Abstract
One of the central puzzles in the study of sociocultural evolution is how and why transitionsfrom 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 understand-ing the ecological dynamics of small and large-scale human groups. By analogy with theinteractions between single-celled and multicellular organisms, we build a theory of grouplifecycles 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, andlarge-scale groups become larger in size and fewer in number over time. Demographic andexpansion behaviours of groups are largely influenced by the distribution and availability ofresources. Our results conform to a pattern of human political change in which religions andnation states come to be represented by a few large units and many smaller ones. Futureenhancements of the model should include decision-making rules and probabilities of frag-mentation for large-scale societies. We suggest that the synthesis of population ecologyand social evolution will generate increasingly plausible models of human group dynamics.