LONGEVITY (Lat. longevitas, from longtv rus, aged, from longus, long ccsum, age). The length or duration of life in the individual is an uncertain quantity, obviously dependent on mani fold environmental circumstances. Eaeb species of plant or animal, as in the case of each in dividual, has its term of existence, its limit of growth, and the duration of life organisms is extremely variable. The natural life of an ephemera is often spanned by four or five hours; that of the baobab-tree of the Cape de Verde Islands by 5000 years. The duration of life has quite a different meaning from that of the pro longation of life by artificial means or by special care and under peculiarly favorable surround ings.
In plants, annuals (more truly semi-annuals) live but a few months, growing up in spring and dying down, after seeding, in the autumn; bien nials die at the end of the second year, while perennials may exist many years. Trees, even of the same order, vary greatly in duration of life; the fir, which is of rapid growth, may decay and die in about 20 years. while the spruce may grow for 150 years. Hufeland states that great age in plants depends (1) on slow growth; (2) it must propagate slowly and late in life; (3) it must have a certain degree of solidity and hardness in its tissues; (4)it must be large and have a considerable extent of surface; and (5) it must rise into the atmosphere. Hildebrand shows that the duration of life in plants is by no means completely fixed and that it may be very considerably changed through the agency of the external conditions of life. Ile points out the fact that in course of time, and under changed conditions of existence, an annual plant may become perennial, or vice versa. That lon gevity depends on the environment, especially temperature, is also proved by the fact observed in botany that in certain genera of plants there are species which are annuals in the temperate zone, while other species in the tropics are tree like and live ninny years.
Great age in animals is by no means confined to the higher vertebrates. A specimen of sea anemone (Aetinia )1 csembryantheinum) lived in an aquarium in Edinburgh fliom 1828 to August 4, 1887. In the Roman fish-ponds lampreys were reputed to have reached their sixtieth year. The crocodile lives a century and continues to grow till it dies; pike and carp are said to bavo lived 150 years; eagles, falcons, and crows a cen tury. A white-headed vulture in the Schbnbrunn Zohlogical Gardens is known to have been in captivity for 118 years. The smallest singing birds live ten. years, while the nightingale and blackbird survive twelve to eighteen years. It is supposed that eider dueks may reach the age of nearly a century. Of mammals, only man, the elephant, and the whale live to be a hundred years old. The horse and bear rarely reach an age of 40 years, the lion 35, the wild boar 25, the sheep 15, the hare 10, and the squirrel and mouse 6 years. As Weisman states, the mini mum duration of life necessary for the species is much lower than among birds.
Of crustacea, the crayfish is said to live 20 years; the queen of the honey-bee lives one or two years, but has been kept for five, while Lubbock kept one female ant over thirteen years and another nearly fifteen years, which continued to lay fertile eggs throughout her life.
The initial and most fundamental cause of longevity in plants is the favorable nature of tho environment, the external conditions of life, par ticularly temperature. It is most probable that this profoundly affects the duration of life in animals. See GROWTH: METABOLISM.
Another factor is heredity. It is well known that longevity runs in families, is hereditary, and that, although individuals who attain a great age may be exposed to the same exigencies of life as those who die young or in middle life, they outlive their generation. The longevity of man is usually given as 100 years, but there are many authentic instances of people reaching LOS years. Beyond that limit, however, cases are very rare. The great majority of long-lived individuals have been of medium height and weight, of quiet, regular habits, moderate eaters and temperate drinkers or abstainers. Tobacco seems to play but small part. Women live longer than men, probably because after the child-bearing period they are less exposed to injury and disease than men. See LIFE, MEAN OF.
That the average length of human life has been nearly doubled within a few centuries is due to improved conditions of living, to the progress of civilization, and especially to improved sanitary conditions. Thus the mean duration of human life in France at the close of the eighteenth century' was 21) years; in the period from 1817 to 1831 the average rose to 39 years, and between Is40 and 1859 to 40 years. For England it has been from :39 to 43. For Massachusetts the average is about 40, and in New York City 33.3. The mean normal longevity may not be the same in all races. The negroes of Senegal develop earlier than the white man, but they are shorter-lived. Yet when reared in the United States they live to a great age. is another proof of the profound influence of the mode and general con ditions of life on longevity.
There is also a chi:se correspondence between the duration of life in the individual and that of the species. Most specific forms are compara tively short-lived. They have originated, flour ished, and died out within the limits of a geo logical epoch; what are called 'persistent' forms, such as Lingutella, Limulus,Corat odus, etc., have by reason of their great vitality outlived en tire faurne and endured for millions of years, and are now flourishing in apparently undimin ished vigor. See EXTINCTION OF SPEUIF.S.
BIBLIOGRAPHY. Weismann. Kssays upon HeBibliography. Weismann. Kssays upon He- redity and Kindred Biological Problems (Eng. trans. Oxford, ISO) ; Lankester, On Com para tire Longerity in Man and the Lower Animals (Lou don, 1870) ; Hildebrand, Lebensdauer. etc., der Ptlanzen," in Englcr's Bolan. lahrbuch, vol. ii. (Leipzig, 1881) ; Thomas, Lmigevity of Man; Hufeland, Art of Prolonging Life; Flourens, De la longerite humaine; Quetelet, Physique sociale.