A conceptual guide to studying multilevel societies

Ettore Camerlenghi, Cyril C. Grueter, Andrea B. Migliano, Elva J.H. Robinson, Julia Fischer, Danai Papageorgiou, Mauricio Cantor, Samuele Ramellini, Lisa Ohrndorf, Dietmar Zinner, Damien R. Farine

1. Multilevel societies—social systems composed of multiple nested social units—have long intrigued scholars in anthropology, behavioral ecology, and evolutionary biology. Classically described in mammals, new evidence shows that multilevel societies are more widespread across taxa than previously acknowledged, raising both conceptual and methodological challenges for comparative research. 2. We propose a taxonomically-inclusive framework for detecting and studying multilevel societies, expanding on the existing definitions to accommodate diverse life histories, seasonal dynamics, and levels of spatial cohesion. The proposed refined criteria consist of a core social unit, temporal stability in group membership, and consistent inter-unit relationships that together form higher social levels within a larger social entity. 3. We synthesize current evidence for multilevel societies in mammals, birds, fish, and insects and demonstrate underappreciated or newly discovered cases—e.g., polydomous ant colonies and seasonal associations in cooperative birds—that meet the criteria for multilevel societies. We also present diagnostic field signatures that can guide early-stage detection of multilevel sociality in under-studied populations, while emphasizing the importance of maintaining definitional rigor to avoid diluting the concept. 4. We offer detailed guidance for how to measure and validate multilevel societies using social network analysis, spatial data, and stability metrics. We suggest approaches to help navigate challenges in conflating social systems and spatial overlap, and describe experimental, modeling, and comparative procedures for testing hypotheses on the function and evolution of multilevel societies. 5. By sharpening definitions, outlining sound empirical approaches, and broadening the theoretical scope and the conceptual toolkit for identifying for multilevel social systems this synthesis aims to foster more consistent and systematic cross-taxonomic social comparisons. A better understanding of the drivers and variation of multilevel societies will shed light on the evolutionary mechanisms that underlie animal sociality more broadly, while offering novel avenues for testing general principles of collective behavior, cooperation, and social complexity.