The Cooperation Ladder: Scale-dependent payoffs and population dynamics create surges, stalls and reversals

The Cooperation Ladder: Scale-dependent payoffs and population dynamics create surges, stalls and reversals | bioRxiv Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results The Cooperation Ladder: Scale-dependent payoffs and population dynamics create surges, stalls and reversals View ORCID Profile Eric Schnell , View ORCID Profile Robin Schimmelpfennig , View ORCID Profile Michael Muthukrishna doi: https://doi.org/10.1101/2021.02.19.432029 Eric Schnell 1 Department of Psychological and Behavioural Science, London School of Economics and Political Science Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Eric Schnell For correspondence: e.r.schnell{at}lse.ac.uk Robin Schimmelpfennig 2 Center for Humans and Machine, Max Planck Institute for Human Development Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Robin Schimmelpfennig Michael Muthukrishna 1 Department of Psychological and Behavioural Science, London School of Economics and Political Science 3 Department of Psychology, New York University Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Michael Muthukrishna Abstract Full Text Info/History Metrics Supplementary material Preview PDF Abstract Human societies have expanded from small bands to large nation-states over the past 12,000 years. Yet, how groups scale up cooperation and why cooperation varies widely between societies, remains a central puzzle. We present a theoretical model that addresses these puzzles by extending the classic Stag Hunt game to (a) multiple players, (b) multiple rewards (“stags”) of different sizes, and (c) endogenous population growth. This framework reveals a “cooperation ladder” where each rung corresponds to a reward that requires a threshold number of cooperators. As cooperation increases, larger rewards become attainable. Securing a larger reward raises carrying capacity (e.g. by providing more food or energy), enabling subsequent population growth and unlocking the possibility of further cooperative gains. However, between these thresholds, cooperation can stagnate or reverse, effectively incentivizing free-riders at intermediate levels. We show that history matters. Early cooperation and population growth can set groups on divergent, path-dependent trajectories. Our model predicts multiple stable equilibria, with surges in cooperation when a new threshold is within reach, and stalls when higher rewards seem unattainable. This framework helps explain key patterns including why cooperation can sometimes accelerate rapidly, why some societies get stuck at smaller scales, and how seemingly selfish behavior can persist in cooperative groups. Expanding the scale of cooperation may depend on how incentives correspond to both environmental conditions, existing levels of cooperation, and population dynamics, offering a new lens on historical transitions in social complexity and insights for modern coordination challenges such as climate change. Significance Statement Small groups can sometimes grow into large-scale cooperative societies, while other societies stagnate at smaller scales. Our theoretical model reveals that population growth and cooperative thresholds for accessing resources or energy create a “cooperation ladder.” As a group’s population increases, new larger-scale payoffs become attainable, which in turn fuels further growth. However, between these critical thresholds, cooperation tends to stall and some free-riding is tolerated. This mechanism offers a new explanation for historical bursts in population and cooperation (such as the agricultural and Industrial revolutions), why some societies remain small, and how selfish behavior can persist in cooperative groups. It also provides insights into global coordination challenges like climate change by highlighting the material conditions needed to sustain and expand large-scale cooperation. Competing Interest Statement The authors have declared no competing interest. Footnotes The manuscript has been revised to update the text, figures, and the appendix. The results of the manuscript remain the same as before. These changes reflect the version of the manuscript being submitted for publication. Copyright The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license . Back to top Previous Next Posted March 16, 2026. Download PDF Supplementary Material Email Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. 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