Agent-Based Geosimulation of Yayoi Period Population Dynamics in Kyushu, Japan

Current scholarship in Japanese archaeology recognizes the people and culture of the Yayoi period as being descended from both continental migrants (Toraijin) and the native inhabitants (Jomon people). However, the number of migrants that came to Japan and the degree to which they were directly responsible for the development of Yayoi culture is a topic of debate. Using northern Kyushu as a case study, the author employs an agent-based simulation based on geospatial data to model the spread of population, rice agriculture, and continental genetics during the Early Yayoi period. Multiple simulations are performed with varying parameters related to migrant population size, marriage customs, and the ratio of men to women amongst migrants to test their effect on the demographics of the Yayoi period. Simulation results were compared to population estimates and the distribution of mitochondrial DNA in order to determine their validity. Experiment 1 showed that the average number of continental migrants was likely in the order of magnitude of 10s of people per year (approx. 40 to 50) during the first 500 years of the Yayoi period. Experiment 2 demonstrated that polygyny can lead to increased population growth and aids in the spread of continental genetics, but without more rigorous evaluation criteria it is difficult to conclude whether it was practiced during the period. The methods used in this study demonstrate how agent-based simulations can model realistically sized populations moving through geographic space by basing simulation inputs on geospatial data and population estimates.