title: A Life-Cycle Model of Human Social Groups Produces a U-Shaped Distribution in Group Size.
abstract: One of the central puzzles in the study of sociocultural evolution is how and why transitions from small-scale human groups to large-scale, hierarchically more complex ones occurred. Here we develop a spatially explicit agent-based model as a first step towards understanding the ecological dynamics of small and large-scale human groups. By analogy with the interactions between single-celled and multicellular organisms, we build a theory of group lifecycles as an emergent property of single cell demographic and expansion behaviours. We find that once the transition from small-scale to large-scale groups occurs, a few large-scale groups continue expanding while small-scale groups gradually become scarcer, and large-scale groups become larger in size and fewer in number over time. Demographic and expansion behaviours of groups are largely influenced by the distribution and availability of resources. Our results conform to a pattern of human political change in which religions and nation states come to be represented by a few large units and many smaller ones. Future enhancements of the model should include decision-making rules and probabilities of fragmentation for large-scale societies. We suggest that the synthesis of population ecology and social evolution will generate increasingly plausible models of human group dynamics.
authors.affiliation: Institut des Sciences de l'Evolution, Université de Montpellier, Place E Bataillon, 34095, Montpellier, Cedex 5, France; Department of Anthropology, University College London, 14 Taviton Street, London, WC1H 0BW, United Kingdom.
authors.forename: Gul Deniz
authors.initials: GD
authors.lastname: Salali
authors.affiliation: Institute of Cognitive and Evolutionary Anthropology, University of Oxford, Oxford, OX2 6PN, United Kingdom.
authors.forename: Harvey
authors.initials: H
authors.lastname: Whitehouse
authors.affiliation: Institut des Sciences de l'Evolution, Université de Montpellier, Place E Bataillon, 34095, Montpellier, Cedex 5, France; Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico, 87501, United States of America.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hochberg
mesh_terms: D003468:Cultural Evolution; D006126:Group Processes; D006801:Humans; D008962:Models, Theoretical; D012919:Social Behavior; D012931:Social Environment