Ours is a world of hope and possibility, a world where the human family is larger than ever before. It is a world in which we are collectively living longer and, on balance, enjoying better health, more rights and broader choices than at any other point in human history. Ours is also a world of anxieties: the tensions of everyday life are rapidly accumulating amid economic uncertainty, the existential question of climate change, the still-rising toll of the COVID-19 pandemic and the ongoing ravages of conflict.

In November 2022, the United Nations announced that the human population had surpassed 8 billion people, and also that two thirds of people were living in places where fertility rates had fallen below the so-called “replacement level” of 2.1 births per woman. These trends offer a nuanced look at demographic transition — the shift from higher to lower mortality and fertility — as it unfolds.