Why don't we live forever?
Your life is not programmed to end, you simply wear out. But why don't your genes equip your body to live forever? One answer to this may lie in the past: our ancestors lived short, dangerous lives. They had children and passed on their genes while they were still young and fit. So, any genes that countered the effects of ageing (for example, those enabling better repair of the damage caused by free radicals) were not favoured by natural selection.