From Science Daily, a fairly content-light piece on researcher Tom Kirkwood's views on aging, evolution and genetics: "there is no single gene for aging. Throughout time, Humans have used energy to get food, produce offspring and survive danger - not to repair and maintain cells. So the maintenance system in the body slowly breaks down. ... But genetic factors do exist. 'Approximately 25 percent of how a person ages is inherited from parents. Stress, environment, nutrition, lifestyle and immunity play an additional role. Great variation between individuals can be seen in organisms such as round worms - and in humans.'" A much better summary of Kirkwood's views can be found in an EMBO Reports article from earlier this year.