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 Because of changes in the genetic material (mutations) these have new characteristics and in the course of their individual lives they are tested for optimal or better adaptation to the environmental conditions. Immortality would disturb this system--it needs room for new and better life. This is the basic problem of evolution.