170 BIOLOGY OF DEATH 



resent true organic relationship and not mere chance. 

 All of the other coefficients are certainly significant, hav- 

 ing regard to their probable errors. Furthermore, they 

 are aU positive in sign, which implies that a variation in 

 the direction of increased duration of life in one relative 

 of the pair is associated with an increase in expectation 

 of life in the other. It will be noted that the magnitude 

 of the correlation between brother and brother is about 

 twice as great as in the case of correlation of father with 

 son. From this it is provisionally concluded that the 

 intensity of the hereditary influence in respect of duration 

 of life is greater in the fraternal relationship than in the 

 parental. It evidently makes no difference, broadly 

 speaking, so far as these two sets of material are con- 

 cerned, whether there are included in the correlation table 

 all adult sons, whatever their age, or only adult sons over 

 50 years of age. The coefficients in both, cases are es- 

 sentially of the same order of magnitude. 



Perhaps someone will be inclined to believe that the 

 correlation between father and son, and brotherl and 

 brother, in respect of the duration of life arises as a 

 result of similarity of the environments to which they 

 are exposed. Pearson's comments on this point are 

 penetrating, and I believe absolutely sound. He says : 



There may be some readers who will be inclined to consider that much 

 of the correlation of duration of life between brothers is due to there being 

 a likeness of their environment, and that thus each pair of brethren is 

 linked together and differentiated from the general population. But it is 

 difScult to believe that this really affects adult brothers or a father and his 

 adult offspring. A man who dies between 40 and 80 can hardly be said 

 to have an environment more like that of his brother or father, who died 

 also at some such age. than like any other member of the general popula- 

 tion. Of course, two brothers have usually a like environment in infancy, 

 and their ages at death, even if they die adults, may be influenced by their 

 rearing. But if this be true, we ought to find a high correlation in ages 



