Biological immortality

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Biological immortality can be defined as the absence of a sustained increase in rate of mortality as a function of chronological age. A cell or organism that does not experience, or at some point ceases experiencing, aging is biologically immortal.

There is no organism or individual cell that is literally immortal. Any "immortal" cell or organism can be killed by cutting or crushing.

Biologists have chosen the word immortal to designate cells that do not undergo cellular sensecence (the state wherein cells no longer divide because of dna damage or shortened telomeres). The term immortalization was first applied to cancer cells that developed the telomere-lengthening enzyme telomerase, and thereby avoided cellular senescence.

Bacteria can be said to be biologically immortal, but only as a species. An individual bacterium can can easily die. The two daughter bacteria resulting from cell division of a parent bacterium can be regarded as unique individuals or as members of a biologically "immortal" species. The two daughter cells can be regarded as "rejuvenated" copies of the parent cell because damaged macromolecules have been split between the two cells and diluted. This is the exact same sense in which stem cells and gametes can be regarded as "immortal". Similarly, Hydra, lobsters and a number of other species are regarded as never aging because they are composed entirely of cells that never cease dividing (and diluting damaged molecules).

Some life extensionists have the hope that humans may someday become biologically immortal. This would not be the same as being literally immortal because people can always be murdered or die in accidents. Many people practice cryonics with the expectation that humans will someday achieve biological immortality. Notable books by cryonicists along this line are The First Immortal by James L. Halperin, The Prospect of Immortality by Robert Ettinger and Forever For All by Dr. R. Michael Perry. Such views have been bolstered by the promise of nanotechnology, and specifically of nanomedicine.

Another ambitious project for achieving biological immortality in humans and mammals is that of biogerontologist Aubrey de Grey of Cambridge University. Dr. de Grey proposes that damage to macromolecules, cells, tissues and organs can be repaired by advanced biotechnology. He calls his project SENS (Strategies for Engineered Negligible Senescence). Dr. de Grey has created a Methuselah Mouse Prize which awards money to researchers who can extend the lifespan of mice or rejuvenate mice.

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