LONGEVITY is a term that may be applied to express either the length or duration of life of any organism, or the prolongation of life to an advanced age. The first meaning is the more scientific of the two, as it may be applied to the duration of the life of any organism, although that duration may be relatively short; thus, we may contrast the longevity of the mould which lives only a few hours with that of the forest tree which has survived for centuries, or the longevity of the ephemeral insect with that of an eagle or a swan, whose lives may be prolonged to over a century. On the other hand, the second meaning is the more common, as when an instance of very advanced age is spoken of as an example of great longevity.
The information we possess as to the natural duration of iife of the lower forms of plants and animals is very meagre, and it can scarcely be asserted that in all there is a natural period of ilife. A simple organism composed of cells, or even one more complicated but still having the organs necessary to life constructed upon a simple type, may continue to live and grow so long as external conditions are favourable. There may be no tendency to decay of tissue inherent in the organism, so that life may be prolonged until a change in external conditions, quickly or slowly, so affects the processes of nutrition as to make the continuance of life impossible beyond a certain time. It is also highly probable that in both the animal and vegetable worlds comparatively few individuals are permitted to live undisturbed for a sufficient length of time to allow any inherent tendencies to decay to show themselves. In the struggle for existence few individuals even reach maturity ; at an early period they are used to support the lives of other and perhaps stronger organisms.
Excluding the lower forms of plants, as to the duration of whose lives we know nothing, the higher plants may bo classed, according to duration of life, as follows :annuals, or semi-annuals, which grow up in spring and die in autumn; biennials, which die at the end of the second year; and perennials, the duration of which may last from four to thousands of years. Succulent plants have a short life, lasting only one or two years ; the formation of wood is necessary for prolonged vegetable existence. It has been pointed out that strongly scented plants have often a longer duration of life than those destitute of smell. Thus thyme, mint, hyssop, marjoram, sage, &c, can live for two years or longer; whilst lettuce, wheat, oats, barley, live no more than a year. Trees of rapid growth, such as fir, birch, horse-chestnut, form soft wood, and have a comparatively short life; whilst hard-wood trees, such as the oak, grow slowly and live long. It is not, however, an invariable rule that trees yielding hard wood live longest. The beech, cypress, juniper, walnut, and pear all form hard wood, but they do not live so long as the lime, which forms a soften wood. Trees which are long in producing leaves and fruit, and which also retain these for a long time, live longer than those in which these changes occur quickly. Fruit-bearing trees, producing a sour harsh fruit in the wild state, have longer lives than those bearing sweet fruits in the cultivated state. By skilful pruning, or lopping off the branches and buds, the term of life of even short-lived plants may be lengthened.
== TABLE ==
According to Hufeland, the chance any plant has of attaining a great age depends on the following conditions : (1) it must grow slowly ; (2) it must propagate slowly and late in life ; (3) it must have a certain degree of solidity and hardness in its organs, a sufficiency of wood, and the sap must not be too watery ; (4) it must be large and have a considerable extent of surface ; and (5) it must rise into the atmosphere. If we view a tree as consisting of an enormous number of buds clustered on a common stem in which the vessels or channels for the circulation of the sap remain pervious, and in which also new wood is formed annually, there seems to be no limit to age, provided external conditions are favourable. Many large trees have reached a vast age, as shown by the following table compiled by De Candolle :
== TABLE ==
In the animal kingdom there is great variety as regards the duration of life, but no accurate data have yet been collected. Certain Infusoria have been watched during the whole period of their existence, which has not lasted more than forty-eight hours; on the other hand, Actinise, or sea anemones, may live to a long age, as shown by the case of a specimen of Actinia mesembryantliemum, still alive in Edinburgh, which belonged to Sir John Dalyell, and which must be at least about seventy years of age. It is highly probable that cold-blooded animals, such as fishes, frogs, toads, in which tissue-changes go on with extreme slowness, especially during a period of muscular inactivity, may live for many years. In the imperial fish-ponds of ancient Rome lampreys were said to have attained their sixtieth year; pike and carp have been ascertained to live a hundred and fifty years; tortoises have reached the age of one hundred years ; and it is alleged by natives of India that the crocodile may live for at least a hundred years, and that there seems to be no limit to its time of growth. Many birds have a long period of life. Eagles and crows have been known to live a hundred years, and parrots have been kept in confinement for sixty years. Peacocks attain an age of twenty years; barn-door fowls live for a much shorter period, from six to twelve years. Small birds seem to have shorter lives than large ones. Blackbirds, gold-finches, and canaries have been known to live for twenty years ; but many of the smaller birds attain an age of only five or six years.
Amongst mammals, the elephant is supposed to attain the greatest age, reaching above a hundred years; the camel generally lives to fifty years, and may live to eighty; the horse does not live more than forty years; the deer, thirty years; the ox, fifteen to twenty years; sheep, goats, foxes, hares, rabbits, from seven to ten years; and dogs and pigs from fifteen to twenty years Certain general state-ments may be made, which do not deserve to be termed laws, but which briefly express relations that undoubtedly exist in many cases between the degree of longevity enjoyed by any species of animal and the conditions of its existence.
1. A relation can often be traced between the duration of life and the time of the development of the animal in utero. To this statement there are many exceptions, as will be apparent from the following table, in which the periods of gestation are given on the authority of Professor Owen \Comp. Anat. and Phys. of Vertebrates, vol iii.):
== TABLE ==
In the case of birds no relation of this kind can be discovered. For times of incubation of many birds see Owen, op. cit, vol. ii. p. 257.
2. It would appear that the sooner a being attains maturity the sootier it propagates, and the shorter will be the duration of its life. The reproductive act may be regarded as the culminating act of the organism, requiring the highest degree of vitality, and involving the largest expenditure of energy. This act will therefore be performed when the organism has reached maturity; in some cases the animal reaches maturity late, in other cases early; but in all the epoch of maturity may be taken as about a fifth part of the whole duration of life. Thus the elephant and the human being do not reach maturity till say the twentieth year, and the period of longevity is about a hundred years ; the horse, ass, and bull are mature in the third or fourth year, and live from fifteen to twenty years; sheep come to maturity in the second year, and live from eight to ten years; whilst rabbits and guinea pigs are mature within one year, and live only from four to five years. Here again there are exceptions, as, for example, the cat is mature before the end of the first year, and still it may live to the age of twenty years. Much information is still required on these points before a law can be formulated.
The question of longevity, however, probably presents the greatest interest in its relation to man. It is still a popular belief that the earliest inhabitants of the world possessed an incredible strength, were of an enormous size, and lived to a very great age ; and the ages of the patriarchs before the flood are often taken literally, although the conditions making such long lives possible are at variance with those of human existence at the present day. In ancient history there are instances given of heroes who attained the age of several hundred years, but these must be regarded as mythical. For an interesting account of these, see Hufeland's Art of Prolonging Life, p. 62 sq.
The following are a few instances of extreme longevity which have been placed on record :Margaret Patten, 137; the countess of Desmond, 145; Thomas Parr, 152; Thomas Damme, 154; John Rovin, 172; and Peter Torton, 185. There can be little doubt that the ages of these persons have been much exaggerated. They lived at a time when no accurate chronological records were kept, and when it was the habit to fix the dates of occur-rences by comparing them in the memory with other events believed to have happened about the same time. Thus there were many sources of fallacy, although the narrators no doubt believed their statements to be quite accurate. Still these were instances of prolongation of human life far beyond the usual limits, and there is no reason for doubting that they all lived till they were upwards of a hundred years of age.
Perhaps the best authenticated instance of this kind is that of the famous Thomas Parr of Shropshire. "He was a poor far-mer's servant, and obliged to maintain himself by daily labour. When above one hundred and twenty years of age he married a widow for his second wife, who lived with him twelve years, and who asserted that during that time he never betrayed any signs of infirmity of age. Till his one hundred and thirtieth year he per-formed all his usual work, and was accustomed even to thresh Some years before his death his eyes and memory began to fail, but his hearing and senses continued sound to the last. In his one hundred and fifty-second year his fame had reached London ; and, as the king was desirous of seeing so great a rarity, he was induced to take a journey thither. This, in all probability, shortened his existence, which he otherwise might have preserved some years longer ; for he was treated at court in so royal a manner, and his mode, of living was so totally changed that lie died soon after, at London, in 1635. He was one hundred and fifty-two years and nine months old, and had lived under nine kings of England. What was most remarkable in regard to this man is that, when his body was opened by Dr Harvey (the discoverer of the circulation of the blood), his internal organs were found to be in the most perfect state, nor was the least symptom of decay to be discovered in them. His cartilages even were not ossified, as is the case in all old people. The smallest cause of deatli had not yet settled in his body ; and he died merely of a plethora, because he had been too well treated."Hufeland, p. 71.
The late Sir George Cornewall Lewis attempted to show that all such narratives were so inaccurate as to reduce the ages of the parties to something under a hundred years, and he was disposed to think that there had been no instance of a human being attaining the age of a hundred years. But subsequent cases have shown that a few have attained that great age. In these cases the evidence has not been of a collateral kind, nor has it depended on human memory, but it has been established by written records. Scarcely a year passes without instances occurring in which the evidence that the deceased attained a hundred years cannot be controverted, and there is no doubt that,, when a sufficient time from the beginning of the system of registration of births has elapsed, such cases will be more common.
The average duration of life in Europe is about thirty-four years. It oscillates between 28T8 years (Prussia) and 39'8 years (Schleswig-Holstein, Lauenburg). Io Naples it is quoted at 31 -65 years. This falls far short of the possible longevity, a circumstance chiefly to be accounted for by the great mortality in the early years of life. According to De Quatrefages, the duration of life is almost universally the same amongst the best known peoples. Laplanders live to a great age, men of from seventy to ninety years of age being common among them. The American Indians have apparently as long a life, on the average, as the white men living in the same locality. It would appear to be the same in the case of the negro. Pilchard quotes from an official document of the State of New Jersey, showing that the census gave one negro centenarian in the 1000, but only one white centenarian in 150,000 ; on the other hand, the negro of the Senegal ages early, and does not live long. In his native place he is exposed to unhealthy influences which tell upon him, although he resists the bad effects of these longer and better than the white man; but when he is transplanted to America he enjoys a longer life.
The manner of life and nature of the occupation, apart from hereditary and special causes, have a most important influence on the duration of life. Few emperors or kings have attained the age of eighty; and, of more than three hundred popes, only six. have exceeded the age of eighty. It would seem that brain work is not Unfavourable to longevity. It is almost proverbial that statesmen and judges often reach an advanced age. Many men famous in literature and science have lived to an old age. Thus from fifty to sixty we have Tasso, Virgil, Shakespeare, Moliere, Dante, Pope, Ovid, Horace, Racine, Demosthenes; from sixty to seventy, Lavater, Galvani, Boccaccio, Fenelon, Aristotle, Cuvier, Milton, Rousseau, Erasmus, Cervantes; from seventy to eighty, Dryden, Petrarch, Linnaeus, Locke, Handel, Galileo, Swift, Eoger Bacon, Charles Darwin ; from eighty to ninety, Thomas Carlyle, Young, Plato, Buffon, Goethe, Franklin, Sir W. Herschel, Newton, Vol-taire, Halley; and from ninety to one hundred, Sophocles, Leeuwenhoek, Michelangelo, Titian. Physicians are often long lived: Boerhaave, Haller, Gall, Darwin, Van Swieteu, Fallopius, Jenner, Cullen, Galen, and Spallanzani died between seventy and eighty years of age, and Harvey, Duhamel, Pinel, Morgagni, Heberden, and Ruysch be-tween eighty and ninety; whilst the father of medicine, Hippocrates, is credited with one hundred and nine years.
A valuable set of statistics have been collected by Hirt (Die Krankheiten der Arbeiter) regarding the influence of trades on longevity. An abstract of these will be found in Buck's Hygiene and Public Health, vol. ii. pp. 71, 72.
The best indication of longevity in a community is given by the expectation of life from any given age. It is obtained by adding together the number of years which the entire population live from any specified age, and dividing the resulting total "years of life" by the number living at the year of age for which the expectation of life is desired (English Life Table, p. xxxiii). Thus we may find the duration of the portion of human life which an individual at any age may expect to enjoy. Such calcula-tions are of great value in connexion with assurance, and indeed in all pecuniary transactions in which the value of life contingencies are taken into account. They are the bases of all systems of life assurance. Life assurance companies have now been able to collect sufficient numbers of cases of their own experience on which to find trust-worthy calculations showing the expectation of life at different ages. Such tables have really been compiled from selected cases, namely, from those who have assured, and consequently differ somewhat from those compiled on the broader data obtained from the whole population. The following table, derived from both sources of informa-tion, is given briefly to indicate the expectation of life, or the longevity, from various ages, reference being made for details to the article INSURANCE. The table to be read thus : a person at thirty years of age has an average expectation of living 33'3 years longer, or of attaining the age of 63-3 years.
== TABLE ==
What are the physiological conditions in the human being that determine longevity? In the first place, there is the inlluence of heredity. Certain peculiarities of tissue are transmitted from parent to offspring that determine whether or not the tissue will remain for a lengthened period of time in a normal condition, or whether it will quickly yield to external influences and take on an abnormal action. As the life of the body is really the sum of the lives of its constituent parts, or in other words, of the cellular elements composing it, it is evident that anything affecting the healthy action of these elements will affect the life of the body as a whole. In some individuals the tissues have what may be termed a hereditary taint, by which is meant a want of stability, so that they pass readily from a normal into an abnormal condition ; and this is unfavourable to longevity.
In the next place, even healthy tissues capable of resist-ing ordinary influences may be unable to resist long-continued unfavourable conditions. In course of time slow changes begin in the tissue; these in turn affect the organ in which the tissue exists, and the organ, by improperly performing its functions, injures the organism. Thus it is that habitually breathing an impure atmosphere, eating improper food, saturating the body with drugs or with alcohol, over-exerting the nervous system by excitement or prolonged brain-work or worry, and sexual excesses de-bilitate the body by working slow but sure changes in the tissues which will inevitably tell upon the longevity of the individual.
But even in the most favourable conditions there seems to be a limitation to the healthy action of tissues, and old age comes on. Whether this is or is not the result of long hereditary transmission it is not of much practical import-ance to ask, as it is a state of things all flesh is heir to. But, if it be hereditary, as is highly probable, there is the satisfaction of knowing that hereditary states can be slowly influenced by individuals living in the best possible con-ditions and transmitting the influences of good moral and physical hygiene. If bad hereditary qualities are trans-mitted, good qualities have even a better chance of being perpetuated, as they favour the individual in the struggle for existence. Thus a race which has a low degree of longevity may acquire, by persistent attempts to live in the best conditions, a long average duration of life. This is also true, though to a less extent, of an individual life.
Each tissue has a life of its own ; it is developed, reaches maturity, declines, and dies. It may be replaced by successive generations of similar tissues, but the power of reproduction of tissue becomes weakened, and by slow degrees the tissue may disappear, or it may become so altered as to be quite unlike what it was at first. By these tissue-changes functional changes of great importance to the body are brought about. Thus, as age comes on, the blood becomes poorer; respiration is less active; the vital I capacity of the chest, that is the working-quantity of air, is diminished ; the temperature of the body is slightly ! increased, so that the aged are more sensitive to cold ; the digestive organs are less vigorous ; the walls of the arteries become hardened by earthy matter, and lose their elasticity ; the veins become dilated, and the circulation is not efficiently performed ; the teeth decay and disappear ; the cartilages become calcified and hard ; the skin is shrivelled | and dry, and cutaneous respiration and excretion are less perfect; the hair whitens or falls off; the stature and the weight diminish. By and by muscular movements are less energetic and less precise ; the hands tremble and the head shakes ; and there is a tottering gait. The cartilages of the larynx ossify, the vocal cords lose their elasticity and the voice becomes a shrill treble. Then the involuntary muscular tissues are affected so that the bladder is less powerful and defaecation is feeble. The transparent media of the eye become dimmed, the near point of vision is pushed back so that the old man becomes presbyopic, or far-sighted, and the power of accommodation, or focussing of the eye, is entirely lost; the delicate mechanism of the drum and bones of the ear is impaired, so that deafness results; and even touch becomes less delicate. Slowly the intellectual faculties become weakened, the emotions are blunted, and the memory becomes by degrees less trustworthy, and at last vanishes. Much of the time is now spent in sleep, and unless some intercurrent disease snaps the thread of life there is a slow ebbing of existence into natural death. Essentially these phenomena are due to delicate changes in the tissues, visible only with the aid of the microscope. These changes are those of wasting or atrophy, meaning a failure of nutrition, or fatty changes, or those caused by infiltration into the tissue of earthy matter, which soon destroys its healthy functions.
Literature.Elliotson, Human Physiology; Hufeland, Art of Prolonging Life; P. Flourens, De la Longévité Humaine, et de la Quantité de Vie sur la Globe ; Quetelet, Physique Sociale, vol. i. p. 308 ; De Quatrefages, The Human Species ; An Account of Persons remarkable for their Health and Longevity, by a Physician, London, 1829 ; Sir G. Cornewall Lewis's Letters ; Thorns, On Longevity. (J. G. M.)
The above article was written by J. M. Mc Kendrick, M.D., Professor of the Institutes of Medicine, University of Glasgow.