Longevity
Longevity is a term that generally refers to 'long life' or 'great duration of life'.  Reflections on longevity have usually gone beyond acknowledging the basic shortness of human life and have included thinking about methods to extend life. Longevity has been a topic not only for the scientific community but also for writers of travel, science fiction and utopian novels. There are many difficulties to authenticate the longest human lifespan ever, because of inaccurate birth statistics in the past; though fiction, legend, and mythology have proposed or claimed vastly longer lifespans in the past or future and longevity myths frequently allege them to exist in the present.
The word 'longevity' is sometimes used as a synonym for 'life expectancy' in demography. However, this is not the most popular or accepted definition, . For the general public as well as writers, the word generally connotes 'long life', especially when it concerns someone or something lasting longer than expected (an 'ancient tree', for example).

# Presently
Various factors contribute to an individual's longevity.  Significant factors in life expectancy include gender, genetics, access to health care, hygiene, diet, exercise, lifestyle, and crime rates.  Below is a list of life expectancies in different types of countries:
- First World: . . . 77-83 years (eg. Canada: 80.1 years, 2005 est)
- Third World:. . . 35-60 years (eg. Mozambique: 40.3 years, 2005 est)
Population longevities can be seen as increasing due to increases in life expectancies around the world:
- Spain:. . . . . 81.02 years in 2002, 82.31 years in 2005
- Australia: . . 80      years in 2002, 80.39 years in 2005
- Italy:. . . . . . 79.25 years in 2002, 79.68 years in 2005
- France: . . . .79.05 years in 2002, 79.60 years in 2005
- Germany: . . 77.78 years in 2002, 78.65 years in 2005
- UK: . . . . . . 77.99 years in 2002, 78.4  years in 2005
- USA: . . . . .  77.4       years in 2002,   77.7  years in 2005
The current validated longevity records can be found in the list of supercentenarians. Notable individuals include:
- Jeanne Calment (1875-1997, 122 years and 164 days) - the oldest person in history whose age has been verified by modern documentation.  This defines the human lifespan, which is set by the oldest documented individual who ever lived
- Shigechiyo Izumi (1865-1986, 120 years 237 days, disputed) - the oldest male ever recognized by the Guinness Book of World Records; this is widely questioned by scholars, who believe that conflation of dates has occurred and this has compromised the authenticity of Izumi's age
- Christian Mortensen (1882-1998, 115 years 252 days) - the oldest male widely accepted by scholars.

# History
Reaching an old age has fascinated people for ages. There are many organizations dedicated to exploring the causes behind aging, ways to prevent aging, and ways to reverse aging. Despite the fact that it is no more than human nature to not wish to surrender to old age and death, a few organizations are against antiaging, because they believe it sacrifices the best interests of the new generation, that it is unnatural, or unethical. Others are dedicated towards it, seeing it as a form of transhumanism and the pursuit of immortality. Even among those who do not wish for eternal life, longevity may be desired to experience more of life, or to provide a greater contribution to humanity.
A remarkable statement mentioned by Diogenes Laertius (c. 250) is the earliest (or at least one of the earliest) references about (plausible centenarian) longevity given by a scientist, the astronomer Hipparchus of Nicea (c. 185  c. 120 B.C.), who, according to the doxographer,  assured that the philosopher Democritus of Abdera (c. 470/460  c. 370/360 B.C.) lived 109 years. All other account given by the ancients about the age of Democritus, appears to, without giving any specific age, agree in the fact that the philosopher lived over 100 years; possibility that turns out to be likely given, not only by the fact that many ancient Greek philosophers are thought to have lived over the age of 90 (e.g.:  Xenophanes of Colophon, c. 570/565  c. 475/470 B.C., Pyrrho of Ellis, c. 360 - c. 270 B.C.,  Eratosthenes of Cirene c. 285  c. 190 B.C., etc.), but also because of the difference that the case of Democritus evidences from the case of, for example, Epimenides of Crete (VII, VI centuries B.C.) of whom it is said to have lived 154, 157 or 290 years, like it has been said about countless elders even during the last centuries (as well as in present time) being these cases most likely (or at least in most cases), exaggerations if not deliberate frauds.

# Religion
The Bible contains many accounts of long-lived humans, the oldest being Methuselah living to be 969 years old (Genesis 5:27). Today some maintain that the unusually high longevity of Biblical patriarchs are the result of an error in translation: lunar cycles were mistaken for the solar ones, and that the actual ages being described would have been 12.4 times less (a lunar cycle being 29.5 days). This makes Methuselah's age only 78. This rationalization, however, seems doubtful too since patriarchs such as Mahalalel (ibid 5:15) and Enoch (ibid 5:21) were said to have become fathers after 65 "years". If the lunar cycle claim were accepted this would translate to an age of about 5 years and 3 months.
One Christian apologist claim is that the life span of humans has changed; that originally man was to have everlasting life, but due to man's sin, God progressively shortened man's life in the "four falls of mankind" -- first to less than 1000 years, then to under 500, 200, and eventually 120 years. After those long living people died around the time of the Biblical Flood, God decided that humans would not be permitted to live more than 120 years (Genesis 6:3.) However, since later biblical figures (and more recent people) such as Sarah lived for longer than that, 120 years should be considered the "usual" upper  limit to man's lifespan. Some individuals can live slightly longer than that.
Another theory proposed by a self described rational faith apologist is based on the fact that some longevity specialists propose that aging occurs primarily due to telomere shortening during cell replication. Each time a cell replicates itself telomeres lose length until finally, replication cannot occur and the cells die. The theory postulates that prior to the flood there existed a thick cloud cover as described in Genesis. This cover protected DNA from UV and other radiation and their subsequent destructive mutation. Post flood with the cloud cover removed, UV rays and radiation could have caused both DNA and cellular destruction; specifically the type that cause telomere shortening or accelerated telomere shortening. As this mutation was passed on, shorter life spans would result for presumably both human and animals.
It has been hypothesized that there is a trade-off between cancerous tumor suppression and tissue repair capacity, and that by lengthening telomeres we might slow aging and in exchange increase vulnerability to cancer (Weinstein and Ciszek, 2002). Experimentation with telomeres on worms has yielded increased worm life spans by about 20% (Joeng et al., 2004).
Even if further study shows that telomeres specifically are not tied to aging, the concept that some sort of DNA damage can cause genetically accelerated aging cannot be abandoned, thus providing a rational explanation for longevity and a subsequent reduction of longevity post-flood.
Many cultures like the Sumerians and Indus Valley also document groups of people who lived many 100s of years. Both cultures show reduced life spans after the flood.
Furthermore, starting with reformers John Calvin and Martin Luther, an alternative explanation has arisen : 120 years would not refer to man's lifespan but to the amount of time left before the flood.]
A more commonly accepted explanation is that such stories are longevity myths; age exaggeration tends to be greater in "mythical" periods in many cultures; the early emperors of Japan or China often ruled for more than a century, according to tradition. With the advent of modern accountable record-keeping, age claims fell to realistic levels; even later in the Bible King David died at 70 years; other kings in their 30s, 40s, and 50s.

# Future
The mainstream view on the future of longevity, such as the US Census Bureau, is that life expectancy in the USA will be in the mid-80s by 2050 (up from 77.85 in 2006) and will top out eventually in the low 90s, barring major scientific advances that can change the rate of human aging itself, as opposed to merely treating the effects of aging as is done today. The Census Bureau also predicted that the USA would have 5.3 million people aged over 100 in 2100 (Which means that, if this turns out to be true, those people are children and toddlers today).
Recent increases in the rates of lifestyle diseases, such as obesity, diabetes, hypertension, and heart disease, may however drastically slow or reverse this trend toward increasing life expectancy in the developed world.
Oeppen and Vaupel (see Science):1029, 2002) have observed that since 1840 record life expectancy has risen linearly for men and women, albeit more slowly for men. For women the increase has been almost three months/year.  In light of steady increase, without any sign of a cap, the suggestion that life expectancy will top out must be treated with caution.  Oeppen and Vaupel observe that experts who assert that "life expectancy is approaching a ceiling ... have repeatedly been proven wrong."It is thought that life expectancy for women increased more dramatically due to the considerable increases in medicine related to childbirth.
Some argue that molecular nanotechnology will greatly extend human lifespans. See medical nanotechnology.

# Non-human biological longevity
Living:
- Methuselah (tree) -  4,700-year-old bristlecone pine in the White Mountains of California, the oldest known living tree.
- Cheeta - a 75-year old chimpanzee, the longest lived known chimpanzee.
Dead:
- Adwaitya - an Aldabra Giant Tortoise, died 2006 at between 150-255 years old, the oldest known animal.
- A Bowhead Whale killed in a hunt was found to be approximately 211 years old, the longest lived mammal known.
- Lamellibrachia luymesi, a deep-sea cold seep tubeworm, is estimated to reach ages of over 250 years based on a model of its growth rates.

# Scientific books on longevity
- Leonid A. Gavrilov & Natalia S. Gavrilova (1991), The Biology of Life Span: A Quantitative Approach. New York: Harwood Academic Publisher, ISBN
- John Robbins' Healthy at 100 garners evidence from many scientific sources to account for the extraordinary longevity of Abkhasians in the Caucasus, Vilcabambans in the Andes, Hunzas in Central Asia, and Okinawans.
- Beyond The 120-Year Diet, by Roy L. Walford, M.D.
- Forever Young: A Cultural History of Longevity from Antiquity to the Present Door Lucian Boia,2004 ISBN 1861891547

# Longevity in fiction
- Abh: "Crest of the Stars"
- James Hilton: Lost Horizon
- P.D. James: The Children of Men
- James L. Halperin: The First Immortal
- John Wyndham: Trouble with Lichen
- Robert A. Heinlein: Time Enough for Love, Methuselah's Children, and others.
- Poul Anderson: The Boat of a Million Years
- Arthur C. Clarke: 2001: A Space Odyssey
- David Brin & Gregory Benford: Heart of the Comet
- Kim Stanley Robinson's Mars trilogy
- Roger Zelazny: This Immortal, Lord of Light, *The Amber series
- J. K. Rowling: Harry Potter and the Philosopher's Stone (The Philosopher's Stone and Nicolas Flamel)
- J. R. R. Tolkien: The Silmarillion (Dunedain)
- J. R. R. Tolkien: The Lord of the Rings (Aragorn, Bilbo and Gollum)
- Bruce Sterling: Holy Fire
- Yoda: Star Wars
- Chewbacca: Star Wars
- Isaac Asimov: The Robot Novels (R. Daneel Olivaw, The Spacers)
- Tom Robbins: Jitterbug Perfume
- Frank Herbert: Dune universe
- Robert Jordan: The Wheel of Time
- Peter F. Hamilton: Misspent Youth
- James Blish: Cities in Flight
- Jonathan Swift: Gulliver's Travels (The Struldbrug)
- Jack L. Chalker: Well World Series character "Nathan Brazil" - is an immortal'"
- Goa'uld, Ancients (Stargate), Wraith (Stargate): Stargate SG-1 and Stargate Atlantis
- Joe Haldeman: The Long Habit of Living
- Anne McCaffrey: The Ship Who Sang, The Ship Who Searched and others in the Brain Ship series
- Andrew Martin: The Bicentennial Man
- Sid Meier: Sid Meier's Alpha Centauri (Longevity Vaccine)

# Notes
-  Jump up to: 3.0 3.1 CIA World Fact Book
-  CIA World Fact Book 2002