In understanding why cultures differ from one another, one might consider their ecology: the social and physical features of the environment relevant to an organism’s fitness. Multiple theories propose that cultures and the individuals within them respond to the threats and opportunities offered by the ecology in predictable and adaptive ways. This dissertation demonstrates how ecology can -- but does not always -- explain a significant portion of cultural variation. The three published, first-authored, peer-reviewed articles featured in this work leverage best practices in archival data to demonstrate the relationship between ecology and cultural variation. Chapter 2 describes the creation of the Eco-Cultural Dataset which contains data on 11 ecological variables and 72 cultural variables in up to 220 countries. Chapter 3 utilizes this dataset to estimate the effect of ecology on culture, writ large. Chapter 4 explores the potential role of pathogens in the existence and prevalence of food taboos in religious and cultural groups. The final chapter reviews the limitations of utilizing archival data to investigate ecology and culture, as well as proposing exciting future directions for the field.

Infectious disease presents a serious threat to our fitness. The biological immune system provides several mechanisms for dealing with this threat. So too does another system: the behavioral immune system. This second system is proposed to consist of a set of evolved cognitive, affective, and behavioral strategies for reducing the likelihood of infection, including xenophobia, traditionalism, and food neophobia. In the present work, I investigate how another suite of fairly novel culturally-learned disease avoidance strategies, namely hygiene behaviors and knowledge of germ theory, are related to the behavioral immune system. Across two studies, I find that individuals who engage in more hygiene behaviors show less evidence of reliance on several elements of the behavioral immune system (i.e., xenophobia, traditionalism, food neophobia). Similarly, individuals who know more about germ theory show less engagement in behavioral immune system components. These findings suggest that effective cultural strategies for avoiding infectious disease may supplant older, evolved psychological strategies with the same purpose.

One salient aspect of most world religions is an emphasis on reproductive morality—rules about which types of sexual behaviors and familiar structures are acceptable. In Chapter 1, I introduce the theoretical background of the dissertation, including the Reproductive-Religiosity Model. Then, in one theoretical paper (Chapter 2) and two empirical papers (Chapters 3 and 4), I consider the cultural and social implications of religious proscriptions on sexual behavior. In Chapter 2, I review the Reproductive-Religiosity Model, which posits that religions are especially attractive to people who desire monogamous, long-term mating strategies. I also discuss the implications of this model for cultural evolution. In Chapter 3, I look at the social implications of these religious proscriptions. That is, if restricted attitudes toward sexuality are strongly linked to religious belief, it follows that people’s stereotypes of religious people may track this relationship. Three studies showed that people tended to trust religious targets more than nonreligious targets, but that this effect seems to be due to inferences about religious targets’ reproductive strategies—that is, people trusted religious targets because they perceived them more likely to be interested in starting a family. In Chapter 4, I examine patterns of religiosity across the world through a rational choice lens, positing that people are more likely to be religious when religion can help them fulfill their goals. Analysis of two global datasets shows that men, more so than women, tend to be less religious in countries with greater gender equality. Finally, Chapter 5 summarizes results and discusses future directions for this line of research.

Humans are biased toward teleological explanations of natural phenomena. The promiscuous teleology account posits that this proclivity is rooted in the detection of supernatural agency behind the design of the natural world. This idea is supported by numerous positive correlations of religious belief and agreement with teleological explanations of natural phenomena, but it is challenged by findings that non-believers often agree with them as well, suggesting the need for an adjudicating experiment. The current experiment tested whether considering similar teleological explanations of nature causes explicitly theistic and atheistic people to think about God, which would suggest that the teleological bias has roots in agency detection. Participants (N = 608) were randomly assigned to consider teleological explanations of either human-caused phenomena or natural phenomena, with the main prediction that considering the natural item set would make theists relatively faster to categorize God as real but make atheists relatively slower to categorize God as imaginary. The data did support this hypothesis, suggesting that people across the theistic belief spectrum automatically think of God when thinking about nature’s purpose, and thus the teleological bias might be rooted in the detection of supernatural agency. Implications for theories of teleology, study limitations, and potential future directions are discussed.