In contrast, African birthrates, having declined from averages of nearly 7 children per women, stand at more than 4 children per woman, with some countries, such as Mali, Niger and Uganda, continuing to have rates above 6 children per woman. Such fertility rates, though expected to decline, translate into rapid population growth for most sub-Saharan African countries for the coming decades. For example, with a current fertility rate of 5.5 children per woman projected to decline to 3.5 children per woman by 2050, Nigeria's population of 162 million more than doubles to 390 million over the next 40 years. Similar patterns of population doubling, in some cases population tripling, are foreseen for many African countries, including the Democratic Republic of Congo, Niger, Mali and Uganda.
Fifth, a major consequence of declining birthrates, as well as increasing life expectancies, is population aging, a global transition to increasing proportions in the older age groups. The more developed countries are leading the way in this historic demographic shift. Some countries such as Germany, Italy and Japan have 20 percent or more of their populations aged 65 years and older (Figure 2). Although the proportions of elderly are lower, the pace of population aging among less developed countries is more rapid; Brazil, China and Indonesia are expected to see elderly proportions double within 25 years.
Sixth, due to increasing longevity, the numbers of oldest people, those aged 80 years and older and the most in need of old-age assistance and health care - are growing comparatively rapidly. Over the next 25 years, the numbers of the oldest, of which nearly two-thirds are women, are expected to increase from 105 million to 246 million, reaching 3 percent of world population, or double today's proportion.
Among developed countries, the proportions of oldest by 2035 will set record highs: 14 percent for Japan, near 10 percent for Germany and Italy. Also, in countries such as China, Indonesia and South Korea, the proportion aged 80 years and older are expected to triple over the next 25 years.
Population aging and increased longevity are of mounting significance for policymakers in both more developed and less developed countries. Population aging, in particular, raises serious concerns about the financial viability of pensions and healthcare systems for the elderly. With the number of workers declining relative to those in the retirement category and growing numbers surviving to advanced ages, especially women, nations will face unavoidable fiscal challenges requiring thorny and unpopular economic decisions.
Seventh, as a result of differences in population growth and age-structures as well as in living standards between the more and less developed countries, powerful push-pull factors continue to produce large streams of international migrants. On the one hand, relative declines in the labor force and increases in the retired elderly present many wealthier nations with a difficult choice of more immigrants or fewer and older citizens. On the other hand, the populations of many developing nations, including India, Nigeria, Pakistan and the Philippines, continue to grow rapidly with many of their young men and women seeking opportunities in the urban centers of wealthier countries.
The consequences of these major demographic changes affect every aspect of human society, including food, natural resources, economic well-being, security, revenue, politics, employment and healthcare. Neither political rhetoric nor wishful thinking can dispel the enormous impacts. On the contrary, sustained critical attention, informed decision making and essential economic and social reforms, too often in short supply, are required to adjust to major population trends.
Economic uncertainty should not provide a pretext to avoid dealing with the great, undeniable demographic trends underway globally. Against this backdrop the policies and actions by governments, businesses, civil society and individuals will determine human well-being in the coming decades.