Theoretical Model of Longevity Extension in Social Species

Improved health and increased longevity in societies sets in motion a self-perpetuating system of longevity extension. This positive feedback relationship is based on the demographic tenet that (all else being equal) increased survival from birth to sexual maturity reduces the number of children desired by parents (15). Because of the reduced drain of childbearing and child rearing, parents with fewer children remain healthier longer and thus raise healthier children. The higher survival rate of these children fosters yet further reductions in fertility. Greater longevity of parents also increases the likelihood that they can contribute as grandparents to the fitness of both their children and their grandchildren. And, the self-reinforcing cycle continues.

In an essay on the formation of human capital, Abramovitz

(16) noted that the decline in mortality rates during the early stages of industrialization in the United States was probably one of the forces behind the expansion of educational effort and growing mobility of people across space and between occupations. Whereas previous conditions of high mortality and crippling morbidity effectively reduced the prospective rewards to investment in education during the preindustrial period

(17), prolonged expectancy for working life span must have made people more ready to accept the risks and costs of seeking their fortunes in distant places and in new occupations. The positive feedback of gains in longevity on future gains involves a complex interaction among the various stages of the life cycle with long-term societal implications in terms of the investment in human capital (16), intergenerational relations (18), and the synergism between technological and physiological improvements—so-called "technophysio evolution" (Chapter 1) (19). In other words, long-term investment in science and education

TABLE 2 Estimates of Longevity for Fossil Hominids

TABLE 3 Classification and Brief Description of Main Theories of Aging

Biological level/ theory

Description

TABLE 2 Estimates of Longevity for Fossil Hominids

Hominid species

Life span (yr)a

Incremental change

Australopithicus afarensus

How to Stay Young

How to Stay Young

For centuries, ever since the legendary Ponce de Leon went searching for the elusive Fountain of Youth, people have been looking for ways to slow down the aging process. Medical science has made great strides in keeping people alive longer by preventing and curing disease, and helping people to live healthier lives. Average life expectancy keeps increasing, and most of us can look forward to the chance to live much longer lives than our ancestors.

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