USE-INHERITANCE AN EVIL. 133 



generally beneficial up to a certain point ; for 

 natural selection has 'sanctioned or evolved organs 

 which possess the property or potentiality of de- 

 veloping to the right extent under the stimulus 

 of use or nourishment. But ust-inferitance would 

 cumulatively alter this individual adaptability, 

 and would tend to fix the size of organs by the 

 average amount of ancestral use or disuse rather 

 than by the actual requirements of the individual. 

 Of course under changed conditions involving 

 increased or lessened use of parts it might 

 become advantageous ; but even here it may 

 prove a decided hindrance to adaptive evolution in. 

 some respects as well as an unnecessary aid in 

 others. Thus in the case of animals becoming 

 heavier, or walking more, it would lengthen the 

 legs although natural selection might require them 

 to be shortened. In the Aylesbury duck and the 

 Call duck, if use-inheritance has increased the 

 dimensions of the bones and tendons of the leg, 



