Theories of Biological Aging

While it is clear that longevity is genetically determined, it is widely believed that specific age-related changes cannot have evolved by natural selection, because most aspects of aging manifest themselves well after reproduction has ceased in humans. This does not mean that aging cannot be altered by genetic intervention. Work begun in the 1980s, and continued with great success in the 1990s, demonstrated clearly that life span in diverse invertebrate organisms can be dramatically extended by mutations in, or overexpression of, specific genes (e.g., antioxidant enzyme genes), often referred to as longevity assurance genes. These genes also code for a wide variety of proteins involved in processes such as signal transduction, hormone production, protein synthesis, and metabolic regulation. It has also been possible to isolate a long-lived strain of fruit flies by selecting for female flies that reproduce late in life, suggesting that certain gene combinations may be particularly beneficial in slowing aging. However, although it is clear that genes do control longevity and the rate of aging, this does not mean that aging is precisely genetically programmed in most organisms.