Evolutionary theories of ageing are based on the observation that the efficacy of natural selection decreases with age. This is because, even without ageing, individuals will die of environmental causes, such as predation, disease and accidents. Ageing is thought to have evolved as the result of optimising fitness early in life. A second process, namely the progressive accumulation of mutations with effects late in life, will reinforce this result. Longevity of a species is therefore determined by the amount of environmental mortality caused by the ecology of a species. The experimental data concerning the relative roles of both processes are reviewed here. Recent discoveries of the levelling of mortality curves, and of age specific mutations in mutation accumulation lines of Drosophila melanogaster, require adjustments to the original models of the evolution of ageing and species longevity. These adjustments do not invalidate the underlying rationale of evolutionary theories of ageing. With current developments in QTL mapping and genetic association studies, the unravelling of the ageing process has the potential to progress rapidly.