Achieving sustainable population: Fertility decline in many developing countries follows modern contraception, not economic growth

The human population is projected to increase by 2.4 billion to 2100, endangering, for example, food security and biodiversity. Population growth depends strongly on fertility level, lowering of which is often assumed to depend on economic growth. Here we test this hypothesis using data from 136 developing countries, 1970–2014. We formed four country groups at different initial economy, and used graphical analyses, with estimates of variation. Falling fertility rates 1970–2000 showed little or no association with economy (GDP or household consumption). Fertility decreased regardless of whether the economy grew, was stagnant, or declined. But falling fertility was closely associated with increasing use of modern contraception, which was largely independent of changes in economy. Fertility decline hence was not caused by economic development, but followed contraceptive use. Family planning programs, with advice on family size and modern contraception, offer promising routes to sustainably low fertility where it has not yet been achieved.