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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. but it 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.
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 naked mole-rat, 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 the genus Heterocephalus.
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.
The age of onset is the age at which an individual acquires, develops, or first experiences a condition or symptoms of a disease or disorder. For instance, the general age of onset for the spinal disease scoliosis is "10-15 years old," meaning that most people develop scoliosis when they are of an age between ten and fifteen years.
Enquiry into the evolution of ageing, or aging, aims to explain why a detrimental process such as ageing would evolve, and why there is so much variability in the lifespans of organisms. The classical theories of evolution suggest that environmental factors, such as predation, accidents, disease, and/or starvation, ensure that most organisms living in natural settings will not live until old age, and so there will be very little pressure to conserve genetic changes that increase longevity. Natural selection will instead strongly favor genes which ensure early maturation and rapid reproduction, and the selection for genetic traits which promote molecular and cellular self-maintenance will decline with age for most organisms.
Eternal youth is the concept of human physical immortality free of ageing. The youth referred to is usually meant to be in contrast to the depredations of aging, rather than a specific age of the human lifespan. Eternal youth is common in mythology, and is a popular theme in fiction.
Brandt's bat or Brandt's myotis is a species of vesper bat in the family Vespertilionidae. It is native throughout most of Europe and parts of western Asia.
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. 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.
The rate of living theory postulates that the faster an organism’s metabolism, the shorter its lifespan. First proposed by Max Rubner in 1908, the theory was based on his observation that smaller animals had faster metabolisms and shorter lifespans compared to larger animals with slower metabolisms. The theory gained further credibility through the work of Raymond Pearl, who conducted experiments on drosophila and cantaloupe seeds, which supported Rubner's initial observation. Pearl's findings were later published in his book, The Rate of Living, in 1928, in which he expounded upon Rubner's theory and demonstrated a causal relationship between the slowing of metabolism and an increase in lifespan.
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.
Steven N. Austad is the Protective Life Endowed Chair in Health Aging Research, a Distinguished professor and Chair of the Department of Biology at the University of Alabama at Birmingham.
The disposable soma theory of aging states that organisms age due to an evolutionary trade-off between growth, reproduction, and DNA repair maintenance. Formulated by Thomas Kirkwood, the disposable soma theory explains that an organism only has a limited amount of resources that it can allocate to its various cellular processes. Therefore, a greater investment in growth and reproduction would result in reduced investment in DNA repair maintenance, leading to increased cellular damage, shortened telomeres, accumulation of mutations, compromised stem cells, and ultimately, senescence. Although many models, both animal and human, have appeared to support this theory, parts of it are still controversial. Specifically, while the evolutionary trade-off between growth and aging has been well established, the relationship between reproduction and aging is still without scientific consensus, and the cellular mechanisms largely undiscovered.
The mitochondrial theory of ageing has two varieties: free radical and non-free radical. The first is one of the variants of the free radical theory of ageing. It was formulated by J. Miquel and colleagues in 1980 and was developed in the works of Linnane and coworkers (1989). The second was proposed by A. N. Lobachev in 1978.
The mutation accumulation theory of aging was first proposed by Peter Medawar in 1952 as an evolutionary explanation for biological aging and the associated decline in fitness that accompanies it. Medawar used the term 'senescence' to refer to this process. The theory explains that, in the case where harmful mutations are only expressed later in life, when reproduction has ceased and future survival is increasingly unlikely, then these mutations are likely to be unknowingly passed on to future generations. In this situation the force of natural selection will be weak, and so insufficient to consistently eliminate these mutations. Medawar posited that over time these mutations would accumulate due to genetic drift and lead to the evolution of what is now referred to as aging.
Lifespan: Why We Age – and Why We Don't Have To is a book by David A. Sinclair.
This timeline lists notable events in the history of research into senescence or biological aging, including the research and development of life extension methods, brain aging delay methods and rejuvenation.
The Siberian bat or Siberian whiskered myotis is a species of vesper bat in the family Vespertilionidae. It is found throughout northeastern Asia, primarily in Siberia. It is known for its high life expectancy relative to its body size, approximately twice that of humans, and holds the record for the oldest bat; in 2005, one individual was discovered in a cave in Siberia that had been banded in 1964, making the bat at least 41 years old.
References
- ↑ Austad, S. N.; Fischer, K. E. (1 March 1991). "Mammalian Aging, Metabolism, and Ecology: Evidence From the Bats and Marsupials". Journal of Gerontology. 46 (2): B47–B53. doi:10.1093/geronj/46.2.B47. PMID 1997563.
- ↑ Austad, Steven N. (2022). Methuselah's Zoo: What Nature Can Teach Us about Living Longer, Healthier Lives. MIT Press. ISBN 978-0-262-04709-8. OCLC 1286312358.[ page needed ]
- ↑ Prothero, John; Jürgens, Klaus D. (1987). "Scaling of Maximal Lifespan in Mammals: A Review". Evolution of Longevity in Animals. Vol. 42. pp. 49–74. doi:10.1007/978-1-4613-1939-9_4. ISBN 978-1-4612-9077-3. PMID 3325028.
{{cite book}}:|journal=ignored (help) - ↑ Austad, S. N. (January 2010). "Methusaleh's Zoo: how nature provides us with clues for extending human health span". Journal of Comparative Pathology. 142 (Suppl 1): S10–21. doi:10.1016/j.jcpa.2009.10.024. PMC 3535457 . PMID 19962715.
- ↑ Buffenstein, R. (1 November 2005). "The Naked Mole-Rat: A New Long-Living Model for Human Aging Research". The Journals of Gerontology Series A: Biological Sciences and Medical Sciences. 60 (11): 1369–1377. doi:10.1093/gerona/60.11.1369. PMID 16339321.
- ↑ Wilkinson, Gerald S.; Adams, Danielle M. (April 2019). "Recurrent evolution of extreme longevity in bats". Biology Letters. 15 (4): 20180860. doi:10.1098/rsbl.2018.0860. PMC 6501359 . PMID 30966896.
- ↑ Podlutsky, A. J.; Khritankov, A. M.; Ovodov, N. D.; Austad, S. N. (1 November 2005). "A New Field Record for Bat Longevity". The Journals of Gerontology Series A: Biological Sciences and Medical Sciences. 60 (11): 1366–1368. doi: 10.1093/gerona/60.11.1366 . PMID 16339320.
- ↑ Hulbert, A. J.; Pamplona, Reinald; Buffenstein, Rochelle; Buttemer, W. A. (October 2007). "Life and Death: Metabolic Rate, Membrane Composition, and Life Span of Animals". Physiological Reviews. 87 (4): 1175–1213. doi:10.1152/physrev.00047.2006. PMID 17928583.