“Arteriosclerosis, removing people from active life when the period of maximum fertility has passed, is of benefit to the young if it relieves them of the care of parents, or brings them an inheritance as they enter adult life. . . . Any attempts to eradicate such a disease from the urban population will be frustrated by natural selection and the survival of more grandchildren in families with few grandparents. Those best fitted to survive in a world growing more urban are those who cease to require support as soon as their roles as parents have been completed. Atherosclerosis and hypertension are now the chief factors in determining that we do not overstay our allotted span of life too long.”