204 THE WONDER OF LIFE 



memory ; the theory is that in the course of generations 

 the capacity of going through the routine is somehow 

 ingrained in the germ-plasm, becoming part and parcel 

 of the inheritance. On this attractive view, heredity is 

 the racial analogue of memory, and development is a kind 

 of recollection. 



The next important step in the history was Weismann's 

 critique of the transmission of acquired characters or 

 modifications. These may be defined as individually 

 acquired changes of bodily structure, which are directly 

 due to changes or pecuharities either in function or in 

 environment, and which so transcend the Umits of organic 

 elasticity that they persist after the inducing conditions 

 have ceased to operate. That these are of common occur- 

 rence is a matter of everyday observation ; that they 

 are ever transmitted as such or in any representative 

 degree has not yet been securely proved in a single instance. 

 It is likely that biologists will return on a higher turn of 

 the spiral to a recognition of the importance of ' Nurture ' 

 in evolution, but there cannot be any return to the crude 

 belief in the transmission of individually acquired charac- 

 ters that was general before Weismann's criticism. It is 

 very difficult to see, in connexion with habit for instance, 

 how the estabhshment of a definite brain- track can repre- 

 sentatively affect the germ-plasm, and unless it does that 

 it cannot be transmitted. Thus, if Weismann's critique 

 be sound, it forbids the assumption which is fimdamental 

 to the Lamarckian theory, that instincts are due to the 

 inherited results of experience. Intellectual ability may 

 be transmitted, for it is primarily due to a germinal varia- 

 tion in the direction of increased sagacity ; but intellectual 

 agility due to practice is not transmitted. Thus, Weismann 



