i The biological clock ii Why dying is beneficial iii The ageing process of men and women iv Prolonging your life v Limitations of life span vi Modes of development of different species vii A stable life span despite improvements viii Energy consumption ix Fundamental differences in ageing of objects and organisms x Repair of genetic material Animals which save energy by hibernation or lethargy (e.g. bats or hedgehogs) live much longer than those which are always active.