Death, Aging, Rejuvenation (part )

Aging How did aging appeared? If mechanism of Death was chosen by evolution, how was aging chosen? Why for example at certain age animals do not die instantly and just give the room for the next generation. Nurturing is one explanation at least for human society. But lets say new generation of young adults already reached puberty . Why would not old generation die in an instant. Why do they age? Actually there is nothing impossible. Some butterflies grow couple years, mate, produce new generation and die in one day. Some plants live year, some live years and then invariably die. Some live years. Lemmings, having overgrowth of population, just go and massively commit suicide in the sea. No questioned asked. Why aging in other animals take several years? It might be selected by cut-throat evolution during another catastrophe. A relatively mild Cataclysm happened in the same time when all adults died programmed to do so. Older animals would survive the disaster. But they died instantly from internal timer. Younger generation did not tolerate the mishap. All species that did it - just disappeared. Younger animals were not adapted to new conditions. Only animals with mechanism of aging were selected. Maybe the aged animals are not so good as younger ones. They already slightly deteriorated. But it is better than nothing. Anyway. It makes sense why Death and Aging were selected during the Evolution. - continued in Part