Longevity

The word "longevity" is sometimes used as a synonym for "life expectancy" in demography or known as "long life", especially when it concerns someone or something lasting longer than expected (an ancient tree, for example).

Reflections on longevity have usually gone beyond acknowledging the brevity 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 in authenticating the longest human life span ever by modern verification standards, owing to inaccurate or incomplete birth statistics. Fiction, legend, and folklore have proposed or claimed life spans in the past or future vastly longer than those verified by modern standards, and longevity narratives and unverified longevity claims frequently speak of their existence in the present.

A life annuity is a form of longevity insurance.

History
A remarkable statement mentioned by Diogenes Laertius (c. 250 AD) 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 BC), who, according to the doxographer, was assured that the philosopher Democritus of Abdera (c. 470/460 – c. 370/360 BC) lived 109 years. All other accounts given by the ancients about the age of Democritus appear, without giving any specific age, to agree that the philosopher lived over 100 years. This possibility is likely, given 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 BC, Pyrrho of Ellis, c. 360 – c. 270 BC,  Eratosthenes of Cirene, c. 285 – c. 190 BC, etc.). The case of Democritus is different from the case of, for example, Epimenides of Crete (7th, 6th centuries BC), who is said to have lived 154, 157 or 290 years, as has been said about countless elders even during the last centuries as well as in the present time. These cases are not verifiable by modern means.

Present life expectancy
Various factors contribute to an individual's longevity. Significant factors in life expectancy include gender, genetics, access to health care, hygiene, diet and nutrition, exercise, lifestyle, and crime rates. Below is a list of life expectancies in different types of countries:
 * First World: 77–83 years (e.g. Canada: 81.29 years, 2010 est.)
 * Third World: 32–80 years (e.g. Mozambique: 41.37 years, 2010 est.)

Population longevities are increasing as life expectancies around the world grow:
 * Spain: 79.08 years in 2002, 81.07 years in 2010
 * Australia: 80 years in 2002, 81.72 years in 2010
 * Italy: 79.25 years in 2002, 80.33 years in 2010
 * France: 79.05 years in 2002, 81.09 years in 2010
 * Germany: 77.78 years in 2002, 79.41 years in 2010
 * UK: 77.99 years in 2002, 79.92 years in 2010
 * USA: 77.4 years in 2002, 78.24 years in 2010

Long-lived individuals
The Gerontology Research Group validates current longevity records by modern standards, and maintains a list of supercentenarians; many other unvalidated longevity claims exist. Record-holding individuals include:
 * Jeanne Calment (1875–1997, 122 years, 164 days): the oldest person in history whose age has been verified by modern documentation. This defines the modern human life span, which is set by the oldest documented individual who ever lived.
 * Sarah Knauss (1880-1999, 119 years, 97 days): The second oldest documented person in modern times and the oldest American.
 * Christian Mortensen (1882-1998, 115 years, 252 days): the oldest man in history whose age has been verified by modern documentation.
 * Besse Cooper (1896-): Celebrated her 115th birthday in August 2011, making her the fourth person documented as having exceeded 114 years.

While various other individuals have lived between 110 and 114 years, the above-mentioned people are the only ones known to have lived longer than 114.

Longevity and lifestyle
Evidence-based studies indicate that longevity is based on two major factors, genetics and lifestyle choices. Twin studies have estimated that approximately 20-30% of an individual’s lifespan is related to genetics, the rest is due to individual behaviors and environmental factors which can be modified. In addition, it found that lifestyle plays almost no factor in health and longevity after the age of 80, and that almost everything in advanced age is due to genetic factors.

In preindustrial times, deaths at young and middle age were common, and lifespans over 70 years were comparatively rare. This is not due to genetics, but because of environmental factors such as disease, accidents, and malnutrition, especially since the former were not generally treatable with pre-20th century medicine. Deaths from childbirth were common in women, and many children did not live past infancy. In addition, most people who did attain old age were likely to die quickly from the above-mentioned untreatable health problems. Despite this, we do find numerous examples of pre-20th century individuals attaining lifespans of 75 years or greater, including Benjamin Franklin, Thomas Jefferson, John Adams, Cato the Elder, Thomas Hobbes, and Michaelangelo.

For example, an 1871 census in the UK (the first of its kind) found the average male life expectancy as being 44, but if infant mortality is subtracted, males who lived to adulthood averaged 75 years. The present male life expectancy in the UK is 77 years for males and 81 for females (the United States averages 74 for males and 80 for females).

Studies have shown that African-American males have the shortest lifespans of any group of people in the US, averaging only 69 years (white females average the longest). This reflects overall poorer health and greater prevalence of heart disease, obesity, diabetes, and cancer among African-American men.

Women normally outlive men, and this was as true in pre-industrial times as today. Reasons for this include smaller bodies (and thus less stress on the heart), a stronger immune system (since testosterone acts as an immunosuppressant), and less tendency to engage in physically dangerous activities. It is also theorized that women have an evolutionary reason to live longer so as to help care for grandchildren and great grandchildren.

Study of the regions of the world known as blue zones, where people commonly live active lives past 100 years of age, have shown that longevity is related to a healthy social and family life, not smoking, eating a plant-based diet, frequent consumption of legumes and nuts, and engaging in regular physical activity. In another well-designed cohort study, the combination of a plant based diet, frequent consumption of nuts, regular physical activity, normal BMI, and not smoking accounted for differences up to 10 years in life expectancy. The Alameda County Study discovered three additional lifestyle characteristics that promote longevity: limiting alcohol consumption, sleeping 7 to 8 hours per night, and not snacking (eating between meals).

Longevity traditions
Longevity traditions are traditions about long-lived people (generally supercentenarians), and practices that have been believed to confer longevity. A comparison and contrast of "longevity in antiquity" (such as the Sumerian King List, the genealogies of Genesis, and the Persian Shahnameh) with "longevity in historical times" (common-era cases through twentieth-century news reports) is elaborated in detail in Lucian Boia's 2004 book Forever Young: A Cultural History of Longevity from Antiquity to the Present and other sources.

The Fountain of Youth reputedly restores the youth of anyone who drinks of its waters. The New Testament, following older Jewish tradition, attributes healing to the Pool of Bethesda when the waters are "stirred" by an angel. After the death of Juan Ponce de León, Gonzalo Fernández de Oviedo wrote in Historia General y Natural de las Indias (1535) that Ponce de León was looking for the waters of Bimini to cure his aging. Traditions that have been believed to confer greater human longevity also include alchemy, such as that attributed to Nicolas Flamel. In the modern era, the Okinawa diet has some reputation of linkage to exceptionally high ages.

More recent longevity claims are subcategorized by many editions of Guinness World Records into four groups: "In late life, very old people often tend to advance their ages at the rate of about 17 years per decade .... Several celebrated super-centenarians (over 110 years) are believed to have been double lives (father and son, relations with the same names or successive bearers of a title) .... A number of instances have been commercially sponsored, while a fourth category of recent claims are those made for political ends ...." The estimate of 17 years per decade was corroborated by the 1901 and 1911 British censuses. Mazess and Forman also discovered in 1978 that inhabitants of Vilcabamba, Ecuador, claimed excessive longevity by using their fathers' and grandfathers' baptismal entries. Time magazine considered that, by the Soviet Union, longevity had elevated to a state-supported "Methuselah cult". Robert L. Ripley regularly reported supercentenarian claims in Ripley's Believe It or Not!, usually citing his own reputation as a fact-checker to claim reliability.

Future
The U.S. Census Bureau view on the future of longevity is that life expectancy in the United States 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 United States would have 5.3 million people aged over 100 in 2100. The United Nations has also made projections far out into the future, up to 2300, at which point it projects that life expectancies in most developed countries will be between 100 and 106 years and still rising, though more and more slowly than before. These projections also suggest that life expectancies in poor countries will still be less than those in rich countries in 2300, in some cases by as much as 20 years. The UN itself mentioned that gaps in life expectancy so far in the future may well not exist, especially since the exchange of technology between rich and poor countries and the industrialization and development of poor countries may cause their life expectancies to converge fully with those of rich countries long before that point, similarly to the way life expectancies between rich and poor countries have already been converging over the last 60 years as better medicine, technology, and living conditions became accessible to many people in poor countries. The UN has warned that these projections are uncertain, and caution that any change or advancement in medical technology could invalidate their projections.

Recent increases in the rates of lifestyle diseases, such as obesity, diabetes, hypertension, and heart disease, may drastically slow or reverse this trend toward increasing life expectancy in the developed world.

Scientist Olshansky examined how much mortality from various causes would have to drop in order to boost life expectancy and concluded that most of the past increases in life expectancy occurred because of improved survival rates for young people. He states that is seems unlikely that life expectancy at birth will ever exceed 85 years.

However, 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 per year. In light of steady increase, without any sign of limitation, the suggestion that life expectancy will top out must be treated with caution. Scientists 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 has increased more dramatically owing to the considerable advances in medicine related to childbirth.

Some argue that molecular nanotechnology will greatly extend human life spans. If the rate of increase of life span can be raised with these technologies to a level of twelve months increase per year, this is defined as effective biological immortality and is the goal of radical life extension.

Non-human biological longevity
Currently living: nonliving:
 * Methuselah: 4,800-year-old bristlecone pine in the White Mountains of California, the oldest currently living organism known.
 * Possibly 250 million year-old bacteria, bacillus permians, were revived from stasis after being found in sodium chloride crystals in a cavern in New Mexico. Russell Vreeland, and colleagues from West Chester University in Pennsylvania, reported on October 18, 2000 that they had revived the halobacteria after bathing them with a nutrient solution. Having survived for 250 million years, they are the oldest living organisms ever recorded. However, their findings have not been universally accepted.
 * A bristlecone pine nicknamed "Prometheus", felled in the Great Basin National Park in Nevada in 1964, found to be about 4,900 years old, is the longest-lived single organism known.
 * A quahog clam (Arctica islandica), dredged from off the coast of Iceland in 2007, was found to be from 400 to 410 years old, the oldest animal documented. Other clams of the species have been recorded as living up to 374 years.
 * 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.
 * Hanako (Koi Fish) was the longest-lived vertebrate ever recorded at 226 years.
 * A Bowhead Whale killed in a hunt was found to be approximately 211 years old (possibly up to 245 years old), the longest lived mammal known.
 * Tu'i Malila, a radiated tortoise presented to the Tongan royal family by Captain Cook, lived for over 185 years. It is the oldest documented reptile. Adwaitya, an Aldabra Giant Tortoise, may have lived for up to 250 years.

Biological Immortality
Certain exotic organisms do not seem to be subject to aging and can live indefinitely. Examples include Tardigrades and Hydras. That is not to say that these organisms are invincible, merely that they only die as a result of disease or injury rather than age-related deterioration (and that they are not subject to the Hayflick limit).