Dhaka, Jan. 23 -- The world is entering a period of demographic divide that few policymakers are prepared to confront openly. Over the past seven decades, global fertility rates have fallen by more than half. Today, more than half of all countries-including every advanced economy, and a growing number of middle-income countries-have fertility rates below the replacement level.From Japan and Italy to the United States and the United Kingdom, ageing populations and shrinking workforces are becoming the defining economic challenge of the coming decades.

At the same time, parts of the Global South, including Bangladesh, face the opposite challenge: youthful populations, expanding labour forces, and a chronic shortage of productive domestic j...