INADEQUACY OF NATURAL SELECTION, ETC. 621 



that those of the fore limbs will undergo co-adaptation similar in 

 their complexity, but dissimilar in their kinds ; and that the two 

 sets of co-adaptations will be effected pari passu. If, as may be 

 held, the probabilities are millions to one against the first set of 

 changes being achieved, then it may be held that the probabilities 

 are billions to one against the second being simultaneously 

 achieved, in progressive adjustment to the first. 



There remains only to notice the third conceivable mode of 

 adjustment. It may be imagined that though, by the natural 

 selection of miscellaneous variations, these adjustments cannot be 

 effected, they may nevertheless be made to take place appro- 

 priately. How made ? To suppose them so made is to suppose 

 that the prescribed end is somewhere recognized ; and that the 

 changes are step by step simultaneously proportioned for achiev- 

 ing it is to suppose a designed production of these changes. In 

 such case, then, we have to fall back in part upon the primitive 

 hypothesis ; and if we do this in part, we may as well do it 

 wholly may as well avowedly return to the doctrine of special 

 creations. 



What, then, is the only defensible interpretation ? If such 

 modifications of structure produced by modifications of function 

 as we see take place in each individual, are in any measure 

 transmissible to descendants, then all these co- adaptations, from 

 the simplest up to the most complex, are accounted for. In some 

 cases this inheritance of acquired characters suffices by itself to 

 explain the facts ; and in other cases it suffices when taken in 

 combination with the selection of favourable variations. An 

 example of the first class is furnished by the change just con- 

 sidered ; and an example of the second class is furnished by the 

 case, before named, of development in a deer's horns. If, by 

 some extra massiveness spontaneously arising, or by formation of 

 an additional " point," an advantage is gained either for attack 

 or defence, then, if the increased muscularity and strengthened 

 structure of the neck and thorax, which wielding of these some- 

 what heavier horns produces, are in a greater or less degree 

 inherited, and in several successive generations are by this 

 process brought up to the required extra strength, it becomes 

 possible and advantageous for a further increase of the horns to 

 take place, and a further increase in the apparatus for wielding 

 them, and so on continuously. By such processes only, in which 

 each part gains strength in proportion to function, can co-opera- 

 tive parts be kept in adjustment, and be re-adjusted to meet new 

 requirements. Close contemplation of the facts impresses me 

 more strongly than ever with the two alternatives either there 

 has been inheritance of acquired characters, or there has been no 

 evolution. 



