Individual morality.—History of two brothers brought up in the same circumstances, but whose conduct was quite different.—Late development of the sense of life.—Evolution of sympathy.—The sphere of egoism in moral conduct.—Christian morality.—Morality of Herbert Spencer.—Danger of exalted altruism 316 IV ORTHOBIOSIS Human nature must be modified according to an ideal.—Comparison with the modification of the constitution of plants and of animals.—Schlanstedt rye.—Burbank’s plants.—The ideal of orthobiosis.—The immorality of ignorance.—The place of hygiene in the social life.—The place of altruism in moral conduct.—The freedom of the theory of orthobiosis from metaphysics 325 THE PROLONGATION OF LIFE PART I THE INVESTIGATION OF OLD AGE I THE PROBLEMS OF SENILITY Treatment of old people in uncivilised countries—Assassination of old people in civilised countries—Suicide of old people—Public assistance in old age—Centenarians—Mme. Robineau, a lady of 106 years of age—Principal characters of old age—Examples of old mammals—Old birds and tortoises—Hypothesis of senile degeneration in the lower animals In the “Nature of Man” I laid down the outlines of a theory of the actual changes which take place during the senescence of our body. These ideas, on the one hand, have raised certain difficulties, and, on the other, have led to new investigations. As the study of old age is of great theoretical importance, and naturally is of practical value, I think that it is useful to pursue the subject still further. Although there exist races which solve the difficulty of old age by the simple means of destroying aged people, the problem in civilised countries is complicated by our more refined feelings and by considerations of a general nature. In the Melanesian Islands, old people who have become incapable of doing useful work are buried alive. In times of famine, the natives of Tierra del Fuego kill and eat the old women before they touch their dogs. When they were asked why they did this, they said that dogs could catch seals, whilst old women could not do so.