In Chapters 2–9 we have reviewed the literature bearing upon economic and related consequences of population aging and its causes – a phenomenon that, according to Sauvy, tended to escape notice despite its obviousness. The tendency toward population aging will be accentuated should fertility descend below the replacement level or should a “gerontic revolution” get under way. Whether a decline in a nation's fertility and eventually in its population in conjunction with further population aging constitutes a serious economic problem turns on “the capacity of our societal institutions to cope with the changes that can be anticipated” and realize the potential advantages of a longer life (see Myers).

Fertility is currently below the replacement level in a number of highly developed countries, according to the United Nations Demographic Yearbook. Among these countries in 1973–4, besides Canada, Japan, and the United States, were Austria, Belgium, Denmark, England and Wales, Finland, both Germanies, Netherlands, Scotland, Sweden, and Switzerland. Should fertility persist at these levels, the age composition will include more persons over 65 than would a corresponding stationary population.

Should life expectancy at higher ages increase, the fraction of the population 65 and over would increase somewhat. For example, in the ultimately stationary population projected for the United States made in 1975, the median age would be 37.8 years, with 17.05 percent 65 and over and 58.93 percent aged 18–64 years. As a result mainly of the upward adjustment of anticipated life expectancy in the stationary population, projections constructed in 1977 illustrate further population aging in the future stationary state (U.S. Bureau of the Census, July 1977, pp. 1–11).