28 Environmental Factors and Gene Activities That Influence Life Span

Abstract

I. THE STUDY OF LIFE SPAN
How the rate of aging is determined is unknown. It is often assumed that aging is the result of an inevitable process of decay and degeneration. However, there are reasons to believe that the aging process is actively regulated. For example, germ cells and transformed cells do not age, which indicates that aging is not a necessary feature of eukaryotic cells. In addition, the rate of aging is strikingly different in different species; e.g., the life spans of mice, canaries, and bats (all small warm-blooded animals) are 2, 13, and 30 years or more, respectively (for an extensive review of the phylogenetic variation of aging rates, see Finch 1990). In addition, control of the rate of aging by the endocrine system has been implicated in many different types of organisms; e.g., marsupial mice and certain species of salmon and insects undergo a rapid process of senescence following reproduction, and the endocrine system has been shown to delay senescence in the queen bee. Life span can also be extended in many species that enter a state of diapause or dormancy under unfavorable environmental conditions, an extreme example of which is the Caenorhabditis elegans dauer larva. The rate of aging in vertebrates and many other animals can also be altered in response to food availability.

Together, these observations suggest that the rate of aging is actively regulated. As with other biological processes, it may be possible to dissect the aging process using genetics, and in fact,...