A recent study published in Evolution and Human Behavior offers new insights into the complex motivations behind female infidelity. The findings reveal that women who cheat are typically more physically attracted to their affair partners but view their primary partners as better co-parents. This suggests that women may cheat to obtain “good genes” for their offspring while relying on their primary partners for parenting support. Additionally, the study highlights several other motivations for infidelity, including relationship dissatisfaction, the desire for variety, and revenge.
Understanding why women commit infidelity is an ongoing debate in evolutionary psychology. Traditionally, infidelity in men has been explained through the desire to increase reproductive success by mating with multiple partners. However, this explanation does not translate directly to women, who do not gain the same reproductive benefits from having multiple mates. A woman’s reproductive output is limited by the number of pregnancies she can have, not by the number of mates she has, unlike men who can potentially father many more offspring with multiple partners.
Consequently, having multiple mates does not significantly increase a woman’s reproductive success in the same way it does for men. This discrepancy has led scientists to explore other potential evolutionary reasons for female infidelity, resulting in two main hypotheses: the mate-switching hypothesis and the dual-mating strategy.
The mate-switching hypothesis suggests that women might engage in infidelity to find a better long-term partner, essentially laying the groundwork to replace their current mate with someone of higher mate value. On the other hand, the dual-mating strategy posits that women might seek to obtain the best possible genetic material from an affair partner while retaining the parental investment from their primary partner. This strategy would mean prioritizing physical attractiveness and genetic benefits in affair partners while valuing their primary partners for their parental qualities.
“It might sound funny, but the evolutionary drivers of female infidelity in humans is an area of vigorous debate in my part of academia. In a way, there are too many good explanations for it!” said study author Macken Murphy, a PhD student at the University of Melbourne and host of the “Species” podcast.
The researchers used Prolific Academic to survey a sample of 254 heterosexual English-speaking men and women who had engaged in infidelity. The survey collected data from participants across 19 countries, making the sample more representative of different socioecological contexts compared to previous studies often limited to specific populations like American undergraduates.
The survey measured three main components of attraction — physical (appearance and sexual desirability), personal (how much they liked their partners’ personal qualities and enjoyed their company), and parental (perceived parenting abilities and suitability for raising children together) — towards both the affair partner and the primary partner using modified versions of the Interpersonal Attraction Scale and the Mate Value Scale. These scales are well-established in the literature and were chosen for their reliability and validity.
In addition to quantitative measures, the survey included qualitative questions to gather more nuanced data about participants’ motivations for infidelity. Participants were asked to describe, in their own words, what motivated them to have an affair. This qualitative component allowed the researchers to capture a broader range of motivations and to identify recurrent themes and patterns in the reasons people cheat.
Women in the study generally rated their affair partners as more physically attractive but less suitable as co-parents compared to their primary partners. This pattern aligns with the dual-mating strategy, where the primary goal of an affair is to combine “good genes” from an affair partner with the parenting support of the primary partner.
Contrary to the mate-switching hypothesis, the study found no evidence that women preferred their affair partners overall or saw them as better long-term mates. Women did not rate their affair partners higher in terms of mate value or personality compared to their primary partners. This indicates that women are not typically seeking to replace their primary partners with their affair partners. Instead, they seem to maintain a clear distinction between the roles of their primary and affair partners, valuing different qualities in each.
Interestingly, the study also found that men exhibited similar patterns to women in their infidelity behavior. This suggests that men, like women, may also engage in infidelity to seek genetic benefits from physically attractive affair partners while valuing their primary partners for parental investment.
“Finding that men were strategically dualistic as well — prioritizing physical attraction in affair partners and parental ability in primary partners — was a surprise,” Murphy told PsyPost. “However, it’s consistent with some past research, some of which suggests men are even more dualistic than women in their affairs.”
The qualitative data provided further insights into the diverse motivations behind infidelity. Some participants’ responses aligned with the dual-mating strategy. For example, several women mentioned being physically attracted to their affair partners and wanting to experience being with someone more attractive than their primary partner.
Although the findings did not support the mate-switching hypothesis overall, some participants indicated that they had affairs in search of a better long-term partner. A few women mentioned falling in love with their affair partners or wanting to be with them long-term, which reflects the mate-switching strategy. This indicates that while mate-switching may not be the dominant motive, it is still relevant for a subset of individuals.
Both men and women cited a desire for variety and novelty as a reason for their affairs. This motivation aligns with the idea that individuals seek new and exciting experiences outside their primary relationships. For instance, one woman mentioned being bored in her relationship, and a man described wanting to “sow his wild oats” while still young. These responses suggest that the drive for new sexual or romantic experiences can be a significant factor in infidelity.
A significant number of participants, particularly women, mentioned relationship dissatisfaction as a key motivator for their affairs. This included feelings of neglect, lack of emotional support, and general unhappiness with their primary partners. Women were notably more likely than men to cite their partner’s lack of investment and support as reasons for cheating.
Some participants reported infidelity as a form of revenge against their primary partners, particularly in response to their partner’s infidelity. Women were more likely than men to cite revenge as a motivation, reflecting a desire to retaliate and restore a sense of justice or balance. For example, one woman mentioned discovering her partner’s emails seeking other women, which prompted her to cheat as a form of payback.
A few participants indicated that their affairs were driven by a desire to validate their attractiveness and desirability. For example, one woman wanted to know that other men still found her desirable and wanted to gain more sexual experience. This reflects a motive to acquire information about one’s own value and attractiveness in the mating market.
Although less commonly cited, the multiple investors hypothesis was supported by a few responses. This hypothesis suggests that women might engage in infidelity to secure additional resources and support from multiple partners, thereby enhancing their offspring’s survival and well-being. This strategy is particularly relevant in environments where the primary partner’s investment is insufficient, prompting women to seek supplementary help from other men. For example, one woman mentioned getting closer to another man who was always available to help her and her child, suggesting she sought additional investment and support outside her primary relationship.
Finally, some participants mentioned unique or situational factors that influenced their decision to cheat. These included stress, long-distance relationships, and the influence of drugs and alcohol. These responses highlight that infidelity can be influenced by a range of external and situational factors, beyond the primary evolutionary strategies.
“Infidelity is a tactic that serves a variety of evolutionarily coherent strategies, including obtaining additional resources, switching to a new primary mate, and, especially in our study, acquiring genetic benefits for offspring,” Murphy said. “However, while humans evolved to cheat, that doesn’t mean we should, and most people don’t.”
But as with all research, there are some limitations. For example, the study relied on self-reported data, which can be influenced by social desirability bias, meaning participants might not fully disclose socially unacceptable motivations for their infidelity.
In addition, Murphy highlighted three important caveats to consider: “1) most women don’t cheat, and many women who do aren’t pursuing a dual mating strategy, and so the vast majority of women are not enacting a dual mating strategy, 2) this study isn’t about conscious motivations, directly, but the evolved psychology underlying them, and 3) the phrase ‘good genes’ comes from evolutionary biology, so it can sound fairly crazy when applied to humans. ‘Good,’ here, is meant in a fitness sense, not in a moral sense — nobody has better genes than anybody else.”
It is also important to note that providing an evolutionary explanation for a behavior, such as infidelity, is not the same as justifying or excusing it. “Just because cheating is natural doesn’t make it alright,” Murphy said.
The study, “Why women cheat: testing evolutionary hypotheses for female infidelity in a multinational sample,” was authored by Macken Murphy, Caroline A. Phillips, and Khandis R. Blake.
