Humanity has passed one of its greatest milestones, and yet almost nobody has noticed. We have reached peak child: the total number of babies in the world is no longer increasing. There will never be more children than there are today: the world’s population will continue to grow, but only because almost everybody is living longer.

We worry about political turmoil, and terrorism, and technology, and for good reason. But demographics remains destiny, and it is therefore impossible to exaggerate the significance of what is happening.

In 1966, the average woman in the world had five children; today, it is 2.5, an average propped up by still high fertility rates in Africa. The global mean is thus only a little higher than Britain’s 1.81 children per woman. Humanity’s great demographic transition, which began with the Industrial Revolution in Britain, is entering its final phase. We have moved from a poor, agrarian society in which we have lots of children, most of whom die early, to a rich, advanced world where we have far fewer offspring, but almost all live to be very old. This is one of the biggest, most welcome, transformations in human history, and the greatest possible liberation for billions of women.