Prejudice and “Racism” Is Hardwired from Evolution: To Avoid Disease Contagion



…because of similarities between sickness behaviors and symptoms of some mental disorders, it was hypothesized that mental illness stigma could be partially explained as a function of behavioral immune system biases designed to avoid potential sources of contagion.

…Some evidence suggests that the mental disorders that are most stigmatized as dangerous are the ones believed to be due to organic causes, or “brain disease,” and include schizophrenia and bipolar disorder, among others.

In response to the recurrent threat of infectious disease, a variety of species appear to have evolved behavioral adaptations to counter pathogen threat… Among humans, it is believed that infectious disease was perhaps the single greatest contributor to morbidity and mortality ancestrally. In response, there exists a behavioral immune system – a psychological system designed to promote the avoidance of potential pathogen carriers. When pathogen concerns are salient, people respond to heuristic disease cues with a range of affective (e.g., disgust), cognitive (e.g., attention), and behavioral (e.g., avoidance) reactions that ultimately serve to protect oneself from possible sources of infection. The imperfect relationship between potential disease cues (e.g., facial discolorations, missing limbs) and actual infectious disease presents a signal detection problem. Over perceiving disease cues and frequently committing false-positive errors is an adaptive response to ambiguous environmental threat. This bias leads people to interpret any deviation from the norm to be evidence for parasitic infection, and has been used to explain prejudice towards immigrants and foreigners, the physically disabled, the elderly, and the obese. However, no study to date has tested whether the behavioral immune system is activated in response to a potential heuristic disease cue that is less visually obvious – mental illness.

When humans and other animals are combating infectious disease, they exhibit a characteristic suite of responses that include lethargy, decreases in appetite, inability to concentrate, sleepiness and fatigue, and a loss of interest in activities they would otherwise find pleasurable. While these behaviors might be evolutionarily adaptive in that they allow the body to conserve enough energy to mount a healthy immune response, the symptoms of these sickness behaviors are similar to symptoms exhibited by those with mental disorders such as depression, some anxiety disorders, and sleep disorders, among others . Importantly, the biological basis of sickness behaviors include increases in pro-inflammatory cytokines that have been implicated in both healthy immune response to disease and in some psychological disorders such as depression. Given the physiological and behavioral similarities between normal immune responses and mental disorders, it is plausible that an oversensitive behavioral immune system would misperceive mental illness cues as physical illness.

… implicit measures also show predictive validity with behavioral measures of bias and discrimination that differ from patterns derived from explicit measures, we focused exclusively on implicit perceptions of mental illness in the present study.

Overview of Current Experiments
Despite a large body of evidence linking explicit mental illness stigma with danger, we predicted that:
people would implicitly associate mental illness with disease over danger
Additionally, we hypothesized that people who are particularly concerned about disease will demonstrate a stronger implicit association between mental illness and disease.

Results and Discussion
… In summary, our prediction that people overall would implicitly associate mental illness with disease over danger was supported. Additionally, we found that those that had been recently ill (and thus had heightened behavioral immune system concerns) tended to implicitly associate mental illness with sickness to a greater degree, and that men might make a stronger implicit association between mental illness and disease than women.

… Results and Discussion
Consistent with our hypothesis, our planned contrast revealed that those in the disease salience condition implicitly associated mental illness with sickness to a significantly greater degree than those in the average of the crime salience and the economic salience conditions…Experimental manipulation of disease salience increases the implicit association between mental illness and sickness.

In summary, in a second experiment it was found that people implicitly associate mental illness with disease over danger, an effect that is enhanced among those who are primed with disease concerns. Importantly, the results indicate that the association between mental illness and sickness appears to be more strongly elicited by pathogen concerns relative to the elevated arousal level of more general threats.

General Discussion Across two experiments we found that people overall implicitly associate mental illness with disease over danger…individuals that have heightened behavior immune system concerns – whether as a result of recent illness or a situational disease prime – are more likely to make this implicit link…the stigma against the mentally ill is due, in part, to people associating mental illness with disease cues…men made a stronger implicit association between mental illness and disease….


Source: Evolutionary Psychology – 2014. 12(4): 706-718

Sick in the Head? Pathogen Concerns Bias Implicit Perceptions of Mental Illness. – Erik M. Lund, et. al.


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