A dynamic model of human dispersal in a land-based economy

This paper presents a dynamic state variable model that examines human disp ersal in a land-based economy. In humans, like other animals, many individu als disperse during their lifetimes, with extensive variability in the timi ng and likelihood of dispersal by individuals of different slates. The mode l places human and non-human dispersal in a common framework, specifically by utilizing a cost-benefit approach. As with other animals, individual acc ess to resources likely plays an important rule in shaping human dispersal, and the model explores the mechanisms underlying this relationship. Over a series of time steps, individuals must decide whether to stay in their nat al area or disperse, given their states (wealth, marital, and inheritance s tatus) and the environmental constraints on dispersal. Costs of dispersal i nclude time and an initial drop in wealth, while the benefit is the potenti al of the dispersal area to increase wealth. The model determines whether d ispersing or staying results in the highest fitness, where fitness is a fun ction of individual wealth and years married. The model shows that dispersa l is favorable under a wide range of environmental conditions, but: that it also varies predictably according to individual states. Men of middle weal th values disperse under a wider variety of circumstances than poorer or we althier men. Wealthy men, who are particularly sensitive to the time cost a nd mortality risk associated with dispersing, appear to adopt a more conser vative dispersal strategy than poorer men, who are more sensitive to the we alth cost and wealth growth rate associated with dispersing. Dispersal beha vior is also contingent on its effects on an individual's probability of ma rrying or inheriting wealth. Finally, the model fosters an examination of h ow the interaction of life events, and their directions of causation, can b e studied.