HUMAN LONGEVITY 53 



ing past eighty years, and great human longevity means being 

 a nonagenarian or centenarian. Progress in medicine and im- 

 provement in the public health have done little or nothing 

 about enabling the individual to achieve such a goal, as the cold 

 statistical facts about the order of human dying make abundantly 

 clear. The s-pan of human life has not been lengthened, and there 

 is no present prospect that it soon will be. The average duration 

 of life is all that has been altered, and that has been accomplished 

 chiefly by giving more babies a fairer start in life's journey than 

 they used to have. Because more of them get by the early and 

 very diflicult hurdles, absolutely more of them survive at later 

 ages. But the terms of the bet that any individual man aged 

 seventy today can safely say that he will be alive at ninety ap- 

 pear to be not quite so good as they were fifty years ago. 



IV 



Why is it that some individuals alive at any given age will 

 live thereafter longer than others? In principle the duration of 

 life of any individual is the net resultant of the interplay between 

 his own innate biological make-up and the forces acting upon it, 

 favorable or unfavorable, external and internal. This is a com- 

 plete and sufficiently logical statement of the case, but not so im- 

 mediately useful as might be wished for the purpose of dis- 

 appointing eager morticians. 



One of the most often quoted things that Oliver Wendell 

 Holmes ever said was that if one is setting out to achieve "three 

 score years and twenty," the first thing to be done, "some years 

 before birth, is to advertise for a couple of parents both belong- 

 ing to long-lived families." "Especially," said he, "let the 

 mother come of a race in which octogenarians and nonagenarians 

 are very common phenomena." When this statement was made 

 its only foundation was the general impression of a wise physi- 

 cian who had spent his own life in a region where octogenarians 

 and nonagenarians were common phenomena. To what extent or 

 degree has this impression been supported by exact, quantita- 

 tive investigation? 



As the first and simplest approach to the question let us 



