Characters, Hereditary and Acquired. 67 



the blending in single individuals of adaptations 

 previously distributed among different individuals ; 

 it has to do with the simultaneous appearance in 

 single individuals of a co-adaptation of parts, none 

 of which could ever have been of any adaptive 

 value had it been previously distributed among 

 different individuals. Consequently, where Darwin 

 comes to consider this particular case (or the case 

 of co-adaptation as distinguished from the blending 

 of adaptations), he freely invokes the aid of the 

 Lamarckian principles l . 



Wallace, on the other hand, refuses to do this, and 

 says that " the best answer to the difficulty " of sup- 

 posing natural selection to have been the only cause 

 of co-adaptation may be " found in the fact that 

 the very thing said to be impossible by variation 

 and natural selection, has been again and again 

 affected by variation and artificial selection 2 ." This 

 analogy (which Darwin had already and very properly 

 adduced with regard to the blending of adaptations] 

 he enforces by special illustrations ; but he does not 

 appear to perceive that it misses the whole and 

 only point of the " difficulty " against which it is 

 brought. For the case which his analogy sustains 

 is not that which Darwin, Spencer, Broca and others, 

 mean by co-adaptation: it is the case of a blending 

 of adaptations. It is not the case where adaptation 

 \sfirst initiated in spite of intercrossing, by a fortuitous 

 concurrence of variations each in itself being with- 

 out adaptive value : it is the case where adaptation 

 is afterwards increased by means of intercrossing \ 



1 E. g. Origin of Species, p. 178. 

 a Darwinism, p. 418. 



F a 



