Large-Scale Genealogies Distinguish Frontier from Steady-State Internal Migration

Many studies of human migration focus on modern issues such as economics, politics, urbanization, and commuting. Here, we seek foundational patterns by using very large genealogies to measure migration centuries before modern technologies or census data became available. In Europe and North America from 1400 to 1950 we find two distinct patterns of internal lifetime migration: in most locations and eras we find “steady-state” migration with a power–law distribution of migration distance. A very different “frontier” distribution appears suddenly in North America after 1740; it is not a simple power law and has much longer average distances. All datasets (both patterns) are well fit by a three-parameter model; the temporal and geographic patterns of the fitted parameters give new insight to American internal expansion 1620–1950. In addition, we find that frontier migration is highly directional and asymmetric; gravity models do not apply. The American frontier pattern arises from the colonial-era steady-state within two generations, plateaus, and then returns to a more mobile steady-state. This frontier pattern is enabled by large-scale technological or numeric imbalance and geographic opportunity; when these forces abate, a new steady-state begins.