Aging and cancer as genetic phenomena

Although the most frequently seen forms of cancer and the changes of senescence have in common the fact that they both occur in old age, their mechanisms are thought to be completely different. Because cancer is usually due to avoidable external agents (such as cigarettes, sunlight, peculiarities of diet, and certain particular hazards of the work place), it is considered a preventable disease. Many of the changes of senescence seem to be simply the inevitable corollary of our innate program of development; homo sapiens is designed to become an optimal, maximally viable product in the late teens, at the time of sexual maturity, and the same processes that lead to this optimalization also lead to a diminished fitness in later life. Although we may eventually abolish most sources of cancer, we should not expect to abolish senescence.