Toxoplasma-infected women scored higher in tribalism and lower in cultural liberalism, compared with the Toxoplasma-free control group; infected men scored higher in economic equity

Le Petit Machiavellian Prince: Effects of Latent Toxoplasmosis on Political Beliefs and Values. Robin Kopecky et al. Evolutionary Psychology, July 29, 2022. https://doi.org/10.1177/14747049221112657

Abstract: Humans infected by Toxoplasma gondii express no specific symptoms but manifest higher incidence of many diseases, disorders and differences in personality and behavior. The aim of this study was to compare the political beliefs and values of Toxoplasma-infected and Toxoplasma-free participants. We measured beliefs and values of 2315 responders via an online survey (477 Toxoplasma-infected) using the Political Beliefs and Values Inventory (PI34). This study showed Toxoplasma-infected and Toxoplasma-free participants of our cross-sectional study differed in three of four factors of PI34, scoring higher in Tribalism and lower in Cultural liberalism and Anti-Authoritarianism. We found sex differences in political beliefs associated with Toxoplasma infection. Infected women scored higher in tribalism and lower in cultural liberalism, compared with the Toxoplasma-free control group, while infected men scored higher in economic equity. These results fit with sexual differences in behavior and attitude observed after toxoplasmosis infection. Controlling for the effect of worse physical health and mental health had little impact, suggesting that impaired health did not cause these changes. Rather than adaptation to prevalence of parasites, as suggested by parasite-stress theory, the differences might be side-effects of long-term mild inflammatory reaction. However, to get clear picture of the mild inflammation effects, more research focused on different infectious diseases is needed.

Keywords: Toxoplasma gondii, manipulation hypothesis, political beliefs, stress, infectious diseases, parasite threat, pathogen avoidance

Discussion

The present study showed that Toxoplasma-infected and Toxoplasma-free participants of our cross-sectional study differed in three of four factors measured with Political inventory, namely scored higher in Tribalism and lower in Cultural liberalism and Anti-authoritarianism. These results are in line with previous broad research, showing that individuals in parasite affected areas are more likely to be conservative and authoritarian (Murray et al., 2013).

Furthermore, we observed sex differences in the studied factors associated with the Toxoplasma infection. Indeed, Toxoplasma-infected men scored higher in Economic Equity, showing a preference for a more equal and less competitive society, while women infected with toxoplasmosis scored higher in tribalism and lower in cultural liberalism. These associations were not reduced when the effect of worse physical health and mental health were controlled, suggesting that impaired health of infected subjects is not the cause of changes in political beliefs. The same conclusion was also supported by the fact that the changes go in the same direction in men and women, because stress coping-associated behavioral and personality changes mostly go in different directions in men and women.

It was suggested by Lindová et al, (2006, 2012) that these associations might be the results of a mild chronic stress caused by the toxoplasmosis infection instead of the result of the toxoplasmosis itself. The presence of a chronic stress not only explain the presence of behavioral and political differences with the non-infected control group, but also the presence of sex differences in these behavior and ideologies as different responses to chronic stress in the two sexes, involving differences in the immune system response and in the coping strategies used. Many of the behavioral changes observed in toxoplasmosis infected people correlate with the function of dopamine in the brain and they may have more broad implications, including political ideologies. In line with our results, previous studies (Flegr et al., 2003, Skallová et al., 2005) showed that infected subjects scored lower in novelty seeking, a factor that contributes to a conservative and political opinion (Carney et al., 2008). Indeed, in our sample the infection was associated with higher tribalism and lower cultural liberalism, specifically in women. While we expected differences in the political ideologies of infected men and women, we did not expect a higher score in economic equity in infected men. Typically, men affected with toxoplasmosis showed higher risk propensity and higher entrepreneurial activities (Johnson et al., 2018) more compatible with a competitive type of economy. The association of toxoplasmosis and the preference for an egalitarian economy in men needs to be better explored in future works.

Several studies have found that societies that are more affected by infectious pathogens also exhibit higher levels of conservative political attitudes such as xenophobia and traditionalism (Bennett & Nikolaev, 2020; Murray et al., 2013; Nikolaev & Salahodjaev, 2017; Thornhill et al., 2009). Similar results have also been found in our study performed on the individual level. The hypothesis that has been proposed is that the attitudes exhibited are connected to pathogen avoidance behaviors aimed at minimizing contact with outsiders (intergroup effect) (Aarøe et al., 2017) who may be carrying new pathogens as well as the maintenance of social traditions that may serve to help protect against pathogens (intragroup effect) (Fincher & Thornhill, 2012), with evidence from a recent cross-national study favoring the intragroup effect (Tybur et al., 2016). Significantly, however, both the effects – and the intragroup effect in particular – seem potentially open to the interpretation that they are generalized responses to stress, rather than to a pathogen (Brown et al., 2016; Currie & MacE, 2012; Hruschka & Henrich, 2013; Ma, 2020).

While the present study examines differences found in association between a parasitic infection and political values in context of increased stress at individual level, the results can be seen as an alternative to the parasite stress theory (Fincher et al., 2008; Thornhill & Fincher, p. 2014) for the following two main reasons: Parasite-stress theory aims to be the ultimate evolutionary explanation of changes in traits that differ with varied geographical parasite stress levels, yet this study focuses directly on the difference between actual infected and non-infected subjects in one small region, where the intensity of the parasite stress is mostly constant (and low). Second reason is that it has been shown that primarily non-zoonotic diseases have a relation to human personality and societal values (Thornhill et al., 2010). However, toxoplasmosis is primarily a zoonotic disease with very specific and limited spread between people – the only intrapersonal route of infection was suggested from male to female or between two male partners through sexual transmission (Flegr, Klapilová, et al., 2014; Flegr, Prandota, et al., 2014; Hlaváčová et al., 2021; Kaňková et al., 2020).

This being said, there might be a possible connection between the present study and the parasite-stress theory after all. An extensive body of research confirms association between infectious (and in most cases parasitic) diseases and changes in personality profile of animals from molluscs (Seaman & Briffa, 2015) and minnows (Kekäläinen et al., 2013) to migratory birds (Marinov et al., 2017) and mammals (Boyer et al., 2010) including men (Webster, 2001). There are also well studied associations between personality traits and political views, e.g. (Furnham & Fenton-O’Creevy, 2018; Harell et al., 2021; Verhulst et al., 2010; Wang, 2016). While the direction of causality needs to be studied further (Bakker et al., 2021) and while the human-centred field of parasite induced changes in personality traits is regrettably understudied and quite complex (Friedman, 2008), we might expect at least some effect of infectious diseases on political attitudes caused by shifts of personality traits. A possibility thus exists, that at least part of the reported difference in political attitudes in countries with different parasitic disease burdens is not caused by parasite-avoidance but results from a significant part of the population being infected with one or multiple pathogens. This hypothesis is supported by studies that linked a change in personality traits with clear connection to political attitudes (e.g., conservatism) with chronic diseases, although not the infectious ones (Mendelsohn et al., 1995; Sutin et al., 2013). On the other hand, some results suggest stronger prediction of personality traits by historical prevalence of diseases rather than by the current situation, suggesting parasite-avoidance as a factor with greater importance in personality shifts (Schaller & Murray, 2008).

Since the available body of literature discussing possible causal relationships between infectious diseases and political beliefs and values is very sparse, this direction of research might provide interesting and important insight into the changing political climate in certain countries. Studies focused on a wider range of infectious diseases besides toxoplasmosis and severe debilitating illnesses such as neurocysticercosis or AIDS would be especially valuable.

The present study showed a 19% prevalence of toxoplasmosis in men and 28% in women. The most recent Czech epidemiological study performed between 2014–2015 (Flegr, 2017) showed the prevalence of 25% in men and 36% in women aged 30–39 years. It is known, however, that prevalence of toxoplasmosis decreases relatively quickly in most developed countries, including the Czech Republic. For example, a large epidemiological study performed on Czech male soldiers 20 years ago found a prevalence of 35% for the age strata 30–35 years (Kolbekova et al., 2007). It is, therefore, possible that the observed seroprevalence reflects the actual situation in the Czech general population.

Limitations

The main limitation of the present study was the fact that the participants of the study were self-selected. Their subpopulation probably represents a specific (more altruistic and more curious) segment of the Czech population, rather than a random sample of the Czech internet population. In addition, people with impairments or severe diseases as well as those from the lowest socioeconomic strata were unable to participate. It is not therefore clear to which extent the results can be generalized to the general Czech (or the World) population.

Another limitation of the study is the moderate number of Toxoplasma-infected men (90). The reason of imbalanced sex ratio was the fact that women are often tested for toxoplasmosis during pregnancy and therefore a larger fraction of women than men know their toxoplasmosis status. Due to the lower number of men, the associations of toxoplasmosis with Cultural liberalism and Anti-authoritarianism were not significant in men, despite being stronger in men than in the more numerous (518) women.

Since this study dealt with the effect of pathogen-caused stress, there is a possible interference of the global COVID-19 pandemics. However, only 6% of the respondents participated in the period between April 2020 when the first infection in Czechia was observed, and the end of data collection in April 2021.

In the present study, we calculated aggregate indices of physical and mental health and used these indices in our statistical models. In future studies, it will be valuable to analyse the effects of individual health-related variables to disentangle the complex relationships between toxoplasmosis, mental and physical health, psychological traits and political beliefs. Such research could also answer important questions related to the causal direction of the observed correlations.

The associations found in the present study are based on correlations and we cannot infer the direction of causality. It cannot be ruled out that the explanation of the effect is in the opposite direction, that e.g., higher tribalism itself, by an unknown mechanism, increases the chance of being infected by Toxoplasma gondii. Like nearly all past studies, also this one was cross-sectional in nature. It is very difficult to study the relationship between Toxoplasma infection and personality using a longitudinal design. The frequency of the Toxoplasma infection in adulthood is low, and thousands of participants should be recruited to find several dozens of subjects who will acquire the infection during the study. Until such a study is performed, any conclusion about the causality behind the correlation between the infection and human personality must be based only on analogies with animal models (Skallová et al., 2006; Hodková et al., 2007) or on the existence of a correlation between length of infection and observed personality trait changes (Flegr et al., 1996, 2000) and must be therefore considered only provisional.

Further research is also needed to better clarify the extension and the implication of the associations we found between toxoplasmosis infection and political ideologies, and to clarify the role of sex differences.