OPTIMALITY THEORY, GOMPERTZ LAW, AND THE DISPOSABLE SOMA THEORY OF SENESCENCE

The ''disposable soma'' theory for the evolution of senescence suggest s that senescence arises from an optimal balancing of resources betwee n reproduction and somatic repair. Dynamic programming models are cons tructed and analyzed to determine the optimal relationship between rep roduction, diversion of resources from repair, and added senescent mor tality. Of particular interest is the relationship between the repair- reproduction trade-off and the form of the mortality-rate-versus-age c urve predicted. The models analyzed in the greatest detail assume that the relationship between reproduction and added senescent mortality d oes not change with age. These suggest that mortality should increase at an increasing rate with age, but may approach a linear rate as mort ality becomes very high. General results are derived for the shape of the mortality curves early and late in the senescing part of the life span, and mortality curves for specific trade-off functions are illust rated. An exponential increase in death rate with age (Gompertz' Law) corresponds to only one of many possible relationships between reprodu ction and aging. The ''Law'' is unlikely to hold generally if the disp osable soma theory accounts for a large fraction of the observed senes cent increase in mortality with age. However, support for the generali ty of Gompertz' Law is weak, and other theories have not produced an e volutionary explanation for the law. The disposable soma theory is con sistent with some of the exceptions to Gompertz' Law that have been ob served.