Proceedings of the Royal Society B: Biological Sciences
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The complex structure of hunter–gatherer social networks

Marcus J Hamilton

Marcus J Hamilton

Department of Anthropology, University of New MexicoAlbuquerque, NM 87131, USA

[email protected]

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,
Bruce T Milne

Bruce T Milne

Department of Biology, University of New MexicoAlbuquerque, NM 87131, USA

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,
Robert S Walker

Robert S Walker

Department of Anthropology, University of Colorado at Denver and Health Sciences CenterDenver, CO 80217, USA

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Oskar Burger

Oskar Burger

Department of Anthropology, University of New MexicoAlbuquerque, NM 87131, USA

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and
James H Brown

James H Brown

Department of Biology, University of New MexicoAlbuquerque, NM 87131, USA

Santa Fe Institute, 1399 Hyde Park RoadSanta Fe, NM 87501, USA

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    In nature, many different types of complex system form hierarchical, self-similar or fractal-like structures that have evolved to maximize internal efficiency. In this paper, we ask whether hunter-gatherer societies show similar structural properties. We use fractal network theory to analyse the statistical structure of 1189 social groups in 339 hunter-gatherer societies from a published compilation of ethnographies. We show that population structure is indeed self-similar or fractal-like with the number of individuals or groups belonging to each successively higher level of organization exhibiting a constant ratio close to 4. Further, despite the wide ecological, cultural and historical diversity of hunter-gatherer societies, this remarkable self-similarity holds both within and across cultures and continents. We show that the branching ratio is related to density-dependent reproduction in complex environments and hypothesize that the general pattern of hierarchical organization reflects the self-similar properties of the networks and the underlying cohesive and disruptive forces that govern the flow of material resources, genes and non-genetic information within and between social groups. Our results offer insight into the energetics of human sociality and suggest that human social networks self-organize in response to similar optimization principles found behind the formation of many complex systems in nature.

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    Figure 1 and paragraph 3 of page 2 are now presented in the correct form.

    10 July 2007

    Notice of correction