Is Aging Inevitable?
Gerontology Seeks to Understand the Enigma of Aging
Turtles don’t seem to die of old age; the oldest known of, at over 150 years, died of a freak accident. Turtles succumb only when something kills them (and something always does, eventually). The adult mayfly has a lifespan as brief as three hours whereas the ocean quahog clam is estimated to live 220 years and the red sea urchin 200 years. However, a mouse is elderly if it makes it four years and if protected from violent death, bacteria may nigh be immortal. Such incongruities cannot help but generate questions – What is aging? (or senescence to use the gerontologists’ term) Is aging inevitable? Why do some animals live so much longer or shorter than others? For that matter, why should the public care?
Is Aging Inevitable?
Why an animal ages (or in some cases doesn’t age) is very much an open question in the world of research gerontology. It seems obvious – animals age because they get old, right? Not really, it turns out. No one knows if animals die because their time is up or because illness, injury, or deprivation does them in. When scientists attempt to look at aging in the absence of disease, they discover that the pathological changes thought of as aging are also the pathological changes associated with disease. That being said, should aging be regarded as a “disease?” A host of animal aging studies suggest answers, some unexpected, some hotly debated.
Physiologists have known for some time that mammals, pound for pound, expend the same energy during their lifetimes, suggesting that each species has a fixed metabolic potential. If true, small individuals with fast metabolisms should die sooner than would their larger more metabolically sluggish counterparts. The so-called rate-of-living theory of aging supposes that the daily act of living is harmful and that deterioration is an inevitable outcome of cell metabolism or “biological rust” if you will.
As a predictor of life span, the rate-of-living theory does appear to hold true for some animals, especially mammals – the most elderly elephants live over 70 years, chimps about 44 years, and house mice about 5 years. (Humans have lived 120 years but as a species we must be disqualified from this list because of our advanced medical technology and ample food supply.)
Is Aging Genetically Programmed?
But if the large are suppose to outlive the small, why do birds far outlive rodents of the same size? Why do cats (32 years) outlive dogs (20 years)? Something else must be going on. A different theory views an animal’s life span as genetically programmed. This notion, known as the evolutionary theory of aging, supposes that natural selection has determined each species’ life span. The difficulty for evolutionary gerontology lies in determining the adaptive benefit of the particular life span allotted any particular species. Shortly after spawning, the entire adult population of adult sockeye salmon perish, ravaged from within by a flood of adrenal hormones yet healthy turtles never stop reproducing, no matter how many decades old. How and why did natural selection shape the genetic constitution and thus the fate of salmons and turtles so totally differently?
More Questions than Answers
Research continues to raise more questions about aging. The life span of fruit flies prevented from flying jumps from the usual two weeks or so to three months. Why? (Unfortunately for dedicated couch potato humans, these results apply only to insects.) Opossums on an island off the Georgia coast not only live as much as 25 percent longer than their mainland kin but they also stay fertile longer and age more slowly physiologically. Why?
Numerous studies of mice, rats, and other animals have found that populations fed one third to one half as much food as what they would eat freely live up to 50 percent longer. Why? (If this applies to humans, would the extra time be worth it if you spend it constantly hungry?) Such are the mysteries of aging that continue to challenge evolutionary gerontology.
If natural selection has indeed already time-stamped our genes with an inevitable life span, what is the use of further research into gerontology? Age researchers would be quick to point out that through their research humanity continues to gain valuable insights and further understanding of the aging process, and that such understanding could lead to drugs and therapies to combat the afflictions of elderly humans thus making the fixed time we all have healthier and happier.
Is Human Aging Inevitable?
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