EVOLUTIONARY PERSPECTIVES ON HUMAN SENESCENCE

Species have evolved adaptive strategies for ensuring reproductive success. Reproduction concentrated early in life suggests that extreme mortality at young ages has been a common demographic characteristic among all forms of life. Because it operates through the differential reproductive success of individuals, natural selection, the arbiter of evolution, is not effective after the reproductive period ends. Requiring survival beyond the reproductive period for senescence to be expressed suggests that senescence is not genetically programmed, but neither is there an active program for immortality. What we call senescence may simply bc the inadvertent consequence of surviving beyond reproductive period. As survival is further extended, inevitable declines in physiological function and a proliferation of fatal and nonfatal degenerative diseases that become progressively less amenable to modification would be predicted. This model of senescence can provide a theoretical framework for demographers in their development or evaluation of models of human mortality.