The evolutionary foundations of cooperation and human ultrasociality

• Applicant: Liran Samuni, Ph.D.
• Subject Area: Evolution, Anthropology ; Sensory and Behavioural Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513871869

Humans’ capacity to cooperate across time and social scales launched our lineage on an evolutionary trajectory that allowed us to thrive across the globe. During evolution, our ability to work together likely enabled us to conquer new challenging environments (that would otherwise have induced competition) and to win in warfare. The need to collaborate to overcome these challenges is hypothesized to have led to interdependence (i.e., mutual reliance) of people within groups – an evolved psychology that still modifies our social biases and social motivations today. However, while there is a consensus that cooperation has contributed to our success, identifying the evolutionary trajectories of human cooperative traits has been a major scientific hurdle, particularly given the limited ability to infer behavior from fossil remains. Exploring how natural environmental and social challenges impact cooperation in our closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), is a critical step in revealing the unique human adaptations that allow us to thrive. Chimpanzees and bonobos not only share phylogenetic proximity with humans but also possess a suite of characteristics parallel to human social systems. In addition to the strong similarities between them, bonobos and chimpanzees show drastic differences in domains thought to underlie human interdependence, with greater environmental variation and challenges and stronger out-group conflict faced by chimpanzees in comparison to bonobos. Capitalizing on natural variation within and between bonobos and chimpanzees, I propose to conduct a comprehensive examination of the ecological and social pressures that impact cooperation and prosociality. Utilizing large datasets of behavior, demography, and physiology of 650+ individuals from four populations across Africa, my research group will compare the prosocial and cooperative tendencies of chimpanzees and bonobos living in similar environments (similar ecology, differing out-group conflict) and of chimpanzee populations across an environmental gradient (similar out-group conflict, differing ecology). Further, capitalizing on natural temporal variation in out-group conflict and the ecology within populations, my group will investigate the extent of a population’s behavioral plasticity, a valuable tool allowing individuals to adapt to changing circumstances. Comparing the cooperative and prosocial capacities of our closest living relatives is a timely topic that has never been explored at this scale, and therefore this project has the potential to significantly advance our understanding of human evolution.

• DFG Programme: Independent Junior Research Groups