TY - JOUR
T1 - Hunter-Gatherers Maintain Assortativity in Cooperation despite High Levels of Residential Change and Mixing
AU - Smith, Kristopher M.
AU - Larroucau, Tomás
AU - Mabulla, Ibrahim A.
AU - Apicella, Coren L.
N1 - Funding Information:
Support comes from the University of Pennsylvania, National Institute on Aging ( P01-AG031093 ), The Science of Generosity Initiative of the University of Notre Dame (supported by the John Templeton Foundation), Canadian Social Sciences and Humanities Research Council , and The Beacon Project at Wake Forest University (supported by the Templeton Religion Trust). We thank Nicholas Christakis, Joseph Henrich, James Fowler, Pat Barclay, and reviewers for feedback, and we thank Hadza participants.
Publisher Copyright:
© 2018 Elsevier Ltd
PY - 2018/10/8
Y1 - 2018/10/8
N2 - Widespread cooperation is a defining feature of human societies from hunter-gatherer bands to nation states [1, 2], but explaining its evolution remains a challenge. Although positive assortment of cooperators is recognized as a basic requirement for the evolution of cooperation, the mechanisms governing assortment are debated. Moreover, the social structure of modern hunter-gatherers, characterized by high mobility, residential mixing, and low genetic relatedness [3], undermines assortment and adds to the puzzle of how cooperation evolved. Here, we analyze four years of data (2010, 2013, 2014, 2016) tracking residence and levels of cooperation elicited from a public goods game in Hadza hunter-gatherers of Tanzania. Data were collected from 56 camps, comprising 383 unique individuals, 137 of whom we have data for two or more years. Despite significant residential mixing, we observe a robust pattern of assortment that is necessary for cooperation to evolve; in every year, Hadza camps exhibit high between-camp and low within-camp variation in cooperation. We find little evidence that cooperative behavior within individuals is stable over time or that similarity in cooperation between dyads predicts their future cohabitation. Both sets of findings are inconsistent with models that assume stable cooperative and selfish types, including partner choice models. Consistent with social norms, culture, and reciprocity theories, the strongest predictor of an individual's level of cooperation is the mean cooperation of their current campmates. These findings underscore the adaptive nature of human cooperation—particularly its responsiveness to social contexts—as a feature that is important in generating the assortment necessary for cooperation to evolve. For cooperation to evolve, cooperators must interact with other cooperators. Smith et al. use panel data from a population of extant hunter-gatherers to show how assortativity in cooperation is maintained.
AB - Widespread cooperation is a defining feature of human societies from hunter-gatherer bands to nation states [1, 2], but explaining its evolution remains a challenge. Although positive assortment of cooperators is recognized as a basic requirement for the evolution of cooperation, the mechanisms governing assortment are debated. Moreover, the social structure of modern hunter-gatherers, characterized by high mobility, residential mixing, and low genetic relatedness [3], undermines assortment and adds to the puzzle of how cooperation evolved. Here, we analyze four years of data (2010, 2013, 2014, 2016) tracking residence and levels of cooperation elicited from a public goods game in Hadza hunter-gatherers of Tanzania. Data were collected from 56 camps, comprising 383 unique individuals, 137 of whom we have data for two or more years. Despite significant residential mixing, we observe a robust pattern of assortment that is necessary for cooperation to evolve; in every year, Hadza camps exhibit high between-camp and low within-camp variation in cooperation. We find little evidence that cooperative behavior within individuals is stable over time or that similarity in cooperation between dyads predicts their future cohabitation. Both sets of findings are inconsistent with models that assume stable cooperative and selfish types, including partner choice models. Consistent with social norms, culture, and reciprocity theories, the strongest predictor of an individual's level of cooperation is the mean cooperation of their current campmates. These findings underscore the adaptive nature of human cooperation—particularly its responsiveness to social contexts—as a feature that is important in generating the assortment necessary for cooperation to evolve. For cooperation to evolve, cooperators must interact with other cooperators. Smith et al. use panel data from a population of extant hunter-gatherers to show how assortativity in cooperation is maintained.
KW - evolution of cooperation
KW - homophily
KW - hunter-gatherers
KW - partner choice
KW - social influence
KW - social norms
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U2 - 10.1016/j.cub.2018.07.064
DO - 10.1016/j.cub.2018.07.064
M3 - Article
C2 - 30245106
AN - SCOPUS:85054157753
SN - 0960-9822
VL - 28
SP - 3152-3157.e4
JO - Current Biology
JF - Current Biology
IS - 19
ER -