Towards a formal theory for the evolution of human social complexity: report on a workshop


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When we launched the Social Evolution Forum a few months ago, one of our declared goals was to advertise future conferences and workshops and publish reports on completed ones. Today we begin to deliver on this promise with a report on the investigative workshop on social evolution theory that took place at NIMBioS last month. Comments are welcome from both participants and other interested parties.

NIMBioS Investigative Workshop
Towards a formal theory for the evolution of human social complexity
February 6-8, 2012; Knoxville, TN

Peter Turchin, Univ. of Connecticut
Laura Fortunato, Santa Fe Institute
Sergey Gavrilets, Univ. of Tennessee

National Institute for Mathematical and Biological Synthesis

Background. The great majority of humans today live in complex societies, which can exist only on a basis of extensive cooperation among large numbers of individuals. Ultrasociality, the ability of humans to cooperate in large groups of genetically unrelated individuals, presents a puzzle to both evolutionary and social theory. Its emergence likely involved the evolution of cooperation in small groups, characterized by an egalitarian social structure, followed by a reversal of this trend starting around 5–10 kya, with the rise of the first nonegalitarian complex societies. Theories to explain how complex societies evolved span the biological, social, and historical sciences, but they largely rely on verbal reasoning: until recently, formal models have focused on the evolution of cooperation in small groups, while the transition from small- to large-scale societies has been mostly neglected.

Objectives. The aim of this workshop was to bring together a diverse group of modelers with anthropologists, archaeologists, and other social scientists to (i) synthesize the state of knowledge in formal models of the evolution of social complexity, (ii) identify unresolved issues, and (iii) set an agenda for future collaborative work. The workshop was organized around the following general themes: What theories and data are available? What are the empirical patterns that cannot be explained by the existing theories and data? How can we adapt existing models to make full use of the available data? What kinds of data are needed to better inform the models? What new modeling techniques and methods need to be developed?


The workshop started with a brief discussion of general goals and some conceptual issues, followed by five half-day sessions, each dealing with one of the general themes specified in the proposal.

Session 1 focused on general patterns in the transition from small- to large-scale societies. Specific topics addressed were (i) the growth in the information-processing capacity of human beings, both individually and in groups, and how that could drive the evolution of social complexity; (ii) the driving forces and constraints in the evolution of archaic states with an emphasis on “pristine” states; and (iii) effects of population growth after the Neolithic transition on the evolution of hierarchic leadership and increasing scale of public goods provision.

The discussion focused on general patterns associated with growing social complexity: increasing population density and size of sociopolitical groups; emergence of permanent leaders; evidence for public goods; and increasing formalization of social institutions. Other patterns and process discussed were: cross-generation transmission of wealth; the scale of “emotive participatory rituals” (measured by the area of public spaces where they could take place); spatial scale and magnitude of taxation; differentiation of functions within a society; trends in the welfare of nonelites. Key issues involved in the transition to complex societies are: How is trust maintained and how does this interact with scale? How is social alignment and coordination achieved? What are the effects of variability in production and distribution (inicluding role of climates at various temporal scales)? What are the rate constraints in these processes? What is the balance of scales (levels) of selection (in a multilevel set-up)? What are the mechanisms of cultural groups selection – conflict with “outside” groups? Attrition by “voting with feet”?

Session 2 dealt with general theories of growth of social complexity. Presentations (i) reviewed the state of theory starting from the nineteenth century evolutionists, (ii) discussed the roles of warfare, bureaucracy, and the applicability of population ecology methods, and (iii) examined theoretical explanations of cyclicity in the evolution of societies.

The discussion continued with a focus on general patterns associated with state emergence, but also began to engage with mechanisms that could explain these patterns. Specific issues included: continuity versus discontinuity in the emergence of states (including the possibility of multiple dynamic equilibria and transitional phases); unicentric versus polycentric systems (also ideological versus political unity). There was an intense discussion of issues involved in cultural group selection, including differences between biological and cultural modes (and coevolution of these modes); transition from initial sociality (small-scale, “simple”) to complexity; dynamic roles of boundaries. Other questions discussed were: How does bureaucracy get larger and change? What is the role of variations in bureaucratic strategies? Resistance against bureaucratic control? Do we need different models for the emergence of “pristine” (primary) and secondary states?

Session 3 summarized a variety of mathematical modeling techniques used for studying the evolution of social complexity. It also included several presentations with novel modeling developments focusing on the emergence of leadership, evolution of languages, cooperation and warfare.

The discussion centered on what mechanisms and processes need to be modeled. Proposals included: dynamics of polity size and complexity; ethnic markers and cultural boundaries; social stratification; cultural evolution and learning; and cooperation, altruism, group selection, kinship. General processes included: yielding autonomy for gains in group/polity size/power; creating norms and institutions that alter individual (or subgroup) payoffs to favor increasing complexity. There was a substantial degree of consensus on the most important modeling goals: articulating spatial models into a coherent theory that can span a range of social systems; identifying institutions and mechanisms involved in each move “up” the scale (e.g., from chiefdoms to complex chiefdoms, then to archaic states, etc); linking social evolution to evolved (human) psychology; determining how material constraints shape evolution of social complexity.

Session 4 focused on the data available to inform theoretical models of the emergence of human social complexity and test their predictions. Two of the presentations related to available cross-cultural archaeological, historical, and ethnographic data; the other three related to data from field-based projects with small-scale populations in Bolivia, Kenya, and India.

The session concluded with a general discussion of issues raised by the presentations. Topics addressed during the discussion session include:

  • how to map cultural variation at all scales, from the level of households all the way up to the level of large-scale societies?
  • how to link rates of change in the frequency of cultural variants to explanatory models?
  • is the analogy of cultural relatedness to kin relatedness a useful approach?
  • what is the effect of migration on changes in social complexity?
  • what pattern will cultural group selection leave at the macro-evolutionary (i.e. cross-cultural) level?
  • can we trace the changes in social complexity with data on institutional change (e.g. legal codes), from which to derive proxies for group effectiveness?

Session 5 discussed possible approaches to integrating theories, models, statistical methods, and data. Talks focused on linking dynamic models to data; evolution of capacity for social complexity in deep human history, and the role of phylogenetic methods. The last talk summarized the state of knowledge in the field of multilevel evolution.

The discussion focused on activities after the workshop. The group discussed specific initiatives by workshop participants to develop models and databases; how our efforts can be better integrated; how graduate students could be involved; and plans for future working groups (at NIMBioS and elsewhere).

Public Session. After the conclusion of the workshop several participants took part in a public debate on the role of warfare in the evolution of early social complexity, which generated a lot of interest on campus, drawing on the order of 100 participants.

Background: In the last 10,000 years, human societies have evolved from highly egalitarian bands of a few dozen people to the huge societies of today with great economic and social divisions, thousands of professions, and elaborate governing structures. How this transition occurred is one of the greatest puzzles in science. To throw some light on this fascinating topic, NIMBioS hosted a debate, focusing on the role of warfare in explaining the transition from simple to complex societies.

Thesis: Warfare has transformed us from living in villages to living in huge states, building cities and civilizations, and ultimately making our lives more peaceful.

Antithesis: Warfare is an unfortunate side-effect of the evolution of social complexity, but it was other evolutionary mechanisms that resulted in highly complex human societies.

For the thesis: Peter Turchin (University of Connecticut), Jeremy Sabloff (Santa Fe Institute)

For the antithesis: Sander van der Leeuw (Arizona State University), Tim Kohler (Washington State University)

Laura Fortunato (Santa Fe Institute), Sergey Gavrilets (NIMBioS)

To find out more about the debate and a link to view it, click here.

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