, Volume 14, Issue 1, pp 53-72

Social network size in humans

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This paper examines social network size in contemporary Western society based on the exchange of Christmas cards. Maximum network size averaged 153.5 individuals, with a mean network size of 124.9 for those individuals explicitly contacted; these values are remarkably close to the group size of 150 predicted for humans on the basis of the size of their neocortex. Age, household type, and the relationship to the individual influence network structure, although the proportion of kin remained relatively constant at around 21%. Frequency of contact between network members was primarily determined by two classes of variable: passive factors (distance, work colleague, overseas) and active factors (emotional closeness, genetic relatedness). Controlling for the influence of passive factors on contact rates allowed the hierarchical structure of human social groups to be delimited. These findings suggest that there may be cognitive constraints on network size.

This project was funded by a grant from Hewlett Packard Research Laboratories (Bristol) and the Economic and Social Research Council (ESRC). The support of the ESRC is gratefully acknowledged. This work was part of the programme of the ESRC Research Centre for Economic Learning and Social Evolution (ELSE).
Russell Hill (B.Sc., M.Phil, Ph.D.) is an Addison Wheeler Research Fellow at the University of Durham. His main research interests are in the evolution of mammalian social systems. Robin Dunbar (B.A., Ph.D.) is a professor of evolutionary psychology at the University of Liverpool. His research interests span mammalian behavioral ecology, including humans, cognitive mechanisms, and Darwinian psychology.