524 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



again itself ultimately forms reproductive cells, and thus the life of 

 the species is continued. It is only in the sense of its propagation in 

 this way from one generation to another that we can speak of the 

 mdefinite continuance of life; we can only be immortal through our 

 descendants! 



AVERAGE DURATION OF LIFE AND POSSIBILITY OF ITS PROLONGATION. 



The individuals of every species of animal appear to have an aver- 

 age duration of existence.* Some species are known the individuals 

 of which live only for a few hours, whilst others survive for a hundred 

 years.^ In man himself the average length of life would probably 

 be greater than the tln-ee-score and ten years allotted to him by the 

 Psalmist if we could eliminate the results of disease and accident; 

 when these results are included it falls far short of that period. If 

 the terms of hfe given in the purely mythological part of the Old 

 Testament were credible, man would in the early stages of his history 

 have possessed a remarkable power of resisting age and disease. 

 But, although many here present were brought up to believe in their 

 hteral veracity, such records are no longer accepted even by the 

 most orthodox of theologians, and the nine hundred odd years with 

 which Adam and his immediate descendants are credited, culmi- 

 nating in the 969 of Methuselah, have been relegated, with the 

 account of Creation and the Deluge, to their proper position in Ht- 

 erature. When we come to the Hebrew Patriarchs, we notice a 

 considerable diminution to have taken place in what the insurance 

 officers term the "expectation of life." Abraham is described as 

 having hved only to 175 years, Joseph and Joshua to 110, Moses to 

 120; even at that age "his eye was not dim nor his natural force 

 abated." We can not say that under ideal conditions aU these 

 terms are impossible; indeed, Metchnikoff is disposed to regard them 

 as probable; for great ages are stiU occasionally recorded, although 

 it is doubtful if any as considerable as these are ever substantiated. 

 That the expectation of Hfe was better then than now would be in- 

 ferred from the apologetic tone adopted by Jacob when questioned 

 by Pharaoh as to his age: "The days of the years of my pilgrimage 

 are an hundred and thirty ^'■ears; few and evil have the days of the 

 years of my life been, and have not attained unto the days of the 

 years of the life of my fathers in the days of their pilgrimage. " Da\dd, 

 to whom, before the advent of the modern statistician, we owe the 

 idea that 70 years is to be regarded as the normal period of hfe,^ 



' This was regarded by Bufion as related to the period of growth, but the ratio is certainly not constant. 

 The subject is discussed by Ray Lankester in an early work, On Comparative Longevity in Man and Ani- 

 mals, 1S70. 



" The approximately regular periods of longevity of different species of animals furnishes a strong argu- 

 ment against the theory that the decay of old age is an accidental phenomenon, comparable with disease. 



» The expectation of life of a healthy man of oO is still reckoned at about 20 years. 



