Life Span and Life Expectancy
Theory of Life Span
These articles on life span, and gerontologists, talk about two kinds of life span. One is maximum life span, the greatest age reached by any member of a species. In humans the life span is 120 years, we think. The other is average life span, the average age reached by members of a population. Life expectancy, the number of years an individual can expect to live, is based on average life spans.
Average life span and life expectancy in the United States have grown dramatically in this century, from about 47 years in 1900 to about 78 years in 2000. This advance in age is mostly due to improvements in sanitation, the discovery of antibiotics, and medical care. Now, as scientists make headway against chronic diseases like cancer and heart disease, some think it can be extended even further.
Maximum human life span seems to be another matter. There is no evidence that the life span for humans has changed for thousands of years despite fabled fountains of youth and biblical tales of long-lived patriarchs. However, very recently, the dream of extending the human life span has shifted from legend to laboratory. As gerontologists explore the genes, cells, and organs involved in aging, they are uncovering more and more of the secrets of longevity. As a result, life extension may now be more than the stuff of myth and the retardation of disease and disability, it is here now and getting more effective every day.
Gerontology is often described in terms of its major theories. These fall into two main groups, one emphasizing internal biological clocks or "programs," and the other external or environmental forces that damage cells and organs until they can no longer function adequately.
Aging processes can be divided into three general categories -- genetic, biochemical, and physiological. The rest of this article describes what we know and don't know in each territory and where we think we are likely to find answers to questions about aging and longevity.
Theories of Aging
The theories of aging fall into two groups. The "programmed" theories hold that aging follows a biological timetable, perhaps a continuation of the one that regulates childhood growth and development. The damage or error theories emphasize environmental assaults to our systems that gradually cause things to go wrong. Many of the theories of aging are not mutually exclusive. Here is a brief and very simplified rundown of the major theories. For more information, see Selected Readings.
Programmed Senescence. Aging is the result of the sequential switching on and off of certain genes, with senescence being defined as the time when age-associated deficits are manifested and you cells simply stop working effectively.
Endocrine Theory. Biological clocks act through hormones to control the pace of aging.
Immunological Theory. A programmed decline in immune system functions leads to an increased vulnerability to infectious disease and thus aging and death.
Wear and Tear. Cells and tissues have vital parts that wear out.
Rate of Living. The greater an organism's rate of oxygen basal metabolism, the shorter its life span.
Cross-linking. An accumulation of cross-linked proteins damages cells and tissues, slowing down bodily processes.
Free Radicals. Accumulated damage caused by oxygen radicals causes cells and eventually organs to stop functioning.
Error Catastrophe. Damage to mechanisms that synthesize proteins results in faulty proteins which accumulate to a level that causes catastrophic damage to cells, tissues, and organs.
Somatic Mutation. Genetic mutations occur and accumulate
with increasing age, causing cells to deteriorate and malfunction.
Please take the time to educate yourself. If you don't care for yourself no one else can or will. Read more...
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Robert Bohen - President
AntiAging Research Laboratories
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