The falling birth rate has some experts worried that America will be left with too few people of working age to support its burgeoning elderly population — both by paying into programs like Social Security andby filling jobs in fields such as health care and home assistance. "If we stay at 1.76, it's not a huge issue," says Bradford Wilcox, director of the National Marriage Project, a nonpartisan research group at the University of Virginia that examines trends in family and childbearing. "If we continue to see a decline in fertility, that would be more likely to lead to some importa...