THE INHERITANCE OF DURATION 173 



points out that the minus sign in the case of these correla- 

 tions of adult with minor exhibits the effect of the inheri- 

 tance of the mortality of youth. Minors dying from 16 

 to 20 are associated with adults dying from 21 to 25. 

 That is, minors dying late correspond to adults dying 

 early. This situation may be a peculiarity of the Quaker 

 material with which this work deals. There is urgent 

 need for further study of the inheritance of the duration 

 of life on more and better material than any which has 

 hitherto been used for the purpose. I have under way 

 in my own laboratory at the present time an extensive 

 investigation of this kind, in which there will be hundreds 

 of thousands of pairs of relatives in the individual 

 correlation tables instead of thousands, and all types of 

 collateral kinship will be represented. Because of the 

 magnitude of the investigation, however, it will be still 

 a number of years before the results will be in hand 

 for discussion. 



The facts which have been presented leave no doubt 

 as to the reality of the inheritance factor as a prime 

 determinant of the length of the life span. 



At the beginning it was pointed out that it was on 

 a priori grounds highly probable that duration of life 

 is influenced by both heredity and environment, and that 

 the real problem is to measure the comparative effect of 

 these two general sets of factors. "We have seen that the 

 intensity of inheritance of duration of life, taking aver- 

 ages, is of the order indicated by the following coefficients. 



Parental correlation (adult children) r = . 1365 

 Fraternal correlation (adults) r=.2831 



Now we have to ask this question : What are the values 

 of parental and fraternal correlation for characters but 

 slightly if at all affected in their values by the environ- 

 ment? Happily, Pearson has provided such values in his 



