The prospect for increasing life expectancy further is a subject of intense scientific debate. Projections of life expectancy can have a significant influence on anticipated changes in social programs, such as Social Security and Medicare, that are influenced by the future size and health status of the older population. Some scientists have argued that life expectancy at birth for humans cannot practically exceed about eighty-five years (Olshansky et al., 1990). This conclusion is based on the facts that (1) survival up to and beyond the age of 110 is as rare in the early twenty-first century as it has always been; (2) the rapid increase in death rates from aging-related diseases that begins in the second decade of life has not changed in recorded history—instead, death rates have shifted down at comparable rates for most age groups; (3) the reduction in death rates required at every age to increase average life expectancy at birth to eighty-five years is extremely large—in fact, larger than what would occur with the elimination of cancer and heart disease; and (4) life expectancy has been shown to be a demographic statistic that becomes less sensitive to declining death rates as it approaches higher levels. Taken together, these facts point clearly to the difficulty in achieving the reduction in death rates required to increase life expectancy past eighty-five years.
Other researchers have argued that theoretically, average life expectancy at birth could reach 100 years (Manton et al.; Ahlburg and Vaupel). Several conditions are required for this to occur. Under one scenario, everyone in the population would have to adopt an "optimal" risk-factor profile, maintain their physical functioning throughout life, retain the risk-factor status of a thirty-year-old for the duration of life, and respond in the same beneficial way to a fixed regime of risk-factor modifications (Manton et al.). This means that everyone would have to eliminate behaviors such as smoking, drinking, and overeating, and somehow avoid the health problems, such as arthritis and sensory impairments, that now tend to compromise physical functioning in older ages.
In a second scenario, a life expectancy of 100 could be achieved if death rates declined by 2 percent at every age for every year for the next century (Ahlburg and Vaupel). Recent evidence indicates that mortality declines of this magnitude have been rare in the historical record of the United States (Olshansky and Carnes), and that such models lead to death rates that are inconsistent with evolutionary theories about the onset and progression of death rates from aging-related causes (Carnes and Olshansky). It is doubtful that either of these scenarios is practicably achievable, although they do represent laudable goals for healthcare planners.
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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.