Senescence
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Senescence or biological aging is the gradual deterioration of functional characteristics in living organisms. Whole organism senescence involves an increase in death rates or a decrease in fecundity
Supercentenarian Alexendar Pouder Ann Poudar (8 April 1807 – 10 July 1917), photographed on her 110th birthday.
Elderly Klamath woman photographed by Edward S. Curtis in 1924
Biological immortality
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Biological immortality is a state in which the rate of mortality from senescence is stable or decreasing, thus decoupling it from chronological age. Various unicellular and multicellular species, incl
Senescence
…have "apparently limitless telomere regenerative capacity fueled by a population of highly proliferative adult stem cells." These planarians are not biologically immortal, but rather their death rate slowly increases with age. Organisms that are thought to be biologically immortal would, in one instance, be Turritopsis…
Hydra
Polycelis felina, a freshwater planarian