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.