88 THE THEORIES OF EVOLUTION 



ism. The truth is, however, that such is rarely the 

 case, and that every modification of an organ corre- 

 sponds closely to other modifications bearing upon all 

 the parts which co-operate with it in its physiological 

 functions. Hence, another objection against the all- 

 sufficiency of natural selection, and which Spencer has 

 formulated as follows: 



"If there occurs some change in an organ, say, by 

 increase of its size, which adapts it better to the crea- 

 ture's needs, it is admitted that when, as commonly 

 happens, the use of the organ demands the co-opera- 

 tion of other organs, the change in it will generally 

 be of no service unless the co-operative organs are 

 changed. If, for instance, there takes place such a 

 modification of a rodent's tail as that which, by suc- 

 cessive increases, produces the trowel-shaped tail of 

 the beaver, no advantage will be derived unless there 

 also take place certain modifications in the bulks and 

 shapes of the adjacent vertebrae and their attached 

 muscles, as well, probably, as in the hind limbs, en- 

 abling them to withstand the reactions of the blows 

 given by the tail." 4 



Likewise a certain mode of locomotion supposes 

 co-operation and co-adaptation of the forelimbs and 

 hindlimbs. How could this co-adaptation have been 

 brought about by natural selection? There is no rea- 



* The Inadequacy of Natural Selection. Contemporary Review, March, 

 1893. 



