> Already, most people live in countries with less than replacement fertility (i.e. with a total fertility rate (TFR) below 2.1 births per woman). This is a te

> Already, most people live in countries with less than replacement fertility (i.e. with a total fertility rate (TFR) below 2.1 births per woman). This is a textbook example of what unsustainable means. In the long run most people will live in the countries with the highest fertility rates.