As noted in the WSJ here, the fertility rate is falling among a certain group, which will lead to a changing America:

Forget the debt ceiling. Forget the fiscal cliff, the sequestration cliff and the entitlement cliff. Those are all just symptoms. What America really faces is a demographic cliff: The root cause of most of our problems is our declining fertility rate.

The fertility rate is the number of children an average woman bears over the course of her life. The replacement rate is 2.1. If the average woman has more children than that, population grows. Fewer, and it contracts. Today, America’s total fertility rate is 1.93, according to the latest figures from the Centers for Disease Control and Prevention; it hasn’t been above the replacement rate in a sustained way since the early 1970s.

The nation’s falling fertility rate underlies many of our most difficult problems. Once a country’s fertility rate falls consistently below replacement, its age profile begins to shift. You get more old people than young people. And eventually, as the bloated cohort of old people dies off, population begins to contract. This dual problem—a population that is disproportionately old and shrinking overall—has enormous economic, political and cultural consequences.