According to a "parasite stress" hypothesis, authoritarian governments are more likely to emerge in regions characterized by a high prevalence of disease-causing pathogens. Recent cross-national evidence is consistent with this hypothesis, but there are inferential limitations associated with that evidence. We report two studies that address some of these limitations, and provide further tests of the hypothesis. Study 1 revealed that parasite prevalence strongly predicted cross-national differences on measures assessing individuals' authoritarian personalities, and this effect statistically mediated the relationship between parasite prevalence and authoritarian governance. The mediation result is inconsistent with an alternative explanation for previous findings. To address further limitations associated with cross-national comparisons, Study 2 tested the parasite stress hypothesis on a sample of traditional small-scale societies (the Standard Cross-Cultural Sample). Results revealed that parasite prevalence predicted measures of authoritarian governance, and did so even when statistically controlling for other threats to human welfare. (One additional threat—famine—also uniquely predicted authoritarianism.) Together, these results further substantiate the parasite stress hypothesis of authoritarianism, and suggest that societal differences in authoritarian governance result, in part, from cultural differences in individuals' authoritarian personalities.

Copyright: © 2013 Murray et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

Systems of governance differ widely, and one important dimension on which they vary is authoritarianism. In contrast to liberal democratic forms of governance (characterized by popular participation in the political process, and by protection of individual civil rights and ideological freedoms), authoritarian governance is defined by highly concentrated power structures that repress dissent and emphasize submission to authority, social conformity, and hostility towards outgroups [1], [2]. Why is governance in some states and societies more authoritarian than in others? Economic variables—including the overall availability of economic resources and the manner in which those resources are distributed—provide partial answers to that question [3], [4], [5], [6]. Ecological variables may play a role as well. Recently, it has been suggested that societal variability in authoritarian governance may result, in part, from variability in the prevalence of disease-causing parasites [7]. (In this context, “parasite” is used to refer broadly to any pathogenic organism, including bacteria and viruses as well as helminths). Although results from several initial studies support this “parasite stress” hypothesis of authoritarian governance [7], [8], alternative explanations for those results remain unaddressed. Here, we report results from two additional investigations designed to test the parasite stress hypothesis and to address inferential limitations of previous studies.

Why might there be a causal link between the prevalence of infectious diseases in the local ecology and an authoritarian system of governance? The hypothesis follows from an analysis of several defining characteristics of authoritarian political systems (such as institutionalized emphasis on social conformity, intolerance of dissent, and ethnocentrism) that may have implications for the spread of infectious disease. Because many disease-causing parasites are invisible, and their actions mysterious, disease control has historically depended substantially on adherence to ritualized behavioral practices that reduced infection risk [9]. Individuals who openly dissented from, or simply failed to conform to, these behavioral traditions therefore posed a health threat to self and others. Thus, while there can be societal costs associated with any collective behavioral tendency toward obedience and conformity (e.g., inhibition of technological innovation), there can be disease-specific benefits too (presuming that a greater proportion of these behavioral traditions serve to mitigate, rather than propagate, the spread of disease). These benefits would have been greater (and more likely to outweigh the costs) under circumstances in which disease-causing parasites placed greater stress on human welfare—circumstances in which those parasites were especially virulent and/or prevalent.

This logical analysis has implications for predictable variation in individuals' attitudes and values, and for worldwide societal differences too. At a psychological level of analysis, empirical evidence reveals that the subjective perception of infection risk causes individuals to be more conformist, to prefer conformity and obedience in others, to respond more negatively toward others who fail to conform, and to endorse more conservative socio-political attitudes [10], [11], [12], [13], [14]. At a societal level of analysis, empirical evidence reveals that in countries and cultures characterized by historically higher prevalence of parasitic diseases, people are less individualistic, exhibit lower levels of dispositional openness to new things, are more likely to conform to majority opinion, and more strongly endorse "binding" moral values that emphasize group loyalty, obedience, and respect for authority [15], [16], [17], [18], [19].

In addition to their intolerance of nonconformity, authoritarian political systems are also characterized by nepotism and ethnocentrism [20]. These behavioral tendencies too have been empirically linked to the threat of disease. At a psychological level of analysis, individuals who are—or who merely perceive themselves to be—more vulnerable to infection tend to endorse more xenophobic and ethnocentric attitudes [21], [22], [23]. At a societal level of analysis, countries characterized by higher prevalence of parasitic diseases are also characterized by stronger family ties, increased frequency of intrastate ethnic conflict, and several indicators of increased ethnocentrism [24], [25], [26], although the interpretation of some these results remains a matter of some disagreement [27], [28].

To the extent that institutionalized forms of governance reflect the attitudes and values of the individuals who populate the local ecology, these lines of research have implications for predicting worldwide variability in authoritarian governance: In places where parasitic diseases have posed greater stress on human health and welfare, authoritarian forms of governance may be especially likely to emerge and to persist over time.

Thornhill and colleagues [7] empirically tested this parasite stress hypothesis, using modern geopolitical entities (e.g., countries) as units of analysis. The hypothesis was tested on four different measures of democratization and/or authoritarianism, using a parasite stress measure derived from a modern epidemiological database. Consistent evidence was observed across all measures: Higher levels of parasite stress were associated with less democratic, more highly authoritarian political systems (N’s >192, absolute r’s >.45, p’s<.001). These relationships remained statistically significant when statistically controlling for measures of economic development and economic inequality (as assessed by a country’s GDP per capita and GINI coefficient respectively). Additional analyses revealed that country-level differences in authoritarian governance were even more strongly predicted by a measure of historical (rather than modern-day) parasite prevalence [29]—a finding consistent with the hypothesis that authoritarian governance is a consequence (rather than a cause) of parasite stress.

However, nontrivial inferential issues arise from the use of contemporary nation-states as units of analysis [30]. Until these issues are addressed empirically, it is difficult to draw confident conclusions about the relationship between parasite stress and authoritarian governance.

One issue pertains to the history of European colonization, and its consequences. When countries colonize other geographic regions, they often impose their own political and economic institutions onto those regions; those institutions may persist even after those regions attain independence. It has been argued that ecological variables (such as the prevalence of infectious diseases) predict societal outcomes primarily because of their influence on particular patterns of colonial settlement, such that European colonial powers were more likely to establish long-lasting democratic political systems and economic institutions in regions characterized by lower incidences of infectious diseases [31], [32]. This represents a very different causal process than that implied by the parasite stress hypothesis.

We conducted two separate investigations, using two different empirical strategies, to address this inferential issue and thus to more rigorously test the hypothesized relation between parasite stress and authoritarian governance.

The first study revisits the country-level analyses reported previously [7]. The alternative explanation—differential colonial establishment of political institutions—is tested by examining relations not only between disease prevalence and state-level authoritarianism evident in government institutions, but also by examining the relation between those variables and authoritarian attitudes expressed by individuals who populate the country. The colonial-establishment-of-institutions explanation implies a direct causal influence of disease prevalence on state-level authoritarian governance, which may in turn have downstream consequences for individual-level authoritarian attitudes. Conversely, the parasite stress hypothesis implies a more direct causal influence of disease prevalence on individuals' authoritarian attitudes, which in turn would be expected to have a consequent influence on state-level systems of government. In statistical analytic terms, the alternative explanation implies an indirect relation between disease prevalence and individuals' authoritarian attitudes that is statistically mediated by authoritarian governance, whereas the parasite stress hypothesis implies an indirect relation between disease prevalence and authoritarian governance that is statistically mediated by individuals' authoritarian attitudes.

In addition to testing the alternative explanation, the results of this study also have implications for our understanding of individual-level authoritarian attitudes as they relate to societal outcomes. Research on “the authoritarian personality” of individuals indicates some relation between politically entrenched authoritarian systems of governance and individually expressed authoritarian personality traits (as such governments and individuals have in common their emphasis on adherence to conventional values, repression of dissent, and devotion to order and hierarchy [1], [2], [33]). But the direction of causality is unclear: To what extent does the correlation reflect the influence of government institutions on individuals' personalities, versus the influence of individuals' personalities on systems of governance? By introducing an additional variable into the analysis, and testing statistical mediation, our results may contribute toward some resolution to this question.

The second study further addresses alternative explanations based on European colonialism by testing the parasite stress hypothesis on a sample of more traditional societies documented within the Standard Cross-Cultural Sample [34]. The Standard Cross-Cultural Sample (SCCS) consists of 186 worldwide cultural populations, many of which are small-scale aboriginal societies. Cashdan and Steele [15] employed the SCCS dataset to test several other hypothesized consequences of disease prevalence that had previously been tested only with cross-national comparisons; their results provided important substantiation for the relationship between disease prevalence and collectivist values—especially those values pertaining to adherence to group norms. We employed the same strategy to provide an empirically complementary test of the hypothesis that ecological variation in disease prevalence predicts societal variation in authoritarian governance.

Drawing on an extensive ethnographic database, the cultures that comprise the SCCS are described by hundreds of numerically coded variables gathered by dozens of different ethnographers—including multiple variables pertaining to systems of governance [35]. These variables, in conjunction with two indicators of disease prevalence [15], [36], allow a statistically rigorous test of the relation between parasite stress and authoritarian governance in small-scale societies. Additional variables assess the prevalence of conceptually distinct threats to human welfare within these societies (e.g., famine, warfare). This allowed us to test the unique predictive effects of parasite stress, while statistically controlling for any effects associated with these other threats.