Published online by Cambridge University Press: 05 April 2015
There has been a long and enduring interest in the demographic structure of human populations, past and present. Thomas Malthus (1798), founder of the science of demography, linked mortality, survival, and success of a population to the food supply – populations with adequate nutrition and lower disease loads will grow, but malnutrition and disease will limit their size. The dynamic interplay between fertility, mortality, and available food resources formed a key element of Charles Darwin’s (1859) theory of natural selection. Darwin concluded that individuals having characteristics that promote their ability to survive, such as the successful acquisition of food and resources generally, will live to adulthood and reproduce. The various demographic measures of the success (or failure) of human populations – mortality, fertility, survivorship, longevity, and life expectancy – have endured as important foci of inquiry by social, behavioral, biological, and medical scientists into the twenty-first century and will continue to do so for the foreseeable future.
Although fertility, mortality, and other key parameters of demographic analysis are important measures of success in today’s world, life expectancy remains the gold standard for evaluating health and well-being around the globe, especially in comparative perspective. Life expectancy of 79 years in the United States versus just 58 years in Rwanda (United Nations, 2011) speaks to the chasm that exists in health and well-being between these two nations, implying a considerably healthier living environment in the former than in the latter. Similarly, increased life expectancy is an indicator of improving living conditions. In the United States, for example, life expectancy increased from 50 years in 1910 to nearly 80 years in 2010, clearly due, in part, to expansion in the availability of healthcare and improved nutrition. If life expectancy (and other demographic parameters) can be measured in ancient populations, then their age structures can provide a powerful perspective on health and conditions of life.