STORY Oct 08, 2018

A changing world population

There were 3 billion people in the world in 1960. In less than three decades, the population surpassed 5 billion in 1987. Today, another three decades later, there are around 7.5 billion people in the world. Since 1975, the global population has grown by one billion about every 12 years. However, over the same period, the composition of the world population has changed and diverged from historical patterns.

The most populous countries and regions are changing

China and India – in that order – have been the most populous countries in the world through this entire period. Today, China has nearly 1.4 billion people, and India is a close second with 1.3 billion, and together, they represent every 1 in 3 people of the global population. In fact, China and India are individually bigger than Sub-Saharan Africa. However, recent population projections suggest that India will surpass China as the most populous country in the world in 2022, and that Sub-Saharan Africa’s population will more than double by 2050.

Births, deaths and migration drives the change

In human history, the youngest age group has typically made up the largest proportion of the population. People have tended to have more children than the replacement level of fertility at which a population replaces itself from one generation to the next (which for most countries is around equal to 2.1 births per woman). The proportion gradually gets smaller with older age groups because people can be born only at age zero but can die at any age, making the population distribution shaped like a pyramid.

However recent rapid changes in the pattern of births, deaths and migration have resulted in a proportion and size of the current population that is atypical of human history. In many countries the number births per woman has declined resulting in low fertility, and timing of deaths has shifted to old age, resulting in high life expectancy.

Worldwide, birth and death rates have been falling over time, from 34 births and 13 deaths per 1000 people in 1965, to less than 19 births and fewer than 8 deaths per 1000 in 2017. In Sub-Saharan Africa, where birth and death rate are both still relatively high, there is a large gap between death and birth rates resulting in high population growth. In contrast, Europe and Central Asia already had a very low death rate in 1960 which has since remained low and steady. At the same time, the birth rate has fallen dramatically, thus closing the gap between the birth and death to nearly zero.


As a result of such changes, three diverging patterns are shaping the populations around the globe:

Countries with low fertility and high life expectancy over the last several decades: The shape of the population composition for such countries has changed from being pyramid shaped to being barrel shaped, like in Norway where there are similar proportions of people in all age groups up to age 70.

Countries with rapidly falling fertility over the last several decades: The shape of the population composition looks like a vase for such countries, for example in South Korea. Here, the composition of the population by age has shifted from children to working population.

Countries with high fertility and low life expectancy: With a higher population growth rate than any other region, many countries in Sub-Saharan Africa have a young population - with largest proportion of people between ages 0-14. The shape of the population for Sub-Saharan Africa looks like an actual pyramid, with largest proportion people at the bottom of the pyramid and gradually smaller proportion of people as the age increases.

The composition of the world population is changing in terms of both age and geographic composition. Understanding births, life expectancy and people’s movements is key to shed light on these changing patterns.