Global Population Falling as Human Fertility Declines

Written by Max Roser, University of Oxford

Global human population is on the decline. The fertility of half of the world’s population is already below the replacement ratio, according to a new study from the University of Oxford. The latest facts run counter to the traditional story of an out of control soaring world population.

In a comprehensive data study entitled ‘Fertility’ found in full at OurWorldInData.org researcher Max Roser reports, “The decline of fertility is one of the most fundamental social changes that happened in human history.” He adds, “The richer the people, the lower the fertility.”

Below are selected extracts:

The first chart shows the total fertility rate for the entire world population at 5 different points in time. The total fertility rate is the number of children born per woman. More specifically, it tells you the average number of children that would be born to a woman (who would live until the end of her childbearing years) if she were to experience the exact current age-specific fertility rates through her lifetime.

How to read the following graph: On the x-axis you find the cumulative share of the world population. The countries are ordered along the x-axis descending by the country’s fertility rate. This makes it possible to see the fertility rate for each country, and it is also possible to see which share of the world population had a fertility rate higher than a given level. For the blue line – referring to the latest data (2005-10) – we see that 20% of the world population have a fertility rate of higher than 3.

For 1950-55 (red line), you see that the countries on the very left – Rwanda, Kenya, the Philippines and others that are not labelled – had a fertility rate of more than 7. China had a fertility rate of just over 6 and India a fertility rate of just under 6! On the very right of the red line you see that in 1950-55 there was only one country in the world  with a fertility rate below 2: tiny Luxembourg.

Looking at the orange line, you see that until 1975-80 some countries substantially reduced their fertility: India’s fertility rate fell to a still very high 4.9, and China’s fell to 3. Other countries maintained very high fertility levels. In Yemen, the fertility rate was 8.6 children per woman.

The latest data from the UN refers to 2005-2010. 80% of the world population lives in countries where women have on average fewer than 3 children. The global average fertility rate is 2.5. This means that global fertility is barely higher than the global replacement fertility. The replacement fertility is the total fertility rate at which the population size stays constant. If there were no mortality in the female population until the end of the childbearing years, the replacement fertility would be exactly 2. With the current level of mortality the global replace fertility is 2.3 – the narrow gap between the current global fertility and the global replacement rate means that the increase of the world population is due to the increasing length of life and population momentum.1

We also see convergence in fertility rates: the countries that already had low fertility in the 1950s only slightly decreased fertility, while many of the countries that had the highest fertility back then saw a rapid reduction of the number of children per woman.

Comparing the red, orange and blue lines also makes it possible to see the change in single countries: In Iran, the fertility rate in 1980-85 was 6.3; in the latest data we see that it is down to the level of Sweden: 1.9 children per woman. In Thailand, the fertility rate in 1950-55 was 6.14, in 1980-85 it was 3.92, and today it is 1.49.

In the chart I have also included the projections for the 21st century. The UN – which has a very good track record for its past demographic projections – expects global fertility to fall further in most countries so that the rate will be below 2 by the end of the century.

World population by level of fertility over time, 1950-2050

World population by level of fertility over time, 1950-2050 – Max Roser

Fertility was high in the time before population growth

The table shows that in European countries one woman gave on average birth to 4.5 to 6.2 children in the 18th century. The population of a society does not increase when every woman is replaced on average by two children. As the tables presents fertility rates when the population did not yet grow rapidly we can infer that on average 2.5 to 4.2 children died per woman.

Age of Marriage of Women and Marital Fertility in Europe before 17904
Country or Region Mean age at first marriage Births per married women Percentage never married Total fertility rate
Belgium 24.9 6.8 6.2
France 25.3 6.5 10 5.8
Germany 26.6 5.6 5.1
England 25.2 5.4 12 4.9
Netherlands 26.5 5.4 4.9
Scandinavia 26.1 5.1 14 4.5

Fertility can decline extremely fast

The decline of fertility is one of the most fundamental social changes that happened in human history.

It is therefore especially surprising how very rapidly this transition can indeed happen. As we see from the chart below it took Iran only 10 years for fertility to fall from more than 6 children per woman to fewer than 3 children per woman. (Iran made this transition under a conservative Muslim government.)

We also see from the chart that the speed with which countries can achieve low fertility has increased over time. A century ago it took the United Kingdom 95 years and the US 82 years to reduce fertility from more than 6 to less than 3. This is a pattern that we see often in development: those countries that first experience social change take much longer for transitions than those who catch up later: Countries that were catching up increased life expectancy much faster, they reduced child mortality more quickly and were able to grow their incomes much more rapidly.

Years-it-took-Fertility-to-fall-from-6-to-below-3

When more infants survive – fertility goes down

On the y-axis we measure the number of annual live births per 1,000 people. On the x-axis we measure how many infants, who were born alive, survive their 1st year of life – this is the infant survival rate.

The chart shows how these two aspects changed over the course of the 20th century: At the beginning of the century all 4 countries can be found in the upper left corner – they are characterized by high fertility and an infant survival rate below 85%. If we follow the 4 lines we are taken to the bottom right corner and see that women have fewer children when the mortality rate of babies goes down.

The causal link between infant survival and fertility is established in both directions: Firstly, increasing infant survival reduces the parents’ demand for children. And secondly, a decreasing fertility allows the parents to devote more attention and resources to their children.

This link between fertility and child mortality is an immensely important insight and tells us what drives the acceleration and slowdown of population growth: In the initial stage of the transition, when fertility rates are still high but health is already improving, the population starts to grow. But then, a bit later, we see that this transition works to decrease population growth since improving health of the children leads to lower fertility. It is an important part of the mechanism behind the demographic transition.

A very cynical view is that a decrease in child mortality is bad for the world since it would contribute to the overpopulation of the planet. The chart above shows that this opinion is not just contemptuous of human life but plainly wrong: When more infants survive fertility goes down and the temporary population growth comes to an end. If we want to ensure that the world’s population increase comes to an end soon we must work to increase child survival.

Infant survival and fertility through time – Max Roser5

Scatter-Fertility-vs-Infant-Survival

Read the full study: Max Roser (2016) – ‘Fertility’. Published online at OurWorldInData.org. Retrieved from: https://ourworldindata.org/fertility/ [Online Resource]