Christianity spread faster in small, politically structured societies

Cross-national analyses require additional controls to account for the non-independence of nations

Cross-national analyses test hypotheses about the drivers of variation in national outcomes. However, since nations are connected in various ways, such as via spatial proximity and shared cultural ancestry, cross-national analyses often violate assumptions of non-independence, inflating false positive rates. Here, we show that, despite being recognised as an important statistical pitfall for over 200 years, cross-national research in economics and psychology still does not sufficiently account for non-independence. In a review of the 100 highest-cited cross-national studies of economic development and values, we find that controls for non-independence are rare. When studies do control for non-independence, our simulations suggest that most commonly used methods are insufficient for reducing false positives in non-independent data. In reanalyses of twelve previous cross-national correlations, half of the estimates are compatible with no association after controlling for non-independence using global proximity matrices. We urge social scientists to sufficiently control for non-independence in cross-national research.

Is Religion Special?

Religion makes unique claims (e.g., the existence of supernatural agents) not found in other belief systems, but is religion itself psychologically special? Furthermore, religion is related to many domains of psychological interest, such as morality, health and well-being, self-control, meaning, and death anxiety. Does religion act on these domains via special mechanisms that are unlike secular mechanisms? These could include mechanisms such as beliefs in supernatural agents, providing ultimate meaning, and providing literal immortality. We apply a critical eye to these questions of specialness and conclude that although it is clear that religion is psychologically important, there is not yet strong evidence that it is psychologically special, with the possible exception of its effects on health. We highlight what would be required of future research aimed at convincingly demonstrating that religion is indeed psychologically special, including careful definitions of religion and careful attention to experimental design and causal inference.

Food storage facilitates professional religious specialization in hunter-gatherer societies

Professional religious specialists centralised religious authority in early human societies and represented some of the earliest instances of formalised social leadership. These individuals played a central role in the emergence of organised religion and transitions to more stratified human societies. Evolutionary theories highlight a range of environmental, economic and social factors that are potentially causally related to the emergence of professional religious specialists in human history. There remains little consensus over the relative importance of these factors and whether professional religious specialists were the outcome or driver of increased socio-cultural complexity. We built a global dataset of hunter-gatherer societies and developed a novel method of exploratory phylogenetic path analysis. This enabled us to systematically identify the factors associated with the emergence of professional religious specialists and infer the directionality of causal dependencies. We find that environmental predictability, environmental richness, pathogen load, social leadership and food storage systems are all correlated with professional religious specialists. However, only food storage is directly related to the emergence of professional religious specialists. Our findings are most consistent with the claim that the early stages of organised religion were the outcome rather than driver of increased socio-economic complexity.

Cultural similarity among coreligionists within and between countries

Cultural evolutionary theories suggest that world religions have consolidated beliefs, values, and practices within a superethnic cultural identity. It follows that affiliation with religious traditions would be reliably associated with global variation in cultural traits. To test this hypothesis, we measured cultural distance between religious groups within and between countries, using the Cultural Fixation Index ([Formula: see text]) applied to the World Values Survey (88 countries, n = 243,118). Individuals who shared a religious tradition and level of commitment to religion were more culturally similar, both within and across countries, than those with different affiliations and levels of religiosity, even after excluding overtly religious values. Moreover, distances between denominations within a world religion echoed shared historical descent. Nonreligious individuals across countries also shared cultural values, offering evidence for the cultural evolution of secularization. While nation-states were a stronger predictor of cultural traits than religious traditions, the cultural similarity of coreligionists remained robust, controlling for demographic characteristics, geographic and linguistic distances between groups, and government restriction on religion. Together, results reveal the pervasive cultural signature of religion and support the role of world religions in sustaining superordinate identities that transcend geographical boundaries.

A phylogenetic analysis of revolution and afterlife beliefs

Beliefs about the fate of humanity and the soul after death may structure behaviours of religious groups. Here we test theories from religious studies: that belief in an imminent apocalypse co-evolved with and facilitated revolutionary violence, whereas belief in reincarnation caused people to acquiesce to existing social orders and withdraw from political activism. We test these hypotheses by building a cultural phylogeny of historical Islamic sects and schools from the seventh to twentieth centuries and use phylogenetic comparative methods to show that these two types of belief display distinct relationships with intergroup violence. There is substantial evidence that apocalyptic beliefs co-evolved with revolutionary violence, whereas reincarnation beliefs were evolutionarily stable in peaceful groups. In both cases, violence precedes the emergence of beliefs, which suggests that conditions that generate revolutionary violence changed beliefs rather than beliefs generating violence. We also found that apocalyptic beliefs are associated with accelerated group extinction, although causal relationships cannot be determined.

How cultural learning and cognitive biases shape religious beliefs

What explains the ubiquity and diversity of religions around the world? Widespread cognitive tendencies, including mentalizing and intuitive thinking, offer part of the explanation for recurrent features of religion, and individual differences in religious commitments. However, vast diversity in religious beliefs points to the importance of the cultural context in which religious beliefs are transmitted. Cultural evolutionary theory provides the basis of a unified explanation for how cognition and culture interact to shape religious beliefs, in ways that are uniquely adapted to local ecological pressures. These insights lay the groundwork for future research regarding how cultural learning interacts with other evolved aspects of human psychology to generate the recurrent and the diverse forms of religious commitments observed around the world.