Biological immortality Edit

Hydras may not may not grow old Main article: Biological immortality If the mortality rate of a species does not increase after maturity, the species does not age and is said to be biologically immortal. Many examples exist of plants and animals for which the mortality rate actually decreases with age, for all or part of the lifecycle.[1] If the mortality rate remains constant, the rate determines the mean lifespan. The lifespan can be long or short, though the species technically "does not age". Hydra species were observed for four years without any increase in mortality rate.[2] Other species have been observed to regress to a larval state and regrow into adults multiple times. The hydrozoan species Turritopsis dohrnii (formerly Turritopsis nutricula ) is capable of cycling from a mature adult stage to an immature polyp stage and back again. This means no natural limit to its lifespan is known. [3] However, no single specimen has been observed for any extended period, and estimating the age of a specimen is not possible by any known means.

(formerly ) is capable of cycling from a mature adult stage to an immature polyp stage and back again. This means no natural limit to its lifespan is known. However, no single specimen has been observed for any extended period, and estimating the age of a specimen is not possible by any known means. At least one hydrozoan ( Laodicea undulata [4] ) and one scyphozoan ( Aurelia sp.1 [5] ) can also revert from medusa stage into polyp stage.

) and one scyphozoan ( sp.1 ) can also revert from medusa stage into polyp stage. The larvae of skin beetles undergo a degree of "reversed development" when starved, and later grow back to the previously attained level of maturity. The cycle can be repeated many times.[6]

Revived into activity after stasis Edit

List of longest-living organisms Edit

See also Edit

Further reading Edit

Rachel Sussman (2014). The Oldest Living Things in the World. Chicago: University of Chicago Press. ISBN 9780226057507.