EVOLUTIONARY PERSPECTIVES ON HUMAN SENESCENCE

Species have evolved adaptive strategies for ensuring reproductive suc cess. Reproduction concentrated early in life suggests that extreme mo rtality at young ages has been a common demographic characteristic amo ng all forms of life. Because it operates through the differential rep roductive success of individuals, natural selection, the arbiter of ev olution, is not effective after the reproductive period ends. Requirin g survival beyond the reproductive period for senescence to be express ed suggests that senescence is not genetically programmed, but neither is there an active program for immortality. What we call senescence m ay simply bc the inadvertent consequence of surviving beyond reproduct ive period. As survival is further extended, inevitable declines in ph ysiological function and a proliferation of fatal and nonfatal degener ative diseases that become progressively less amenable to modification would be predicted. This model of senescence can provide a theoretica l framework for demographers in their development or evaluation of mod els of human mortality.