INHERITANCE OF ACQUIRED CHARACTERS 59 



of species. Still, they add in some measure to the 

 weight of recent evidence which points to the con- 

 clusion that many specific structures have had a 

 different method of origin. We have already pointed 

 out that there are two alternative methods, each of 

 which has its adherents. Before passing to a con- 

 sideration of the now prevalent view of mutation, 

 something still remains to be said with regard to the 

 remaining theory the theory of Lamarck. 



Darwin himself, as we have seen, admitted the 

 minor importance of the inheritance of acquired 

 characters, as well as that of the phenomenon of 

 sporting, regarding both these processes as causes of 

 the origin of new species subsidiary to the action of 

 natural selection upon individual differences, whilst he 

 looked upon the latter as the main process in organic 

 evolution. 



Later writers, however, have asserted that natural 

 selection is the sole cause of the origin of species, and 

 in particular they have denied any effect to the in- 

 heritance of acquired characters the Lamarckian 

 factor asserting that there is not, and cannot be, 

 any such inheritance. Among the most distinguished 

 opponents of the theory of use-inheritance were A. R. 

 Wallace, the co-discoverer of natural selection ; and 

 Professor Weismann, who has argued the case with 

 particular ability. Much the most able defender of 

 the principle of use-inheritance was Herbert Spencer, 

 who was one of the few who had thoroughly convinced 

 themselves of the truth of the theory of evolution 

 years before the ' Origin of Species ' made its appear- 



