ONE of the arguments in favour of the European Union is that it allows good ideas and policies to spread quickly across the continent. Together with enhanced trade within the single market, that should, in theory, cause countries that entered the club with vastly different societies and levels of wealth to become more similar over time. Full economic parity remains a long way off, as the EU’s eastern and southern countries are still poorer than their western brethren. However, some social indicators do reveal impressively rapid convergence. Among the most striking is the age at which women give birth for the first time.

In the mid-1990s, women in western Europe typically became mothers for the first time in their late 20s, with the next-biggest group doing so in their 30s. In southern Europe, they got to the task when they were slightly younger. But the post-communist countries of eastern Europe looked very different. Most women there became mothers in their early 20s, with lots of births by teenagers and very few by women over 30.

By 2015 this disparity had almost entirely disappeared. Western European countries maintained their earlier pattern, but southern and eastern European ones moved sharply towards the western model. The two most important causes of this shift in the former communist countries were the increasing availability of modern contraceptives—rarely used in the region before the 1990s—and women postponing marriage to go to university. In several eastern European countries, the share of women with university degrees nearly tripled between 2002 and 2016.

European countries have converged in another way. Everywhere, the fertility rate is between one and two, meaning a woman can expect to have that many children, on average. With such few babies, the populations of most European countries are set to shrink—unless they admit immigrants or progress in medicine and public health extends lifespans, or both.