Sex Differences in Jealousy The Evolutionary Psychology of Jealousy in Romantic Relationships: Evidence for a Sexually Dimorphic Response Mechanism in Humans by REBECCA M. ALLEN A thesis submitted in partial fulfillment of the requirements for the Degree of Bachelor of Arts with Honors in Psychology WILLIAMS COLLEGE Williamstown, Massachusetts May 11,2005 Sex Differences in Jealousy Abstract Evolutionary psychologists have proposed that men and women differ in their relative responses to sexual vs. emotional infidelity in a romantic relationship, a proposal based upon the presumption of evolved sex differences in mating strategies. Because sexual infidelity signals the possibility of being cuckolded and emotional infidelity signals the possible withdrawal of resources, men are expected to be relatively more jealous over the former whereas women are expected to be relatively more jealous over the latter. Although past research has demonstrated robust support for the evolutionary hypothesis, this support has been called into question on both empirical and conceptual grounds. In this thesis, I test the claims of the evolutionary hypothesis using a novel experimental paradigm designed to address previous methodological concerns. In two studies, participants (college students in Study 1; married adults in Study 2) were asked to consider a series of hypothetical scenarios depicting cues to either sexual or emotional infidelity and to rate their responses on a variety of continuous measures. Across both studies, as expected, women were found to be significantly more bothered by emotional cues than were men. Contrary to expectations, however, women and men displayed similar responses to sexual cues, with women having a slight tendency to be more bothered than men. The latter effect was less consistent than the former, however, giving rise to a reliable two-way interaction between sex and infidelity type (sexual vs. emotional). Although these findings were only partly supportive of my predictions, they nonetheless demonstrate that humans display a sexually dimorphic jealousy response, and provide support for the contention that this is an evolved mechanism. Discussion addresses a number of additional findings, as well as avenues for future research. Sex Differences in Jealousy Contents I. Introduction . I1. Study . 30 - Method 34 - Results 38 - Discussion . -44 I11. Study . 48 - Method 49 - Results 50 - Discussion 54 IV. General Discussion . -59 V. References . 66 VI. Acknowledgements 71 VII. Appendix .-72 VIII. Tables and Figures .82 Sex Differences in Jealousy The Evolutionary Psychology of Jealousy in Romantic Relationships: Evidence for a Sexually Dimorphic Response Mechanism in Humans "O! beware, my lord, of jealousy; It is the green-eyed monster which doth mock The meat it feeds on." - William Shakespeare, Othello Anyone who has ever been in a romantic relationship probably has a firsthand understanding of the emotional distress that any threat to this relationship may cause. The very suspicion that one's mate may be romantically interested in a rival is enough to inspire a negative reaction in anyone, such as sadness, insecurity, hurt feelings, or anger in some cases, even enough anger to attack one's partner or the object of their affection (Daly & Wilson, 1988). All of these negative feelings that arise in response to a romantic partner's past or imminent infidelity can be commonly understood as manifestations of jealousy. Jealousy over romantic relationships is a universal phenomenon that can be seen in men and women across cultures and age groups (Buunk, Angleitner, Oubaid & Buss, 1996; Buss, Shackelford, Kirkpatrick, Choe, Lim, Hasegawa, Hasegawa & Bennett, 1999; Wiederman & Kendall, 1999; Harris, 2003). Evolutionary theorists have proposed that jealousy is a response mechanism that has been naturally selected for in humans because over the course of evolution, those who had a negative response to signs of a mate's infidelity would be more apt to prevent this infidelity and thus experience higher rates of reproductive success (Wiederman & Allgeier, 1993). This explanation appears likely when we consider the fact that many other animals have also evolved mechanisms to reduce the possibility that their mate will engage in extradyadic copulation. For example, among Plecia nearcticas, aptly laown as "love bugs," after a male gains access to a sexually receptive female he remains attached Sex Differences in Jealousy to her in a copulatory embrace that can last for days, thereby preventing other males from fertilizing her eggs. Another species of insect, Johannseniella nitida, adopts an even more drastic strategy: Males of that species actually leave their genitalia behind, broken off inside the female, after insemination - presumably to seal off the female's reproductive opening and thus forestall takeovers from rival males (Buss, 2003). Considering the fact that even lowly insects have evolved specialized behaviors to prevent the likelihood of losing their mate to a rival, it is reasonable to surmise that humans have also evolved an innate sense of jealousy to accomplish the same purpose. However, a specific aspect of the evolutionary theory of jealousy that has come under intense scrutiny is the hypothesis that humans have evolved sexually dimorphic jealousy mechanisms that cause males and females to be differentially upset by different types of infidelity. Specifically, this theory postulates that men will be relatively more jealous about their mate's sexual straying, whereas women will be relatively more jealous at the prospect of their mate's emotional involvement with a rival (Buss, Larsen, Westen & Semmelroth, 1992). A great deal of research has been done to investigate this question, and while considerable support has been found for the hypothesis, there is much debate in the field over whether jealousy is really an evolved sexually dimorphic mechanism, or if gender differences in jealousy can be explained by other, more social or cultural influences (Harris, 2003). The goal of this thesis is to offer an unbiased examination of the arguments for and against the evoXutionary theory of human jealousy and to build on previous studies by developing and implementing an experimental paradigm that addresses the limitations of these studies. I ultimately intend to determine a) whether there really is a sex difference Sex Differences in Jealousy in jealousy response to different types of infidelity, and b) if so, whether this difference can be attributed to evolved mechanisms or a more socially learned explanation. Understanding the Evolutionavy Argument Human males and females, over the course of evolutionary history, have undoubtedly faced differing environmelltal pressures and circumstances affecting mating behavior. Some of the effects of these pressures can be seen in the sex-differentiated psychological tendencies and preferences shown by men and women - for instance, countless studies have demonstrated that men worldwide tend to be attracted to women with physical attributes of youth and fertility, which indicate an ability to bear healthy children, whereas women are more attracted to signs of social dominance and material wealth, which are cues to a man's ability to provide resources for her offspring (e.g. Buss, 1989; Kenrick & Keefe, 1992). Attraction to certain characteristics in the opposite sex is not the only way that past evolutionary pressures might manifest themselves in human psychology; in order to preserve their chances of reproductive success, males and females may have also needed to be sensitive to different types of cues that could indicate a potential threat to their mating relationship. This idea is where the evolutionary theory of jealousy has its origin. For any species of animal that employs internal fertilization, the males are faced with a reproductive dilemma: It is impossible for a male to be certain that his mate's offspring are the result of his own fertilization or a competitor's. Different species have evolved different methods of countering this uncertainty of paternity, from mate-guarding behaviors to infanticide to simply impregnating as many females as possible (Buss 8& Shackelford, 1997; Buss, 2003). As humans are a relatively monogamous species, Sex Differences in Jealousy meaning that a man's investment of time and resources in his mate tends to be high, it would be especially costly to him if his mate were sexually unfaithful, because all of his energy would be devoted towards raising offspring that did not carry his own genes. Thus it follows that over the course of evolution, human males who were sensitive to indications of their mate's sexual straying such that they could minimize or forestall it altogether would have been more successful at passing down their genes than males who were not bothered when their mate showed signs of sexual interest in another man. Females, on the other hand, can be 100% certain that their offspring carries their own genes, so this should not have been a primary concern for them. However, since the female was the one who bore and consequently raised her children, she would have had a much higher probability of success if she could be certain that her mate remained emotionally devoted to her, providing his material support and protection for the extended time that it takes to raise a child to adulthood. A man's brief sexual dalliance, although potentially troubling, would not have been harmful to his mate's reproductive success so long as he stayed emotionally attached and willing to share his resources with her. Women who were vigilant to signs that their mate's affection (and hence his resources) was being diverted to another, such that they could minimize or forestall this occurrence, therefore should have held an evolutionary advantage over those who were oblivious to these indications of emotional interest and attention towards a competitor. From the logic of these scenarios comes the evolutionary theory ofjealousy: Although members of both sexes should be upset by any type of infidelity on the part of their mate since emotional and sexual infidelity frequently co-occur (Harris & Chistenfeld, 1996; DeSteno & Salovey, 1996), men are predicted to be relatively more upset by sexual Sex Differences in Jealousy infidelity than women, and women are expected to be relatively more upset by emotional infidelity than men (Buss et al., 1992). The idea of increased male sexual jealousy has been supported with statistics on morbid jealousy, spousal abuse, and homicide in response to sexual infidelity, all of which are more commonly found in men than women (Daly & Wilson, 1988). Additionally, it has been found that women place a much higher importance on emotional investment in a relationship than men do; a man's ability to commit is a key factor in a woman's assessment of his potential as a mate, and women who repeatedly engaged in sex without a high degree of emotional investment were found to have heightened levels of anxiety and distress despite holding the "liberal" opinion that uncommitted sex was morally acceptable (Townsend, 1995). In another study, when 15 committed undergraduate couples were asked to list as many jealousy evoking situations as they could think of, men were significantly more likely to list sexual scenarios, whereas women tended to list situations in which their partner spent more time with or showed emotional attachment to a potential rival (Francis, 1977, as cited in Wiederman & Allgeier, 1993). Despite the fact that these and many other studies appear to support the evolutionary hypothesis, we must be cautious in our interpretation of the data. Men commit more violent crimes than women in response to sexual infidelity, but this may simply be a reflection of the fact that men commit more violent crimes overall than women do. Also, as Harris points out in her 2003 review, people who are morbidly jealous or who commit murder as a reaction to jealousy represent extreme, possibly mentally unstable cases, and "observations about population extremes are likely to offer a Sex Differences in Jealousy very unreliable guide to species-typical characteristics" (p. 108). In the case of the undergraduate couples listing the predicted types of scenarios that would make them jealous, this could just be because men tend to think about sex in general more than women do, and women tend to think more about emotional issues, so these were the exemplars that happened to spring to mind. Obviously, one cannot rely on homicide statistics or general jealousy studies as proof of the evolutionary hypothesis - in order to truly examine its worth, we must turn to studies that have been specifically designed to test the question of whether the sexes differ in their sensitivity to infidelity, as predicted by evolutionary theory. Robust Support for the Evolutionary Theory One groundbreaking study performed by Buss and his colleagues in 1992 provided direct support for the evolutionary theory of jealousy. In a simple experimental design, Buss presented participants with two hypothetical scenarios. Participants were asked to imagine that their romantic partner either formed a "deep emotional attachment" to or had "passionate sexual intercourse" with another person, and were then asked to choose which of the two would upset or distress them more. An additional set of questions asked whether their partner "trying different sexual positions" or "falling in love" with another person would upset them more. The results fiom this simple, forcedchoice measure were as predicted by the evolutionary hypothesis: Significantly more men than women chose the instance of sexual infidelity as more upsetting, for both sets of scenarios. In this same study, Buss also found preliminary physiological evidence in support of the hypothesis, reporting that men showed more electrodema1 activity (EDA) Sex Differences in Jealousy 10 and a higher pulse rate (PR) when imagining sexual infidelity than emotional infidelity, whereas women displayed the opposite tendencies (Buss et al., 1992). These findings in support of the evolutionary theory ofjealousy have been replicated by many subsequent studies employing the same or similar forced-choice methodology (Wiederman & Allgeier, 1993; Buunk et al., 1996; DeSteno & Salovey, 1996; Wiederman & Kendall, 1999; Buss et al., 1999; Cramer, Abraham, Johnson, & Manning-Ryan, 2001; DeSteno, Bartlett, Braverman, & Salovey, 2002; Harris, 2002; Pietrzak, Laird, Stevens & Thompson, 2002; and for a meta-analysis, see Harris, 2003). Different populations have been sampled, different cultures have been tested, and the phrasing of the scenarios has been altered slightly, but across them all, one very robust effect is that when people are asked to choose between the two different types of infidelity, significantly more men than women indicate that sexual infidelity is worse, and significantly more women than men choose emotional infidelity as worse. The reliability of this finding is undeniable, even in samples from cultures as diverse as Germany, the Netherlands, Sweden, Japan, and Korea (Buunk et al., 1996; Wiederman & Kendall, 1999; Buss et al., 1999). Similar results have also been found when asking men and women which type of infidelity they would be more likely to forgive, and which would lead them to break up with their partner (Shackelford, Buss, & Bennett, 2002). But the support for the evolutionary hypothesis isn't as clear-cut as it might first appear. One finding that throws a snag into the evolutionary argument is the fact that, though the percentage of men who are more upset by sexual infidelity is significantly higher than the percentage of women who are, that number is still frequently lower than 50%. This means that the majority of men in many samples chose emotional infidelity as Sex Differences in Jealousy 90 +Male - Female 8.42 9.55 6.18 7.87 5.39 7.02 5.34 7.19 2.89 4.54 2.32 2.87 2.03 -3.26 Scenario Secret love letter Deep emotional attachment Expensive bday present, Busy schedule Inside joke Laughs at rival's joke Takes care of sick friend = p < .05, A = p < .10 Sexual Scenarios I - Male -Female 8.95 9.47 7.78 8.23 4.5 6.09 1 4.76 5.15 / 3.47 3.89 3.37 3.68 1.78 2.74 Scenario Passionate sex with another Drunk one-night stand Dancing closely with stranger Sensual massage Sexual M W games Audition for lussing role in play Night out at strip club + =p[...]... has been played out in the literature on jealousy Many opponents of the evolutionary theory of jealousy argue against it based on a particular interpretation of what the theory maintains Some critics have adopted a very specific, narrow, rather simplistic definition that can be referred to as "JSIM," the "jealousy as a specific innate module" definition According to JSIM, "because sexual jealousy arose... The goal of evolutionary psychology is not to distill human behavior into a catalog of instincts and mechanical responses bred into us by natural selection, but to examine how humans interact with thelr environment and determine what role, if any, Sex Differences in Jealousy 26 evolution may have played in shaping those interactions (Wiederrnan & Allgeier, 1993) Thus, any theory of evolutionary psychology. .. Buss et al., 1999) A meta-analysis of the data from these studies grouped by region (US, Asia, and Europe) found that this variable was not a significant moderator of gender differences in jealousy (Harris, 2003) Culture certainly does influence participants' overall pattern of responses - for instance, a higher percentage of American men than Japanese men chose sexual infidelity as the most upsetting... physiological response to the baseline sexual and the sexual infidelity - in other words, imagining a sexual situation was more arousing to men than imagining an emotional situation, regardless of whether that situation involved infidelity or not (Harris, 2000) A reasonable interpretation of these mixed results may thus be that this method of measurement is simply not useful for assessing sex differences in jealousy. .. emotional responses after the infidelity situation has already come and gone This being the case, until someone can Sex Differences in Jealousy 21 design a study that examines immediate reactions to actual infidelity without arousing ethical concerns, hypothetical situations of infidelity are the best method available for assessing jealous responses Potential Moderating Factors As we have seen, there are many... of jealousy at all Buss and his colleagues chose to measure participants' electroderrnal activity (EDA), pulse rate (PR), and electromyographic activity (EMG) as methods of assessing their physiological arousal in response to situations of imagined infidelity (1992) They found that men showed greater EDA for sexual infidelity than for emotional, women showed greater EDA for emotional infidelity than... jealousy Reactions to Actual vs Hypothetical Infidelity One common theme thoughout all of these different methods of measuring jealousy is that they all rely on the Sex Differences in Jealousy 20 participants' ability to imagine a hypothetical situation of infidelity and react to it as if they were actually experiencing it Clearly, this is not an optimal way of measuring someone's actual jealousy reaction... this original pool of participants, data from seven (all females) were eliminated due to previous knowledge of the evolutionary theory of jealousy that could potentially bias their responses, leaving a total sample of 85 participants (47 female and 38 male) Only one participant described herself as bisexual, and all other participants described themselves as heterosexual, so no data were eliminated due... together for life and is very difficult to break Consequently, married individuals have a much greater assurance that their relationship will be safe against rivals This assurance is purely a result of the contract and all of the societal regulations that accompany it - the institution of marriage would not have existed early on in human evolutionary history, so our ancestors would not have had this type of. .. this trend was the same for American and Japanese women as well, so across cultures, the sex difference remains robust (Buss et al., 1999) Sexual Orientation as a Moderating Factor Homosexuality has always posed an interesting conundrum for evolutionary psychologists, because as of yet there is no convincing Darwinian explanation for why some people would find themselves attracted to members of their . in Jealousy 1 The Evolutionary Psychology of Jealousy in Romantic Relationships: Evidence for a Sexually Dimorphic Response Mechanism in Humans by REBECCA M. ALLEN A thesis submitted in. baseline sexual and the sexual infidelity - in other words, imagining a sexual situation was more arousing to men than imagining an emotional situation, regardless of whether that situation. copulation. For example, among Plecia nearcticas, aptly laown as " love bugs, " after a male gains access to a sexually receptive female he remains attached Sex Differences in Jealousy 5