Do you want to live a longer life in good health? Simple practices can make some difference, such as exercise or calorie restriction. But over the long haul all that really matters is medical biotechnology: progress towards therapies that can repair and reverse the known root causes of aging. The sooner these treatments arrive, the more lives will be saved. Find out how to help  Here is a framework for thinking about aging and longevity: various forms of low-level biological damage accrue as a result of the operation of metabolism, degrading organs and tissues and ultimately causing death. Where natural selection favors longer-lived individuals, mechanisms will evolve to repair, minimize, or resist the effects of this damage. So aging is driven by damage, but genetic programs interact with that damage, evolved to try to do something about it. In spite of exciting new insights into regulatory mechanisms that modulate the aging process, the proximal cause of aging remains one of the unsolved big problems in biology. An evolutionary analysis of aging provides a helpful theoretical framework by establishing boundary conditions on possible mechanisms of aging. The fundamental insight is that the force of natural selection diminishes with age. This does not preclude senescence (age-related decrease in individual fitness) from occurring in natural populations. Senescence can develop because some genes have non-separable, but typically different or opposite, functions in reproductive-age and in old individuals. Such genes, selected according to their "youthful" function, may thus impose a distinct senescent phenotype in old