There is something clearly right about the analysis offered by Hibbing et al. It appears that no matter how you slice (or measure) it, liberals and conservatives differ in psychologically basic ways in their responses to threatening or aversive stimuli. Hibbing et al. present compelling evidence that these low-level psychological differences account for some of the observed variation in social, moral, and political attitudes.

One strength of this analysis is the elegance with which it unifies findings from seemingly disparate literatures under one conceptual umbrella. On this approach, the separate relationships between political attitudes and individual differences in attention to risk and threat, sensitivity to disgust, and valuing of order and consistency can all be described as reflecting a deeper underlying relationship between responsiveness to negative stimuli and political ideology.

However, this level of abstraction, while providing a useful framework for disseminating the work of psychologists to political scientists and others, also leaves many questions to be answered – as the authors themselves acknowledge.

One important question is the nature and scope of disgust's influence on political attitudes and ideology. Hibbing et al. ask: “Is sensitivity to disgust pertinent only to attitudes regarding homosexuality, to attitudes on all sexually related issues (e.g., support for abstinence-only sex education, opposition to pornography, and opposition to abortion rights), or to conservatism more generally? Empirical evidence can be found for all of these conclusions” (sect. 6.2, para. 5).

In our work, we have focused on the relationship between disgust and moral and political attitudes. As we have recently argued elsewhere (Inbar & Pizarro Reference Inbar, Pizarro, Wright and Sarkissian2014), we believe that disgust's connection to specific social/political issues – as well as to broader ideological commitments – can be parsimoniously explained by its role as part of the behavioral immune system, an evolved motivational system that responds to physical contamination threats (Schaller & Park Reference Schaller and Park2011). Our primary claim is that disgust evolved in part to keep individuals safe from disease by motivating them to avoid disease-bearing foods, substances, individuals, and groups. As such, in addition to causing rejection and avoidance of basic contamination threats (such as rotten meat, blood, and feces; Rozin et al. Reference Rozin, Haidt, McCauley, Lewis, Haviland-Jones and Barrett2008) disgust also motivates a range of social judgments. These include negative evaluations of acts that are associated with a threat of contamination (e.g, moral norm violations pertaining to food and sex; Haidt et al. Reference Haidt, Koller and Dias1993); negative attitudes towards unfamiliar groups who might pose the threat of contamination through physical contact (e.g, outgroups characterized by these moral norm violations, or who are unfamiliar; Inbar et al. Reference Inbar, Pizarro, Knobe and Bloom2009b; Navarrete et al. Reference Navarrete, Fessler and Eng2007); and greater endorsement of certain social and political attitudes that minimize contamination risk (such as increased sexual conservatism, reduced contact between different social groups, and hostility towards foreigners; Inbar et al. Reference Inbar, Pizarro and Bloom2009a; Terrizzi et al. Reference Terrizzi, Shook and McDaniel2013). We see this argument as consistent with, and complementary to, the argument advanced by Hibbing et al., but it explains why the same emotion should be related to many superficially different attitudes (because they all involve disease and contamination threats), and why disgust is related to politics both at the specific-issue and broad-ideology levels (because more conservative attitudes at both levels minimize these threats).

The disease avoidance approach to understanding disgust also sheds light on another question posed by Hibbing et al. – that of the relationship between oxytocin and political ideology. They point to two theoretically plausible but conflicting possibilities. On the one hand, oxytocin might give rise to a “liberalizing” effect in due to its association with trust and “warmth;” on the other, oxytocin's promotion of in-group favoritism (de Dreu et al. Reference De Dreu, Greer, Van Kleef, Salvi and Handgraaf2011) might mean that it would instead boost politically conservative attitudes. We can offer a preliminary suggestion based on work in the animal literature. Kavaliers et al. (Reference Kavaliers, Choleris, Ågmo and Pfaff2004) demonstrated a critical role for oxytocin in motivating parasite avoidance in mice. Mice respond to olfactory cues indicating parasitic infection by avoiding the infected individual, protecting the non-infected mouse from potential contagion. The authors found that mice missing a gene critical for the production of oxytocin lose this ability to identify infected conspecifics. Given this link between oxytocin and disease avoidance, and given the relationship between disease avoidance, disgust, and political conservatism in humans, we believe that oxytocin administration will move individuals toward the more conservative end of the political spectrum – consistent with its promotion of in-group favoritism.

One final important question is how the findings reviewed by Hibbing et al. can be reconciled with the fact that higher neuroticism (lower emotional stability) is typically correlated with liberalism, not conservatism (e.g., Gerber et al. Reference Gerber, Huber, Doherty, Dowling and Ha2010). Similarly, in data collected by our collaborator, Ravi Iyer at www.yourmorals.org, liberals score higher than conservatives on a self-report measure of Behavioral Inhibition System strength, which taps sensitivity to negative outcomes (the BIS/BAS scale; Carver & White Reference Carver and White1994). This is, on the face of it, inconsistent with the view of conservatives as anxious, fearful, and threatened. One possibility is that conservatives are more likely to respond to threats with externalizing emotions, such as anger or disgust, whereas liberals are more likely to respond with internalizing emotions, such as anxiety and distress (Tomkins Reference Tomkins and White1963; Reference Tomkins, Tomkins and Izard1965; Reference Tomkins and Demos1995). Again, more research is needed to shed light on the complex relationship between these variables.

The idea that basic individual differences in responses to threatening or aversive stimuli can account for high-level differences in social, moral, and political opinions is, we believe, an important insight. What remains is to work out the details.