This essay explains how the emotion of disgust is approached by evolutionary psychology (EP) and cultural evolution (CE), by analysing biological forms of disgust towards objects, and social forms of disgust towards outgroups. I argue both sub-fields are complementary, and disgust can operate under a universal disease avoidance mechanism suggested by EP, that is capable of varying across societies through different social transmission processes suggested by CE.
EP classifies disgust as a mechanism to avoid diseases, known as the behavioural immune system (BIS). The BIS uses sensory cues such as smell or sight to detect potential threats to the immune system, eliciting disgust to prompt avoidance (Schaller, 2011). Curtis and Biran (2001) further emphasized that BIS could have developed during ancestral times to help humans avoid objects which are likely to infect them with disease. This is evident in the consistent correlations found between the usual elicitors of disgust, and high bacterial rates: faeces, corpses, etc, and it is due to their high risk of infection, that these objects are universally considered ‘disgusting’ across human societies (Oaten et al, 2009). Moreover, in a subsequent experiment by Curtis et al (2004), they showed that by giving participants two nearly-identical photos, in which one was made to indicate cues of infection, the ‘infectious’ photo will always be rated as significantly more disgusting than the ‘non-infectious’ one. For example, a blue-stained cloth is not rated as disgusting, but a yellow-stained cloth would be rated as disgusting. Such effects were found for participants across diverse ranges of cultures, which highlights the universality of disease avoidance as a precursor to disgust in most societies.
The universality of disgust is also evident in physiological responses. Notably, while there is growing evidence that facial expressions of disgust vary slightly across Eastern and Western societies (Fang et al, 2022). Objective measures like the Facial Action Coding System (FACS) have concluded that across cultures, disgust expressions can be classified according to a general set of facial actions, including combinations of a wrinkled nose, tightened eyelids, or a dropped jaw (Reschke et al, 2019). These sets of physiological responses fit into the disease avoidance hypothesis proposed by EP. Susskind et al (2008) explain that actions like wrinkling nose during disgust may serve a function of limiting pathogen contact through vital sensory pathways. They infer this through an experiment which compares the air-flow velocity through nasal pathways when participants pull a ‘disgusted’ expression and a ‘fearful’ expression. They showed that air-flow velocity significantly decreased when participants made a disgusted expression, while significantly increased with a fearful expression. Evolutionary, it would be logical that fearful expressions should increase air-flow, to prepare for potential dangers, while disgust expressions should decrease air-flow, to limit ingestion of potential air-borne pathogens.
The BIS is also applicable to social domains of disgust towards people. Schaller (2011) proposes that, ancestrally, humans may have developed the tendency to be disgusted by foreign groups, as outgroup humans could carry novel diseases. This relationship between disgust and outgroup is revealed through Aaroe et al’s (2017) study. Their metanalysis highlighted that a strong empirical link is found between individuals’ disgust sensitivity, how easily they feel disgusted, and prejudice towards immigrants. They further conducted a correlational test of disgust sensitivity and anti-immigration attitudes, while controlling for factors like political ideologies. They discovered that even among liberals, who ideologically should support immigration, those with high disgust sensitivity tend to support more anti-immigration policies than liberals with low disgust sensitivity. These findings imply that disgust underlies the tendencies of prejudice and negative attitudes towards social outgroups,
Furthermore, Faulkner et al (2004) elucidates the relationship between outgroup disgust and disease avoidance by showing that prejudice is mediated by the salience of disease to individuals. Their experiment revealed that when disease-salience is primed in Canadian students, such as thinking about their own vulnerabilities to illness, they become significantly less likely to endorse the arrival of Nigerian immigrants, but more likely to endorse Scottish immigrants. But, when disease-salience is not primed, endorsements for Nigerians immigrants were equal to Scottish immigrants. These results imply that not only does perception of disease threats induce prejudice towards outgroup members, the prejudice is also exclusive for more unfamiliar kinds of outgroup, like Nigerians as opposed to the Scottish for Canadians. Thus, the more ‘foreign’ the outgroup, the more disgust is generated for avoidance. By all means, I am not suggesting that prejudice is inevitable as a part of humans’ disgust mechanism, this point will be elaborated on from the perspective of CE.
CE approaches disgust as a behaviour that is socially learnt. A case for this can be made with children’s acquisition of disgust and food preferences. Stevenson et al (2010) discovered a significant relationship between parent and child’s responses to disgust elicitors. For example, a parent who expressed more disgust to their child when faced with disgusting stimuli together, would lead to the child displaying higher avoidant behaviour when faced with the stimuli alone. The same kind of parent-child transmission is observable with food. According to Paroche et al (2017), children’s preferences for food is primarily shaped by observational learning processes like imitation of parents. Understandably, some foods that are nutritious, like vegetables, can initially elicit disgust in children that need to be overcome. Their experimental study tested how parents’ eating of novel food would impact their children’s own intake of novel food. Presenting parent and child with semolina dyed with either matching or differing colours, findings showed that children are more likely to eat semolina after observing parents eat one of the same colour, but not when they were different colours (Addessi et al, 2005). These results imply that social transmissions, particularly by parents, can determine our disgust and avoidance towards objects.
Expanding on this idea, Siegal et al (2011) suggest that disgust does not always conform to disease avoidance rules, and cultural contexts dictate how pathogen risks are responded to. Using rural Benin as an example, they explain that while industrialized places have developed a toilet-training culture, rural Benin faces a historical open-defecation problem. Therefore, disgust sensitivity to faecal contamination may be lower due to regular exposure. This is reflected in Jenkins and Curtis’ (2005) survey, which highlighted that the major motivations behind installing latrines for households in rural Benin were seldom factors for cleanliness or disease avoidance, but instead, revolved around prestige and comfort. If cultural elements influence our disgust sensitivity, we would also expect variations in disgust sensitivity across societies. This is indeed the case, Gallo et al’s (2024) created a cross-cultural mapping of disgust sensitivity showed, by analysing how samples in five countries (Hong Kong, Germany, Palestine, Spain, & USA) describe and exemplify disgust. They revealed significant variations across societies, for instance, food domains of disgust, like spoiled milk etc, were only mentioned by Western countries, and activities like ‘not showering’ was significantly rated as more disgusting by Palestinians than other countries. These studies illustrate that ‘what we are disgusted by’, is shaped by the community we inhibit.
In a similar vein, disgust towards social outgroups is not always guided by disease avoidance, because outgroups that lack indications of illness or dirtiness are able to elicit disgust nonetheless. In Landy et al’s (2023) experiment, self-identified Democrats and Republicans were presented with a set of faces, paired with personal information about the individual, including political affiliation, i.e. “proud Republican.”. Participants were tasked with rating the faces in terms perceived grossness, and healthiness. The results highlighted a trend, that Democrats tend to significantly judge Republican’s faces to look more gross, but just as healthy as political ingroups’ faces. As Murray and Mulvaney (2012) propose, political identification is robustly linked to socio-cultural factors like parenting style, for instance, authoritative parents were found to pass on political partisanship to children more effectively than permissive parents. Taken together, these findings challenge the accounts of outgroup disgust given by the disease avoidance hypothesis, they signify that ‘who we are disgusted by’, is shaped through the group identity we adopt.
Subsequently, intervention methods to reduce outgroup disgust serve as a reminder that prejudice can be socially unlearnt just as well as learnt. Hodson et al (2014) explained that an individuals’ intergroup disgust sensitivity (ITG-DS), how easily they feel disgusted by foreign groups, predicts their prejudice towards outgroups. For example, comparing the attitudes towards homeless people between participants with high and low ITG-DS. They concluded that people with high ITG-DS hold more negative attitudes and are less trusting towards the homeless compared to those with low ITG-DS. However, by using contact simulation, like getting participants to imagine a positive interaction with a homeless person, the prejudice levels of those with high ITG-DS can be significantly reduced. Additionally, the more elaborate the imagined contact, such as imagining cooperation and physically touching the homeless, the more prejudice is reduced. Therefore, disgust towards an outgroup is not fixed by an individual’s disgust sensitivity, and through social interventions like anti-prejudice programmes, disgust is reversible.
Although I have listed conflicting approaches to disgust, I emphasize that both sub-fields are essentially complementary. For one, Curtis and Augner (2011) posits that it makes more sense for disgust to be an adaptive system built mainly around disease avoidance, but still allows for culturally specific developments, since human lifestyles inherently change across time and place. An example of disgust’s adaptiveness is detailed by Nichols (2002), he explains that as social manners develop over time in a society’s history, manners that are related to disgust tend to be preserved and even refined, compared to non-disgust related manners. By conducting a statistical comparison between historical and contemporary manuals about etiquette, Nichols revealed that old manuals often describe actions such as twisting one’s neck, laughing loudly, and spitting as bad manners. Yet, today, only spitting is unanimously considered bad manners. Furthermore, manners surrounding spitting only developed to be stricter over time. For instance, during the 17th century, spitting before someone was permissible, as long as it was covered with one’s foot, but by the 18th century, the norm had changed into spitting into a handkerchief. I believe this study perfectly integrates CE and EP perspectives on disgust. It shows that behaviours against disgust (not spitting) exhibits an advantage within cultural evolution, and are likely to be socially transmitted as ‘good manners’. Yet, many ‘bad manners’ is ultimately connected to disease, like spreading bacteria from spitting, that humans may be evolutionary predisposed to avoid.
In conclusion, EP approaches disgust as an emotion based around disease-avoidance, thus, objects and even outgroup members that pose potential disease threats evoke disgust to facilitate avoidance. CE approaches disgust as a behaviour socially learnt through parents and culture, evident in how disgust sensitivity varies across societies. Both perspectives are complementary, able to produce a fitting model of disgust as a disease-avoidance driven emotion that allows for developments within and across cultures.
*** This essay was submitted as an assignment for fourth-year module at the University of St. Andrews (PN4107 Evolution of Human Behaviour and Culture), where it achieved a grade of 19/20. No generative AI was used in the process of writing this essay. ***
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