Social networks show striking structural regularities1,2, and both theory and evidence suggest that networks may have facilitated the development of large-scale cooperation in humans3,4,5,6,7. Here, we characterize the social networks of the Hadza, a population of hunter-gatherers in Tanzania8. We show that Hadza networks have important properties also seen in modernized social networks, including a skewed degree distribution, degree assortativity, transitivity, reciprocity, geographic decay and homophily. We demonstrate that Hadza camps exhibit high between-group and low within-group variation in public goods game donations. Network ties are also more likely between people who give the same amount, and the similarity in cooperative behaviour extends up to two degrees of separation. Social distance appears to be as important as genetic relatedness and physical proximity in explaining assortativity in cooperation. Our results suggest that certain elements of social network structure may have been present at an early point in human history. Also, early humans may have formed ties with both kin and non-kin, based in part on their tendency to cooperate. Social networks may thus have contributed to the emergence of cooperation.
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This work was supported by grant P01-AG031093 from the National Institute on Aging and by the Science of Generosity Initiative of the University of Notre Dame (supported by the John Templeton Foundation). We are grateful for comments from S. Bowles, D. Eisenberg, F. Fu, H. Gintis, J. Henrich, P. Hooper, D. Hruschka, M. Nowak, D. Rand, P. Richerson and C. Tarnita. We thank A. Mabulla, I. Mabulla, M. Peterson, C. Bauchner and L. Meneades for help with data collection and preparation. We are grateful to D. Stafford and A. Hughes for sharing data regarding two villages in Honduras, as used in the Supplementary Information.
The authors declare no competing financial interests.
This file contains Supplementary Methods, Supplementary Statistics and Results, Supplementary Tables 1-51, Supplementary Figures 1-13 with legends and Supplementary References. (PDF 9453 kb)
This file contains a 3-D movie of the male and female campmate social networks - see page 9 of the Supplementary Information file for full legend. (MOV 13586 kb)
This file contains a 3-D movie of the male and female campmate social networks - see page 9 of the Supplementary Information file for full legend. (MOV 13944 kb)
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Apicella, C., Marlowe, F., Fowler, J. et al. Social networks and cooperation in hunter-gatherers. Nature 481, 497–501 (2012). https://doi.org/10.1038/nature10736
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