ii2 An Examination of Weismannism. 



relative importance of natural selection and the 

 Lamarckian factors in the process of organic evolution. 



It may be perfectly true — and I myself believe it 

 is perfectly true — that Darwin attributed too large 

 a measure of importance to the Lamarckian factors ; 

 but whether or not he did so is quite a different 

 question from that which obtains between his theory 

 of pangenesis and Weismann's theory of germ-plasm. 

 The former question is whether we are to "modify" 

 the theory of pangenesis, so as to constitute it the 

 theory of stirp ; the latter question is whether we are 

 to " abolish " the theory of pangenesis, in favour of its 

 logical antithesis, the theory of germ-plasm. And 

 this question remains to be dealt with in my next 

 volume. 



Coming then, lastly ; to the companion postulate 

 of germ-plasm as absolutely stable since the first 

 origin of sexual propagation, we had to observe 

 that, unlike the one we have just been considering, 

 there is an immensely strong presumption against it 

 on merely antecedent grounds. That the most com- 

 plex substance in nature should likewise be the most 

 stable substance with regard to complexity of i; mole- 

 cular structure " ; that the greater its complexity 

 becomes the greater becomes its stability, so that 

 while in the comparatively simple unicellular organ- 

 isms it is eminently susceptible of modification by 

 external conditions, it entirely ceases to be thus 

 susceptible when it becomes evolved into the incom- 

 parably more complex and immensely more varied 

 structures which form the bases of heredity in the 

 multicellular organisms — where, also, it must come 



