By the end of this century, almost every country in the world could have a shrinking population. Although people are living longer due to advances in healthcare and a decline in poverty, they are also having fewer babies. Over the past 50 years, the global fertility rate — the total number of births per woman — has roughly halved to 2.3. In most advanced economies it is already well below the replacement rate of 2.1, where the population replaces itself from one generation to the next, taking into account mortality. Developing nations are on a similar downward trajectory. The upshot is a decline in the working-age population across the developed world, which will bring significant social, economic and political costs if left unaddressed. Some blame a dystopian outlook among millennials and Gen Z — from the harms their children may cause to the climate, to the harms the climate may also do to them. But while a child-free life has gained appeal among some youngsters, for multiple reasons, the vast majority of under-30s in America who do not have kids still want them.

Rather, the long-term drop in the fertility rate is mostly the result of positive socio-economic trends. First, global female labour force participation and education levels have risen over the past half century. This has led to fewer children, or having them later in life. Second, economic development, better welfare systems and lower childhood mortality have reduced the need to have several children to support financial security.

In the developing world, fertility rates are still above the “wanted rate” — an estimate of what the fertility rate would be if all unwanted births were avoided — according to data compiled by the World Bank. But, in advanced economies couples tend to have fewer children than they want. This is because the hurdles to bringing up children have also risen.