Influence of Environment _>_>- 



Opinions of Lamarck and Darwin. — It is well known thai La- 

 marck taught that characters due to desire or need, use or disuse, 

 and to changed environment or conditions of life were inherited 

 and thus brought about progressive evolution. Long ago desire 

 or need was repudiated as a factor of evolution. Lowell satir- 

 ized it in his Biglow Papers in these words : 



"Some filosifers think that a fakkilty's granted 



The minnit it's felt to be thoroughly wanted, 



* * * * * 



That the fears of a monkey whose holt chanced to fail 

 Drawed the vertibry out to a prehensile tail." 



Darwin wrote to Hooker, "Heaven forfend me from Lamarck's 

 nonsense of adaptation from the slow willing of animals" ; 

 but although he repudiated this feature of Lamarckism he held 

 that characters due to use or disuse and to changed conditions of 

 life might be inherited and he proposed his hypothesis of pan- 

 genesis in order to explain the process of the transmission of 

 such characters to the germ cells. 



Weismann's Theories. — Weismann introduced a new era in 

 biology by denying the inheritance of all kinds of acquired char- 

 acters, and by challenging the world to produce evidence that 

 would stand a rigorous analysis. But Weismann's greatest ser- 

 vice lay in his constructive theories rather than in destructive 

 criticism ; he forever disposed of theories of pangenesis and the 

 like by showing that the germ cells are not built up by contribu- 

 tions from the body and that characters are not transmitted from 

 generation to generation ; but on the other hand that there is 

 transmitted a germ plasm which is relatively independent of the 

 body and which is relatively very stable in organization. This 

 epoch-making theory of Weismann's has naturally undergone 

 some changes, as the result of new discoveries. It is no longer 

 believed that the germ plasm is really independent of the body, 

 nor that it is absolutely stable, as Weismann at one time held. 

 There is no doubt that the germ cells and the germ plasm are 



