Longevity

Longevity is defined as long life or the length of a person's life (life expectancy). Reflections on longevity have usually gone beyond acknowledging the basic shortness of human life and have included thinking about methods to extend life. There are many dificulties to authenticate largest human lifespan ever, because of inaccurate birth statistics in 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.

Presently
Various factors contribute to an individual's longevity. Significant factors in life expectancy include gender, genetics, access to health care, hygiene, diet, exercise and lifestyle. 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)

Tobacco smoking is generally accepted to significantly reduce longevity, and is one of the main statistical factors explaining differences in life expectancy between advanced nations. This may be offset by other factors; Japan, a country with a high rate of tobacco consumption, has one of the highest life expectancies in the world (81.15 years, 2005 est ). Hong Kong, a dense 7 million people city with constant stress, recently reported a higher life expectancy than Japan (81.39 years, 2005 est ) Population longevities can be seen as increasing due to increases in life expectancies around the world :
 * Australia: . . 80     years in 2002, 80.39 years in 2005
 * Spain:. . . . . 81.02 years in 2002, 82.31 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

Records
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) - oldest person ever whose age has been verified by modern documentation; born 1875. 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) - oldest male ever recognized by the Guinness Book of World Records; authentication largely questioned by modern conflation.
 * Christian Mortensen (1882-1998, 115 years 252 days) - 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, 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.

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.

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 296(5570):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."

Some argue that molecular nanotechnology will greatly extend human lifespans. See medical nanotechnology.

Non-human biological longevity
Living: Dead:
 * Methuselah (tree) - 4700-year-old bristlecone pine in the White Mountains of California, the oldest known living organism.
 * Chimpanzee - a 74-year old chimpanzee, the longest lived known chimpanzee.
 * Adwaitya - an Aldabra Giant Tortoise, died 2006 at 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 3-7186-4983-7

John Robbins' Healthy at 100 (see ) 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.