July 18, 2019 | News | New Publication

Fertility in the Global South: Decline not equally pronounced across regions

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How have birth rates in urban and rural areas developed in countries of the Global South? Mathias Lerch discusses the similarities and differences he identified in his PLOS ONE article just published.

“In rural areas it usually takes a little longer for birth rates to fall during demographic transition, especially in Sub-Saharan Africa,” says Mathias Lerch, Deputy Head of the Fertility and Well-Being Laboratory at the Max Planck Institute for Demographic Research (MPIDR) in Rostock.

A population’s fertility and mortality are constantly changing. The theory of demographic transition identifies regularities therein and describes the process of development. The transition sets in when mortality falls as the population lives longer, the result of sanitary and medical progress. Because the birth rate often remains high for some time, the population grows rapidly.

As soon as the population has adapted its reproductive behaviors to the new circumstances, fewer children are born, thus fertility decreases. When the population grows no further, the demographic transition ends. Countries of the Western world went through this development during 19th- and 20th-century industrialization.

In the countries of the Global South, mortality rates fell rapidly in the 1950s, but fertility started to decline at different points in time from region to region. The decline began in Latin America and Asia in the 1960s and 1970s, in Sub-Saharan Africa it set in as late as in the past 30 years.

Accurate comparison reveals regularities

Mathias Lerch took a detailed look at the falling birth rate for 60 countries of the Global South, divided into four regions. He looked at the ratio of fertility in urban and rural areas over time, based on data from the "World Fertility Surveys (WFS)" and the "Demographic and Health Surveys (DHS)" as well as publicly available samples from census data (IPUMS). Notably, Lerch compared the data of the individual countries on corresponding phases of demographic transition rather than on historically identical time periods. "This way, we do not compare apples with oranges and can better identify regularities in this process," says Lerch.

Lerch found that the trends in fertility decline in the countries of North Africa, the Middle East, and Latin America are similar: Fertility falls first in the cities, but little more than ten years later the same process starts in the rural regions.

Only in rural Sub-Saharan Africa does fertility develop differently: It takes about 20 years to adapt to the trend of having fewer children. Once the process begins, the birth rate falls more slowly than in the cities of Sub-Saharan Africa or other rural regions of the world.

Better forecasts thanks to more accurate fertility rates

Asian countries deviate from the usual regularities, too: Fertility in the cities and in the countryside declined almost at the same time and at the same rate. This lead to the fastest demographic transition in the world.

Lerch will study the explanations for these atypical trends in his future work. But he emphasizes: "If we know more about the differences between urban and rural fertility, we can also make better predictions about population trends." This is important because the crucial population developments of the 21st century would take place almost exclusively in the cities of the Global South.

Original Publication

Lerch, M.: Regional variations in the rural-urban fertility gradient in the Global South. PLOS ONE (2019) DOI: 10.1371/journal.pone.0219624


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The Max Planck Institute for Demographic Research (MPIDR) in Rostock is one of the leading demographic research centers in the world. It's part of the Max Planck Society, the internationally renowned German research society.