Negligible senescence

Negligible senescence is the lack of symptoms of aging in some organisms. Negligibly senescent organisms do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly senescent organisms do not increase with age as they do in senescent organisms.

There are many examples of species for whose organisms scientists have not detected an increase in mortality rate after maturity. This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age.

Study of negligibly senescent animals may provide clues that lead to better understanding of the aging process and influence theories of aging. The phenomenon of negligible senescence in some animals is a traditional argument for attempting to achieve similar negligible senescence in humans by technological means.

There are also organisms that exhibit negative senescence, whereby mortality chronologically decreases as the organism ages, for all or part of the life cycle, in disagreement with the Gompertz–Makeham law of mortality (see also Late-life mortality deceleration). Furthermore, there are species that have been observed to regress to a larval state and regrow into adults multiple times, such as Turritopsis dohrnii.

Recent studies have indicated a connection between phenomena related to negligible senescence and the general stability of an organism's genome, specifically transcription processes, over its lifetime.

Some fish, such as some varieties of sturgeon and rougheye rockfish, and some tortoises and turtles are thought to be negligibly senescent, although recent research on turtles has uncovered evidence of senescence in the wild. The age of a captured fish specimen can be measured by examining growth patterns similar to tree rings on the otoliths (parts of motion-sensing organs).

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