Organisms lacking senescence
Cellular senescence is not observed in some organisms, including perennial plants, sponges, corals, and lobsters. In those species where cellular senescence is observed, cells eventually become post-mitotic when they can no longer replicate themselves through the process of cellular mitosis; i.e., cells experience replicative senescence. How and why some cells become post-mitotic in some species has been the subject of much research and speculation, but it has been suggested that cellular senescence evolved as a way to prevent the onset and spread of cancer. Somatic cells that have divided many times will have accumulated DNA mutations and would therefore be in danger of becoming cancerous if cell division continued. As such, it is becoming apparent that senescent cells undergo conversion to an immunogenic phenotype that enables them to be eliminated by the immune system.
^ Burton; Faragher (2015). “Cellular senescence: from growth arrest to immunogenic conversion”. AGE. 37. doi:10.1007/s11357-015-9764-2. PMC 4365077. PMID 25787341.