Infectious disease has posed a greater threat to human survival and welfare throughout both our recent and distant past. Given the implications of disease-causing parasites throughout human (and non-human) history, they have unsurprisingly long been a subject of intense study throughout the sciences — in biology, immunology, behavioral ecology, and even economics, just to name a few. More surprisingly, however, is the fact that the potential influence of disease threat on human cognition and behavior was a topic that was almost completely ignored by social psychologists until relatively recently.

Our immune system is a testament to the immense selective pressure that pathogens and parasites have exacted on humans throughout our evolutionary history. This extraordinarily sophisticated system has the ability, for example, to generate billions of unique antibodies as it calibrates to our local ecologies. However, it’s not the only disease-management tool we have.

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Another disease-management strategy is to simply avoid disease-causing objects whenever possible. We do this in our daily lives almost unconsciously, given that much of this avoidance is affectively motivated by the emotion of disgust. Previous research overwhelmingly indicates that, around the world, we’re grossed out the most by things that have historically posed the greatest risk of disease transmission, such as rotting food, squirmy bugs, and bodily secretions. We also have cultural strategies that mitigate disease transmission. Many culture-specific norms develop and persist due to their disease-buffering benefits — how to prepare and cook certain foods, how to avoid macroparasites with hygienic practices, even how to construct certain types of shelters.

Of course, despite the fact that disease is a ubiquitous threat, it is a threat that varies in magnitude. Any given person’s vulnerability to disease is influenced by both their internal processes (i.e. their immune system) and the environments in which they spend their time. This logically implies that it is more beneficial for some people to engage in behavioral disease avoidance strategies than others. But behavioral disease-avoidance strategies have costs too, which must be factored into the implicit cost-benefit calculus.

Using this type of adaptive cost/benefit framework, recent psychological research has begun to illuminate the numerous cognitive and behavioral constructs that are influenced by both real and perceived disease threat. We can find one intuitive example within the domain of sexual behavior. While sexually promiscuous behavior can have both hedonic and reproductive benefits, it has disease-specific costs too. These costs are more likely to be outweighed by the benefits for people who are more vulnerable to disease; thus, an adaptive framework predicts that higher vulnerability to disease should be associated with less promiscuous attitudes and behaviors. And this is exactly what the research to date suggests: people who perceive themselves to be more vulnerable to disease are less attitudinally and behaviorally inclined towards promiscuity, and experimentally making the threat of disease salient makes people high in trait-like germ aversion report more restrictive sexual attitudes. Similarly, at the cross-cultural level, people living in countries with higher levels of disease are, on average, less attitudinally favorable towards promiscuity.

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In a more recent set of studies, we were interested in how the perceived threat of disease might predict people’s sensitivity to moral violations (people’s “moral vigilance”). Similar cost/benefit logic links disease threat to moral vigilance. Failure to follow moral proscriptions has historically had implications for the spread of infectious disease.

Because many disease-causing parasites are invisible and their actions mysterious, disease control has historically depended substantially on adherence to normative proscriptions that reduced infection risk. People who openly dissented from these normative moral proscriptions, therefore, posed a health threat to both themselves and others. Thus, while there are costs associated with unequivocal conformity to established rules (such as inhibition of creative problem-solving and innovation), there are disease-specific benefits too. These benefits would have been more likely to outweigh the costs under circumstances in which the threat of disease is (or is perceived to be) higher. Thus, to the extent that following moral proscriptions confers the benefit of mitigating disease threat, we predicted that greater perceived disease threat would be associated with greater sensitivity to moral violations.

We tested this hypothesis across three studies, using both online and student samples (all participants were currently living in the United States). In all studies, we used as our outcome variable a scale assessing sensitivity to moral violations across the six moral domains suggested by Moral Foundations Theory. This scale had people rate the perceived wrongness of hypothetical violations (ranging from “not at all wrong” to “extremely wrong”) in the moral domains of purity (“you see a teenager urinating in the wave pool at a crowded amusement park”), loyalty (“you see an employee joking with competitors about how badly his company did last year”), authority (“you see a woman refusing to stand when the judge walks into the courtroom”), liberty (“you see a man blocking his wife from leaving home or interacting with others”), fairness (“you see a student copying a classmate’s answer sheet on a final exam), emotional care (“you see a teenage boy chuckling at an amputee he passes by while on the subway), animal care (“you see a woman swerving her car in order to intentionally run over a squirrel”), and physical care (“you see a woman slapping another woman who she is arguing with in the parking lot”). Overall moral vigilance was calculated as the average of these eight categories. As has been done previously we also distinguished “binding” moral vigilance (the value placed on authority, loyalty, and purity) and “nonbinding” (or individualizing) moral vigilance (the average of the five remaining domains).

Across the three studies, higher dispositional worry about disease threat consistently predicted higher levels of moral vigilance. Subsequent analyses revealed that this relationship was strongest between worry about disease threat and sensitivity to violations of the “binding” moral domains — authority, loyalty, and purity. These are the domains that may be most pertinent to inhibiting pathogen transmission. Of course, these are only correlations, and it’s important to distinguish whether these relationships are specific to worry about disease avoidance or anxiety about potential threats or dangers more generally. Indeed, further analyses revealed that worry about physical threats predicted sensitivity to moral violations as well, but when controlling for these relationships the relationship between perceived disease threat and moral vigilance remained.

Of most inferential utility was the third study, in which we experimentally manipulated the perceived threat of disease by making participants talk, for a few minutes, about a time in their lives in which they felt most vulnerable to germs or disease (in the two control conditions, participants talked about either a time that they felt vulnerable to physical harm or simply what they did yesterday). These experimental results revealed that participants who discussed being vulnerable to disease subsequently expressed greater moral vigilance than participants in both of the control conditions. This experimental effect was true for both Binding and non-Binding vigilance.

Overall, then, our results suggested that dispositional germ aversion was more strongly related to binding moral vigilance. This is consistent with research at the cross-cultural level of analysis suggesting that higher levels of real disease threat predict higher levels of binding moral vigilance. However, experimentally-manipulated disease salience amplified moral vigilance in both binding and nonbinding moral violations. Although currently we can only speculate, it is possible that whereas chronic worry about germs and disease leads to the calibration of moral cognition that more specifically facilitates enforcement of norms in disease-relevant domains, temporary disease salience results in an overgeneralized reaction of increased sensitivity to violations in any domain. Such overgeneralized reactions are consistent with previous work suggesting that evoked disease threat is associated with conformity to norms that are not disease-specific. However, these results are preliminary. Much further research remains.

These findings are described in the article entitled On Disease and Deontology: Multiple Tests of the Influence of Disease Threat on Moral Vigilance, recently published in the journal Social Psychological and Personality Science.

About The Author

Damian Murray is a research scientist at Tulane University. Dr. Murray's research programs follow two themes: 1) The consequences of a disease-avoidance motive for interpersonal relationships, social attitudes, personality, and cultural differences, and 2) The dynamics of new interpersonal relationships—the individual differences that predict formation, stability, and satisfaction in new romantic relationships, and the implications of these relationships for physiology and health.