Evidence that disgust evolved to protect from risk of disease

Disgust is a powerful human emotion that has been little studied until recently. Current theories do not coherently explain the purpose of disgust, nor why a wide range of stimuli can provoke a similar emotional response. Over 40 000 individuals completed a web-based survey using photo stimuli. Images of objects holding a potential disease threat were reported as significantly more disgusting than similar images with little or no disease relevance. This pattern of response was found across all regions of the world. Females reported higher disgust sensitivity than males; there was a constant decline in disgust sensitivity over the life course; and the bodily fluids of strangers were found more disgusting than those of close relatives. These data provide evidence that the human disgust emotion may be an evolved response to objects in the environment that represent threats of infectious disease.     

Social neuroscience of disgust

Disgust can be thought of as an affective system that has evolved to detect signs of pathogens, parasite and toxins as well as to stimulate behaviors that reduce the risk of their acquisition. Disgust incorporates social cognitive mechanisms to regulate exposure to and, or anticipate and avoid exposure to pathogens and toxins. Social cognition entails the acquisition of social information about others (ie, social recognition) and from others (ie, social learning). This involves recognizing and assessing other individuals and the pathogen/parasite/contamination/toxin threat they pose and deciding about when and how to interact with and, or avoid them. Social cognition provides a frame‐work for examining the expression of disgust and the associated neurobiological mechanisms. Here, we briefly consider the relations between social cognition and pathogen/parasite/toxin avoidance behaviors. We briefly discuss aspects of: (1) the odor mediated social recognition of actual and potentially infected individuals and the impact of parasite/pathogen threat on disgust mate and social partner choice; (2) the roles of “out‐groups” (strangers, unfamiliar individuals) and “in‐groups” (familiar individuals) in the expression of disgust and pathogen avoidance behaviors; (3) individual and social learning of disgust and empathy for disgust; (4) toxin elicited disgust and anticipatory disgust; (5) the neurobiological mechanisms, and in particular the roles of the nonapeptide, oxytocin and estrogenic mechanism associated with social cognition and the expression of disgust. These findings on the social neuroscience of disgust have a direct bearing on our understanding of the roles of disgust in shaping human and nonhuman social behavior.     

Disgust as an adaptive system for disease avoidance behaviour

Disgust is an evolved psychological system for protecting organisms from infection through disease avoidant behaviour. This 'behavioural immune system', present in a diverse array of species, exhibits universal features that orchestrate hygienic behaviour in response to cues of risk of contact with pathogens. However, disgust is also a dynamic adaptive system. Individuals show variation in pathogen avoidance associated with psychological traits like having a neurotic personality, as well as a consequence of being in certain physiological states such as pregnancy or infancy. Three specialized learning mechanisms modify the disgust response: the Garcia effect, evaluative conditioning and the law of contagion. Hygiene behaviour is influenced at the group level through social learning heuristics such as 'copy the frequent'. Finally, group hygiene is extended symbolically to cultural rules about purity and pollution, which create social separations and are enforced as manners. Cooperative hygiene endeavours such as sanitation also reduce pathogen prevalence. Our model allows us to integrate perspectives from psychology, ecology and cultural evolution with those of epidemiology and anthropology. Understanding the nature of disease avoidance psychology at all levels of human organization can inform the design of programmes to improve public health.     

Disgust: the disease-avoidance emotion and its dysfunctions

This review analyses the accumulating evidence from psychological, psychophysiological, neurobiological and cognitive studies suggesting that the disease-avoidance emotion of disgust is a predominant emotion experienced in a number of psychopathologies. Current evidence suggests that disgust is significantly related to small animal phobias (particularly spider phobia), blood-injection-injury phobia and obsessive-compulsive disorder contamination fears, and these are all disorders that have primary disgust elicitors as a significant component of their psychopathology. Disgust propensity and sensitivity are also significantly associated with measures of a number of other psychopathologies, including eating disorders, sexual dysfunctions, hypochondriasis, height phobia, claustrophobia, separation anxiety, agoraphobia and symptoms of schizophrenia--even though many of these psychopathologies do not share the disease-avoidance functionality that characterizes disgust. There is accumulating evidence that disgust does represent an important vulnerability factor for many of these psychopathologies, but when disgust-relevant psychopathologies do meet the criteria required for clinical diagnosis, they are characterized by significant levels of both disgust and fear/anxiety. Finally, it has been argued that disgust may also facilitate anxiety and distress across a broad range of psychopathologies through its involvement in more complex human emotions such as shame and guilt, and through its effect as a negative affect emotion generating threat-interpretation biases.     

Pathogen disgust,but not moral disgust,changes across the menstrual cycle

The Compensatory Prophylaxis Hypothesis (CPH) proposes that during periods of increased susceptibility to infections, e.g., during the luteal phase of the menstrual cycle when progesterone suppresses immune function, women should feel more disgust toward pathogen cues and behave prophylactically. We investigate differences in disgust sensitivity and contamination sensitivity during different phases of the menstrual cycle in regularly cycling, healthy 93 rural and urban Polish women using the within-subject design. Disgust sensitivity was measured during two different phases of a menstrual cycle: 1) the follicular phase (the 5th or 6th day of the cycle) and 2) the luteal phase (on the 5th day after a positive ovulatory test or on 20th day of a cycle if the result of the ovulatory test was not positive). In the luteal phase, women scored higher on the Pathogen Disgust of the Three-Domain Disgust Scale, the Contamination Obsessions and Washing Compulsions Subscale of Padua Inventory, and on ratings of photographs showing sources of potential infections than in the follicular phase. Moral Disgust of the Three-Domain Disgust Scale did not differ between cycle phases. Hence, results suggest that women feel more disgusted toward cues to pathogens during the luteal phase, when susceptibility to infection is greater. We suggest that it is necessary to incorporate ovulatory testing as well as to conduct repeated measurements of disgust sensitivity in future tests of the CPH. Moreover, we believe that understanding how the feeling of pathogen disgust varies across the menstrual cycle and in relation to progesterone levels could be useful in designing effective infectious diseases prevention strategies for women.     

Disgust and the Politics of Sex: Exposure to a Disgusting Odorant Increases Politically Conservative Views on Sex and Decreases Support for Gay Marriage

Disgust has been implicated as a potential causal agent underlying socio-political attitudes and behaviors. Several recent studies have suggested that pathogen disgust may be a causal mechanism underlying social conservatism. However, the specificity of this effect is still in question. The present study tested the effects of disgust on a range of policy preferences to clarify whether disgust is generally implicated in political conservatism across public policy attitudes or is uniquely related to specific content domains. Self-reported socio-political attitudes were compared between participants in two experimental conditions: 1) an odorless control condition, and 2) a disgusting odor condition. In keeping with previous research, the present study showed that exposure to a disgusting odor increased endorsement of socially conservative attitudes related to sexuality. In particular, there was a strong and consistent link between induced disgust and less support for gay marriage.     

Domain-specific variation in disgust sensitivity across the menstrual cycle

Disgust operates in many domains of behavior. On the presumption that facets of this emotion evince adaptive design, we conducted a cross-sectional study of 307 women, investigating changes in disgust sensitivity across the menstrual cycle. Two hypotheses were tested, namely (i) sexual disgust is an adaptation that serves to reduce participation in biologically suboptimal sexual behaviors, and (ii) many facets of disgust sensitivity compensate for cyclic changes in immunological robusticity via patterned alterations in behavioral prophylaxis against pathogens. Hypothesis (i) was supported, as disgust sensitivity in the sexual domain, and only in the sexual domain, was positively correlated with presumed conception risk as assessed on the basis of self-reported position in the menstrual cycle. Hypothesis (ii) was not supported, as no facet of disgust sensitivity changed as a function of the presumed level of immunosuppression assessed on the basis of self-reported position in the menstrual cycle. Results are discussed in light of published ethnographic evidence indicating that, in disparate cultures, disgust is elicited by aberrant sexual behaviors, and sex is equated with eating. Together with published findings on an animal model of sexual conditioning, this corpus suggests that sexual disgust may be a panmammalian adaptation.     

Disgust versus Lust: Exploring the Interactions of Disgust and Fear with Sexual Arousal in Women

Sexual arousal is a motivational state that moves humans toward situations that inherently pose a risk of disease transmission. Disgust is an emotion that adaptively moves humans away from such situations. Incongruent is the fact that sexual activity is elementary to human fitness yet involves strong disgust elicitors. Using an experimental paradigm, we investigated how these two states interact. Women (final N=76) were assigned to one of four conditions: rate disgust stimuli then watch a pornographic clip; watch a pornographic clip then rate disgust stimuli; rate fear stimuli then watch a pornographic clip; or watch a pornographic clip then rate fear stimuli. Women’s genital sexual arousal was measured with vaginal photoplethysmography and their disgust and fear reactions were measured via self-report. We did not find that baseline disgust propensity predicted sexual arousal in women who were exposed to neutral stimuli before erotic content. In the Erotic-before-Disgust condition we did not find that sexual arousal straightforwardly predicted decreased image disgust ratings. However, we did find some evidence that sexual arousal increased self-reported disgust in women with high trait disgust and sexual arousal decreased self-reported disgust in women with low trait disgust. Women who were exposed to disgusting images before erotic content showed significantly less sexual arousal than women in the control condition or women exposed to fear-inducing images before erotic content. In the Disgust-before-Erotic condition the degree of self-reported disgust was negatively correlated with genital sexual arousal. Hence, in the conflict between the ultimate goals of reproduction and disease avoidance, cues of the presence of pathogens significantly reduce the motivation to engage in mating behaviors that, by their nature, entail a risk of pathogen transmission.     

Disgust sensitivity is negatively associated with immune system activity in early pregnancy: Direct support for the Compensatory Prophylaxis Hypothesis

According to the Compensatory Prophylaxis Hypothesis (CPH), disgust may be considered a part of the behavioral immune system, adjusting as a function of immunocompetence. Early pregnancy involves modulation of a complex network of various immune-related factors, but only a few studies so far have focused on disgust sensitivity in pregnant women in the context of the CPH. This study aimed to examine associations between disgust sensitivity and immune activity indices, cytokine levels, and white blood cell (WBC) count in pregnant women. The sample included 78 women in the 1st trimester of pregnancy. Higher disgust sensitivity (Disgust Scale-Revised; DS-R) was significantly associated with decreased levels of IL-1β, IL-2 IL-4, IL-7, IL-17, Eotaxin, MCP-1 (MCAF), and RANTES in blood serum. This model explained 17.5% of the total DS-R score variability. Using the DS-R subscales, the Contamination disgust was significantly associated with levels of FGF basic, IFN-γ, IL-1β, IL-2, IL-4, IL-7, IL-17A, G-CSF, MCP-1 (MCAF), MIP-1α, PDGF-BB, and RANTES, and the Core disgust was significantly associated with levels of IL-1β, IL-2, IL-4, IL-7, IL-17A, Eotaxin, G-CSF, IP-10, MCP-1 (MCAF), PDGF-BB, and TNF-α. Disgust sensitivity was not associated with WBC count. Disgust may reflect and compensate for insufficient immune adaptation in early pregnancy, suggesting the potential clinical significance of this common prenatal symptom.     

Risk of parasite transmission influences perceived vulnerability to disease and perceived danger of disease-relevant animals

Adaptationist view proposes that emotions were shaped by natural selection and their primary function is to protect humans against predators and/or disease threat. This study examined cross-cultural and inter-personal differences in behavioural immune system measured by disgust, fear and perceived danger in participants from high (Turkey) and low (Slovakia) pathogen prevalence areas. We found that behavioural immune system in Turkish participants was activated more than those of Slovakian participants when exposed to photographs depicting disease-relevant cues, but not when exposed to disease-irrelevant cues. However, participants from Slovakia, where human to human disease transmission is expected to be more prevalent than in Turkey, showed lower aversion in Germ Aversion subscale supporting hypersensitiveness of the behavioural immune system. Having animals at home was less frequent both in Turkey and in participants who perceived higher danger about disease relevant animals. Participants more vulnerable to diseases reported higher incidence of illness last year and considered perceived disease-relevant animals more dangerous than others. Females showed greater fear, disgust and danger about disease-relevant animals than males. Our results further support the finding that cultural and inter-personal differences in human personality are influenced by parasite threat.     

Does food play a prominent role in visual attention to disgusting stimuli?

Journal of Ethology - Disgust is a basic emotion which protects individuals from potential contamination. It is hypothesized that disgust evolved primarily as a mechanism against oral contamination...     

Different Timing Features in Brain Processing of Core and Moral Disgust Pictures: An Event-Related Potentials Study

Disgust, an emotion motivating withdrawal from offensive stimuli, protects us from the risk of biological pathogens and sociomoral violations. Homogeneity of its two types, namely, core and moral disgust has been under intensive debate. To examine the dynamic relationship between them, we recorded event-related potentials (ERPs) for core disgust, moral disgust and neutral pictures while participants performed a modified oddball task. ERP analysis revealed that N1 and P2 amplitudes were largest for the core disgust pictures, indicating automatic processing of the core disgust-evoking pictures. N2 amplitudes were higher for pictures evoking moral disgust relative to core disgust and neutral pictures, reflecting a violation of social norms. The core disgust pictures elicited larger P3 and late positive potential (LPP) amplitudes in comparison with the moral disgust pictures which, in turn, elicited larger P3 and LPP amplitudes when compared to the neutral pictures. Taken together, these findings indicated that core and moral disgust pictures elicited different neural activities at various stages of information processing, which provided supporting evidence for the heterogeneity of disgust.     

Reprint of Hormonal correlates of pathogen disgust: testing the compensatory prophylaxis hypothesis

Raised progesterone during the menstrual cycle is associated with suppressed physiological immune responses, reducing the probability that the immune system will compromise the blastocyst's development. The Compensatory Prophylaxis Hypothesis proposes that this progesterone-linked immunosuppression triggers increased disgust responses to pathogen cues, compensating for the reduction in physiological immune responses by minimizing contact with pathogens. Although a popular and influential hypothesis, there is no direct, within-woman evidence for correlated changes in progesterone and pathogen disgust. To address this issue, we used a longitudinal design to test for correlated changes in salivary progesterone and pathogen disgust (measured using the pathogen disgust subscale of the Three Domain Disgust Scale) in a large sample of women (N?=?375). Our analyses showed no evidence that pathogen disgust tracked changes in progesterone, estradiol, testosterone, or cortisol. Thus, our results provide no support for the Compensatory Prophylaxis Hypothesis of variation in pathogen disgust.     

Disgust sensitivity and the neurophysiology of left-right political orientations

Disgust has been described as the most primitive and central of emotions. Thus, it is not surprising that it shapes behaviors in a variety of organisms and in a variety of contexts--including homo sapien politics. People who believe they would be bothered by a range of hypothetical disgusting situations display an increased likelihood of displaying right-of-center rather than left-of-center political orientations. Given its primal nature and essential value in avoiding pathogens disgust likely has an effect even without registering in conscious beliefs. In this article, we demonstrate that individuals with marked involuntary physiological responses to disgusting images, such as of a man eating a large mouthful of writhing worms, are more likely to self-identify as conservative and, especially, to oppose gay marriage than are individuals with more muted physiological responses to the same images. This relationship holds even when controlling for the degree to which respondents believe themselves to be disgust sensitive and suggests that people's physiological predispositions help to shape their political orientations.     

Hormonal correlates of pathogen disgust: testing the compensatory prophylaxis hypothesis

Raised progesterone during the menstrual cycle is associated with suppressed physiological immune responses, reducing the probability that the immune system will compromise the blastocyst's development. The Compensatory Prophylaxis Hypothesis proposes that this progesterone-linked immunosuppression triggers increased disgust responses to pathogen cues, compensating for the reduction in physiological immune responses by minimizing contact with pathogens. Although a popular and influential hypothesis, there is no direct, within-woman evidence for correlated changes in progesterone and pathogen disgust. To address this issue, we used a longitudinal design to test for correlated changes in salivary progesterone and pathogen disgust (measured using the pathogen disgust subscale of the Three Domain Disgust Scale) in a large sample of women (N = 375). Our analyses showed no evidence that pathogen disgust tracked changes in progesterone, estradiol, testosterone, or cortisol. Thus, our results provide no support for the Compensatory Prophylaxis Hypothesis of variation in pathogen disgust.     

Disease avoidance as a functional basis for stigmatization

Stigmatization is characterized by chronic social and physical avoidance of a person(s) by other people. Infectious disease may produce an apparently similar form of isolation-disease avoidance-but on symptom remission this often abates. We propose that many forms of stigmatization reflect the activation of this disease-avoidance system, which is prone to respond to visible signs and labels that connote disease, irrespective of their accuracy. A model of this system is presented, which includes an emotional component, whereby visible disease cues directly activate disgust and contamination, motivating avoidance, and a cognitive component, whereby disease labels bring to mind disease cues, indirectly activating disgust and contamination. The unique predictions of this model are then examined, notably that people who are stigmatized evoke disgust and are contaminating. That animals too show avoidance of diseased conspecifics, and that disease-related stigma targets are avoided in most cultures, also supports this evolutionary account. The more general implications of this approach are then examined, notably how it can be used to good (e.g. improving hygiene) or bad (e.g. racial vilification) ends, by yoking particular labels with cues that connote disease and disgust. This broadening of the model allows for stigmatization of groups with little apparent connection to disease.     

When is it socially acceptable to feel sick?

Disease is a ubiquitous and powerful evolutionary force. Hosts have evolved behavioural and physiological responses to disease that are associated with increased survival. Behavioural modifications, known as ‘sickness behaviours’, frequently involve symptoms such as lethargy, somnolence and anorexia. Current research has demonstrated that the social environment is a potent modulator of these behaviours: when conflicting social opportunities arise, animals can decrease or entirely forgo experiencing sickness symptoms. Here, I review how different social contexts, such as the presence of mates, caring for offspring, competing for territories or maintaining social status, affect the expression of sickness behaviours. Exploiting the circumstances that promote this behavioural plasticity will provide new insights into the evolutionary ecology of social behaviours. A deeper understanding of when and how this modulation takes place may lead to better tools to treat symptoms of infection and be relevant for the development of more efficient disease control programmes.     

The behavioral immune system and social conservatism: a meta-analysis

The behavioral immune system (BIS) is a cluster of psychological mechanisms (e.g., disgust) that have evolved to promote disease-avoidance (Schaller M. (2006). Parasites, behavioral defenses, and the social psychological mechanisms through which cultures are evoked. Psychological Inquiry, 17, 96–101). Recent evidence suggests that the BIS may promote avoidance of outgroup members, an historical source of contamination, by evoking social conservatism (Terrizzi JA Jr, Shook NJ, & Ventis WL. (2010). Disgust: A predictor of social conservatism and prejudicial attitudes toward homosexuals. Personality and Individual Differences, 49, 587–592; Terrizzi J, Shook N, Ventis L. (2012). Religious conservatism: An evolutionarily evoked disease-avoidance strategy. Religion, Brain & Behavior, 2, 105–120.). That is, the BIS mechanisms may encourage the endorsement of socially conservative beliefs, which promote social exclusivity, tradition, and negativity toward outgroups. The current study provides a systematic review and meta-analysis of 24 studies to evaluate the hypothesis that the BIS is predictive of social conservatism. The results indicate that behavioral immune strength, as indicated by fear of contamination and disgust sensitivity, is positively related to social conservatism (i.e., right-wing authoritarianism, social dominance orientation, religious fundamentalism, ethnocentrism, collectivism, and political conservatism). These findings provide initial evidence that socially conservative values may function as evolutionarily evoked disease-avoidance strategies.     

Sociality and health: impacts of sociality on disease susceptibility and transmission in animal and human societies

This paper introduces a theme issue presenting the latest developments in research on the impacts of sociality on health and fitness. The articles that follow cover research on societies ranging from insects to humans. Variation in measures of fitness (i.e. survival and reproduction) has been linked to various aspects of sociality in humans and animals alike, and variability in individual health and condition has been recognized as a key mediator of these relationships. Viewed from a broad evolutionary perspective, the evolutionary transitions from a solitary lifestyle to group living have resulted in several new health-related costs and benefits of sociality. Social transmission of parasites within groups represents a major cost of group living, but some behavioural mechanisms, such as grooming, have evolved repeatedly to reduce this cost. Group living also has created novel costs in terms of altered susceptibility to infectious and non-infectious disease as a result of the unavoidable physiological consequences of social competition and integration, which are partly alleviated by social buffering in some vertebrates. Here, we define the relevant aspects of sociality, summarize their health-related costs and benefits, and discuss possible fitness measures in different study systems. Given the pervasive effects of social factors on health and fitness, we propose a synthesis of existing conceptual approaches in disease ecology, ecological immunology and behavioural neurosciences by adding sociality as a key factor, with the goal to generate a broader framework for organismal integration of health-related research.     

COVID-19 one year later: a retrospect of CRISPR-Cas system in combating COVID-19

Coronavirus disease 2019 (COVID-19), an infectious disease caused by Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has posed a persistent global threat. The transmission of SARS-CoV-2 is wide and swift. Rapid detection of the viral RNA and effective therapy are imperative to prevent the worldwide spread of the new infectious disease. Clustered Regularly-Interspaced Short Palindromic Repeats (CRISPR)- CRISPR-associated protein (Cas) system is an RNA-directed adaptive immune system, and it has been transformed into a gene editing tool. Applications of CRISPR-Cas system involves in many fields, such as human gene therapy, drug discovery and disease diagnosis. Under the background of COVID-19 pandemic, CRISPR-Cas system shows hidden capacity to fight the emergency in many aspects. This review will focus on the role of gene editing in COVID-19 diagnosis and treatment. We will describe the potential use of CRISPR-Cas-based system in combating COVID-19, from diagnosis to treatment. Furthermore, the limitation and perspectives of this novel technology are also evaluated.