Fincher & Thornhill (F&T) are to be commended for revealing and explicating the importance of parasitic stress as one of several ecological factors that may influence the evolutionary creation of human culture. This commentary presents cross-national research to suggest that, compared with parasitic stress, climatic and economic factors may be even more convincing predictors of national culture. Our alternative explanation builds on prior research demonstrating that climatic stress is associated with considerable cultural differences, but that these effects can be observed only if we distinguish between poor and rich residential areas.

The climato-economic theory of culture (Van de Vliert Reference Van de Vliert2009) proposes that humans create cultures in adaptive response to climatic stress by using income resources to turn detrimental effects of climate into beneficial effects of climate. For a warm-blooded species like humans, livability is optimal in temperate climates because of existential needs for thermal comfort, nutrition, and health. Climates with temperatures around 22°C (about 72°F) provide psychophysiological comfort, abundant nutritional resources, and relatively healthy habitats. Cold or hot climates, lacking the climatic resources of temperate areas, are more demanding and thus require greater cultural adaptation. Income resources can alter the effects of adverse climates through investments in climate-compensating goods and services, including clothing, housing, household energy, meals, drinks, and medical cure and care. Consequently, cash and capital are more important influences on culture in colder or hotter and thus more stressful habitats. In support of this theory, inhabitants of lower-income areas appear to appraise climatic stresses as threats and adapt to cold or heat by falling back more on their in-groups for achieving goals. Inhabitants of higher-income areas, however, appear to appraise climatic stresses as challenges and adapt to them by falling back more on their individual selves for achieving goals (Fischer & Van de Vliert Reference Fischer and Van de Vliert2011; Van de Vliert Reference Van de Vliert2011a; 2011b).

That F&T ignore climatic stress is therefore a serious omission, all the more because parasitic stress is confounded with climatic stress. The prevalence of nonzoonotic infectious diseases is higher in countries with both hotter climates (r=.54, n=174, p<.001) and less thermal variation between winters and summers (r=−.48, p<.001). This raises the possibility that effects of parasitic stress are epiphenomena of the effects of climatic stress. Admittedly, F&T discuss economic livability (Inglehart & Baker Reference Inglehart and Baker2000) as a competing explanation, but they ignore the interactive effects of climatic stress and economic livability. The climato-economic theory of culture is able to predict two salient cultural outcomes that are also targeted in F&T's parasite-stress model: societal collectivism versus individualism (see our comment above), and political autocracy versus democracy (Van de Vliert Reference Van de Vliert2011a; Van de Vliert & Tol Reference Van de Vliert and Tol2011). Both societal collectivism and political autocracy are strongest in lower-income countries with more demanding cold or hot climates, moderate in countries with temperate climates irrespective of income per head, and weakest in higher-income countries with more demanding cold or hot climates.

In sum, there are conceptual and empirical reasons to view parasitic stress and climato-economic livability as competing explanations of national culture. We combined databases from the target article and the public sources mentioned below, in order to test the hypothesis that climato-economic livability is a stronger predictor than parasitic stress of cross-national differences in societal collectivism and political autocracy. After introducing how we measured parasitic stress, climato-economic livability, and collectivistic and autocratic culture, we present and briefly discuss the results.

The prevalences of nonzoonotic and zoonotic diseases were taken from the target article's Electronic Supplement 2. Nonzoonotic and zoonotic disease burdens, and their interaction, were included as predictors. As is usual in our novel line of climato-economic research, livability was represented by climatic demands, income resources, and their interaction. Climatic demands were measured across each country's major cities as average absolute deviations from 22°C in the coldest and hottest months, respectively (source: Van de Vliert Reference Van de Vliert2009). Data on income resources, measured as the natural logarithm of the purchasing power product per capita in 2002, were available for 174 nations (source: United Nations Development Programme 2004). For societal collectivism, we used an internally consistent and externally valid 121-nation index of familism, nepotism, and compatriotism (source: Van de Vliert Reference Van de Vliert2011b). Finally, for political autocracy, Pemstein et al.'s (Reference Pemstein, Meserve and Melton2010) integrated index of ten measures of regime type was chosen over other indices because the breadth of its domain did in no way undermine its internal reliability. The modest overlap between societal collectivism and political autocracy (r=.55, n=121, p<.001) made separate analyses meaningful.

As shown in Table 1, hierarchical regression analysis with standardized predictors estimating societal collectivism in 121 nations, and political autocracy in 174 nations, yielded three results. First, reconfirming and refining F&T's interesting finding that nonzoonotic rather than zoonotic infectious diseases explain in-group assortive sociality (target article, sect. 5.1.1), zoonotic disease stress has no significant main or interactive effects on societal collectivism and political autocracy. Second, when parasitic stress is first controlled for, climato-economic livability still accounts for the largest part of the variation in societal collectivism (ΔR ²=.31; total R ²=.47) and political autocracy (ΔR ²=.21; total R ²=.35). Third, when climato-economic livability is first controlled for, parasitic stress cannot additionally account for any variation in societal collectivism (ΔR ²=.00; total R ²=.47) and political autocracy (ΔR ²=.00; total R ²=.35).

Table 1. Results of hierarchical regression analyses predicting societal collectivism and political autocracy.

***p<.001, **p<.01, *p<.05 (n=121 for societal collectivism; n=174 for political autocracy). Unstandardized beta weights shown in the B columns are from the final step in both prediction models. There was no multicollinearity (VIFs<5.22), and there were no outliers (Cook's Ds<.23).

It is important to emphasize that the parasite-stress model has been successfully applied to a spectrum of components of culture, so these disconfirmatory results do not invalidate the model. It is clearly the case that parasitic stressors may influence cultural values and practices. Yet, it is also likely that the evolution of culture in humans, just like evolution in animals and plants, has climatic underpinnings. In comparison with latent concerns over parasites, it would appear that climato-economic livability is the more powerful predictor of cultural orientations towards collectivism and autocracy.