34 IOWA ACADEMY OF SCIENCES. 



the possibility of the transmission of acquired characters. 

 It is in connection with this hypothesis that he has become 

 most widely known, and it is upon the affirmative or neg- 

 ative decision in regard to it that the biologists of the 

 world to-day stand divided into two opposing schools. 

 Neo-Darwinians, following Weismann in not being able to 

 account for the evolution of forms in any degree by the 

 transmission of acquired characters, have been forced into 

 the position of accounting for all such evolution through 

 the distinctively Darwinian factors, natural selection and 

 sexual selection. 



Neo-Lamarckians, in accepting the possibility of the 

 transmission of acquired characters, have been compelled 

 to deny the validity of the theory of the continuity of germ 

 plasm, at least when that theory is held, as by Weismann's 

 school, to include the idea of the absolute independence of 

 the germ plasm of all representative influences derived 

 from the somatoplasm. Of course it is not necessary in 

 holding this view to discard the Darwinian factors, and in 

 fact most Neo-Lamarckians accept these as effective, but 

 attribute to them greatly varying degrees of relative 

 importance. 



The Neo-Darwinians, whether they be right or wrong, 

 have intrenched themselves in a very strong position, from 

 which it is difficult to dislodge them. Presenting strong 

 presumptive evidence against the inheritance of acquired 

 characters, they ask those who believe in such inheritance 

 to present proof of a single case in which an undoubted 

 acquired character has become congenital. Now, such 

 proof is very difficult to obtain, and indeed some of the 

 most eminent Neo-Lamarckians have acknowledged that 

 it has not yet been forthcoming. 



Neo-Lamarckians have, as has been said, generally 

 accepted as untenable the theory of pangenesis. There 

 has been accumulated, however, a mass of evidence to 

 prove that selection (natural or sexual) is insufficient to 

 account for all the observed facts of evolution. This evi- 

 dence is particularly abundant in paleontology. Before 

 selection can act, a variation must possess some utUity; 



