Ageing and death are necessary evolutionary components in the life of multicellular organisms. The survival of a species requires death of its individuals at a given time. Only on this basis can a new generation arise with a new combination of genes. At the cellular level, programmed cell death (apoptosis) in different tissues and at the right time is required for normal embryonic development. All living organisms have a species-specific lifespan. This is closely related to the process of ageing. All genes required to reach and complete the reproductive phase of an organism are subject to natural selection. In contrast, selective pressure is alleviated for genes that are required later on, after the reproductive phase has been completed. The rate of ageing appears to be influenced by genetic factors. In particular, different types of stem cells play an important role. Under the influence of specialized genes, stem cells retain the ability to remain undifferentiated and continue to divide without signs of ageing until the death of the individual.