Social Evolution Forum
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Commentary on Dunbar

In “Networking Past and Present” Dunbar offers a brief, but important overview of the importance of understanding the role of complex network structures in all types of human organizations and societies, from the internal substructure of traditional subsistence societies to the frequency of friending on Facebook. Remarkably, the empirical statistical structures of these seemingly very different types of networks are often very similar (Arenas et al. 2004).  Human social networks, and the organizations they form, are commonly 1) modular, in that there is a discrete substructure to the basal units within the network, such as nuclear families in populations, or cliques within friendship networks;  2) hierarchical, in the sense that interactions between individuals occur at multiple levels of social organization; and 3) nested, such that basal modular units are aggregated into larger groups at higher hierarchical levels, facilitating the flows of energy, materials, and information between individuals. These fundamental features of human social networks are in fact fundamental features of all kinds of complex systems in nature (Oltvai & Barabasi 2002; Ravasz & Barabasi 2003), and seem to represent a common solution to the problem of building complex systems by integrating flows over multiple scales of interaction in living systems. Therefore, we might well ask whether it is in fact surprising that there may be general principles that describe how humans organize themselves into groups for mutual benefit across the socioeconomic and cultural evolutionary spectrum. After all, humans across the anthropological spectrum share the same cognitive and communicative abilities, and it is our differential access to technologies that alter the scale over which these basic interactions can occur.

As complex networks are fundamental features of human societies, understanding their ecological and evolutionary dynamics will play a fundamental role in developing a 21st century anthropological science.  This development will require both the inductive, empirical analysis of common patterns that emerge from anthropological, ethnographic, archaeological, and sociological data (such as the origin and potential universality of “Dunbar’s numbers”) and the development of quantitative mechanistic theory to explain how these structures evolved, theory that must be derived from the first principles of physics, chemistry, and biology, and so internally consistent across the sciences. Now that we understand the ubiquity of network structures in human social organization, we need to explore what this means for understanding the ecological and evolutionary dynamics of human systems, and the role of more fundamental scientific processes in these dynamics.

Marcus J. Hamilton
Santa Fe Institute


Arenas, A., Danon, L., Díaz-Guilera, A., Gleiser, P. M. & Guimerá, R. 2004 Community analysis in social networks. European Physical Journal B 38, 373-380.

Oltvai, Z. N. & Barabasi, A.-L. 2002 Life’s Complexity Pyramid. Science 298, 763-764.

Ravasz, E. & Barabasi, A.-L. 2003 Hierarchical organization in complex networks. Physical Review E 67, 026112.


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