Time of our lives. What controls the length of life?

Abstract

What controls the length of life?

Figure 1

Survival curves for organisms in wild and protected environments. In the wild, the level of age-independent extrinsic mortality tends to be high, so that animals rarely reach an age where senescence makes its mark. For this reason, the ageing process has evolved mainly within the 'selection shadow' where natural selection is powerless to select for any kind of clock that might actively drive senescence.

Figure 2

Underlying the ageing process is a progressive, gradual accumulation of molecular damage. Such damage is intrinsically random in nature but its rate of accumulation is regulated by genetic mechanisms for maintenance and repair. As cell defects accumulate, the effects on the body as a whole are eventually revealed as age-related frailty, disability and disease. This model accommodates the observed effects on length of life through environmental factors such as stress, nutrition, and exercise, which—in the case of adverse factors—can exacerbate the exposure to damage, and which—in the case of beneficial factors—can assist the body's maintenance and repair functions. The model therefore accommodates genetic, environmental and intrinsic chance effects on the ageing process.