160 



BIOLOGY OF DEATH 



We see that the longest average duration of life, or 

 expectation of life, was of that group which had both 

 mothers and fathers living to age 80 and over. The 

 average duration of life of these persons was 52.7 years. 

 Contrast this with the average duration of life of those 

 whose parents both died under 60 years of age, where 



TABLE 16 



Showing the influence of a considerable degree of longevity in both father 



and mother upon the expectation of life of the offspring. [After Bell). 



{In each cell of the table the open figure is the average duration of 



life of the offspring and the bracketed figure is the number of 



cases upon which the average is based). 



the figure is 32.8 years. In other words, it added al- 

 most exactly 20 years to the average life of the first 

 group of people to have extremely long-lived parents, 

 instead of parents dying under age 60. In each column 

 of the table the average duration of life advances as we 

 proceed from top to bottom — that is, as the father's age 

 at death increases — and in each row of the table the aver- 

 age expectation of life of the offspring increases as we 

 pass from left to right — ^that is, with increasing age of 

 the mother at death. However the matter is taken, a 

 careful selection of one's parents in respect of longevity 

 is the most reliable form of personal life insurance. 



