162 HEREDITARY CHARACTERS 



are two ways in which adaptation has occurred in which 

 new characters have appeared. One is by the selection of 

 inborn variations, the other by the transmission to the off- 

 spring of the acquired characters of the parents. But 

 apparently the selection of inborn variations is sufficient 

 to account for all characters, whether they are or are not 

 of such a nature that the transmission of acquirements 

 would have influenced them. The transmission of acquired 

 characters, on the other hand, could at best account for 

 only a part of the process of evolution. It is always 

 dangerous to assume more than is absolutely necessary 

 in explaining any phenomenon, and therefore, even were 

 there no other reason, very strong evidence would be 

 necessary before the inheritance of acquired characters 

 could be accepted as a usual occurrence in nature. As 

 a matter of fact there is very little evidence that suggests 

 that they ever are inherited, and this evidence may be 

 interpreted in an equally plausible manner without making 

 any assumptions beyond the occurrence of variations in 

 all directions, the transmission of such variations, the 

 extermination of individuals with unfavourable variations, 

 and the elimination of all variations that are not in the 

 direction of adaptation to the environment. As much as 

 this must be assumed in either case. 



It must also be borne in mind that the assumption that 

 acquired characters are transmitted implies some extremely 

 complicated and almost inconceivable mechanism by which 

 the acquirements of the individual produce a definite effect 

 upon the germ cells. This effect is not a general effect, but 

 a particular effect. That the germ cells as a whole might be 

 generally injured or generally benefited by some acquirement 

 of the organism in which they are contained, is readily con- 

 ceivable. But it is hard to conceive that some small differ- 

 ence appearing in adult life can so influence the germ cells as 

 to appear in the organisms produced from them, without the 

 germ cells being affected in other ways as well. Such a theory 

 assumes too much, without need, practically without evidence. 



