Whether the population tends towards a long-run stationary value
depends on forces of demographic convergence. One such force is the
result of fertility rates being negatively affected by population
density. We test the existence of such an effect in 44 developing
countries, matching georeferenced data from the Demographic and
Health Surveys for half a million women with population density
grids. We find a causal relationship from population density to
fertility such that a rise in density from 10 to 1,000 inhabitants
per square kilometer corresponds to a decrease in fertility of
about 0.7 children. The corresponding half-life for population
dynamics is of the order of four-five generations.