196 Inheritance of Acquired Characters 



acting also in this same direction throughout a decidedly 

 large number of successive generations. 



"One must admit," says Hartmann, very rightly, 

 "that minute and purely accidental variations even if 

 they are useful, are unable to preserve themselves from 

 disappearing again through crossing. Whatever is to 

 be preserved must, as Darwin also admits, appear in a 

 certain quantity, either all at once or successively, because 

 the number of similar variations must be sufficient to 

 overcome the suppression through crossing. But it is 

 not to be expected that similar variations will appear in 

 such frequence by chance, but only as a result of definite 

 external or internal causes which set a definitely directed 

 modification in the place of accidental ones." 153 



Of the causes of variation which possess this capac- 

 ity of simultaneous similar and constant action, we know 

 at present only functional adaptation aided by the inher- 

 itance of acquired characters. 



The very fixity of many species has been rightly 

 urged against Weismann. Natural selection in fact, 

 because of the smallness of fortuitous individual vari- 

 ations, is forced, on the one side in order to explain by 

 itself the development of species, to fall back upon an 

 excessively great degree of selective capacity; but on 

 the other side if this great degree of selective capacity 

 is accorded, it encounters still greater difficulty in account- 

 ing for the contrary phenomenon presented by a host of 

 other species which have remained unaltered even dur- 

 ing a whole series of long geologic periods. 



The Lamarckian theory does not find any special 



1BS Eduard von Hartmann: Die Abstammungslehre seit Darwin. 

 Annalen der Naturphilosophie, herausg. v. W. Ostwald. Zvv. Bd., 

 Heft. III. Leipzig, May 26, 1903. P. 289. 



