Buss.1992.Jealousy-1

Buss.1992.Jealousy-1 - PSYCHOLOGICAL SCIENCE Research...

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Unformatted text preview: PSYCHOLOGICAL SCIENCE Research Report SEX DIFFERENCES IN JEALOUSY: Evolution, Physiology, and Psychology David M. Buss, Randy J. Larsen, Drew Weston, and Jennifer Semmelroth University of Michigan Abstract—in species with internal female fertilization, males risk both lowered pa- ternity probability and investment in ri- val gametes if their mates have sexual contact with other males. Females of such species do not risk lowered mater- nity probability through partner infidel- ity, but they do risk the diversion of their mates’ commitment and resources to ri- val females. Three studies tested the hy- pothesis that sex differences in jealousy emerged in humans as solutions to the respective adaptive problems faced by each sex. in Study 1, men and women selected which event would upset them more—a partner’s sexual infidelity or emotional infidelity. Study 2 recorded physiological responses (heart rate, electrodermal response, corrugator su- percilii contraction) while subjects imag- ined separately the two types of partner infidelity. Study 3 tested the effect ofbe- ing in a committed sexual relationship on the activation ofjealousy. All studies showed large sex drflerences, confirming hypothesized sex linkages in jealousy ac- tivation. In species with internal female fertil- ization and gestation, features of repro- ductive biology characteristic of all 4,000 species of mammals, including humans, males face an adaptive problem not con- fronted by femalcsm—uncertainty in their paternity of offspring. Maternity proba- bility in mammals rarely or never devi- ates from 100%. Compromises in pater- nity probability come at substantial re- productive cost to the male—the loss of mating effort expended, including time, energy, risk, nuptial gifts, and mating op- portunity costs. A cuckolded male also loses the female‘s parental effort, which becomes channeled to a competitor‘s ga- metes. The adaptive problem of pater- nity uncertainty is exacerbated in spe- cies in which males engage in some p0stzygotic parental investment (Triv- ers, 1972). Males risk investing re- VOL. 3, N0. 4, JULY 1992 sources in putative offspring that are ge- netically unrelated. These multiple and severe reproduc- tive costs should have imposed strong selection pressure on males to defend against cuckoldry. Indeed, the literature is replete with examples of evolved an- ticuckoldry mechanisms in lions (Ber; tram, 1975), bluebirds (Power, 1975), doves (Erickson & Zenone, 1976), nu— merous insect species (Thornhill & Al- cock, 1983), and nonhuman primates (Hrdy, 1979). Since humans arguably Show more paternal investment than any other of the 200 species of primates (Al- exander & Noonan, [979), this selection pressure should have operated especially intensely on human males. Symons (1979); Daly, Wilson, and Weghorst (1982); and Wilson and Daly (in press) have hypothesized that male sexual jeal- ousy evolved as a solution to this adap— tive problem (but see Hupka, 1991, for an alternative View). Men who were in- different to sexual contact between their mates and other men presumably ex- perienced lower paternity certainty, greater investment in competitors’ ga- metes, and lower reproductive success than did men who were motivated to at- tend to cues of infidelity and to act on those cues to increase paternity proba- bility. Although females do not risk mater- nity uncertainty, in species with biparen- tal care they do risk the potential loss of time, resources, and commitment from a male if he deserts or channels investment to alternative mates (Buss, I988; Thorn- hill & Alcock, 1983; Trivers, 1972). The redirection of a mate’s investment to an- other female and her offspring is repro- ductivcly costly for a female, especially in environments where offspring suffer in survival and reproductive currencies without investment from both parents. In human evolutionary history, there were liker to have been at least two sit- uations in which a thman risked losing a man‘s investment. First, in a monoga- Copyright © 1992 American Psychological Society mous marriage, a woman risked having her mate invest in an alternative woman with whom he was having an affair (par- tial loss of investment) or risked his de- parture for an alternative woman (large or total loss of investment). Second, in polygynous marriages, a woman was at risk of having her mate invest to a larger degree in other wives and their offspring at the expense of his investment in her and her offspring. Following Buss (I988) and Mellon (1981), we hypothesize that cues to the development of a deep emo- tional attachment have been reliable leading indicators to women of potential reduction or loss of their mate‘s invest- ment. Jealousy is defined as an emotional “state that is aroused by a perceived threat to a valued relationship or position and motivates behavior aimed at coun- tering the threat. Jealousy is ‘sexual’ if the valued relationship is sexual“ (Daly et al., 1982, p. 11; see also Salovey, 1991; White & Mullen, 1989). It is rea- sonable to hypothesize that jealousy in— volves physiological reactions (auto- nomic arousal) to perceived threat and motivated action to reduce the threat, al- though this hypothesis has not been ex- amined. Following Symons (I979) and Daly et al. (1932), our central hypothesis is that the events that activate jealousy physiologically and psychologically dif- fer for men and women because of the different adaptive problems they have faced over human evolutionary history in mating contexts. Both sexes are hy- pothesized to be distressed over both sexual and emotional infidelity, and pre- vious findings bear this out (Buss, 1989). However, these two kinds of infidelity should be weighted differently by men and women. Despite the importance of these hypothesized sex differences, no systematic scientific work has been di- rected toward verifying or falsifying their existence (but for suggestive data, see Francis, 1977; Teismann & Mosher, I978; White & Mullen, 1989). 251 Sex Differences in Jealousy STUDY 1: SUBJECTIVE DISTRESS OVER A PARTNER’S EXTERNAL INVOLVEMENT This study was designed to test the hypothesis that men and women differ in which form of infidelity—sexual versus emotionalm—triggers more upset and sub- jective distress, following the adaptive logic just described. Method After reporting age and sex, subjects (N : 202 undergraduate students) were presented with the following dilemma: Please think of a serious committed romantic relationship that you have had in the past, that you currently have, or that you would like to have. Imagine that you discover that the per- son with whom you've been seriously in- volved became interested in someone else. What would distress or upset you more (please circle only one): (A) Imagining your partner forming a deep emotional attachment to that person. (B) Imagining your partner enjoying pas- sionate sexual intercourse with that other person. Subjects completed additional ques- tions, and then encountered the next di- lemma, with the same instnictional set, but followed by a different, but parallel, choice: (A) Imagining your partner trying different sexual positions with that other person. (B) Imagining your partner falling in love with that other person. Results Shown in Figure 1 [upper panel) are the percentages of men and women res porting more distress in response to sex— ual infidelity than emotional infidelity. The first empirical probe, contrasting distress over a partner’s sexual involve- ment with distress over a partner’s deep emotional attachment, yielded a large and highly significant sex difference ()3 = 47.56, df = 3, p < .001). Fully 60% of the male sample reported greater distress over their partner's potential sexual infi- delity; in contrast, only 17% of the fe- male sample chose that option, with 83% reporting that they would experience 252 PSYCHOLOGICAL SCIENCE Percentage Reporting More Distress to Sexual Infidelity Sexual Infidelity versus Deep Emotional Infidelity Percentage Reporting More Distress to Sexual Infidelity Have Been in Committed Satual Reiationshrp é Sexual Idelity versus Love Infidelity Have Not Been in Committed Sexual Relatbnshlp Fig. 1. Reported comparisons of distress in response to imagining a partner’s sexual or emotional infidelity. The upper panel shows results of Study l—the percentage of subjects reporting more distress to the sexual infidelity scenario than to the emotional infidelity (left) and the love infidelity (right) scenarios. The lower panel shows the results of Study 3—the percentage of subjects reporting more distress to the sexual infidelity scenario than to the emotional infidelity scenario, presented separately for those who have experienced a committed sexual relationship (left) and those who have not experienced a committed sexual relationship (right). greater distress over a partner's emo- tional attachment to a rival. This pattern was replicated with the contrast between sex and love. The mag— nitude of the sex difference was large, with 32% more men than women report- ing greater distress over a partner‘s sex- ual involvement with someone else, and the majority of women reporting greater distress over a partner’s falling in love VOL. 3, NO. 4, JULY I992 PSYCHOLOGICAL SCIENCE m with a rival (x2 : 59.20, df : 3, p < .001). STUDY 2: PHYSIOLOGICAL RESPONSES TO A PARTNER’S EXTERNAL INVOLVEMENT Given the strong confirmation of jeala ousy sex linkage from Study 1, we sought next to test the hypotheses using physiological measures. Our central measures of autonomic arousal were electrodermal activity (EDA), assessed via skin conductance, and pulse rate (PR). Electrodermal activity and pulse rate are indicators of autonomic nervous system activation (Levenson. 1988). Be— cause distress is an unpleasant subjec- tive state, we also included a measure of muscle activity in the brow region of the face—electromyographic (EMG) activity of the corrugator supercilt'i muscle. This muscle is responsible for the furrowing of the brow often seen in facial displays of unpleasant emotion or affect (Frid- lund, Ekman, & Oster, 1987). Subjects were asked to image two scenarios in which a partner became involved with someone else—one sexual intercourse scenario and one emotional attachment scenario. Physiological responses were recorded during the imagery trials. Subjects Subjects were 55 undergraduate stu— dents, 32 males and 23 females, each completing a 2-hr laboratory session. Physiological Measures Physiological activity was monitored on the running strip chart of a Grass Model 7D polygraph and digitized on a laboratory computer at a 10-Hz rate, folv lowing principles recommended in Ca- cioppo and Tassinary (1990). Electrodermal activity Standard Beckman Ag/AgCl surface electrodes, filled with a .05 molar NaCl solution in a Unibase paste, were placed over the middle segments of the first and third fingers of the right hand. A Wheat- stone bridge applied a 0.5—V voltage to one electrode. VOL. 3, NO. 4, JULY 1992 Pulse rate A photoplcthysmograph was attached to the subject’s right thumb to monitor the pulse wave. The signal from this pulse transducer was fed into a Grass Model 7P4 cardiotachometer to detect the rising slope of each pulse wave, with the internal circuitry of the Schmitt trig— ger individually adjusted for each subject to output PR in beats per minute. Electromyographlt‘ activity Bipolar EMG recordings were ob- tained over the corrugator snpercilii muscle. The EMG signal was relayed to a wide-hand AC-preamplifier (Grass Model 7P3), where it was band-pass fil- tered, full-wave rectified, and integrated with a time constant of 0.2 5. Procedure After electrode attachment, the sub- ject was made comfortable in a reclining chair and asked to relax. After a 5-min waiting period, the experiment began. The subject was alone in the room during the imagery session, with an intercom on for verbal communication. The instruc- tions for the imagery task were written on a form which the subject was re- quested to read and follow. Each subject was instructed to engage in three separate images. The first image was designed to be emotionally neutral: “Imagine a time when you were walking to class, feeling neither good nor bad, just neutral.” The subject was instructed to press a button when he or she had the image clearly in mind, and to sustain the image until the experimenter said to stop. The button triggered the computer to begin collecting physiological data for 20 s, after which the experimenter in- structed the subject to “stop and relax." The next two images were infidelity images, one sexual and one emotional. The order of presentation of these two images was counterbalanced. The in- structions for sexual jealousy imagery were as follows: “Please think of a seri- ous romantic relationship that you have had in the past, that you currently have, or that you would like to have. Now imagine that the person with whom you're seriously involved becomes inter- ested in someone else. Imagine you find out that your partner is having sexual David M. Buss et a1. intercourse with this other person. Try to feel the feelings you would have if this happened to you." The instructions for emotional infidel- ity imagery were identical to the above, except the italicized sentence was re- placed with “Imagine that your partner is falling in love and forming an emo- tional attachment to that person." Phys- iological data were collected for 20 5 following the subject's button press indi- cating that he or she had achieved the image. Subjects were told to “stop and relax” for 30 s between imagery trials. Results Physiological scores The following scores were obtained: (a) the amplitude of the largest EDA re- sponse occurring during each 20-3 trial; (b) PR in beats per minute averaged over each 20-s trial; and (c) amplitude of EMG activity over the corrugator supercilii averaged over each 20-s trial. Difference scores were computed between the neu- tral imagery trial and the jealousy induc— tion trials. Within-sex t tests revealed no effects for order of presentation of the sexual jealousy image, so data were col- lapsed over this factor. Jealousy induction effects Table 1 shows the mean scores for the physiological measures for men and women in each of the two imagery con- ditions. Differences in physiological re- sponses to the two jealousy images were examined using paired-comparison t tests for each sex separately for EDA, PR, and EMG. The men showed signifi- cant increases in EDA during the sexual imagery compared with the emotional imagery (t : 2.00, df = 29, p < .05). Women showed significantly greater EDA to the emotional infidelity image than to the sexual infidelity image (t = 2.42, df = 19, p < .05}. A similar pattern was observed with PR. Men showed a substantial increase in PR to both im- ages. but significantly more so in re- sponse to the sexual infidelity image (t = 2.29, df = 3|, p < .05). Women showed elevated PR to both images, but not dif- ferentially so. The results of the corru- gator EMG were similar, although less strong. Men showed greater brow con- traction to the sexual infidelity image, 253 Sex Differences in Jealousy Table 1. Means and standard deviations on physiological measures during two imagery conditions Imagery type Mean Measure Males Sexual 1 .30 3 .64 Emotional * 0.1 l 0.76 Pulse Sexual 4 .76 7.80 rate Emotional 3 .00 5.24 Brow Sexual 6.75 32.96 EMG Emotional 1.16 6.60 EDA Females Sexual ~ 0.01r 0.49 Emotional 0.21 0.78 Pulse Sexual 2 .25 4. 68 rate Emotional 2 .57 4. 37 Brow Sexual 3 .03 8.38 EMG Emotional 8.12 25.60 EDA Note. Measures are expressed as changes from the neutral image condition. EDA is in microsiemen units. pulse rate is in beats per minute. and EMG is in microvolt units. and women showed the opposite pattern, although results with this nonautonomic measure did not reach significance (r = 1.12, d)" = 30, p < .14, for males; 2 = -1.24, (if = 22, p < .12, for females). The elevated EMG contractions for both jealousy induction trials in both sexes support the hypothesis that the affect ex- perienced is negative. STUDY 3: CONTEXTS THAT ACTIVATE THE JEALOUSY MECHANISM The goal of Study 3 was to replicate and extend the results of Studies I and 2 using a larger sample. Specifically, we sought to examine the effects of having been in a committed sexual relationship versus not having been in such a rela- tionship on the activation of jealousy. We hypothesized that men who had ae- tually experienced a committed sexual relationship would report greater subjec- tive distress in response to the sexual in- fidelity imagery than would men who had not experienced a high-investing sexual relationship, and that women who had experienced a committed sexual re- lationship would report greater distress 254 PSYCHOLOGICAL SCIENCE to the emotional infidelity image than Women who had not been in a committed sexual relationship. The rationale was that direct experience of the relevant context during development may be nec- essary for the activation of the sex- linked weighting of jealousy activation. Subjects Subjects for Study 3 were 309 under- graduate students, 133 men and 176 “'0an. Procedure Subjects read the following instruc- tions: Please think of a serious or committed roman— tic relationship that you have had in the past, that you currently have, or that you would like to have. Imagine that you discover that the person with whom you‘ve been seriously involved became interested in someone else. What would distress or upset you more (please circle only one): (A) Imagining your partner falling in love and forming a deep emotional attachment to that person. (B) Imagining your partner having sexual intercourse with that other person. Alternatives were presented in stan- dard forced-choice format, with the or- der counterbalanced across subjects. Following their responses, subjects were asked: “Have you ever been in a serious or committed romantic relationship? (yes or no)" and “If yes, was this a sex- ual relationship? (yes or no)." Results The results for the total sample repli- cate closely the results of Study 1. A much larger proportion of men (49%) than women (19%) reported that they would be more distressed by their part- ner‘s sexual involvement with someone else than by their partner‘s emotional at- tachment to, or love for, someone else (x2 = 38.48, df = 3, p < .001). The two pairs of columns in the bot- tom panel of Figure 1 show the results separately for those subjects who had experienced a committed sexual rela- tionship in the past and those who had not. For women, the difference is small and not significant: Women reported that they would experience more distress about a partner’s emotional infidelity than a partner‘s sexual infidelity, regard- less of whether or not they had experi- enced a committed sexual relationship (x2 = 0.80, df = 1, us). For men, the difference between those who had been in a sexual relation- ship and those who had not is large and highly significant. Whereas 55% of the men who had experienced committed sexual relationships reported that they would be more distressed by a partner’s sexual than emotional infidelity, this fig- ure drops to 29% for men who had never experienced a committed sexual rela- tionship (x2 f 12.29, df : ],p < .001). Sexual jealousy in men apparently be- comes increasingly activated upon expe- rience of the relevant relationship. DISCUSSION The results of the three empirical studies support the hypothesized sex linkages in the activators of jealousy. Study I found large sex differences in reports of the subjective distress individ- uals would experience upon exposure to a partner‘s sexual infidelity versus emo- tional infidelity. Study 2 found a sex link- age in autonomic arousal to imagined sexual infidelity versus emotional infi- delity; the results were particularly strong for the EDA and PR. Study 3 rep- licated the large sex differences in re- ported distress to sexual versus emo- tional infidelity, and found a strong effect for men of actually having experi- enced a committed sexual relationship. These studies are limited in ways that call for additional research. First, they pertain to a single age group and culture. Future studies could explore the degree to which these sex differences transcend different cultures and age groups. Two clear evolutionary psychological predic- tions are (a) that male sexual jealousy and female commitment jealousy will be greater in cultures where males invest heavily in children, and (b) that male sexual jealousy will diminish as the age of the male's mate increases because her reproductive value decreases. Second, future studies could test the alternative hypotheses that the current findings re- flect (a) domain-specific psychological VOL. 3, NO. 4, JULY I992 PSYCHOLOGICAL SCIENCE # David M. Buss et al. adaptations to cuckoldry versus poten- tial investment loss or (b) a more do- main-general mechanism such that any thoughts of sex are more interesting, arousing, and perhaps disturbing to men whereas any thoughts of love are more interesting, arousing, and perhaps dis- turbing to women, and hence that such responses are not specific to jealousy or infidelity. Third, emotional and sexual infidelity are clearly correlated, albeit imperfectly, and a sizable percentage of men in Studies 1 and 3 reported greater distress to a partner‘s emotional infidel- ity. Emotional infidelity may signal sex- ual infidelity and vice versa, and hence both sexes should become distressed at both forms (see Buss, 1989). Future research could profitably explore in greater detail the correlation of these forms of infidelity as well as the sources of within-sex variation. Finally, the in- triguing finding that men who have expe- rienced a committed sexual relationship differ dramatically from those who have not, whereas for women such experi- ences appear to be irrelevant to their se- lection of emotional infidelity as the more distressing event, should be exam- ined. Why do such ontogenetic experi- ences matter for men, and why do they appear to be irrelevant for women? Within the constraints of the current studies, we can conclude that the sex dif— ferences found here generalize across both psychological and physiological methods—demonstrating an empirical robustness in the observed effect. The degree to which these sex-linked elici- tors correspond to the hypothesized sex- linked adaptive problems lends support to the evolutionary psychological frame- work from which they were derived. Al— ternative theoretical frameworks, includ- ing those that invoke culture, social con- struction, deconstruction, arbitrary parental socialization, and structural powerlessness, undoubtedly could be VOL. 3, N0. 4, JULY 1992 molded post hoc to fit the findings— something perhaps true of any set of findings. None but the Symons (1979) and Daly et al. (1982) evolutionary psy- chological frameworks, however, gener— ated the sex-diflerentiated predictions in advance and on the basis of sound evo— lutionary reasoning. The recent finding that male sexual jealousy is the leading cause of spouse battering and homicide across cultures worldwide (Daly & Wil- son, 19883, 1988b) offers suggestive evi- dence that these sex differences have large social import and may be species- wide. Acknowledgments—This research was supported in part by National Institute of Mental Health (NIMH) Grant MH-44206— 02 to David M. Buss; Research Scientist Development Award KOliMHOOT/(M and NIMH Grant MH-42057 to Randy Larsen; and Biomedical Research Support Grant $07 RR07050—25 from the National Insti- tutes of Health to Randy Larsen and David M. Buss through the University of Michigan Office of the Vice President for Research. The authors thank Michael Chen, Martin Duly, Todd DeKay, Bruce Ellis, Arlelte (,lreer, Kurt Hoop, Tim Ketelaar, Neil Malamuth, David Schmitt, and Don Symons for helpful suggestions on earlier versions of this article. REFERENCES Alexander, R.D., & Noonan, K.M. (1979). 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