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 Theories 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.
Biological clocks act through hormones to control the pace of aging.
A programmed decline in immune system functions leads to an increased vulnerability to infectious disease and thus aging and death. Error Theories 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.