2. Politics and the subconscious

Extraneous or even subthreshold factors affect a wide range of day-to-day decisions and opinions and moral, religious, and political decisions, and beliefs are not immune to such forces. People sitting in a messy, malodorous room tend to make harsher moral judgments than those who are in a neutral room (Schnall et al. Reference Schnall, Haidt, Clore and Jordan2008), and disgusting ambient odors decrease approval of gays (Inbar et al. Reference Inbar, Pizarro, Knobe and Bloom2009b; see also Inbar et al. Reference Inbar, Pizarro and Bloom2009a; Reference Inbar, Pizarro and Bloom2012a). Sitting on a hard, uncomfortable chair leads to less flexible attitudes than those offered when sitting on something soft and comfortable (Ackerman et al. Reference Ackerman, Nocera and Bargh2010). People reminded of physical cleansing – for example, by the presence of hand sanitizer – render sterner judgments than those who are not given such a reminder (Helzer & Pizarro Reference Helzer and Pizarro2011). Moral judgments can change as a result of hypnotic suggestion (Wheatley & Haidt Reference Wheatley and Haidt2005), and prompting analytical thinking lowers religiosity (Gervais & Norenzayan Reference Gervais and Norenzayan2012). Focusing exclusively on political variables, when churches are employed as polling places people's tendency to cast votes for right-of-center candidates and ballot propositions increases compared with when public schools serve as polling places (Berger et al. Reference Berger, Meredith and Wheeler2008; Rutchick Reference Rutchick2010). Mortality prompts – images of tombstones, hospitals, and the elderly – foster the adoption of conservative political positions (Jost et al. Reference Jost, Fitzsimons, Kay, Greenberg, Koole and Pyszczynski2004; Landau et al. Reference Landau, Solomon and Greenberg2004; although see Castano et al. Reference Castano, Leidner, Bonacossa, Nikkah, Perrull, Spencer and Humphrey2011). Italians who implicitly associated symbols of the United States with negative concepts were more likely to vote against the proposed expansion of a U.S. military base even though they believed themselves undecided on this issue (Galdi et al. Reference Galdi, Arcuri and Gawronski2008).

In a series of studies following the lead of Zajonc (Reference Zajonc1980), political scientist Milt Lodge and his colleagues demonstrated the importance of hot cognition or automaticity in political judgments (Lodge & Hamill Reference Lodge and Hamill1986; Lodge & Taber Reference Lodge and Taber2005). Political stimuli often produce extremely quick emotional reactions that affect more deliberate cognitive processes such as memory recall, attention, and information processing. In one study, images of a happy face flashed for too short a time to register in conscious awareness resulted in participants offering fewer reasons to oppose immigration (Lodge & Taber Reference Lodge and Taber2013), indicating that quick, preconscious responses color political judgments. These concepts receive extensive development in the work of psychologist John T. Jost and colleagues. Jost refers to preconscious biases as motivated social cognition and repeatedly demonstrates that people do not come into political situations unconstrained (Carney et al. Reference Charney2008; Jost Reference Jost2006; Jost & Amodio Reference Jost and Amodio2012; Jost et al. Reference Jost, Glaser, Kruglanski and Sulloway2003). These constraints typically operate outside of conscious awareness though people often insist that their political decisions are solely the result of conscious considerations. Even neuroscientists sometimes express surprise that political orientations are influenced by subthreshold factors (Wade Reference Wade2011).

The relevance of subthreshold factors allows for the possibility that political temperament is systematically related to a range of psychological and physiological response patterns. In the following sections we summarize research showing this possibility is in fact a reality. First, we examine liberal-conservative psychological differences as reflected in (survey) self-reports. Second, we review psychological differences that are not fully accessible to the participants themselves. Third, we describe evidence of physiological differences between liberals and conservatives. Finally, we synthesize the research by arguing that many of the correlations described are tied together by the common thread of differences in response patterns to negative stimuli.

3. Politics and self-reported psychological differences

Mass-scale political preferences systematically correlate with an astonishing variety of psychological characteristics. Perhaps the best known is authoritarianism. The Authoritarian Personality, by Adorno et al. (Reference Adorno, Frenkel-Brunswik, Levinson and Sanford1950), claimed that characteristics such as conventionalism, submission to authority and anti-intellectualism clustered into a distinct, measurable personality trait, and developed the F-scale to measure that trait. Variation on this scale correlated with a wide range of political attitudes, including self-placement on a liberal-conservative dimension. Similarly, McCloskey (Reference McCloskey1958) concluded that traits such as confidence, social behavior, mood, cognitive complexity, social behavior, and preferred leadership styles also distinguished liberals and conservatives.

Since then, some research explicitly rolls politics into personality, whereas other research treats politics as conceptually distinct from personality. A prominent example of the former is Altemeyer's development of a scale to measure Right-Wing Authoritarianism or RWA (Altemeyer Reference Altemeyer1981; Reference Altemeyer1996). To illustrate, one RWA item asks whether respondents agree that “God's laws about abortion, pornography, and marriage must be strictly followed before it is too late, and those who break them must be strongly punished.” Altemeyer's blending of life and political tendencies to capture a personality trait of broad social relevance is part of a pattern in post-Adorno research. Wilson and Patterson (Reference Wilson and Patterson1968) measure conservatism by combining explicitly political stands on issues such as school prayer and the death penalty with preferences on broader lifestyle issues such as modern art and pajama parties (see also Wilson Reference Wilson1973). Bouchard urges combining religion, politics, and authoritarianism into a single concept (Reference Bouchard, Voland and Schiefenhövel2009). Tomkins (Reference Tomkins and White1963) and Tetlock and Mitchell (Reference Tetlock, Mitchell, Mellers and Baron1993) also conflate personality and politics. Others, however, go out of their way to tap authoritarian tendencies without explicitly invoking politics – for example, by measuring nonpolitical authoritarianism with survey items on child rearing (Feldman & Stenner Reference Feldman and Stenner1997; Hetherington & Weiler Reference Hetherington and Weiler2009; Stenner Reference Stenner2005). Those who favor more authoritarian parenting styles are significantly more likely to be political conservatives. Another longstanding concept merging politics and personality is Social Dominance Orientation (SDO) (Pratto et al. Reference Pratto, Sidanius, Stallworth and Malle1994; Sidanius & Pratto Reference Sidanius and Pratto2001) which is based on the observation that people vary in their comfort levels with group-based discrimination and dominance, with some embracing the vision of a hierarchy of groups.

Much recent research takes advantage of personality psychology's growing acceptance of a standard package of five core personality traits, known as the Big Five: conscientiousness, agreeableness, openness to new experiences, extraversion, and emotional stability (Gosling et al. Reference Gosling, Rentfrow and Swann2003; McCrae Reference McCrae1996; Mondak et al. Reference Mondak, Hibbing, Canache, Seligson and Anderson2010). Though Big Five personality batteries are not overtly political, two traits consistently discriminate political orientation across a broad range of studies: Conservatives tend to score higher on conscientiousness and liberals tend to score higher on openness to new experiences (see Caprara et al. Reference Caprara, Barbaranelli and Zimbardo1999; Gerber et al. Reference Gerber, Huber, Doherty, Dowling and Ha2010; Mondak & Halperin Reference Mondak and Halperin2008; Rentfrow et al. Reference Rentfrow, Jost, Gosling, Potter, Jost, Kay and Thorisdottir2009). Other Big Five traits do not correlate as consistently with political orientations but extraversion and emotional stability have been associated with economic (though not social) conservatism (Gerber et al. Reference Gerber, Huber, Doherty, Dowling and Ha2010; Young Reference Young2009) and elements of agreeableness have also been linked to ideology, with conservatives being more polite and liberals more empathetic (Hirsh et al. Reference Hirsh, DeYoung, Xu and Peterson2010). These personality differences encourage researchers to explore the possibility that liberals and conservatives construct and occupy different individual and social environments. For example, consistent with their tendency to report being more conscientious, conservatives' “life spaces” tend to have more cleaning supplies and organizing elements, including calendars, postage stamps, and laundry baskets, and, consistent with their penchant for new experiences, liberals tend to have more art supplies, travel materials, and greater varieties of books and music (Carney et al. Reference Charney2008).

Personality traits are far from the only psychological characteristics that discriminate political orientations. Shalom Schwartz's research focuses on the values that guide an individual's personal life, such as conformity, tradition, security, power, achievement, hedonism, stimulation, self-direction, universalism, and benevolence (Schwartz Reference Schwartz and Zanna1992; for a good overview, see Feldman Reference Feldman, Sears, Huddy and Jervis2003). Relationships among these values are stable across cultures (Piurko et al. Reference Piurko, Schwartz and Davidov2011; Schwartz Reference Schwartz2006) and are consistently related to individual-level variation in political preferences. Conservatives tend to value security and conformity and liberals tend to value self-expression and stimulation – and those values even turn out to be powerful predictors of voting behavior (Schwartz et al. Reference Schwartz, Caprara and Vecchione2010).

Jonathan Haidt and colleagues demonstrate convincingly that liberals and conservatives tend to employ different considerations when making moral judgments. Liberals rely primarily on concerns for equality and harm avoidance, whereas conservatives are more likely to take into account considerations such as purity, authority, and in-group/out-group status (Graham et al. Reference Graham, Haidt and Nosek2009; Haidt & Graham Reference Haidt and Graham2007; Haidt & Joseph Reference Haidt and Joseph2004). As was the case with personality traits and core values, these connections of moral foundations to politics apply in numerous countries (Graham et al. Reference Graham, Haidt and Nosek2009; for additional work on the political relevance of selected moral foundations, see Petersen Reference Petersen2009). The connection between purity concerns and conservatism is consistent with the previously mentioned finding that conservatives tend to have more cleaning supplies in their living spaces (Carney et al. Reference Charney2008). It is also consistent with the finding (replicated cross-nationally) that people with stronger self-reported disgust are more conservative (Inbar et al. Reference Inbar, Pizarro and Bloom2009a; Reference Inbar, Pizarro, Iyer and Haidt2012b; but see Tybur et al. Reference Tybur, Merriman, Caldwell, McDonald and Navarrete2010).

Jost et al.'s (Reference Jost, Glaser, Kruglanski and Sulloway2003) extensive meta-analysis examining the core differences between the left and the right concludes that comfort with change and attitudes toward equality are the two central variables distinguishing liberals and conservatives. The relevance of these traits argues strongly against assertions that ideology has little meaning for most people and is decreasingly relevant to modern life (Bell Reference Bell1960; Converse Reference Converse and Apter1964; Fukuyama Reference Fukuyama1992). Jost (Reference Jost2006) suggests ideology is no more likely to end than personality traits given that ideology is the political reflection of aspects of broader psychology.

Liberal-conservative differences even extend to tastes and preferences. Compared to liberals, conservatives are more likely to prefer simplicity and realism as opposed to complexity and abstractions in art (Wilson et al. Reference Wilson, Ausman and Matthews1973) and puns as opposed to unexpected incongruity in humor (Wilson Reference Wilson1990). A recently collected sample of our own shows statistically significant relationships between political conservatism and preferences for familiar as opposed to unfamiliar foods and music, for poetry that rhymes, and for novels that come to closure (Neiman Reference Neiman2012).

This last finding is consistent with a substantial body of research investigating the relationship between political beliefs and the “need for cognitive closure.” In 1993, Kruglanski et al. introduced a battery now widely used to tap preferences for closure. It includes items such as “I do not like situations that are uncertain,” “I like to have friends who are unpredictable,” and “even after I've made up my mind about something, I am always eager to consider a different opinion.” Cross-nationally this battery consistently suggests individuals who desire cognitive closure tend to self-identify as conservative (Chirumbolo et al. Reference Chirumbolo, Areni and Sensales2004; Federico et al. Reference Federico, Golec and Dial2005; Golec Reference Golec2002; Golec et al. Reference Golec, Cislak and Wesolowska2010; Kossowska & van Hiel Reference Kossowska and Van Hiel2003; Rock & Janoff-Bulman Reference Rock and Janoff-Bulman2010; van Hiel et al. Reference van Hiel, Pandelaere and Duriez2004), identify with conservative political parties (Kemmelmeier Reference Kemmelmeier1997), and adopt conservative positions on specific topics such as the death penalty and general punitiveness (Jost et al. Reference Jost, Kruglanski, Simon, Thompson, Messick and Levine1999), immigration (Chirumbolo et al. Reference Chirumbolo, Areni and Sensales2004), and a variety of other social and economic topics (Golec Reference Golec2002). A meta-analysis (Jost et al. Reference Jost, Glaser, Kruglanski and Sulloway2003) reports relationships between political conservatism and desire for cognitive closure (or related concepts such as intolerance of ambiguity and preference for order) in 20 different samples in an array of countries. As both are consistent with a desire for clear and definite answers, it is not surprising that religious fundamentalism also is related to preferences for closure (Lienesch Reference Lienesch1982).

Historical and cultural context plays an important role in these relationships. In some postcommunist countries individuals with a strong preference for closure are more likely to support socialist economic arrangements (Golec Reference Golec2002; see also Kossowska & van Hiel Reference Kossowska and Van Hiel2003). Thorisdottir et al. (Reference Thorisdottir, Jost, Liviatan and Shrout2007) find that psychological preferences for traditionalism and rule-following lead to right-of-center preferences in both Eastern and Western Europe. On the other hand, preferences for security lead to right-of-center orientations in the West but left-of center orientations in the East (they also find that the effects of openness on politics are particular to region). Presumably the security and familiarity associated with a particular regime style (whatever the ideology) that long shaped people's lives appeals to certain personality traits. Thus, psychological tendencies may be generally related to political beliefs but the particular features and history of a polity undoubtedly modify these relationships from country to country and era to era.

In addition to a desire for cognitive closure, variations in preference for cognitively involved activity (a different concept than cognitive ability) also seem to relate to political preferences. Cacioppo et al. (Reference Cacioppo, Petty, Feinstein and Jarvis1996) developed an instrument suitable for assessing attitudes toward cognition and Sargent (Reference Sargent2004) reports that, in two separate samples, those more comfortable with cognitive effort and attributional complexity are less supportive of punitive responses to lawbreaking.

4. Politics and implicit psychological differences

The studies summarized above show liberal-conservative differences in psychological traits and tendencies but they rely almost exclusively on self-reports. It turns out that differences correlating with political orientations also extend to measures tapping implicit, subthreshold tendencies. Such measures are designed to index variation in the manner in which individuals see, pay attention to, and process stimuli (Wahlke Reference Wahlke1979; for a good summary, see Nosek et al. Reference Nosek, Graham, Hawkins, Gawronski and Payne2010). As such, they tap concepts that are much broader than politics.

A variety of measures of directed attention are available. Common protocols such as the “Emotional Stroop,” “Dot-Probe,” and “Flanker” tasks find that threatening stimuli are consistently more distracting for conservatives (Carraro et al. Reference Carraro, Castelli and Macchiella2011, McLean et al., in press). Negative stimuli such as angry faces appear to grab the attention of conservatives more than they do liberals. Eyetracking is an even more direct way to measure attention. Dodd et al. (Reference Dodd, Balzer, Jacobs, Gruszczynski, Smith and Hibbing2012) asked participants to “free view” collages of images (selected from the widely used IAPS collection) that had been pre-rated as positive (sunsets, happy children, cute animals) or negative (vomit, houses on fire, dangerous animals). They found conservatives spent significantly more time looking at negative images and were significantly quicker to “fixate” on those images, as well. In sum, across research methods, samples and countries, conservatives have been found to be quicker to focus on the negative, to spend longer looking at the negative, and to be more distracted by the negative.

Some evidence suggests conservatives have a lower bar for deeming stimuli and situations negative. When “emotionally ambiguous” faces are shown to research participants, individuals on the political right are more likely to report that the face is expressing a threatening or dominant emotion, such as anger. Those on the political left are more likely to “see” a subordinate emotion such as surprise (Vigil Reference Vigil2010). In a study of our own, a sample of 340 U.S. adults were shown a series of pre-rated IAPS images and asked to report their evaluations from favorable to unfavorable. Consistent with expectations, conservatives perceived the negative images more negatively than did liberals (p < 0.01).

Research also reports liberal-conservative differences in word usage, implicit association tests (IATs), object categorization, and exploratory behavior. Linguist George Lakoff observes that people on the left use the language of the nurturing parent and those on the right the language of the strict parent (Lakoff Reference Lakoff2002; see also, Graham et al. Reference Graham, Haidt and Nosek2009). Compared with liberals, conservatives tend to have stronger implicit attachments to tradition, stability, long-held values, conformity, and order (Jost et al. Reference Jost, Nosek and Gosling2008). Young (Reference Young2009) finds conservatives are more likely to be “hard categorizers” and liberals “soft categorizers,” suggesting that conservatives have a lower tolerance for ambiguity and are more likely to view the world in strongly defined categories (see also Rock & Janoff-Bulman Reference Rock and Janoff-Bulman2010).

Conservative-liberal differences also appear in the way individuals extract and process information from their environments. “BeanFest” is a computer game where participants must choose to accept or reject a series of differently shaped and marked beans. If the bean is accepted, the value of beans with that same shape and marking is revealed (it could be +10 or −10) and participants are rewarded for accumulating points. Strategies of play vary widely across people: Some “accept” many beans, risking points in order to acquire information, whereas others play it safe, accepting only those beans they know to have a positive value. One of the key correlates of variations in these strategies is political orientation. Liberals are significantly more exploratory than conservatives in that they choose far more unknown bean types even though doing so runs the risk of losing points (Shook & Fazio Reference Shook and Fazio2009). Differences also show up in the learning capacities of people with different political orientations. Conservatives are better than liberals at remembering which beans are “bad,” but they are also more likely to misremember the positive beans as “bad.” In short, conservatives are more likely than liberals to follow strategies that lead them to know less about positive aspects of their environment, possibly leading them to conclude that “the world is a relatively harsh place” (Shook & Fazio Reference Shook and Fazio2009).

5. Politics and physiological differences

Liberal-conservative differences in psychology appear in a variety of tasks, samples, and countries – but do these differences extend to the realm of physiology? Research on the relationship between politics and physiology is just starting to take root and often involves neuroimaging. Much of this research focuses on identifying the parts of the brain that are differentially activated by political stimuli regardless of the participant's liberal-conservative orientation (Cacioppo & Visser Reference Cacioppo and Visser2003; Knutson et al. Reference Knutson, Wood, Spampinato and Grafman2006; Lieberman et al. Reference Lieberman, Schreiber and Ochsner2003; Westen et al. Reference Westen, Blagov, Harenski, Kilts and Hamann2006). Still, some recent research reports liberal-conservative neural differences.

Amodio et al. (Reference Amodio, Jost, Master and Yee2007) analyze conflict-related anterior cingulate cortex (ACC) activity by recording two event related potentials (ERP) for 43 participants. They employ a Go/No-Go task where participants habituate to provide a “Go” response but then have to withhold that response (a situation known to be associated with enhanced ACC activity). Self-identified conservatives in this study made more mistakes in giving the habituated response, suggesting they are inclined toward greater persistence than liberals. Moreover, Amodio et al. find that conservative participants have significantly less conflict-related neural activity than liberals when response inhibition is necessary. This is consistent with research showing that conservatives are more likely to be conscientious and to favor cognitive closure and hard categorization. As Amodio et al. put it, “political orientation, in part, reflects individual differences in the functioning of a general mechanism related to cognitive control and self-regulation” (p. 1247; for parallel findings on individuals with strong religious convictions, see Inzlicht et al. Reference Inzlicht, McGregor, Hirsh and Nash2009). Schreiber et al. (Reference Schreiber, Fonzo, Simmons, Dawes, Flagan, Fowler and Paulus2013) report that during a risk-taking task, functional magnetic resonance imaging (fMRI) on 54 participants reveals those who tend to vote Republican show greater amygdala activation, whereas individuals who tend to vote Democratic show greater insula activation.

Kanai et al. (Reference Kanai, Feilden, Firth and Rees2011) provide evidence that there are liberal-conservative differences in neural structure. Using magnetic resonance imaging (MRI), they scanned the brains of 90 college students in London (and 28 more in a replication sample) and found that self-identified liberals tend to have more gray matter in the ACC, whereas self-identified conservatives tend to have increased volume in the right amygdala. Though the amygdala has been connected to intense positive, as well as negative affect processing, these results are consistent with the aforementioned self-regulating, conflict-monitoring differences between liberals and conservatives and with differences in response to threats and facial emotions (responses that have been traced to the amygdala). These similarities lead Kanai et al. to note that their results “converge with previous work to suggest a possible link between brain structure and psychological mechanisms that mediate political attitudes” (p. 677).

Physiological differences between liberals and conservatives are not limited to brain imaging. Electrodermal activity (EDA) is one of the most widely employed measures of sympathetic nervous system activation (Dawson et al. Reference Dawson, Schell, Filion, Cacioppo, Tassinary and Berntson2007) and several studies report that negatively valenced visual stimuli increase electrodermal activity in conservatives more than in liberals (Dodd et al. Reference Dodd, Balzer, Jacobs, Gruszczynski, Smith and Hibbing2012; Oxley et al. Reference Oxley, Smith, Alford, Hibbing, Miller, Scalora, Hatemi and Hibbing2008; Smith et al. Reference Smith, Oxley, Hibbing, Alford and Hibbing2011). In some of these studies EDA response to specific image categories such as disgust correlates with specific conservative issue positions such as those related to gay marriage (Smith et al. Reference Smith, Oxley, Hibbing, Alford and Hibbing2011), whereas in other studies EDA response to a wide range of aversive images correlates with broad conservatism (Dodd et al. Reference Dodd, Balzer, Jacobs, Gruszczynski, Smith and Hibbing2012). Similar research shows that physiological response to outgroup (especially ethnic) stimuli predicts attitudes and behaviors often associated with left-right conflicts on issues like affirmative action (Dambrum et al. Reference Dambrum, Despres and Guimond2003; Vanman et al. Reference Vanman, Saltz, Nathan and Warren2004). Facial electromyography (EMG) is another technique for measuring physiological response and individuals scoring high on right wing authoritarianism tend to have greater muscle activity in the corrugator region (furrowing of the brow) when viewing negative social situations (Fodor et al. Reference Fodor, Wick, Hartsen and Preve2008). Conservatives also tend to display greater blink amplitude (movement of the orbicularis occuli muscle) in response to sudden, unpleasant, and unexpected auditory prompts (Oxley et al. Reference Oxley, Smith, Alford, Hibbing, Miller, Scalora, Hatemi and Hibbing2008).

Endocrine levels are another aspect of physiology that may relate to political orientations. Although no study to date has tested and reported a connection to location on the liberal-conservative spectrum, existing research provides an indication of the possibilities. Madsen (Reference Madsen1985) finds that whole blood serotonin levels correlate with leadership and assertiveness in group situations. Testosterone levels have been shown to decrease (Stanton et al. Reference Stanton, Beehner, Saini, Kuhn and Labar2009) and cortisol levels to increase (Stanton et al. Reference Stanton, LaBar, Saini, Kuhn and Beehner2010) when favored candidates lose an election (see also Apicella & Cesarini Reference Apicella, Cesarini, Hatemi and McDermott2011; Waismel-Manor et al. Reference Waismel-Manor, Ifergaine and Cohen2011). Testosterone levels have been associated with aggressive (simulated) decision making (McDermott et al. Reference McDermott, Johnson, Cowden and Rosen2007) and oxytocin appears to increase trust toward in-group members (Kosfeld et al. Reference Kosfeld, Heinrichs, Zak, Fischbacher and Fehr2005) but may also heighten feelings of ethnocentrism (de Dreu et al. Reference De Dreu, Greer, Van Kleef, Salvi and Handgraaf2011).

6. Negativity bias and politics

As is apparent, the list of empirically demonstrated psychological and physiological differences between liberals and conservatives is long and diverse. Additional studies are needed, however, because much of the extant physiological work is based on small, geographically constrained samples and much of the psychological work relies on college undergraduates who may have yet to form stable political attitudes. Perhaps an even greater need is for theoretical integration of this burgeoning empirical literature and that is what we hope to provide in this section, though we recognize that any effort to provide a theoretical undergirding for the findings summarized will be unavoidably speculative.

Liberals and conservatives vary in their tolerance of social equality and change, their moral foundations, their values, and even their perceptions of the nature and perfectibility of the human condition (Graham et al. Reference Graham, Haidt and Nosek2009; Jost et al. Reference Jost, Glaser, Kruglanski and Sulloway2003; Pinker Reference Pinker2002, Ch. 16; Schwartz et al. Reference Schwartz, Caprara and Vecchione2010; see also Sowell Reference Sowell1987; Tomkins Reference Tomkins and White1963). As valuable as these efforts are, questions immediately arise regarding the precursors of these differences. Why do some people say they value security and some self-expression? Why do some more than others rest their moral judgments on purity and authority? Why do some have a tragic and some a utopian vision of humankind? Why do some embrace change and others avoid it? To answer these questions, it may be useful to incorporate deeper physiological and psychological differences. After all, people's answers to the survey items used to assess moral foundations, personal values, and personality traits must come from somewhere and given the important role of subthreshold forces in political orientations, variations in physiology and deep psychology are likely to play an important role.

We believe a key factor in accounting for people's political predispositions is their orientation to negatively valenced events and stimuli. Negativity bias is the principle that “negative events are more salient, potent, dominant in combinations, and generally efficacious than positive events” (Rozin & Royzman Reference Rozin and Royzman2001, p. 297; see also Baumeister et al. Reference Baumeister, Bratslavsky, Finkenauer and Vohs2001). Essentially, this principle reflects the fact that humans generally tend to respond more strongly, to be more attentive, and to give more weight to negative elements of their environment. This tendency shows up in a wide variety of socially-relevant characteristics – everything from loss aversion (Kahneman & Tversky Reference Kahneman and Tversky1984) to quick recognition of angry versus happy faces in a crowd (Hansen & Hansen Reference Hansen and Hansen1988). People generally tend to be more attuned to negative faces, words, and social information, and both the autonomic and central nervous systems tend to have measurably higher levels of activation in response to negative than positive stimuli (Rozin & Royzman Reference Rozin and Royzman2001). Good evolutionary reasons exist for negativity bias given that negative events can be much more costly in fitness terms than positive events are beneficial; to state the obvious, infection, injury, and death curtail reproductive opportunities.

For our purposes the most notable feature of negativity bias is not that it exists but that it varies so much from individual to individual (Norris et al. 2010). That some people are more attuned to potential threats, more sensitive to sources of contagion, and more desirous of in-group protections is known intuitively and amply demonstrated by a large research literature. These individual differences seem to be stable over time and generalize to a broad category of stimuli (sounds, words, and images; see Norris et al. 2010). Previous research suggests that this individual-level variation also correlates with orientations to the social world, such as risk tolerance (Baumeister et al. Reference Baumeister, Bratslavsky, Finkenauer and Vohs2001). The connection we point out now is that the empirically demonstrated individual variation in negativity bias manifests itself not just in broad social orientations, but also in political preferences.

Negative situations are likely to relate to threats, whether microbial, predatory, or emotional, and people have widely varying orientations to threats. As we have seen, those individuals with politically conservative orientations display elevated physiological response to negative stimuli, devote more attention to negative stimuli, possess distinct self-reported psychological patterns when asked to imagine negative stimuli (i.e., give evidence of high disgust and high threat sensitivity), and perhaps harbor recognizable structural features consistent with elevated responsiveness to negative situations (distinctive substructures of the amygdala and perhaps even genetic differences such as a “short” allele of the dopamine receptor gene DRD4). Consistent with this line of thinking, Schaller and Neuberg observe that “some people seem to go through life more cognizant of threats” (quoted in Culotta Reference Culotta2012; see also Schaller & Neuberg Reference Schaller, Neuberg, Crawford and Krebs2008) before going on to suggest that these variations in general threat awareness likely correlate with political orientations.

Documented differences in response patterns extend beyond overtly threatening situations and into those that are more broadly negative. Environmental stimuli that are unexpected, ambiguous, uncertain, or disorderly also appear to generate more response and attention from conservatives than liberals at a variety of levels, including brain activation patterns, sympathetic nervous system response, cognitive behaviors, and self-reports. In many respects, compared with liberals, conservatives tend to be more psychologically and physiologically sensitive to environmental stimuli generally but in particular to stimuli that are negatively valenced, whether threatening or merely unexpected and unstructured. The consistency of these patterns across diverse research designs with diverse samples in different countries is difficult to miss. In fact, we know of no published study pointing in the opposite direction (i.e., that liberals respond more to negative stimuli or are more bothered by ambiguous or unexpected stimuli).

What could explain this connection? It is not surprising that those attuned to the negative in life might take steps to avoid it, perhaps by refraining from taking chances with the unknown, by following instructions, and by sticking to the tried and true. As an illustration, an adult subject in one of psychologist Jerome Kagan's longitudinal studies who was classified as “highly reactive” to novel, unfamiliar stimuli as a result of behavioral patterns detected when she was just four months old, summed up her approach to life by saying “I don't stray from the rules too much” (quoted in Henig Reference Henig2009). This is exactly the pattern we see in the personality data: Conservatives are less open to new experiences and are more conscientious. As a result, conservatives are less likely both to solicit new, potentially harmful information and to retain positive information concerning an object or perhaps a person or group (Castelli & Carraro Reference Castelli and Carraro2011; Shook & Fazio Reference Shook and Fazio2009). Consequently, not only do political positions favoring defense spending, roadblocks to immigration, and harsh treatment of criminals seem naturally to mesh with heightened response to threatening stimuli but those fostering conforming unity (school children reciting the pledge of allegiance), traditional lifestyles (opposition to gay marriage), enforced personal responsibility (opposition to welfare programs and government provided healthcare), longstanding sources of authority (Biblical inerrancy; literal, unchanging interpretations of the Constitution), and clarity and closure (abstinence-only sex education; signed pledges to never raise taxes; aversion to compromise) do, as well. Heightened response to the general category of negative stimuli fits comfortably with a great many of the typical tenets of political conservatism.

People who are highly responsive to negative sensory input may adopt a prevention focus by diminishing the possibility of negative events occurring or at least by mitigating the consequences of those events. The likelihood of negative encounters can be minimized through personal choices (e.g., not venturing into dangerous neighborhoods after dark) but, in modern democratic societies, also indirectly by political choices (e.g., advocating policies that are tough on criminals). Thus, it is reasonable to hypothesize that individuals who are physiologically and psychologically responsive to negative stimuli will tend to endorse public policies that minimize tangible threats by giving prominence to past, traditional solutions, by limiting human discretion (or endorsing institutions, such as the free market, that do not require generosity, discretion, and altruism), by being protective, by promoting in-groups relative to out-groups, and by embracing strong, unifying policies and authority figures (for an excellent discussion, focusing on promotion/prevention differences, see Janoff-Bulman Reference Janoff-Bulman2009). Such policies generally are associated with conservatism or the political right. On the other hand, individuals who appear to devote fewer psychological and physiological resources to negative encounters may not be as committed to avoiding them and thus may be more willing to condone new lifestyles, reductions in defense and police spending, assistance to out-groups, rehabilitation of criminals, and challenges to traditional authority, positions typically associated with the left (or with liberals as the phrase is used in the U.S.).

In sum, we posit that, due in all likelihood to a combination of genetic, early developmental, and later environmental factors, people's physiological and deep psychological responses to negative life situations vary widely. These variations, in turn, encourage but certainly do not mandate particular social tendencies and, more to the point of this article, particular political beliefs. Both degree of negativity bias and political dispositions obviously can change over the course of a lifetime but both change rather grudgingly and stability is more common than wild fluctuation. Although the theory that variations in negativity bias shape political beliefs has much to recommend it, many valid objections can be raised and we now address several of them.

7. Conclusion: Politics and controversy

The extent to which politics evokes controversy is puzzling. Jost and Amodio ask the pertinent question: “How is it that individuals and groups can be so strongly inspired by an abstract configuration of ideas that they are willing to sacrifice even their own lives?” (Reference Jost and Amodio2012). Along with religion (another abstract configuration of ideas capable of affecting the lives of others), politics is the topic most able to produce conflict at family reunions and on the battlefield. People do not typically come to blows over whether it is better to be an introvert or an extravert, presumably because introverts do not have to worry that they will need to change their behavior as a result of the existence of extraverts. Politics, however, is unavoidably intrusive. The mere presence of liberals [conservatives] creates a very real possibility that conservatives [liberals] in the same polity will not be able to structure society in the fashion they most desire. This potential imposition of values is likely one reason politics is so emotional and explosive (Brader Reference Brader2006; Marcus et al. Reference Marcus, Newman and Mackuen2000; Redlawsk Reference Redlawsk2006; Sullivan & Masters Reference Sullivan and Masters1988; Valentino et al. Reference Valentino, Hutchings, Banks and Davis2008).

The controversial nature of politics makes research on the differences between liberals and conservatives particularly sensitive. People are quick to be defensive and to suspect that their particular ideological beliefs are being defamed. As a result, it is appropriate to note in closing that citing differences in the psychological and physiological traits of liberals and conservatives is not equivalent to declaring one ideology superior to the other. Mounting empirical evidence suggests that, compared to liberals, conservatives are more responsive and attuned to negative stimuli, patterns consistent with their tendency to advocate political solutions designed to protect against threats and disorder – real or perceived. Liberals appear not to notice, respond to, or attend to negative stimuli to the same degree, a pattern consistent with their willingness to advocate political solutions that could lead society to experience new approaches to life and governing but that could also leave society more vulnerable to threats and disorder. The relative advantages of one ideology compared to the other depend upon the circumstances. If a foreign policy threat turns out to be real, the conservative response will be extremely valuable; if it is not real, the liberal approach will be better positioned to cash in on opportunities the conservative response would miss.

Moreover, being more attuned to the dangers of the world does not make for pessimistic, fearful individuals and being less attuned to dangers does not make for carefree, hedonistic individuals. In fact, conservatives are consistently found to score higher than liberals on subjective well-being, even after controlling for socioeconomic status (Vigil Reference Vigil2010). Apparently, being responsive and attentive to negative aspects of the environment does not lead to depressive personalities. In fact, it may be that limiting the consequences of threats is a more manageable and defined goal than is pursuing novel experiences. Along these lines, it is well to remember that responding and attending to negative events is not the same thing as living in fear of them (see Aron Reference Aron1996). Turning to liberals, the desire for stimulation, self-expression and new experiences does not necessarily make for self-absorbed individuals. Liberals consistently score higher than conservatives on empathy scales (Hirsh et al. Reference Hirsh, DeYoung, Xu and Peterson2010). From an evolutionary perspective, insufficient attention and response to negative situations is clearly a problem but it is also the case that unrelenting vigilance and heightened physiological response also become problems at some point.

Finally, just as the tendency to read value judgments into the findings summarized here should be resisted, so should the tendency to conclude the results are stronger than they are. The connection of conservative political orientations and heightened orientation to negative stimuli is surprisingly consistent across designs, studies, and countries but it is also consistently modest in effect size. Many political conservatives are not particularly responsive to negative stimuli and many political liberals are. The reported effects, however, persist even when more traditional explanatory variables, such as standard sociodemographics, are included in the models. Moreover, to provide perspective, the effects of variation in negativity bias and related concepts, though modest, typically are at least as large as many of these standard variables.

A recurring feature of human history seems to be, as Atran puts it, people going “to war without understanding the transcendent drives and dreams of adversaries who see a very different world” (Reference Atran2012). Empirical evidence is increasingly documenting the psychological and physiological differences across people that can lead them to perceive the world so differently. One person focuses on threats but when facing that same situation another person focuses on opportunities. It is not surprising that these different visions of reality lead to fundamentally different sets of political preferences. By documenting that political differences are not necessarily traceable to misinformation or ignorance on the part of one side or the other, scientific understanding of the broader and deeper bases of political diversity may make it possible for Emerson's forces of tradition and innovation to live together, if not more profitably, at least less violently.