Testudo horsfieldii locking into the camera

Negligible senescence is a term coined by

biogerontologist Biogerontology is the sub-field of gerontology concerned with the biological aging process, its evolutionary origins, and potential means to intervene in the process. The term "biogerontology" was coined by S. Rattan, and came in regular use wit ...

Caleb Finch Caleb Ellicott Finch (born July 4, 1939) is an American academic who is a professor at the USC Davis School of Gerontology. Finch's research focuses on aging in humans, with a specialization in cell biology and Alzheimer's disease. Early life ...

to denote organisms that do not exhibit evidence of biological aging (

senescence Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...

), such as measurable reductions in their reproductive capability, measurable functional decline, or rising death rates with age. There are many species where scientists have seen no increase in mortality after maturity. This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age. Study of negligibly senescent animals may provide clues that lead to better understanding of the aging process and influence theories of aging. The phenomenon of negligible senescence in some animals is a traditional argument for attempting to achieve similar negligible senescence in humans by technological means. There are also organisms that exhibit negative senescence, whereby mortality chronologically decreases as the organism ages, for all or part of the life cycle, in disagreement with the

Gompertz–Makeham law of mortality The Gompertz–Makeham law states that the human death rate is the sum of an age-dependent component (the Gompertz function, named after Benjamin Gompertz), which increases exponentially with age and an age-independent component (the Makeham ter ...

(see also

Late-life mortality deceleration In gerontology, late-life mortality deceleration is the disputed theory that hazard rate increases at a decreasing rate in late life rather than increasing exponentially as in the Gompertz law. Late-life mortality deceleration is a well-establi ...

). Furthermore, there are species that have been observed to regress to a larval state and regrow into adults multiple times, such as ''

Turritopsis dohrnii ''Turritopsis dohrnii'', also known as the immortal jellyfish, is a species of small, biologically immortal jellyfish found worldwide in temperate to tropic waters. It is one of the few known cases of animals capable of reverting completely to ...

''. Studies have indicated a connection between phenomena related to negligible senescence and the dynamic stability of an organism's underlying regulatory network over its lifetime. Depending on the parameters of metabolism and the connectivity of the network, on one hand, and the genetic and expressome error elimination rates (repair efficiency), on the other, organisms may function in such a way that damage is either effectively eliminated and kept under control at all times, or the amount of damage is getting exponentially amplified. The two limiting cases may correspond to the distinct regimes of non-aging and "normal" aging, respectively. The boundary between the aging regimes corresponds to the phase transition line, whereas most regulatory networks of living species operate at the stability-instability boundary. If the relation between aging and criticality in genetic regulatory networks and the corresponding explanation behind the negligible senescence is confirmed by further research, it may explain how weak genetic perturbation can produce switching between normal (Gompertzian) aging and negligibly senescent regimes on evolutional time scales.

In vertebrates

Some fish, such as some varieties of

sturgeon Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...

and

rougheye rockfish The rougheye rockfish (''Sebastes aleutianus'') is a rockfish of the genus ''Sebastes''. It is also known as the blackthroat rockfish or the blacktip rockfish and grows to a maximum of about in length, with the IGFA record weight being . Simila ...

, and some

tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a turtle shell, shell to protect from predation and other threats. The shell in tortoises is generally hard, ...

s and

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

s are thought to be negligibly senescent, although recent research on turtles has uncovered evidence of senescence in the wild. The age of a captured fish specimen can be measured by examining growth patterns similar to

tree rings Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...

on the

otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The sa ...

s (parts of motion-sensing organs). In 2018,

naked mole-rat The naked mole-rat (''Heterocephalus glaber''), also known as the sand puppy, is a burrowing rodent native to the Horn of Africa and parts of Kenya, notably in Somali regions. It is closely related to the blesmols and is the only species in th ...

s were identified as the first mammal to defy the Gompertz–Makeham law of mortality, and achieve negligible senescence. It has been speculated, however, that this may be simply a "time-stretching" effect primarily due to their very slow (and cold-blooded and hypoxic) metabolism.

In plants

In plants,

aspen Aspen is a common name for certain tree species; some, but not all, are classified by botanists in the section ''Populus'', of the ''Populus'' genus. Species These species are called aspens: *'' Populus adenopoda'' – Chinese aspen (China ...

trees are one example of

biological immortality Biological immortality (sometimes referred to as bio-indefinite mortality) 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, ...

. Each individual tree can live for 40–150 years above ground, but the

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

system of the

clonal colony A clonal colony or genet is a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor. In plants, an individual in s ...

is long-lived. In some cases, this is for thousands of years, sending up new trunks as the older trunks die off above ground. One such colony in

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

, given the nickname of "Pando", is estimated to be 80,000 years old, making it possibly the oldest living colony of aspens. The world's oldest known living non- clonal organism was the Methuselah tree of the species ''

Pinus longaeva ''Pinus longaeva'' (commonly referred to as the Great Basin bristlecone pine, intermountain bristlecone pine, or western bristlecone pine) is a long-living species of bristlecone pine tree found in the higher mountains of California, Nevada, and ...

'', the bristlecone pine, growing high in the White Mountains of

Inyo County Inyo County () is a county in the eastern central part of the U.S. state of California, located between the Sierra Nevada and the state of Nevada. In the 2020 census, the population was 19,016. The county seat is Independence. Inyo County is o ...

in eastern

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, aged years. This record was superseded in 2012 by another Great Basin bristlecone pine located in the same region as Methuselah, and was estimated to be 5,062 years old. The tree was sampled by Edmund Schulman and dated by Tom Harlan. Ginkgo trees in China resist aging by extensive

gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...

associated with adaptable

defense mechanisms In psychoanalytic theory, a defence mechanism (American English: defense mechanism), is an Unconscious mind, unconscious psychological operation that functions to protect a person from anxiety-producing thoughts and feelings related to interna ...

that collectively contribute to longevity.

In bacteria

Among

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

, individual organisms are vulnerable and can easily die, but on the level of the

colony In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the ''metropole, metropolit ...

, bacteria can live indefinitely. The two daughter bacteria resulting from

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

of a parent bacterium can be regarded as unique individuals or as members of a biologically "immortal" colony. 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. See

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...

Maximum life span

Some examples of maximum observed life span of animals thought to be negligibly senescent are:

Cryptobiosis

Some rare organisms, such as

tardigrade Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ...

s, usually have short lifespans, but are able to survive for thousands of years—and, perhaps, indefinitely—if they enter into the state of

cryptobiosis Cryptobiosis or anabiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop ...

, whereby their

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

is reversibly suspended.

References