EMBRYOLOGY AND HUMAN MORTALITY 149 



in this chapter add one more link to the already strong 

 chain of evidence which indicates the highly important 

 part played by innate constitutional biological factors 

 as contrasted with environmental factors in the deter- 

 mination of the observed rates of human mortality. Here 

 we have grouped human mortality into broad cla,sses 

 which rest upon a strictly biological basis. When this 

 is done it is found that the proportionate subdivision of 

 the mortality among the several causes — ^in short the 

 death ratios in the sense of Fisher — is strikingly similar 

 in such widely dissimilar environments as the United 

 States, England and Southern Brazil. 



