India, Oct. 3 -- Every few months, a fresh alarm is sounded: India's birth rate is falling, the nation is greying, and a demographic cliff awaits. Voices urge couples to have more children; commentators warn of empty classrooms and lonely elders. The anxiety is understandable. It is also, let me be frank, badly out of date.

The arithmetic of an older century

India's total fertility rate has settled at roughly 2.0, a shade below the replacement level of 2.1, and several southern states now sit well under it. This is not a collapse. It is the quiet success of girls' education, better child survival, wider access to contraception and women's growing authority over their own lives. A mother who no longer needs to bear six children so that t...