Perhaps couples will decide to have more children once they perceive that lives have lengthened enough for parents to focus sequentially, if not simultaneously, on children and career. In any case, public policy toward such basic concerns of potential parents as housing, health, and childcare costs is likely to influence decisions to have additional children, especially since investments in careers and homes, as well as children, are concentrated in the early phases of the adult income cycle. In recent decades, improvements in mortality have contributed to U.S. population growth by lengthening Americans' lives. Scientists generally agree that mortality will continue to improve over the next half century, increasing the numbers of older Americans well beyond the level of the current projections by the Social Security Administration. Beyond that, they disagree as to whether natural limits to life expectancy exist, whether devastating new diseases will appear, or whether significant public investments in health research will continue to vanquish old diseases.
Public policy is most important in determining the nature and level of immigration.
It is difficult to imagine that immigration will fall much below current levels, if only because population is growing so rapidly in less developed countries. More than 95 percent of the world's youth currently live in less developed countries where fertility rates, though lower than they were a half century ago, are still much higher than in the United States. As successively larger generations of young people seek their economic future, it is likely that they will continue to look to wealthier countries for work. In fact, public policy might favor admitting more young immigrants, rather than lengthening the work life to accommodate the increasing number of years lived after the official retirement age. Households and families may continue to change shape as mortality improvements increase the number of years adults live after raising their children.