Sex Differences in Jealousy: An Evolutionary Perspective
Jealousy is an intense emotional reaction that affects all types of people in different cultures all over the world (Buss, 2001). Having a wide variety of implications, jealousy is most often associated with negative, anxiety induced behaviours, and in relationships it is most often in response to a relationship threat by a third party with desirable qualities. Current literature on the topic suggests that there is a general consensus that the main function of jealousy is to protect a valuable relationship from loss to a desirable rival (Buss & Haselton, 2005). However despite this primary function, there are clear sex differences with regards to thoughts about emotional and sexual infidelity (Daly, Wilson & Weghorst, 1982). There exists a lot of evidence to support the finding that men find sexual infidelity worse than emotional infidelity, whereas women find the opposite (Buss et al., 2001; Daly et al., 1982). It has been found that 60% of men choose sexual infidelity as worse, and 74% of women choose emotional infidelity (Sagarin et al., 2012). Moreover, these findings have been replicated in numerous countries, which encourage the perspective that these sex differences are evolutionary based (Buunk & Angleitner, 1996). The parental-investment model states that these differences occur because men want to be sure of the paternity of their children, not invest their resources to genetically unrelated offspring, and consequently lose reproductive resources. Women, however, find emotional infidelity worse because they want mates who will invest in their offspring’s chance of survival (Trivers, 1972). Nonetheless, there still remains considerable controversy over whether these sex differences really do exist. Forced-choice compared to continuous measures have yielded different results, with forced-choice measures revealing sex differences and continuous measures showing no differences (DeSteno, 2010). When using the Buss Infidelity Questionnaire, participants are asked which out of two scenarios would distress them more: their partner having intense, sexual intercourse with another person, or their partner have a deep emotional attachment to another person. Using this measure, it was found that 60% of men and 17% of women reported that sexual infidelity is worse (Sagarin et al., 2012). When using continuous measures, participants are asked to report how much each scenario would upset them on a scale, for example, from one to seven. When continuous measures have been used, a common finding concludes that both women and men rate sexual infidelity as more distressing than emotional infidelity, however there are also studies concluding significant gender differences (DeSteno, Bartlett, Braverman, & Salovey, 2002). Although both genders believe that sexual infidelity would be more distressing, it is still important to recognize that when given a forced-choice option between which would be hypothetically more upsetting, there are still distinct sex differences.
There have also been issues with replicating sex differences when measures are based on actual life experiences of infidelity compared to hypothetical situations. It has been demonstrated that when asked to recall specific, real life situations where cheating has occurred, both and men and women report that they focus more on emotional infidelity, and there are no significant gender differences (Harris, 2002). This study used the forced-choice method of measuring infidelity rather than continuous. Contrary to this finding, Edlund et al. (2006) found that when asked to think about a past experience when a partner has cheated, men reported that sexual infidelity was more upsetting more often than women, and women recounted that emotional infidelity was more upsetting more often than men. These results were found for both forced-choice and continuous measures and included separate samples of university students and working adults.
Attachment theory has attempted to explain the differences that have been repeatedly found by using the forced-choice measurement style. Attachment theory is an evolutionary-based theory that hinges on the assumption that an infant’s behaviour towards their caregivers increases their likelihood of protection and survival, subsequently creating a foundation for social learning (Bowlby, 1988). The sense of attachment that an infant has towards their caregiver creates a working model for relationships later in life. Hazan and Shaver (1987) used the theory of childhood attachment to form a new theory that romantic relationships are modelled off of these pre-existing working models from infancy and also involve similar processes when forming new attachments. Four major styles were used to describe adult romantic attachment: secure, fearful, preoccupied, and dismissive. Using these four attachment styles, Levy and Kelly (2010) investigated the within-sex differences of jealousy by identifying romantic attachment style of participants and having them complete the Buss Infidelity Questionnaire. They found that there were distinct sex differences, however these differences were strongly related to self-reported attachment style. Secure males and females were both more likely to report emotional infidelity as worse, whereas dismissive males were 26 times more likely to report sexual infidelity as worse than dismissive females. Moreover, the majority of those with secure, pre-occupied and fearful attachment styles reported emotional infidelity as worse, whereas dismissive styles reported sexual infidelity as worse. These findings indicate that sex differences in jealousy are more multifaceted than parental investment theory suggests, and that at least two evolutionary theories are at play when determining jealous reactions in romantic relationships. A considerable amount of studies have used the hypothetical approach to determine sex differences in jealous reactions, and a growing number have begun to evaluate actual past experiences of infidelity. There is no current research using a traditional experimental design, where researchers create jealous reactions in a laboratory setting. Because of the discrepancy in results when measuring hypothetical and actual experiences, this kind of research would advance the knowledge in the field of jealousy as an evolutionary mechanism. There are, however, ethical issues when provoking jealous reactions in human participants; using couples and putting them in scenarios which cause jealousy can interfere with the dynamics of the relationship, as well as the emotional well-being of the participants. This leads to the question of whether sex differences in jealousy emerge in response to evoked jealous reactions when using both forced-choice and continuous measures. Due to the finding that adult romantic attachment style strongly relates to the difference in responses to sexual and emotional infidelity, an analysis of whether attachment style is related to real jealous reactions would be beneficial. Jealousy will be conceptually defined as an emotional reaction to a potential or imagined relationship threat, whereas adult romantic attachment style will be defined as the type of attachment processes that one uses as a schema for their belief about appropriate behaviours in a relationship. The majority of research has continuously found that men consider sexual infidelity as worse, and women consider emotional infidelity as worse. Although continuous measures and retrospective studies have yielded non-significant results, many of them have still found distinct sex differences. Therefore, my first hypothesis states that there will be a significant difference between men and women in terms of which type of jealousy they find more distressing. Specifically, men will report that sexual infidelity is worse than emotional infidelity when using both continuous and forced-choice measures. Comparatively, women will report emotional infidelity as worse than sexual infidelity for both continuous and forced-choice measures. My second hypothesis is that these between-group differences will partially be a result of romantic adult attachment style. Specifically, dismissive individuals will report that sexual infidelity is more distressing, and secure individuals will report that emotional infidelity is more distressing. The basis for the prediction that dismissive individuals will be more like to report sexual infidelity is rooted in two findings. First, dismissive individuals have been found to be more focused on the sexual aspects of relationships, and less on the intimate aspects (Schachner & Shaver, 2004). Secondly, Levy and Kelly (2010) have found that dismissive individuals are more likely to report sexual infidelity as worse when thinking about hypothetical situations. This research design will be experimental, with three different experimental groups being measured in addition to a control group. Participants will be recruited from the university campus, and must be in a current heterosexual romantic relationship in order to participate, with each participant receiving a small monetary reward for participating in the experiment. Informed consent will be obtained before beginning the experiment, where participants will be told that they may experience minor emotional distress. All participants will be completing the Buss Infidelity Questionnaire to measure jealousy, where participants will be forced to choose either emotional infidelity or sexual infidelity as more distressing (the forced-choice measure). Participants will also score themselves on two 7-point Likert scales: one measuring how much distress would be caused by sexual infidelity, and the other measuring how much emotional infidelity would distress them. This scale will be named the Continuous Scale of Infidelity and the end points of the scale will consist of “not at all” and “completely” distressing. Attachment style will be measured using the Relationship Questionnaire (Bartholomew & Horowitz, 1991). The Relationship Questionnaire consists of four vignettes each depicting one of the four attachment styles in relationships. The respondent chooses which vignette most accurately describes their relationship style. These self-report measures will be completed at the end of the experiment.
To begin the experiment, participants will be divided into three groups: the first group, called the sexual cue condition, will watch a short video depicting an intense sexual interaction between a male and female. This video will not be too explicit, but explicit enough to create an awareness of the intensity of the situation. Prior to watching the video, participants will be instructed to imagine the situation taking place with their current romantic partner and the anonymous other person in the video. When the video is complete, each person will complete the Buss Infidelity Questionnaire (the forced-choice measure), the Continuous Scale of Infidelity, and the Relationship Questionnaire. The second group, named the emotional cue condition, will watch a short video depicting an intense love connection between two anonymous people. Before watching the video, participants will be instructed to picture their current romantic partner as the person in the video of the same gender having the intense love connection with the other anonymous person. Afterwards, all participants will complete the Buss Infidelity Questionnaire, the Continuous Scale of Infidelity, and the Relationship Questionnaire. The separation of the two videos into the sexual cue condition and emotional cue condition is essential to determine whether the vivid images affect the elicited response by the participants. The third group, called the combined cue condition, will watch both the sexual and emotional videos, and will be instructed to imagine their current romantic partner with the anonymous other person in the videos. The participants from the combined cue condition will then complete the Buss Infidelity Questionnaire, the Continuous Scale of Infidelity, and the Relationship Questionnaire. The fourth group, which is the control group, will watch a short video about a historical Canadian event, and will then be instructed to think of a hypothetical situation of their partner cheating. The participants will then complete the Buss Infidelity Questionnaire, the Continuous Scale of Infidelity, and the Relationship Questionnaire. The independent variables in this study are sexual and emotional video clips and gender, and the dependent variables are the responses to each of the questionnaires.
To analyze the data, two MANOVAs will be run. The first MANOVA will test whether there are gender differences in jealous reactions based on the four different cue conditions. The independent variables in this MANOVA will be gender and condition groups, and the dependent variables will be the Buss Infidelity Questionnaire and the Continuous Scale of Infidelity (jealousy). For the second MANOVA, the jealousy measures and the attachment styles from the Relationship Questionnaire will be mean centered to create interaction terms. If the interaction effects are significant, this will indicate a moderator effect, specifically that attachment style moderates the relationship between gender and jealousy. Post-hoc tests will then be run to determine which attachment styles moderate the relationship.
The results of this study will hopefully clarify the relationship between gender and jealousy due to the confusion from the different results that have been found when different measures have been used. The wide array of conflicting results include continuous measures indicating no sex differences, however a preference for both genders to choose sexual infidelity as more distressing, and retrospective studies indicating that both males and females report that emotional infidelity is more distressing. Furthermore, retrospective studies have also yielded significant sex differences with males finding sexual infidelity worse, and females finding emotional infidelity worse. Due to the controversial evidence in the current literature, a design that uses both forced-choice and continuous methods of measurement as well as an experimental design that evokes real jealous reactions should hopefully bring some answers to the forefront. The implications of understanding jealous reactions in response to infidelity would not only bring closure to the debate, but also allow more insight into the evolutionary function of jealousy.

References
Bartholomew, K., & Horowitz, L. M. (1991). Attachment styles among young adults: A test of a four-category model. Journal of Personality and Social Psychology, 61(2), 226–244. doi:10.1037/0022-3514.61.2.226
Bowlby, J. (1988). A secure base: Parent-child attachment and healthy human development. New York, NY US: Basic Books.
Buss, D. M. (2001). Human nature and culture: An evolutionary psychological perspective. Journal of Personality, 69(6), 955–978.
Buss, D. M., & Haselton, M. (2005). The evolution of jealousy: Comment. Trends in Cognitive Sciences, 9(11), 506–507. doi:10.1016/j.tics.2005.09.006
Buss, D. M., Larsen, R. J., Westen, D., & Semmelroth, J. (2001). Sex differences in jealousy: Evolution, physiology, and psychology. In W. G. Parrott (Ed.), (pp. 143–149). New York, NY US: Psychology Press.
Buunk, B. P., & Angleitner, A. (1996). Sex differences in jealousy in evolutionary and cultural perspective: Tests from the Netherlands, Germany, and the United States. Psychological Science, 7(6), 359–363.
Daly, M., Wilson, M. I., & Weghorst, S. J. (1982). Male sexual jealousy. Ethology & Sociobiology, 3(1), 11–27. doi:10.1016/0162-3095(82)90027-9
DeSteno, D. (2010). Mismeasuring jealousy: A cautionary comment on Levy and Kelly (2010). Psychological Science, 21(9), 1355–1356. doi:10.1177/0956797610378688
DeSteno, D., Bartlett, M. Y., Braverman, J., & Salovey, P. (2002). Sex differences in jealousy: Evolutionary mechanism or artifact of measurement? Journal of Personality and Social Psychology, 83(5), 1103–1116. doi:10.1037/0022-3514.83.5.1103
Edlund, J. E., Heider, J. D., Scherer, C. R., Fare, M., & Sagarin, B. J. (2006). Sex differences in jealousy in response to actual infidelity. Evolutionary Psychology, 4, 462–470.
Harris, C. R. (2002). Sexual and romantic jealousy in heterosexual and homosexual adults. Psychological Science, 13(1), 7–12. doi:10.1111/1467-9280.00402
Hazan, C., & Shaver, P. (1987). Romantic love conceptualized as an attachment process. Journal of Personality and Social Psychology, 52(3), 511–524. doi:10.1037/0022-3514.52.3.511
Levy, K. N., & Kelly, K. M. (2010). Sex differences in jealousy: A contribution from attachment theory. Psychological Science, 21(2), 168–173. doi:10.1177/0956797609357708
Sagarin, B. J., Martin, A. L., Coutinho, S. A., Edlund, J. E., Patel, L., Skowronski, J. J., & Zengel, B. (2012). Sex differences in jealousy: A meta-analytic examination. Evolution and Human Behavior, 33(6), 595–614. doi:10.1016/j.evolhumbehav.2012.02.006
Schachner, D. A., & Shaver, P. R. (2004). Attachment dimensions and sexual motives. Personal Relationships, 11(2), 179–195. doi:10.1111/j.1475-6811.2004.00077.x
Trivers, R, (1972). Parental investment and sexual selection. In B. Campbell (Ed.), Sexual selection and the descent of man. 1871–1971 (pp. 136–179). Chicago: Aldine.