INHERITANCE OF ACQUIRED CHARACTERS 65 
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- 
