longevity, term denoting the length or duration of the life of an animal or plant, often used to indicate an unusually long life. The average human life-span of threescore and ten years cited in the Bible has been attained only in recent years in areas of the world where man has been largely freed from disease and social and economic disadvantages. In the period around the American Revolution, the average life span was less than 35 years. By 1920, in the United States, the average life span had risen to 54 years; and by 1992 the median life span was 75.8 years. Studies indicate that females are likely to live longer than males. Shigechiyo Izumi of Japan, the longest-lived person authenticated, lived 120 years. The whale averages 60 years. The eagle and the swan have the longest lives among birds; of the fishes, the carp and pike are believed to live as long as 150 years. Among plants, the bristlecone pine of California has the greatest longevity, over 4,600 years. See geriatrics.

Time between birth and death. It ranges from a mayfly's day to certain trees' thousands of years. Its limit appears to depend on heredity, but such factors as (in humans) disease, natural disasters, war, diet, and habits such as smoking reduce it. Maximum life span is theoretical; more meaningful is average life span, which life-insurance companies and actuaries analyze and tabulate. Long-lived progenitors tend to beget long-lived descendants. A very-low-calorie diet appears to prolong life. Reduced infant mortality and improved sanitation and nutrition account for much of the increase since circa 1800—from about 35 to over 70 years in most industrialized countries. The oldest well-documented age reached by a human is 122 years.

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