Joel Kotkin makes a basic but important point about population growth:
[O]verall the biggest demographic problem stems not from too many people but from too few babies. This is no longer just a phenomenon in advanced countries. The global “birth dearth” has spread to developing nations as well. Nearly one-third of the 59 countries with “sub-replacement” fertility rates — those under 2.1 per woman — come from the ranks of developing countries. Several large and important emerging countries, including Iran, Brazil and China, have birthrates lower than the U.S. In the short run this is good news. It gives these countries an opportunity to leverage their large, youthful workforce and declining percentage of children to drive economic growth. But over the next two or three decades — by 2030 in China’s case – these economies will be forced to care for growing numbers of elderly and shrinking workforces.