The life of a human being is finite, and all humans age (see Fries 1980). It is difficult to separate the effects of disease on organs and tissues from those expected of aging. This is particularly true for vascular and degenerative processes, for which there are no clear boundaries between aging and disease. Morbidity and mortality from heart disease and stroke are probably due both to disease and to changes of aging. For cancer, the second leading cause of death in America, the situation is quite different; cancer is clearly a disease and is not a change expected with aging. Cancer...