158 



BIOLOGY OF DEATH 



These striking resiilts demonstrate at once that there 

 is a definite and close connection between the average 

 longevity of parents and that of their children. Ex- 

 tremely long-lived children have a much higher percent- 

 age of extremely long-lived parents than do shorter lived 

 children. While the diagrams demonstrate the fact of 

 this connection, they do not measure its intensity with 

 as great precision as can be obtained by other methods 

 of dealing with the data. A little farther on we shall 

 take up the consideratioji of this more precise method 

 of measurement of the hereditary influence in respect 

 of longevity. 



In the preceding diagrams we have considered each 

 parent separately in connection, with the offspring in 



TABLE 15 

 Longevity of parents of persons dying at 80 and over. {From Bell) 



regard to longevity. We shall, of course, get precisely 

 the same kind of result if we consider both parents to- 

 gether. For the sake of simplicity, taking only the cases 

 of extreme longevity, namely, persons living to 80 or 

 over — the essential data are given in Table 15. 



From this table it is seen that where neither parent 

 lived to be 80, only 5-3 per cent, of the offspring lived to 

 be 80 or over, the percentage being based upon 827 



