The Hypothesis of the Mobility Transition

OCIAL scientists are guided in their gropings toward pattern and regularity in human activities by their small hoard of paradigms. In the fields of geography and demography, such broad intellectual designs have been especially scarce.' Indeed, there are probably no more than three major geographical paradigms in active use today. The first, which might be called the geographic axiom, so basic and instinctive as to be seldom articulated, is the conviction that there is genuine significance in the spatial patterning of physical and social events on and near the surface of the earth. Next is the notion of the spatial diffusion of innovations, sired jointly by anthropologists and geographers and recently explored with highly interesting results. Finally, geographers have borrowed the principle of least effort, or economic optimization, from economists and have grafted it onto the geographic axiom. This hybridization has spawned a number of hypotheses concerning the territorial arrangement of economic and related activities. In demography we can discern only twNo such axiomatic items: the theory of the demographic transition and the so-called laws of migration. The first is the assertion that, on attaining certain thresholds of socioeconomic development, every community will pass from a premodern near-equilibrium, in which high levels of mortality tend to cancel out high levels of fertility, to a modern near-equilibrium, in which low fertility almost matches low mortality but with the decline in births lagging far enough behind the decline in deaths to ensure a substantial growth in numbers during the transitional phase.2 The laws of migration, first enunciated by Ravenstein in 1885, later modified by Thomas and Stouffer, and most recently improved and codified