Negligible senescence

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Some tortoises show negligible senescence. Testudo horsfieldii locking into the camera.jpg
Some tortoises show negligible senescence.

Negligible senescence is a term coined by biogerontologist Caleb Finch to denote organisms that do not exhibit evidence of biological aging (senescence), such as measurable reductions in their reproductive capability, measurable functional decline, or rising death rates with age. [1] There are many species where scientists have seen no increase in mortality after maturity. [1] 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. [2]

Contents

Study of negligibly senescent animals may provide clues that lead to better understanding of the aging process and influence theories of aging. [1] [3] The phenomenon of negligible senescence in some animals is a traditional argument for attempting to achieve similar negligible senescence in humans by technological means.

In vertebrates

Some fish, such as some varieties of sturgeon and rougheye rockfish, and some tortoises and turtles [4] are thought to be negligibly senescent, although recent research on turtles has uncovered evidence of senescence in the wild. [2] The age of a captured fish specimen can be measured by examining growth patterns similar to tree rings on the otoliths (parts of motion-sensing organs). [5]

In 2018, naked mole-rats 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. [6] [7] [8]

In plants

In plants, aspen trees are one example of biological immortality. Each individual tree can live for 40–150 years above ground, but the root system of the clonal colony 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, given the nickname of "Pando", is estimated to be 80,000 years old, making it possibly the oldest living colony of aspens. [9]

The world's oldest known living non-clonal organism was the Methuselah tree of the species Pinus longaeva , the bristlecone pine, growing high in the White Mountains of Inyo County in eastern California, aged 4855–4856 years. [10] 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. [11]

Ginkgo trees in China resist aging by extensive gene expression associated with adaptable defense mechanisms that collectively contribute to longevity. [12]

In bacteria

Among bacteria, individual organisms are vulnerable and can easily die, but on the level of the colony, bacteria can live indefinitely. 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" colony. [13] 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. [14] See asexual reproduction.

Maximum life span

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

Rougheye rockfish 205 years [15] [16]
Aldabra giant tortoise 255 years
Lobsters 100+ years (presumed) [17]
Hydras Observed to be biologically immortal [18]
Planaria Observed to be biologically immortal [19]
Sea anemones 60–80 years (generally) [20]
Red sea urchin 200 years [21]
Freshwater pearl mussel 210–250 years [22] [23]
Ocean quahog clam 507 years [24]
Greenland shark 400 years [25]

Cryptobiosis

Some rare organisms, such as tardigrades, usually have short lifespans, but are able to survive for thousands of years—and, perhaps, indefinitely—if they enter into the state of cryptobiosis, whereby their metabolism is reversibly suspended.[ citation needed ]

Negative senescence

There are also organisms[ which? ] that exhibit negative senescence, [26] 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 [27] (see also Late-life mortality deceleration). Furthermore, there are species that have been observed to regress to a larval state and regrow into adults multiple times, such as Turritopsis dohrnii . [28]

See also

Related Research Articles

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 involves an increase in death rates and/or a decrease in fecundity with increasing age, at least in the later part of an organism's life cycle. However, the resulting effects of senescence can be delayed. The 1934 discovery that calorie restriction can extend lifespans by 50% in rats, the existence of species having negligible senescence, and the existence of potentially immortal organisms such as members of the genus Hydra have motivated research into delaying senescence and thus age-related diseases. Rare human mutations can cause accelerated aging diseases.

Life extension is the concept of extending the human lifespan, either modestly through improvements in medicine or dramatically by increasing the maximum lifespan beyond its generally-settled limit of 125 years. Several researchers in the area, along with "life extensionists", "immortalists", or "longevists", postulate that future breakthroughs in tissue rejuvenation, stem cells, regenerative medicine, molecular repair, gene therapy, pharmaceuticals, and organ replacement will eventually enable humans to have indefinite lifespans through complete rejuvenation to a healthy youthful condition (agerasia). The ethical ramifications, if life extension becomes a possibility, are debated by bioethicists.

<span class="mw-page-title-main">Longevity</span> Longer than typical lifespan, especially of humans

Longevity may refer to especially long-lived members of a population, whereas life expectancy is defined statistically as the average number of years remaining at a given age. For example, a population's life expectancy at birth is the same as the average age at death for all people born in the same year.

Maximum life span is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the maximum amount of time that a member of a given species could survive between birth and death, provided circumstances that are optimal to that member's longevity.

The free radical theory of aging states that organisms age because cells accumulate free radical damage over time. A free radical is any atom or molecule that has a single unpaired electron in an outer shell. While a few free radicals such as melanin are not chemically reactive, most biologically relevant free radicals are highly reactive. For most biological structures, free radical damage is closely associated with oxidative damage. Antioxidants are reducing agents, and limit oxidative damage to biological structures by passivating them from free radicals.

<span class="mw-page-title-main">Biogerontology</span> Sub-field of gerontology

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 with the start of the journal BIOGERONTOLOGY in 2000. It involves interdisciplinary research on the causes, effects, and mechanisms of biological aging. Biogerontologist Leonard Hayflick has said that the natural average lifespan for a human is around 92 years and, if humans do not invent new approaches to treat aging, they will be stuck with this lifespan. James Vaupel has predicted that life expectancy in industrialized countries will reach 100 for children born after the year 2000. Many surveyed biogerontologists have predicted life expectancies of more than three centuries for people born after the year 2100. Other scientists, more controversially, suggest the possibility of unlimited lifespans for those currently living. For example, Aubrey de Grey offers the "tentative timeframe" that with adequate funding of research to develop interventions in aging such as strategies for engineered negligible senescence, "we have a 50/50 chance of developing technology within about 25 to 30 years from now that will, under reasonable assumptions about the rate of subsequent improvements in that technology, allow us to stop people from dying of aging at any age". The idea of this approach is to use presently available technology to extend lifespans of currently living humans long enough for future technological progress to resolve any remaining aging-related issues. This concept has been referred to as longevity escape velocity.

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, including some vertebrates, achieve this state either throughout their existence or after living long enough. A biologically immortal living being can still die from means other than senescence, such as through injury, poison, disease, predation, lack of available resources, or changes to environment.

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<span class="mw-page-title-main">Ageing</span> Biological process of getting older

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The anti-aging movement is a social movement devoted to eliminating or reversing aging, or reducing the effects of it. A substantial portion of the attention of the movement is on the possibilities for life extension, but there is also interest in techniques such as cosmetic surgery which ameliorate the effects of aging rather than delay or defeat it.

<span class="mw-page-title-main">Biomarkers of aging</span> Type of biomarkers

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<span class="mw-page-title-main">Genetics of aging</span> Overview of the genetics of aging

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<span class="mw-page-title-main">Rochelle Buffenstein</span> American biologist

Rochelle (Shelley) Buffenstein is an American comparative biologist currently working as Research Professor at the University of Illinois Chicago. Previously, she was a senior principal investigator at Calico Life Sciences, an Alphabet, Inc. funded research and development company investigating the biology that controls aging and lifespan where she used the extraordinarily long-lived cancer resistant naked mole-rat as an attractive counter-example to the inevitability of mammalian aging; for at ages greatly exceeding the expected maximum longevity for this mouse-sized rodent, they fail to exhibit meaningful changes in age-related risk of dying or physiological decline. As such these rodents likely provide the blueprint for how to stave off myriad adverse effects of aging and provide proof of concept that age-related health decline can be avoided in humans.

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<span class="mw-page-title-main">Relationship between telomeres and longevity</span>

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References

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  2. 1 2 Warner DA, Miller DA, Bronikowski AM, Janzen FJ (June 2016). "Decades of field data reveal that turtles senesce in the wild". Proceedings of the National Academy of Sciences of the United States of America. 113 (23): 6502–6507. Bibcode:2016PNAS..113.6502W. doi: 10.1073/pnas.1600035113 . PMC   4988574 . PMID   27140634.
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  9. ↑ Quaking Aspen by the Bryce Canyon National Park Service.
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  15. ↑ Munk K (2001). "Maximum Ages of Groundfishes in Waters off Alaska and British Columbia and Considerations of Age Determination". Alaska Fishery Research Bulletin. 8: 1.
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  17. ↑ "140-year-old lobster's tale has a happy ending". Associated Press. January 10, 2009.
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  24. ↑ Munro D, Blier PU (October 2012). "The extreme longevity of Arctica islandica is associated with increased peroxidation resistance in mitochondrial membranes". Aging Cell. 11 (5): 845–855. doi: 10.1111/j.1474-9726.2012.00847.x . PMID   22708840.
  25. ↑ Pennisi E (11 August 2016). "Greenland Shark May Live 400 Years, Smashing Longevity Record". Science Magazine.
  26. ↑ James W Vaupel 1 , Annette Baudisch, Martin Dölling, Deborah A Roach, Jutta Gampe. "The case for negative senescence". PubMed. Archived from the original on 2023-09-18.{{cite web}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  27. ↑ Ainsworth C, Lepage M (2007). "Evolution's greatest mistakes". New Scientist. 195 (2616): 36–39. doi:10.1016/S0262-4079(07)62033-8.
  28. ↑ "Cheating Death: The Immortal Life Cycle of Turritopsis". 8e.devbio.com. Archived from the original on 2010-04-02. Retrieved 2010-03-17.
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