130 ARE THE EFFECTS OF USE INHERITED? 



required by natural selection ; and it is clear that 

 the latter factor must at least have reduced use- 

 inheritance to the very minor position of compara- 

 tive feebleness and harmlessness assigned to it 

 by Darwin. 



f Use-inheritance would be ruinous through 

 causing unequal variation in co-operative parts 

 of which Mr. Spencer may accept his own in- 

 stances of the jaws and teeth, and the cave-crab's 

 lost eyes and persistent eye-stalks, as typical 

 examples. That the variation would be unequal 

 seems almost self-evident from the varying rapidity 

 and extent of the effects of use and disuse on 

 different tissues and on different parts of the 

 general structure. The optic nerve may atrophy in 

 a few months from disuse consequent on the loss 

 of the eye. Some of the bones of the rudimentary 

 hind legs of the whale are still in existence after 

 disuse for an enormous period. Evidently use- 

 inheritance could not equally modify the turtle 



