India and Niger do not belong in one demographic category simply because both are less affluent than Western Europe. The phrase “developing world” conceals places that have already moved below replacement, places close to it, and places where families still average four or more children.
India shows how quickly the old map can change. Its 2019–21 National Family Health Survey estimated a national TFR of 2.0. The country can continue growing because it has a vast young population, not because current fertility remains high everywhere. The same survey found a range from 3.0 in Bihar to 1.1 in Sikkim. India’s demographic future is the sum of transitions already at different stages within one country.
Latin America moved from high fertility to low fertility in a few generations. Mexico’s 2023 estimate was 1.6. Brazil, Chile, Colombia, and Uruguay also sit below replacement in the UN’s 2024 estimates. The region is younger than Europe, but its window between falling fertility and intensive aging is narrower than Europe’s was.
Northern Africa and Western Asia resist one story. Fertility has fallen sharply in Iran and Turkey, while Yemen remained above four in 2024. Income and religion do not fix one family size, and political boundaries group populations with different marriage, education, health, and migration patterns.
Where high fertility remains
The largest concentration of high fertility is now in sub-Saharan Africa. Of the 63 countries and areas the United Nations expects to reach low fertility only after 2054, 42 are in that region. Together, the full group contained about 1.8 billion people in 2024. Their average TFR fell from 5.9 in 1994 to 4.1 in 2024, so continued growth and fertility decline are occurring at the same time.
A young age structure with growth already built in Niger’s population by single year of age in 2020. Even a substantial fertility decline would work through the large cohorts approaching adulthood. via Wikimedia Commons
Sub-Saharan Africa is not moving on one clock. Fertility decline began later and has generally proceeded more slowly than it did in Asia and Latin America, especially in Middle and Western Africa. Eastern and Southern Africa have often moved faster. Desired family size, child survival, women’s education, marriage, contraception, urbanization, and the economic role of children differ within the region as they do elsewhere.
The contrast with affluent societies also complicates a common claim about affordability. Children cost money everywhere, but absolute income cannot explain why richer societies so often have fewer of them. The relevant costs include housing, time, foregone earnings, schooling expectations, available kin, and the place children occupy in family and economic life. Chapter 3 will follow those differences more closely.
For the next several decades, much of the world’s growth will come from countries with young populations, particularly in sub-Saharan Africa, while countries elsewhere shrink. That does not place Africa outside the demographic turn. It shows why the turn is uneven: today’s births act through age structures made by yesterday’s births.
That interaction is population momentum. It is the mechanism that lets global growth and national contraction occur together—and that can keep a country shrinking after fertility begins to recover.
Citations
- Government of India, Ministry of Health and Family Welfare, Health and Family Welfare Statistics in India 2023, table C.4.
- Instituto Nacional de Estadística y Geografía, Encuesta Nacional de la Dinámica Demográfica 2023, 2024.
- United Nations, Department of Economic and Social Affairs, Population Division, World Fertility 2024, 2025.