Individuals diagnosed with morbid jealousy have hypersensitive jealousy mechanisms that cause them to have irrational thoughts about their partner's fidelity and to exhibit extreme behaviors. Using a newly constructed database of 398 cases of morbid jealousy reported in the literature from 1940 to 2002, we tested four evolutionarily informed hypotheses about normally functioning jealousy mechanisms and applied them to this novel population of individuals diagnosed with morbid jealousy. We hypothesized that a greater percentage of men than women diagnosed with morbid jealousy would be focused on a partner's sexual infidelity and on indicators of a rival's status and resources and that a greater percentage of women than men diagnosed with morbid jealousy would be focused on a partner's emotional infidelity and on indicators of a rival's youth and physical attractiveness. All four hypotheses were supported. The results suggest continuity between normal jealousy and morbid jealousy and highlight the heuristic value of using archival databases to test evolutionarily informed hypotheses.
Sexual jealousy has been studied extensively by evolutionary scientists and has been shown to be a normal emotional reaction to perceived or actual partner infidelity. This research has provided evidence for sex differences in jealousy, as well as an explanation as to why the sexes have different reactions to infidelity. When asked which type of partner infidelity would be more upsetting, men are more likely to select sexual infidelity and women are more likely to select emotional infidelity (Buss et al., 1992, Buss et al., 1999, Schützwohl, 2004, Schützwohl, 2005, Schützwohl & Koch, 2004, Shackelford et al., 2002 and Shackelford et al., 2004).
Men and women also differ in reports of the characteristics of rivals that produce jealousy, due to the different characteristics that men and women prefer in a mate. When asked to rate a potential mate's characteristics, women place greater importance on the ability to invest in offspring than do men, and men place greater importance on characteristics indicating health and fertility than do women (Buss, 1989, Buss, 2003, Buss & Schmitt, 1993, Kenrick et al., 1990, Li et al., 2002 and Schmitt et al., 2001). It is has been hypothesized that men and women are particularly upset by rivals who display these particular characteristics (Buss, 2000). Research supports this hypothesis: When asked to identify the characteristics of a potential rival that are upsetting, men are more likely than women to identify characteristics related to resource acquisition or holdings, whereas women more than men report upset when confronted with potential rivals who display youthfulness and attractiveness (Brase et al., 2004 and Buss et al., 2000).
These findings have been well documented in normal adult populations but have not yet been investigated in individuals diagnosed with morbid jealousy. These individuals have irrational thoughts about their partner's fidelity (APA, 2000), and they incessantly make unwarranted or unverified accusations about their partner's infidelity (e.g., Kingham & Gordon, 2004, Shepherd, 1961 and Vauhkonen, 1968). Morbid jealousy can be thought of as hypersensitive jealousy, as these individuals experience jealous reactions at a much lower threshold than normal individuals.
