What this chart shows:

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 – that I heard more than one time as a reply on my twitter – 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.

Data Sources:

The data is taken from the International Historical Statistics (IHS), edited by Palgrave Macmillan Ltd. (April 2013). The online version is available here. As a printed version it is published by Palgrave. The child survival rate is calculated using the IHS Data ‘Deaths Of Infants Under One Year Old Per 1,000 Live Births’.

Link to OurWorldInData.org

You find this chart and much more information about this topic in the data entry on fertility.