SEX DIFFERENCES IN JEALOUSY:

Zn species with internal female fertilization, males risk both lowered paternity probability and investment in rival gametes i f their mates have sexual contact with other males. Females of such species do not risk lowered rnaternity probability through partner infidelity, but they do risk the d i i ~ ~ i ~ n of their mates' commitment and resources to rival females. Three studies tested the hypothesis that sex differences in jealousy emerged in humans as solutions to the respective adaptive problems faced by each sex. In Study I , 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 supercllii contraction) while subjects imagined separately the two types of partner infidelity. Study 3 tested the effect of being in a committed sexual relationship on the activation of jealousy, 21 studies showed large sex digerences, confirming hypothesized sex linkages in jealousy activation. In species with internal female fertilization and gestation, features of reproductive biology characteristic of all 4,000 species of mammals, including humans, males face an adaptive problem not confronted by females--uncertainty in their paternity of offspring. Maternity probability in mammals rarely or never deviates from 100%. Compromises in paternity probability come at substantial reproductive cost to the male-the loss of mating effort expended, including time, energy, risk, nuptial gifts, and mating opportunity costs. A cuckolded male also loses the female's parental effort, which becomes channeled to a competitor's gametes. The adaptive problem of paternity uncertainty is exacerbated in species in which males engage in some postzygotic parental investment (Trivers, 1972). Males risk investing resources in putative offspring that are genetically unrelated. These multiple and severe reproductive costs should have imposed strong selection pressure on males to defend against cuckoldry. Indeed, the literature is replete with examples of evolved anticuckoldry mechanisms in lions (Bertram, 19751, bluebirds (Power, 19751, doves (Erickson & Zenone. 1976), numerous insect species (Thornhill & Alcock, 1983), a& nonhuman primates (Hrdy, 1979). 'Since humans arguably show more pater? %investment than any other of the 200 species of primates (Alexander & Noonan, 19791, this selection pressure should have oper d especially intensely on human m a a S y m o n s (1979); Daly, Wilson, and Weghorst (1982); and Wilson and Daly (in press) have hypothesized that male sexual jealousy evolved as a solution to this adaptive problem (but see Hupka, 1991, for an alternative view), Men who were indifferent to sexual contact between their mates and other men presumably experienced lower paternity certainty, greater investment in competitors' gametes, and lower reproductive success than did men who were motivated to attend to cues of infidelity and to act on those cues to increase paternity probability. I Although Females do not risk maternity uncertainty, in species with biparental 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, 1988; Thornhill & Alcock, 1983; Trivers, 1 9 7 g T h e redirection of a mate's investment to another female and her offspring is reproductively 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 likely to have been at least two situations in which a woman risked losing a man's investment. First, in a monogamous maniage, a woman risked having her mate invest in an alternative woman with whom he was having an affair (partial loss of investment) or risked his departure for an alternative woman (large or total loss of investment). Second, in polygynous mamages, a woman was at risk of having her mate invesr ro a larger degree in other wives and their offspring at the expense of his investment in her and her offspring, Following Buss (1988) and Mellon (1981), we hypothesize that cues to the development of a deep emotional attachment have been reliable leading indicators to women of potential reduction or loss of their mate's investm e 5 1rJealousy is defined as an emotional ' L s g t e that is aroused by a perceived threat to a valued relationship or position and motivates behavior aimed at countering the threat. Jealousy is 'sexual' if the valued relationship is sexual" (Daly et al., 1982, p. 1 I ; see also, Salovey, 1991; White & Mullen, 1 9 a I t is reasonable to hypothesize thamalousy involves physiological reactions (autonomic arousal) to perceived threat and motivated action to reduce the threat, although this hypothesis has not been examined. Following Symons (1979) and Daly et al. (1982). our central hypothesis is that the events that activate jealousy phy siologicaUy and psychologically differ for men and women because of the different adaptive problems they have faced over human evolutionary history in mating contexts. Both sexes are hypothesized to be distressed over both sexual and emotional infidelity, and previous findings bear this out (Buss, 1989). However, these two kinds of infidelity should be weighted dierently by men and women. Despite the importance of these hypothesized sex differences, no systematic scientific work has been directed toward verifying or falsifying their existence (but for suggestive data, see Francis, 1977; Teismann & Mosher. 1978; White & Mullen, 1989). VOL. 3. NO. 4. JULY 1992 Copyright