Passage to Methuselah: Some Demographic Consequences of Continued Progress Against Mortality

Suppose progress continues to be made in reducing mortality rates at all ages. What impact would this progress have on the size and age composition of the U.S. population? The supposition that mortality rates will continue to fall is admittedly questionable. The view popularized by James F. Fries is that "the median natural human life span is set at a maximum of 85 years with a standard error of less than one year" (Fries and Crapo, 1981). Paul Demeny, in making long-term population forecasts for the World Bank, assumes that even by the year 2100 there will be no country with a life expectancy above 82.5 years. Demeny notes that in some countries life expectancy seems to be slowly decreasing. The possibility of a general decline in life expectancy cannot be ruled out. On the other hand, as Demeny points out, "the upper limit to life expectancy" of 82.5 years "may yield to technological changes in medicine and to changes in life styles, perhaps even within the next few decades" (Demeny, 1984). As documented by Crimmins (1981), remarkably rapid progress in reducing mortality rates was made in the United States from 1968 to 1977. This progress has continued and even accelerated from 1977 to 1983. At most ages, including older ages, mortality rates over the last decade have been declining at a rate of one or two percent per year. Hope that this progress might continue is butressed by recent advances in the biological, medical, and gerontological sciences. The life sciences appear to be poised at roughly the point the physical sciences were a century ago and breakthroughs comparable to electricity, automobiles, television, and computers may be forthcoming in the areas of genetic engineering, prevention and treatment of such diseases as atherosclerosis, cancer, and diabetes, and perhaps understanding and control of the process of aging itself (see, e.g. Walford (1983), Bulkley (1983), and Rosenfeld (1976)). In this note, we explore three possibilities: no change in mortal