Introduction to our research
Humans are unusual animals, but many of the things that make us special – our complex institutions, our systems of religion and ritual, and our collective behaviors such as migration and warfare – are not produced by single individuals, but are emergent phenomena that develop from the interactions of multiple people. Those interactions can be distributed across space, such as people forming coalitions to attack another group, or across time, such as group transmitted practices, iteratively giving rise to complex culture. They can be intentionally constructed, or they can emerge through non-deliberative processes.
Although phenomena like institutions, warfare, and group rituals come from the interactions of individual humans, they in turn change how people behave – for example, by influencing the shape of a person’s networks, where they live, who they consider kin, their experiences with outgroup members, and even physiological measures. These can then feedback into emergent phenomena. We refer to these emergent phenomena and interacting levels as systems and we study how they develop and how they affect behavior. To do so, we incorporate tools from diverse fields including social network analysis, GPS technology, behavioral ecology, cultural anthropology, social psychology, evolutionary biology, and social physics.
Our research can be grouped into the following themes but individual projects often overlap thematically. We also have smaller and ancillary projects on questions that don’t neatly fit into any of these.
If you’re interested in discussing any of these ideas or collaborating, please send me an email!
Coordination and Collective Behavior
Human societies function because of shared expectations and conventions. Language requires common understandings of what words mean; we interact with people assuming they know the many norms underlying social life; and even walking through a crowded public space involves coordination to create informal lanes of traffic.
We know a decent amount about the principles of coordination and the mechanisms that can sustain collective behavior; yet, we know astonishingly little about how humans actually solve basic coordination problems. For example, how do we learn to navigate public spaces with multi-directional flows of pedestrians? Or agree on the referents (names) of objects or develop sets of shared expectations? The problems are even more acute in subsistence contexts where daily decisions may have life or death consequences (e.g. who to hunt with, where to move camp, and when). We develop conventions to solve many of these types of problems (which are often non-obvious) but what are they and how do we do so? Our lab focuses on understanding how humans solve real coordination problems and produce collective behavior.
Proceedings of the National Academy of Sciences, 2017
Media Coverage: Daily Mail, Yale News, Psychology Today.
Leadership solves collective action problems in small-scale societies. Philosophical Transactions of the Royal Society B: Biological Sciences, 2017
Philosophical Transactions of the Royal Society B: Biological Sciences, 2017
Collective action relies on the ability to coordinate with others and frequently involves investment in others. Solving the problems inherent in it is a key ability underlying the success of our species.
If you are reading this, you are likely a member of a WEIRD (western, educated, industrialized, rich, democratic) population and share with other readers a set of cultural values and expectations about the social and natural environment. These affect your beliefs, inferences, and decisions. Yet, the range of cosmological and metaphysical assumptions humans can hold seems nearly limitless. For example, many societies historically held beliefs that children with minor deformities or whose parents had died would bring bad luck and should be killed motivating infanticide, or that illness and death by natural causes were really the work of witches and shaman who could later be targeted for revenge. Beliefs such as these can give rise to norms (e.g. infanticide), institutions (e.g. partible paternity), and group dynamics (e.g. group fissioning, intergroup conflict) that are hard to understand in isolation without considering underlying belief structures.
The social sciences have scarcely considered the vast diversity of human psychologies and as a result we know little about the psychological realities that humans experience. Given that these shape norms and institutions, better understanding culturally-specific psychology can reveal aspects of humans systems that are otherwise hard to understand.
A systems approach focuses on the interaction between individuals and emergent social and behavioral phenomena. In this vein, our research is concerned with understanding (1) how and why groups see the world in the way that they do, (2) what this means for their decision-making and other behavior, and (3) how this variation contributes to different group-level outcomes (such as the spread of ideas, the development of institutions, and types of intergroup conflict). For example, our research has shown that different modes of production drive variation in interdependence, and that this in turn modulates people’s reliance on social information. Future projects will examine how factors including hierarchy, social networks, and residence influence the development of emergent behaviors.
Nature Human Behaviour, 2017
Coverage: Commentary in NHB.
Our research has shown that interdependence in daily tasks is associated with increased reliance on social information.
Norms and Institutions
Rules, norms, and institutions are a key means through which humans solve coordination problems, enabling us to adapt to a multitude of ecological and social contexts. But they are also fascinating and often intricately evolved pieces of cultural machinery tuned to specific socio-ecological environments. Where do they come from? How are they sustained? How do they respond to changing conditions?
Our research is less about any specific set of norms or institutions but rather about how groups come to adopt norms and create institutions. We primarily approach this from the perspective of self-interested agents whose decisions and behaviors at an aggregate level produce norms and institutions.
Relatedly, we are developing projects to uncover patterns in the organization of human societies and develop tools to improve the specificity of how we describe human groups.
The emergence of locally adaptive institutions: insights from traditional social structures of East African pastoralists.
Human Nature, 2018
Humans are able to inhabit an astonishing range of environments not through biological adaptations but through cultural adaptations including complex technology and social institutions such as kinship (see above figure for an example from one society). Many features of social systems emerge regularly likely through convergence (such as bilateral cross-cousin marriage) but others appear to be tailored to specific environments (social or ecological).
Much research on the origins of cooperation focuses on transactional relationships, such as A pays a cost to benefit B. However, human sociality is also enabled by processes-oriented behaviors and interactions, where the costs and benefits are often not obvious. These can include behaviors such as music, ritual, and religion, which can facilitate group bonding, promote cooperation, and drive cultural evolution. They are also fascinatingly human specific—ritual, religion, dance, music!
Our research strives to understand how process-oriented behaviors arise, why individuals participate in them, and what their individual and social consequences are. To do so, we seek to build ethnographically rich descriptions in the societies we study that will enable us to better understand how these processes function, how they shape and drive the evolution of other cultural traits, and why and how human groups the world over come to have these peculiar and fascinating processes.
For the past few years, we have focused extensively on music, which appears to promote group cohesion and facilitate many process-based interactions. Much of this research occurs as part of the Natural History of Song Project, which I co-direct with Sam Mehr and Manvir Singh. NHS systematically explores the features and social functions of music cross-culturally with the aim of developing a more complete, data-driven understanding of the social functions of music.
Current Biology, 2018
Media Coverage: NY Times, The Atlantic, The Economist.
Media Coverage: Wall Street Journal, Newsweek, Smithsonian.
Music from diverse societies exhibits recurrent form-function relationships.
Violence and Warfare
Collective aggression has a deep evolutionary history and was likely a major selective force in human evolution. Yet, we still know little about the proximate psychological mechanisms, evolutionary significance, and cultural determinants of violence.
Despite the aversion many people have to physical risk and injuring others, violent conflict is common. What explains this? How do biology, cultural background, and beliefs motivate individuals to violence? What are the processes by which collective, group-based violence emerges?
Separately, we aim to understand how societies regulate conflict, especially through dampening processes or incentivizing mechanisms. These questions strike at the heart of one of the most vexing issues in understanding humans—how our hyper-prosociality exists alongside our propensity to willfully hurt others.
To study these questions, we use a combination of archival research, experimental paradigms, modeling, and field studies conducted with people experiencing intergroup violence. Much of our fieldwork focuses on small-scale groups in east Africa who experience regular intergroup conflict, accounting for up to 40% of the male mortality rate. These societies lack centralization, and warfare is usually conducted without larger political objectives and institutional leadership, both of which fundamentally affect individual motivations and the social dynamics of participation.
Journal of Economic Behavior and Organization, 2020
Proceedings of the National Academy of Sciences, 2015
Media Coverage: Wall Street Journal, LA Times, Science.
Nature Human Behaviour, 2017
A group of raiders in East Africa. Across cultures, conflict usually involves mostly young men.
We study how collective violence can arise from within-group processes. Much of our work has focused on understanding the functional significance at an individual level. Figure from Isakov et al. 2016.