CHAPTER X. 



Heredity (continued') — The Principle of Structural Mean — Pre-potency — 

 Physiological and Pathological Blendings. 



The Principle of Structural Mean. — This has already 

 been denned. Inasmuch as two individuals are engaged in 

 the reproductive process, the offspring cannot be exactly like 

 either of them, but must, on the contrary, be some sort of 

 mean between the two. There is probably an ideal or standard 

 mean which they all tend to approach, but this is subject of 

 course to such differences as depend upon the principle of 

 sexual heredity, so that the case will be more accurately put 

 thus: The male offspring all tend toward a certain fixed standard, 

 the female offspring to a certain other fixed standard. 



Whatever differences occur between brothers on the one hand, 

 and sisters on the other, are due to differences of the E, which, as 

 we shall see, has a considerable power in altering S. This will be 

 more particularly shown in treating of E as a power capable of 

 modifying structure, and w r e shall then be the better able to 

 understand how utterly impossible it is for the E to be anything 

 like the same in any two cases. Such differences in E must 

 inevitably cause corresponding differences among the brothers 

 on the one hand, and among the sisters on the other. The 

 only point about which there can be any doubt is whether this 

 is the sole cause of the difference. I contend that it is. 



It will be observed that the above hypothesis assumes an 

 ideal, standard E. It is- obviously impossible to scientifically 

 define such an ideal ; but in reality all that is necessary is to 

 assume one. The hypothesis is rendered sufficiently clear by 

 the statement that all the male progeny on the one hand, and all 

 the female on the other, would be exactly alike under the same E. 



It must not be thought that the structural mean of which I 

 am speaking is an exact mean of the two parental structures. 



