These theories assert that aging is an essential and innate part of the biology of people, and that aging is programmed into our body systems. The three main systems that are connected with aging are the endocrine (hormonal) system, the immune system and our genes. These systems change over time. These changes cause the symptoms and signs of aging.
The Body is NOT a Machine:
We like to compare the human body to a machine. But this is not a very good comparison. Unlike a machine, which has only the parts it was built with, the human body continually repairs and replaces cells. Every seven years, 90 percent of the cells in your body are new. The human body is an amazing, open, dynamic system. To understand aging, we have to forget about machines and think about living systems.
Aging Is About Evolution, Not Biology:
There is really no reason that the human body should "wear out" as long as it can repair and renew itself. Something other than time must be at play to cause the inevitable effects of aging. The programmed theory of aging believes that aging and death are necessary parts of evolution, not of biology. If a species did not have the genetic capacity for aging and death, then it would not be forced to replicate to survive. Individuals in the species would just keep on living until a climate or other change wiped them all out. The key point here is that if biological individuals live forever, there would be no evolution.
Programmed Aging:
Aging, therefore, must be inherent in the organism and not simply a result of environmental factors or disease. So aging and death, according to this theory, are not a result of wear and tear or exposure, but are a programmed, natural and necessary part of genetics. In short, we are programmed to age and die.
The Evidence:
The evidence supporting this theory is that there is not a great deal of variation in lifespan within species. Elephants die around 70, spider monkeys die around 25, and people die around 80. Some changes can be made based on nutrition and medical care -- but overall lifespan within species is fairly constant. The programmed theory asserts that if aging were due to "wear and tear" there would be more variation in lifespan within each species.
Sources:
Prinzinger, Roland. Programmed ageing: the theory of maximal metabolic scope.
EMBO Rep. 2005 July; 6(S1): S14–S19.
