Abstract
In industrialised countries, mortality and morbidity are dominated by age related chronic degenerative diseases. The health and health care needs of future populations will be heavily determined by these conditions of old age. Two opposite scenarios of future morbidity exist: morbidity might decrease ("compress"), because life span is limited, and the incidence of disease is postponed. Or morbidity might increase ("expand"), because death is delayed more than disease incidence. Optimality theory in evolutionary biology explains senescence as a by product of an optimised life history. The theory clarifies how senescence is timed by the competing needs for reproduction and survival, and why this leads to a generalised deterioration of many functions at many levels. As death and disease are not independent, future morbidity will depend on duration and severity of the process of senescence, partly determined by health care, palliating the disease severity but increasing the disease duration by postponing death. Even if morbidity might be compressed, health care needs will surely expand.