Life expectancy is a concept in demography that measures the mean number of years of life for babies born in a specified year. It is heavily influenced by the rate of infant mortality. But when infant mortality drops below 20 deaths per 1000 births, life expectancy switches and depends on the lifetimes of older people. It is a common fallacy to read that "life expectancy was 40 years" and deduce that few people lived beyond age 40.
There has been much speculation about an upper limit of average life expectancy--90? 100? higher? Is expectancy now approaching this hypothetical limit? For 160 years, best-performance life expectancy has steadily increased by a quarter of a year per year, an extraordinary constancy of human achievement. Mortality experts in the past often asserted life expectancy is close to its ceiling; these experts have repeatedly been proven wrong. The apparent leveling off of life expectancy in various countries is an artifact of laggards catching up and leaders falling behind.
- Robert William Fogel. The Escape from Hunger and Premature Death, 1700-2100: Europe, America, and the Third World (2004)
- James C. Riley. Rising Life Expectancy: A Global History (2001)
- Jim Oeppen and James W. Vaupel, "Enhanced: Broken Limits to Life Expectancy," Science (May 10 2002): Vol. 296. no. 5570, pp. 1029 - 1031
- Helmut Wendel, and Christopher S Wendel. Vital Statistics of the United States Births, Life Expectancy, Deaths and Selected Health Data (2006)
- Oppen and Vaupel (2002)