This study developed a multi-level evolutionary model of pre-industrial agricultural societies to simulate the evolution of family systems and determine how each adapts to environmental conditions and forms a characteristic socio-economic structure. The model shows four basic family systems emerge (nuclear or extended, with equal or biased inheritance), depending on land resources and societal pressures. Analysis reveals higher poverty in extended families and accelerated wealth accumulation in families with biased inheritance. Empirical data verifies the model's predictions on environmental conditions, family systems, and socio-economic structures.

Kenji Itao, Kunihiko Kaneko