A simulation model for migrations and dispersals of prehistoric human populations.

A new simulation model was constructed to estimate demographic processes of prehistoric human populations who migrated and dispersed, particularly to uninhabited habitats. The characteristics of the simulation model are: the minimum component is an individual with sex and age properties; each individual's death is determined in each year by comparing the age-specific probability of dying and a random number; childbirth of each woman of reproductive age in each year is determined by the age-specific probability of childbirth and a random number; sex ratio at birth is fixed at 1.05, and each newborn baby's sex is determined by a random number; people live in settlements; each settlement is located in a cell on a hexagonal-linkage land and the cells temporarily number 64 (8x8); each cell has its own optimal carrying capacity; and the net reproduction rate (NRR) is used for determining the speed of population increase in each cell. The preliminary trial applied the following conditions: 64 cells, carrying capacity of each cell is 160, age-specific probability of dying was based on the life table of prehistoric Maori in New Zealand (infant mortality rate of 157/1000 and life expectancy of 23.49 years). 500-year-interval changes of the total population of all cells increased almost exponentially to the year 2000 from 346 persons at year 500 to 2208 at year 2000. It gradually increased further and peaked at about 10,000 at the year 5000. By year 8000 all the cells were inhabited with a total population of 10,978. The population in the year 2000 was 27.6 times more than in year zero. The intergenerational interval of 25 years yielded a NRR of 1.042. During the period between the year 2000 and the year 4000 the population increased by 3.42 times corresponding to a NRR of 1.015. After the year 5000 population increase declined to almost zero with a NRR of almost 1.00. Preliminary trials have produced satisfactory results.