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).

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 in authenticating the longest human lifespan ever, due to inaccurate birth statistics; 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.

A life annuity is a form of longevity insurance.

History

Longevity according to the psalms of the Bible was estimated on average to be "threescore and ten", that is 70 years, and "by reason of strength be extended to fourscore", that is 80 years. In addition, Solon, the famous lawgiver of Ancient Greece, in his dialogue with Croesus stated 70 as the allotted length of life for man. fact: date=July 2008 The longest living person as recorded in the Old Testament was Methuselah, who was said to have lived nearly a millennium.

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 human nature not to 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 and/or that it is unnatural and/or unethical. Others are dedicated to 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 accounts given by the ancients about the age of Democritus appear to, without giving any specific age, agree on the fact that the philosopher lived over 100 years. This is a possibility that turns out to be likely, given 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.) and because of the difference that the case of Democritus evidences from the case of, for example, Epimenides of Crete (VII, VI centuries B.C.), 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.