, which, in turn, increases the chance that betrayal will occur. (pg.247)

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Feldman, S. S., & Cauffman, E. (1999). Your cheatin' heart: Attitudes, behaviors, and correlates of sexual betrayal in late adolescents. Journal of Research on Adolescence, 9(3), 227–252. https://doi.org/10.1207/s15327795jra0903_1

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Multivariate model fitting to infidelity and number of sexual partners (log transformed) confirmed that a Cholesky model containing parameters for additive genetic factors and the unique environment, but without shared environmental factors, provided the best explanation of the observed correlation between the two variables. The resulting genetic correlation between the two traits was .47, so nearly half the genes impacting on infidelity also affect number of sexual partners. (pg.652-653)

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Cherkas, L., Oelsner, E., Mak, Y., Valdes, A., & Spector, T. (2004). Genetic Influences on Female Infidelity and Number of Sexual Partners in Humans: A Linkage and Association Study of the Role of the Vasopressin Receptor Gene (AVPR1A). Twin Research, 7(6), 649-658. https://doi.org/10.1375/twin.7.6.649

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The residents of Promiscuous America are predictable in many ways. They’re less likely to be married and more likely to be divorced. They’re several times as likely as their less adventurous peers to have cheated on a spouse.

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Wolfinger, N. H. (2018, April 18). Promiscuous America: Smart, secular, and somewhat less happy. Institute for Family Studies. Retrieved December 13, 2021, from https://ifstudies.org/blog/promiscuous-america-smart-secular-and-somewhat-less-happy (https://archive.md/F2Kf7)

Nicholas Wolfinger is Professor of Family and Consumer Studies and Adjunct Professor of Sociology at the University of Utah.

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As it relates to sexual history later in life, promiscuity is linked to a higher likelihood of cheating in long-term, serious relationships. Vrangalova thinks the reason may be that many promiscuous people aren't really built for monogamy.

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Kubota, T. (2015, October 20). What the number of sexual partners says about you. Men's Journal. Retrieved December 3, 2021, from https://www.mensjournal.com/health-fitness/what-the-number-of-sexual-partners-says-about-you-20151020/ (https://archive.md/7wOAo)

Dr. Zhana Vrangalova is a NYC-based sex educator and adjunct professor of human sexuality at New York University.

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When compared with their peers who report fewer partners, those who self-report 20 or more in their lifetime are:

Three times as likely to have cheated while married (pg.89)

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Regnerus M. (2017). Cheap sex : the transformation of men marriage and monogamy. Oxford University Press.

Mark Regnerus is Professor of Sociology at the University of Texas at Austin

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Contrary to the myth, partners who’ve had many partners have a harder, not easier, time remaining monogamous. They are significantly more at risk of straying than those with little or no prior sexual experience.

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Staik, A. (2019, March 28). 10 Predictors of Infidelity and Gender Differences: Why Do Partners Cheat?. Psych Central. Retrieved on July 15, 2020, from https://blogs.psychcentral.com/relationships/2014/08/a-look-at-infidelity-why-do-partners-cheat/ (https://archive.is/bPRPy)

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An indicator of whether or not the respondent has had previous sex partners is included and identifies the number of male sex partners the woman had previous to her relationship with her current primary partner… A history of numerous sex partners indicates a pattern or habit of sexual behavior that we expect will negatively influence sexual exclusivity in the current relationship. (pg.37)

Having previous sexual partners greatly increased the likelihood that a woman would have a secondary sex partner. In particular, a woman with 4 or more male sex partners prior to her primary relationship was about 8.5 times more likely to have a secondary sex partnerthan a woman with no previous sex partners… Having previous sex partners also increased the likelihood that dating and married women would have secondary sex partners. In particular, married women with 4 or more previous partners were 20 times more likely to have secondary sex partners than married women with no previous sex partners (pg.41)

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Forste, R., & Tanfer, K. (1996). Sexual exclusivity among dating, cohabiting, and married women. Journal of Marriage and the Family, 58(1), 33–47. https://doi.org/10.2307/353375

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Regarding other sexual behaviors, we examined whether number of prior sex partners and viewing pornography predicted ESI. As has been found in prior research (Feldman & Cauffman, 1999; Treas & Giesen, 2000), having had more prior sex partners predicted future ESI (pg.12)

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Maddox Shaw, A. M., Rhoades, G. K., Allen, E. S., Stanley, S. M., & Markman, H. J. (2013). Predictors of Extradyadic Sexual Involvement in Unmarried Opposite-Sex Relationships. Journal of Sex Research, 50(6), 598–610. https://doi.org/10.1080/00224499.2012.666816

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For people who reported four or fewer lifetime sexual partners, the rate of infidelity in the current marriage dropped to 11%, while for those who had five or more sexual partners the number was nearly double (21%)

McQuivey, J. L. (2019, October 14). The road to infidelity passes through multiple sexual partners. Institute for Family Studies. https://ifstudies.org/blog/the-road-to-infidelity-passes-through-multiple-sexual-partners