Humans are unique for our exceptional prosociality. We cooperate on vast scales with strangers yet this ability also enables us to harm and kill one other with great effectiveness. These two traits – our hyper-cooperativeness and our propensity for aggression against outgroups – have a deep evolutionary history and were likely major selective forces in human evolution. Thus, understanding these phenomena can yield fundamental insights into our species. My research program asks two overlapping questions related to the evolution of these characteristics: First, how do individuals with competing interests coordinate to produce collective behavior? Second, what are the proximate and ultimate bases of human aggression? Theoretically, I look for adaptive explanations of behavior that are rooted in self-interest, focusing on proximate mechanisms as a means to identify and assess tradeoffs

I use a methodologically diverse approach to explore questions about human behavior. My fieldwork in small-scale subsistence populations incorporates behavioral and ethnographic data collection as well as paradigms from social psychology and behavioral economics. My research questions share a common thread in seeking to understand how individuals with competing interests coordinate to produce complex behavior. If you are interested in learning more about these projects or collaborating, please send me an email

Aggression and Coalitionary Violence

My research seeks to understand how and why individuals and groups engage in violent conflict. Humans are generally harm-averse, yet participating in conflict creates risks for aggressors. How do individuals overcome aversion to risk? How do inter-individual differences create group level effects? How does culture influence individual preferences and likelihood of participation? At a macro level, I seek to understand the processes by which societies regulate conflict, especially through dampening processes or incentivizing mechanisms. I investigate these questions focusing on the cultural modulation of aggression, inter-individual differences, and social networks. I am also a co-organizer of a recent workshop on the Evolution of Warfare hosted by the National Institute of Mathematical and Biological Synthesis. 

Collective Action 

Understanding how humans solve collective action problems outside of formal institutions is one of the central challenges of evolutionary anthropology. Using data from small-scale traditional societies I study 1) the mechanisms that sustain cooperation in the absence of formal institutions, 2) how informal regulation of the commons develops, 3) how inter-individual differences, such as in personality, can catalyze collective behavior. These questions extend to the processes by which high-risk collective action, such as big-game hunting or warfare, occurs in small-scale societies, as well as how institutions that promote collective action, such as age organization, territorial sections, or cultural reward systems, develop. I am a co-editor of a recent issue of Philosophical Transactions of the Royal Society on inter-individual differences and collective action. 

Norms and Institutions  

How do norms, institutions and group functional culture arise among self-interested agents in acephalous social environments? How are they maintained without formal sanctioning systems? Along with colleagues Manvir Singh and Richard Wrangham, I have developed an agent-based approach for understanding how self-interested agents can produce rules, norms, and group functional culture. I am beginning to test these ideas through research into the development of cultural institutions in small-scale societies.

Cultural Psychology   
If you are reading this, you are likely a member of a WEIRD (western, educated, industrialized, rich, democratic) population and share a set of cultural values and expectations about the social and natural environment. Yet in many societies, individuals have profoundly different conceptions of self and causality as well as differing norms and social expectations. Little is known about the cultural psychology of traditional populations compared to WEIRD societies or the psychological changes invoked by demographic transitions. Research into this area is nascent but I am developing projects on norms and the processes of cultural transitions. 

Ritual, Group Cohesion, and Crowd Behavior    
Along with Samuel Mehr and Manvir Singh, I co-direct the Natural History of Song Project which systematically explores the features and social functions of music cross-culturally. I am also developing tools to advance conceptual models on human behavior in groups, including ritual. I am interested in the interaction between biology and social psychology and am working to develop better models to probe the psychological processes and social dynamics of participation in these contexts.