Aging as alteration.

Aging is a normative biological process, and not simply a physical one. It is not accurate to define it by the fact that life has an entropic cost, and to characterize it as a pure imbalance between exergonic and endergonic reaction in metabolism (the free radical theory of aging) or finally as an imbalance between the excessive formation of reactive oxygen species and limited antioxidant defenses. In connective tissues, aging is alteration. And alteration is more than destruction or degradation. It deals with self-destruction and with the so-called molecular vicious circles of aging. In worms, in yeast, and in other organisms, aging is also opposed to longevity that counteracts this self-destruction process, as if longevity was something like a developmental constraint (delay) opposed to an evolutionary one (alteration).