Heredity
The influence of heredity has often been insisted upon and is perhaps the most important factor in longevity. Out of 824 persons between 80 and 100 years of age analysed by Humphry, 406, or 49·4 per cent, came of long-lived families. Numerous striking examples of such families are on record, but a few only need be given. Roy[45] quotes the case of Dr. Iverex, who died in 1700 at the age of 104, his father at 112, his mother 107, and his grandfather 130 years, and gives four other examples of three centenarians in the same family. Another remarkable family group was that of Joseph Retas who died at Tarbes at the age of 118 in 1888, and was the son of a man aged 111 years and had a brother aged 114 years. Two centenarian twin sisters were recorded in a village near Athlone[46]; centenarian sisters and brothers are not so very exceptional. Sir Hermann Weber[47] recorded two families, in one of which the average age of ten children was over 90 years and in the other of eight children nearly 90 years.
A good stock may ensure long life in the face of adverse environment, such as town life and alcoholism; thus Dr. John Brownlee[48] showed statistically that while persons dying at the age of 51 in the average environment would have, had they lived in the country, a mean life of seven years longer, this difference was less at higher ages, and remarks that a person who has the potentiality of living to the age of 80 years has a force of life which is more or less independent of environment. Sir George Savage[49] often noted that of two aged members of the same family one was sober the other intemperate; and a good many centenarians have taken alcohol in quantities that would be too much for ordinary people.
Heredity is not an all-powerful factor, for an individual whose family history is not remarkable for longevity may greatly prolong his life by carefully correcting unfavourable hereditary tendencies. Thus the late Sir Hermann Weber, who lived to the age of 95 as the result of practising the maxims of his Prolongation of Life, mentions that his mother died of cardiac failure before she was 60 and his father at 60 from cerebral haemorrhage, and he gives other instances of the same happy result of wise management. Not unfrequently husband and wife both live to an advanced age, no doubt often as the result of favourable environment. A photograph of a married couple both 101 years old appears as the frontispiece of Sir George Humphry’s book on Old Age, and must of course be accepted; but the same cannot be said of the frontispiece to volume ii. of Sir John Sinclair’s Code of Health and Longevity (1807), representing the Hungarian husband and wife, aged respectively 172 and 164 years, who had been married 147 years.
It has been suggested that “cell-memory” by providing experience as to the proper way to behave at the different periods of life has a bearing on the coming of old age; Samuel Butler[50] argued that cells without hereditary memory of past existence at, say, 75 years, would become puzzled and so disordered as to die. Parkes Weber[51] has modified this view by assuming a failure of the wish to live on the part of the nerve cells of the brain, a want which might also be hereditary. The possession by the cells of “the will to live” would be an important factor in longevity and should be obtained by individual effort or in other words be an acquired character, though the reverse conditions such as physical mutilations,[52] often spoken of as acquired characters, are known not to be inherited.
In different countries and in different individuals the cells of the body may differ in the rate at which they live; they have, as Sir James Paget[53] said, a different “time-rate”; in some the time-rate is rapid, for example in the natives of hot climates where maturity comes early and old age at a time that seems very premature by our standard; in others the body, sometimes the mind, works slowly, is set at a more leisurely rate and therefore takes longer to run its course. In some persons this appears to be shown by a slow pulse, a characteristic that may also be hereditary.
Fig. 8.—John Rovin and Sarah his wife, Hungarians, at their reputed ages of 172 and 164 years respectively; their married life lasted 147 years.
Of the hereditary factors most concerned in longevity the inherent vitality of the central nervous system is the most essential; physiological death in man and the higher animals is probably due to failure of the cells of the brain, which do not multiply after birth and are less capable of rejuvenescence than those of the other organs. The integrity of the cardio-vascular system is also most important; in Sir William Osler’s[54] words much depends “on the quality of arterial tissue (vital rubber) which the individual has inherited.” According to Sir Clifford Allbutt[55] there are two modes of hereditary transmission of arteriosclerosis, the direct and the indirect; the direct which he calls decrescent or primary, consisting in an original frailty or toxic susceptibility which like other peculiarities may run in families; and the indirect or hyperpietic, a secondary event due not to inherent taint in the arterial walls but to metabolic changes causing high arterial pressure; it is in such families with hereditary high blood pressure that cerebral haemorrhage occurs in one generation after another about the same age (65–70). In examining people the discovery of a blood pressure low for their age often justifies, in the absence of any pathological condition, the suggestion that the family is long-lived. The frequency of cardiac hypertrophy (43 per cent of Councilman’s cases), even though it be a pathological condition, shows that its reserve power is good. Death among the aged very commonly depends on some morbid change in the cardio-vascular system; thus at the Royal Hospital, Chelsea, Majors R. J. C. Thompson and R. E. Todd[56] found that among 169 deaths of pensioners with an average age of 77·2 years the largest number 64, or 38 per cent, were due to this cause; lesions of the respiratory system, pneumonia, and bronchopneumonia, coming next with 41 deaths, or 24 per cent, malignant disease being responsible for 22, or 13 per cent. The nervous and circulatory systems are intimately correlated with each other, disorder or disease of one, particularly of the cardio-vascular system, exerting an evil influence on the other. In a negative manner weakness of the digestive system may favour longevity by preventing the excesses which vigorous individuals may for a time at any rate indulge in with impunity; but as a rule the digestion of the long-lived is good.
The first-born is significantly handicapped, as Karl Pearson[57] has shown, and more subject to tuberculosis, insanity, and criminality. But out of 71 centenarians analysed by Sir George Humphry 17, or 24 per cent, were firstlings, and 24 per cent of 824 persons between 80 and 100 were first-born. It must be remembered that first-born are more numerous than any others, and some of the above were only children. The most frequent position in the family among these 895 old people analysed by Sir George Humphry was the third.