160 THE FIRST PRINCIPLES OF HEREDITY 



on the cross-points of the horizontals and verticals drawn 

 for equal heights i.e., the heights of the sons would be 

 identical with that of the fathers, and we should have 

 complete correlation. On the other hand, if the line AB 

 were horizontal going through O, the height of all the 



Height of Fathers. 



FIG. 72. DIAGRAM OF CORRELATION. (After Lock.) 



sons would be that of the average population, 69 inches, 

 irrespective of the class of fathers to which they belong 

 i.e., there would be no correlation between the height of the 

 fathers and that of the sons, for all the fathers, irrespective 

 of their own height, would have sons of the same medium 



