Kinship, Distance, and Reciprocity Underpin Economic Support in the Pantanal Wetland

Abstract The behavioural phenomenon of cooperation has been a focus of study in a variety of disciplines. Evolutionary anthropologists often use quantitative methods to test hypotheses on cooperation, grounded in theories such as kinship and reciprocal altruism: people are more likely to help those to whom they are related and who repay the cost of the altruistic act. That said, empirical results are somewhat mixed; numerous factors may cause social structures to vary across contexts. Here, we advance this line of inquiry in an underexplored freshwater fishery of the 179 300 km 2 Pantanal region in Brazil. In doing so, we examine the underlying structures of sociality within an economic-based support system at the household level ( ). Exponential random graph models reveal that households tend to engage in support with kin, nearby neighbours and reciprocal partners across the network. These results affirm longstanding evolutionary theories of cooperation while challenging preconceived assumptions regarding wealth differentials in offering and requesting aid; they may also inform debates on inequitable nature-based solutions in conservation, the practical implications of which could lead to better-adapted local policy interventions and feedback to communities to support regional initiatives.