1 1 Inter-ethnic Interaction, Strategic Bargaining Power, and the Dynamics of 2 Cultural Norms: A Field Study in an Amazonian Population 3 4 John Andrew Bunce1,2,3 and Richard McElreath1,2 5 6 1Department of Human Behavior, Ecology, and Culture, Max Planck Institute for Evolutionary 7 Anthropology, Leipzig, Germany 8 2Department of Anthropology, University of California, Davis, CA USA 9 3Department of Anthropology, Indiana University, Bloomington, IN USA 10 11 Corresponding author: John Andrew Bunce (tel: +49 341 3550 347, email: 12
[email protected]) 13 14 ORCID 15 John Andrew Bunce: 0000-0003-4092-485X 16 Richard McElreath: 0000-0002-0387-5377 17 18 In press in Human Nature 2 19 ABSTRACT 20 Ethnic groups are universal and unique to human societies. Such groups sometimes have 21 norms of behavior that are adaptively linked to their social and ecological circumstances, and 22 ethnic boundaries may function to protect that variation from erosion by inter-ethnic interaction. 23 However, such interaction is often frequent and voluntary, suggesting that individuals may be 24 able to strategically reduce its costs, allowing adaptive cultural variation to persist in spite of 25 interaction with out-groups with different norms. We examine five mechanisms influencing the 26 dynamics of ethnically-distinct cultural norms, each focused on strategic individual-level choices 27 in inter-ethnic interaction: bargaining, interaction frequency-biased norm adoption, assortment 28 on norms, success-biased inter-ethnic social learning, and childhood socialization. We use 29 Bayesian item response models to analyze patterns of norm variation and inter-ethnic interaction 30 in an ethnically-structured Amazonian population.