INHERITANCE OF PARENTAL MODIFICATIONS 73 



those of the third or fourth or tenth or fiftieth ? If parental 

 modifications be inherited, the plants of the later generations 

 should be larger than those of the first, the inherited effect 

 of increased size accumulating from generation to genera- 

 tion. We do not, however, find this to be the case. It is 

 not by this method that large plants have been produced 

 by the gardeners. They have been produced by selecting 

 the larger plants to breed from and continuing this process 

 from generation to generation, the same process of selection 

 that goes on in nature. 



Let us look at an illustration of the reputed inheritance 

 of the effects of use and disuse and see if we can accept this 

 influence as a factor in the evolution of the higher animals 

 and plants. We have referred to the increase in size that 

 follows the use of a muscle, and the decreased size that 

 results from its disuse. Are these effects inherited by the 

 offspring ? Does the man who is strong because he leads 

 an active life have stronger children than he would have 

 if he led an inactive life? Notice this: The fact that he 

 does develop strong muscles as the result of exercise shows 

 that he must have had an innate capacity for developing 

 strong muscles by exercise. If he inherited from his parents 

 the ability to develop strong muscles under the stimulus of 

 an active life, his offspring in turn will inherit from him the 

 same ability. A blacksmith has a son who becomes an office 

 clerk and takes no exercise. Does the son have any stronger 

 right arm than he would have had if his father had been 

 an office clerk ? Of course the son will have the same 

 capacity for developing a strong arm that his father had 

 before him, but will the fact that the father developed this 

 capacity and became strong give the son any greater strength 



