The idea is that evolution is not about individuals, it is about a population as a whole. Every generation brings new genetic combinations, and the best ones ha

The idea is that evolution is not about individuals, it is about a population as a whole. Every generation brings new genetic combinations, and the best ones have to survive and spread. From an evolution point of view, you don't want the older individuals to stick around too much once they have passed on their genes. All other things being equal, there is usually a benefit in being there for a longer time. This is especially true for intelligent and social animals: you know the place, you have a social network. Therefore, older individuals need a handicap for the competition to be level with the new generation. Without aging, a population would simply stall as strong individuals who were there first would systematically squash younger competition. > It seems intuitive to me that keeping an old body from falling apart takes great resources / evolutionary focus Actually, it looks increasingly like aging is an additional feature, not a constraint, of life. Some organisms (some shrimps, naked mole rats, galapagos turtles...) seem to have inadvertently switched off aging.