The Oxford Handbook of Infidelity (2023) is the most comprehensive scientific reference on why people cheat, bringing together leading researchers to provide a global, evidence-based picture of who is most likely to be unfaithful, why, and with what consequences.

Notes

About the Authors:
Each chapter of The Oxford Handbook of Infidelity (2023) is authored by leading scholars and researchers in psychology, sociology, evolutionary biology, and related fields. The editors are:

Todd K. Shackelford, PhD – Distinguished Professor of Psychology at Oakland University, where he directs the Evolutionary Psychology Lab. He has over 500 scholarly publications and extensive editorial experience in evolutionary psychology. He also edited the Cambridge Handbook of Evolutionary Sexual Behavior (4 volumes), and the Oxford Handbook of Evolutionary Psychology and Romantic Relationships.

Tara DeLecce, PhD – Assistant Professor of Psychology at California State University, San Bernardino. Her research focuses on romantic and sexual relationships, infidelity, and the psychological and cultural factors that influence mating strategies.

Chapter 1: Are Certain People More Prone Toward Infidelity?

Authors: Emma E. Altgelt, James K. McNulty, Andrea L. Meltzer

This chapter reviews how personality traits and individual differences predict infidelity in both the individual and their partner.
Findings show consistent links between low conscientiousness, low agreeableness, and higher infidelity, with added risk from extraversion and (for women) neuroticism. The Dark Triad (narcissism, psychopathy, Machiavellianism) is strongly associated with cheating. Attachment insecurity and unrestricted sociosexuality also predict infidelity. Partner traits matter as well—being with a partner low in conscientiousness increases the likelihood of straying.

• Low conscientiousness and low agreeableness are consistent predictors of higher infidelity.
• Extraversion and female neuroticism track higher risk, though effects are smaller.
• Dark Triad traits correlate strongly with cheating, via low empathy and manipulativeness.
  • Sexual narcissism is most predictive of infidelity (McNulty & Widman, 2014), rather than general narcissism, which can sometimes be inconsistent 🙋🏼‍♂️ Lucio’s note: narcissism as a whole may also lead to mixed findings when vulnerable narcissism is included. I’d expect vulnerable narcissists to cheat less because of fewer options
• Attachment insecurity increases infidelity likelihood, especially avoidance.
  “people higher in attachment avoidance see others as relatively unreliable and thus engage in cognitive and behavioral strategies aimed at gaining distance from partners (Mikulincer & Shaver, 2003)”
• Unrestricted sociosexuality robustly predicts infidelity, beyond other traits.
• Partner low conscientiousness raises your cheating risk, indicating partner effects.

🙋🏼‍♂️ Lucio’s suggestion: fantastic work and opening chapter. For the tables, I’d suggest considering a more immediately clear visual representation. For example, green, grey, or red cell for positive, no, or negative correlation—paired with textual annotations indicating the strength of each relationship

Chapter 2: Predicting Infidelity in the Context of Race and Ethnicity

Authors: Kelly Campbell, Tiffany L. Brown, Brandyn-Dior McKinley

This chapter examines infidelity prevalence across U.S. racial and ethnic groups. The findings are blunt: infidelity rates are highest among African Americans, followed by Latinos, then Whites, and lowest among Asian Americans.

The authors stress that race itself rarely serves as a direct predictor of infidelity. Instead, it’s the factors that correlate with race, such as cultural norms, socioeconomic pressures, religiosity, and social exchange dynamics and sexual marketplace dynamics. <—🙋🏼‍♂️ Lucio’s note: This may partly read like a CYA for the cultural zeitgeist. It’s likely partially true. Still, I don’t remember having seen definitive evidence that would fully rule out a contribution of race/ethnicity.

Religiosity suppresses infidelity across groups, while acculturation stress raises risks in immigrant populations.

• Infidelity prevalence is highest among African Americans, with some estimating that African American men are twice as likely as White men to have relationships outside their primary partnership (Pinderhughes, 2002)
  • Followed by Latinos, Whites
  • Lowest infidelity is among Asian Americans, because of emphasis on family union, sex for procreation and, potentially, options, since Asian American men have less sexual experience than women

Write the authors on the difference in sexual experience between male and female Asians:

A partial explanation for this difference is the influence of sexual stereotypes that portray Asian women as submissive and exotic sexual objects and Asian men as asexual, emasculated nerds and outsiders (Mukkamala & Suyemoto, 2018; Wong et al., 2012). Possibly, the eroticization of Asian women exposes them to more sexual opportunities relative to men

🙋🏼‍♂️ Lucio’s note: Asian women may have some more opportunities, although I’m doubtful and it largely depends on individual’s behavior and attractiveness. I suspect the main difference lies in the fewer options than their male counterparts, rather than the more options of Asian women

• African American men have more options than African American women leading to ‘man sharing’ for some women.
  The reasons are:
  • Black women outnumber men: Largely due to higher mortality and incarceration rates, as well as disproportionate rates of substance abuse and poor healthcare related to racism (Penn et al., 1997), there are more available female partners than there are men within the Black community (Utley, 2011)
  • Black men can ‘date outside their race’
  • 🙋🏼‍♂️ Lucio’s note: Another issue for American women is the even larger education gap. See this article on ‘difficult dating markets for successful women‘
• Religiosity suppresses infidelity rates across groups.
  • Conservative political attitude may also suppress infidelity, mention the authors
• Acculturation stress elevates risk, especially for immigrants.
  • The value of individualism relates to infidelity because people prioritize personal fulfillment over relational, family, or collective goals, potentially feeling entitled to fulfill their needs through EDI, even if it damages the primary relationship (Attridge & Berscheid, 1994).

Power In Relationships

At the relational (micro) level, power stems from controlling valued resources such as money or sex. The more a partner desires that resource, the more power the provider holds (Lennon, Stewart, & Ledermann, 2013). Power also shifts toward the less dependent or less committed partner—typically the one with better alternatives. Dependence and commitment are shaped by the ability to secure valued resources elsewhere.

At the macro level, societal structures (e.g., gender, race, class) influence power dynamics within couples (Coontz, 1997). Partners bring intersecting dominant or minority statuses into the relationship, and mismatches may lead to tension. The more powerful partner may falsely assume both have the same freedom, but only they do. If they deny or ignore their power, the other cannot initiate change.

Across cultures, men tend to hold more macro-level power, making women more relationship-dependent and more vulnerable to infidelity and exploitation. In interracial or interethnic couples, the partner from the dominant group (e.g., European American) typically holds more dyadic power as well, increasing the risk of conflict or exploitation.

The authors also point out that while the higher power partner may assume the other shares similar freedoms, only the powerful partner can act freely.
And more equitable change is only possible by admitting the power gap. I quote: ‘When a person with power does not acknowledge their power or pretends not to have it, the other partner cannot implement change; they require recognition of the imbalance by the power-holder to achieve desired outcomes‘.

Power also fluctuates in predictable patterns depending on the relationship phase.

Also see:

• Stages of relationship power

Value exchanges overlap with power dynamics

A crucial concept we also unveiled on this website, value exchanges and power dynamics overlap, as the authors correctly note:

In terms of equity, those who feel overbenefited (i.e., receiving more outcomes than they deserve) as well as underbenefited (i.e., receiving fewer outcomes than they deserve) report more EDI than those in equitable relationships. Equity is linked to power, in that people who are less dependent on their partner for rewards (satisfying outcomes) have more power in a relationship and are more inclined toward EDI (Prins, Buunk, & VanYperen, 1993)

Macro power differential may explain the gender gap in infidelity

A variety of intrapersonal factors predict EDI across racial/ethnic groups. In nearly every culture studied, men are more likely than women to engage in EDI (Mark et al., 2011); however, a major reason for this gender difference may relate to power differentials between the sexes. When comparisons are made between men and women with similarly high levels of power and status, infidelity rates are comparable (Lammers et al., 2011)

Chapter 3: Hormonal Predictors of Infidelity

Authors: Lindsay Bochon, Brian M. Bird

Hormones strongly influence mating behavior. T
estosterone, estradiol, oxytocin, vasopressin, and cortisol interact with life history strategies to predict infidelity. Higher testosterone is linked with more short-term mating and extradyadic sex. Women’s estradiol peaks correlate with greater attraction to alternatives around ovulation. Oxytocin and vasopressin promote bonding but, when dysregulated, can weaken exclusivity. Cortisol interacts with stress and opportunity, amplifying risk.

• Higher testosterone aligns with greater extra-pair interest, especially short-term mating.
  • Testosterone in men is associated with continued mating efforts
  • Men with unrestricted sociosexuality retain testosterone similar to single men
  • Mothers with higher postpartum testosterone show reduced affectionate behavior toward offspring (Fleming et al., 1997), suggesting that reductions in testosterone are necessary for nurturing behavior
• Testosterone adapts to needs: T, similar to other hormones, can drive behavior, but also responds flexibly to environmental cues of challenge and/or mating opportunities
• Fertile-phase estradiol shifts increase attraction to alternatives, particularly in some partnered women.
• Bonding hormones can stabilize or destabilize exclusivity, depending on regulation and context.
• Fast life-history strategies predict more cheating, reflecting short-term orientation.

Extra notes

• Sociosexual orientation is malleable: men become relatively more restricted as mating opportunities become scarce (Arnocky et al., 2016) and as they transition from single into marriage and fatherhood (Gettler et al., 2019)
• High T women prefer masculine men: Research by Welling and colleagues suggests that preferences for these sexually dimorphic facial characteristics—including women’s attractiveness ratings of masculine men’s faces (Welling et al., 2007) are associated with elevated endogenous testosterone concentrations (but see Marcinkowska et al., 2019)
  • High T men prefer feminine faces (Welling et al., 2008)
• Status and power matter: polygynously married men had equivalent testosterone levels compared to their monogamously married counterparts (Gray et al., 2007) Polygynously married men, however, are older than men in monogamous marriages, suggesting that age and the continued acquisition of wealth and sociopolitical power is more important for marital status than testosterone-mediated behavior.

Chapter 4: Operational Sex Ratio and Infidelity

Author: Daniel J. Kruger

The balance of men to women in a population changes infidelity dynamics.
Where men are scarce, men cheat more and commit less; where women are scarce, women extract commitment and resources, but men still may stray. Skewed sex ratios affect not only relationships but social stability, divorce, culture, and public health outcomes.

• Male scarcity increases male infidelity and reduces commitment.
• Female scarcity lets women secure more commitment, though cultural sanctions may limit female infidelity.
• Women marry younger when there are more men: Because women can secure male commitment earlier in relationships, they tend to marry at younger ages (Kruger et al., 2010).
  • Some men also marry younger to secure a prospective partner before another man does, but on average:
• The variance in male marital age increases with more men, because men need to acquire greater social status and resources to be considered eligible for marriage (Kruger et al., 2010).
• Skewed sex ratios correlate with higher STIs and instability, affecting public health.

Sex Ration Changes Cultures

In post-Roman Europe, Germanic invasions, population collapse, and rural subsistence with a preference for sons led to male-biased sex ratios (Herlihy, 1973; Coleman, 1976) and the birth of courtly love can be traced back to sex ratio, with men also idealizing unconsummated relationships and married women (“courtly love”; Guttentag & Secord, 1983).

In the late Middle Ages, this shifted because of losses of men to the Crusades, monastic life, and plague mortality. The new female-biased sex ratios sparked early feminist thought. Unmarried women formed Beguine communities—quasi-secular female communes—that produced radical proto-feminist literature and advocated for education and autonomy, though most women remained uneducated and unaware of these movements (Bolton, 1976; Herlihy, 1973).

By the 19th century, female-biased ratios coincided with a resurgence of feminist movements advocating for female independence (Gordon, 1976; Herlihy, 1973).

Cultural shifts continued into the 20th century, where fluctuating sex ratios influenced media and relationship behavior: male-biased decades (1930s–50s) emphasized male commitment, while female-biased periods (1960s–70s) saw more casual male sexual strategies and rising divorce rates (Pedersen, 1991; Guttentag & Secord, 1983).

Chapter 5: It’s Not You, It’s Us—Relationship-Based Predictors

Authors: Jana Hackathorn, Brien K. Ashdown

Relationship factors are stronger predictors of infidelity than personality. The key is commitment, shaped by satisfaction, investments, and alternatives. Infidelity risk spikes with low satisfaction, high-quality alternatives, and boredom. Cohabiting couples show more infidelity than married couples. Risk also changes over time: women’s risk peaks around 7 years, men’s later, around 18 years.

Satisfaction within various domains in one’s primary relationship predicts a person’s attitudes toward infidelity, and less satisfaction increases the likelihood to engage in an affair, as individuals who are happy tend not to stray from the things that make them happy

• Low satisfaction and commitment are strong predictors of infidelity.
  Conversely:
• Relationship quality lowers infidelity: quality is negatively related to intense attraction to others and to infidelity (Gibson et al., 2016).
• higher quality of alternatives is among the strongest predictors of cheating (Emmers-Sommer et al., 2010)
• Cohabitation shows higher cheating risk than marriage, partly due to weaker constraints.
• The earlier the marriage, the higher the cheating: Respondents who were married at a young age (i.e., 16 years or younger) reported four times more infidelity than those who were married in their early 20s.
  The likelihood of infidelity decreases steadily as the age at which participants were married increases (Atkins et al., 2001).
• Dependent women cheat more: Lower relative income (i.e., economic dependency on one’s current partner) is associated with higher odds of infidelity (Munsch, 2015). For women, those who are economically dependent on their partner are more likely to engage in infidelity than either women who provide all the income in a household (i.e., the breadwinners) or women who are in an economically equal relationship (Munsch, 2015). <— 🙋🏼‍♂️ Lucio’s suggestion & note: This was super interesting to find out, and something I suspected based on experience and power dynamics. I really wanted to see here there effect size or at least a directional estimate—how much more likely? I’d advice the authors to share the effect size whenever possible
• Risk timing differs by sex, peaking ~7 years for women and ~18 years for men.

However, remember that infidelity can also happen in happy relationships:

(while) demographic and individual characteristics are inconsistently associated with infidelity, relationship variables are the most consistent and robust across multiple studies (Haseli et al., 2019; Vowels et al., 2020). However, this research on relationship factors accounts for, on average, only one-fourth of the variance in infidelity behavior (e.g., Atkins et al., 2001; Blow & Hartnett, 2005; Tsapelas et al., 2010), leaving a large amount of variance unexplained. Simply put, infidelity does sometimes occur in happy relationships (Perel, 2017)

Social Exchange, Commitment & Infidelity (Handbook of Infidelity)

The investment model of commitment—validated and replicated across cultures—is based on social exchange theory, which holds that people seek relationships where rewards outweigh costs (Nye, 1979; Rusbult et al., 1998). Commitment is strongest when satisfaction is high, alternatives are low, and investment is substantial (Le & Agnew, 2003).

Low satisfaction, weak interdependence, and abundant alternatives predict infidelity across groups (Treas & Geisen, 2000; Atwood & Seifer, 1997; Nowak et al., 2014). In contexts like the African American community, gender imbalances and structural inequality reduce investment and increase infidelity risk (Adamopoulou, 2013; Penn et al., 1997). Religiosity can act as a protective factor (Atkins et al., 2001).

Globally, economic-sexual exchanges—such as transactional relationships—also contribute to infidelity, especially where emotional fulfillment is lacking (Smith, 2010; Lang & Smart, 2002; Scelza et al., 2020).

Chapter 6: Social Versus Sexual Monogamy

Authors: Catherine Salmon, Jessica Hehman

This chapter offers an important differentiation between social monogamy, when couples pair bond and live together, and sexual monogamy, which entails sexual exclusivity.
‘Genetic monogamy’ can occur without sexual monogamy if no extrapair paternity occurs.

Humans often practice social monogamy (long-term bonds) with expected but not guaranteed sexual exclusivity.
Evolution shaped dual strategies: pair-bonding for cooperation and occasional extra-pair sex for genetic diversity or status. Cultures differ in how strictly they enforce sexual monogamy.

• Social monogamy does not imply sexual exclusivity, even in stable bonds.
• Extra-pair sex is common in socially monogamous societies, varying with norms and enforcement.

Interesting notes

• Polygyny is more common overall, but monogamy is more common in societies with more evolved political systems (Sanderson, 2001)

Chapter 7: Cultural Differences and Similarities in Correlates of Infidelity

Authors: Inmaculada Valor-Segura, Gemma Sáez, Abraham P. Buunk

Cross-cultural data show universal predictors—low satisfaction, high alternatives—while culture shapes expression and stigma.
Cultures of honor (e.g., Mediterranean, Middle Eastern) punish women’s infidelity more harshly. Religious and collectivist cultures have lower infidelity prevalence, while urban, individualist settings foster higher rates.

infidelity is not typically accepted or approved in Western countries such as Spain, Great Britain, or the United States, and is seriously disapproved of in many Islamic countries, with often serious consequences for the adulterer. On the other hand, in many African countries infidelity is sometimes tolerated, while in Eastern countries such as Thailand, people are more tolerant because sex has traditionally been marketed, thus increasing the approval or consent of extradyadic sex (Mackay, 2001)

• Male infidelity is more accepted: Mackey and Immerman’s review (2001) of 216 cultures showed that male infidelity is less unacceptable than female infidelity. Even today many cultures view it as more ‘understandable’ if a betrayed party sought revenge (Buunk et al., 2018).
• Low satisfaction and high alternatives predict infidelity universally, across cultures.
• Honor cultures penalize women’s infidelity harshly, shaping behavior and reporting.
• Modernization and urbanization expand opportunities, weakening sanctions.

Chapter 8: Predicting Online Infidelity

Authors: Carey J. Fitzgerald, Crystal Moreno, Jody Thompson

Online spaces expand opportunities for infidelity: sexting, private messaging, pornography alternatives, and dating apps. Hidden apps and passwords may help keep it hidden. Many people consider these behaviors infidelity, even without physical sex.

Chapter 9: Predicting Infidelity in Nonheterosexual Relationships

Authors: Jonathan M. Bowman, Benjamin L. Compton

Infidelity in nonheterosexual couples follows many of the same patterns as heterosexual couples: low satisfaction, weak commitment, and good alternatives. But there is a key difference: many LGBTQ couples negotiate consensual nonmonogamy. Infidelity is thus defined not by sex with others per se but by breaking the couple’s agreed rules.

• Low satisfaction and commitment predict cheating across orientations, mirroring heterosexual patterns.
• Men perceive same-sex cheating as less threatening (Confer & Cloud, 2011; Denes et al. 2015; Compton & Bowman, 2017)

Interesting notes:

• Bisexual women are more likely to rate higher on Machiavellianism than straight or lesbian women (Lippa, 2020) and on the Dark Triad (Semenyna et al., 2018) <— 🙋🏼‍♂️ Lucio’s note: this reminds me of the book ‘Confessions of a Sociopath’, where the author states that bisexuality is her red flag for possible sociopathy

Chapter 17: Infidelity in Nonheterosexual Relationships

Authors: Justin J. Lehmiller, Dylan Selterman

Patterns of infidelity in nonheterosexual couples parallel heterosexual dynamics but with unique stressors. Minority stress, secrecy, and smaller dating pools shape behavior. Consensual nonmonogamy is more common, but infidelity still occurs when agreements are broken. Gay men report higher rates of sexual infidelity than lesbians, but less distress if agreements are clear.

• Rule clarity defines fidelity in CNM, not monogamy itself.
• Gay men report higher sexual infidelity, lesbians lower but more emotional boundary issues.
• Minority stress elevates secrecy and boundary challenges, impacting trust.

Chapter 10: Emotional and Sexual Infidelity—Evolutionary Origins

Authors: Julie A. Planke, Jacqueline M. Di Santo, Glenn Geher

This chapter explains why men and women differ in what they find most threatening.
Both sexes find infidelity of any type distressing. But men, on average, evolved to be more distressed by sexual infidelity (risk of paternity uncertainty), while women, on average, evolved to be more distressed by emotional infidelity (risk of losing resources and commitment).
Large-scale cross-cultural data support this pattern, though individual variation exists.

• Men report greater distress at sexual infidelity, women at emotional infidelity.
• These sex differences appear cross-culturally, consistent with evolutionary threats.
• Individual differences modulate reactions, including orientation, attachment, and culture.

Chapter 11: Sexual Novelty Motivations for Infidelity

Authors: Limor Y. Gottlieb, David P. Schmitt

A powerful driver of infidelity is the search for novelty. People cheat not only because of dissatisfaction but because novelty is inherently rewarding. Cross-cultural surveys show both men and women report sexual variety as a major motive, with men slightly higher. Evolutionarily, novelty seeking could spread genes and maintain excitement.

• Men are higher in novelty-seeking, though present in women.
• Novelty seeking operates even in satisfied relationships, not just those with deficits.
• Psychopathy predicts novelty-seeking, the robust link between psychopathy and novelty-seeking and infidelity (in both men and women) could indicate a reproductive strategy (Mealey, 1995) aligned with a fast life history strategy (Jonason, Koenig, & Trost, 2010).

Machiavellianism vs Psychopathy

Psychopathy predicts infidelity in men, while both psychopathy and Machiavellianism predict it in women.

One explanation: women face higher relational costs for infidelity (e.g., breakup risk; Brand et al., 2007), so Machiavellian traits—like planning, impulse control, and secrecy (Jones & Paulhus, 2011b)—may help them cheat more strategically and avoid detection.

Unlike psychopaths, Machiavellian individuals are less likely to destroy their relationships after infidelity. This suggests that novelty-seeking women may use Machiavellian strategies to maximize genetic or sexual benefits while minimizing social risk.

Chapter 12: The Mate Switching Hypothesis

Authors: Mike Abrams, Lidia Dengelegi Abrams

Infidelity often functions as a mate-switching strategy. Cheating may signal the end of one relationship and the start of another, especially when the new partner is perceived as higher value. Affairs often precede divorces. This hypothesis explains why many long-term affairs result in new committed partnerships.

• Infidelity often serves as a mate-switching tactic, paving the way for a new partner.
• Affairs frequently convert into primary relationships, especially with higher perceived mate value.
• Women more often use affairs as exit strategies, when dissatisfied or unsafe.

Interesting Notes

• Infidelity is heritable, especially in men: a study of 7,378 twins revealed that extrarelationship sex had a heritability of 62% in men and 40% in women (Zietsch et al., 2015).
  The higher heritability of infidelity in men is concordant with men’s larger fitness benefits from infidelity
• Low self-esteem pushes away partners: Low self-evaluations may inadvertently convince a partner that this is the case.
  The solicitations the self-effacing partner offers may prompt a re-evaluation of relationship equity (Schmitt, & Buss, 2001; Arnocky et al., 2013)

Also read:

• Dating women with low self-esteem

Why Jealousy Is Inborn

A man in such an epoch spending even a year or two providing sustenance and care to the progeny of another male paid a devastating price in genetic fitness. Men who were vigilant for competing males, put significant effort into mate guarding, and responded with violent rage when their monogamy was threatened, were more successfully in avoiding cuckoldry.
(…)
An early human who took a laissez-faire approach to his mate’s behavior would have an increased chance of investing in other males’ offspring and a diminished likelihood of leaving his own offspring and genes to survive in posterity. As a result, “jealous” genes are more prevalent in modern men

Dual Sexuality Hypothesis

Sexual infidelity in relationships in which a partner perceives their mate to have less value may be explained by the “good genes hypothesis.”
Women have evolved a dual mating strategy—obtaining parental and other investment from one man while surreptitiously seeking and mating with those they find more sexually attractive. A woman drawn to a more sexually attractive man represents her nonconscious quest for “better” genes. Indeed, the willingness of many women to risk the consequences of an affair denotes the compelling attraction to someone with a superior genome. The quest for better genes is more motivation for women than for men, who, unlike women, will often have affairs even when satisfied with their current relationship (Shackelford & Buss 1997b). Their motives are the quest for novelty and opportunity to propagate their genes (consciously or unconsciously).

Read more in our article reviewing the corresponding manosphere mantra:

• Low status provides, high status has sex?

Mate Value Dissonance & Subconscious Devaluation

The authors describe an interesting subconscious process.

Mate switching as the result of a slow, subconscious shift in assessment. When one partner’s self-perceived mate value rises—due to aging differences, career gains, or social advancement—they may begin to feel increasingly mismatched with their partner (Schmitt & Buss, 2001).

This internal dissonance builds gradually and often leads to attributing dissatisfaction to the partner’s flaws (Abrams, 2012). As attraction fades, infidelity becomes more likely—and infidelity feels justified based on the partner’s flaws, rather than regretted.
The unfaithful partner may then devalue their current mate while idealizing the new lover, paving the way for infidelity to evolve into full mate switching.

🙋🏼‍♂️ Lucio’s Note: Survival of the relationship may not depend much on the partner’s attractiveness

The authors say that as love fades, relationships are more likely to survive if one or both partners possess high mate value—such as male status and masculine features (Jacob et al., 2002), or female markers of reproductive health like a .7 waist-to-hip ratio and facial neoteny.

However, I think that the survival of either love or the relationship may depend less on a partner’s absolute attractiveness, and more on how well the partners’ mate values match, and how those values compare to available alternatives.

Paradoxically, partners who are not much in demand or lower in confidence may be hold up better and happier together.

Chapter 20: Formation of a Primary Relationship with an Infidelity Partner

Authors: Charlene F. Belu, Lucia F. O’Sullivan

Some affairs evolve into primary relationships. However, these new relationships face challenges: lower trust, fear of repeat cheating, and stigma. Success rates are lower than relationships formed outside infidelity contexts, but some do stabilize if partners rebuild trust.

• Affair partners sometimes become primary partners, but trust deficits linger.
• Trust erosion and suspicion remain elevated, challenging stability.
• Relationships born from affairs break up more often, relative to typical starts.

Mate Poaching May Lead to Poor Relationships Because of Poachers’ Traits

In line with traits that cue dominance, successful mate poaching by males was best predicted by their height, greater self-esteem, criminal tendencies, and greater display of cold affect (Sunderani et al., 2013). Targets of mate poaching attempts were higher on average in physical attractiveness (Sunderani et al., 2013). Together, these profiles indicate that the traits that characterize those who engage in infidelity or who are likely to be lured away from an exclusive relationship are not traits conducive to long-term committed relationships

Chapter 13: Deception and Secrecy in Infidelity

Author: Susan M. Hughes

Infidelity requires deception—concealing time, digital activity, finances, and emotions. People use verbal lies, technology tricks, and behavioral cover-ups. Detecting infidelity is difficult because cheaters refine concealment. Gender differences exist: men more often deny, women more often omit or emotionally redirect.

• Gaslighting, a term used to describe the manipulation of information and distortion of reality in such a way that the victim questions their own sanity (Gass & Nichols, 1988). Cheaters may lie, falsify the facts, and distort reality to convince their mates that they are crazy and that what their mate perceives is not happening
  • Also read ‘signs of gaslighting‘ to protect yourself
• Most infidelity victims remain ignorant, which allows the transgressors the ability to sustain their primary relationship (Weiser & Weigel, 2015). Dowd (2012) found that most participants (78%) in the study never disclosed their infidelity to their partner, so it remained unknown
• Withdrawal (39.5%) was the most commonly reported sign of a partner’s infidelity in Dowd’s study (2012). Different types of withdrawal patterns included less frequency in phone contact, less physical contact, a diminishing sex life, a general loss of interest in their partner, being less communicative, emotional detachment, and breaking patterns of usual behavior (Dowd, 2012; Shackelford & Buss, 1997).
• People can identify infidelity in others’ romantic relationships: Lambert et al. (2014) found that participants who watched a short video clip of a couple interacting could accurately detect which targets had cheated on their romantic partners. They found that this detection was mediated by ascriptions of commitment and trustworthiness of the persons they were observing
• Men more likely to be suspicious (Brand et al., 2007), to judge their partner will be unfaithful in the future, and to detect infidelity (Andrews et al., 2008).
  This is explained by ‘error management theory’: since men’s costs of infidelity are higher, they err on the side of caution
• Men more often deny; women more often omit or redirect, in disclosure patterns.
• Greater relationship satisfaction leads to more confessions: individuals who reported having greater satisfaction with their relationship were more likely to reveal their infidelity secret to their partner than those in less satisfying relationships (Dowd, 2012)
• Women are more likely to disclose infidelity than men (Brand et al., 2007). But it may not all be because of ‘honesty’, but as a step to terminate the relationship:
  • Women were also marginally more likely than men to break up with their partner after they had cheated and subsequently more likely to then start a new relationship with the affair partner
• Securely attached partners less likely to cheat and more likely to confess or consider confessing
• Men seeking extrapair concealed the relationship, while women were more likely to reveal they had a committed partner

Interesting Notes

• Mate value influences reactions to infidelity. Those who perceived themselves to be high in mate value reported greater levels of indignation in response to infidelity, whereas those who perceived themselves to be lower in mate value reported greater levels of insecurity (Phillips, 2010)
• Masculinity is an important facial indicator: Facial masculinity seemed to mediate women’s accuracy, with women rating more masculine-looking men as more likely to be unfaithful and as having a sexual history of being unfaithful. Women were correct in their estimates because masculinity ratings correlated significantly with men’s infidelity
• Lower-pitched voices judged more likely to cheat for both sexes (Hughes and Harrison, 2017), while higher pitched voices more trustowrthy (O’Connor & Barclay, 2017)

Men and Women’s Approaches to Concealing Infidelity

When attempting to attract a new partner while still in a committed relationship (i.e., mate poaching), men and women use different tactics to conceal their intentions from both their current partner and their social circle.

• Men tend to increase displays of commitment to their current partner to conceal infidelity. This includes talking about a shared future, expressing emotional closeness, showing satisfaction with the relationship, and fulfilling the partner’s resource and emotional needs. Men also hide the affair socially by withholding information and isolating the extradyadic relationship from their broader network (Schmitt & Shackelford, 2003).

• Women, on the other hand, maintain stable routines to avoid drawing attention. They often increase sexual and romantic behavior with their current partner, making the extradyadic interest less detectable through consistent behavior and apparent emotional investment (Schmitt & Shackelford, 2003).

In short, men perform over-investment; women maintain consistency and increase intimacy—both aimed at hiding infidelity.

Machiavellian’s Strategic Approach to Deception

Individuals high in Machiavellianism tend to control what information they reveal, making them more capable of plausible and convincing lies (Giammarco et al., 2013).

They often endorse lying for personal gain and feel confident in their ability to deceive, which makes them more likely to engage in blatant lies rather than subtle omissions (Brewer & Abell, 2015).

However, because they’re also risk-averse when it comes to detection, especially in cases like infidelity, they still employ strategic caution in how they lie (Adams et al., 2014).

Learn more:

• How to be a good Machiavellian, using the positives within an honorable man’s approach

Chapter 14: Infidelity Across the Ovulatory Cycle

Authors: Virginia E. Mitchell, Jenna M. Lunge, Alex Orille, Mercedes Hughes, Lisa L. M. Welling

Women’s sexual interest fluctuates across the ovulatory cycle. During fertile phases, women are more likely to show attraction to men with markers of genetic quality, sometimes outside their primary partner. This creates a predictable window of higher infidelity risk, though it does not apply equally to all women or all relationships.

• Attraction to alternatives increases near ovulation, for some partnered women.
• Testosterone and estradiol are positively associated with women’s preferences for facial masculinity (e.g., Bobst et al., 2014; Welling et al., 2007; although see Marcinkowska et al., 2019; for estradiol, see Dixson et al., 2018; Roney & Simmons, 2016; Roney et al., 2011).
  Estradiol levels are also positively associated with women’s preferences for masculine male voices (e.g., Feinberg et al., 2006; Pisanski et al., 2014) and behavioral displays of dominance (e.g., Lukaszewski & Roney, 2009, although these authors used estimated rather than measured hormonal assessments)
  • Progesterone is negatively associated with facial masculinity preferences (e.g., DeBruine et al., 2019; Marcinkowska et al., 2018)
  • 🙋🏼‍♂️ Lucio’s note: Estradiol is more strongly associated with feminine traits, fertility, sexually selective behavior and even mate value.
    Progesterone is more associated with nurturance and long-term bonding, higher post-ovulation, and inversely related to masculine preference.

🙋‍♂️Lucio’s Question: Is masculinity preferred by feminine or masculine women?

Lucio:
The authors refer to women high in both testosterone and estradiol as preferring masculine men.

However, the two seem to be opposite: testosterone is associated with masculinity and dominance (and not most attractive in women), and estradiol with femininity (and often more attractive).

I wonder how these two square off together, if at all.

I found out that these two hormones seem to be moderately correlated.
So I suppose it’s possible for a woman to be high testosterone, but not high estradiol, and the opposite.

Is it a coincidence that both prefer masculine men, or not?

Finally, progesterone seems to be negatively correlated with testosterone and be a stereotypically ‘feminine hormone’.
Shouldn’t this make a woman more likely to be feminine? 🤔

• Infidelity risk peaks around ovulation, especially when partner satisfaction is low.
• Partner mate-guarding intensifies during fertile windows, reflecting evolved counter-strategies.
• Hormonal contraceptives change tastes and behaviors:
  • Exotic dancers don’t get extra tips during ovulation when using HCs (Miller et al., 2007)
  • Reduced preferences for male masculinity (Feinberg et al., 2008; Gori et al., 2014; Little et al., 2002; Little, Jones, & Burriss, 2007; but see Jones, Hahn, Fisher, Wang, Kandrik, Han, et al., 2018)

Theories of Women’s Sexual Strategies

1. Dual Mating Hypothesis

Main idea:
Women evolved a dual mating strategy:

• Long-term mates: chosen for investment, reliability, and cooperation
• Short-term mates (at peak fertility): chosen for genetic quality (e.g., masculinity, symmetry, health markers)
  (Pillsworth & Haselton, 2006a)

Message: Women may seek good genes via extrapair sex while keeping a dependable long-term partner.

Support:

• Some support from cycle-based shifts in preferences (e.g., increased attraction to masculine men near ovulation)
• But replication is mixed, and newer studies question how strong or consistent the effect is across individuals and cultures.

Also, it’s possible that women may be in a relationship with high mate value partners, in which case the ‘ovulatory shift’ in attraction may favor the current patner:

Moreover, women with more sexually desirable partners report feeling closer to their partners and experiencing more relationship satisfaction around ovulation than women who have less sexually desirable partners.
Conversely, women with less sexually desirable partners report being less critical of and feeling closer to their partner during low-fertility versus high-fertility points in their menstrual cycle (Larson et al., 2013)

2. Extended Sexuality Theory

Main idea:
Women’s sexual behavior extends beyond fertile windows and serves a bonding function, especially in low-fertility (luteal) phases
(Grebe et al., 2013; Thornhill & Gangestad, 2008)

Message: Non-conceptive sex helps maintain long-term bonds, ensure male investment, and protect against risks (e.g., coercion, resource loss) during pregnancy.

Support:

• More support than Dual Mating in explaining why women engage in sex when not fertile
• Aligns well with human pair-bonding and concealed ovulation patterns.

Concealed Ovulation

Main idea:
Unlike many mammals, women show no obvious signs of ovulation (Nunn, 1999), and have sex across the cycle (Dixson & Altmann, 2000).

Message: Concealed ovulation evolved to:

• Increase paternal investment (men can’t time their effort just around ovulation)
• Reduce paternity certainty to deter male infanticide (Hrdy, 1979)
• Allow covert extrapair mating at peak fertility

Support:

• Strong theoretical grounding
• Supported by comparative research and observed human mating patterns
• Fits well with both Dual Mating and Extended Sexuality theories

In chart:

Chapter 15: Long-Term Infidelities

Authors: Dana A. Weiser, Jaclyn Cravens Pickens, Adam V. Thomas

Long-term infidelities involve emotional bonding and sometimes parallel relationships. These affairs can last years and involve deep secrecy. They often coexist with otherwise stable marriages, showing that infidelity is not always about dissatisfaction but can create a “dual life.”

Chapter 16: Cultural Differences in the Nature of Infidelity

Author: Farid Pazhoohi

Cultures differ not just in prevalence but in type. In more gender-equal societies, women report more sexual infidelity; in patriarchal societies, men dominate infidelity rates.
Punishments also differ: in some Middle Eastern countries, female infidelity is punishable by death, while male infidelity may be tolerated. In contrast, Western cultures often normalize male infidelity but stigmatize female cheating less than in the past.

• Greater gender equality correlates with higher reported female infidelity, narrowing gaps.
• Patriarchal cultures harshly punish women’s infidelity, while tolerating men’s more.
• Western societies show narrowing gender gaps, with shifting norms.
• Higher male provisioning = higher infidelity punishment: both men and women viewed male more than female sexual and emotional infidelities more harshly in cultures in which direct paternal investment and provisioning is higher
  • Frequency and permissiveness of social norms toward extramarital sex were associated with higher female-biased sex ratios and lower paternal investment (Scelza et al., 2020a)
• Infidelity acceptance and rates may be rising: from 2000 to 2016, the percentage of American adults who report that extramarital sex is always wrong has declined from 79.4% to 75.8%
  • In China, infidelity rates have risen over the period 2000–2015 from 12.9% to 33.4% for men, and from 4.7% to 11.4% for women (Zhang et al., 2021).

• 🙋🏼‍♂️Nature may beat culture: It is argued that women from male-dominated societies such as Japan in the 1970s do not approve of extramarital infidelity; however, once they are exposed to such an opportunity they are as likely as American women to be unfaithful (Maykovich, 1976).

Chapter 18: Relationship Dissolution Following Infidelity

Authors: Caroline E. Shanholtz, David A. Sbarra

Infidelity is the number one predictor of divorce worldwide. Most relationships do not survive discovery of cheating, especially sexual infidelity. Factors influencing whether couples stay together include presence of children, financial dependence, and willingness to forgive. But overall, infidelity is the leading cause of breakup across societies.

• Infidelity is the leading global cause of divorce, across societies.
• Testosterone has been associated with precursors to unforgiveness, including more anger rumination (Herschl et al., 2012) and less empathy (Hermans et al., 2006).
• Infidelity can be a catalyst toward growth after a separation: women who end very low-quality marriages show gains in psychological well-being over time and appear to be relatively free of the tumultuous period of adjustment that often surrounds the end of marriage (Bourassa et al., 2015)
• Couples with children and shared resources are likelier to stay, despite betrayal.
• Emotional affairs can be as breakup-inducing as sexual ones, depending on values.

Chapter 19: Forgiveness for a Partner’s Infidelity

Authors: Megan R. Dillow, Amanda Denes

Forgiveness after infidelity is rare but possible. Predictors include high relationship investment, religious values, and genuine partner remorse. Women are slightly more forgiving of emotional infidelity, men of sexual infidelity. But forgiveness does not always restore satisfaction—it sometimes only prolongs the relationship.

• Forgiveness depends on remorse, investment, and values, more than time.
• Gendered forgiveness patterns exist, with women more forgiving of emotional, men of sexual infidelity.
• Forgiveness does not guarantee satisfaction recovery, and may only extend the relationship.
• Forgiveness can be healthy: forgiveness-granting has been associated with decreased anxiety, depression, stress, and negative affect; in addition, it improves positive affect and overall life satisfaction (Riek & Mania, 2012; Toussaint et al., 2016). Conversely,
• Unforgiveness has been related to increased subclinical anxiety and depressive symptoms (J. Davis et al., 2015)
• ⚠️ Careful forgivingthose who don’t deserve it, like repeat offenders

Women’s forgiveness of a partner’s abuse may reinforce unequal power distributions and may be equated with tolerance of abuse (Lamb, 2002). Dominant abusers who are able to elicit empathy from their female targets are more likely to be forgiven, implicating a vicious cycle wherein empathy-driven forgiveness is associated with continued patterns of abuse (Tsang & Stanford, 2007)

Forgiveness-Seeking Tactics

Checkmarks that one that seemed to work better, x the ones that didn’t.

• ✅ Explicit acknowledgment — apologizing, expressing regret, taking responsibility, directly asking for forgiveness
• ✅ Nonverbal assurances — behaving especially nicely, showing affection, attentive behavior
• ✅ Compensation — doing favors, buying gifts, offering to “do anything”
• Explanation — giving reasons or context for the offense
• ❌ Humor — joking about the situation or trying to lighten the mood (rare and ineffective for serious transgressions)

What seems to work best then, as predicted by power dynamics theory, is to re-empower the cheated partner.

Sincere apologies, visible remorse, and accepting responsibility increase empathy and forgiveness (Metts & Cupach, 2007; Davis & Gold, 2011; McCullough et al., 1997).
and commitment to change and offering reparations further improve chances of being forgiven

Chapter 21: Renewed Love Between Partners After Infidelity

Authors: T. Joel Wade, Rebecca L. Burch, Maryanne L. Fisher

Some couples experience renewed passion after infidelity, triggered by jealousy, fear of loss, or honest confrontation. These cases are uncommon but show that crises can sometimes reignite attraction. Still, the new closeness often fades with time as post-infidelity passion tend to be ‘spikes’ in attraction.

Chapter 22: Relationship Quality Without Renewed Love

Authors: Mohammad Hassan Asayesh, Elaheh Golpasha

When couples stay together after infidelity without renewed love, the relationship often declines in quality. Trust erodes, communication worsens, and dissatisfaction increases. These marriages often continue due to obligation (children, finances) but are marked by low well-being.

• Children and finances keep couples together, despite chronic dissatisfaction.
  • Some victims form child coalitions, 🙋🏼‍♂️ Lucio’s note: some coalitions can turn toxic and against the cheating partner. I’ve experienced this from an ex’s family

Chapter 23: Violence and Homicide Following Infidelity

Authors: Steven Arnocky, Adam Davis, Ashley Locke, Larissa McKelvie, Tracy Vaillancourt

Infidelity is a leading trigger for intimate partner violence and homicide. Men are more likely to respond violently, especially when paternity uncertainty is threatened.

• Biparental care provides benefits but also risks, including infidelity.
  • Infidelity is a major reproductive challenge
• Violent reactions correlate with male sexual proprietariness: the many potentially violent consequences to real or suspected infidelity (ie.: psychological, physical, or sexual violence against partner, violence against affair partner, abuse and killing of children) all are robustly links to (typically) male sexual proprietariness, which embodies men’s attempts to control and monopolize the reproductive decisions of women to stymie infidelity, reduce paternity uncertainty, and prevent women’s attempts to defect from the romantic relationship (Daly & Wilson, 1988; Taylor, 2012; Wilson & Daly, 1996).
• There is a link between infidelity and abuse, several studies show. Taken together, this body of evidence highlights that infidelity and IPV frequently intersect; real or suspected female infidelity likely precipitates and maintains, but does not justify, violence against women
  • Women who committed infidelity during their prior relationship were more likely to experience sexual and physical abuse at the hands of their partner (Shields and Hanneke, 1983)
  • Men who suspected a partner was likely to cheat reported more controlling behavior, which in turn predicted violence against intimate partners (Cousins & Gangestad, 2007)
  • Arnocky, Sunderani, et al. (2015) supported positive correlations between anticipated partner infidelity and IPV (physical assault, partner injury, sexual coercion, and psychological aggression) in a sample of college-aged men
• IPV may be considered a form of cost-inflicting mate retention behavior, including emotional manipulation, controlling behavior, and physical abuse, that functions to stymie women’s and men’s infidelity and to reduce the likelihood of defection from the mateship (Albert & Arnocky, 2016; Davis et al., 2018; Miner, Shackelford, et al., 2009; Miner, Starratt, et al., 2009)
• IPV may be adaptive, with several lines of evidence
  • Domestic assault appears to function primarily to prevent infidelity, whereas in-pair sexual assault seems to be a response after infidelity has been committed (Camilleri & Quinsey, 2009; Daly & Wilson, 1992; Goetz & Shackelford, 2006)
  • ⚠️ Don’t jump to conclusions, though: it is difficult to determine the extent to which infidelity directly leads to abuse. Abused individuals may instead be more likely to be unfaithful (Arnocky, Sunderani, et al., 2015). And men suspected of infidelity are also more likely to commit IPV (WHO & LSHTM, 2010) (…)
    IPV is also risky, including violent retaliation, increased odds of relationship termination (discussed in Davis et al., 2018, Duntley & Shackelford, 2012, and Miner, Starratt, et al., 2009), and women deciding to terminate pregnancies when victims of IPV
• IPV isn’t male only, women can also perpetrate, particularly in gender-parity cultures women and men perpetrate common forms of emotional and physical violence to a similar extent (Archer, 2006, 2018; Graham-Kevan & Archer, 2003; Straus, 2009).
  • Most IPV appears to be bilateral, whereby both partners are engaged in mutual violence toward one another (Babcock et al., 2019; Madsen et al., 2012).
• Intimate partner homicide is considered an extreme form of male sexual proprietariness (Daly & Wilson, 1988)
  • Uxoricide may best qualify as an evolutionary byproduct rather than the designed behavioral output of an adaptation because of its high costs and smaller payoffs <—- 🙋🏼‍♂️ Lucio’s note: I agree. And was surprised the author didn’t list what seemed to be the strongest cost of uxoricide: losing one’s mate with an act that may make it even harder to find a new one
• Culture of honors may promote IPV, men are more tolerant of male jealousy and male-perpetrated IPV, and men tend to seek power and dominion over women and are more likely to treat them as sexual objects

Interesting Notes

• Women focus on female rivals, men focus on their women: women focus their attention on threats to infidelity from potential rivals (other women), compared to men who focus on monitoring their own partner’s intents to commit infidelity (Ein-Dor et al., 2015).

🙋🏼‍♂️ Lucio’s note on the chapter: Steven Arnocky and his team stand out for their scientific rigor and critical thinking process. Rather than proposing hypotheses based on confirming evidence, they critically examined the data and concurrent explanations both for and against each claim. This balanced, falsification-aware approach is exactly what strengthens theoretical credibility and what we need more of. Both in the world, and in evolutionary psychology specifically.

Chapter 24: Male Sexual Coercion in Response to Infidelity

Authors: Lidia Dengelegi Abrams, Mike Abrams

Some men respond to suspicion or discovery of infidelity with sexual coercion, using sex as a form of control or punishment. This behavior is linked to evolutionary mate-guarding instincts but we shouldn’t fall for the ‘naturalistic fallacy’ and can still condemn it as highly destructive and abusive.

• Some men escalate to sexual coercion after suspicion or discovery, as abusive mate-guarding.
• There is no specific mechanism for rape although it’s evolved. Such as, rape emerges from other evolved male strategies for reproductive competition like aggression, jealousy, mate guarding, sperm competition, lower empathy in some individuals etc., but not because there’s a specific neural system or module that evolved just for rape.
  • Male mate guarding is an adaptation to prevent infidelity and cuckolding, even in its most violent manifestations
• Genetic differences explain 40% of sexual coercion and shared environment explain only 2%. The data directly contradicts the social science model holding that sexual is learned
• Men feeling less desirable than partner deploy more forced in-pair copulation, and more when she is in, or close to, estrus (e.g., Buss & Shackelford, 1997; Goetz et al., 2005)
• Sexual violence does not correlate with dominance in the relationship (Gage & Hutchinson, 2006), contrary to authors who relate sexual partner abuse with need for control and domination (Basile, 2002; Bergen, 1996)

Interesting Notes

• Emotional vs sexual jealousy may depend on lover/provider strategies, rather than genders: A study by Jones and associates (2007) shows that individuals who express high mating effort, characterized by short-term relationships and inconsistent partner-guarding, are more likely to be upset over sexual infidelity than emotional infidelity. Conversely, individuals with low mating effort, who conduct more mate guarding behaviors, but in a way that preserves the future of a relationship, are more likely to be upset by emotional infidelity than sexual infidelity. Moreover, the high-mating-effort individuals are more likely to react punitively to all types of infidelity.

Sexual coercion is part of a cluster of cost-inflicting tactics

Starratt et al. (2008) find a correlation between partner-directed insults and accusations of sexual infidelity and sexual coercion. Resource manipulation, commitment manipulation, and defection threats are correlated with accusations of infidelity and partner insults. Insults such as derogating her physical attractiveness, her value as a partner, her mental capacity, or her value as a person correlate with sexual coercion and can be seen as a type of mate guarding. Lowering the partner’s perceived self-value and self-esteem is meant to diminish her likelihood of attempting to stray

People Constantly Assess Market Value

partners to continuously assess their own mate value relative to their current partner and potential new partners. This challenge to relationship fidelity is exacerbated by the inevitable change of a person’s status, appearance, health, and emotional stability over the life span. When time treats one partner more harshly than the other, there will emerge an increased disparity in relative mate value
(…)
A man’s or woman’s finding someone they believe to be both available and more suitable can lead to a breakdown in the continuing effort to sustain monogamy. For example, a woman who has a close friendship with a male coworker of a higher status or more physically attractive than her husband may progress to a sexual affair if her husband loses his job or otherwise becomes less desirable in her eyes

However, a good bond can go a long way to keep a partner attracted and in the relationship:

Conjugate or companionate love can foster a bond that is resistant to the allure of another potential partner. (…)
Unhappily, many relationships do not develop a strong enough familial bond (…) The combination of relationship fragility and the common practice of evaluating potential new partners may motivate a partner’s focus on someone who seems to offer more

Dominance, Submission, & Sexuality

Rape and sexual coercion may reflect exaggerated but evolutionarily grounded mechanisms that evolved to facilitate reproduction.

Across species, females become less aggressive and less cautious when sexually aroused, particularly during estrus.
Even predators like hyenas or lions adopt submissive postures to permit copulation when fertile (East et al., 1993). This behavioral shift is hormonally mediated—primarily by estrogen—and linked to a submission circuit in the mammalian brain that reduces defensiveness to allow close contact with potentially dangerous males (Pfaff et al., 1994; Ciaccio et al., 1979). The theory holds that evolution had to override the natural caution of females to make reproduction possible, given the risks involved.

Freud (1933) misinterpreted this sexual submission as evidence of innate female masochism, but in fact, sexual masochism is more common in men than women (Abrams et al., 2019; Donnelly & Fraser, 1998). Studies on sexual fantasies show that:

• Men’s submission fantasies often involve BDSM, pain, or humiliation
• Women’s submission fantasies typically center on being dominated by a sexually committed male (Abrams, 2016)

This female preference is consistent with ancestral mating logic, where larger, socially dominant males provided protection for women and offspring (Buss, 2004).
Even modern socially dominant women often report fantasies of sexual submission to dominant men (Hawley & Hensley, 2009), suggesting underlying sexual submission/dominance modules.

There is of course overlap in masculine/feminine responses; some men acquire a more submissive sexual response and some women a more aggressive one.

At the extreme end of these dynamics are sadism and masochism, which reflect overamplified versions of dominance and submission. Sadism exaggerates the drive for dominance to the point where inflicting pain is sexually rewarding. Masochism does the reverse—turning submission into a need for degradation or pain as a condition for arousal.
Given that sadistic and masochistic fantasies are nearly universal (Brown et al., 2020; Joyal & Carpentier, 2017), they likely reflect deep evolutionary structures, originally tied to reproductive strategies involving dominance, submission, and mate choice.

Chapter 25 – 26: Nonhuman Animals & Future Directions

Author: Yu-Hsun Hsu

Infidelity occurs across species. Birds, mammals, and primates show extra-pair mating despite pair bonds. Consequences include paternal uncertainty, mate guarding, infanticide, and sperm competition. Animal studies highlight evolutionary roots of human infidelity.

Chapter 26: Future Directions for Infidelity Research

Author: Tara DeLecce

The book closes by urging clearer definitions of infidelity, better measurement (including digital and emotional), and more diverse global samples. Future research should focus on domain-specific personality traits (e.g., sexual narcissism), cultural variation, and the growing role of technology. Understanding both predictors and consequences is crucial for building realistic models of human mating.

SHARPEST INSIGHTS

These are the insights that struck us the most.
We use the authors’ quotes and research, but the titles and interpretations are our own—and may not reflect the authors’ intent.
Credit for the insight goes to them; blame for the interpretation is on us.

Being Too Nice May Increase Odds of Infidelity?

From chapter 1:

a study of almost 900 older married individuals that controlled for multiple confounding variables (e.g., demographics, the other Big Five personality traits, religiosity) demonstrated that people higher in agreeableness reported more instances of their partner engaging in infidelity (Mahambrey, 2020). The authors speculated that “perhaps individuals with agreeable spouses become accustomed to their highly understanding and accommodating partners, so much so that they assume even infidelity—if discovered—will be pardoned” (p. 294). Consistent with such speculation, other work suggests people do take advantage of partners who appear particularly accommodating (McNulty & Russell, 2016)

However, the findings are inconsistent on this, so it would be incorrect to say ‘the more agreeable, the more you get cheated on’.

I suspect that the difference here is in the variables that sometimes go unmentioned in research, including:

• Gender: it’s not the same for a man or woman to be overly agreeable
• Power awareness: being nice with those who deserve it
• Social strategy: being nice in the appropriate situations
• Personal value: high value and agreeable is good. Low value and agreeable screams ‘overcompensating’
• Masculinity/dominance as the baseline behavior with ‘agreeable on top’

Ie.: I suspect that being too agreeable, naive, lower-value and submissive for men increases the odds of being cheated on.

It may not be the same for women.

And it’s probably not the same for men who are ‘contextually and smartly agreeable’. Such as, being agreeable without being overly agreeable (optimum balance), and knowing when not to be agreeable.

On how to combine being agreeable with getting respect and attraction:

• High agreeable, and high power

Does Western’s ‘Expectation of Monogamy’ Set Up People For Failure?

In chapter 12 Mike Abrams and Lidia Dengelegi Abrams write:

The forces that drive people to seek new mates are in a continual battle with a socially endorsed ideal of lifelong bonds (…) Despite the best efforts of many well-intentioned individuals, innate inclinations often overwhelm the imperatives imposed by marriage or partners’ strong intentions of fidelity. We humans simply are not evolved to remain with one partner exclusively and indefinitely. When we nevertheless do so, it is often with frustration and resentment.
(…)
In an era with long life spans and permanent marriages, love’s relative brevity tends to lead to disappointment. Romantic love almost inevitably fades within a few years, leading to diminished commitment and broken vows

And from chapter 2 by Kelly Campbell et al.:

The prevailing expectation of monogamy, which appears difficult to uphold considering EDI rates, causes individuals to feel devastated when infidelity occurs (Campbell et al., 2012; Coontz, 2005).
(…)
The Western norm of monogamy therefore does not work well, and it would be worth identifying different models that could help individuals and relationships thrive.

I agree with this.
It’s understandable that anyone would be distraught by a cheating partner.

Yet there is also an element of naivete in the assumption that ‘monogamy is the norm, cheating does not happen (to me)’.
And the higher the pain, the more one has bought into that unrealistic ideal.

Long-term monogamy CAN work for many and potentially even most couples within certain cultural contexts and societies (ie.: high social and religious conservatism, fewer options, rural areas, fewer women at work, etc. etc.).
However, that may just not be the case anymore for most Western countries. And it’s been so for decades now.

Also linked, is this:

Naivete May Be Linked to Bigger Trauma After Infidelity

From chapter 22 by Mohammad Hassan:

Balman (1992, as cited in Lusterman, 1998) noted that people who have suffered a severe trauma feel fundamental confusion about the nature of the world cognitively and existentially. Based on Balman’s reports, these people had three basic assumptions in their mind before experiencing the trauma: (1) the world is a source of goodness, (2) the world is purposeful and meaningful, and (3) the self is valuable. Following the trauma of unfaithfulness, these assumptions are shattered.

Believing that ‘the world is a source of goodness’ is an indicator of excessive naivete, unless one also believes the world can be a sourch of ‘not goodness’ as well.

The More He Spends, The More She Cheats (Power-Imbalance Hypothesis of Infidelity)

From chapter 5 by Jana Hackathorn, Brien K. Ashdown:

Lower relative income (i.e., economic dependency on one’s current partner) is associated with higher odds of engaging in infidelity (…)
For women, those who are economically dependent on their partner are more likely to engage in infidelity than either women who provide all the income in a household (i.e., the breadwinners) or women who are in an economically equal relationship (Munsch, 2015).

This is something I noted and aligns with power dynamics.

As usual, mate value plays an important role.
Female breadwinners may be more likely to be in a partnership with a more attractive or player type in an unspoken exchange of money for mate value.

For men, the more he earns compared to her, the less likely it is that it’s a relationship between equals.
A relationship with higher power imbalance may seem good for the dominant party on paper, but it presents unique challenges.

Unless he’s careful and highly power-aware, his financial contributions may turn the relationship transactional (even if she initially likes him for his qualities, the ‘crowding out effect’ of intrinsic motivation).

Submissive parties tend to avoid assertiveness and instead resort to passive aggression, sneakiness… And cheating behind the dominant party’s back.

I’ve seen these dynamics often, including with Western men traveling to poorer countries, and this includes younger and good-looking guys, not just the retired ones.
Some of these ‘passport bros’ believe they struck gold with local, submissive women. But front-facing submissiveness rarely translates to faithfulness.

I suspect that relationships with a high power imbalance may inherently increase ‘in your face submissiveness’, but at the cost of increasing ‘behind your back sneakiness’.

Men: Don’t Be Too Vulnerable

From an interesting clinical example of a man who made the mistake of ‘seekign reassurance’:

In his despair, Val made the common mistake of seeking reassurance from a spouse going through an emotional crisis of her own. <— 🙋🏼‍♂️ Lucio’s note: Instead a masculine steadying presence, he added his own crisis
Karen’s priorities were her child and child to be, and their life quality now seemed at risk. Her anxieties were leading her to question the trajectory of their marriage. Val’s new self-effacing demeanor and his apologetic efforts to do more at home had the paradoxical effect of diminishing his status in Karen’s eyes. <— 🙋🏼‍♂️ Lucio’s note: Giving more in this situation can be framed as a (desperate) effort ot make up for an ever-growing mate value discrepancy
She now pitied him, and pity is not attractive. As this tension in their marriage increased, their sexual encounters radically decreased in frequency

And then she went on to cheat on him.
I was quite surprised to see such a lucid, power-aware, real-life case study in a handbook.
The authors analyzed this example perfectly well, a TPM-level passage. These are the types of therapists that can put a man back on track.

Also read ‘vulnerability without losing power‘.

QUOTES

On the reality of humans’ (subconscious) calculativeness:

Partners in relationships are continually assessing their own and their mate’s “market value,” and their self-appraised mate value will often guide the treatment of their partner and decision of whether to be unfaithful.

On morality vs evolutionary logic:

Since moral virtue was not an attribute that added to fitness during the epochs in which the preponderance of hominin and human behavior evolved, violence had many upsides and fewer downsides

🙋🏼‍♂️ Lucio’s Analysis

This was an exemplary handbook: it analyzed infidelity both broadly and deeply, there was little overlap between chapters to maximize time to insights, and the authors wrote like true scientists.

Just take these examples:

• it should be noted that this integrative data analysis was based on newlywed couples, a time when infidelity is rare and thus we are hesitant to draw strong conclusions from this single analysis <— This is how you critically analyze a sample and think about possible faults with it, rather than immediately generalize the findings
  (Chapter 1, Emma E. Altgelt, James K. McNulty, and Andrea L. Meltzer)
• and behavioral displays of dominance (although these authors used estimated rather than measured hormonal assessments). <— The author highlights and uncovers an importantant limitation for the readers’ benefit (Chapter 14, Virginia E. Mitchell et al.)
• there are reasons to question whether IPV in response to infidelity constitute adaptations. Cost-inflicting mate retention is a risky reproductive strategy because it may result in violent retaliation and increase the likelihood of termination of the relationship (discussed in Davis et al., 2018, Duntley & Shackelford, 2012, and Miner, Starratt, et al., 2009) <— this is good critical thinking skills, without jumping to easy conclusions. This is how you make you good evolutionary psychology, without falling for easy storytelling (Chapter 23, Steve Arnocky)

REVIEW

The Oxford Handbook of Infidelity (2023) is an exceptionally insightful and well-crafted volume, written with the rigor and clarity one expects from top researchers.

Each chapter not only summarizes the state of the science but also highlights limitations, unresolved debates, and where evidence remains mixed or merely hypothetical.

I hope more researchers will follow this example.
For TPM, I was able to update and improve several articles. I’m grateful to the authors, and I look forward to learning more from them 🙏🏼.

Check the best evolutionary books or get this book on Amazon.

The Oxford Handbook of Infidelity: Summary & Review

The Oxford Handbook of Infidelity (2023) is the most comprehensive scientific reference on why people cheat, bringing together leading researchers to provide a global, evidence-based picture of who is most likely to be unfaithful, why, and with what consequences.

URL: https://thepowermoves.com/the-oxford-handbook-of-infidelity-summary-review/

Author: Lucio Buffalmano

Editor's Rating:
5