Why do people cheat on their romantic partners? This is an old question to which science has for a while been struggling to provide answers. While infidelity—or "extradyadic involvement" as it is inelegantly termed in the scientific literature—is condemned almost universally, it is also quite consistently and cross-culturally persistent and prevalent.
Infidelity is also highly consequential. It’s the most often-given reason for divorce across cultures; it is often accompanied by personal distress, not to mention harsh social and professional implications, the spread of STIs, and, all too often, violence.
Its prevalence and considerable consequences make infidelity a worthy target for scholarly investigation. Alas, studying infidelity well is difficult to do, for several reasons. First, infidelity is by definition secretive, and people are wary about giving away their secrets, even with the promise of anonymity. Second, people often provide inaccurate information when asked about sex, whether intentionally (to feel or look good), or unintentionally (because they are confused, unaware, or uninformed).
Moreover, people who are asked to explain themselves in retrospect often construct answers that serve to rationalize behavior rather than accurately account for it. The story we tell looking back is often different in self-serving ways than how and why the story unfolded in real-time.
Further, consensus is lacking: Different people define infidelity differently. For some, only extradyadic intercourse qualifies as infidelity, while for many others, lesser sexual behaviors such as necking, petting, and kissing constitute infidelity, as does any extradyadic, secretive emotional attachment. Infidelity, to a significant extent, is in the eyes of the betrayed.
Finally, because of ethical considerations (you can’t randomly assign people to satisfying and unsatisfying marriages, for example), controlled experimentation is impossible to pursue in this area of research, which means that we know little about cause and effect.
These difficulties notwithstanding, psychological theorists and researchers have ventured to understand and explain the phenomenon looking for predictors of infidelity and the motivating forces behind it.
Evolutionary explanations have focused on the fitness benefits both men and women may gain by cheating. For men, "spreading their seed" among secret paramours provides a form of genetic insurance since they cannot know for sure that their pregnant partner is actually carrying their offspring. Women, seeking their own advantage, may be motivated to secretly poach high-quality sperm from testosterone-heavy types and bring it back to be raised by loyal and caring types, or use affairs as preparation for "trading up" for a more fit male if the current relationship sours.
- Men would be motivated to guard more against sexual infidelity since it puts at risk their access to the woman’s womb.
- Women, on the other hand, supposedly are more sensitive to emotional infidelity on the part of their partner, since they stand to lose the most if their male partner leaves for good and takes his resources elsewhere.
Debate over these predictions continues; so far, robustly supportive evidence has emerged mostly for the latter hypothesis.
Another well-researched model relies on social exchange theory in predicting infidelity. This so-called investment model argues that the decision to stray is formed on the basis of three calculations.
- One’s satisfaction level in the relationship (are my expectations being met?).
- The availability of quality alternatives (are there other potential mates around?).
- The level of unrecoverable investment (how many resources that cannot be retrieved have I already poured into the relationship?).
When satisfaction and investment levels are low, and high-quality alternatives are abundant, infidelity is more likely.
Another influential framework through which to make sense of infidelity is attachment theory. According to attachment theory, patterns of parent-child interactions in infancy lead children to internalize certain mental representations (expectations) of how relationships work. These early templates are carried into adulthood to inform romantic relations.
Children who have developed a secure attachment style tend to assume that others are trustworthy and accessible to them and can help meet their needs. Those who’ve developed an insecure attachment style fall into one of two camps: anxious or avoidant. Both groups expect others to be less accessible and less competent in meeting their needs. Specifically, anxious individuals cope with their fear of abandonment by becoming demanding and clingy. Avoidant individuals cope with the fear of disappointment by maintaining emotional distance and low intimacy needs.
Both these types of insecurity predict marital infidelity, as anxious individuals will often look elsewhere in hope of satisfying their unmet intimacy needs while avoidant individuals, feeling less committed and emotionally attached in a given relationship, will find it inherently easier to stray.
Much of the empirical literature on infidelity has looked into people’s motivations for having affairs, often by asking participants directly. Predictably, people’s reasons are multiple and varied.
For example, in a recent study, Dylan Selterman of the University of Maryland and his colleagues, using an Internet-based questionnaire, asked 495 young adult participants about their motivations for infidelity. Answers ranged broadly from lack of love (“I had ‘fallen out of love with’ my primary partner”) and low commitment (“I was not very committed to my primary partner”), to esteem needs (“I wanted to enhance my popularity”), a desire for sexual variety (“I wanted a greater variety of sexual partners”), and specific situational factors (“I was drunk and not thinking clearly”).
One robust general finding in psychological research is that past behavior predicts future behavior. This appears to hold true with regard to infidelity. For example, Kayla Knopp of the University of Denver and colleagues followed 484 adult participants longitudinally through two heterosexual romantic relationships. Their findings showed that those who reported engaging in extra-dyadic sex in the first relationship were three times more likely to report engaging in such behavior in their next relationship (compared to those who did not report engaging in affairs in the first relationship).
In addition, those who knew that their partners in the first relationships had engaged in extradyadic sex were twice as likely to report the same behavior from their next relationship partners (compared to those whose partners did not have affairs). Those who suspected their first-relationship partners of having an affair were four times more likely to suspect their future partners. The authors conclude that “prior infidelity emerged as an important risk factor for infidelity in next relationships."
Research on the predictors of infidelity has linked the behavior to an array of personality, situational, and demographic variables. While some of those, such as low religiosity or marital dissatisfaction, are intuitive, others are not. For example, one study has identified the wife’s pregnancy as a risk factor for the husband’s infidelity.
Recently, Frank Fincham and Ross May of Florida State University published a summary of “the current state of research on the prediction of infidelity” in which they highlighted several interesting findings.
For example, the authors estimate that 20-25 percent of marriages experience infidelity at some point. Infidelity tends to increase in the summer, likely due to increased travel during that season, which provides easier opportunities for covert activity. Moreover, infidelity rates increased markedly between the early 1990s and the mid-2000s, particularly in older individuals, likely due in part to the introduction of erection drugs such as Viagra. Cohabitation before marriage is associated with an increased likelihood of cheating (perhaps through its association with more permissive attitudes about sex).
Like most complex human social behaviors, infidelity is multiply determined, which means that it has many causes that may interact in complex ways. One example: Relationship dissatisfaction strongly predicts infidelity, but only in people who are not very religious. Acknowledging this complexity, Fincham and May nevertheless identify four main classes of infidelity determinants:
Demographic variables: Men are more likely to have affairs than women—the disparity is due in part to the fact that more men than women visit prostitutes—although the gap appears to be closing, particularly among young people (in part due to women’s increased financial independence and social mobility).
Individual characteristics: People high in narcissism and neuroticism are more prone to infidelity. As mentioned earlier, an insecure attachment style is also a predictor, as is a history of promiscuity and more permissive attitudes toward sex. A history of parental infidelity also predicts infidelity. Unfaithful parents beget unfaithful children, although of course, many exceptions exist.
Relationship variables: The best proximal predictor of infidelity appears to be relationship satisfaction. Not surprisingly, relationship commitment is also strongly predictive. Research has suggested that satisfaction and infidelity have a reciprocal relationship, influencing each other. Finally, partners who are more alike (in religion, values, education, etc.) are less likely to stray (perhaps in part because similarity begets a more satisfying relationship).
Context: Work environment is related to the likelihood of infidelity, according to research. Specifically, work that requires much travel, and/or involves personal contact with potential mates and a large proportion of opposite-sex coworkers predicts higher odds of infidelity. Family constellations with one working and one stay-at-home spouse are also at higher risk for infidelity.
Religiosity is another factor. Specifically, the attendance of religious services is reliably predictive of a lower rate of affairs. Additionally, those who take the bible as the literal word of God are also less likely to stray.
Finally, as with all things sexual, the internet provides a new context within which infidelity occurs. In general, people who seek sex on the internet are more likely to have affairs, and a majority of those who look for sex online end up having real-world sex with the partner they met online, often in secret. Moreover, "internet infidelity," although difficult to define and research, is increasingly becoming a source of relationship stress and strife deserving of further study—as well as its own future column.