Nature of Heredity and Problem of Mechanism 313 



cal germ-plasm so much as the observable fact that or- 

 ganic development, whether hereditary or not, is first and 

 foremost transformative rather than transmissive. 



Tendency to Confuse Heredity with Causes of Heredity 



Again there is appearing in the strictly modern studies of 

 heredity a conception that seems both scientifically unwar- 

 rantable and fraught with possibilities of much harm. This 

 is the failure to distinguish between heredity itself and the 

 causes of heredity. Pearl has given this the most positive 

 expression I have come upon. "By heredity is meant the 

 complex of causes, not now further specified or defined, 

 which, taken together, determines this likeness or resemblance 

 between individuals genetically related to each other." 5 It 

 is to be hoped Doctor Pearl would not wish to be taken quite 

 literally in this. Indeed, other passages give some ground 

 for supposing he would not. The point here raised is 

 probably more an aspect of the general theory of natural 

 causation than of the specific question of cause and effect in 

 heredity. 



The concept "cause" is meaningless except in relation with 

 the concept "effect," and since causes and their effects 

 can not be identical, effects must be as much realities of 

 nature as causes are; so if science is to maintain its claim to 

 objectivity it must devote itself as sedulously to the ascer- 

 tainment of what the effects are in any given case as to what 

 the causes are. The eye-color of a child which resembles 

 the eye-color of an ancestor is an effect and not a cause, 

 and must be accepted whole-heartedly as such before the 

 student is in a proper frame of mind to consider the question 

 of what the cause or causes mav be of the observed effects. 

 To define heredity in a way that implies a disregard of this 

 general principle can but lead to unbalanced thinking and 

 effort and to results strongly tinctured with error. If the 

 position be taken and unfortunately it is taken by many 



