The evolution of jealousy.

Two decades ago, mainstream psychologists explained jealousy as a pathology, social construction, or by-product of capitalist society, manifested identically in men and women [1]. Evolutionary psychologists, in contrast, hypothesized that jealousy is an evolved adaptation, activated by threats to a valuable relationship, functioning to protect it from partial or total loss [2–4]. Because the reproductive consequences of infidelity and partner loss are parallel for men and women in some respects, and asymmetric in others, the sexes were predicted to have similar psychologies in some respects, and different psychologies where their adaptive problems recurrently diverged. This program initially focused on a few core design features of jealousy, but has since expanded to study many more. Sexual similarities include the following. Jealousy (i) is an emotion designed to alert an individual to threats to a valued relationship, (ii) is activated by the presence of interested and more desirable intrasexual rivals, and (iii) functions, in part, as a motivational mechanism with behavioral output designed to deter ‘the dual specters of infidelity and abandonment’ ([1], p. 35). (iv) ‘[B]oth sexes are hypothesized to become distressed over sexual and emotional infidelity’ because both forms of infidelity provide important cues to the loss of reproductively valuable resources ([4], p. 251). When there is a discrepancy in mate value, (v) the lower-value partner will experience more intense jealousy [1]. There are at least 13 distinct hypothesized sexdifferentiated design features, and 13 out of 13 have been confirmed empirically. Men and women differ psychologically in the weighting given to sexual and emotional cues that trigger jealousy, such that (i) men more than women become upset at signals of sexual infidelity, which portend both paternity uncertainty and loss of reproductive resources to a rival; and (ii) women more than men become upset at signals of a partner’s emotional infidelity, which threaten a loss of commitment and resources to a rival [1,5]. When jealousy is activated by interlopers, (iii) women become especially distressed by threats from physically attractive rivals, whereas (iv) men become especially distressed by rivals with more resources [6]. Within committed mateships (v) men paired with physically attractive women exhibit elevated jealous mate-guarding, whereas (vi) women paired with more resource-endowed men exhibit more jealous mate-guarding [7]. (vii) Near ovulation – the critical window in which a man’s paternity