The human population is aging at a rate “without parallel in the history of humanity” (United Nations, Department of Economic and Social Affairs, Population Division, 2001: xxviii). The aging of the world population is driven by two trends. First, there has been a dramatic increase in life expectancy. In the United Kingdom, for example, 10 million people are over 65 years old (roughly, 1 in 6 individuals). The latest projections are for 5½ million more elderly people in 20 years' time, and the number will have nearly doubled to around 19 million (roughly, 1 in 4 individuals) by 2050 (Cracknell, 2010). In the United States, older persons (officially denoted as 65+ years) numbered 39.6 million in 2009, when they represented 12.9% of the population, about one in every eight Americans. By 2030, there will be about 72.1 million older persons, more than twice their number in 2000 (Administration on Aging, 2014). Globally, the increase in life expectancy reflects both a reduction in deaths from infectious and parasitic diseases (e.g., smallpox, polio, measles) and a general movement toward healthier lifestyles. Second, as a result of more effective birth control and improved education, there has been an equally dramatic decline in fertility rates. The world's total fertility rate has already dropped by about half, from 5.0 children per woman in 1950–1955 to 2.5 children per woman in 2010–2015; it will fall below replacement by 2050 (United Nations, 2013).