Introduction

Romantic jealousy, which refers to the jealousy experienced in response to real or perceived threats to an intimate relationship, is an unpleasant emotion that people do not wish to experience (DeSteno et al., 2002; Buss, 2000). It is also associated with various negative consequences, including relationship dissolution (Apostolou & Wang, 2021), divorce (Betzig, 1989), depression, and suicide attempts (Carson & Cupach, 2000), as well as domestic violence (Buss, 2000; for a comprehensive review of jealousy literature, refer to Martínez-León et al., 2017). It has been argued that these adverse outcomes are outweighed by jealousy’s protective effect against infidelity (Buss, 2000). The current research aims to test several predictions derived from this hypothesis within the context of Greek culture. We will initiate our discussion by exploring the evolutionary logic of cheating.

The Evolutionary Logic of Infidelity

In order for individuals to be unfaithful to their partners, they must first be in a committed relationship. Consequently, the evolution of infidelity followed the evolution of long-term mating, which we will discuss first. Human mating is strategic in that individuals employ specific strategies to direct their mating efforts towards specific goals (Gangestad & Simpson, 2000). Various factors have favored the evolution of long-term mating strategies, where individuals form enduring intimate relationships.

To begin with, human children require significant, reliable, and prolonged parental investment before reaching sexual maturity and being able to reproduce themselves. Consequently, the formation of long-term intimate relationships is associated with reproductive benefits, as parents can combine their efforts to provide the necessary investment for their children (Lancaster & Lancaster, 1987). Additionally, a long-term mate can be a valuable source of support, particularly in ancestral human societies that lacked social protection systems (Apostolou & Wang, 2021). Furthermore, long-term mating is associated with a lower risk of contracting sexually transmitted diseases compared to casual mating (McLeod & Day, 2014). These survival and reproductive or fitness benefits have made long-term mating the dominant mating strategy. For example, throughout different times and cultures, most people form enduring relationships with the goal of having and raising children within the institution of marriage (Coontz, 2005).

There are several potential fitness benefits associated with having extra-pair partners. Firstly, men can have a higher number of children with less parental investment, while women can obtain material goods or secure better genes for their children (Buss & Schmitt, 1993, 2019; Schacht & Kramer, 2019). Both sexes can establish relationships with desirable individuals who could become their partners if their legitimate partners abandon them or die (Buss & Schmitt, 1993). Similarly, both men and women who wish to switch mates can probe future partners before ending their current relationship (Buss et al., 2017). These potential benefits have favored an infidelity strategy in which individuals in long-term relationships engage in extra-pair mating (Buss, 2000). Due to its secretive nature, it is challenging to determine the exact prevalence of this strategy; however, different lines of evidence suggest that it is widespread. For example, studies in the USA have indicated that approximately one in three married men and one in five married women are expected to have an extramarital affair during their lifetime (Greeley, 1994; Tafoya & Spitzberg, 2007; for a review of infidelity research, see Fincham & May, 2017; Haseli et al., 2019).

The Evolutionary Logic of Romantic Jealousy

An intimate partner’s infidelity can have detrimental fitness consequences. To begin with, individuals risk losing their partners’ investment to other individuals and their children. They also risk losing their partners to others and forfeiting all the investment they have made in maintaining the relationship. Additionally, there is a risk of contracting a sexually transmitted disease, while men risk unknowingly raising another man’s children (Buss, 2000; Greiling & Buss, 2000). These potential fitness costs create strong selection pressures favoring the evolution of mechanisms that protect individuals from their partners’ infidelity (Platek & Shackelford, 2006). One such mechanism is romantic jealousy (Buss, 2000).

In more detail, romantic jealousy reduces the costs of infidelity by generating a negative emotion that prompts corrective action to eliminate it. Jealousy mechanism is sensitive to clues indicating that a partner is cheating. When such clues are detected, jealousy triggers and enables individuals to take corrective actions such as monitoring their partners more closely or searching their belongings to determine if infidelity is actually occurring (Mullen & Martin, 1994; see also Apostolou & Ioannidou, 2021). Jealousy can also trigger adverse reactions such as ending the relationship or being physically aggressive toward the partner. The fear of these reactions serves as a deterrent for partners to be unfaithful (Buss, 2000).

Moreover, jealousy is sensitive to situations or contexts where there are increased opportunities for a partner to cheat, such as going on a business trip. Jealousy triggers motivating actions such as frequent calls to partners or insisting on accompanying them. Furthermore, jealousy can preemptively trigger before partners find themselves in high-risk situations to prevent them from actually encountering such situations. For example, driven by jealousy, people may insist on accompanying their partners when they go out, reducing the latter’s opportunities to engage with potential extra-pair mates (for further discussion, see Apostolou & Ioannidou, 2021).

Predictions

Based on the above theoretical framework, we can derive several predictions regarding the workings of romantic jealousy. Firstly, we expect jealousy to be triggered in contexts or situations where there is an increased probability of an intimate partner cheating. One such context is when a partner’s mate value exceeds one’s own (Buss & Shackelford, 1997; Sidelinger & Booth–Butterfield, 2007). In this scenario, partners with higher mate value experience an opportunity cost, equivalent to the fitness benefits they could gain by being in a relationship with someone of similar mate value, but forego by staying with their current partners. To minimize this cost, they would be motivated to seek either parallel relationships with higher mate value partners or terminate the current relationship and seek a higher mate value partner. In the case of the latter, they may remain in the current relationship while exploring prospective mates (Buss et al., 2017). Overall, discrepancies in mate value would be associated with a higher risk of cheating, consequently triggering higher levels of jealousy (H1). Consistent with this prediction, Sidelinger and Booth–Butterfield (2007) conducted a study with a sample of 179 undergraduate students in the USA, and found that having an intimate partner with a higher mate value was associated with increased jealousy.

Individuals vary considerably in their inclination towards infidelity. Some are strictly monogamous, while others are inclined to be unfaithful at every opportunity (Buss, 2016). Therefore, another context associated with a higher probability of being unfaithful is having an intimate partner likely to adopt a cheating strategy. The adoption of such a strategy is reflected in attitudes toward cheating, considering it appropriate, for instance, if the partner never finds out. We expect that the romantic jealousy mechanism is sensitive to detecting such attitudes, leading to the prediction that having a partner with positive attitudes toward infidelity would trigger jealousy in the other partner (H2). Furthermore, frequent interactions with individuals of the opposite sex is a context that could potentially provide more opportunities for cheating. Accordingly, we predict that higher levels of opposite-sex interactions would be associated with higher levels of partner jealousy (H3).

Moving on, for jealousy to protect against infidelity, it would need to constrain partners’ freedom to find themselves in compromising situations. This leads to the prediction that higher levels of partner jealousy would be associated with less freedom to flirt with others (H4). One pathway for this to occur is through higher jealousy being linked to more negative reactions when infidelity is detected, and the fear of such reactions would limit people’s freedom to flirt with others. Therefore, we predict that higher levels of partner’s jealousy would be associated with a greater fear of negative reactions, which in turn would be associated with less freedom to flirt with others (H5).

Methods

Participants

The research was performed at private university in the Republic of Cyprus, and has received ethics clearance from the institution’s ethic’s review board. Participants were recruited by promoting the link of the study as an ad on social media (Facebook, Instagram, Twitter), with the target audience being adult people residing in Greece and in the Republic of Cyprus. In addition, we forwarded the link to students enrolled in our classes at the time of the study, and to colleagues in our department with the request to forward it to their network of friends and acquaintances. Participation was on a voluntary basis. In total, 333 (197 women, 135 men, and one participant who did not indicate her/his sex) Greek-speaking participants took part. The mean age of women was 33.9 (SD = 9.3), and the mean age of men was 37.5 (SD = 11.2). Moreover, 54.4% of the participants indicated that they were in a relationship, and 45.6% that they were married. In addition, 94.6% of the participants indicated that they were attracted exclusively or predominantly to members of the opposite sex, 3.3% exclusively or predominantly to members of the same sex, and 2.1% to both members of the opposite and same sex.

Materials

The questionnaire was in Greek and was created using Google Forms. It consisted of nine parts. In the first part, participants were asked to indicate their relationship status (single, in a relationship, married, other). Only participants who indicated that they were in an intimate relationship (i.e., in a relationship or married) were allowed to proceed to the next part. In the second part, participants were asked to rate their partners’ mate value, while in the third part, they were asked to rate their own mate value. For this purpose, we employed a four-item instrument that participants had to rate on a seven-point scale (Edlund & Sagarin, 2014). For this scale, Cronbach’s alpha was 0.89. A higher mean score indicated a higher mate value.

In the fourth part, participants were asked to assess their partners’ jealousy using a seven-item instrument. Participants had to rate the items on a seven-point Likert scale, with a higher mean score indicating higher levels of jealousy. The instrument was developed by Apostolou and Antonopoulou (2022) and was based on a larger instrument developed by Pines and Aronson (1983a) (see Appendix A). We chose the shorter version because the Pines and Aronson (1983b) original instrument measured subjective variables including how people feel about their financial or mental condition, which were of not interest here. Furthermore, the items were adapted to measure partner’s jealousy. For instance, the “How jealous you consider yourself to be?” was changed to “In general, how jealous you consider your partner to be?” Cronbach’s alpha for this scale was 0.74. In the fifth part, we measured participants’ attitudes toward cheating using a four-item instrument that we developed for this purpose (see Appendix B). We developed a new scale because we were unable to find an existing one in the literature. Participants responded to the items using a five-point Likert scale: 1 – Strongly disagree, 5 – Strongly agree. The Cronbach’s alpha for this scale was 0.91. A higher mean score indicated more positive attitudes toward cheating.

In the sixth part, we measured the frequency of participants’ interactions with members of the opposite sex. Participants were asked the following questions: “I often go out with people of the opposite sex” and “I have friends of the opposite sex.“ Participants’ responses were recorded on a five-point Likert scale: 1 – Strongly disagree, 5 – Strongly agree. In the seventh part, we measured participants’ freedom to flirt using the following question: “I have limited freedom to flirt with others.“ In the eighth part, we measured participants’ fear of their partner’s reactions using the following question: “I am afraid of my partner’s reactions if he/she finds out I have cheated on him/her.“ In both parts, participants’ answers were recorded on a five-point scale: 1 – Strongly disagree, 5 – Strongly agree. Finally, in the ninth part, demographic information was recorded, including sex, age, and sexual orientation (attracted exclusively or predominantly to members of the opposite sex, attracted about the same to members of the same or opposite sex, attracted exclusively or predominantly to members of the same sex).

Statistical Analysis

We conducted an ANCOVA test with partner’s jealousy as the dependent variable. The independent continuous variables included attitudes toward cheating, frequency of interaction with opposite-sex individuals, and age. The independent categorical variables were discrepancy in mate value and sex. The frequency of interactions with the opposite sex variable was created by averaging the responses to the two questions that measured this dimension.

To create the discrepancy in mate value variable, we followed this procedure: First, we estimated the partner’s mate value and the participant’s own mate value, and then subtracted the latter from the former. We then classified these scores into three categories: If the participants’ mate value was between − 0.25 and 0.25 units, they were classified as “own similar to partner’s mate value.“ If the participant’s own mate value exceeded their partner’s mate value by more than 0.25 units, they were classified as “own higher than partner’s mate value.“ If their partners’ mate value exceeded the participants’ own mate value by 0.25 units they were classified as “partner’s higher than own mate value.“

In our sample, 44.7% of the participants indicated that their partners had a similar mate value to their own, 32.6% indicated that their partners had a higher mate value than their own, and 22.7% indicated that their partners had a lower mate value than their own.

Furthermore, we conducted a mediation analysis with participants’ responses to the question about freedom to flirt with others as the dependent variable, partner’s jealousy as the predictor, and fear of partner’s reactions as the mediator (see Fig. 1). Sex and age variables were included as covariates. Unstandardized indirect effects were computed for each of the 10,000 bootstrapped samples, and the 95% confidence interval was determined by examining the indirect effects at the 2.5th and 97.5th percentiles. The analysis was performed using SPSS version 28 and the PROCESS version 4.2 macro.

Fig. 1
figure 1

The figure above depicts the direct and indirect effect of partner’s jealousy on freedom to flirt with others

Full size image

Results

We aimed to test the hypothesis that one context which is likely to trigger partners’ jealousy is interactions with individuals of the opposite sex. However, this is unlikely to be true for homosexual people. Thus, for our analysis, we excluded participants who indicated that they were only attracted to members of the same sex (11 participants). Our results indicated that there was a significant main effect of mate value differential on partner’s jealousy [F(1,296) = 17.60, p = .006. ηp2 = 0.034]. More specifically, post-hoc analysis using Bonferroni indicated that participants who reported that they had a higher mate value than their partners, indicated the latter to be significantly more jealous (M = 3.88, SD = 1.34) than participants who reported their partners’ mate value to be similar (M = 3.34, SD = 1.19) or lower to their own (M = 3.25, SD = 1.02). Note that there was no statistical difference between the latter two categories. In addition, there was a significant main effect of attitudes toward cheating on partner’s jealousy [F(1,296) = 17.60, p = .002. ηp2 = 0.032]. The coefficient of attitudes was positive (0.213) indicating that the more positive attitudes participants had toward cheating, the more jealous they reported their partners to be.

Furthermore, there was no significant main effect of the opposite-sex interactions variable (p = .904), but there was a significant interaction between sex and opposite-sex interactions variable [F(1,296) = 17.60, p = .002. ηp2 = 0.032], indicating that the opposite-sex interactions had a different effect on men and on women. Accordingly, we repeated the analysis separately for male and female participants. For men, the effect was not significant (p = .060), and the coefficient was to the opposite than the predicted direction (i.e., negative). On the other hand, for women the effect was significant [F(1,296) = 7.48, p = .007. ηp2 = 0.040]. The coefficient was positive (0.200) indicating that the more women indicated that they were interacting with opposite-sex individuals the higher their partners’ jealousy. In addition, with respect to reducing freedom to flirt, there was a significant main effect of partner’s jealousy [F(1,315) = 11.18, p = .001. ηp2 = 0.034] with a positive coefficient (b = 0.212) indicating that the higher partner’s jealousy was the more participants indicated that they had reduced opportunities to flirt. Note that we did not detect any significant interactions between our independent variables.

We would also like to examine whether there was a sex difference in the fear of a partner’s reactions. For this purpose, we run an ANCOVA test, where the fear of a partner’s reactions was entered as the dependent variable, and participants’ sex and age as the independent variables. The results indicate that there was no significant main effect of sex (p = .224).

Mediation Analysis

In running mediation analysis, homosexual participants were also included. The results indicated that there was a direct effect of partner’s jealousy on freedom (c’) (p = .007). The coefficient was positive [b = 0.18 (CI-95: 0.05–0.30)] indicating that the more jealous participants indicated their partners to be, the more they indicated that they had limited freedom to flirt with others. Moreover, partner’s jealousy had an effect on the fear of partner’s reactions (a) (p < .001), with a positive coefficient [b = 0.22 (CI-95: 0.08–0.35)]. In addition, there was a significant indirect effect of partner’s jealousy on flirting through fear of reactions (a*b) [b = 0.03 (CI-95: 0.00-0.06)]. The total effect (direct plus indirect) was 0.21 indicating that one unit increase in partner’s jealousy was associated with a 0.21 units increase in participants’ reporting that they had limited freedom to flirt with others. The bulk of this increase was due to jealousy having a direct effect (0.18), but there was also a small indirect effect through the fear of partner’s reactions (0.03).

Discussion

In the current study, we found that an intimate partner’s jealousy is predicted by discrepancy in mate value, attitudes toward cheating, and interactions with opposite-sex individuals. However, the effect of interactions with opposite-sex individuals was limited to male participants. Additionally, we found that higher romantic jealousy in a partner was associated with reduced freedom to flirt with others. This effect was both direct and indirect, mediated by increased fear of partner’s reactions.

Consistent with our original prediction, having a higher mate value than a partner was associated with the partner exhibiting more romantic jealousy. Previous research has also shown that individuals who rated their partners as having a higher mate value than their own exhibited higher jealousy (Sidelinger & Booth-Butterfield, 2007). This finding provides evidence for the protective nature of the romantic jealousy mechanism. If intimate partners have a higher mate value, they are more likely to cheat, which triggers jealousy and keeps people vigilant. In addition, it could be advantageous in terms of reproductive success to have intimate partners of similar mate value as they are less likely to cheat (see Luo, 2017), and romantic jealousy could promote the formation of such relationships. In particular, having an intimate partner with a higher mate value frequently triggers jealousy, which, from an evolutionary perspective, could be interpreted as a ‘punishment’ for being in a fitness-decreasing situation. To avoid this punishment, people may seek to escape such situations by terminating the relationship and finding a partner with a similar mate value.

In line with our original prediction, more positive attitudes toward cheating were associated with a partner exhibiting higher jealousy. The evolutionary argument suggests that positive attitudes toward infidelity would be associated with a higher likelihood of cheating, triggering jealousy and increasing vigilance. However, as discussed earlier, it is also possible that experiencing jealousy serves as a ‘punishment’ for being in a fitness-decreasing situation, such as having a partner who is likely to be unfaithful. This punishment may lead individuals to seek more fitness-increasing situations, such as having an intimate partner with negative attitudes toward cheating. Thus, jealousy could have a dual effect: Being vigilant to prevent infidelity and considering partners who are less likely to cheat. Yet another possibility is that expressing jealousy may indicate how partners value each other, leading to the renegotiation of relationship rules and ultimately more satisfying relationships (Guerrero et al., 1995).

We predicted that frequent interactions with opposite-sex individuals would be associated with increased romantic jealousy in a partner. However, this effect was only found in male participants, indicating that women exhibit jealousy when their male partners interact with other women, while men do not exhibit the same level of jealousy when their female partners interact with other men. We do not have a working hypothesis to explain the absence of this effect in female participants, and future studies should attempt to replicate our findings in different samples.

Consistent with our original prediction, higher partner jealousy was associated with less freedom to flirt with others. This finding demonstrates the protective nature of the romantic jealousy mechanism, which limits opportunities for infidelity. We also found an indirect effect: Higher partner jealousy was associated with greater fear of adverse reactions, which in turn was associated with less freedom to flirt with others. However, the indirect effect was small, suggesting that this is not the primary mechanism through which jealousy leads to a reduction in the freedom to flirt. Therefore, future research should examine other ways in which higher jealousy constrains a partner’s freedom to cheat.

There are several factors that could moderate the relationships we found here, such as personality or emotional closeness between partners. For instance, the effect of the partner’s jealousy on the fear of reactions to infidelity may be moderated by the closeness of the relationship. For instance, people who are closer to their partner may worry more about their reactions in case of infidelity. Additionally, jealousy can directly affect the closeness of the relationship. Specifically, some individuals may experience high levels of romantic jealousy, which motivates them to guard their partners and reduces the possibility of infidelity. However, this jealousy could strain the relationship, leading to emotional distance between the parties involved. Future research should consider additional variables such as emotional closeness that could have effects on the relationships identified in the current study.

Moving on, infidelity can be emotional or sexual. In particular, intimate partners may have romantic feelings for extra-pair mates without being sexually involved with them. Additionally, they may have sexual relationships without being emotionally involved, with the use of prostitution being an obvious example. Men, as opposed to women, face the risk of cuckoldry, which involves raising other men’s children without being aware of it. Sexual infidelity greatly increases this risk. On the other hand, historically women have been dependent on the resources provided by their partners, which could be lost if their partners become emotionally involved with other women. Based on this reasoning, it has been argued that men would be more upset in instances of actual or suspected sexual infidelity, while women would be more upset in instances of actual or suspected emotional infidelity (Buss et al., 1992). Considerable empirical work (e.g., Sagarin et al., 2003) has found support for this hypothesis (for a review, see Edlund & Sagarin, 2017). Our study did not distinguish between emotional and sexual infidelity, and future research should extend our work by considering this dimension of infidelity. For instance, we found that a partner’s jealousy was associated with a decreased freedom to flirt, both directly and indirectly through fear of negative reactions (see Fig. 1). This model could be extended to consider emotional or sexual infidelity as triggers of jealousy and examine the different pathways for men and women.

One limitation of the current research is that it relied on self-report instruments, which are susceptible to various biases, including participants providing inaccurate answers. Additionally, our instruments measured perceived rather than objective scores (e.g., mate value). For example, we measured how people perceive their partner’s jealousy rather than directly measuring the partner’s jealousy. However, in our theoretical framework, for jealousy to be effective in protecting against infidelity, it needs to be manifested in behavior, such as individuals constantly checking on their partners. Thus, jealousy is not a latent trait, and people can have a generally accurate idea of how jealous their partners are. In other words, if your partner is highly jealous without outwardly manifesting it, you might perceive that you can freely engage in cheating without consequences. Furthermore, to test our hypotheses, we required a measure of perceived jealousy rather than actual jealousy. For instance, we hypothesized that people’s freedom to flirt with others would be reduced due to their fear of their partner’s reactions. If partners’ jealousy is not expressed, people would not perceive it, and as a result, they would not fear their partners’ reactions.

Furthermore, for measuring specific dimensions of interest, such as freedom to flirt with others, we used single-item instruments. While we believe that these instruments adequately capture the dimensions of interest, future research may develop alternative instruments for this purpose. Moving on, when measuring participants’ attitudes toward infidelity, we asked them about ‘cheating’ without providing clarification regarding its specific meaning. Since cheating can manifest in different forms (emotional or sexual, as discussed earlier), future research should investigate attitudes toward each type and explore their relationship with triggering a partner’s jealousy. Furthermore, when examining the effect of the fear of partners’ reaction to infidelity, we did not investigate the specific nature of participants’ fears. Exploring this aspect could potentially reveal sex differences, with women, for example, being more concerned about physical retaliation, while men might be more apprehensive about their partner dissolving the relationship as a reaction. Future research should expand upon our findings by precisely identifying the reactions people are fearing.

Although there has been considerable theorizing on the evolved nature of romantic jealousy, empirical research in this area remains limited. The current research has tested several predictions derived from the hypothesis that romantic jealousy has a protective effect against infidelity. Further research is necessary to better understand the mechanisms of this behavioral adaptation.