Appendix II. 311 



these causes can ever have acted independently. In point 

 of fact, as we have seen in the foregoing chapters, such has 

 probably and frequently been the case under the influences 

 of isolation, climate, food, sexual selection, and laws of 

 growth ; but I may here adduce some further remarks with 

 regard to yet another possible cause. If the Lamarckian 

 principles are valid at all, no reason can be shown why in 

 some cases they may not have been competent of themselves 

 to induce morphological changes of type by successive 

 increments, until a transmutation of species is effected by 

 then- action alone as, indeed, Weismann believes to have 

 been the case with all the species of Protozoa *. That such 

 actually has often been the case also with numberless species 

 of Metozoa, is the belief of the neo-Lamarckians ; and 

 whether they are right or wrong in holding this belief, it is 

 equally certain that, as a matter of logical reasoning, they are 

 not compelled by it to profess any disbelief in the agency of 

 natural selection. They may be mistaken as to the facts, as 

 Darwin in a lesser degree may have been similarly mistaken ; 

 but just as Darwin has nowhere committed himself to the 

 statement that all species must necessarily have been originated 

 by natural selection, so these neo-Lamarckians are perfectly 

 logical in holding that some species may have been wholly 

 caused by the inheritance of acquired characters, as other 

 species may have been wholly caired by the natural selection 

 of congenital characters. In short, unless we begin by 

 assuming (with Wallace and against Darwin) that there 

 can be no other cause of the origin of species than that which 

 is furnished by natural selection, we have no basis for 

 Professor Huxley's statement " that every species has been 

 originated by selection " ; while, if we do set out with this 

 assumption, we end in a mere tautology. What ought to 

 be done is to prove the validity of this assumption ; but, as 



1 Since the above was written Professor Weismann has transferred 

 this doctrine from the Protozoa to their ancestors. 



