Disgust Sensitivity and Political Ideology: A Brief Review

For more than a decade, research conducted across multiple disciplines has uncovered a growing body of empirical evidence that individual variation in disgust sensitivity correlates positively with aspects of political ideology (for a meta-analysis, see Terrizzi, Shook, & McDaniel, 2013). Inbar, Pizarro, and Bloom (2009), for instance, found that self-report measures of disgust sensitivity were positively associated with political conservatism in both a sample of U.S. adults recruited from swing states in the 2004 presidential election and in U.S. undergraduates, consistent with a range of studies suggesting that disgust forms a more important component of moral judgment for conservatives than for liberals (e.g., Graham et al., 2009; Haidt & Graham, 2007; see also Hatemi & McDermott, 2012). The relationship between disgust sensitivity and political orientation is not restricted to the United States: In a large Internet sample of adults born and raised outside the United States, greater disgust sensitivity predicted social conservatism, and it did so when analyzed separately in 10 distinct world regions and nations (Inbar, Pizarro, Iyer, & Haidt, 2012; see also Brenner & Inbar, 2015). Nor is this relationship restricted to self-report measures of disgust sensitivity: Smith, Oxley, Hibbing, Alford, and Hibbing (2011; see also Hibbing & Smith, 2014) found that neurophysiological responses to disgust-eliciting images were associated with self-described conservative political orientation—particularly for social issues pertaining to sexuality—even after controlling for self-reported disgust sensitivity.

Together, these findings complement prior work of evolution-minded researchers, who suggested that disgust sensitivity relates to out-group avoidance, in-group attraction, and xenophobic opposition to foreign immigrants (Faulkner, Schaller, Park, & Duncan, 2004; Navarette & Fessler, 2006), each of which underlies conservative political values (Terrizzi et al., 2013). Although not all studies support the claim that disgust sensitivity predicts political orientation (e.g., Tybur, Merriman, Hooper, McDonald, & Navarrete, 2010), a meta-analysis of 24 studies indicated that disgust sensitivity relates to ideological conservatism (specifically, social conservatism) with a moderate effect size estimated to be r = .25 after correcting for publication bias (Terrizzi et al., 2013). Thus, converging evidence attests to a robust association of disgust sensitivity with a socially conservative political orientation. Researchers have yet to determine, however, why this association exists and what it might mean.

Explaining the association: The pathogen-avoidance model

One hypothesis to explain the correlation between disgust sensitivity and a conservative political orientation suggests that disgust sensitivity reflects investment in pathogen avoidance: Social conservatism functions as a strategy for mitigating the threats posed by infectious disease (Terrizzi et al., 2013). The logic behind this pathogen-avoidance model derives from considerations of the fitness costs that pathogens and parasites impose upon their hosts (Tybur et al., 2010). This intense and enduring selection pressure has led to the evolution of elaborate innate and adaptive immune systems that are metabolically expensive to maintain, as well as to the evolution of sexual reproduction, which levies costs in the form of mate search, specialized systems for mating, and sexual recombination (Tooby, 1982; Van Valen, 1973).

But the innate and adaptive immune systems and sexual reproduction are not the only evolved defenses against the threat of pathogens. Evolutionary theorists point to a suite of psychological and behavioral responses that function to avoid or reduce pathogen threat, an adaptive nexus termed the “behavioral immune system” (Schaller, 2006, 2011). Many evolutionary-minded emotion researchers agree that disgust serves as a key component of the behavioral immune system; disgust motivates the avoidance of cues that inform the probability that pathogens are present (Haidt et al., 1994; Oaten, Stevenson, & Case, 2009; Schaller, 2006, 2011; Tybur, Lieberman, & Griskevicius, 2009; Tybur, Lieberman, Kurzban, & DeScioli, 2013). Such cues include visual and olfactory indicators of spoiled food, feces, sores or pus on the human body, and animals linked to the spread of disease such as cockroaches and rats (Tybur et al., 2009). Of particular relevance here, other individuals are also sources of infectious disease.

The pathogen-avoidance account of ideology rests atop three propositions: (1) individuals who are more easily disgusted are more heavily invested in pathogen avoidance, (2) individuals who are more heavily invested in pathogen avoidance will be more readily drawn to social and political ideologies that reinforce this investment, and (3) socially conservative ideologies most strongly endorse and reinforce investment in pathogen avoidance. In explaining why more pathogen-avoidant individuals might be drawn toward socially conservative political positions, researchers distinguish between the pathogen risks that originate outside one’s social group and the pathogen risks endemic to group living (Inbar & Pizarro, 2016; Tybur et al., 2016; Tybur, Inbar, Güler, & Molho, 2015a).

Researchers who focus on external pathogen threats argue that the disgust system is activated by superficial visible markers of ethnically and culturally unfamiliar out-groups (Faulkner et al., 2004; Navarrete & Fessler, 2006). These arguments imply that individuals more highly invested in pathogen avoidance tend toward social conservatism by way of disgust-mediated out-group avoidance. Researchers have thus referred to this path to conservatism as the out-group avoidance pathway (Inbar & Pizarro, 2016; Tybur et al., 2015a, 2016).

The question of why cues to unfamiliar out-groups elicit disgust remains a matter of debate (Aarøe, Petersen, & Arceneaux, 2017). Some researchers emphasize that variation in immunity to infectious disease is highly group-dependent and that exposure to other groups poses a pathogen threat (Faulkner et al., 2004), as the recent historical record demonstrates (Diamond, 1997). On this view, ancestral intergroup contact was associated with heightened pathogen threat, promoting a selection for psychological and behavioral mechanisms to mitigate that threat by identifying and responding adaptively via disgust-mediated aversion (Faulkner et al., 2004; Fincher & Thornhill, 2012). That is, disgust-mediated out-group avoidance might be an evolved adaptation.

Alternatively, however, cues to unfamiliar out-groups might activate the disgust system as a by-product of the disgust system’s “hypervigilance” (Aarøe et al., 2017). Because pathogens pose high risks to fitness (e.g., illness and death), the costs of the disgust system producing a false negative (inferring pathogens are not present when in fact they are) likely outweigh the costs of the system producing a false positive (inferring pathogens are present when in fact they are not; Tybur & Lieberman, 2016). The asymmetric costs of error imply that the disgust system should respond to an overly inclusive range of cues—some of which may not reliably indicate a disease threat—rather than to a smaller set of perfectly accurate markers (Tybur & Lieberman, 2016). A by-product view, then, suggests that the physical (and perhaps cultural) markers of unfamiliar out-groups are among these “overinclusive” cues taken as an input by a system erring on the side of caution (Aarøe et al., 2017; see also Petersen, 2017; van Leeuwen & Petersen, 2018).

Regardless of whether the disgust system responds to unfamiliar out-groups as an adaptive feature or as a by-product of one, a variety of studies have shown that such a link does indeed exist. For instance, in an online sample of U.S. citizens, Navarrete and Fessler (2006) found that greater perceived vulnerability to infectious disease was associated with increased ethnocentrism and that increased disgust sensitivity was associated with elevated negativity toward foreigners. Across four studies on Canadian undergraduates, Faulkner et al. (2004) found that self-reported vulnerability to infectious disease correlated negatively with various measures of xenophobia and opposition to foreigners including attitudes toward immigration in general, implicit associations of Africans with danger, opposition to the immigration of Africans to Canada, and opposition to the immigration of out-groups with foreign and unfamiliar culinary and hygienic practices. Two additional studies drawn from the same population reported that increased disease salience (as manipulated via a photo prime) was associated with more negative attitudes toward foreign (vs. familiar) out-groups (see also Hodson et al., 2013; Huang, Sedlovskaya, Ackerman, & Bargh, 2011, but see van Leeuwen & Petersen, 2018).

Studies that examine the association between degree of pathogen threat in the local ecology and attitudes toward out-group members provide corroborating evidence at the level of culture and nation-state (Fincher & Thornhill, 2008; Fincher, Thornhill, Murray, & Schaller, 2008; Thornhill, Fincher, & Aran, 2009; Thornhill, Fincher, Murray, & Schaller, 2010). In a worldwide survey of 98 culturally distinct geopolitical regions, for instance, Fincher et al. (2008) showed that the regional prevalence of pathogens correlated positively with collectivism (vs. individualism), a construct that blends a propensity toward ethnocentrism, a tendency to strongly distinguish coalitional in-group members from out-group members, and an overall favoritism displayed toward the in-group.

As mentioned above, pathogen-avoidant individuals might also be drawn toward socially conservative political positions due to threats internal to the group (Tybur et al., 2016). On this view, which researchers have termed the traditional norms pathway, cultural and societal norms function in part to mitigate infectious disease threat by reinforcing specific practices (Murray & Schaller, 2012; Schaller & Murray, 2008; Tybur et al., 2015a; Van Leeuwen, Park, Koenig, & Graham, 2012). Cultural norms may promote, for instance, practices that reduce food spoilage (e.g., Billing & Sherman, 1998) or that improve interpersonal hygiene, thereby reducing exposure to pathogens. In contrast to the out-group avoidance account, the traditional norms view is fundamentally an intragroup rather than an intergroup model: Defense of group norms guards against the emergence of behaviors that risk pathogen transmission (Tybur et al., 2016).

The traditional norms model may predict opposition to some out-group members, but in contrast to the out-group avoidance model, such opposition is not predicated upon cues to a foreign origin per se. Instead, the traditional norms pathway predicts that social conservatives oppose out-group members who refuse to adopt existing cultural norms (e.g., common pathogen transmission mitigation practices), as well as in-group members who violate traditional norms (Tybur et al., 2016). By way of contrast, social conservatives focused on out-group avoidance are predicted to express even greater hostility and avoidance toward those immigrants who assimilate, precisely because assimilation would increase intergroup contact and raise the risk of exposure to novel pathogens. Consistent with predictions of the traditional norms pathway, multiple studies (e.g., Olatunji et al., 2007; Terrizzi, Shook, & Ventis, 2010; see Terrizzi et al., 2013) report that disgust sensitivity relates to religiosity, a variable tied strongly to traditionalism but only weakly to standard measures of out-group avoidance (Duckitt, Bizumic, Krauss, & Heled, 2010; Tybur et al., 2016).

Numerous studies have documented an association of various measures of social conservatism specifically with pathogen-related disgust (i.e., disgust reported in response to those elicitors that are most closely associated with pathogen exposure), thus providing evidence consistent with the pathogen-avoidance model overall (Terrizzi et al., 2013). But researchers have recently begun to pit the two potential pathways—out-group avoidance and traditional norms—against one another. Tybur et al. (2016), for instance, argued that the two pathways yield different predictions regarding which domains of social conservatism should be most strongly associated with pathogen-related disgust. The out-group avoidance pathway, they suggest, should result in a stronger association of pathogen-related disgust with social dominance orientation (SDO), a measure of the extent to which the individual endorses differences in intergroup equality (Pratto, Sidanius, Stallworth, & Malle, 1994), than with traditionalism, as assessed by the traditionalist facet of the Authoritarianism–Conservatism–Traditionalism Scale (Duckitt et al., 2010). The traditionalist pathway, conversely, should yield a stronger association of pathogen-related disgust with traditionalism than with SDO. In a large cross-cultural sample ranging across 30 nations, Tybur et al. (2016) found greater support for the traditionalist pathway: Pathogen-related disgust sensitivity at the individual level was more strongly related to traditionalism than to SDO. Thus, pathogen disgust appears to be related to conservative ideology via intragroup, not intergroup, processes.