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Persecutory delusions: reminiscence of ancestral hostile threats?

Julia Zolotova, Martin Brüne

1. Introduction

2. Methods

3. Results

4. Discussion

Acknowledgment

References

Copyright

1. Introduction

Persecutory delusions have repeatedly been interpreted as the consequence of an evolved psychological mechanism of social threat recognition gone awry. Whereas the formal aspect of delusional beliefs of persecution has been linked to specific mistakes in inferring the intentions of other individuals (Charlton & McClelland, 1999) and to heightened vigilance toward threat perception in facial expressions of emotion (Green & Phillips, 2004), it has been suggested that the content of persecutory delusions could reflect threats from the human ancestral environment that differ for men vs. women: Walston, David, and Charlton (1998) proposed that women would project such delusional beliefs of being threatened onto female conspecifics, because for women, it was vital to cooperate with other nonkin women to build social support networks (Essock Vitale & McGuire, 1985). For men, by contrast, potential ancestral threats might have lain in marauding bands of strange males, because, due to strong resource competition between unrelated communities in ancestral human environments, men formed coalitions to defend territory and engage in warfare (Wrangham, 2004).

In support of this proposal, Walston et al., (1998) found that women suffering from persecutory delusions felt threatened by familiar persons, whereas the majority of deluded men feared persecution by strangers. However, the sample size was fairly small, ratings were made in retrospect, the study did not examine the nature of the perceived threat (e.g., physical violence, sexual coercion, or ostracism), and there was no cross-cultural comparison, which could provide further evidence in favor of the hypothesis of pathologically distorted human universals for dealing with social threat detection in psychiatric disorders associated with persecutory delusions (Brown, 1991).

In the present prospective study, we sought to address these open questions. Specifically, we hypothesized the following: (1) Men with persecutory delusions project their threat perception onto groups of strange males. (2) Deluded women feel persecuted by persons from their familiar social environment (both men and women). (3) Physical violence including death is the predominating nature of perceived threat in deluded men. (4) Women's fears focus on physical violence or sexual coercion if threatened by males, and ostracism if threatened by other females. (5) In light of the arbitrariness of categories of current diagnostic systems (i.e., DSM-IV 4th edition, American Psychiatric Association, 1994), these findings are expected to be independent of psychiatric diagnosis. (6) The anticipated sex differences are cross-culturally similar.

2. Methods

Patients admitted to the Center for Psychiatry, Psychotherapy, and Psychosomatics, University of Bochum, Germany, were screened for the presence of delusional beliefs of persecution. Sixty-four cases with persecutory delusions were identified and examined using a semistructured interview. The interview addressed patients' demographic variables (age, sex, and marital status) and the predominant nature of the perceived threat (physical violence, sexual coercion, ostracism, or loss of social status), the number of persecutors (single persons or groups), the sex of the perceived persecutors (males, females, or both), and whether the perceived persecutors were familiar to the deluded subjects (family members, neighbors, or colleagues), or strangers (e.g., police, Mafia, secret service, etc., were subsumed under the term “hostile gangs”).

A diagnosis was made according to DSM-IV criteria (APA, 1994), and psychopathology was rated using the Positive and Negative Symptom Scale (PANSS, Kay, Opler, & Lindenmayer, 1989). Fifty-seven patients (25 males, 32 females) were German born, whereas seven (1 male, 6 females) were from various other cultural backgrounds and had lived for quite a short time in Germany.

The same procedure was followed to assess a group of 63 inpatients (31 males, 32 females) of the Department of Psychiatry, University of St. Petersburg, Russia.

3. Results

In the German sample, 30 patients were diagnosed with schizophrenia, 14 with delusional disorder, 6 with schizoaffective disorder, 2 with affective disorder, and 5 with organic psychotic disorder. In the Russian sample, 50 patients were diagnosed with schizophrenia, 2 delusional disorder, 1 schizoaffective disorder, 1 affective disorder, and 9 organic psychosis according to DSM-IV (APA, 1994). Five of the patients living in Germany from a different cultural background were classified as schizophrenic, one as schizoaffective, and one as organic psychotic disorder.

The demographic variables of the samples are summarized in Table 1. The German and Russian samples did not differ with respect to age [F(2,120)=0.50, p=.61], sex distribution [χ2(1,120)=0.58, p=.47], or psychopathology ratings as measured using the PANSS [F(2,120)=0.17, p=.84]. Likewise, a multiple analysis of variance did not reveal any significant interaction between the diagnostic categories and nationality in terms of psychopathology [F(6,127)=0.35, p=.91] or age [F(6,127)=0.38, p=.89].

Table 1.

Demographic data, diagnostic categorization, and psychopathology (as measured using the PANSS, Kay et al., 1989) of German and Russian patients with delusions of persecution

Variable German patients Russian patients Statistics (p values)
N 57 63
Age 44.95±14.7 46.38±12.04 .608, n.s.
Sex (m : f) 25:32 32:31 .47, n.s.
Diagnostic category
Schizophrenia (N) 30 50
Delusional disorder (N) 14 2
Schizoaffective disorder (N) 6 1
Affective disorder (N) 2 1
Organic psychotic disorder (N) 5 9
Psychopathology
PANSS positive symptoms 24.47±6.65 24.05±7.04 .93, n.s.
PANSS negative symptoms 23.42±7.84 24.89±5.93 .284, n.s.
PANSS general psychopathology 51.14±11.21 49.46±11.16 .689, n.s.
PANSS sum score 98.67±21.11 98.35±19.93 .841, n.s.

As predicted, the majority of male patients (69.4%) with delusions of persecution projected their delusional fears onto strangers, whereas the majority of delusional women (68.3%) attributed their fears to familiar people. This sex differences was highly significant in the entire patient group [χ2(2,125)=24.42, p<.001], as well as in separate analyses in both German [χ2(2,57)=15.12, p<.001] and Russian patients [χ2(2,61)=8.70, p=.013]. Moreover, as expected, no difference between German and Russian patients emerged in respect of either female preference for familiar persons as perceived persecutors [χ2(2,58)=3.74, p=.15] or male preference for strangers as perceived persecutors [χ2(2,61)=1.81, p=.41].

We further hypothesized that males would feel persecuted mainly by other males, whereas females would be more likely to feel persecuted by other females. Overall, most males felt persecuted by other males (46.0%) or members of both sexes (52.4%). Contrary to our expectations, however, female patients with persecutory delusions projected their fears onto other females in only 17.5% of cases, whereas 44.4% felt persecuted by males and 38.1% by both sexes. Contrariwise, 10 of 11 patients who projected their delusional beliefs onto females were women. The difference between male and female patients was statistically significant [χ2(2,126)=9.77, p=.008]. Again, there was no difference between German and Russian male and female patients regarding the number of female persecutors [χ2(2,12)=1.53, p=.47], male persecutors [χ2(2,57)=1.28, p=.53], or perceived persecution from members of both sexes [χ2(2,57)=4.11, p=.13].

As regards the number of perceived persecutors, we predicted that male patients would feel persecuted by groups, whereas females would more often feel persecuted by single persons. Overall, 84.1% of male patients felt persecuted by groups; however, only 33.3% of female patients projected their fears onto single persons, the sex difference being nevertheless significant [χ2(1,126)=5.18, p=.023]. Interestingly, here, we found differences between German and Russian patients: In both nationalities, males felt persecuted by groups in 84% of the cases, but 53.1% of the German female patients felt persecuted by single persons vs. only 10% in the Russian sample. Thus, the sex difference in the entire group was due to the difference in the German sample [χ2(1,57)=8.31, p=.004], whereas in the Russian sample, no sex difference in the number of perceived persecutors was detected [χ2(1,62)=.44, p=.51].

We hypothesized that fear of physical violence would be more prevalent in male patients, and sexual violence in women. This was not the case. In the entire sample, men and women with delusions of persecutions did not differ in this regard [χ2(3,125)=3.27, p=.35]. In delusional men, the fear of physical violence was present in 85.3%; the percentage of female patients who primarily felt threatened by physical violence was even slightly higher (89.1%). The respective figures of males and females for fear of sexual coercion were 6.6% and 7.8%, for fear of ostracism 3.3% and 3.1%, and for loss of social status 4.9% in men and 0% in women. These figures were by and large similar in German and Russian patients, except that all German patients who feared sexual coercion were women (two patients were diagnosed with schizophrenia, two with delusional disorder), whereas the majority of Russian patients (80%) who felt threatened by sexual coercion were men.

In addition, we hypothesized that, due to the imprecision of DSM-IV categories, no differences would emerge between diagnostic categories. Due to small N for schizoaffective, affective, and organic psychotic disorder, we performed statistical analyses in patients with schizophrenia and patients with delusional disorder only. As expected, the differences between male and female patients regarding the identity of perceived persecutors remained significant in patients with schizophrenia [χ2(2,83)=20.44, p<.001] and in patients with delusional disorder [χ2(1,16) =9.35, p=.002]. As for the sex of the perceived persecutors, the sex differences remained significant only in the schizophrenia group [χ2(2,84)=6.59, p=.037]. Regarding the number of perceived persecutors, no statistically significant sex difference emerged in either the schizophrenic [χ2(1,84)=1.92, p=.17] or the delusional disordered group [χ2(1,16)=3.31, p=.069]. Similarly, no sex differences were found in the nature of perceived threat in either group. These results are summarized in Table 2.

Table 2.

Summary of findings pertaining to the main hypotheses of the study in German and Russian patients with persecutory delusions

German patients Russian patients
Males Females Males Females
Identity of persecutors
Strangers 18 (78%) 8 (26%) 21 (72%) 10 (34%)
Familiar persons 5 (22%) 23 (74%) 8 (28%) 19 (66%)
(100%) (100%) (100%) (100%)
Sex of persecutors
Males 10 (40%) 12 (38%) 18 (56%) 16 (53%)
Females 6 (19%) 1 (3%) 4 (13%)
Both sexes 15 (60%) 14 (43%) 13 (41%) 10 (33%)
(100%) (100%) (100%) (100%)
Number of persecutors
Single 4 (16%) 17 (53%) 6 (16%) 3 (10%)
Groups 21 (84%) 15 (47%) 27 (84%) 27 (90%)
(100%) (100%) (100%) (100%)
Nature of perceived threat
Physical violence 22 (92%) 28 (88%) 24 (77%) 28 (90%)
Sexual violence 4 (12%) 4 (13%) 1 (3%)
Ostracism 2 (8%) 2 (7%)
Loss of social status 3 (10%)
(100%) (100%) (100%) (100%)

Finally, we were interested in which of the variables would best predict the odds of being a female or male patient with delusions of persecution. Therefore, we performed a logistic regression analysis fitting the identity, the sex, and the number of perceived persecutors as independent variables in the equation. All variables were significant zero-order predictors. Nagelkerke's R2 of the model was .297. The sex of 75.8% of male patients and 70.5% of female patients was correctly predicted on the basis of the model. The most significant predictor of the odds of being a female or male patient with persecutory delusions was the identity of the perceived persecutor [stranger or familiar person; regression coefficient B=1.693, exp(B)=5.436, p<.001]. The item “sex of the perceived persecutors” approached statistical significance [regression coefficient B=0.677, exp(B)=1.967 p=.052), whereas the number of persecutors (groups of single individuals) was not a significant predictor in the model [regression coefficient B=0.182, exp(B)=1.200, p=.75].

However, we found minor differences between German and Russian patients. In the German sample (values for the Russian sample shown in italics and square brackets), the identity of persecutors predicted best the odds of being a male or female patient. Of the male and female patients, 80.0% [80.6%] and 71.9% [57.1%], respectively, were classified correctly on the basis of the model. For “identity of persecutors,” the regression coefficient B was 1.317, exp(B)=3.731, p=.029, [regression coefficient B=2.339, exp(B)=10.366, p=.001]; for “sex of persecutors,” the regression coefficient B was 0.549, exp(B)=1.732, p=.311, n.s. [regression coefficient B=1.054, exp(B)=2.870, p=.105, n.s.]; and for the item “number of persecutors,” the figures were regression coefficient B=0.782, exp(B)=3.048, p=.154 [regression coefficient B=−1.921, exp(B)=.146, p=.086].

4. Discussion

In the present study, we sought to test the hypothesis of Walston et al., (1998) that the content of persecutory delusions may reflect ancestral hostile threats of the human environment of evolutionary adaptedness, and to expand on their proposal that male patients with persecutory delusions would feel threatened by strangers, whereas females would more likely project their delusional fears onto familiar people of their own group. We addressed whether male and female patients differed in the identity, sex, and number of perceived persecutors, and in the nature of the anticipated threat, in patients of two nationalities, and across diagnostic categories according to DSM-IV (APA, 1994).

Consistent with Walston et al., (1998) hypothesis, our study suggests that the majority of male patients with persecutory delusions felt threatened by groups of strange males, which is consistent with the evolutionary scenario where—like our closest relatives, the chimpanzees—early human males were probably threatened by territorial competition with other males and warfare (Wrangham, 2004). By contrast, women with persecutory delusions more often felt persecuted by familiar persons from their social environment. Not only were our figures strikingly similar to those reported by Walston et al., (1998), but in a logistic regression analysis, we found the identity of the perceived persecutor to be the most significant predictor of the patient's sex. In further support of the evolutionary background of delusional fears, our findings were cross-culturally similar in two German and Russian samples of patients matched for age, sex distribution, and level of psychopathology, and also, at least in part, similar across different diagnostic categories. One notable exception, however, was the difference between German and Russian female patients regarding the number of the perceived persecutors. Whereas in the German sample, approximately 50% of the female patients felt persecuted by single persons, only 10% of the Russian women felt persecuted by single persons. This difference could not be accounted for by the higher prevalence of delusional disorder in the German sample, because the figures were similar for schizophrenic and delusional women. Our findings therefore cannot rule out all impacts of cultural differences. Similarly, Parsons (1969) found cultural differences between U.S. American patients with paranoid schizophrenia and patients from Southern Italy; in her study, the majority of American patients projected their delusional fears onto institutions or ideological background such as advertising agencies or communists, whereas most Italian patients' projections were centered on specific persons in the patients' family or neighborhood. However, the study of Parsons (1969) did not address sex differences, leaving open to speculation the possibility that men were overrepresented in the American sample and women in the Italian sample.

Contrary to our expectations, fear of sexual coercion in female delusional patients was almost absent. Arguably, this could indicate either that sexual coercion was not a major threat in the environment of evolutionary adaptedness, which would speak against the proposed evidence of female adaptations against rape (Thornhill & Palmer, 2000), or, perhaps more likely, that fears of being sexually coerced were simply underreported by female patients due to shame or embarrassment. We also cannot rule out the possibility that differences between German and Russian patients and between this and other studies were partly due to the divergent diagnostic distribution of patients, or to factors pertaining to the length of hospitalization, duration of illness, or other illness-related factors, which could have influenced the accuracy of the patients' verbal report. These issues ought to be addressed in further studies.

In any event, in both sexes and across cultures, males and females with persecutory delusions felt threatened mainly by acts of physical violence. Indeed, this might have played a vital role in ancestral conditions, as reports on hunter–gatherers of the Andaman Islands (Radcliffe-Brown, 1948) and New Guinea horticulturalists (Schiefenhövel, 1995) suggest. For example, in the Eipo people of Western New Guinea, who until recently lived in conditions perhaps similar to human ancestral environments, the rate of unnatural deaths from intertribal conflicts is extremely high. Up to 25% of men die in combat, and approximately 13% of women die violent deaths (Schiefenhövel, 1995). If such scenarios were sufficiently persistent throughout major parts of human evolutionary history, and provided that delusions of persecution are indeed reminiscent of ancestral threats, then it becomes plausible why a substantial proportion of deluded females was afraid of being physically attacked.

In further support of the hypothesis that delusional beliefs could be reminiscent of “real” ancestral threats, a previous study on erotomania—the delusional belief of being loved by another person—revealed sex differences in the characteristics of the perceived lover and the actual behavior oriented toward the “love object” (Brüne, 2001). Overall and across diagnostic categories, erotomania was most prevalent in unmarried female patients in their late reproductive age. Erotomanic women preferentially chose older men of high social rank as love objects, were fixated on single love objects, and tried to increase their mate values, which altogether could be interpreted as pathological exaggeration of a long-term mating strategy (Buss & Schmitt, 1993). In contrast, evolution-minded studies of delusional jealousy would presumably evince a typical “male” behavioral profile (Charlton & McClelland, 1999), but this assertion warrants empirical testing (Daly, Weghorst & Wilson, 1982).

In sum, our study provides additional evidence for the hypothesis that delusions of persecution may reflect ancestral threats. In a more general vein, we conclude that the content of delusional beliefs could be interpreted as pathological variants of adaptive psychological mechanisms relating to social selection pressures (Charlton & McClelland, 1999).

Acknowledgments

We are grateful to Professor Alexej Y. Egorov for providing us with the data on the Russian sample and to all patients for their willingness to participate in the study.

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Center for Psychiatry, Psychotherapy and Psychosomatics, University of Bochum, 44791 Bochum, Germany

Corresponding author. Tel.: +49 234 5077 155; fax: +49 234 5077 235.

PII: S1090-5138(05)00063-2

doi:10.1016/j.evolhumbehav.2005.08.001

 



2007:12:08