People live longer than ever before. This, as I noted recently, has created opportunities and challenges. But postponing death is only a part of the demographic story. The other is the decline in births. The combination of the two is creating huge changes in the world we inhabit.

The notion of a “demographic transition” is almost a century old. Human societies used to have roughly stable populations, with high mortality matched by high fertility. In England and Wales in the 18th and 19th centuries, death rates plummeted. But fertility did not. The result was a population explosion until, at last, fertility rates also collapsed.

Financial Times