Information theoretical aspects of the aging process of organismic systems.

The aging process is understood as the temporally changing ability of the organism to maintain the degree of inner order and organisation which is necessary for viability. This inner order and organisation may be represented by a multidimensional state variable 'vitality'. The quantity 'vitality entropy' is defined in a manner similar to information theoretical or thermodynamical entropy. It is an aggregate measure of the age-dependent distribution of vitality in the state space. In these terms a mathematical description of the aging process may be given as temporal changes of the extension of this distribution. In an initial phase of differentiation of an organism the vitality entropy decreases to a minimum as the distribution becomes concentrated at the optimal states. With aging in the narrower sense, the distribution spreads in the state space with the decrease of order and organisation, and the consequent increase of vitality entropy.