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.

This study explores aggression among siblings. Specifically, this study tests whether different types of aggression among siblings occur more or less frequently than toward friends and acquaintances. This study also examines whether sex differences in aggression between siblings resemble sex differences in aggression among friends and acquaintances. Results suggest that direct aggression occurs much more frequently among siblings than among friends and acquaintances, but that indirect aggression occurs far less frequently among siblings than among friends and acquaintances. In addition, the findings suggest that certain sex differences in aggression, such as males directly aggressing more often than females, are diminished when the aggression occurs between siblings. Both males and females report high levels of direct aggression toward their siblings.